30 (2005) H. 3

Klaus Herfurth, Solingen (D),Dipl.-Ing. Henrik Elmkvist,TASSO, Odense (DK),

Dipl.-Ing. Klaus Reif, Munkebo (DK)

Special edition from

Continuous cast ironfor innovative parts

manufacture

Prof. Dr.-Ing. habil. Klaus Herfurth, Solingen,coordinator of the DGV’s „Continuous Casting“ad hoc working party

Klaus Herfurth, Solingen

Continuous cast iron for innovativeparts manufactureThere are numerous examples of how grey (GJL) and SG (GJS) iron can be usedto technical and financial advantage. The advantages of these cast iron materialshave mainly been described for static casting. The following article looks atcontinuous cast iron in the form of cast semi-finished products, from whichcomponents for all sorts of applications can be manufactured. Continuous castiron has not yet been standardised. On the initiative of the German FoundryAssociation (DGV) in Düsseldorf, therefore, four European continuous castingfoundries assessed the current development status of continuous cast iron,which is described below.

1 IntroductionIn the manufacture of continuous castiron solidification begins in a water-cooled, open-ended die. Because thethermal conditions are different fromthose for sand casting, solidification isfaster. Depending on the process, thisresults in properties that differ from thoseobtained by sand casting and a parti-cularly close-grained, dense materialstructure. Very high pressure-tightnessin respect of liquids and gases is a fea-ture of continuous cast iron [1, 2].

There are no international (ISO), Euro-pean (EN) or national standards for thiscontinuous cast iron. Representatives ofthe following four firms therefore ana-lysed the current production status ofcontinuous cast iron and came up withan initial proposal for future standardi-sation:

- ACO Guss, Kaiserslautern (D)- Contifonte Groupe Kuhn, Saverne (F)- Gontermann-Peipers, Siegen (D)- TASSO, Odense (DK)

2 Principles ofcontinuous casting

Continuous cast grey and SG iron ismanufactured using the horizontal con-tinuous casting method. Figure 1 showsthe three main subassemblies in a hori-zontal continuous casting plant: a receiverwith a flange-mounted, water-cooled,open-ended die that can be changedquickly, a driving and pulling mechanismwith an electronic control system, and acutting and breaking mechanism. As themost important subassembly, the open-ended die is largely responsible for thesurface quality of the cast strand, freedomfrom defects, crystalline structure andcasting speed. It is made of graphite andis enclosed by a water-cooled jacket.

The cubic capacity of the receiver de-pends on the production rate of the con-tinuous casting plant and the supply cyclefor the molten iron. The receiver is replen-ished with molten iron at regular intervalsduring the continuous casting process,ensuring that the process is uninter-rupted.

Having been tapped from the meltingfurnace, the molten iron is treated

(magnesium addition, inoculation) be-fore being poured into the receiver. Thisprocess is repeated every 15 to 30 minu-tes, depending on the strand size andcasting speed. Depending on what sizeof strand is being cast, the temperatureof the molten iron in the holding furnaceis between 1180 and 1300°C. Becauseof the thermal balance, the thinner thestrand being cast, the higher the over-heating temperature must be.

The external, supporting, solid skin of thestrand forms during the initial coolingphase of the cast iron in the open-endeddie – primary cooling. This is followed bysecondary cooling, where the strandsare allowed to cool in still air. When thestrand leaves the open-ended die, it hasnot yet solidified all the way through. Thecore of the strand remains molten for atime. The continuous casting die, whichis largely made of electrographite, per-forms the task of shaping and, by virtueof its physical properties and coolingintensity, sets the strand’s rate of coolingto what is required. The water cooling ofthe open-ended die can be regulated.This allows the cooling intensity to bevaried. The lubricating effect of the graph-ite reduces friction between the con-tinuous casting die and the strand. Theferrostatic head of the molten metal inthe holding furnace acts on the strandlike a feeder. The liquid and solidificationcontraction of the material is equalisedby the constant flow of molten metal. Atthe same time, the expansion of the ma-terial that occurs during solidification asa result of graphite separation coun-teracts cavitation. Continuous castingtherefore produces a cavity- and pore-free structure that is particularly denseand homogeneous.

Figure 1: Schematic diagram of horizontal continuous casting,1 – receiver, 2 – open-ended die, 3 – supporting rollers, 4 – feed unit,5 – cutting wheel, 6 – breaking unit, 7 – broken-off strand lengths

The strand is pulled by a drive unit, which,together with the electronic control sys-tem, undertakes the intermittent with-drawal of the strand with the open-endeddie stationary. The withdrawal cycle isgenerally made up of a movement phaseand a rest phase (waiting time). Thestrand movement, which is made up of asequence of pulling and rest phases, isvery pronounced in continuous iron cast-ing. Depending on the strand size andthe type of cast iron, the pulling lengthcan be between 30 and 80 mm. Beforethe casting process commences, thedischarge end of the continuous castingdie is sealed with a dummy bar. The driveunit is followed by devices for dividing

Figure 2: Various continuous casting plantsa) Continuous casting plant for one strand with the receiver being filled in the background (picture: Contifonte, Saverne (F))b) Continuous casting plant for one strand (picture: TASSO, Odense (DK))c) Continuous casting plant for two strands (picture: Contifonte, Saverne (F))d) Continuous casting plant for four strands (picture: TASSO, Odense (DK))

Figure 3: A continuous casting warehouse with a variety of different sections, sizesand lengths (picture: K. Vollrath, Rees)

a) b)

c) d)

Figure 4: Manufacturing sequences when making parts from continuous cast iron

the strand into individual strand lengths.The moving strand is cut part of the waythrough with a cutting device (saw or gascutter), which moves parallel to thestrand. The resulting strand length isthen broken off by a breaking device.

Figure 2 shows various continuous cast-ing plants in operation with receiver,continuous casting die and one, two orfour strands. Continuous cast iron is oftenrequested at very short notice. The cus-tomer or middleman will therefore de-mand excellent supply readiness andfast, punctual delivery of the material bythe supplier. So as to be able to deliver atany time despite all the different types ofcast iron and strand sizes, foundriesmaintain a permanent stock of their fullrange (figure 3). The strand cross-sec-tion is mainly round, square or rectan-gular. This produces round, square andflat bars, which come in various sizesand lengths.

The manufacturing process for contin-uous cast iron is illustrated in figure 4in two different variants. Variant 1 showswhat has generally been the case untilnow: the foundry delivers the strandlength in the required dimensions andwith specific mechanical properties to thecustomer, who manufactures parts bymeans of machining. Nothing is done toimprove the properties of the materialand the usage properties of the com-ponent further.

Figure 5 presents the manufacturingprocess for variant 1 on the left oncemore, this time in visual form. It alsoincludes heat treatment after continuouscasting, which may be necessary insome cases. Comprehensive qualitycontrol at the end of the foundry’smanufacturing process is a matter ofcourse these days. Extensive in-process

Figure 5: Manufacturing sequence for continuous iron casting (picture: Gontermann-Peipers, Siegen (D))

inspection takes place throughout theproduction process.

In variant 2 (figure 4, right), on the otherhand, processes are carried out afterrough machining to improve the materialproperties in the direction of greaterstrength/resistance and other usageproperties by means of targeted heattreatment and coating or surface re-forming.

Table 1 lists the various test methods forquality control by continuous cast ironmanufacturers. These test methods in-clude visual and dimensional inspection,evaluation of the microstructure, chemicalanalysis, quantification of mechanicalproperties by means of tensile testingand Brinell hardness testing, and non-destructive tests: dye penetration testing,

Figure 6: Rough cutting of continuous cast iron lengths as aservice to the customer (picture: ACO Guss, Kaiserslau-tern (D))

Figure 7: With blocks that have been rough-machined to the rightoutside dimensions, precision machining can start immediately.(Picture: K. Vollrath, Rees)

ultrasonic testing and magnetic particletesting.

Continuous cast bars of a certain lengthare traditionally supplied unmachined ormachined by the manufacturer. All-overmachining to finished size as percustomer specifications is also offeredby manufacturers (figures 6 and 7). Thissaves the customer having to carry outadditional machining operations. Squareand rectangular bars are machined onsix sides. Angular precision is < 0.05 mmper 100 mm, while plane parallelismand length tolerance are < 0.04 mm per100 mm.

Drilled retaining holes and precise pre-centring of drilling positions are alsoavailable. Round bars can be accuratelymachined to a required size [2].

Figure 8: Glass mould manufacture is aninteresting and important area of appli-cation for continuous cast iron. (Picture:ACO Guss, Kaiserslautern (D))

Table 1: Selected test methods for continuous cast iron

Test method

Visual inspection

Dimensional inspection

Hardness test

Structure

Analysis

MechanicalcharacteristicsDye penetration test

Ultrasonic testing

Magnetic particle testing

Machining-state

rawmachinedrawmachinedrawmachinedrawmachinedrawmachinedrawmachinedrawmachinedrawmachinedrawmachined

Type of cast iron

GJL

xxxxxxxxxxxx-x---x

GJS

xxxxxxxxxxxx-x-x-x

Standards

DIN EN 1559-1, 1559-3DIN EN 1559-1, 1559-3DIN ISO 8062

EN 10003-1EN 10003-1EN ISO 945EN ISO 945

EN 10002-1, 10045-1EN 10002-1, 10045-1as per DIN-EN 571-1DIN-EN 571-1as per DIN-EN 583DIN-EN 583-1

DIN EN 1561, 1563, 13835DIN EN 1561, 1563, 13835

DIN EN 1561, 1563, 13835DIN EN 1561, 1563, 13835as per DIN EN 1371-1DIN EN 1371-1as per DIN EN 12680-3DIN EN 12680-3

DIN EN 1369

3 Cast iron materialsThere are several groups of cast iron,including:

- grey iron – GJL (DIN EN 1561) [3]

- vermicular iron – GJV (VDG (GermanFoundrymen’s Association) BulletinW 50, March 2002) [4]

- SG iron – GJS (DIN EN 1563) [5]

- austempered ductile cast iron – ADI(DIN EN 1564) [6, 7, 8]

- malleable cast iron – GJMB/GJMW(DIN EN 1562) [9]

- austenitic cast iron – GJLA-X/GJSA-X(DIN EN 13835) [10, 11]

- wear-resistant cast iron – GJN (DINEN 12513) [12]

The technical literature quoted [3 to 13]provides a detailed description of thebasic metallurgy of cast iron materialstogether with their properties, standard-isation and areas of application.

The materials are classified on the basisof the shape of the graphite crystals pre-cipitated, the formation of a special basicstructure by alloying or heat treatment,or, in the case of malleable cast iron, theprecipitation of the graphite from thestructure by means of heat treatmentonce it has solidified to white cast iron.

The following remarks only relate to greyand SG iron. These cast irons are iron-carbon-silicon materials with a carboncontent of 2 - 4 % and a silicon content of

Figure 9: Fe-C-Si diagram (pseudobinary section at 2.4 % silicon) [13]

2 - 3 %. If no other alloying elements areadded to these materials, they are re-ferred to as unalloyed despite the highsilicon content. The metallic matrix ofthese cast iron materials is on a par witha eutectoid steel with a carbon content ofaround 0.7 % and a silicon content of 2 -3 %, in which graphite crystals of differentshapes are embedded.

The phase and structure transformationsthat take place during manufacture or heattreatment therefore have to be describedwith the phase diagrams for ternary sys-tems (Fe-C-Si). These phase diagramshave four variables and so can normallyonly be displayed in three dimensions. If,however, a section is taken at a constantvalue for one of the variables, a two-di-mensional diagram can be producedonce more. Just such a pseudobinarysection through the Fe-C-Si ternary sys-tem at 2.4 % silicon suffices to describethe transition processes that occur (fig-ure 9).

A distinction is made between two trans-formation stages (graphitisation stages)in the structure formation from the moltenmetal or the structure transformation inthe solid state of aggregation. The firstgraphitisation phase lies between theliquidus temperature and the eutectoidtransformation. This stage decides whethergraphite crystals will be produced (greysolidification) during solidification ofthe cast iron or not (white solidification).Whether the molten metal solidifies towhite or grey cast iron depends on itschemical composition and the rate ofcooling during solidification. The secondgraphitisation stage lies in the area of

the eutectoid transformation. Dependingon the process conditions, this stagedetermines whether the matrix will bepearlitic or ferritic. A third possibility whenit comes to influencing the outcome is toinoculate the molten metal, which pro-motes solidification to grey cast iron.

If the chemical composition is the same,the mechanical properties of the castiron are dependent on the rate of cooling.In practice this fact means that themechanical properties are dependent onthe wall thickness of the casting – theyare section sensitive. A small wall thick-ness means a fast rate of cooling, whilea large wall thickness means a slow rateof cooling. This sensitivity of the mechan-ical properties to wall thickness is greaterfor grey iron than for SG iron.

The hardness (usually Brinell hardness)of cast iron materials is always mixed.Such materials have a hard, steel-like,metallic matrix in which graphite crystalsof a lower hardness are embedded. Thehardness of the metallic matrix can onlybe determined by means of microhard-ness measurements.

The density of cast iron materials isaround 10 % lower than that of steels asa result of graphite crystals of very lowdensity (approx. 10 % by volume) beingembedded in the steel-like, metallicmatrix. If the component geometry is keptthe same, this difference in densitymeans a weight saving, and therefore alightweight effect, if cast iron is usedinstead of steel.

Figure 10: The large range of dimensionsand the various cored bar sections meanthat all sorts of different components canbe manufactured with a minimum of ma-chining. (Picture: TASSO, Odense (DK))

3.1 Grey iron (GJL)Grey iron (GJL) is a traditional materialthat remains very successful today: globalannual production of grey iron is morethan all the other cast materials com-bined. Its cost effectiveness in terms ofmaterial, manufacturing, operating anddisposal costs continues to be excellent.Attention can be drawn to its goodmechanical, physical and technologicalproperties, not to mention its good cast-ing characteristics.

According to EN 1561, grey iron is a iron-carbon cast material in which the freecarbon is largely present in the form oflamellar or flake graphite. The materialdesignation is GJL (EN 1560). For sandcasting the above standard offers ma-terial grades with tensile strength of 100 -350 N/mm2 and Brinell hardness of 155 -265 units.

The graphite flakes form a cohesivestructure of foliaceous components in aeutectic cell (figure 11). The arrangementof the graphite flakes can vary. It dependson the chemical composition of the castiron, the cooling conditions and, to a largedegree, also the nucleation behaviour ofthe molten metal, which can be stronglyinfluenced by inoculation. With the rightcomposition and inoculation to suit thecasting process, flake graphite with aregular arrangement as per type A of thestandard structure series (EN ISO 945)is produced. Depending on the process,not only A-graphite, but also B-graphite,is produced in continuous cast iron.

The mechanical properties of grey ironare largely determined by the quantity

The machinability of cast iron materialsis better than that of steels. Higher cuttingspeeds and bigger advances or longertool lives are possible with cast iron. Thegraphite crystals in the cast iron act asboth chip breaker and lubricant. The formand quantity of the graphite are of sub-sidiary importance. More important is thenature of the metallic matrix. Ferritictypes are easier to machine than pearlitictypes.

Cast iron materials are very suitable forgliding and rolling wear, that is to say theabrasion stress that occurs when ma-chine elements move against each other.The graphite crystals provide additionallubrication. The wrenching of graphitecrystals from the skin leaves small„pockets“, in which lubricant collects. Thisproduces good anti-seizure perfor-mance. Of the normal types, varieties ofcast iron with a pearlitic matrix offer thebest wear resistance relatively speaking.Wear resistance can be greatly increasedby means of surface hardening, thermo-chemical treatment or isothermal aus-tenite transformation.

The arguments in favour of ecologicallysensible and therefore sustainable pro-duction are gaining ground. Cast ironmaterials are made from cast iron scrap,steel scrap and pig iron. In Germany in2003 the proportion of pig iron, whichtakes a great deal of energy to manu-facture, was 8.7 % of the total quantity ofthe aforementioned materials to beused. This means that more than 90 %of these metallic materials come fromthe secondary cycle.

Cast iron materials are therefore se-condary materials and continuous castiron is a secondary product. As materials,cast irons are virtually unbeatable fromthis point of view. They are also eco-logically compatible to manufacture anduse. They can be recycled in their entirety,with virtually nothing being left over. Therecycling rate has been very high formany years and can scarcely be improvedon. Production and product waste havealways gone back into the material cycle.Recycling does not mean a reduction inquality – that is to say, there is no down-cycling. But an improvement in quality,upcycling, is not a problem. It is possible,for example, to make grey iron withtenacity of 200 or 250 N/mm2 from scrapgrey iron with tenacity of 150 N/mm2.

-

Figure 11: Three-dimensional structureof lamellar graphite [13]

Figure 12: Using bars that have beenrough-machined to his specification at thefoundry (top), the customer can manu-facture end-products quickly and eco-nomically (bottom). (Picture: K. Vollrath,Rees)

and type of the graphite flakes. Thenature of the essentially steel-like metal-lic matrix has only a limited impact.The graphite flakes weaken the bearingcross-section and cause stress concen-tration at the flake tips, which act likeinternal notches. These two circum-stances are the reason for the relativelylow strength values and low plasticity.

The mechanical properties of grey ironare manifestly dependent on the rate ofcooling – which means for practical pur-poses the wall thickness of the casting.The dependence of mechanical proper-ties on wall thickness is described in EN1561 and must be taken into accountwhen choosing a material.

Grey iron has a high damping capacity –in other words it is able to reduce ex-ternally imposed mechanical vibrations.The mechanical vibrations decay rapidly.The decay time for a vibration in grey ironis in a ratio of 1:4.3 to that for steel.

A detailed description of the propertiesof grey iron with details of its mechanicalproperties with regard to cyclical stress,its mechanical properties at high and lowtemperatures, its mechanical fracturingproperties, its physical properties (den-sity, coefficient of linear thermal expan-sion, thermal conductivity, specific ther-mal capacity, coercive field strength,hysteresis loss, specific electrical re-sistance) and its tribological properties(friction and wear) can be found in [3].

iron the elongation at rupture of the gradeof cast iron used was an order ofmagnitude smaller than that of the gradeof steel (3 % as against 20 %). Todaymore than 90 % of all cars and vans haveSG iron crankshafts that display perfectlyadequate fatigue limits for flexion andtorsion.

Elongation describes deformation (e. g.malleability) as a first approximation andso is a processing property rather than ausage property. Since cast parts areclose to their final contours after solidi-fying and cooling, no forming process isnecessary. Approximately 90 % of thefractures in machine elements are endur-ance fractures resulting from materialfatigue. The residual fracture in suchcases is always a brittle failure, evenin steels with very high elongation atrupture.

The fatigue limits (fatigue strength underreversed bending stresses) for an un-notched sample is in the 180 - 320 N/mm2

range for SG iron, including austem-pered ductile cast iron. SG iron is lessnotch sensitive than steel. As regardsdamping capacity for mechanical vi-brations, the values for SG iron comebetween steel and grey iron. The ad-vantages of SG iron over steel aresummarised in table 2.

Information on further static mechanicalproperties, fatigue limit, properties athigh and low temperatures, machining,welding and wear behaviour can befound in [5].

Figure 13: Three-dimensional structureof spheroidal graphite [13]

3.2 SG iron (GJS)There has been industrial production ofcastings made from SG iron for 60 years.Compared with grey iron, SG iron is arelatively „recent“ material. Graphitespheres were observed in cast iron forthe first time ever in the foundrydepartment of the Aachen University ofTechnology in 1937. At around the sametime the British Cast Iron ResearchInstitute succeeded in manufacturingSG iron by adding cerium to the molteniron. But it was not until InternationalNickel Inc. in the USA discovered that SGiron could be made by adding a nickel-magnesium master alloy that thefoundations for the industrial productionof this group of materials were laid. Andso began the triumphal procession of thesteel-like SG iron. In the years thatfollowed, SG iron was substituted forsteel and cast steel with greatcommercial success on numerous occa-sions. This substitution process is stillgoing on.

According to EN 1563 and EN 1564 SGiron is an iron-carbon material in whichthe free carbon is largely present inspheroidal form (spheroidal graphite) asper forms V and VI in EN ISO 945 (figure13). The material designation is GJS (EN1569). The European standards lay downthe following mechanical properties forsand casting:

- Normal grades: tensile strength 350 -900 N/mm2, 0.2 % permanent elon-gation limit 220 - 600 N/mm2, elonga-tion at rupture 2 - 22 %, Brinell hard-ness 130 - 330 units.

- High-tenacity grades: tensile strength800 - 1400 N/mm2, 0.2 % permanentelongation limit 500 - 1000 N/mm2,elongation at rupture 1 - 8 %, Brinellhardness 130 - 330 units.

In EN 1564 the high-tenacity grades aredesignated as austempered ductile castiron or ADI.

The presence of graphite spheres in asteel-like metallic matrix does away withthe internal notch effect described above,minimising interruption of the metallicmatrix. As with steel, the properties of themetallic matrix are shown to fulladvantage. The yield point/tensilestrength ratio of SG iron is usually better

than that of steels. For steel this ratio is0.44 - 0.53, whereas for SG iron it is 0.6 -0.7. SG iron has been used in placeof steel (cast steel, forged steel, rolledsteel) to great commercial advantage formore than 60 years and this trend iscontinuing.

With steel the elongation at rupture forcomparable strength is greater than forSG iron. However, that is no disadvan-tage for these grades of cast iron, ashas been demonstrated in numerousinstances. An example from the past hasbeen cited in this connection: the carcrankshaft. The changeover from forgedsteel to SG iron for these crankshaftsstarted in the sixties. For the same ten-sile strength and yield point (permanentelongation limit) in forged steel and SG

Table 2: The advantages of SG iron over steel

Its strength (tensile strength, permanent elongation limit) extends well intothe range offered by steel.Its yield point/tensile strength ratio is better than for steel.Its smaller elongation at rupture (reduction in area at breaking) is not adisadvantage.Its hardness satisfies many requirements.Its fatigue limits extend well into the range offered by steel.Its density is about 10% lower.Its strength/weight ratio is higher.Lightweight construction is possible with cast iron.Its damping capacity for mechanical vibrations is better.It offers better machinability.It has good tribological properties.It can be almost completely recycled.Cast iron is a recycled material – cast iron parts are recycling products.There is no downcycling, but upcycling is always possible.Less energy is used for smelting.Cast iron is non-toxic.The use of cast iron instead of steel results in cost savings.

4 Continuous cast ironVarious peculiarities have to be taken intoaccount for continuous cast iron asopposed to sand casting. They aredescribed in detail below.

4.1 Mechanical properties ofcontinuous cast iron

The mechanical properties of grey iron(GJL) and SG iron (GJS) can be orderedin accordance with the Europeanstandards (EN 1561, EN 1563 and EN1564 for sand casting) on the basis ofeither tensile strength or hardness(Brinell hardness) as the characteristicproperty. The manufacturing processesfor the individual grades of cast iron, theirchemical composition, the type of cast

Figure 14: Microstructure of continuous cast alloys (pictures: Gontermann-Peipers, Siegen (D))a) GJL-150C b) GJL-250C c) GJL-300Cd) GJS-400-15C e) GJS-500-7C f) GJS-600-3C

a) b) c)

d) e) f)

treatment and the heat treatmentmethod are at the manufacturer’sdiscretion unless the customer specifiesotherwise.

Table 3 shows chemical analyses forcontinuous cast iron for informationpurposes. These analysis values are inno way binding, however, as there iscurrently no national standard, no Euro-pean standard (EN) and no internationalstandard (ISO) for continuous cast iron.The foundries that supply continuouscast iron set out the mechanical prop-erties of their products in brochures. Themetallic matrix can be made ferritic,ferritic-pearlitic and pearlitic (figure 14).

The standardisation of grey and SG ironhas long contained a number of spec-ifications that are also reflected in

the European standards (EN 1561, EN1563 and EN 1564). In order to describethe mechanical properties of continuouscast iron, which differ from those for sandcast iron, however, depending on theprocess used, traditional specificationsare adopted on the basis of the Europeanstandards for sand cast iron and adap-ted to the process-related peculiaritiesas

- The grades of continuous cast ironare identified in accordance with EN1560.

- For SG iron the graphite structuremust predominantly correspond toforms V and VI as per EN ISO 945.

- The manufacturing processes forgrey and SG iron, cast treatment, chem-ical composition and heat treatment

In the case of SG iron this high rate ofcooling in the skin leads to a clearincrease in the sphere count comparedwith the centre of a cast iron strand (figure17). Y. S. Lerner [14] gives the distributionof the sphere count over the cross-sectionfor a continuous cast round bar of SGiron with a diameter of 110 mm (figure18). The sphere count of 450/mm2 nearthe surface declines towards the centreof the bar. It achieves a value of 115/mm2

at a distance of approximately 30 mmfrom the surface and remains constantto the centre of the strand.

are at the manufacturer’s discretion.Chemical analyses for grey and SGiron are given in table 4, but they arenot standardised and therefore notbinding.

- The grades of cast iron can be or-dered on the basis of both tensilestrength and hardness as the charac-teristic property.

- The mechanical properties are clas-sified according to the controlling wallthickness. The controlling wall thick-ness is twice the modulus or ratio ofvolume to surface area. To provide asimplified overview, the mechanicalproperties for continuous cast iron arealso specified as a function of dia-meter in the case of round bars.

- There are traditionally three sam-pling variants:

• separately cast test pieces (designa-tion S),

• attached test pieces (designation U), • test pieces removed from casting

(designation C).

These designations are defined in EN1560. Separately cast test pieces arenot used for continuous cast iron inpractice. Attached test pieces are notpossible owing to the process used.In the case of continuous cast iron,therefore, the test pieces are removedfrom the strand and the expected val-ues in the casting (strand) taken con-sistently as the basis for the mechan-ical properties.

- The specifications in EN 1561, EN1563 and EN 1564 apply to tensiletesting, hardness testing and repeattesting.

Figure 15: Position of test pieces for con-tinuous cast iron

Table 3: Chemical composition of continuous cast iron, reference values

Chemicalelement

CSiMnPSCrCuNiMg

Grey ironGJL [%]

2.80 – 3.702.25 – 3.990.40 – 1.000.08 – 0.25

> 0.030.05 – 0.500.05 – 0.600.05 – 0.80

SG ironGJS [%]

3.00 – 3.852.00 – 3.000.10 – 0.80

< 0.04< 0.01< 0.01

0.05 – 1.200.05 – 1.00

0.025 – 0.080

Extensive statistical analyses have beencarried out by the four firms involved witha view to laying down real values for themechanical properties of continuous castiron (see appendix). The results of thesestatistical analyses showed that theaforementioned expected values werethe minimum values for tensile strengthor Brinell hardness.

The mechanical properties for contin-uous cast iron are set out in tables 4 to7. In the case of grey iron, four grades ofcast iron covering a tensile strengthrange of 80 to 220 N/mm2 are offered.Brinell hardness is in the 110 - 290 unitsrange. In the case of SG iron the fourgrades offered cover a tensile strength

range of 370 to 600 N/mm2. The tensilestrength, permanent elongation limit,elongation at rupture and hardness aredependent on the strand diameter orcontrolling wall thickness. This sensitivityof the mechanical properties to wallthickness is much more pronounced forgrey iron than for SG iron.

Table 8 sets out the existing continuouscast iron materials of the four firmsinvolved (trade names, registered trade-marks) for the aforementioned gradesof cast iron with the material designationsbrought into line with European stan-dardisation. This means that customersknow where they stand, the existingnames that are familiar on the marketare not lost and the manufacturers’rights are protected. Figure 15 shows theposition of the test pieces taken from thestrand for round, square and rectangularcross-sections.

Process-related peculiarities occur inthe skin of grey iron. A very high rate ofcooling occurs during solidification of theskin owing to the influence of the water-cooled, open-ended die. This producesgrey iron with graphite structure type Dand also some type E as per EN ISO945. This very feathery, interdendriticallystructured graphite gives rise to acompletely ferritic metallic matrix as aresult of very short diffusion paths (figure16). The thickness of the skin withgraphite structure type D and type E isdependent on strand diameter and isgreater than 25 % for 25 to 50 mm,approximately 15 % for >50 to 200 mmand approximately 10 % for >200 to350 mm. The data for the thickness ofthis skin are not binding, but for in-formation purposes only. Free carbidesare also present in this skin.

Brinellhardness

[units]

110 - 180

140 - 210

170 - 240

220 - 290

Table 5: Continuous cast iron, GJS, characteristic property: tensile strength

grey and SG iron. Figures 19 and 20illustrate the machining allowances andstraightness.

4.2 Machining allowances,straightness

For the manufacture of static cast ironusing sand casting processes thegeneral tolerances and machiningallowances have been standardised asa function of linear size for grey and SGiron (compare DIN 1685-1 and DIN ISO8062). As things stand, there is no suchstandardisation for continuous cast iron.The firms involved in this project haveproposed the values contained in tables

C – test piece taken from casting (DIN EN 1560)

1 Depending on the process, these material grades contain small quantities of free carbides, whichcan be removed by heat treatment.C – test piece taken from casting (DIN EN 1560)

Table 6: Continuous cast iron, GJL, charac-teristic property: hardness

Stranddiameter

[mm]

30 - > 60 60 - > 200200 - > 370

30 - > 60 60 - > 200200 - > 400

30 - > 60 60 - > 200200 - > 400

30 - > 60 60 - > 200200 - > 400

Controllingwall thickness

[mm]

15 - > 30 30 - > 100100 - > 200

15 - > 30 30 - > 100100 - > 200

15 - > 30 30 - > 100100 - > 200

15 - > 30 30 - > 100100 - > 200

GJS-500-7C, pearlitic-ferritic

GJS-600-3C, predominantly pearlitic

Tensile strengthmin.

[N/mm²]

400 390 370

400390370

500450420

600550550

Permanentelongation limit

min. [N/mm2]

250250240

250250240

320300290

360340340

GJS-400-15C, ferritic, annealed

GJS-400-7C, ferritic-pearlitic1

Elongationat rupturemin. [%]

181512

7711

775

311

Stranddiameter

[mm]

30 - > 60 60 - > 200200 - > 370

30 - > 60 60 - > 200200 - > 400

30 - > 60 60 - > 200200 - > 400

30 - > 60 60 - > 200200 - > 400

Table 7: Continuous cast iron: GJS, charac-teristic property: hardness

GJS-HB245, predominantly pearlitic

GJS-HB155C, ferritic, annealed

GJS-HB160C, ferritic-pearlitic

GJS-HB205C, pearlitic-ferritic

Controllingwall thickness

[mm]

15 - > 30 30 - > 100100 - > 200

15 - > 30 30 - > 100100 - > 200

15 - > 30 30 - > 100 100 - > 200

15 - > 30 30 - > 100100 - > 200

C – test piece taken from casting (DIN EN 1560)

Brinellhardness

[units]

130 - 180

130 - 190

170 - 240

200 - 290

GJL-150C ACO Eurobar® GG-F CONTIFONTE® CF 15 TASSO GG-F-BlackGJL-200C CONTIFONTE® CF 20 TASSO GG-FFP-GreenGJL-250C ACO Eurobar® GG-FP CONTIFONTE® CF 25 TASSO GG-FP-RedGJL-300C ACO Eurobar® GG-P CONTIFONTE® CFP TASSO GG-P-Yellow

GJS-400-15C ACO Eurobar® GGG-40 CONTIFONTE® CFS 40 TASSO GJS-400-15GJS-400-7C ACO Eurobar® GGG-40/50GJS-500-7C ACO Eurobar® GGG-50 CONTIFONTE® CFS 50 TASSO GJS-500-7GJS-600-3C ACO Eurobar® GGG-60 CONTIFONTE® CFS 60 TASSO GJS-600-3

Table 8: Grades of continuous cast iron with trade names

Grey iron

SG iron

9 and 10 for the machining tolerancesand straightness of the strand lengthsas a function of strand dimensions for

Stranddiameter

[mm]

30 - > 40 40 - > 160160 - > 300

30 - > 40 40 - > 160160 - > 300

30 - > 40 40 - > 160160 - > 300

30 - > 40 40 - > 160160 - > 300

Table 4: Continuous cast iron, GJL, characteristic property: tensile strength

Controllingwall thickness

[mm]

15 - > 2020 - > 8080 - > 150

15 - > 2020 - > 8080 - > 150

15 - > 2020 - > 8080 - > 150

15 - > 2020 - > 8080 - > 100

GJL-250C, ferritic-pearlitic

GJL-300C, predominantly pearlitic

Tensile strengthApproximate value

min. [N/mm²]

110 95 80

155130115

195170155

220200185

GJL-150C, ferritic, annealed

GJL-200C, predominantly ferritic

Controllingwall thickness

[mm]

15 - > 2020 - > 8080 - > 150

15 - > 2020 - > 8080 - > 150

15 - > 2020 - > 8080 - > 150

15 - > 2020 - > 8080 - > 150

GJL-HB255C, predominantly pearlitic

GJL-HB145C, ferritic, annealed

GJL-HB175C, predominantly ferritic

GJL-HB205C, ferritic-pearlitic

Stranddiameter

[mm]

30 - > 40 40 - > 160160 - > 300

30 - > 40 40 - > 160160 - > 300

30 - > 40 40 - > 160160 - > 300

30 - > 40 40 - > 160160 - > 300

C – test piece taken from casting (DIN EN 1560)

-

a) b)

5 Heat treatment ofcast iron

The heat treatment of metallic materialsdivides into

- thermal treatment- thermochemical treatment- thermomechanical treatment

The properties of cast iron can be posi-tively influenced to a large extent usingthermal and thermochemical heattreatment. Thermomechanical treat-ments are not relevant in the case of castiron because, apart from surface re-forming, reforming is not part of the man-ufacturing sequence.

The structural transformations possiblewith heat treatment, and the resultingchanges in properties, are more ex-tensive and varied with cast ironmaterials than with steel. The highersilicon content of 2.0 to 3.5 % that isalways present in the unalloyed mate-rials, for example, means that the eutec-toid temperature in the Fe-C diagrambecomes a eutectoid area in the Fe-C-Sidiagram. There is, of course, an „internal“carbon source in the form of the graphitecrystals, which means that the austenitecan always be carburised until saturatedwith carbon. As with solidification, thesilicon content delays the formation ofiron carbides. The interactions betweenthe stable and metastable Fe-C-Si canalso be put to good use.

Figure 17: Sphere count for continuous cast GJS (picture: ACO Guss, Kaiserslautern(D)) a) - in rim area b) - in centre

5.1 Thermal treatments

Fundamental changes in microstructureand consequently in properties can beachieved using thermal heat treatment.Figure 21 shows the temperature-timesequences of important heat treatmentvariants in the form of a schematicdiagram.

5.1.1 Stress-relief annealing

It is not practically possible to manu-facture a cast product without internalstresses owing to the different rates ofcooling within the product. The size anddirection of these internal stresses aredependent on the geometry of the cast

components, their design and theprocess conditions during casting.Stress-relief annealing is a heat treatmentthat is used specifically to reduce internalstresses. The annealing temperaturesof between 500 and 550 °C are belowthe area of eutectoid transformation, soan unwanted change in structure andtherefore a change in the mechanicalproperties during the annealing processis avoided. To prevent new internalstresses developing during stress-relief annealing as a result of heating andcooling, rates of heating of between 10and 50 K/h and rates of cooling ofbetween 25 and 35 K/h up to at least300 °C must be ensured. Stress-reliefannealing is only used on continuouscast iron in special cases.

a) b) c)

Figure 16: Microstructure of GJL in rim area (picture: Gontermann-Peipers, Siegen)a) fine D-graphite, outside b) transition from D- to E-graphite c) predominantly E-graphite inside

5.1.2 Soft annealing athigh temperature

If cast parts that have solidified to greycast iron are to display their typicalmechanical properties, they must not asa rule have any structure content that hassolidified to white cast iron. If there is anycontent of eutectic (ledeburitic) carbidesor even primary carbides during castingand solidification, an annealing tem-perature well in excess of the eutectoidinterval between 900 and 950 °C mustbe chosen in order to remove it. The rateof cooling is chosen on the basis ofwhether a pearlitic or ferritic basicstructure is wanted.

5.1.3 Soft annealing atlow temperature

This heat treatment is used to turn pear-lite into ferrite. Whereas the soft an-nealing of steel only coalesces lamellarpearlite into granular pearlite, the softannealing of cast iron results in a com-pletely ferritic basic structure without anyeutectic iron carbide content. The an-nealing temperature in this case is justbelow the eutectoid interval at around700 °C. The rate of cooling is 50 K/h. Inthe manufacture of the GJL-150C andGJS-400-15C grades of continuous castiron heat treatment generally forms partof the manufacturing chain in the foundry.

5.1.4 Two-stage soft annealingIf SG iron has to satisfy the highest tenac-ity requirements, the necessary prop-erties can only be achieved in unalloyed

Figure 18: Variation in sphere count overthe cross-section of a strand for GJS [14]

Table 9: Machining allowances for continuous cast iron

Figure 20: Straightness

Figure 19: Machining allowance for continuous cast iron

Key, left: do – maximum machined diameter on finished partz – machining allowancedR – theoretical diameter of unmachined part DR = d0 + z

Key, centre: a0 – maximum machined edge length on finished partz – machining allowanceaR – theoretical edge length of unmachined part aR = a0 + 2z

Key, right: b0, s0 – maximum machined width/thickness on finished partz – machining allowancebR, sR – theoretical width/thickness of unmachined partbR = b0 + z, sR = s0 + z

grades by means of two-stage heattreatment. This consists of austenising at850 - 920 °C, followed by furnace or aircooling and then holding (5 to 10 h) at theeutectoid interval between 650 and 740 °C.Quenching is followed by tempering in acoolant.

5.1.5 Isothermal annealing

Isothermal annealing aims to set a com-pletely or partially pearlitic structure with aview to achieving certain strength prop-erties or homogenising the structurein different wall thickness areas. Thisprocess is also called normalisationbased on the heat treatment of steel. In iso-thermal annealing the component is heatedto temperatures between 900 and 920°C,reaching the austenite region above the

eutectoid interval. Then acceleratedcooling is carried out in order to sup-press ferrite formation. Depending onthe component size, the optimum rateof cooling is achieved using still air orwater spray. This heat treatment variantis also used in the foundry’s manufac-turing chain for continuous cast iron.

5.1.6 Hardening

As an iron-carbon-silicon material, castiron can be hardened just like steel. Thehardening of cast iron is either aimedat forming a wear-resistant skin (sur-face hardening) or used as the firststage of the combined hardening andtempering process. It gives the cast ironhigh hardness values of 45 to 60 HRCand therefore high wear resistance.

SG ironGJS

654

Table 10: Straightness (deviation from straight line) for continuous cast iron

Size[mm]

30 – 100> 100 – 200> 200 – 440

unannealed

433

Deviation from straight line [mm/1000 mm]

Grey ironGJL

annealed

654

Format

Round bars

Square bars

Strand size[mm]

30 – 100> 100 – 200> 200 – 440

40 – 60> 60 – 150> 150 – 200> 200 – 300

Grey ironGJL

81216

8101216

Machining allowance z [mm]

SG ironGJS

101418

10121618

With hardening, the component is heatedabove the eutectoid interval at tem-peratures of 850 - 950 °C. During aus-tenising the austenite is carburised untilsaturated. The sources of carbon for thisare the eutectoid carbide of the pearliteand the graphite crystals. The rapidcooling (quenching) that follows preventsthe formation of ferrite or pearlite andleads to transformation into martensiteand residual austenite. The high rates ofcooling required are achieved by immers-ing the component in oil, emulsions orwater. Hardening the entire volume of thecomponent is the first stage in thecombined hardening and temperingprocess.

Using special technologies, it is alsopossible to harden just a thin skin on thecomponent in order to improve wearresistance. With this surface hardeningthe skin is heated to a temperature in theaustenite region with a flame, inductioncurrent or laser and quenched rapidly.

Figure 21: Heat treatment variantsKey: Red – furnace cooling, Blue – air cooling, Black – quenching in oil

Figure 22: Cast iron gear wheels and gear rims are typical end-products of continuous casting that stand out for their high, uniformhardness and good machinability. (Picture: Contifonte, Saverne (F))

Figure 23: The fine, compact structure of continuous cast iron isideal for manufacturing pressure- and gas-tight hydrauliccomponents. (Picture: Contifonte, Saverne (F))

Laser remelting is a special processused to change the skin with the aim ofimproving wear or corrosion resistance.To do this, the skin is melted with the laser.Owing to the high thermal conductivity ofthe material below the skin, solidificationtakes place at a high rate of cooling. Inthe case of cast iron this produces a veryhard skin that has solidified to white castiron. Using this remelting technology, it isalso possible to add alloying elements tothe molten metal in order to achievespecial properties in the skin.

5.1.7 Combined hardening andtempering

In this process hardening is followed bytempering (reheating). The temperingresults in further optimisation of prop-erties. In the case of SG ironcombined hardening and tempering canbe used to achieve mechanical prop-erties similar to those for heat-treatablesteels, but plasticity and tenacity remain

below the values achievable for thesteels. Tempering dismantles the quench-ing structure produced by hardening(martensite and residual austenite).Depending on the properties to beachieved, the tempering temperature isbetween 150 and 650 °C. As the tem-pering temperature goes up, the tensilestrength, 0.2 % permanent elongationlimit and hardness decline, while elon-gation at rupture and notched-bar impactstrength increase. Several temperingstages are passed through before thehigher tempering temperatures arereached and, unlike with steels, can resultin a carbide-free state in the case ofcast iron owing to the silicon content.

Tempering at high temperatures alsocauses secondary graphite to form in aferritic basic structure.

Combined hardening and temperingcan be a good way of improving thestrength values of SG iron in manycases. It does not produce very good val-ues for plasticity and tenacity, however.

Figure 24: Nitriding curve (as per DIN50190)

5.1.8 Isothermal austenitetransformation

Isothermal austenite transformation attemperatures below the pearlite stageand above the martensite stage isotherwise known as austempering (DIN17014). In the case of cast iron this treat-ment with complete bainitic transfor-mation did not produce particularly goodproperties. However, a special heattreatment variant with incomplete iso-thermal austenite transformation hascome about in this area and offers anexcellent combination of mechanicalproperties.

In isothermal austenite transformationthe cast iron is first completely aus-tenised at 875-920 °C. If the cast ironparts are then quickly transferred to a saltbath at a temperature of between 300and 400 °C, austenite transformationcommences with the formation of ferriteneedles and saturation of the remainingaustenite content with carbon, whichleads to stabilisation of this residualaustenite. Carbide formation does nothappen and austenite transformationvirtually stops. This is incomplete iso-thermal austenite transformation. Oncethe cast iron has cooled to room tempera-ture, it has a basic structure of needleferrite and a high residual austenitecontent of up to 40 %.

Isothermal austenite transformation hasgained in importance for SG iron. In thecase of parts manufacture it leads to highstrength values combined with favour-able values for plasticity and tenacity [6to 8]. This means that it can be substi-tuted for heat-treatable steels.

5.2 Thermochemicaltreatments

Thermochemical treatments are heattreatments in which the chemicalcomposition of a material is deliberatelychanged by diffusing one or more ele-ments in or out. These thermochemicaltreatments include nitriding, aluminising,siliconising, boronising and chromising,which produce positive changes in prop-erties in cast iron as well as steel.

5.2.1 NitridingNitriding is a thermochemical treatmentthat produces the diffusion saturation ofthe surface layer of a grade of steel orcast iron with nitrogen by heating in asuitable medium. The purpose of nitrid-ing is to enhance the hardness, wearresistance, fatigue strength and also the

corrosion resistance of a workpiecethrough the absorption of nitrogen into thesurface.

The processes involved in nitriding arebased on the iron-nitrogen phase dia-gram. In the case of nitriding below theeutectoid temperature the α mixed crystalis saturated with nitrogen first. Then thenitride Fe4N (γ-phase) forms. Once it hasbeen saturated, the nitride Fe2N forms asa further phase, known as the ε-phase.The outcome of the prolonged operationof atomic nitrogen on the surface of a steelor cast iron component is the formationof the follow layers from the skin to thecore: ε-phase, γ-phase, α mixed crystal. Ifthe nitrided component is slowly cooledto room temperature, the nitrogen solu-bility of the ε- and α-phases declines andthe γ-phase is eliminated from theselayers.

5.2.2 Nitriding and otheralloying elements

If iron materials are nitrided with alloyingelements that form special nitrides, thestructure of the nitride layer is more com-plicated. Alloying elements, such as Cr,Al, Mo or V, that have a great affinity withnitrogen form very hard special nitrides.Cast iron always has higher silicon con-tents, which lead to an increase in hard-ness, with this being ascribed to thepresence of aluminium in the ferrosiliconused.

A distinction is made between the com-pound layer and the diffusion zone in anitrided component. The hardness char-acteristic from the surface to the core ofthe nitrided component is shown in figure24. This characteristic, which showshardness as a function of the distancefrom the surface, is used to determinethe effective case depth after nitriding. Theeffective case depth after nitriding is thevertical distance from the surface of anitrided workpiece to the point at whichthe hardness corresponds to a limit valuethat has been set for the purpose. Thelimit value within the meaning of thisstandard is the hardness number, which

is referred to as the limit hardness. Thelimit hardness refers to the state specifiedin the manufacturing documentation forthe nitrided component. The limit hard-ness should be defined as Vickers hard-ness HV:

Limit hardness = (actual core hardness + 50)HV (1) (rounded to 10 HV)

The hardness HV0.5 measured at approxi-mately three times the effective casedepth after hardening should be used asthe core hardness. The limit hardness isgenerally specified as Vickers hardnessHV0.5.

5.2.3 The nitriding process

Nitriding is carried out in salt baths or thegas phase. Bath nitriding is done in cya-nide baths and is really carbonitridingbecause of the carburisation that takesplace at the same time. The salt bathsused consist of either sodium cyanide orcalcium cyanide with chlorides added insmall quantities.

Gas nitriding is based on the use of am-monia, which dissociates thermally at thetemperatures of between 500 and 560 °Cthat are used. This makes the necessaryatomic nitrogen available at the surface ofthe component. The degree of dissocia-tion for the ammonia depends on thepressure and temperature in the nitridingfurnace. Nitriding takes a relatively longtime. For a normal nitriding steel and anitriding depth of 0.6 mm it takes 100hours, for example. The nitriding time canbe reduced by using glow dischargesand adding oxidising gases (particularlyoxygen for the ammonia).

In this case SG was nitrided in the flow ofammonia gas. The relevant hardness gra-dient curves are shown in figure 25 formaterial grade GJS-400-15C. A nitridingtemperature of 510 °C and nitriding timeof 36 hours produced an effective casedepth after hardening of 0.2 mm (curve a),while a nitriding temperature of 580°C anda nitriding time of 5 hours produced aneffective case depth after hardening of0.1 mm (curve b).

These investigations show that SG ironcan be successfully nitrided in the sameway as steel. Gas nitriding was used for agear rim made of SG iron in grade GJS-400-15C (figure 26). This gear rim hasthe following characteristics: module 3.5,20 teeth, base circle 63 mm, 44 units mini-mum hardness on nitrided tooth profiles(effective case depth after hardening 400HV0.1), inside and outside diameter plussides ground after nitriding. The nitridedgear rim satisfied all the requirements infull, just like a steel gear rim.

Figure 26: Gear rim (picture: Bucher Maschinen-bau, Klettgau (D))

Figure 25: Nitriding curve for GJS-400-15C (picture: Carl Gommann, Rem-scheid-Hasten)

8 Use of continuouscast iron

Unlike static cast iron, where use isunequivocally fixed by the manufactureof cast parts that are close to final dimen-sions, continuous cast iron is a semi-finished cast product that can be usedfor all sorts of applications. Continuouscast iron is therefore extremely versatile.It can be used to manufacture a widevariety of components for every branch ofindustry.

Important areas of application are il-lustrated by figures 8, 10, 12, 22, 23 and27, for example. These pictures dem-onstrate the diversity of possible uses.

9 Concluding remarksAn ad hoc working party under the Ger-man Foundry Association (DGV) in Düs-seldorf has assessed and described thecurrent manufacturing status of contin-uous cast grey and SG iron. This alsorepresents a first attempt with a view tofuture standardisation.

The firms involved are thanked for theirexpert and constructive cooperation.Thanks go to the following individuals inparticular: Dipl.-Ing. Klaus Reif (leaderof ad hoc working party (DK)), MarcoAntes and Dipl.-Ing. Wolfgang Giese(ACO guss (D)), Dipl.-Ing. ChristopheAncel, Bernard Linder, Dipl.-Ing. HansSattel and Dipl.-Ing. Franck Kootz(Contifonte (F)), Dipl.-Ing. Klaus Beute(Gontermann-Peipers (D)) and Dipl.-Ing.Henrik Elmkvist (TASSO (DK)).

-

Literature

[1] ACO Eurobar® - ein Qualitätsstranggussaus Gusseisen. konstruieren + giessen29 (2004) H. 2, pp. 41 - 42.

[2] Vollrath, K.: Hydraulikguss –Zusatznutzendurch Dienstleistungen nach Maß. kons-truieren + giessen 29 (2004) H. 3, pp. 25 -26.

[3] Werning, H., u. a.: Gusseisen mit Lamel-lengraphit. konstruieren + giessen 25(2000) H. 2, pp. 1 - 82 (offprint).

[4] Steller, I.: Das neue VDG-Merkblatt W 50:Gusseisen mit Vermiculargraphit konstru-ieren + giessen 28 (2003) H. 2, pp 22 - 24.

[5] Werning, H., u. a.: Gusseisen mit Kugel-graphit. konstruieren + giessen 13 (1988)H. 1, pp. 1 - 98 (offprint).

[6] Röhrig, K.: 2. Europäische ADI-Entwick-lungskonferenz – Eigenschaften, Bauteil-entwicklung und Anwendungen. konstru-ieren + giessen 28 (2003) H. 1, pp. 2 - 14.

[7] Herfurth, K: Austenitisch-ferritischesGusseisen mit Kugelgraphit, Teil 1: Aus-tenitisierung. Giesserei-Praxis (2003) H.3, pp. 99 - 106.

[8] Herfurth, K.: Austenitisch-ferritischesGusseisen mit Kugelgraphit, Teil 2: Un-vollständige isothermische Austenitum-wandlung. Giesserei-Praxis (2003) H. 4,pp. 137 - 142.

[9] Werning, H.: Schwarzer Temperguss –Herstellung, Eigenschaften, Anwendun-gen. konstruieren + giessen 25 (2000) H.1, pp. 27 - 42.

[10] Röhrig, K.: Die neue Norm für AustenitischeGusseisen. konstruieren + giessen 28(2003) Nr. 3, pp. 31 - 32.

[11] Röhrig, K.: Austenitische Gusseisen.konstruieren + giessen 29 (2004) H. 2,pp. 2 - 33.

[12] Röhrig, K.: Verschleißbeständige weißeGusseisenwerkstoffe. konstruieren +giessen 24 (1999) H. 1 (offprint).

[13] Herfurth, K., Ketscher, N., Köhler, M.: Gies-sereitechnik kompakt - Werkstoffe, Ver-fahren, Anwendungen. Giesserei-VerlagGmbH, Düsseldorf 2003.

[14] Lerner, Y. S.: Microstructure and proper-ties of continuous cast ductile cast iron.AFS Transactions, pp. 349 - 354.

6 Coating continuous cast partsCoating is the conscious creation of ser-viceable layers on pre-treated surfaceswithout essentially changing the mac-rostructure of the components. Coatingincludes both the application of amor-phous or foil-like substances and thechemical or electrolytic application oflayers. All the numerous coating pro-cesses aim to protect componentsagainst corrosion and wear, or to achievea decorative effect.

A wide variety of coatings are also usedon cast iron, including painting, enam-elling, chromium plating and nickelplating.

7 Surface reforming(deep rolling, shotpeening)

In surface reforming only the skin of acomponent is compacted with a ball orroller tool, which is moved over a surfacewith a specific vertical force and a definedspeed, or by blasting with spherical shot(shot peening). This causes compres-sive stresses.

Such surface reforming has been suc-cessfully used on the transition radii ofcrankshaft castings made from SG iron,for example. The internal compressivestresses thus created increased com-pressive strength noticeably.

The firms involved in this articlemeasured and statistically analysedmechanical properties as a function ofstrand diameter/modulus over an ex-tended period of production.

Tensile strength and Brinell hardnesswere measured for grey iron, while tensilestrength, 0.2 % permanent elongationlimit, elongation at rupture and Brinellhardness were measured for SG iron.The familiar sensitivity of mechanicalproperties to wall thickness was alsoclearly apparent for continuous cast iron.This sensitivity is much more pronouncedfor grey iron than for SG iron.

Appendix: Statistical analysis for mechanical properties

Figure 27: Various components madefrom grey and SG iron that clearly dem-onstrate the varied use of continuouscastings. (Picture: ACO Guss, Kaisers-lautern (D))

examples of the statistical analysis arepresented in figures I and III to V formaterial grades GJL-250C and GJS-400-15C.

Figure II shows the correlation betweentensile strength and Brinell hardness forgrey iron. Based on the testing of themechanical properties of grey iron, forwhich mostly separately sand cast testpieces (round samples with a diameterof 30 mm) are used, the possible tensilestrength for a strand diameter of 30 mmwas fixed as the reference quantity forcontinuous casting. Please note in thisrespect that the tensile strength valuesare for test pieces removed from thecasting.

The data contained in tables 5 to 8 wascollated on the basis of the resultsobtained in this way. Some selected

Figure I: Tensile strength in relation to strand diameter forGJL-250C, round bars, sample position D/4

Figure II: Tensile strength in relation to hardness for GJL,tensile strength = f(hardness) for sample position D/4

Figure III: Tensile strength in relation to strand diameter forGJS-400-7C over modulus (D/4), unannealed

Figure IV: 0.2 % permanent elongation limit in relation tostrand diameter for GJS-400-7C over modulus (D/4),unannealed

Figure V: Elongation at rupture in relation to strand diameterfor GJS-400-7C over modulus (D/4), unannealed

A/S Tasso, Odense, Reg. No. 4890Hjallesegade 45, 5260 Odense SDenmarkTel: +45 6613 1313Fax: +45 6591 4022Email: mail@tasso.dkWebsite: www.tasso.dkBank: Den Danske BankA/C No. 3574 4700162001Swift code: DABADKKKODEVAT No. DK 37 85 15 15