1

(1) INTRODUCTION

The Rails account for large proportion(from 30%- 50%) of the cost of new infrastructure. .Management of this asset ,its maintenance and its renewal costs play a key role in the optimization of track maintenance cost. Rail is also the components which are directly subject to stresses and undergo direct wear by rolling stock. They are subject to loads and dynamic forces, which they transfer to the infrastructure through sleeper and ballast, amplified by the surface defects in the rail. Rail to be used for heavy hauled traffic laid with radii as low as 300 M will require to exert very high lateral forces .Therefore rail material should be such that can withstands manifold and high forces , the rails must meet the following requirements:- * High resistance to wear.

* High resistance to compression. * High resistance to fatigue. * High yield strength, tensile strength and hardness. * High resistance to brittle fracture. * Good weldability. * High degree of purity. * Good surface quality. * Evenness and observance of profile and * Low residual stress after manufacturing. * To carry desired axle load with required speed

In briefs, it should have resistance to (i) Mechanical forces (vertical, lateral load) through train action which includes during acceleration and retardation by the wheel of locomotive. (ii) Thermal forces induced by change in ambient temperature from the “neutral” or force free temperature of rail these forces are both tensile and compressive in nature depending upon the temperature is above or below the force free temperature. Bending and longitudinal stresses play an important factor in the rail designing process. Contact stresses are most important in maintenance process causes rail fatigue. (iii) Rail life is determined on the basis of wear so material should be hard for lesser wear. The defects are transverse, longitudinal, web, base, surface etc which are mainly caused by manufacturing process. These defects during manufacturing can be controlled by precise manufacturing process. (iv). Defects in service such as scabbing of rail head, fatigue rail head, corrugation of rails etc are main problem experienced in past days.

(v). It should be economical by material in respect of per meter cost.

2

(2) INDIAN RAILWAY PRESENT STATUS (i) The following are the rail section commonly used in Indian railway.

The service life of 90 UTS Rail is about 50% higher than of medium Manganese

rail having 72 UTS. 90 UTS rail have much superior wear characteristics hardness of about 270 BHN as against 220 BHN of medium manganese rail with 72 UTS. The allowable shear stresses of 90 UTS are much higher (22.5Kg/mm2) than 72 UTS rail (18.0 Kg/mm2). Due to induction of BOX N stock, there is not only higher shear stress of the order of 20.0Kg/mm2 is induced but also excessive wear of rail was noticed due to cast wheel of higher hardness of BOX N wagons. 110 UTS Rail (imported) have been laid Mumbai division of Central Railway.

(ii) Rail Chemical composition

Grade

C % Mn % Si % S % Max.

P % Max.

Al % Max.

Hydrogen contents in liquid form ppm(max.)

880 (IRS-T-12-96

0.6to 0.8

0.8 to 1.3

0.1 to 0.5

0.035 0.035 0.02 3.0

_ 1080 (IRS/T-12-88)Head hardened rail

0.72 to 0.82

0.75 to 1.05

0.05 to 0.30

0.035 max.

0.035 max.

-

Rail Section Type of section

Weight per meter in Kg

Area of Cross Section in Sq mm

Max axle load that rail can carry (Thumb Rule) 560xSectional weight of rail

Life of rail in GMT

90lbs

RBS 44.61 5895 22.5 MT These rail are not laid in now - days except old track

52 Kg/m

IRS 51.89 6615 29.12 MT 72UTS- 350GMT 90UTS-525 GMT

60Kg/m

UIC 60.34 7686 33.79 MT 90UTS -800 GMT

3

(iii) Axle Load (i) Indian railway is carrying 20.32 t axle load on most of the BG routes.

(ii) In order to enhance throughput to meet increasing traffic demands, Railway board has permitted running of BOX N wagons, loaded up to CC+6+2t (Axle load of 22.32 t) on identified 55 route in 2005

(iii) Railway board has permitted running of BOX N wagons, loaded up to

CC+8+2.(axle load of 22.82t) on identified iron ore routes (34 sections) on ER,SER,SCR , SWR, Eco R ,SECR, SR. .

(iv) 25t axle loads are to be introduced on IR during the year 2006-07 initially on two routes Dallirajahara – Bhilai, Banspani – Daitari. As per Track policy circular no2 of 2006 dtd19th July, 60 Kg 90UTS, PSC Sleeper 1660No/Km, ballast cushion 300 mm are to be provided in these routes.

Till such time, numbers of precautions monitoring mechanisms have been prescribed for these sections. Minimum track structure 52/60 Kg 72 UTS rails, sleeper density M+7 and depth of ballast cushion 250mm for running of these freight trains at maximum permissible speed of 60Kmph and on 90R rails 30 KMPH.

(iv) Need to go for heavier axle load

In view of growth national economy is expected around 8%, substantial growth in volume of railway traffic will be a challenged for Indian railway because most of the main routes are heavily saturated. IR is planning to universalize 22.82t axle load. Construction of dedicated freight corridors fit for 32.5 t axle loads , four quadrilaterals is planned with 68 Kg(90UTS or higher) Rails. Feeder route required for connecting existing route to DFC are to be for minimum 25t axle load. So there is need to improve in metallurgy of rail to carry 32.5 t axle load which in terms of having property greater resistance against rail wear caused by wheel interaction as well as longer life (GMT).

(3) Elements of Rail Metallurgy

Steel and cast irons are iron-carbon alloys. Solidified steel is composed of crystal. Each crystal structure has a cubic unit cell with atom located at all eight corners and a single atom at cube center which called body-centered cubic (BCC) crystal structure as shown in figure 1(a) . It is stable at low temperature and is called Ferrite (�-iron).

4

Figure 1(a) Figure 1(b) Another crystal structure has a unit cell with atoms located at each of

the corners and center of the entire cube surface. It is called the face centered cubic (FCC) crystal structure as shown in figure 1(b). It is stable at high temperatures and is called Austenite (� – iron)

It can be realized that steel of a fixed chemical compositions (like iron

and carbon) may have the different crystallographic structure depending upon the rate of cooling temperature which has different strength and hardness properties.

First take case of pure iron ( Fe ) to exhibit the cooling effect

.Immediately after solidification at about 1538˚ C,iron forms BCC structure (�-ferrite ) and on further cooling at 1394 to 912˚ C iron transforms to an FCC structure called (� – iron), or austenite. As cooling continue at 912˚ C iron transforms back to the BCC structure called ferrite (� –iron). The crystallographic structure of the iron and its mechanical properties depend upon its temperature. This has been shown in graph temperature versus Fe and carbide .

5

Figure 2 ( Iron – Iron carbide Phase diagram)

Ferrite Cementite

Figure-3 (a) Microstructure of pearlite

6

Figure 3(b) Scanning electron micrographs of pearlite Now consider the iron-carbon alloy of eutectoid composition that contains 0.77% C by weight. The cooling process is represented by the vertical dashed line ‘ab’ that corresponds to 0.77% C. At point ‘a’ ie. at the temperature of about 900˚C this alloy is composed entirely of �- iron (austenite) as shown in fig. As the alloy is cooled, no changes occur until the eutectoid temperature, 727˚C is reached. Upon slowly crossing this temperature, say to point ‘b’ the �- iron transforms by decomposing into � iron (ferrite) and the iron carbide (Fe3C). Fe3C is also referred to as cementite, The micro structure of the resulting steel consist of alternating layers of lamellae of the two phases, � and Fe3C, that form simultaneously during the transformation it is called pearlite . The Fe3C is extremely hard and brittle. By controlling its amount, size, and shape, the degree of dispersion strengthening and the properties of steel are controlled as indicated in figure -4. Proof stress will increase if interlamellar spacing decreases. The quantitative interrelationship is given by

Proof –stress( 0.2%)= 85.9+ 8.3 / (s) ½

Figure-4

7

Figure-5 Temperature transformation is to be governed by time; therefore time temperature

transformation curve is plotted in above fig -5. In Eutectic iron carbon alloy (0.77% C) temperature transformation is held constant throughout the duration the isothermal reaction. It contains two solid curves that are constructed from transformation time measurements as shown in above fig. One curve represents the time required to begin the transformation and the other represents the conclusion of the transformation. To the left of the ‘begin’ transformation curve only austenite is present, whereas to the right of the ‘completion ‘curve only pearlite exists. Between these curves, the austentite is in the process of transforming to pearlite and thus both micro constituents are present.

Note that both curves are nearly parallel and that they approach the eutectoid

temperature line 727˚C. At temperature just below the eutectoid, very long times are required to complete the transformation from austenite to pearlite, therefore at these

8

temperatures the reaction rate is very slow. With the decreasing temperature, that transformation rate increases. For example for the material temperature of 675˚C about 180 seconds are needed to the transformation from austenite to pearlite but at 570˚C only about 8 seconds are needed. Just below eutectoid (727˚C) temperature, relatively thick layer of both ferrite and Fe3C phases are produced. This microstructure is called coarse pearlite. With decreasing temperature the layer become progressively thinner. The thin- layered structure produced in the vicinity of 540˚ C is called fine pearlite .The fine grained pearlitic steels are tougher than the coarse-grained pearlitic steels .Also ‘the yield point and tensile strength increase ‘as distance between the lamellae decreases. Therefore the preferred way to increase tensile strength, yield strength, yield point, hardness, and toughness is to reduce the spacing between the pearlite lamellae. This can be achieved by transforming austenite at the lowest temperature, without forming bainite and martensite.

Figure-6

(i) Bainite is the transformation product in the temperature range between about 540˚ to 215˚ C. It was found that once some portion of an alloy has transformed to either pearlite or bainite .It consists of very fine microstructure of ferrite and cementite (Fe3C) phases. The transformation to other microcontituent is not possible without reheating to form austenite.

9

(ii) Martensite

When austenized iron-carbon alloy are rapidly cooled (for example critical quenching rate) to a relatively low temperature (near ambient ) a different microconstituent called martensite is formed. Martensite transformation occurs when quenching rate is enough to prevent carbon diffusion. Since this transformation does not involve diffusion, it occurs almost instantaneously. Martensite is very hard and so brittle that it cannot be used for most of the applications. Any internal stresses induced during quenching have weakening effects. The ductility and toughness of martensite may be enhanced and internal stresses relived by heat treatment known as tempering.

(4) Elements Influencing Rail Steel Desired property of rail can be obtained by (i) By adding, different chemical composition in steel alloy of rail. ie, in plain carbon

steel carbon is the prime alloying elements, other elements may be added in specific amount to improve the mechanical properties and to expedite the heat treatment process. The other alloying elements are Manganese, Silicon, Nickel, Chromium, Molybdenum and Vanadium .When the carbon content is increased the tensile strength, hardness and yield point of steel increases, however the ductility decreases. Manganese makes the steel more resistant to the abrasive forces by increasing the strength, toughness, and elasticity. Higher percentage of silicon produces denser steel. Vanadium, Chromium and Molybdenum are also effective alloys. Aluminum is required for killing the molten steel. Excess quantity of aluminum produces lamina inclusions which is very hard in nature and harmful. Alloying with copper and molybdenum rails are two times better than ordinary carbon steel rail as corrosion resistance .These alloys are very costly however an alternate micro alloying Nb, micro alloying vanadium . Chromium and copper elements makes steel of higher yield strength and UTS. Phosperous (P) is the most detrimental impurity in rail steel since it makes it brittle when cooled, thus reduces its ability to resist impact. For this reason, the phosperous content is to be kept very low. Also, the slightest amount of sulphur is considered detrimental in rail steel because of its effect on cracking during the hot rolling process. Thus great care must be taken to eliminate these impurities, as well as slag and gases.

(ii) By controlling cooling temperature of rail. - In pearlitic steel the mechanical

properties are largely governed by the distance between the cementite (Fe3C) lamellae, their thickness and by the grain size. The influence of the interlamellar spacing on the yield point, tensile strength and reduction of area depends upon isothermal reaction. These micro structures of the same steel are dependent absolutely to different cooling rates, which lead to different rate of diffusion of carbon at the austenite, pearlite growth front

10

(iii) Chemical Analysis for Standard Chemistry Rail Steel as per AREMA 2003

Chemical Analysis Weight percent

Product Analysis, Weight percent Allowance beyond limits of specified chemical analysis

Major elements

Minimum Maximum Minimum Maximum Carbon 0.74 0.84 0.04 0.04 Manganese 0.75 1.25 0.06 0.06 Phosphorus - 0.020 - 0.008 Sulphur - 0.020 - 0.008 Silicon 0.10 0.60 0.02 0.05 Trace elements

Additional trace elements may be included in the chemistry analysis when agreed upon by the purchaser and the supplier

/Nickel - 0.25 - - Chromium - 0.25 Molybdemum 0.060 Vanadium 0.010 Aluminium 0.010

Rail Hardness:-Standard rail 300BHN, High Strength Rail 370 BHN.

(iv) High wear resistance requires sufficient hardness. It has been established that for pearlitic steels rail wear decline as the tensile strength increases. Thus, a high – tensile strength is desirable mechanical rail property. (v) High yield point. This is necessary for reducing the large progressive plastic deformations that occur at, and below, the running rail surface. This includes also rail corrugations. Pearlite steels with increased tensile strength is also accompanied by an increase of yield point. (vi) Resistance to fatigue damage. For many decades, it was assumed that the lengthening service life of rails was to increase the wear resistance of steel of rail. With the recent introduction of lubrication and resulting reduction of rail head wear, however, fatigue defects caused by maximum shear stresses in upper part of the rail head and by stress concentrations near coarse nonmetallic inclusions emerged as a major rail replacement. Purity from nonmetallic inclusions must be maintained during manufacturing, especially for freight railways. Therefore, in order to avoid long term damage, a high degree of rails is desirable. The impurity level should be below ultrasonic delectability. Fatigue damage may also take place because of stress concentration near bolt holes, scratches, or sharp notches. Sharp nicks or deep scratches in any part of rail should be eliminated.

11

. Figure-7 Yield tensile ratio for different rail steel

Figure -8 Tensile v/s Fatigue

12

Tests revealed that for rail steel, an increase in tensile strength is also accompanied by an increase in fatigue strength. This is another indication why high-tensile strength is a desirable rail property. Because of the ever increasing wheel loads and train speeds, and the quest for improving further the economics associated with track maintenance, various studies are being conducted to further improve the performance of rail-in-track. (5) Rail Hardness

The hardness is related to the mechanical properties such as resistance to penetration, scratching, wears, abrasion and cutting. Process such as cold working or heat treating is often used to change the hardness of the material. Brinell Hardness Number (BHN) is the ratio of load in kgf and the area of the permanent spherical indentation in mm2 left on the surface. BHN = 3000kgf/Indentation area (mm2) In the recent past the rail manufacturers of European Countries has produced the rail with BHN up to 400. Based on the tests conducted, the correlation between hardness and tensile strength is expressed below.

Brinell hardness number (BHN) = Tensile strength/ 500 (Tensile strength in psi units)

This relation shows that the higher the tensile strength of the steel larger is the rail hardness and therefore the lower is the corresponding rail wear Tensile strength is considered an essential parameter for classifying the rails. The resistance of the rail head against wear is closely related to tensile strength of the rail steel. Under high axle load the rail wear can be kept low by using high tensile (strength) rails.

At the same time great improvement in the steel cleanliness where achieved by introducing the continuous casting process in the rail manufacture. This method significantly reduces the number of included impurities, compare to the traditional ingot steel rails. This clean premium rails offers not only much better wear resistant than a standard rail, but it also lead to reduced failures from internal defects (because these inclusions and impurities cause stress concentrations and then fatigue failures)

(i) Naturally Hard Rail-

These are naturally hardness Rail. These pearlitic rails are, named according to the crystallization condition. The rate of wear on the rail top will be approximately 0.7 to1.0 mm per 100 million tones on straight track and of 2 to3 mm in curves with radius of about 600 M.

13

(ii) Thermally treated rails Naturally hard rails is to undergo a thermal treatment to increase the strength by head hardening process .This can be done by off-line hardening ,in line hardening.

When off-line hardening is applied, the rail is heated up inductively to

temperature 850-950˚ C within 2-6 minutes. Then the head is quenched by compressed air, water spraying or fog to 650-500˚ C. The accelerated cooling is proportioned in such a way that the very fine pearlitic structure with high hardness and strength is achieved. In off-line hardening the quenching case is limited, the rail have to be straightened before and after thermal treatment.

In in-line hardening the rail is brought to the hardening plant directly out of the rolling process. Its temperature is still more than 800˚ C. The entire head is quenched in a hardening bath (water with synthetic admixtures). The cooling agent forms in a layer on the rail which reduces the cooling intensity of water. This ensures the required even cooling conditions. Immersion time is about 2.5 minutes. When the rail is cooled down to approximately 60˚ C, it is straightened and tested. The figure shows hardness gradient of head hardened rails and of the rails with natural hardness from the outer surface of the rail head inwards. Figure -9 Hardness distribution of head – hardened rails with and rails with natural hardness.

14

Figure -10

Figure-10 shows stress - strain diagram of head hardened rails and “naturally” hard rails. Nominal tension at maximum tensile force Fm is defined as tensile strength Rm.

The service life of HH rails (1200HH) is up to 7 times longer than the service life

of wear resistance rails of 900A qualities. Both the rails were tested in 300 M radius curve and no lubrication was applied between wheel rail contacts. Refer graph in figure 11.

15

Figure-11 High wear resistance

Figure 12, compare the resistance to wear of various types to the resistance of

the 200 rail type. It shows the significantly reduced wear of thermally treated rails with hardness value of 350 HB up to (ultra – high- carbon) sorts.

A long term study (three years, 90million tones) load carried out on lines of the

DB, AG compared the properties of head hardened rails under operational load with 900A & 800 rails. The development and growth of head checks, corrugation growths and

16

wear of the rails is shown in figure 13. The results show that the depth of crack is only one third of the depth which develops on rails of 900A standard quality.

The corrugations that had developed on HSD rails (after 66 million tones) had a

wavelength of 20-40 mm and average depth of 0.026 mm. The corrugation on rails of the 900A quality had a wavelength of 40-60 mm and an average depth of 0.04 mm. So the growth of corrugation on HSH rails is one third lower than that on 900A Standard quality rails.

Fig 14 shows the wear of the tested rails in both height and surface area. It proves

that the wear of the HSH rails is by 40% below the wear of 900A quality rails.

Figure-12 Increased resistance to wear of very high quality rails compared to the

quality 200

17

Figure 13 Depth of cracks on rails of different hardness

Figure-14

18

Figure-15 The principle of the so called magic wear -rate

These results combined with the findings that head checks mainly develop with the radius of 1500-2000 M, suggest using HSH rails not only for smaller radii but also for this medium range of radii. (iii) HIGH ALLOY RAILS

The disadvantage of High-alloy steels is their increase welding sensitivity and decreases the fracture toughness. To avoid the formation of undesirable structure parts causing brittleness, it is necessary to pay specials attention to the cooling down speed after welding. The minimum cooling time of the chromium-manganese steels in the range of 800-500˚ C is 220-200sec, therefore the mobile flash butt welding machines provides reheating by current pulses after shearing of the welding beads to keep the cooling down speed within the safe range. (iv) BAINITIC RAILS Since Pearlitic steels appear to approach their limit of development, a number of railway manufacturers and research organizations are focusing on improving the Bainitic and Martensitic steels.

Pearlitic rail material has a ribbon—grain structure of ferrite and cementite, with inclusions of other elements in the form of carbides and nitrides. Bainite is a multi-component structure consisting of strongly tensioned ferrite with inclusions of carbides, martensite or residual austenite as a second phase.

19

Bainitic rails (1400 quality) have also shown very good wear resistance in tests carried out on the OFOT railway. Their wear rate was eight times lower than that of standard rail qualities.

Chemical Composition Rm

Quality Mill finish Designation

C Si Mn Cr V (N/mm2)

700 Natural hardness

Standard quality

0.5 0.2 1 - - 680

900A Natural hardness

Wear-resistant quality

0.7 0.3 1 - - 860

1100 Natural hardness

0.72 0.6 1.1 0.9 0.1 1080

1200 Natural hardness

0.77 1 1.1 0.9 0.15 1180

1200HH Head-hardened

Highly wear resistant special qualities

0.77 0.3 0.9 0.1 - 1175

1400 Natural hardness

(Bainitic) 0.3 1.8 2 2-3 - 1400

Nowadays rails are frequently manufactured by continuous casting followed by immediate rolling. The tensile strength (crushing yield point) amounts to approximately 60% of the yield point. The admissible bending tensile strength is determined in a long-time test – it is 50% below tensile strength.

The grade and structure of the steel used hard grade steels and extra hard grade

steel. It is recommended that rails of 900 grade steel manufactured by the oxygen process, if possible by continuous casting, be used.

(6) The Rail profile- UIC and Others

Worldwide many different rail profiles are in use such as German section UIC section, American section, British section and some other various sections like India 52, Netherlands SA42, Denmark Form V, VII, Switzerland SBB1, South Africa SAR48, China 43, & China 50.

As regard of uniformity UIC had recommended the use of standard profiles internationally.

-UIC 54

-UIC 60

For mainly connected with fatigue strength, it is recommended that the UIC 60 profile be used on heavily-loaded and high speed lines.

20

Although the drafting group of CEN tried to reduce the number of profiles, still

21 different profiles with sections heavier than 46 kg/m are in used in Europe. According to new CEN standards, rail profiles are indicated by the mass per meter followed by the letter E and a serial number starting with 1. The old profile UIC 54 and UIC 60 are now indicated as 54 E1 and 60E1 respectively

In Europe normally rails of UIC standard grades according to UIC leaflet 860-0

were employed. in the year 2001 anew European standard for rails were introduced, referred to as EN 13674-1, which would replace the UIC leaflet. In the new standard, the rail grades are no longer indicated by the tensile strength but by the Brinell hardness. The specifications according to UIC,BS and AREA standards are listed below the table (Figure-16). The standard grades could be designated as R200 (700), R260 (900A), R260 Mn (900 B)and R320 Cr (1100) represented by the Brinell Hardness. For completeness the minimum tensile strength is indicated between brackets varying from 700-1100 N/ mm2.

Figure-16 Rail grades used in Europe and America

21

8 Finishing stands 1 9 Finishing stands 2

Figure-17 The rail manufacturing process at Thyssen

22

Blast Furnace Schematic

23

Basic Oxygen Furnace Filling Process of Converter

24

(7) RAIL MANUFACTURING PROCESS (i) The ore is found in the form of iron oxide in rocks. The ore is graded and crushed and some of the finer ore is taken to the sinter plants where it is mixed with coke and limestone and heated to form an iron- rich clicker known as sinter.

(ii) Blast furnace – This sinter is fed into the tip of the blast furnace together with more iron ore, coke and limestone in the controlled proportions and the whole is fired i.e.- 1.6% ore ,0.6 % coke. Great heat is generated and fanned to white hot intensity by blasts of super heated air. By means of this process the iron ore is reduced. The iron in the sinter and ore melts to form a pool of molten metal at the foot of the furnace being higher density and which has an air temperature of approximately 1500˚ C. The limestone combine with impurities in the iron ore, forming a liquid slag which being of lighter density, floats on top of it. Both slag and molten metal are simultaneously tapped off periodically.

(iii) Basic oxygen furnace: -Currently steel for rail is produced by basic oxygen process or by electric arc furnace process. The mixture of scrap about 30% by weight and molten pig iron that is poured into refractory lined vessel (converter) from the blast furnace. The reaction start immediately and temperature reaches to about 1536˚ C. Carbon, manganese, and silicon are oxidized which are reduced to desired levels by adding lime and fluxes. These extract impurities such as phosphorus and sulfur in the form of liquid slag floats on top being lighter than molten metal which periodically tapped and removed. During the process, various ingredients are added to ensure the desired chemistry. Blast furnace process is continuous, and often goes on for four years or more, before the heat resistance brick lining of the furnace begins to deteriorate. It takes charge of 150-350 tones or more at a time and converts it into steel in 40 minutes.

(iv) The casting of liquid steel to form either ingots or continuously cast blooms. : The furnace is tilted and molten steel is poured from the furnace into ladle. From it is then teemed into ingot molds, or allowed to flow at a controlled rate into the tundish which feeds a continuous caster. The ladle phase allows for a more precise control of the chemistry, deoxidation, desulfurization, and temperature of the liquid steel. For example, inert gas stiring is used immediately after taping molten steel from the basic oxygen or electric arc furnace to achieve uniform chemistry and temperature, and to promote cleanliness of the steel by aiding the floatation of nonmetallic inclusion into slags. Argon is generally used as the inert gas for rail steel.

(v) Rolling process. Ingots/ blooms are sent to soaking pit where they are reheated to prescribed, uniformly distributed, rolling temperature of about (1288˚ C). They are then moved to the primary rolling plant where it goes number of rolling passes to take approximate shape .In secondary rolling plant, the rolling of rails to their final form is obtained directly from the blooms or continuous casting process The rail temperature at the end of the rolling process is generally below (1038˚ C). Descaling equipment removes the mill scale , there by permitting a consistently smooth product surface before the final rolling.

25

(vi) Rail finishing:- Rails are moved cooling bed for their cooling up to (538˚ C). Next these rails are transferred to an insulated container, where they are controlled cooled to reduce hydrogen contents and to improve the strength and wear resistance of the rails (hardness) by altering the internal (crystallographic) structure of the rails steel. After the rails are removed from the control cooling container they pass one at a time, through rollers, where they are straightened vertically and laterally. This precision roller may exert forces on a rail as high as 180 tons. During straightening the rails are plastically deformed and residual stresses are introduced. Then the rails are sent to inspection bed for continuous inspection process. After sorting out the storage, shipment is done. (8) Rail surface treatment

(i) Laser hardening Laser glazing liquefies the surface of layer of the rail with the help of a high performance laser .Due to good deflection of the rail heat the surface layer solidifies immediately and forms a very hard layer with a lower coefficient of friction. The coefficient of friction between wheel and rail is reduced by up to 40%.

(ii) Plasma coating – for plasma coating an ionized gas is charged with powder which coats the rail with protective layer. This plasma coating ensures a lower frequency of lubrication and leads to lower coefficients of friction.

(iii) Laser coating – This technology has been developed by the DUROCRAIL Company, SWEDEN. A hard layer highly resistance to wear is applied to rail by using a high performance laser and by adding alloying constituents and ceramic additives. The field test has shown very high resistance to cracking, a low coefficient of friction and excellent resistance to wear, when a 24 –mm Broad layer with the name “Duroc222” was applied. The tests were carried out on the Swedish iron ore railway Malmbnan. After application hardness of the layer increased from 390HV to540 HV after an operational load of 7M-Tons.After above 18 M-Tons of track load the rail coated with the Duroc222 layer still does not show any cracks.

(iv) Rail Lubrication - Some rail roads lubricate rails to reduce wheel and rail wear and save fuel. But some experiments have also shown the occurrence of fatigue – crack formation increases significantly in lubricated rails(Steele and Reiff, 1982) .Wear is the principal life- limiting factor for rail, but as wear life is extended, many more rails stay in service long enough for fatigue cracks to form and propagate .The research studies on rail lubrication have been conducted by the AAR at the TTC, and have been empirical in nature.

(v) Rail Grinding and Wear - Some world railway grinds the rail head to maintain specific profile shapes. The intent of rail grinding is primarily to control rolling contact conditions and rail wear.

26

(9) CONCLUSION

Feasibility of advance materials for rail - Improvement in metallurgy of rail steel quality in terms fatigue, fracture, and wear resistance have been achieved conventionally by :

(i) Increasing carbon content- as carbon content increases, tensile strength is also increased. Hardness and yield point of steel increases but decreases ductility.

(ii) Adding alloy elements– Other elements of alloy are such as manganese (Mn) silicon (Si), nickel (Ni), chromium (Cr), molybdenum (Mo) and vanadium (V). Manganese makes steel more resistance to abrasive forces, increase strength, toughness and elasticity. Higher percentage of silicon produces denser steel. Vanadium, Chromium, Molybdenum are also effective alloys. Phosperous is a impurity which makes rail brittle when cooled, thus reduces ability to reduce impact. Phosperous is kept as low as possible. Sulphur in rail steel effect in cracking during hot rolling process. Great care is required to eliminate the impurities as well as slag (non metallic elements) and gases (hydrogen contents).

(iii) Heat treatment - In Pearlitic steel, Fe3C is extremely hard and brittle. By controlling its amount, size and shape, the degree of dispersion strengthening and properties of the steel are controlled. This can be achieved by regulating the desired cooling temperature in required time.

(iv) Improving metallurgical cleanliness by reducing inclusions – Metallurgical cleanliness can be quantified in terms of chemical composition by the oxide and sulphide contents. By improving the cleanliness in steel, introducing continuous casting process in rail manufacturing which improves not only much better wear resistant than a standard rail obtained from traditional ingot steel but also reduces failures from internal defects.

(v) Work hardening – Tensile strength is directly related to Brinell hardness number of rail which can be increased by hardening the rail. This can be achieved by Head Hardening. If the greater is the hardness, lesser will be wear in rail head.

Rail quality improvements through these methods have strived to maintain Pearlitic microstructure. For future rail applications, however, alternate methods to improve the rail qualities may be required to offset the railroad industry’s trend in carrying heavier axle loads over the rails. One possible method to achieve in improvements fatigue, fracture and wear resistance may be the production of rail steel with the carbide free or Bainitic microstructure. Such a microstructure could be attained by controlling the in-line quenching during rail production and/or altering the rail steel chemical composition by adding alloys such as chromium, vanadium and molybdenum. Other potential methods to improve rail strength may be investigated such as maraging (have low carbon content, but contain relatively large percentage of nickel and other hardening elements) steels and ultrahigh carbon (UHC) steels. Finite element analyses modeling heat treatment of rail may be useful to evaluate the options to improve rail

27

strength. A thermoplastic finite element model has been developed to examine the problem of designing quenching schedules for the production of bainitic rail. The results of this model suggest that further study is needed to determine whether bainitic rail can be straightened, by means of conventional cold-rolling process, without leaving excessive residual stresses in the rail when it enters service.

(10) SUGGESTION Different alloys rails can be used at different location as per condition prevails of the region such as coastal area, north India region where temperature variation are at extreme and region where temperature does not vary much and corrosion problem is not considerable.

(i) In coastal region rails are more prone to corrosion where rail renewals are 50%earlier than its actual life. Corrosion resistance rails ( copper, Nb,molybedenum)alloys steels are more effective, should be used in such problem area.

(ii) Region where temperature variation are very much ,Rail with greater ratio of high yeild point/ ultimate tensile strength (Cr& Cu) alloys steel should be used. (iii) Ordinary carbon steel rail (pearlite} UIC-900 grade can be used .

For heavy axle load tracks, steel grades were developed with minimum tensile strength values between 1100-1200 N/mm2. This is achieved by increasing silicon content adding chromium and sometimes vanadium. Heat treated rails have a larger tensile strength and thus a great wear resistance, while at the same time they are relatively tough. Therefore, they replace alloy steels in heavy haul applications and in heavily loaded curve tracks.

28

CONTENTS

1.0 INTRODUCTION 2.0 INDIAN RAILWAY PRESENT STATUS 3.0 ELEMENTS OF RAIL METALLURGY 4.0 ELEMENTS INFLUENCING RAIL STEEL 5.0 RAIL HARDNESS 6.0 RAIL PROFILE-UIC AND OTHERS 7.0 RAIL MANUFACTURING PROCESS 8.0 RAIL SURFACE TREATMENT 9.0 CONCLUSION 10.0 SUGGESTION

29

PROJECT REPORT

IMPROVEMENTS IN RAIL STEEL METALLURGY FOR 32.5 T AXLE LOAD

COURSE N0. 721 SENIOR PROFESSIONAL COURSE

(P.WAY)

KAMLESH KUMAR JAIN R. MURTHY DY.CE/P&D/GORAKHPUR DY.CE/WORKS/MAS N.E.RAILWAY SOUTHERN RAILWAY