Development of intelligent hot forging tools with increased...

06.10.2016

© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier

Seite 1 | TOOL 2016 | 04-07 Okt. 2016

Development of intelligent hot forging tools with

increased wear resistance by cyclic edge-zone

hardening

Oleksandr Golovko1, Jan Puppa2, Florian Nürnberger1,

Dmytro Rodman1, Hans Jürgen Maier1, Bernd-Arno Behrens2

1 Institut für Werkstoffkunde (Material Science)2 Institut für Umformtechnik und Umformmaschinen (Forming Technology and Machines)


Seite 2 | TOOL 2016 | 04-07 Okt. 2016

Heinemeyer, D.: Untersuchung zur Frage der Haltbarkeit von

Schmiedegesenken, Dissertation, Universität Hannover, 1976

Stress- and damage types of tools by hot forging

damage types:

• Thermal- Long-term thermal load due to

increased base tool temperature

- Thermal cycle load with heated

workpiece and cooling lubricant

• Mechanical- High mechanical stresses

through the deformation forces

• Tribological- Interlayer: lubricant, scale

- Friction conditions on the contact

• Chemical- Oxidation processes and chemical

reactions, incl. lubricant additives

Thermal, mechanical, tribological and chemical loads always affect in combination

Combined loads lead to the showed damage types

upper die

lower die

Wearing

Mechanical cracking

Plastic deformation

Thermal cracking

loads:


Seite 3 | TOOL 2016 | 04-07 Okt. 2016

Temperature profile and microstructural

changes in a forging tool

rehardened

structure

(white layer)

cyclic

annelead

structure

200 forging cycles 1000 forging cycles

temperature profile

in the tool

(surface layer)

distance from the surface [µm]

tem

pe

ratu

re[°

C]

fine martensite annealed structure tempered structure

⇩

Smart materials are designed materials that have one or more properties that can be

significantly changed in a controlled external conditions, such as stress, temperature etc.

without external regulation.

decreasing of

Ac1b- temperature

improvement of

the wear resistance

increasing of the

hardened layer

Ttempering

Ac1b


Seite 4 | TOOL 2016 | 04-07 Okt. 2016

Alloy development and material characterisation

AlloyChemical composition (wt.-%)

Ac1b-

temperature

0.2%

yield strength

[MPa]

UTS

[MPa]

A

[%]C Si Mn Cr Mo V Ni Co

1.2365 0.29 0.29 0.31 2.72 2.61 0.41 0.24 0.01 851 ± 3 °C 1409 1595 8.8

A2 0.22 0.18 1.81 2.26 2.47 0.28 1.53 1.16 753 ± 8 °C 1322 1535 4.6

A3 0.38 0.16 3.94 3.14 2.47 0.30 1.77 0.02 723 ± 5 °C 1285 1513 2.2

A4 0.46 0.15 2.33 3.35 2.55 0.37 1.18 0.01 744 ± 6 °C 1272 1438 3.7

A5 0.18 0.10 2.03 2.13 2.52 0.22 1.59 0.02 745 ± 9 °C 1225 1443 13.6

influence of manganese, nickel and

cobalt on the Ac1b-temperature

evaluation of Ac1b -temperature

by dilatometry

temperature [C]

len

gth

ch

an

gin

g D

l[µ

m]


Seite 5 | TOOL 2016 | 04-07 Okt. 2016

Laboratory hot forging tests

Tool steel: 1.2365 (ref.)

1.2365+Mn+Ni+Co(mod.)

Workpiece steel: 1.0503 (C45)

Tool temperature: 250 °C

Workpiece temperature: 1150 °C

Tact time: 8 s

Quantity of forging cycles: 1, 100, 500, 1000

eccentric press Eumuco SP30d

1 – forging press

2 – inductor

3 – feeder

4 – LLC feeder

2 – inductor

3 – handling equipment

tool system for die forgingcontoured model tool


Seite 6 | TOOL 2016 | 04-07 Okt. 2016


microstructure in the edge layer at the convex mandrel radii

after 500 forging cycles

locations that were analysed


Seite 7 | TOOL 2016 | 04-07 Okt. 2016


micro hardness depth profiles in the edge layer

of the convex mandrel radius

100 µm

Härteeindrücke

Werkzeug-oberfläche

scheme of micro hardness measuring in the

surface layer of the convex mandrel radius

Hardness

imprints

Tool

surface


Seite 8 | TOOL 2016 | 04-07 Okt. 2016

Tool wear behaviour under industrial conditions

taper

punch radius

(wear-critical area)

convex

radius

bottomKind & Co., Edelstahlwerk, KG

producing of billets

Chemical composition (wt.-%)

modelling alloy – A5

Hardness 250-285 HB

final heat treatment (1160 C, 7 h)

forging (1160 850 C), Rr = 3.5

annealing (680 C, 24 h)

cooling in furnace

casting

diffusion annealing (1280 C, 24 h)

punch


Tool HRC

1 1.2367 nitr. 50.3

2 1.2365 mod. 48.3

3 1.2365 mod.+nitr. 47.4

• Press: automatic multi-station;

horizontal ram movement

• Workpiece: cylindrical part

(65 90 mm, steel 1.1157)

• Heating: inductive to 1240 C

• Cycle time: 1 s

• Basic punch temperature: 100 C

C – 0.25 Mo – 2.47

Si – 0.27 V – 0.26

Mn – 1.98 Ni – 1.60

Cr – 1.98

two step preheating

(600 900 C)

holding at hardening

temperature (1020 C, 40 min)

tempering (560 C, 2 h)




Seite 9 | TOOL 2016 | 04-07 Okt. 2016


microstructure in the edge layer of a nitrided punch made of

steel 1.2367 after 89 % of the tool life

nitrided layer

plastic deformation

cracks

cracks

flaking

thick

annealed zone

thin annealed

zone

nitrided

layer

thin annealed

zone

nitrided

layer



Seite 10 | TOOL 2016 | 04-07 Okt. 2016


plastic deformation thick white

layer

cracks

cracks

thin annealed

zonethin white layer

annealed zone

annealed zone

microstructure in the edge layer of a punch made of modified steel

1.2365mod without nitriding after 92 % of the tool life



Seite 11 | TOOL 2016 | 04-07 Okt. 2016


after 89%

of tool lifeafter 92%

of tool life

• top area (zone A) – softening

• zones B and C – hardening

• zone B: 880 HV0.025 (surface)

550 HV0.025 (bulk material)

• under the hardened zone – annealed

area (HV down to 400 HV0.025)

• zone D – hardening (HV0.025 up to

700 HV0.025)

• tool surface – up to 1260 HV0.025 (nitriding)

• nitride layer 100-200 µm HV drops abruptly

• zones B, C – HV (to 270 HV0.025) - nitride

layer degraded, annealed zone at 500 µm

• zones D, E nitride layer had partially degraded

• below the nitride layer – annealed zone (depth

120 µm, approx. 500 HV0.025)

Locations that

were analysed

reference steel modified steel


Seite 12 | TOOL 2016 | 04-07 Okt. 2016


nitrided layer

thick white

layer

cracks

thin annealed

zonenitrided layer

microstructure in the edge layer of a nitrided punch made of modified steel

1.2365mod after 133 % of nominal tool life



Seite 13 | TOOL 2016 | 04-07 Okt. 2016


after 133%

of tool life

• zone C: nitriding affects the hardness up to 200 µm; greatest hardness change due to a

cyclic hardening to 960 HV0.025.

• in zone D hardening effect is less present – only near the surface (to 50 µm)

• zone E – annealed area with a softened microstructure

• bottom of the punch (zone F) – hardness is still high due to the existence of the initial nitride

layer (up to 1045 HV0.025)


modified nitrided steel - 1.2365mod


Seite 14 | TOOL 2016 | 04-07 Okt. 2016

Conclusions

• Lowering the material-specific Ac1b-temperature by alloying promotes the cyclic hardening effect in

the tool’s surface layers.

• The modified hot working tool steel showed distinct white layers compared to conventional steels.

These white layers mostly develop in wear-critical areas of the tool like convex radii. Exceeding the

Ac1b-temperature followed by a subsequent quenching results in the formation of a hardened zone in

these areas. This hardened zone increases the wear resistance in the surface layer.

• A softened annealed zone vulnerable to abrasive wear can develop in areas that are not austenitised.

Hence, the intelligent hot working tool steel can only be used efficiently when tailored to the forging

parameters.

• For the tools examined, an additional nitriding treatment would be necessary to increase wear

resistance in the weakened areas efficiently. This was evident after testing a nitrided punch made of

the modified hot working tool steel. The punch endured a nominal tool life of 133 %.

• The objective of future research will be to test to what extent the wear resistance of forging tools can

be increased with a combination of the modified alloy and a material-specific nitriding treatment.

Acknowledgement

The IGF-project „Development of intelligent materials for wear reduction of forging tools“, IGF-Project No.

445 ZN, by the “Forschungsvereinigung Stahlanwendung e. V.” (FOSTA) was sponsored through the AiF

in line with the program “Förderung der industriellen Gemeinschaftsforschung” (IGF) by the federal

ministry of economy and energy


Seite 15 | TOOL 2016 | 04-07 Okt. 2016

Thank You for attention!

To contact:

Dipl.-Ing. J. Puppa

Institut für Umformtechnik und Umformmaschinen

(Forming Technology and Machines)

Tel.: +49 511 762 2168

E-Mail: [email protected]

To contact:

Dr. sc. techn. O. Golovko

Institut für Wekstoffkunde

(Material Science)

Tel.: +49 511 762 4402

E-Mail: [email protected]

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