development of intelligent hot forging tools with increased...
TRANSCRIPT
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)
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
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:
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
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
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
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]
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
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
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
Seite 6 | TOOL 2016 | 04-07 Okt. 2016
Laboratory hot forging tests
microstructure in the edge layer at the convex mandrel radii
after 500 forging cycles
locations that were analysed
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
Seite 7 | TOOL 2016 | 04-07 Okt. 2016
Laboratory hot forging tests
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
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
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
locations that were analysed
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)
tempering (530 C, 2 h)
tempering (530 C, 2 h)
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
Seite 9 | TOOL 2016 | 04-07 Okt. 2016
Tool wear behaviour under industrial conditions
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
locations that were analysed
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
Seite 10 | TOOL 2016 | 04-07 Okt. 2016
Tool wear behaviour under industrial conditions
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
locations that were analysed
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
Seite 11 | TOOL 2016 | 04-07 Okt. 2016
Tool wear behaviour under industrial conditions
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
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
Seite 12 | TOOL 2016 | 04-07 Okt. 2016
Tool wear behaviour under industrial conditions
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
locations that were analysed
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
Seite 13 | TOOL 2016 | 04-07 Okt. 2016
Tool wear behaviour under industrial conditions
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)
locations that were analysed
modified nitrided steel - 1.2365mod
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
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
© Leibniz Universität Hannover, IW, Prof. Dr.-Ing. Hans Jürgen Maier
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]