Transcript Vergleich AFP Stahl und 20MnCrMo7

New High Strength Bainitic Steel
20MnCrMo7 for Automobile Applications
in Powertrains
Dr.-Ing. Serosh Engineer,
Dipl.-Ing. Charlotte Merkel
EZM EdelstahlZieherei Mark GmbH, Wetter
Automotive Steels
June 2013
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Agenda
Steel development 20MnCrMo7
Steel design and microstructure
Mechanical Properties
Examples of Automotive Applications
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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Development of a New Steel: Requirements
• Use for components in common-rail-diesel engines with
pressures ≈ 3 000 bar and high alternating loads
• Possibility of manufacturing components directly on cooling from
hot rolling /forging temperatures
• Steel with 1200 – 1500 N/mm² tensile strength and good
ductility due to fine grained bainitic microstructure
• Acceptable weldability (CE<0.8)
• Microstructure suitable for autofrettage (process to improve
alternating stress resistance on tube surfaces)
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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Steel Design
• Carbon content < 0,23% for acceptable weldability
• Manganese (Mn), Chromium (Cr) and Molybdenum (Mo)
additions to obtain bainitic microstructure directly on cooling
from hot rolling/forging temperatures
• Niobium (Nb), Titanium (Ti) and Nitrogen (N) to allow fine grain
sizes stable up to temperatures of 1 050°C
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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Microstructure of 20MnCrMo7 Wire Rod Ø 21 mm
Longitudinal sample, magnification 100:1
surface
core
• Homogeneous fine grained structure (finer than 8 ASTM)
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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TiN / TiCN Inclusions
• Particles of ≤ 20 µm are embedded in a ductile bainitic matrix
• No negative influence on the technological properties has
been determined as yet (up to pressures of 3 500 bars).
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
Bildquelle: Dr. Härtel
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Hardenability of 20MnCrMo7 and 18CrNiMo76
Jominy Test
1.7911
1.6587
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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Mechanical Properties 20MnCrMo7 vs 50CrMo4, 34CrNiMo6
Tensile strength
Rm
[Mpa]
Yield strength
Rp0,2% [MPa]
Elongation A
Reduction in
Area Z
DVM Notch
Impact [J]
Automotive Steels
June 2013
20MnCrMo7
50CrMo4
34CrNiMo6
(1.7911)
(1.7228)
(1.6582)
air cooled from hot rolling
Ø 21mm
Quenched & Tempered
Ø 16-40 mm
Quenched &Tempered
Ø 16-40 mm
1262
1000-1200
1100-1300
856
≥ 780
≥ 900
18 %
≥ 10 %
≥ 10 %
62 %
≥ 45 %
≥ 45 %
40
≥ 30
≥ 45
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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Fine Grain Stability of 20MnCrMo7 (1.7911)
Grain Size in accordance with ASTM E 112 / EN ISO 643. Ø 21mm
• Fine grained structure is essentially stable up to 1 050°C and 20h
holding time.
source SCT 2011 [1]
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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Microstructure after AC-Annealing for Cold Forging
• Spherodized annealed
microstructure suitable
for cold forging
Magnification: 1000:1
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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Strain Hardening Behaviour 20MnCrMo7 (1.7911)
Low strain hardening rate after spherodized annealing
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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Case Hardening Behaviour of 20MnCrMo7 (1.7911)
• Corresponding data of 18CrNi8 at 250°C and 300°C are less
favorable
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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20MnCrMo7 as Case Hardening and Q&T-Steel
•
•
•
20MnCrMo7 can be used in the quenched and tempered as well as in
the case hardened state
Properties of 20MnCrMo7 are comparable to or better than more
expensive NiCr-Steels
20MnCrMo7 has lower alloy
surcharge due to lower
Ni content
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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Machinability Results 20MnCrMo7: Turning
Fc= cutting force
Ff= feed force
Fp= passive force
•
f =feed rate , re= Edge radius, VB=flank wear
Cutting depth 1 mm
Cutting speed 200m/min
source: CIRP 2013 [2]
Tool life is improved by adjusting tool geometry and tool
material composition
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Applications in Common Rail Diesel Engines
Common Rail
Connection Bolt
Injector
Nozzle Nut,
connects Injector
and
Nozzle Body
Source: SCT 2008 [3]
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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20MnCrMo7 – A Promising Steel Development
Summary
• The new fine grained bainitic steel is very suitable for
applications at high pressures.
• This steel has a higher strength AND ductility in comparison to
the microalloyed ferritic pearlitic steels developed for the
automotive industry approximately 35 years ago.
• 20MnCrMo7 can also be used as quenched and tempered or
case hardening steel. In comparison to NiCr steels,
20MnCrMo7 has comparable properties at lower cost.
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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New High Strength Bainitic Steel
20MnCrMo7 for Automobile Applications
in Powertrains
Thank you for your attention!
Automotive Steels
June 2013
Dr.-Ing. S. Engineer
High Strength Bainitic Steel 20MnCrMo7
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References
[1] Engineer, S., Janßen, P., Härtel, M., Hampel, C., Randelhoff, F.: „ Technological Properties of
the New High Strength Bainitic Steel 20MnCrMo7”, Proceedings of the 3rd International
Conference on Steels in Cars and Trucks, Salzburg 2011, pp 404-411
[2] Biermann, D. , Hartmann, H., Terwey, I., Merkel, C., Kehl, D.: „Turning of high - strength
bainitic and quenched and tempered steels”, 46th CIRP Conference on Manufacturing
Systems, May 26th -29th 2013, Setúbal, Portugal (in Press)
[3] Langner, H., Beyer, C., Engineer, S., Franke, A., Hölzl, H., Janßen, P.: ,, A new high strength
steel 20MnCrMo7“ , Proceedings of the 2nd International Conference on Steels in Cars and
Trucks, Wiesbaden 2008, p. 72
[4] Biermann, D., Felderhoff, F., Engineer, S., Justinger, H.: “Machinability of high-strength bainitic
steel 20MnCrMo7“, Proceedings of the 3rd International Conference on Steels in Cars and
Trucks, Salzburg 2011, pp 567-574