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

Steel development 20MnCrMo7 Steel design and microstructure Mechanical Properties Examples of Automotive Applications Agenda Automotive Steels June 2013 Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo7 2

Development of a New Steel: Requirements Use for components in common-rail-diesel engines with pressures ≈ 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 3

Steel Design 4 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

Microstructure of 20MnCrMo7 Wire Rod Ø 21 mm Longitudinal sample, magnification 100:1 Homogeneous fine grained structure (finer than 8 ASTM) Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo7 5 core surface Automotive Steels June 2013

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 bars). Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo76 Bildquelle: Dr. Härtel Automotive Steels June 2013

Hardenability of 20MnCrMo7 and 18CrNiMo Automotive Steels June 2013 Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo7 7 Jominy Test

20MnCrMo7 (1.7911) air cooled from hot rolling Ø 21mm 50CrMo4 (1.7228) Quenched & Tempered Ø mm 34CrNiMo6 (1.6582) Quenched &Tempered Ø mm Tensile strength Rm [Mpa] Yield strength R p0,2% [MPa] 856≥ 780≥ 900 Elongation A18 %≥ 10 % Reduction in Area Z 62 %≥ 45 % DVM Notch Impact [J] 40≥ 30≥ 45 Mechanical Properties 20MnCrMo7 vs 50CrMo4, 34CrNiMo6 Automotive Steels June 2013 Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo7 8

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] 9 Automotive Steels June 2013 Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo7

Microstructure after AC-Annealing for Cold Forging Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo7 10 Spherodized annealed microstructure suitable for cold forging Magnification: 1000:1 Automotive Steels June 2013

Strain Hardening Behaviour 20MnCrMo7 (1.7911) Low strain hardening rate after spherodized annealing Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo711 Automotive Steels June 2013

Case Hardening Behaviour of 20MnCrMo7 (1.7911) Corresponding data of 18CrNi8 at 250°C and 300°C are less favorable Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo712 Automotive Steels June 2013

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 Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo7 13 Automotive Steels June 2013

Tool life is improved by adjusting tool geometry and tool material composition Machinability Results 20MnCrMo7: Turning Fc= cutting force Ff= feed force Fp= passive force f =feed rate, r  = Edge radius, VB=flank wear Cutting depth 1 mm Cutting speed 200m/min source: CIRP 2013 [2] 14

Applications in Common Rail Diesel Engines Automotive Steels June 2013 Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo7 15 Common Rail Injector Nozzle Nut, connects Injector and Nozzle Body Connection Bolt Source: SCT 2008 [3]

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. 17 Automotive Steels June 2013 Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo7

New High Strength Bainitic Steel 20MnCrMo7 for Automobile Applications in Powertrains Thank you for your attention! Dr.-Ing. S. Engineer High Strength Bainitic Steel 20MnCrMo7 18 Automotive Steels June 2013

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 [2]Biermann, D., Hartmann, H., Terwey, I., Merkel, C., Kehl, D.: „Turning of high - strength bainitic and quenched and tempered steels”, 46 th CIRP Conference on Manufacturing Systems, May 26 th -29 th 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