The Application of Hot Stamped Boron Steel 15B22 on the Automotive Parts Cheng-Kai ChiuHuang Co-authors: S.W. Wang, P.K. Lee, T.R. Chen Product Application Research Section Iron & Steel Research & Development Department China Steel Corporation 2016/11/15 1
Outline Background Hot Stamping Manufacturing Process Characteristics of CSC Boron Steel 15B22 Examples of Hot Stamping Die Tryout Conclusions 2
Background Body Structure lightweight and safety are the main driving forces for the development of hot stamping process. The strength of the parts made by hot stamping is higher than the traditional forming technology. 3
The Application and Global Market for Hot Stamping Parts Due to the CO 2 emission regulation and vehicle safety issue, the application of hot stamping parts on the body structure shows a fast growth. Schuler forecasts that the hot stamping market will reach 5.7 billion Pcs by 2018. Ref: www.gestamp.com Ref: www.schuler.com 4
Hot Stamping Manufacturing Process The blank is heated to 910 degree Celsius in the furnace. Then the blank is transferred to the die within 6 secs. Die closing for 15-20 secs to quench the blank. The part is trimmed by laser cutting. Direct Process Ref: www.stampingjournal.com December 2006 5
Mechanical Properties of Boron Steel 15B22 The blank is heated to austenite state followed by fast die quenching. The critical cooling rate to obtain the martensite microstructure is 27 K/sec. 15B22 Annealed 15B22 Ref: Garcia Aranda et al., 2002 6
Pros and Cons of Hot Stamping Process Pros High Strength (TS > 1500 MPa) Good Formability (Forming at high Temperature) Lower Press Capacity Required (<1000 Ton) Good Part Dimension Control (No Springback) Cons Higher Energy Consumption (Furnace for blank heating) Higher Die manufacturing cost (Cooling ducts required) Higher Investment for the Production line 7
Example: U-Hat Hot Stamping Die CSC 200 Ton Hydraulic Press U-Hat Hot Stamping Die 8
CAE Model: Forming and Drawing Blank Holder 9
Temperature Distribution and Phase Fraction Top Side wall Quench 2 Sec Flange Quench 10 Sec Top Side wall Quench 2 Sec Flange Quench 10 Sec 10
CSC Hot Stamping R&D Capability Outlet Inlet Die Design Cooling ducts design Computer Computer Simulation (Forming) Computer Simulation (Water Flow) 11
Springback Comparions for Different Materials Hot stamping parts have good size stability (No Springback). Al 5182 270 Mild Steel 15B22 (No Springback) 12
Strength (MPa) Hardness (HRC) Strength and Hardness Verification The strength meet the requirement of GM and Volkswagen standard. GMW14400: TS 1000~1700MPa YS 950~1250MPa EL 5% min TL4225: TS 1300~1650MPa YS 1000~1250MPa EL 5% min Location Location 13
Mechanical Properties Before and After Hot Stamping 1600 1400 CSC HC 15B22 1200 Sterss (MPa) 1000 800 600 400 200 0 Before H.T. After H.T. 0 5 10 15 20 25 Strain (%) Blank Status Yielding Strength (MPa) Tensile Strength (MPa) Elongation(%) GL=50mm Hardness (HRC) Before H.S. 280 450 20 - After H.S. 950 ~ 1250 1300 ~ 1650 6 40~49
Microstructure after Die Quenching With appropriate die design, a uniform high-strength martensite structure can be obtained after die quenching. Drawing 15B22 t=1.4 mm Flat Area Corner Flat area Side wall Side Wall Corner Forming 15B22 t=1.4 mm Flat Area Corner Side Wall 15
CSC HC 15B22 Microstructure (Before and After Die Quenching) Before Hot Stamping Ferrite + Pearlite Hardness 80 ~ 90HRB After Hot Stamping (Die quenching) Martensite Hardnbess 43 ~ 47HRC (Heating to 930,Transfer to the die in 5 secs followed by 15 secs die quenching) 16
Hot Stamping R&D Capacity-Cooperate with Local Research Institute 800 Ton Press Double-layered Furnace Automatic blanking Bumper (15B22) Blank Transfer A pillar (15B22) 17
Automotive Parts Developed by Hot Stamping CSC 15B22 Patchwork B-pillar A-pillar and Door Beam Patchwork B Pillar 30% Lightweight compared to the coldstamping design 18
Conclusions The demand for the hot stamping parts from the automotive industry shows a strong growth. The annual demand is predicted to reach 5.7 billion pcs by 2018. China Steel Corporation has successfully developed non-coated and coated high temperature oxidation resistant 15B22 boron steel for the hot stamping process. After hot stamping (die quenching), the YS, TS and Elongation of CSC 15B22 can reach 1090 MPa, 1510 MPa and 6.75% respectively. Through the test, it is sure that the developed 15B22 steel can meet the requirement of GM standard (GM 14400) and VW standard (TL4225) for hot stamping. 19