Research Papers

Introduction to a Third-Generation Automobile Steel and Its Optimal Warm-Stamping Process

[+] Author and Article Information
Ying Chang

School of Automotive Engineering,
National Key Laboratory of Industrial Equipment
Structural Analysis,
Dalian University of Technology,
Dalian 116024, China

Cunyu Wang, Han Dong

East China Branch of Central Iron & Steel
Research Institute (CISRI),
Beijing 100081, China

Kunmin Zhao

School of Automotive Engineering,
National Key Laboratory of Industrial Equipment
Structural Analysis,
Dalian University of Technology,
Dalian 116024, China
e-mail: kmzhao@dlut.edu.cn

Jianwen Yan

Industrial and Equipment Technology Institute,
Hefei University of Technology,
Hefei 230601, China

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received June 13, 2015; final manuscript received September 14, 2015; published online October 27, 2015. Assoc. Editor: Wayne Cai.

J. Manuf. Sci. Eng 138(4), 041010 (Oct 27, 2015) (7 pages) Paper No: MANU-15-1284; doi: 10.1115/1.4031636 History: Received June 13, 2015; Revised September 14, 2015

The medium-Mn steel is a promising third-generation automobile steel. Its chemical composition, microstructure, and thermal and mechanical properties are introduced and a warm-stamping process for the medium-Mn steel is proposed. The optimal process parameters are identified through the design of experiments (DOE) and range analysis. The evaluated experimental indexes include tensile strength, elongation, and hardness. The optimal forming process consists of an austenitization temperature of 840 °C, a soaking time of 4 min, and an initial stamping temperature of 500 °C. The proposed process was applied to the warm stamping of an automotive B-pillar. The microstructure of ultrafine, uniform, and complete martensite laths was obtained. The formed part exhibits approximately 1420 MPa tensile strength, over 11% elongation and 460 HV hardness. The optimal warm-stamping process has proved effective and applicable for forming medium-Mn steel parts. It will help promote the application of the third-generation automotive steels.

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Fig. 1

The CCT curves of the medium-Mn steel sheet

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Fig. 2

(a) Microstructure examined by transmission electron microscopy (TEM) (austenite with stacking fault and/or annealing twin) and (b) microstructure characterized by electron backscatter diffraction (EBSD) (white-colored phase is the retained austenite)

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Fig. 3

Tensile test specimen of the as-received material

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Fig. 4

Tensile test specimen cut from the B-pillar

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Fig. 5

The effect of process parameters on tensile strength (a), elongation (b), and Vickers hardness (c)

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Fig. 6

The warm-stamped B-pillars of medium-Mn steel

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Fig. 7

The micrograph of the B-pillar at selected locations

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Fig. 8

The mechanical properties of medium-Mn steel part at examined locations




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