STUDY OF Mn AND P SOLUTE DISTRIBUTIONS AND THEIR EFFECT ON THE TENSILE BEHAVIOR IN ULTRA LOW CARBON BAKE HARDENING STEELS
WANG Hua, SHI Wen, HE Yanlin, FU Renyu, LI Lin
College of Materials Science and Engineering, Shanghai University, Shanghai 200072
Cite this article:
WANG Hua SHI Wen HE Yanlin FU Renyu LI Lin. STUDY OF Mn AND P SOLUTE DISTRIBUTIONS AND THEIR EFFECT ON THE TENSILE BEHAVIOR IN ULTRA LOW CARBON BAKE HARDENING STEELS. Acta Metall Sin, 2011, 47(3): 263-268.
Abstract With the increasing requirement of vehicle weight reduction and energy conservation from automobile industry, the investigation and development of high strength steel sheet has been stressed extensively. Bake hardening steel, as a new kind of automotive steel, exhibits low strength and good formability before drawing, after which increases obviously in the yield strength during baking process, and is then widely used in the outer plate of modern cars. Mn and P are often added to sheet steel to increase the strength, and their distributions have significant effect on drawability, bake hardening property and surface quality of bake hardening steels. In this paper, the distributions of Mn and P and their effect on tensile behavior in bake hardening steels were studied. For investigation, two kinds of bake hardening steels (BH–Mn and BH–P steels) were heated to 800 ℃, held for 2 min and cooled by water quenching. Three dimensional atom probe (3DAP) technique, internal friction experiments and tensile tests were carried out to analysis the effect of Mn and P distribution patterns on the interstitial atom distribution and Cottrell atmosphere in the matrix, so as to obtain the influence of solute istributions on tensile behavior. The results indicate that P segregates mainly in bake hardening steel, and part of P segregates together with C, which strongly pin the dislocations and is the main reason that induces the yield point elongation during tensile process. In BH–Mn steel, Mn hardly segregates in the matrix and C segregates very little, so the strength of BH–Mn steel is lower than that of BH–P steel, whereas the plasticity is better than BH–P steel. The segregation of P together with C and its pinning of dislocations will influence Snoek–Ke–Koster internal friction, and mkes the disappearance of Snoek–Ke–Koster peak.
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