Mn和P在超低碳烘烤硬化钢中的分布形态及其对拉伸行为的影响研究

来源期刊：金属学报2011年第3期

论文作者：王华 史文 符仁钰 李麟

文章页码：263 - 268

关键词：超低碳烘烤硬化钢； 三维原子探针 (3DAP)； 固溶元素分布； 屈服平台； 内耗

Key words：ultra low carbon bake hardening steel； three dimensional atom probe (3DAP)； solute distribution； yield point elongation； internal friction

摘    要：将2种不同成分的烘烤硬化钢(BH-Mn钢和BH-P钢)加热至800℃,保温2 min后水淬;采用3DAP技术、内耗实验及拉伸性能检测分析Mn和P对超低碳BH钢的间隙原子分布及Cottrell气团的影响,从而得出固溶元素分布对拉伸行为的影响机制.结果显示,在BH-P钢中,P以明显的偏聚形式存在,并和C发生共偏聚现象,从而造成对位错的强烈钉扎,这是导致拉伸过程中BH-P钢产生明显屈服平台的主要原因;在BH-Mn钢中,由于固溶Mn几乎不产生偏聚,而且固溶C的偏聚也很少,因此BH-Mn钢的强度低于BH-P钢,塑性则优于后者;P和C的共同偏聚及其对位错的强烈钉扎能够影响Snoek-Ke-Koster内耗,使Snoek-Ke-Koster峰消失.

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 distributions 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 makes the disappearance of Snoek-Ke-Koster peak.