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金属学报  2020, Vol. 56 Issue (4): 429-443    DOI: 10.11900/0412.1961.2020.00003
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热冲压成形钢的强度与塑性及断裂应变
易红亮1,2(),常智渊1,才贺龙1,杜鹏举1,杨达朋1
1.东北大学轧制技术及连轧自动化国家重点实验室 沈阳 110819
2.育材堂(苏州)材料科技有限公司 苏州 215123
Strength, Ductility and Fracture Strain ofPress-Hardening Steels
YI Hongliang1,2(),CHANG Zhiyuan1,CAI Helong1,DU Pengju1,YANG Dapeng1
1.State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China
2.Easyforming Materials Technology Co. , Ltd. , Suzhou 215123, China
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摘要: 

轻量化是支撑汽车电动化和智能化的重要赋能技术之一。抗拉强度为1500 MPa的热冲压成形用硼钢(22MnB5)是目前最经济有效的车身轻量化技术解决方案,而汽车工业对轻量化需求的日益提高正引领热冲压成形钢向着更高强度、更高塑性及更高断裂应变的方向发展。本文首先分析了车身轻量化对碰撞过程中构件变形抗力和断裂抗力的要求,解释了强度与塑性及断裂应变等材料的力学性能参量对碰撞变形抗力和断裂抗力的影响,然后介绍了作者及其他研究人员在研究开发更高强度、更高延伸率、更高断裂应变的新一代热冲压成形钢的最新进展:(1) 提出了一种新的强韧化方法,在热冲压成形钢的马氏体基体组织内引入大量纳米级的VC析出物,从而在获得2000 MPa强度的同时保持了与常规1500 MPa热冲压钢22MnB5相当的延伸率和断裂应变。(2) 在热冲压成形钢的微观组织中引入残余奥氏体,利用相变诱导塑性效应显著提升热冲压成形钢的延伸率;具体的工艺实施途径包括模具外淬火-配分工艺、淬火-闪配分工艺、淬火-回火配分工艺等。(3) 介绍了热冲压成形钢的新一代Al-Si镀层技术以及Al-Si镀层板断裂应变改善方面的最新研究进展;通过降低Al-Si镀层与钢板基体之间的合金化扩散来减少界面C富集,从而达到显著提高Al-Si镀层热冲压成形钢断裂应变的目的。

关键词 轻量化热冲压钢Al-Si镀层延伸率冷弯角断裂抗力    
Abstract

Press-hardening steels (PHS) are increasingly used for vehicle body structure components because of their lightening potential owning to superiorly high strength, adequate ductility and fracture resistance. New PHS grades with higher strength and enhanced fracture resistance are being widely studied now for achieving further vehicle weight reduction, and the recent development in this field is reviewed in this article. Combining quenching and partitioning (Q&P) with the hot stamping process has been explored by some researchers, as well as tempering after the hot stamping using the medium-Mn steels. A certain amount of austenite could remain by the above processes and the resulted tensile strength can exceed 1500 MPa while tensile ductility of 10%~16% can be achieved utilizing the transformation-induced plasticity (TRIP) effect. A V micro-alloyed steel (34MnB5V) for hot stamping has been designed, utilizing both grain refinement and precipitation strengthening of VC. The tensile strength of the newly developed 34MnB5V exceeds 2000 MPa which is much higher than that of the most commonly used PHS 22MnB5 (1500 MPa). Meanwhile, the ductility and bending properties of the above two steels are comparable. Al-Si coated PHS is usually adopted to avoid oxidation during heating and improve its corrosion resistance after stamping. However, its bendability after forming is lower than that of the bare grade when surface decarburization is absent. The thickness of the brittle Fe2Al5 phase was reduced and the carbon enrichment at the interface of α-Fe and martensite matrix was weakened after hot stamping by thinning of the Al-Si coating. Thus, the bending property was improved. The applicability of the new designed processes for the existing production lines should be considered in future studies. The bending test should be adopted for the deformability evaluation rather than the uniaxial tensile test simply. The welding property and the mechanism of hydrogen embrittlement should also be studied for industrial application of the new developed steels.

Key wordslight weighting    hot stamping steel    Al-Si coating    ductility    bendability    fracture resistance
收稿日期: 2020-01-03     
ZTFLH:  TG142.41  
基金资助:国家自然科学基金项目(51722402);国家自然科学基金项目(U1560204);中央高校基本科研业务费项目(N170705001);111计划项目(B16009)
通讯作者: 易红亮     E-mail: hlyi@ral.neu.edu.cn
Corresponding author: Hongliang YI     E-mail: hlyi@ral.neu.edu.cn
作者简介: 易红亮,男,1981年生,教授,博士

引用本文:

易红亮,常智渊,才贺龙,杜鹏举,杨达朋. 热冲压成形钢的强度与塑性及断裂应变[J]. 金属学报, 2020, 56(4): 429-443.
Hongliang YI, Zhiyuan CHANG, Helong CAI, Pengju DU, Dapeng YANG. Strength, Ductility and Fracture Strain ofPress-Hardening Steels. Acta Metall Sin, 2020, 56(4): 429-443.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2020.00003      或      https://www.ams.org.cn/CN/Y2020/V56/I4/429

图1  汽车零件弯曲压溃吸能实验
图2  VDA 238-100弯曲示意图与弯曲过程中的厚度方向应变的分布
SteelCSiMnTiBVFe
22MnB50.220.221.330.0290.0031-Bal.
34MnB5V0.340.321.390.0300.00250.11~0.30Bal.
表1  22MnB5和34MnB5V的化学成分[14] (mass fraction / %)
图3  22MnB5、34MnB5V原奥氏体晶界和34MnB5V的TEM像
图4  22MnB5和34MnB5V的拉伸曲线和三点尖弯曲载荷-角度曲线
图5  34MnB5V热冲压钢车门防撞梁和实车碰撞测试
图6  淬火-配分(Q&P)工艺与热冲压成形工艺的示意图
图7  22MnB5与不同处理工艺下热冲压钢的力学性能[17,18,19,20,21,36]
图8  淬火-闪配分(Q&FP)热冲压钢的TEM像
图9  22MnB5与Q&FP热冲压钢的工程应力-应变曲线
图10  中锰钢温成形的工艺路线图及其典型的拉伸曲线
图11  中锰热冲压钢淬火-回火配分(Q-T&P)和淬火-烘烤配分 (Q-B&P)的工艺路线图及其典型拉伸曲线
图12  预涂覆25 μm厚的Al-Si镀层热冲压钢的SEM像
图13  Al-Si镀层合金化之后与硼钢基体界面间高碳致脆模型
图14  预涂覆约10 μm厚的Al-Si镀层热冲压钢的SEM像
图15  Al-Si镀层板热冲压后α′基体与α-Fe相C浓度分布
图16  Al-Si镀层热冲压零件涂装烘烤之后的弯曲载荷-位移曲线以及压溃后零件裂纹扩展情况
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