亚稳奥氏体和微合金元素对冷轧高强汽车钢性能的影响

介绍了亚稳奥氏体和微合金元素（Nb、V）对TRIP钢、TWIP钢和Q＆P钢等冷轧高强汽车钢性能的影响。主要包括调控冷轧高强汽车钢亚稳奥氏体组织的成分体系和连续退火工艺、亚稳奥氏体组织特征及测量方法,及其对高强汽车钢强塑积、拉伸曲线形状等性能的影响等。同时介绍了微合金元素（V、Nb）对冷轧高强汽车钢成形性、强度等级、延迟断裂等个性化性能的影响。     

钒钛资源综合利用国家重点实验室验收又一项开放课题

<正>2017年11月5日,在重庆大学电镀中心会议室,钒钛重点实验室办公室主任陈永主持召开了2014年度实验室开放课题"微合金化超高强钢氢致延迟断裂基础研究"验收会议。该课题于2014年立项,目标是开展钒微合金化氢致延迟断裂行为研究,研究含钒钢中影响氢致延迟断裂的钒及其第二相的相关因素,研究钒含量、组织结构与钢氢致塑性损伤之间的数学关系模型。     

钢中铌、钒、钛微合金化的主要作用

<正>微合金化理论被誉为20世纪物理冶金学领域所取得的最重要进展,极大地推动了微合金化钢的研究、生产与应用,钢中最常用的微合金化元素是铌、钒和钛等,其主要作用是细化晶粒与沉淀强化。钢中添加微合金铌元素可显著提高再结晶温度、细化晶粒,有利于提高钢的工艺性能及使用性能,但降低钢的高温塑性,恶化钢的焊接性能。     

铌和稀土对厚规格轮辐钢板组织和性能的影响

 通过对汽车轮辐用钢板的铌和稀土微合金化试验和生产实践,分析了铌、稀土元素对汽车车轮用钢组织和性能的影响。结果表明：铌微合金化可以细化晶粒;钢中加入稀土,可改变夹杂物形状和尺寸,铌、稀土可以提高钢材的综合性能,尤其是提高了钢板的耐疲劳性能。     

Nb微合金化和含铌钢的发展及技术进步

叙述了国际上铌微合金化技术的发展历史及铌作为微合金化元素在钢中应用的经济性和技术性优势。国际市场铌铁价格的长期稳定使铌微合金化技术成为钢铁工业持续稳定发展的重要伙伴,是保持含铌高强度钢技术创新和使用铌的动力。介绍了高强度管线钢、汽车工业用高级钢板带材及微合金化非调质钢和结构钢等领域中铌微合金化技术的发展经验。     

汽车用TWIP钢的基础研究现状

 概述了汽车用孪晶诱导塑性钢(TWIP)的基础研究现状及进展,介绍了TWIP钢不同成分配比与力学性能的关系,不同合金元素对TWIP钢组织及性能的影响,TWIP效应产生机理,以及不同温度、应变速率和加工工艺对TWIP钢组织和性能的影响。     

热装板坯中微合金元素析出行为研究

正低合金高强度(HSLA)钢用途广泛,涵盖建筑结构、汽车和管线行业。它们由于加入少量合金元素如铌、钒和钛而称为HSLA钢,典型碳含量小于0.1%。合金加入量通常不到0.1%,从而被称作微合金化。微合金化元素通过碳化物、氮化物和碳氮化物的析出,改善HSLA钢的力学性能。析出物尺寸、分布、析出分数及析出物类型都是决定钢的使用性能的重要因素。析出物延迟和/或阻止奥氏体再结晶并在最终基体中产生析出强化,在热轧过程中,     

钛对高强度钢耐延迟断裂性能的影响

在42CrMo钢中加入不同含量的微合金元素钛，研究了钛对高强度钢耐延迟断裂性能的影响。试验结果表明，钢中添加适量的钛能够改变高强度钢的耐延迟断裂性能，这种影响主要来自于析出物TiC的氢陷阱作用和晶粒细化作用。     

热成形钢氢致延迟断裂的研究现状及展望

热成形钢是汽车实现轻量化和提高安全性的关键材料。然而，热成形钢的发展面临着氢致延迟断裂的巨大挑战。文中总结了热成形钢氢致延迟断裂的研究现状，综述了热成形钢的可扩散氢检测技术、氢含量变化规律、氢致延迟断裂评价技术和氢致延迟断裂改善方法。同时，对今后的热成形钢氢致延迟断裂研究进行了展望。     

热装板坯中微合金元素析出行为研究

正低合金高强度钢用途广泛,涵盖建筑结构、汽车和管线行业。它们由于加入少量合金元素如铌、钒和钛而称为HSLA钢,典型碳含量小于0.1%。合金加入量通常不到0.1%,从而被称作微合金化。微合金化元素通过碳化物、氮化物和碳氮化物的析出,改善HSLA钢的力学性能。析出物尺寸、分布、     

先进高强度汽车用钢氢致延迟断裂研究进展

摘要：随着汽车、机械装备、航空航天、船舶等工业领域的快速发展，降低成本、提性减重、实现节能减排已成为各个行业为之努力而奋斗的目标，而高强度钢材是实现汽车工业产品轻量化和安全性的重要依托。然而，随着汽车用钢强度的不断提升，氢致延迟断裂问题越发突出，已经成为阻碍高强度汽车用钢广泛应用的一个关键因素。主要介绍先进高强度汽车用钢（热成形钢、双相（DP）钢、淬火配分（Q&P）钢）最新的研究成果，并对其氢致延迟断裂特性、机制和测试评价技术方法等方面做了简要介绍，为相关领域的研究人员提供参考。     

Effects of Niobium and Vanadium on Hydrogen-Induced Delayed Fracture in High Strength Spring Steel

 Influence of vanadium and/or niobium additions on delayed fracture behavior in high strength spring steel was studied by hydrogen permeation method and slow strain rate technique (SSRT), and its mechanism was analyzed. The results show that apparent diffusion coefficient of hydrogen in microalloyed spring steels Nb V steel and Nb steel is lower than that in non microalloyed steel 60Si2MnA. Percentage of strength reduction in SSRT in air after precharged hydrogen of the microalloyed steels is smaller than that of 60Si2MnA. Addition of the microalloys changes the fracture characteristics. Thence, vanadium and/or niobium additions are a very effective and economy means to improve the hydrogen induced delayed fracture resistance of high strength spring steel.     

汽车用高锰TWIP钢的研究现状

高锰TWIP钢的塑性机制与其堆垛层错能有关。采用试验法和热力学计算法确定TWIP钢层错能的研究结果存在差异,TWIP效应与层错能的对应关系也未达成一致。高锰TWIP钢凝固温区宽,凝固时容易形成疏松、偏析等铸态缺陷。铸态TWIP钢高温时的断面收缩率均低于40%,可能导致连铸弯矫时开裂。水平连铸和双辊薄带连铸在TWIP钢生产上具有突出优势。TWIP钢的热轧温度区间窄,与其固相线温度低和高温塑性差有关。冷轧后连续退火温度和退火时间也尚在摸索之中。Fe-Mn-Si-Al系TWIP钢的强化机制以孪晶形成动态细化晶粒为主,而Fe-Mn-C-(-Al)系TWIP钢中动态应变时效可能是主导作用。TWIP钢的延迟断裂敏感性可通过Al合金化来改善,其主要机制是在试样表层下形成的α-Al2O3层阻止氢的渗入。     

Delayed Fracture Resistance and Mechanical Properties of 30MnSi High Strength Steel

To investigate the effect of heat treatment on mechanical properties and delayed fracture resistance of high strength steel, 30MnSi prestressed concrete (PC) steel bars are quenched and tempered. Tensile results show that, after 950 °C quenching and about 430 °C tempering, 30MnSi PC steel bars have superior mechanical properties and delayed fracture resistance. Microstructural observation shows that 30MnSi steel bar is mainly composed of fine tempered sorbite (troostite) with carbide distributed along the lath martensite boundaries. It can be concluded that thermal refining is an effective way to improve mechanical properties and delayed fracture resistance of 30MnSi PC steel bar.     

Study on hydrogen induced delayed fracture of 1500 and 2000MPa hot stamping steels

The application of hot-stamping steel (HS) in the automobile is an inevitable trend, but the hydrogen embrittlement sensitivity of HS steel still needs to be studied and improved. The hydrogen diffusion behavior and hydrogen embrittlement sensitivity of 1500 and 2000MPa hot stamping steels were studied by means of hydrogen penetration, slow strain rate tensile (SSRT), and fracture analysis. The results show that the apparent diffusion coefficient Dap (1.71×10-7cm2/s) of 1500HS is significantly less than the Dap (3.45×10-7cm2/s) of 2000HS; delayed fracture resistance of 1500HS is superior to 2000HS. From the fracture analysis, under the same hydrogen charging conditions, the fracture morphology of 1500HS changed from typical dimple ductile fracture to quasi cleavage brittle fracture, while 2000HS changed from dimple morphology to intergranular brittle fracture with the increase of hydrogen charging current density. While the deformation degree of 2000HS was very small, the local hydrogen content and stress value had reached the critical deal. The hydrogen reduced the bonding force between grains, resulting in the nucleation and propagation of microcracks. Therefore, with the improvement of the strength of HS steel, Ti and V micro alloyed elements should be properly added to form nano precipitates, as irreversible hydrogen traps to capture hydrogen atoms, hinder their diffusion and segregation, and effectively refine the structure and pinning dislocations, to improve the resistance to hydrogen induced delayed fracture of HS steel.     

高强度高塑性TWIP钢的开发研究

通过调整成分,研究了一种新型的高锰钢成分对组织结构和TWIP效应以及对强度、塑性的影响。结果表明,该钢在变形后基体中存在大量细小的形变孪晶,室温下可具有相变诱导塑性和孪晶诱导塑性的TWIP效应,因而具有高的强度(1000MPa以上)和极高的伸长率(60％～90％)。该钢种是很有前途的高强度、高塑性钢种,满足下一代汽车制造对钢铁材料的需求。     

Residual Stress Effect on the Delayed Fracture of Twinning-Induced Plasticity Steels

Residual stress effect of the deep drawn TWIP steel on delayed fracture was investigated. Microstructural features of the TWIP steels did not change after stress relief annealing, while the elastic lattice strain dropped to 0.0007. Delayed fracture of the drawn TWIP steel occurred after 203 hours of HCl immersion testing, but did not occur in the annealed one. It is clear that residual stress after the drawing is the primary reason for the delayed fracture of TWIP steels.     

Residual Stress Analysis in Deep Drawn Twinning Induced Plasticity (TWIP) Steels Using Neutron Diffraction Method

In Twinning Induced Plasticity (TWIP) steels, delayed fracture occurs due to residual stresses induced during deep drawing. In order to investigate the relation between residual stresses and delayed fracture, in the present study, residual stresses of deep drawn TWIP steels (22Mn-0.6C and 18Mn-2Al-0.6C steels) were investigated using the finite element method (FEM) and neutron diffraction measurements. In addition, the delayed fracture properties were examined by dipping tests of cup specimens in the boiled water. In the FEM analysis, the hoop direction residual stress was highly tensile at cup edge, and the delayed fracture was initiated by the separation of hoop direction and propagated in an axial direction. According to the neutron diffraction analysis, residual stresses in 18Mn-2Al-0.6C steel were about half the residual stresses in 22Mn-0.6C steel. From the residual strain measurement using electron back-scatter diffraction, formation of deformation twins caused a lot of grain rotation and local strain at the grain boundaries and twin boundaries. These local residual strains induce residual stress at boundaries. Al addition in TWIP steels restrained the formation of deformation twins and dynamic strain aging, resulting in more homogeneous stress and strain distributions in cup specimens. Thus, in Al-added TWIP steels, residual stress of cup specimen considerably decreased, and delayed fracture resistance was remarkably improved by the addition of Al in TWIP steels.     

Strain Effect on the Microstructure,Mechanical Properties and Fracture Characteristics of a TWIP Steel Sheet

Twinning-induced plasticity (TWIP) steels are a highly promising group of steels for the production of complex structural components in cold forming operations for car body manufacturing. In this work, the effect of cold rolling strain on the microstructure, mechanical properties and fracture characteristics of a TWIP steel sheet used for automobile body structure was studied by means of optical microscopy, scanning electron microscopy, electron back-scattered diffraction technique, microhardness measurement, tensile test and fractography. TWIP steel sheets were cold rolled with reductions of 0, 15 and 30%. An increase of the cold rolling strain led to an increase of deformation twinning activity in certain favourably oriented grains and resulted in significant increase in ultimate tensile strength and hardness of TWIP steel. However, the ductility of TWIP steel significantly decreased with increasing degree of cold rolling strain. The increase in the ultimate tensile strength was almost linear with the increase in cold rolling strain. After cold rolling reduction of 30%, the ultimate tensile strength increased by approximately 50%, whereas the elongation decreased by approximately 85%. The size and depth of the dimples in the fracture surface decreased with the increase of the twin boundaries at 30% cold rolling strain, leading to highly limited plasticity through the tensile testing.