超级钢板料冲压性能的拉伸试验研究

将超级钢应用于国产汽车冲压件的生产中不仅可以提高汽车质量,而且可以降低汽车的成本、减小汽车重量、降低能源消耗和减少环境污染.为了在汽车工业中更好地使用超级钢,概述了板材冲压性能的评价指标,介绍了拉伸试验值对板材冲压性能的影响,并对超级钢进行了拉伸试验.研究了超级钢板的硬化指数、塑性应变比、屈服强度、极限强度、均匀延伸率等机械性能,并分析了超级钢板的冲压成形性能,超级刚具有较好的胀形性能、拉深性能、弯曲性能,抗起皱性能等冲压性能,可以广泛地应用于汽车冲压零件生产中.     

卷取温度对冷轧DC01钢板显微组织与成形性能的影响

通过拉伸试验、金相检验和成形试验,分析了热轧卷取温度对冷轧DC01钢板显微组织和成形性能的影响。结果表明：随卷取温度由680℃升高至730℃,冷轧DC01钢板的屈服强度和抗拉强度均呈不同程度的下降趋势,下降幅度在20～30 MPa,断面收缩率A₈₀提升约2%,最高可达41.5,塑性应变比r提升约0.4,最高可达2.05,加工硬化指数n变化不大,冷轧DC01钢板的综合成形性能与罩式退火DC01钢板的相当;在730℃高温卷取条件下,DC01钢板的热轧组织和冷轧组织均为铁素体+少量珠光体,冷轧过程中再结晶阻力较小,有利于γ纤维织构的形成,使材料的塑性应变比r大幅提高,从而改善材料的冲压成形性能;在730℃高温卷取条件下,冷轧DC01钢板的相对锥杯值和胀形高度与罩式退火DC01钢板的相当,其冲杯高度达到了罩式退火DC01钢板的86%,综合成形性能良好。     

冷却条件对超级钢焊接接头组织和性能的影响

400MPa级超级钢主要特征是高洁净度和超细晶粒组织。采用钨极氩弧焊对400MPa级超级钢施焊,并对其空冷和水冷两种冷却方式下的显微组织和力学性能进行分析。结果表明,空冷条件下焊接接头热影响区（HAZ）晶粒严重长大、强度下降,并出现软化区;焊接过程采用喷水冷却加快了冷却速度,有效抑制了焊接接头热影响区晶粒的长大,改善了接头组织,提高了贝氏体和低碳马氏体的含量,进而改善了接头的综合力学性能,满足实际焊接要求。     

超细晶粒钢的疲劳性能

采用常规疲劳试验方法分别对400MPa级和500MPa级两种热轧态超细晶粒钢进行了疲劳试验,分析了这两种超细晶粒钢的疲劳性能,并研究了超细晶粒钢疲劳裂纹萌生的机制。结果表明：由于500MPa级超细晶粒钢的晶粒尺寸相比400MPa级钢的更细小,因此其疲劳性能优于400MPa级钢的;在应力比R=-1、正弦波加载、循环周次基数N=5×10^6次的条件下,500MPa级和400MPa级超细晶粒钢的条件疲劳强度分别为270MPa和220MPa;两种超细晶粒钢的疲劳裂纹均在试样表面形核,且呈单源特征。     

数值模拟在超级钢焊接中的应用

本文综述了超级钢焊接温度场的数值模拟方法及研究现状,以及超级钢焊接热影响区微观组织的预测方法及研究现状,论述了超级钢的强化机制及细晶原理。超级钢作为一种性能好、成本低的新型材料,有着广阔的应用前景,但其焊接工艺尚不完善。数值模拟方法能够准确的模拟超级钢焊接温度场,预测超级钢焊接热影响区微观组织,这对了解超级钢焊接机理有很大帮助,并为优化焊接工艺提供指导和依据。     

Si和Nb对高强热轧高扩孔钢组织和性能的影响

为了研究Si和Nb对高强热轧高扩孔钢板显微组织、力学性能和扩孔性能的影响,在CSP连轧线上进行了3种成分试验钢的热轧试制,并对试验钢在扩孔过程中裂纹的形成和扩展行为进行了分析.研究表明:3种成分热轧钢板的显微组织均由铁素体和贝氏体组成,钢板的抗拉强度均高于610 MPa,伸长率大于24.5%,扩孔率高于104%;Si含量的增加,提高了组织中铁素体的含量,钢板的强度、伸长率和扩孔率得到提高;Nb含量的增加,细化了钢板的组织,钢板的强度和扩孔率增加明显,伸长率变化不大;试验钢在扩孔过程中裂纹主要沿铁素体和贝氏体的晶界处扩展,部分裂纹穿过铁素体晶粒.     

1200 MPa级冷轧双相钢组织性能及其热塑性

在实验室分别采用C-Si-Mn-Cr-Nb系及C-Si-Mn-Nb系成分设计试制了1 200MPa级冷轧双相钢,并对其热塑性进行了研究。结果表明,试验钢冷轧后连退板的抗拉强度分别达到了1 205 MPa、1 235 MPa,屈服强度分别为545 MPa、530 MPa,屈强比分别为0.45、0.43,伸长率分别为11.5%、10.5%,C-Si-Mn-Cr-Nb系成分设计的试验钢各项力学性能明显优于C-Si-Mn-Nb系试验钢。采用热模拟仪对试验钢的热塑性进行研究,发现1 200 MPa级冷轧双相钢在实验条件下,C-Si-Mn-Nb系试验钢出现第Ⅰ脆性区和第Ⅲ脆性区,而C-Si-Mn-Cr-Nb系试验钢仅出现第Ⅲ脆性区;C-Si-Mn-Nb系和C-Si-Mn-Cr-Nb系两种试验钢在600~1 100℃均出现热塑性降低,在750℃时降到这一区间的最低点,原因在于Nb(C,N)和AlN发生了沿奥氏体晶界析出。     

氮对淬火-配分超级马氏体不锈钢组织和性能的影响

对超级马氏体不锈钢进行氮合金化并进行淬火-配分工艺处理,使用OM、SEM、TEM、EBSD、BSD、万能试验机和维氏硬度计等手段对不含氮和氮含量(质量分数)分别为0.23%、0.35%的三组超级马氏体不锈钢进行表征,研究了氮元素对其组织和性能的影响。结果表明：氮的添加细化了实验钢中的马氏体板条,使其平均宽度由2.93 μm减小到0.65 μm。在配分处理过程中较高的氮富集度为逆变奥氏体的生成提供了驱动力,并使其稳定到室温。在钢中添加氮元素使钢的强度和塑性均明显比0 N试验钢的高,0.23 N和0.35 N试验钢的抗拉强度和延伸率分别为1510 MPa、24.2%和1215 MPa和35.1%。由此可见,氮合金化有利于提高超级马氏体不锈钢的力学性能。     

应用炉卷轧机开发700MPa级高强韧性钢板

700MPa级高强韧性钢板具有强度高、低温韧性好以及焊接性能优良的特点.然而,传统的铁素体/珠光体钢的屈服强度一般低于500MPa,不能满足强度要求.本研究采用现代炉卷轧机并结合控轧控冷工艺在安阳钢铁公司研制开发出700MPa级高强韧性钢板,其屈服强度大于560MPa、抗拉强度大于670MPa、延伸率大于16%、-40℃冲击功大于47J.     

异种钢的焊接研究现状

异种钢焊接时由于其化学成分与性能的较大差异,容易导致焊接裂纹、焊缝组织不均匀及性能稳定性差等问题,许多研究者对不同强度级别的低合金高强钢、异种不锈钢以及复合钢板的焊接进行了大量试验研究及理论分析。针对不同类型的异种钢焊接研究进行了综述,分析了异种钢焊接的特点,并对常见的问题进行了探讨,概述了国内外异种钢的焊接方法、工艺措施及接头性能等方面的研究现状,并对异种钢的焊接研究及其应用进行了展望。     

不同厂家直缝埋弧焊钢管的主要性能差异

通过对比测试采用不同厂家生产的钢板制成同规格、同钢级JCOE钢管成分、拉伸和冲击等性能,同时分析了不同厂家钢管的主要性能差异。结果表明,国内钢厂钢管比国外钢厂钢管具有较好的强度和低温夏比冲击韧性,其中钢管的屈服强度比国外钢厂钢管的屈服强度高33MPa,其母材冲击功比国外钢厂的要高107J;同时从基体成分分析了直缝埋弧焊管强度和韧性高于国外钢厂焊管的原因。     

390MPa级Ti+Nb超低碳高强度BH钢组织性能研究

对Ti+Nb+B复合处理超低碳高强度BH钢的热轧、冷轧和连续退火进行实验。结果表明:试制的超低碳高强度BH钢退火板的屈强比为0.536,烘烤硬化值为44MPa,具有较为优良的成形性能和烘烤硬化性能,抗拉强度为394MPa,达到了390MPa级超低碳高强度BH钢板的强度要求。物理化学相分析表明:添加在超低碳高强度BH钢中的B除了析出了2mg/kg的BN,大部分的B在钢中以间隙固溶的形式存在,对超低碳高强度BH钢基体起到了固溶强化的作用。     

Evaluation of local fatigue strength in spot weld by small specimen

It has been reported that high strength steel sheet cannot improve fatigue strength of components with a spot weld. The purpose of this study is to discuss the dominant factors on the fatigue strength of spot weld in order to clarify the reasons. A new fatigue testing technique is developed for a small specimen with a total length of less than 3 mm, and the local fatigue strength of heat‐affected zone (HAZ), which is the crack initiation site in the joint, in a mild steel sheet (270MPa‐grade) and a high strength steel sheet (590MPa‐grade) are evaluated by this technique. The fatigue strength of HAZ is almost equal in both steels although the tensile strength of the 590MPa steel is higher than that of the mild steel. The stress in the tensile‐shear spot‐welded joint under cyclic loading and the residual stress by the spot‐welding are evaluated by finite element analyses. The residual stress is tensile in both steels. However, the plastic deformation takes place in the joint of the mild steel and this releases the residual stress. On the other hand, the stress in the 590MPa steel is elastic and the residual stress decreases the allowable alternating stress. The stress under the condition of the experimental fatigue limit of the joint considering the residual stress coincides well with the fatigue limit diagram of HAZ, which means that the fatigue limit of the joint is determined by the fatigue limit of HAZ and the residual stress.     

高强贝氏体基体钒微合金化TRIP钢的性能

对一种钒微合金化TRIP钢进行冷轧连续退火,研究了钢的组织特征和力学性能。结果表明,贝氏体基TRIP钢的组织由贝氏体/马氏体和少量的残余奥氏体组成。随着贝氏体区等温时间的延长,钢的抗拉强度下降,屈服强度和延伸率提高。残余奥氏体由块状向薄膜状转变,体积分数增加,薄膜状残余奥氏体主要分布在贝氏体板条间,厚度为50-90 nm。在400℃等温180 s连续退火钢板呈现出相对低抗拉强度(960 MPa)、高屈服强度(765 MPa)和高延伸率(22.0%)的特性,而且加工硬化指数(0.20)、各向异性指数(0.94)和强塑积(21120 MPa.%)也较为优良。     

高强钢焊接构件工字形横截面残余应力试验及统一分布模型研究

为研究不同强度等级高强钢焊接工字形截面残余应力的变化规律,采用分割法对960MPa钢材试件进行测量,得到了残余应力分布。将试验结果与大量其他强度等级(包括235MPa、345MPa、460MPa以及690MPa)钢材焊接工字形截面的残余应力进行对比分析,研究了残余拉应力和残余压应力随钢材强度的变化规律。研究结果表明,焊缝和翼缘焰切边附近残余拉应力与截面几何尺寸无明显相关性,且呈现随钢材强度增大而增大的变化规律,并始终低于钢材强度;翼缘和腹板的残余压应力与钢材强度无明显关系,但随板件宽厚比及板厚的增大而明显减小。基于这一规律及大量试验数据,提出了不同强度等级钢材焊接工字形截面残余拉应力和压应力的计算方法,确定了分布范围,制定了统一分布模型,为不同强度等级高强钢结构的研究提供了基础条件。     

Microstructures and Mechanical Properties of Si-AI-Mn TRIP Steel with Niobium

Microstructure consisting of ferrite, bainite and retained austenite can be obtained through intercritical annealing and isothermal treatment in bainite transformation region for low silicon TRIP （transformation induced plasticity） steel containing niobium. Effects of strain rate, Nb content and soaking temperature in bainite region on microstructure and mechanical properties of test steels were investigated. It is shown that as strain rate ranges from 10^-2 to 10^-4 s^-1, the volume fraction of transformed martensite from retained austenite, as well as tensile strength, elongation rate and strength-ductility product, increases. When Nb is added, the volume fraction of retained austenite decreases, but tensile strength and yield strength increase. While Nb content reaches 0.014%, the steel exhibits high elongation and combination of strength and ductility. Higher retained austenite volume fraction and good mechanical properties are obtained in the test steels when the soaking temperature in bainite region is 400℃. The maximum values of tensile strength, total elongation rate and strength-ductility product can reach 739 MPa, 38% and 28082 MPa%, respectively.     

Application of nanoengineering to research and development and production of high strength steel sheets

Abstract

The design concepts and properties of three unique high strength steel sheets developed utilising nanoengineering are reviewed. The first steel is developed by optimising the distribution of nanoprecipitates and exhibits low yielding ratio in spite of being strengthened by grain refinement and precipitation hardening. The second is the ferrite single phase tensile strength 780 MPa grade advanced high strength steel sheet utilising the thermally stable nanosized precipitates, which possesses significantly well balanced elongation and stretch flangeability. These two were already commercialised. The last is the ultrahigh strength steel, of which the formability is enhanced by optimising the combination of hard phases. The steel consists of bainite, retained austenite and tempered martensite and exhibits 35% of elongation with 1470 MPa of tensile strength. Although further optimisation of the composition and the processing are needed to produce and commercialise the steel, the results indicate that the approach has the potential to improve formability dramatically.     

The Study on 400 MPa Class Plain Carbon Structure Steel

New generation of structure steel has been developed to meet the uninterruptedly increasing needs of the economic construction and development of society, and such material is characterized by ultra-fine grain. In this paper, 400MPa class plain carbon structure steel has been studied, making its yield strength doubled and service life doubled on the basis of good comprehensive properties in large quantity utilization. The deformation behavior and the stain induced transformation of SS400 steel at different temperature were investigated in the laboratory, and the industrial rolling test was carried out in 2 050mm HSM of Baosteel. Not only the laboratory studies but also the industrial test show that the technical route of the experimentis correct and the industrial test results on the basis of low carbon plain steel indicate that the grain size of ferrite was near to 4 ～ 5 μm, elongation was more than 30% , impact property was good, the yield strength can reach 400 MPa.