980MPa级先进高强钢的发展

选用轻量化汽车材料时应综合考虑材料的性能、质量和成本。目前,先进高强钢被广泛用于汽车工业。先进高强钢有双相钢、相变诱导塑性钢、马氏体钢、复相钢、淬火-配分钢、DH钢等。综述了980 MPa及以上高强钢的分类和主要钢种,汽车用高强钢的化学成分、显微组织、力学性能和使用性能,并结合实际零件的制造过程对这些高强钢的焊接和成形性能作了较深入的探讨,简述了其发展现状和研究进展。

Ballistic impact response of resistance-spot-welded(RSW) double-layered plates for Q&P980 steel

Ballistic impact response of resistance-spot-welded(RSW)double-layered(2×1.6 mm)plates(190 mm×150 mm)for Q&P980 steel impacted by a round-nosed steel bullet(12 mm diameter and 30 mm length)was investigated by using gas gun and high-speed camera system.The RSW specimens were spot welded using a 6 mm diameter electrode face producing a 7.2 mm diameter fusion zone of the spot weld.The ballistic curve and energy balance for the tests of the spot weld of the RSW specimens at different velocity were analyzed to characterize the ballistic behavior of the RSW specimens under bullet impact.The fracture mechanisms of the RSW specimens under bullet impact were presented.For the tests below the ballistic limit,the cracks initiated from the notch-tip and propagated along the faying surface or obliquely through the thickness depending on the impact velocity.For the tests above the ballistic limit,the plug fracture in the front plate of the RSW specimen could be caused by the thinning-induced necking in the BM near the HAZ,while the plug fracture in the rear plate of the RSW specimens may be consist of the circumferential cracking from the rear surface and the bending fracture of the hinged part of material.The effects of the electrode indentation and the weld interfaces on deformation and fracture of the RSW specimens under bullet impact were revealed.For the tests above the ballistic limit,the circumferential fracture from the rear surface of the RSW specimens was always initiated along the interior periphery of the electrode indentation and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface.When the circumferential crack also formed outside the electrode indentation,the fracture on the BM/HAZ interface could be found.On the front plate of the RSW specimens,the shear/bending induced cracking from the notch-tip were observed and the crack paths were along the FZ/CGHAZ or CGHAZ/FGHAZ interface.

Effects of Cover Sheets on the Nugget Growth and Fracture Behavior of Resistance Spot Welded Q&P980 Steel Joints

The resistance spot weldability of galvanized ultra-high-strength steels is not satisfed,the joints are prone to interfacial fracture and the weldable current range is narrow.To solve the problems,a novel method called resistance spot welding with double-sided cover sheets was introduced to weld a galvanized Q&P980 steel with the thickness of 1.2 mm.Two thin SPCC mild steel sheets were chosen as cover sheets and were placed symmetrically at both sides between the Q&P980 steels and the electrodes,then the RSW process was carried out.Compared with the traditional RSW method,the joints obtained by using the novel method achieved larger tensile shear strength and energy absorption,which increased by 26.9%and 52.6%,respectively.With increasing the welding current,the failure mode transferred from interfacial fracture to nugget pull-out fracture or base metal tearing fracture.By contrast,the joints always showed interfacial fracture without cover sheets.The improvement of the joint performance was mainly attributed to the enlargement of the nugget.With the help of fnite element simulation,it was found that the cover sheets helped increase the contact area and reduced the current density during welding,which postponed the expulsion,and a larger area could be evenly heated.The application of the novel method can be easily extended to the resistance spot welding of other ultra-high-strength steels with various thicknesses.

组织特征对980 MPa级先进超高强钢成形性能和拉伸行为的影响

以CP980钢、DP980钢、QP980钢为研究对象,采用单轴拉伸试验并结合数字图像相关技术,研究了组织特征对980 MPa级先进超高强钢单轴拉伸行为以及全局、局部成形性的影响。结果表明:QP980钢由马氏体、铁素体、残余奥氏体组织组成,在均匀变形阶段奥氏体相变产生的相变诱导塑性效应使该钢具有最优的全局成形性,但是新生马氏体相与其他相的硬度差较大,导致其局部成形性最差并形成准解理断裂;DP980钢由铁素体和马氏体组织组成,其强化机制以马氏体硬相强化和铁素体位错强化为主,全局成形性居中,同时因铁素体和马氏体之间具有一定的协调变形能力,其局部成形性较好,断裂形式主要为韧性断裂;CP980钢为铁素体、贝氏体、马氏体的多相组织,各相硬度差小,协调变形能力较强,局部成形性最好,断裂形式为韧性断裂。

980钢超窄间隙熔化极气体保护焊研究

以厚板980钢为对象,进行了超窄间隙熔化极混合气体保护自动对接焊试验,并依据《JB4708-2000钢制压力容器焊接工艺评定》国家标准,对980钢超窄间隙MAG焊接头进行了拉伸、弯曲和冲击试验,分析了显微组织、显微硬度和宏观形貌。结果表明,接头所有技术指标均满足国家标准要求,且焊接热影响区很窄,该区塑韧性损伤极小。

980钢焊接接头在谱载荷作用下的疲劳裂纹扩展

对 98 0钢焊接接头在谱载荷作用下的疲劳裂纹扩展行为进行了初步研究。用 980钢焊接接头制成两种标准CT试件 ,裂纹分别开在焊缝金属上和焊趾处平行于焊缝方向 ,在两种谱载荷下进行了疲劳裂纹扩展试验。采用Wheeler模型进行谱载荷作用下裂纹扩展分析 ,得到焊缝金属的载荷延滞效应明显 。

980MPa级高强钢焊接接头HAZ的组织和性能

采用焊接热模拟的方法,研究一种980MPa级低碳贝氏体高强钢焊接接头HAZ不同区域,通过对各个区域的组织及相的分析,以及相应的拉伸及冲击试验研究了此类高强钢的组织和性能.结果表明,粗晶区的冲击性能最好,细晶区的冲击性能最低,为热影响区的薄弱环节.粗晶区组织为均匀粗细相间的板条贝氏体组织;在板条贝氏体上弥散析出碳化物;板条贝氏体界面上的奥氏体薄膜的存在是粗晶区韧性提高的原因.细晶区为孪晶马氏体+少量的板条马氏体,孪晶马氏体是导致细晶区性能下降的主要原因.

980MPa级高强钢焊接接头HAZ冲击性能的分析

采用焊接热模拟方法,对NiCrMoV系980MPa级低碳贝氏体高强钢焊接接头HAZ单次及多次热循环进行了热模拟试验.在室温和-50℃下研究了该钢焊接接头HAZ不同区域的冲击性能.结果表明,在室温和-50℃粗晶区的冲击性能最好,细晶区的冲击性能最差,为焊接接头的薄弱环节;二次粗晶区循环改善其性能,二次细晶区循环降低其性能;粗晶区晶粒比较粗大主要为低碳板条贝氏体组织;断口上表现为大而深的韧窝的融合,且韧窝之间融合较紧密;细晶区晶粒细小主要为孪晶马氏体,断口上表现为小而浅韧窝之间的连接,存在少数较大的韧窝.

980MPa级钢配套焊丝电弧形态和熔滴过渡试验分析

利用激光为背景光的成像系统,摄取电弧形态和熔滴过渡的高速图像,试验了新研制的屈服强度为980MPa级钢配套的两种焊丝电弧形态和熔滴过渡形式.试验在典型焊接参数条件下,采用不同配比的氩、氦混合保护气体MIG焊接方法,对所研制的焊丝与普通焊丝H08Mn2SiA进行了电弧形态和熔滴过渡对比试验.结果表明,所研制的焊丝不仅其熔敷金属力学性能满足要求,而且熔滴过渡性能也优于常用的普通焊丝,为所研制焊丝的焊接工艺性能和实际应用奠定了试验基础.

980MPa耐蚀钢轨U68CuCr的开发和应用

通过制定合理成分和铁水脱硫-120 t顶底复吹转炉-吹氩-LF—RH-280 mm×380 mm坯连铸-轧制工艺,开发了980 MPa热轧耐蚀钢轨U68CuCr（/%：0.65~0.75C,0.40~0.80Si,1.00~1.30Mn,≤0.030P,≤0.025S,≤0.50Cu,≤0.50Cr,≤0.05Nb）。试验结果表明,耐蚀钢轨U68CuCr抗拉强度≥1060 MPa,伸长率≥12%,踏面硬度HB值为300~310,珠光体片间距为0.2μm,耐磨性能优于同一强度级别的U75V钢轨。2%NaCl溶液腐蚀试验显示,耐蚀钢轨U68CuCr腐蚀速率为U75V钢轨的57%。在京广线使用3年,通过总重量超过3亿吨,耐蚀钢轨U68CuCr使用性能良好,其各项指标均满足铁路运输要求。

980钢加工表面疑似“裂纹”的分析与对策

在以980钢为母材的风洞柔板加工过程中,980钢加工表面出现了大量的疑似“裂纹”,为搞清楚疑似“裂纹”是什么,回答能否应用于在建风洞的问题,开展了材料化学成分检测、无损检测、金相研究、加工工艺研究、腐蚀研究、疲劳试验等工作,研究成果应用于改进后的加工工艺,消除了疑似“裂纹”,用980钢加工的柔板也成功应用于在建风洞。

一种新型980MPa高强钢的低温四点弯曲断裂行为

在不同试验温度（-196～200℃）下对一种新型980MPa高强钢进行了带缺口试样的四点弯曲试验，并用扫描电镜对其断口进行了观察，研究了该钢的断裂行为。结果表明：随着试验温度升高，该钢的韧性逐步提高；在-100℃及以上温度时，该钢的断裂形态为韧性断裂，韧性较好；在-100℃以下，逐渐由韧性向脆性断裂过渡，在-196℃时，为脆性准解理断裂。

980 MPa高强钢焊接接头薄弱环节的确定

通过在低温下进行拉伸试验、冲击试验以及扫描电镜下的断口观察,对屈服强度为980 MPa新型高强钢的MAG和TIG焊接接头的性能和断裂机理进行了研究,并在此基础上确定焊接接头的薄弱环节,提出其薄弱环节对接头整体性能的影响规律.结果表明,这两种焊接方法焊缝金属的抗拉强度与母材相差不大,但其断面收缩率有所降低;焊缝金属尤其原始焊缝是整个焊接接头的薄弱环节;原始焊缝比例和焊缝比例共同决定着焊接接头的整体性能.MAG焊试样的冲击韧性要比TIG焊相应的韧性小很多;MAG焊焊缝断口为准解理断裂,而TIG焊焊缝断口则是韧性断裂.出现这种现象的原因主要是以下两个方面:一方面是由于TIG焊焊丝的镍含量比MAG焊焊丝的要高,致使其韧性好于MAG焊;另一方面是因为MAG焊焊缝金属含有大量夹杂物,且夹杂物尺寸大于TIG焊焊缝金属中夹杂物尺寸,大量大尺寸的夹杂物容易形成起裂源,使其诱发早期脆性准解理断裂.

HAZ Characterization and Mechanical Properties of QP980-DP980 Laser Welded Joints

The QP980-DP980 dissimilar steel joints were fabricated by fiber laser welding.The weld zone(WZ)was fully martensitic structure,and heat-affected zone(HAZ)contained newly-formed martensite and partially tempered martensite(TM)in both steels.The supercritical HAZ of the QP980 side had higher microhardness(~549.5 Hv)than that of the WZ due to the finer martensite.A softened zone was present in HAZ of QP980 and DP980,the dropped microhardness of softened zone of the QP980 and DP980 wasΔ21.8 Hv andΔ40.9 Hv,respectively.Dislocation walls and slip bands were likely formed at the grain boundaries with the increase of strain,leading to the formation of low angle grain boundaries(LAGBs).Dislocation accumulation more easily occurred in the LAGBs than that of the HAGBs,which led to significant dislocation interaction and formation of cracks.The electron back-scattered diffraction(EBSD)results showed the fraction of LAGBs in sub-critical HAZ of DP980 side was the highest under different deformation conditions during tensile testing,resulting in the failure of joints located at the sub-critical HAZ of DP980 side.The QP980-DP980 dissimilar steel joints presented higher elongation(~11.21%)and ultimate tensile strength(~1011.53 MPa)than that of DP980-DP980 similar steel joints,because during the tensile process of the QP980-DP980 dissimilar steel joint(~8.2%and 991.38 MPa),the strain concentration firstly occurred on the excellent QP980 BM.Moreover,Erichsen cupping tests showed that the dissimilar welded joints had the lowest Erichsen value(~5.92 mm)and the peak punch force(~28.4 kN)due to the presence of large amount of brittle martensite in WZ and inhomogeneous deformation.

TS980QC钢焊接工艺试验

采用φ(Ar)80%+φ(CO2)20%的熔化极气体保护焊接方法,对8 mm厚TS980QC钢板进行焊接试验,研究了材料抗冷裂敏感性、焊接热输入对焊接质量的影响,以及焊接接头综合质量。结果表明:预热温度高于50℃时,TS980QC高强钢焊接可以避免冷裂纹产生;该钢对焊接热输入较为敏感,过高或过低的热输入均会导致性能下降;试验选用的焊丝在合适工艺条件下能较好地匹配TS980QC钢的性能。

980钢焊接工艺研究

本文介绍了980钢的可焊性,并采用焊条电弧焊(SMAW)方法利用不同预热温度、后热处理对板材进行了焊接工艺试验,通过拉伸性能、冲击韧性和显微硬度测试对不同预热、后热温度获得的焊接接头进行评定。试验结果表明,采用焊接材料V840,焊接方法为焊条电弧焊及合理的焊接工艺参数,可以获得焊接接头的综合力学性能良好,且满足工程要求的焊接接头。

980 MPa级冷轧双相钢连退断带原因分析及改进措施

分析了980 MPa级别冷轧双相钢在连退线入口非焊缝处断带的产生原因,结果显示,热轧显微组织为铁素体-马氏体两相组织,且两相分布均匀,钢板通宽方向上硬度分布均匀。冷硬钢板组织为典型的纤维状两相组织,且宽度方向上硬度分布也比较均匀。断口呈撕裂状,且存在较多的韧窝,为典型的韧性断裂。断口附近存在较多大小不一的裂口,且钢板板形较差,存在较严重的中浪,而入口张力辊张力高达15 kN。综上,导致980 MPa级冷轧双相钢连退入口断带的主要原因是张力过大、边裂和板形较差综合作用结果。通过降低入口张力、改善酸轧板形、减少边裂,可以有效降低断带的风险。

高强钢摆动电弧窄间隙GMAW组织与性能研究

采用摆动电弧窄间隙GMAW方法对42 mm厚的10Ni5Cr Mo V钢进行了焊接,并对其接头形貌、显微组织、硬度分布、拉伸性能和冲击韧性进行了测试分析。结果表明,该方法得到了成形良好、无任何宏观缺陷的窄间隙焊缝;焊缝组织由针状铁素体和粒状贝氏体及少部分马氏体组成;热影响区中的过热区以粗大的板条状马氏体组成,是整个焊接接头最薄弱区域,但其宽度较窄;窄间隙焊接接头具有较好的强度和韧性,无软化及脆化现象,满足使用要求。

Effect of sulfate-reducing bacteria on hydrogen permeation and stress corrosion cracking behavior of 980 high-strength steel in seawater

980 high-strength steel has been widely used in marine engineering structures due to its high strength and toughness.However,it is easily affected by the harsh environmental conditions(such as the presence of sulfate-reducing bacteria,SRB),leading to the risk of stress corrosion cracking(SCC).In this paper,the effects of SRB and its metabolites on hydrogen permeation and SCC mechanism of 980 steel in seawater solution were investigated by slow strain rate tensile test,scanning electron microscope,Xray energy spectroscopy,Raman spectroscopy and Devanathan-Stachurski double electrolytic cell.Results demonstrated that the SCC susceptibility of 980 steel was promoted in the presence of SRB,which was related to the cultivation time of the bacteria.When SRB were cultivated for 3 d and 6 d,the SCC mechanism was controlled by hydrogen-induced cracking(HIC);while the cultivation time extended to 11 d,the SCC of 980 steel was under the combined effect of the anodic dissolution(AD) and HIC mechanism.When cultivated for 16 d,the SCC of 980 steel was caused by the dominant AD.Both the SRB accelerated hydrogen permeation under cathodic depolarization process and SRB assisted AD(pitting corrosion)played an enhancing role in promoting SCC susceptibility of 980 steel.

Abrasive Wear Resistance of Dual Phase Steels DP980 and DP600

The abrasive wear resistance of dual phase （DP） steels DP980 and DP600 was investigated by using an ASTM rubber wheel abrasion tester. At 2.40 m ·s-1 sliding speed under 19.9 N load with 180--355μm abrasive sands, the wear rates of DP980 and DP600 were 1.01 × 10^-11 and 0.86 ×10^-11 m3 · m-1 , respectively, correspond- ing to about 1.9 and 2.3 times of the relative wear resistance of normal low-carbon steel ASTM A283C. Using di- rectly water quenching from austenitic temperature, the abrasive wear resistance of DP980 samples under 19.9 N load could be improved by 1.65 times. The wear rates of DP980 and DP600 samples decreased respectively with in- creasing sliding speed and abrasive particle size and decreasing applied load. The experimental results reveal that the effect of martensite on the wear resistance not only depends on the volume fraction but also depends on the morphol- ogy, distribution and grain size.