On failure mode of resistance spot welded DP980 advanced high strength steel

Abstract

This paper aims at investigating the correlation between metallurgical and mechanical characteristics of DP980 dual phase steel resistance spot welds with attention focused on the transition in failure mode from interfacial to pullout mode during the tensile shear test. It was studied whether the conventional/industrial weld size criteria can produce pullout failure modes for DP980 spot welds. Based on theoretical analysis and experimental results, there is a minimum fusion zone size which beyond that the interfacial failure mode is avoided. Results showed that by increasing welding current, pullout failure mode was promoted due to increasing the fusion zone size and encouraging martensite tempering in subcritical heat affected zone (HAZ). Fusion zone size was proved to be key factor controlling mechanical properties of DP980 welds in terms of peak load, ductility and failure energy.

Ce document vise à examiner la corrélation entre les caractéristiques métallurgiques et mécaniques de soudures par points par résistance de l’acier biphasé DP980, en mettant l’accent sur la transition du mode de défaillance de mode d’interface à mode par arrachement lors de l’essai de traction-cisaillement. On voulait savoir si les critères conventionnels ou industriels de taille de la soudure pouvaient produire des modes de défaillance par arrachement des soudures par points de DP980. L’analyse théorique et les résultats expérimentaux indiquent qu’il y a une taille minimale de la zone de fusion au-delà de laquelle on évite le mode de défaillance d’interface. Les résultats ont montré qu’en augmentant le courant de soudage, le mode de défaillance par arrachement était favorisé, à cause de l’augmentation de la taille de la zone de fusion et de l’encouragement du revenu de la martensite dans la HAZ sous critique. On a démontré que la taille de la zone de fusion constituait une composante clé contrôlant les propriétés mécaniques des soudures de DP980 en ce qui a trait à la charge de pointe, à la ductilité et à l’énergie de défaillance.     

TRIP600 高强钢的点焊工艺研究

对1．8mm规格的TRIP600钢进行了点焊试验、拉剪试验和接头的金相分析,研究了焊接电流、焊接时间等点焊工艺参数对接头力学性能的影响。结果表明,焊接时间为0．20、0．24、0．30S,TRIP600钢的可焊电流范围分别为11-12、10．5～12、10-11．5kA,拉剪试验失效模式为扣式或母材撕裂、且无飞溅的焊点,拉剪力达到27-30kN。     

GB／T20564．2—2006汽车用高强度冷轧双相钢国家标准制订情况介绍

介绍了GB／T20564．2—2006汽车用高强度冷轧双相钢国家标准的制订原则,及其主要技术内容。     

Peak load and energy absorption of DP600 advanced steel resistance spot welds

The paper aims at investigating the microstructure, failure mode transition, peak load and energy absorption of DP600 dual phase steel during the tensile-shear test. It was found that the welding current has profound effect on the load–displacement characteristics. In the low welding current, welds failed in interfacial failure mode. Increasing welding current resulted in sufficient weld nugget growth to promote double-sided pullout failure mode with improved mechanical properties. Further increase in the welding current caused expulsion and failure mode was changed to single-sided pullout with reduced energy absorption capability. It was found that the fusion zone size is the key parameter controlling the mechanical properties of DP600 resistance spot welds in terms of peak load, maximum displacement and failure energy.     

高强度汽车大梁用钢W610L的研制

采取在碳锰钢中添加适量的铌和钛,通过细晶强化和沉淀强化成功开发出高强度汽车大梁用钢W610L。该钢钢质纯净、晶粒细小、强度高、韧性好,成功应用于国内多家知名汽车制造厂的汽车纵梁、横梁、支撑结构件等构件的制作。     

汽车用先进高强度钢开发和研究的进展

先进高强度钢已经在汽车上得到了广泛应用,并在汽车的减重、安全、节能、环保等方面表现出广阔的前景。强度更高、成型性更好的新型先进高强度钢的开发也得到越来越多的重视。对正在开发的新型先进高强度钢开发和研究现状进行了简述,并对下一代高强度钢的研究进行了预测。     

两相区热处理对工程结构用高强钢低周疲劳性能的影响

为提高工程结构用高强钢的低周疲劳性能,通过光学显微镜、扫描电子显微镜、X射线衍射仪、疲劳试验等方法,研究了两相区热处理工艺条件下工程结构用钢的显微组织演变及低周疲劳断裂行为.结果表明:两相区热处理组织由细小且形状不规则的回火态马氏体与条带状铁素体组成,马氏体体积分数约为61.7%,残余奥氏体体积分数为2%~5%。试样具有优良的综合性能,与传统调质工艺相比,具有较低的屈强比及较高的低温冲击韧性.同时,两相区热处理后呈现出较高的抗低周疲劳性能,因为塑性变形能力提高,降低了过早形成疲劳裂纹的概率并减小裂纹扩展速率,使高应变低周疲劳性能提高.     

高强度焊接结构钢微裂纹控制

通过对高强度焊接结构钢板和铸坯表面裂纹进行取样分析,结合生产工艺,查找微裂纹产生的原因,从结晶器保护渣选用、结晶器冷却制度、二次冷却制度几个方面进行优化,取得了良好控制效果。     

采用在线热处理工艺开发高强钢的研究进展

简述了采用直接淬火（DQ）和在线回火（HOP）工艺开发高强度钢板的研究进展,介绍了屈服强度690 MPa级、800 MPa级9、60 MPa级和1 100 MPa级超高强度钢板试制结果。试制钢的微观组织为超细贝氏体及与马氏体的混合组织,此类组织具有良好的强韧性。采用HOP工艺以较快的加热速度热处理,形成的细化渗碳体和分布均匀的马奥组元。细化的渗碳体均匀地分布在基体中,可提高钢板的强度和低温冲击功。研究认为,在线淬火及回火技术未来将成为高强结构钢的重要发展方向。     

钢种补偿在冷轧高强钢厚度控制中的应用

酸轧产线生产高强钢时,X射线测厚仪测出的带钢厚度和实际厚度有明显偏差,容易产生批量厚度不符的质量事故。分析了厚度偏差产生的原因,推导出了厚度离线钢种补偿的方法。该方法在产线应用后,X射线测厚仪测出的高强钢厚度偏差小于0.01 mm,满足了对高强钢厚度精度控制的要求。     

Microstructure and forming characteristics of spray-formed M42 high speed steel

M42 high speed steel(HSS),a high grade alloy,was produced using the spray forming technology.Optical metallography(OM),X-ray diffraction(XRD) and scanning electron microscope(SEM) were used to investigate the microstructures of the as-sprayed M42 HSS and the as-atomized powders.It is found that as-sprayed M42 HSS is composed of martensite,retained austenite and carbides.The grain size,as well as the morphology,size and distribution of the carbides have been greatly improved compared with those of the as-cast M42 steel(a traditional process).The size of the powder obtained at a high cold speed was ranged from 50 μm to 100 μm in diameter.Its representative microstructures include dendrite,dendritic fragments,a mixture of dendrites,equiaxed grains and dendritic fragments,and equiaxed grains.The rapid solidification in the spray forming is a key factor to cause the refinement of the M42 HSS.     

Research and development of hot-rolled ultra-high strength steel at Baosteel

The effects of the composition and cooling process on the microstructures and properties of hot-rolled ultra-high strength low alloy(HSLA)steel,complex phase steel and martensite steel were studied in the laboratory.And S700MC and MP1200 ultra-high strength steels were trial produced at the 1 880 mm hot-rolling line of Baosteel.Compared with conventional hot-rolled high strength products,the idea that water is alloy was applied in the newly developed hot-rolled ultra-high strength steel.By the use of the economical composition design and controlled cooling after hot-rolling effectively,ultra-high strength steel of different steel grades can be obtained.     

冷轧双相钢DP800生产工艺及性能研究

探讨了800 MPa级冷轧双相钢的成分体系、冷却处理工艺、组织及性能;研究了退火温度、冷却速率对双相钢性能的影响,分析了双相钢的强化机理,并且优化了退火工艺参数。结果表明,冶炼过程采用C-Si-Mn-Cr-V成分体系,轧制过程采用650℃±20℃的中温卷取,连续退火过程中快冷段投入高氢(H2含量20%)冷却,冷速达到42~50℃/s,能够得到由铁素体和马氏体组成的冷轧双相钢DP800,综合力学性能优良。     

Study on non-metallic inclusions in Al killed high strength alloy steel refined by high basicity and high Al_2O_3 content slag

Laboratory and industrial studies were carried out to investigate non-metallic inclusions in high strength alloy steel refined by high basicity and high Al₂O₃ slag.It was found that the steel/slag reaction time largely affected non-metallic inclusions.With the reaction time increased from 30 min to 90 min in laboratory study,MgO-Al₂O₃ spinels were gradually changed into CaO-MgO-Al₂O₃ system inclusions surrounded by softer CaO-Al₂O₃ surface layers.By using high basicity slag which contained as much as 41%Al₂O₃ in the laboratory study,ratio of low melting temperature CaO-MgO-Al₂O₃ system inclusions was remarkably increased to above 80%.In the industrial experiment,during the secondary refining,the inclusions changed in order of "Al₂O₃→MgO-Al₂O₃→CaO-MgO-Al₂O₃".Through the LF and RH refining,most inclusions could be transferred to lower melting temperature CaO-Al₂O₃ and CaO-MgO-Al₂O₃ system inclusions.     

500MPa高强度热轧型钢的生产实践

为了满足高端工业车辆对高强度型材的需求,莱钢通过采用钒氮微合金化成分设计及再结晶控制轧制工艺,开发出500 MPa高强度热轧型钢。对此产品进行了拉伸、冲击性能、布氏硬度及金相检验,其力学性能良好,屈服强度Re L达到556 MPa,金相组织为铁素体加珠光体,完全满足工业车辆用热轧型钢的要求。     

CT100高强度连续油管用钢卷的开发与应用

介绍了宝钢CT100高强度连续油管用钢卷的开发及应用。宝钢开发的CT100高强度连续油管用钢卷具有低的硫磷含量、均匀的显微组织、合适的力学性能,钢卷的屈强比低于0.80,且不同部位强度性能差异在50 MPa以内,符合连续油管的制造需求。采用研制的钢卷钢制造的连续油管各项力学性能均满足API Spec 5ST规范对CT100钢级连续油管的要求,且具有优良的抗疲劳性能。     

高强IF钢的高速应变行为

利用拉伸实验装置研究了高强IF钢在高应变速率下的变形特性。结果表明：高强IF钢是应变速率敏感性材料,在应变速率10-4～103/s的范围内,应变速率对高强IF钢的应变硬化率与屈服强度的影响具有2阶段性。在第一阶段,应变速率较低,应变硬化率与屈服强度对应变速率的敏感性较小;在第二阶段,应变速率较高,随应变速率的增加,应变硬化率迅速降低,屈服强度迅速增加。     

Q420B高强度角钢工艺研究与控制

介绍了Q420B高强度角钢的工艺研究与质量控制,认为通过采用合理的钒氮微合金化工艺和合理的冶炼、精炼、连铸工艺,能生产出质量和轧材性能均符合有关标准要求的Q420B高强度角钢。     

温成形温度对双相钢B340/590DP拉深性能的影响

研究了再结晶温度以下不同温度的双相钢B340/590DP的拉深性能.数值模拟显示B340/590DP钢随着温度的上升拉深过程中材料的等效应力是下降的,但材料的实际拉深性能在300℃以内并未随温度的升高而改善,在温度超过400℃以后材料的拉深性能明显改善,在500℃时材料的拉深极限系数由常温的0.52降为0.5.实验结果表明,当温度加热至400℃以上时,板料的实际成形性能提高,拉深试样的厚度分布更加均匀.