含钼双相钢DP600相变研究和工艺实践

采用热模拟试验研究了含钼双相钢DP600在不同冷却模式、转变温度和冷却速率时的显微组织转变,分析了相变后的马氏体比例和晶粒度级别,根据热模拟结果设计了DP600钢的生产工艺,并探讨了钼元素对双相钢的影响。结果表明,DP600钢在热轧组织转变时,两段式冷却工艺比一段式工艺形成的马氏体细小,且晶粒度提升1级。奥氏体向铁素体转变过程中,存在最佳相变温度平衡点;590 ℃以上减缓DP600钢铁素体＋珠光体的过冷转变速率,可以细化晶粒、增加马氏体比例。生产的DP600钢金相显微组织为铁素体＋马氏体,马氏体比例为17%,晶粒度为11级;纵向、横向抗拉强度分别为592和620 MPa,伸长率分别为28.5%和26.5%。钼元素可以强烈抑制C- Si- Mn- Cr- Mo系DP600钢的铁素体转变,缩小铁素体转变区。     

高强度热轧双相钢的低周疲劳性能

从热轧双相钢的实际应用需求出发,研究了高强度热轧双相钢DP600的低周疲劳性能。采用轴向应变控制方法对DP600钢进行了低周疲劳试验,并对试验数据进行拟合计算,得到DP600钢的循环应力-应变曲线、应变-寿命曲线和过渡疲劳寿命。通过扫描电镜观察疲劳断口,结果显示低周疲劳条件下,DP600钢断裂裂纹起源于试样表面,裂纹扩展前期呈现部分脆性断裂特征,后期则以明显的韧性断裂为主。     

Warm deformation and fracture behaviour of DP1000 advanced high strength steel

The effect of temperature has been investigated on the mechanical properties and fracture behaviour of DP1000 advanced high-strength steel. The variation of the mechanical properties depending on temperature has been determined by performing uniaxial tensile tests at the temperatures of 25, 100, 200, 300°C at the rolling directions of 0° (rolling), 45° (diagonal), and 90° (transverse) at the strain rate of 0.0083?s^?1. The yield strength and tensile strength have showed a slight decrease tendency between 25 and 200°C, but the highest value has been reached by showing an increase at 300°C temperature. The amount of elongation has not been affected significantly with the increase of the temperature. While hardening coefficient has increased due to the rising temperature, no effect has been observed on strength coefficient between 25 and 100°C, but an increase has occurred at higher temperature values.     

DP980钢及DP980钢激光焊接接头的高周疲劳性能

摘要：为了研究DP980钢的高周疲劳性能,采用疲劳试验机对DP980钢和DP980钢激光焊接接头进行高周疲劳试验,得到Basquin方程,并利用光学金相显微镜和扫描电镜进行组织和断口分析。结果表明：DP980钢激光焊接接头的焊缝根部和顶部出现形状凹陷,焊接接头的质量为中等。DP980钢疲劳极限为341MPa,DP980钢激光焊接接头的疲劳极限为148MPa,激光焊接接头的疲劳极限较母材的疲劳极限降低约50%。对于DP980钢而言,铁素体/马氏体晶界是裂纹萌生的主要位置,疲劳断口为准解理断口。对于DP980钢激光焊接接头而言,疲劳裂纹源位于焊缝凹陷处,而非热影响区及母材,疲劳断口为解理断口。DP980钢和DP980钢激光焊接接头的疲劳裂纹扩展区均有明显的疲劳条带,并伴随有二次裂纹。     

High cycle fatigue behavior of DP980 steel and DP980 steel laser welded joints

For the study of the DP980 steel high cycle fatigue property, high fatigue tests of DP980 steel and DP980 steel laser welded joints were carried out with fatigue testing machine, the Basquin equation was concluded. Microstructures and fractures were analyzed by optical microscope and scanning electron microscope. The results show that DP980 steel laser welding joints have the weld concavity at the welding root and top, the quality of welded joints is medium. The fatigue limit of DP980 steel is 341MPa, the fatigue limit of DP980 steel laser welded joint is 148MPa, the fatigue limit decreases by 50% compared with the fatigue limit of the base metal. For DP980 steel, the crystal boundary of the ferrite/martensite is the main location of micro cracks initiation, the fatigue fracture of DP980 steel is the quasi cleavage fracture. For DP980 steel laser welding joints, the fatigue cracks initiation is located in the weld concavity, not in the heat affected zone, the fatigue fracture is cleavage fracture. DP980 steel and DP980 steel laser welding joints crack propagation is characterized by the obviously fatigue striations coupled with secondary cracks.     

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.     

热轧双相钢DP600组织性能的研究

选择添加铬、钼合金元素的碳、锰、硅系的高强双相钢DP600为研究对象,选择Gleeble-3800热模拟试验机为研究方法测定了DP600动态CCT曲线,并模拟DP600双相钢热轧过程。采用金相组织观察、织构分析及力学性能测试等手段分析了不同工艺制度下双相钢组织及织构变化规律以及对性能的影响,从中获得最佳组织配比及优化的热轧工艺参数。根据优化的中试结果,进行了热轧双相钢DP600的工业试制。结果表明,试制样品的显微组织为铁素体及马氏体;屈强比均小于0.65,抗拉强度均在600 MPa以上;伸长率在24%以上;其拉伸曲线均为连续曲线,无屈服点伸长,具有典型的双相钢特征。     

600MPa级高强钢热轧卷取工艺研究及应用

为了探究卷取过程热轧带钢的氧化铁皮和组织性能的变化规律,采用扫描电镜、电子探针、光学显微镜、透射电镜和拉伸试验机等研究了不同卷取温度和冷却方式对600 MPa级热轧带钢表面质量和组织性能的影响。结果表明,650、600℃卷取温度下,与缓慢冷却方式相比,采用快速冷却方式可有效改善热轧带钢表面氧化铁皮的结构,使氧化铁皮中FeO比例提高10%～15%,氧化铁皮厚度下降25%～30%,同时有效减弱热轧带钢表面氧化铁皮与基体界面硅元素和锰元素富集;不同冷却工艺下热轧带钢中的晶粒尺寸相近;650℃卷取+快速冷却工艺下热轧带钢的屈服强度最高,试样断口的位错密度最高,但断后伸长率并未明显下降。     

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。     

高强DP钢的关键轧制技术开发与应用

为了解决高强钢生产过程中的诸多问题,从热轧、冷轧制中存在的问题以及工序管理控制的角度出发,制定了先进高强钢关键轧制技术研究方案,最终解决了热轧带钢性能稳定性控制、带头上翘、冷轧带钢厚度波动、冷轧板形突变等问题。另外,在热轧轧制工艺、温度精准控制、冷轧轧制力模型优化,一级AGC厚度自动控制系统开发、全流程压下负荷分配优化等方面开展了大量研究工作,积极探索创新,开发了一系列先进高强钢轧制关键技术,并在产线生产中得到应用,取得良好效果。     

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.     

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。     

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。     

高强度无取向电工钢疲劳性能及断裂机制

测试了高强无取向电工钢的S-N曲线,并借助光学显微镜、扫描电子显微镜、透射电子显微镜分析了实验钢组织,疲劳断口形貌和位错结构.结果 表明:室温条件下,频率为20 Hz,应力比R为0.1,循环107周次时,实验钢的疲劳强度为360 MPa,疲劳裂纹萌生于实验钢的次表面,裂纹萌生点附近有沿晶开裂现象,疲劳裂纹扩展区域有解理台阶与疲劳条纹,瞬间断裂区是韧性断裂,有大量韧窝.实验钢在循环应力作用下基体中产生了大量位错,并有驻留滑移带终止在晶界位置.     

Tempering process of high strength and high toughness Cr- Mo- V bulb- flat steel

Aim at the problems that the heat treatment process of high strength and high toughness Cr- Mo- V bulb- flat steel was difficulty and the granular bainite was not fully decomposed, the influence of different tempering temperatures and tempering holding times on the microstructure and mechanical properties of high strength and high toughness Cr- Mo- V bulb- flat steel were studied by optical microscopy, SEM, TEM and mechanical property tests. The results show that the metastable granular bainite in the steel can be recovered and transformed to quasi- polygonal ferrite by tempering at temperatures above 600?? and holding for more than 2h. The large- sized and long- shaped M- A islands in the original microstructure are decomposed and transformed into granular M- A islands. With the increase of the tempering temperature, the granular bainite in the steel can be further decomposed to make the particles finer and more dispersed, which significantly improves the low- temperature toughness of the steel and obtains a good comprehensive performance. For this steel, the best heat treatment process to get good match of strength and toughness is tempering at 660-680?? and holding for 3. 0-3. 5h.     

高强耐磨稀土高锰黄铜的组织与性能

设计一种用于制造同步器齿环的CuZnMnAlSiFeCeB复杂黄铜合金,利用水平连铸,热挤压和快速水冷的工艺制备合金型材.利用金相显微镜和扫描电镜以及能谱分析的手段研究合金的铸态组织,挤压态组织. 合金铸态组织均匀,无气孔和夹杂等缺陷. 挤压淬火态合金组织为β+少量α+均匀分布强化相. 合金挤压淬火后的性能为抗拉强度783 MPa,断后伸长率5.89 %.      

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。     

先进高强度汽车钢的发展趋势与挑战

 高强钢在汽车轻量化、节能减排、成本方面具有一定的优势与潜力,目前,仍是汽车的主要材料。高强钢的使用比例逐年增加,并且向更高强度方向发展,生产方式呈现出钢板“以热代冷”、零件成形“以冷代热”的低成本发展趋势,依靠亚稳奥氏体增强、增塑的第三代汽车钢成为先进高强钢的重要发展方向,然而,先进高强钢的发展给材料、工艺、装备等带来了新的挑战。     

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.