400 MPa级超细晶粒热轧带肋钢筋焊接接头的组织和性能

研究了超细晶粒钢筋焊接接头的组织和力学性能。结果表明：经过焊接热循环的作用，虽然热影响区的晶粒明显粗化，但由于所获得的二次组织形态与钢筋原始组织不同，热影响区未发生软化，也不存在焊接接头强度下降的问题。超细晶粒钢筋的碳当量低，具有优良的焊接性，适于采用电渣压力焊、闪光对焊和电弧焊等方法焊接。     

超声冲击对P355NL1钢焊接接头超高周疲劳性能影响

 通过超声疲劳试验探究超声冲击对P355NL1钢焊接接头超高周疲劳性能的影响。结果表明,由疲劳[S-N]曲线可知,在105～109寿命区间内,冲击态试样的疲劳性能要高于焊态试样,在1.0×108的疲劳寿命下,焊态试样的疲劳强度为139 MPa,冲击态的疲劳强度为217 MPa,冲击态疲劳强度相较于焊态提高了56%,这表明超声冲击可以明显提高焊接接头的疲劳强度。利用扫描电镜（SEM）观察断口形貌可以发现,裂纹源位于焊接接头焊根区表面。P355NL1钢焊接接头疲劳断裂为准解理断裂,超声冲击可以提高焊接接头的疲劳强度,但不会改变其疲劳失效机理。超声冲击可以降低焊根处应力集中,引入有益压应力和表面晶粒细化,从而提高焊接接头的疲劳强度。     

薄规格380MPa级轮辋钢焊接组织与性能研究

采用光学显微镜、扫描电镜、维氏硬度计、万能试验机等设备对不同闪光电流密度、闪光电压条件下380 CL车轮钢闪光对焊接头的显微组织和力学性能进行了研究,结果表明:380 CL车轮钢闪光对焊接头显微组织可划分为界面区、粗晶区、重结晶区、部分重结晶区四个部分;闪光电流和闪光电压不同,焊接接头各个区域的显微组织存在较大差异,热输入量越大晶粒尺寸越粗大;焊缝熔合线处的组织包括块状铁素体+魏氏体+渗碳体,组织尺寸较粗大;闪光电压升高,焊缝处魏氏体组织和渗碳体增多,焊缝处的硬度峰值较高,硬度下降趋势减缓,塑韧性降低;当380CL级车轮钢闪光对焊熔合线结晶良好、无焊接缺陷时,焊接接头峰值硬度虽然较母材高16.67%～43.84%、出现马鞍点,但是焊接接头拉伸及弯曲性能依然良好,熔合线处未出现裂纹和断裂。     

HRB400细晶粒热轧带肋钢筋焊接试验

用昆钢开发生产的HRB400细晶粒热轧带肋钢筋作为母材．采用闪光对焊工艺进行焊接。对焊接接头进行力学性能、维氏硬度和金相检验．说明了在焊接热循环作用下,重新奥氏体化后再结晶形成的组织对母材强度有影响。结合焊接接头硬度及金相组织的变化规律。对焊接接头的抗拉强度进行探讨。结果表明．钢筋焊接后焊缝的抗拉强度低于母材．只有将焊接件镦粗。使焊缝有效截面积大于母材截面积的1．1倍．才能保证HRB400细晶粒热轧带肋钢筋焊接接头抗拉强度指标大于该钢种的抗拉强度指标．使焊接接头不发生焊缝断裂。     

400MPa级超细晶粒钢的焊接

对超细晶粒钢在焊接热循环作用下晶粒长大和组织、性能变化的规律进行了研究。400 MPa级钢由于不存在第Ⅱ相粒子对晶粒长大的钉扎作用,晶粒长大趋势明显,焊接热输入越大,长大程度越严重。无论是焊接热模拟试件还是焊接接头硬度测试均表明HAZ不存在软化问题,接头拉伸试验断在远离热影响区的母材上。HAZ粗晶区有较多的侧板条铁素体,但缺口冲击功未显示热影响区的冲击韧性低于母材,尽管试件断口分析说明粗晶区的韧性低于母材。     

30 mm厚TA1电子束焊接头疲劳断裂原因分析

为探究30 mm板厚TA1电子束焊接头发生疲劳断裂的原因,针对接头开展疲劳试验,获得了接头S-N曲线及条件疲劳极限。针对TA1接头开展宏观、微观组织及力学性能检验,结合对典型低寿命接头的疲劳试样断口分析,获得了接头断裂特征。结果表明:电子束焊接过程使TA1焊缝及热影响区得到强化,整个接头无明显软化区。TA1电子束焊接头S-N曲线数据符合线性拟合规律,其拟合的疲劳极限值163 MPa,为接头抗拉强度的48.7%,接头疲劳强度符合金属材料结构件疲劳设计的一般规律。焊缝内部"微米级"焊接气孔的存在是导致接头发生疲劳断裂的主要原因,部分接头则是因焊接夹渣导致疲劳断裂。     

铌微合金化HRB400钢筋的电渣压力焊接

介绍了铌微合金化HRB400钢筋及其电渣压力焊接试验。试验结果表明：铌微合金化HRB400利筋电渣压力焊接性能良好，接头符合相关标准规定。     

高炉炉壳钢板BB503焊接性研究

从焊接角度分析 BB503钢板的化学成分,进行粗晶区奥氏体晶粒长大,焊接接头脆性断裂、抗裂性等焊接试验研究,根据现场焊接工艺作焊接接头力学性能测试。试验结果表明,BB503钢是一种较理想的高炉炉壳用钢。     

HRB500E钢筋高应变低周疲劳性能研究

针对钢筋在地震载荷下的失效模式,在恒应变条件下对HRB500E钢筋的高应变低周疲劳性能进行系统测试。利用威布尔双参数方法对疲劳寿命进行了统计分析,得出了不同置信度下的疲劳寿命和95%置信度下的循环韧度。并对疲劳机理和进一步提高高强钢筋高应变低周疲劳性能的途径进行了讨论。     

SAE1018盘条闪光对焊后接头脆断原因分析

对SAE1018热轧盘条连续闪光对焊后接头出现的脆断现象进行了分析.结果表明,焊接头脆断是热影响区过热引起的.采取降低焊接二次电压、高温区快冷、降低钢中S含量等措施,可使SAE1018盘条闪光对焊焊接接头过热倾向明显改善.     

SS400超细晶粒钢及其焊接接头的疲劳裂纹扩展速率

SS400钢是一种细晶强化的新一代钢铁材料．焊接对其疲劳性能的影响是人们关注的问题。笔者参照美国材料试验学会标准ASTME647—83的规定．采用紧凑拉伸CT试件对SS400钢及其焊接接头CT试件的疲劳裂纹扩展速率进行了测试。发现：母材的疲劳裂纹扩展存在两个不同速率的阶段,焊缝及热影响区的疲劳裂纹扩展速率均低于母材;热影响区的疲劳裂纹扩展速率介于焊缝与母材之间;焊接接头组织和性能的变化并未导致SS400钢疲劳性能的降低。     

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.     

The use of hot spot stress for estimating the fatigue strength of welded components

The relatively complex geometry of welded joints makes an assessment of fatigue strength rather difficult in many cases, especially if the common nominal stress approach is applied. An alternative to this method is the hot spot stress approach which considers structural stress concentration factors at a welded discontinuity, in which a unified S‐N curve is used to estimate fatigue strength, rather than using numerous curves corresponding to welded joint categories of welded structures. In this paper, using numerical and experimental results for a variety of welded joint models, a unified S‐N curve was derived, which is independent of structural stress concentration factors. Based on a fatigue test of a real welded joint in a train bogie frame, it could be confirmed that the unified S‐N curve can be directly applied to the estimation of fatigue strength and fatigue design for general welded steel constructions.     

Evaluation on Fatigue Performance and Fracture Mechanism of Laser Welded TWIP Steel Joint Based on Evolution of Microstructure and Micromechanical Properties

The fatigue performance and fracture mechanism of laser welded twinning induced plasticity(TWIP)steel joint were investigated experimentally based on the evolution of microstructure and micromechanical properties.The optical microscopy was used to analyze the evolution of microstructure.The variation of composition and phase structure of fusion zone were detected by energy dispersive X-ray and X-ray diffraction spectrometers.The micromechanical behaviors of the various zones were characterized using nanoindentation.The static tensile test and high cycle fatigue test were performed to evaluate the mechanical properties of welded joint and base metal.The microstructures,tensile properties and fatigue strength of base metal as well as welded metal were analyzed.The fatigue fracture surfaces of base metal and welded joint were observed by means of scanning electron microscopy,in order to identify fatigue crack initiation sites and propagation mechanisms.Moreover,the fatigue fracture characteristics and mechanisms for the laser welded TWIP steel joints were analyzed.     

A Study of Thickness Effect on Fatigue in Thin Welded High Strength Steel Joints

It is well known that the fatigue strength of welded joints decreases when plate thickness increases. This decrease in fatigue strength is known as the thickness effect. In many standards for fatigue design the thickness effect is taken into account for joints with plate thickness typically greater than 25 mm. Previous work has mainly been focused on joints with plate thickness between 12‐200 mm. Less attention has been paid to thinner joints. Published investigations on joints with sheet thickness 2‐12 mm show an increase of fatigue strength with decreasing sheet thickness. In the present study results from constant amplitude fatigue testing of non‐load carrying welded joints in high strength steel of thickness 3‐12 mm are presented. The results show an increase in fatigue strength with decreasing sheet thickness down to 3 mm. Fracture mechanics calculations confirm the test results.     

Optimisation of flash welding parameters for wheel rim manufacture using continuously cast steels

Continuously cast steels are nowadays commonly employed for the manufacture of wheel rims, and the flash welding process is generally employed for that purpose. The current work addresses the flash welding of a continuously cast material (carbon steel with carbon segregation in it), in the wheel rim manufacturing process route, with emphasis on the control of process parameters on the quality of weld joints. It has been established in this research work that the controlled post weld heat cycles, during the flash welding process, Improve the quality of joints and also eliminate or at least drastically decrease the failure susceptibility of such flash welded joints during subsequent manufacturing operations.     

低碳汽车薄钢板点焊构件疲劳寿命统计分析

本文研究了文献的两种点焊工艺条件下的W08A1点焊构件疲劳寿命统计分析,认为焊接电流的变化,对点焊构件中寿命区的疲劳寿命无显著影响,但增大电流,对提高长寿命区的疲劳寿命是有益的。     

使用状态对Q690CFD焊接接头性能的影响

针对煤矿机械、港口机械等对低成本焊接结构用高强钢的需求,宝钢开发了低成本TMCP高强钢Q690CFD,具有优异的综合力学性能和抗冷裂纹性能.对于高强钢厚板而言,焊后热处理工艺非常关键,它对接头的力学和使用性能有重要影响.在制造过程中,根据用户不同的服役条件,焊接结构要求不同的使用状态,比如焊态、消氢处理态和消应力处理态.按照相关的国家标准,采用实芯焊丝BH700-Ⅱ,制作了Q690CFD的富氩气保焊接头,分析接头的不同使用状态,包括焊态、300℃消氢处理和580℃消应力处理对Q690CFD/BH700-Ⅱ接头性能的影响.结果表明,焊态、消氢处理态和消应力处理态下,接头的力学性能均满足相关国家标准;按接头性能优劣来分,从好到差的顺序为：消氢处理态、焊态、消应力处理态.消氢处理可以一定程度上增加接头的冲击性能,但消应力处理使接头的冲击性能变差.     

Influence of Nonuniform Microstructure on High-Cycle Fatigue Properties of the Electron-Beam-Welded Joint of High-Strength Steel

The relatively weak fatigue property of electron beam (EB)-welded joints is one of the key issues restricting their wide application. Herein, the impact of accelerating voltage, specifically the process-induced nonuniform microstructure, is investigated on the high-cycle fatigue properties of 15CrMnMoVA steel EB-welded joints. It is indicated in the results that increasing the accelerating voltage from 120 to 150 kV (150-specimen) results in a longer fatigue life and an 11.8% improvement in fatigue limit for the welded joint with the locking bottom structure. However, even after removing the locking bottom structure, the fatigue life of the 150-specimen is still inferior to that of the base metal. The shorter fatigue life is primarily due to stress concentration and premature fatigue failure caused by the nonuniform distribution of grain size and crystallographic orientation across the EB-welded joint. Thus, further optimization of the welding process is necessary to improve the fatigue reliability of EB-welded joints by obtaining a more uniform microstructure.