超细晶Q460高强钢焊接接头组织与韧性研究

采用手工焊条电弧焊和熔化极活性气体保护焊对超细晶Q460钢进行了焊接,分析表征了焊接接头的组织结构、显微硬度和冲击韧性的变化规律。研究结果表明,采用E5515焊条焊接,焊缝金属主要为先共析铁素体、多边形铁素体与少量珠光体。采用ER55-G焊丝,熔化极活性气体保护焊,焊缝金属主要由针状铁素体和少量多边形铁素体组成,焊丝中Ti元素的添加有利于获得针状铁素体组织。采用较小的焊接线能量,超细晶Q460钢热影响区粗晶区组织为粒状贝氏体组织。焊缝金属的显微硬度高于热影响区和母材的显微硬度,热影响区未出现软化现象。冲击试验表明,焊缝金属和热影响区均具有较高的冲击韧性,而且热影响区的韧性高于焊缝金属的韧性。     

X70管线钢的局部脆化

研究了X70管线钢模拟热影响区的局部脆化现象和临界再热粗晶区粒状贝氏体的形成及其对韧性的影响规律.结果表明,二次峰值温度为780℃时,M-A组元在原奥氏体晶界成链状分布;二次峰值温度为840℃时,原粗晶区晶界位置生成了细晶贝氏体带,及大颗粒的M-A组元;二次峰值温度为900℃时,M A组元弥散分布,原粗晶区的奥氏体晶界消失.在二次加热过程中奥氏体主要在原粗晶区晶界形核长大.X70钢的粗晶区出现再加热脆化现象,它的脆化温度区间是一个比Ac1-Ac3更窄的温度区间,主要在T2P=Ac1-840℃温度范围内.临界再热粗晶区脆化的主要原因是在晶界上有链状分布的M-A组元.     

热输入对Q1100钢焊接接头低温韧性及耐蚀性能的影响

采用10 kJ/cm和15 kJ/cm两种焊接热输入对Q1100超高强钢进行熔化极气体保护焊,研究焊接接头的组织性能及局部腐蚀行为。结果表明：两种热输入焊接接头的焊缝组织主要为针状铁素体和少量的粒状贝氏体,粗晶区组织均为板条贝氏体,细晶区组织均为板条贝氏体和粒状贝氏体,临界相变区组织为多边形铁素体、马奥岛和碳化物的混合组织。两种热输入焊接接头中电荷转移电阻均为母材>热影响区>焊缝区,母材耐蚀性最好,热影响区次之,焊缝区耐蚀性最差。在腐蚀过程中,焊缝区作为阳极最先被腐蚀,当腐蚀一定时间后,腐蚀位置发生改变,阳极腐蚀区域转移到母材区,而焊缝区作为阴极得到保护。热输入为10 kJ/cm时,焊接接头具有更好的低温韧性和耐蚀性,其焊缝和热影响区-40℃冲击功分别为46.5 J和30.2 J。     

大电流MAG焊接接头弯曲性能研究

采用无氦多元气体保护大电流MAG焊接技术焊接了A5 72接头 ,对接头进行了弯曲性能试验 ,用光学显微镜、扫描电镜和EDAX分析了接头侧弯脆性断口。结果表明 ,弯曲试验时产生的脆断与焊缝金属中有非金属夹杂物、焊缝金属中C、Ti含量较高以及焊缝金属中有马氏体组织等因素密切相关。在弯曲时 ,焊缝金属中存在的非金属夹杂物形成裂源 ,在小线能量焊接时焊道间热影响区组织中存在的大量粗大马氏体组织 ,使焊缝金属在裂纹萌生区和开始扩展阶段为解理断裂。在大电流MAG焊时 ,适当增大线能量以利于非金属夹杂物的逸出并避免马氏体的形成 ,降低焊缝金属中的C、Ti含量 ,从而改善接头韧性。     

低碳贝氏体钢双面埋弧焊接头的组织和低温韧性

对低碳贝氏体钢进行双面埋弧焊焊接,并用光学显微镜和PSW750型示波冲击试验机对焊接接头进行表征,研究了钢的显微组织和低温韧性。结果表明:低碳贝氏体钢双面埋弧焊后,焊缝区的组织为针状铁素体和粒状贝氏体;HAZ的组织为贝氏体铁素体和粒状贝氏体;HAZ熔合线附近的硬度最高,远离熔合线硬度降低并逐渐接近母材金属的硬度;随着温度的降低焊接过程中的凝固偏析、高度集中的位错源来不及松弛应力集中以及分布在晶界上的Ti、Mo等微合金元素形成的碳氮化物,导致焊接接头焊缝区和HAZ韧性降低并在-20℃和-60℃发生韧脆转变。     

Ti-Nb微合金钢焊接粗晶热影响区组织及韧性

利用碳萃取复型技术研究了Ti-Nb微合金钢及其模拟粗晶区(CGHAZ)中的第二相粒子,并利用OM、TEM及系列冲击试验对Ti-Nb微合金钢焊接粗晶区的组织及韧性进行了研究.研究结果表明,Ti-Nb微合金钢中含有大量的、尺寸细小的TixNb1-x(CyN1-y)粒子,粒子中Nb的相对含量在0.25～0.82之间,形状接近球形.这些粒子具有很高的稳定性,在焊接过程中这些粒子能有效地阻止奥氏体晶粒长大、抑制粗大贝氏体的形成、促进针状铁素体析出及M-A组元的分解,从而显著善低合金高强钢焊接粗晶热影响区的韧性,t8/5越大,这种改善作用越明显.     

一种铜沉淀强化铁素体钢焊接热影响区性能研究

通过Gleeble热模拟试验,研究了一种低碳铜沉淀纳米相强化铁素体钢焊接热影响区组织及性能,测试了试验钢粗晶区焊接CCT曲线。结果表明,试验钢焊接粗晶区组织主要为贝氏体,其它区域均为铁素体;铜沉淀纳米强化相随热循环不同而发生不同演变,从而引起热影响区性能变化。试验钢粗晶区冲击功及硬度与基体相当,细晶区、临界区及亚临界区冲击功均高于基体,有一定软化现象。在试验t8/5范围内,试验钢粗晶区对焊接热输入较为敏感,随t8/5的增加,组织粗化,并产生较多的粒状贝氏体组织,冲击功降低明显。     

焊接方法对X90管线钢焊接接头性能的影响

目前,关于焊接方法对X90管线钢焊接接头组织性能的影响相关报道较少。采用手工电弧焊(SMAW)、熔化极气体保护焊(GMAW)、埋弧焊(SAW)3种焊接方法对X90管线钢进行对接焊。利用金相显微镜(OM)、扫描电镜(SEM)及能谱仪(EDS)对焊接接头及冲击断口进行显微组织及成分分析,分析了焊接方法对X90管线钢焊接接头组织性能的影响规律。结果表明:焊缝区组织主要为粒状贝氏体和针状铁素体;SMAW粗晶区组织主要为多边形铁素体、粒状贝氏体及M/A组织,GMAW和SAW粗晶区组织主要为粗大的铁素体、粒状贝氏体及板条贝氏体;3种焊接接头硬度分布趋势一致,盖面层硬度最高;SMAW、GMAW和SAW焊接接头抗拉强度依次为714,771,790 MPa,断后伸长率依次为23.3%,22.9%,20.0%;SAW与GMAW熔合线处20℃冲击吸收功比SMAW高约40 J,断裂机制为微孔聚集型,在韧窝底部有金属碳化物粒子析出。     

高强低合金钢电子束焊接接头的组织与性能研究

采用电子束焊接了厚度为9 mm的15CrNi3MoV高强低合金钢试板,焊接接头成形良好,无内部缺陷,经热处理后焊接系数达到0.98以上。通过研究焊接接头组织和力学性能,发现热处理后,接头组织以贝氏体组织为主,在焊缝和热影响区粗晶区中出现索氏体组织,热影响区的细晶区存在粒状贝氏体组织,焊接接头的冲击韧性与母材相比得到提升;散焦修饰使原始焊缝的柱状晶碎化,能够改善焊缝处的显微硬度。     

焊接热循环对一种低合金船体钢组织及性能的影响

通过焊接热循环模拟试验,对试样进行微观组织结构观察和低温韧性测试,研究了不同条件的热循环过程对一种低合金高强度船体钢组织及性能的影响。结果表明:在一定的焊接线能量范围内,t8/5对试验钢的组织及性能影响不大,模拟粗晶区组织主要为马氏体和贝氏体;峰值温度对试验钢热影响区组织及低温韧性影响较大,粗晶区为热影响区薄弱环节,二次热循环可提高试验钢粗晶区的低温韧性;试验钢经历两次粗晶区热循环后仍保持有细小的板条结构及条间奥氏体,冲击韧性较为稳定。     

X80管线钢焊接粗晶区韧化因素的研究

采用热模拟技术研究了不同热循环对X80管线钢焊接粗晶区低温冲击韧度的影响.实验结果表明,随着冷却时间t8/5的增加,第二相粒子的数量减少且出现聚集现象,晶粒尺寸增加,但是当t8/5小于6.8s时,粒状贝氏体含量较高,板条束贝氏体细小且方向性较弱,试样的冲击韧性较高;而当t8/5超过6.8s后,粒状贝氏体含量逐渐下降,板条贝氏体逐渐粗大、平行,试样韧性又逐渐降低.M-A组元由于其含量低,尺寸小,对韧性的影响不显著.因此为提高焊接粗晶区的韧性,应采用小线能量和合适的预热温度来控制晶粒尺寸和组织形态.     

热输入对Q890高强钢焊缝组织及性能的影响

针对国内某钢厂最新研制的Q890高强钢,采用三种不同的热输入对其进行气体保护焊接,研究了不同热输入对焊缝金属组织、硬度及冲击韧性的影响.结果表明,3种热输入下,焊缝组织主要以板条贝氏体为主,并含有粒状贝氏体、少量的板条马氏体和残余奥氏体.随着热输入的增大,焊缝组织中贝氏体铁素体板条粗化,板条马氏体逐渐减少,而粒状贝氏体逐渐增多,部分残余奥氏体由薄膜状向块状转变;焊缝金属硬度随着热输入的增大而下降;焊缝金属的冲击韧性亦呈逐渐下降的趋势.     

Effect of Post-weld Heat Treatment on Microstructure and Fracture Toughness of 30CrMnSiNi2A Steel Welded Joints

The electron beam local post-weld heat treatment (EBLPWHT) is a rather new method that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. This paper studies the effect of two post-weld heat treatment processes on the microstructure, mechanical properties and fracture toughness of an electron beam welded joints in 30CrMnSiNi2A steel. EBLPWHT, in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were compared. The experimental results show that, after EBLPWHT treatment, the main microstructure of weld was changed from coarse acicular martensite into lath rnartensite, HAZ was changed from lath martensite, bainite into lower bainite, and base metal was changed from ferrite and pearlite into upper bainite and residual austenite. The microstructures of different zones of joints in FWPWHT condition were tempered sorbite. The properties of welded joints can be improved by the EBLPWHT in some extent, and especially largely for the fracture toughness of welded joints. However the value of fracture toughness of base metal is comparatively low, so appropriate heat treatment parameters should be explored in the future.     

高强度结构钢及其接头热影响区的疲劳及断裂性能分析

采用焊条电弧焊对48 mm厚高强度结构钢进行焊接,对焊接接头热影响区疲劳裂纹扩展门槛值ΔK_th、裂纹扩展速率da/dN和断裂韧度K_IC进行研究并与基体进行对比。结果表明,在室温下,焊接接头热影响区具有更好的疲劳和断裂性能;随着与熔合线距离的增大,热影响区的组织依次为粗大板条状贝氏体+奥氏体薄膜、细粒状贝氏体、回火索氏体+细粒状贝氏体,硬度逐渐下降;在室温下,焊接接头热影响区和基体冲击韧性均位于上平台。热影响区的残余奥氏体薄膜和硬度较高的贝氏体是影响其疲劳和断裂性能的重要因素。      

Fabricating Defect-Free API X65 Steel Welds under Underwater Wet Conditions using Friction Taper Plug Welding

The experiment on API X65 steel was carried out using friction taper plug welding (FTPW) under underwater wet conditions at room temperature. Sound weld formation can be achieved vastly at axial force ranging from 25 to 40 kN and a rotating speed of 7000 rpm. The microstructure of the weld zone consists of lath martensite, upper bainite, granular bainite, polygonal ferrite, and acicular ferrite. The microstructure of heat affected zone (HAZ) mainly consists of lath bainite as well as a bit of lath martensite and granular bainite. The tensile properties of defect-free welds are excellent. The maximum impact energy of the V-notch of bonding area can reach 110 J, which was conducted at 0°C with an error of ±12.5 J. The typical SEM impact fracture morphology presents areas of cleavage, quasi-cleavage, and dimples.     

不同热输入下F460钢焊接粗晶热影响区韧脆转变的内在机理

使用Gleeble 3800热模拟试验机模拟F460钢单道次焊接条件下焊接粗晶热影响区的热循环过程,通过光镜(OM)、扫描电镜(SEM)分析热影响区的显微组织、确定临界事件,通过ABAQUS软件计算临界解理断裂应力σf,进而系统分析不同焊接热输入E下韧脆转变温度变化的内在机理。结果表明:随着E的提高,焊接粗晶热影响区显微组织依次为少量板条马氏体和大量细密的板条贝氏体,板条贝氏体较多的板条/粒状贝氏体,粒状贝氏体较多的板条/粒状贝氏体,粗大的粒状贝氏体。原始奥氏体晶粒、贝氏体团的最大尺寸随着E的提高而变大。在完全解理断裂的冲击断口上,寻找停留在缺口尖端附近的残留裂纹,通过对比残留裂纹长度、原始奥氏体晶粒大小、贝氏体团尺寸,发现不同E下解理断裂的临界事件尺寸都是贝氏体团大小,而临界事件尺寸越小,韧脆转变温度越低。此外,通过有限元模拟缺口尖端的应力分布得到σf,σf越大冲击韧度越好,随着E的提高σf降低,故进一步说明随着E的提高韧脆转变温度Tk上升的内在机理。     

Effects of heat treatment process and niobium addition on the microstructure and mechanical properties of low carbon steel weld metal

The mechanical properties and microstructure were evaluated and analyzed by optical microscopy (OM) and transmission electron microscopy (TEM) for micro-alloy carbon steel weld metal with and without Nb addition, respectively, under different heat treatment processes including stress relief annealing, normalizing, and no treatment after welding. The strength and elongation of the weld metal without treatment after welding were improved with the addition of Nb element, and the impact toughness was not affected obviously with the Nb addition. After stress relief annealing, the strength decreased for the Nb-free weld metal, while the elongation and impact toughness increased. However, for the Nb-bearing weld metal, stress relief annealing improved the strength of the weld metal significantly, and deteriorated the elongation and impact toughness. In the case of normalizing treatment to the weld metal, it was shown that with the increase of the holding time at the normalizing temperature of 920 °C, for both the weld metals with and without Nb addition, the microstructure of the columnar grain zone (CGZ) was transformed from one of columnar grain into one of equiaxed grain. The grain size of the equiaxed grain zone (EGZ) increased initially, then remained almost unchanged with the prolonging of the holding time. The mechanical properties of the weld metal with and without Nb addition showed no obvious change with the increasing holding time. With the increase of the normalizing temperature, the strength of the Nb-bearing weld metal increased, while the elongation and impact toughness decreased significantly. OM and TEM analysis found that the fine NbC particles were precipitated at the normalizing temperature of 920 °C, which refined the grains of the weld metal and increased the impact toughness. With the increase of the normalizing temperature, the content of widmanstatten ferrite (WF) in the Nb-bearing weld metal increased, whereas the quantity of the NbC particles decreased, which improved the strength and lowered the impact toughness.