718合金TIG焊热影响区组织变化

以不同热输入对轧制、铸态、铸后均匀化热处理3种2.8 mm厚Inconel-718薄板进行TIG焊试验.观察各接头母材与HAZ(焊接热影响区)组织,分析热输入对3种母材接头HAZ晶粒结构、大小的影响.发现随热输入增大,轧制母材焊接接头HAZ沉淀相大量溶解,等轴晶晶粒长大明显,速度为铸态或均匀化接头4.6倍.铸态或均匀化母材呈树枝晶,晶粒较大;HAZ偏析区扩散消失,奥氏体成分趋于均匀,树枝晶结构痕迹减弱;沉淀相残留于原枝晶间位置,在抑制HAZ晶粒长大的同时,保留部分树枝晶结构痕迹;铸态母材焊接接头HAZ沉淀相多于均匀化接头,更接近树枝晶结构.     

In-situ microscopy study of grain refinement in the simulated heat-affected zone of high-strength low-alloy steel by TiN particle

High-strength low-alloy steels subjected to high heat input welding are susceptible to failure due to low toughness caused by grain coarsening. The effect of TiN on grain refinement in the simulated heat-affected zone (HAZ) was investigated. Because of small amount of Ti addition, abundant dispersed nanoscale TiN precipitates were formed. The TiN precipitates tended to be stable at high temperature and effectively retarded the austenite grain growth by refining the grain size during thermal cycle. Furthermore, the TiN also covered on the surface of Al–Ti complex oxide with MnS and caused low interface energy with ferrite. The acicular ferrite grains nucleated on complex inclusion in austenite grains at intermediate temperature and induced the austenite grain transform to the fine-grained mixed microstructure of acicular ferrite and bainite. The crystallographic grain size became small in the simulated HAZ due to the effective pinning effect and acicular ferrite formation.     

GMAW焊接传热及其对HAZ奥氏体晶粒长大过程的影响

精确分析熔化极气体保护电弧焊（ＧＭＡＷ）焊接传热过程的前提是对施加于工件表面上的焊接热输入分布模式有一个恰当的、合乎实际的描述。本文作者根据电弧物理的基本原理和熔滴与熔池的交互作用,建立了双峰分布的电弧热流密度分布模型,确定了熔滴热焓量在熔池内部的分布区域。以此为基础,建立了ＧＭＡＷ焊接传热的数学模型,给出了焊接热影响区奥氏体晶粒长大的动力学方程。采用数值模拟技术研究了低碳钢和ＨＱ１３０钢ＨＡＺ的     

热循环对高铌管线钢焊接热影响区冲击韧性的影响

采用Gleeble-3500型热模拟试验机,研究了焊接热循环对Mn-Mo-Nb和高铌 HTP X80管线钢焊接热影响区(HAZ)冲击韧性的影响.结果表明,随焊接热输入量的增加,两种X80管线钢粗晶HAZ的冲击韧性均降低,但在相同的焊接热输入条件下,高Nb钢粗晶HAZ的冲击韧性均高于Mn-Mo-Nb管线钢.其原因是高Nb钢中由于未溶Nb(CN)状的存在,抑制奥氏体晶粒长大,在高的线能量条件下,能够保证奥氏体晶粒的细小均匀.     

EQ70钢激光电弧复合焊焊接热循环及其对热影响区组织演变的影响

采用Visul Environment 软件建立了EQ70钢激光电弧复合焊的三维模型,并利用SYSWELD软件对激光电弧复合焊焊接温度场进行了有限元数值模拟,结合热电偶测温法和热影响区的微观组织表征分析了激光电弧复合焊热循环特点及其对热影响区组织演变的影响. 结果表明,采用双椭球体+峰值递增锥体组合型热源可以准确模拟复合焊温度场,电弧区、过渡区、激光区相同热影响区微区具有相近的热循环,热影响区加热速度可达400 ℃/s,1 100 ℃以上停留时间为0.79～1.33 s,t_8/5为4～6 s. 粗晶区、细晶区组织为板条马氏体,临界区组织为马氏体+晶界碳化物,亚临界区组织为回火马氏体. 激光电弧复合焊具有快速加热、高温停留时间短的特点,在一定程度限制了奥氏体晶粒的长大,粗晶区和细晶区平均晶粒尺寸分别为42.7,19.8 μm.     

一种稀土高强钢焊接热影响区组织与性能

机械装备的整体性能和寿命随着高强钢的大量使用而大幅提高，但性能薄弱区仍然是焊接热影响区. 应用恰当的处理技术，能生成形态、尺寸和分布有益的稀土夹杂物，在焊接中抑制原奥氏体晶粒长大改善钢的焊接性能. 试验制备了一种0.18%C的稀土高强钢，采用Gleeble-3500热模拟机模拟4种热输入下的热循环过程，采用光学显微镜观察了试验钢的焊接热影响区显微组织转变，用冲击试验机测试了焊接热影响区的冲击吸收能量，测量了不同冷却速度下的原始奥氏体晶粒尺寸的变化. 结果表明，焊接热输入值为25 kJ/cm时，HAZ组织主要为马氏体，晶粒尺寸细小，这时的冲击韧性和硬度值最高. 当焊接热输入值大于50 kJ/cm以上时，钢中生成了上贝氏体和粒状贝氏体，晶粒也逐渐长大，出现了韧性下降和软化. 试验钢的C含量为0.18%，在热循环中焊缝中出现了粗大的马氏体组织，形成淬硬组织，未生成针状铁素体组织.     

Ferrite to austenite reverse transformation process in B containing 9%Cr heat resistant steel HAZ

Abstract

Creep properties of the high Cr heat resistant steel welded joint can be improved by adding B due to prevention of the grain refinement in heat affected zone (HAZ). In the present study, phase transformation behaviour of the B steel HAZ has been investigated to understand suppression mechanism of the grain refinement. During reverse transformation, fine austenite was formed through diffusional transformation at the prior austenite grain boundary in the first stage, and then coarse austenite was formed at the same location of the original austenite. The volume fraction of the fine austenite increased with increasing perk temperature of the weld thermal cycle. This phenomenon can be explained if the coarse austenite contains high density of dislocations. Clear surface relief was observed during the reverse transformation by a confocal laser microscope. These results indicate that martensitic or displacive reverse transformation takes place during welding and it prevents the grain refinement in HAZ.     

工业纯铝焊接热影响区微观组织模拟

将蒙特卡罗(MC)技术引入到晶粒生长模拟中，结合焊接工艺和热模拟试验，模拟了单相合金焊接热影响区(HAZ)晶粒生长过程。首先应用实验和统计学的方法确定了材料晶粒生长的动力学模型，然后计算了焊接热循环，同时基于蒙特卡罗技术编制了模拟程序。最后在不同焊接热输入情况下，模拟了晶粒生长过程。模拟结果动态演示了晶粒生长过程，并且体现了焊接热钉扎效应。模拟得出数据与试验结果非常接近，为评定焊接工艺和材料可焊性提供了依据。     

TiNbV微合金钢焊接接头HAZ晶粒长大及相变原位观察

采用激光共聚焦显微镜原位观察方法,研究了大热输入用TiNbV微合金钢在模拟焊接热循环作用下焊接热影响区(HAZ)晶粒长大过程及相变的规律. 热循环过程中加热温度升高至860 ~ 980 ℃时,发生由铁素体和珠光体向奥氏体的转变,1 100 ℃时,奥氏体晶粒开始有明显长大的趋势,1 300 ~ 1 400 ℃时,晶粒以合并长大方式迅速长大;冷却过程中温度降低至1 400 ~ 1 350 ℃时,晶粒以晶界迁移方式缓慢长大,660 ~ 580 ℃时,发生奥氏体迅速向贝氏体转变,焊接HAZ主要由贝氏体与铁素体组成,贝氏体的尺寸是由奥氏体晶粒大小决定的. 热循环高温停留时间延长,奥氏体与贝氏体的形成、终了、转变温度区间均有下降. 结果表明,组织中先共析铁素体含量先降低后增加,贝氏体含量降低,多边形铁素体消失,先共析铁素体含量增加,冷却组织趋于均匀粗大. 焊接过程中,选择合适的高温停留时间可提高组织中IAF的含量,提高力学性能.     

工业纯铝焊接热影响区晶粒生长的模拟

结合焊接工艺试验和热模拟试验,运用蒙特卡罗(MC)技术模拟了工业纯铝L1060焊接热影响区(HAZ)晶粒生长过程。首先应用试验和统计学的方法确定了工业纯铝L1060晶粒生长的动力学模型,然后计算了焊接热循环,同时基于蒙特卡罗技术编制了模拟程序,最后在不同焊接热输入情况下,模拟了晶粒生长过程。模拟结果与试验结果非常接近,为评定焊接工艺和材料焊接性提供了依据。     

焊接热影响区晶粒长大过程的微观组织模拟

利用蒙特卡罗方法(MC)结合焊接工艺试验，模拟了单相合金焊接热影响区(HAZ)的晶粒长大过程。文中首先应用试验方法确定了材料的晶粒长大动力学方程，在不同峰值温度和冷却速度等热输入的情况下，模拟结果再现了晶粒长大的动态过程，并体现出热钉扎效应。得出了与焊接实际过程相一致的模拟结果。为以后进行三维焊接热影响区晶粒长大模拟奠定了可靠的基础。     

Influence of Welding Thermal Cycle on Microstructure and Properties in Heat-affected Zone of X80 Pipeline Steel

Single welding thermal–cycles with different input linear energies (ILE)(15, 20, 30, 40, 50 kJ/cm) and peak temperatures (PT) (900, 1050, 1200, 1300, 1350 ℃) were simulated by MMS-300 to study the correlation of toughness and microstructure in heat-affected zone (HAZ) of a X80 pipeline. The evolution characteristics of microstructure were investigated by OM, SEM and EBSD. The results show that numerous polygonal ferrites and grain boundary ferrites appear, and the sizes apparently decrease as the heat input decreases. Heat input in single welding should be less than 35 kJ/cm to ensure well Charpy impact toughness. The toughness of course grain zone is the lowest when welding heating temperature is 1350 ℃ and it is the weakness part in welded zone. The uniformity of prior austenite grain is worsened as increasing the heat input. Moreover, the characteristics of M-A constituents and high angle grain boundaries (HAGB) are influenced by heat input and PT. In the case of low heat input and PT, higher density of HAGBs, dispersed and fine M-A constituents were observed. Otherwise, with high heat input (≥40 kJ/cm), the effective grain size is almost the diameter of prior austenite grain, and it will decrease the density of HAGB, moreover, coarse M-A constituents which are prone to crack initiation will be generated, thus, the impact toughness of the coarse grain zone will be worsened obviously in welding HAZ.     

400MPa级新一代钢铁材料焊接热影响区晶粒长大图

新一代钢铁材料将是21世纪的主要结构材料，脉冲MAG焊是适合它的一种传统熔焊方法，为了促进400MPa新一代钢铁材料的焊接性研究及其工程应用，首先根据实测脉冲MAG焊的热循环曲线，确定了400MPa级新一代钢铁材料脉冲MAG焊的焊接热循环方程，并以此为基础建立了焊接HAZ的奥氏体晶粒长大方程和晶粒长大图，通过晶粒篚图，可以预测焊接HAZ各个部位的奥氏体晶粒篚的情况，研究结果表明，400MPa级新一代钢铁材料焊接热影响区的晶粒长大图的预测结果与其热模拟的实测数据吻合很好。     

超低碳QT钢焊接二次热循环的组织转变与局部脆化

采用焊接热模拟实验及透射电镜分析技术研究了一种超低碳QT钢在多道焊接二次热循环过程中的组织转变与韧性间的关系,结果表明,由于在一次焊接热循环过程中的晶粒粗化和未回火马氏体的形成,使得粗晶我的韧性明显降低,在多道焊的二次热物质 时,实验钢不存在临界粗晶区局部脆化现象,但表现为亚临界粗晶区局部脆化,引起亚临界粗晶区局部脆化的原因是碳化物的析出粗化和残余奥氏体的热失稳分解。     

A stochastic model for austenite phase formation during arc welding of a low alloy steel

Modeling the microstructure of heat-affected zone (HAZ) in weld area can be useful in predicting mechanical behavior of the weldment. A multi-scale model is proposed to calculate the temperature distribution and to predict the microstructure evolution within the HAZ. Finite difference method was used to develop a computer model for studying the cooling curves during welding, and a stochastic method to analyze the austenite formation and its grain growth in HAZ. The droplet of liquid metal detached from electrode in manual arc metal welding is an important concern in studying the temperature distribution and the austenite grains growth. Both heat content of liquid metal detached from electrode and heat generated by electrical arc were used in calculation of temperature distribution. The stochastic model simulates the austenite phase formation and its growth during welding based on the kinetics of these processes. With this model, it is possible to visualize the topology of austenite phase. This multi-scale model was applied to the welding of low alloy steel. The observed morphology was in good agreement with that predicted by the model.     

铁素体不锈钢焊接热影响区晶粒长大过程模拟

提出一种用Monte Carlo模拟单相合金的热影响区（HAZ）晶粒长大方法,可以将焊接实际时间与模拟过程对应起来,应用有限元方法计算出焊接热循环,并结合晶粒长大的Arrhenius公式,模拟了铁素体不锈钢EB26-1在一定规范下HAZ晶粒的演变情况,模拟结果表明,此方法可以预测HAZ中晶粒的分布以及存在于HAZ中很陡的温度梯度对晶粒长大的阻碍作用。     

610MPa级大热输入高强钢焊接性能热模拟研究

利用Gleeble1500热模拟试验机研究了610 MPa级高强度钢板在60～120 kJ/cm热输入下的焊接热影响区性能,分析了影响焊接性能的显微结构因素。试验结果表明:试验钢在60～100 kJ/cm的大热输入焊接热模拟后拉伸强度和低温韧性良好,而在120 kJ/cm大热输入下机械性能下降较大但仍满足要求;试验钢中大量弥散分布的细小TiN粒子在热循环过程中能够钉扎奥氏体晶界和促进铁素体晶内形核,能有效抑制热影响区组织长大,保证了试验钢的大热输入焊接性能。     

TCS不锈钢复合热源焊接热影响区晶粒长大的预测

根据等温条件下的铁索体晶粒长大公式,推导出了焊接热影响区(HAZ)铁索体晶粒长大的动力学方程,并结合焊接热循环的数值分析结果对TCS不锈钢热影响区晶粒长大进行了预测.在此基础上,对复合焊新型焊接工艺条件下TCS不锈钢HAZ的晶粒长大情况进行了数值计算,得到了3种工艺参数下TCS不锈钢复合焊HAZ内的晶粒尺寸.基于TCS不锈钢复合焊接接头的金相图片,测量了HAZ内的平均晶粒尺寸,对数值模拟结果进行了验证.初步讨论了晶粒尺寸随热循环温度的长大情况和热循环温度差异对晶粒长大的影响规律.     

工程机械用800MPa低合金高强度钢焊接热影响区断裂韧性评价

随着工程机械的大型化,需要采用800MPa低合金高强度钢结构。为了保证焊接接头具有良好的韧性,必须合理控制焊接热作用,避免焊接接头脆化。本研究采用热模拟试件,研究了焊接冷却时间及加热温度对800MPa低合金高强度钢焊接热影响区(HAZ)断裂韧性的影响及其显微组织特征。发现在t8/5为18s时,HAZ具有最好的断裂韧性。随着t8/5的增加,奥氏体晶粒逐渐长大,马氏体的体积分数逐渐降低,粒状贝氏体的数量不断增加,断裂韧性逐渐下降。t8/5大于45s,LT方向试件出现脆性失稳现象。焊接接头各区的韧性分布是,过热区的断裂韧性最好,两相区的断裂韧性最差,粗晶区的韧性优于细晶区。影响HAZ韧性的主要因素是贝氏体的形态和分布。研究结果为制定合理的焊接工艺和大型工程机械的断裂安全评定奠定基础。     

计算机模拟在焊接微观组织中的应用

介绍了计算机模拟在焊接热影响区（HAZ）微观组织模拟过程中应用的重要性，利用物理模拟方法建立了HAZ晶粒长大的模型，研究了铁素体不锈钢EB26-1（单相合金）焊接热影响区的晶粒长大过程，预测了HAZ中晶粒的分布，以及不同的热输入对HAZ晶粒长大的影响和HAZ中晶粒长大的热钉扎效应，指出了目前研究中存在的不足和今后的发展方向。