Simulation of hydrogen diffusion in welded joint of X80 pipeline steel

Hydrogen diffusion coefficients of different regions in the welded joint of X80 pipeline steel were measured using the electro-chemical permeation technique. Using ABAQUS software, hydrogen diffusion in X80 pipeline steel welded joint was studied in consideration of the inhomogeneity of the welding zone, and temperature-dependent thermo-physical and mechanical properties of the metals. A three dimensional finite element model was developed and a coupled thermo-mechanical-diffusion analysis was performed. Hydrogen concentration distribution across the welded joint was obtained. It is found that the postweld residual hydrogen exhibits a non-uniform distribution across the welded joint. A maximum equivalent stress occurs in the immediate vicinity of the weld metal. The heat affected zone has the highest hydrogen concentration level, followed by the weld zone and the base metal.Simulation results are well consistent with theoretical analysis.     

X80/X100异种钢激光-MIG复合焊接头显微组织和性能

采用激光-MIG复合焊对X80管线钢和X100管线钢进行焊接,研究了激光功率对复合焊接头的焊缝形貌、显微组织、硬度、强度和韧性的影响规律.结果表明,激光功率从2.0 k W增大至3.5 k W时,盖面焊缝熔宽和熔深增加,激光区熔深明显增加;激光区焊缝中AF含量增加、LB含量减少,X100侧粗晶热影响区和细晶热影响区中条状贝氏体含量减少,X80侧粗晶热影响区和细晶热影响区中准多边形铁素体含量增加.复合焊接头硬度分布并不对称,最高硬度出现在X100侧熔合区部位.复合焊接头的抗拉强度基本不随激光功率变化,拉伸试样断裂位置均为X80侧母材.随着激光功率增大,焊接接头最高硬度和韧性均下降.     

X80管线钢焊接冷裂纹敏感性研究

采用BOHLER E9010G纤维素焊条进行斜Y形坡口焊接裂纹试验和最高硬度试验,结合显微组织分析和斜Y形坡口焊接裂纹试验的残余应力分析,系统研究了X80管线钢的冷裂纹敏感性。结果表明,不进行预热时,X80管线钢存在一定的冷裂纹敏感性,一定程度的预热可以有效降低其冷裂纹敏感性,且接头中等效残余应力峰值水平下降;当预热温度为150℃时,断面裂纹率最低;但当预热温度高于150℃后,粗晶区显微组织变得粗大,且焊接接头中横向残余应力峰值和等效残余应力峰值均上升,不利于降低冷裂纹敏感性。     

水下湿法多层焊接头显微组织和应力分析

采用美国BROCO水下焊条对16mm厚的Q345钢板分别进行陆上和水下湿法焊接试验,分析陆上和水下焊接接头的显微组织和接头硬度分布,计算焊接过程的温度场分布和残余应力场分布,并研究焊接电流对温度场和残余应力场的影响。结果表明,相同的电流条件下,水下焊接接头的显微组织类型和构成与陆上焊接接头不同,焊缝可以获得更细的侧板条铁素体组织和针状铁素体,粗晶区组织主要为高硬度的马氏体;增加水下焊接电流,焊缝中侧板条铁素体增加。计算结果表明,170 A电流的水下焊接相比陆上焊接可获得较低的焊接温度、更快的焊后冷却速度和更高的等效残余应力峰值水平;水下焊接电流增加到190A时,焊接最高温度有所升高,焊后冷却速度略有降低,等效残余应力峰值水平下降。     

X80管线钢焊接接头氢分布的数值模拟

利用ABAQUS有限元软件,建立了三维有限元模型,对X80管线钢焊接接头的氢扩散行为进行了模拟. 通过对不同焊接条件下温度场、应力场、氢扩散的三场耦合模拟,研究了焊接工艺参数对焊接接头中氢扩散及分布的影响. 结果表明,焊接热影响区残余应力水平最高,是整个接头的应力集中部位,也是焊接接头中的富氢地带. 适当地提高预热温度和焊接热输入,均有利于焊接接头中氢的扩散逸出,降低氢在焊接热影响区的聚集程度,从而降低氢致裂纹的敏感性.     

焊接工艺参数对9%Ni钢热影响区低温韧性的影响

采用热模拟技术研究了热输入和层间温度对9％Ni钢焊接热影响区中四个亚区域低温韧性的影响,并利用光学显微镜、X射线衍射仪对各亚区域的组织形态和数量分布进行了观察分析。结果表明,临界热影响区低温韧性对热输入和层问温度的变化不敏感;层间温度是影响粗晶区低温韧性的主要工艺参数;热输入则是影响过临界粗晶区和临界粗晶区低温韧性的主要工艺参数。热输入越大,晶粒和组织越粗大,低温韧性恶化;层间温度提高,马氏体的自回火作用越显著,低温韧性改善。因此,焊接9％Ni钢时,应采用较小的焊接热输入,配合较高的层间温度。     

冷热循环处理对钛基非晶合金摩擦学性能的影响EI北大核心CSCD

钛合金的耐磨性较差,在钛合金活动部件表面制备钛基非晶合金涂层是一种保持钛合金优势又提升其耐磨性的选择。采用X射线衍射仪、差示扫描量热仪、SEM、摩擦磨损试验机,对冷热循环处理前后钛基块体非晶合金的组织结构与摩擦行为进行比较研究。结果表明:经过冷热循环处理后的钛基块体非晶合金仍然保持着完全非晶态,弛豫焓提升11%。冷热循环处理后钛基非晶合金的平均纳米硬度从6.84 GPa降低到6.59 GPa,平均弹性模量从118.70 GPa降低到103.43 GPa,但硬度与弹性模量的比值增大。冷热循环处理后,钛基块体非晶合金在5 N和10 N的载荷下磨损率减小了约10%。与TC4合金相比,其在5 N和10 N载荷下的磨损率分别减小了20%和50%。TC4合金由于硬度较低,呈现较为严重的黏着磨损。冷热循环处理后,钛基非晶合金的磨损机制从铸态的磨粒磨损为主向磨粒磨损、黏着磨损和氧化磨损共同作用转变,且随着载荷的增大,黏着磨损减轻,磨粒磨损占据主导。因此,冷热循环处理是提升钛基块体非晶合金摩擦学性能的一种有效方法。     

Cold cracking susceptibility of X100 pipeline steel

The y-groove Tekken test has been performed to evaluate the cold cracking susceptibility of X100 pipeline steel. The impact of preheating state on the microstructure, distribution of hardness, and the stress-strain state in the welded joint was analyzed. The results show that X100 pipeline steel reveals a low susceptibility to cold cracking with cracking ratios below 20%. It is found that elevated preheating temperature leads to longer cooling time in the welded specimen and ultimately results in a lower cold cracking susceptibility. Preheating temperatures of up to 100 ℃ are favorable in decreasing the cold cracking susceptibility due to a relative fine microstructure and low M-A constituent amount in coarse grained heat affected zone, a low hardenability, and low-level residual stress and strain. However, excessive preheating temperatures of 150 ℃ and 200 ℃ lead to grain coarsening, higher M-A constituent amount, higher residual stress level and increasing strain level in the Tekken specimens. Preheating temperature above 150 ℃ is not favorable for decreasing the cold cracking susceptibility of X100 steel.     

9%Ni钢斜Y形坡口裂纹试验的数值模拟

利用 SYSWELD 有限元计算软件,采用双椭球焊接热源模型,对 9%Ni 钢斜 Y 形坡口裂纹试验中不同预热温度下的试件进行了焊接温度场和应力场的数值模拟.研究了试件的焊接温度场和应力场的分布规律,分析了预热温度对焊接热过程和焊后残余应力的影响.结果表明,提高预热温度时,一方面焊后冷却速度降低,有利于氢的逸出和马氏体的自回火作用;另一方面,横向残余应力水平增加,试件总体应力水平增加,冷裂纹敏感性增加.因此,焊接 9%Ni 钢时,不宜采用过高的预热温度.

Abstract：

With SYSWELD software, the temperature and stress field of 9% Ni steel Y-slit weldments with different preheat temperatures were simulated by applying double-ellipsoid heat source. Distribution laws of welding temperature and stress field were studied. Effects of preheat temperature on welding heat cycles and residual stress were analyzed. Results show that with increasing preheat temperature, cooling rate decreases facilitates escaping of hydrogen and self-tempering of martensite, the average stress level and cold-cracking susceptibility of the weldments increase, so high preheat temperature shall be avoided for 9% Ni steel welding.