析出强化超细晶粒钢焊接热影响区粗晶区的组织和性能

为研究焊接对800 MPa级Ti、Nb复合微合金化析出强化超细晶粒钢组织性能的影响.运用Gleeble3500热模拟试验机,对实验钢进行单道次焊接热循环试验,并研究冷却速度、冷却时间t8/5对焊接热影响区粗晶区(CGHAZ)组织、性能的影响.结果表明:冷却速度5~15℃/s,CGHAZ的组织为贝氏体,冷却速度进一步增大,会出现马氏体.随着冷却时间t8/5的增加,原奥氏体晶粒尺寸逐渐增加,硬度值逐渐降低,冲击韧性先上升后下降.t8/5为20~120 s时,CGHAZ显微硬度(223~250.4 HV)均小于母材的显微硬度(270.6 HV),出现软化现象,t8/5为20 s时,冲击吸收功最高,为18.2 J,但仅有母材的25.3%.经历焊接热循环后,奥氏体晶粒粗化以及CGHAZ出现贝氏体组织是导致脆化的主要原因.     

冷却时间对TMCP890钢焊接热影响区组织和性能影响

使用Gleeble-3800热模拟试验机研究了在800-500℃冷却时间(t8/5)对TMCP890钢焊接热影响区(HAZ)粗晶区组织转变规律和性能的影响,结果表明:冷却时间t8/5为6-20 s时粗晶区组织为板条马氏体,硬度值为334-328HV10;t8/5为20-60 s时粗晶区组织为板条马氏体+板条贝氏体,硬度值为328-305 HV10,Bs点在490-510℃;t8/5为150-2000 s时粗晶区组织为板条贝氏体+粒状贝氏体,Bs点在530-570℃,硬度值保持在270 HV10。稻垣道夫经验公式适用于TMCP890钢实际焊接过程中t8/5的计算,热输入E在10-20 k J/cm、T0在50-150℃变化时粗晶区的硬度值为318-335HV10,硬度值的波动幅度较小,性能稳定。     

1 200 MPa级HSLA钢的SH-CCT曲线及其热影响区组织与性能

为在工程应用中对焊接工艺的合理选取与制定提供理论和试验依据,采用焊接热模拟技术研究了800~500℃冷却时间(t8/5)对1 200 MPa级低合金高强钢焊接热影响区粗晶区(CGHAZ)显微组织和性能的影响.结果表明:t8/5为6~20 s时,该钢热影响区的粗晶区组织为板条马氏体,硬度为477~456 HV5;随着冷却时间的延长,组织中开始出现板条贝氏体,在t8/5为60 s时硬度下降到380 HV5;当t8/5为60~600 s时,粗晶区组织为板条贝氏体和粒状贝氏体,硬度为380~300 HV5;t8/5600 s时粗晶区组织主要为粒状贝氏体,硬度为300~315 HV5.试验钢碳当量为0.626%,冷裂纹敏感系数为0.335%,说明其淬硬倾向较大,焊接热影响区容易产生裂纹.     

10CrNi3MoV钢焊接热影响区组织和晶粒度研究

采用焊接热模拟技术研究了590MPa级船用高强度结构钢焊接热影响区组织和晶粒度的变化规律．研究结果表明：10CrNi3MoV钢热影响区粗晶区(CGHAZ)经峰值温度在临界相变点Ac1和Ac3温度范围二次热循环后，具有粗大组织或粗大晶粒遗传现象．焊接线能量(t8/5时间)对粗大晶粒遗传没有影响，但对粗大组织遗传具有显著影响．当t8/5较小时，能够产生粗大组织遗传．当t8/5较大时，仅仅产生粗大晶粒遗传．并且，随着t8/5值增加，产生粗大组织遗传的温度区间减小。     

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.     

1.4003铁素体不锈钢与Q235-C钢焊接接头的组织和力学性能

采用室温拉伸、不同温度冲击、硬度及金相检验等分析方法对用熔化极混合气体保护焊焊接的1.4003铁素体不锈钢与Q235-C钢焊接接头的显微组织和性能进行了研究.试验结果表明:该焊接接头的抗拉强度与母材相当,焊缝的冲击性能略低于母材,1.4003铁素体不锈钢的热影响区(HAZ)冲击性能较差,焊缝为奥氏体+铁素体双相组织;Q235-C钢的熔合区出现明显界限,1.4003铁素体不锈钢焊接热影响区为晶粒粗大的单一铁素体组织.     

0Cr19Ni9 TIG焊接接头的抗蚀性及电弧重熔

研究了低碳奥氏体不锈钢０ｃＲ１９Ｎｉ９手工钨极氩弧焊（ＴＩＧ）焊接接头表面抗蚀性能及电弧重熔对其抗蚀性能的影响。实验结果表明,受焊接热循环的作用,焊接接头热影响区的抗蚀性能,以及焊缝金属的抗蚀性能,较母材有所降低。但经微束等离子弧表面重熔后,由于接头表面重熔层的快速凝固作用,细化了支组织,减小了显微的,抑制了碳铬化合物在晶界的沉淀析出,焊接接头的抗蚀性能得以显著提高。     

高速列车A6005A铝合金焊接接头断裂韧性研究

为了研究高速列车常用A6005A铝合金材料抵抗裂纹扩展能力,对其焊接接头断裂韧性和冲击韧性进行了求解.采用三点弯曲法、扫描电子显微镜等求出焊接接头各部位冲击韧性、断裂韧性以及断口形貌,得到断裂韧性CTOD值δm(8)和J积分值Jm(8).试验结果表明,热影响区的冲击功为16.3 J;母材冲击功为11.5 J;焊缝区域最差,冲击功为5.5 J.CTOD数据表明,HAZ处δm(8)=0.373 9 mm,母材δm(8)=0.089 2 mm,焊缝δm(8)=0.069 7 mm.J积分数据表明,HAZ处Jm(8)=109.454 kJ/m2,母材Jm(8)=38.249 kJ/m2,焊缝Jm(8)=16.231 kJ/m2.热影响区断口上韧窝比母材上韧窝大,其韧性更好.焊缝上气孔、夹杂较多,其塑性较差,冲击吸收功很低.冲击韧性和断裂韧性表征规律一样,热影响区值抵抗裂纹扩展能力最好,母材次之,焊缝区最差.     

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。     

Cr含量和组织对含1%Cr管线钢焊接接头抗CO2腐蚀性能影响

采用高温高压反应釜和电化学技术对含1%(质量分数)Cr管线钢焊接接头的CO2腐蚀行为进行研究,目的在于揭示Cr含量和组织对焊接接头抗CO2性能的影响.结果表明,Cr含量较高的焊缝区,腐蚀产物膜出现Cr元素富集,膜较其他区域更厚更致密,抗CO2腐蚀性能更佳.而Cr含量相同、组织不同的热影响区和母材,腐蚀产物膜特征相似.对于含1%Cr管线钢焊接接头,抗CO2腐蚀性能起主要作用的是Cr含量而非组织.电化学测试表明,在CO2腐蚀介质中焊接接头的母材区域易作为阳极首先发生腐蚀,焊缝和热影响区作为阴极得到保护.     

焊接热输入对06CuNiCrMoNb钢HAZ组织与性能的影响

研究了热输入对06CuNiCrMoNb钢焊接热影响区不同部位组织和性能的影响,重点分析了粗晶区的韧性与组织之间的关系。结果表明,模拟焊接热影响区没有出现"软化"现象,但是当线能量大于30kJ/cm情况下,粗晶区低温韧性迅速下降。对粗晶区的分析显示,线能量17kJ/cm条件下贝氏体铁素体呈细小板条状,在板条间存在着残余奥氏体薄膜,随线能量的增大,块状的铁素体数量增多,并且出现不规则片状M+A组元。     

Effects of nitrogen content and weld cooling time on the simulated heat-affected zone toughness in a Ti-containing steel

An increase of nitrogen content in a 0.02 wt% Ti-containing carbon-manganese steel resulted in a low coarsening rate of TiN particles in the heat-affected zone (HAZ), which led to an accelerated ferrite transformation instead of ferrite side plates during weld cooling cycle. The mixed microstructure of ferrite side plate, acicular ferrite and grain boundary polygonal ferrite in the simulated HAZ produced higher toughness. However, the increase of nitrogen content gradually increased the free nitrogen content in the HAZ and deteriorated HAZ toughness. Impact energy of the simulated HAZ (with Δt_8/5 ∼60 s) at –20 °C deteriorated by about 97 J per 0.001 wt% free nitrogen, in the free nitrogen range from 0.0009 wt% to 0.0034 wt%, even though the HAZ has the tough mixed microstructure. Cooling time after welding influenced the HAZ microstructure and toughness as well, and maximum toughness was obtained when cooling produced the tough mixed microstructure. Therefore, for a high HAZ toughness, both nitrogen content and cooling time should be controlled to obtain the tough mixed microstructure and to keep the free nitrogen content low. The optimal nitrogen content and cooling time from 800 °C to 500 °C were 0.006 wt% and between 60 s and 100 s, respectively, in this experiment.     

The effect of repeated repair welding on mechanical and corrosion properties of stainless steel 316L

The purpose of this study is to evaluate changes in the mechanical, micro structural and the corrosion properties of stainless steel 316L under repeated repair welding. The welding and the repair welding were conducted by shielded metal arc welding (SMAW). The SMAW welding process was performed using E316L filler metals. Specimen of the base metal and different conditions of shielded metal arc welding repairs were studied by looking in the micro structural changes, the chemical composition of the phases, the grain size (in the heat affected zone) and the effect on the mechanical and corrosion properties. The microstructure was investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The chemical composition of the phases was determined using energy dispersive spectrometry (EDS). The corrosion behavior in 1 M H₂SO₄ + 3.5% NaCl solution was evaluated using a potentiodynamic polarization method. Tensile tests, Charpy-V impact resistance and Brinell hardness tests were conducted. Hardness of the heat affected zone decreased as the number of repairs increased. Generally an increase in the yield strength (YS) and the ultimate tensile strength (UTS) occurred with welding. After the first repair, a gradual decrease in YS and UTS occurred but the values of YS and UTS were not less than values of the base metal. Significant reduction in Charpy-V impact resistance with the number of weld repairs were observed when the notch location was in the HAZ. The HAZ of welding repair specimen is more sensitive to pitting corrosion. The sensitivity of HAZ to pitting corrosion was increased by increasing the number of welding repair.     

Pitting of 316L stainless steel in flare piping of a petrochemical plant

Pitting was observed on a 6-in. (15 cm) flare piping made of stainless steel ASTM A312 Gr. Tp 316L, prior going into service in a petrochemical plant. The pits were in the heat-affected zone (HAZ) and fusion zone (FZ) boundary of the pipe seam welds. The FZ was also uniformly corroded. The SEM photomicrographs showed large inclusions in the welded area, while EDS analysis indicated that the inclusions were rich in Al, Si, and S. The Streicher test indicated no sensitization in the welded area. The Huey test confirmed that the corrosion rate of samples from welded area were higher that of samples from base metal in a boiling nitric acid test.The results indicated the presence of a high level of inclusions in the welded area. Pitting initiation in HAZ and FZ may be attributed to existence of large inclusions in the welded area. The general corrosion of the FZ can be attributed to the galvanic effect between inter-dendrite delta ferrite and the cored austenitic in the welded area which could be prevented by proper annealing after welding. It is plausible to claim that the general corrosion of these areas could trigger the pitting initiation as well.     

Effects of Carbon on the CG HAZ Toughness and Transformation of X80 Pipeline Steel

X80 pipeline steel produced by TMCP has high strength and high toughness with ultrafine grain microstructure. The microstructure coarsens and the toughness worsens at the coarse grained (CG) HAZ apparently after weld simulation. The experimental results indicated that the bainitic ferrite and the second phases formed at cooling are differently as the variation of carbon in base metal. In low carbon steels, the bainitic ferrite laths are long and narrow, the second phases are complex including residual austenite, martensite, the M-A constituent and the Fe3C carbide. The formation of Fe3C carbide is the main reason of the poor toughness in CG HAZ. The ultralow carbon in base metal, however, can improve the CG HAZ toughness through restraining the formation of carbides, decreasing the M-A constituent, increasing the residual austenite content, which are beneficial to the CG HAZ toughness.     

模拟冷却水中304不锈钢的耐蚀性影响因素研究

用电化学方法研究了Cl^-、S^2-、NO3^-、温度以及某电厂水质稳定剂对304不锈钢耐蚀性的影响。极化曲线表明：在[Cl-]／[SO4^2-]约为0．56时，点蚀电位开始下降，并随着Cl-浓度的增大逐渐降低；S2-的加入使钝化电流显著增大；NO3-浓度增加使点蚀电位逐渐升高；溶液温度的提高使点蚀电位降低，钝化电流也有所增大，钝化膜的耐蚀性降低;实验表明采用的某厂水质稳定剂可引起304不锈钢点蚀电位的下降。Mott-Schottky图显示S2-浓度的增加使体现p-型半导体(氧化铬)性质的直线段发生较大变化，说明硫离子影响了铬氧化物的性质。     

Microstructural study and electrochemical behavior of low alloy steel weldment

Submerged arc welding (SAW) was applied to SA516 (Grade 70) pressure vessel and boiler steel. The microstructural and electrochemical corrosion study of base metal (BM), weld zone (WZ) and heat affected zone (HAZ) was carried out to understand the effect of welding cycle by optical microscopy, X-ray diffraction (XRD), potentiodynamic polarization and linear polarization resistance (LPR) method to correlate corrosion kinetic parameters with microstructural changes in tap water and 0.5% (w/v) NaCl solution under plain and aeration conditions at room temperature. From microstructural study, the morphology of ferrite in WZ and HAZ showed different electrochemical behavior and corrosion rate than that of BM.     

铝合金6082和5083 MIG焊接头的微观组织和性能

对高速列车车体常用铝合金6082与5083板材进行熔化极氩弧焊(MIG)对接,利用光学显微镜和扫描电镜分析异种材料焊接接头的显微组织特点,利用显微硬度计、拉伸试验机和电化学工作站对接头的力学性能和耐腐蚀性能进行测试和分析。研究结果表明,焊缝成型良好,焊缝区由细小的胞状树枝晶和等轴晶构成,熔合线附近为粗大的柱状晶;焊接接头抗拉强度为199.92 MPa,断后伸长率为5.18%,断裂位置在铝合金6082的焊接热影响区(HAZ),为韧性断裂,接头的正弯性能较差,背弯性能良好;铝合金5083侧的热影响区宽为4mm,6082侧的热影响区宽为15mm,接头两侧的硬度分布有明显差别,在6082侧距焊缝中心12.5mm的显微硬度最低为63HV;6082-5083异种铝合金焊缝的耐蚀性能优于母材5083,但比母材6082差。     

铸造双相不锈钢点腐蚀行为研究

采用化学浸泡腐蚀试验及微观组织和化学成分分析研究了5种铸造双相不锈钢在6%Fe Cl3溶液中的点腐蚀行为,并与316L奥氏体不锈钢进行了对比。结果表明,铸造双相不锈钢的抗点腐蚀性能均优于316L的,腐蚀速率和点腐蚀深度均小于316L奥氏体不锈钢的;双相不锈钢主要耐点蚀能力合金元素在奥氏体和铁素体相内分布不均匀,铬、钼更多地分配于铁素体相内,而镍、氮则更多地分配于奥氏体相内,铁素体相的耐点蚀指数PRE(Cr%+3.3Mo%+16N%)大于奥氏体相;双相不锈钢的耐点腐蚀性能与化学成分有关,随着PRE的增加,双相不锈钢的耐点腐蚀性能提高,铜元素在铁素体内析出的富铜相导致点蚀优先在铁素体内发生和发展。     

Corrosion behaviour of a thin section martensitic stainless steel GTA weldment in chloride solutions

A thin section martensitic stainless steel was welded by gas tungsten arc welding and characterized for the microstructure, hardness and corrosion behaviour in chloride solutions. Welds free from defects could be produced by autogenous welding under the optimized welding conditions. The weld metal was over-matched in terms of mechanical properties (hardness, tensile strength). The general corrosion resistance and the passivation behaviour of the weld metal/heat affected zone (HAZ) region were on par with that of the parent material in chloride and sulphuric acid test electrolytes; however, in terms of pitting corrosion resistance, the martensitic-structured weld metal/HAZ region was marginally inferior compared to its parent material.