Influence of Aging treatment on the microstructure and mechanical properties of T92/Super 304H dissimilar metal welds

Influence of aging treatment on the microstructure and mechanical properties of T92/Super 304H dissimilar steel joints was investigated. The microstructure of T92/Super 304H dissimilar steel joints was characterized using optical microscopy, scanning electron microscopy and energy dispersive spectrometer. The results show that the tensile strength of dissimilar metal welds (DMWs) after 10,000 h aging treatment met the ASME T92 and Super 304H standards. Rupture positions were located in the T92 base metal because of the precipitates formed along the sub grain and prior grain boundaries. The tensile strength of DMWs initially increased with time up to 4000 h, then decreased between 4000 to 6000 h, and finally came to almost a constant value from 8000 to 10,000 h exposure. The decrease in the tensile strength resulted from the nucleation and growth of Laves phases at the sub-grains and prior austenitic grain boundaries. The low absorption of impact energy in the weld metal was related to the coarse grains and its grain orientation.     

Microstructures and mechanical properties of T92/Super304H dissimilar steel weld joints after high-temperature ageing

T92/Super304H dissimilar steel weld joints, fabricated through a gas tungsten arc welding (GTAW) technique using a Ni-based welding wire of ERNiCrMo-3, were aged at 650 °C for time up to 3000 h. Microstructures, fractographies and mechanical properties of the joints were then investigated. The results show that as the aging time increased, in the T92 side heat-affected zone (HAZ) and base metal (BM), the second-phase particles aggregate and coarsen along the austenite grain boundaries/in the austenite grains. In the Super304H side HAZ and BM, the growth of the austenite grains and that of the second-phase particles are slight. The fracture positions of the aged joints are always in the T92 BM. The tensile strengths and the hardness values of the joints drop firstly, then rise, and finally tend to be stable. The impact toughness values of the joints are monotonously decreases with the ageing time.     

690 MPa级低合金高强钢焊接接头组织性能

为探讨690 MPa级低合金高强钢焊接接头组织与性能的关系,采用手工电弧焊(SMAW)和埋弧焊(SAW)获得成形良好的焊接接头,经过拉伸、冲击、弯曲试验及光学显微镜、扫描电镜和透射电镜分析,对两种焊接方法的接头组织性能进行研究.结果表明:两种焊接方法的焊缝组织主要为板条状贝氏体和少量针状铁素体,粗晶区为粗大贝氏体和少量马氏体;焊缝中含有大量分布均匀的微小球形夹杂物;两种焊接方法所得焊接接头都具有较高力学性能,-50℃的冲击断口形貌为韧窝、准解理混合型;埋弧焊焊缝冲击韧性低于手工电弧焊,手工电弧焊熔合线处冲击吸收功小于埋弧焊,但随距熔合线距离增加其值增加更快.显微组织和夹杂物是影响接头性能的主要因素.     

Characterization on strength and toughness of welded joint for Q550 steel

Q550 high strength steel was welded using gas shielded arc welding and three different welding wires without pre- or post-heat treatments. The paper investigates the influence of welding wire on the microstructure, tensile strength and impact toughness of Q550 steel weld joints. Results showed that the microstructure of the weld metal of joints produced using ER50-6 wire was a mixture of acicular ferrite and grain boundary ferrite including pro-eutectoid ferrite and ferrite side plate. Acicular ferrite was mainly obtained in the weld metal of the joints produced using MK·G60-1 wire. Pro-eutectoid ferrite was present along the boundary of prior austenite. Crack initiation occurred easily at pro-eutectoid ferrite when the joint was subjected to tensile. Tensile strength and impact toughness were promoted with increasing acicular ferrite. Tensile strength of the joint fabricated using MK·G60-1 wire was close to that of base metal. And tensile samples fractured at location of the fusion zone, which had lower toughness and thus became the weak region in the joint. Impact absorbing energy was the highest in the heat affected zone. Fibrous region in fracture surfaces of impact specimens was characterized as transgranular fracture with the mechanism of micro-void coalescence. Acicular ferrite microstructure region corresponded to relatively large dimples while boundary ferrite microstructure corresponded to small dimples.     

Microstructure, Impact Toughness and TEM Analysis in the CGHAZ of HQ130 High Strength Steel

1.IntroductionThedifferentpartsintheheat-affectedz0neofthehighstrengthsteelexperienceddifferentweldthermalcycles,inwhichthechangeofmicrostructureandper-formanceinthecoarsegrainheat-affectedzone(CG-HAZ)nearthefusionzoneismost0bvious,andcoldcrackingiseasytobeproducedandspreadinthiszone.CGHAZwasconsideredasone0fthem0stweakpositioninwholeweldingjoilltzone,andllu-merousinvestigatorshavepaidcl0seattentiontotheCGHAZl1'2].HQ130steel,whichhastensilestrength(UTs)ofmorethan1300MPa,isanewlydevelop…     

Effect of welding wire and groove angle on mechanical properties of high strength steel welded joints

Mechanical properties of high strength steel welded joints strictly depend on the welding process, the filler material composition and the welding geometry. This study investigates the effects of using cored and solid welding wires and implementing various groove angles on the mechanical performance of weld joints which were fabricated employing the gas metal arc welding process. It was found that weld joints of low alloy, high strength steels using low alloy steel cored welding wires exhibited higher tensile strength than that of low alloy steel solid wire and chromium‐nickel steel bare welding wire when the method of gas metal arc welding is employed. The effect of groove angle on the strength and toughness of V‐groove and double V‐groove butt‐joints was investigated. V‐groove joints, with higher tensile strength than double V‐groove joints in the whole range of groove angles, were superior in toughness for small groove angles, but impact toughness values of both joints were comparable for large angles. The effect of heat input and cooling rate on the weld microstructure and weld strength was also investigated by performing thermal analysis employing the commercial software ANSYS. It was concluded that cooling rate and solidification growth rate determined the microstructure of the weld zone which had great consequences in regard to mechanical properties.     

T92/Super304H异种钢焊接接头的性能研究

根据新型耐热钢T92和Super304H钢的焊接特点制定了适宜的焊接工艺,研究了焊制的T92/Su-per304H异种钢焊接接头的力学性能。结果表明,T92/Super304H异种钢接头的各项力学性均能满足使用要求。焊缝金属的韧性远低于T92钢侧热影响区,焊缝金属的结晶形态对焊缝韧性有很大的影响。焊接接头中焊缝金属的硬度值最高,而T92钢侧热影响区硬度最低,并且不同热影响区部位显微硬度变化较大,Super304H钢侧热影响区硬度变化不大。     

12CrNi5MoV锻钢焊接热影响区组织与性能研究

采用热模拟技术研究了12CrNi5MoV锻钢焊接热影响区粗晶区的组织与性能。结果表明,经历一次焊接热循环后,材料粗晶区的抗拉强度与原始态试样相比显著升高,而冲击韧性明显降低;冷却过程中冷却速度加快引起材料组织中孪晶马氏体与残余奥氏体含量的增加是其粗晶区力学性能变化的主要原因。     

石油储罐钢焊接热影响区模拟研究

采用焊接热模拟技术,研究不同焊接热输入条件下焊接热循环对石油储罐钢焊接热影响区粗晶区(CGHAZ)的组织和性能的影响.结果表明:实验钢在80～100kJ/cm的大热输入下,热影响区仍能够保持良好的低温韧性;随着焊接热输入的增加,实验钢CGHAZ组织变粗大,低温冲击功下降;钢中弥散分布着大量细小TiN粒子,在焊接热循环中...     

Experimental investigation of local tensile and fracture resistance behaviour of dissimilar metal weld joint: SA508 Gr.3 Cl.1 and SA312 Type 304LN

The aim of the paper is to evaluate the local tensile and fracture toughness properties of the dissimilar metal weld joints between SA508Gr.3 Cl.1 and SA312 Type 304LN pipe. Weld joints have been prepared by manual gas tungsten arc welding (GTAW) process with conventional V‐groove and automatic hot wire gas tungsten arc welding with narrow gap using different filler wires/electrode such as Inconel 82/Inconel 182 and ER309L/ER308L. The tensile and fracture toughness test specimens have been machined from different regions of dissimilar metal weld such as heat affected zones, fusion lines, buttering layer, weld metal and both base metals. Tensile and fracture toughness tests have been carried out as per the ASTM standard E8 and E1820 respectively. Tensile and fracture toughness results of all the regions of dissimilar metal weld joints have been discussed in this paper. Metallurgical and fracture surface examinations have also been reported to substantiate the tensile and fracture toughness results. Need for the local properties for integrity assessment of the dissimilar metal weld joints has also been brought out.     

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。     

C和W对低合金Cr-Mo钢焊缝金属组织和冲击韧性的影响

使用OM、SEM、EPMA、EBSD等手段并进行热膨胀和冲击等实验,研究了C和W元素对第四代钠冷快堆用低合金Cr-Mo钢钨极氩弧焊(TIG)熔敷金属微观组织和冲击韧性的影响.结果 表明:多道次焊接热循环使多层多道焊缝金属的组织分布不均匀,分为表层焊缝组织和中间焊缝组织.表层焊缝组织,可分为熔化区(MZ)、粗晶区(CGH...     

Application of local approach to inhomogeneous welds. Influence of crack position and strength mismatch

In steel welds there is often a large variation in fracture toughness and mechanical properties between the weld metal, base material and the various heat affected zone (HAZ) microstructures. The stress field in front of a crack in a weldment can be noticeably affected by the strength mismatch between the weld metal, HAZ and the base material. The crack position relative to the various microstructures will clearly influence the strength mismatch effect. In this paper the influence of crack tip positioning on the fracture performance of strength mismatched steel welds has been studied both experimentally and by FEM analysis. For a mismatched weld with local brittle zones small changes in crack tip location can give considerable changes in the fracture performance of a CTOD specimen. A high degree of strength mismatch increases the effect of crack positioning. Weld metal overmatch increases the stress level in the heat affected zone due to material constraint and thereby reduces the cleavage fracture resistance of the weldment when the coarse grained HAZ (CGHAZ) controls the fracture. The detrimental effect of high overmatch is most pronounced for specimens with notch position at fusion line and a short distance into the brittle CGHAZ. The Weibull stress has been shown to be a suitable fracture parameter in the case where one microstructure clearly controls the cleavage fracture and the calculation of the Weibull stress therefore can be limited to this zone.     

汽车高强钢SG1000激光复合焊接力学性能研究

目的 针对汽车高强钢SG1000焊接接头恶化等问题,研究了SG1000激光复合焊接的力学性能。方法 选用等强匹配焊丝MG90-G对高强钢SG1000进行激光复合焊接,对焊接接头进行拉伸和低温冲击韧性试验,并结合扫描和硬度监测等手段对焊缝组织和断口形貌进行分析。结果 由于激光的预热作用,高强钢SG1000激光复合焊接成形件的焊缝美观,焊接过程稳定可靠,焊接熔池深度较大,有效改善了传统焊接的咬边、飞溅、气孔等缺陷。焊缝组织主要由板条马氏体和奥氏体晶粒组成,热影响区的过热区内部板条马氏体和奥氏体晶粒比较粗大,而焊接母材主要为细小的板条马氏体和奥氏体晶粒。焊接拉伸断口主要为细小且较浅的韧窝,且韧窝底部存在第二相粒子及夹杂物,焊接拉伸断口断裂于热影响区且微观形貌为韧性断裂;冲击微观形貌主要由准解理小平面及河流花样组成,且存在一定数量大小不一的韧窝交错分布,焊接冲击断口断裂于热影响区且微观形貌也为韧性断裂。结论 焊缝热影响区的晶粒比非热影响区的晶粒粗大,拉伸和冲击断裂均发生于热影响区;随着激光功率的增大,复合焊接接头的力学性能呈现逐渐增强的趋势;随着焊接速度的增大,复合焊接接头的力学性能呈现先增强后削弱的趋势。高强钢SG1000激光复合焊接最佳工艺参数如下:激光功率为9.5 kW,焊接速度为0.8 m/min,对应屈服强度为1 072 MPa,抗拉强度为1 175 MPa,断裂伸长率为13.5%,冲击断裂吸收的能量为30.8 J、焊缝中心显微硬度为342 HV。     

Mechanical and Structural Properties of Similar and Dissimilar Steel Joints

The mechanical properties of specimens from similar and dissimilar weld joints were examined. A ferritic steel (St37-2) and an austenitic stainless steel (AISI 304) were joined by the gas tungsten arc weld (GTAW) process using an austenitic filler metal. Mechanical and metallographic properties of the specimens were obtained by means of microhardness testing, tensile testing, bending fatigue testing, and light optical and scanning electron microscopy. The highest microhardness values were recorded on the ferritic–austenitic dissimilar weld joint, whereas the highest tensile strength and bending fatigue life were obtained with the austenitic–austenitic joints. Ferritic and pearlitic structures were observed in the microstructure of the ferritic–ferritic joint. The microstructures of austenitic–austenitic and austenitic–ferritic joints showed small recrystallization grains in addition to the typical austenitic and ferritic structures. Scanning electron microscopy was used to observe the fracture surfaces of the specimens and the origins of the fatigue cracks.     

S275低合金钢焊接接头的组织与力学性能

通过拉伸、冲击、硬度测试和金相检验等方法对S275低合金钢熔化极活性气体保护焊(MAG)焊接接头的力学性能与显微组织进行了研究。结果表明:采用JM一56焊丝对S275低合金钢进行焊接时,接头具有较好的抗剪强度;开45。坡口,拉伸后均断在离焊缝位置较远的母材上,焊接接头抗拉强度满足技术要求。焊缝组织晶内为细小密集的针状铁素体,有极少量珠光体,焊缝局部有魏氏组织;熔合区、过热区为沿晶界析出的块状先共析铁素体和向晶内生长的条状铁素体以及少量的珠光体;正火区组织为细小的铁素体和珠光体;母材组织为铁素体和珠光体,晶粒也比较细小。最后得出S275低合金钢用于转向架焊接构架是可行的。     

不同强度级别双相不锈钢激光焊接头的组织与力学性能

目的 为了合理制定不同强度等级DP钢同种和异种接头的激光焊接工艺,研究激光焊接工艺对接头组织性能的影响。方法 采用SEM、硬度试验、拉伸试验等手段,研究不同强度等级DP钢同种和异种激光焊接接头的微观组织和力学性能。结果 对于同种DP钢激光焊接,由于接头各个区域经历的热循环不同,因此其马氏体体积分数和形态、含碳量等存在明显差异。在焊缝熔合区,由于冷却速度较高,因此马氏体体积分数较高且为细条状,硬度高于母材硬度。在热影响区,由于马氏体发生了回火分解,因此其硬度值低于母材硬度,且软化的程度和范围大小与DP钢的强度级别相关。软化的热影响区成为接头的薄弱区域,降低了接头的拉伸性能。在异种DP钢激光焊接接头中,焊缝熔合区的硬度也明显高于母材硬度。靠近高强度级别母材侧的热影响区范围更大,软化程度更明显,接头硬度分布不再对称。接头的抗拉强度与低等级DP钢母材的抗拉强度基本一致。结论 激光焊接工艺对不同强度等级DP钢同种和异种接头组织性能的影响存在较大的差异,DP钢强度级别越高,接头或接头对应侧的热影响区软化程度越明显,这在制定焊接工艺以及焊后处理工艺过程中需要予以考虑。     

Carbide precipitates and mechanical properties of medium Mn steel joint with metal inert gas welding

Medium Mn steel was metal inert gas(MIG)welded with NiCrMo-3 and 307Si filler wires.The effect of filler wires on the microstructure and mechanical properties of joint was investigated,and the carbide precipitates were contrastively discussed.The results revealed that the microstructure of weld metal,heat-affected zone and base metal are austenite.Obvious grain coarsening occurred in the heat-affected zone(HAZ),and the maximum grain size grew up to 160 pm.In HAZ,C and Cr segregated at grain boundaries,the carbides was identified as Cr7C3.The dispersive(Nb,Mo)C phase was also found in weld metal with NiCrMo-3 filler wire.All the welded joints failed in HAZ during tensile tests.The tensile strength of welded joint with NiCrMo-3 filler wire was 675 MPa,which is much higher than that with 307Si filler wire.In comparison to base metal,higher microhardness and lower impact toughness were obtained in HAZ for these two welded joints,which was attributed to the precipitation of Cr7C3 phase and grain coarsening.The impact toughness around the fusion line is the worst for these two welded joints.     

Effects of weld strength undermatch on fracture toughness of HAZ notched weldments in a HSLA steel

In the present work the effects of weld strength undermatch on fracture toughness of heat affected zone (HAZ) have been studied. In the investigation a high strength low alloyed steel (HSLA) with 800 MPa strength class was used, and the undermatched welded joints were made with two weld strength mismatch levels. Three-point bending test specimens with crack depth to specimen width ratio a/W ranging from 0.05 to 0.5 were extracted from the welded joints. The test results show that strength mismatching gives an obvious influence on the fracture toughness of coarse grained HAZ for the undermatched joints. The lower the weld strength mismatching, the higher the fracture toughness of the HAZ. In addition the tendency of fracture toughness change with crack depths is much the same as in previous studies on base metals or weld metals, that is, fracture toughness of the HAZ is increased with reduction of crack depths. From the measured results it shows that the macroscopically mechanical heterogeneity of the welds may have more important influence on the fracture toughness of the HAZ than the meso-heterogeneity in the reheated coarse grained HAZ. Furthermore, numerical verification indicates that the stress triaxiality at crack tip may be the essential reason for the change of fracture toughness of HAZ. It is also shown that the yield strength of HAZ determined by the limit load in the three-point bend test represents the combinative effects of HAZ and its surrounding materials. This revised version was published online in August 2006 with corrections to the Cover Date.