Effect of welding heat input on HAZ character in ultra-fine grain steel welding

In this essay, we studied how heat input affected the microstructure, hardness, grain size and heat-affected zone(HAZ) dimension of WCX355 ultra-fine grain steel which was welded respectively by the ultra narrow-gap welding (UNGW) process and the overlaying process with CO 2 as protective atmosphere and laser welding process. The experimental results show when the heat input changed from 1.65 kJ/cm to 5.93 kJ/cm, the width of its HAZ ranged from 0.6 mm to 2.1 mm.The average grain size grew up from 2～5 μm of base metal to 20～70 μm and found no obvious soften phenomenon in overheated zone. The width of normalized zone was generally wide as 2/3 as that of the whole HAZ, and the grain size in this zone is smaller than that in base metal. Under the circumstance of equal heat input, the HAZ width of UNGW is narrower than that of the laser welding.

Effects of welding wire composition and welding process on the weld metal toughness of submerged arc welded pipeline steel

The effects of alloying elements in welding wires and submerged arc welding process on the microstructures and low-temperature impact toughness of weld metals have been investigated. The results indicate that the optimal contents of alloying elements in welding wires can improve the low-temperature impact toughness of weld metals because the proeutectoid ferrite and bainite formations can be suppressed, and the fraction of acicular ferrite increases. However, the contents of alloying elements need to vary along with the welding heat input. With the increase in welding heat input, the contents of alloying elements in welding wires need to be increased accordingly. The microstructures mainly consisting of acicular ferrite can be obtained in weld metals after four-wire submerged arc welding using the wires with a low carbon content and appropriate contents of Mn, Mo, Ti-B, Cu, Ni, and RE, resulting in the high low-temperature impact toughness of weld metals.

Effect of the heat input on microstructure and properties of submerged arc welded joint of 08Cr19MnNi3Cu2N stainless steel

SAW308L submerged arc welding wire and SJ601A submerged arc welding flux were selected to weld the 12 mm 08Cr19MnNi3Cu2N low nickel and high nitrogen austenitic stainless steel plates with three different welding heat input,and microstructure,tensile properties,microhardness and corrosion properties of the welded joints were studied.The results show that no defects are found in the three groups of welded joints,and the welded joints have better performance.The tensile strength of 08Cr19MnNi3Cu2N stainless steel welded joints with different heat input is slightly lower than that of the base metal,and fracture occurs in the weld zone,and the hardness of the weld zone is lower than that of the base metal.The weld microstructure of stainless steel welded joints with different heat input is composed of austenite+δferrite,and ferrite is uniformly distributed in austenite.With the increase of the welding heat input,the ferrite content in the weld zone decrease gradually,the grain size in the thermal affected zone increase gradually,and the impact toughness reduce.

Effect of Zr-Ti combined deoxidation on impact toughness of coarse-grained heat-affected zone with high heat input welding

In this study, the effects of Zr-Ti combined deoxidation and AI deoxidation on the impact toughness of coarse- grained heat-affected zone in high-strength low-alloy steels were investigated. More fine oxides were formed in the Zr-Ti-killed steel than in Al-killed steel. It was also found that more acicular ferrite grains were formed in the coarse-grained heat-affected zone in the Zr-Ti-killed steel than in Al-killed steel. The impact toughness of coarse-grained heat-affected zone of Zr-Ti-kiUed steel was higher than that of Al-killed steel. The good impact toughness was attributable to the pinning effect of fine oxides and the formation of acicular ferrite grains on fine oxides.

Review of GTAW Welding Parameters

Welding as a fabrication process is one of the vital production routes for most manufacturing industries. Several factors are involved in the choice of welding process for specific applications;notable among these are compositional range of the material to be welded, the thickness of the base materials and type of current. Most metals oxidize rapidly in their molten state, and therefore, the weld area needs to be protected from atmospheric contamination;this is achieved in gas tungsten arc welding GTAW by a shielding gas (argon, helium, nitrogen). GTAW technique is one of the major processes for joining austenitic stainless steels (ASS) and ferritic stainless steel (FSS) fabrication. However, the microstructural change that occurs during welding and at weld joint is still a major challenge today as it affects both the corrosion resistance and the mechanical properties. Therefore, this present paper reviews past research findings on GTA welding of ASS and FSS. Results of the findings have confirmed that, depending on the amount of heat input, which can be controlled by welding parameters (welding speed, voltage and current), welded joints particularly, heat affected zones (HAZs) of both grades of steels can undergo mechanical failure and can be susceptible to corrosion attack if the joints are produced with a less ideal combination of welding parameters.

Laboratory development of high performance steel plates with excellent HAZ toughness at large heat inputs

Presented in this study is the result of steel plates developed at laboratory by using the technique of chemistry design based on microstructure evolution.It has been shown that the produced 50mm thickness steel plates with yield and tensile strength being 420 MPa and 530 MPa respectively exhibit excellent large heat input weldability:the Charpy impact tests in the whole range of heat affected zone(HAZ) including the fusion line at the welded joint with large heat input of 100 -300 kJ/cm showed uniform impact toughness of above 140 J at -40℃.Welding simulations were also performed for heat inputs of 200-600 kJ/cm,which showed far better toughness at -20℃.Analysis on the results of the simulations and the practical welding tests were done and the microstructure evolution mechanisms were proposed.Finally suggestions were given to improve the simulation processes as well as chemistry modification.

The Influence of Welding Parameters on Brittle Fracture of Liquefied Natural Gas Storage Tank Welded Joint

Many applications operate at sufficiently low temperature conditions where most structural steels become very brittle and, therefore, unsuitable for use in safety-critical structures. So the materials used in the vessels or storage tanks which keep the natural gas at liquefaction temperatures need to remain ductile and crack resistant with a high level of safety. The material also needs to have high strength in order to reduce the wall thickness of the container and it must permit welding without any risk of brittle fracture. 9% Ni steel plates are one of most common used materials in the LNG storage tank application. However, the welding procedure for 9% Ni steel plates requires high level of skills of welding that is strictly controlled welding parameter for balancing avoidance of cold and hot cracking and maintenance of high strength. Mechanical properties are important characteristics of the weldment that must confirm to the application feasibility as well as functional requirements of the welded joint. The only way to enhanced the mechanical properties of welded joint by controlling the parameters of using welding process. From the main variables of the arc welding process are the heat input and interpass temperature where the two variables control the thermal cycle of welding process. The experiment show that for thin test specimen with thickness ≤ 14 mm, the heat input range from 1.4 to 2 KJ/mm and controlling interpass temperature within 80°C give high tensile strength with improving the toughness properties of welded joint and reduce the probability of brittle fracture happened by increase the ductility and reduce the yield strength and increased the transition temperature.

Microstructure and properties of SAF2507 superduplex stainless steel welded joints

SAF2507 plates （ 12 mm thickness ） were welded using shield metal arc welding （SMAW） process with E2594 electrode. The microstructure, o-phase, and impact fraetograph of the welded joints were analyzed using optical microscope and scanning electron mieroseope. The results show that the fusion zone consists of ferrite, chromium nitride, and secondary aastenite precipitation when welding is performed at low heat input （0. 5 kJ/mm）. However, the increase in heat input causes precipitation of brittle o＂ phase at the y/c~ interface in weld metal and heat-affected zone, as well as a brittle fracture along the grain boundary. Heat input in the range of O. 5 kJ/mm to 1.5 kJ/mm is suitable for joining SAF2507 plates.

On the heterogeneous microstructure development in the welded joint of 12MnNiVR pressure vessel steel subjected to high heat input electrogas welding

Microstructure features of 12 MnNiVR pressure vessel steel welded joint deposited by the high heat input electrogas welding have been systematically investigated. It is revealed that the welded joint is featured by a heterogeneous juxtaposition. The coarse grained heat-affected zone(CGHAZ) primarily consists of lath bainites and minor granular bainites. The fine grained heat-affected zone(FGHAZ) is dominated by polygonal ferrites, pearlites, and fine cementite particles. Moreover, electron backscatter diffraction results further demonstrate that the CGHAZ is populated by coarse prior austenite grains(PAGs) with high frequency(61.3%) of low angle grain boundaries(LAGBs). On the other hand, the FGHAZ is filled with fine PAGs with a lower frequency(19.6%) of LAGBs. Such microstructural differences may likely contribute to differed mechanical properties for samples tested at designed positions.

Progress in the technological development of oxide metallurgy for manufacturing steel plates with excellent HAZ toughness

In the present study, the market needs for the （HAZ） toughness are analyzed, and the mechanism of the development of steel plates with excellent heat affected zone decrease in the HAZ toughness during high-heat input welding is discussed.The important countermeasure for improving the HAZ toughness is to employ the technology of oxide metallurgy ,namely,to make use of fine inclusion particles for improving the microstructure of HAZ. The progress and theories of oxide metallurgy technologies developed in the Nippon Steel Corporation （ NSC）, the JFE Steel Corporation and the Kobe Steel Group are illustrated. Steel plates developed by these three companies with excellent HAZ toughness are introduced.

Influence of Ti on Weld Microstructure and Mechanical Properties in Large Heat Input Welding of High Strength Low Alloy Steels

The influence of Ti on weld microstructure and mechanical properties in large heat input welding of high strength low alloy steels is investigated. The results indicate that a moderate amount of Ti is still effective for grain refinement even under larger heat input and a large amount of acicular ferrite （AF） is formed in the weld metal when Ti content is within 0. 028%--0. 038%. With increasing Ti content, proeutectoid ferrite in the weld metal decreases, whereas bainite and M-A constituent increase. The type of inclusion in the welds varies from Mn-Si-AI-O to Ti-Mn- A1-O and finally to Ti-A1-O as Ti content increases from 0 up to 0. 064%. As for adding 0. 028%--0. 038% Ti, high weld toughness could be attained since most inclusions less than 2 tim which contain Ti20s provide the effective nu- clei for aeicular ferrite formation. However, the toughness of the weld metals severely reduces when Ti content is over the optimum ranRe of 0. 028%--0. 038%.

Heterogeneous Microstructure-Induced Mechanical Responses in Various Sub-Zones of EH420 Shipbuilding Steel Welded Joint Under High Heat Input Electro-Gas Welding

Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy,electron backscatter diffraction and mechanical testing.Comparing with the coarse-grained heat-affected zone(CGHAZ),the weld metal presents higher toughness(129.3 J vs.37.3 J)as it contains a large number of acicular ferrites with high-angle grain boundaries(frequency 79.2%)and special grain boundary∑3(frequency 55.3%).Moreover,coarse austenite grains in CGHAZ and slender martensite–austenite constituents between bainite laths may likely facilitate crack propagation.Polygonal ferrites and tempered pearlites formed at the junction of the fine-grained heat-affected zone and the intercritical heat-affected zone induced a softened zone with an average hardness of 185 HV0.5,which is the main reason for the occurrence of tensile fracture.

Influence of laser energy input mode on joint interface characteristics in laser brazing with Cu-base filler metal

The flange butt joints of 1 mm-thick galvanized steel sheets were brazed with CuSi3 as filler metal at different laser heating modes.The microstructures and element distributions of joint interface were investigated by SEM and EDS.The results show that there is no obvious interface layer with the circular individual beam heating and lamellar Fe-Si intermetallic compound layer is found with dual-beam laser spot heating.With the irradiation of rectangular laser spot,the joint interface layer is also formed.The layer thickness is larger than that of dual-beam brazing and the layer shape is flat so that intermetallic compounds trend to grow into cellular crystals.Moreover,the interface layer shape also depends on its position in the joint.Under the high heat input,dendritic or granular intermetallic compounds dispersively distribute in brazing seam adjacent to the interface,which is caused by the melting or dissolving of the base metal.According to the results,the brazing quality can be controlled by laser heating mode and processing parameters.

Low Cost High Performance Steel Plate With Superior HAZ Toughness for Large Heat Input Welding

In this paper, a laboratory study has been made to develop low cost high performance steel plates with superior HAZ toughness for large heat input welding. Simulated results show that the absorbed impact energy of heat-affected zone (HAZ) at -20℃reaches above 200J when large heat inputs of 100 to 400kJ/cm were applied, suggestive of superior HAZ toughness for large heat input welding of developed steel plate. The microstructures in HAZ are transformed from mainly fine ferrite and bainite at 100kJ/cm, through an intermediate stage of ferrite, bainite and pearlite at 200 and 300kJ/cm, to nearly fine ferrite and pearlite at 400kJ/cm. The prior austenite grain size and ferrite grain size in HAZ are controlled to ～50 and ～20μm, respectively. The high HAZ toughness is due to the inhibition of prior austenite grain size at high temperatures and the formation of beneficial microstructures to HAZ toughness during continuous cooling.

X80钢补焊残余应力模拟与试验验证

X80管线钢在铺设或者使用过程中会产生裂纹、气孔等缺陷而需要进行补焊修复。利用ABAQUS有限元分析软件建立了X80钢平板补焊模型,模拟分析了补焊前后X80钢焊接残余应力的变化情况,同时研究了3种不同补焊热输入量对焊接残余应力的影响。为验证模拟结果的准确性,开展了3种对应热输入量的补焊试验。模拟及试验研究结果表明,补焊残余应力高于初始焊残余应力,补焊后横向残余应力峰值较初始焊增加55.52%,补焊后纵向残余应力峰值已超过材料屈服强度。随着补焊热输入量的增大,Mises等效残余应力峰值和纵向残余应力无明显改变,但不同路径的横向残余应力变化规律有所不同。试验测量的残余应力值与模拟结果接近,两者的变化趋势一致。

焊接热输入对0Cr13Ni4Mo马氏体不锈钢电弧焊接头组织与性能的影响

在不同焊接热输入(9,13,17 kJ·cm^(-1))下对0Cr13Ni4Mo马氏体不锈钢板进行多层多道电弧焊,研究了焊接热输入对焊接接头显微组织与力学性能的影响。结果表明:不同焊接热输入下所得焊接接头焊缝和热影响区的组织均为板条马氏体、少量δ铁素体和残余奥氏体;随着焊接热输入的增大,焊缝和热影响区的板条马氏体变粗大,δ铁素体含量增多;不同焊接热输入下焊接接头的抗拉强度和屈服强度分别约为810,600 MPa,均高于母材且符合项目规定,屈强比均小于0.9,接头的拉伸性能良好,拉伸后均在母材处断裂;随着焊接热输入增大,冲击吸收能量减小,焊接热输入为9,13 kJ·cm^(-1)下冲击断口中的韧窝尺寸略大且均匀,接头的冲击韧性更好;不同焊接热输入下焊缝的硬度为310~340 HV,其平均硬度高于热影响区和母材,随着焊接热输入的增加,焊缝和热影响区的硬度均略微降低。

焊接热输入对P91钢焊接修复微观组织及性能的影响

为进一步揭示补焊热输入对补焊接头焊缝区微观组织与性能的影响规律,本文通过微观组织表征、显微硬度测试、拉伸实验和冲击实验等方法,对比研究了焊接热输入对P91钢焊接接头焊接缺陷、微观组织和力学性能的影响。结果表明,热输入为10kJ/cm时,补焊区焊缝金属中树枝晶呈平行状;热输入增加到15kJ/cm时,补焊区焊缝组织呈现出交叉互锁的燕尾搭接状形态;而热输入进一步增加到20kJ/cm时,补焊区的焊缝组织以平行状树枝晶为主和少量的交叉互锁的燕尾搭接状树枝晶组成。补焊区的析出相主要由NbC、Cr_(23)C6和Fe_(2)Nb(Laves相)组成,且随着热输入的增加,析出相熟化长大。力学性能分析表明,补焊区焊缝金属的强度和冲击韧性随热输入的增加均呈现出先增加后降低的变化趋势。热输入为15kJ/cm时,补焊区焊缝金属的枝晶形态和析出物形态所导致的“协同效应”使得显微裂纹形核、发育、扩展所需的能量阈值有所不同,进而补焊区的焊缝金属可以保持相对较高的韧性,因此热输入为15kJ/cm时,补焊区焊缝组织的强韧匹配最优。而3种热输入下的补焊区的焊接热影响区由于晶粒粗大以及补焊过程中的高拘束应力使得该区域的冲击韧性最差。

焊接热输入对690 MPa级HSLA钢焊缝金属组织与力学性能的影响

采用自研直径4.0 mm的焊条对厚度为27 mm的690 MPa级HSLA钢进行不预热焊接,研究了焊接热输入对焊缝金属组织和性能的影响及强韧化机理.结果表明,焊接热输入由13 kJ/cm提高至19 kJ/cm对焊缝金属组织结构及其强韧性产生了显著影响,对接接头抗拉强度、硬度呈现降低趋势,焊缝金属−50℃冲击吸收能量呈现先升高后降低趋势.16 kJ/cm热输入条件下获得了良好的强韧性,对接接头抗拉强度为828 MPa,焊缝中心−50℃冲击吸收能量为71~90 J,均值为80 J.13 kJ/cm及19 kJ/cm热输入条件下焊缝金属强韧性较低,前者与焊缝金属中板条贝氏体及侧板条铁素体形成有关,后者与其中粗大的M-A组元形成相关.热输入16 kJ/cm条件下,充分形成了塑性良好的针状铁素体组织,针状铁素体和贝氏体呈交织分布,同时,细小弥散分布的M-A组元并未对其韧性产生显著的负面作用,焊缝金属获得了良好的强韧性配合.

热输入对440 MPa级HSLA钢埋弧焊对接接头组织及性能的影响

采用20 kJ/cm,25 kJ/cm,30 kJ/cm三种焊接热输入进行440 MPa级HSLA钢埋弧焊试验,使用光学显微镜、扫描电子显微镜、透射电子显微镜、维氏硬度仪以及冲击试验机等实验仪器,研究了焊接热输入对接头显微组织和力学性能的影响。结果表明,三种不同的热输入下的焊缝金属的显微组织主要由先共析铁素体、侧板条铁素体、针状铁素体以及少量残余奥氏体组成,粗晶热影响区的显微组织主要由粒状贝氏体组成。随着焊接热输入的增加,焊缝金属中针状铁素体的含量不断降低,先共析铁素体和侧板条铁素体的含量逐渐升高;粗晶热影响区中粒状贝氏体的晶粒尺寸明显增大,焊缝金属中直径大于1μm的夹杂物占比从40.7%逐渐升高至59.9%,因此使得焊缝金属的强度和低温冲击韧性下降。当热输入为20 kJ/cm时,焊缝金属的平均硬度值最高,且低温冲击韧性达到最优;当热输入从20 kJ/cm开始增大时,焊缝冲击功从186 J下降至130 J,冲击断口中韧窝尺寸逐渐减小,深度变浅,断口形貌由韧性断裂向准解理断裂过渡,降低了裂纹扩展所需的能量,使得冲击吸收功不断减小。

高强钢焊接接头优化方法研究现状

高强钢以出色的力学性能在焊接结构的应用量急剧增加,其焊接接头性能已逐步成为研究焦点。为了解决高强钢焊接易出现冷裂纹、热影响区软化脆化、低温冲击韧度不高等问题,获得高强钢焊接接头优良强韧匹配。在使用熔化极气体保护焊接工艺的基础上采用不同的高强钢焊接接头优化方法,对严格控制热输入、焊前预热并控制热输入和研发并采用药芯焊丝这3种焊接接头优化方法进行分析总结,对3种优化方法下的焊接接头微观组织及力学性能进行分析,发现通过这3种接头优化方法可避免焊接接头产生裂纹、获得良好的韧性组织和力学性能优良的焊接接头。