焊后热处理对DH36钢焊接接头断裂韧性的影响

文中对DH36钢埋弧焊焊接接头进行了焊后热处理,并根据BS7448标准对焊缝和热影响区进行裂纹尖端张开位移CTOD测试,研究焊后热处理对断裂韧性的影响.结果表明,焊后热处理对焊缝断裂韧性的影响并不一定是好的效果,热处理后,焊缝δ值有的升高有的降低;焊后热处理对热影响区粗晶区的断裂韧性有不利影响,热处理后,热影响区粗晶区的δ值均有所下降.经过焊后热处理,90 mm厚焊缝试样的δ值略有下降,60mm厚焊缝试样的δ值明显升高;90mm厚热影响区试样的δ值明显下降,60mm厚热影响区试样的δ值略有下降.     

Microstructure Characterization of Laser-Welded Nb-Microalloyed Silicon-Aluminum TRIP Steel

This work presents the results of a microstructural characterization of welds in Nb-microalloyed TRIP steel with silicon partially replaced by aluminum. Tests of laser welding of thermomechanically processed sheet samples were carried out using keyhole welding and a solid-state laser. Welding penetration tests were conducted for heat input values between 0.037 and 0.048 kJ/mm. Identification of different microstructural constituents was carried out using light microscopy and scanning electron microscopy in the fusion zone (FZ), heat-affected zone (HAZ), and base metal. Special focus was put on the effect of cooling conditions on the stabilization of retained austenite in different zones. The intercritical, fine-grained, and coarse-grained regions of the HAZ were identified. It was determined that enriching austenite with carbon in the intercritical HAZ stabilizes this phase at a level close to the base metal, i.e., a 15% volume fraction. Despite a high cooling rate in the FZ and HAZ, interlath retained austenite is also present in these zones. The research involved microhardness measurements and characterizing non-metallic inclusions formed in the fusion zone. A good correlation between microstructures formed in different weld regions and microhardness results was obtained.     

Welding of aluminum alloy door units for large SUVs using a compound laser method

A study was made on the relation between CTOD value and M–A constituent for the single-heat-cycled weld heat-affected zone (HAZ) of YS 320–360 N/mm² class thermomechanical control process steels with increased heat input. It was found that the M–A constituent disappeared and lost its deterioration effect on the HAZ CTOD toughness when the heat input exceeded about 15 kJ/mm, although this boundary heat input depended on the steel chemistry. On the other hand, the austenite grain size increased monotonically with increasing the heat input. But the austenite grain size could not be the controlling factor of the HAZ toughness, and its effect deferred between base metals. However, the HAZ toughness was related to the fracture facet size for the large heat input conditions. This fracture facet size, which represents the fracture toughness, is considered to be a measure of the uniformity of the transformed microstructure from austenite in the HAZ.     

大热输入焊接EH36船板钢接头力学性能

以EH36高强度船板钢为研究对象,通过拉伸和冲击分析试验手段,对EH36船板钢不同热输入埋弧焊接头进行了力学性能测试,同时采用扫描电镜对冲击试样断口形貌进行分析.结果表明,所有断裂均发生在拉伸试样的母材区,EH36船板钢在大焊接热输入条件下,焊缝和焊接热影响区的强度好于母材,并没有出现热影响区软化现象;随着焊接热输入增加焊缝的冲击韧性降低,从焊缝和熔合区断口形貌来看,断裂类型为韧性断裂和准解理断裂的混合断裂.随着远离熔合线距离的增加,冲击吸收功有增加的趋势,在距离熔合线4 mm处的冲击吸收功跟母材接近,说明该位置处韧性基本不受焊接热循环的影响.     

局部脆性区对直接淬火回火钢焊接热影响区断裂韧性的影响

通过焊接热模拟和厚板焊接接头ＣＴＯＤ断裂性能试验,研究了直接淬火回火钢焊接热影响区局部脆性区组织和性能及对厚板焊接接头断裂韧性的影响,结果表明,在γ＋α二相区的内再次加热的粗晶区（ＩＣＣＧＨＡＺ）具有最低冲击韧性值,是焊接接头中最薄弱环节,该区在原奥氏体晶界上分布着“项链”状,ＭＡ组元,引发多层焊热影响区脆断起裂,降低热影响区断裂韧性,局部脆性区韧性的高低和尺寸的大小是控制直接淬火回火钢多层焊热和     

INFLUENCE OF LOCAL BRITTLE ZONE ON THE FRACTURE TOUGHNESS OF HIGH-STRENGTH LOW-ALLOYED MULTIPASS WELD METALS

1.IntroductionManyillvestigatiolls[1--5]havefOllndthattilelocalbrittlezone(LBZ)playsanimportantroleinfyacturetoughnessofheat--affectedzoneinthebasemetalfornormalizedandthermomechanicallycontrolledprocessingsteels,aswellasdirectquellchedandtemperedsteels.Therearefewreportsaboutthisphellomellainhigh-strengtllmllltipassweldmetals.Inmultipasswelds,thereareprimaryweldmetalandweldmetalreheatedtovarioustemperaturesbythesubsequentbeads[6'71.Thereheatedregionfinderabeadcanbedividedintoacoarsegrainedz…     

Fracture toughness and safety assessment of X65 offshore pipeline welded joints

0Introduction Weldedjointsaretheweaknesslocationinthewelded structureofoffshorepipeline.Duetothein servicecondi tionssuchaslowtemperatureandoceanwave,crackiniti ation,extensionandevencollapsearefrequentlyfoundin thejoints.Thematerialwithhightoughnessatl…     

A model of heating a flux-cored wire in arc metallizing and analysis of the structure of the coating

Summary

This paper describes HAZ‐notched CTOD tests of multipass welds in SMYS = 420–460 MPa class high‐strength steels for offshore structural applications. The weld metal strength overmatch causes different fracture behaviour depending on the actual CGHAZ toughness. When the CGHAZ is completely embrittled, the weld metal strength overmatch leads to the lower bound critical CTOD value. This is due to elevation of the local stress in the CGHAZ caused by the restraint effect of the overmatched weld metal. The fracture surface is generally flat, and brittle fracture originates from the CGHAZ sampled by the fatigue crack front. A larger fraction of the CGHAZ along the crack front gives a smaller critical CTOD value. When the CGHAZ has moderate toughness, however, the weld metal strength overmatch may produce a higher critical CTOD value at brittle fracture initiation. This is due to crack growth path deviation towards the base metal. Plastic deformation preferentially accumulates to a greater extent on the softer base metal side before the critical stress conditions for brittle fracture initiation occur in the CGHAZ. This asymmetrical plastic deformation promotes deviation of ductile crack growth from the crack tip CGHAZ. In this case, the critical CTOD value does not always reflect the CGHAZ toughness itself.

A notch location nearer the weld metal sometimes causes fracture initiation in the weld metal if the fatigue crack tip samples the CGHAZ. Such experimental data do not reflect the real CGHAZ toughness.

The significance of the critical CTOD value obtained in the tests must be determined in the fracture toughness evaluation of the weld CGHAZ. This paper presents a procedure for evaluation of CTOD test results obtained for HAZ‐notched welds that considers the strength mismatch effect.     

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。     

国产06Ni9DR 钢焊接热影响区组织和低温韧性

采用扫描电镜(SEM)、背散射电子衍射(EBSD)和焊接热模拟技术,研究了单次热循环不同峰值温度对国产06Ni9DR 钢焊接热影响区(HAZ)显微组织和低温冲击韧性的影响. 结果表明,06Ni9DR 钢HAZ的-196 ℃冲击吸收能量均低于母材,HAZ整体发生了脆化. 粗晶区脆化最为严重,原因是原始奥氏体晶粒粗大及其导致的有效大角度晶界较少,残余奥氏体量少且不稳定,以及较大的位错密度和粗大马氏体的存在. 晶界呈链状分布的大块逆转奥氏体和M-A组元的存在导致回火区脆化程度仅次于粗晶区. 细晶区和不完全脆化区的韧性低于母材,主要是因为淬火马氏体的存在和残余奥氏体的低温稳定性差.     

欧标低合金结构钢粗晶热影响区组织和韧性的热模拟研究

利用Gleeble-3500热模拟试验机模拟粗晶热影响区的焊接热循环,研究了热输入对欧标低合金结构钢粗晶热影响区晶粒长大、硬度及韧性和组织的影响。结果表明,随着峰值加热温度的提高和高温停留时间的延长,奥氏体晶粒将发生不同程度的长大,粗晶热影响区的最高硬度也逐渐提高;同时随着t_(8/5)的延长,粗晶热影响区的组织将由少量低碳马氏体、针状铁素体以及粒状贝氏体和大量块状铁素体组织,逐渐转化为大量侧板条贝氏体、粒状贝氏体以及粗大长条状M-A组元,甚至出现一定数量的上贝氏体,使得粗晶热影响区的低温冲击韧度急剧下降,由低温韧性断裂转化为低温脆性断裂。     

Weldability characteristics of shielded metal arc welded high strength quenched and tempered plates

High strength, quench and tempered (Q&T) plates having yield strength of a minimum of 670 MPa and conforming to SA 517 Gr. F specification were successfully developed at Rourkela Steel Plant in plates up to 40 mm thickness. The plates are used extensively for the fabrication of impellers, penstocks, excavators, dumpers, and raw material handling devices, where welding is an important processing step. SA 517 Gr. F plates, characterized by a relatively high carbon equivalent (CE: ∼0.6) and alloyed with Ni, Cr, Mo, Cu, and V, are susceptible to a crack-sensitive microstructure and cold cracking during welding. In view of the above, the present study investigated the weldability properties of 20 mm thick plates using the shielded metal arc welding (SMAW) process. Implant and elastic restraint cracking (ERC) tests were carried out to assess the cold cracking resistance of the weld joint under different welding conditions. Preheat of 100 °C, partial or full rebake, and a heat input of 14.9 to 15.4 KJ/cm resulted in static fatigue limit (SFL) values well in excess of the minimum specified yield strength (MSYS) of 670 MPa and a critical restraint intensity (K _cr) value of 34,650 MPa, indicating adequate cold cracking resistance. Lamellar tear tests conducted using full thickness plates at heat input levels ranging from 9.7 to 14.4 KJ/cm and weld restraint loads (WRL) of 510 to 685 MPa showed no incidence of lamellar tear upon visual, ultrasonic, and four-section macroexamination. The weld joint, based on optimized welding parameters, exhibited adequate tensile strength (812.4 MPa) and low temperature impact toughness 88.3 and 63.4 J (9.2 and 6.6 kg-m) at −40 °C for weld metal (WM), and heat-affected zone (HAZ) properties, respectively. The crack tip opening displacement (CTOD) values of WM and HAZ (0.40 and 0.36 mm, respectively) were superior to that of the parent metal (0.29 mm), indicating adequate resistance of weld joint to brittle fracture. It was concluded that the weld joint conforms to the requirements of SA 517 Gr. F specification and ensures a high integrity of the fabricated products.     

TP347H钢焊接接头微观组织及断口形貌分析

采用了ER316L和H1Cr18Ni9Ti焊丝对TP347H钢的焊接性进行了研究,测试了焊接接头在常温下的力学性能,对焊缝金属和热影响区进行微观组织观察,并对冲击试件进行了SEM断口形貌分析.发现氧化物等杂质容易聚集在热影响区,内充氩不当在焊缝根部极易形成氧化裂纹,焊接参数大容易引起焊缝区未熔合,在启裂处有脆性断裂迹象.通过分析对TP347H钢的焊接性及工艺参数有了更清楚的认识,对大参数火电机组和核电机组材料的焊接具有一定的帮助.     

TA15钛合金电子束焊焊接接头力学性能

钛合金材料以及相关制造技术是实现飞机先进性的重要基础之一,电子束焊接是钛合金板材一种先进的焊接形式.对TA15钛合金板材电子束焊接试样进行了金相分析和静力试验、疲劳试验和扫描电镜(SEM)分析.结果表明,TA15板材电子束焊焊接接头的焊缝、热影响区和母材的微观组织差别明显;焊缝韧性降低,抗拉强度高于母材;热影响区尺寸较小,在1～2 mm左右,是焊接接头的薄弱部位;疲劳裂纹大多萌生于焊接热影响区区域,疲劳破坏试样断口的SEM分析表明,疲劳裂纹大多起源于焊接热影响区的气孔处.     

Effects of strength matching and crack depth on the fracture parameters for welded joints

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添加N2保护对CMT-P复合电弧焊接头组织与性能的影响

以UNS S32750超级双相不锈钢为研究对象,采用冷金属过渡脉冲(cold metal transfer pulse,CMT-P)复合电弧焊接技术,运用光学显微镜、扫描电子显微镜、透射电子显微镜、X射线衍射仪和电子探针组织表征手段以及显微硬度和低温冲击韧性性能测试方法,对比研究了纯Ar和Ar+2%N₂气体保护对焊接接头的微观组织、硬度和低温韧性的影响规律.结果表明,与纯Ar保护气相比,添加2%N₂保护的焊接过程飞溅较少,焊缝平整笔直,鱼鳞纹更加细致紧密.此外,热影响区主要由过量的铁素体和少量的奥氏体组成,并伴随有害的Cr₂N析出.因此,与CMT-P复合电弧焊接头的其它区域相比,热影响区的硬度较高和韧性较低.添加2%N₂气体保护增加了焊缝和热影响区奥氏体含量和N原子在铁素体与奥氏体内的固溶量,从而提高了接头各区域的低温韧性.     

On the Microstructural Strengthening and Toughening of Heat-Affected Zone in a Low-Carbon High-Strength Cu-Bearing Steel

In this article, the influence of simulated thermal cycles for the heat-aff ected zone(HAZ) on the microstructural evolution and mechanical properties in a low-carbon high-strength Cu-bearing steel was investigated by microstructural characterization and mechanical tests. The results showed that the microstructure of the coarse-grained heat-aff ected zone(CGHAZ) and the fine-grained heat-aff ected zone(FGHAZ) was mainly comprised of lath martensite, and a mixed microstructure consisting of intercritical ferrite, tempered martensite and retained austenite occurred in the intercritically heat-aff ected zone(ICHAZ) and the subcritically heat-aff ected zone(SCHAZ). Also, 8–11% retained austenite and more or less Cu precipitates were observed in the simulated HAZs except for CGHAZ. Charpy impact test indicated that the optimum toughness was obtained in FGHAZ, which was not only associated with grain refinement, but also correlated with deformation-induced transformation of the retained austenite, variant confi guration as interleaved type and a relatively weak variant selection. The toughness of ICHAZ and SCHAZ exhibited a slight downtrend due to the presence of Cu precipitates. The CGHAZ has the lowest toughness in the simulated HAZs, which was attributed to grain coarsening and heavy variant selection. In addition, the contribution of Cu precipitates to yield strength in simulated HAZs was estimated based on Russell–Brown model. It demonstrated an inverse variation trend to toughness.     

Effect of weld metal chemistry on stress corrosion cracking behavior of AISI 444 ferritic stainless steel weldments in boiling chloride solution

The influence of the weld metal chemistry on the susceptibility of AISI 444 ferritic stainless steel (FSS) weldment to stress corrosion cracking (SCC) in hot chloride was investigated by constant load tests and metallographic examination. Two types of filler metal of austenitic stainless steel (E316L and E309L) were used in order to produce fusion zones of different chemical compositions. The SCC test results showed that the interface between the fusion zone (FZ) and the heat affected zone (HAZ) was the most susceptible region to SCC. Results also showed that the AISI 444 stainless steel weldment with E309L weld metal presented the best SSC resistance. Microstructural examinations indicated that the cracks initiated in the weld metal and propagated to the HAZ of the AISI 444 FSS, where the fracture occurred and it was observed a considerable amount of precipitates. Additionally, the higher SCC resistance of the AISI 444 FSS weldment with E309L weld metal may be attributed to the presence of a discontinuous delta‐ferrite network in its microstructure, which acted as a barrier to cracks propagation from the fusion zone to the HAZ/fusion zone interface of AISI 444 FSS. Fractrography analyses showed that the transgranular quasi‐cleavage fracture mode was predominant in the AISI 444 weldment with E316L weld metal and the mixed fracture mode was the predominant in the AISI 444 weldment with E309L weld metal.