Mitigation of hot cracking of alloy 52M overlay on cast stainless steel CF8A

Abstract

Effects of ER308L buffer layer and welding parameter slope down time on the hot cracking susceptibility of alloy 52M overlay on CF8A base metal were studied. The results indicated that Si segregation was a critical factor affecting Alloy 52M hot cracking. Applying ER308L buffer layers between CF8A and Alloy 52M can reduce the dilution of Alloy 52M weld beads and minimise the contribution of Si from CF8A into Alloy 52M, thereby alleviating Si segregation and the hot cracking susceptibility of Alloy 52M. When the Si content in the grain boundary region was lower than 0·81 wt-%, the hot cracking in the weld bead could be mitigated completely. In many cases, crater cracks occurred in the end crater of the weld bead. Increasing the number of ER308L buffer layers and extending the slope down time could reduce crater crack susceptibility. However, the Si content in the grain boundary region should be controlled to be lower than 0·63 wt-% to prevent crater cracking.     

A Feasibility Study of Applying SS 307Si Buffer Layer for Mitigating the Hot Cracking of Ni-Based Weld Overlay

The hot cracking behavior of Ni-based Alloy 52M weld overlay with respective SS 307Si and SS 308L buffer layers was investigated. The dilution level of SS 307Si buffer layer is a little higher than that of SS 308L. However, the hot crack length of overlay with SS 307Si buffer layer is shorter and the SS 307Si layer has higher mechanical properties than that of SS 308L layer. As observed by SEM and EBSD, ferrites precipitated in SS 307Si buffer layer are in vermicular skeletons dotted with lathy precipitates, which have a little higher local stain than that of SS 308L weld. However, Alloy 52M weld around SS 307Si fusion boundary has a lower degree of local distortion. The results generalize that the SS 307Si buffer layer is marginally better for reducing hot cracking susceptibility, owing to its lower local stain and slightly higher mechanical strength.     

The effect of solidification behaviour of austenitic stainless steel on the solidification cracking susceptibility

0Introduction Oneofthemainproblemsinweldingausteniticstain lesssteelsishotcracking[1,2].Inweldingofsingle phase austeniticstainlesssteels,thetendencyofhotcrackingis moreserious[3].Inordertopreventhotcrackingofthis kindofmaterial,itwasattemptedtogaintwo p…     

Effect of dilution on the behavior of solidification cracking in PTAW overlay deposit on Ni-Base superalloys

In this study, the effects of dilution on the solidification cracking susceptibility of PTAW (Plasma Transferred Arc Welding) Inconel 625 and 718 overlay on Nimonic 80A were observed. In order to evaluate solidification cracking susceptibility, the Varestraint test was utilized. A possible mechanism of solidification cracking was suggested on the basis of microstructural examination and thermal analysis. The present study showed that the solidification temperature range and the amount and distribution of γ/NbC and γ/Laves eutectic phases formed along the solidification grain boundaries. As dilution increased, the C/Nb ratio increased and the amount of eutectic phases decreased. In addition, the solidification temperature range decreased with increasing dilution in each overlay.     

Controlling End-Grain Corrosion of Austenitic Stainless Steels

SS 304L is widely used as a structural material in applications handling nitric acid such as nuclear fuel processing plants and nuclear waste management facilities. Bar, wire, and tubular products of this material are especially susceptible to end-grain corrosion in nitric acid environment. Such an attack takes place on the tubular and forged surfaces that are perpendicular to the hot-working direction and occurs as localized pitting type attack. This study shows that the possible reasons for the directional nature of end-grain attack are the manganese sulfide inclusions aligned along the hot-working direction and/or segregation of chromium along the flow lines during the fabrication stage itself. It has been shown in this study that controlled solution annealing, laser surface remelting, and weld overlay can be used to avoid/minimize end-grain corrosion. Different annealing heat-treatments were carried out on two heats of SS 304L tube and susceptibility to corrosion was measured by ASTM A 262 practice C and electrochemical potentiokinetic reactivation (EPR) test. Solution annealing at 950 °C for 90 min has been shown to increase the resistance to end-grain corrosion. Laser surface remelting using continuous wave CO₂ laser under argon shield and weld deposition (overlay) using SS 308L material were done on the end faces of the tubes. These samples were completely resistant to end-grain corrosion in nitric acid environments.     

Research on Prediction Method of Liquation Cracking Susceptibility to Magnesium Alloy WeldsEI北大核心CSCD

Magnesium alloys has a wide application prospect due to their good properties, such as high specific strength and specific stiffness, but the susceptibility of liquation cracking is also pretty high. The liquation in partially melted zone of AZ-series magnesium alloys were investigated with circular-patch welding test. The AZ91, AZ31 base alloys were welded with AZ61 and AZ92 filler wires by using the cold metal transter metal inert-gas (CMT-MIG) welding. The results show that, the liquation occurred along the weld edge of AZ91 with the eutectic reaction occurring between gamma(Mg17Al12) phase and Mg-rich phase. The liquation susceptibility of AZ31 was pretty low as gamma(Mg17Al12) was not present in base metal of AZ31. Meanwhile, a new method for predicting liquation cracking based on binary phase diagram was proposed. When the initial solidification temperature of weld is higher and the solidification temperature range of weld is shorter than those of base metal, the liquation crack susceptibility of weld is mostly higher. When the initial solidification temperature of weld is close to or below that of base metal, and the solidification temperature range of weld is close to or longer than that of base metal, the liquation cracking susceptibility of weld is lower. This method worked well on predicting the effect of composition of base metal and filler wires on liquation cracking, and the predicting results are consistent with the experimental results. That is, the liquation cracking susceptibility is higher with AZ91 base metal used than that with AZ31 base metal. And, the liquation cracking susceptibility is lower with AZ92 filler wire than that with AZ61 filler wire.     

A comparison of hydrogen embrittlement susceptibility of two austenitic stainless steel welds

Slow displacement rate tensile tests were carried out to assess the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of AISI 316L and 254 SMO stainless steel (SS) plates and welds. 254 SMO generally exhibited a better resistance to hydrogen embrittlement than 316L. The strain-induced transformation of austenite to martensite in the 316L SS was responsible for the high hydrogen embrittlement susceptibility of the alloy and weld. Sensitized 254 SMO (i.e., heat-treated at 1000 °C/40 min) base plate and weld comprised of dense precipitates along grain boundaries. Interfacial separation along solidified boundaries was observed with the tensile fracture of 254 SMO weld, especially the sensitized one. Dense grain boundary precipitates not only reduced the ductility but also raised the susceptibility to sulfide stress corrosion cracking of the sensitized 254 SMO plate and weld.     

Microcracking in multipass weld metal of alloy 690 Part 3 – Prevention of microcracking in reheated weld metal by addition of La to filler metal

Abstract

The effect of addition of La to a filler metal on microcracking (ductility dip cracking) in the multipass weld metal of alloy 690 was investigated with the aim of improving its microcracking susceptibility. The susceptibility to ductility dip cracking in the reheated weld metal could be greatly improved by adding 0·01–0·02 wt-%La to the weld metal. Conversely, excessive La addition to the weld metal led to liquation and solidification cracking in the weld metal. Hot ductility of the weld metal at the cracking temperature was greatly improved by adding 0·01–0·02 wt-%La to the weld metal, implying that the ductility dip cracking susceptibility was decreased as a result of the desegregation of impurity elements of P and S to grain boundaries due to the scavenging effect of La. The liquation and solidification cracking resulting from excessive addition of La to the weld metal is attributed to the formation of liquefiable Ni–La intermetallic compound. A multipass welding test confirmed that microcracks in the multipass weldment were completely prevented by using a filler metal containing an addition of 0·01 wt-%La.     

Microstructural characterization of electron beam welded joints of TiAl-based intermetallic compound

The feasibility to use election beam welding to join the nominal composition Ti-48Al-2Cr-2Nb (at.%) alloy was assessed. The microstructure characterization and cracking susceptibility of the joints were evaluated by means of OM, SEM, XRD, and microhardness.It was found that the welded microstructure exhibited columnar and     

Effects of heat treatment and chromium content on the environmentally assisted cracking behavior of the dissimilar metal welds in simulated BWR coolant environments

The environmentally assisted cracking behavior of dissimilar metal (DM) welds, including Alloy 52 – A508 and Alloy 82 – A508, under simulated BWR coolant conditions was studied. Effects of postweld heat treatment (PWHT) on the SCC and corrosion fatigue crack growth rates of DM welds were evaluated. PWHT brought about a change of the carbide precipitate distribution and strain localization, thus leading to a redistribution of the weld residual stress. It is concluded that Cr content in the weld may not be the sole factor governing the SCC resistance; the localized strain concentration could also play an important role.     

不锈钢厚板焊接凝固裂纹驱动力的三维数值模拟

利用双椭球形热源模型研究了SUS310不锈钢的三维焊接温度场,并与实验测量进行了比较．在计算温度场的基础上,重点研究了材料在凝固裂纹敏感温度区间内,焊缝金属应变场和位移场的动态场演变过程,得到了10mm厚板的凝固裂纹驱动力曲线,并利用动态单元再生方法,消除了焊接凝固过程对应变场的影响．模拟计算得到的驱动力曲线与前人实验测量的凝固裂纹阻力曲线进行了比较,初步预测了SUS310不锈钢凝固裂纹敏感性．     

Effect of minor elements on hot cracking susceptibility of austenitic stainless steel welds

This research evaluates the effects of Si, N and REM on the hot cracking behavior of specially designed austenitic stainless steels. Varestraint hot cracking tests and microstructural examination revealed that solidification cracking of 304 can be minimized by a suitable addition of Si, N and control of the solidification mode. Further, the addition of N to “fully” austenitic 316 weld metal decreased solidification cracking susceptibility. REM additions were also effective in reducing solidification and weld metal HAZ liquation cracking in 347, but was ineffective for reduction in base metal HAZ liquation cracking.     

AZ31镁合金双面对称搅拌摩擦焊接头疲劳性能

试验选用ZK61, AZ31, AZ61和AZ91镁合金进行焊接凝固裂纹敏感性的分析. 首先进行了双速模式下的横向移动裂纹敏感性试验,获得了4种镁合金的临界横向移动速度,并对凝固裂纹敏感性进行了评估和排序：ZK61 > AZ31 > AZ61 > AZ91,与单速模式试验结果以及基于│dT/d(f_S)^1/2│_max作为裂纹敏感指数得到的计算预测结果一致,验证了双速模式的横向移动裂纹敏感性试验用于评估镁合金凝固裂纹敏感性的有效性.凝固裂纹尖端及周边存在液相回填特征,ZK61镁合金的晶间回填液相呈非连续状且回填通道较窄,难以起到愈合裂纹效果,增大了凝固裂纹敏感性;AZ91镁合金液相回填通道宽度最大,有利于晶间液相回填,降低了凝固裂纹敏感性.     

The effect of annealing twin-generated special grain boundaries on HAZ liquation cracking of nickel-base superalloys

The susceptibility to weld heat-affected-zone (HAZ) liquation cracking of wrought Waspaloy and Alloy 718 was quantified by using hot ductility testing. The intergranular (IG) cracking behavior of these alloys was influenced by long term isothermal heat treatments. Such long holds at the solution temperature resulted in continuous grain growth in Waspaloy. However, the IG liquation cracking was not solely controlled by grain size. Annealing twin-generated special grain boundaries increased in volume fraction as grain size increased and reduced the tendency for IG cracking. Intense δ phase precipitation occurred in Alloy 718 following the long isothermal holds. δ phase pinning of grain boundaries restricted grain growth and hence the fractional increase of special grain boundaries. However, special grain boundaries did provide resistance to IG liquation cracking once the δ-phase was dissolved using a “rejuvenation” heat treatment.     

A method of measuring the heat generation parameters in the resistance spot welding in single phase AC machines

In the fabrication of reactors (made of Cr–Mo steel modified with vanadium) operating in high hydrogen pressure and high-temperature service, internal cladding in austenitic stainless steel (typically made of AISI 347) is required in order to guarantee satisfactory corrosion resistance against the process fluids desulphurized hydrocarbons. Application of an electro-slag strip cladding (ESSC) process for internal weld overlay and clad restoring on heads, barrels and nozzles of 2¼Cr–1Mo–¼V reactors (with single-layer or double-layer technique) is described in the paper. The first part of the paper is focused on metallurgical aspects, cracking phenomena (hydrogen cracking, solidification cracking, under-clad cracking and hydrogen-induced disbonding) and cladding residual stresses referable to ESSC process. The second part of the paper is focused on operating aspects of the ESSC process and UT examination of weld overlay and clad restoring, optimized for the detection of planar defects under cladding.     

Delamination failures of Stellite hardfacing in power plants: a microstructural characterisation study

In recent years, several incidents of cracking and failures have been observed in Stellite (Stellite is a registered trademark of the Deloro-Stellite Corporation) hardfacing used in valves of modern high temperature combined cycle gas fired power plants. These hardfacing layers are applied as an overlay onto a steel substrate, such as CrMo steel (i.e. Grade 22, WC9) or creep strength enhanced ferritic steel (i.e. Grade 91, C12A). Cracking has been observed in valve components at the Stellite/steel interface and in the weld dilution zone formed between the steel and clad. Ultimately, disbonding or delamination of the weld hardfacing from the valve body occurs and has resulted in collateral damage to components in the plant (such as to the turbine) or valve failure. In this study, the microstructure formed near the Stellite/steel interface is investigated. Based on thermodynamic modelling, microstructure formed at these regions is hypothesised and a simple methodology is proposed to predict the occurrence of these failures.     

热丝脉冲TIG堆焊Inconel625成型质量优化与性能

基于中心复合试验设计方法,采用热丝脉冲TIG工艺在AISI 4130基体上堆焊Inconel 625合金。借助响应面法建立了焊缝几何特征与工艺参数之间的数学模型。根据优化后的工艺参数,获得了平坦、连续、无缺陷的多道两层堆焊层。堆焊层微观组织主要由柱状晶组成,在融合界面附近存在少量的平面晶与胞状晶,其顶部组织为等轴晶与转向晶。利用动态极化曲线法对基体与堆焊层的耐腐蚀性能进行了评价。结果表明：堆焊层的耐腐蚀性随着Fe含量的增加而降低,但增加堆焊层的层数可以显著提高耐腐蚀性能。而且,两层堆焊层试样与铸态Inconel 625的耐腐蚀性能基本相当。     

A corrosion study of nickel–copper and nickel–copper–palladium welding filler metals

In an effort to reduce the release of fumes containing carcinogenic Cr⁶⁺ during arc welding of stainless steel, Cr‐free filler metals for welding of SS304 have been developed. Corrosion studies were carried out on 304L stainless steel samples welded with these Cr‐free consumables. The corrosion properties of gas tungsten arc (GTA) and shielded metal arc (SMA) welds fabricated with Ni? Cu and Ni? Cu? Pd consumables were found to be comparable to those of welds fabricated with SS308L, the standard filler metal used with SS304. Although the breakdown potentials of the welds made using both welding processes were lower than that of the SS308L GTA weld, the repassivation potentials of these welds were much higher. Generally, the repassivation potential is a more conservative measure of susceptibility to localized corrosion. Accordingly, the Ni? Cu and Ni? Cu? Pd welds were more resistant to crevice corrosion than SS308L welds. The addition of a small amount of Pd improved the corrosion resistance relative to Ni? Cu welds, which is consistent with previous studies from specially‐prepared button samples and bead‐on‐plate samples. Other corrosion studies such as creviced and uncreviced long time immersion, atmospheric exposure, and slow strain rate testing suggest that Ni? Cu? Pd filler metal can be a potential replacement for the conventional SS308L filler metal for joining SS304.     

In situ corrosion testing of various nickel alloys at Måbjerg waste incineration plant

The majority of waste in Denmark is disposed via waste to energy (WTE) incineration plants which are fabricated from carbon steel. However, due to the increasing corrosiveness of waste over the years, more corrosion resistant alloys are required. In Denmark, Inconel 625 (UNSN06625) is the weld overlay material currently being used to give improved corrosion resistance. In order to assess the use of alternative nickel alloys, test panels have been manufactured and inserted into Måbjerg waste incineration plant. Inconel 625 as a 50% weld overlay, two layered weld overlay and as a spiral weld overlay was exposed. Other nickel materials exposed were weld overlay Alloy 686, Alloy 50 and Sumitomo Super 625 coextruded tube. Exposure has been undertaken from 2003 to 2009 in the first pass and 2005–2009 in the second pass, and sections have been removed and investigated during this period. The composition of the deposits from the exposed waterwall panels was also analysed each time sections were removed. This paper will compare the various nickel alloys in the two areas and assess the results of the long‐term testing project.     

Multicycle fatigue strength of welded joints of steel S500MC

Microcracking susceptibility in the dissimilar multipass weld metal of alloy 690 and low-alloy steel A533B was evaluated, and the effect of dilution on hot cracking (ductility-dip and liquation cracking) behaviour was investigated. In order to simulate the dissimilar multipass weld metal of alloy 690 to A533B steel, the A533B plate was welded under various dilution ratios using alloy 690 filler metal with different contents of P and S. Several weld metals, which had different alloy compositions at the fixed (P+S) content, were manufactured, and then ductility-dip and liquation cracking susceptibilities of the reheated weld metals were evaluated by the spot-Varestraint test. Ductility-dip cracking susceptibility heightened as the dilution ratio was increased even when the amounts of P and S were fixed. The increased dilution ratio (contamination of Fe into the weld metal) should reduce the tortuous character of the grain boundary (GB) due to inhibiting the constitutional supercooling (the instability of the solidification boundary), as well as enhance the GB embrittlement due to promoting the GB segregation of P and S. Furthermore, the liquation cracking susceptibility slightly heightened with an increase in the dilution ratio at the fixed (P+S) content. The increased liquation cracking susceptibility would be attributed to the enhancement of solidification segregation of P and S with increasing the dilution ratio.