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为了研究焊后热处理对8万吨模锻压机主缸材料20MnNiMo焊接接头残余应力的影响,制定了窄间隙焊接方案和15 h×(550±10)℃焊后热处理方案,并通过盲孔法对焊接接头表面残余应力进行了测定和记录。得到了15 h×(550±10)℃焊后热处理对20MnNiMo厚板焊接接头残余应力场分布的影响。结果表明:15 h×(550±10)℃去应力退火可以很好的减小20MnNiMo厚板焊接残余应力,去应力效果显著,可以很好地改善20MnNiMo焊接残余应力的分布,该热处理方案满足实际产品需要,可以用于实际焊接生产中。 相似文献
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Edmund Tasak Aneta Ziewiec Barbara Wasilewska Jarosław Walczyk 《Welding International》2013,27(8):608-613
This paper reviews the results of investigations on how post-weld heat treatment (PWHT) influences the hardness and microstructures of welded joints in stainless steel X3Cr-NiMo 13-4. It is known that welding leads to high segregation of components in the solidification process, which has an influence on phase transitions in PWHT. The investigated steel has a very narrow PWHT range, about 600–620°C, which provides optimum levels of hardness and toughness. Excessive annealing temperature leads to decreased toughness, which in turn causes exceeding of the Ac1 temperature in the segregation range, which then leads to increased ‘fresh’ martensite content. 相似文献
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The behavior of Cu precipitates in the weld coarse-grained heat-affected zone (CGHAZ) of 1.5 wt% Cucontaining high strength low-alloy (HSLA) steel subjected to a thermal/thermo-mechanical welding cycle and post-weld heat-treatment (PWHT) was evaluated. The welding cycles of CGHAZ and PWHT were simulated by the Gleeble system. The hardness was measured at each PWHT condition, and observation and analysis of the Cu particles were performed using HRTEM. The hardness decreased initially with an increasing PWHT time at 550 °C. However, the peak hardness resulting from precipitation of Cu particles occurred after about 60 min at 550 °C. In the thermo-mechanical cycle, the peak hardness appeared at an earlier PWHT time. These results correspond with the HRTEM observations in which Cu particles were observed at an earlier PWHT time and larger Cu particles were observed at the same given PWHT time after the thermo-mechanical cycle. Thus, this paper confirms that the kinetics of Cu precipitation can be accelerated by an intrinsic mechanical cycle during the welding cycle. 相似文献
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为了得到SA508-3钢特厚板焊接残余应力分布及焊后热处理对残余应力分布的影响,利用有限元方法对焊接及焊后热处理进行了模拟计算,计算结果表明:焊后热处理对试板焊接应力分布趋势影响较小,但焊后热处理可以大大减小接头应力数值,其中,纵向应力最大减小幅度为72%,横向应力最大减小幅度为70%;焊接接头存在应力分布准稳定区,且接头内部残余应力水平最小,其次为接头上表面,接头下表面应力水平最大;通过残余应力测定试验与模拟结果比对,两者结果吻合度很高,说明计算模型及计算方法可靠,可以指导实际SA508-3钢特厚板焊后热处理生产. 相似文献
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Abhishek Mitra N. Siva Prasad G. D. Janaki Ram 《Journal of Materials Engineering and Performance》2016,25(4):1384-1393
Ferritic steel weldments are invariably post-weld heat treated for relieving the residual stresses. However, the long duration of post-weld heat treatment (PWHT) required for very thick weldments can adversely affect the mechanical properties and fracture toughness. Thus, there is a need to establish the relative importance of temperature and time of PWHT with respect to stress relief. Accordingly, in the present work, the phenomenon of stress relief (due to PWHT) in an 800-mm-thick steel weldment was investigated using finite element analysis and the results were validated against experimental measurements. An analytical study was also carried out to determine the relative influence of temperature and time of PWHT on stress relief. It was found that time of PWHT plays a more significant role in case of relatively lower PWHT temperatures. It was also found that, for a given value of Hollomon parameter, different combinations of PWHT temperature and time can be employed to achieve the same level of stress relief. A mathematical relationship has been established between Hollomon parameter and magnitude of residual stress after PWHT. It has been shown that residual stress is a monotonically decreasing function of the Hollomon parameter. 相似文献
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采用粘弹塑性有限元方法从应力释放角度讨论了Cr-Mo钢局部热处理下各种优化加热条件.研究表明,局部热处理过程产生的瞬态和残余应力受蠕变性能和温度关系弹性模量等因素的影响.当加热宽度足够大时,局部热处理后的应力与炉中热处理的应力接近.通过与现有标准的比较,从应力释放角度位于焊缝中心5√Rt的加热宽度较为合理.提出了考虑焊接冷却过程Cr-Mo低温膨胀现象的相变模型.给出了焊接残余应力与局部焊后热处理应力的试验结果与模拟结果的对比. 相似文献
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Sanghoon Kim Jongho Lee Byoungchul Hwang Chang Gil Lee Changhee Lee 《Metals and Materials International》2011,17(1):137-142
The present study focuses on the effect of Cu and post-weld heat treatment (PWHT) on the microstructure and mechanical properties
in the coarse grained heat affected zone (CGHAZ) of Cu containing high strength low alloy (HSLA) steel welds. For this study,
HSLA steels with and without Cu were prepared in laboratory. Mechanical properties were estimated by Vickers hardness and
Charpy impact tests. As a result, despite PWHT, the Vickers hardness did not change noticeably; however, the impact toughness
deteriorated significantly with increasing PWHT time. In case of Cu added steel, intergranular brittle fractures occurred
after PWHT, due to the strengthening of the grain interior by precipitation of Cu particles. Additionally, the formation of
a soft denuded grain boundary zone also played a significant role in lowering the fracture toughness during PWHT. 相似文献
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Austenitic stainless steel welds with different ferrite contents (4 and 12 FN) were obtained by the Submerged Arc Welding (SAW) strip cladding process, and some clads were remelted by TIG. The welds were post weld heat treated (PWHT) at 600, 800, 1000°C for 1 h. Pitting potentials were measured in 1 N H2SO4 + 0.5 N NaCl. Etching at the pitting potentials was carried out in the same solution in order to locate the pit sites; pitting studies were also conducted in 10% FeCl3 solution. The results showed that an increase in ferrite content decreases pitting resistance. PWHT at 800°C decreases pitting resistance, too, whereas PWHT at 1000°C results in increased pitting resistance at austenite/ferrite interfaces. TIG samples showed less pits than their SAW counterparts. 相似文献
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Walter Jesus Paucar Casas Sérgio Luiz Henke Nilceu Novicki 《Welding International》2013,27(3):166-172
CA6NM quenched and tempered steel is used in hydraulic turbine rotors, pumps and compressors. The objective of this research is to determine the fracture toughness of tempered and quenched CA6NM alloy, and of its welded joints without post-welded heat treatment (PWHT). To this end, compact tension (CT) test pieces are milled from pieces of CA6NM steel for evaluation of the toughness of the alloy used in a hydraulic turbine. Due to the elasto-plastic condition of the material, the test pieces are tested by means of the J integral concept, setting out the resistance curve J–R and the crack initiation J IC. In welded joints produced from ingots, without PWHT, the fragility they show does not allow the J–R curve for the CT test pieces to be drawn up, and the toughness is characterized by means of the K IC concept. The welding procedure looks at the probable conditions for repair of cavitation wear to the turbine, where PWHT cannot be carried out. The results confirmed the higher toughness for the CA6NM steel, with values approximately three times higher than those obtained in the welded joints without PWHT. In terms of the fracture, the CA6NM steel shows ductile behaviour while the welded joint without PWHT shows fragile behaviour. 相似文献
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分析了T23/12Cr1MoV异种钢焊接接头焊后热处理裂纹的宏观和微观特征、断口形貌及接头的显微组织,测试了接头的硬度分布,在此基础上讨论了裂纹的性质及形成原因,并提出了防止裂纹的措施。结果表明,裂纹启裂于T23钢侧焊趾部位,沿粗晶粒热影响区(CGHAZ)晶界扩展,为典型的再热裂纹。焊后热处理明显降低了异种钢焊接接头两侧热影响区的硬度,T23钢侧CGHAZ产生再热裂纹与其在焊后热处理过程中晶界析出碳化物有关,其析出促进了孔洞的形成。在焊后热处理前,对异种钢焊接接头进行一次550 ℃×1 h的中间热处理有利于抑制再热裂纹的产生。 相似文献
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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. 相似文献
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Jingjing Wang Jian Sun Xinhai Yu Guohong Chen Qiuhua Fu Chao Gao Wenming Tang 《Journal of Materials Engineering and Performance》2017,26(10):4659-4666
Small-caliber, thick-wall 12Cr1MoVG seamless steel tube welded joints were fabricated in this study by gas tungsten arc welding and shielded metal arc welding techniques, then the microstructures, mechanical properties, and residual stress distributions of the joints with or without post-weld heat treatment (PWHT) were compared. The welded joints are mainly composed of bcc ferrite (F), Fe3C, and M7C3 carbides. PWHT did not cause an apparent microstructure evolution in the joints, but promoted granular pearlite decomposition and growth of F grains and carbides, therefore decreasing the yield, tensile strength, and hardness while increasing the impact toughness and elongation of the welded joints. PWHT also released the circumferential residual stress and altered the stress state in the joint from tensile to compressive. Although the mechanical properties and bending performance of the small-caliber, thick-wall 12Cr1MoVG seamless welded joints without PWHT are acceptable, our results show that the joints with PWHT are more reliable. 相似文献
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针对设计院和制造厂提出的越来越严格的模焊工艺要求,结合136 mm厚钢板研究了极限模焊工况对大厚度SA387Gr11CL2钢力学性能的影响。结果表明,在保温温度690 ℃、保温时间24 h、装出炉温度200 ℃、升降温速率30 ℃/h的极严格模焊工艺制度下,钢的全厚度(表面下1.6 mm、板厚1/4处及板厚1/2处)室温拉伸性能尚可,但0 ℃及以下随着冲击温度的降低,相应冲击吸收能量逐渐下降,板厚1/2处-20 ℃冲击吸收能量已经接近标准要求的下限,富余量很小,结合金相和扫描电镜进行组织分析,表明过分加严模焊工艺会引起显微组织中碳化物沿晶界偏聚并长大,使钢板韧性明显变差。 相似文献
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升温速率是P91钢管道局部焊后热处理的关键参数之一,决定着热处理的效率和质量. 文中以?575 mm × 35 mm的P91钢管道为对象,进行79 ~ 479 ℃/h 之间的5个升温速率下的局部焊后热处理试验,并分析升温速率对实际升温时间(管道外壁温度达到稳态的名义升温时间+管道内壁温度达到稳态的滞后时间)、管道轴向和径向温度梯度的影响,然后建立P91钢管道焊后热处理有限元计算模型,优化升温速率参数. 结果表明,提高升温速率减小整个管道接头的实际升温时间,可以提高热处理效率. 当升温速率小于179 ℃/h时,提高升温速率明显缩短实际升温时间;当升温速率超过179 ℃/h时,提高升温速率缩短实际升温时间的作用减小. 升温速率的变化对径向温度梯度影响较小,对轴向温度梯度影响则较大. 基于轴向温度梯度控制准则和优化计算结果,得到了不同壁厚P91钢管道局部焊后热处理最大升温速率的计算公式,最后提出了工程上快速选取焊后热处理最大升温速率的应用方案. 相似文献
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Austenitic claddings of type 316 were obtained by SMAW (Shielded Metal Arc Welding) and SAW (Submerged Arc Welding) processes, using type 316 L electrodes on low carbon boiler steel (SA 515 Gr 60) with type 309 L as a barrier layer deposited by the SAW process. Welding heat input was changed in order to obtain different ferrite contents in the cladding. The clad samples were post-weld heat treated at 650°C for 50 and 200 h. The top layer of the cladding was removed and the specimens were then subjected to intergranular corrosion tests (ASTM A-262-75, practices A, B, C and E, viz. 10% oxalic acid electrolytic etch; ferric sulfate ?50% sulfuric acid; 65% nitric acid and copper-copper sulfate ?16% sulfuric acid tests) and controlled potential etching test. The study indicated that the ferrite content of the cladding decreases with increasing current. Ferrite transformed after PWHT (post weld heat treatment) was relatively more in claddings obtained with low heat input and containing high ferrite content in the as-clad condition. PWHT led to brittle fracture of high ferrite claddings (above 10 FN). The corrosion attack of ferrite was found to depend on environment. 65% nitric acid attacked ferrite preferentially, whereas in acid-ferric sulfate, ferrite was intact and austenite was attacked. No sample exhibited susceptibility to intergranular corrosion in the as-clad or PWHT conditions in the copper-copper sulfate ?16% acid test. However, PWHT specimens with low ferrite contents (3.55 FN) exhibited grain boundary precipitation at the interface of two adjacent layers. In general, ferrite was found to be beneficial in controlling corrosion rates of clad metals after PWHT. Heat input, within the range studied, did not affect the corrosion rates significantly. 相似文献