焊后热处理对2.25Cr-1Mo钢堆焊处显微组织及剥离开裂的影响

研究了在2.25Cr-1Mo钢上堆焊不锈钢的焊后热处理(PWHT)对其显微组织和剥离开裂的影响。采用690℃加热后空冷的一般PWHT时,界面附近的不锈钢一层侧生成新的马氏体(FM)。充氢试验结果表明,一段PWHT产生剥离开裂是因生成FM所致,由其导致的裂纹沿着奥氏体晶界扩展。但若在一段PWHT后进行600℃回火的二段PWHT,则FM消失,不发生剥离开裂。由此得出结论:控制剥离开裂的显微组织是一段PWHT所生成的FM。     

焊后热处理对2.25Cr—1Mo钢堆焊处显微组织及剥离开裂的影响

研究了在２．２５Ｃｒ－１Ｍｏ钢上堆焊不锈钢的焊后热处理（ＰＷＨＴ）对其显微组织和剥离开裂的影响。采用６９０℃加热后空冷的一般ＰＷＨＴ时，界面附近的不锈钢一层侧生成新的马氏体（ＦＭ）。充氢试验结果表明，一段ＰＷＨＴ产生剥离开裂是因生成ＦＭ所致，由其导致的裂纹沿着奥氏体晶界扩展。但若在一段ＰＷＨＴ后进行６００℃回火的二段ＰＷＨＴ，则ＦＭ消失，不发生剥离开裂。由此得出结论：控制剥离开裂的显微组织是一段Ｐ     

不锈钢堆焊层氢致剥离断裂的途径

本文通过一系列电解充氢试验研究了不锈钢堆焊层的氢致剥离断裂。利用光学显微镜、电子显微镜和微区分析的手段，对试块氨剥离的断裂途径进行了深入的研究。研究表明，氢致剥离裂纹在脆性相解理开裂或脆性相与基体晶粒界面处形核，并沿晶界生长和传播。     

焊接检验及其设备

奥氏体不锈钢堆焊层熔合区剥离原因分析 使用超声波检测热壁加氢反应器时,发现剥离裂纹。采用奥氏体不锈钢双丝带极埋弧堆焊2．25Cr-1Mo钢试板。根据奥氏体不锈钢的焊接性,提出了合理的焊接工艺参数。通过对2．25Cr-1Mo奥氏体不锈钢堆焊试件,模拟加氢反应器不同工况条件下运行试验,然后对堆焊试件解剖,并进行无损检验、力学性能测试、显徽组织观察等,     

焊接检验及其设备

奥氏体不锈钢堆焊层熔合区剥离原因分析 使用超声波检测热壁加氢反应器时,发现剥离裂纹。采用奥氏体不锈钢双丝带极埋弧堆焊2．25Cr-1Mo钢试板。根据奥氏体不锈钢的焊接性,提出了合理的焊接工艺参数。通过对2．25Cr-1Mo奥氏体不锈钢堆焊试件,模拟加氢反应器不同工况条件下运行试验,然后对堆焊试件解剖,并进行无损检验、力学性能测试、显徽组织观察等,     

不锈钢带极埋弧堆焊防剥离工艺优化研究

对不锈钢带极埋弧堆焊层进行热模拟试验，研究高温停留时间对堆焊层过渡区硬化层厚度的影响，用剪切试验检测不同硬化层厚度条件下的界面结合强度，用焊接数值模拟分析堆焊层数对界面残余应力的影响。研究结果表明：随着高温停留时间增加，堆焊层过渡区硬化层厚度增大，堆焊层与母材的结合强度降低。随着堆焊层数的增加，界面残余应力增大，堆焊层数达到6层残余应力为380 MPa。较小的热输入、较低的预热温度和层间温度、较少的堆焊层数，可以减小不锈钢带极埋弧堆焊过渡区硬化层厚度，提高堆焊层与母材结合强度，降低堆焊层界面残余应力，防止堆焊层剥离。     

金属材料疲劳损伤的界面效应

总结了不同金属材料在低周疲劳过程中典型的晶界、孪晶界、相界和微电子互连界面的损伤开裂行为. 纯Cu中疲劳裂纹萌生的难易顺序为: 小角度晶界、驻留滑移带和大角度晶界. 对于纯Cu与铜合金中退火孪晶界, 是否萌生疲劳裂纹与合金成分有关, 随合金元素的加入降低了层错能, 退火孪晶界相对容易萌生疲劳裂纹. 对于Cu--Ag二元合金, 由于存在不同的晶界和相界面, 是否萌生疲劳裂纹取决于界面两侧晶体的取向差, 通常两侧取向差大的界面容易萌生疲劳裂纹. 在微电子互连界面中, 疲劳裂纹萌生位置与焊料成分和时效时间有关,对于Sn--Ag/Cu互连界面, 疲劳裂纹通常沿焊料与界面化合物结合处萌生; 对于Sn--Bi/Cu互连界面, 随时效时间增加会出现明显的由于Bi元素偏聚造成的界面脆性.     

低合金高强钢表面不锈钢带极堆焊的研究

采用不锈钢带极双层堆焊,在低合金高强钢表面堆焊不锈钢耐蚀层。研究了过渡层、表面层带极成分对堆焊层的成分、组织及堆焊层δ铁素体含量的影响,并对堆焊试样进行横向侧弯和纵向侧弯测试。结果表明:过渡层采用309L、表面层采用347L宽50 mm带极,在焊接电流700~850 A、焊接速度140~160 mm/min条件下,可获得与低合金高强钢基体结合良好的堆焊层,堆焊层的增碳层无明显M脆化倾向,堆焊层组织为均匀的奥氏体+δ铁素体双相组织,δ铁素体含量在4.5%~5.5%之间,奥氏体晶粒明显细化。     

植入铸造317L不锈钢在Hank’s模拟体液中腐蚀疲劳裂纹的萌生和扩展

利用往复弯曲疲劳试验机和SEM研究了铸造317L不锈钢材料在Hank’s模拟体液中的腐蚀疲劳裂纹的萌生和扩展行为.铸造317L不锈钢具有晶间腐蚀敏感性,首先在晶界上孕育萌生初始疲劳裂纹,继而扩展,形成主裂纹,发生断裂.在断口上产生了疲劳辉纹,二次裂纹和疲劳台阶.     

奥氏体不锈钢堆焊层熔合区剥离原因分析

使用超声波检测热壁加氢反应器时,发现剥离裂纹。采用奥氏体不锈钢双丝带极埋弧堆焊2．25Cr—1Mo钢试板,根据奥氏体不锈钢的焊接性,提出了合理的焊接工艺参数。通过对2．25Cr-1Mo奥氏体不锈钢堆焊试件,模拟加氢反应器不同工况条件下运行试验,然后对堆焊试件解剖,并进行无损检验、力学性能测试、显微组织观察等,分析堆焊层熔合区剥离的原因及形成过程,为以后加氢反应器的安全运行和完善操作条件提供依据。     

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.     

Evaluation of Microstructure and Mechanical Properties in Dissimilar Austenitic/Super Duplex Stainless Steel Joint

To study the effect of chemical composition on microstructural features and mechanical properties of dissimilar joints between super duplex and austenitic stainless steels, welding was attempted by gas tungsten arc welding process with a super duplex (ER2594) and an austenitic (ER309LMo) stainless steel filler metal. While the austenitic weld metal had vermicular delta ferrite within austenitic matrix, super duplex stainless steel was mainly comprised of allotriomorphic grain boundary and Widmanstätten side plate austenite morphologies in the ferrite matrix. Also the heat-affected zone of austenitic base metal comprised of large austenite grains with little amounts of ferrite, whereas a coarse-grained ferritic region was observed in the heat-affected zone of super duplex base metal. Although both welded joints showed acceptable mechanical properties, the hardness and impact strength of the weld metal produced using super duplex filler metal were found to be better than that obtained by austenitic filler metal.     

Scanning AES and chemical investigation of materials failure due to phosphorus and sulphur grain boundary segregation in type AISI 304L stainless steel

Investigations have been performed on the influence of heat treatment on grain boundary segregation in austenitic stainless steel. In the present work segregation behaviour at type AISI 304L austenitic stainless steel containing relatively high amount of P and/or S has been examined after heat treatment at 550°C/1000 hours. In order to make grain boundaries accessible, the preparation conditions for a high intergranular fracture part have been determined. This procedure is based on cathodic hydrogen charging followed by thermal exposure and straining up to the yield stress. The enrichment of P and S at grain boundaries has been detected directly by means of Auger Electron Spectroscopy after in situ fracture in ultra high vacuum and indirectly by the Coriou test. Significant evidence for segregation of P and S at grain boundaries has been found after the heat treatment only. The segregation causes increasing intergranular stress corrosion susceptibility and embrittlement indicated by CERT (Constant Extension Rate Test).     

Microstructure and Mechanical Properties of Laser Welded Joints of DZ125L and IN718 Nickel Base Superalloys

The microstructure and mechanical properties of the laser welded joint of DZ125L and IN718 nickel base superalloys were investigated. The results show that the fusion zone (FZ) mainly consists of fine dendrite structure with fine γ′, Laves phases and MC carbides inhomogeneously distributed. The high welding temperature induces the partial dissolution of γ′ in the heat-affected zone (HAZ) of DZ125L and liquation of grain boundaries in both of the HAZs. After post-weld heat treatment (PWHT), fine γ″ and γ′ phases precipitate in the FZ, IN718 HAZ and IN718 base metal (BM), and fine γ′ precipitate in the γ channel of the HAZ and BM of DZ125L. With tensile testing, the joints after PWHT show higher strengths than that of the weaker DZ125L alloy. Plastic deformation mainly concentrates in the weaker DZ125L and the joint finally fails in the DZ125L BM.     

Arrest of weld-decay in 304 austenitic stainless steel by twin-induced grain boundary engineering

A twin-induced grain boundary engineered 304 austenitic stainless steel with a high frequency of coincidence site lattice boundaries produced by a one-step thermomechanical process was arc-welded. The heat-affected zone was examined by orientation imaging microscopy and corrosion tests. The results indicated that the intergranular corrosion due to sensitization in the heat-affected zone were perfectly suppressed, because the high frequency of coincidence site lattice boundaries and the optimum grain boundary character distribution were stable in the grain boundary engineered stainless steel during arc-welding. The grain boundary engineering can arrest the weld-decay of austenitic stainless steel effectively.     

Evaluation of solidification cracking susceptibility of Fe–18Mn–0·6C steel welds

Solidification cracking susceptibilities of high Mn steel welds were evaluated in the present study. A longitudinal Varestraint technique was utilised to assess the solidification cracking behaviours of the fusion zone. High Mn steel welds were more susceptible to solidification cracking than 304 and 202 austenitic stainless steel welds, however, they were less susceptible than 310S austenitic stainless steel welds. Extensive segregations of Mn and C took place at the dendritic and grain boundaries in the weld metal, and accordingly contributed to the increase of the hot cracking susceptibility of high Mn steel by the enlargement of solidification temperature range. Further, continuous γ-(Fe,Mn)₃C eutectic phases formed at 1090°C along the grain boundary primarily resulted in the increase of solidification cracking sensitivity in high Mn steel.     

FSS/ASS厚壁异种钢“TIG冷焊 + UNGW”组合焊的接头组织与力学性能

为了有效解决铁素体不锈钢的焊接热影响区晶粒易粗化问题，以及奥氏体不锈钢焊接时在接头部分熔合区及其附近热影响区内因易形成蠕虫状δ铁素体而显著降低该区域耐腐蚀性的问题，提出了“TIG冷焊 + UNGW”的组合焊接工艺，并进行了1Cr17/1Cr18Ni9Ti厚壁异种不锈钢的焊接，同时对所得接头的显微组织、力学性能及耐腐蚀性进行了测试与分析. 结果表明，组合焊接头的1Cr17母材热影响区晶粒未发生粗化，并且1Cr18Ni9Ti母材部分熔合区及其附近热影响区内未形成蠕虫状δ铁素体；组合焊接头的抗拉强度优于1Cr17母材，并且1Cr17母材热影响区的冲击吸收能量与1Cr17母材相当；组合焊接头的熔敷层、1Cr18Ni9Ti母材、1Cr17母材、UNGW焊缝区及完整接头的耐腐蚀性呈依次下降的趋势.     

奥氏体不锈钢-铜钎料钎焊界面反应行为分析

针对电弧钎焊奥氏体不锈钢时,易产生裂纹的问题,采用316LN不锈钢母材和多种铜基钎料,研究了电弧钎焊、炉中钎焊和真空钎焊316LN不锈钢和铜基钎料时的界面反应行为.结果表明,电弧钎焊条件下钎料对母材的润湿性随着电流的加大而提高,钎料沿母材晶界的扩散不明显,在电流较高时母材局部熔化,且易形成沿晶界裂纹.炉中钎焊过程中钎料沿母材晶界扩散明显,但不易形成裂纹;真空钎焊过程中钎料沿母材晶界扩散显著,形成较厚的界面层,但无裂纹出现.较大的焊接热应力以及钎料沿母材晶界扩散造成的晶界弱化是形成界面裂纹的必要条件.     

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 CO2 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 O. 6 mm to 2. 1 ram. The average grain size grew up from 2 ~ 5 pln of base metal to 20～70 um and found no obvious soften phenomenon in overheatedzone. 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.     

经济型铁素体不锈钢焊接接头组织与耐蚀性能

采用ER-309焊丝焊接了TCS345,T4003,Nirosta 4003,JFE410RW四种铁素体不锈钢,用金相方法分析了四种母材、接头的显微组织,通过电化学极化曲线测量,对母材和焊接接头的耐腐蚀性能进行了评价.结果表明,TCS345和T4003铁素体不锈钢与Nirosta 4003和JFE410RW铁素体不锈钢的主要区别是钛和锰含量偏低,尤其是钛含量少,导致TCS345和T4003铁素体不锈钢的晶粒长大倾向较Nirosta 4003和JFE410RW铁素体不锈钢的明显.铁素体不锈钢焊接接头存在较大的热影响区,热影响区的组织与母材晶粒相比,其晶粒明显粗大;TCS345铁素体不锈钢的晶粒长大严重,Nirosta 4003和JFE410RW铁素体不锈钢的铁素体晶粒尺寸比TCS345略小,晶粒长大不明显.在1mol/L Na2SO4溶液中,TCS345和JFE410RW不锈钢母材的腐蚀性能优于T4003和Nirosta 4003.