Microstructure and mechanical properties of similar and dissimilar metal gas tungsten constricted arc welds:Maraging steel to 13-8 Mo stainless steel

Maraging steel (250) and 13-8 Mo stainless steel plates were joined by gas tungsten constricted arc welding(GTCAW) process in similar and dissimilar metal combinations using 13-8 Mo stainless steel filler wire. The similar and dissimilar metal welds made in solutionized condition were subjected to standard post weld hardening treatments direct ageing at 485 ℃, soaking for 31/2 hours followed by air cooling(ageing treatment of maraging steel) and direct ageing at 510 ℃, soaking for 4 h followed by air cooling(ageing treatment of 13-8 Mo stainless steel). The joint characterization studies include microstructure examination, microhardness survey across the weldments and transverse weld tensile test.Similar and dissimilar metal weldments responded to both the post weld ageing treatment. After post weld aging, increase in yield strength, UTS and slight reduction in % elongation of similar and dissimilar metal were observed. The observed tensile properties were correlated with microstructure and hardness distribution across the welds.

PH13-8Mo高强不锈钢在不同温度时效后的析出相及其对力学性能的影响

将PH13-8Mo高强不锈钢先在925℃进行固溶处理,然后再分别于510,540,550,565,595℃下进行时效处理,研究了不同温度时效后试验钢中析出相的种类和含量,以及析出相对试验钢力学性能的影响。结果表明:在较低温度时效后,试验钢中的析出相以六方结构的M_2C为主,中温时效后的析出相为六方结构的M_2C、面心立方的M_(23)C_6和Ni_3Al以及体心立方结构的NiAl,高温时效后以体心立方的NiAl与面心立方的M_(23)C_6析出相为主;随着时效温度升高,析出相的含量逐渐增加,试验钢的抗拉强度与屈服强度逐渐降低,塑韧性不断提高;时效过程中析出的第二相粒子能起到阻碍位错运动的作用,从而提高试验钢的强度;试验钢在925℃固溶、540℃时效处理后可获得最佳的综合力学性能。

Stress corrosion cracking behavior of PH13-8Mo stainless steel in Cl^- solutions

The stress corrosion cracking（ SCC） behavior of PH13-8Mo precipitation hardening stainless steel（ PHSS） in neutral NaCl solutions was investigated through slow-strain-rate tensile（ SSRT） test at various applied potentials. Fracture morphology,elongation ratio,and percentage reduction of area were measured to evaluate the SCC susceptibility. A critical concentration of 1. 0 mol / L neutral NaCl existed for SCC of PH13-8Mo steel. Significant SCC emerged when the applied potential was more negative than -0. 15 VSCE,and the SCC behavior was controlled by an anodic dissolution（ AD） process.When the applied potential was lower than -0. 55 VSCE,an obvious hydrogen-fracture morphology was observed,which indicated that the SCC behavior was controlled by hydrogen-induced cracking（ HIC）.Between -0. 15 and -0. 35 VSCE,the applied potential exceeded the equilibrium hydrogen evolution potential in neutral NaCl solutions and the crack tips were of electrochemical origin in the anodic region; thus,the SCC process was dominated by the AD mechanism.

Effect of solution pH,Cl- concentration and temperature on electrochemical behavior of PH13-8Mo steel in acidic environments

The effect of solution pH,Cl;concentration and temperature on the electrochemical corrosion behavior of PH13-8Mo steel in acidic solution was investigated by using the electrochemical tests,scanning electron microscopy and X-ray photoelectron spectroscopy.The PH13-8Mo martensitic precipitation hardened stainless steel is in the passivity state when the pH value is above 3.0,below which the anodic polarization curves of the steel are actively dissolved.The corrosion current density gradually decreases with increasing the solution pH and decreasing Cl;concentration and solution temperature.Pits are initiated on the sample surface in the presence of the Cl;and gradually developed into uniform corrosion with increasing the Cl;concentrations.Moreover,the corrosion is more serious with an increase in solution temperature.

时效处理对PH13-8Mo高强不锈钢耐局部腐蚀行为的电化学研究

采用极化曲线,电化学阻抗谱和Mott-Schottky曲线研究了不同时效温度下,PH13-8Mo高强不锈钢在3.5%NaCl溶液中形成的钝化膜性能。结果表明:时效温度对PH13-8Mo高强不锈钢耐点蚀性能有影响,具体表现为:时效时间为4 h,随时效温度升高,于480~595℃温度区间点蚀电位持续降低,温度升至621℃时,点蚀电位升高。电化学阻抗谱结果表明:随时效温度升高,钝化膜表面阻抗先增大后减小,温度升高到621℃,阻抗增大,与极化曲线测试结果一致。Mott-Schottky测试结果表明,不同时效温度下PH13-8Mo高强不锈钢表面钝化膜的致密性不同。