模拟煤制气环境下X80管线钢及HAZ的氢脆敏感性

Hydrogen embrittlement susceptibility of X80 steel substrate and HAZ in simulated coal gas environment

煤制气中含有一定量的氢气,氢致失效成为输送管线的潜在问题,HAZ的存在增加了氢脆失效的敏感性.选用X80钢,通过焊接热模拟制备了HAZ试样.采用高压煤制气环境下的拉伸试验对比研究了X80钢及HAZ各区的氢脆敏感性.结果表明,经模拟煤制气环境充氢后,X80钢及HAZ各区的性能均稍有降低,氢对材料的性能有一定影响.粗晶区的氢脆敏感性最高,结合金相和电子背散射衍射分析发现,主要是由于粗晶区在高温作用下发生晶粒长大,致使大角度晶界减少,氢的扩散速率及其在裂纹尖端的富集程度增加,止裂性能变差,断口呈明显的脆性断裂特征.

Coal gas contains a certain amount of hydrogen gas,so hydrogen-induced failure becomes the potential safety problem of pipelines, especially in the heat-affected zone( HAZ) of welded joint. HAZ samples of X80 pipeline steel were experimentally prepared using a welding simulator. The hydrogen embrittlement susceptibility of X80 pipeline steel substrate and different sub-regions of HAZ were evaluated by tensile test under high pressure coal gas environment. The results show that the mechanical properties of X80 pipeline steel substrate and different sub-regions of HAZ slightly decreased under coal gas environment,and this means hydrogen gas has a negative effect on the steel performance. Coarse grained heat-affected zone( CGHAZ) had the highest hydrogen embrittlement susceptibility,since obvious grain growth occurred and high angle grain boundaries decreased in this region based on analysis with optical microscope( OM) and electron backscatter diffraction( EBSD).The hydrogen diffusion speed in CGHAZ and hydrogen concentration at crack tip would increase,comparing to steel substrate,and thus the crack arrest property decreased. Consequently,the fracture surface presented apparent brittle features.