少无氧扩散处理对热浸镀铝奥氏体钢氧化开裂影响的实验研究

Effect of Diffused Heat Treatment with Little or No Oxygen on High Temperature Oxidation Cracks of Hot-dip Aluminizing Austenitic Stainless Steel

对扩散热处理后的热浸镀铝1Cr18Ni9Ti奥氏体不锈钢进行1000℃高温氧化试验,发现直接扩散处理试样在氧化120 h后表面出现明显开裂,而少无氧扩散处理试样经500 h氧化后表面完好。通过金相显微镜、扫描电镜和能谱仪的观察及分析表明,由于扩散前期在外扩散层形成的Fe-Al合金(脆性相Fe2Al5和条状FeAl2)为氧提供了扩散通道,导致直接扩散试样的合金层内产生了内氧化空洞,在高温氧化阶段,内氧化占据主导地位,使镀层表面开裂。少无氧扩散能够防止氧进入合金层内部,而且随着扩散的进行,合金层的相组成及形态变化也对氧向内扩散起阻碍作用。少无氧扩散试样的高温氧化由外向内进行,延缓了合金层的开裂和脱落。

Tests of oxidation resistance at 1000 ℃ was done on hot-dip aluminizing austenitic stainless steel after diffused heat treatmem. Some cracks appeared on the surface of specimen with heat treatment in the air after oxidation for 120 h. By contrast, an unbroken surface was obtained after oxidation for 500 h by heat treatment with little or no oxygen. The analysis by OM, SEM and EDS shows that Fe-A1 alloy （brittle Fe2Al5 and strip-type FeAl2） in outer diffusion layer provides diffusing channel for oxygen in the former period of diffused heat treatment. Heat treatment in the air can cause internal oxidation voids in alloy layer. Internal oxidation is dominant during high temperature oxidation, which can lead to cracks in the surface. Heat treatment with little or no oxygen can prevent oxygen from entering alloy layer. Alloy phase compositions and forms change with the heat treatment going on, which can also hinder the diffusion of oxygen into the matrix. The oxygen at high temperature is from outside to inside for specimen after heat treatment with little or no oxygen, which can delay the cracks and spalling of alloy layer.