Low carbon steel was surface modified by the quench-polish-quench salt bath treatment process ( QPQ) . The modi-fied surface was systematically characterized. The results reveal that the nitrided sample surface consists of Fe3 N/Fe24 N10/FeN0. 0939 , while the post-oxidized sample surface consists of Fe3 O4/Fe2 N/α-Fe. The Fe3 N in the outer-layer and Fe24 N10/FeN0. 0939 in the sub-layer were transformed as Fe3 O4/Fe2 N and α-Fe, respectively, after conducting post-oxidation process. After post-oxidi-zing, many cracks and pores were observed on the outer-layer and sub-layer. The hardness profile of post-oxidized sample de-creased about 50～100 HV0. 025 with comparison to nitrided sample. The polarization curves results reveal that the corrosion current den-sity (icor ) of post-oxidized sample decreased about 0. 055 μA . cm-2 with comparison to nitrided sample, indicating an improvement of corrosion resistance. However, the corrosion potential ( Ecor ) decreased about 79 mV, which may be caused by the cracks and pores formed on the compound layer by post-oxidizing process.%用QPQ盐浴复合处理技术对低碳钢进行表面改性处理,对处理后的低碳钢表面进行系统表征.结果表明:QPQ氮化处理后低碳钢试样表面从外至内由Fe3 N/Fe24 N10/FeN0.0939组成,氧化处理后,试样表面从外至内的组成物变成了Fe3 O4/Fe2 N/α-Fe,氧化处理使外层氮化层由Fe3 N转变成Fe3 O4/Fe2 N,内层氮化层由Fe24 N10/FeN0.0939转变成α-Fe;氧化处理后,分别在外层氮化层和内层氮化层上出现大量的显微裂纹和孔状结构;与只进行过氮化处理的试样相比,氧化处理后试样的表面硬度降低了50～100 HV0.025.通过极化曲线可以看出,与氮化试样相比氧化处理后腐蚀电流密度下降了0.055μA.cm-2,腐蚀电位也降低了79 mV.这表明氧化处理能有效提升试样的耐腐蚀能力,而氧化过程中产生的表面缺陷可能导致了腐蚀电位下降.
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