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采用电化学试验、交流阻抗谱测试、失重试验、中性盐雾试验及SEM、EDS、XRD分析,研究了不同热处理工艺下塑料模具钢P20的耐腐蚀性能,并对腐蚀机制进行了研究。研究结果表明,860℃空冷得到的贝氏体/马氏体双相组织和860℃油冷得到的单相马氏体组织的耐蚀性优于785℃油冷得到的铁素体/马氏体双相组织。组织为贝氏体/马氏体及马氏体的试样分别经过450和620℃回火后,马氏体及贝氏体发生分解,碳化物大量析出,耐蚀性下降。经电化学试验后,试样表面腐蚀产物分为两层,外层为疏松的FeOOH,内层为致密的Fe3O4;阳极反应为铁的溶解,阴极反应为析氢反应。钢在0.5mol/L的NaCl溶液中的点蚀主要发生在夹杂物周围。
The corrosion resistance of plastic mold steel P20 under different heat treatment processes was studied by electrochemical test, AC impedance spectroscopy, weight loss test, neutral salt spray test, SEM, EDS and XRD. The corrosion mechanism was also studied. The results show that the corrosion resistance of bainite / martensite dual phase microstructure obtained by air cooling at 860 ℃ and single phase martensite obtained by oil cooling at 860 ℃ is better than that of the ferrite / Body biphasic tissue. After being tempered at 450 and 620 ℃ respectively, the samples with bainite / martensite and martensite structure were decomposed into martensite and bainite, and a large amount of carbides were precipitated and the corrosion resistance decreased. After electrochemical test, the corrosion products on the surface of the sample are divided into two layers, the outer layer is loose FeOOH, the inner layer is dense Fe3O4; the anode reaction is the dissolution of iron, the cathodic reaction is the hydrogen evolution reaction. Pitting of steel in 0.5 mol / L NaCl solution mainly occurred around inclusions.