熱處理模具鋼深冷與QPQ處理對機械性質及耐腐蝕性影響

王中彥(Chung-Yen Wang)

指導教授 ： 施登士

國立中央大學/工學院/機械工程學系/碩士(2015年)

摘要

本研究中，準備M333，SKD61和M390三種型號模具鋼，予以固溶處理再進行-60及-196℃深冷處理，再實施QPQ探討對模具鋼機械性質的影響。觀察深冷處理後顯微結構及殘留沃斯田鐵的變化，QPQ處理後氮﹑氧層之膜厚及物相分析。根據XRD顯示出深冷處理後比高溫回火殘留沃斯田鐵顯著減少，及氧﹑氮化層物相為Fe3O4﹑ Fe2-3N﹑ CrN等有利於硬度及耐磨的提升。
電位極化曲線試驗顯示出經QPQ處理後與深冷處理比較未有較好的耐蝕能力，是由於氮化期間過多的CrN析出導致表面及基材 Cr 含量急遽減少導致耐蝕性下降，另一原因氮化層有少數裂紋產生。
EPMA maping分析元素強度分佈可看到三種鋼材氮化層厚度不一(10~15µm)主要因材料Cr含量不同Cr元素會抑制N原子之擴散之故。利用TEM穿透式電子顯微鏡觀察深冷與QPQ處理之碳化物之變化，發現氮化物大小形狀種類並無明顯變化，因QPQ處理溫度介於500~600℃之間無直接影響到碳化物溶解與成長。

關鍵字

模具鋼 ； 深冷處理 ； QPQ處理 ； X-ray繞射 ； 氮化膜 ； 氧化膜

並列摘要

In the study，three types of die steels(M333，SKD61，M390) were prepared via austenitiling treatment quenched to room temperature the followed by cryogenic treatment(-60 and -196℃) for 8hrs.All sample were temepered twice at 500℃ for 2hrs. Quench-Polish-Quench (QPQ) treatment was also conducted for surface hardening.The microstructure and retained austenite of the cryogenic treated sample were observed measured. The thickness of oxide films and nitride films and phase analyses of the QPQ Treated sample were investigated by SEM and OM.
Accodding to XRD analyses retained austenitic was significantly decreased sample matrix after cryogenic treatment.The analyzed phase displayed that oxide films and nitride films were mainly Fe¬3¬O4，Fe2-3N and CrN，which hardness increase.

The QPQ treated sample displayed poor corrosion than that without QPQ treated samples due to excessive CrN precipitated during nitriding,so that the content of Cr dereased in their matrix to result in decreasing corrosion resistance.

EPMA mapping analyses show the thickness of nitride layer and oxide layer on different sample. Particles of CrN and FeN were also Identified film mapping analyses.No significant variation of carbide size were observed by TEM between with/without QPQ treated samples size.

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