本研究探討JIS SKD61熱作模具鋼經淬火回火及氣體氮化、氣體軟氮化、鹽浴軟氮化處理之微結構及耐熱疲勞性變化。SKD61試片使用1025°C持溫20分鐘，進行2 kg/cm2 氮氣氣淬及620°C回火處理，部分回火試片並進行530°C × 20小時氣體氮化、570°C × 2、4、6及8小時氣體軟氮化及570°C × 2、4、6及8小時鹽浴軟氮化。SKD61經氣淬並以620°C回火之微觀組織可以發現回火麻田散體組織，硬度為45±1 HRC，氮化及軟氮化處理後，試片表面可達1000HV以上，氮化層深度在80μm~120μm以下。綜合裂紋面積百分比及損傷因子結果顯示，氣體軟氮化處理4小時試片皆較低，故較佳。鹽浴軟氮化試片經熱疲勞試驗後，沒有明顯熱疲勞裂紋，又處理2小時試片表面平整、凹凸程度較低，抗熱疲勞以處理2小時效果最好。氣體氮化試片及氣體軟氮化8小時試片受循環熱應力後，表面有剝落現象故抗熱疲勞性最差。30~580℃環境下比較各處理參數之損傷因子以及裂紋狀態，發現鹽浴軟氮化2小時有最佳之耐熱疲勞性。

This study investigates in thermal fatigue resistance of the surface treatment effect on the thermal fatigue behavior of JIS SKD61 hot-work using different nitriding and nitrocarburizing processes. Selected specimens, austenitized at 1025°C for 20 min and then gas quenched to room temperature and tempered at 620°C, were gas and salt bath nitrocarburized for 2, 4, 6 and 8 hours and gas nitrided for 20 hours. Microstructure, microhardness, X-ray diffraction and thermal fatigue tests were conducted. The hardness values of SKD61 specimen with nitriding and nitrocarburizing were above 1000 HV. The decreasing of thermal fatigue resistance of the specimen nitrided was caused by a brittle compound layer which would be flaked after thermal fatigue test. After salt bath nitrocarburized treatment, there are higher microhardness value than gas nitrocarburized treatment, there are two sides to one coin, the surface treated by salt bath nitrocarburing which had harder and more ductile than gas nirocarburized specimens makes better thermal fatigue resistance. Thermal fatigue tests showed that the best resistance of the specimen is the one salt bath nirtocarburizied for 2 hours which with the lowest value of damage factor and unobvious crack condition.

中文摘要 (CHINESE ABSTRACT) i
英文摘要 (ENGLISH ABSTRACT) ii
目錄 iii
圖目錄 vi
表目錄 xi
Chapter 1 前言 1
Chapter 2 文獻回顧 3
2.1 模具鋼 3
2.1.1 模具材料 3
2.1.2 熱作模具鋼 3
2.1.3 JIS SKD61 熱作模具鋼 4
2.1.4 添加合金元素的影響 8
2.2 真空熱處理 8
2.2.1 熱作模具鋼之熱處理 10
2.2.2 二次回火 10
2.2.3 合金碳化物 11
2.3 表面處理 12
2.3.1 氮化處理 12
2.3.2 氮化用鋼 14
2.3.3 氣體氮化法 15
2.3.4 滲氮碳化 15
2.3.5 鹽浴軟氮化法 16
2.3.6 電漿氮化法 17
2.4 壓鑄模具之損耗 18
Chapter 3 實驗步驟 23
3.1 試片製備 23
3.2 實驗儀器 24
3.3 實驗流程與參數 25
3.4 微觀結構觀察 26
3.4.1 光學顯微鏡觀察 26
3.4.2 電子顯微鏡觀察 26
3.5 X-ray繞射分析 26
3.6 硬度量測 27
3.7 熱疲勞試驗 27
Chapter 4 結果與討論 31
4.1 微觀結構觀察 31
4.1.1 收料組織 31
4.1.2 氣體氮化微觀組織 33
4.1.3 氣體軟氮化微觀組織 34
4.1.4 鹽浴軟氮化微觀結構 36
4.2 微硬度試驗 39
4.3 X-ray 繞射分析 41
4.4 熱疲勞試驗 44
4.4.1 熱疲勞縱向平面裂紋觀察 44
4.4.2 熱疲勞裂紋之損傷因子量測分析 59
Chapter 5 結論 63
References 65

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