改良麻淬火應用於精密機械元件鋼料淬火之研究

A Study of Modified Marquenching Application on Quenching of Steels for Precision Machine Parts

陳祖豪(Tzu- Hau Chen)

指導教授 ： 曾春風

國立虎尾科技大學/工程學院/材料科學與綠色能源工程研究所/碩士(2014年)

摘要

改良麻淬火(Modified Marquenching)是用高溫熱油浴取代鹽浴，解決傳統麻淬火熱處理過程恆溫槽使用硝酸鹽或亞硝酸鹽等鹽浴所造成的危險、環保及後續處理的問題。此法係將沃斯田鐵化的鋼料急冷於MS點以下的熱油浴中，恆溫適當時間使表面與心部的溫度一致後取出空冷。適當的選擇熱油溫度及在熱油中持溫時間可減低元件鋼料表面與心部之溫度差，可有效地減少熱應力及淬火變形量，降低精密元件後續因淬火變形所須加工成本或元件廢棄費用。
本研究旨在探討不同熱油溫度、持溫時間及攪拌流速之改良麻淬火參數，對JIS-S45C、JIS-SCM440、JIS-SNCM439、JIS-SKD61等精密機械元件用鋼料之硬度分佈、硬化深度、淬火變形量及顯微組織的影響。並在試樣可硬化的情況下，尋找降低淬火變形量之最佳參數；最後與傳統油淬火(油溫70°C)比較其淬火變形量的改善情形。
實驗結果顯示，硬化深度方面，隨熱油溫度或攪拌流速的提高，中等硬化能鋼JIS-SCM440之硬度及硬化深度均得到提升；但是對於JIS-SNCM439、JIS-SKD61硬化能良好的鋼之硬度及硬化深度均無太大影響，而持溫時間的增加對上述鋼料之淬火硬度及硬化深度亦無太大影響。JIS-S45C在設定之改良麻淬火參數下淬火皆無法硬化成功。
JIS-S45C 尺寸Φ10x100mm試樣在設定之改良麻淬火參數下淬火仍無法成功硬化，故不適用於此改良麻淬火處理。而在試樣可硬化的情況下，JIS-SCM440、JIS-SNCM439、JIS-SKD61試樣隨熱油溫度由120°C提高到140°C及160°C時，淬火變形量明顯的下降；隨持溫時間由5、10、15分鐘增加到30分鐘時的淬火變形量變小，但時間由30分鐘增加到60分鐘就無明顯變化；隨攪拌流速由0.1m/s提高至0.3m/s淬火變形量會隨之增加。
在試樣可硬化的情況下，JIS-SCM440、JIS-SNCM439、JIS-SKD61淬火變形量最小之改良麻淬火最佳參數為攪拌流速0.1m/s，熱油溫度160°C，持溫時間30分鐘。與傳統油淬火比較，改良麻淬火處理之淬火變形量得到明顯的降低。

關鍵字

改良麻淬火 ； 傳統麻淬火 ； 淬火變形量 ； 攪拌流速 ； 最佳參數 ； 傳統油淬

並列摘要

Modified Marquenching uses hot oil to replace molten salt for solving the dangerous and environmental problems which arise from heat treating process of marquenching by using nitrate or nitrite molten salt bath. The austenitized steel was quenched in the hot oil bath at a temperature below the Ms point and held isothermally with appropriate time until the temperature is uniform throughout steel specimen, and then cooled to room temperature in air. Proper choice of hot oil temperature and holding time in hot oil bath can decrease the temperature difference between the surface and the center of steel part so as to reduce effectively the thermal stress and quenching distortion, and also to decrease the processing and part abandoned costs arising from quenching distortion.
The purpose of this study is to investigate the effect of modified marquenching parameters of hot oil temperature, holding time in hot oil bath and fluid agitation velocity on hardness distribution, hardening depth, quenching distortion and microstructure of JIS-S45C, JIS-SCM440, JIS-SNCM439, JIS-SKD61 steels for precision machine parts. Furthermore, the study also looks for the optimum parameters to reduce the quenching distortion based on hardenable condition. Finally, a comparison was conducted on the improvement condition of quenching distortion between modified marquenching and conventional oil (temperature at 70 ° C) quenching for steels.
The experimental results show that both hardness and hardening depth of middle hardenability steel JIS-SCM440 will increase while hot oil temperature or fluid agitation velocity increase. However, the increasing of hot oil temperature and fluid agitation velocity have no effect on hardness and hardening depth of JIS-SNCM439 and JIS-SKD61 which have good hardenability, and holding time in hot oil bath has no significant effect on hardness and hardening depth, too. The JIS-S45C cannot be quenched harden successfully under the modified marquenching parameters.
JIS-S45C specimen with size Φ10x100 mm cannot be hardened successfully under the setting parameter of modified marquenching, hence modified marquenching is not applicable to hardening of low hardenability steel JIS-S45C. On the condition of hardening, when oil temperature raises from 120°C to 140°C and 160°C, quenching distortion of JIS-SCM440、JIS-SNCM439 and JIS-SKD61 will be significantly decreased. When the holding time in hot oil bath increases from 5minutes to 30minutes by 5minutes interval, quenching distortion will be obviously decreased; but it has no significant change as holding time is increased from 30 minutes to 60 minutes. When fluid agitation velocity raises from 0.1m/s to 0.3m/s, the quenching distortion of specimen will increase.
On the condition of hardening, the optimum parameter of minimum quenching distortion is the fluid agitation velocity of 0.1m/s, hot oil temperature 160°C, and holding time (in hot oil bath) 30 minutes. Comparing with conventional oil quenching, the quenching distortion has been significantly decreased in the modified marquenching.

並列關鍵字

modified marquenching ； hot oil temperature ； holding time ； quenching distortion ； fluid agitation velocity ； optimum parameter ； conventional oil quenching

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