臺灣博碩士論文加值系統

本研究係以高合金冷作工具鋼AISI D2藉超深冷處理中以各種不同之冷卻速率和低溫持溫時間及隨後之回火於不同溫度，探討從殘留沃斯田體到麻田散體的變態過程，並以微觀組織觀察、硬度、殘留沃斯田體含量檢測及耐磨耗性的比較來評估不同處理過程對於D2工具鋼所造成的的差異，藉以找出最佳之超深冷處理的條件。實驗結果得知淬火後之試片以直接浸入液態氮而後經低溫回火者，其耐磨耗性最佳。

This research is to study the transformation of retained austenite and try to find an optimum condition for transformation mechanism by virtue of different cooling rates and different holding times in cryogenic temperature as well as the subsequent tempering processes. Cold work tool steel AISI D2 has been used as specimens material. The wear resistance evaluations have been made by use of the microstructures, hardness, retained austenite content of the specimens derived from different treatment conditions. The experiment results show that the specimens being directly dipped in liquid nitrogen and then followed by low temperature tempering exhibited the best wear resistance.

Table of Content
摘要………………………………………………………………………………………Ⅰ
Abstract………………………………………………………………...………………..Ⅱ
Table of Content………………………………………………………..……………….Ⅲ
The List of Table……………………………………………………...…………………Ⅴ
The List of Figure……………………………………………………..………………...Ⅵ
1. Introduction………………………………………………………..…………………1
2. Literature review………………………………………………………………..……3
2.1 Introduction of high alloy cold work tool steel AISI D2…………………………..3
2.2 Cryogenic treatment process………………………………………………………4
2.2.1 Snap tempering…………………………………………………………….5
2.2.2 Cooling rate………………………………………………………………..5
2.2.3 Soaking time……………………………………………………………….5
2.2.4 Tempering………………………………………………………………….6
2.3 Reduction of retained austenite……………………………………………………7
2.4 Precipitation of fine carbides………………………………………………………7
2.5 Wear mechanism…………………………………………………………………..8
3. Experimental details……………………………………………………………..….11
3.1 Preparation of specimens…………………………………………………………11
3.2 Heat treatment……………………………………………………………………12
3.2.1 Vacuum heat treatment…………………………………………………...12
3.2.2 Conventional heat treatment……………………………………………...12
3.2.3 Cryogenic treatment……………………………………………………...12
3.3 Hardness test……………………………………………………………………...13
3.4 Retained austenite estimate………………………………………………………14
3.5 Scanning electron microscopic observation……………………………………...15
3.6 Wear resistance test………………………………………………………………15
4. Results and discussion…………………………………………………………..…..17
4.1 Hardness………………………………………………………………………….17
4.2 Content of retained austenite……………………………………………………..18
4.3 Microstructure observations..…………………………………………………….19
4.3.1 Comparison between conventional heat treatment and cryogenic treatment on microstructure………………………………………………………....19
4.3.2 Effects of cooling rate and soaking time in cryogenic treatment on microstructure…………………………………………………………….20
4.4 Wear test………………………………………………………………………….21
4.4.1 Effect of cooling rate on cryogenic treatment followed by low temperature tempering…………………………………………………………………22
4.4.2 Effect of soaking time on cryogenic treatment followed by high temperature tempering……………………………………………………22
4.4.3 Wear behavior…………………………………………………………….23
4.5 Effects of snap tempering and double high temperature tempering……………...24
4.5.1 Effect of snap tempering…………………………………………………24
4.5.2 Effect of double high temperature tempering…………………………….25
5. Conclusion………………………………………………………………………...…27
References……………………………………………………………………………29

References
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