D-6ac合金鋼之熱處理研究
Date Issued
2004
Date
2004
Author(s)
Chang, Shi-Da
DOI
zh-TW
Abstract
The purpose of this work is to determine the best heat-treatment condition of D-6ac steel, which including the austenitizing temperature, tempering temperature, and cooling rate after tempering. The correlation between the microstructures and the mechanical properties will be discussed. The microstructures were observed by Optical Microscope(OM), Transmission Electron Microscope(TEM) and Scanning Electron Microscope(SEM). Furthermore, the toughness is seriously influenced by the position, type, distribution, and size of the carbide precipitating in the tempered structure.
The results show that the specimens oil-quenched from 850℃ and then tempered in the range 200~250℃ would have high strength and sufficient toughness (1899~2116MPa, 1.17~1.48kg-m). If the specimens were oil-quenched from 850℃ and then tempered in the range 600~650℃, they would have high toughness and sufficient strength (1239~1460MPa, 4.58~6.15kg-m). Tempered martensite embrittlement (TME) will happen when D-6ac is tempered at 350℃. Since the retained austenite at lath boundary have transformed to discontinuous cementite along the lath boundary. When tempered at 550℃, slow cooling will cause the tempered embrittlement (TE). However, it can be prohibited by rapid cooling after tempering.
Executing the subzero cooling after austenitizing can efficiently reduce the amount of retained austenite. Thus the tempered martensite may uniformly precipitates cementites and prompt it to raise its impact toughness. Two-stage tempering (200℃×1hr + 550℃×2hr) can improve the toughness due to a great deal of ε-carbides were precipitated during first-stage tempering and the ε-carbides will enhance the cementites to precipitate and aggregate during second-stage tempering.
Subjects
合金鋼
D-6ac
Type
thesis
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