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1/8 Strengthening via the formation of strain-induced martensite instainless steels 授課老師：戴子堯 老師 班級：碩研二甲 學號：MA110119 姓名：鄧文斌 機械工程系所 精密製造實驗室 102年12月23日 2/8 I、Introduction The interaction of plasticity and phase transitions represents a rich area for future work both because it enables new structures to be explored and because from a practical viewpoint, it provides a route to develop materials with exceptional combinations of strength and ductility. The objective of the current paper is to explore the evolution of the martensite structure as a function of imposed plastic strain and to delineate how the FCC– BCC composite formed by deformation acts in order to enhance the strength level, i.e., to examine the role of the BCC phase produced by deformation on the strength and ductility of the material. 機械工程系所 精密製造實驗室 102年12月23日 3/8 II、 Experimental methods In this study, 304L and 316L austenitic stainless steel in bar form was used. The composition of the materials is given in Table 1. Tensile samples were machined with the tensile axis in the direction of the bar extrusion axis. These samples were then annealed at 1050℃ for 30 min in an atmosphere of high-purity helium, to ensure they were in the fully austenitic condition. The grain size after annealing was nominally 90 Micron. 機械工程系所 精密製造實驗室 102年12月23日 4/8 III 、 Results 3.1. Transformation rate and mechanical behaviour (a) Mechanical response at both 77 and 300K with volume fraction data superimposed (b) work hardening rate at 77 and 300 K. 機械工程系所 精密製造實驗室 102年12月23日 5/8 3.2. Formation of strain-induced martensite In the annealed condition, the austenite contains many annealing twins and when deformed at room temperature the austenite exhibits planar slip. As a consequence of the decreaseof stacking fault energy with temperature, deforming the austenite at 77K results in the extensive formation of stacking faults. In the 304L stainless steel alloy examined in the present work, the sequence of martensite formation was observed to be as follows: 機械工程系所 精密製造實驗室 102年12月23日 6/8 3.3. Behaviour of the martensite as a reinforcing phase It was observed that the ε phase that forms in prestrained samples is very fine in scale. In the case of monotonic deformation at 77K the ε sheets are roughly 100 nm thick, but when formed after a room-temperature prestrain they were ∼10 nm thick, as shown in Fig. 4. Fig. 4. Image of fine bands of ε phase in the transformation front of a sample prestrained 16% at room temperature, and strained 7% at 77 K. 機械工程系所 精密製造實驗室 102年12月23日 7/8 IV 、 Discussion Mechanical response of the austenite and martensite in a sample with 30% martensite. 機械工程系所 精密製造實驗室 102年12月23日 8/8 Reference material http://www.sciencedirect.com/science/article/pii/S0921509304006896 麻田散體、沃斯田體 機械工程系所 精密製造實驗室 102年12月23日 報 告 完 畢 謝 謝 大 家 機械工程系所 精密製造實驗室 102年12月23日