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동적변형시효현상이 304 오스테나이트계 스테인레스강의 변형률속도감도에 미치는 영향에 관한 연구
한준희,문한규 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.5
The dynamic strain aging effect which had been commonly identified with the serrations on the stress-strain curve, was studied by observing the strain rate sensitivity, if., the stress change due to the sudden change of strain rate during deformation. The new experimental method attempted in this study was to change the strain rate at the same stress and strain on the cyclically stabilized stress-strain curve so that the work hardening effect could be eliminated. The initial stress change and the gradual stress change accompanying the strain rate change were measured seperately identifing the form or with the viscous effect and the latter with the dynamic strain aging effect. The experiment was performed in a relatively large strain rate range of 3.2×10^(-7) to 3.2×10^(-3) and a temperature range of 20℃ to 800℃. Among the substitutional alloys which were of our interests for the current study, 304 austenitic stainless steel was chosen as a test material because its dynamic strain aging temperature and strain rate ranges could be obtained with our experimental facilities. The main conclusions are that the dynamic strain aging effect could be studied quantitatively and the strain rate change method is very effective for the purpose, and that, for 304 austenitic stainless steel, the dynamic strain aging effect appears most strongly at the strain rates of 10^(-6), 10^(-5), 10^(-4) and 10^(-3) for the temperatures of 300℃, 400℃, 500℃, and 600℃, respectively.
준안정 오스테나이트계 스테인리스강의 4K 에서의 하중제어 인장 특성에 미치는 시험편 크기의 영향
박종서,윤기봉,변수일,이해무,문한규 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.10
In load-controlled tensile tests at 4K, an abrupt and large discontinuous yielding behavior occurs, which remarkably differs from the discontinuous yielding observed in displacement-controlled tests. The tensile properties under a load control mode may, therefore, be different from that obtained under a displacement control mode. A series of tensile tests has been performed in this regard using 304 and 316 metastable austenitic stainless steels at 4K under a load control mode to examine the effect of specimen size and loading rate on the discontinuous yielding behavior. Four different stress rates ranging from 0.154 to 154 MPa/s were used, while the diameters of tensile specimens were 4.5, 6.35 and 8㎜. Both the stress rate and the specimen diameter were found not to affect the yield strength. However, the stress and strain at the onset of discontinuous yielding decreased as the stress rate and specimen diameter increased. The discontinuous yielding behavior under a load control mode was then compared with that under a displacement control mode.