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TRIP형 Duplex Stainless 강의 상온 인장 특성에 미치는 N 함량의 영향
지정훈(J. H. Ji),김세라(S. R. Kim),황시우(S. W. Hwang),최점용(J. Y. Choi),박경태(K. T. Park) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
(1) 저 Ni 계 이상(duplex) STS 강을 개발하기 위해 Fe- 20Cr- 5Mn- 0.2Ni- xN (x=0.1, 0.2, 0.3, 중량%)강 냉연소둔재의 인장특성과 인장변형 중 미세조직 변화에 미치는 N 첨가의 영향을 조사하였다. (2) Fe- 20Cr- 5Mn- 0.2Ni- xN (x < 0.3) STS 강의 경우 N 함량 증가에 따라 강도 및 연신율은 증가하였다. 이는 N 함량 증가에 따른 austenite 분율 증가에 의한 austenite 소성변형 중 일어나는 TRIP의 기여도가 증가하기 때문이다. In the present study, room temperature tensile behaviors of duplex stainless steels with the low Ni content were investigated to examine the effect of nitrogen addition. For this purpose, nitrogen of 0.1~0.3 wt.% was added to the steels. The steels were cold rolled (~70 % reduction) and then annealed at 1100 C for 5 min. Both strength and ductility increased with increasing the N content. Especially, in the case of the steel containing 0.3 wt.% N, tensile strength exhibited ~1000 ㎫, and the elongation became ~50 %. Deformation of austenite in the present duplex stainless steel was dominated by transformation induced plasticity, and greatly affected the overall deformation.
냉간 압연에 따른 N 함유 저 Ni계 Duplex Stainless Steel의 변형거동
최점용(J. Y. Choi),황시우(S. W. Hwang),지정훈(J. H. Ji),김세라(S. R. Kim),박경태(K. -T. Park) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.5
The effects of nitrogen addition on the strain induced martensitic transformation (SIMT) behavior of duplex stainless steel (D-STS) with the low nickel content were examined in a wide range of strain by means of cold rolling. Nitrogen of 0.1,0.2 and 0.3 wt.% was added into Fe-20Cr-5Mn-0.2Ni D-STS (in wt.%) and cold rolling was conducted up to the effective strain of ~1.45 after annealing at 1100 C for 30 min. In the as-annealed state, the austenite fraction increased with increasing the N content. Regardless of the N content, the ferrite grain size was coarser than that of austenite. The stacking fault energy of austenite of the present D-STSs inferred by the element partitioning analysis was low enough so that SIM transformation is available. Accordingly, during cold rolling, SIMT occurred in austenite with a sequential manner of austenite → ε martensite → α’ martensite with increasing strain. By contrast, the deformed microstructure of ferrite was dominated by dislocation cells.
초미세 결정립 구조를 갖는 OFHC Cu 대형봉재의 미세조직 및 기계적 특성
박경태(K.-T. Park),박이주(L. J. Park),김형원(H. W. Kim),황시우(S.W. Hwang),지정훈(J.H. Ji),이종수(C.S. Lee) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.5
Bars of OFHC Cu with the diameter of 45mm were processed by equal channel angular pressing up to 16 passes via route Be, and homogeneity of their microstructrues and mechanical properties was examined at every four passes which develop the equiaxed ultrafine grains. Cross-sectional hardness exhibited a concentric distribution. Hardness was the highest at the center of bar and it decreased gradually from center to surface. After 16 passes, overall hardness decreased due to recovery and partial recrystallization. Regardless of the number of passage, yield strength and tensile strength were quite uniform at all positions, but elongation showed some degree of scattering. At 4 passes, coarse and ultrafine grains coexisted at all positions. After 4 passes, uniform equiaxed ultrafine grains were obtained at the center, while uniform elongated ultrafine grains were manifested at the upper half position. At the lower half position, grains were equiaxed but its size was inhomogeneous. It was found that inhomogeneity of grain morphology and grain size distribution at different positions are to be attributed to scattering in elongation but they did not affect strength.