• Proceedings of the KWS Conference
• /
• 2002.05a
• /
• pp.224-227
• /
• 2002

• Proceedings of the KWS Conference
• /
• 2005.06a
• /
• pp.88-90
• /
• 2005

• Proceedings of the Korean Society of Laser Processing Conference
• /
• 2004.10a
• /
• pp.78-81
• /
• 2004

• Journal of the Korean Society for Heat Treatment
• /
• v.12 no.3
• /
• pp.231-239
• /
• 1999

Volume fraction and morphology of retained austenite, tensile properties of TRIP type high strength steel sheet with Fe-C-Si-Mn-Cu chemical composition have been investigated. The retained austenite of granular, bar and film type existing in specimen was obtained after intercritical annealing and austempering. The granular type retained austenite increased with increase of intercritical annealing and austempering temperature. With increase of intercritical annealing temperature, retained austenite and carbon contents increased. Maximum contents of retained austenite was obtained by austempering at $400^{\circ}C$. The maximum tensile strength was obtained by austempering at $450^{\circ}C$ and maximum elongation was obtained at $400^{\circ}C$. T.S${\times}$E.L value increased with increase of retained austenite contents due to the elongation strongly controlled by contents of retained austenite, but tensile strength was affected with various factors such as bainitic structure etc.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2012.05a
• /
• pp.252-253
• /
• 2012

음극전기분해법을 이용하여 고강도 DP강과 TRIP강에 수소를 강제 주입시켜, 시험편 내 수소량을 정량적으로 분석하였고, 표면하 미소경도분포 측정과 소형펀치시험 및 파단면 관찰을 통하여 수소주입량에 따른 고강도 박강판재의 수소침투 및 수소취화거동을 평가하고자 하였다. DP강은 강도가 클수록 높은 수소량으로 조사되었고, TRIP강은 DP강에 비해 주입된 수소량이 적은 것으로 조사되었다. 또한 미소경도분포 및 소형펀치시험에서도 DP강은 TRIP강에 비해 수소취성에 민감성이 높은 것으로 평가되었다.

• Transactions of Materials Processing
• /
• v.19 no.1
• /
• pp.44-49
• /
• 2010

It has been widely reported that carbide-free bainitic steels or super-bainite TRIP (SB-TRIP) steels for the automotive industry are a new family of steels offering a unique combination of high strength and ductility. Hence, it is important to exactly evaluate the volume fraction of RA and to identify the 3-D morphology of constituent phases, because it plays a crucial role in mechanical properties. Recently, as electron back-scattered diffraction (EBSD) equipped with focused ion beam (FIB) has been developed, 3-D EBSD technique for materials science are used to these steels. Moreover, newly developed atom probe tomography (APT) technique can provide the exact distribution and chemical concentration of alloying elements in a sub-nm scale. The APT analysis results indicate exactly the distribution and composition of alloying elements in the austenite and bainite phases of SB-TRIP steels with the atomic-scale resolution. And thus, no partitioning of aluminum and manganese atoms was showed between the austenite containing $7.73{\pm}0.39$ at% C and the bainitic ferrite associated with $0.22{\pm}0.06$ at% C in SB-TRIP steel.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.27 no.4
• /
• pp.265-271
• /
• 2014

304L stainless steel sheets are used as a primary barrier for the insulation of membrane-type liquefied natural gas(LNG) carrier cargo containment system. 304L stainless steel is a transformation-induced-plasticity(TRIP) steel that exhibits complex material behavior, because it undergoes phase transformation during plastic deformation. Since the TRIP behavior is very important mechanical characteristics in a low-temperature environment, significant amounts of data are available in the literature. In the present study, a uniaxial tensile test for 304L stainless steel was performed to investigate nonlinear mechanical characteristics. In addition, a viscoplastic model and damage model is proposed to predict material fractures under arbitrary loads. The verification was conducted not only by a material-based comparative study involving experimental investigations, but also by a structural application to the LNG membrane of a Mark-III-type cargo containment system.

• Korean Journal of Materials Research
• /
• v.13 no.7
• /
• pp.453-459
• /
• 2003

In this paper the effect of interstitial heat treatment on the microstructure and mechanical properties was examined both in the 0.15C-6Mn steels and 0.15C-6Mn steels added with Nb or Ti. This result will be applied into the development of a steel which has the properties of high strength and high ductility resulted from the transformation induced plasticity. The strength-elongation combination was increased as the holding time was increased when the temperature is at $625^{\circ}C$. However, the strength-elongation combination was decreased sharply as the holding time was increased when the temperature is at $675^{\circ}C$. The tensile strength and elongation of a reverse transformed steels added with Ti or Nb was 93 kg/$\textrm{mm}^2$ and 40%, respectively. This steel shows higher strength more than 10% of the 0.15C-6Mn steel without loss of ductility. The autenite formed from the reverse transformed treatment has a fine lath type, which has the width size of 0.1-0.3 $\mu\textrm{m}$. The TRIP sequence normally transforms the austenite to martensite, however, some of the sequence will produce retained austenite \longrightarrow deformation twin \longrightarrow martensite

• Journal of Welding and Joining
• /
• v.24 no.1
• /
• pp.56-63
• /
• 2006

The characteristics of $CO_2$ or Nd:YAG laser welded 600MPa ade TRIP steel was investigated. He or Ar gas was used as a shield gas in case of $CO_2$ laser welding, but the shield gas was not used in case of Nd:YAG laser welding. Bead on plate welding was performed with various welding conditions. Defects in the joints of both welding type occurred at 1.8m/min but were not observed over the welding speed of 2.1m/min in case of Nd:YAG laser welding. However, porosity occurred in $CO_2$ laser welding and the tendency of decreasing with the increase of welding speed. The hardness was the highest at heat affected zone near fusion zone as well as at the fusion zone and decreased on approaching the base metal. In a perpendicular tensile test to the weld line, all specimens that have been welded at optimum conditions were fractured at the base metal, and the tensile properties showed the rather higher than those of raw material. In a parallel tensile test, the strength of the joints was higher than that of the base metal. Elongation was found to be lower than that of the raw material. Forming height by Erichsen test and elongation were deeply related with the ratio of base metal/weld metal and the maximum hardness of the weld metal. Also porosity induced to decrease the strength and the elongation. The maximum formability was recorded at approximately 80% as compared with that of the raw material with the optimum condition.

• 한국전자현미경학회:학술대회논문집
• /
• 2005.11a
• /
• pp.194-195
• /
• 2005