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열피로에 의한 Fe-Cr-Ni-Cr 계 스테인리스강 피복층의 미세조직 변화
안상호,백응율,정재영 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.3
The thermal cycling fatigue behavior on the microstructure of hardfacing Fe-Cr-Ni-C stainless steels has been investigated using optical microscopy, scanning and transmission electron microscopy. x-ray diffractometry, differential scanning calorimeter, and high temperature tensile testing. The as-welded microstructures of Fe-Cr-Ni-C stainless steels exhibit a fully martensitic structure except for Fe-14%Cr-1Ni-0.11C alloy consisting of the small amount of δ-ferrite and the martensite. The thermal cycling fatigued microstructure varied as the distance of penetration increased from the top-surface to the inner region. A recrystallized ferrite structure of equiaxed grains followed by a lath-shaped ferrite structure and a tempered martensite structure were observed depending on C and Ni contents. The increase in the high thermal expansion coefficient due to low C and high Ni contents accelerated plastic deformation during thermal fatigue in hardfacing Fe-Cr-Ni-C stainless steel. In the case of alloys containing relatively high C and low Ni, the recrystallized ferrite region was not observed in thermally damaged region. This can be explained by low thermal expansion coefficient combined with the pinning effect of carbides.
탄도충격을 받은 2층 육성용접 장갑판재의 균열생성 및 전파거동 연구
이성학,추성훈,백응율 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.7
The objective of this study is to investigate microstructural characteristics of a two-layer hardfaced armor plate after ballistic impact. In order to deaelop the newly-designed armor plate, high hardness, hypereutectic high Cr white iron and ductile SUS 309 stainless steel were hardfaced nn an HY l00 steel plate using self-shielding flux cored arc welding method. This hardfaced plate was ballistically impacted, and metallurgical observations of the area near the perforated region were conducted. The high Cr white iron hardfaced layer was obseved to block effectively a fast traveling prajectile, although microcracks were initiated at coarse primary carbides of the high Cr hardfaced layer, and propagated to form longer cracks However, very few cracks were found in the stainless steel hardfaced layer, which tended to hinder the propagating crack. These foundings suggest that ballistic performance of the multi-layered armor plates fabricated by hardfacing technique might be improved.
고크롬 철계 합금 육성용접층의 파괴인성에 미치는 미세조직의 영향
안상호,이성학,김낙준,추성훈,백응율 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.7
This study aims at investigating the effect of matrix microstructure of high Cr white iron hardfacing alloys on fracture toughness and abrasion resistance. The hardfacing alloys were deposited twice on a mild steel plate using self-shielding flux cored arc welding method. In order to examine the matrix effect, different matrices such as pearlite, austenite, and mixture of pearlite and austenite were employed by changing the ratio of Mn/Si, while the total volume fraction of carbides was fixed. As the volume fraction of austenite in the matrix was increased, hardness and abrasion resistance were nearly constant, but fracture toughness was increased. In-situ observation of fracture process showed that cracks initiated at large primary M_7C₃ carbides tended to be blocked at the austenitic matrix, whereas they propagated through the pearlitic matrix. It could be concluded that abrasion resistance was controlled mainly by the volume fraction of primary carbides, while fracture toughness was controlled mainly by the amount of austenite in the matrix. Considering both abrasion resistance and fracture toughness, thus, the austenitic matrix was preferred for the high Cr white iron hardfacing alloys.
Fe-(12-17) %Cr-(0.19-0.32) %Cr 스테인레스 강으로 육성된 융접층의 미세조직과 기계적 특성에 미치는 C 및 Cr 함량의 영향
안상호,이성학,김낙준,추성훈,백응율,정재영 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.10
Fe-Cr-C hardfacing stainless steels were deposited on S45C carbon steel using a submerged arc welding process. The effects of C and Cr contents on the as-welded structures of Fe-(12-17)%Cr-(0.19-0.32)%C hardfacing stainless steels have been studied by microstructural observation and mechanical testing. The variation of as-welded structure as a function of C and Cr contents was compared with the microstructure predicted by the Schaeffler diagram. In Fe-12%Cr-(0.19-0.32)%C stainless steels, carbon solute atoms were primarily segregated in the interdendritic regions. And Cr-rich carbides tends to precipitate along the interdendritic regions in the stainless steels having C contents higher than 0.2%C. This explains why that the abrupt decreases of mechanical properties and the cleavage fracture surfaces appear in the stainless steels having C contents higher than 0.20%. The sliding wear mechanism varied from the adhesion to tribochemical reaction with increasing hardness of weld metal. However, the wear resistance tends to be affected by the introduction of abrasion. wear mode due to the hard carbide particles. This can be confirmed by the fact that its wear resistance increases with the increase of matrix hardness of weld metal.