逆変態未再結晶オーステナイトから生成したFe-24%Niラスマルテンサイトの強度とミクロ組織

抄録

Steel is one of the most important materials because of its wide strength level by using heat treatment and processing. Martensitic transformation can strengthen steel highly because shear deformation introduce a lot of dislocations during the transformation. Dislocations can be inherited into martensite or austenite through forward or reverse transformations. So we can generate strengthened austenite by the reverse transformation at an unrecrystallization temperature in order to keep dislocations in austenite. In addition, by the transformation to the martensite again, the martensite with dislocations in the austenite is generated, resulting in strengthened martensite. In this work, we performed microstructure observation and tensile properties of the lath martensite formed from unrecrystaliized austenite in an Fe-24Ni alloy, and compared the results with those from recrystallized austenite. Before the tensile tests, we characterized blocks in the lath martensite by color etching. Characterized blocks enable us to acquire digital image correlation based strain mapping corresponding to blocks. Electron back scattered diffraction analysis showed higher density of high angle boundaries in the martensite formed from unrecystallized austenite. The tensile strength was higher in the marteniste formed from unrecrystallized austenite. The deformation behavior was discussed with the strain maps.