Microstructure and Mechanical Properties in B-Doped Fe-31.9Ni-9.6Co-4.7Ti Alloys

Abstract

Effects of the addition of boron on grain boundary precipitation, martensitic transformation temperatures, and mechanical properties were investigated for Fe-31.9Ni-9.6Co-4.7Ti alloy sheets. Grain boundary precipitation of the g-Ni3Ti phase with the D024 structure, which significantly deteriorates the mechanical properties, is effectively suppressed by the addition of a small amount of B. Both the transformation temperature and the thermal hysteresis slightly increase with increasing B composition. Tensile fracture elongation is improved to be about 1.3 % by addition of 0.05 % B, but no superelastic property was detected in the cyclic stress-strain curve. The features in the mechanical properties are discussed with the texture properties in the sheet specimen.

Shape Memory Effect Induced by Stress-induced α′ Martensite in a Metastable Fe–Cr–Ni Austenitic Stainless Steel

“…Consequently, the metastable c phase can be transformed to alpha prime martensite (a 0 ) and epsilon martensite (e) when it is deformed below the M d temperature, the highest temperature where stress-induced martensitic transformation can take place [5,6]. Many studies showed that a good shape memory effect (SME) can be realized in high manganese Fe-Mn-Si-Cr-Ni-based austenitic stainless steels and in Fe-Ni-C and Fe-Ni-Co-Ti alloys by the stress-induced e and a 0 martensite, respectively [6][7][8][9][10][11][12][13][14][15][16]. However, to our knowledge, so far only a very poor SME was reported in 304 stainless steels due to the stressinduced e martensite, while the SME realized by the stressinduced a 0 martensite has not been reported [17][18][19].…”