Abstract
Wire specimens of a TRIP steel and several commercial austenitic stainless steels were torsionally strained both by continuous monotonic twist to fracture and by following various pause and reverse twist regimens. Progress of the phase transformation to ferromagnetic martensite, induced by the extensive plastic strain, was monitored by in situ dynamic measurements of the cyclic axial magnetizations due to alternating circular and alternating axial magnetic fields. By these means, various anisotropic features, as well as the relative concentration of the transformation products, were indicated. In the TRIP steel the dominant anisotropy is found to be magnetoelastic, whereas the Cr-Ni steels are found to develop a helical magnetic anisotropy, interpreted as resulting from the shape of the emergent martensite. While the TRIP steel transformation followed closely upon the advent of plastic strain, the Cr–Ni steels showed strain thresholds. Measurements following incremental surface metal removal of post fracture specimens indicated a negative radial gradient in martensite concentration from the surface, correlating with the similar gradient in accumulated strain.
Published Version
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