Abstract
To improve the formability of two kinds of 18%Ni maraging steels through transformation-induced plasticity during cooling from the solution-treating temperature, the effects of deformation temperature and strain rate upon the ductility were investigated in uniaxial tensile tests. The maximum elongation, which is approximately ten times that of the solution-treated material at room temperature, was obtained at a suitable temperature and strain rate. The deformation behaviour in the entire range of strain is verified by the work-hardening characteristic of austenite at small strains and subsequent work hardening accompanying strain-induced martensite formation at large strains. 100% martensite formation is found to produce the maximum elongation. The heat generated by deformation at high strain rates decreases the elongation, but by giving a prestrain in the temperature range of austenite, large elongation is obtained and the temperature range over which the large elongation is produced is significantly broadened.
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