Open Access Conference Proceedings

Low carbon low alloyed TRIP steel with partial substitution of silicon by aluminium was thermo-mechanically treated to obtain a multiphase microstructure typical for TRIP steels. The processing consisted of soaking at 900°C and two compressive deformations applied during the cooling to the isothermal hold temperature of 425°C. The microstructure was predominantly bainitic with about 17% of retained austenite and little proeutectoid ferrite. Bainite consisted of the mixture of bainitic ferrite and retained austenite laths. The samples underwent tensile test with five different strain rates, 0.003, 0.3, 1, 10, 100 s-1. Mechanical properties show some dependency on strain rate, tensile strengths of 832-925 MPa were achieved together with total elongation of 30-38%. Significantly higher strain rates of 380, 470 and 520 s-1 were produced by impact test with various initial positions of the pendulum (90°, 120°, 150°). In these cases, only the impact energy was evaluated, showing the increasing values with increasing deformation rate. The effect of increasing strain rate on the stability of retained austenite was also evaluated by the means of X-ray diffraction phase analyses. The microstructure after the straining was documented by scanning electron microscopy, as well as fracture surfaces.

Keywords: TRIP steel, strain rate, retained austenite, multiphase microstructure, aluminum

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