Microstructure and Mechanical Properties of Direct Quenched Versus Conventional Reaustenitized and Quenched Plate

Direct quench processing of steels may be employed as a more cost efficient mechanism to produce low-carbon martensitic plate steels. However, the strengthening mechanisms of direct-quenched (DQ) steels, which can include grain size, dislocation density, and precipitation, are not well understood. Three experimental alloys containing 0.19 wt.% carbon with microalloy additions of Nb and V were developed to compare direct-quench processed steels to steels processed through reaustenitizing and quenching, the more conventional method to produce martensitic plate steels. Two different direct quench processing routes, conventional controlled rolling and recrystallization controlled rolling, with variations in the amount of final rolling reduction were investigated with two of the alloys. The third alloy was processed through reaustenitizing and quenching. The microstructures were quantified using light optical microscopy, scanning electron microscopy, and electron backscattered diffraction and correlated with tensile test results to assess the strengthening mechanisms in each of the conditions. The strength of the DQ steels was similar and matched that of the reaustenitized and quenched steel. It was found that the martensite block size was constant across the experimental conditions, and might play a major role in strengthening the DQ plates.