Abstract: Effect of deformation in non-recrystallization region on microstructure evolution and microhardness of EH47 crack arrest steel was studied by single pass compression test using MMS-200 thermal simulator. The results show that when the deformation increases from 15% to 60%, the length-width ratio of the prior austenite grain increases from 1.2±1.4 to 2.7±2.3, the microstructure changes from coarsened bainite to refined ferrite and bainite, the proportion of high-angle grain boundaries(HAGB) increases from 34.6% to 61.7%, the effective grain size decreases from 4.5±5.9 μm to 3.4±4.2 μm, and the microhardness decreases from 230 HV50 to 211 HV50. The austenite grains of the specimen with 60% deformation have an effective interfacial area per unit volume of 106.7 mm^-1 before the phase transformation, which is the main reason for the refined and uniform microstructure. The ferrite grains nucleated, grown and then intercontacted at the prior austenite grain boundaries enhances the proportion (21.5%) of HAGB within the misorientation range of 20° to 47°, resulting in a crucial aspect for its possession of 61.7% HAGB. The main reasons for the decrease of microhardness are the high content of ferrite, the decrease of dislocation density and the increase of the proportion of recrystallized grains.

Key words: EH47 crack arrest steel, deformation, prior austenite grain, microstructure, hardness