奥氏体变形状态对EH960海工钢组织与性能的影响

控制轧制中未再结晶区变形量是调控 DQ-T钢板组织与性能的关键参数。针对EH960钢板,将3 块 60 mm 厚钢坯热轧至 40 mm 厚度中间坯,待温至 850 ℃ 后再轧至 10、15、30 mm 厚度,随后进行直接淬火(DQ10、DQ15 和 DQ30)和 620 ℃ 回火(DQ10-T、DQ15-T 和 DQ30-T)热处理,研究了控制轧制中未再结晶区变形量对DQ钢板及DQ-T钢板组织与性能的影响。结果表明:提高未再结晶区变形量,可以有效地细化直接淬火后DQ钢板的马氏体板条组织。高温回火后的DQ-T钢板中遗传自马氏体板条的高密度晶体缺陷促进了碳化物的析出,提高了屈服强度;由于其原始奥氏体变形而呈现压扁形态,在冲击过程中产生断口分层扩大了纤维区,从而提高了低温韧性。但是,奥氏体变形量过大会导致淬火时马氏体相变偏向于某一取向,不利于马氏体区块等亚结构的形成,从而减少了大角度晶界的密度,不利于钢板低温冲击韧性。DQ15-T钢板具有较好的综合力学性能,其屈服强度为1 070 MPa,抗拉强度为1 098 MPa,-40 ℃冲击功为100 J。

Effect of austenite deformation on the microstructure and mechanical properties of EH960 steel for offshore engineering

For direct-quenched and tempered (DQ-T) plate, the extent of deformation below the non-recrystallization temperature (T_nr) is crucial for adjusting its microstructure and mechanical properties. For the EH960 steel plate, three 60 mm-thick slabs were hot rolled into 40 mm-thick plates above T_nr, which were subsequently hot rolled into final plates with thickness of 10 mm, 15 mm, and 30 mm, respectively, after being held in the air until temperatures dropped to about 850 ℃. The three finishing rolled plates were directly quenched in water (referring to DQ10, DQ15, and DQ30) and then were subsequently tempered for 2 h at 620 ℃ (referring to DQ10-T, DQ15-T, and DQ30-T).The influence of deformation extent below T_nr on the microstructure and mechanical properties of DQ and DQ-T plates were investigated. The results show that increasing deformation extent below T_nr can effectively refine direct-quenched martensitic structure, within which the high-density crystal defects inherited from the deformed austenite, promoted the precipitation of carbides during tempering, increasing the yield strength of plate. Due to the pancaked austenite grains, delamination fracture occurred during impact tests, the low-temperature toughness is thus improved by increasing the area of fiber zone. However, excessive deformation in the non-recrystallization region strengthens a specific orientation of martensite transformation during direct quenching, which reduces the amount of substructure blocks and large-angle grain boundaries,unfavorable for low temperature impact toughness of plate. The DQ15-T plate, which has a yield strength of 1 070 MPa, a tensile strength of 1 098 MPa, and an impact energy of 100 J at -40 ℃, thereby exhibits the optimum combination of mechanical properties.