Water-Cooling Process Optimization of Q460 Steel Plate with 90 mm Thickness for Construction Machinery after Hot-rolling

The 90 mm thick Q460 steel plates were produced by clean steel smelting, rough rolling in austenite recrystallization zone and fine rolling in austenite non-recrystallization zone with the composition design of low carbon and adding micro-alloying elements such as niobium, vanadium, titanium and chromium. The steel plates were water-cooled by one-time water-cooling process with large flow and low roll speed control strategy and three-time reciprocating water-cooling process with small flow and intermittent water control strategy after hot-rolling. The effects of different water-cooling processes on the microstructure and mechanical properties of steel plates were studied in order to obtain suitable water-cooling process. The results show that the microstructure of the test steel plate produced by one-time water-cooling process was mainly acicular ferrite + a small amount of pearlite, while that of the test steel plate produced by three-time reciprocating water-cooling process was mainly polygonal ferrite + pearlite + a small amount of granular bainite. Compared with that by three-time reciprocating water-cooling process, the microstructure in thickness direction of the test steel plate produced by one-time water-cooling process was more uniform and finer, and acicular ferrite was formed. The tensile properties and impact toughness of the test steel plates produced by the two kinds of water-cooling processes met the standard requirements, but the impact toughness of the test steel plate produced by one-time water-cooling process was significantly better than that produced by three-time reciprocating water-cooling process at −40 ℃, and the impact toughness in the thickness direction was more uniform. The suitable water-cooling process for Q460 steel plate with a thickness of 90 mm after hot-rolling was one-time water-cooling process, and the steel plate had the yield strength of 495–512 MPa, tensile strength of 604–616 MPa, percentage elongation after fracture of 23%–24%, and impact absorption energy of more than 200 J at −40 ℃.