The Effect Of Rolling And Cooling Ways On The Microstructure And Mechanical Property Of Extra-thick Steel Plate Q460

With the widen and heavy plate production lines putting into produce gradually, as well as proposed by the state that build the widen and heavy plate production lines into the world's high-grade, quality timber production basement plans into implementation stage, the plate enterprises are increasing high value-added plates' research and production. As the request of large-scale and efficient construction, using a large single-wide respecial extra-thick steel plate can reduce the weld. The use of extra-thick steel plate is widespread, it is mainly used on pipelines and ships, and it is also widely used on Boiler containers, pressure vessels, chemical synthesis tower, high temperature and high pressure fuel oil desulfurization unit, hydropower turbines, bridges, machinery and components base, weapons, mold, armor, and building components and so on.The research of this paper is under the background of the Shouqin Metal Material Co. Ltd. HSLA structural steel extra-thick steel plate R & D issue. The main work and results are as follows:1.The experiments of Q460 steel were made at the MMs-300 thermo-mechanical simulator in austenite without deformation and 40% compressive deformation with different deformation pass. The continuous cooling transformation (CCT) curves were constructed in austenite without deformation and 40% compressive deformation at 900℃. Microstructure in different conditions were analysised. From the research, it was found that as the cooling rate increase, the yâ†'a phase transformation point reduced, and also refined the first eutectoid ferrite grain size.The austenite deformation obviously refined ferrite crystal grain, increased the ferrite percentage, and caused the organization to distribute more uniform, while accelerated the ferrite transformation. The austenite deformation promoted the Q460 steel transformation, increased the transformation temperature.2. Laboratory experiments were carried out.Microstructure analysis of the test steel shows that with both two-stage controlled rolling and direct rolling craft,the organization are ferrite and pearlite. Rolling path has little effect on the tensile and impact properties of the tested steel, but cooling way obviously affects it, the water-cooling makes steel plate's yield strength and tensile strength enhance approximately 60MPa than that by air-cooling. 3. EDS analysis was carried out to precipitates of the test plate. It shows that the precipitates contain TiN, TiC, Nb (CN), VN, and the precipitated sequence is TiN, TiC, Nb(CN), VN. As the size of TiN particle first precipitated is larger,it make little contribution to inhance material properties, while because of the smaller size the latter precipitates (such as Nb(CN)) prevent austenite grain growth, refines the organization, and improves the strength and toughness of the test steel.4. Normalizing experiments were carried out on the tested steel, it made the yield strength of steel reduced 60～80MPa, tensile strength lowered 90～100MPa, however, low-temperature impact toughness of steel was significantly improved,-20℃impact energy was increased more than 150J,made it reach to the national standard of Q460D. By SEM analysis to the impact of fracture at -20℃after normalizing ductile fracture.5. Through industrial pilot to Q460 (100mm thick) steel, appropriate rolling craft route to Q460C (100mm thick) plate in the Shouqin is performed. Two stages controlled rolling is adopted, in which the first stage rolling starts above 1050℃, the thickness of temperature holding is 160mm, the second stage rolling starts at 890±10℃, the final rolling temperatures are 820～850℃; finish cooling temperature is 600～660℃, cooling rate is 5～7℃/s.