Applied Investigation On Process Of Controlled Rolling And Controlled Cooling In Stead Of Normalizing For High Strength Ship-plate

It is found out that impact toughness and strength are the main index influencing the qualification rate of properties of high-strength ship plate, through the analysis to the high-strength ship plate properties, produced under the ordinary hot-rolled process conditions in the Plate Mill of Chongqing Iron and Steel Company (CGGS). The parameters of Thermomechanical Controlled Process (TMCP) have been researched, for improving the strength and toughness of high-strength ship plate, such as heat process, rough rolling process, rolling temperature & distortion amount in austenite crystallization area and rolling temperature, finishing rolling temperature, cooling speed in austenite non-crystallization area. The TCMP process for the existing production equipment of CGGS Plate Mill has been proposed as follow: the slab heating temperature: 1150-1250 ℃, accumlative reduction ratio of rough rolling : ≥70%, pass distortion mount : 10~ 20%; beginning temperature of finish rolling : ≥1000℃C, pass distortion mount in the first rolling process of finish rolling : 10~18%, controlled rolling process: in austenite low-temperature area (namely non-recrystallization area) during the second rolling process of finish rolling, the beginning rolling temperature: less than 950℃, the thickness of temperature control : thicker than or equal to about 2 times of the thickness of the finished product, distortion mount of the second rolling pass: 8~15%, accumlative reduction ratio : more than 50%, finish rolling temperatur: 810~860℃, cooling speed after rolling: 3~8℃/s, finish strengthening temperature: 650~720℃. The properties and structures of high-strength ship plate produced with TMCP could approach or exceed that of normalized steel. Within half a year, 23,500ton high-strength ship plate has been rolled with TMCP replacing of normalization process at the Plate Mill of CGGS. The qualification rate of hot-rolling properties exceeds 90%. Tts properties characteristic value is in higher level steadily. The average of impact energy is up to about 100J, so the high-strength ship plates produced by custom-built TMCP process replacing of normalization process after rolling can be delivered directly. By mathematical statistics of actual composition and properties of high-strength ship plate produced with above-mentioned TMCP, the actual steel-making performance has been confirmed. And in the case of not increasing the production cost of the steel making, the internal chemicalcomposition scope for high-strength ship plate in CGGS has been established.