中厚板中间坯冷却过程中晶粒长大及控制方法

为控制中厚板中间坯长时间待温导致的晶粒长大，研究了中间强制水冷却对奥氏体组织的影响．通过对Q345B钢和含Nb-Ti钢采用1050℃变形后快冷至1050-950℃预定温度保温的热模拟方法，确定了中间坯冷却过程中的晶粒尺寸变化规律，提出了中厚板冷却过程中晶粒长大的控制方法，建立了Q345B钢和含Nb-Ti钢在中间冷却过程中的晶粒长大模型．在中间冷却过程中，Q345B钢晶粒稳定性较差，而含Nb-Ti钢晶粒稳定性良好，归因于以铌为主的析出相对奥氏体晶界的钉扎作用．中间坯的强制冷却可控制奥氏体晶粒长大，63mm厚中间坯强制冷却可有效减小平均晶粒尺寸约20μm．在实际生产中，经中间强制冷却后16mm厚度Q345B钢板的冲击韧性提高25％-70％．

Grain growth and its control method of intermediate slabs for plates during cool- ing processes

The effect of forced intermediate water cooling on austenite grains in plates was studied to find a method of controlling grain growth in intermediate slabs due to staying for cooling.Changes in grain size of the intermediate slabs of low alloy steel Q345B and Nb-Ti bearing steel during cooling processes were analyzed by thermal simulating,which includes deforming at 1 050 ℃ and then rapidly cooling to scheduled temperature from 1 050 to 950 ℃ for a certain time.Control methods of grain growth were suggested for plates during cooling processes and grain growth models were established for Q345B steel and Nb-Ti bearing steel during the intermediate cooling process.The stability of austenite grains is poor for Q345B steel during the intermediate cooling process,whereas austenite grains in Nb-Ti bearing steel have good stability due to the pinning effect of precipitates,which mainly consist of niobium.Austenite grain growth in the intermediate slabs can be controlled by forced water cooling.The average grain size of 63 mm-thick intermediate slabs after forced water cooling reduces by about 20 μm.In actual production the impact toughness of 16 mm-thick Q345B steel plates after forced intermediate water cooling increases by 25% to 70%.