Influence of Heat Treatment on Mechanical Properties and Microstructure of Q390RSteel
In order to study the process adaptability of Q390R steel in the manufacturing process of pressure vessel and provide basic data for the industrial application of the steel,this paper studies the microstructure and mechanical properties of Q390R steel under annealing state,hot forming(air cooling)and hot forming+normal ignition(air cooling).The test results show that Q390R steel exhibits a band like structure composed of ferrite and pearlite approximately parallel to the rolling direction in its microstructure after annealing at 630 ℃ × 6 hours,hot forming at 910 ℃ × 40 minutes,and normalizing at 880 ℃ × 60 minutes,as well as in its original state.However,under hot forming at 910 ℃ × 40 minutes,the microstructure is equiaxed with almost no band like structure.The tissue of Q390R steel plate is composed of ferrite and pearlite,and the ribbon tissue composed of ferrite and pearlite appears along the rolling direction after thermoforming+ignition(air cooling).The mechanical properties of the three heat treatment states are between 516 MPa and 550 MPa,and the mechanical properties and low-temperature impact toughness can meet the requirements of engineering technical conditions.The highest hardness test of welding thermal influence area measured Q390R steel with the sensitivity of welding cold crack method,and finally determined the best preheating temperature before welding.The test results show that appropriate preheating measures before welding can effectively reduce the cold crack tendency of Q390R steel.
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