超快冷工艺对高强船板组织与性能的影响

Effect of ultra-fast cooling on microstructure and properties of high strength steel for shipbuilding

通过拉伸性能和冲击韧性试验及显微组织观察分析了厚板生产线控制轧制(CR)后采用超快冷(UFC)和层流冷(AcC)两种冷却工艺对AH32高强船板力学性能、焊接热影响区(HAZ)冲击韧性和显微组织的影响。结果表明,与AcC钢板相比UFC钢板性能明显提高,其屈服强度提高54 MPa且塑性不恶化,-60℃冲击功达到260 J以上,韧脆转变温度大幅降低。UFC使钢的显微组织明显细化,晶粒尺寸达到11.5级,且厚度方向显微组织更均匀,而AcC钢晶粒尺寸为9.5级。UFC对钢的焊接热模拟试样冲击韧性没有明显影响。用铁素体(α)形核动力学和Hall-Petch效应分析了晶粒细化机理及对强韧性影响。UFC降低了奥氏体(γ)转变温度,提高了α形核速率而细化了铁素体晶粒,同时也细化了贝氏体和珠光体,明显提高了钢的力学性能。

The effect of ultra-fast cooling( UFC) and conventional accelerated cooling( AcC) on the mechanical properties and microstructure of controlled rolled AH32 grade steel plates on industrial scale were investigated using tensile test,Charpy impact test,welding thermal simulation,and microscopic analysis.The results show that the properties of the plate produced by UFC are improved considerably comparing to that by AcC.The yield strength is increased by 54 MPa without deterioration in the ductility and the impact energy is improved to more than 260 J at- 60 ℃ with much lower ductile-to-brittle transition temperature( DBTT).The ferrite grain size is refined to ASTM No.11.5 in the UFC steel with uniform microstructure throughout the thickness direction,while that of the AcC steel is ASTM No.9.5.The effect of the cooling processes on the toughness of simulated heat affected zone( HAZ) is negligible.The analysis of nucleation kinetics of α-ferrite indicates that the microstructure is refined due to the increased nucleation rate of α-ferrite by much lower γ→α transition temperature through the UFC process.The Hall-Petch effect is quantified for the improvement of the strength and toughness of the UFC steel attributed to the grain refinement.