10Ni5CrMoV钢焊缝针状铁素体相变热力学分析

Thermodynamic Analysis on Phase Transformation of Acicular Ferrite in Weld of 10Ni5CrMoV Steel

基于各种相变热力学模型,计算了10Ni5CrMoV钢焊缝针状铁素体相变热力学模型,通过对焊缝金属相变驱动力的计算,以期揭示10Ni5CrMoV钢焊缝奥氏体变成针状铁素体机制。利用传统扩散模型、类珠光体转变模型和贫碳区切变模型探讨热力学的转变机制,结果表明,针状铁素体相变驱动力与原奥氏体中C含量相关,C含量越低,其驱动力越大。随着奥氏体转变针状铁素体的温度降低,贫碳区C原子的活度增大,针状铁素体的长大驱动力变大,从而温度的降低有利于针状铁素体的形成。在中温相变温度区间,700 K时的针状铁素体相变驱动力约为950 K时的6.1倍。基于热力学计算推测10Ni5CrMoV钢焊缝主要以贫碳区切变模式形成针状铁素体。适当延长焊接时中温相变停留时间,是提高针状铁素体含量的较好工艺选择。

Based on various thermodynamic models of phase transformation, the thermal model of acicular ferrite transformation in 10Ni5CrMoV steel weld was calculated. The driving force of weld metal transformation was calculated to reveal the mechanism of austenite transforming into acicular ferrite in 10Ni5CrMoV steel weld. The traditional diffusion model,pearlite transformation model and carbon lean zone shear model were used to explore the thermodynamic transformation mechanism. The results show that the lower the carbon contents in the original austenite, the greater the driving force of the acicular ferrite transformation. When the temperature of the austenite transforming into acicular ferrite reduces, the activity of carbon atoms in the carbon poor zone increases, and the growth driving force of acicular ferrite improves, which is conducive to the formation of acicular ferrite. The driving force of acicular ferrite transformation at 700 K was about 6.1 times of that at 950 K. Based on thermodynamic calculation, it is inferred that acicular ferrite is formed mainly in the form of shearing transition in carbon poor zone. It’s a better process choice to increase the content of acicular ferrite by prolonging the residence time of medium temperature transformation during welding process.