RAFM钢应变补偿本构关系及热加工图

Strain compensation constitutive equation and hot processing map of RAFM steel

低活化铁素体/马氏体(RAFM)钢具有较低的辐照肿胀率和优异的力学性能,被认为是聚变堆首选的结构材料。然而,低活化钢强度高、冷塑性变形抗力大的特点,使其难以通过冷加工或低温加工实现大规模生产。使用MMS-200型热模拟试验机,在变形温度为950~1200℃、应变速率为0.1~5 s-1和最大变形量为50%条件下,进行了低活化铁素体/马氏体钢(0.11C-9.4Cr-1.35W-0.22V-0.05Si-0.11Ta-0.50Mn)单道次热压缩试验,研究其热变形行为。基于动态材料模型构建了不同应变量下的低活化钢变形本构方程和热加工图,确定了最优热加工参数,结合金相结果分析了材料变形过程中微观组织演化规律,为低活化钢的热加工成形工艺及组织优化提供理论参考。结果表明,在相同应变速率下,随着变形温度升高,流变应力逐渐降低,在一定变形温度下,流变应力随应变速率增大而增大;温度和应变速率对组织的影响主要取决于变形过程中材料内部发生的动态回复和再结晶等机制的交互作用。使用六阶多项式拟合进行应变补偿建立的低活化钢变形本构方程具有较高的预测精度,平方相关系数为0.972。显微组织和热加工图分析结果表明,温度升高为再结晶提供了充足能量,材料软化机制由动态回复转变为动态再结晶;减小应变速率,能量有足够时间扩散,有利于动态再结晶的进行;在变形温度为1060~1130℃、应变速率为0.13~0.36 s^(-1)条件下和合金耗散系数η达到36%的最佳热加工参数范围,可获取到均匀动态再结晶组织。

Reduced activation ferritic martensitic(RAFM)steels have low irradiation swelling rates and excellent mechanical properties,which are considered to be the preferred structural materials for fusion reactors.However,the high strength of RAFM steels and the high resistance to cold plastic deformation make it difficult to achieve large-scale production through cold or low-temperature processing.The thermal simulation compression test investigated the single-pass thermal compression experiment of the RAFM steel(0.11 C-9.4 Cr-1.35 W-0.22 V-0.05 Si-0.11 Ta-0.50 Mn)in the MMS-200 thermal simulator under the temperature of 950℃to 1200°C,strain rate of 0.01 sto 5 s,and maximum deformation of 0.5.Based on the dynamic material model,a strain compensation constitutive equation and hot processing map of RAFM steel under different strain rates were constructed,and the optimal hot deformation parameters were determined.The law of microstructure evolution during the deformation process was observed by a metallographic microscope,which provides a theoretical reference for the hot processing forming process and microstructure optimization of RAFM steel.The results show that the flow stress of nuclear power steel gradually decreases with the increase of deformation temperature at the same strain rate,and the flow stress increases with the increase of strain rate at a certain deformation temperature.The effect of temperature and strain rate on the microstructure is mainly determined by the dynamic,recrystallization,and other softening mechanisms that occur inside the metal.The mathematical model of RAFM steel was established by a sixth-order polynomial.It has high prediction accuracy with a square correlation coefficient of 0.972.The results show that the rising temperature provides sufficient energy for recrystallization,and the softening mechanism of materials changed from dynamic recovery to dynamic recrystallization.When the strain rate decreases,the energy has enough time to diffuse,which is beneficial to dynamic recrystallization.The optimal range of hot processing parameters for obtaining a uniform dynamic recrystallized structure of RAFM steel is that the deformation temperature is 1060-1130℃,the strain rate is 0.13-0.36 s^(-1),and the alloy dissipation coefficientηreaches 36%.