The fracture toughness K_Jc of ferritic steels in the ductile-to-brittle transition region is important for analyzing the structural integrity of structures subjected to large temperature variations. In this study, a σ_YS-based lower-bound (LB) K_Jc master curve (MC) was developed to overcome the failure of the ASTM E1921 MC to predict K_Jc above room temperature (RT). The characteristic K_Jc, was first identified after finding K_Jc for the load P₅, which is the upper limit load for K_Ic defined in ASTM E399. It can be approximated as K_L = 0.6σ_YS (W)^1/2 for various materials and specimen types. Then, the characteristic σ_YS was selected to be σ_YSRT/σ_YS. Assuming that K_Jc > K_LRT at RT, K_LRT was assumed to give an LB, which is empirically true for materials tested in accordance with ASTM E1921. Finally, the MC was formulated as K_JcLB = K_LRT (σ_YSRT/σ_YS)^5.5, by applying the critical distance scaling method. K_JcLB was successfully a LB for 715 unirradiated K_Jc data points, including eight heats of reactor pressure vessel (RPV) steel and seven heats of non-RPV steel. This MC can be constructed without conducting fracture toughness tests if σ_YSRT is known, because a temperature-based σ_YS MC exists.

铁素体钢在韧性到脆性过渡区的断裂韧性K _{J c}对于分析承受较大温度变化的结构的结构完整性非常重要。在这项研究中，σ _YS基于下限（LB）ķ _{Ĵ Ç}主曲线（MC）的开发是为了克服ASTM E1921 MC的故障预测ķ _{Ĵ Ç}高于室温（RT）。在找到负载P _5的K _{J c}之后，首先确定特性K _{J c}，这是K的上限负载。_IC在ASTM E399中定义。它可以近似为ķ_大号 = 0.6 σ _YS（w ^）^1/2对各种材料和标本类型。然后，特征σ _YS被选择为σ _YSRT / σ _YS。假设在室温下K _{J c}  >  K _LRT，则假定K _LRT给出LB，根据ASTM E1921进行测试的材料在经验上是正确的。最后，将MC表示为K _{J cLB}  =  K _LRT（σ _YSRT / σ _YS）^5.5，通过应用临界距离的缩放方法。K _{J cLB}成功地获得了715个未辐照的K _{J c}数据点的LB ，其中包括反应堆压力容器（RPV）钢的八种热量和非RPV钢的七种热量。此MC可以在不进行是否断裂韧性试验来构造σ _YSRT是已知的，因为一个基于温度的σ _YS MC存在。