本文研究了S20A钢的断裂特点。无论加稀土与否,在J积分试验中P-△曲线都出现一个小平台。载荷未达到平台值时,裂纹不扩展;达平台值时裂纹启裂;越过平台值时,裂纹失稳扩展。试验证明,取P-△曲线上平台值的起点作为开裂点,计算J_(IC)值即方便又准确。本文还讨论了稀士元素的加入,改变了S20A钢中夹杂物的形状,因而横向J_(IC)值提高一倍。 This article studies the fracture characteristics of S20A steel. Regardless of the addition of rare earth or not, a small platform appears in the P-curve in the J-integral test. When the load does not reach the plateau value, the crack does not expand; when the plateau value is reached, the crack initiates; when the plateau value crosses the plateau value, the crack propagates instability. Experiments show that taking the starting point of the platform value on the P- curve as the cracking point, the calculation of the J IC value is convenient and accurate. This article also discusses the addition of rarefied elements that change the shape of the inclusions in S20A steel, thereby doubling the lateral J_ (IC) value.