海底管线钢CTOD性能探讨

Discussion about CTOD properties of submarine pipeline steel

应用MTS动态测试系统对海底管线钢X65MO进行了CTOD(δ)性能试验。CTOD(δ)试验采用3点弯曲试样,预制疲劳裂纹为降K法,疲劳应力比为0.1,位移控制单调加载应力强度因子在0.5~3.0 MPa·m^(1/2)/s之间。试验结果表明,X65MO组织为铁素体+珠光体+少量贝氏体,晶粒度12.0级,-20、0、20℃CTOD(δm)分别为0.956、1.101、1.216 mm,远高于API 5L PSL2 X65Mo级热轧钢带标准0.30 mm的要求。试样断口显示,试样边缘发生较大的塑性变形,呈现剪切裂纹形成及扩展的特征,说明材料韧性性能较好,CTOD(δm)为典型的塑性裂纹扩展特性。

The MTS dynamic testing system was used to test the CTOD( δ) properties of submarine pipeline steel X65MO.Three-point bending method was employed in the CTOD( δ) experiment. Prefabricated fatigue crack adopted K-decreasing method. The fatigue stress ratio was 0. 1. The stress intensity factors of displacement controlled monotonic loading were between 0. 5-3. 0 MPa·m^(1/2)/s. The test results showed that the microstructure of X65MO was ferrite + pearlite + a little bainite. The grain size was 12. 0 grade. CTOD( δm) at-20,0 and 20 ℃ were 0. 956,1. 101 and 1. 216 mm,respectively,which were much higher than the standard of 0. 30 mm of API 5L PSL2 X65Mo grade hot rolled strip. The fracture surface of the sample showed that the edge of the sample had a large plastic deformation,presenting the characteristic of formation and extension of shearing crack. It indicated that the material had good toughness. The CTOD( δm) was a typical plastic crack growth characteristic.