常规淬火工艺宏观断口形貌有明显得裂纹存在，进一步观察发现，表面存在因大型共晶碳化物脱落留下的孔洞，同时未脱落的碳化物表面形成了微裂纹。而在双淬火工艺中这种现象并不明显，显然经双淬火后，由于降低了共晶碳化物的圆整度，裂纹沿基体与碳化物之间萌生的概率大大降低，因而提升了韧性，但对强度的提升并不明显。

There are obvious cracks in the macro fracture morphology of the conventional quenching process. Further observation shows that there are holes left on the surface due to the shedding of large eutectic carbide, and microcracks are formed on the surface of the carbide that does not fall off. However, this phenomenon is not obvious in the double quenching process. Obviously, after double quenching, because the roundness of eutectic carbide is reduced, the probability of crack initiation along the matrix and carbide is greatly reduced, so the toughness is improved, but the strength is not significantly improved.