The hardness values of the substandard and standard products are shown in Table 1. The result shows that the hardness of the substandard product was higher than that of the standard product. The high hardness in crystalline materials could cause the strong rigidity, but resulting in the lack of enough toughness. Therefore, the substandard product was easily fractured under overloading condition. After quenching and tempering, the strength and hardness of 4Cr13 stainless steel increased, but it had severe crack sensitivity. During heat treatment or spot welding, the crack was easily formed.