It was pointed out that the main cause is stress corrosion cracking, including transcrystalline stress corrosion cracking by chloride iron and sulfide as well as intergranular stress corrosion cracking by polythionic acid. 有氯离子和硫化物引起的穿晶型应力腐蚀开裂,也有连多硫酸引起的沿晶型应力腐蚀开裂。