The welding process of thick wall multi-layer ball valve welding is a process of repeated heating and cooling of metal materials, resulting in uneven and inferior welding joint organization, resulting in high residual stress, and even welding defects.
焊接球阀厚壁多层焊接过程是金属材料多次反复加热和冷却的过程，导致焊接接头组织的不均匀性和劣质化，产生较高的残留应力，甚至产生焊接缺陷。
Welding is the last process after the assembly of the product, there are non-metallic sealing materials rubber and polytetrafluoroethylene plastic in the valve chamber, which cannot be heat-treated after welding.
焊接又是该产品组装后的最后一道工序，阀腔内有非金属密封材料橡胶和聚四氟乙烯塑料，不能进行焊后热处理。
Welding ball valve Mn can also improve the performance, form and distribution of sulfide.
焊接球阀Mn还能改善硫化物的性能、形态及其分布等。
Therefore, in order to prevent the formation of joint cracks, there are certain requirements for the M-S value in the weld metal.
因此，为了防止产生结品裂纹，对焊缝金属中的M可S值有一定要求。
How large the M can S value is conducive to preventing crystallization cracks, and it is also related to the carbon content.
M可S值多大才有利于防止结晶裂纹，还与含碳量有关。
The higher the C content, the higher the value of M is required.
含C量愈高，要求M此值也愈高。
