*5CrMo  has high endurance strength and creep strength at high temperature, good impact toughness at low temperature, good hardenability, no overheating tendency, small quenching deformation, acceptable plasticity at cold edge forming and medium processability. Poor weldability, preheating before welding, post welding heat treatment and stress relief are generally used after quenching and tempering, and can also be used after high and medium frequency surface quenching or quenching and low and medium temperature tempering.
*4CrMo4 / *5CrMo is used as important structural parts working under high load, such as transmission parts of vehicles and engines; The rotor, main shaft and transmission shaft with heavy load of turbo generator, the large section part *4CrMo4 is used to manufacture forgings with higher strength and larger quenching and tempering section than *5CrMo steel, such as large gear for locomotive traction, booster transmission gear, rear shaft, connecting rod and spring clamp with great load. *4CrMo4 can also be used for drill pipe joints and fishing tools in oil deep wells below ***0m.*4CrMo4 Gas Cylinder Pipe, mainly used in automobile gas cylinder installation, fire protection, medical fields, industry equipment, etc.
The carbon equivalent value CEQ of *5CrMo steel is 0.*2%. It can be seen that the weldability of this material is poor, and its hard tendency is large during welding. The hot crack and cold crack tendency of the heat affected zone of *5CrMo alloy pipe will be large. Especially when welding in the quenched and tempered state, the cold crack tendency of the heat affected zone will be very prominent. Therefore, on the basis of selecting appropriate welding materials and reasonable welding methods, higher pre welding preheating temperature Under the condition of strict process measures and proper interpass temperature control, the purpose of product welding can be achieved.