Grounds for choice of ply steel for making vessels auxiliary mechanisms

In the modern wide spectrum of construction materials the combined weldments from bimetal steels can be differentiated by alloying materials distribution in them, steels to be welded combinations, operating conditions and applications. A special group of the combined constructions are the bimetallic constructions in which not individual parts are made from alloyed steel, but just the superficial layers of them that are in immediate contact with the aggressive environment, or with the source of intensive wear. Such constructions of bimetals are used mainly for vessels, working under pressure and under the influence of aggressive environments in chemical and petroleum machine building, and in atomic power plants as well. Ply steels are widely used in machines parts of various purpose if the superficial layers of them are subjected to wear of different character or are under heavy pressure. The nomenclature of the materials used in the combined constructions is rather exten-sive and comprises most wieldable steels. As to the combination of materials in one knot it is expedient to distinguish two basic groups of constructions: with the steel weldments of one structural class, but different alloying; and steel weldments of different structural classes. At welding steels of one structural class there are not usually requirements either to the choice of a welding method or to its mode, taking into account the heterogeneity of connection. Within one structural class thermal and physical properties of steel do not differ. The characteristics of transitional layers of parent metal in similar connection in most cases do not substantially differ from the characteristics of thefiller metal