Heat-resistant steels and alloys as a special type of structural materials began to be used quite intensively in connection with the development of the turbine-building industry. Turbines in the form of a converter or an energy source are used in heat power equipment, aircraft and marine engines. More recently, gas turbine structures for ground rolling stock (trucks, locomotives) have become widespread.
As the inlet gas temperature rises, the specific fuel consumption per unit of power decreases. In this regard, in a fairly short time, heat-resistant steels appeared. Today, these materials in turbine designs account for up to 50% of the total mass.
Heat-resistant steel is a material that works not only at elevated temperatures. It is applicable in the condition of a difficult state during a given time period. The main characteristic that determines the operability of the specified material is heat resistance.
This quality is understood to mean the stress that does not lead to the destruction of a given deformation, which is able to withstand a metal material in a certain structure at a given temperature for a specific time period. When time and voltage are specified, the characteristic is called ultimate strength (long-term). If deformation, time and stress are determined, then quality is called the creep limit.
Heat-resistant steels possess, in addition to strength, ductility, which must be maintained until the end of operation. The reliability margin of metal is estimated by the plasticity margin indicators.
An important characteristic of the material is its sensitivity to notching. This quality is determined in the form of the ratio of the time elapsed before the destruction of a smooth and notched sample, tested at the same voltage temperature. Heat resistant steels are considered insensitive to notching at a ratio equal to or greater than unity.
Due to the fact that the increase to the working temperature occurs over time, while the beginning of work corresponds, as a rule, to the external temperature, much attention is paid to the values of elasticity and strength. It is important that the values possessed by the material at room temperature are sufficiently high.
Due to the fact that heat-resistant steels work under conditions of a difficult stress state, which is characterized by a constant change in the sign and magnitude of the loads, a high fatigue resistance indicator is also important.
Today, the use of complex technical solutions when creating designs makes it necessary to have metallic materials with high technological characteristics. So, in the manufacture of blades in gas turbine engines , forging, precision stamping, grinding, mechanical processing of finished products and rods, precision casting, polishing are used. The production of combustion chambers from heat-resistant metal sheets is carried out using pressing, cold stamping, spot welding and other technologies. The most common technologies are electrode welding, friction, diffusion welding, soldering of products. All these manipulations require high quality characteristics of the material used.
Heat-resistant alloys and steels by their nature are able to maintain high strength indicators, both to working and to process temperatures. This, in turn, leaves a specific imprint on the entire applicable technology of metal redistribution, from the deformation of the ingot to the final operations to refine the products to the required surface cleanliness and required dimensions.