Heat-resistant alloy, also known as high-temperature alloy, is an alloy with structural stability and excellent mechanical, physical and chemical properties under high temperature conditions. Including heat-resistant steel, heat-resistant aluminum alloy, heat-resistant titanium alloy, high-temperature alloy, refractory alloy and so on. Heat resistant alloys have certain tensile, creep, fatigue properties, physical, chemical properties and process properties at elevated temperatures.

Introduction

Heat resistant alloys are alloys that have high oxidation resistance, creep resistance and long-lasting strength at high temperatures, also known as high temperature alloys. With the development of modern science and technology (especially aviation, rockets, etc.), the working temperature of metal materials or products is constantly increasing. In the field of superalloys, iron-based, nickel-based and cobalt-based superalloys are mainly used in large quantities. From the viewpoint of the strength of the alloy crystal structure, three basic characteristics of high temperature strengthening:

(1) Improve the resistance of the dislocation movement at the slip interface, that is, increase the deformation resistance of the slip deformation mechanism.

(2) A diffusion-type motion process that slows down dislocations to suppress the progress of the diffusion-type deformation mechanism.

(3) Improve the crystal structure state to increase the grain boundary strengthening effect; or cancel the grain boundary to eliminate the weak link of the grain boundary at high temperature.

Heat resistant alloy classification

According to the matrix elements, it can be mainly divided into iron-based superalloys, nickel-based superalloys, cobalt-based superalloys and powder metallurgy superalloys. According to the strengthening method, there are solid solution strengthening type, precipitation strengthening type, oxide dispersion strengthening type, and fiber strengthening type. Superalloys are mainly used to manufacture high temperature components such as turbine blades, guide vanes, turbine disks, high pressure compressor disks and combustion chambers for aerospace, naval and industrial gas turbines; they are also used in the manufacture of spacecraft, rocket engines, nuclear reactors, petrochemical plants, and Energy conversion devices such as coal conversion. Superalloys should have high creep strength and long-lasting strength, good thermal and mechanical fatigue resistance, good oxidation and gas corrosion resistance, and structural stability, with creep strength and long-lasting strength being the most important.

Heat-resistant alloys metallurgy production process

Superalloys containing no or less aluminum and titanium are generally smelted in an electric arc furnace or a non-vacuum induction furnace. When high-temperature alloys containing aluminum and titanium are smelted in the atmosphere, elemental burning is difficult to control, and gas and inclusions are more intensive, so vacuum smelting should be used. In order to further reduce the content of inclusions, improve the distribution of inclusions and the crystal structure of the ingot, a double process combining smelting and secondary remelting may be employed. The main means of smelting are electric arc furnace, vacuum induction furnace and non-vacuum induction furnace; the main means of remelting are vacuum self-consumption furnace and electroslag furnace.

Solid solution strengthened alloys and alloy ingots containing aluminum and titanium (the total amount of aluminum and titanium are less than about 4.5%) can be forged blanks; alloys containing aluminum and titanium are generally extruded or rolled. Then hot rolled into a material, some products need to be further cold rolled or cold drawn. Larger diameter alloy ingots or cakes are forged with a hydraulic press or a fast forging hydraulic press. Alloys with a high degree of alloying and non-deformation are currently widely used for precision casting, such as casting turbine blades and guide vanes. In order to reduce or eliminate grain boundaries perpendicular to the stress axis in the cast alloy and to reduce or eliminate looseness, a directional crystallization process has been developed in recent years. In addition, in order to eliminate all grain boundaries, a manufacturing process of single crystal blades has been studied in recent years.