Metal materials and various scientific activities as well as economic society has a close connection, the development of human society to today. With the progress of The Times and the development of science and technology, metal substitutes have been constantly developed, and the heat treatment technology of metal materials has also been improved unprecedentedly. The following will briefly describe and analyze its development status and future development direction.
Key words: Heat treatment technology of metal materials; The status quo. The development direction
preface
Metal materials are one of the most important materials for human development. No matter which era, metal materials are playing a huge role in people's life. According to its characteristics, metal materials have the characteristics of high toughness, hardness and strength, and metal materials are easy to obtain, and many metals are easy to make. With the development and promotion of modern metal technology, the development and expansion of science and technology, metal materials in machinery production, national defense, industry, agriculture, electronic information and other industries, have obvious cost-effective advantages and broad prospects for development of the market.
1. Current status of metal heat treatment technology
1.1 Ordinary heat treatment
The purpose of ordinary heat treatment is to improve the metal structure, adjust the strength, hardness, toughness, improve the processing performance of the metal, do not change the chemical composition of the metal. The main processes are annealing, normalizing, quenching and tempering.
Annealing is a heat treatment process in which steel is heated to the required value of the process, held for a certain time, and then slowly cooled to obtain an equilibrium state. The main purpose of annealing is to reduce the hardness, in order to facilitate the metal mechanical performance; Refine grain, improve plasticity and toughness; Eliminate internal stress.
Normalizing is a heat treatment process in which steel is heated to 30-50℃ above Ac3 or 30-50℃ above Acm and cooled in air after holding. The role of normalizing is to heat the steel to the austenite zone, so that the steel recrystallized, so as to solve the problem of coarse grain and uneven structure of the steel.
Quenching is a process of heating steel to Ac3 or Ac1 above 30-50℃, and then cooling it rapidly in quenching medium after holding, so that the supercooled austenite is transformed into martensite or bainite. Because the workpiece is prone to crack or deformation during quenching, the heating temperature of quenching should be strictly controlled, the quenching medium should be reasonably selected, and the quenching method should be correctly selected in order to obtain better quenching effect.
Tempering is to reheat the quenched steel to a temperature below Ac1, and then cool it to turn it into a stable tempered structure. The main purpose of tempering is to eliminate the internal stress of quenching, reduce the brittleness of steel, prevent cracks, and obtain the required mechanical properties of steel.
Common heat treatment technology is widely applied in Chinese machinery industry production, and it develops well in equipment and technology. For example, in the production of high-pressure gas cylinders, the cup body formed by the steel plate drawing for many times needs to be annealed after each drawing to refine the grain, eliminate the internal stress, and prevent fracture and deformation in the subsequent drawing operation.
1.2 Surface heat treatment
Surface heat treatment is a metal heat treatment process in which the surface of steel is heated and cooled to change the surface mechanical properties. The main processes are surface quenching and chemical heat treatment.
Surface quenching is a local quenching method in which the surface layer of steel is quenched to a certain depth while the core remains unquenched. The main purpose of surface quenching is to obtain a high hardness, high wear resistance surface, while the core still maintains good toughness, often used in machine tool spindle, gear, engine crankshaft, etc.
Chemical heat treatment is to put the workpiece in a certain chemical medium to heat, heat preservation, so that the active atoms in the medium into the surface of the workpiece, in order to change the chemical composition and organization of the surface of the workpiece, obtain the required mechanical properties and physical and chemical properties. According to the infiltration of different elements, chemical heat treatment can be divided into carburizing, nitriding, boronizing, aluminizing and so on. If two or more elements are infiltrated at the same time, it is called co-osmosis, such as carbon and nitrogen co-osmosis, chromium aluminum and silicon co-osmosis, etc.
