Quenching of steel is to heat the steel to the critical temperature Ac3a (sub-eutectic steel) or Ac1 (over-eutectic steel) above the temperature, hold for a period of time, so that all or part of the austenitization, and then faster than the critical cooling rate of the cooling rate of the fast cooling to Ms below (or Ms near the isothermal) for the transformation of martensite a (or bainite) heat treatment process. Usually also aluminum alloys, copper alloys, titanium alloys, tempered glass and other materials solid solution assistant “or with rapid cooling process heat treatment process called quenching”.
The purpose of quenching:
(1) Improve the mechanical properties of the metal into material or parts.
(2) improve the material properties or chemical properties of some special steel
Quenching methods: mainly single-liquid quenching, double-liquid fire, graded quenching, isothermal quenching, localized quenching and so on.
Tempering is the quenched metal into a material or part heated to a certain temperature, after holding a certain period of time, cooled in a certain way of heat treatment process, tempering is an operation immediately after quenching, usually is also the workpiece for heat treatment of the last process, and thus the joint process of quenching and tempering is called the final treatment.
The role of tempering is to:
(1) improve the stability of the organization, so that the workpiece in the use of the process no longer occurs in the organization of the transformation, so that the workpiece geometry and properties remain stable.
(2) Eliminate internal stresses in order to improve the performance of the workpiece and stabilize the geometry of the workpiece.
(3) adjust the mechanical properties of steel to meet the requirements of use.
Tempering requirements: different uses of the workpiece should be tempered at different temperatures to meet the requirements in use. (1) cutting tools, bearings, carburizing quenched parts, surface quenched parts are usually tempered at 250 ℃ below the low-temperature tempering, low-temperature tempering after the hardness does not change much, the internal stress is reduced, the toughness is slightly improved. (2) spring in 350 ~ 500 ℃ under medium temperature tempering, can obtain high elasticity and necessary toughness. (3) medium-carbon structural steel parts made of high-temperature tempering usually at 500 ~ 600 ℃, in order to obtain the appropriate strength and toughness of a good match.
Normalizing is a kind of heat treatment to improve the toughness of steel, the steel components are heated to the Ac3 temperature above 30 ~ 50 ℃, after holding a period of time out of the air-cooled. The main feature is that the cooling rate is faster than the return and lower than the quenching, normalizing can be slightly faster cooling in the crystalline grain refinement of steel, complementary single can get satisfactory strength, and can significantly improve the small capriciousness (AKV value), reduce the tendency to cracking of the component, some low alloy hot rolled steel plate, low alloy steel forgings and castings by normalizing, the comprehensive mechanical properties of the material can be played to improve, but also improve the Cutting performance.
Annealing is the metal is slowly heated to a certain temperature, maintained for a sufficient period of time, and then at a suitable rate of cold zone of a metal heat treatment process. Annealing heat treatment is divided into complete annealing, incomplete annealing and stress relief annealing. Mechanical properties of annealed materials can be used tensile test to Kinze, can also be detected by hardness test. Many steel materials are supplied in a returned heat-treated condition, steel hardness testing can be used Locke's hardness tester, test HRB hardness, for thinner steel plates, steel strips, and thin-walled steel tubes, you can use the surface Locke's hardness tester, building materials HRT hardness.
The purpose of quenching and annealing: 1 to improve the goods to eliminate the rigid thee in the casting, forging, rolling and welding process caused by a variety of organizational defects, as well as residual stresses, to prevent deformation of the workpiece, cracking. 2 to soften the workpiece in order to carry out cutting. 3 to refine the grain, improve the organization in order to improve the mechanical properties of the workpiece. 4 for the final heat treatment (quenching, tempering) to do a good job of organization standards.
Commonly used annealing processes are:
(1) complete annealing. Used to refine the middle and bottom carbon steel by casting, forging and welding after the emergence of poor mechanical properties of coarse superheated tissue.
(2) spheroidal annealing. Used to reduce the high hardness of tool steel and bearing steel after forging.
(3) isothermal annealing. Used to Jiangdu certain nickel, chromium content angle steel alloy structural steel high hardness.
(4) recrystallization annealing. Used to trolley metal wire, sheet in the cold drawing, cold rolling process of hardening phenomenon (hardness increases, plasticity decreases)
(5) graphitization annealing. Used to make the cast iron containing a large number of carburized body into malleable cast iron with good plasticity.
(6) diffusion annealing. Used to make the chemical composition of alloy castings uniform, improve its performance.
(7) stress relief annealing. Used to eliminate the internal stress of steel castings and weldments.
Post time: Dec-01-2024
