(1) normalizing
1) Definition of normalizing: Normalizing, also known as normalization, is to heat the workpiece to Ac3 (Ac refers to the final temperature at which free ferrite is completely transformed into austenite during heating, generally between 727°C and 912°C ) or Acm (Acm is the critical temperature line for complete austenitization of hyper eutectoid steel in actual heating) above 30~50°C, after holding for a period of time, take it out from the furnace and cool it in the air or by spraying water, spraying or blowing Metal heat treatment process.
2) The purpose of normalizing: ①Remove the internal stress of the material; ②Increase the hardness of the material.
3) The main application ranges of normalizing are ① used for low carbon steel; ② used for medium carbon steel; ③ used for tool steel, bearing steel, carburizing steel, etc.; ④ used for steel castings; ⑤ used for large forgings; ⑥ for ductile iron.
(2) Annealing
1) Definition of annealing: It refers to slowly heating the metal to a certain temperature, keeping it for a sufficient time, and then cooling it at an appropriate speed (usually slow cooling, sometimes controlled cooling).
2) The purpose of annealing: ① reduce hardness, improve machinability; ② eliminate residual stress, stabilize size, reduce deformation and crack tendency; ③ refine grain, adjust structure, eliminate structure defects; ④ uniform material structure and composition, improve Material properties or tissue preparation for later heat treatment.
3) The main application range of annealing: ①Complete annealing is mainly used for castings, forgings and weldments of hypereutectoid steel to eliminate structural defects, make the structure thinner and uniform, and improve the plasticity and toughness of steel parts; ②Incomplete annealing is mainly used for forging and rolling of medium-carbon and high-carbon steel and low-alloy structural steel, which makes the grains thinner, reduces hardness, eliminates internal stress, and improves machinability; ③Spheroidizing annealing is only used for The medium annealing method of steel, in which medium carbon steel and high carbon steel have low hardness, good machinability, and large cold deformation ability; The residual stress in the medium stabilizes the size and shape of the workpiece, and reduces the deformation and crack tendency of the parts during cutting and use.
(3) Quenching
1) Definition of quenching: a metal heat treatment process in which a metal workpiece is heated to an appropriate temperature and maintained for a period of time, and then immersed in a quenching medium for rapid cooling. Commonly used quenching media are brine, water, mineral oil, air, etc.
2) The purpose of quenching: to improve the mechanical properties of steel parts, such as hardness, wear resistance, elastic limit, fatigue strength, etc.; to improve the physical or chemical properties of some special steels, such as enhancing the ferromagnetism of magnetic steel and improving the resistance of stainless steel corrosion, etc.
3) The scope of application of quenching: widely used in various tools, molds, measuring tools and parts that require surface wear resistance (such as gears, rolls, carburized parts, etc.). The important parts in machinery, especially the steel parts used in automobiles, airplanes and rockets, are almost all quenched.
(4) Tempering
1) Definition of tempering: tempering is generally carried out immediately after quenching, and the quenched workpiece is reheated to an appropriate temperature below the lower critical temperature and is cooled in air, water, oil and other media after a period of heat preservation. .
2) The purpose of tempering: ① Eliminate the residual stress generated when the workpiece is quenched to prevent deformation and cracking; ② Adjust the hardness, strength, plasticity and toughness of the workpiece to meet the performance requirements; ③ Stabilize the structure and size to ensure accuracy; ④ Improve and improve processing performance.
3) Application range of tempering: tempering is divided into low-temperature tempering, medium-temperature tempering and high-temperature tempering, among which low-temperature tempering is mainly used in cutting tools, measuring tools, molds, rolling bearings, carburized and surface quenched parts, etc.; medium temperature tempering Tempering is mainly used in springs, forging dies, impact tools, etc.; high-temperature tempering is widely used in various important structural parts, such as connecting rods, bolts, gears and shaft parts.
