Thermal processing, a method of simultaneously causing plastic deformation and recrystallization of a metal material at a temperature higher than a recrystallization temperature. Thermal processing typically involves casting, hot-rolling, forging, and metal heat treatment, sometimes including welding, hot cutting, and thermal spraying. Thermal processing enables the metal part to improve its structure while forming, or to change the formed part to a crystalline state to improve the mechanical properties of the part. For low melting point metal materials, such as lead, zinc, tin, etc., the recrystallization temperature is low, and plastic processing of them at room temperature is also a thermal process.
Hot-rolled sheet has low hardness, easy processing, good ductility, relatively low strength, poor surface quality (low oxidation/smoothness), but good plasticity, generally medium and heavy plate, hot-rolled steel sheet, mechanical properties are far less than cold processing, Secondly than forging, but with good toughness and ductility.
Cold-rolled sheet: high strength, high hardness, relatively difficult to process, but not easy to deform, high surface finish, generally thin sheet, can be used as a stamping sheet; due to a certain degree of work hardening, low toughness, but can achieve better The yield ratio is used to cold-bend spring parts and other parts. At the same time, because the yield point is closer to the tensile strength, the danger is not predictable during use, and accidents are likely to occur when the load exceeds the allowable load. Most cold rolled steel sheets have a thickness of 4.5 mm or less. Cold rolled sheet has high hardness and high strength
Medium and heavy plate refers to a steel plate with a thickness of 4.5-25.0mm, a thick plate with a thickness of 25.0-100.0mm, and a thick plate with a thickness exceeding 100.0mm.
(1): Annealing: A heat treatment process in which a metal material is heated to an appropriate temperature for a certain period of time and then slowly cooled. Common annealing processes are: recrystallization annealing, stress relief annealing, spheroidizing annealing, complete annealing, and the like. The purpose of annealing: mainly to reduce the hardness of metal materials, improve plasticity, to facilitate cutting or pressure processing, reduce residual stress, improve the homogenization of the structure and composition, or prepare the tissue for the subsequent heat treatment.
(2): Normalizing: refers to a heat treatment process in which steel or steel is heated to above Ac3 or Accm (the upper critical point temperature of steel) and is kept at a temperature of 30 to 50 ° C for a suitable period of time. The purpose of normalizing is to improve the mechanical properties of low carbon steel, improve machinability, refine grains, eliminate tissue defects, and prepare for post-heat treatment.
(3): quenching: refers to heating the steel to a temperature above Ac3 or Ac1 (the lower critical temperature of the steel) for a certain period of time, and then obtaining martensite (or bainite) at an appropriate cooling rate. The heat treatment process of the tissue. Common quenching processes include salt bath quenching, martensite quenching, bainite austempering, surface quenching and partial quenching. The purpose of quenching: to obtain the desired martensite structure of the steel, to improve the hardness, strength and wear resistance of the workpiece, and to prepare the tissue for the subsequent heat treatment.
(4): Tempering: refers to the heat treatment process in which the steel is hardened and then heated to a temperature below the critical point AC1 for a certain period of time and then cooled to room temperature. Common tempering processes are: low temperature tempering, medium temperature tempering, high temperature tempering and multiple tempering. The purpose of tempering: mainly to eliminate the stress generated by the steel during quenching, so that the steel has high hardness and wear resistance, and has the required plasticity and toughness.
(5): quenching and tempering: refers to the composite heat treatment process of quenching steel and steel parts and high temperature tempering. Steel used for quenching and tempering is called quenched and tempered steel. It generally refers to medium carbon structural steel and medium carbon alloy structural steel.
(6): Carburizing: Carburizing refers to a process in which carbon atoms are infiltrated into a steel surface layer. It also makes the low carbon steel workpiece have the surface layer of high carbon steel, and after quenching and low temperature tempering, the surface layer of the workpiece has high hardness and wear resistance, while the central part of the workpiece still maintains the toughness of low carbon steel. Plasticity.
Annealing→heating the workpiece to the appropriate temperature, using different holding times according to the material and the workpiece size, and then slowly cooling (the slowest cooling rate), in order to achieve or close to the equilibrium of the internal metal structure, and obtain good process performance and use. Performance, or preparation for further quenching.
Normalizing→The workpiece is heated to a suitable temperature and then cooled in the air. The effect of normalizing is similar to annealing, except that the obtained structure is finer, which is often used to improve the cutting performance of materials, and sometimes used for some less demanding parts. As the final heat treatment.
Quenching → After heating and holding the workpiece, it is rapidly cooled in a quenching medium such as water, oil or other inorganic salts or organic aqueous solutions. After quenching, the steel becomes hard but becomes brittle at the same time. In order to reduce the brittleness of the steel, the quenched steel is subjected to long-term heat preservation at a suitable temperature higher than room temperature and lower than 710 ° C, and then cooled. This process is called tempering. Annealing, normalizing, quenching and tempering are the "four fires" in the overall heat treatment. The quenching and tempering are closely related, and often used together, they are indispensable;