| Name | heat treatment process | heat treatment purpose | 1. Annealing | steel heated to a certain temperature, holding a certain period of time, and then slowly cooled to room temperature. | ① reduce the hardness of steel, plastic, in order to facilitate cutting and cold deformation processing; (2) the grain refinement and uniform steel organizations to improve the performance of the steel and for the subsequent heat treatment for preparation; ③ to eliminate the internal stress of the steel. Prevent parts processing, deformation and cracking. | (1) fully annealed | steel heated to a critical temperature (the critical temperature of the different steel generally is 710-750 ° C, the critical temperature of the individual alloy steel up to 800-960 º C) 30-50 º C, thermal insulation a certain period of time, and then slowly cooled with the furnace (or buried in the sand cooling). | grain refinement, uniform organization, and reduce the hardness, and fully eliminate the internal stress of the fully annealed carbon content (mass fraction) in O. Less than 8 percent of forgings or steel castings. | (2) spheroidization annealing | the steel is heated to above the critical temperature 20 ~ 30 ° C, after the insulation after slow cooling to below 500 ℃ and then cooled baked. | reduce the hardness of the steel to improve the cutting performance, prepare for, and after quenching, deformation and cracking in order to reduce the quenching, the ball annealing carbon content (mass fraction ) is greater than O. 8% of the carbon steel and alloy tool steel. | (3) to stress annealing | steel heated to 500 ~ 650 º C, thermal insulation of a certain period of time, then slowly cooled (usually followed by furnace cooling). | eliminate the internal stress generated in the steel welded and cold straightening, eliminating the machining of precision parts of the internal stress to prevent deformation after processing and process. Stress relief annealing for a variety of castings, forgings, weldments and cold extrusion. | 2. Normalizing | the steel is heated to above the critical temperature 40 ~ 60 º C, thermal insulation a certain period of time, and then cooling in air. | ① to improve the organizational structure and the cutting performance; ② less demanding parts of the mechanical properties, commonly used normalizing as the final heat treatment; (3) the elimination of internal stress. | 3. Quenching | steel heated to quenching temperature, holding for some time, and then rapid cooling in air), water, brine or oil (the individual materials. | ① the steel to obtain a higher hardness and wear resistance; ② the steel in tempering after a particular performance, such as high strength, elasticity and toughness. | quenching category | The (1) single liquid quenching | steel heated to quenching temperature, after the insulation after cooling in a quenching agent. The single liquid quenching is only applicable to relatively simple shapes, technical requirements are not too high carbon steel and alloy steel. Quenching, the diameter or thickness greater than 5 ~ 8mm carbon steel, the choice of saline or water cooling; alloy steel selection oil cooling. | (2) Two-quenching | steel heated to quenching temperature, the first in the water after the insulation after rapid cooling to 300-400? C, and then transferred into the cooling oil. | (3) flame surface hardening | sprayed into the combustion flame of acetylene and oxygen surface of the part, so that part rapidly heated to quenching temperature, and then immediately with water injection to the part surface. Flame surface hardening applies to a single piece or small batch production, hard surface requirements while wear-resistant and can withstand large impact loads in carbon steel and carbon steel, such as crankshaft, gear and rail. | (4) surface induction hardening | steel on the sensor, the sensor in the role of a certain frequency of the AC magnetic field, the steel in the magnetic field induced current, so that the steel surface rapid heating (2-l0min) to the quenching temperature, then immediately the water sprayed onto the steel surface. Surface induction hardening of parts, surface hard and wear-resistant, while the core part to maintain good strength and toughness. Surface induction hardening medium carbon steel and alloy steel of medium carbon content. | 4. Tempering | hardened steel is heated to below the critical temperature, thermal insulation for some time, and then cooling in air or oil. Tempering followed by quenching and is heat-treated process. | ① obtain the required mechanical properties. Under normal circumstances, the strength and hardness of the parts after quenching has greatly improved, but the ductility and toughness has decreased significantly, while the actual working conditions of the parts require good strength and toughness. Select the appropriate tempering temperature tempering, you can obtain the required mechanical properties; ② stable organization, stability, size; (3) the elimination of internal stress. | tempering category | (1) low-temperature tempering | will be hardened steel is heated to 150-50 º C. At this temperature, thermal insulation a certain period of time, and then cooling in air, low-temperature tempering is used for cutting tools. measuring tools, molds, Rolling and carburizing parts. | eliminate the internal stress of the steel due to quenching. | (2) | quenching of steel heated to 350 to 450 percent by the holding period of time to cool down, generally used for all kinds of springs and hot die parts. | steel to obtain a higher flexibility, toughness and hardness. | (3) high-temperature tempering | hardened steel is heated to 500 to 650 º C. After cooling, after the insulation is mainly used for important structural components requiring high strength, high toughness, such as the spindle crankshaft, cams, gears and connecting rods. | to obtain better mechanical properties of steel, high strength and toughness and hardness, to eliminate the internal stress of the steel due to quenching. | 5. Quenched and tempered | hardened steel at high temperature (500 ~ 600 º C) tempering used for important structural parts such as shafts, gears, connecting rod, quenched and generally in the rough after. | grain refinement, the steel to obtain higher toughness and of sufficient strength, it has a good comprehensive mechanical properties. | 6. Aging treatment | (1) artificial aging | hardened steel is heated to 100 ~ 160 ° C, followed by cooling after a long period of insulation. | eliminate stress, reduce part deformation, stability, size, high precision parts is more important. | (2) natural aging | casting on the open air; steel (such as the long axis of the screw, etc.) on the sea or long-term suspension or tapping the natural aging parts. best to rough. | 7. Chemical treatment | steel containing certain active atoms (such as carbon, nitrogen, chromium, etc.), chemical medium, by heating, insulation, cooling, so that the medium some atoms penetrate to the steel surface, thereby to change the steel surface chemical composition of the steel surface with a special performance. | chemical treatment categories | (1) | carbon atoms into the steel surface. Commonly used in wear-resistant and shock parts, such as: wheels, gears, shafts, piston pin and so on. | surface has high hardness (to HRC60 ~ 65) and wear resistance, while the center remains high toughness. | (2) the nitrogen permeability of steel | nitrogen atoms penetrate the surface of steel. Commonly used in important parts of bolts, nuts, pins, etc.. | steel surface hardness, wear resistance, corrosion resistance. | (3) steel cyanide | carbon and nitrogen atoms also penetrate to the steel surface is applicable to low-carbon steel, carbon steel or alloy steel parts, high-speed steel cutting tools can also be used. | improve the hardness and wear resistance of the steel surface. | 8. Black | metal parts on a very strong alkali and oxidant solution heated oxidation, the metal parts of the surface layer of magnetic iron oxide thin films commonly used in low-carbon steel, low carbon alloy tool steel. Materials and other factors, the black layer film color blue-black, black, red, brown, tan, of a thickness of 0.6 ~. O. 8μm. | rust-proof, to increase the metal surface appearance and gloss, to eliminate the stress in the quenching process. |