70mn spring steel heat treatment and microstructure specifications: Heat treatment specifications: quenching 830 ℃ ± 20 ℃, oil cooling; tempering 480 ℃ ± 50 (when special needs, ± 30 ℃). Microstructure: fine pearlite and a small amount of eutectoid ferrite. 70Mn spring steel hardness of spring steel 70Mn spring steel 70Mn composition price performance of spring steel 70Mn spring steel 70Mn manganese alone polishing properties such as spring steel 65Mn, the manganese content is 0.90 to 1.20%. Increasing the manganese content improves hardenability and strength of steel, reducing decarbonization tendencies; drawback is overheating sensitivity and temper brittleness, and easy to produce quenching cracks, so only suitable for the manufacture of various small size flat spring, round spring . Silico-manganese spring steel is a major hot-rolled alloy spring steel, China has 55Si2Mn, 60Si2Mn, 60Si2MnA, 70Si3MnA four steel. A silicon content of 1.50 to 2.80%, a manganese content of 0.60 to 0.90%. Plus silicon steel can significantly increase the elastic limit and yield ratio, improve the tempering stability; it is easy to form silicate inclusions increase decarbonization sensitivity. When the carbon content in steel and silicon are high, easy-graphitizable carbon. Such steel is widely used in the production of cars, tractors, damping spring and coil spring locomotive, as well as requirements to withstand high stress spring. For the manufacture of spring or spring-like properties of the parts of steel type. With a high elastic limit, fatigue limit (especially notch fatigue limit) as well as certain toughness and ductility, mainly used under dynamic loads or long cycle alternating stress shocks and vibration. So the spring working in various states should have a good surface quality and high fatigue resistance. In the process performance, to be quenched and tempered spring steel, should have a certain hardenability, easy removal, low thermal sensitivity and high plasticity, easy to shape in a hot state. Manufacture of small size steel springs have uniform hardness and a certain plasticity. Category spring steel according to production methods can be divided into hot-rolled and cold-drawn spring steel (rolled) spring steel. Hot rolled spring steel spiral process including manufacturing performance springs used in the shock, vibration, or long-term cross-stress, it requires a high spring steel tensile strength, elastic limit, high fatigue strength. In the process requires a certain degree of spring steel hardenability, easy removal, good surface quality carbon spring steel that is the carbon content of WC within 0.6% -0.9% range of high-quality carbon structural steel. Silicomanganese alloy spring steel is mainly the Department of steel, their lower carbon content, mainly by increasing silicon content Wsi improve performance; in addition to Ge, tungsten, vanadium alloy spring steel. In recent years, with China's resources, and designed according to the requirements of new technology cars, tractors, developed a boron, niobium, molybdenum and other elements on the basis of in silico-manganese steel new steel to extend the spring of life and improve the quality of the spring . Performance requirements for use in the spring under the impact, vibration, or long-term cross-stress, it requires a high spring steel tensile strength, elastic limit, high fatigue strength. In the process requires a certain degree of spring steel hardenability, easy removal, good surface quality carbon spring steel that is the carbon content of WC within 0.6% -0.9% range of high-quality carbon structural steel. Silicomanganese alloy spring steel is mainly the Department of steel, their lower carbon content, mainly by increasing silicon content Wsi improve performance; in addition to Ge, tungsten, vanadium alloy spring steel. In recent years, with China's resources, and designed according to the requirements of new technology cars, tractors, developed a boron, niobium, molybdenum and other elements on the basis of in silico-manganese steel new steel to extend the spring of life and improve the quality of the spring . Production process is generally available spring steel furnace, open-hearth, or oxygen converter production; better quality or have special properties of high-quality spring steel, electric furnace or vacuum furnace slag refining. The main provisions of spring steel elements carbon, manganese, silicon and other content narrower, must strictly control the chemical composition of smelting. Easy to form bubbles and other defects at higher silicon content, after cooling wrought ingot was not easy to produce white spots. Therefore, the smelting of raw materials must be dry, try to remove gas and inclusions, but also to avoid superheat. Spring steel surface decarburization and pay special attention to the quality of the rolling process. When the steel surface decarbonization serious, it will significantly reduce the fatigue limit of steel. For high-silicon spring steel as 70Si3MnA, should be taken to avoid graphitization. Thus, when the thermal processing temperature should not stop rolling low (≥850 ℃), easier to avoid the formation of graphitization temperature range (650 ~ 800 ℃) long residence time. Rear springs made by shot peening make spring surface residual compressive stresses to offset part of the work on the surface stress, inhibit the formation of surface cracks, which can significantly increase the fatigue limit of the spring. Heat-treated spring steel require high strength and fatigue limit, usually in the quenching and tempering of state used in order to obtain a high elastic limit. Heat treatment technology to the intrinsic quality of the spring has a crucial impact. So, how to further improve the fatigue life of the spring, further research is needed, especially chemical surface modification heat treatment, shot peening and so have a major impact on the spring fatigue life. To further strengthen the valve spring surface strength, increased stress, improve fatigue life, after forming the valve spring, to further after nitriding, carbonitriding or cryogenic liquid sulfur and nitrogen permeation, and then by shot peening. For example, Japan will f4mm of si-cr oil quenched steel wire 450 ℃ × 4.5h hypothermic carbonitriding and after 400 ℃ × 15min tempering comparison, the fatigue limit can be increased 240mpa. Nitrogen infiltration, not only to eliminate the adverse effects of decarbonization, but also improve the residual compressive stress, while low-temperature liquid nitriding and carbonitriding temperature strength valve springs increase the amount of deformation at 150 ℃ 0.2% (provision of 0.5%), the amount of deformation 250 ℃ 0.56%, increased valve spring thermal stability and resistance to relaxation stability, but liquid nitriding and carbonitriding time should be strictly controlled, otherwise it will form a network sulfide and net nitride, but it will reduce its fatigue strength. Definition of spring steel is steel due to the elasticity in the quenched and tempered condition, and specifically for the manufacture of springs and elastic components. Spring steel depends on its ability to elastically deform, i.e., within the prescribed range, the ability to withstand a certain elastic deformation so that the load does not occur in the permanent deformation after the load is removed. Spring steel should have excellent properties such as mechanical properties (especially elastic limit, ultimate strength, yield ratio), ballistic performance reduction (ie anti decreased elasticity properties, also known as sag resistance), fatigue properties, hardenability physical and chemical properties (heat resistance, low temperature, oxidation, corrosion, etc.). To meet these performance requirements, spring steel with excellent metallurgical quality (high purity and uniformity), good surface quality (strict control of surface defects and decarburization), the exact shape and size. According to GB / T 13304 "Steel classification" standard, according to the basic performance characteristics and use of a spring steel is a mechanical structural steel; according to quality grade, is a special quality of steel, that is, in the production process requires strict control of the quality and performance of special steel . According to Chinese custom, spring steel is a special steel, spring steel production when the technical requirements are relatively high, excellent technology directly determine the level of quality. Research strength levels of traditional spring steel can not meet the requirements of modern industrial development, it is known under the mechanical properties of spring steel material quality assurance in the premise depends on the heat treatment process, and the heat treatment process should be determined according to the materials, high-strength spring steel One important way is to give full play to the role of alloying elements to achieve the best effect of alloying.