Spring steel hardness after heat treatment

Spring steel heat treatment processing of heat treatment characteristics of spring steel heat treatment depends on the spring forming method, generally can be divided into hot forming spring and cold forming spring two broad categories: 1) Hot forming spring of section size> 10 mm all kinds of large and complex shape spring adopt hot forming ( Such as hot rolling, hot roll) , such as cars, tractors, train plate spring and spring. Its simple processing route is: heating, bending or flat or round steel cutting winding to quenching medium temperature tempering, surface peening treatment, using the state organization for tempering austenite. Shot peening strengthening surface and improve the quality of the surface of the spring, significantly improve the fatigue performance. 2) Spring cold forming sectional dimension of < 10 mm small spring can use cold forming ( Such as cold rolled, cold rolled) , such as the instrument of the spiral spring, spring and spring leaf, etc. This kind of spring for cold drawn before forming ( Cold rolled) Isothermal quenching, quenching medium temperature tempering or lead bath after cold drawing ( Rolling) Strengthening; Then using the cold forming process, this process will further strengthen the metal, but also produce a large internal stress and brittleness, so should be done after low temperature annealing ( Generally 200 ~ 400 ℃) Measures to improve the quality of spring, 1) Thermomechanical treatment - - - - - - - The deformation of steel strengthening and heat treatment strengthening both combined, to further improve the strength and toughness of steel. Has high, medium and low temperature thermomechanical treatment. High temperature thermomechanical treatment is produced in the condition of austenite deformation immediately after quenching, can also be combined with forging or hot rolled, namely thermoforming immediately after quenching. Thermomechanical treatment is applied to automobile plate spring production. ( 2) Isothermal quenching - spring - - - - - - For small diameter or through permeability enough spring can use isothermal quenching, it not only can reduce the deformation, but also can improve the tenacity, best again after isothermal quenching tempering, can improve the elastic limit, tempering temperature and isothermal quenching temperature are the same. ( 3) Spring relaxation - processing - - - - - - Spring for a long time work under external force, as a result of stress relaxation will produce trace amounts of permanent ( Plastic) Spring deformation, especially the high temperature, under high temperature stress relaxation phenomenon is more serious, reduce the precision of the spring, for the general precision spring is not allowed. Therefore, this type of spring in quenching and tempering - should be relaxed after the treatment - For spring preload, make its deformation than the spring work possible deformation. Then work in the above temperature 20 c under the condition of heating, heat preservation 8 - 24h。 ( 4) Carbonitriding - at low temperature - The tempering and carbonitriding (at low temperature Soft nitriding) With the combination of technology, can significantly improve the fatigue life of spring and corrosion resistance, it is more for coil spring. ( 5) Shot blast - - Surface defects such as scratches, folding, oxidation decarburization tend to become spring work place of stress concentration and fatigue fracture source. If with tiny steel shot high speed spray the surface of the spring, not only improve the surface quality of the spring, to improve the surface strength, and the surface in the compressive stress state, and thus improve the spring fatigue strength and service life. Operating considerations ( 1) Check whether there is surface decarburization before heat treatment, such as crack defects. These surface defects will seriously reduce the fatigue limit of spring. ( 2) Quench heating should pay special attention to prevent overheating and decarburization, completes the salt bath deoxidization, control of furnace gas atmosphere, strictly control the heating temperature and time. ( 3) In order to reduce the deformation, the spring in the heating furnace charging ways, jig form and cooling quenching cooling method. ( 4) As soon as possible after quenching tempering, heating to scoop. Tempering, quick cold can prevent the temper brittleness and compressive stress caused by surface, improve the fatigue strength.