Knowledge of steel.The carbon content of tempered steel is generally o. 35% ~ 0.55% (carbon steel), or o. 25% ~ 0.50% (alloy steel).If the carbon content is low, the toughness and plasticity are good and the strength is insufficient.When the carbon content is medium, it can have appropriate strength, toughness and plasticity at the same time.The main role of the alloy elements in the tempered steel is to improve the hardenability and comprehensive mechanical properties, so the alloy elements can improve the mechanical properties of steel in the tempered state, relative to carbon steel, the same carbon content of the alloy steel of high strength, plasticity and toughness, so it is often used as an important tempered parts.Quenched steel according to the degree of hardenability, can be divided into low hardenability steel, medium hardenability steel and high hardenability steel, respectively as follows.
(1) low hardenability steel
The critical diameter of oil quenching of this kind of steel is not more than 30mm.Common brands are 45, 40Mn2, 45Mn2, 42Mn2V, 35SiMn, 40B, 40MnB, 40MnVB, 40Cr, 40CrSi, 40CrV, 50(r, rV, etc.), carbon steel hardenability is low, poor mechanical properties, generally used to make small cross section and unimportant parts;Chromium steel has better hardenability, has higher tempering stability than carbon steel, quenching temperature is wide, not easy to overheat, deformation and cracking tendency is small, so it is widely used;The function of manganese steel is similar to that of chromium steel. Manganese reduces the critical cooling rate of steel and improves the strength and hardness of steel.Boron steel in boron significantly improved the hardenability of steel, its performance is close to 40Cr, the critical diameter of oil quenching in 20 ~ 30mm, commonly used for automotive half shaft, worm, spline shaft, etc.
(2) medium hardenability steel
This kind of steel oil quenching directly in 40 ~ 60n, m, the commonly used steel has chromium molybdenum steel, chromium manganese steel.Common grades of 35 (jrMn, 42 crmo, 35 l: rMnV, 40 CRMN, 35 crmnsi, 30 crmnsi, 35 (: rMnTi, 40 crmnti, 40 crni, chrome molybdenum steel with high hardenability, high temperature and high strength, good stability and organization, eliminate the temper brittleness, 42 crmo used to produce high strength requirement, large cross section of the conditioning parts, such as gear, large steam turbine generator shaft, the load of the connecting rod, etc., at the same time also can be made in five (:) o ℃ under the long-term work of the parts;The hardenability and strength of chromium-manganese steel are high, the toughness is not reduced, 30(: rMnsi is a high strength steel, with good weldability, used for the manufacture of high-pressure blower compression sheet, high-speed load sand wheel shaft and other important parts.
(3) high hardenability steel
The critical diameter of oil cooling is 60 ~ 1 OO mm.Common material brands are 30Mn2MoW, 40CrMnMo, 30(: rNi3, 37CrNi3, 40CrNiMc), 45CrNiMov, 25cr2Ni4w, etc., 40CrMnMo is a commonly used high hardenability steel, with small tempering brittleness, small overheating tendency and other characteristics, used to make cross-sectional area, high strength and high toughness of the parts, such as large heavy-duty car half axle.