Heat treatment process of high quality medium carbon structural steel 45 steel
45 steel, is the name in GB,JIS called :S45C,ASTM called 1045,080M46,DIN called :C45; 45 steel is a high-quality carbon structural steel, chemical composition: carbon (C) content is 0.42~0.50%, Si content is 0.17~0.37%, Mn content is 0.50~0.80%, Cr content < =0.25%. The cold and hot processing performance is good, the mechanical properties are good, and the price is low, the source is wide, so it is widely used. Its biggest weakness is low hardenability, large cross-section size and relatively high requirements of the workpiece should not be used.
45 Steel heat treatment recommended temperature: normalizing 850, quenching 840, tempering 600.
①45 steel after quenching without tempering, hardness greater than HRC55 (up to HRC62) is qualified. The maximum hardness for practical application is HRC55 (high-frequency quenching HRC58).
②45 steel does not use carburizing quenching heat treatment process.
45 steel tempering: 45 steel quenching temperature in A3+(30~50)℃, in actual operation, generally take the upper limit. High quenching temperature can accelerate the heating speed of the workpiece, reduce surface oxidation, and improve the work efficiency. In order to homogenize the austenite of the workpiece, sufficient holding time is required. If the actual amount of furnace loading is large, it is necessary to appropriately extend the holding time. Otherwise, there may be insufficient hardness due to uneven heating. However, if the holding time is too long, there will also be coarse grains, serious defects of oxidation and decarburization, which will affect the quality of quenching.
If the loading amount is greater than the requirements of the process document, the heating and holding time should be extended by 1/5. Because of the low hardenability of 45 steel, a 10% brine solution with a large cooling rate should be used. After the workpiece enters the water, it should be quenched, but not cold, if the workpiece is cold in salt water, it is possible to crack the workpiece, because when the workpiece is cooled to about 180 ° C, the austenite is rapidly transformed into martensite, resulting in excessive organizational stress.
Therefore, when the quenched workpiece is quickly cooled to the temperature area, the method of slow cooling should be taken. Because the temperature of the water is difficult to master, it must be operated by experience, when the workpiece in the water stops shaking, the water can be air-cooled (such as oil cooling is better). In addition, the workpiece should be moved into the water should not be static, should be in accordance with the geometric shape of the workpiece, make regular movement. The static cooling medium coupled with the static workpiece leads to uneven hardness, uneven stress and large deformation of the workpiece, and even cracking.
The hardness after quenching of steel tempering parts should reach HRC56~59, the possibility of a large cross-section is lower, but not lower than HRC48, otherwise, it means that the workpiece has not been completely quenched, there may be sostenite or even ferrite organization in the organization, this organization through tempering, still retained in the matrix, can not achieve the purpose of tempering. 45 steel quenching after high temperature tempering, heating temperature is usually 560~600℃, hardness requirements HRC22~34. Because the purpose of conditioning is to obtain comprehensive mechanical properties, the hardness range is relatively wide.
However, if the drawings have hardness requirements, the tempering temperature should be adjusted according to the requirements of the drawings to ensure hardness. If some shaft parts require high strength, high hardness requirements; And some gear, with the keyway of the shaft parts, because of the quality after milling, insert processing, hardness requirements are lower. Regarding the tempering holding time, depending on the hardness requirements and the size of the workpiece, the hardness after tempering depends on the tempering temperature, which has little relationship with the tempering time, but must be back through, the general tempering holding time of the workpiece is always more than one hour.
If carburizing 45 steel is used, hard and brittle martensite will appear in the core after quenching, losing the advantages of carburizing treatment. Now the use of carburizing process materials, carbon content is not high, to 0.30% core strength can reach very high, rarely seen in applications.
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