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Introduction
45# steel is a kind of medium carbon steel, it contains 0.42 - 0.50% of carbon, 0.17- 0.37% of silicon and 0.3-0.60% of manganese. It is often used to make parts in machinery, engine and construction industry. Heat treated steel 45# can be made into variety of components. In this article, an electron microscope and Section technique will be used to reveal microstructure and mechanical properties of heat treated 45# steel.
Physical Structure of Heat Treated 45# Steel
Under an optical microscope, heat treated 45# steel is found to be a mature pearlitic structure and a combination of ferrite and cementite which are widely dispersed in the microstructure (Fig1). The length of cementite particle mainly lies between 1-2 µm and that of ferrite particle lies between 1-7 µm.
Fig.1 Heat treated 45# steel microstructure under optical microscope
Mechanical Properties of Heat Treated 45# Steel
The mechanical properties of heat treated 45# steel can be generally evaluated by hardness test and tensile test. In this article, the Vickers test is performed to measure the hardness of 45# steel before and after heat treatment. After heat treatment, the hardness of 45# steel is 390HV (Fig2). In addition, tensile test is further employed to show theyield strength and ultimate tensile strength of 45# steel. The results show that the yield strength is 654 MPa, the ultimate tensile strength is 814 MPa, the elongation of 35# steel is 20.3% (Fig3).
Fig.2 Vickers hardness test of heat treated 45# steel
Fig.3 Tensile test results of heat treated 45# steel
Corrosion Resistance of Heat Treated 45# Steel
Corrosion resistance is an important property of 45# steel. Accelerated corrosion tests are performed to study the corrosion behavior of 45# steel. It shows that heat treated 45# steel exhibits superior corrosion resistance compared to untreated 45# steel. This is mainly due to the formation of a protective oxide layer on the surface of the steel during heat treatment.
Conclusion
In conclusion, heat treated 45# steel has a mature pearlitic structure, with ferrite and cementite widely dispersed in the microstructure. The hardness, yield strength and ultimate tensile strength of heat treated 45# steel are 390HV, 654 MPa and 814 MPa respectively. Heat treated 45# steel also shows superior corrosion resistance, mainly because of the formation of a protective oxide layer on the surface of the steel during heat treatment.
由此可见，热处理45＃钢具有成熟的珠光体结构，铁素体和水石渣在显微结构中被广泛分散。45＃钢的硬度，屈服强度和抗拉强度分别为390HV，654MPa和814MPa。热处理45＃钢还显示出优异的耐腐蚀性，这主要是由于热处理过程中钢面上形成的一层保护氧化物层的形成。
