Study on the effect of different heat treatment processes on the microstructure and properties of 45 # steel

Through different heat treatment processes, the changes of microstructure and mechanical properties of 45# steel were studied, and the best heat treatment process was found. The results show that different heat treatment processes have a certain influence on the microstructure and properties of 45 # steel. When the quenching temperature is 800 °C, the mechanical properties are the best, and the martensite structure is finer.
The cost performance of 45 # steel is relatively good. It belongs to carbon structural steel and has been widely used in industrial production. Therefore, it is particularly important to study the related properties of 45 # steel. In this paper, by changing the heat treatment process system, to find out the 45 # steel structure to achieve the best performance of a heat treatment process.

1. Test materials and methods

1.1 Test materials

In this experiment, 8 samples of 45 # steel test samples, 4 % nitric acid alcohol and alcohol were selected. The chemical composition of the samples was mainly: C: 0.43 %, Si: 0.24 %, Mn: 0.66 %, P: 0.03 %, S: 0.03 %, Ni: 0.22 %, Cu: 0.23 %, Fe: residual.

1.2 Test equipment

Heating equipment : box resistance furnace; tissue observation equipment : upright metallographic microscope. Hardness testing instrument : automatic Rockwell hardness tester.

1.3 Test method

Divide 8 samples of 45 # steel into four groups, with two samples in each group. Heat them to 760 ℃, 780 ℃, 800 ℃, and 830 ℃ respectively, and then hold them for 30 minutes. Quench these samples in water; Afterwards, one sample from each group was subjected to corrosion and its structure was observed. The other sample was subjected to hardness testing to obtain the hardness value of the sample, and the four groups of samples were subjected to the same repeated operation.

2. Test results and analysis

2.1 Mechanical properties analysis

Table.1 Rockwell hardness value of 45 # steel after quenching

Heating temperature/°C	Cooling method	Average hardness value/HRC	Average strength value/MPa
760°C	Water-cooling	33.9	801.143
780°C	Water-cooling	55.2	909.687
800°C	Water-cooling	59.3	1288.211
830°C	Water-cooling	58.1	1176.347

From Table 1, it can be seen that the hardness obtained is different with different heat treatment processes. The four samples were quenched in water and heated at 760 °C, 780 °C, 800 °C and 830 °C respectively. The hardness values of the samples were 33.9HRC, 55.2HRC, 59.3HRC and 58.1HRC respectively, and the average strength values were 801.143 MPa, 909.687 MPa, 1288.211 MPa and 1176.347 MPa respectively. It can be known from the above data that when the quenching heating temperature is 800 °C, the hardness and strength of 45 # steel are larger. This is because the microstructure contains a small amount of ferrite, which is dispersed in the matrix and inhibits the growth of austenite. Therefore, the obtained martensite is relatively small, which produces the effect of fine grain strengthening.

2.2 Metallographic microstructure analysis

The 45 # steel is quenched by water, and different quenching temperatures will get different structures, so the hardness and strength values will be different. When the quenching temperature is 760 °C, there is more ferrite in the microstructure. As the temperature increases, the ferrite gradually decreases and the martensite structure gradually increases. When the quenching temperature is 800 °C, the martensite structure is finer, which is because ferrite hinders the growth of austenite. The martensite grain structure at 830 °C is relatively larger.

3. Conclusion

• (1) Different heat treatment processes have a certain influence on the properties of 45# steel. When the quenching temperature is 800 °C, the mechanical properties are the best.
• (2) Different heat treatment processes have a certain effect on the microstructure of 45# steel. When the quenching temperature is 800 °C, the obtained martensite structure is finer.

Author: An Shuaijie