Experimental study on compression of 20CrMnTi gear steel

The compression test is carried out by Gleeble-1500 thermal simulation testing machine to find out the influence law of heating temperature and strain rate on the rheological stress of 20CrMnTi steel, analyze the microstructure change of isothermal compression, and then preliminarily analyze its deformation mechanism.

1.Selection of test equipment

Gleeble-1500 thermal simulation testing machine is adopted for compression test equipment. The main parameters are shown in Table 1:

Temperature range0~1200℃/8~1700℃
Displacement velocity0.001~1200mm/s
Heating speed0~10000℃/S
Maximum cooling rate140 ℃ / S (at 1000 ℃)
Maximum displacement±100mm

2.Gear steel sample material

The compression test material is gear steel 20CrMnTi. 20CrMnTi is alloy carburized steel with carbon content less than 0.25%. It is often used in small parts (diameter less than 30cm) with high hardness and wear resistance on the surface but low strength requirements. On the basis of low carbon steel, chromium, manganese, titanium, vanadium and other elements are added to refine the grain of alloy carburized steel and improve the hardenability. The contents of main elements are shown in Table 2.

Numerical value0.17-0.230.80-1.100.17-0.371.00-1.390.04-0.1≤0.035≤0.035

3.Preparation of gear steel sample

Processed by wire cutting φ 10mm × 15mm cylindrical bar, and then grind both ends flat on the grinder. In order to reduce the influence of friction, apply lubricant (graphite and oil) on both ends of gear steel sample during compression test.

4.Compression test scheme

The deformation rate is 10-2s-1, 10-1s-1100s-1 and 5s-1 respectively. The deformation temperatures are 900 ℃, 950 ℃, 1000 ℃, 1050 ℃ and 1100 ℃ respectively. The expected variable is 0.693.

In the compression test, the effects of deformation temperature, deformation speed and deformation amount on flow stress and microstructure during deformation are mainly studied. During the test, the gear steel sample is heated to 1200 ℃ at the heating rate of 10 ℃ / S (stage 1 in the figure), held for 5 minutes to fully austenitize it (stage 2 in the figure), then cooled to the deformation temperature at the rate of 5 ℃ / S (stage 3 in the figure), held for 15 seconds to eliminate the temperature gradient inside the gear steel sample (stage 4 in the figure), and finally isothermal forming at the deformation temperature (stage 5 in the figure). All gear steel samples shall be quenched rapidly after deformation. During deformation, argon is used for protection.

The gear steel sample quenched by compression test is cut along the axis, the cross section of the gear steel sample is ground with 100 ~ 1000 different types of sandpaper, and then the gear steel sample is polished on the polishing machine. The surface of the test gear steel sample is polished by P-2 metallographic gear steel sample polishing machine. The disc diameter is 200mm, the rotating speed is 1400R / min, and the working voltage is 380V. The polishing process is manually operated. When the section of the gear steel sample is as smooth as a mirror, the surface is eroded with 4% nitric acid alcohol and saturated picric acid aqueous solution + detergent, and the microstructure changes of the gear steel sample are observed on the scanning electron microscope.

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