Experimental materials and methods of heat treatment process on corrosion performance of Automobile Gears

1. Material preparation

The automobile gear steel 20mncr5, which is widely used, is selected as the experimental material. The energy dispersion X-ray fluorescence analyzer is used to analyze the composition of the prepared test material. The results are shown in Table 1, which meets the composition design requirements of the material.

2. Material heat treatment

After forging at 1200 ℃, the above materials are heat treated by normalizing and isothermal annealing respectively.

Normalizing process: heat the forged test material to 940 ℃ for 1 h, and then conduct air cooling.

Isothermal annealing process: heat the forged test material to 940 ℃ for 0.5 h, then isothermal at 630 ℃ for 1 h, and then air cooling.

3. Material corrosion test

For the salt spray corrosion test of test materials, the test materials after heat treatment shall be cut into 2 cm respectively × 1 cm × 0.5 samples of CM were 3 pieces, then the samples were pre treated by grinding and degreasing. Then the sample plane was 25 degrees in the vertical direction and placed in the FDYE-03E type salt spray testing machine. The salt spray concentration was 3.5wt%, the salt spray temperature was (23 + 1) centigrade, the spray pressure (0.75 + 0.05) MPa, and the sedimentation volume 0.05mL/ (H cm2), intermittent spraying method was adopted. After 72 h salt spray test, the surface corrosion morphology was observed on leitz-mm6 optical microscope.

For the full immersion corrosion test of the test material, first remove the surface oxide with 200 ~ 500 mesh sandpaper, then fully immerse the test material after heat treatment in 0.6 mol / L NaCl solution for uniform corrosion for 240 h, take out the sample every 12 h, wash it with distilled water for 3 times and then dry it, and quickly weigh and record the mass loss of the material with a precision electronic balance, Draw the mass loss rate time curve.

The electrochemical corrosion test of the test material is carried out with a three electrode system. The auxiliary electrode is platinum black electrode, the reference electrode is calomel electrode, the electrolyte is 0.6mol/l NaCl solution, and the working electrode is the electrode prepared after heat treatment of the test material. When making the working electrode, one surface of the sample shall be ground flat as the test surface, and the electrode lug (copper wire) shall be welded on the other surface. All surfaces except the test surface shall be completely sealed with paraffin. The electrochemical workstation is lk98b Ⅱ microcomputer electrochemical analysis system. After 180 s of potentiostatic (- 1.0V) polarization to remove surface oxides, Tafel curve test was carried out at 25 ℃ and 0.001v/s scanning speed.

Scroll to Top