Study on Vacuum Enabling Weak Nitrogen Carbon Inclusions

The operating temperature is the main factor affecting the thickness of the penetrating layer and the composition of carbonitrides. Similar to other gas nitrocarburizing methods, the temperature of the vacuum pulse nitrocarburizing method can also be used at 480°C and 570°C. According to our tests and considering the actual hardness of the mold substrate, our working temperature is set at 510°C-560°C. °C.

The time of infiltration is based on the research of “Vacuum Pulse Nitriding Process Research” of our institute. The time increases, the hardness increases, and when the compound layer appears, the hardness increases more obviously and the penetration layer also deepens. Therefore, the time of infiltration depends on different requirements and is set at 416h. The ratio of pressure between C and NH. IV-46 According to the data and our experiments show that the nitriding speed and carburizing ability mainly depend on the relationship between C pressure and positive ratio. , Co: too little, the effect is not obvious; too much C02, the brittleness of the penetrating layer increases, in the C pressure: NH3 two (510): (95-90), can obtain a higher hardness value.

The pulse time test shows that the pulse time is too long, the depth of the penetration layer is not significant; the pulse time is too short, the surface brittleness of the sample increases, and the effect is good at 1.52.smin. Furnace pressure is set at a higher upper limit (at 0 to 0, 1 MPa), and the depth and hardness of the infiltration layer are better. The lower limit of the furnace pressure is that the vacuum layer has a high hardness and a high hardness.

The experimental example has been sent to us by our customer for n pieces of H13 forging die, the size is 180x150ltln which has been quenched and ten times of fire treatment, but due to equipment failure caused by low hardness and surface decarburization, after testing as 42 and 43HRc customer requirements, do not re-quench To improve the hardness, the best in 4852HRc.

Through analysis, it is considered that vacuum pulsing with low-temperature nitrocarburizing can improve the microstructure and improve the hardness. After soliciting the approval of the customer, the process is as follows: temperature T (°C) time T vacuum degree, process parameters: adopted (515°C xIOh 560°C x 6h) The second stage of co-permeation, according to C02 is 10% ratio, the pulse period of 2 minutes, the furnace pressure limit of a 0.olMpa, the lower limit of a 0.08Mpa.

After treatment, the test result was: 5657 HRC, and after treatment under vacuum conditions at 540°C x 6 h, the result was: 5354HRc, accepted by the customer. After actual use, the working conditions are the same as those of direct quenching and tempering (hardness index 48 “52HRC”), and the service life is the same, so as to achieve the purpose of reducing mold scrap.

When the low-temperature nitrocarburizing of the vacuum pulse is analyzed, a small amount of carbon atom is also infiltrated into the nitrogen, and the resulting Fe—Fe:(Nc) compound has good wear resistance, corrosion resistance and other properties. Using a two-stage vacuum pulse low-temperature nitrocarburizing process, the lower surface temperature (520 ± 10°C) and high nitrogen and carbon potential infiltration are used to make the surface obtain a higher concentration of nitrogen and carbon, and then increase the temperature of co-permeability (560 persons). 10°C) Reducing the nitrogen-carbon potential, so that the surface of the nitrogen atoms, carbon atoms to accelerate inward diffusion, and nitrocarburizing reaction diffusion, according to the first law of diffusion: dm = a Ddf.de / dxdt type: dm pass The physical quantity of the cross section, the odd-diffusion-diffusion, the df-cross-sectional area, the dt-time, and the dc/dx-concentration gradient are related by the cross-sectional mass and the diffusion coefficient, the cross-sectional area, the concentration gradient, and the time.

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