PRODUCT CATEGORIES

Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

1Cr18Ni9Ti stainless steel vacuum nitriding

1Cr18Ni9Ti austenitic stainless steel has strong corrosion resistance in air, seawater, acid, alkali and salt solution, etc., and high temperature resistance, good processability, and is widely used in petrochemical, machinery manufacturing, food hygiene and Metal structural materials in medicine and other fields. However, the surface hardness is low, wear-resistant, and the service life is short, which also limits the scope of its use. Nitrogen infiltrating the steel surface and the nitrides formed by iron and its alloys have the advantages of stable chemical properties, high hardness and good wear resistance. Therefore, surface nitriding of stainless steel is an effective method to improve its surface hardness and wear resistance. Gas nitriding has the advantages of simple process, wide adaptability, low cost, small deformation and uniform nitriding. It is still a difficult problem to obtain a nitride hardened layer with high hardness, high wear resistance and a certain thickness on the surface of stainless steel in a short time. Vacuum nitriding has the advantages of high surface activity, good quality of the nitriding layer, and short nitriding time.

Vacuum nitriding process

1.Materials

The material is a medium 15 mm 1Crl8Ni9Ti austenitic stainless steel bar, cut into a cylindrical sample of φ15 mm x 6 mm.

The photographic sandpaper is ground from coarse to fine and cleaned with alcohol.

Vacuum pulse nitriding was carried out in a tube furnace, using ammonia gas as the nitriding medium, the nitriding temperature was 580C, the nitriding time was 8 h, and the nitriding pressure was 50-60 kPa. The concrete method is: load the sample into the furnace and carry out vacuuming, and the vacuum degree is 5～20 Pa, then the furnace temperature is raised to the nitriding temperature and the vacuum pump is closed for 30 minutes, and then ammonia gas is introduced into the furnace to carry out nitriding for 30 minutes. min, followed by vacuuming for 30 min, and then filling with ammonia gas, repeating the above process, and performing periodic pumping/inflating pulse nitriding to the specified time.

Figure 2 shows the XRD patterns of the surface of the 1Cr18Ni9Ti austenitic stainless steel as-is and nitrided. It can be seen from the figure that the surface phase of the stainless steel without nitriding is only γ-Fe phase. After vacuum pulse nitriding, the γ-Fe diffraction peak on the surface is weakened, and the nitride phases y’-Fe, N and γ-Fe appear at the same time. CrN, it can be seen that the surface phase of 1Cr18Ni9Ti austenitic stainless steel after vacuum pulse nitriding is mainly composed of γ-Fe, y’-Fe, N and CrN. 1Crl8Ni9Ti stainless steel is a single-phase austenite solid solution in which nitrogen has a large solid solubility. During vacuum nitriding, a nitrogen-containing solid solution is first formed. With the nitriding, the solid solution gradually transforms into y’-FesN. The CrN phase appeared on the surface during the vacuum pulse nitriding process, mainly because the nitrogen-dissolving ability of the γ phase decreased during the nitriding cooling process.

Figure 3 shows the metallographic structure of the infiltrated layer of 1Cr18Ni9Ti austenitic stainless steel after vacuum pulse nitriding at 5609 °C for 8 h. It can be seen from Figure 3 that after nitriding 1Cr18Ni9Ti austenitic stainless steel, a nitriding layer of a certain thickness is formed, and the thickness of the nitriding layer is about 200 um. For the 1Cr18Ni9Ti austenitic stainless steel, vacuum pulse nitriding is used, and the vacuum is continuously evacuated. The adherents on the surface of the stainless steel are discharged, the atmosphere in the furnace is purified, the surface activity is increased, and the gas is continuously circulated, and the atmosphere in the furnace is constantly replaced, which increases the activity. Therefore, vacuum pulse nitriding can greatly shorten the nitriding time of stainless steel and improve the quality of the surface nitriding layer.

2.Hardness

Figure 4 shows the hardness distribution of nitriding layer after vacuum pulse nitriding of 1Cr18Ni9Ti austenitic stainless steel. It can be seen from the figure that the surface hardness of 1Cr18Ni9Ti austenitic stainless steel after nitriding is between 1 100 and 1 200 HV, and the hardness of the matrix is 290 to 310 HV. The layer depth reaches 160 um, and the hardness decreases slowly from the surface to the inside. This shows that vacuum pulse nitriding can greatly increase the surface hardness of stainless steel. The reason is that a large amount of nitrides are produced on the surface of 1Cr18Ni9Ti austenitic stainless steel after vacuum pulse nitriding. At the same time, nitrogen has a large solid solubility in austenite, which has a solid solution strengthening effect, so that the hardness decreases slowly along the direction of the nitrided layer.

3.Heavy wear and tear

Table 2 shows the weight loss of the original 1Cr18Ni9Ti austenitic stainless steel and the vacuum nitriding sample after the load is 200N, the rotational speed is 200r/min, and the wear is 30min. It can be seen from the table that the weight loss of the stainless steel without nitriding is 74.9 mg, while the weight loss of the stainless steel after vacuum nitriding is only 9.38 mg, which is about 1/8 of the weight loss of the original 1Cr18Ni9Ti austenitic stainless steel after vacuum infiltration. The wear resistance after nitrogen is greatly improved. This is mainly because the nitriding layer of 180 μm is obtained after nitriding the stainless steel, and the hardness is as high as 1100HV or more. Therefore, the wear loss of the stainless steel after nitriding is significantly reduced compared with that of the non-nitriding sample, and the wear resistance is significantly improved.

4.Conclusion

1) The surface phase of 1Cr18Ni9Ti austenitic stainless steel after 560 C vacuum pulse nitriding for 8 h is composed of y-Fe, y’-FeN and CrN, and a nitrided layer with a thickness of about 200 μm is formed. The use of vacuum pulse nitriding can greatly shorten the nitriding time of stainless steel and improve the quality of the surface nitriding layer.

2) The surface hardness of 1Cr18Ni9Ti austenitic stainless steel after vacuum pulse nitriding is between 1100-1200HV, which is about 4 times higher than that of the substrate. When the wear test is carried out under the same conditions, the wear weight of the stainless steel sample after vacuum pulse nitriding is about It is 1/8 of the original wear loss, the wear scar width is greatly reduced after nitriding, and the wear resistance is greatly improved.

Selection of vacuum nitriding equipment: The RVN series vacuum nitriding furnace produced by SIMUWU is a high-quality product for the vacuum nitriding process of tooling and molds. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum nitriding process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing.