Thick-walled stainless steel pipes have many advantages, such as resistance to high-temperature oxidation, strong corrosion resistance, good plasticity, and excellent weldability, making them widely used in various civilian and industrial fields. However, due to the relatively low hardness and wear resistance of stainless steel, the application of thick-walled stainless steel pipes is limited in many situations, especially in environments where multiple factors, such as corrosion, wear, and heavy loads, coexist and influence, significantly shortening the service life of stainless steel materials. So, how can the surface hardness of thick-walled stainless steel pipes be increased?
Currently, there is a method to increase the surface hardness of thick-walled stainless steel pipes through ion nitriding to improve wear resistance and thus extend their service life. However, austenitic stainless steel pipes cannot be strengthened through phase transformation, and conventional ion nitriding, due to its high nitriding temperature (generally above 500℃), results in the precipitation of chromium nitrides in the nitrided layer, leading to chromium depletion in the stainless steel matrix. While significantly increasing the surface hardness of thick-walled stainless steel pipes, the surface corrosion resistance is severely weakened, thus losing the inherent characteristics of thick-walled stainless steel.
Using a DC pulse ion nitriding equipment to perform low-temperature ion nitriding treatment on austenitic steel pipes can enhance the surface hardness of thick-walled stainless steel pipes while maintaining their corrosion resistance essentially unchanged. This increases the wear resistance of the thick-walled stainless steel pipes, and the data comparison with samples treated with ion nitriding at conventional nitriding temperatures shows a significant improvement.
The experiment was conducted in a 30kW DC pulse ion nitriding furnace. The DC pulse power supply parameters were adjustable voltage from 0-1000V, adjustable duty cycle from 15%-85%, and frequency of 1kHz. The temperature measurement system used an IT-8 infrared thermometer. The sample material was austenitic 316 thick-walled stainless steel pipe, with a chemical composition of 0.06% carbon, 19.23% chromium, 11.26% nickel, 2.67% molybdenum, 1.86% manganese, and the remainder being iron. The sample size was Φ24mm × 10mm. Before the experiment, the sample was polished with water-based sandpaper to remove oil stains, then cleaned with alcohol and dried before being placed in the center of the cathode disk and evacuated to below 50Pa.
Ion nitriding of austenitic 316 stainless steel welded pipes using both low-temperature and conventional nitriding temperatures can achieve a microhardness exceeding 1150 HV. Low-temperature ion nitriding results in a thinner nitrided layer with a higher hardness gradient. After low-temperature ion nitriding, the wear resistance of austenitic steel can increase by 4-5 times, while its corrosion resistance remains unchanged. While ion nitriding at conventional temperatures can also enhance wear resistance by 4-5 times, the precipitation of chromium nitrides on the surface of thick-walled austenitic stainless steel pipes can reduce their corrosion resistance to some extent.
Post time: Apr-15-2026