How to increase the hardness of the surface of thick-walled stainless steel pipes

How to increase the hardness of the surface of thick-walled stainless steel pipes Thick-walled stainless steel pipes have many advantages, such as high-temperature oxidation resistance, strong corrosion resistance, good plasticity, excellent welding performance, etc., and are widely used in various civil industrial fields. However, due to the low hardness and low wear resistance of stainless steel, its application in many occasions will be limited, especially in an environment where multiple factors such as corrosion, wear, and heavy load exist and affect each other, the service life of stainless steel materials will be significantly shortened. So, how to increase the hardness of the surface of thick-walled stainless steel pipes? Now there is a method to increase the surface hardness of thick-walled pipes by ion nitriding to improve wear resistance and thus extend its service life. However, austenitic stainless steel pipes cannot be strengthened by phase change, and conventional ion nitriding has a high nitriding temperature, which is higher than 500°C. Chromium nitrides will precipitate in the nitriding layer, making the stainless steel matrix chromium-poor. While the surface hardness is significantly increased, the surface corrosion resistance of the pipe will also be severely weakened, thereby losing the characteristics of thick-walled stainless steel pipes. The use of DC pulse ion nitriding equipment to treat austenitic steel pipes with low-temperature ion nitriding can enhance the surface hardness of thick-walled steel pipes while keeping the corrosion resistance unchanged, thereby increasing their wear resistance. Compared with the ion nitriding treated samples at conventional nitriding temperature, the data comparison is also very obvious. The experiment was carried out in a 30kW DC pulse ion nitriding furnace. The parameters of the DC pulse power supply are adjustable voltage 0-1000V, adjustable duty cycle 15%-85%, and frequency 1kHz. The temperature measurement system is measured by an infrared thermometer IT-8. The material of the sample is austenitic 316 thick-walled stainless steel pipe, and its chemical composition is 0.06 carbon, 19.23 chromium, 11.26 nickel, 2.67 molybdenum, 1.86 manganese, and the rest is iron. The sample size is Φ24mm×10mm. Before the experiment, the samples were polished with water sandpaper in turn to remove oil stains, then cleaned and dried with alcohol, and then placed in the center of the cathode disk and vacuumed to below 50Pa. The microhardness of the nitrided layer can even reach above 1150HV when ion nitriding is performed on austenitic 316 stainless steel welded pipes at low temperatures and conventional nitriding temperatures. The nitrided layer obtained by low-temperature ion nitriding is thinner and has a high hardness gradient. After low-temperature ion nitriding, the wear resistance of austenitic steel can be increased by 4-5 times, and the corrosion resistance remains unchanged. Although the wear resistance can be enhanced by 4-5 times by ion nitriding at conventional nitriding temperature, the corrosion resistance of austenitic stainless steel thick-walled pipes will be reduced to a certain extent because chromium nitrides will precipitate on the surface. Post time: Aug-23-2024