The Aging Study On Microstructure And Properties Of High Nitrogen Austenitic Stainless Steel

At present, high nitrogen austenitic stainless steel becomes one of the most popular materials to be studied in the world, which is largely due to its excellent mechanical properties and corrosion resistance. However, the poverty of nickel resources restricts its further development. In order to solve this problem, the nitrogen element in high nitrogen austenitic stainless steel is used to replace nickel element, leading to a remarkably reduce in production costs. What’s more, there are many advantages of the high nitrogen steel alloying process that completed through the addition of nitrogen element. Unfortunately, brittle fracture is more liable to occur in low temperature, resulting from the increase in nitrogen content. In addition, during the high-temperature heat treatment of the high nitrogen steel, carbon-nitrogen compounds and intermetallic compounds which exert an effect on material properties can precipitate from the austenite phase, resulting in a reduction in the stability of the austenite phase. Therefore, it is of great significance to conduct the research about the precipitation behaviour, as well as about its effect on properties of the high nitrogen steel.In this paper, the effect of solid-solution and aging behaviour on the micro structure and properties of 0Cr21Mn17Mo2NbN austenite stainless steel is primarily researched by various test methods. The conclusions obtained through analysis of the experimental results are shown as follows:1.There was a transition of the matrix structure to the austenite after the solid-solution treatment of 0Cr21Mn17Mo2NbN austenite stainless steel. When the aging treatment was conducted, it was found that nitride precipitation behaviour occurred with the upper limit temperature of 950～1000℃, along with the range of the lower limit temperature from 600℃～650℃. The mos sensitive temperature of nitride precipitation is in the temperature range of 750℃～800℃.2. After the solid-solution treatment of 0Cr21Mn17Mo2NbN austenite stainless steel, the main phase that can precipitate in every temperature range is (Cr, Fe, Mn)2(N, C) (M2N and σ), of which the M2N phase was mainly composed of Cr2N with a hexagonal closepacked structure. Following the reaction:γâ†'σå'ŒÎ±-Feâ†'σ, σ phrase of a cubic structure precipitated along with Cr2N phrase, and it would not appear until the aging time was long enough.3. With the completion of 0Cr21Mn17Mo2NbN austenite stainless steel aging treatment, Rockwell hardness value of the aging is larger than that of the solid solution state. During isothermal aging at 800℃, the general trend of hardness curve firstly rose and then declined, finally rose once more, with maximum hardness value reaching 40.1HRC. With aging temperature rising from 700℃ to 900℃, the hardness firstly increased and then decreased, what’s more, it reached a maximum value in the temperature range of 750℃-800℃.4. The steel strength and toughness was significantly improved than the original samples after the solid-solution treatment. During the isothermal aging process, the steel strength showed normal distribution features which presented firstly a increase and then a decrease, while the roughness took on a continuously rising trend.