On Ingots Quality Of High Nitrogen Stainless Steel Under High Pressure

As an important alloying element, nitrogen can improve the mechanical, such as yield strength and tension strength, corrosion and wear properties of high nitrogen steel greatly, which can be only obtained if nitrogen remains in solid solution after quenching or is precipitated as coherent and fine chromium nitride particles after tempering.Now the research of HNS in high pressure condition is few. High-pressure metallurgy as one of the important direction for the future development of HNS, study of casting quality solidified under high pressure is especially important. The nitrogen behavior in the solidification process of molten steel and the microstructure and the distribution of nitrogen in the ingot are analyzed.The research uses thermodynamic software Fact Sage to calculate the phase diagrams of Cr12 N alloy under high pressure, and the results are in agreement with the experimental ones. With the increasing of nitrogen pressure,nitrogen solubility in solid phase increases, and the rate decreases above 0.6MPa. The ? and gas+? phase area has a linear relation with the (P_N2)^1/2. The changes of the solidification under high pressure depend on the balance between the solid phase, chromium nitride and nitrogen gas. High pressure promotes the stability of Cr N phase which is precipitated instead of Cr2 N above0.6MPa.Simulation results of high-pressure solidification show that the nitrogen concentration in steel distributes more uniformly with the increasing nitrogen pressure.The mechanism of nitrogen movement with the increasing pressure is studied theoretically. Using software Fact Sage, the partition coefficient of nitrogen is calculated which has a lot to do with the nitrogen distribution in steel.The experimental results show that high pressure can fragment the carbide along the grain boundary. Both the total and interstitial nitrogen concentration increase with increasing pressure, thus improving the comprehensive performance.