| Stainless steel is very popular since its inception, but the production of stainless steel needs a large number of nickel, and the world nickel resources reserves is insufficient to meet the demand of stainless steel. High nitrogen austenitic stainless steel (hereinafter referred to as the advent of high nitrogen steel) solved this problem, it is a kind of resource conservation stainless steel which use nitrogen, Mn partly displaced or completely replaced the nickel to save nickel element. Nitrogen is a strong austenitic stabilization element, and a small amount of nitrogen can achieve stability austenitic phase. Carbon, nitrogen joint action to make high nitrogen steel strength greatly raised, to room temperature difference, and the toughness of local corrosion resistant materials were improved.Domestic production in recent years has started to product high nitrogen steel, the current largest production is the generator protect ring steel Cr18Mn18N. But there are many problems with the production and application of high nitrogen steel, such as the joining of nitrogen, toughness of steel will reduce, sensitization will take place in intermediate temperature, second-phase separates out in high temperature, plastic brittle transition in low temperature and so on. This paper will focus on the organization performance of high nitrogen steel casting ingot, high temperature resistant thermoplastic, the rules of second phase separating, in addition to explore the rules of high nitrogen steel in low temperature ductile to brittle transition. The results of the study indicate that:1.Cr-Mn-N high nitrogen steel casting ingot has coarse grains, it is due to the high atomic diffusion speed of high content of Mn, C and N in high temperature. In the induction furnace there are serious gathering of more Cr, Mn, C, Si atoms in the crystal casting ingot branch intergranular slant segregation, except N atoms. Electricity slag remelting although can improve this kind of composition segregation and organizational inhomogeneity, but no effect to the grain refinement. Fe3C shaped perfectly round ball appeared in casting ingot of high nitrogen austenitic stainless steel, and connected to reticular shape.2. It is found that in the thermal simulation experiment Of Cr18Mn18N high nitrogen steel:In 1000-1100℃, it present low shrinkage and surface plastic zone is only 30%, the fracture is intergranular fracture And in 1150-1200℃, it present higher shrinkage and low surface deformation resistance, surface shrinkage rate is over 60% and present dimple fracture. The strength of the sample reduced as temperature increasing. And at the same temperature conditions, more the deformation rate is, the greater the tensile strength is.3. After the normal temperature tensile testing of the quenched forging sample, it is found that the brittle fracture of high nitrogen steel changed into ductile fracture as quenching temperature increased, carbide became smaller.4. After the observation of the fracture surface microstructure, it is found that the grain are abnormal bulky, and grain boundaries are fuzzy with the increase of temperature, the grain grow to coarse gradually. In 1100℃the metallographic vision of grain boundaries cannot be observed. Ferrite start to precipitate in 1200℃, there are a lot of ferrite and ferrite had grown up when it is 1300℃.5.During the studying of the law of Cr18Mn18N precipitation in different temperature, only Cr3C2, ferrite and a handful of TiN was observed, Cr2N has not been found. Separation material law and phase diagram does not conform to the state, from different condition obtained. In the thermodynamic equilibrium calculation results that represent phase change and phase composition with the condition of cooling or heating gradually But the heating and cooling speed in the experiment is faster. 6. The "V" thermosplasitic rule stems from the underlying tisssues. During the temperature 800℃to 950℃, Fe3C has dissolve in substrate, but Cr3C2 was not yet massively separate out. So, it has well plasticity. While the plastic will reduce during 1000℃to 1100℃for Cr3C2 not only separates from crystal boundary but from transgranular massively, and also the crystal grain seriously thick. When the temperature continues to elevate to 1150℃, Cr3C2 has dissolved, high nitrogen steel will be in well thermosplastic for it has been pure austenite area. The austenite substrate will separate out ferrite since 1200℃which will grow up along with temperature increment.7. High nitrogen austenitic stainless steel has the ductile to brittle transition phenomenon. The temperature of ductile to brittle transition is distinct for the different ingredient. And the temperature will raise along with the increase of nitrogen content. The ductile to brittle transition of Cr18Mn18 stainless steel in-110℃to-196℃, and Cr22Mn16N is-80℃to-110℃8. The ductile to brittle transition process of high nitrogen steel is dimple fracture→dreich dimple fracture→mixed type break→intergranular fracture. The element of nickel will increase austenite stabilizing degree. Nickle is good for the toughness of high nitrogen for it will reduce carbon separate out. Carbon and sulfide will separate out from grain boundary when it is not solution heat treatment sufficiently which will lead to material failure finally.
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