Surface Mechanical Nanocrystallization And Thermal Stability Of High Nitrogen Austenitic Stainless Steel

High nitrogen austenitic stainless steel with high strength, good ductility and fracture toughness, creep resistance big, strong corrosion resistance and excellent low magnetic or non-magnetic properties, excellent performance, and thus the field of military industry, marine engineering and petrochemical in inside has a very good prospect. In particular the non-magnetic properties of HNS, both in non-magnetic drill collars, or in military equipment manufacturing and other areas have unique advantages. In addition, nitrogen generation of nickel stainless steel preparation techniques can greatly reduce dependence on nickel stainless steel production areas, and has very positive implications for strategic reserves of nickel scarce resources. Meanwhile, the relative scarcity of nickel elements, the low price of nitrogen also makes high-nitrogen austenitic stainless steel without nickel price advantage is obvious. With atmospheric nitrogen steel smelting technology matured and improved production costs of stainless steel can be effectively controlled, enterprise, large-scale production has become possible. Excellent performance and low price will promote rapid adoption of HNS applications and in various fields.Recently, it was discovered that the use of plastic deformation techniques can prepare metal nano-materials, to achieve improved surface properties of materials and expand its applications. Such a material surface or rolling mechanical polishing process may be obtained from the base to the surface layer of the grain size is gradually reduced to nanometer scale gradient nanostructures. Gradient type multistage build nanostructures not only excellent performance nanostructured materials can play out, but also to overcome the performance deficiencies of nanomaterials, is a new way of nano materials and applications. In this paper, thermoforming Fe-21Cr-17Mn-2.43Mo-Nb-0.83N nitrogen austenitic stainless steel for the study, it is subject to 1150℃, diffusion annealing, quenching 10h of water; then use to design embedded friction ball milling head on the plate of polished smooth conduct time was 4h, surface pressure rolling mill machinery processing 6h,8h, the pressure and the mechanical rolling mill after the sample processing different vacuum heat treatment temperature and time. Using X-ray diffraction, micro-hardness tester, scanning electron microscopy, transmission electron microscopy experimental means, before and after solution treatment, focusing on the front and back surfaces of the mechanical rolling mill and pressure vacuum heat treatment samples were characterized before and after the system explores the high nitrogen austenitic stainless nanostructured gradient mechanism and thermal stability, with some reference value for expansion of HNS applications.In this paper, the main research results are as follows:1) This study provides a surface layer of nanostructures prepared new technology-surface mechanical pressure grinding method, and can be prepared by this method gradient nanostructured metallic materials.2) high nitrogen austenitic stainless 0Cr21Mn17Mo2NbN0.83 after 240min,360min, 480min after mechanical grinding pressure treatment, the total thickness of the surface layer and the buffer layer nano refinement than 700μm, and the hardness value increased more than doubled;3) high nitrogen austenitic stainless steel 0Cr21Mn17Mo2NbN0.83 mechanical pressure on the surface of the grinding and subsequent heat treatment process, did not generate a new phase, which is always a single austenite;4) heat treatment temperature on the mechanical grinding of high nitrogen austenitic stainless steel pressure gradient nanostructures 0Cr21Mn17Mo2NbN0.83 greater impact, the temperature rises to 923 K, the surface of the nano-layer thickness will be reduced and the transition zone will reply recrystallization phenomenon;5)In less than 873K, the holding time of high nitrogen austenitic stainless 0Cr21Mn17Mo2NbN0.83 gradient nanostructure stability less affected, no significant changes in the microstructure, microhardness values will not change significantly, but at 873K for a long time (300min) insulation in the process, part of the organization of the transition zone of high strain rate will revert recrystallization occurs, the stability of the gradient will be affected nanostructures.