Study On Preparation Of Nanostructure 430L Stainless Steel Materials By HEBM-SPS

In this thesis, the preparation of 430L nanocrystalline stainless steel powders by high energy ball milling was investigated at first. The crystalline grain size was calculated according to the test results of XRD. The average particle size of milled 430L stainless steel powders were analyzed by Mastersizer 2000. The morphology and microstructure of samples was observed by SEM. The experiments for preparation of 430L nanocrystalline stainless steel powders with different weight ratio of balls to powders and the same ball milling time were performed. The research results indicated the crystalline grain size of the powders reduced rapidly with the increasing of weight ratio of balls to powders, the average crystalline grain size reduced from 32nm to 23nm as weight ratio of balls to powders increased from 5:1 to 20:1. As the weight ratio of balls to powders increased further, the crystalline grain size reduced slowly. It was 19nm as the weight ratio of balls to powders reached to 30:1. The experiments with various ball milling time and the same weight ratio of balls to powders were also performed. The research results showed that the crystalline grain size of the powders decreased drastically at the early stage (0-10h), which rapidly reduced to 23nm, then decreased slowly. After 50h ball milling, it reached to 15nm. The observation results of SEM and MS2000 indicate that cold welding, fragmentation and work harden occurred during high energy ball milling. The changes of particles size of 430L stainless steel powders could be divided into four stages: at the initial stage (0-10h), the particle size of the powders increased quickly because of cold welding, and the average particle size of the powders reached to 330μm; in the second stage(10-20h), the particle size of the powders decreased because of fragmentation, the average particle size reduced to 100μm.; in the third stage (20-30h), the particle size of the powders has less change, the average particle size was about 98μm, the dynamical equilibrium was held between cold welding and fragmentation; in the final stage(30-50h), the particle size of the powders decreased slowly, the average particle size reduced to 55μm, the dominative role was also fragmentation at this stage .Nanocrystalline 430L stainless steel cermets produced using spark plasma sintering was also investigated. Bulk densities of the samples were determined by Archimedes method in distilled water, the hardness and the tensile strength were measured using Vickers hardness tester and MTS810 materials testing machine, the crystalline grain size was observed by TEM. Nanocrystalline 430L stainless steel powders prepared by high-energy ball milling(weight ratio of balls to powders 20:1 for ball milling time of 30h) were sintered by spark plasma sintering at 800-1000℃for holding time of 3 to 15min. Comparison with sample sintered at 800℃, the properties of samples sintered at 900℃has improved much. After having sintered at 900℃for...