The Study Of Non-equilibrium Grain-boundary Segregation Of Stainless Steels

Non-equilibrium grain-boundary segregation has been investigated since 30 years ago, and has formed a complete theory system. It has been applied to explain intergranular embrittlement. In order to develop processing and service potential of materials, four following aspects have been carried out based on the theory of NGS in this paper:1. Unified mechanism of intergranular embrittlementAccording to the research results in articles, the unified mechanism of intergranular embrittlement for the temper embrittlement, intergranular corrosion embrittlement and intermediate temperature embrittlement has been pointed out based on non-equilibrium grain-boundary segregation. At the same time, it was pointed out that the intermediate temperature embrittlement is a kind of measurement uncertainty of mechanical property in high temperature tensile test.2. Non-equilibrium grain-boundary segregation mechanism of hot ductility for austenitic and ferritic stainless steelsWe calculate the critical time and effective time of the austenite and ferrite stainless steels based on the non-equilibrium grain-boundary segregation. It is successfully explained that the hot ductility of an austenitic steel decreases with decreasing strain rate while the hot ductility of a ferritic steel increases.3. Measurement uncertainty of metallic ductility in tensile tests:intermediate temperature embrittlement and strain rate embrittlementThrough analyzing the reduction of area of a variety of alloys with the change of the strain rate, founding that the reduction of area appears minimum with increasing strain rate, and the embrittlement achieves maximum, which is caused by non-equilibrium grain-boundary segregation of impurity atoms. Then puting forward the measurement uncertainty of metallic ductility in tensile tests based on the non-equilibrium grain-boundary segregation.4. Strain rate embrittlement for 17Cr ferritic stainless steelAfter solution treatment at high temperature of 1100℃ for 30min, the 17Cr ferritic stainless steel was measured by elevated temperature tensile test, which were tested at 500℃ and different strain rates from 10-6s-1 to 100s-1 and the element concentration at grain boundary has been tested by electron probe micro-analyser (EPMA). It is concluded that the embrittlement is induced by the grain-boundary segregation of S atoms.