Corrosion Fatigue of Austenitic Stainless Steels for Nuclear Power Engineering
Significant structural steels for nuclear power engineering are chromium-nickel austenitic stainless steels. The presented paper evaluates the kinetics of the fatigue crack growth of AISI 304L and AISI 316L stainless steels in air and in corrosive environments of 3.5% aqueous NaCl solution after the application of solution annealing, stabilizing annealing, and sensitization annealing. Comparisons were made between the fatigue crack growth rate after each heat treatment regime, and a comparison between the fatigue crack growth rate in both types of steels was made. For individual heat treatment regimes, the possibility of the development of intergranular corrosion was also considered. Evaluations resulted in very favourable corrosion fatigue characteristics of the 316L steel. After application of solution and stabilizing annealing at a comparable ∆K level, the fatigue crack growth rate was about one half compared to 304L steel. After sensitization annealing of 316L steel, compared to stabilizing annealing, the increase of crack growth rate during corrosion fatigue was slightly higher. The obtained results complement the existing standardized data on unconventional characteristics of 304L and 316L austenitic stainless steels.
The intergranular fragility index — an engineering materials parameter
Abstract Residual elements affect the performance of engineering alloys through their ability to concentrate at grain boundaries, and this in turn may lead to certain forms of intergranular failure in various metallurgical situations. In order to identify the most potent residuals occurring in alloys of commercial purity, an evaluation exercise was conducted on a range of commercial engineering alloys which had exhibited various forms of intergranular failure in service. The results were assessed according to several behaviour categories: high temperature (e.g. creep, stress relief cracking), low temperature (e.g. temper brittleness) and reaction with the environment (e.g. intergranular stress corrosion cracking). For each such distinguishable category there exist a different hierarchy of effective elements. Here we introduce a generalized engineering parameter, the fragility index, which allows a rapid assessment of the quality of a steel cast in relation to the above specific behaviour categories and in terms of an assessed dominant impurity equivalent. Thus for the above behaviour categories this index is expressed as a tin or phosphorus or copper equivalent depending on the phenomenon. Another engineering parameter, the relative fragility, forms the basis of a screening test for identifying the most probable embrittling elements. These parameters may be derived either from metallurgical test data or from the appropriate model presented here which requires only a knowledge of the bulk composition and segregation data.
Numerical Simulation of Induction Heating Process of Continuous Casting Slab
Compared with traditional blazing furnace, the Continuous Casting-Direct Rolling is an advanced manufacturing steel technology, which can reduce energy waste, decrease pollution and enhance efficiency. The characteristics of steels during induction heating are complex, the change of material properties with temperature makes exact analysis methods very difficult to implement. Therefore, a powerful computer aided numerical tool (i.e., finite difference analysis) is selected to numerically model the induction heating process in this paper. The mathematic model coupling with electromagnetic field and thermal field was established, and it was solved by finite difference method (FDM), thus the slab temperature distribution and its variation with time were obtained, and the characteristics in whole induction heating process were studied. To validate the program feasible, the results were evaluated and compared with experiment results, which showed that the simulation results are reliable and effective. The skin effect in heating process from the two results was studied and demonstrated, the temperature change caused by different parameters such as the induced power intensity and the corner radian were also presented, which indicate that the slab temperature can be heated uniformly through adjusting these parameters, thus the continuous casting slab can meet the rolling requirement.