Properties of creep resistant steels depend on composition, processing technology and parameters, termomechanical and heat treatment. In the case of thermomechanical treatment influencing parameters are temperature and deformation rate. This part of research was focused on the effect of additional rolling, including temperature and deformation rate on the microstructure and creep resistance of 10% Cr steel. Microstructural analysis and results of creep resistance revealed that additional rolling has practically no effect on creep resistance. However, larger deformation rate provides fine grained microstructure with better mechanical properties.
F.10 Improvements to an existing technological process or technology
COBISS.SI-ID: 1228714Purpose of this investigation was to determine optimal creep testing conditions, effect of heat treatment parameters on microstructure and creep resistance, define correlations between mechanical properties and creep resistance and define elements of microstructure affecting creep resistance. Results show, that first tempering temperature has practically no influence on the size and number of precipitates and thus no effect on time to rapture. Effect of second tempering is more pronounced and negative. Higher 2nd tempering temperature reduces number of precipitates, but makes them larger and interparticles distance, which leads to reduced creep resistance. The most direct effect is shown by austenitizing temperature. Increasing austenitizing temperature increases number of precipitates and reduces their size and distance. In this way up to 4-times better creep resistance was obtaind, indicating size and number of pecipitates as the most important constituents of the microstructure.
F.02 Acquisition of new scientific knowledge
COBISS.SI-ID: 1292970In the case of high Cr creep resistant steels the main microstructural components are martensitic matrix, primary and secondary carbonitides as well as non-metallic inclusions. Within this research it was found that the most critical component from the creep resistance point of view are Al2O3 non-metallic inclusions. Presence of such inclusion results in up to 3-times reduced creep resistance. By optimizing steel composition (mainly N and Nb content), parameters of ESR process and using proper termomechanical treatment number of non-metallic inclusions was greatly reduced and their type changed. At the same time finer and more stable precipitates were obtained leading to greatly improved creep resistance.
F.07 Improvements to an existing product
COBISS.SI-ID: 1293226