Papers by Keyword: T24 Steel

Abstract: A progressive increase of plant efficiency calls for new requirements of heat-resistantsteels used in the boiler and piping systems. In this paper, high-temperature creep behavior of T23and T24 steels were studied. Creep tests over a long period of time have been conducted for bothsteels at different temperatures. The creep mechanisms of the two steels have been clarified byanalyzing the minimum creep rate versus stress data. Besides, the creep rupture data from the creeptests were in good accordance with theoretical simulation on the basis of the CDM model over a longtime. Creep temperature has great effects on the rupture strength of the two steels. By creep ruptureexperiments and appropriate modelling, the high-temperature creep behavior can be well described.

Abstract: 7CrMoVTiB10-10 (T24) steel is recommended for fabrication of boiler components such as water walls, water panels or headers without post weld heat treatment (PWHT). The chemical composition of this steel and cooling conditions after welding influence the susceptibility to cracking in weld metal during and after welding. TEM investigations showed that in the as-welded microstructure mixtures of bainite and martensite were dominating. This has an important implication for technological properties.

Abstract: The T24 steel belongs to a new group of bainitic steels introduced currently to the power industry. Higher requirements connected with applying higher steam parameters in power units are the reason why the low-alloy steels used so far can no longer be applied. Therefore, new T24 steel has been developed in Europe on the basis of 10CrMo9-10 (10H2M) steel, which has been used in the power industry for many years, as a result of modification in its chemical composition. This modification consisted in introducing additions and microadditions of titanium, vanadium, boron and nitrogen into the base steel. As a result of the modification the new-found T24 steel is characterized by higher mechanical properties in comparison with the base steel, which allows to use the steel for tight shields in the new supercritical power units. The material for research was low-alloy bainitic T24 steel. Samples for examination were taken from a pipe section of the following size: outside diameter 44.5mm, wall thickness 7mm. Samples were isothermally aged in the air atmosphere, at the temperature of 580°C and at times up to 12 000 hours. Changes in the microstructure were observed and recorded by means of high-resolution electron microscope, JOEL JEM 3010. Identification of the precipitates was made using carbon extraction replicas and thin foils with the SAED method. The aim of research was the analysis of precipitation processes. They are extremely important in the context of long-term service and maintaining strength parameters above the minimum level. The tests were performed on T24 steel for the as-received condition (after heat treatment) and after 12 000 hours of ageing at the temperature of 580°C. The research made it possible to determine the morphology of precipitates. It also allowed to establish the sequence of precipitation process for the examined steel.

Abstract: The paper presents results of research on the influence of ageing on the microstructure and mechanical properties of T24 steel. The examined material was in the form of longitudinal samples taken from a pipe section (with the pipe size of 44.5x6.7 mm). The research is focused on degradation of the base material (T24 steel) where the steel samples, after initial heat treatment, were aged at the temperature of 580°C and time up to 6000hrs in a furnace with air atmosphere. This contribution summarizes the experimental results of mechanical and structural measurements and provides relations between them.