Ferritic heat-resistant steel and method for production thereof

Abstract

A ferritic heat-resistant steel which comprises, in wt %, 1.0 to 13 % of chromium, 0.1 to 8.0 % of cobalt, 0.01 to 0.20 % of nitrogen, 3.0 % or less of nickel, 0.01 to 0.50 % of one or more elements selected from the group consisting of vanadium, niobium, tantalum, titanium, hafnium and zirconium, which form MX type precipitates, and 0.01 % or less of carbon, as constituting elements, the balance being substantially composed of iron and inevitable impurities, and has a metal structure wherein MX type precipitates are formed over the whole of grain boundaries and the surface within grains and M23C6 type precipitates are present on grain boundaries in an area percentage of 50 % or less. The ferritic heat-resistant steel exhibits excellent creep characteristics even at a high temperature exceeding 600 DEG C.

Description

technical field [0001] The present invention relates to ferritic heat-resistant steel and its manufacturing method. More specifically, it relates to a ferritic heat-resistant steel excellent in creep characteristics even at high temperatures exceeding 600° C. and a method for producing the same. Background technique [0002] Austenitic heat-resistant steels or ferritic heat-resistant steels are used as materials for high-temperature components, such as boilers and steam turbines for power generation, nuclear power generation equipment, and chemical industrial equipment, etc. Wait. Among them, ferritic heat-resistant steels are cheaper than austenitic heat-resistant steels, have a lower coefficient of thermal expansion, and have better thermal fatigue resistance, so they are often used as materials for high-temperature parts whose operating temperatures reach around 600°C. [0003] On the other hand, in recent years, thermal power plants have been researching high temperatu...

AI Technical Summary

Problems solved by technology

However, carbon is necessary to ensure the hardenability of ferritic heat-resistant steel, and if carbon is reduced alone, sufficient quenching will not be possible, and the effect of improving the strength due to the introduction of dislocations during quenching will be reduced.

From the above, it can be seen that ferritic heat-resistant steel with high creep strength for a long time at a high temperature exceeding 600°C has not been provided so far.

Images