Enhanced high-temperature mechanical properties of ARAA by thermo-mechanical processing

We studied effects of thermo-mechanical processing (TMP) on microstructure and mechanical properties of the Korea RAFM steel, ARAA, as a feasibility study for enhancement of creep-resistance. Austenitized ARAA plates were subjected to three different TMP schedules: i) 20% hot-rolling at 1000 degrees C, ii) 20% hot-rolling at 700 degrees C, and iii) 20% hot-rolling at 700 degrees C followed by 30% cold-rolling, all of which were then subjected to tempering at 750 degrees C. 20% hot-rolling resulted in strengthening effects on the as-tempered ARAA in both tensile and short-term creep tests, the extents being greater for that rolled at lower temperature. However, additional cold-rolling promoted recrystallization of tempered martensite structure, leading to a significant loss of strength. Enhanced tensile and creep strength of the TMPed ARAA can be attributed to the larger number of fine MX carbides and slightly higher density of dislocations. It is concluded that ausforming, which is simple and readily applicable to industry, is a method that can effectively improve the high-temperature creep strength of ferritic-martensitic steels without a loss of impact toughness.