Grain-refining ability of ultra-rapid annealing for low-carbon steel: severe plastic deformation

Abstract

To study the grain-refinement ability of ultra-rapid annealing (URA), heating rates from 0.3°C/s up to 1200°C/s with conventional annealing and URA in the intercritical temperature range were performed on severely deformed low-carbon steel. The results show that recrystallization in conventional annealing is completed below the critical temperature of Ac1 without grain refinement. URA up to 730°C at a heating rate of 200°C/s causes grain refinement due to full interaction between the recrystallization and phase transformation. URAs up to 730°C with heating rates of 600°C/s and 1000°C/s lead to partial grain refinement and no grain refinement, respectively. During annealing with a heating rate of 1200°C/s, the temperature should reach 760°C for the occurrence of recrystallization leading to grain refinement. The sample URAed at 600°C/s up to 730°C shows the maximum hardness due to fine grains being partially formed. Keywords: conventional annealing, ultra-rapid annealing, interaction, severe plastic deformation Za {tudij sposobnosti udrobnjenja zrn pri zelo hitrem`arjenju, so bile uporabljene hitrosti segrevanja od 0,3°C/s do 1200°C/s pri obi~ajnem in zelo hitrem`arjenju v interkriti~nem temperaturnem obmo~ju na mo~no deformiranem malooglji~nem jeklu. Rezultati ka`ejo, da je rekristalizacija pri konvencionalnem`arjenju zaklju~ena pod kriti~no temperaturo Ac1 brez udrobnjenja zrn. Zelo hitro`arjenje do 730°C pri hitrosti ogrevanja 200°C/s povzro~i udrobnjenje zrn, zaradi polne interakcije med rekristalizacijo in fazno premeno. Zelo hitro`arjenje do 730°C , s hitrostjo ogrevanja 600°C/s in 1000°C/s povzro~i delno udrobnjenje zrn oz. udrobnjenja zrn ni. Med ogrevanjem s hitrostjo 1200°C/s je potrebno dose~i temperaturo 760°C, da se pojavi rekristalizacija, ki povzro~i udrobnitev zrn. Vzorec po zelo hitrem`arjenju z 600°C/s do 730°C ka`e maksimalno trdoto zaradi delnega nastanka drobnih zrn.