Coarse grains occurred in the non-quenched-tempered steel 48MnV (% : 0. 45 ~0. 51C
0. 90 ~ 1. 20Mn
0. 05 〜0. 10 V ) produced by 100 t EAF-LF ( VD) -300 mm x 320 mm casting-continuous rolling process. As added 0. 030% 〜0. 050% Ti in steel
the rating of grain in 125 mm x 125 mm square bar rolled with 13 passes was 3 ~ 4 ; the rating of grain in Φ141 mm roun(i bar ( contained 0. 030% 〜0.053% Ti) rolled with 9 passes was 4 ~5; but as added 0. 018% ~0. 035% Ti and 0. 021 % 〜0. 029% Nb in steel
the rating of grain in Φ141 mm round bar rolled with 9 passes was 5. 5 〜6. 5 in order to obviously increase strength and toughness of steel.