The test steel 42CrMoTiB and RE microalloying steels 42CrMoTiBRE (/% : 0.41 -0.43C

0. 36 ~0. 38Si

0.59~0.72Mn

0.018 ~ 0.020P

0.005 ~0.010S

1.08-1. 13Cr

0. 16~0. 19Mo

0. 06 ~ 0.08Ti

0. 003 ~ 0.004B

0~ 0. 020Ce or Sm

0.001 3 ~0.001 5 T [O

]

) are melted by an 150 kg vacuum induction furnace

casting average cross section 165 mm x 165 mm ingot then forged to 120 mm x 120 mm billet. The effect of Ce or Sm on inclusions and mechanical properties of steel 42CrMoTiB forged billet is studied. Results show that as compared with non-adding RE steel 42CrMoTiB

the inclusion amount in steel 42CrMoTiBRE with adding 0. 18RE ( R

E content in steel- 0. 019% ~0. 020% ) decreases obviously

the inclusion rating units of heavy series A

B and D respectively decrease from 0. 5

2. 0 and 0. 5 to 0

0 ~ 0. 5 and 0

and that of thin series respectively decrease from 0. 5

1. 5 and 2. 0 to 0

1. 0 and 1. 0; The morphology of inclusions in steel is modified by adding RE to form spherical RE oxysulfide ； and the plasticity and toughness of steel markedly increase by adding RE

as compared with non-adding RE steel 42CrMoTiB the transverse reduction of area (Z) and Charpy V-notch impact energy of steel 42CrMoTiBCe increase respectively from 22% and 17 J/cm

2

to 30% and 28 J/cm

2

.