Test steel 508-3 (/% : 0. 19C

0. 26Si

1.48Mn

0. 009P

0. 007S

0. 78Ni

0. 50Mo

0.003Al) is melted by a vacuum induction furnace and cast to 50 kg ingot

forged at 1 150 to Φ16 mm bar

end forging ≥900℃.The effect of normalizing temperature (900 ~ 1 200 °C) and multi-normalizing process (900 〜1 200℃ 1 h-900℃ 1 h-890 °C 1 h) on austenite grain size of steel 508-3 has been studied. Results show that as normalizing at 900 ~ 1 200 °C

with increasing normalizing temperature the austenite grain size of steel coarsens obviously

the rating of austenite grain coarsens from No 6. 5 to No 3 ； with subsequent secondary normalizing at 900 °C the original course austenite grains in steel are refined to rating of No 6

then with third normalizing at 890 °C the effect of refining of austenite grains is not obvious. Multistep- normalizing treatment is available to refining the coarse austenite grains of steel 508-3

but repeating normalizing at same temperature is not obvious to refining the austenite grains in steel.