Based on the model of isothermal austenite grain growth of steel 42CrMo for bearing ring of shield tunneling machine

the model of austenite grain growth during continuous heating process of steel has been established by using the principle of additivity. The effect of original austenite grain size is considered in the established model

it is included in established models of grain size d

i

and soaking time t

i

*

during interval time (t

i-1

t

i

). With using Gleeble-1500 thermal simulation machine the austenite grain size of forged billet ( finishing forging at 850 ℃)of steel 42CrMo (/% : 0. 40C

0. 23Si

0. 60Mn

0. 016P

0. 001S

1. 08Cr

0. 22Mo) with 100

℃/s heated to 1000-1300 °C and water cooling has been tested and measured. Results show that with increasing austenitizing temperature from 1 000 ℃ to 1 100 ℃ the grain size of austenite in steel 42CrMo increases from 16. 3 μm to 30. 3 μm

the grain size of steel rapidly increases as heating temperature is more than 1100 °C and the austenite grain size in steel heating at 1300 °C is 112. 5 μm； the predicted value by model and measured value of austenite grain size in steel are better identical.