The microstructure and property of the coarse grained heat affected zone( CGHAZ) of 960QT steel was studied under t

8/5

by using thermal simulation technology

and the continuous cooling transformation curve of the heat affected zone(SH-CCT diagram)was acquired. The results show that

the microstructure of the CGHAZ consists of lath martensite and the hardness values change little as t

8/5

is 3 - 6 s. When t

8/5

= 10 s

lath bainite appears. With increase of t

8/5

the lath martensite reduces and lath bainite increases

and the microhardness of CGHAZ gradually reduct. When t

8/5

reaches 150 s

granular bainite in structure is found the microhardness is further reduced. As t

8/5

> 600 s

the CGHAZ mainly consists of granular bainite. Based on the measured heat affected zone 5

the relationship between tg/5 values and heat input E of steel 960QT is established. As t

8/5

is 30 s

the microhardness of CGHAZ (325 HV1) is equal to the base metal(330 HV1). So the heat input should be controlled to ensure that t

8/5

is less than 30 s. Under non-preheating conditions

the heat input should be less than 1.4 kj/mm.