Abstract:
Coarse-grained heat affected zone (CGHAZ) samples of 9Ni steel joint were prepared with Gleeble-3500 type thermal simulator at
t8/5 (cooling time from 800℃ to 500℃) of 6,10,30,60,100 s, respectively, and then cryogenic impact tests were carried out on the samples. The effects of
t8/5 on the microstructure and cryogenic toughness of CGHAZ were investigated. The results show that the microstructure of CGHAZ was mainly composed of lath martensite. The granular bainite appeared at
t8/5 of 30 s and the amount increased with increasing
t8/5. With increasing
t8/5, the size of martensite lath in CGHAZ increased slightly and then decreased; the ductile-brittle transition temperature rose and then decreased. The impact energy at -100℃ and -125℃ of CGHAZ prepared at different values of
t8/5 was higher than 200 J. With decreasing impact temperature, the impact fracture morphology changed from dimple to quasi-cleavage.