Abstract： In the field of ocean engineering，there is an urgent demand for thick steel plate with high heat input welding and excellent lowtemperature toughness. Through microalloying technology and quenching and tempering process，Baosteel has developed E550 grade ocean engineering steel for high heat input welding. The inclusions and microstructure of the offshore steel for high heat input welding were investigated by smelting，rolling，quenching and tempering，thermal simulating test，SEM observation statistical analysis of inclusions and metallographic observation. The results were compared with the existing offshore steel E550 in Baosteel. The results show that the inclusions of the developed offshore steel H1 are Al2O3，MnS，Al2O3Ti3O5，Al2O3MnS，TiNMnS，Al2O3Ti3O5MnS. The inclusions of the E550 are Al2O3，CAx，CaOCaS，CAxCaS，CAxCaSTiN. The mechanical properties of steel H1 can meet the requirements of E550 grade offshore steel and can meet the requirements for 50 kJ/cm and 100 kJ/cm weld heat input. The mechanism of HAZ toughness improvement is as follows， low silicon and low aluminum content are beneficial to reduce local brittle zone；Ti content reduction is beneficial to inhibit TiC embrittlement and improve HAZ toughness.
王毓男，蒋晓放. 大线能量焊接用海工钢的夹杂物与组织[J]. 钢铁, 2019, 54(8): 209-215.
WANG Yunan，JIANG Xiaofang. Investigation on inclusions and microstructure of #br#
offshore steel for high heat input welding. Iron and Steel, 2019, 54(8): 209-215.
