Study On Microstructure And Properties Of Marine Engineering Steel E36 For High Heat Input Welding

At present,thick steel plates have been widely used in large-scale welding structures such as shipbuilding,high-rise buildings,and offshore platforms.In order to improve the welding efficiency and quality,and then increase the economic benefits,the heat input to welding continues to increase.As the high heat input welding process,the grain structure of the heat affected zone of the steel plate will become coarse,resulting in a significant reduction in the toughness of the heat affected zone of the steel plate welding,and seriously affecting the mechanical properties of the welded joint.Therefore,while ensuring the strength of the steel plate,how to effectively improve the toughness of the heat-affected zone has become a major problem that people need to solve.In this paper,the E36 steel for marine engineering,which is in urgent need of high heat input welding performance,is used as the target steel grade,and the steel plate is trial-produced using the oxide metallurgy process.The effects of rolling process and normalizing temperature on its microstructure and properties were studied,and the related thermal input welding thermal simulation experimental study was carried out.In order to study the effect of different normalizing temperatures on the microstructure and properties of marine engineering steel E36,smelting steels were treated under the same rolling process and different normalizing temperature conditions.The microstructures were observed by optical microscope,and the impact tests were performed.Tensile test was used to test the mechanical properties of the steel plate.The results show that the impact energy of normalized steel at 910°C is higher than the impact energy of rolled steel at impact temperature of-40°C,while the impact energy of normalized steel at 890°C and 870°C is lower than that of rolled steel.The 910°C normalized steel has the highest yield strength,elongation and impact energy;the 870°C normalized steel has the highest tensile strength;the 890°C normalized steel has relatively poor overall performance,while the 910°C normalized steel has the best comprehensive performance.In order to study the effect of high heat input on the microstructure and low temperature toughness of the heat affected zone of the steel plate,a welding heat simulation experiment was conducted on 910 °C normalized steel.The results show that the heat input of 920 °C normalized steel at 200 kJ/cm heat input Under simulated conditions,the microstructure is grain boundary ferrite,polygonal ferrite,and acicular ferrite.At this time,the steel plate has good low temperature toughness,but when the steel also contains bainite,the toughness of the steel plate will be declined.Through the analysis of relevant inclusions,the results show that the composite inclusions containing titanium compounds in the range of 0.2-5 um can effectively promote the nucleation of acicular ferrite.Under the guidance of the above experimental results,the steel plate was industrially trial-produced,and the results showed that the mechanical properties of the high heat input marine engineering steel that was trial-produced on the industrial production line using the new process were in line with national standards and the regulations of various classification societies.The simulated welding heat input can reach 200kJ/cm.In the actual gas-electricity vertical welding,the heat affected zone still has qualified performance under the condition of heat input of 304kJ/cm.