Effect of Heat Input on the Microstructure and Cryogenic Toughness of the Simulated Heat-Affected Zone of High Manganese Steel During Welding
As a novel cryogenic material,high manganese steel has advantages of cost-effectiveness and excellent cryogenic mechanical properties,as well as broad application prospects in liquefied natural gas(LNG)storage tanks.However,during welding,its cryogenic toughness usually deteriorates in a specific subzone(the FL+3 subzone)of the heat-affected zone,which is located 3 mm away from the fusion line.To solve this problem,welding thermal simulations of the FL+3 subzone were conducted under different heat inputs.A scanning electron microscope,an electron probe X-ray microanalyzer,and a transmission electron microscope were used to observe the grain boundary proportion,segregation,and precipitate.The result showed that the FL+3 subzone had good cryogenic toughness,and the fracture morphologies were characterized by numerous dimples.However,with increasing heat input,the impact absorbed energy decreased.The-196℃impact absorbed energies at 10 kJ/cm,15 kJ/cm,30 kJ/cm,and 45 kJ/cm were 177 J,172 J,138 J,and 112 J,respectively.The FL+3 subzone consisted of single-phase austenite.With increasing heat input,the grain size did not change significantly,while the proportion of low-angle grain boundaries increased.A higher heat input aggravated the C-Cu grain boundary and Mn band segregation in the FL+3 subzone,increasing the stacking fault energy and critical shear stress for twinning in the segregating region.This made it difficult to activate the twinning mechanism,weakened the toughening effect of deformation twins,and reduced the cryogenic toughness.When the heat input was 15 kJ/cm,granular and massive Cr23C6 carbides with a size of about 200 nm were precipitated,and the size and quantity of the precipitates further increased with increasing heat input.The carbide precipitates caused stress concentration and crack initiation,deteriorating the cryogenic toughness of the FL+3 subzone.
high manganese steelheat inputwelding thermal simulationgrain boundary proportionsegrega-tionprecipitatecryogenic toughness
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维普
