HYDROGEN ABSORPTION BEHAVIOR OF 1500 MPa--GRADE HIGH STRENGTH STEEL 42CrMoVNb

Abstract

Hydrogen absorption behaviors of a newly developed 1500 MPa-grade high strength steel 42CrMoVNb at different austenitizing temperatures and tempering temperatures were studied using cathodic charging and hydrogen thermal desorption analysis,which were also compared with commercial structural steel 42CrMo.The results show that the hydrogen escape peak temperatures (θ_p) in hydrogen evolution curves of hydrogen charged 42CrMoVNb specimens are between 200℃to 300℃both at as-quenched condition and as-tempered condition.The absorbed hydrogen content of 42CrMoVNb specimen increases slowly with increasing tempering temperature up to 500℃.When the tempering temperature exceeded 500℃,the absorbed hydrogen content increases sharply and reaches its peak,6.6×10~(-6),for the specimen tempered at 600℃,which is 5 times as much as that of the as-quenched specimen.Thereafter the absorbed hydrogen content declines sharply as the tempering temperature was gone up sequentially.When the specimen was tempered at 400℃,the absorbed hydrogen content decreases slightly with austenitizing temperature increasing,and in the microstructure no fine dispersed(V,X)C carbide precipitated,while when the specimen was tempered at 600℃, the absorbed hydrogen content increases sharply with austenitizing temperature increasing,and more fine dispersed(V,X)C precipitated.These results indicate that fine dispersed(V,X)C precipitate could be regarded as a strong hydrogen trap,and the trap activation energy,E_a,is equal to about 28.7 kJ/mol,which was obtained by change heating rate.