STUDY ON THE DELAYED CRACKING OF ULTRA HIGH STRENGTH STEEL

The hydrogen induced cracking and the stress corrosion cracking in weld joints of 37 SiMnCrMoV steel are investigated by means of four-point bending test and surface crack test,respectively.High environment humidity increases the susceptibility to hydrogen induced cracking and stress corrosion cracking.Scanning electron microscope fractography shows the intergranular character of hydrogen induced cracking.The effect of microstructure of HAZ(partially melted zone and quenched zone) on cracking susceptibility is studied by scanning electron microscope and optical microscope.Welding procedures are adjusted to prevent brittle failure of high pressure vessel.