Study On Solidification Cracking Susceptibility Of Single-phase Austenitic Alloys During Laser Welding

Aiming at the problem of solidification cracking will occur during laser welding for austenitic alloys such as austenitic stainless steel and nickel-based alloys,based on Schaeffler phase diagram,this paper took SUS304 stainless steel as the base material and seven nickel-based alloys with different chemical compositions as the welding materials to prepare the welding joint of dissimilar austenitic alloy with different chemical compositions.Used to develop a new type of hot crack test method for quantitative research on the solidification cracking susceptibility,proven Schaeffler diagram of single-phase austenitic area distribution characteristics,solidification cracking susceptibility by optical microscope,scanning electron microscope,electron back scattering diffraction analysis and electron probe micro analysis methods such as analysis of weld organization,clarify single-phase austenitic alloy solidification cracking generation mechanism.Specific research is as follows:（1）A new hot cracking evaluation method called trapezoidal hot cracking test was developed to evaluate the solidification cracking susceptibility.The solidification cracking rate is an important index to evaluate solidification cracking susceptibility.With increasing of the ratio,the solidification cracking susceptibility tended to increase.Meanwhile,the reliability of the new test method was verified through metallurgical factor and process factor.The sequence of solidification cracking susceptibility is SUS310>SUS316>SUS304.Moreover,the solidification cracking susceptibilities of SUS310 and SUS304 tended to decrease and increase with increasing welding speed from 1.0 m/min to 2.0 m/min.（2）The dissimilar austenitic alloys welded joint could be obtained by changing nickel-based alloys and dilution,which distributed in the middle part of single-phase area on the Schaeffler diagram(Ni_eq<40%).The new test method would be employed to evaluate their solidification cracking susceptibilities.The Cr_eq/Ni_eqincreased from0.4 to 1.2 approximately,the solidification cracking rate tended to decrease.The solidification cracking susceptibility was relatively high on the left side and upper part of right side,relatively low in the middle and lower part of right side on the Schaeffler diagram.（3）The theoretical equation was employed to verify the reliability of solidification cracking susceptibility of dissimilar austenitic alloys welded joint.The relationship between trace elements and the solidification cracking rate was analyzed.With increasing Nb,the solidification cracking rate tented to increase.While,the effect of other trace elements on the solidification cracking rate was relatively not obvious or complex.Moreover,Nb C and Laves appeared in the microstructure,which verified the effect of Nb on the solidification cracking susceptibility.This revealed the mechanism of the solidification cracking.