Research On CO₂Laser Welding Of30Cr3Ultra-High Strength Steel

The laser weldability of30Cr3ultra-high strength steel was studied forthe first time in China, the welding parameters of pure laser welding andlaser welding with filler wire were analyzed, meanwhile, themicrostructure and mechanical properties were studied.The influence of the laser power, welding speed, side blowing flow,defocus and joint preparation on the weld appearance and penetration werediscussed. Then a research on critical laser power under the welding speedof1.5m/min to3.5m/min was carried out. No weld defects such as poreand crack was observed with the optimized parameters. Microstructure ofweld metal (WM) was martensite, martensite and pearlite were observed inheat affected zone (HAZ), and many second phase particles distributed inHAZ. Mechanical properties test showed that maximum microhardnesswas in WM and the fracture occurred in base material (BM). Post-weldand before-weld heat treatment were carried out, results showed that microstructure changed to tempered martensite after quenched andtempered, leading to ultra-high strength of1745MPa, on the contrary, softzone appeared in the specimen which was quenched and tempered beforewelded.In the welding with filler wire, laser power, laser incident angle andlaser incident height were studied. Microstructure analysis andmicrohardness test were carried out on the welded joint, which was welllapped and with beautiful surface morphology.Weld quality control of the starting point and finishing point wasstudied. Results indicated that energy attenuating at the weld finishingpoint can get well overlapped appearance, the entire weld was smooth andcontinuous. In the welding with filler wire, control mode with wire feedingahead laser starting could eliminate burn-through and pits at the startingposition, at the contrary, extra wire feeding at the finishing position shouldbe adopted after energy attenuating to improve the formation of the weldedjoints.