Effect of quenching and tempering process on the microstructure and mechanical properties of 40CrNiMoA steel welded joints was studied in this paper. The test results indicated that by quenching + tempering at 830 ~ 870 °C + 550 - 650 °C the 40CrNiMoA steel 3 nun plate at 90A 10V welded joint hardness difference between weld zone

heat affected zone

and base metal zone is reduced significantly

and tempered sorbite structure is formed. The higher quenching and tempering temperature

the more uniform microstructure among the weld zone

heat affected zone and base metal of welded joint

and the cementite particle grew up in structure. The 40CrNiMoA steel welded joint after oil quenching at 850°C and tempering at 600 勾 has higher strength (905 MPa) and plasticity (13. 5% ). In this case

the comprehensive mechanical properties are best.