Influence of welding heat input on microstructure and properties of 12MnNiVR steel joints
We weld 12MnNiVR steel by gas-electric vertical welding method and study the influence of welding heat input on the microstructure and mechanical properties of the joint and focus on the impact toughness of the joints.The results show that the microstructure of weld is mainly composed of acicular ferrite and granular bain-ite.Martensite-Austenite(M-A)components are also observed.The microstructure of the coarse-grained heat-affected zone is lath ferrite,and the inclusions are identified as TiN.With increasing welding heat input,acicu-lar ferrite and lath ferrite gradually transform into massive ferrite.The size of massive ferrite increases gradually and the number and size of M-A components also increas.The microhardness of the weld seam and the maxi-mum microhardness of the heat-affected zone both decrease with increasing welding heat input.The tensile and bending properties of the joints meet the standards.The impact toughness decreases with increasing welding heat input and the impact fracture at the weld seam presents dimple characteristics.With increasing welding heat in-put,the fracture mode of the impact fracture at the heat affected zone changes from ductile fracture to quasi cleavage fracture.Finally,this paper proposes that the welding heat input of 12MnNiVR steel with a thickness of 21.5 mm should be controlled below 100 kJ/cm to ensure that the joint has good comprehensive mechanical properties and high production efficiency.
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