Study on heat affected Zone of low alloy wear-resistant plate welding
The manufacture of low-alloy wear-resistant plates for high-pressure towers can not only increase the overall strength of the tower, reduce the amount of steel used, but also greatly increase the life of the tower, which has been increasingly used. However, the wear-resistant plate has a larger tendency to harden, a higher hardness, and a larger tendency to crack (especially cold crack) after welding, which affects the quality of the tower.
For the research on welding heat affected zone, many literatures generate welding heat affected zone samples by welding heat affected zone simulator based on actual welding process parameters. Although this method can enlarge welding heat affected zone for convenience of research, some literatures also point out that there are errors between sample parameters obtained by welding heat affected zone simulator and those obtained in actual welding. Based on the above considerations, welding experiments were carried out to study the welding heat affected zone (HAZ) of wear-resistant plates. The effects of welding heat input (E) on the microstructure and mechanical properties of HAZ were studied under different preheating temperatures (TP), providing theoretical and experimental references for the control of cracks in the welding of wear-resistant plates in UHV welding towers.
The experimental material is hot rolled JFE-C400 wear-resistant plate, the size is 300mm×200mm×10mm, and its chemical composition (mass fraction, %) is: 0.203C, 0.043Si, 1.26Mn, 0.006P, 0.001S, 0.046Nb, 0.019Ni, 0.012Cr, 0.29Al, 0.018Cu. 45° L-shaped bevel with a blunt edge of 2mm. The welding material is Φ1.2mm ER55-G welding wire. The welding method is CO2 gas shielded welding, the welding equipment model is YM-500KR, and the single pass butt welding is adopted. After welding, it is air-cooled at room temperature and then tested for impact and hardness.
When the welding line energy of the wear-resistant plate is 10kJ/cm, the width of the welding heat affected zone is about 4mm, and 40kJ/cm will reach about 9mm. The grain size of the coarser zone is very different under different wire energy input. The average grain size of the coarser zone when the wire energy is 40kJ/cm is almost twice that of 10kJ/cm. This shows that the wear-resisting plate has limited inhibitory effect on austenite grain at high linear energy, while the nailing effect of Nb(C,N) will hinder austenite grain growth at low linear energy. At the low welding energy (10kJ/cm), preheating before welding can refine the hardened microstructure such as martensite and M-A block compared with no preheating, which has a favorable effect on the toughness of coarse-grained zone. However, under high line energy (40kJ/cm), preheating before welding will not only make the coarse-grained zone more coarse-grained structure, but also more easily produce the microstructure with relatively poor mechanical properties such as upper bainite, which seriously reduces the toughness of the coarse-grained zone, which needs attention in welding.
