Study On High Toughness Submerged Arc Welding Wire For The Marine Engineering

The purpose of this study is to develop a kind of submerged arc welding wire with good toughness under a wide range of heat input for 420 MPa level of marine engineering steel. According to the mechanics demand of marine engineering steel, meanwhile considering of the microstructure characteristic of welding joint and result of mechanical properties, acicular ferrite is chose to be the malleableize phase. Based on above condition, the Mn-Ni-Si-Ti-B was chose as alloy system for TM13 submerged arc welding wire by analyzing the effect of alloy elements in the weld metal and the mechanism of strengthening and toughening. Submerged arc welding with different basicity flux was carried out to get the deposited metal. The results indicated that the deposited metal has excellent strength and toughness when matches with high basicity TMF105 flux, and the microstructure is mainly of acicular ferrite and a small amount of proeutectoid ferrite.The influences of Mn and Ni concentrations on toughness and microstructure in weld metals of high strength low alloy steels have been studied. Results indicated that Mn and Ni have considerable effect on the weld metal microstructure, and both Mn and Ni promote acicular ferrite at the expense of grain boundary ferrite and ferrite side plates. Based on the properties and impact resistance, the optimum levels of Mn and Ni were suggested to be 0.6-0.9% and 2.5-3.5%, respectively. Additions beyond this limit promoted the formation of segregation structures and granular bainite, which may be detrimental to weld metals toughness.The weld metals have good low-temperature toughness under a wide range of heat input when using TM13 wire matches with TMF105 flux. The microstructure of weld metals is mainly composed of proeutectoid ferrite, side plate ferrite, acicular ferrite and pearlite composition. With the increase of heat input, the proportion of proeutectoid ferrite increases, acicular ferrite begin coarsening, and the content of carbide precipitates at the original austenite grain boundary increases.Thick plate butt test was carried out under the heat input of 22 k J·cm-1 and 32 k J·cm-1, then several tests including CTOD and Charpy impact had been performed on the welded joints to identify the toughness. The results show that the weld metals have good low-temperature toughness, and the microstructure of the welded metals mainly consists of acicular ferrite and fine equiaxed ferrite.