| 10CrNi3MoV steel has good strength and toughness, but the poor weldability limits its more application. The cold cracking could be only prevented by preheating through single arc welding. Efficiency enhancement and improvement of welding quality can be guaranteed through double-sided arc welding. Then it is necessary to study the effect of DSAW to 10CrNi3MoV steel. Based on temperature field simulation and thermal simulation method to analyze microstructure and toughness of HAZ in backing weld. Superiority of DSAW to single arc welding is described.First, Temperature field simulation is used to research the relationship between thermal circular principle and morphology characteristics of molten pool. Double pool and peak temperature have gradually shown and the minimum temperature gradually decreased with the increasement of distance between two wires when the large heat input is 33.2KJ/cm. The minimum temperature is above Ms point between Ms and Mf with the increasing distance between two wires, lower than Mf respectively. t8/5 of the back arc and front arc get rise to about twice with increasing heat input.Second, Thermal simulation is used to reconstruct the area of HAZ to obtain macroscopic sample. Microstructure and mechanical properties are going to be analyzed. microstructure like lath martensite, bainite are obtained through the first and second coarse grained thermal cycling when the small heat input is 21.7 KJ/cm. pro-eutectoid ferrite, granular bainite and carbide are obtained with the increasing heat input. The distribution of M-A constituent is more uniform and the form is changed from block to stripy feature. Structure inheritance is obtained in the heat-affected zones through coarse grained and then incomplete quenching thermal cycling. The grain size decreases with the increase of distance between two wires and increases with the increase of heat input through the measurement of original austenite grain size and the size of martensite lath. The ratio of original austenite grain size to the size of martensite lath(dp/dγ) remains unchanged when the original austenite grain size reaches in a certain value.At last, the impact toughness of DSAW is greater than single arc welding regardless of the heat input, when the distance between two wires is 40 and 60 mm, the impact toughness is larger than 10 and 20 mm. The impact toughness remains unchanged with the increase of distance between two wires in the large heat input, but larger than the value of impact toughness in small heat input. This is because the ratio of original austenite grain size to the size of martensite lath of 40 and 60 mm is higher than the value of 10 and 20 mm.And the value of dp/dγ in large heat input remains the same. Hence, the impact toughness is decided by the size of martensite lath. The relation between the lowtemperature impact toughness and fracture mode is researched. Experimental results indicate that the fracture mode is changed from quasi-cleavage fracture to tough fracture with the increase of distance between two wires. The fracture mode is essentially tough fracture with the large heat input. Cracks near the fracture propagate largely along the austenite grain boundary and the lath boundary. Course grained zone obtained from DSAW is occupied by essentially transgranular fracture, while course grained zone obtained from single arc welding is occupied by essentially Intergranular fracture. Commonly, the energy needed in transgranular fracture is higher than Intergranular fracture.In a conclusion, microstructure and toughness of HAZ in backing weld of 10CrNi3MoV steel with proper parameters is good to promote huge Superiority. |
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