| Today,as energy is drying up,nuclear energy has a wide use value as a clean energy source in the energy field.The nuclear island primary circuit equipment is the core of the pressurized water reactor nuclear power plant,and the SA508 low alloy steel is widely used in the manufacture of reactor pressure vessels due to its excellent performance.The manufacture of reactor nuclear primary equipment requires the use of a large number of welding consumables,of which low alloy steel welding consumables are mainly used for the welding of the main bearing welds of the main equipment of the primary circuit system.At present,the mature welding consumables that can be used in the manufacture of nuclear pressure vessels in China are mainly concentrated on submerged arc welding wires and manual arc welding electrodes,while the welding wires that can be used for tungsten argon arc welding mainly rely on imports.It is difficult to achieve 150 J of low-temperature impact absorption work for subm erged arc welding and manual welding.Therefore,it is of great significance to study the tungsten-argon-arc welding low-alloy steel welding wire with independent property and stable performance in the key equipment manufacturing problem.In this paper,four different heat input conditions were used to test the deposited metal of 508-IIIB low alloy steel TIG welding wire,and all of them obtained high and strong low temperature toughness and stable performance indexes.The precipitation process of the second phase was studied from the perspective of thermodynamics,and the phase types and distribution laws of the precipitates were analyzed.It is found that the types of precipitated phases of the deposited alloys of the three alloy components are the same,all of which are alloy cementite and(Ti,Nb)C,and no nitride is found.The precipitation phase TiC is first precipitated in the austenite solid phase temperature range,and then NbC precipitates around it with the primary TiC phase as the core.As the heat input increases,the effect of precipitation phase strengthening is weakened.The effects of changes in heat input on the metallurgical process of inclusion nucleation and the growth and distribution of inclusions were investigated.The results show that the size,number and area ratio of inclusions change correspondingly with the increase of heat input.However,under the four heat inputs,the inclusion types are(Al2O3,SiO2,TiO,MnS)composite inclusions.In the process of metallurgical reflection,after the deoxidation of Al and Ti is completed,Si and Mn are also involved in the metallurgical reaction process of the molten pool in turn,and finally several inclusions aggregate and grow to form a composite inclusion.As the heat input increases,the grain size increases from 3.07 um to 3.85 um,and the acicular ferrite contents are: 79.2%,85.1%,90.3%,and 70.3%,and inclusions induce acicular ferrite nucleation.The ability of inclusions to induce acicular ferrite nucleation is first increased and then decreased.Through the change of the microstructure and properties of the deposited metal during the increase of heat input,it is found that the microstructure of the deposited metal is composed of acicular ferrite and lath bainite,and in the process of the heat input increases from 9kJ/cm to 15 kJ,the heat of the molten pool is gradually increased,the metallurgical reaction process is more intense,the cooling rate is slowed down,the tissue transformation period becomes longer,and the crystal grains are gradually roughened.Under the four heat input,the tensile strength of the deposited metal is greater than 630 MPa,and the impact absorption at-30 °C is greater than 250 J.The value of the impact absorption work increases first and then decreases with the increase of heat input;When the input is 13kJ/cm,the deposited metal has the best performance,the impact absorption power is 310 J,and the ductile-brittle transition temperature is-77 °C. |
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