Study On The Microstructure And Properties Of 20mm Thick 10Ni5CrMoV Steel Weld Austenitic Wire By MIG Welding

With the development of large-scale and heavy-duty equipment,the requirements for the strength and thickness of low alloy high-strength steel continue to increase.As an important steel for pressure vessels and ships,10Ni5CrMoV steel has become one of the research hotspots in this field for welding under large thickness and high constraint conditions.At present,when welding thick plate 10Ni5CrMoV steel in China,there are few types of welding materials available,with low strength,poor crack resistance,and low welding efficiency.It is urgent to develop welding materials and matching welding processes to improve the crack resistance,strength,plasticity,and other properties of large thickness and high constraint welded joints.In view of this,this article focuses on 20mm thick 10Ni5CrMoV steel,selects four types of austenitic welding materials,and uses MIG welding to study the microstructure and mechanical properties of austenitic welding wire deposited metal and welded joints.Finally,the optimal gas shielded welding wire and process suitable for welding 10Ni5CrMoV steel are obtained,providing new research directions and important theoretical basis and technical support for the application of austenitic gas shielded welding wire in the field of welding large thickness and high-strength steel,Filling the domestic gap in this field.The main research results are as follows:For thick plate 10Ni5CrMoV steel,four types of austenitic welding wires were used for the first time,and MIG welding was used.Research has found that the commonly used shielding gas component Ar+CO₂ for MIG welding is not suitable for austenitic welding wires.Therefore,a ternary shielding gas component He+Ar+N₂ was designed to form high-quality deposited metal and welded joints.2.For thick plate 10Ni5CrMoV steel,the deposited metal and welded joint microstructure and properties of austenitic stainless steel welding wires（numbered 1#and 2#）were studied.（1）The research on deposited metal showed that the quality of the deposited metal is good,and the microstructure of both deposited metals is composed of austenite matrix and precipitation phase;At room temperature,the tensile strength（R_m）,yield strength(R_p0.2),elongation after fracture（A）,and reduction of area（Z）of 1#welding wire are 767MPa,560MPa,38%,and 46%,respectively,and their plasticity was higher than that of 2#welding wire;In the low-temperature impact tests at room temperature and-50℃,2#had 130J and 119J respectively,with higher impact toughness than 1#welding wire;In the hardness test,the average hardness value of 1#welding wire was higher than that of 2#welding wire.（2）The study of welded joints showed that the two kinds of welds were composed of austenite matrix and precipitated phase,and the coarse grain zone was composed of Flat noodles martensite and bainite;There were significant differences in the elements of the 1#joint,with a wider fusion line,while the 2#joint elements were excessively stable,with a narrower fusion line;The tensile strength values of the two were similar,indicating plastic fracture;In the impact test,the WM,FL,and HAZ of 2#welding wire were 165J,174J,and 143J,respectively,higher than 1#;In the hardness test,the hardness trend of the two welding joints was the lowest in the weld area and the highest in the Heat-affected zone.The hardness of the welding joint of wire 1#is higher than that of wire 2#.3.The microstructure and properties of two nickel based welding wire deposited metals were studied for thick plate 10Ni5CrMoV steel.（1）Research on deposited metal showed that the welding process of ERNi Cr Mo-4 was superior to that of ERNi Cr Mo-3;The metallographic structure of ERNi Cr Mo-3deposited metal was mainly composed ofγThe phase,Nb C,carbide,and laves phases are composed of ERNi Cr Mo-4,which was mainly composed ofγPhase,P-phase,andμPhase composition;The tensile properties of the two deposited metals were similar,with both having higher average impact absorption energies,reaching 104J,85J,130J,and 119J at room temperature and-50℃,respectively;The hardness value of ERNi Cr Mo-3 was higher than that of ERNi Cr Mo-4.（2）The research on the microstructure and properties of the welded joint showed that the chemical composition of the weld and the Heat-affected zone were different,and the weld grains of the two welded joints did not have strong orientation;ERNi Cr Mo-4 welding wire had a more stable arc during the welding process,better weld formation,and an average tensile strength value of 858MPa for welded joints;In the impact test,both types of welded joints had high plasticity and toughness,and the impact performance of each part was good;There was no fracture during the lateral bending test;In the hardness test,the hardness value of ERNi Cr Mo-4 joint was higher than that of ERNi Cr Mo-3.4.For thick plate 10Ni5CrMoV steel,by using the four types of welding wires mentioned above,welding processes were developed to study the deposited metal and the microstructure and properties of welded joints.The optimal welding wire for MIG welding of 20mm thick 10Ni5CrMoV steel was ERNi Cr Mo-4.The process parameters were:（1）The shielding gas component was Ar+47%He+3%N₂.（2）The voltage was25V～27V.（3）The current was 160A～170A.（4）The heat input was less than 10KJ/cm.（5）The interlayer temperature was less than 120℃.And under this condition,further vertical and overhead welding tests were conducted,and welding joints with good forming quality and performance were obtained,indicating that ERNi Cr Mo-4 is also suitable for all position welding of thick plate 10Ni5CrMoV steel.