The present work is aimed at studying the microstructure and pitting corrosion behaviour of shielded metal arc welded high nitrogen steel made of Cromang-N electrode. Basis for selecting this electrode is to increase ...The present work is aimed at studying the microstructure and pitting corrosion behaviour of shielded metal arc welded high nitrogen steel made of Cromang-N electrode. Basis for selecting this electrode is to increase the solubility of nitrogen in weld metal due to high chromium and manganese content. Microscopic studies were carried out using optical microscopy(OM) and field emission scanning electron microscopy(FESEM). Energy back scattered diffraction(EBSD) method was used to determine the phase analysis, grain size and orientation image mapping. Potentio-dynamic polarization testing was carried out to study the pitting corrosion resistance in aerated 3.5% NaCl environment using a GillAC electrochemical system. The investigation results showed that the selected Cr-Mn-N type electrode resulted in a maximum reduction in delta-ferrite and improvement in pitting corrosion resistance of the weld zone was attributed to the coarse austenite grains owing to the reduction in active sites of the austenite/delta ferrite interface and the decrease in galvanic interaction between austenite and delta-ferrite.展开更多
The spreading effect of atmospheric pressure microplasma jets(APμPJ)on the surface of materials will increase the etching area,and controlling the diameter of the jet can improve the precision of surface treatment.In...The spreading effect of atmospheric pressure microplasma jets(APμPJ)on the surface of materials will increase the etching area,and controlling the diameter of the jet can improve the precision of surface treatment.In this work,a two-dimensional axisymmetric simulation model is established to analyze the effect of nitrogen(N_(2))shielding gas on helium(He)from gas dynamics.In addition,by etching the polyethylene terephthalate fllm,the relationship between the etching effect and aerodynamic analysis is verifled.The simulation results are similar to the experimental results,indicating that N2 shielding gas has a focusing effect which is related to the N_(2)flow rate,distance difference between the inner and outer tubes,and outer tube nozzle diameter.It is hoped that the results of this work can provide a certain reference for the use of shielding gas to control the jet flow of APμPJ.展开更多
High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grad...High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grade steel owing to its low cost, excellent mechanical properties and better corrosion resistance.Conventional fusion welding causes problems like nitrogen desorption, solidification cracking in weld zone, liquation cracking in heat affected zone, nitrogen induced porosity and poor mechanical properties.The above problems can be overcome by proper selection and procedure of joining process. In the present work, an attempt has been made to correlate the microstructural changes with mechanical properties of fusion and solid state welds of high nitrogen steel. Shielded metal arc welding(SMAW), gas tungsten arc welding(GTAW), electron beam welding(EBW) and friction stir welding(FSW) processes were used in the present work. Optical microscopy, scanning electron microscopy and electron backscatter diffraction were used to characterize microstructural changes. Hardness, tensile and bend tests were performed to evaluate the mechanical properties of welds. The results of the present investigation established that fully austenitic dendritic structure was found in welds of SMAW. Reverted austenite pools in the martensite matrix in weld zone and unmixed zones near the fusion boundary were observed in GTA welds. Discontinuous ferrite network in austenite matrix was observed in electron beam welds.Fine recrystallized austenite grain structure was observed in the nugget zone of friction stir welds.Improved mechanical properties are obtained in friction stir welds when compared to fusion welds. This is attributed to the refined microstructure consisting of equiaxed and homogenous austenite grains.展开更多
文摘The present work is aimed at studying the microstructure and pitting corrosion behaviour of shielded metal arc welded high nitrogen steel made of Cromang-N electrode. Basis for selecting this electrode is to increase the solubility of nitrogen in weld metal due to high chromium and manganese content. Microscopic studies were carried out using optical microscopy(OM) and field emission scanning electron microscopy(FESEM). Energy back scattered diffraction(EBSD) method was used to determine the phase analysis, grain size and orientation image mapping. Potentio-dynamic polarization testing was carried out to study the pitting corrosion resistance in aerated 3.5% NaCl environment using a GillAC electrochemical system. The investigation results showed that the selected Cr-Mn-N type electrode resulted in a maximum reduction in delta-ferrite and improvement in pitting corrosion resistance of the weld zone was attributed to the coarse austenite grains owing to the reduction in active sites of the austenite/delta ferrite interface and the decrease in galvanic interaction between austenite and delta-ferrite.
基金supported by National Natural Science Foundation of China(No.51905002)Anhui Provincial Natural Science Foundation(Nos.2008085QE230,2108085ME174)+2 种基金Open Project of Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials(No.GFST2021KF06)Open Project of Anhui Province Key Laboratory of Special and Heavy Load Robot(No.TZJQRO03-2021)Open Project of Anhui Province Engineering Laboratory of Intelligent Demolition Equipment(No.APELIDE2021B001)。
文摘The spreading effect of atmospheric pressure microplasma jets(APμPJ)on the surface of materials will increase the etching area,and controlling the diameter of the jet can improve the precision of surface treatment.In this work,a two-dimensional axisymmetric simulation model is established to analyze the effect of nitrogen(N_(2))shielding gas on helium(He)from gas dynamics.In addition,by etching the polyethylene terephthalate fllm,the relationship between the etching effect and aerodynamic analysis is verifled.The simulation results are similar to the experimental results,indicating that N2 shielding gas has a focusing effect which is related to the N_(2)flow rate,distance difference between the inner and outer tubes,and outer tube nozzle diameter.It is hoped that the results of this work can provide a certain reference for the use of shielding gas to control the jet flow of APμPJ.
文摘High nitrogen stainless steel(HNS) is a nickel free austenitic stainless steel that is used as a structural component in defence applications for manufacturing battle tanks as a replacement of the existing armour grade steel owing to its low cost, excellent mechanical properties and better corrosion resistance.Conventional fusion welding causes problems like nitrogen desorption, solidification cracking in weld zone, liquation cracking in heat affected zone, nitrogen induced porosity and poor mechanical properties.The above problems can be overcome by proper selection and procedure of joining process. In the present work, an attempt has been made to correlate the microstructural changes with mechanical properties of fusion and solid state welds of high nitrogen steel. Shielded metal arc welding(SMAW), gas tungsten arc welding(GTAW), electron beam welding(EBW) and friction stir welding(FSW) processes were used in the present work. Optical microscopy, scanning electron microscopy and electron backscatter diffraction were used to characterize microstructural changes. Hardness, tensile and bend tests were performed to evaluate the mechanical properties of welds. The results of the present investigation established that fully austenitic dendritic structure was found in welds of SMAW. Reverted austenite pools in the martensite matrix in weld zone and unmixed zones near the fusion boundary were observed in GTA welds. Discontinuous ferrite network in austenite matrix was observed in electron beam welds.Fine recrystallized austenite grain structure was observed in the nugget zone of friction stir welds.Improved mechanical properties are obtained in friction stir welds when compared to fusion welds. This is attributed to the refined microstructure consisting of equiaxed and homogenous austenite grains.
