SMA490BW Steel's CCT Curve Testing And Welding Thermal Simulation Experimental Research For High-speed Train's Bogie

SMA490BW weather-resistance structural steel is used mainly in the railway,vehicles,Bridges and towers,these steel structures are long exposed to the atmosphere.With the constant improvement of railway vehicle speed,the safety and reliability of welding railway bogie structures is more and more important,Heat affected zone is in the weak position of the welding joints,the structure and properties in heat affected zone has an important influence on welding joints' safety and reliability.So it's quite necessary to study structures and properties in heat affected zone' s subregion.Whereas,due to welding heat affected zone being very narrow,it's so difficult to observe and analyze it directly.This article uses Gleeble 3,500 thermal simulation tester resistance to simulate all the regional areas of welding heat affected zone of SMA490BW weathering resistant steel,then testing and analyzing their structure and mechanical performance.Main contents including measuring average crystallite size,analyzing the influence of welding heat cycle and heat input on grain size,testing hardness and impact toughness and analyzing low temperature embrittlement of sensitivity and fracture mechanism.Expansion curves of specimens in different cooling rates were simulated by Gleeble-3500.And their microstructure,quantitative metallography and hardness were also carried out to construct SHCCT curve.Test results show that regional areas' organizations are different,organizations of ICHAZ are many polygons ferritic to a small flake pearlite presenting ribbon distribution,CGHAZ's are granular bainite and quilted bainite,IRCGHAZ's are granular bainite and small amounts of acicular ferrite and SRCGHAZ's are granular bainite and a little side attrib wattle ferritic;welding heat cycle's peak temperature has great influence on the grain size with the same other conditions,the higher peak temperature is,the bigger grain size is;in different welding thermal cycling conditions,line energy affects grain size differently;when the welding energy is 10KJ/cm,the heat affected zone's hardness will be reduced.According to static CCT curve,to ensure high strength,the cooling rate should be higher than 3?/s in the subsequent heat treatment,which could avoid the banded pearlite ferrite;to obtain a certain toughness,the colding rate should range from 7.5 C/s to 15 C/s.When the colding rate is lower,banded structure will be formed,which will have a serious influence on toughness.By analyzing the actual bogie's stress relieving welding joint,it can be found that there are banded structures of ferrite and pearlite in the internal zone.