Microstructure And Properties Control Of 1Cu-2Ni Low Carbon Bainite Weathering Steel

In recent years,in order to meet the development needs of various industries to increase weight reduction,energy saving,emission reduction,and to increase the service life of materials,the research and development of high strength weathering steel has attracted much attention.For engineering materials,good welding performance is often essential.In order to ensure good welding performance,low-carbon or even ultra-low-carbon steel is often used,which inevitably reduces the mechanical strength of the material.A large number of past research and production practices have shown that titanium microalloying technology and controlled rolling and controlled cooling technology are an effective way to develop and produce low-cost,high-strength,low-carbon weathering steel.In this paper,on the basis of titanium microalloying,choose a low-carbon,Cu-Cr-Ni corrosion-resistant composition system,by increase the content of copper and nickel elements,designed a 1Cu-2Ni low-carbon bainite weathering.Through thermal simulation tests,pilot hot rolling mills and ultra-fast cooling devices,the effects of different deformations,deformation temperatures,and cooling methods on the microstructure evolution of 1Cu-2Ni low-carbon bainite weathering steel during the controlled rolling and controlled cooling process have been systematically studied,Provide theoretical basis and technical support for the research and development of low-carbon bainite weathering steel.The main work of this paper is as follows:1?Based on the requirements of high strength,toughness,corrosion resistance and weldability,a high strength weathering steel with composition of 0.05C-1.5Mn-0.5Cr-1Cu-2Ni-0.1Ti(mass.%)was designed and prepared.The microstructure evolution of 1Cu-2Ni low carbon bainitic weathering steel was studied under the condition of rapid co oling(20?/s)to 300?(hold for 1 min)and air cooling after deformation at dif ferent deformation temperature and deformation amount.The results show that with th e increase of temperature,lath bainite can be easily obtained by 15%and 30%defor mation at 950?,the bainite cluster size is about 21?m,and the Vickers hardness is about 320 HV;when the deformation increases to 50%,the microstructure coarsens,th e bainite cluster size is 32?m,and the Vickers hardness decreases to 310 HV.Granul ar bainite with fine structure can be easily obtained by deformation at 900?.Under different deformation conditions,the size of massive and quasi polygonal ferrite is ab out 10?m,and the Vickers hardness is about 280 HV.Generally speaking,the effect of deformation temperature on microstructure is greater than that of deformation amou nt.2?The phase transformation of 1Cu-2Ni low carbon bainite weathering steel with continuous cooling is studied under the conditions of 50%deformation at 900?and 30%deformation at 950?,respectively.The results show that 1)Deformation inhibits the formation of lath bainite;2)Under the same deformation condition,with the increase of cooling rate,the granular bainite structure gradually decreases,and the lath bainite structure gradually increases,at the same time the microstructure is gradually refined.The Vickers hardness increases with the increase of cooling rate;3)Compared with the air-cooled microstructure after a short stay at 300?,it is found that the formation of lath bainite can be more easily promoted after a short stay at 300?.3?After large deformation in the austenite recrystallization zone,the weathering steels with different microstructure and properties were prepared by five cooling methods:air cooling,fast cooling(10-20?/s),ultra-fast cooling(40-60?/s),air cooling and water cooling after ultra-fast cooling to 300?.The results showed that:Rolling 1Cu-2Ni low carbon weathering steel at the temperature of austenite recrystallization zone in multiple passes,followed by super-fast cooling of the steel plate to 300?,followed by air cooling to room temperature,is the best process for preparing high strength and toughness weathering steel.The tensile strength of the steel can reach about 950 MPa,the yield strength can reach about 630 MPa,and the yield strength ratio is 0.66.At-20?,the impact energy reaches more than 170 J,and the corrosion rate in 3.5 wt%Na Cl solution is only 3.122×10^-3mm/y.