Research Of Phase Transformation And Recrystallization Behavior Of CSP High Strength Saw Steel Bearing Nb-V

The steel for saw blades is widely used for the processing of wood and metal due to its excellent cutting performance.The thickness of the s teel for saw blades is reduced,and the increase in the diameter of the saw blade will increase the cutting efficiency,which promotes development in the direction of large diameter and thin gauge.Thin slab continuous casting and rolling(CSP)technology has outstanding advantages in the production of thin gauge steel billets.It is an inevitable trend to use CSP technology to produce steel for saw blades.The dynamic recrystallization of 55MnCr niobium-containing or niobium-containing vanadium steel at deformation temperature(900?1000?1080?1150?)and strain rate(0.1?1?5?10s-1)and the law of dynamic CCT was studied by using a thermal simulator to provide experimental data and theoretical basis for the CSP process.The main conclusions are as follows:(1)The true stress-strain curve at high temperature is analyzed in the single compression tests.The influence of convection stress on thermal deformation parameters is studied by using the data of stress-strain curve,and the corresponding constitutive equation and dynamic recrystallization model are cons tructed.The calculated res ults agree well with the experimental results and can be used.Recrystallization activation energy of niobium containing steel:Q1=328.02kJ·mol-1,corresponding constitutive equation:?=4.536 × 1012[sinh(0.0082?)]5.532exp(-328020/RT);dynamic recrystallization critical strain model:?c=0.0015[?exp(39454/T)]0.1678;dynamic recrystallization activation energy of yttrium vanadium steel:Q2 = 389.34kJ·mol-1,the corresponding constitutive equation:?= 2.009 × 1015[sinh(0.0072?)]6.330 exp(-389340/RT);dynamic recrystallization critical strain model:?c=0.0005[?exp(46829/T)]0.1751.(2)Dynamic recrystallization occurs at 1080 ? and 1150 ? for niobium-containing steel and niobium-vanadium steel at a strain rate of 0.1/s.As the strain rate increases to 1/s and 10/s,the deformation temperature decreases and the deformation resistance increases.At the same deformation temperature and deformation rate,the grain size of niobium-bearing steel is larger than that of niobium-vanadium steel,which indicates that niobium-vanadium composite can refine the dynamic recrystallization grain.Thermodynamic calculation and transmission electron microscope analysis show that the precipitation of niobium steel precipitates niobium carbide and vanadium niobium steel precipitates hinders dynamic recrystallization in the deformation temperature range.(3)The continuous cooling phase transition behavior of niobium-containing steel and niobium-vanadium s teel was analyzed by thermal simulation experiment.The results show that the average lamellar spacing of pearlite is 247nm at a cooling rate of 0.1?/s,168nm at a cooling rate of 0.4 ?/s,and 117nm when the cooling rate reaches 0.8 ?/s of niobium-bearing steel.When the cooling rate is 0.1 ?/s,the interlayer spacing is 172nm,and when the cooling rate is increased to 0.4 ?/s,the interlayer spacing is reduced to 145nm of niobium-vanadium steel.In contrast,the pearlite lamellar spacing of niobium-bearing steel is larger than that of niobium-vanadium steel at the same cooling rate,indicating that the effect of niobium-vanadium composite action on grain refinement is better than that of pure niobium element.At the same cooling rate,the Vickers hardness of niobium-vanadium steel is higher than that of niobium-bearing steel.With the increase of cooling rate,the difference between niobium-vanadium steel and niobium-vanadium steel becomes smaller and smaller,indicating that the composite effect of niobium and vanadium is better than niobium in improving hardness.