| In this paper, the Ti40alloy that had been ring rolled was compressed intemperature range of950～1100℃，strain rates of1.0～0.001s-1and true strain of0.11～0.92by isothermal and constant strain rate compression tests, it’s hot deformationbehavior was studied and constitutive relationship with high accuracy was established,and the evolution of deformation microstructure follow deformation parameters of testswas also obtained. The studied results could provide theoretical guidence forformulating suitable hot deformation parameters of the material.The analysis for flow stress curves showed that, at different deformation conditions,flow stress was quickly increased to peak value with the increase of strain and then thecurve turned to steady flow in the main. Flow stress was sensitive to both deformationtemperature and strain rates, and it was decreased with the increase of deformationtemperature and the decrease of strain rate. Further analysis for flow stress curveindicated that, constitutive relationship was suitable to establish by using Arrheniusequation of hyperbolic sine type, and constitutive relationship with high accuracy wasestablished by adding Z parameter into Arrhenius equation of hyperbolic sine type.Error analysis showed that, the points which the error of constitutive relationship wasless than10percent were94.41percent by all points of the tests, it could well predictthe hot deformation behavior for the material.The influence of deformation temperature and strain rates to the evolution ofdeformation microstructure was studied at60%of height reduction. The results showedthat, dynamic recrystallization was viewed in all deformation parameters of differentdegree, and dynamic recrystallization was developed gradually from grain boundary tointernal grain with the increase of deformation temperature and the decrease of strainrate. The fraction and diameter of dynamic recrystallization was increased with theincrease of deformation temperature at a same strain rate, while at1.0s-1, it wasapproximately in the range of8.02%～28.69%and8.77μm～30.36μm respectively;while at0.1s-1, it was approximately in the range of5.32%～23.74%and7.93μm～13.82μm respectively; while at0.01s-1, it was approximately in the range of31.56%～87.27%and10.72μm～40.26μm respectively; while at0.001s-1, it was approximately inthe range of74%～100%and36.08μm～90.23μm respectively. While at a same deformation temperature, the fraction and diameter of dynamic recrystallization wasdecreased slightly when strain rate decline from1.0s-1to0.1s-1, the maximum changerange was7.59%and16.54μm respectively, however, when strain rate decline from0.1s-1to0.001s-1, they were increased significantly, the maximum change range was83.21%and76.41μm. By considering improve workability, while temperature was inthe range of＜1050℃, the preferable strain rates should be in the range of≤0.01s-1；while temperature was in the range of≥1050℃, the preferable strain rates shouldextend to1.0s-1～0.01s-1.By studying deformation microstructure scientifically at different height reductionof the same deformation temperature and strain rate showed that, initial beta grains werestretched and flatted more and more obviously with the increase of strain at a majorityof deformation parameters.While deformation temperature was in the range of950～1100℃and strain rate was equal to0.001s-1, the critical stain of being occured dynamicrecrystallization was the minimum one, and the critical stain will increase with theincrease of strain rate while strain rate was more than0.001s-1. Furthermore, the fractionand diameter of dynamic recrystallization were all increased with the increase of strainat a same deformation temperature and strain rate. For instance, while strain wasincrease from0.11to0.92at1000℃and0.001s-1, the fraction and diameter of dynamicrecrystallization was approximately in the range of2.69%～84.48%and19.67μm～42.16μm respectively. However, the average diameters of deformation microstructurewere keeping decreasing with the increase of strain, therefore, the initial beta grainswere turn to fine. When deformation microstructure was in different strain, as strain ratedecrease from1.0to0.001, the mechanism of dynamic recrystallization changedgradually from nucleated recrystallization to continuous recrystallization. |
PDF Full Text Request