Powder Metallurgy Pure Tungsten Plate Rolling Process Controlling And Optimization

With the rapid development of nuclear industry and aviation industry, the use of tungsten plates has become increasingly common. However, due to high melting point of tungsten and ductile-brittle transition temperature, crocodiling, lamination and cracking were easily formed in roll processing. Moreover, grain sizes of tungsten plates are too coarse in engineering practice, leading to a decrease of the mechanical properties and a compromise to the quality of the end product. Therefore, controlling and optimizing the process parameters aiming at reducing grain size is particularly important to tungsten plate industry.The samples were taken from the rolled tungsten plates with different thickness. The grain size of the tungsten plates were measured from26.9-57.1μm by optical metallographic microscope; X-diffraction analysis shows that a-W is the only phase in the tungsten plates; The annealing experiments shows that:heated to1000℃, hold time of30min, cooled down to400℃in the stove, and continued to cool in natural, the residual stress decreased, the fibrous tissue of tungsten plate arrange closely.The effective strain field of the rolled tungsten plates is obtained by simulation of actual rolling process with Deform software. The average effective strain of the samples and the actual measured grain sizes were analyzed, and there was a regression relationship between them. The relationship can be expressed asSetting target value of average grain size as20μm, the effective strain value of the end pass should be2.16based on the calculation. The process parameters such as rolling deformation rate, billet temperature, roll speed, friction coefficient were adjusted in order to make the effective strain value equal to2.16. Then a reasonable set of ideal process parameters were obtained.The average grain size was measured as21.886μm with the ideal process parameters. The relative error between actual and target value is9.43%, which is lower than allowable range, therefore, the relationship between the effective strain and grain size is correct. The measured grain size with the ideal process parameters was compared with the original parameters. It is found that the grain size with the ideal process parameters was much lower. The fining degree is up to34.45%, demonstrating that the ideal process parameters are feasible.