On the Abnormal Microstructure Formed in Hot Rolled Plates and Sheets of α+β Titanium Alloys

In order to make clear the formation process, the property and the effect on tensile property of abnormal microstructure formed in hot rolled plates and sheets of α+β titanium alloys, experiment was carried out on Ti-5Al-2Cr-1Fe, Ti-4Al-3Mo-1V, Ti-6Al-4V, and Ti-8Mn alloys. Hot rolling was carried out under various conditions so as to investigate the formation process of the abnormal microstructure observed by optical microscopy, and hardness of that microstructure formed was measured by the microhardness tester.Concentration of alloying elements at the abnormal microstructure was also measured by means of electron probe microanalyzer. Tensile test was carried out on hot rolled plates and sheets with and without the abnormal microstructure to obtain the effect of the said microstructure. The results are summarized as follows:(1) The abnormal microstructure in hot rolled plates and sheets is formed, with an elongated shape, by rolling from the abnormal microstructure already existing in slab.(2) Formation of the abnormal microstructure depends on hot rolling temperature; that is, the temperature around and over β transus makes severe one.(3) The abnormal microstructure has high hardness and contains more β stabilizing elements compared to its surroundings.(4) On plates and sheets with the abnormal microstructure, the elongation, especially in the tensile property, decreases singnificantly and also severe anisotropy is detected.