AIŠMAN David University of West Bohemia

Spoluautoři PILEČEK Vít, JENÍČEK Štěpán

Mini-thixoforming is processing method consisting of forming of metals in the semi-solid state at temperatures between solidus and liquidus. Small amount of the metal could be rapidly heated and subsequently solidified with high precision and dynamics. Thanks to this facts, even the materials with narrow semi-solid state interval, which are unsuitable for conventional processing methods, can be processed. To the group of conventional materials belongs also tool steels with ledeburitic microstructure. Their microstructures after thixoforming consist mostly of polyhedral grains of metastable austenite surrounded by carbide network. To obtain unconventional microstructures, steels with specific chemical composition produced by powder metallurgy were used. Wide range of alloying elements contents were chosen to cover the effect of individual alloying elements, particularly of vanadium, chromium, molybdenum and tungsten. New steels CPM 15V, CPM S30V, K190 and CPM REX121 were chosen for experimental program. Necessary forming parameters were first calculated for all the materials in JMatPro software. Based on these parameters, the first semi-solid forming tests were carried out. Identification of suitable parameters of semi-solid state processing resulted in desired filling of the cavity of the form and good surface quality of the products. All materials possessed after mini-thixoforming austenitic-martensitic matrix with various types of carbides. This caused significant increase of compression yield strength and hardness. For example yield strength of CPM 15V steel increased from the original 627MPa to 1990MPa. This was also reflected by hardness increase after thixoforming from 298 HV 10 to 728 HV 10.

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