Estudo da reutilização do aço uddeholm vanadis® 8 superclean pela rota da metalurgia do pó a partir da técnica de moagem de alta energia (mechanical milling)

Abstract

Uddeholm Vanadis®8 Superclean steel corresponds to the grade of cold work tool steels containing high contents of carbon, vanadium, chromium and molybdenum, high wear resistance, high mechanical strength and hardness, dimensional stability and good toughness, being used in various applications as in the manufacture of dies for mechanical forming, extruders, cutlery. They are supplied to demand in the form of ingots and billets which need to be machined to form the final product. The chips generated in the machining process are often remelted and/or maybe even discarded, which harms the environment, in addition to the loss of the material's added value. In order to reuse metallic waste, the Powder Metallurgy (PM) route has proven to be an efficient alternative for having high use of raw material, low energy consumption, production of parts / components with structural and mechanical homogeneity and good superficial finish. Thus, this work had as objective the production of metallic powders by the process of high energy ball milling (HEBM) from the reuse of Vanadis®8 steel chips with and without addition of carbides. As a comparative effect on the efficiency of the HEM, three series were determined: with addition of vanadium carbides (V8VC), a mixture of vanadium, chromium and molybdenum carbides - V8(VMoCr)C and without addition of carbides (V8SC). The morphology and granulometry analyzes of the powders at different milling times were performed by scanning electron microscopy and particle size analysis by laser diffraction. The structural and mechanical characterization of the sintered, quenched and tempered were performed by scanning electron microscopy, optical microscopy, X-ray diffraction, bulk density via Archimedes and by MO, Vickers microhardness and compression testing. The results reveal that all the usual conditions in the HEBM were efficient, with an emphasis on the V8(VMoCr)C series, with an average particle size of 11.48 µm. The sintering parameters improve, increasing the average density by 86.31% in relation to the CR material, with an emphasis on a V8SC series (87.46%), evidenced by the lower apparent porosity. The quenching and tempering heat treatments promoted an increase in the microhardness and compressive strength of the new materials developed, mainly after the tempering, where the microhardness was close to the CR material, also treated. Regarding the results of maximum compressive strength and modulus of elasticity, as three series presented approximately equal values, considering the standard deviation, with emphasis on the additions of V8VC, which presented high compressive strength of 1710.29 MPa, and for the samples V8(VMoCr )C wich presented an elastic modulus of 17945.28 MPa. The microstructural transformations for the materials developed in this work were similar to Vanadis®8 steel as received. Therefore, the PM process using the HEBM technique proves to be an efficient alternative route in the reuse of Vanadis®8 tool steel chips.