Microstructure and Mechanical Behavior of a Mini-Thixoformed Tool Steel
- PDF / 544,557 Bytes
- 5 Pages / 593.972 x 792 pts Page_size
- 49 Downloads / 257 Views
forming (thixoforming) of metals is an innovative technology for producing complex-shaped specimens in a single step.[1] The high temperature of the processing method as well as intensive simultaneous deformation with rapid cooling and solidification under high pressure in some cases lead to the generation of entirely different and unique microstructures with interesting features and novel properties.[2,3] In this study, we consider a recent modification of this technique, termed mini-thixoforming: By scaling down the thixoforming equipment, small dimension specimens with thicknesses of ~1 mm can be produced. Furthermore, this laboratory-scale process is particularly optimized for a precise temperature control that allows a detailed materials science analysis of processing parameters and their effect on microstructure–property relations. One promising potential application of the mini thixoforming technique is the near-net shape forming of hard and wear-resistant materials such as crucible particle metallurgy (CPM) tool steels that are very difficult to machine conventionally, INDRANI SEN, Visiting Scientist, MARCUS BO¨HME, Research Assistant, and MARTIN F.-X. WAGNER, Professor, are with the Chemnitz University of Technology, Institute of Materials Science and Engineering, D-09107 Chemnitz, Germany. Contact e-mails: indrani. [email protected]; [email protected] HANA JIRKOVA´, Research Assistant, and BOHUSLAV MASˇEK, Professor, are with the University of West Bohemia, Research Centre of Forming Technology—FORTECH, 30614 Pilsen, Czech Republic. Manuscript submitted March 29, 2012. Article published online July 7, 2012 3034—VOLUME 43A, SEPTEMBER 2012
especially in smaller dimensions.[3–7] To the best of our knowledge, this study represents the first attempt ever to characterize microstructures and properties of a CPM tool steel after mini-thixoforming. We discuss the microstructures before and after mini-thixoforming in a CPM15V (nominal composition in wt pct: Fe-3.4C5.25Cr-14.5V-1.3Mo-0.5Mn-0.9Si) steel that, owing to its higher vanadium content compared to other steels of similar category, exhibits exceptionally high hardness and wear resistance but reduced machinability. Moreover, we use nanoindentation to assess the local mechanical performance of the resulting phases and to rationalize how the microstructural modifications achieved by mini-thixoforming affect the hardness of the tool steel—a key parameter for its practical application that is frequently related to wear resistance. Generally, for thixoforming to be effective, a specimen is typically heated to a critical temperature between the solidus and liquidus temperatures that leads to ~60 pct of solid spheroids in the liquid matrix. The material in the semisolid state can then flow with the application of shear.[8] In case of a eutectic system, with a process temperature just above the eutectic temperature, the liquid transforms into a two-phase mixture, and the contour of the primary solid globules remains well defined.[7] The operating temperature plays an
Data Loading...
