The Breakdown of Carbide Network in a H23 Tool Steel by Hot Axisymmetric Compression Meilinda Nurbanasari 1,a , Panos Tsakiropoulos 2,b , and Eric J. Palmiere 3,c 1 Department of Mechanical Engineering, Institut Teknologi Nasional, Bandung, Indonesia Jl. PHH. Mustapha 23, Bandung, 40124, West Java, Indonesia 2,3 Department of Materials Science and Engineering, The University of Sheffield, Mappin street, S1 3JD, Sheffield, United Kingdom a meilinda@itenas.ac.id, b p.tskiropoulos@sheffield.ac.uk, c e.j.palmiere@sheffield.ac.uk Keywords: axisymmetric compression, carbide, solutioning temperature, microstructure Abstract. The effects of hot axisymmetric compression to break down the primary carbide network of the H23 tool steels were studied. This current study only focused on one strain rate of 0.01 s -1 . The samples were deformed at 3 different temperatures (1000, 1050 and 1100 o C) with solutioning temperatures 1100 and 1250 o C, respectively. Afterwards, the samples were cooled by water quenching. The techniques used in this current study for investigation were the optical and electron microscopes and Vickers hardness test. The results show that hot axisymmetric compression had broken down the primary carbide network in the direction perpendicular to the compression axis and the carbides became finer. Although the highest hardness (274 HV) was achieved after solutioning at 1250 o C, followed by deformation at 1000 o C, however the microstructure analysis indicated that the optimum hot axisymmetric compression condition was solutioning at 1250 o C and deformation at 1000 o C. Introduction The H23 tool steel contains high alloying elements, namely W and C (each at around 12 wt%), which are carbide forming elements. The carbides give a very significant contribution to determine mechanical properties of tool steels. The formation of carbide network in tool steels during solidification leads to detrimental their mechanical properties. The thermo mechanical processing (TMP) of tool steels is of great interest from both fundamental and industrial viewpoints due to the formation of carbides’ network in the ingot that remain throughout processing. The TMP refers to high temperature deformation at T > 0.6 T m where T m is the melting temperature in degrees Kelvin [1]. At temperatures above 0.6 T m , plastic deformation is strongly affected by thermally activated processes, thus the flow stress and structure changes are mainly functions of material, temperature and strain rate. The increase in peak stress of tool steel is more sensitive to the presence of carbides than alloying elements in solution in the austenite matrix. The hard carbide precipitates cause increase in flow stress and Q def . According to Milovic, Manojlovic et al [2] and Imbert, Ryan et al [3] the Q def suddenly increases when M 23 C 6 carbides precipitate around 1000 o C. Another study by Imbert and McQueen [4] showed that the Q def of a M2 tool steel was 14 % higher than that of a A2 tool steel due to greater alloy carbide content. The peak stress of tool steels is in general greater than that of carbon and HSLA steels due to greater amounts of alloying elements [5]. In this study, the effects of high axisymmetric compression parameters, namely solutioning and deformation temperatures on the microstructure and hardness of the H23 tool steels were studied. Special attention was paid to establish the deformation conditions that lead to break down of the carbide network occurred during solidification. Experimental Method The investigated H23 tool steel was melted using vacuum induction furnace with air cooling. The chemical composition (% wt) of the ingot was 0.3 %C, 0.4 %Mn, 0.5 %Si, 12.3 %Cr, 0.4 %Ni, 12.3 Advanced Materials Research Vol. 1043 (2014) pp 149-153 Submitted: 13.08.2014 Online available since 2014/Oct/20 at www.scientific.net Accepted: 13.08.2014 © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.1043.149 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 183.91.86.34-23/10/14,08:20:43) For personal use only