Journal of Materials Processing Technology 210 (2010) 1632–1635 Contents lists available at ScienceDirect Journal of Materials Processing Technology journal homepage: www.elsevier.com/locate/jmatprotec Semisolid structure for M2 high speed steel prepared by cooling slope Behnam Amin-Ahmadi ∗ , Hossein Aashuri Department of Materials Science and Engineering, Sharif University of Technology, Azadi Ave., Tehran, Iran article info Article history: Received 17 February 2010 Received in revised form 18 May 2010 Accepted 21 May 2010 Keywords: Globular structure M2 steel Semisolid processing Cooling slope Angle Super heat Molten metal abstract Effects of cooling slope angle and the temperature of molten metal on the globular structure of M2 high speed steel after holding at the semisolid state have been investigated. The globular structure was achieved by pouring the molten metal at 1595 ◦ C on the ceramic cooling slope with the length of 200 mm and the angle of 25 ◦ . The globular structure of M2 high speed steel in the form of rolled–annealed and as cast condition after holding at semisolid state has been achieved. The size of globular grains of cool- ing slope sample was smaller than that of the rolled–annealed and as cast samples. Solid particles of rolled–annealed sample after holding at semisolid state had better roundness compared with cooling slope sample. Dissolution of carbides in the austenite phase at grain boundaries leads to formation of globular particles in the semisolid state. MC-type and M 6 C-type eutectic carbides reprecipitate during cooling cycle along grain boundaries. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Semisolid processing is an attractive technology which offers the ability to produce components for the automotive industry. The thixoforming method combines the near net shape capabili- ties of die casting process with the final mechanical properties of the forging process, resulting in a very sound product (Birol, 2007). Many studies have been done on semisolid metal forming (ssm) of light alloys like aluminum and magnesium alloys. In the last decades, many research works have been based on thixoforming of high temperature materials or ferrous alloys (Bramann et al., 2004). Thixoformed parts have higher quality (improved elongation) compared with the ones which are produced by die casting method. They have lower cost than forging parts. Although thixo- forming offers significant advantages compared with traditional metal forming methods, the process requires special feedstock. Thixoforming uses semisolid slurries with globular solid particles uniformly distributed in a liquid matrix. There are many methods to achieve semisolid slurry such as strain-induced melt activated (SIMA), the isothermal treatment and casting using a cooling slope (Haga and Suzuki, 2001; Haga and Kapranos, 2002). In the cooling slope method, the alloy with an appropriate superheat is cast over an inclined cooling plate. It is common to use a simple water-cooled plate in the thixoforming of aluminum alloys (Haga and Kapranos, 2002). The fragmented dendrites on the surface of cooling slope ∗ Corresponding author. Tel.: +98 21 66165227; fax: +98 21 66005717. E-mail address: behnam.aminahmadi@gmail.com (B. Amin-Ahmadi). plate become spherical after being maintained in the semisolid state (He et al., 2008). The fragmentation of dendrites during pouring of the molten metal on the cooling slope occurs by a number of mechanisms: (a) fragmentation of dendrites due to applying the stress. The stress is created by melt flow (b) remelting of the root of secondary den- drites assisted by the diffusion of melt into the inter-dendritic regions, (c) remelting of dendrite arms due to increase in melt tem- perature resulted in the turbulence of molten metal during pouring on the cooling slope, (d) decreasing of the melting point of dendrite arms due to rejection of alloying elements during solidification, (e) plastic deformation of dendrite arms due to melt flow and forma- tion of grain boundaries. Grain boundaries will form due to the high concentration of dislocations in the deformed regions. These high energy grain boundaries are unstable and become wet easily by the molten metal (Pahlevani et al., 2004). The produced samples by using cooling slope cannot become globular without being held at the semisolid state (Birol, 2008). In the present research work, effects of cooling slope angle and the temperature of molten metal on the globular structure of M2 high speed steel after holding at the semisolid state have been investigated. Besides, The globular structures of M2 high speed steel in the form of the rolled–annealed and as cast conditions was investigated for comparison of results. 2. Materials and methods The experiments were carried out by melting the steel grade HS6-5-2 inductively. HS6-5-2 (1.3343) is a high speed steel which is applied for cutting tools. M2 high speed steel with chemical com- 0924-0136/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2010.05.011