Abstract
M2 tool steel was used as a feedstock material for casting from the the semisolid range between 1310-1350oC corresponding to 25 - 50 % of the liquid phase. The chemical composition of the investigated steel is following: 0.85%C, 3.9 %Cr, 6.7 %W, 4.7 %Mo and 1.7 % V. A specially constructed machine allowed thixoforming in a protective argon atmosphere and semisolid forming at a high piston velocity powered by a high air pressure. After heating of the feedstock using induction heating by the stamping of semi-liquid sample to a graphite mould pre-heated by resistance heating. The material after thixoforming from 1315oC shows a globular microstructure with a relatively small globule’s size between 30-50 μm. The crystal structure of globules contained, austenite and martensite, while that of the eutectic, ferrite and W2C, Fe3C, Mo2C, M23C6 and VC carbides as determined by X-ray studies and confirmed using electron diffraction studies. The alloying elements like Mo, W and V are concentrated in the eutectic, while Cr only in thixoformed samples segregates to the carbides and indeed M23C6 was identified. The hardness significantly increases up to 780 HV after thixo-forming due to formation of martensite. The other part was cast from the liquid phase at 1450o C using melt spinning method allowing high cooling rate. The microstructure of melt spun ribbon shows a cellular microstructure of austenitic and martensitic structure without the eutectic. The WC and M23C6 carbides were located at the cell’s boundariers. The microhardness near 1300 HV of the ribbon was much higher than that of semisolid formed samples.
Highlights
The application of Semi Solid Metal (SSM) processing for steels is still at the development stage due to a high melting temperatures and the narrow liquidus-solidus range for a low carbon steels, which are of interest for a common use
SSM processing has been investigated for several steels compositions, starting with experimentally easier high carbon, mostly X210CrW12 tool steels with a broad semisolid range [1,2,3], through intermediate like M2 steels [3,4,5], up to a low carbon containing steels [6,7]
As results from the X-ray diffraction taken from the thixocast steel presented in Fig.2 the globules consists of austenite and ferrite
Summary
The application of Semi Solid Metal (SSM) processing for steels is still at the development stage due to a high melting temperatures and the narrow liquidus-solidus range for a low carbon steels, which are of interest for a common use. In order to obtain an easy flow of the semi-solid slurry, a microstructure of the alloy prior to forming should consist preferably of solid solution metal spheroids in a liquid matrix [2,3,4,5,6,7]. Such a microstructure can be obtained when the steel is initially cold or hot deformed prior to heating to a semisolid range [1,2,3,4,5,6,7]. In the X210CrW12 steel it was reported [2] that after
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
