Sains Malaysiana 43(8)(2014): 1213–1219

Morphological Evolution during Partial Re-Melting of AISI D2 Cold-Work Tool Steel

(Perubahan Morfologi Keluli Kerja Sejuk AISI D2 melalui Peleburan-Semula-Separa)

M.N. MOHAMMED, M.Z. OMAR*, J. SYARIF & M.S. SALLEH

Department of Mechanical and Materials Engineering, Faculty of Engineering and Built Environment

Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

Received: 28 December 2012/Accepted: 26 November 2013

ABSTRACT

The impact of isothermal temperature and holding time on the microstructural evolution process is studied. This process is used to produce globular microstructures during partial re-melting of AISI D2 cold work tool steel. The experimental results showed that the optimum process factors should be selected according to the criteria for average grain size and shape factor and also by acknowledging the distribution of the liquid phase around the grains. With increasing isothermal temperature and holding time, the liquid phase starts to diffuse into the grain boundaries and spread more evenly. Also, the equiaxed grains were transformed into near-globular shape, which makes the grain size and shape factor more favourable for thixoforming. The work shows that the optimal process condition for the thixoforming of AISI D2 is 1340°C and 5-min holding time, having a shape factor of 1.13 and a particle size of 51 μm.

Keywords: AISI D2; direct partial re-melting; microstructure evolution; thixoforming

ABSTRAK

Kesan suhu dan masa memegang proses evolusi mikrostruktur telah dikaji. Proses ini digunakan untuk menghasilkan mikrostruktur globular untuk besi gred AISI D2. Keputusan uji kaji menunjukkan bahawa proses optimum dipilih mengikut kriteria untuk saiz ira purata dan faktor bentuk dan juga menggunakan pengagihan fasa cecair sekitar ira yang terbentuk. Dengan peningkatan suhu dan masa, fasa cecair mula meresap ke dalam sempadan ira dan tersebar lebih merata. Ira juga telah berubah ke dalam bentuk bulat, yang menjadikan saiz ira dan faktor bentuk yang lebih baik untuk kerja pembentukan-tikso. Kerja-kerja ini menunjukkan bahawa keadaan proses yang optimum untuk pembentukan-tikso D2 AISI ialah 1340°C dan masa yang diambil ialah 5 min. Ia mempunyai faktor bentuk 1.13 dan saiz zarah 51 μm.

Kata kunci: AISI D2; evolusi mikrostruktur; mengarahkan sebahagian lebur semula; pembentukan-tikso

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*Corresponding author; email: zaidi@eng.ukm.edu.my