Sains Malaysiana 39(6)(2010): 999–1006

Effect of Copper Addition on Grain Refinement of Austenite in Fe-8wt.%Ni-(0-3)wt.%Cu Alloy

(Kesan Penambahan Kuprum terhadap Pengecilan Butiran  Austenit di dalam Aloi Fe-8%bt.Ni-(0-3)%bt.Cu)

Junaidi Syarif* & Zainuddin Sajuri

Department of Mechanical and Materials Engineering

Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia

43600 UKM Bangi, Selangor, Malaysia

Received: 16 September 2009 / Accepted: 10 March 2010

ABSTRACT

The effect of copper addition on martensitic structure and reversion from martensite to austenite behaviours upon heating were investigated to clarify mechanism of grain refinement of austenite in Fe-8wt.%Ni-Cu alloys. Upon water-quenching, the alloys underwent a martensitic transformation that exhibited a typical lath-martensitic structure. It was found that prior-austenite grain and martensite-packet sizes were refined with increasing copper content. The grain refinement was not due to a decrease of grain growth rate of the austenite. However, it was found that nucleation rate of the austenite on reversion was increased by the copper addition. In Fe-8wt.%Ni alloy heated in (austenite+ferrite) region, reversed austenite grains were formed at high angle boundaries such as prior austenite grain boundary and packet boundary. On the other hand, TEM observation of the Fe-8wt.%Ni-3wt.%Cu alloy revealed that fine copper particles precipitated within the martensitic structure and the reversed austenite grains also formed within lath-structures and lath boundary. It means that the copper addition promoted formation of the reversed austenite within martensitic matrix and resulted in the grain refinement of the prior-austenite in Fe-8wt.%Ni-Cu alloy.

Keyword: Austenite grain; copper addition; grain refinement; refinement martensitic steel; martensitic-austenitic reversion

ABSTRAK

Kesan penambahan kuprum terhadap struktur martensit dan pemendakan butiran kuprum serta kelakuan kebalikan daripada martensit kepada austenit pada pemanasan telah dikaji untuk mengenalpasti mekanisme pengecilan butiran austenit di dalam aloi Fe-8%bt.Ni-Cu. Selepas proses lindap kejut air dilakukan, berlaku penjelmaan martensit pada aloi berkenaan yang dibuktikan melalui kewujudan struktur lazim martensit berbilah. Butiran austenit-terdahulu dan saiz martensit-paket menjadi kecil dengan penambahan kandungan kuprum. Pengecilan butiran bukan disebabkan oleh penurunan kadar pertumbuhan butiran austenit. Sebaliknya, kadar penukleusan austenit daripada proses kebalikan meningkat dengan penambahan kuprum. Untuk aloi Fe8%bt.Ni yang dipanaskan di dalam kawasan fasa-duaan (austenit+ferit), butiran austenit berbalik terhasil pada sempadan sudut tinggi seperti sempadan butiran austenit-terdahulu dan sempadan paket. Daripada sudut yang lain, pencerapan TEM terhadap aloi Fe-8%bt.Ni-3%bt. Cu memperlihatkan butiran halus kuprum termendak di dalam struktur martensit dan butiran austenit berbalik juga terhasil di dalam dan di antara sempadan bilah martensit. Penambahan kuprum memberi kesan kepada pembentukan austenit berbalik di dalam matriks martensit, dan menyebabkan pengecilan butiran austenit-terdahulu pada aloi Fe-8%bt.Ni-Cu.

Kata kunci: Butiran austenit; kebalikan martensit-austenit; keluli martensit; penambahan kuprum; pengecilan butiran

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*Corresponding author; email: syarif@eng.ukm.my