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
Diserahkan: 16
September 2009 / Diterima: 10 Mac 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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*Pengarang untuk
surat-menyurat; email: syarif@eng.ukm.my
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