Küresel grafitli dökme demirlerin aşınma davranışına alüminyum ilavesinin ve östemperleme ısıl işleminin etkilerinin incelenmesi

Alüminyum (Al) içermeyen ve ağırlıkça %3 Al içeren küresel grafitli dökme demirler kum kalıba döküm yöntemiyle üretilmiştir. Üretim sonrası, 900 °C’de 90 dk süreyle östenit sahada tutulan numuneler, 300 °C’ye hızla soğutulmuş ve bu sıcaklıkta 60 dk boyunca bekletilmiştir. Yapılan östemperleme işleminin, dökme demirlerin mikroyapı ve aşınma özelliklerine etkisinin incelenmesi amacıyla, optik mikroskop, SEM, sertlik ve disk üzeri bilya tipi aşındırma cihazları kullanılmıştır. Al miktarı arttıkça, matristeki ferrit oranı ve grafit miktarının arttığı, buna karşılık grafitlerin küreselliğinin bozulduğu belirlenmiştir. Al ile alaşımlandırma, malzemeye daha yüksek sertlik ve daha iyi aşınma dayanımı kazandırmıştır. Östemperleme sonrası numunelerde, kalıntı östenit ve beynitik ferrit matris yapısı elde edilmiştir. %3 Al içeren numunede, östemperleme sonrası oluşan ferrit miktarının arttığı görülmüştür. Numunelerin aşınma yüzeylerinde abrazif ve adhezif aşınmanın dominant karakterde olduğu belirlenmiştir. %3 Al ile alaşımlama aşınma direncini artırırken, östemperleme işlemi alaşımsız numunenin aşınma dayanımında daha iyi sonuç vermiştir.

Anahtar Kelimeler:

Östemperleme, Küresel grafitli dökme demir, Aşınma, Alüminyum, Alaşımlama

Investigation of the effects of aluminum addition and austempering heat treatment on wear behavior of ductile cast irons

Ductile cast irons, which do not contain aluminum (Al) and contain 3 wt.% Al, were produced by the sand mold casting method. After production, the samples kept in the austenite field at 900 ° C for 90 min were rapidly cooled to 300 ° C and held at this temperature for 60 min. Optical microscope, SEM, EDS, and ball-on-disc type wear devices were used to examine the effect of austempering on the microstructure and wear properties of the cast irons. It was determined that as the amount of Al increased, the ferrite ratio and the amount of graphite in the matrix increased, whereas the nodularity of the graphite deteriorated. Alloying with Al provided higher hardness and better wear resistance. After austempering, retained austenite and bainitic ferrite matrix structure were obtained. It was observed that the amount of bainite formed after austempering decreased in the sample containing 3% Al. It was determined that abrasive and adhesive wear was predominant on wear surfaces of the samples. While alloying with 3% Al increased the wear resistance, austempering process gave better results in the wear resistance of the unalloyed sample.

Keywords:

Austempering, Ductile cast iron, Wear, Aluminum, Alloying,

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