FRICTION-WEAR CHARACTERISTICS OF PLASMA NITRIDED COLD WORK TOOL STEELS

Year 2020, Volume: 25 Issue: 1, 609 - 622, 30.04.2020

Ahmet Yılmaz Hakan Aydın

https://doi.org/10.17482/uumfd.630430

Abstract

D2,
D6 and Calmax cold work tool steels were heat treated in vacuum hardening, made
grinding and plasma nitrided in 75% N₂ + 25% H₂
atmosphere at 450 °C for 12 h at 2 mbar.
Characterization of samples has been carried out by means of surface roughness,
microstructure, microhardness and wear-friction. Wear-friction characteristics
of samples have been investigated using a ball-on-disc tribosystem with a WC-Co ball.
Plasma nitriding increased the surface roughness of samples. However, this
effect was decreased with higher surface roughness of base metal. Fe₄N
(γ'), Fe₃N (ε) and CrN phases were obtained on the surfaces of
samples. Higher surface hardness was obtained in the plasma nitrided D2 and D6
steels. No significant mass loss was observed in the ball on-disc tribosystem. So,
the wear of samples was characterized
with the worn surfaces using a
scanning electron microscope (SEM). Plasma nitriding improved the wear
resistance and decreased the friction coefficient of steels. Plasma nitrided D2
steel showed the highest wear resistance, whereas plasma nitrided Calmax steel
exhibited the lowest wear resistance. However, plasma nitrided Calmax tool
steel had relatively lower friction coefficient than the other plasma nitrided
steels. In general, brittle layer fractures have determined the friction
coefficient.

Keywords

Cold work tool steels, Plasma nitriding, Microhardness, Friction coefficient, Wear surface characterization

Supporting Institution

TUBITAK

Project Number

Project No. 3180859

Thanks

This work was funded by Scientific and Technological Research Council of Turkey (TUBITAK) (Project No. 3180859). The authors acknowledge to TUBITAK for financial support.

Plazma Nitrürlenmiş Soğuk İş Takım Çeliklerinin Sürtünme-Aşınma Karakteristikleri

Abstract

D2,
D6 ve Calmax soğuk iş takım çelikleri vakum altında sertleştirildi, taşlandı ve
75% N₂ + 25% H₂ atmosferinde 450 °C sıcaklıkta ve 2 mbar
basınç altında 12 saat süre ile plazma nitrürlendi. Numuneler yüzey
pürüzlülüğü, mikroyapı, mikrosertlik ve aşınma-sürtünme testleri ile
karakterize edildi. Aşınma-sürtünme karakteristiklerinin belirlenmesinde WC-Co
bilyasına sahip ball-on-disk sürtünme-aşınma sistemi kullanıldı. Plasma
nitrürleme numunelerin yüzey pürüzlülüğünü arttırmıştır. Ancak, bu etki temel
malzemenin daha yüksek yüzey pürüzlülüğü ile azalmıştır. Plazma nitrürlenmiş numunelerin
yüzeylerinde Fe₄N (γ'), Fe₃N (ε) ve CrN
fazları elde edilmiştir. Plazma nitürlenmiş D2 ve D6 çeliklerinde daha yüksek
yüzey sertlikleri elde edilmiştir. Ball-on-disk sürtünme-aşınma sisteminde
numunelerde önemli bir kütle kaybı meydana gelmemiştir. Bu yüzden,
numunelerdeki aşınma taramalı elektron mikroskobu (SEM) ile karakterize
edilmiştir. Plazma nitrürleme çeliklerin aşınma dayanımını iyileştirmesinin
yanında sürtünme katsayısını da düşürmüştür. Plazma nitürlenmiş D2 çeliği en
yüksek aşınma dayanımına sahip olurken, plazma nitrülenmiş Calmax çeliği ise en
düşük aşınma dayanımı sergilemiştir. Ancak, plazma nitrürlenmiş Calmax çeliği
diğer plazma nitrülenmiş çeliklere nazaran nispeten daha düşük sürtünme
katsayısına sahip olmuştur. Genel olarak, aşınma ürünü kırılgan nitrür
parçacıkları sürtünme katsayısını belirleyici rol oynamıştır. 

Keywords

Soğuk iş takım çelikleri, Plazma nitrürleme, Mikrosertlik, Sürtünme katsayısı, Aşınma yüzeyi karakterizasyonu

Project Number

Project No. 3180859

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