Nursel Altan Özbek

This study aimed to determine the effects of cryogenic treatment to increase the hardness, wear resistance, and tensile strength of AISI 431 martensitic stainless steel. After austenitizing, quenching, and tempering, the steel samples were subjected to shallow cryogenic treatment at −80 °C and deep cryogenic treatment at −180 °C. Samples were cryopreserved for 12 and 24 h in each case. Following these processes, a tempering heat treatment was applied at 200 °C for 120 min. Experimental results revealed that cryogenic treatment positively affected the mechanical properties of AISI 431 steel. Samples that underwent a 24-h deep cryogenic treatment, however, yielded the best mechanical characteristics. Wear resistance was most significantly affected by cryogenic treatment. Compared to the sample with only conventional hardening, the wear rate of the sample with deep cryogenic treatment for 24 h was 82% lower. Between shallow and deep cryogenic treatment types, samples treated with deep cryogenic treatment exhibited superior properties. In both species, longer cryogenic treatment holding time resulted in greater improvement in mechanical properties. Deep cryogenic treatment for 24 h provided approximately 5.61%, 7.49% and 1.75% increase in hardness, yield strength and tensile strength, respectively. In addition, cryogenic treatment has been shown to effectively reduce residual austenite, providing more homogeneous carbide distribution and new carbide precipitation.

In this work, the microstructure, hardness, tensile and yield strength, and wear resistance of X210CrW12 steel are examined in relation to the impacts of deep cryogenic treatment. In order to achieve this, deep cryogenic treatment at −180 °C was applied to X210CrW12 steel samples for 12, 18, 24, and 36 h following quenching. Following the cryogenic treatments, a tempering heat treatment was applied to the samples at 300 °C for two hours. Experimental results showed that deep cryogenic treatment significantly improved the mechanical properties of X210CrW12 steel. The best mechanical properties were obtained after applying deep cryogenic treatment for 24 and 36 h. The cryogenic treatment showed the most dominant effect on wear resistance. As a result of the wear tests performed with the pin-on-disk method, it was determined that the wear rate of the sample subjected to cryogenic treatment for 36 h was 59.37% less than that of the conventionally hardened sample. The deep cryogenic treatment applied for 36 h provided the highest hardness increase of 12.06%. Compared to the conventionally hardened sample, the tensile and yield strength in the steel subjected to deep cryogenic treatment for 24 h is up to 11.02% and 11.35% higher. As a result of microstructural analysis, it was determined that it provides cryogenic new carbide precipitation, increases carbide density, and provides a more homogeneous carbide distribution.

This study investigates the effects of shallow cryogenic treatment on the microstructure, hardness and wear resistance of 1.2436 steel. For this purpose, quenched (QT) 1.2436 steel samples were subjected to shallow cryogenic treatment at -80 °C for 12 hours (SCT12) and 18 hours (SCT18). Hardness measurement and wear test were carried out on the samples and the samples were examined microstructurally. As a result of the study, it was observed that the cryogenic treatment provided a denser and homogeneous carbide distribution in the microstructure of 1.2436 steel. The amount of carbide in the microstructure increased by 18.80% with shallow cryogenic treatment for 18 hours. As a result of the hardness and wear tests, it was determined that the cryogenic treatment positively affected the hardness and wear resistance of 1.2436 steel. Compared to the quenched sample alone, the sample cryogenically treated for 18 hours exhibited 9.28% higher hardness and 34.37% less wear.

This study investigated the effects of shallow and deep cryogenic treatment on the microstructural and mechanical properties of Sverker 21 tool steel. After conventional heat treatment, shallow cryogenic treatment at −80 °C for 2, 12, and 24 h and deep cryogenic treatment at −180 °C for 2, 18, and 36 h were applied on the steel samples. After that, the samples were tempered at 200 °C for 2 h. As a result of these treatments, the steel samples’ hardness, toughness, and wear rate changes were determined, and their microstructural properties were investigated. As a result of the study, it was observed that the cryogenic treatment had positive effects on the mechanical and microstructural properties of Sverker 21 steel. Mechanical properties also improved with increasing holding time for both cryogenic treatment types. It has been found that the deep cryogenic treatment provides better mechanical properties compared to the shallow cryogenic treatment. The maximum hardness and wear resistance were obtained in the deep cryogenically treated sample for 36 h. Compared to the CHT sample, the hardness and impact energy of the DCT(36) sample increased by approximately 11.75% and 17.36%. An improvement of approximately 64% was observed in the wear rate.

The AISI 4140 and AISI 4340 tempered steels are widely used in industry. This study investigated the effects of the tempering temperature on the mechanical properties of these steels. The steels were kept at 850 °C for 30 min, left in an oil environment, and then subjected to hardening. The samples were then tempered for 1 h at four different temperatures (300, 450, 550, and 650 °C). Hardness measurements were performed to determine the mechanical properties of the materials. In addition, the samples were subjected to tensile, notch impact, and wear tests. The samples were also examined microstructurally. The results revealed that the hardness, impact energy, and wear rates of samples of both steels decreased when tempering was applied after quenching. As the tempering temperature was increased, these values tended to decrease. However, the impact value increased in parallel with the tempering heat treatment and tempering temperature.

This study investigated the effects of cryogenic treatment and tempering temperature applied after cryogenic treatment on the mechanical and microstructural properties of AISI 431 martensitic stainless steel. After conventional heat treatment (CHT), the steel samples were cryogenically treated at -180 °C for 6 hours and then tempered at 200 °C (CT200) and 300 °C (CT300) for 2 hours. After these processes, hardness measurement, tensile test, and abrasion test were carried out to determine the mechanical properties of the steel samples. In addition, microstructure photographs were taken to determine the microstructural properties. As a result of the study, it was observed that the cryogenic treatment applied after the conventional heat treatment was effective on the mechanical properties of AISI 431 martensitic stainless steel. Cryogenic treatment and tempering temperature showed the greatest effect on wear resistance. CT200 and CT300 samples were 62% and 56% less worn than the CHT sample. Compared to the CHT sample, the yield strength of CT200 and CT300 samples increased by 6.95% and 7.03%, while the hardness increased by 3.89% and 3.52%.

This study evaluated the effects of cutting tool coating type and process parameters on flank wear and surface roughness in the turning of hardened 1.2343 hot work tool steel. Two different coated tungsten carbide cutting tools (CVD TiCN/Al ₂ O ₃ /TiN and PVD TiAlN/TiN), three different cutting speeds and three different feedrates were used for the experimental tests. Turning tests were designed based on the Taguchi method (L18). Experimental results demonstrated that the PVD TiAlN/TiN tool performed better under all cutting conditions. Analysis of variance results determined the feedrate, with an impact ratio of 82.61%, to be the parameter with the most impact on surface roughness, while flank wear was most affected by the cutting tool, with 89.12%.

Bu çalışmada, AISI H11 sıcak iş takım çeliğinin tornalanmasında kriyojenik işlemin kesici takım performansı üzerine etkileri araştırılmıştır. Deneylerde TiAlN+TiN kaplı tungsten karbür takımlar kullanılmıştır. Kesici takımlar üzerine 6 saat süre ile -80 °C’de sığ kriyojenik işlem (SCT6), 6 saat süre ile -196 °C’de derin kriyojenik işlem (DCT6) ve 24 saat süre ile -196 °C’de derin kriyojenik işlem (DCT24) uygulanmıştır. Tornalama deneyleri 0,6 mm kesme derinliği, 0,18 mm/dev ilerleme hızı ve 320, 360, 400 ve 440 m/dak olmak üzere dört farklı kesme hızında gerçekleştirilmiştir. Deneysel sonuçlar kriyojenik işlemin kesici takımın aşınma direncini artırdığını göstermiştir. En düşük kesici takım aşınması ve yüzey pürüzlülüğü değerleri DCT24 takımla elde edilmiştir. Yanak aşınmasında %13-28 oranlarda, yüzey pürüzlülüğünde ise %7-14 oranlarda iyileşmeler gözlenmiştir. Diğer yandan kriyojenik işlemin kesici takımların sertliğinde %4,4-8,7 oranlarda artış sağladığı tespit edilmiştir. En yüksek sertlik artışı da DCT24 takımda meydana gelmiştir.

Islah çelikleri, kimyasal bileşimleri özellikle karbon miktarı bakımından, sertleştirilmeye elverişli olan ve ıslah işlemi sonunda belirli bir çekme dayanımında yüksek tokluk özelliği gösteren, alaşımlı ve alaşımız makine imalat çelikleridir. Sunulan bu çalışmada, sanayide geniş kullanım alanına sahip olan AISI 4140 ıslah çeliğinin su verme işleminden sonra uygulanan temperleme ısıl işlemi sıcaklığının çeliğin mekanik özellikleri üzerine etkileri araştırılmıştır. Numunelere 850 °C sıcaklıkta su verme işlemi uygulanmış ve ardından numuneler 300, 450, 550 ve 650 °C olmak üzere dört farklı sıcaklıkta 1 saat süre ile temperleme işlemine tabi tutulmuştur. Mekanik özelliklerinin belirlenmesi için; numunelerin sertlik ölçümleri yapılmıştır. Ayrıca numuneler çekme ve darbe deneylerine tabi tutulmuştur. En düşük temperleme sıcaklığı olan 300 °C’de sertlik değeri maksimuma ulaşmıştır. En yüksek çekme ve akma dayanımı değeri de yine bu sıcaklıkta elde edilmiştir. Artan temperleme sıcaklığı ile birlikte numunelerin çekme ve akma dayanımı değerlerinde azalma görülmüştür.