Farklı ebatlardaki H tipi çelik konstrüksiyon profillerde hızlandırılmış soğutma ile mekanik özelliklerin incelenmesi
Küçük Resim Yok
Tarih
2022
Yazarlar
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Karabük Üniversitesi
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
Bu çalışmada, HEA 120 ile 140 ve HEB 120 ile140 ebatlarındaki S275JR kalite çelik profillerin "Hızlandırılmış Soğutma ve Kendi Kendini Temperleme (HS-KT)" ısıl işlemi sonrasında mikroyapı ve mekanik özelliklerinde meydana gelen değişiklikler incelenmiştir. HS-KT ısıl işlemi, hava+su karışımını pülüverize şekilde profil yüzeyine püskürten özel tasarlanmış ve imal edilmiş sistemle gerçekleştirilmiştir. Profillere HS-KT ısıl işlemi 4, 8 ve 12 bar hava basıncında, 10, 20 ve 30 saniye soğutma süresinde uygulanmıştır. HS-KT uygulanmış ve uygulanmamış profillerin mikroyapı incelemesi optik ışık mikroskobu, EDS donanımlı SEM analizi ve EBSD incelemesi ile gerçekleştirilmiştir. Mekanik özellikler sertlik ölçümü ve darbe testleri ile yapılmıştır. Sertlik ölçümü 750 kg yük altında 5 mm çaplı bilya ile HB cinsinden belirlenmiştir. Darbe testleri 450 J kapasiteli Charpy tipi test cihazı ile V çentikli numuneleri oda sıcaklığında kırarak gerçekleştirilmiştir. Kalıntı gerilimleri, web ve flanş bölgelerine yapıştırılan gerinim ölçerler yardımıyla kesme metodu kullanılarak ölçülmüştür. En yüksek soğutma hızı, HEA 120 profilin web bölgesinde soğutma plakası ile malzeme arasındaki mesafenin 2 kat, hava basıncı 12 bar ve soğutma süresinin 30 saniye olduğu HS-KT işlemi ile 118°C/sn. olarak elde edilmiştir. En düşük soğutma hızıda profillerin flanş bölgesinde minimum 4°C/sn. olarak tespit edilmiştir. Isıl işlemsiz malzemelerin mikroyapı Ferrit+Perlit yapısındayken, 9°C/sn.'lik bir soğuma hızına kadar yapının asiküler ferrit ve/veya poligonal ferrite dönüştüğü, 30°C/sn.'lik bir soğuma hızına kadar üst beynit ve/veya sorbit yapısının hakim olduğu, 30°C/sn.'nin üzerindeki soğuma hızlarında da alt beynit ve/veya martenzit fazının oluştuğu bulunmuştur. Isıl işlem görmemiş profillerde ki 106-120 HB aralığındaki sertlik değerinin, HEA 120 profilin web bölgesinde 118°C/sn. soğuma hızında 214 HB'ye yükseldiği, flanş bölgesindeki düşük soğuma hızından (4°C/sn.) kaynaklı olarak ısıl işlemsiz profillerin sertliğine eşdeğer olduğu tespit edilmiştir. En yüksek 118°C/sn. soğuma hızına maruz kalan HEA 120 web bölgesin -515 MPa'lık kalıntı basma gerilmesi ölçülürken flanş bölgesinde 10°C/sn.'lik bir soğutma hızında ise 332 MPa'lık kalıntı çekme gerilmesi değeri elde edilmiştir. Daha kalın kesitli olmasından dolayı HEB ebatlı profillerde hem kalıntı basma gerilmesi hem de kalıntı çekme gerilmesi daha dar aralıklarda ölçülmüştür.
In this study, microstructure and mechanical properties of S275JR quality steel sections in HEA 120 and 140 and HEB 120 and 140 sizes after "Accelerated Cooling and Self Tempering (AC-ST)" heat treatment were investigated. AC-ST heat treatment system that sprays the air+water mixture on the surface of the section in a pulverized manner is designed specially and manufactured. AC-ST heat treatment was applied to the sections at 4, 8 and 12 bar air pressure, 10, 20 and 30 seconds cooling time. Microstructure examination of AC-ST applied and untreated sections was performed by optical light microscope, EDS equipped SEM analysis and EBSD examination. Mechanical properties were made by hardness measurement and impact tests. The hardness measurement was determined in HB with a 5 mm diameter ball under a load of 750 kg. Impact tests were carried out by breaking V-notched specimens at room temperature with a Charpy type tester with a capacity of 450 J. Residual stresses were measured using the shear method with the help of strain gages adhered to the web and flange regions. The highest cooling rate was obtained as 118°C/sec in the web region of the HEA 120 section with the AC-ST process where the distance between the cooling plate and the material was 2 fold, the air pressure was 12 bar and the cooling time was 30 seconds. At the lowest cooling rate, minimum 4°C/sec in the flange area of the section was detected. While the microstructure of non-heat-treated materials is Ferrite+Pearlite, the structure changes to acicular ferrite and/or polygonal ferrite up to a cooling rate of 9°C/sec and the upper bainite and/or sorbite structure up to a cooling rate of 30°C/sec. It was found that the lower bainite and/or martensite phase is formed at cooling rates above 30°C/sec. It was determined that the hardness value in the range of 106-120 HB in the unheated sections increased to 214 HB at a cooling rate of 118°C/sec in the web region of the HEA 120 section, and was equivalent to the hardness of the non-heat-treated profiles due to the low cooling rate (4°C/sec) in the flange region. While the residual compressive stress of -515 MPa was measured in the HEA 120 web region exposed to the highest cooling rate of 118°C/sec a residual tensile stress value of 332 MPa was obtained in the flange region at a cooling rate of 10°C/sec. Due to the thicker section, both the residual compressive stress and the residual tensile stress were measured in narrower intervals in HEB sized sections.
In this study, microstructure and mechanical properties of S275JR quality steel sections in HEA 120 and 140 and HEB 120 and 140 sizes after "Accelerated Cooling and Self Tempering (AC-ST)" heat treatment were investigated. AC-ST heat treatment system that sprays the air+water mixture on the surface of the section in a pulverized manner is designed specially and manufactured. AC-ST heat treatment was applied to the sections at 4, 8 and 12 bar air pressure, 10, 20 and 30 seconds cooling time. Microstructure examination of AC-ST applied and untreated sections was performed by optical light microscope, EDS equipped SEM analysis and EBSD examination. Mechanical properties were made by hardness measurement and impact tests. The hardness measurement was determined in HB with a 5 mm diameter ball under a load of 750 kg. Impact tests were carried out by breaking V-notched specimens at room temperature with a Charpy type tester with a capacity of 450 J. Residual stresses were measured using the shear method with the help of strain gages adhered to the web and flange regions. The highest cooling rate was obtained as 118°C/sec in the web region of the HEA 120 section with the AC-ST process where the distance between the cooling plate and the material was 2 fold, the air pressure was 12 bar and the cooling time was 30 seconds. At the lowest cooling rate, minimum 4°C/sec in the flange area of the section was detected. While the microstructure of non-heat-treated materials is Ferrite+Pearlite, the structure changes to acicular ferrite and/or polygonal ferrite up to a cooling rate of 9°C/sec and the upper bainite and/or sorbite structure up to a cooling rate of 30°C/sec. It was found that the lower bainite and/or martensite phase is formed at cooling rates above 30°C/sec. It was determined that the hardness value in the range of 106-120 HB in the unheated sections increased to 214 HB at a cooling rate of 118°C/sec in the web region of the HEA 120 section, and was equivalent to the hardness of the non-heat-treated profiles due to the low cooling rate (4°C/sec) in the flange region. While the residual compressive stress of -515 MPa was measured in the HEA 120 web region exposed to the highest cooling rate of 118°C/sec a residual tensile stress value of 332 MPa was obtained in the flange region at a cooling rate of 10°C/sec. Due to the thicker section, both the residual compressive stress and the residual tensile stress were measured in narrower intervals in HEB sized sections.
Açıklama
Lisansüstü Eğitim Enstitüsü, Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı, Metalurji ve Malzeme Mühendisliği Bilim Dalı
Anahtar Kelimeler
Metalurji Mühendisliği, Metallurgical Engineering
