Yapı çeliklerinin mikroyapısı ve faz dönüşümleri üzerine hava soğutmalı ısıl işlemin etkisi

Yıl 2025, Cilt: 14 Sayı: 1, 360 - 369, 15.01.2025

Semih Mahmut Aktarer

https://doi.org/10.28948/ngumuh.1578719

Öz

Bu çalışmanın amacı, S235JR, S275JR ve S355JR yapısal çeliklerinin hava soğutmalı ısıl işlem sonrası mikro yapısını, faz dönüşümlerini ve sertlik değişimini incelemektir. Çelik numuneleri, 1000°C’de östenitleştirdikten sonra havada soğutulmuş ve soğuma esnasında numune sıcaklıkları bir termokupl ile kaydedilmiştir. Numunelerin mikro yapı incelemeleri ile faz dönüşümleri hem deneysel yöntemlerle hem de Faz Diyagramlarının ve Termokimyanın Bilgisayarla Birleştirilmesi (CALPHAD) malzeme özelliği yazılımıyla analiz edilmiştir. Yapı çeliklerinde artan karbon ve mangan içeriği faz dönüşüm sıcaklıklarını düşürerek beynit oluşumunu arttırdığı, ferrit ortalama tane boyutunu küçülttüğü ve bu yüzden de sertlik değerlerinde artışa yol açtığı görülmüştür. Yazılım ile belirlenen faz oranları ve sertlik değerleri, deneysel sonuçları %3'ten düşük bir sapma ile tahmin etmiştir. Bu sonuçlar, hava soğutma ile dengeli bir ferrit ve beynit faz dağılımının elde edildiğini ve malzeme özellik yazılımının bu faz dönüşümlerini başarılı bir şekilde modelleyebildiğini göstermektedir.

Anahtar Kelimeler

Yapısal çelikler; Havada soğutma, Mikroyapı, Faz dönüşümü, CALPHAD

The effect of air-cooling heat treatment on the microstructure and phase transformations of structural steels

Öz

The aim of this study was to investigate the microstructure, phase transformations, and hardness changes of S235JR, S275JR, and S355JR structural steels after air-cooled heat treatment. The steel samples were austenitized at 1000°C and then cooled in air, and the sample temperatures were recorded with a thermocouple during cooling. The microstructure and phase transformations of the samples were analyzed both experimentally and with the Computerized Combining Phase Diagrams and Thermochemistry (CALPHAD) material property software. It was observed that higher carbon and manganese levels in structural steels lower the phase transformation temperatures, promote bainite formation, reduce the average ferrite grain size, and consequently lead to an increase in hardness. The phase ratios and hardness values were determined by the predicted experimental results with a deviation of less than 3%. These results show that a balanced ferrite and bainite phase distribution is achieved air cooling and the software effectively models these transformations.

Anahtar Kelimeler

Structural steels, Air cooling, Microstructure, Phase transformation, CALPHAD

Kaynakça

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