Makine imalat sanayi için düşük karbonlu beynitik çelikalaşım ve proses tasarımı
Küçük Resim Yok
Tarih
2022
Yazarlar
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Bursa Teknik Üniversitesi
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
Bu çalışmada uzun yarı mamul üretiminde üretim maliyeti yüksek ıslah çeliklerinin yerine alternatif olarak kullanılabilecek ve üretim maliyeti daha düşük yeni bir beynitik çelik alaşımın, alaşım ve proses tasarımı yapılmıştır. Makine imalat endüstrisinin kullanımına yönelik olarak tasarlanan yeni beynitik çelik alaşımın mekanik özelliklerinin ve kaynaklanabilirlik özelliğinin ıslah çeliklerine göre aynı veya daha yüksek performans göstermesi hedeflenmiştir. Bu çalışmada 42CrMo4+QT çelik alaşımının mekanik özellikleri referans olarak alınmıştır. Malzeme modelleme simülasyonlarında kullanılan JMatPro – Hesaplamalı Malzeme Mühendisliği programı desteği ile malzemenin metalürjik özellkleri hesaplanmış, kaynaklanabilirlik ve rekristalizasyon sıcaklığı hesaplamaları yapılmış ve elde edilen sonuçlara göre öngörülen çelik alaşımların laboratuvar ölçekli üretimi gerçekleştirilmiştir. Pilot ölçekli üretim sonrası laboratuvarda gerçekleştirilen mikroyapı ve mekanik karakterizasyon çalışmaları ile de final alaşım olan yeni bir düşük karbonlu beynitik (DKB) çelik alaşımı geliştirilmiştir. Teorik hesaplamalar ile elde edilen alaşımlar (2 alaşım) ile mangan ve krom oranları farklı ilave 2 alaşımın (toplam 4 alaşım) 100 kg kapasiteli vakum indüksiyon ergitme ocağında (VIM) ingot üretimi gerçekleştirilmiştir. Üretilen ingotların şekillendirme işlemi standart haddeleme prosesi (SHP) ve termomekanik haddeleme prosesi (TMHP) parametrelerine göre şahmerdanda uygulanan deformasyon ile gerçekleştirilmiştir. İngotlar şahmerdanda östenit rekristalizasyon sıcaklığının üzerinde (SHP: Tdef > TNR) ve altında (TMHP: Tdef < TNR) 30 mm çapa dövülmüştür. SHP ve TMHP uygulamalı olarak dövülen parçalardan çıkarılan mekanik test numunelerine oda sıcaklığında çekme testi ve -40°C, -20°C, 0°C ve oda sıcaklığında Charpy çentik darbe testi uygulanmıştır. Optik mikroskop (OM) ile malzemelerin faz yapıları tayin edilirken taramalı elektron mikroskobu (SEM) ile de faz yapıları daha detaylı incelenmiştir. Ayrıca beynitik ferrit plakaları ve sementit fazı (Fe3C) kalınlıkları ölçülerek TMHP prosesi ile hedeflenen ince beynit yapısının oluşumu incelenmiştir. 42CrMo4+QT (16-40 mm çap aralığı) referans mekanik özellikleri en iyi sağlayan kompozisyon nihai alaşım olarak belirlenmiştir. Elektron geri saçılım kırınımı (EBSD) tekniği ile nihai çelik alaşımda TMHP'nin mikroyapı, tane yönlenmesi ve tane boyut dağılımına olan etkisi incelenmiştir. Teorik hesaplamalar ve pilot öçekli üretim sonrasında nihai alaşımın kimyasal kompozisyonu '0,1C-3Mn-0,2Cr-1Si + Mikroalaşım elementleri (MAE)' olarak belirlenmiştir. Mekanik değerleri SHP koşulunda; Akma mukavemeti (Rp0,2) 785 MPa, çekme mukavemeti (Rm) 1095 MPa ve uzama (%A) 7,2 olarak belirlenmiştir. TMHP koşulunda ise Rp0,2 879 MPa, Rm 1215 MPa ve %A 9,5 olarak gerçekleşmiştir. Charpy çentik darbe test sonuçları, -40°C, -20°C, 0°C ve oda sıcaklığında sırasıyla SHP koşulunda 18 J, 27 J, 30 J ve 45 J, TMHP koşulunda ise 37 J, 39 J, 39 J ve 46 J olarak ölçülmüştür. Mikroyapı incelemeleri sonrasında yapının ince yapılı alt beynit ve granülar beynit karışımı ile bir miktar martenzitten oluştuğu görülmüştür. Sonuç olarak, ıslah çelikleri yerine kullanılabilecek, 42CrMo4+QT mekanik özelliklerini karşılayan, alaşım elementleri bakımından daha düşük maliyetli, ilave bir ısıl işlem gerektirmeyen ve proses süresi daha kısa olan ekonomik yeni bir beynitik çelik alaşımın tasarımı yapılmıştır.
In this study, alloy and process design of a low-cost bainitic steel grade that can be used as an alternative to high-cost quench and temper (QT) treated steels in the production of semi-finished long products has been carried out. It is aimed that the mechanical properties and weldability of the new low-cost bainitic steel grade designed for use in the machinary industry illustrate a similar or better performance compared to those of the QT treated steels. In this study, mechanical properties of 42CrMo4+QT were taken as the reference values. The chemical composition of low carbon bainitic (LCB) steel alloy was selected with the support of JMatPro – Computational Materials Engineering program used in material modeling simulations, calculations of the weldability and recrystallization temperature followed by the laboratory-scale production and finally microstructure and mechanical characterization studies carried out in our laboratory. Following theoretical calculations four different steel grades with different manganese and chromium content were produced in a 100 kg capacity vacuum induction melting (VIM) furnace. In order to perform a physical simulation of the standart rolling process (SRP) along with the thermomechanical rolling process (TMHP), the produced ingots were forged to 30 mm round pieces at two deformation temperature (Tdef) which are above (SRP: Tdef > TNR) and below (TMHP: Tdef < TNR) the austenite recrystallization temperature (TNR) respectively and subsequently they were left to cool down in still air. Charpy notch impact tests at -40°C, -20°C, 0°C and room temperature and tensile test were carried out on the mechanical test specimens machined from forged pieces. While the phase structure of the materials were investigated by optical microscope (OM), the thickness of the ferritic bainite plates and cementite were measured by scanning electron microscope (SEM), and the formation of thin bainite packages were observed. The crystallographic orientation and grain size distribution of austenite grains of the final steel grade were investigated for both SHP and TMHP conditions. After theoretical calculations, physical casting and shaping activities, the final steel grade was determined as 0.1C-3Mn-0.2Cr-1Si with microalloying elements (MAE). The mechanical properties of the final steel grade were determined as follows: yield strength (Rp0,2) 785 MPa, tensile strength (Rm) 1095 MPa and elongation 7.2% for standart rolling conditions and Rp0,2 879 MPa, Rm 1215 MPa and elongation 9.5% for TMHP. Charpy notch impact test results at -40°C, -20°C, 0°C and room temperature were measured as 18 J, 27 J, 30 J and 45 J for SHP condition and 37 J, 39 J, 39 J and 46 J for TMHP condition, respectively. Microstructural investigations revealed that the structure consisted of fine lower bainite and granular bainite with some amount of martensite phase. Consequently, in this study an economical novel bainitic steel grade has been designed that meets the mechanical properties of 42CrMo4+QT steels and has a lower cost in terms of not containing high cost alloying elements and not requiring additional heat treatment. This novel steel grade can be used instead of standart QT steel grades.
In this study, alloy and process design of a low-cost bainitic steel grade that can be used as an alternative to high-cost quench and temper (QT) treated steels in the production of semi-finished long products has been carried out. It is aimed that the mechanical properties and weldability of the new low-cost bainitic steel grade designed for use in the machinary industry illustrate a similar or better performance compared to those of the QT treated steels. In this study, mechanical properties of 42CrMo4+QT were taken as the reference values. The chemical composition of low carbon bainitic (LCB) steel alloy was selected with the support of JMatPro – Computational Materials Engineering program used in material modeling simulations, calculations of the weldability and recrystallization temperature followed by the laboratory-scale production and finally microstructure and mechanical characterization studies carried out in our laboratory. Following theoretical calculations four different steel grades with different manganese and chromium content were produced in a 100 kg capacity vacuum induction melting (VIM) furnace. In order to perform a physical simulation of the standart rolling process (SRP) along with the thermomechanical rolling process (TMHP), the produced ingots were forged to 30 mm round pieces at two deformation temperature (Tdef) which are above (SRP: Tdef > TNR) and below (TMHP: Tdef < TNR) the austenite recrystallization temperature (TNR) respectively and subsequently they were left to cool down in still air. Charpy notch impact tests at -40°C, -20°C, 0°C and room temperature and tensile test were carried out on the mechanical test specimens machined from forged pieces. While the phase structure of the materials were investigated by optical microscope (OM), the thickness of the ferritic bainite plates and cementite were measured by scanning electron microscope (SEM), and the formation of thin bainite packages were observed. The crystallographic orientation and grain size distribution of austenite grains of the final steel grade were investigated for both SHP and TMHP conditions. After theoretical calculations, physical casting and shaping activities, the final steel grade was determined as 0.1C-3Mn-0.2Cr-1Si with microalloying elements (MAE). The mechanical properties of the final steel grade were determined as follows: yield strength (Rp0,2) 785 MPa, tensile strength (Rm) 1095 MPa and elongation 7.2% for standart rolling conditions and Rp0,2 879 MPa, Rm 1215 MPa and elongation 9.5% for TMHP. Charpy notch impact test results at -40°C, -20°C, 0°C and room temperature were measured as 18 J, 27 J, 30 J and 45 J for SHP condition and 37 J, 39 J, 39 J and 46 J for TMHP condition, respectively. Microstructural investigations revealed that the structure consisted of fine lower bainite and granular bainite with some amount of martensite phase. Consequently, in this study an economical novel bainitic steel grade has been designed that meets the mechanical properties of 42CrMo4+QT steels and has a lower cost in terms of not containing high cost alloying elements and not requiring additional heat treatment. This novel steel grade can be used instead of standart QT steel grades.
Açıklama
Lisansüstü Eğitim Enstitüsü, İleri Teknolojiler Ana Bilim Dalı
Anahtar Kelimeler
Metalurji Mühendisliği, Metallurgical Engineering
