Farklı kimyasal bileşimlerdeki  sert dolgu aşınma plakalarının özelliklerinin incelenmesi, geliştirilmesi ve optimizasyonu
Characterization, improvement and optimization of different chemical composition hardfacing wear plates
Yazar: UMUT DOĞAN TURUNÇ
Danışman: PROF. DR. İSMAİL YILMAZ TAPTIK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı / Üretim Metalurjisi ve Teknolojileri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Makine Mühendisliği = Mechanical Engineering ; Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Sistem ekipmanlarının aşınması sanayide karşılaşılan en önemli ve en yaygın problemdir. Sektörlerde süregelen pahalı kesintiler ve makine bileşenlerinin değiştirilmesinin maliyetini azaltmak için yöntemler ve malzemeler geliştirmek için sürekli bir mücadele olmuştur. Sert dolgu işlemi çok yönlü tekniklerden en önemlisi olup metal altlık üzerine çeşitli metal ve alaşımları sert ve aşınmaya dayanıklı tabakalar şeklinde kullanıcıya sunmaktadır. Sadece aşınmaya dayanımı arttırmakla kalmayıp, servis ömrünü uzatmaya ve maliyetleri düşürmeye yardımcı olmaktadır. Sertdolgu kaynak yöntemiyle üretilen aşınma plakaları;  abrasif aşınma etkisi altında çalışan sistemlerin üretilmesi ve aşınmış sistem yüzeylerinin yenilenmesi için maliyeti de azaltarak sanayiye hizmet eden güncel çözümdür. Aşınma plakaları birçok kaynak uygulamasının yerine doğrudan uygulanarak tamir - bakım masraf ve zaman kayıplarının önüne geçmektedir. Bu sayede  abrasif aşınma içeren birçok uygulamada çalışabilmeye olanak sağlamıştır. 
Bu akademik çalışmada, şu anda ülkemizde gelişime açık durumda olan sertdolgu aşınma plakalarının  gerektirdiği teknolojik ve bilimsel bilgiye ulaşmak istenmektedir. Yapılan araştırmada Fe-Cr-C esaslı ve Si, Mn ihtiva eden sertdolgu aşınma plakalarının karmaşık kimyasal bileşiminin geliştirilerek abrasif aşınma dayanımlarının iyileştirilmesi amaçlanmıştır. Yapılan deneyler; kimyasal bileşim deneyleri, metalurjik mikroyapı incelemeleri, abrasif aşınma dayanımı deneyleri, sertlik deneyleri, aşınma deneyi sonrası mikroyapı incelemeleri kontrol edilerek standartlara ve proje hedeflerine uygun olup olmadığı belirlenmiştir. 
Bu tez çalışma aşamasında aşınma plakaları melez bir toz altı kaynak yöntemiyle sertdolgu kaynakları yapılmıştır. ASTM G65 abrasif aşınma testi esas alınarak ve Avrupa standardı EN 14700 standardı çerçevesinde yapılan karakterizasyon deneyleri ile çeşitli miktarda element içeren aşınma plakalarının mekanik ve mikroyapısal özellikleri birbirleri ile karşılaştırılmıştır. Daha sonra bu veriler ve literatür çalışmaları değerlendirilerek yeni aşınma plakası tasarımları yapılmıştır. Yapılan beş aşınma plakası tasarımıyla birlikte istenilen mekanik değerlere ulaşarak gelişme sağlanmış ve başarılı olunmuştur.
Aşınma plakalarının özelliklerin incelenmesi ve karakterizasyonu için deney planı oluşturulmuştur. Bu deney planına göre kaynak deneyleri gerçekleştirilmiştir. Elde edilen tecrübeler doğrultusunda sert dolgu kaynağıyla üretilen aşınma plakaları uygulamalarına özelleştirilmiş balık kılçığı hazırlanmıştır. Literatürdeki diğer çalışmalar ile karşılaştırmalar yapılarak elde edilen sonuçların geçerliliği araştırılmıştır.  
 
Elde edilen sonuçlar doğrultusunda Aşınma Plakalarının sanayideki birçok alanda kullanımının yaygınlaştırılması amaçlanmaktadır. Aşınma Plakalarının kullanımının yaygınlaşması sonucunda sanayi kuruluşlarında aşınmaya bağlı üretim ve hizmet kesintisinin daha aza indirilmesiyle beraber maliyetlerde belirgin azalma öngörülmektedir.
Deneysel çalışmalar kapsamında aşınma plakaları istenilen kaynak kalitesini sağlamakla beraber tasarım aşamasından sonra uygulamanın gerekli mekanik ve kimyasal özellikleri sağladığı görülmektedir. Aşınma plakaları diğer muadil malzemelere göre üstünlük sağlamaktadır. Abrasif aşınma dayanım performansı ve fiyatı gibi tekno-ekonomik faktörler de göz önüne alındığı takdirde aşınma plakaları birçok uygulama için rakipsiz konuma gelmektedir.

Abstract:
Wear of the system equipment is the most important and the most common problems encountered in the industry. To reduce the cost of replacing expensive ongoing interruptions and machine components; industry has been in a constant struggle to develop methods and materials. Hard-facing process as one of the most important versatile techniques offers the user various metals and alloys in the form of hard and wear-resistant layers on the metal base. Not only increase wear resistance and helps extend the service life and reduce costs. Wear plates produced by the hard-core welding- through developing working systems under the influence of abrasive wear, and reducing the cost of system renewal of worn surface-is the current solution serves the industry. Wear plates when applied directly instead of multiple welding applications, prevents repair and maintenance costs and time loss. Thus, providing an opportunity to be able to work with many applications involving abrasive wear.
In this academic work, it is desired to achieve clear technological and scientific knowledge that is required by technical hard-facing wear plates which is currently in development. The survey aimed to improve the abrasive wear resistance  of Fe-Cr-C based, and Si-Mn containing hard-facing wear plates by developing the complex chemical composition. Verified by experimental studies; chemical composition tests, metallurgical micro-structure examinations, abrasive wear resistance tests, hardness tests, and determined whether it is appropriate to wear tests with standards and project objectives.
In this thesis, hard-facing wear plates are made with a hybrid open-submerged arc welding method. Under ASTM G65 abrasive wear test basis and within the framework of the European standards of EN 14700 standards characterization experiments has been conducted through which mechanical and micro-structural properties of wear plates containing various amounts of elements are compared with each other.
An experimental design (test plan) to investigate the characterization and properties of wear plates has been formed and welding test carried out according to this test plan. In accordance with the experience obtained, a fish-bone has been prepared which is customized to the applications produced by hard-facing wear plates. The validity of the results obtained by comparison with other studies in the literature have been investigated.
Based on the results obtained to extend the use of wear plates in many areas of the industry has been aimed. As a result of widespread use of Wear Plates in industrial establishments minimizing interruptions in production and service due to wear and  a significant cost reduction is expected. Following the characterization studies above mentioned, the following results were obtained:
 
•	After hardfacing coating process has been carried out, the investigation of the properties of the wear plate and characterization has been performed and conformity to standards EN 14700 FE-14 through chemical composition and hardness values of samples investigated and verified.
•	During cross sectional upper surface examination of the micro-structure through optical microscope and scanning electron microscope, except for Sample number 3 expected in all wear plate samples containing the primary chromium carbides hyper-eutectic system occurs and hexagonal M₇C₃ primary chromium carbide has been observed. In the wear plate number 3 in, unwanted lower-eutectic primary austenite structure which is assumed to occur from the failure of the carbon content and to affect adversely the strength properties, and M₇C₃ eutectic carbides dispersed in the primary austenitic phase has been detected. The results of EDX analysis of all wear plates samples has been confirmed consistency with the experimental results of the chemical composition. When results of cross-sectional EDX analysis are analyzed the carbon content of primary chromium carbides has increased as expected while moving towards the surface of the coating from the metal base of the coating.
•	Hardness test results supporting micro-structure analysis results to be the lowest and under the usual was obtained in the wear plate sample number 3.
•	Wear tests has been conducted in accordance with ASTM G 65 test by providing the most appropriate test equipment and components within the framework of standard ASTM G65 procedure A which is most suitable to abrasive wear seen with work environment in targeted areas of the wear plate. Abrasion resistance tests have also been clearly observed to be compatible with other test results; as per No. 3 sample showed the significant lowest abrasion resistance among wear plates. As another but important results of the ASTM G65 abrasive wear test the samples of abrasive wear plates have been found to show very high abrasion resistance as compared to the samples of Hardox S235JR. Wear test results showed parallelism with the sample hardness.
•	Considering the above assessments, the wear plate sample No.3 although associated with chemical composition, range values of hardness standard; due to not meeting expected value in terms of wear resistance performance and hardness value as per ASTM G65 the new wear plate designs have been realized. 
Provided that, wear resistance and toughness properties of designed wear plates based on the Fe-Cr-C phase diagrams is at least 3.5% carbon content under the operating temperature. Thus, the prediction of expected formation and requested basic features rise due to the increase of (Cr,Fe)₇C₃ of (M₇C₃), carbide density rise, significant increase of the hardness and abrasion resistance rate have been assumed; and after the development studies on the five wear plate designs the following results have been achieved;
•	In the first three wear plate design, carbon ratio has been increased gradually. Then the element C is kept constant but Si and Mn ratio is increased. The chemical % composition of the final fifth wear plate design formed as; C: 5.0 / Cr: 28.2 / Si: 1.03 / Mn: 1.29. When both cross-sectional of and upper surface images of the welding area of the T5 wear plate analyzed by optical microscopy and scanning electron microscopy, the desired primary chromium carbides M₇C₃ has been observed. M₇C₃ hexagonal chromium carbide grains are observed comfortable than the previous samples. And EDX analyses are consistent with the chemical composition analysis. Due to improved micro-structure and carbide 
 
density of the T5 design has achieved better abrasion resistance values than the other samples. This result supports the result of the improvement in wear resistance performance.
•	Average hardness values as of the status in the final design results as compared to the initial sample No. 3, increased by 10 Rockwell C. In this case, increase of the rate C is in the foreground.
•	Depending on the % weight loss compatible with the increase of the hardness of abrasion resistant material even though there is no linear relationship between hardness and wear resistance.
•	The amount of carbide is increasing due to the increase of carbon content, and thus hardness and abrasive wear resistance increase too.
•	Chemical composition of all design values have been in accordance with standards EN 14700 FE-14, FE-15. Therefore, in all wear plate designs the micro-structure content specified in the standards have been observed. Moreover, all the hardness test results of the design are consistent with hardness range of the same standards and abrasive wear resistance, which are consistent with standard usage.
•	After the abrasive wear test ASTM G65, regions subject to wear and not exposed to wear has been studied. Abrasive wear of the eutectic phase has been found to be more. Hexagonal primary chromium carbide grains are making stops as barrier effect against abrasive wear, they prevent erosion and have been identified fragmentation not completed.
Within in the scope of the experimental applications, although the wear plates provide the quality desired by welding work, but it is seen that the required mechanical and chemical properties provided only after the design stage. Wear plates is superior as compared to other similar materials. If techno-economic factors such as abrasive wear resistance and price are taken into consideration the wear plates reach unbeatable competitive performance and position for many applications.