Nizamettin Kahraman

Wear behaviour of bulldozer rollers welded using a submerged arc welding process

Abstract The submerged arc welding process is commonly used due to its easy applicability, high current density and its ability to deposit a large amount of weld metal using more than one wire at the same time, especially in restoration of worn parts, which is of great importance to manufacturers. In this study, worn parts were welded using the submerged arc welding process. Various wires and fluxes were used for this purpose. These welded parts were subjected to wear tests under different loads, and changes in the hardness and microstructures were examined. A pin-on-disk wear test apparatus was used. The results showed that the hardest weld metal showed the highest wear resistance, while the least hard weld metal showed the least wear resistance. The weld hardness and wear resistance obtained were found to be dependent on the chemical composition of the weld wire and flux.

Abrasive wear behaviour of powder flame sprayed coatings on steel substrates

The main purpose of thermal spraying method is to produce wear resistant surfaces. Easy applicability, very low possibility of metallurgical changes and low distortion of coated parts due to low heat transfer to the substrate and salvation of worn parts are some of the practical advantages of this process. In this study, abrasive wear behaviour of powder flame sprayed coatings on steel substrates has been investigated. Coating was carried out onto both hot and cold substrates by using four types of powders. Prior to the wear tests, the coated specimens were machined on a lathe and surface roughness and hardness measurements were carried out on the machined surfaces. Heating the substrates prior to the coating led to the decrease in the hardness of the coating layers. Abrasive wear resistance of flame sprayed coatings was seen to be dependent on the chemical composition and characteristics of coating materials and coating condition.

A novel approach to diffusion bonding of copper to stainless steel

In this study, austenitic stainless steel and copper materials were bonded through the diffusion welding method, one of the solid-state welding processes. The welding process was carried out at 875°C temperature for 30 minutes under 3 MPa pressure. Two different methods were employed in the welding process. In the first method, the conventional diffusion welding procedure was followed. In the second one, an external electrical current was applied to the parts to be joined with the help of a system that was added to the conventional system. By doing so, the aim was to determine the diffusion amount and length for the specimens obtained with and without current. The weld quality of the diffusion welded specimens was examined using the tensile and hardness test. In addition, microstructural analyses were done using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The highest hardness value was obtained in regions next to the interface and it was decreased gradually as the distance from the interface increased on both sides of the interface. The results indicated that the highest interface strength was obtained for the specimens joined when the external current was applied. According to the EDS and EDS line element analyses results, it can be seen that the specimens joined by applying the external current had a higher amount of diffusion and length than the specimens joined by the conventional technique.

Investigation of the Microstructural, Mechanical and Corrosion Properties of Grade A Ship Steel-Duplex Stainless Steel Composites Produced via Explosive Welding

AbstractGrade A ship-building steel-AISI 2304 duplex stainless steel composite plates were manufactured via explosive welding. The AISI 2304 plates were used to clad the Grade A plates. Optical microscopy studies were conducted on the joining interface for characterization of the manufactured composite plates. Notch impact, tensile-shear, microhardness, bending and twisting tests were carried out to determine the mechanical properties of the composites. In addition, the surfaces of fractured samples were examined by scanning electron microscopy (SEM), and neutral salt spray (NSS) and potentiodynamic polarization tests were performed to examine corrosion behavior. Near the explosion zone, the interface was completely flat, but became wavy as the distance from the explosion zone increased. The notch impact tests indicated that the impact strength of the composites decreased with increasing distance from the explosion zone. The SEM studies detected brittle behavior below the impact transition temperature and ductile behavior above this temperature. Microhardness tests revealed that the hardness values increased with increasing distance from the explosion zone and mechanical tests showed that no visible cracking or separation had occurred on the joining interface. The NSS and potentiodynamic polarization tests determined that the AISI 2304 exhibited higher corrosion resistance than the Grade A steel.

AISI 8620 çelik malzemelerin plazma püskürtme yöntemiyle kaplanması ve kaplamaların karakterizasyonu

Bu calismada, sementasyon islemi gormus AISI 8620 celik malzemenin asinan yuzeyleri farkli kimyasal icerige sahip tozlarla, plazma puskurtme yontemiyle kaplanarak tekrar kullanima uygun hale getirilmesi amaclanmistir. Kaplamalarin servis sartlarindaki asinma dayanimlarini belirlemek icin asinma testi, kaplama tabakasi ve arayuzeylerin karakterizasyonu icin sertlik testi yapilmistir. Ayrica kaplama numuneleri uzerinde arayuzey ozelliklerini belirlemek icin, taramali elektron mikroskobu (SEM/EDS) calismalari gerceklestirilmistir. Yapilan sertlik olcumleri sonucunda; en fazla yuzey sertligine sahip kaplamanin 72F-NS kaplamasi oldugu tespit edilmistir. Asinma testleri sonucunda en yuksek asinma direnci CRC-106 kaplamasindan elde edildigi ve onu sirasiyla 68 F-NS-1, 72F-NS AMDRY 962 takip ettigi bulunmustur. SEM/EDS incelemeleri sonucunda kaplama tabakalarinin lamelli oldugu ve kaplama tabakasi ile arayuzeyde oksitlerin olustugu gozlenmistir.

S235JR karbon çeliği ile AISI 430 ferritik paslanmaz çeliğin mig kaynak yöntemi ile kaynak edilebilirliğinin incelenmesi

Bu calismada farkli kimyasal bilesime ve mekanik ozelliklere sahip, dusuk karbonlu celik (S235JR) ile ferritik paslanmaz (AISI 430) celik malzemeler MIG kaynak yontemi ile farkli tel ilerleme hizlarinda (kaynak akimi) birlestirilmislerdir. Kaynak uygulamasi gerceklestirilmis kaynakli birlestirmenin mekanik ozelliklerini belirlemek icin kaynakli baglantilara cekme deneyi yapilmis, ayrica kaynak bolgesinde sertlik olcumleri gerceklestirilmistir. Son olarak kaynak metalinde meydana gelen olusumlar ve ITAB’daki degisimleri belirlemek icinde mikroyapi calismalari yapilmistir.

Effect of Continuous and Pulsed Currents on Microstructural Evolution of Stainless Steel Joined by TIG Welding

Abstract In this study, AISI 316L series austenitic stainless steel sheets were joined by tungsten inert gas welding method in continuous and pulsed currents. Regarding microstructural investigation and hardness values of weld metal, samples were welded to investigate the effect of current type on grain structures of weld metal. Results showed that samples welded by using pulsed current had considerable different properties compared to the samples welded by using continuous current. While the weld metals of joinings obtained by using continuous current displayed a coarse-grained and columnar structure, weld metals obtained by using pulsed current had a finer-grained structure. It was also found that hardness values of samples, which were welded with continuous and pulsed current, were quite different.

Tozaltı Ark Kaynak Yöntemi ile Birleştirilen X60, X65 ve X70 Çeliklerin Kaynak

Bu calismada, petrol ve dogal gaz hatlarinda kullanilan, dusuk alasimli, ince taneli ve yuksek mukavemetli X60, X65 ve X70 celikleri, tozalti ark kaynak yontemi ile iki farkli tel (S1 ve S2Mo) ve toz (LN761 ve P223) kullanilarak birlestirilmistir. Kaynakli birlestirmelere, oncelikle yuzey ve yuzey alti kusurlarin belirlenebilmesi icin tahribatsiz muayene yontemlerinden gozle ve ultrasonik muayeneye teknikleri uygulanmis, sonrasinda birlestirmelerin dayanimlarini belirlemek amaciyla, cekme ve egme testi uygulanmistir. Ayrica numuneler uzerinde sertlik ve makroyapi calismalari gerceklestirilmistir. Kaynakli numuneler uzerinde yapilan gozle ve ultrasonik muayene sonucunda, kaynak bolgesinde herhangi bir kaynak hatasina rastlanilmamistir. Yapilan cekme testleri sonucunda, tum numunelerde kopma, ana malzemeden gerceklesmis ve butun baglanti dayanimlari, ana malzemelerden daha yuksek bulunmustur. Egme testleri sonucunda, kaynak bolgesinde herhangi bir catlak, yirtik vb. hata gorulmemistir. Yapilan sertlik testleri sonucunda, en yuksek sertlik degerleri kaynak metalinden olculurken onu sirasiyla ITAB ve ana malzeme takip etmektedir. Makroyapi resimleri incelendiginde kaynak bolgesinde catlaklara, yirtilmalara, bosluklara, ergime/nufuziyet azligina, curuf kalintilarina ve yanma oluklarina rastlanilmamistir. Deney sonuclari genel olarak degerlendirildiginde, X70 malzemede kullanilan, S2Mo teli ve P223 tozu en verimli mekanik test sonuclari vermistir.

INVESTIGATION OF THE MECHANICAL PROPERTIES OF DIFFERENT THICKNESS OF THE GRADE A SHIP PLATES JOINED BY SUBMERGED ARC WELDING

In this study, a large part of the ship used in the manufacture of three different thickness of Grade A ship plates were joined by submerged arc welding method. In order to determine the strength of welded joints to the tensile and charpy impact test were applied, as well as hardness and microstructure studies were conducted on samples. Tensile tests showed that rupture occurred in the base metal of all samples. From the results of charpy impact test, the highest charpy notch values were obtained from base metal and this is followed by HAZ and the weld metal. It was seen that all the welding parameters, weld metal hardness is higher than the HAZ and the base metal.