Serap Gümüş

Modeling and thermal analysis of solidification in a low alloy steel

In this study, solidification of a low alloyed steel used for armor material was simulated at various transformation temperatures by the help of thermodynamical calculations using Thermo-Calc software. Differential thermal analysis (DTA) was carried out to determine the critical transformation temperatures for the phases and results were compared with those calculated by Thermo-Calc. It is concluded that the temperatures calculated by Thermo-Calc software are in good agreement with the results obtained from DTA. These results will be very useful to determine the proper austenization temperature having an important effect on the properties of steel serving as an armor material.

Properties of modified ethylene terpolymer/poly(lactic acid) blends based films

In order to explore an alternative method instead of plasticization for improving the toughness, flexibility and processability of PLA based packaging films, two different kinds of modified polyethylene based elastomers, such as glycidyl methacrylate or maleic anhydride functionalized ethylene-acrylate based elastomers, were melt blended with PLA. Their properties were compared with conventional PEG plasticized PLA. The chemical interaction between end groups of PLA and epoxide or maleic anhydride functional groups of elastomers was shown by FTIR. Scanning electron microscopy showed that up to 20 % PEG loading, one phase morphology was achieved, however beyond this point, a phase separation was observed for plasticized PLA. For PLA/elastomer blends, a two-phase morphology was obtained as a result of immiscible nature of PLA and elastomers. Tensile and dynamic mechanical properties indicated that elastomer based blends were better than plasticized PLA independently from elastomer type. Differential scanning calorimeter (DSC) analysis exhibited that the Tg value was remarkably lowered in the plasticized PLA; however, it did not change in the case of elastomers. In terms of oxygen permeability and biodegradability, plasticized PLA was found to be better than elastomer based blends.

Effect of matrix toughness and grain morphology on fracture of steels

The microstructure and fracture surfaces of steel X42 (type 09G2S) and of an experimental bainitic steel (0.23% C, 0.18% Mn, 0.04% Ni, 2.35% Co, 1.40% Cr, 0.50% Mo, 0.08% Nb, 0.08%V, 0.02% Ti) are studied after quenching and tempering. The influence of the toughness of the matrix on the fracture behavior of the steels is determined. It is shown that the fracture toughness changes depending on the tempering temperature, and the nucleation and propagation of cracks depends on the presence of secondary phases and on the morphology of the grain structure.

A case study of a stress corrosion cracking failure in an AA5083 mold material used for curing rubber compounds

In this study the failure analysis of an AA5083 mold material, used for curing rubber compounds, was carried out. The problem revealed itself as the formation of bubbles on the mold surface during curing process and caused quality problems in the final product. Preliminary microanalysis studies showed that there was an accumulation of both Mg and Cl in the bubble. Several samples were taken out from the inner/outer part of the mold material and examined using scanning electron microscope and energy dispersive X-ray spectrometer. It was concluded that (i) the contamination by Cl ions was due to the cutting oil used to open vent holes during mold cleaning, (ii) the outer part of mold material had finer α-Al grains whereas the inner part in contact with the compound had coarse grains due to the thermal effect of curing process, (iii) β-phase (Al3Mg2) formed at the grain boundaries after a sufficient exposure to temperatures above 50°C, (iv) the grain boundaries had Mg-rich phase showing anodic behavior, while the grains had Al-rich phase showing cathodic behavior, (v) the cracks initiated and propagated through the grain boundaries as stress corrosion cracking which resulted in the separation of grains and the accumulation of gases appeared as bubbles due to thermo-mechanical aging and effects of corrosive medium.

Characterization of the fracture behaviour of X42 microalloyed pipeline steel

Purpose – The purpose of this paper is to investigate the fracture of grade X42 microalloyed steel used as pipe material after tensile test at room temperature and impact tests at 0, −20 and −40°C, respectively. Design/methodology/approach – In the first stage of the study, X42 steels in the form of sheet and pipe materials were selected and etched samples were characterized using light microscope. In the second stage, mechanical properties of steels were obtained by microhardness measurements, static tensile and impact tests and all the broken surfaces were examined by scanning electron microscope to determine the fracture type as a function of both microstructure and loading. Findings – The examinations revealed that: first, the sheet material had a typical ferritic-pearlitic matrix, second, the transverse section of the sheet steel exhibited a matrix consisting of polygonal ferrite-aligned pearlite colonies and the longitudinal one had elongated ferrite phase and pearlite colonies in the direction of r...

Determination of the Microstructure of Powder Tool Steels by Different Etching Techniques

The microstructure of three powder high-speed steels is studied in quenched and tempered conditions by methods of light and scanning electron microscopy. Several types of carbides with different morphology are detected by using various methods of etching of specimens. The composition of the carbide phases is determined by the method of energy dispersive local analysis.

MICROSTRUCTURAL CHARACTERIZATION OF CARBIDES IN A CAST HIGH SPEED STEEL USING DIFFERENT METALLOGRAPHIC TECHNIQUES

Abstract High-speed steels are mostly manufactured by casting and they exhibit a characteristic dendritic microstructure with primary carbides. In this study, the morphology of carbides in a cast high-speed steel is investigated using light and scanning electron microscopes. The morphology and structure of the carbides were revealed by means of different metallographic techniques such as chemical and electrolytic etching and color metallography. The combination of these metallographic techniques gives different approaches to how different primary carbide morphologies can be observed in the martensitic structure. Besides, microanalysis was carried out to determine the chemical composition of primary carbides using SEM/EDX.