Ahmet Güral

Warm deformation and fracture behaviour of DP1000 advanced high strength steel

ABSTRACT The effect of temperature has been investigated on the mechanical properties and fracture behaviour of DP1000 advanced high-strength steel. The variation of the mechanical properties depending on temperature has been determined by performing uniaxial tensile tests at the temperatures of 25, 100, 200, 300°C at the rolling directions of 0° (rolling), 45° (diagonal), and 90° (transverse) at the strain rate of 0.0083 s−1. The yield strength and tensile strength have showed a slight decrease tendency between 25 and 200°C, but the highest value has been reached by showing an increase at 300°C temperature. The amount of elongation has not been affected significantly with the increase of the temperature. While hardening coefficient has increased due to the rising temperature, no effect has been observed on strength coefficient between 25 and 100°C, but an increase has occurred at higher temperature values.

Microstructure and dry sliding wear properties of 3Si–2Ni and 3Si–2Mn powder metallurgy steels with different graphite content:

In this study, plain iron powder (ASC.100.29) was mixed with 0.35–1.1 % graphite + 3 % Si + 2 % Ni and 0.35–1.1 % graphite + 3 % Si + 2 % Mn powders. While coarse pearlitic structure with homogeneous distribution of Mn was obtained in Mn-added specimens, Ni-rich austenitic areas with divorced pearlite structure were observed in Ni-added specimens. Wear tests were carried out at a load of 50 N. The experimental results showed that the highest wear resistance was obtained in the Ni-added specimen. While subsurface brittle cracking caused more wear in the Mn-added specimens, the wear occured by plastic deformation of surface Ni-added specimens.

Effect of Repeated Quenching Heat Treatment on Microstructure and Dry Sliding Wear Behavior of Low Carbon PM Steel

The effect of repeated quenching heat treatment on microstructure and dry sliding wear behavior of low carbon PM steel was investigated. For this purpose, atomized iron powder was mixed with 0.3 % graphite and 1 % Ni powders. The mixed powders were cold pressed and sintered at 1200°C for 30 min under pure Ar gas atmosphere. Some of the sintered specimens were intercritically annealed at 760°C and quenched in water (single quenching). The other sintered specimens were first fully austenized at 890°C and water quenched. These specimens were then intercritically annealed at 760°C and re-quenched in water. The martensite volume fraction in the double quenched specimens was higher than that of the single quenched specimen. Wear tests were carried out on the single and double quenched specimens under dry sliding wear condition using a pin-on-disk type machine at constant load and speed. The experimental results showed that the wear coefficient effectively decreased in the double quenched specimen.

Processing of Zinc-Based MgAl2O4 Composite and Effect of Fly Ash Addition

The properties of ceramic-metal (Cermet) composites as tensile strength, hardness and resistance to corrosion and high temperature are superior than ceramics and metals. Because of the enhanced characteristics of cermets, they are commonly used in various applications and industries. The main objective of this study is to produce a cheap, easy produced, strong and high corrosion resistant composite material. For these purposes, zinc is used for its natural capacity against corrosion, low density, low melting point and softness. Magnesium aluminates spinel oxide (MgAl2O4) is chosen because of its high melting point and low density. Fly ash is a waste from coal power plant having puzzolanic properties. In this study, the effect of various amounts of zinc and fly ash addition on density and hardness behaviour of zinc-based MgAl2O4 composites was investigated. The experimental results showed that zinc and fly ash addition improved the hardness behavior of zincbased MgAl2O4 composite.

Influence of strain rate on tensile properties and fracture behaviour of DP600 and DP780 dual-phase steels

The influences of the strain rate on the tensile properties and fracture behaviour of DP600 and DP780 advanced high-strength sheet steels have been studied. The variation of their mechanical properties depending on the strain rate have been researched by applying uniaxial tensile tests at three different strain rates (0.001, 0.01, 0.06 s−1). The influences of strain rate on fracture behaviour have been investigated by displaying the fracture surfaces of the material. Strain rate increase has been determined to increase the yield strength, tensile strength, total elongation and hardening rate. The strain hardening coefficient has been found not to be significantly affected by the strain rate. It has been determined that, the fracture has occurred faster during necking while load-carrying capacity has increased with strain rate increase.

Comparison of Heat Treatments on the Toughness of 1.7Ni-1.5Cu-0.5Mo Pre-alloyed P/M Steels

Abstract Effects of quenching plus tempering and intercritical annealing plus quenching heat treatments on the impact toughness properties of 1.7Ni-1.5Cu-0.5Mo pre-alloyed powder metallurgy steels with 0.2 (in mass%) graphite were investigated. Specimens were prepared by pressing at 670 MPa and sintering at 1250 °C. Different heat treatments, namely quenching and tempering, directly intercritically annealing and fully austenization plus intercritically annealing were carried out on the sintered specimens. The results showed that the impact toughness decreased with increasing intercritical annealing temperature in ferrite plus martensite dual phase powder metallurgy steels and with increasing tempering temperature in the quenched plus tempered specimens. Besides, impact toughness of fully austenizated plus intercritically annealed specimens was higher than those of quenched plus tempered and directly intercritically annealed specimens at the same hardness levels.

High Temperature Tensile Properties of Equal Channel Angular Pressed Al-Zn-Mg-Cu Alloy

Abstract In this study, ultra fine-grained microstructure was produced in Al–Zn–Mg–Cu alloy by equal channel angular pressing (ECAP) at 200 °C and a pressing speed of 2 mm s−1 using route C. The microstructure of the specimens was characterized by transmission and scanning electron microscopes. The results showed that the mean grain size of the specimens effectively decreased with increasing pass number. That is, while the grain size of unECAPed specimen was 10 µm, this value decreased to 300 nm after 14 passes. High temperature tensile tests were carried out at a strain rate of 1 × 10− 2 and temperature of 250 °C in the specimens with different pass number. It was seen that the flow stress decreased and the elongation to failure significantly increased with increasing pass number. The highest elongation to failure value of 90% was obtained in the specimen after 14 passes.

Equal Channel Angular Pressing (ECAP) and Its Application to Grain Refinement of Al‐Zn‐Mg‐Cu Alloy

Microstructure of a metal can be considerably changed by severe plastic deformation techniques such as high pressure torsion, extrusion and equal‐channel angular pressing (ECAP). Among these methods, ECAP is particularly attractive because it has a potential for introducing significant grain refinement and homogeneous microstructure into bulk materials. Typically, it reduces the grain size to the submicrometer level or even nanometer range and thus produces materials that are capable of exhibiting unusual mechanical properties. In the present study, a test unites for equal channel angular pressing was constructed and this system was used for Al‐Zn‐Mg‐Cu alloy. After the optimization tests, it was seen that the most effective lubricant for the dies was MoS2, the pressing pressure was around 25–35 ton and the pressing speed was 2 mm/s. By using these parameters, the Al‐Zn‐Mg‐Cu alloy was successfully ECAPed up to 14 passes at 200 °C using route C. After ECAP tests, the specimens were characterized by transm...

Influence of Tempering Temperature and Microstructure on Wear Properties of Low Alloy PM Steel with 1-2 % Ni Addition

The effect of tempering temperature and microstructure on dry sliding wear behavior of quenched and tempered PM steels was investigated. For this purpose, atomized iron powder was mixed with 0.3 % graphite and 1-2 % Ni powders. The mixed powders were cold pressed and sintered at 1200°C. The sintered specimens were quenched from 890°C and then tempered at 200°C and 600°C for 1 hr. Wear tests were carried out on the quenched+tempered specimens under dry sliding wear conditions using a pin-on-disk type machine at constant load and speed. The experimental results showed that the wear coefficient effectively increased with increasing tempering temperature. With increasing Ni content, the wear coefficient slightly decreased at all tempering temperatures due to the high amount of Ni-rich austenitic areas.

Comparing Microstructures and Tensile Properties of Intercritically Annealed and Quenched-Tempered 1.7Ni–1.5Cu–0.5Mo–0.2C Powder Metallurgy Steels

The aim of this study was to compare the influence of intercritical quenching (IQ), step quenching (SQ) and quenching plus tempering (QT) heat treatments on the microstructure and tensile properties of 1.7Ni–1.5Cu–0.5Mo–0.2C pre-alloyed powder metallurgy (P/M) steels. In the microstructures of the IQ and SQ specimens partial martensite having Ni-rich phases formed up in the soft ferritic matrix. It was observed that unlike Mo, a Cu alloying element dissolved homogeneously in the specimens. The martensite volume fraction (MVF) in the SQ specimens was higher than that in the IQ specimens. It was found that macrohardness, yield and tensile strengths increased, whereas microhardness of ferrite and elongation decreased with increasing MVF. However, with this increase, microhardness values of martensite phases decreased in the IQ specimen, while they increased in SQ specimens. It was observed that the yield, tensile, and elongation values of the QT specimens were lower than those of all intercritically annealed specimens having the same hardness values.