C. Hakan Gür

Numerical investigation of non-homogeneous plastic deformation in quenching process

Abstract The aim of the study is to investigate the evolution of internal stresses and non-homogeneous plastic deformation in quenching by numerical simulation. This paper presents the finite element model of quenching of axisymmetric components and the results of various numerical experiments. In the simulation, first the temperature distribution is determined as a function of geometry and time. Then, a model is described to give the volume fractions of phases as a function of time for the corresponding cooling curves. Next, thermo–elastic–plastic approach is applied to describe the stress–strain response during cooling, and to predict the residual stresses of the first order. The computer program was written in Fortran, and material properties were input as a function of the individual phases and temperature.

Nondestructive investigation of the effect of quenching and tempering on medium-carbon low alloy steels

The aim of the study is to investigate the effect of quenching and tempering on sound velocity of steels, and to contribute to the nondestructive control and optimisation of the quenching/tempering systems. Disk-shaped specimens were prepared from AISI/SAE 4140 and AISI/SAE 5140 steel bars. All specimens were austenised and quenched identically to eliminate the effect of grain size on sound velocity, and a constant tempering time was chosen. Microstructures of the samples were characterised by metallographic examinations and hardness measurements. The reference values were obtained for as-quenched and tempered structures by measuring sound velocities for both longitudinal and transversal waves. The sound velocity is lowest in the as-quenched martensite, and however, increases after tempering as a function of tempering temperature. The changes in sound velocity can be explained primarily by differences in the elastic modulus that is affected by the degree of lattice distortion and misorientation in the microstructure.

Characterization of duplex stainless steel weld metals obtained by hybrid plasma-gas metal arc welding

Despite its high efficiency, autogenous keyhole welding is not well-accepted for duplex stainless steels because it causes excessive ferrite in as-welded duplex microstructure, which leads to a degradation in toughness and corrosion properties of the material. Combining the deep penetration characteristics of plasma arc welding in keyhole mode and metal deposition capability of gas metal arc welding, hybrid plasma - gas metal arc welding process has considered for providing a proper duplex microstructure without compromising the welding efficiency. 11.1 mm-thick standard duplex stainless steel plates were joined in a single-pass using this novel technique. Same plates were also subjected to conventional gas metal arc and plasma arc welding processes, providing benchmarks for the investigation of the weldability of the material. In the first place, the hybrid welding process enabled us to achieve less heat input compared to gas metal arc welding. Consequently, the precipitation of secondary phases, which are known to be detrimental to the toughness and corrosion resistance of duplex stainless steels, was significantly suppressed in both fusion and heat affected zones. Secondly, contrary to other keyhole techniques, proper cooling time and weld metal chemistry were achieved during the process, facilitating sufficient reconstructive transformation of austenite in the ferrite phase.

Investigation of as-quenched and tempered commercial steels by Magnetic Barkhausen Noise method

This study aims to characterise as-quenched and tempered steels by the Magnetic Barkhausen Noise method, and to contribute to optimisation of heat treatment processes. Identical austenitisation and quenching procedures were applied to SAE 1040 and SAE 4140 specimens to eliminate the effect of grain size. Samples were tempered at 200°C and 600°C for 2 hours. Microstructures were characterised by metallographic examinations and hardness measurements. Amplitude, position and frequency spectrum of signals were evaluated using a commercial system. As the tempering temperature increases, in contrast to the reduction in hardness, magnetic response increases due to the enhancement of domain wall displacement.

Investigation of the Variations in Microstructure and Mechanical Properties of Dual-Matrix Ductile Iron by Magnetic Barkhausen Noise Analysis

The variations in the microstructure and tensile properties of dual-matrix ductile irons have been investigated non-destructively by Magnetic Barkhausen Noise (MBN) method. Specimens have been intercritically austenitised at 795°C and 815°C for 20 minutes, and then oil-quenched to obtain different martensite volume fractions. Two specimens, namely as-cast and oil-quenched from 900°C, were prepared for comparison purpose. To investigate the effect of tempering, some specimens were tempered at 500°C for 1 h and 3 h. The results showed that there is a good correlation between MBN response and variations in microstructure and mechanical properties. The volume fraction of martensite can be controlled to modify the mechanical properties, and all changes in the microstructure can be nondestructively monitored by MBN.

NUMERICAL AND EXPERIMENTAL ANALYSIS OF QUENCH INDUCED STRESSES AND MICROSTRUCTURES

Numerical and experimental studies have been carried out to investigate the evolution of residual stresses and microstructures in quenched steel components. In the numerical analysis, a finite element model is implemented for predicting the temperature field, phase changes with their associated internal stresses in axisymmetrical components. The model is verified by several comparisons with other known numerical results. Case studies are performed to investigate the effects of the quench bath temperature and the specimen geometry. Specimen geometry has been analyzed by introducing a hole in a cylinder and varying hole diameter and its eccentricity. Experiments include microstructural examination and X-ray diffraction measurements of surface residual stresses.

Simulation of Quenching: A Review

Quenching is an important part of the production chain of steel components. The final properties of the product are largely determined during this stage, and this renders quenching as one of the most critical stages of production, requiring design and optimization specific to the product. The simulation of quenching requires the solution of a multi-scale/multi-physics problem with complex boundary conditions because of the simultaneously occurring heat transfer, phase transformation, and mechanical interactions. The aim of this paper is to provide an updated review of research studies on the simulation of quenching. The subject is covered from the pioneering work up to very recent advances in the field, with special emphasis on future research needs for improving the industrial usage of heat treatment simulations.

A new framework for simulation of heat treatments

In this study, a mathematical framework based on finite element method (FEM) capable of predicting temperature history, evolution of phases and internal stresses during thermal treatment of metals and alloys was developed. The model was integrated into the commercial FEA software MSC.Marc® by user subroutines. The accuracy of the model was verified by simulating the quenching of eccentrically drilled steel cylinders. Simulation results were justified via SEM observations and XRD residual stress measurements.

Applicability of the Magnetic Barkhausen Noise Method for Nondestructive Measurement of Residual Stresses in the Carburized and Tempered 19CrNi5H Steels

ABSTRACT There exist no materials and/or structures of technical importance without residual stresses. The residual stress management concept has gained importance in industrial applications aiming to improve service performance and useful life of the product. Thus, the industry requests rapid, reliable, and nondestructive methods to determine residual stress state. The aim of this article is to investigate the applicability of the Magnetic Barkhausen Noise (MBN) method to measurement of surface residual stresses in the carburized steels. To comprehend the differences in the surface residual stress state, 19CrNi5H steel samples were carburized at 900°C for 8 and 13 hours, and then, tempered in the range of 180°C and 600°C. The MBN measurement results were correlated with those obtained by the X-ray diffraction (XRD) measurements. Microstructural investigations and hardness measurements were also conducted. For this particular study, it was concluded that both techniques give similar qualitative results for monitoring of the residual stress variations in the carburized and tempered steels. Since the MBN method is much faster than the XRD method, from the industrial point of view it is a very strong candidate for qualitative monitoring of residual stress variations. With an appropriate pre-calibration by considering the effect of microstructure, the MBN method may give reliable quantitative results for residual stress.

Nondestructive Characterization of Microstructures of Heat-Treated Steels by Magnetic Barkhausen Noise Technique

Optimization and control of the microstructure is important for improving the properties of steel components. Development of non-destructive techniques for microstructure characterization is a critical task. Magnetic Barkhausen Noise (MBN) technique is a promising and challenging non-destructive technique for automated evaluation of microstructures in steel components in a fast and reliable manner. This paper presents the results of MBN measurements for microstructure characterization of the quenched and tempered steels.