Blanking of sheet steels is one of the most frequently used processes in the manufacturing indust... more Blanking of sheet steels is one of the most frequently used processes in the manufacturing industry. During blanking processes, the wear of punches occurs due to the cyclic contact of the opposite surfaces. Therefore, the punch is exposed to high stresses and requires high resistance against wear. When worn tools are used, the tool surface directly affects the quality of sheet products and causes some surface defects. The PVD coating of the punch with a surface layer of improved hardness and low friction may reduce wear. The aim of the present study is to characterize the tool wear of AlCrN coated punch used for the sheet-steel blanking. The worn punch surfaces were examined by scanning electron microscopy. The results showed that wear take place due to the abrasion, adhesion, and delamination along sliding flank surfaces. Edge rounding and fracture of cutting edges were also observed. After blanking tests, the tool wear volume of punches and the burr height of blanked parts were also measured. The wear volumes were determined by means of profile measurements of the worn punch carried out after the completion of a large amount of blanked parts.
Journal of Thermal Analysis and Calorimetry, Jan 17, 2013
Thermodynamical modeling and thermal analysis are practical tools for determining of phase transf... more Thermodynamical modeling and thermal analysis are practical tools for determining of phase transformations in steels. The thermodynamical modeling provides knowledge about the phase transformation in the equilibrium state of steels, whereas thermal analysis is very useful for the choice of heat treatment parameters in the industrial applications. In this study, firstly various transformation temperatures were simulated by using thermodynamical calculations using Thermo-Calc software during solidification of a low alloyed steel. Secondly, differential thermal analysis (DTA) was carried out to determine critical transformation temperature for phases and was compared with those of calculated by Thermo-Calc. It is concluded that the temperatures calculated by Thermo-Calc software are well agreement with the results obtained from DTA.
In the current research, we studied the role of the solution treatment and aging on the microstru... more In the current research, we studied the role of the solution treatment and aging on the microstructure of a Co-28Cr-5Mo-0.3C alloy. We used metallographic observations, scanning electron microscopy (SEM), and hardness measurements for the evaluations. We also made a comparison between the phase equilibrium calculated with Thermo-Calc, using TCFE8 and TCNI8 thermodynamic databases and experimental findings. The experimental results showed that the transformation of the metastable FCC phase to the HCP phase during aging was extremely sensitive to the solution treatment prior to aging. The effect of the increase in the solution temperature and time was detectable through promotion of the martensitic transformation during quenching in which HCP 1 (straight bands) and HCP 2 (lamellar-type constitution) phases had developed. In contrast, a low solution temperature and time caused most of the primary carbides to remain in an undissolved condition in the matrix; therefore, during aging, no sign of the FCC to HCP 1 (straight bands) phase transformation could be observed. However, we observed the formation of the HCP 2 phase (lamellar-type constitution) at the grain boundaries. In addition, the X-ray diffraction pattern indicated that the sample solution treated at lower temperatures and shorter times had a stronger martensitic transformation during aging compared to the sample solution treated at higher temperatures and longer times. Hardness measurements confirmed the results. Thermodynamical calculations showed that an agreement existed between the experiments and calculations. We also discuss the results from the TCFE8 and TCNI8 databases.
It is known that the mechanical properties of steels are dependent on the final microstructure re... more It is known that the mechanical properties of steels are dependent on the final microstructure resulting from phase transformation during heat treatments. Hot rolled mine support profiles are produced generally from unalloyed quality steels. After the hot rolling, heat treatments of quenching and tempering result in a tempered martensite microstructure with high strength and toughness. The retained austenite phase may also be expected in the microstructure due to the lack of alloying elements. In this study a microstructural characterization of a mine support profile is carried out before and after the quenching and tempering to investigate the effect of heat treatments on the microstructure. A dilatometric analysis is performed to detect the phase transformation temperatures. Dilatometric analysis is carried out at different cooling rates from austenite phase region. Depending on the different cooling rates, ferrite, pearlite and bainite phases are determined using dilatation curves, light microscope, and Vickers hardness tests. The results indicate that critical temperatures can be determined by dilatometric analysis.
The decarburization layer can be detrimental and lead failures in press hardened steels. This wor... more The decarburization layer can be detrimental and lead failures in press hardened steels. This work investigates the effect of decarburization layer on the fatigue crack origination and growth on press hardened parts of uncoated 22MnB5 steel. The decarburization layer was analyzed by light microscope, scanning electron microscope, and microhardness measurements. It was found that decarburization layer has two distinct zones indicating complete and partial decarburization. To understand the effect of decarburization on crack origination, high cycle fatigue tests were performed on samples from press hardened parts in decarburized and polished (nondecarburized) conditions. The results have shown that the fatigue performance of press hardened steels in polished condition outperforms the fatigue samples in decarburized condition. In fractographic investigations, it was seen that decarburization is not only responsible for crack origination but also affects crack propagation by having full and partial decarburization zones. The full decarburization zone was acted as surface crack origination source. In the partial decarburization zone, the crack propagation behavior was changed by a complex phase microstructure of bainite, ferrite, and martensite.
The microstructure evolution of dual-phase steel during partial austenitization was investigated ... more The microstructure evolution of dual-phase steel during partial austenitization was investigated for different intercritical annealing temperatures between Ac1 and Ac3 temperatures. Partial austenitization may result in different austenite volume fraction, chemical composition, and grain size of austenite depending on the intercritical annealing temperature. This study examines the effect of intercritical annealing temperature on Ms and Bs temperatures for dual-phase steels. Ms and Bs were measured experimentally for different intercritical annealing temperatures by using dilatometry and were compared with calculated values from empirical formulas. The grain sizes of the final microstructures were also quantitatively analyzed. It was shown that Ms depends on the intercritical annealing temperature and austenite grain size. It was concluded that this double effect is attributed to the intercritical annealing temperature, which is responsible for both austenite chemical composition and grain size.
In this study, the suitability for producing dual phase steel from hot rolled medium carbon steel... more In this study, the suitability for producing dual phase steel from hot rolled medium carbon steel for mining industry and the effect of annealing temperature on hardness and microstructure has been investigated. The critical equilibrium temperatures and phase diagram were calculated using Thermo-Calc software for 0.37C-0.87Mn steel. In experimental studies using dilatometer, microstructures containing ferrite and martensite were produced by intermediate quenching method with annealing at different temperatures followed by water quenching. Before the intermediate quenching, the specimens were first quenched to form martensite from austenitizing temperature of 1100 °C. Fully martensitic samples were then annealed respectively at 725, 730, 740, 750 °C for 15 min and quenched. During the annealing, the austenite nucleates and grows at former boundaries of the martensite plates resulting fibrous microstructure of martensite and ferrite. Microstructural investigations were carried out using light microscope and scanning electron microscope to investigate the effect of the increasing annealing temperature on the microstructure. Vickers test was applied to specimens. The calculations and experimental results show that hot rolled medium carbon steels are suitable to produce a dual phase microstructure. It was observed that increasing annealing temperature increases the amount of martensite and hardness because martensite is the main phase controls the hardness value of steel. It is observed that the A1 and A3 temperatures are very close and the percentage of austenite is much more than conventionally produced dual phase steels. It is related to including more carbon content than conventionally produced dual phase steel.
Metallurgical and Materials Transactions, Jan 2, 2022
The typical final microstructure of bearing steels is composed of coarse carbides in a martensiti... more The typical final microstructure of bearing steels is composed of coarse carbides in a martensitic matrix due to coarse carbides in the initial microstructure obtained by the soft annealing. In this work, the effect of the initial microstructure on the final microstructure and wear performance of bearing steels was studied. In dilatometer experiments, the effect of different initial microstructures on the phase transformations was examined through the hardening at 840 °C. The wear tests were performed using a ball-on-disk tribometer. Microstructural characterization and hardness test have been carried out after the wear testing. The results showed that martensitic and bainitic initial microstructures markedly reduce the size of carbides in the final microstructure. The new heat treatment method for bearing steels meets higher hardness and outstanding resistance against wear owing to finer carbides in the final microstructure.
Journal of Materials Engineering and Performance, Dec 28, 2013
ABSTRACT This paper presents a study concerning phase transformations during quenching of a mediu... more ABSTRACT This paper presents a study concerning phase transformations during quenching of a medium carbon dual phase steel using thermodynamic equilibrium calculations and dilatometry. Medium carbon steel was subjected to the intermediate quenching to produce a fine grained ferrite/martensite dual phase steel. 4 samples quenched after intercritical annealing at 725, 730, 740, and 750 °C. Martensite-start and bainite-start temperatures were calculated from dilatometric curves using plastodilotemeter. Experimental findings are supported by calculated phase diagrams and equilibrium phase compositions using ThermoCalc® and calculations from different empirical formulas. It is concluded that martensite-start temperature depend on chemical composition and grain size of austenite.
Bu çalışmada, 100Cr6 çeliğinde kısmi ve tam östenitleme koşullarında sementit çözünme kinetiği in... more Bu çalışmada, 100Cr6 çeliğinde kısmi ve tam östenitleme koşullarında sementit çözünme kinetiği incelenmiştir. 840 °C ve 1050 °C sıcaklıkta farklı sürelerde ısıl işleme tabi tutulan numunelerde sementit hacim oranındaki ve boyutundaki değişim belirlenmiştir. ImageJ yazılımı ile SEM mikrografları analiz edilerek karbürlerin boyutu ve hacim oranları belirlenmiştir. Elde edilen istatistiksel veriler "lineer olmayan eğri uydurma" yöntemi kullanılarak çözünme eğrilerine dönüştürülmüştür. Tam ve kısmi östenitleme işlemlerinin başlangıcında sementit çözünme hazının yüksek olduğu belirlenmiştir. Bir model kurularak DICTRA yazılımında karbür çözünmesi hesaplanmıştır. Elde edilen çözünme eğrileri DICTRA sonuçları ile karşılaştırılmıştır. SEM mikrograflarından elde edilen istatistikler ile DICTRA hesaplamalarının uyumlu olduğu görülmüştür. Elde edilen hesaplama sonuçlarına göre başlangıçtaki hızlı karbür çözünmesinin nedeni, C atomları difüzyonu ile kontrol edilen ve Cr difüzyonunun ihmal edildiği "ihmal edilebilir yerel denge" modunda çözünmenin gerçekleşmesidir.
In this study, the effect of microstructure on hot deformability of high nitrogen X50CrMnNiNbN21-... more In this study, the effect of microstructure on hot deformability of high nitrogen X50CrMnNiNbN21-9 valve steel was investigated. Phase transformations and precipitation were thermodynamically modeled as well as experimentally determined via microstructural characterization. Hot tensile and compression tests were used to simulate the hot deformation at temperatures between 900 oC-1300 oC. Hot tensile test determined the high temperature properties. The effect of temperature on cracking sensibility during hot deformation was investigated using hot compression test. The results showed hot deformability depends on primary and secondary precipitates of carbides and nitrides.
This study deals with the effect of initial microstructure on final microstructure of mediumcarbo... more This study deals with the effect of initial microstructure on final microstructure of mediumcarbon dual-phase steels by two different annealing methods. In experimental studies, initial microstructures martensite and ferrite+pearlite annealed at same annealing temperatures and quenched applying different annealing durations. The influence of initial microstructures on microstructural evolution is studied using scanning electron microscope (SEM). The manganese distribution in ferrite and martensite is analyzed by energy-dispersive X-ray spectroscopy (EDS). The experimental study was supported by phase field modeling using Thermo-Calc and Diffusion-Controlled TRAnsformations (DICTRA) softwares. Experimental results showed that dual phase microstructure has inhomogeneity of martensite islands and fibers in ferritic matrix after intermediate quenching. Martensite formation occurred at prior austenite grain boundaries and martensite laths. In the case of intercritical annealing, pearlite regions are transformed to austenite and eventually martensite islands after quenching.
ABSTRACT Stickstofflegierte Stähle zeichnen sich im Vergleich zu konventionellen nichtrostenden a... more ABSTRACT Stickstofflegierte Stähle zeichnen sich im Vergleich zu konventionellen nichtrostenden austenitischen Stählen durch eine erhöhte Streckgrenze und Zugfestigkeit sowie eine verbesserte Warmfestigkeit aus. Sie weisen weiterhin eine verbesserte Korrosionsbeständigkeit, Lochfraßbeständigkeit und Beständigkeit gegen Spannungsrisskorrosion auf. Diesen Vorteilen können je nach Legierung Probleme bei der Warmumformung gegenüber stehen. So können Kanten- und Flächenabplatzungen sowohl als auch Risse während des Schmiedens auftreten. Diese Risse erfordern eine aufwendige Nachbearbeitung des Gussblockes, welches einen Nachteil in der Wirtschaftlichkeit des Prozesses bedeutet. In dieser Arbeit wurde ein Schmiedefenster für die wirtschaftliche Warmumformung von stickstoffhaltigen Stählen unter Berücksichtigung der Modellierung von Ausscheidungen und experimenteller Simulationen von Umformungen identifiziert. Dazu wurden drei hoch stickstofflegierte Stähle 1.4452, 1.4501 und 1.4882 und ein Referenzstahl 1.4301 untersucht. Zur Ermittlung des Ausscheidungsverhaltens und der Phasenumwandlungen werden mit Hilfe des Programms Thermo-Calc® die Phasenzustandsdiagramme simuliert. In Verbindung mit den Untersuchungen der Ausscheidungen werden Rückschlüsse auf die auftretenden Phasen und die Auflösungstemperaturen der Ausscheidungen gezogen. Für die experimentelle Simulation von Umformungen werden Heißzug- und Stauchversuche durchgeführt. Durch Heißzugversuche werden die Hochtemperatureigenschaften bei den Umformtemperaturen von 900ºC bis 1300ºC untersucht. In Stauchversuchen wird der Einfluss der Umformtemperatur auf die Rissanfälligkeit ermittelt. Mit diesen Ergebnissen wird ein Schmiedefenster erstellt. Die Untersuchungen zeigen, dass die Umformtemperaturbereiche für die austenitischen Werkstoffe 1.4452 und 1.4882 stärker eingeschränkt sind als die für den nicht stickstofflegierten Referenzstahl 1.4301 und den hoch stickstofflegierten Superduplex-Stahl 1.4501. High nitrogen steels (HNS) differ from conventional austenitic steels on their higher yield and tensile strength as well as improved high temperature strength. HNS show also a better corrosion resistance, pitting resistance and stress corrosion cracking resistance. However, these advantages are accompanied with some problems during hot deformation of HNS. Edges and surface cracks as well as forging cracks may appear. Time consuming and expensive finishing operations are required for these cracks which mean a serious drawback to economic processing of forging blocks. The aim of this thesis is the identification of a forging window for an economical production of HNS under consideration of the modeling of precipitation and the experimental simulation of deformation. The experiments were made on three HNS 1.4452, 1.4501, and 1.4882 and a reference steel 1.4301. On the modeling of precipitation, the phase diagrams were calculated with Thermo-Calc® software in order to determine precipitation characteristics and phase transformations. The investigation of precipitations helps to draw conclusions from appearing phases and dissolving temperatures. In order to simulate the deformation, the high temperature properties were determined at deformation temperatures between 900ºC and 1300ºC via hot tensile tests. The compression test defines also the effect of deformation temperature on the crack sensibility. As a result of experimental simulations, a forging window was determined. The results show the deformation temperature window is restricted for austenitic HNS 1.4452 and 1.4882 in compare to reference steel 1.4301 and super duplex HNS 1.4501.
This paper provides a study of carbide dissolution during heating of bearing steel using computat... more This paper provides a study of carbide dissolution during heating of bearing steel using computational thermodynamics and kinetics. 100Cr6 steel was used for the experimental work and calculations using the Thermo-Calc and DICTRA. Carbide dissolution was calculated at different full and intercritical austenization temperatures from 840 to 1200 C. The calculations also give the distribution of the alloying elements at carbide and austenite phase boundaries. In experimental work, SEM was used to study microstructures. SEM micrographs were evaluated with line intercept technique and carbide size and quantity were determined. The experimental results were compared with calculations providing good correlation.
IOP Conference Series: Materials Science and Engineering, 2017
The effects of heat treatment and initial microstructure on tensile properties of 22MnB5 and 30Mn... more The effects of heat treatment and initial microstructure on tensile properties of 22MnB5 and 30MnB5 high-strength hot stamping steels with martensite-ferrite matrix were investigated. Hot stamping steels possessed limited elongations of about 5% in a tensile strength ranging from 1300 to 1500 MPa when quenched at temperatures above A3 temperatures. The total elongations were tried to improve by partial austenization between Ac1 and Ac3 temperature and quenching. Ac1 and Ac3 temperatures were calculated via ThermoCalc. Microstructural characterization was made by using Light Microscope and Scanning Electron Microscope. Microstructure is composed of ferrite+martensite. It was seen that annealing temperature affects the volume fraction of phases. It was concluded that initial microstructure is an important parameter for the final microstructure. This method can be used for automobile parts which require higher TE with sufficient yield and tensile strength. Also this process may be a way of using Zn coated steel sheets in hot stamping process.
Blanking of sheet steels is one of the most frequently used processes in the manufacturing indust... more Blanking of sheet steels is one of the most frequently used processes in the manufacturing industry. During blanking processes, the wear of punches occurs due to the cyclic contact of the opposite surfaces. Therefore, the punch is exposed to high stresses and requires high resistance against wear. When worn tools are used, the tool surface directly affects the quality of sheet products and causes some surface defects. The PVD coating of the punch with a surface layer of improved hardness and low friction may reduce wear. The aim of the present study is to characterize the tool wear of AlCrN coated punch used for the sheet-steel blanking. The worn punch surfaces were examined by scanning electron microscopy. The results showed that wear take place due to the abrasion, adhesion, and delamination along sliding flank surfaces. Edge rounding and fracture of cutting edges were also observed. After blanking tests, the tool wear volume of punches and the burr height of blanked parts were also measured. The wear volumes were determined by means of profile measurements of the worn punch carried out after the completion of a large amount of blanked parts.
Journal of Thermal Analysis and Calorimetry, Jan 17, 2013
Thermodynamical modeling and thermal analysis are practical tools for determining of phase transf... more Thermodynamical modeling and thermal analysis are practical tools for determining of phase transformations in steels. The thermodynamical modeling provides knowledge about the phase transformation in the equilibrium state of steels, whereas thermal analysis is very useful for the choice of heat treatment parameters in the industrial applications. In this study, firstly various transformation temperatures were simulated by using thermodynamical calculations using Thermo-Calc software during solidification of a low alloyed steel. Secondly, differential thermal analysis (DTA) was carried out to determine critical transformation temperature for phases and was compared with those of calculated by Thermo-Calc. It is concluded that the temperatures calculated by Thermo-Calc software are well agreement with the results obtained from DTA.
In the current research, we studied the role of the solution treatment and aging on the microstru... more In the current research, we studied the role of the solution treatment and aging on the microstructure of a Co-28Cr-5Mo-0.3C alloy. We used metallographic observations, scanning electron microscopy (SEM), and hardness measurements for the evaluations. We also made a comparison between the phase equilibrium calculated with Thermo-Calc, using TCFE8 and TCNI8 thermodynamic databases and experimental findings. The experimental results showed that the transformation of the metastable FCC phase to the HCP phase during aging was extremely sensitive to the solution treatment prior to aging. The effect of the increase in the solution temperature and time was detectable through promotion of the martensitic transformation during quenching in which HCP 1 (straight bands) and HCP 2 (lamellar-type constitution) phases had developed. In contrast, a low solution temperature and time caused most of the primary carbides to remain in an undissolved condition in the matrix; therefore, during aging, no sign of the FCC to HCP 1 (straight bands) phase transformation could be observed. However, we observed the formation of the HCP 2 phase (lamellar-type constitution) at the grain boundaries. In addition, the X-ray diffraction pattern indicated that the sample solution treated at lower temperatures and shorter times had a stronger martensitic transformation during aging compared to the sample solution treated at higher temperatures and longer times. Hardness measurements confirmed the results. Thermodynamical calculations showed that an agreement existed between the experiments and calculations. We also discuss the results from the TCFE8 and TCNI8 databases.
It is known that the mechanical properties of steels are dependent on the final microstructure re... more It is known that the mechanical properties of steels are dependent on the final microstructure resulting from phase transformation during heat treatments. Hot rolled mine support profiles are produced generally from unalloyed quality steels. After the hot rolling, heat treatments of quenching and tempering result in a tempered martensite microstructure with high strength and toughness. The retained austenite phase may also be expected in the microstructure due to the lack of alloying elements. In this study a microstructural characterization of a mine support profile is carried out before and after the quenching and tempering to investigate the effect of heat treatments on the microstructure. A dilatometric analysis is performed to detect the phase transformation temperatures. Dilatometric analysis is carried out at different cooling rates from austenite phase region. Depending on the different cooling rates, ferrite, pearlite and bainite phases are determined using dilatation curves, light microscope, and Vickers hardness tests. The results indicate that critical temperatures can be determined by dilatometric analysis.
The decarburization layer can be detrimental and lead failures in press hardened steels. This wor... more The decarburization layer can be detrimental and lead failures in press hardened steels. This work investigates the effect of decarburization layer on the fatigue crack origination and growth on press hardened parts of uncoated 22MnB5 steel. The decarburization layer was analyzed by light microscope, scanning electron microscope, and microhardness measurements. It was found that decarburization layer has two distinct zones indicating complete and partial decarburization. To understand the effect of decarburization on crack origination, high cycle fatigue tests were performed on samples from press hardened parts in decarburized and polished (nondecarburized) conditions. The results have shown that the fatigue performance of press hardened steels in polished condition outperforms the fatigue samples in decarburized condition. In fractographic investigations, it was seen that decarburization is not only responsible for crack origination but also affects crack propagation by having full and partial decarburization zones. The full decarburization zone was acted as surface crack origination source. In the partial decarburization zone, the crack propagation behavior was changed by a complex phase microstructure of bainite, ferrite, and martensite.
The microstructure evolution of dual-phase steel during partial austenitization was investigated ... more The microstructure evolution of dual-phase steel during partial austenitization was investigated for different intercritical annealing temperatures between Ac1 and Ac3 temperatures. Partial austenitization may result in different austenite volume fraction, chemical composition, and grain size of austenite depending on the intercritical annealing temperature. This study examines the effect of intercritical annealing temperature on Ms and Bs temperatures for dual-phase steels. Ms and Bs were measured experimentally for different intercritical annealing temperatures by using dilatometry and were compared with calculated values from empirical formulas. The grain sizes of the final microstructures were also quantitatively analyzed. It was shown that Ms depends on the intercritical annealing temperature and austenite grain size. It was concluded that this double effect is attributed to the intercritical annealing temperature, which is responsible for both austenite chemical composition and grain size.
In this study, the suitability for producing dual phase steel from hot rolled medium carbon steel... more In this study, the suitability for producing dual phase steel from hot rolled medium carbon steel for mining industry and the effect of annealing temperature on hardness and microstructure has been investigated. The critical equilibrium temperatures and phase diagram were calculated using Thermo-Calc software for 0.37C-0.87Mn steel. In experimental studies using dilatometer, microstructures containing ferrite and martensite were produced by intermediate quenching method with annealing at different temperatures followed by water quenching. Before the intermediate quenching, the specimens were first quenched to form martensite from austenitizing temperature of 1100 °C. Fully martensitic samples were then annealed respectively at 725, 730, 740, 750 °C for 15 min and quenched. During the annealing, the austenite nucleates and grows at former boundaries of the martensite plates resulting fibrous microstructure of martensite and ferrite. Microstructural investigations were carried out using light microscope and scanning electron microscope to investigate the effect of the increasing annealing temperature on the microstructure. Vickers test was applied to specimens. The calculations and experimental results show that hot rolled medium carbon steels are suitable to produce a dual phase microstructure. It was observed that increasing annealing temperature increases the amount of martensite and hardness because martensite is the main phase controls the hardness value of steel. It is observed that the A1 and A3 temperatures are very close and the percentage of austenite is much more than conventionally produced dual phase steels. It is related to including more carbon content than conventionally produced dual phase steel.
Metallurgical and Materials Transactions, Jan 2, 2022
The typical final microstructure of bearing steels is composed of coarse carbides in a martensiti... more The typical final microstructure of bearing steels is composed of coarse carbides in a martensitic matrix due to coarse carbides in the initial microstructure obtained by the soft annealing. In this work, the effect of the initial microstructure on the final microstructure and wear performance of bearing steels was studied. In dilatometer experiments, the effect of different initial microstructures on the phase transformations was examined through the hardening at 840 °C. The wear tests were performed using a ball-on-disk tribometer. Microstructural characterization and hardness test have been carried out after the wear testing. The results showed that martensitic and bainitic initial microstructures markedly reduce the size of carbides in the final microstructure. The new heat treatment method for bearing steels meets higher hardness and outstanding resistance against wear owing to finer carbides in the final microstructure.
Journal of Materials Engineering and Performance, Dec 28, 2013
ABSTRACT This paper presents a study concerning phase transformations during quenching of a mediu... more ABSTRACT This paper presents a study concerning phase transformations during quenching of a medium carbon dual phase steel using thermodynamic equilibrium calculations and dilatometry. Medium carbon steel was subjected to the intermediate quenching to produce a fine grained ferrite/martensite dual phase steel. 4 samples quenched after intercritical annealing at 725, 730, 740, and 750 °C. Martensite-start and bainite-start temperatures were calculated from dilatometric curves using plastodilotemeter. Experimental findings are supported by calculated phase diagrams and equilibrium phase compositions using ThermoCalc® and calculations from different empirical formulas. It is concluded that martensite-start temperature depend on chemical composition and grain size of austenite.
Bu çalışmada, 100Cr6 çeliğinde kısmi ve tam östenitleme koşullarında sementit çözünme kinetiği in... more Bu çalışmada, 100Cr6 çeliğinde kısmi ve tam östenitleme koşullarında sementit çözünme kinetiği incelenmiştir. 840 °C ve 1050 °C sıcaklıkta farklı sürelerde ısıl işleme tabi tutulan numunelerde sementit hacim oranındaki ve boyutundaki değişim belirlenmiştir. ImageJ yazılımı ile SEM mikrografları analiz edilerek karbürlerin boyutu ve hacim oranları belirlenmiştir. Elde edilen istatistiksel veriler "lineer olmayan eğri uydurma" yöntemi kullanılarak çözünme eğrilerine dönüştürülmüştür. Tam ve kısmi östenitleme işlemlerinin başlangıcında sementit çözünme hazının yüksek olduğu belirlenmiştir. Bir model kurularak DICTRA yazılımında karbür çözünmesi hesaplanmıştır. Elde edilen çözünme eğrileri DICTRA sonuçları ile karşılaştırılmıştır. SEM mikrograflarından elde edilen istatistikler ile DICTRA hesaplamalarının uyumlu olduğu görülmüştür. Elde edilen hesaplama sonuçlarına göre başlangıçtaki hızlı karbür çözünmesinin nedeni, C atomları difüzyonu ile kontrol edilen ve Cr difüzyonunun ihmal edildiği "ihmal edilebilir yerel denge" modunda çözünmenin gerçekleşmesidir.
In this study, the effect of microstructure on hot deformability of high nitrogen X50CrMnNiNbN21-... more In this study, the effect of microstructure on hot deformability of high nitrogen X50CrMnNiNbN21-9 valve steel was investigated. Phase transformations and precipitation were thermodynamically modeled as well as experimentally determined via microstructural characterization. Hot tensile and compression tests were used to simulate the hot deformation at temperatures between 900 oC-1300 oC. Hot tensile test determined the high temperature properties. The effect of temperature on cracking sensibility during hot deformation was investigated using hot compression test. The results showed hot deformability depends on primary and secondary precipitates of carbides and nitrides.
This study deals with the effect of initial microstructure on final microstructure of mediumcarbo... more This study deals with the effect of initial microstructure on final microstructure of mediumcarbon dual-phase steels by two different annealing methods. In experimental studies, initial microstructures martensite and ferrite+pearlite annealed at same annealing temperatures and quenched applying different annealing durations. The influence of initial microstructures on microstructural evolution is studied using scanning electron microscope (SEM). The manganese distribution in ferrite and martensite is analyzed by energy-dispersive X-ray spectroscopy (EDS). The experimental study was supported by phase field modeling using Thermo-Calc and Diffusion-Controlled TRAnsformations (DICTRA) softwares. Experimental results showed that dual phase microstructure has inhomogeneity of martensite islands and fibers in ferritic matrix after intermediate quenching. Martensite formation occurred at prior austenite grain boundaries and martensite laths. In the case of intercritical annealing, pearlite regions are transformed to austenite and eventually martensite islands after quenching.
ABSTRACT Stickstofflegierte Stähle zeichnen sich im Vergleich zu konventionellen nichtrostenden a... more ABSTRACT Stickstofflegierte Stähle zeichnen sich im Vergleich zu konventionellen nichtrostenden austenitischen Stählen durch eine erhöhte Streckgrenze und Zugfestigkeit sowie eine verbesserte Warmfestigkeit aus. Sie weisen weiterhin eine verbesserte Korrosionsbeständigkeit, Lochfraßbeständigkeit und Beständigkeit gegen Spannungsrisskorrosion auf. Diesen Vorteilen können je nach Legierung Probleme bei der Warmumformung gegenüber stehen. So können Kanten- und Flächenabplatzungen sowohl als auch Risse während des Schmiedens auftreten. Diese Risse erfordern eine aufwendige Nachbearbeitung des Gussblockes, welches einen Nachteil in der Wirtschaftlichkeit des Prozesses bedeutet. In dieser Arbeit wurde ein Schmiedefenster für die wirtschaftliche Warmumformung von stickstoffhaltigen Stählen unter Berücksichtigung der Modellierung von Ausscheidungen und experimenteller Simulationen von Umformungen identifiziert. Dazu wurden drei hoch stickstofflegierte Stähle 1.4452, 1.4501 und 1.4882 und ein Referenzstahl 1.4301 untersucht. Zur Ermittlung des Ausscheidungsverhaltens und der Phasenumwandlungen werden mit Hilfe des Programms Thermo-Calc® die Phasenzustandsdiagramme simuliert. In Verbindung mit den Untersuchungen der Ausscheidungen werden Rückschlüsse auf die auftretenden Phasen und die Auflösungstemperaturen der Ausscheidungen gezogen. Für die experimentelle Simulation von Umformungen werden Heißzug- und Stauchversuche durchgeführt. Durch Heißzugversuche werden die Hochtemperatureigenschaften bei den Umformtemperaturen von 900ºC bis 1300ºC untersucht. In Stauchversuchen wird der Einfluss der Umformtemperatur auf die Rissanfälligkeit ermittelt. Mit diesen Ergebnissen wird ein Schmiedefenster erstellt. Die Untersuchungen zeigen, dass die Umformtemperaturbereiche für die austenitischen Werkstoffe 1.4452 und 1.4882 stärker eingeschränkt sind als die für den nicht stickstofflegierten Referenzstahl 1.4301 und den hoch stickstofflegierten Superduplex-Stahl 1.4501. High nitrogen steels (HNS) differ from conventional austenitic steels on their higher yield and tensile strength as well as improved high temperature strength. HNS show also a better corrosion resistance, pitting resistance and stress corrosion cracking resistance. However, these advantages are accompanied with some problems during hot deformation of HNS. Edges and surface cracks as well as forging cracks may appear. Time consuming and expensive finishing operations are required for these cracks which mean a serious drawback to economic processing of forging blocks. The aim of this thesis is the identification of a forging window for an economical production of HNS under consideration of the modeling of precipitation and the experimental simulation of deformation. The experiments were made on three HNS 1.4452, 1.4501, and 1.4882 and a reference steel 1.4301. On the modeling of precipitation, the phase diagrams were calculated with Thermo-Calc® software in order to determine precipitation characteristics and phase transformations. The investigation of precipitations helps to draw conclusions from appearing phases and dissolving temperatures. In order to simulate the deformation, the high temperature properties were determined at deformation temperatures between 900ºC and 1300ºC via hot tensile tests. The compression test defines also the effect of deformation temperature on the crack sensibility. As a result of experimental simulations, a forging window was determined. The results show the deformation temperature window is restricted for austenitic HNS 1.4452 and 1.4882 in compare to reference steel 1.4301 and super duplex HNS 1.4501.
This paper provides a study of carbide dissolution during heating of bearing steel using computat... more This paper provides a study of carbide dissolution during heating of bearing steel using computational thermodynamics and kinetics. 100Cr6 steel was used for the experimental work and calculations using the Thermo-Calc and DICTRA. Carbide dissolution was calculated at different full and intercritical austenization temperatures from 840 to 1200 C. The calculations also give the distribution of the alloying elements at carbide and austenite phase boundaries. In experimental work, SEM was used to study microstructures. SEM micrographs were evaluated with line intercept technique and carbide size and quantity were determined. The experimental results were compared with calculations providing good correlation.
IOP Conference Series: Materials Science and Engineering, 2017
The effects of heat treatment and initial microstructure on tensile properties of 22MnB5 and 30Mn... more The effects of heat treatment and initial microstructure on tensile properties of 22MnB5 and 30MnB5 high-strength hot stamping steels with martensite-ferrite matrix were investigated. Hot stamping steels possessed limited elongations of about 5% in a tensile strength ranging from 1300 to 1500 MPa when quenched at temperatures above A3 temperatures. The total elongations were tried to improve by partial austenization between Ac1 and Ac3 temperature and quenching. Ac1 and Ac3 temperatures were calculated via ThermoCalc. Microstructural characterization was made by using Light Microscope and Scanning Electron Microscope. Microstructure is composed of ferrite+martensite. It was seen that annealing temperature affects the volume fraction of phases. It was concluded that initial microstructure is an important parameter for the final microstructure. This method can be used for automobile parts which require higher TE with sufficient yield and tensile strength. Also this process may be a way of using Zn coated steel sheets in hot stamping process.
Uploads
Papers by Ersoy Erişir