The tendency for fish-scale formation of the enamelled products is characterized by the hydrogen ... more The tendency for fish-scale formation of the enamelled products is characterized by the hydrogen permeability. The permeation rate is established by the diffusivity and the solubility of hydrogen in the steel. The dissolved hydrogen is contained as atomic hydrogen in the interstices of the metal lattice. But in steel exist various traps for hydrogen atoms. Trapping enhances the solubility of hydrogen but decrease the diffusivity. The hydrogen diffusion was examined by electrochemical hydrogen permeation method. The studied hot rolled coil of S235JR grade steel had homogenous microstructure, constituted from ferrite, pearlite and inclusions non-metallic. The hydrogen permeation times were short at each sample (T H = 0.45-0.7). At Al-killed low carbon steel with high coiling temperatures the microstructure of the hot rolled sheets are composed from ferrite and massive carbide (T H gen = 0.6). The hydrogen permeation times were short. During of the cold rolling the massive carbides tend to be broken in fragments, between the carbides were observed micro-cavities. Increasing the dislocation density, with cold rolling the T H values increased. The shear bands are other representative traps at low carbon rimmed steels. After annealing where the massive carbides average areas were 4-7 μm 2 , the hydrogen permeation times were long (at the same samples T H values were higher than 40). The small rounded carbides, smaller then 1μm 2 , have no effect on hydrogen permeability. The ferrite grains sizes have no characteristic effect on hydrogen permeability.
The corrosion resistance of stainless steels depends on a protective, passive film being formed a... more The corrosion resistance of stainless steels depends on a protective, passive film being formed at the steel surface on exposure to the service environment. The use of fusion welding for fabrication leads to local compositional variations within the material, which may significantly alter the stability of the passive layer and hence the corrosion behaviour. In this work were examined the effect of welding parameters (shielding gas, amperage) on corrosion resistance of X6CrNiTi18-10 austenitic stainless steel tubes. The corrosion test was performed according to ASTM G48 standard.
A plasma-nitriding system was built at the BME Department of Materials Science and Engineering. T... more A plasma-nitriding system was built at the BME Department of Materials Science and Engineering. The aim of this surface treatment equipment is to produce nitrided layers on different steels. The aim of our research work is to analyze with SEM-EDS and XRD the surface of tempered steels and stainless steels after plasma-nitriding. We made specimens in our laboratory and for comparing, at an industrial partner in its equipment. Metallographic and hardness testing and microstructural characterization were performed. Corrosion tests were made on stainless steels to prove the properties of preliminary researches.
A plasma-nitriding system was built by plans of professor Blücher at the BME Department of Materi... more A plasma-nitriding system was built by plans of professor Blücher at the BME Department of Materials Science and Engineering. The aim of this surface treatment equipment is to produce nitrided layers on different steels. The aim of our research work is to analyze with SEM-EDS and XRD the surface of tempered steel after plasma-nitriding. We made specimens in our laboratory and, for comparing, at an industrial partner in its equipment. Metallographic and hardness testing and microstructural characterization were performed.
During our investigation lath martensite was produced in low carbon steels by austenitization at ... more During our investigation lath martensite was produced in low carbon steels by austenitization at 1200 °C/20 min, and the cooling of samples in ice water. The samples were tempered at a range of temperatures. The tempering effects on microstructure and on mechanical proprieties were investigated. Some samples with lath martensite microstructure were cold rolled and heat treated at different temperatures. Recrystallization was observed after heat treatment at 600-700 °C.
Lath martensitic microstructures were produced in steels containing 0.15% of carbon and various a... more Lath martensitic microstructures were produced in steels containing 0.15% of carbon and various amounts of molybdenum and nickel. The behavior of the lath martensitic microstructure was studied during cold rolling in steels with six different chemical compositions. All materials have endured 75% deformation without damage. In addition, the effects of heat treatments on microstructures and hardness were investigated as well.
The need for steel materials with increasing strength is constantly growing. The main application... more The need for steel materials with increasing strength is constantly growing. The main application of such advanced high strength steels (AHSS) is the automobile industry, therefore the welding process of different types of AHSSs in dissimilar welding joint was investigated. To simulate the mass production of thin steel sheet constructions (such as car bodies) automated metal inert gas (MIG) welding process was used to weld the TWIP (twinning induced plasticity) and TRIP (transformation induced plasticity) steel sheets together. The welding parameters were successfully optimized for butt welded joints. The joints were investigated by visual examination, tensile testing, quantitative metallography and hardness measurements. The TRIP steel side of the joints showed increased microhardness up to (450-500 HV0.1) through increased fraction of bainite and martensite. Macroscopically the tensile specimen showed ductile behaviour, they broke in the austenitic weld material.
Case hardened, double-walled train wheel, produced in the foundry of Abraham Ganz in 1867 and use... more Case hardened, double-walled train wheel, produced in the foundry of Abraham Ganz in 1867 and used for long time on the railroad tracks, was studied and evaluated by modern methods of materials sciences. The investigations indicated the presence of 0.059m% antimony (Sb), distributed uniformly in the material of the wheel. This quantity is several times higher than the average Sb amounts (<0.01m%) of the other components get into the castings. Sb was detected even in the several mm thick crust; except in the outermost surface layer with < 1 µm thickness. Based on the 20th century comprehensive studies, the antimony content, detected in the wheel, was found to be ideal. In grey iron it is a powerful pearlite stabilizer which has favourable effects on its mechanical properties and serviceability.The investigation of the surface structure proved that the excellent hardness (~600 HV) at the crust surface was due to the “nano-composite” structure formed from the pearlite as a consequence of severe plastic deformation during service. This was also promoted by the high amount (4.09m%) of carbon present in the casting. The microstructure refinement during operation most probably contributes to the long service lifetime of the wheels.The secret of the Abraham Ganz’s train wheels is inherently present – besides the novel construction and production technology (case hardening) – in the above mentioned composition and the structure of the material.
The role of the dislocations on the hydrogen permeation time of Al-killed, unalloyed low carbon s... more The role of the dislocations on the hydrogen permeation time of Al-killed, unalloyed low carbon steels was investigated using a special high resolution double crystal diffractometer operated at a rotating cobalt anode with fine focus. Strain anisotropy gives information about dislocation character and Burgers vector populations. Generally the normalized hydrogen permeation time increases or decreases with dislocation densities but the hydrogen accumulation could be less favourable near a screw dislocation than an edge dislocation.
The solubility of hydrogen in iron and steels are affected by temperature and crystal structure. ... more The solubility of hydrogen in iron and steels are affected by temperature and crystal structure. At lower temperatures (below about 400°C), the excess hydrogen, beyond that which is soluble (and therefore dissolved) interstitially, is retained in the steel in other sites commonly referred to as ”traps”. At room temperature, the dissolved hydrogen may be only a small fraction of the total hydrogen content. The movement of hydrogen in steel occurs by the migration of atoms through the lattice. The hydrogen diffusion takes place with interstitial mechanism. Trapping enhances the solubility of hydrogen but decreases the diffusivity. In practice hydrogen transmissibility is characterized by TH value. We have studied the effect of the cold rolling on the TH value for Al-killed low carbon enamelling-grade steel sheets. The microstructures of the samples were formed from ferrite, carbides and some non-metallic inclusions. Reducing the thickness of the steel sheets by cold rolling in carbide...
ABSTRACT The role of dislocations on hydrogen permeation time of Al-killed, unalloyed low-carbon ... more ABSTRACT The role of dislocations on hydrogen permeation time of Al-killed, unalloyed low-carbon steels was investigated using a special high-resolution double crystal diffractometer operated at a rotating copper anode with fine focus. Information about dislocation character and Burgers vector populations are given by strain anisotropy. Generally, the hydrogen permeability increases or decreases with dislocation densities but hydrogen accumulation proved to be less favourable near a screw dislocation than an edge dislocation.
The tendency for físh-scale formation of the enamelled products is characterized by the hydrogen ... more The tendency for físh-scale formation of the enamelled products is characterized by the hydrogen permeability. The permeation of hydrogen trough steel involves its entrance at one surface and its exit at the other surface. The permeation rate, P, at which hydrogen passes through a slab of thickness, d, per unit area, will be established by the diffusivity and the solubility of hydrogen in the steel. The dissolved hydrogen is contained as atomic hydrogen in the interstices of the metal lattice. In steel exist various traps for hydrogen atoms. Trapping enhances the solubility of hydrogen but decrease the diffusivity. Traps are, for example: grain boundaries, boundaries of second phase particles, steelinclusion interfaces, micro-cavities etc. Traps can be characterized by their nature. A reversible trap being one that hydrogen can both enter and leave. A dislocation core is saturable, reversible trap; while voids and cracks are unsaturable reversible traps. The studied hot rolled coil of S235JR grade steel had homogenous microstructure, constituted from ferrite, pearlite and inclusions non-metallic. There were not micro-cavities. The measured T H values were low (between: 0.45-0.7).
It have been studied the cold rolling effects on the microstructure of samples prepared from Al-k... more It have been studied the cold rolling effects on the microstructure of samples prepared from Al-killed low carbon steel sheets with high coiling temperatures. The microstructure of the hot rolled steels sheet is formed from ferrite and large carbides when the coiling temperature is high. The cold rolling affects the steel mechanical and electrochemical properties due to microstructural changes. We have studied the microstructure by optical microscope and scanning electron microscope. Low angles grain boundaries and the texture of samples were studied by EBSD method.
When the coiling temperature of the hot rolled, Al-killed low carbon enamelling grade steel is hi... more When the coiling temperature of the hot rolled, Al-killed low carbon enamelling grade steel is high; the microstructure is formed from ferrite and large carbides. High finishing temperatures combined with high coiling temperatures can result in the material to appear a coarse degenerate form of pearlite. Due to the cold rolling at the beginning of the process the dislocation density increase. After some % of reducing of the thickness at the ferrite-carbide interfaces appear voids. Increasing the reduction appears cracks in the carbides. After heavy reductions the carbides are broken into fragments, groups of fragments being elongated in the rolling direction. Measuring the hydrogen permeation times we have observed, that the T H value of the hot rolled strip were very short (T H =0.6). At 12-20% reductions it could be discern some voids and few cracks in carbides, the T H = 2.6-3.5. After 25-30% reduction appear some broken carbides. At 37% reduction was observed a jumping in T H value (T H =11.56), where we could discern beautifully broken carbides and microcavity between them. At 51% reduction was observed another jumping in T H value (T H =24.4), here for the microstructure has became characteristic the broken carbides. Other jumping were observed at 60% reduction (T H =47,9) and at 70% reduction of the thickness (T H =101.
The aim of this work was to analyze the performance of joints made by TIG (Tungsten Inert Gas) we... more The aim of this work was to analyze the performance of joints made by TIG (Tungsten Inert Gas) welding process in austenitic and duplex stainless steels with special regards to their corrosion resistance. Three different types of stainless steel were butt welded with TIG method. Ferric-chloride test and electrochemical treatments revealed how does the TIG process affects the corrosion resistance depending upon the alloy used for welding the joint. This work focuses on the weldability of the 2304, 2404 and 304 type stainless steel heterogeneous welds.
The tendency for fish-scale formation of the enamelled products is characterized by the hydrogen ... more The tendency for fish-scale formation of the enamelled products is characterized by the hydrogen permeability. The permeation rate is established by the diffusivity and the solubility of hydrogen in the steel. The dissolved hydrogen is contained as atomic hydrogen in the interstices of the metal lattice. But in steel exist various traps for hydrogen atoms. Trapping enhances the solubility of hydrogen but decrease the diffusivity. The hydrogen diffusion was examined by electrochemical hydrogen permeation method. The studied hot rolled coil of S235JR grade steel had homogenous microstructure, constituted from ferrite, pearlite and inclusions non-metallic. The hydrogen permeation times were short at each sample (T H = 0.45-0.7). At Al-killed low carbon steel with high coiling temperatures the microstructure of the hot rolled sheets are composed from ferrite and massive carbide (T H gen = 0.6). The hydrogen permeation times were short. During of the cold rolling the massive carbides tend to be broken in fragments, between the carbides were observed micro-cavities. Increasing the dislocation density, with cold rolling the T H values increased. The shear bands are other representative traps at low carbon rimmed steels. After annealing where the massive carbides average areas were 4-7 μm 2 , the hydrogen permeation times were long (at the same samples T H values were higher than 40). The small rounded carbides, smaller then 1μm 2 , have no effect on hydrogen permeability. The ferrite grains sizes have no characteristic effect on hydrogen permeability.
The corrosion resistance of stainless steels depends on a protective, passive film being formed a... more The corrosion resistance of stainless steels depends on a protective, passive film being formed at the steel surface on exposure to the service environment. The use of fusion welding for fabrication leads to local compositional variations within the material, which may significantly alter the stability of the passive layer and hence the corrosion behaviour. In this work were examined the effect of welding parameters (shielding gas, amperage) on corrosion resistance of X6CrNiTi18-10 austenitic stainless steel tubes. The corrosion test was performed according to ASTM G48 standard.
A plasma-nitriding system was built at the BME Department of Materials Science and Engineering. T... more A plasma-nitriding system was built at the BME Department of Materials Science and Engineering. The aim of this surface treatment equipment is to produce nitrided layers on different steels. The aim of our research work is to analyze with SEM-EDS and XRD the surface of tempered steels and stainless steels after plasma-nitriding. We made specimens in our laboratory and for comparing, at an industrial partner in its equipment. Metallographic and hardness testing and microstructural characterization were performed. Corrosion tests were made on stainless steels to prove the properties of preliminary researches.
A plasma-nitriding system was built by plans of professor Blücher at the BME Department of Materi... more A plasma-nitriding system was built by plans of professor Blücher at the BME Department of Materials Science and Engineering. The aim of this surface treatment equipment is to produce nitrided layers on different steels. The aim of our research work is to analyze with SEM-EDS and XRD the surface of tempered steel after plasma-nitriding. We made specimens in our laboratory and, for comparing, at an industrial partner in its equipment. Metallographic and hardness testing and microstructural characterization were performed.
During our investigation lath martensite was produced in low carbon steels by austenitization at ... more During our investigation lath martensite was produced in low carbon steels by austenitization at 1200 °C/20 min, and the cooling of samples in ice water. The samples were tempered at a range of temperatures. The tempering effects on microstructure and on mechanical proprieties were investigated. Some samples with lath martensite microstructure were cold rolled and heat treated at different temperatures. Recrystallization was observed after heat treatment at 600-700 °C.
Lath martensitic microstructures were produced in steels containing 0.15% of carbon and various a... more Lath martensitic microstructures were produced in steels containing 0.15% of carbon and various amounts of molybdenum and nickel. The behavior of the lath martensitic microstructure was studied during cold rolling in steels with six different chemical compositions. All materials have endured 75% deformation without damage. In addition, the effects of heat treatments on microstructures and hardness were investigated as well.
The need for steel materials with increasing strength is constantly growing. The main application... more The need for steel materials with increasing strength is constantly growing. The main application of such advanced high strength steels (AHSS) is the automobile industry, therefore the welding process of different types of AHSSs in dissimilar welding joint was investigated. To simulate the mass production of thin steel sheet constructions (such as car bodies) automated metal inert gas (MIG) welding process was used to weld the TWIP (twinning induced plasticity) and TRIP (transformation induced plasticity) steel sheets together. The welding parameters were successfully optimized for butt welded joints. The joints were investigated by visual examination, tensile testing, quantitative metallography and hardness measurements. The TRIP steel side of the joints showed increased microhardness up to (450-500 HV0.1) through increased fraction of bainite and martensite. Macroscopically the tensile specimen showed ductile behaviour, they broke in the austenitic weld material.
Case hardened, double-walled train wheel, produced in the foundry of Abraham Ganz in 1867 and use... more Case hardened, double-walled train wheel, produced in the foundry of Abraham Ganz in 1867 and used for long time on the railroad tracks, was studied and evaluated by modern methods of materials sciences. The investigations indicated the presence of 0.059m% antimony (Sb), distributed uniformly in the material of the wheel. This quantity is several times higher than the average Sb amounts (<0.01m%) of the other components get into the castings. Sb was detected even in the several mm thick crust; except in the outermost surface layer with < 1 µm thickness. Based on the 20th century comprehensive studies, the antimony content, detected in the wheel, was found to be ideal. In grey iron it is a powerful pearlite stabilizer which has favourable effects on its mechanical properties and serviceability.The investigation of the surface structure proved that the excellent hardness (~600 HV) at the crust surface was due to the “nano-composite” structure formed from the pearlite as a consequence of severe plastic deformation during service. This was also promoted by the high amount (4.09m%) of carbon present in the casting. The microstructure refinement during operation most probably contributes to the long service lifetime of the wheels.The secret of the Abraham Ganz’s train wheels is inherently present – besides the novel construction and production technology (case hardening) – in the above mentioned composition and the structure of the material.
The role of the dislocations on the hydrogen permeation time of Al-killed, unalloyed low carbon s... more The role of the dislocations on the hydrogen permeation time of Al-killed, unalloyed low carbon steels was investigated using a special high resolution double crystal diffractometer operated at a rotating cobalt anode with fine focus. Strain anisotropy gives information about dislocation character and Burgers vector populations. Generally the normalized hydrogen permeation time increases or decreases with dislocation densities but the hydrogen accumulation could be less favourable near a screw dislocation than an edge dislocation.
The solubility of hydrogen in iron and steels are affected by temperature and crystal structure. ... more The solubility of hydrogen in iron and steels are affected by temperature and crystal structure. At lower temperatures (below about 400°C), the excess hydrogen, beyond that which is soluble (and therefore dissolved) interstitially, is retained in the steel in other sites commonly referred to as ”traps”. At room temperature, the dissolved hydrogen may be only a small fraction of the total hydrogen content. The movement of hydrogen in steel occurs by the migration of atoms through the lattice. The hydrogen diffusion takes place with interstitial mechanism. Trapping enhances the solubility of hydrogen but decreases the diffusivity. In practice hydrogen transmissibility is characterized by TH value. We have studied the effect of the cold rolling on the TH value for Al-killed low carbon enamelling-grade steel sheets. The microstructures of the samples were formed from ferrite, carbides and some non-metallic inclusions. Reducing the thickness of the steel sheets by cold rolling in carbide...
ABSTRACT The role of dislocations on hydrogen permeation time of Al-killed, unalloyed low-carbon ... more ABSTRACT The role of dislocations on hydrogen permeation time of Al-killed, unalloyed low-carbon steels was investigated using a special high-resolution double crystal diffractometer operated at a rotating copper anode with fine focus. Information about dislocation character and Burgers vector populations are given by strain anisotropy. Generally, the hydrogen permeability increases or decreases with dislocation densities but hydrogen accumulation proved to be less favourable near a screw dislocation than an edge dislocation.
The tendency for físh-scale formation of the enamelled products is characterized by the hydrogen ... more The tendency for físh-scale formation of the enamelled products is characterized by the hydrogen permeability. The permeation of hydrogen trough steel involves its entrance at one surface and its exit at the other surface. The permeation rate, P, at which hydrogen passes through a slab of thickness, d, per unit area, will be established by the diffusivity and the solubility of hydrogen in the steel. The dissolved hydrogen is contained as atomic hydrogen in the interstices of the metal lattice. In steel exist various traps for hydrogen atoms. Trapping enhances the solubility of hydrogen but decrease the diffusivity. Traps are, for example: grain boundaries, boundaries of second phase particles, steelinclusion interfaces, micro-cavities etc. Traps can be characterized by their nature. A reversible trap being one that hydrogen can both enter and leave. A dislocation core is saturable, reversible trap; while voids and cracks are unsaturable reversible traps. The studied hot rolled coil of S235JR grade steel had homogenous microstructure, constituted from ferrite, pearlite and inclusions non-metallic. There were not micro-cavities. The measured T H values were low (between: 0.45-0.7).
It have been studied the cold rolling effects on the microstructure of samples prepared from Al-k... more It have been studied the cold rolling effects on the microstructure of samples prepared from Al-killed low carbon steel sheets with high coiling temperatures. The microstructure of the hot rolled steels sheet is formed from ferrite and large carbides when the coiling temperature is high. The cold rolling affects the steel mechanical and electrochemical properties due to microstructural changes. We have studied the microstructure by optical microscope and scanning electron microscope. Low angles grain boundaries and the texture of samples were studied by EBSD method.
When the coiling temperature of the hot rolled, Al-killed low carbon enamelling grade steel is hi... more When the coiling temperature of the hot rolled, Al-killed low carbon enamelling grade steel is high; the microstructure is formed from ferrite and large carbides. High finishing temperatures combined with high coiling temperatures can result in the material to appear a coarse degenerate form of pearlite. Due to the cold rolling at the beginning of the process the dislocation density increase. After some % of reducing of the thickness at the ferrite-carbide interfaces appear voids. Increasing the reduction appears cracks in the carbides. After heavy reductions the carbides are broken into fragments, groups of fragments being elongated in the rolling direction. Measuring the hydrogen permeation times we have observed, that the T H value of the hot rolled strip were very short (T H =0.6). At 12-20% reductions it could be discern some voids and few cracks in carbides, the T H = 2.6-3.5. After 25-30% reduction appear some broken carbides. At 37% reduction was observed a jumping in T H value (T H =11.56), where we could discern beautifully broken carbides and microcavity between them. At 51% reduction was observed another jumping in T H value (T H =24.4), here for the microstructure has became characteristic the broken carbides. Other jumping were observed at 60% reduction (T H =47,9) and at 70% reduction of the thickness (T H =101.
The aim of this work was to analyze the performance of joints made by TIG (Tungsten Inert Gas) we... more The aim of this work was to analyze the performance of joints made by TIG (Tungsten Inert Gas) welding process in austenitic and duplex stainless steels with special regards to their corrosion resistance. Three different types of stainless steel were butt welded with TIG method. Ferric-chloride test and electrochemical treatments revealed how does the TIG process affects the corrosion resistance depending upon the alloy used for welding the joint. This work focuses on the weldability of the 2304, 2404 and 304 type stainless steel heterogeneous welds.
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