High-pressure steel cylinders (HPSC) are commonly used for applications like industrial gases storage and its transport, storage and transport of compressed natural gas (CNG) and many others. Especially in case of CNG storage, different gas purities are used worldwide. Special field of gases storage is storage and transportation of untreated CNG so called raw gas, meaning not dehumidified and desulphurised natural gas. This kind of gas causes significantly increased speed of corrosion in H2S environment. So far, there were only two solutions. The first one was used for HPSC with very low mechanical properties with limited tensile strength (TS) up to 950 MPa to withstand such conditions. This was conditioned by increased wall thickness and weight of cylinders consequently, leading to low mechanical properties of material. The second solution was an application of inner coatings of HPSC, but this solution is highly expensive and the processes during the gas filling caused the wear of the inner coating and its chipping. The best solution is application of any different material. In this case, the high strength martensitic stainless steel was only an alternative solution to get an increased corrosion resistance and also TS up to 1099 MPa. In this paper, the basic microstructure, mechanical properties and resistance to SSC are evaluated and compared with the 34CrMo4 steel, which is used as the standard material for HPSC production.
The present work deals with the possibility of the evaluation of the descaling rate of the AISI 304 stainless steel. The samples were pre-treated in the reduction melt containing NaOH, Na2O and NaH and the final pickling took place in the mixtures of acids. The cross – sections of the scales formed on the steel as received and those remained after reduction bath treatment and acid pickling were examined by using a scanning electron microscope. The surface analysis was performed by the Raman microspectroscopy and the presence of magnetite was proved for all the samples. The occurrence of this electroactive substance enabled using of the electrochemical methods (cyclic voltammetry, electrochemical impedance spectroscopy and chronocoulometry) for monitoring of the redox reactions taking place on the working electrode formed by the steel sample in 1 M NaOH solution. The application of whichever method provides a quick estimation of the pickled surface state.
When dealing with corroded objects, it is necessary to identify the corrosion products to develop a propper treatment for this particular object. Using X-ray diffraction is still suitable to do the phase composition analysis of the material, however it does the analysis of the material in bulk. It is also possible to use SEM to analyze the structure of the corrosion layers on a cross-section by EBSD method, however this method is time consuming.
It is more suitable to use Raman spectroscopy when studying the structure of corrosion layers. Using propper equipment, such as Raman microscope it is possible to do not only analysis of precisely given point, but it is also possible to do mapping (both 1D and 2D) of the crossection. Taking map of surface also does need time, but is definitelly less time consuming compared to EBSD method
In this study, the impact of corrosion in S400 grade of reinforcing steel bar as for the mechanical performance on seismic loads (low-cycle fatigue LCF) was investigated. The mechanical performance and life expectancy of S400 grade of reinforcing steel bar on seismic loads was evaluated based on the strength degradation (reduction of maximum strength) during its loading time period, under corrosion or not circumstances. The results show that corrosion level, as a parameter, has a negative influence on the seismic performance of steel bar. Therefore, a phenomenological hysteretic model of non-corroded and corroded steel bar, was also conducted considering three levels of imposed deformation (±1%, ±2.5% & ±4%). The effectiveness of material model was validated through comparison with experimental data being in a good agreement with the observed experimental results. At this point, a lower limit value (threshold) of upper tensile and compression load was also introduced, in order to predict the performance and the useful life duration (cycles number) of a Reinforced-Concrete (R/C) member. That could lead to warning signs of awakening in order not to use unreliable parts of R/C in existing structures, prior to their life expectancy.
As the austenitization temperature of these steels can be used as a control measure of the transformation characteristics, the paper analyzes the cavitation behavior of a steel subjected to solution treatment at a lower temperature (950 ºC), after which a primary aging at 700 ºC and a tempering at 450 ºC, were applied. The cavitation tests were conducted on a vibratory facility with piezoelectric crystals, in conformity with the prescription given by the ASTM G32-2010 Standard. The variation curves of mass losses and their speed during the test period, along with the hardness measurements and metallographic examinations explain the degradation mechanism of the surface at the impact of the cavitation bubbles from the hydrodynamic field.
This paper aimed to investigate the advantages of the use of S700MC steel instead of St52 steel widely used in industrial areas. For this purpose, a tensile test, a macro hardness test, a Charpy impact test, and a fatigue life test were performed on St52 steel and S700MC steel specimens. Test results showed that S700MC steel generally exhibited better performance than St52 steel in terms of mechanical properties and fatigue life. In addition, a finite element method (FEM) analysis was conducted on a tandem housing body of a motor grader according to S700MC and St52 scenarios to determine their safety factors and the reduction in its weight with the use of S700MC steel. FEM results showed that the use of S700MC steel led to an increase in the safety factor by about 83 % or a decrease in the weight by about 30 %.
A new surface induction hardening technology was for the first time in Europe designed in BONARTANS GROUP Company for the purpose of increasing the safety and resistance of railway axles to fatigue damage. The operation of railway axles should fulfill two main demands: safety and low operation costs. A significant part of operation costs is given by frequency of regular inspection intervals which should reveal potential fatigue cracks in railway axle. The detection of cracks is of probabilistic approach, therefore some small cracks could be not revealed. For the safety, the existence of potential initial crack should be considered on the axle surface and residual fatigue lifetime should be conservatively determined for this case. Reliable procedure of fatigue lifetime estimation should take into account real geometry, material characteristics and loading of the railway axle. This paper shows methodology for determination of residual fatigue lifetime based on fracture mechanics approach. The calculated lifetime is compared with results of experimental tests of the axle. This paper further present a part of technological benefit such as hardness profile and fatigue characteristics and compare their values with standard heat treated railway axles.
The effect of mean stress on fatigue life and fatigue limit was investigated for S355 NL+N ferritic-pearlitic steel. Changing stress ratio from R=0 corresponding to pulsating regime to R = -1, which is in conformity with alternating regime, the fatigue life was changed when applying the mean stress for the same stress amplitude. Although this phenomenon is generally very well known it is important to investigate it further regarding to commonly applied material. Research results of this topic could help to structure designer better utilize fatigue behaviors of materials as S355 steel which is commonly used for constructions of welded structures. Since this steel is favored for production of structures, it is extremely important how the alternating stress ratio affects their service life. The experimental results show that with increasing mean stress of loaded S355 steel and growing stress ratio, the fatigue limit diminishes and fatigue life is getting shorter. Then for a given value of the limited amplitude the number of cycles up to failure with increasing stress ratio decreases. This effect is much more substantial when the limited amplitude approaches to the fatigue limit for a given value of the stress ratio. Discussed experimental results help to optimize mechanical design of steel welded structures.
A study of fatigue crack initiation and growth in 316 L austenitic stainless steel is reported. Fatigue
experiments were performed at room temperature on full cylindrical specimens cycled axially
(tension-compression) and on hollow cylindrical specimens tested in reversed torsion. The
symmetrical cyclic loading under strain control regime was performed using servohydraulic MTS 809
axial – torsional test system. Microstructure and damage evolution (crack initiation and growth) on
the surface of mechanically and electrolytically polished specimens were observed using light and
electron microscopy. An analysis of both crack density and the orientation of microcracks and
macrocrack(s) which led to failure was made. Relationship between crack initiation and
crystallographic orientation of grains was studied using EBSD technique. Axially loaded specimens
exhibited presence of several microcracks which resulted in macrocrack propagating perpendicularly
to specimen axis. In the case of torsional loading, orientation of macrocrack propagation was
dependent on applied load and presence of notches. High amount of short cracks initiated parallel to
specimen axis. Long cracks exhibited a tendency to bifurcation with crack branches oriented at
approximately 45° to the specimen axis. Bifurcation was observed in case of short fatigue cracks, too.
In this case, the crack does not propagated anymore. In some specimens, hole of diameter 0.3 mm
was drilled. Four fatigue cracks initiated in the hole and propagated in directions of approximately
45° to the specimen axis. It means that the crack initiation stadium was omitted which resulted in shortening of fatigue life.
This paper deals with the analysis of microstructure and mechanical properties of 9 Cr steel after austenitisation at temperatures of 1150°C, 1180°C and 1210°C/2hrs and after tempering at temperature of 790°C/1hr. Microstructure after austenitisation and quenching was formed of lath martensite and uniformly distributed ferritic area. At austenitising temperature of 1150°C were microstructures relatively homogeneous. At higher austenitising temperature 1180°C and 1210°C were microstructure significantly heterogeneous. With increasing austenitising temperature there was a significant increase of the original austenite grain boundaries. After tempering was microstructure formed by tempered martensite, with lath morphology. The results of mechanical properties (Rp0,2, Rm, HBW, KV2) are in good agreement with requirements for grade P91 and P92 according to the relevant norm of STN EN 10216-2+A2. The minimum values of ductility A5 accordance with that norms were not achieved, where values were lower about 1.1 – 2.1% compared with the prescribed value of ductility for grade P92 (min.19%).
Laves phases are the largest class of intermetallic phases, showing very high strength up to temperatures above 1000 °C, but being very brittle at room temperature.
The present work summarizes results obtained from transmission electron microscopy on single-phase Fe2Nb with hexagonal structure before and after compression tests. The compressive stress-strain curves are characterized by a pronounced stress peak in the stress-strain curves at temperatures up to 1200 °C and by steady state flow above 1200 °C.
Undeformed NbFe2 is almost free of dislocations. After deformation at 1200 °C new dislocations are introduced into the material. Widely-extended stacking faults on the basal plane dominate the microstructure. Material deformed at 1300 °C shows a high density of dislocations, which are split into pairs of partial dislocations that bound stacking faults on the basal plane.The main deformation mechanism in the NbFe2 Laves phase is basal slip.
Creep resistance of steels in the field of dislocation creep strongly depends on both thermodynamic and dimensional stability of minor phases. Precipitation of many minor phases in heat resistant steels is now very well documented. But it is not true in the case of some interstitial minor phases in nitrogen-bearing steels. For example, a limited amount of information is available about precipitation of a complex nitride (Nb,V)CrN, so called modified Z-phase, in austenitic steels. This paper deals with the studies on precipitation behaviour of modified Z-phase in an AISI 316 LN steel with vanadium and niobium additions. Thermodynamic equilibrium phases for the steel investigated were simulated using the Thermocalc software. Furthermore, laboratory annealing of specimens was carried out in the temperature interval from 550 to 1250 °C for times 1, 20 and 50 hours. Kinetics of precipitation of modified Z-phase in the austenitic matrix was fast. Precipitation of this minor phase was observed in the temperature range of 750 – 1050 °C which corresponded well with the results of thermodynamic calculations. Solvus temperature of modified Z-phase in the steel investigated was determined to be app. 200 °C lower than that reported for NbCrN type of Z-phase in austenitic steels.
Grain oriented electrical steels (GOES) produced by the „AlN + Cu“ technology usually contain ca 0.5 wt.%Cu. Evolution of microstructure during the final high temperature annealing of GOES is strongly affected by microstructural changes during the individual steps of industrial production process. Inhibition phases, AlN and sulphides, are expected to play an important role in the formation of the final Goss texture.
This paper deals with TEM characterization of sulphides in Cu – bearing GOES after basic steps of industrial production process: hot rolling, decarburization annealing and high temperature annealing. In specimens after hot rolling only sulphides of manganese and complex sulphides of manganese containing a small fraction of copper were identified. Typical size of these sulphides reached several hundreds of nanometres. These results prove a low solvus temperature of Cu rich sulphides in GOES. After decarburization annealing re-precipitation of copper-rich sulphides was observed. Due to low temperature of precipitation typical size of these sulphides reached only several tens of nanometres. Apart from complex sulphides of copper and manganese, fine Cu2S particles were detected. In the paper the effect of Cu – bearing sulphides precipitation on the formation of other minor phases is discussed. Heterogeneous nucleation of AlN particles on fine sulphides was often observed. During high temperature annealing all sulphides gradually dissolved.
To evaluate the resistance to failure of the constructions with cracks usually the fracture criterions are used. One of such criterion used to evaluate failure is J-integral. Calculated value of failure criteria in construction with crack is compared with its critical value for the material the construction is made of. The values of J-integral for the materials are usually experimentally determined. This article presents the methodology for the determination of J-integral using numerical methods. For this purpose the Finite Element (FE) code ABAQUS was used.
The modelling of the J-integral of steel P91 was performed. 2D and 3D FE models were used for this purpose. The experimental stress – strain curve was used as material description. For crack growth calculation the crack opening displacement as fuction of crack length is presented. As a result of investigation the J-integral of steel P91 was determined and numerical modelling data were compared with experiment. Numerically determined J-integral has good coincidence with experiment results. Therefore it can be concluded that presented methodology can be used for study of J-integral.
A physical model describing the diffusion of interstitial atoms was developed and has been repatedly used to study the redistribution of hydrogen, as well as predicting the risk of hydrogen damage during various real manufacturing processes.
A particular advantage of this model is that, contrary to some simplified comercial and academic models, it contemplates diffusion in its most comprehensive description, i.e., with the driving force for atom diffusion being the gradient in chemical activation (and not simply occurring down a composition gradient). As the model also incorporates thermal history, microstructure, matrix solubility, multiple trapping distributions, interaction with the atmosphere and others, it is specially suitable to study real manufacturing processes.
In this case, two applications of interest both to accademia and industry are presented. Fist, the model is aplied to simulate a Thermal Desorption Analysis (TDA) test. By using the model, it is possible to relate desorption fluxes with the redistribution between different trapping sites within the metal.
Then hydrogen permeation is considered. In the case studied hydrogen is transported through a metal wall separating one volume with high hydrogen pressure and temperature from another volume with low hydrogen pressure and temperature. By using such comprehensive physical model, it is possible to study the effects of hydrogen pressure and temperature gradient, wall thickness, metal microstructure and trap distribution on the flux across the wall and on the accumulation of hydrogen within the metal. Furthermore, it makes possible to estimate the embrittlement risk and when necessary the time to fracture.
The key characteristic of austenitic Hadfield steel is itself strengthening during operation. By the influence of mechanical loading is austenit transformed to martensite, it leads to increasing of surface strength (hardness) in combination with keeping good toughness. Very high resistance to abrasive wear is the reached result.
In the respect of very difficult machinability and weldability are final products designed as castings without additional machining or simply as products from rolled sheets.
This paper describes the most frequent defects on rolled sheets and their effects on decresing of abrasion resistance. As samples for testing were selected sheets from available standard production where there were identified following defects: high decarburazed layer, carbides on grain boundaries and martensite structure in delivered conditions before any loading. We have used shot blasting test in the cabinet of shot blasting machine for the comparison of the abrasion resistance of each tested sample. We evaluated weight difference caused by shot blasting on the each sample.
Achieved results confirm, that samples without defect (where the defect was grind off) have the better wear resistance in 25 – 40% than the samples with described defect.
Recent research by the steel industry focuses mainly on the high strength steels with excellent formability. A new look at the role of individual elements generally used for steels and the possibility of new metallurgical technologies application have led to the development of steels with a wide range of mechanical properties and formability used in automotive industry. New possibilities appeared at the beginning of this century when the effect of strain-induced transformation of γ phase was attempted to be applied to austenitic steels. Nowadays, a new group of high-manganese austenitic TWIP steels with variable concentration of Mn, Al and Si was proposed showing their high potential. This paper deals with the description of the strengthening due to the cold rolling on experimental heats of manganese steel with TRIP/TWIP effect. Impacts on microstructure, yield strength and tensile strength are described.
The high alloyed austenitic manganese steel, the Hadfield steel, thanks to its good wear resistance of the work surface and maintaining the high toughness of the internal material in the same time, is successfully applied for casted crossings. The crossings are the most dynamic stressed components in the railway turnouts. Thanks to low surface and sub-surface hardness the occurrence of plastic deformation and the progressive wear of the crossing running surfaces can be found since the initial stages of the crossing operational life. One possibility how to increase the surface and the sub-surface hardness and this way improve the dimensional stability and the crossing lifetime as well is to apply the explosive hardening of the crossing running surfaces. The technology mentioned above means the application of the explosives in the imminent nearness to the running surface of the crossing, when the high pressure wave acting within the extremely short period actuates the plastic deformation of the material structure. The experiments of this work describe the long – term validation, the surface hardness and wear of the running surfaces of 4 explosive hardened crossings made by Hadfield steel already installed into the Czech Republic railway track.
In this study, the quantity, size and type of non-metallic inclusions occurred in laser welded transformation induced plasticity (TRIP) and complex phase (CP) steel joints were identified using SEM and EDS techniques. Both steels include Al, Ti, and Si additions which are characterized by high chemical affinity to oxygen. Microscopic observations of the fusion zones of the TRIP and CP steels showed that the quantity and size of inclusions formed in the CP steel were significantly lower than those observed in the fusion zone of TRIP steel. The presence of oxide-type non-metallic inclusions containing Al, Ti and Si has been primarily revealed.
A hot rolled TRIP steel concept was selected for the laboratory scale process simulation. The ferrite and bainite transformation kinetics on the Run Out Table and during coiling were mapped
as a function of temperature and austenite conditioning by Leblond and Devaux s concept. The updated carbon content in the remaining austenite is the key factor to control following bainite formation.
The microstructure was characterized by LOM, SEM, FEG EPMA. The mean carbon content was taken from the in-situ high energy XRD. This study shows that enough carbon enrichment of austenite can be achieved by forming carbide free bainite alone without the formation of ferrite at higher temperature. However, its fraction can be too low to exhibit the TRIP effect. Therefore, pre-deformation such that in the hot rolling process is still necessary.
This work is deal with the carbide/wear resistance relationship of nitrogen containing high speed tool steel. In this work, carbides presence in steel under consideration after full heat treatment studied using X-ray diffraction, optical microscopy, image analysis. The relationship between the carbide precipitated during solidification of investigating steel with sliding wear resistance are studied and discussed. The experimental result shows that, the microstructure of nitrogen containing steel is more dense, well distributed and contain higher carbides contents. The x-ray result shows that some kind of carbides partially or totally disappears and other carbides appear. From wear resistance point of view, experimental results show that nitrogen containing steel has more wear resistance than traditional steel (nitrogen free steel).
It is well known, that lamellar pearlite austenitization can lead to rapid spheroidisation of cementite. This phenomenon is the base for ASR process – Accelerated carbide Spheroidisation and Refinement. It is possible to obtain fully spheroidised structure from lamellar pearlite within minutes by partial austenitization and divorced pearlitic transformation. Moreover, such structure is significantly finer than spheroidised structure after conventional soft annealing. The size of carbide particles obtained by ASR process depends on the austenitization rate. This is an important fact, because various kinds of heating methods can be applied for steel heat treatment with heating rate differing by decade orders. This article describes cementite morphology during spheroidisation with respect to the austenitization kinetics.
100CrMnSi6-4 with pearlitic structure was austenitized isothermally at different temperatures and continuously at different heating rate. Cementite lamellae fragmentation at interphase boundary perlite/austenite was examined by SEM after deep etching. Size and distribution of resulting cementite globules was characterized. Austenitization kinetics was observed via dilatometric measurement.
The aim of the paper was to determine the influence of used technology on the tribological properties and the erosive resistance of X2CrNi18-9 base sintered materials. In the work was made the analysis of processes the high temperature isostatic pressing and sintering in deep vacuum. For researches were made two sets of samples with variant SiC content in range 0÷5%. To the erosive resistance analysis was used the designed in Czestochowa University of Technology device. To the tribological properties analysis was used the pi on disc test.
This work presents the comparative results of twin-spot laser welding of complex phase and transformation induced plasticity steels. Both steels include Nb and Ti microalloyed elements. Tests of dual beam laser welding were carried out using keyhole welding. The sheets were welded with three different power beam distributions in order to determine the effect of simulated thermal cycles on microstructure and hardness profiles. The power distribution between beams were 50:50, 60:40 and 70:30 %. The microstructural constituents in the fusion zone, heat affected zone and base metal were identified using light microscopy and scanning electron microscopy. It was found that the change of beam distribution affects morphological details of the martensite and hardness behaviour.