High-alloy Cast Research Articles

Effect of Carbide Orientation on Wear Characteristics of High-Alloy Wear-Resistant Cast Irons

Both erosive and abrasive wear are common in mechanical systems and moving components in industrial production. Once they occur in machine parts, the task of breakdown maintenance should be carried out, leading to high production costs. Previous research has shown that high-chromium cast iron (HCCI), a commonly used wear-resistant material, experiences repeated particle impacts that break up the chromium carbides (M7C3) on its surface, resulting in the formation of fine fracture carbides. It has been reported that erosion wear occurs progressively due to the shedding of protrusions caused by the plastic deformation of the material’s matrix. Thus, the erosion wear characteristics of a material are strongly affected by carbides, which come in various shapes and can affect resistance. This research examined the orientation of carbides on the microstructure and their effects on erosion and abrasion properties. The wear tests showed that 27 wt.% chromium content high-alloy cast irons showed the best wear resistance properties due to the coarse strips of M7C3 carbides that effectively suppressed wear propagation. Additionally, the M2C carbides crystallized around the M7C3 carbides which support the M7C3 carbide to reduce plastic deformation and carbide peel-out. Consequently, the wear resistance properties of this material are significantly improved.

Effect of hot isostatic pressing processing parameters on microstructure and properties of Ti60 high temperature titanium alloy

Hot isostatic pressing parameters are critical to Ti60 high temperature titanium alloy castings which have wide application perspective in aerospace. In order to obtain optimal processing parameters, the effects of hot isostatic pressing parameters on defects, composition uniformity, microstructure and mechanical properties of Ti60 cast high temperature titanium alloy were investigated in detail. Results show that increasing temperature and pressure of hot isostatic pressing can reduce defects, especially, the internal defects are substantially eliminated when the temperature exceeds 920 °C or the pressure exceeds 125 MPa. The higher temperature and pressure can improve the microstructure uniformity. Besides, the higher pressure can promote the composition uniformity. With the temperature increases from 880 °C to 960 °C, α-laths are coarsened. But with increasing pressure, the grain size of prior-β phase, the widths of α-laths and α-colony are reduced. The tensile strength of Ti60 alloy is 949 MPa, yield strength is 827 MPa, and the elongation is 11% when the hot isostatic pressing parameters are 960 °C/125 MPa/2 h, which exhibits the best match between the strength and plasticity.

Reserves for Improving the Quality of Metal Layers of the 450Kh30M and 500Kh22B7 Types by Regulation of Silicon Content in Hard-Facing Consumables

An effective way to improve quality of metal layers of the 450Kh30M and 500Kh22B7 types by controlling the silicon content in hard-facing consumables is shown. The influence of silicon and aluminum content in hard-facing consumables on content of silicon, aluminum, chromium and carbon in the hard-faced layer as well as the amount of non-metallic inclusions of silicate type was studied to develop mathematical models and to derive corresponding dependencies. As a result some corrections to the composition of the hard-facing consumables were proposed to improve quality of metal layers of high-alloyed white cast irons of the investigated types.

Key Determinants for High-Alloyed Cast Irons for Mechanical Engineering

This work presents the factors determining cast iron, and particularly austenitic high-alloy cast iron as a construction material, which is ranked among the leading casting alloys of iron with carbon, mainly due to its very good service properties, which makes it dedicated as a material for automotive castings, pipe and fitting castings and components resistant to elevated temperatures, corrosion and abrasive wear. Construction materials currently used in industry have increasingly better properties and their potential is depleting quickly. This forces the manufacturers to adjust the requirements and production capabilities of cast iron using the most modern technologies that give the expected beneficial economic and operating effects. The paper quotes the results of research in the field of the offered technologies that give special surface features to machine parts made of cast iron by modernising the parameters of the technological process of obtaining high-alloy austenitic cast iron, i.e., by applying coatings, as well as by appropriate surface treatment, the aim of which is and reinforce the material surface with those properties which are important in a given application.

Influence of the Material Structure and Properties on the Wear Resistance of Gears with Different Geometries

The article gives the description of experimental studies on the assessment of changes in the state of gear teeth of a mechanical transmission during tests on a stand with a closed power flow. Data on the gears made of cast iron materials are presented. The strength characteristics of gear wheel materials and their chemical composition are given. Operational life testing of gear sets with various geometries of gearing and made of gray cast was carried out. According to the conducted studies, it is found that by the optimization of the gearing parameters it is possible to increase the gear life by one and a half to two times without switching to more wear-resistant and durable materials. It is experimentally proved that the influence of geometrical parameters of gearing with combined displacement on the durability of gears is comparable with the replacement of material. When replacing the material of gears made of gray cast iron with alloy grades of cast iron, preference should be given to high-alloy wear-resistant cast iron with a surface hardness above average, and the effect of their use can be comparable to the effect of optimizing the gearing parameters.

The Influence of H<sub>2</sub>SO<sub>4</sub>- NaCl Electrolyte Composition to the Electrochemical Noise Behaviour of a High-Alloy Cast Steel

In this study, the influence of varying sulphuric acid – sodium chloride electrolyte composition to the electrochemical noise behaviour of a high-alloy cast steel was analysed. The noise analysis was carried out in a bare 0.1 M sulphuric acid solution, in a pure 5 wt.% sodium chloride solution and three solutions with defined ratios of both. The electrochemical current noise signal was recorded with a sampling rate of 100 Hz for 1 hour in each test solution. For the identification of the frequency content of notified characteristic transients, the current-time records were analysed by the continuous wavelet transform (CWT). The characteristic transients were extracted from the noise signal for a further analysis of their frequency and amplitude characteristics. The results show high-frequency transients in the bare sulphuric acid and low-frequency transients in the pure sodium chloride solution. In the combined electrolyte solutions the portion of low-frequency components increases when the NaCl content increases and indicates the enhancing influence of localised damage evolution processes at the steel surface.

Experimental and simulation study for rewelding defects during the flow process of Semi-solid die casting

Semi-solid die casting process due to its advantages of compact process, high performance and low cost is widely applied in automobile, communication and other industries for the preparation with high performance aluminum alloy castings. Compared with liquid metal melt, the filling behavior is laminar flow for semi-solid metal melt with higher apparent viscosity. In the process of semi-solid die casting, the semi-solid metal melt from different directions came together, it will lead to “rewelding” defects if with insufficient fusion or uneven slurry state. In this paper, the formation reasons and forms of flow “rewelding” defects are analyzed. By numerical simulation and experimental analysis, the flow state of semi-solid metal melt at the junction of filling frontier is represented, and the state of “rewelding” defect is characterized. The effect of eliminating defects is analyzed by modifying the mold structure, such as redesigning overflow and venting systems at the confluence position. The results show that the microstructure of the “rewelding” defects in the confluence position of the semi-solid metal melts is the segregati12on of solid and liquid phase, gas, oxidation inclusions and other defects. Different semi-solid die casting process will affect the flow state and defect size at the location of different semi-solid metal melt coming together. By means of the process control and the mold structure optimization, “rewelding ” defects can be removed from the product cavity. The aluminum alloy semi-solid die-casting products with high performance are obtained finally.

Discrete Wavelet Analysis of Electrochemical Current Noise of a High-Alloy Cast Steel in Sulfuric Acid and Sodium Chloride Solution

The electrochemical current noise signal of a high-alloy cast steel was investigated in a 0.1 M sulfuric acid solution and in a 5 wt.% sodium chloride solution. In the sulfuric acid solution, the current time signal reveals characteristic spikes of high amplitudes. In the chloride containing solution, spontaneous power drops with a subsequent recovery of comparatively low intensity characterize the noise signal. Both noise records were analyzed by the discrete wavelet transform. For the noise signal in the sulfuric acid solution, the received wavelet coefficients exhibit the highest values in the fine scale, which signal the dominance of short-time corrosion events that were attributed to the observed hydrogen bubble evolution. In the chloride containing medium, the signal decomposition by the wavelet analysis reveals the highest coefficients predominantly in the coarse scale, indicating a preferred initiation of corrosion processes of high duration. The subsequent observations by scanning electron microscopy, reveal an attack by micro pitting, which is associated with the noise events.

Combination of Electrochemical Noise and Acoustic Emission for Analysis of the Pitting Corrosion Behavior of an Austenitic Stainless Cast Steel

The pitting corrosion behavior of a high alloy cast steel is analyzed in a sodium chloride solution by combination of the electrochemical noise technique and the acoustic emission (AE) method. Four corrosion states are identified on the steel surface after the 70 h noise measurement test. The simultaneously monitored AE exhibits two types of acoustic signals. The first type of AE events is attributed to the local passive oxide breakdown and the pit initiation process and the second type of AE events is related to the subsequent associated hydrogen gas bubble evolution.

Deformation mechanisms and microplasticity of austenitic TRIP/TWIP steel under flyer plate impact

Abstract. The focus of this study is on the deformation mechanisms of high-alloy cast austenitic TRIP/TWIP steel with the nominal composition Fe-16Cr-6Mn-6Ni. Due to its chemical composition, the material exhibits a low stacking-fault energy of 17.5 mJ/m2which facilitates the formation of the deformation-induced γ (fcc) → ε (hep) → α’ (bcc) transformation. Consequently, the steel exhibits a tensile strength of 800 MPa with fracture elongation of 55 % under quasi-static loading. The experiments presented demonstrate the response of this steel to flyer-plate impact (FPI) at room temperature using two different test setups. In the first setup, laser interferometry measurements of the sample free surface were used for determination of the dynamic mechanical properties (Hugoniot elastic limit / HEL. spall strength) after impact with aluminium plates accelerated up to 650 m/s. In the second setup, an experimental shock testing device developed at the Freiberg High-Pressure Research Centre was used for impacting large cylindrical samples without the occurrence of spallation. Subsequently, microstructural investigations were carried out by scanning electron microscopy (SEM) and transmission election microscopy (TEM) in combination with diffraction techniques and magnetic martensite measurements. Their results facilitate the representation of a complete image of deformation mechanisms during shock wave loading.

Development of a new composite material for bits of supporting and centering devices

Research has been conducted on the development of a new composite material for bits of well-supporting and -centering devices. The highly durable composite makes it possible to reduce frictional energy losses on straightline wellbore sections while ensuring a highly destructive effect at wellbore sections that are being explored. High-carbon high-alloy cast irons reinforced with titanium carbide have been proposed as the composite matrix. It has been shown that the hardness of the new material is comparable to that of hard alloys, while the minimum power losses for sliding friction under abrasion are lower than for hard alloys and diamond-bearing materials.

Application of Thermo-Calc TCFE7 to High-Alloyed Mottled Cast Iron

The thermodynamic modeling of alloy systems consisting of stable and metastable phases e.g. high-alloyed mottled cast iron can be problematic. Thermodynamic databases are rather well-developed for low, medium and high alloyed steels (e.g. HSS) but the application of those databases is not yet very common for high-alloyed (mottled) cast irons. The Thermo-Calc software together with the TCFE7 database is used to calculate isopleth and property diagrams, using the CALPHAD method. Additionally Scheil-Gulliver calculations are performed to simulate the effects of microsegregation during solidification. The results from the thermodynamic calculations are compared with measurements on own samples and with literature values. Those measurements include quantitative light-optical analysis, SEM with BSE detector, EDX measurements for the distribution of the alloying elements as well as XRD and DSC measurements. The investigations show the possibilities which are offered by thermodynamic calculations for high-alloyed mottled cast iron as well as the limitations and the compromises which have to be taken into account when calculating stable and metastable phases existing next to each other.

ВИРТУАЛЬНОЕ МОДЕЛИРОВАНИЕ ЦЕНТРОБЕЖНОГО ЛИТЬЯ ВАЛКОВ

The work is devoted to the virtual simulation of a sheet roll working layer formation at a technological stage “casting-solidification”. To form a virtual model of a roller mould pouring and foundry solidification there was used a computer modeling system (CMS) which included initial and boundary conditions for a roller mould pouring process with highalloy cast iron in the field of centrifugal force action. The distribution of a metal working layer along an inner surface of a rotating mould at different technological parameters: mass of highalloy cast iron, its density, temperature and pouring velocity, temperature of metal and non-metal parts of a mould at the initial point of time, modes of rotation and conditions of mould cooling and others were investigated. It is established that under the influence of centrifugal forces a free surface of liquid melt obtains a parabolic form. The influence of basic technological parameters upon the vertex position of a paraboloid of revolution of highalloy liquid melt z0 is revealed. It is shown in the paper that it stipulates for the unevenness of a working layer value along a roller barrel. As a result of computations it is obtained that the value of a working layer at lower flanks of barrels is higher than that of upper sides. The average value of such an exceeding makes 0.012 m. As a result of a simulation analysis of a foundry formation process at different technological parameters it is determined that the distance increase between the vertex of a paraboloid of revolution and the metal area investigated raises the working layer evenness along a roller barrel 3.6 times. Hence, the increase of capacity for work of a rolling tool is expected. The results of investigations presented are basic for the works for the increase of centrifugal roller servicing characteristic increase.

Erosive Wear Behavior of High-Alloy Cast Iron and Duplex Stainless Steel under Mining Conditions

Centrifugal pumps used in the lignite mines encounter erosive wear problems, leading to a disastrous failure of the pump casings. This paper attempts to evaluate the erosive wear resistance of Ni-Hard 4, high-chromium iron, and Cast CD4MCu duplex stainless steel (DSS), for mining conditions. The prepared test coupons were subjected to an erosion test by varying the impingement velocity and the angle of impingement, under two different pH conditions of 3 and 7, which pertained to the mining conditions. XRD analysis was carried out to confirm the phases present in the alloy. The eroded surface was subjected to SEM analysis to identify the erosion mechanisms. The surface degradation of Ni-Hard 4 and high-chromium iron came from a low-angle abrasion with a grooving and plowing mechanism at a low angle of impingement. At normal impingement, deep indentations resulted in lips and crater formations, leading to degradation of the surface in a brittle manner. A combined extrusion-forging mechanism is observed in the CD4MCu DSS surface at all the impingement angles.

Porosity of Castings Produced by the Vacuum Assisted Pressure Die Casting Method

Abstract The paper presents the results of investigations concerning the influence of negative (relative) pressure in the die cavity of high pressure die casting machine on the porosity of castings made of AlSi9Cu3 alloy. Examinations were carried out for the VertaCast cold chamber vertical pressure die casting machine equipped with a vacuum system. Experiments were performed for three values of the applied gauge pressure: -0.3 bar, -0.5 bar, and -0.7 bar, at constant values of other technological parameters, selected during the formerly carried initial experiments. Porosity of castings was assessed on the basis of microstructure observation and the density measurements performed by the method of hydrostatic weighing. The performed investigation allowed to find out that - for the examined pressure range - the porosity of castings decreases linearly with an increase in the absolute value of negative pressure applied to the die cavity. The negative pressure value of -0.7 bar allows to produce castings exhibiting porosity value less than 1%. Large blowholes arisen probably by occlusion of gaseous phase during the injection of metal into the die cavity, were found in castings produced at the negative pressure value of -0.3 bar. These blowholes are placed mostly in regions of local thermal centres and often accompanied by the discontinuities in the form of interdendritic shrinkage micro-porosity. It was concluded that the high quality AlSi9Cu3 alloy castings able to work in elevated temperatures can be achieved for the absolute value of the negative pressure applied to the die cavity greater than 0.5 bar at the applied set of other parameters of pressure die casting machine work.

Investigation on Microstructure and Wear Resistance of the New CrWMoV High-Alloy Wear Resistant Cast Iron

This paper mainly introduces the new CrWMoV high-alloy wear resistant cast iron prepared by the composition design, the composition proportion and the melting and pouring, and analyses its microstructure and wear resistance. Microstructures and phases of the new CrWMoV high-alloy wear resistant cast iron were analyzed by scanning electron microscopy, energy dispersive spectrometer and X-ray diffract meter. Furthermore, the Rockwell hardness, impact toughness and wear resistance of the material were also studied. The result show that the composition of the new CrWMoV high-alloy wear resistant cast iron is mainly (V, W) C particles which is synthesized in-situ and evenly distributed in the composite, as well as a small amount of (Cr, Fe) 7C3 phase and Fe-Cr phase. The average Rockwell hardness of the composite is about 64.5 HRC, the average impact toughness is 9.85 J/cm2, and the relative wear ability of the composite is about 2 times higher than the Cr15Mo2Cu which shows good wear resistance.

Study of Solidification Time and Solidus Velocity on Porosity Formation in High Strength Aluminum Alloy Castings

The purpose of the present study was to discuss the effects of local solidification time and solidus velocity on porosity formation in high strength aluminum alloy casting. With systematic change in the riser size, together with variation of thickness and length, A201 aluminum alloys were cast in 100% silica sand molds. The porosity content of A201 aluminum alloy was affected by the local solidification time and solidus velocity in this study. The correlation between porosity content and solidification time is found to be split into 2 bands, each being associated with one of the two thicknesses of plate castings. The longer the solidification time, the more the porosity content was measured in the A201 aluminum alloy plate casting. And the faster the solidus velocity, the more the porosity content in this study. The porosity content of A201 aluminum alloy was influenced by both of solidification time and solidus velocity at same time in this study. Basically, shorter local solidification time with slow solidus velocity seems get lower porosity content in A201 aluminum alloy castings.

Kinetics of Deformation Processes in a High-Alloy Cast TWIP Steel Determined by Acoustic Emission and Scanning Electron Microscopy

High-alloy cast CrMnNi steels exhibit depending on the chemical composition either transformation induced plasticity (TRIP-effect) or twinning induced plasticity (TWIP effect). Whereas the TRIP effect is caused by a martensitic phase transformation from the f.c.c austenitic phase into the b.c.c α-martensite phase via the formation of deformation bands with high stacking fault density the so-called ε-martensite, the TWIP effect is the result of mechanical twinning during plastic deformation. The occurrence of both effects as well as the underlying microstructural processes are strongly affected by the austenite stability, the stacking fault energy and/or the test temperature. However, the onset stress and the kinetics of these deformation processes are still unknown. The in-situ measurement of acoustic emission signals during the plastic deformation of materials is a powerful tool for the investigation of such dynamic microstructural processes and their kinetics. In the present study acoustic emission measurements were performed during tensile deformation at room temperature on a high-alloy cast TWIP steel. The AE investigations were completed by SEM investigations on the deformed specimens. The statistical and cluster analysis of acoustic emission signals reveals different patterns of acoustic emission signals, which are correlated with underlying microstructural processes.

A thermomechanically coupled material model for TRIP-steel

The transformation behavior of TRIP-steels is strongly dependent on temperature. Especially inelastic deformations lead to a temperature rise, if the heat cannot be dissipated, for instance under high strain rate loadings. Therefore, realistic mechanical models for TRIP-steel need a thermomechanical coupling to take the interaction between strain rate and transformation behavior into account. The objective of this study is the investigation of the thermodynamical consistency of an material model for a high alloyed cast TRIP-steel and the formulation of an appropriate thermomechanical coupling approach. The discussion is given in the framework of thermodynamics of inelastic processes for small deformations. Subsequently, the gained heat equation is adapted to large deformations. A parameter identification procedure is performed to determine the temperature dependent material parameters at low strain rates. Furthermore, a numerical example is given using the identified parameters for a thermomechanical coupling analysis at elevated strain rates. The simulation results at elevated strain rates are in good agreement with experimental data. Therewith, a future support of structure design through simulations is possible.

Experimental Study and Squeeze Casting Process Optimization for High Quality AC2A Aluminium Alloy Castings

This study focuses on the attempt for the production of AC2A aluminium alloy castings through direct squeeze casting process. Samples were prepared for each experimental condition based on L’16 orthogonal array of Taguchi method. Initially, the effect of casting parameters on tensile yield strength was investigated. Taguchi method and genetic algorithm were employed for process optimization in order to produce high quality castings. The effect of squeeze pressure on macrostructure and microstructure was also investigated for various casting conditions. The castings obtained for optimum squeeze casting condition exhibited better grain refinement in microstructure and around 65 % improvement in tensile yield strength than gravity die casting condition. Squeeze pressure was noted to be an important process parameter for producing defect-free, sound, high quality castings. The experimental results show that squeeze casting is noted to be practicable for processing this alloy by applying and holding high level compression directly on the melt up to the time of complete solidification.