This study presents results of stress rupture test of MAR-M-509 cobalt alloy samples, as-cast and after surface refining with a concentrated stream of heat. Tests were conducted on samples of MAR-M-509 alloy castings, obtained using the lost-wax method. Casting structure refining was performed with the GTAW method in argon atmosphere, using the current I = 200 A and electrical arc scanning velocity vs = 100, 150, 200 and 250 mm/min. The effect of rapid resolidification of the MAR-M-509 alloy on the microstructure was examined and significant improvement in stress rupture test was observed.
The paper presents results of examination of material parameters of cast iron with structure obtained under rapid resolidification conditions carried out by means of the nanoindentation method.
The paper proposes a methodology useful in verification of results of dilatometric tests aimed at determination of temperatures defining
the start and the end of eutectoid transformation in the course of ductile cast iron cooling, based on quenching techniques and
metallographic examination. For an industrial melt of ductile cast iron, the effect of the rate of cooling after austenitization at temperature
900°C carried out for 30 minutes on temperatures TAr1
start and TAr1
end was determined. The heating rates applied in the study were the
same as the cooling rates and equaled 30, 60, 90, 150, and 300°C/h. It has been found that with increasing cooling rate, values of
temperatures TAr1
start and TAr1
end decrease by several dozen degrees.
The paper deals with problems related to application of aluminum-silicon alloys for combustion engine cylinder liners
Elaborated shapes of many car components are the reason for which the use of casting techniques to fabricate them is a solution wellfounded
from the economical point of view. Currently applicable regulatory requirements concerning emissions of exhaust fumes force the
carmakers to reduce the overall weight of their products, as this is a basic precondition for reducing fuel consumption. As a result, newly
launched car models contain a continuously increasing share of thin-walled castings made of materials which ensure a satisfactory level of
service properties. At the same time, developing new technological processes allowing to extend the service life of individual components
by means of surface improving becomes more and more important.
The paper presents an analysis of factors affecting the wear of cylinder liners. The effect of the graphite precipitation morphology on the
cylinder liner wear mechanism is presented. Materials used to cast cylinder liners mounted in a number of engines have been examined for
their conformity with requirements set out in applicable Polish industrial standard. A casting for a prototype cylinder liner has been made
with a microstructure guaranteeing good service properties of the part.
The paper deals with the effect of microstructure diversified by means of variable cooling rate on service properties of AlSi7Mg cast alloy
refined traditionally with Dursalit EG 281, grain refining with titanium-boron and modified with sodium and a variant of the same alloy
barbotage-refined with argon and simultaneously grain refining with titanium-boron and modified with strontium. For both alloy variants,
the castings were subject to T6 thermal treatment (solution heat treatment and artificial aging). It turned out that AlSi7Mg alloy after
simultaneous barbotage refining with argon and grain refining with titanium-boron and modified with strontium was characterised with
lower values of representative microstructure parameters (SDAS – secondary dendrite arm spacing, λE, lmax) and lower value of the
porosity ratio compared to the alloy refined traditionally with Dursalit EG 281 and grain refining with titanium-boron and modified with
sodium. The higher values of mechanical properties and fatigue strength parameters were obtained for the alloy simultaneously barbotagerefined
with argon and grain refining with titanium-boron and modified with strontium.
The cooling rate is one of the main tools available to the process engineer by means of which it is possible to influence the crystallisation
process. Imposing a desired microstructure on a casting as early as in the casting solidification phase widens significantly the scope of
technological options at disposal in the process of aluminium-silicon alloy parts design and application. By changing the cooling rate it is
possible to influence the course of the crystallisation process and thus also the material properties of individual microstructure
components. In the study reported in this paper it has been found that the increase of cooling rate within the range of solidification
temperatures of a complex aluminium-silicon alloy resulted in a decrease of values of the instrumented indentation hardness (HIT) and the
instrumented indentation elastic modulus (EIT) characterising the intermetallic phase occurring in the form of polygons, rich in aluminium,
iron, silicon, manganese, and chromium, containing also copper, nickel, and vanadium. Increased cooling rate resulted in supersaturation
of the matrix with alloying elements.
The paper is a presentation of a study on issues concerning degradation of protective paint coat having an adverse impact on aesthetic
qualities of thin-walled cast-iron castings fabricated in furan resin sand. Microscopic examination and microanalyses of chemistry
indicated that under the coat of paint covering the surface of a thin-walled casting, layers of oxides could be found presence of which can
be most probably attributed to careless cleaning of the casting surface before the paint application process, as well as corrosion pits
evidencing existence of damp residues under the paint layers contributing to creation of corrosion micro-cells
The paper deals with the issue of potential for improvement of resistance of wood chip fine grinders to abrasive wear by providing them with WCCoCr coating applied with the use of atmospheric plasma spraying (APS). The study focused on establishing parameters of the technological process of spraying a 250–270 μm thick coating onto surface of ductile cast iron castings used to date as grinder linings. The presented data include results of microstructure examination, chemical composition analysis, HV hardness measurements, and scratch tests for both previous and new variant of linings. The obtained scratch test results indicate that the material of the coating is characterized with definitely lower susceptibility to scratching. The scratch made on coating was 75–84 μm wide and 7.2–8.2 μm deep, while the scratch on cast iron was distinctly wider (200–220 μm) and deeper (8.5–12.8 μm). In case of cast iron, the range of variability in scratch width and depth was definitely larger. This can be explained with large difference in hardness of individual components of microstructure of cast iron and significantly larger plastic deformation of cast iron compared to the coating revealed in the course of indenter motion over surfaces of the two materials. It has been found that application of WCCoCr coating offered better resistance of lining surfaces to scratching which can be considered a rationale for undertaking in-service tests.
A common problem encountered in hydraulic valves is a progressing deterioration of tightness of their water flow cutting-off seats. The seats are provided usually with a copper-alloy insert joined mechanically with cast-iron valve housing. The problem of unreliability of such joints can be solved by providing surface of the seat with a coating, deposited with the use of HVOF method and resistant to abrasive and cavitation wear. The tests were carried out for a sealing-draining seat insert made of CuZn39Pb2Al brass used to date and a specimen taken from the cast-iron valve housing which was the substrate for a plasma-sprayed coating of powder containing 86.1% Cr, 7.2% Ni, and 6.7% C. The coating, 345 ± 15 μm thick, was characterized with good quality of bonding with cast-iron substrate and high compactness of the material. The cavitation wear test on materials used in the study were carried out with the use of Vibra-Cell ultrasonic liquid processor (Sonics) equipped with a piezoelectric probe operating at the frequency of 20 kHz. Based on profilograms taken along a line crossing centers of cavitation craters, measurements of the height parameter Rt, and microscopic observations of surfaces it has been found that the coating plasma-sprayed onto substrate of nodular cast iron demonstrated higher resistance to cavitation compared to copper-alloy inserts used so far in cast-iron hydraulic valves. Cavitation craters on the material used typically for valve seats to date were more distinctly outlined and deeper compared to craters observed on the coating. Larger were also sizes of local tear-outs which resulted in larger difference between the peaks line and the valleys line.
The paper deals with susceptibility of nodular cast iron with ferritic -pearlitic matrix on cavitation erosion . Cavitation tests were carried out with the use of a cavitation erosion vibratory apparatus employing a vibration exciter operated at frequency of 20 kHz. The study allowed to determine the sequence of subsequent stages in which microstr ucture of cast iron in superficial regions is subject to degradation. The first features to be damaged are graphite precipitates. The ferritic matrix of the alloy turned out to be definitely less resistant to cavitation erosion compared to the pearlitic matrix component.
NC11 steel, in view of the specificity of its manufacturing process, is characterised with band-like orientation of carbides. Depending
on the direction of cutting the material for the inserts out of commercially available steel products, carbide bands can be oriented
in parallel or perpendicularly to the direction in which aggregate grains move in the process of pressing stampings. It has been found that
in case of scratches made in direction perpendicular to carbide bands, depth of the scratches is less than this observed when scratches are
made in direction coinciding with prevailing orientation of carbide precipitates.
The paper deals with possibility to improve operating performance of cast-iron heat exchangers by providing them with a copper alloy (CuTi2Cr) with the use of the flame spraying method. A test exchanger was cast of a gray cast iron with vermicular graphite in ferriticpearlitic matrix obtained in production conditions at KAW-MET Iron Foundry with the wire method used to vermicularize the material. The test samples were two plates cast in sand molds, of which one was given a flame-sprayed CuTi2Cr coat on one side. The operating performance of such model cast-iron heat exchangers, with and without CuTi2Cr coating, was tested on a set-up for determining the heat flow rate (thermal power) transferred by the heat exchanger to environment. The obtained results indicate that the value of the heat flow rate characterizing the CuTi2Cr-coated cast-iron heat exchanger was by 10% higher compared to the flow rate of heat conveyed to environment by the heat exchanger without coating.
The present paper is a presentation of results of a study on morphology, chemical composition, material properties (HVIT, HIT, EIT), and nanoindentation elastic and plastic work for carbide precipitates in chromium cast iron containing 24% Cr. It has been found that the carbides differ in chemical composition, as well as in morphology and values characterizing their material properties. The carbides containing the most chromium which had the shape of thick and long needles were characterized with highest values of the analyzed material properties.
The paper presents results of metallographic examination of faults occurring in the course of founding thin-walled cast-iron castings in
furan resin sand molds. A non-conformance of the scab type was Observed on surface of the casting as well as sand buckles and cold
shots. Studied the chemical composition by means of a scanning electron microscope in a region of casting defects: microanalysis point
and microanalysis surface. Around the observed defects discloses high concentration of oxides of iron, manganese and silicon.
A computer simulation of the casting process has been carried out with the objective to establish the cause of occurrence of cold shots on
casting surface. The simulation was carried out with the use of NovaFlow & Solid program. We analyzed the flowing metal in the mold
cavity. The main reason for the occurrence of casting defects on the surface of the casting was gating system, which caused turbulent flow
of metal with a distinctive splash stream of liquid alloy.
The paper presents results of a study on the effect of passage of time on magnesium content in iron alloys and the effect of magnesium content on the number of vermicular graphite precipitations per unit surface area and value of the longitudinal ultrasonic wave velocity for two different vermicularization methods. The study was carried out with the use of inspection bar castings. For specific production conditions, it has been found that in case of application of both the cored wire injection method and the method of pouring liquid metal over magnesium master alloy on ladle bottom, the satisfactory level of magnesium content in the bottom-pour ladle, for which it was still possible to obtain castings with vermicular graphite, was 0.018% Mg. In case of the cored wire injection method, the “time window” available to a pouring station at which castings of vermicular cast iron are expected to be obtained, was about 5 minutes. This corresponds to the longitudinal ultrasonic wave velocity values exceeding 5500 m/s and the number of graphite precipitations per unit surface area above 320 mm–2. In case of the master alloy method, the respective “time window” allowing to obtain castings of vermicular cast iron was only about 3 minutes long. This corresponds to the longitudinal ultrasonic wave velocity value above 5400 m/s and the number of graphite precipitations per unit surface area above 380 mm–2.
The paper presents results of a study concerning an AlSi7Mg alloy and the effect of subjecting the liquid metal to four different processes: conventional refining with hexachloroethane; the same refining followed by modification with titanium, boron, and sodium; refining by purging with argon carried out in parallel with modification with titanium and boron salts and strontium; and parallel refining with argon and modification with titanium, boron, and sodium salts. The effect of these four processes on compactness of the material, parameters of microstructure, and fatigue strength of AlSi7Mg alloy after heat treatment. It has been found that the highest compactness (the lowest porosity ratio value) and the most favorable values of the examined parameters of microstructure were demonstrated by the alloy obtained with the use of the process including parallel purging with argon and modification with salts of titanium, boron, and sodium. It has been found that in the fatigue cracking process observed in all the four variants of the liquid metal treatment, the crucial role in initiation of fatigue cracks was played by porosity. Application of the process consisting in refining by purging with argon parallel to modification with Ti, B, and Na salts allowed to refine the microstructure and reduce significantly porosity of the alloy extending thus the time of initiation and propagation of fatigue cracks. The ultimate effect consisted in a distinct increase of the fatigue limit value.
The study presented in this paper concerned the possibility to apply a heat treatment process to ductile cast-iron thin-walled castings in order to remove excessive quantities of pearlite and eutectic cementite precipitates and thus meet the customer’s requirements. After determining the rates of heating a casting up to and cooling down from 900°C feasible in the used production heat treatment furnace (vh = 300°C/h and vc = 200°C/h, respectively), dilatometric tests were carried out to evaluate temperatures Tgr, TAc1start, TAc1end, TAr1start, and TAr1end. The newly acquired knowledge was the base on which conditions for a single-step ferritizing heat treatment securing disintegration of pearlite were developed as well as those of a two-step ferritization process guaranteeing complete disintegration of cementite and arriving at the required ferrite and pearlite content. A purely ferritic matrix and hardness of 119 HB was secured by the treatment scheme: 920°C for 2 hours / vc = 60°C/h / 720°C for 4 hours. A matrix containing 20–45% of pearlite and hardness of 180–182 HB was obtained by applying: 920°C for 2 hours or 4 hours / vc = 200°C/h to 650°C / ambient air.
The paper presents results of assessment of the unit pressure force within the refractory material volume in the course press-moulding of
stampings for refractory precast shapes. The force was evaluated with the use of physical simulation of deformation undergone by lead
balls placed in the raw refractory mass subjected to pressing in a metal die. To determine the value of unit pressure force applied to the
aggregate grains in the course of stamping press-moulding, physical model of deformation of a sphere induced by the uniaxial stress state
was used.