The results of the modification of austenitic matrix in cast high-manganese steel containing 11÷19% Mn with additions of Cr, Ni and Ti

were discussed. The introduction of carbide-forming alloying elements to this cast steel leads to the formation in matrix of stable complex

carbide phases, which effectively increase the abrasive wear resistance in a mixture of SiC and water. The starting material used in tests

was a cast Hadfield steel containing 11% Mn and 1.34% C. The results presented in the article show significant improvement in abrasive

wear resistance and hardness owing to the structure modification with additions of Cr and Ti.

The paper presents the results of abrasive wear resistance tests carried out on high-vanadium cast iron with spheroidal VC carbides. The cast iron of eutectic composition was subjected to spheroidising treatment using magnesium master alloy. The tribological properties were examined for the base cast iron (W), for the cast iron subjected to spheroidising treatment (S) and for the abrasion-resistant steel (SH). Studies have shown that high-vanadium cast iron with both eutectic carbides and spheroidal carbides has the abrasion resistance twice as high as the abrasion-resistant cast steel. The spheroidisation of VC carbides did not change the abrasion resistance compared to the base high-vanadium grade.

The paper presents the results of tests on the spheroidising treatment of vanadium carbides VC done with magnesium master alloy and mischmetal. It has been proved that the introduction of magnesium master alloy to an Fe-C-V system of eutectic composition made 34% of carbides crystallise in the form of spheroids. Adding mischmetal to the base alloy melt caused 28% of the vanadium carbides crystallise as dendrites. In base alloy without the microstructure-modifying additives, vanadium carbides crystallised in the form of a branched fibrous eutectic skeleton. Testing of mechanical properties has proved that the spheroidising treatment of VC carbides in high-vanadium cast iron increases the tensile strength by about 60% and elongation 14 - 21 times, depending on the type of the spheroidising agent used. Tribological studies have shown that high-vanadium cast iron with eutectic, dendritic and spheroidal carbides has the abrasive wear resistance more than twice as high as the abrasion-resistant cast steel.

The paper presents an innovative method of creating the layered castings. The innovation relies on application the 3D printing insert obtaining in SLM (selective laser melting) method. This type of scaffold insert made from pure Ti powder, was placed into mould cavity directly before pouring by grey cast iron. In result of used method was obtained grey cast iron casting with surface layer reinforced by titanium carbides. In range of studies were carried out metallographic researches using light microscope and scanning electron microscope, microhardness measurements and abrasive wear resistance. On the basis of obtaining results was stated that there is a possibility of reinforcing surface layer of the grey cast iron casting by using 3D printing scaffold insert in the method of mould cavity preparation. Moreover there was a local increase in hardness and abrasive wear resistance in spite of the precipitation of titanium carbides in surface layer of grey cast iron. While the usable properties of composite surface layer obtained in result of use of the method presented in the paper, strongly depend of dimensions of scaffold insert, mainly parameters Re and Ri.

The paper concerns evaluation of the coefficient of friction characterising a friction couple comprising a commercial brake disc cast of

flake graphite grey iron and a typical brake pad for passenger motor car. For the applied interaction conditions, the brake pressure of

0.53 MPa and the linear velocity measured on the pad-disc trace axis equalling 15 km/h, evolution of the friction coefficient μ values were

observed. It turned out that after a period of 50 minutes, temperature reached the value 270°C and got stabilised. After this time interval,

the friction coefficient value also got stabilised on the level of μ = 0.38. In case of a block in its original state, stabilisation of the friction

coefficient value occurred after a stage in the course of which a continuous growth of its value was observed up to the level μ = 0.41 and

then a decrease to the value μ = 0.38. It can be assumed that occurrence of this stage was an effect of an initial running-in of the friction

couple. In consecutive abrasion tests on the same friction couple, the friction coefficient value stabilisation occurred after the stage of

a steady increase of its value. It can be stated that the stage corresponded to a secondary running-in of the friction couple. The observed

stages lasted for similar periods of time and ended with reaching the stabile level of temperature of the disc-pad contact surface.

Currently, due to the economic and ecological aspects, light alloys are increasingly important construction material, in particular in the transport industry. One of the popular foundry magnesium alloys is the alloy AZ91, which among others due to mechanical properties and technological features, is used, for example, for light structural parts.
The paper presents the results of research on modification of the AZ91 alloy surface layer in the plasma electrolytic oxidation process. The change of usable properties of the produced coatings was obtained by introducing additions of silicon carbide or boron nitride. The thickness and hardness of the protective layers produced, resistance to scratches and corrosion resistance were determined. Moreover, the friction coefficient of the coating-steel pair was investigated. The quality of the connections made between the coating and the substrate, i.e. the magnesium alloy, was also evaluated. The results obtained for coatings with silicon carbide or boron nitride additives were always compared to the results obtained for unmodified samples.
On the basis of the obtained results, it was shown that the introduction of boron nitride additive to the AZ91 alloy coating produced in the plasma electrolytic oxidation process significantly improves the resistance to: (i) corrosion and (ii) abrasive wear of the coating.

The resistance of cast iron to abrasive wear depends on the metal abrasive hardness ratio. For example, hardness of the structural

constituents of the cast iron metal matrix is lower than the hardness of ordinary silica sand. Also cementite, the basic component of

unalloyed white cast iron, has hardness lower than the hardness of silica. Some resistance to the abrasive effect of the aforementioned

silica sand can provide the chromium white cast iron containing in its structure a large amount of (Cr, Fe)7C3 carbides characterised by

hardness higher than the hardness of the silica sand in question. In the present study, it has been anticipated that the white cast iron

structure will be changed by changing the type of metal matrix and the type of carbides present in this matrix, which will greatly expand

the application area of castings under the harsh operating conditions of abrasive wear. Moreover, the study compares the results of

abrasive wear resistance tests performed on the examined types of cast iron. Tests of abrasive wear resistance were carried out on a Miller

machine. Samples of standard dimensions were exposed to abrasion in a double to-and-fro movement, sliding against the bottom of

a trough filled with an aqueous abrasive mixture containing SiC + distilled water. The obtained results of changes in the sample weight

were approximated with a power curve and shown further in the study.