The article discusses the results of a study investigating the effect of the number of fine non-metallic inclusions (up to 2 µm in size) on the fatigue strength of structural steel during rotary bending. The study was performed on 21 heats produced in an industrial plant. Fourteen heats were produced in 140 ton electric furnaces, and 7 heats were performed in a 100 ton oxygen converter. All heats were desulfurized. Seven heats from electrical furnaces were refined with argon, and heats from the converter were subjected to vacuum circulation degassing.Steel sections with a diameter of 18 mm were hardened and tempered at a temperature of 200, 300, 400, 500 and 600• C. The experimental variants were compared in view of the applied melting technology and heat treatment options. The results were presented graphically, and the fatigue strength of steel with a varied share of non-metallic inclusions was determined during rotary bending. The results revealed that fatigue strength is determined by the relative volume of fine non-metallic inclusions and tempering temperature.Keywords: steel, structural steel, non-metallic inclusions, fatigue strength, bending fatigue, bending pendulum W pracy przedstawiono wyniki badań wpływu ilości drobnych wtrąceń niemetalicznych, o wielkości do 2 µm, na wytrzymałość zmęczeniową przy zginaniu obrotowym. Badania prowadzono na 21 wytopach wyprodukowanych w warunkach przemysłowych. 14 wytopów wykonano w piecach elektrycznych o pojemności 140 ton i 7 wytopów w konwertorze tlenowym o pojemności 100 ton. Wszystkie wytopy poddawano odsiarczaniu. 7 wytopów pochodzących z pieca elektrycznego poddawano rafinacji argonem, zaś wytopy z konwertora odgazowaniu próżniowemu.Odcinki ze stali o średnicy 18 mm hartowano i odpuszczano w temperaturach: 200, 300, 400, 500 lub 600 • C. Warianty badań zestawiono uwzględniając technologię wytapiania stali opcje obróbki cieplnej. Wyniki przedstawiono w graficznej postaci uwzględniającej zależności wytrzymałości zmęczeniowej przy obrotowym zginaniu z udziałem objętościowym wtrąceń niemetalicznych. Wykazano, że wytrzymałość zmęczeniowa zależy od objętości względnej drobnych wtrąceń niemetalicznych, oraz temperatury odpuszczania.

The microstructure of an unmodified AlSi9Mg alloy comprises large primary α phase dendrites, eutectic β phase crystals and eutectic α phase. This composition is responsible for the alloy's low strength parameters, and it limits the extent of practical applications. The mechanical properties of hypoeutectic silumins can be improved through chemical modification as well as traditional or technological processing. Modification improves the mechanical properties of alloys through grain refinement. This study presents the results of double modification of an AlSi9Mg alloy with strontium, boron and titanium. The influence of the analyzed modifiers on the microstructure and mechanical properties of the processed alloy was presented in graphs. The modification of a hypoeutectic AlSi9Mg alloy improved the alloy's properties. The results of the tests indicate that the mechanical properties of the modified alloy are determined by the sequence in which the components are introduced to the alloy.Keywords: Al-Si alloys, silumin, mechanical properties, modification, boron, titanium, strontium Mikrostruktura niemodyfikowanego stopu AlSi9Mg składa się z dużych dendrytów pierwotnej fazy α, eutektycznych kryształów fazy β i eutektycznej fazy α. Taki skład fazowy jest przyczyną niskiej wytrzymałości stopu, co ogranicza jego praktyczne zastosowanie w praktyce. Właściwości mechaniczne podeutektycznych siluminów można poprawić poddając stop modyfikacji chemicznej, jak również poprzez zastosowanie procesów technologicznych. Modyfikacja poprawia właściwości mechaniczne stopów poprzez rozdrabnianie ziarna. W pracy przedstawiono wyniki podwójnej modyfikacji stopu AlSi9Mg przy użyciu strontu, boru i tytanu. Wpływ badanych modyfikatorów na mikrostrukturę i właściwości mechaniczne obrabianego stopu przedstawiono na wykresach. Modyfikacja podeutektycznego stopu AlSi9Mg poprawiła jego właściwości. Wyniki badań wskazują, że właściwości mechaniczne modyfikowanego stopu zależą od kolejności, w jakiej składniki są wprowadzane do stopu.

The quality of carbon steels working at variable loads mainly depend of microstructure, but also of impurities. The quantity and morphology of non-metallic inclusions and spaces between impurities are correlated with the content of admixtures in the alloy, while their phase composition and structure, in particular shape, dimensions and dispersion, are determined by the course of metallurgical processes. Non-metallic inclusions as impurities found in steel can affect its performance characteristics. Their impact depends not only on their quality, but also, among others, on their size and distribution in the steel volume. The literature mainly describes the results of tests on hard steels. The article discusses the results of a study investigating the effect of the number of large non-metallic inclusions (over 10 μm in size) on the fatigue strength of structural steel during rotary bending. The study was performed on 6 heats produced in an industrial plant. Fourteen heats were produced in 140 ton electric furnaces. All heats were desulfurized and refined with argon. The experimental variants were compared in view of the tempering the research steel. The fatigue strength of steel with an impurity spaces was determined during rotary bending: the results revealed that fatigue strength is determined by the impurity spaces and tempering temperature.

Non-metallic inclusions may be introduced to liquid steel from the outside, usually with charge material, or they may be produced in the metallurgical process. According to literature, if evenly distributed, non-metallic inclusions may affect the functional properties of steel, mainly its fatigue strength. The aim of this study was to determine the quantity and dimensional structure of non-metallic inclusions in high-grade medium carbon steel melted in an electric furnace and subjected to desulfurization. The experimental material consisted of semi-finished products of high-grade, medium-carbon constructional steel containing manganese, chromium, nickel, molybdenum, and boron. The levels of phosphorus and sulphur impurities did not exceed 0.02%. Billet samples were collected to determine the chemical composition, microstructure, the relative volume of non-metallic inclusions, and the size of impurities. The results were processed and presented in graphic form.

Stainless steels are used widely in many industries. A duplex microstructure offers a combination of advantages, including resistance to crevice and stress corrosion, reduced susceptibility to hot cracking in comparison with fully austenitic structures and excellent tensile strength. The paper discusses the effect of aging on the microstructure and corrosion resistance of X2CrNiMoN25-7-4 super duplex stainless steel. Low and predictable corrosion rate is an important parameter for steels operating in aggressive environments. Resistance to intergranular corrosion expressed by corrosion rate (mm/year) was determined in accordance with standard PN-EN ISO 3651-1. Metallographic studies were carried out to evaluate surface degradation and intergranular corrosion. The results support an evaluation of the impact that phase fraction changes caused by aging have on resistance to intergranular corrosion. The results of the corrosion analysis were used to develop mathematical models describing changes in corrosion rate over time for different phase fractions.

Results of studies on the modification of AlSi7Mg alloy with an exotherimc modifier are presented in the paper. MgO, Cr 2 O 3 , Na 2 O 2 , NaNO 3 , Na 2 MoO 4 were used as modifiers in the amount of 0.05, 0.10, 0.15, 0.20 and 0.25%, and Cr 2 O 3 +Al, NaNO 3 +Al, Na 2 MoO 4 +Al were applied as exothermic modifiers with Al as the reducing agent in the amount of 0.04-0.3%. The analyzed modifiers were incorporated in line with factorial design 2 3 . The Inmold modification method was applied. The microstructure of selected modified alloys was presented, and their tensile strength, percentage elongation and Brinell hardness number were given in graphic form. The results of the study indicate that the use of modifiers delivering an exothermic effect influences the effectiveness of silumin modification.Keywords: Al alloys, modification, silumin, exothermic modifier W pracy przedstawiono wyniki badań nad modyfikacją stopu AlSi7Mg modyfikatorem egzotermicznym. Do badań użyto, jako modyfikatorów związków MgO, Cr 2 O 3 , Na 2 O 2 , NaNO 3 , Na 2 MoO 4 wprowadzanych w ilości 0.05, 0.10, 0.15, 0.20 and 0.25% oraz w postaci modyfikatora egzotermicznego z Al jako reduktorem Cr 2 O 3 +Al, NaNO 3 +Al i Na 2 MoO 4 +Al w ilości 0.04-0.3% wprowadzanych zgodnie z planem czynnikowym 2 3 . Modyfikację prowadzono metodą Inmold. Przedstawiono wybrane mikrostruktury stopu po modyfikacji oraz w postaci graficznej wytrzymałość na rozciąganie, wydłużenie procentowe i twardość Brinella. Wykazano, że zastosowanie modyfikatora w postaci mieszanki dającej efekt egzotermiczny wpływa na efektywność modyfikacji siluminu.

This study discusses changes in the value of fractal parameters determined based on functions of structure S(t), generated in different directions of anisotropy of the examined surfaces. The analyzed material consisted of AFM calibration standards TGT1, PG and TGZ1 which were used as models of strongly isotropic and anisotropic surfaces. The topography of the examined surfaces was imaged by atomic force microscopy. The obtained results indicate that all surfaces can be described mathematically to identify fractal parameters in any anisotropic direction.

Abstract. All structural steels offer economical properties of mean strength and low corrosion resistance. There are ferritic-perlitic steels and very often used as construction materials in industrial applications. The purpose of this article is to investigate corrosion resistance using weight loss and profile roughness parameters of typical structural steel in grade S235JR in 20 % NaCl solution in distilled water. Corrosion tests show that the tested steel in both corrosive environments is characterized through continuous corrosion. Roughness parameters for every of the research times determine the size of steel corrosion.Keywords: steel, structural steel, carbon steel, corrosion, corrosion rate, profile roughness. IntroductionSteel is the most popular constructional material. The mechanical, physical and chemical properties of low carbon steel are under the influence of different factors, including the chemical composition and manufacturing technology.The properties and practical applications of all constructional materials, including steel, are determined mostly by their microstructure. The structural low carbon steels have a ferritic-perlitic microstructure. The percentage of each microstructure phase shapes the properties of the steel. The microstructure depends on the manufacturing technology and heat treatments of steel. Corrosion resistance is an important factor of the quality and application of structural steels [1][2][3][4][5][6][7][8][9][10][11][12].Low-carbon steel as a construction material is also very popular. Steels from this group have wide range of industrial applications, mainly as a welded material. The microstructure and properties of these steels are still tested to improve the quality. These steels are willingly used because they are cheap and well welded. Steel structures with low-carbon structural steel can be built by welding quickly at a low price, but still the main problem is their corrosion protection [13][14][15][16].The influence of inner structural stresses caused by the corrosion notches as well as stresses resulting from production with stresses resulting from external load plays an important role in premature destruction of the construction by formation and development of initiation cracks and cracks. Structural stresses also depend on the percentage of each phase in the microstructure and their shape. Microstructure morphology is shaped in the process of manufacturing, heat treatment and welding processes. Corrosion processes are able to extract metal atoms from the metal lattice, which atoms during the process pass to corrosion products. Corrosion causing local diffusion of metal atoms is particularly dangerous [17][18][19][20][21][22][23][24][25]. The problem is huge because low-carbon structural steel is sensitive to corrosion. The corrosion rate first of all depends on different environment [2; 5; 13; 20].One of the corrosive environmental factors are chlorides. They are mainly found on the coast as an aerosol of sea water, and in large quantities in large industrial ar...