Defect and Diffusion Forum Vol. 405

Abstract: Nanomechanical properties of iron borides, FeB and Fe₂B were studied in Fe-Mn-B ternary alloys. The alloys were produced by arc melting method using high purity powders, which were subsequently annealed at temperature of 873 K and 1223 K, until fully equilibrated for a time period of 2160 hours and 1440 hours, respectively. Based on results obtained from experimental study and thermodynamic modeling of Fe-Mn-B system the solubility of Mn in these borides was determined. For the purpose of this study the influence of heat treatment temperature, as well as, the solubility of Mn in these borides on their nanomechanical properties is investigated. Nanomechanical properties, including determination of indentation modulus and hardness were measured using nanoindentation testing machine equipped with Berkovich type diamond indenter. The indentation process was carried out using an indentation depth controlled method, to a maximum depth of 500 nm.

Abstract: Frozen mold casting uses a casting mold in which only water is added as a binder to sand, and the mixture is kneaded, frozen, and solidified. This method can offer the same level of mold strength and productivity as conventional methods, while maintaining a low environmental impact in terms of resource utilization and ensuring pollution-free processing. We studied the simultaneous fabrication of multiple aluminum alloy castings using a frozen mold. No defects associated with the collapse of the mold due to the molten metal heat were found. No entrainment of sand was observed on the surface of the samples.

Abstract: The structures of Fe-28Al-15Si-2Mo iron aluminide in as cast state and in three states after heat-treatments were investigated for the verification of secondary phases stability. Short-term (at 1000 °C for 24 h and at 1200 °C for 2 h) as well as long-term (at 800 °C for 100 h) annealing were performed. Molybdenum addition enhances the high-temperature mechanical properties due to solid solution strengthening, however the mechanism of hardening could be modified (to solid solution strengthening + strengthening by incoherent precipitates) by another alloying element (f. e. Si or C). The phase compositions of alloys were described by means of scanning electron microscopy equipped with energy dispersive analysis. The complex Fe-Si-Mo carbides were found in the structure. The bulk hardness measurement and image analysis were performed for the verification of secondary phase stability. Particles became coarse with increasing temperature of annealing.

Abstract: The structures of Fe-28Al-15Si-0.2Zr iron aluminide in the as cast state and in three states after heat-treatments (at 800 °C for 100 hours, at 1000 °C for 24 hours and at 1200 °C for 2 hours) were investigated for verification of secondary phases stability. The type and distribution of precipitates were described by means of light optical microscopy and scanning electron microscopy equipped with an energy dispersive analysis. The presence of complex carbides based on Fe-Si-Zr was shown. The bulk hardness and image analysis of samples was measured for verification of dissolution of secondary phase particles to the matrix. Short-term annealing did not influence distribution and dissolution of secondary particles significantly, while long-term annealing (at 800 °C for 100 hours) leads to the sporadic formation of fine eutectic areas.

Abstract: The aim of this work was to analyse the microstructural nature of plasticity in ZnAl4Cu1 alloy and its dependence on the processing technology. The alloy condition was analysed after gravity casting, after forging and after ECAP processing. Two alloys with slightly different compositions were studied. For alloy A, the returnable material from a prominent Zn alloy producer was used. For B alloy input raw materials of relatively high purity were used. Tensile testing showed that in the as-cast alloy tensile strength had relatively low levels up to 211 MPa, and particularly low values of ductility only up to 2.5 % were found in B alloy, which was more polluted. By means of ECAP processing of the as-cast alloy, the tensile strength was improved by 50 % (Rm = 312 MPa). In the case of the purer A alloy the majority of samples improved to level A = 27.9 %. Forging of the as-cast alloy preserved strength on a level similar to the ECAP result, but ductility was improved to the level of 34.4 %, although alloy B had lower purity. Further significant ductility improvement was obtained through ECAP processing to A = 147 % of the as-forged alloy. The microstructure of ZnAl4Cu1 consists primarily of segregated η phase (rich in Zn) and fine eutectoid composed of η and alpha phases segregated mostly in dispersive state, but in places also in lamellar form. Close correlation between microstructure and processing method resulted from our fractographic study. In the case of ECAP processing of the forged state the finest microstructure was achieved, which was accompanied by higher plasticity and also by fine dimples of transcrystalline ductile fracture (DTDF).

Abstract: The paper presents comparison of microstructure and fracture surface morphology of the CuAlNi shape memory alloy (SMA) after different heat treatment procedures. The investigation was performed on samples in as-cast state and heat treated states (solution annealing at temperatures of 850 °C / 60’ / H₂O and 920 °C / 60’ / H₂O along with tempering at two different temperature 150 °C / 60’ / H₂O and 300 °C / 60’ / H₂O). The microstructure of the samples was examined by optical (OM) and scanning electron microscope (SEM) equipped with device for EDS analysis. The obtained fracture surfaces were examined by SEM. Optical and scanning electron microscopy showed martensitic microstructure in all investigated samples. However, the fractographic analysis of samples after tensile testing reveals significant changes in fracture mechanism. In both solution annealed states the results shows transgranular type of fracture, but after tempering at two different temperatures the difference is obvious. After tempering at 150 °C, along with transgranular type of fracture appear some areas with intergranular type of fracture. After tempering at 300 °C, fracture surface reveals completely intergranular type of fracture.

Abstract: In the first part of this paper inclusion morphology and factors influencing machinability of structural steels are shortly discussed. In the experimental part of this work the effect of calcium addition on the inclusion morphology transformation and the machinability Bindex (according to Volvo standard) for several grades of structural steels are presented.

Abstract: Cold tube drawing is a metal forming process that enable to manufacturers to produce high precision tubes. The dimensions of the tube are reduced by drawing it through a conical converging die with or without inner tool. There are four types of tube cold drawing process. Their difference relies on the technique used for inner diameter calibration. Therefore, the main objective was determining the difference in development of crystallographic texture and stress-strain state between drawing with the fixed plug and hollow sinking process. The input feedstock (with E235 steel grade) after the recrystallizing anneal was cold drawn (drawing with the fixed plug, hollow sinking) by one drawing passes. Electron BackScatter Diffraction (EBSD) analysis was used to evaluate the changes of grain structure and texture connected with tubes manufacturing. The stress-strain state in the tube material during drawing was calculated using DEFORM-3D software and the crystallographic orientation with respect to the cylindrical reference frame (Z-direction = drawing direction). A significant difference in stress-strain state between drawing with the fixed plug and hollow sinking process was recorded in radial direction.

Abstract: By use of physical simulations, it was studied the influence of finish rolling temperature (from 820 °C to 970 °C) on the microstructural and mechanical properties of seamless tubes with a different wall thickness (from 6.3 to 40 mm) – in the state after rolling as well as after quenching and tempering. In laboratory conditions, by use of the Simulator HDS-20, the bloom piercing and rolling of the seamless tubes from 25CrMo4 low-alloy steel in a pilger mill were in a simplified way simulated. The wall thickness of the tube influenced the total deformation of specimens at anisothermal multi-pass plain-strain compression tests as well as the final cooling rate. The quenching and tempering of the deformed specimens was subsequently performed with use of the electric resistance furnaces. The finish rolling temperature had only insignificant effect on the resulting properties. Markedly lower hardness was obtained only after the simulation of tube production with the wall thickness of 40 mm contrary to the wall thickness of 6.3 and 20 mm. Structural variations of the specimens after rolling simulations were more or less overlapped by the subsequent quenching from the temperature of 850 °C and tempering at the temperature of 680 °C.

Abstract: This paper deals with the analysis of microstructure and substructure of 9CrNB steel, after normalization at temperature of 1070 °C and tempering at 790 °C / 240 min. The tube was second time tempered at the following temperatures and holding times: 760 °C / 30 min (A1), 760 °C / 120 min (C1), 800 °C / 30 min (G1) and 800 °C / 120 min (I1). Microstructure after tempering consists of tempered martensite and bainite with lath morphology, while inhomogeneous redistribution of precipitates is visible. Substructure analysis of state A1 and I1 show, that a relatively large number of irregular, rod-shaped and oval carbide particles, often arranged in clusters, were precipitated at the primary original austenite grain boundaries. In case of state A1, the average size of these carbide particles is 300 nm and in case of state I1 the average size is 350 nm. A relatively large number of rod-shaped and oval shaped particles were found at the interface of the tempered martensite and bainite mainly in the form of clusters and also inside the tempered bainite with higher particle distribution. In the case of the state A1, they reached an average size of 150 nm. In some regions of substructure of the state I1, the fine carbide particles with an average size of 200 nm and coarse carbide particles with an average size of 400 nm were presented within the areas of tempered bainite. Particles were identified by EDX analysis and by selection electron diffraction. The mechanical properties after tempering were evaluated and compared with properties of P91 and P92 steel.