Vol 48, No 7 (2018)

The microstructure and crystalline structure of laser-surfaced 9Kh2MF and 8Kh3SMFA steel samples are studied. Samples are taken from the working rollers of the reversible rolling mill at PAO Uralmashzavod. Sealing of surface cracks in the rollers by means of a laser is regarded as an effective repair method in small-scale production. The goal of the research is to monitor the quality of laser-surfaced steel components. The inspection focuses on metallurgical defects (nonmetallic inclusions, gaps, regions with nonuniform chemical composition) in the surfacing zone and the surrounding thermal influence zone. An ultrasound method is employed. Metallographic study of the microstructure and crystalline structure of laser-surfaced steel samples is necessary in order to develop an ultrasonic monitoring method. Metallurgical defects in steel are mainly found by means of a scanning electron microscope capable of X-ray spectral microanalysis (EDS analysis) and electron back-scattering diffraction (EBSD analysis). The present work employs a Carl Zeiss Auriga Crossbeam scanning electron microscope with EDS analysis of the surface’s elemental composition and EBSD analysis of the surface’s crystalline structure. The metallographic data for the laser-surfaced steel samples from the rollers reveal metallurgical defects along the boundary of the surfacing zone. The microheterogeneities measure 10–50 and 1–3 μm for 9Kh2MF and 8Kh3SMFA steel, respectively. The elements present include Mn, Si, and O for 9Kh2MF steel and Mn, Cr, and Mo for 8Kh3SMFA steel. The surface metal is found to be less textured than the basic metal and has more uniform acoustic characteristics. That must be taken into account in ultrasound monitoring of laser-surfaced steel components. In the ultrasound monitoring of laser-surfaced working rollers, signal recording with reflectivity equivalent to a flat-bottomed hole of 1.5-mm diameter is recommended.

To understand the factors affecting the working life of 40Kh24N12SL steel grating bars in roasting cars, we compare data regarding the grating bars after operation with the results of simulating their operating conditions. The results obtained by finite-element modeling are highly reliable. In modeling, the maximum possible number of boundary conditions is specified on the basis of the data regarding the grating bars already obtained and literature data. Modeling shows that a considerable temperature is formed over the part’s cross section, with local heating zones. The heating is predictable and is associated with the supply of coolant to the working zone in the course of operation. Over time, zones with large internal stress and strain are formed locally in the part. The appearance of these zones depends strongly on the presence of structural inhomogenities of the part and is thought to be associated with the geometric complexity of the casting. In the presence of shrinkage cavities, all of the stress and strain values increase sharply, especially at local maxima. The distribution of the local zones with high stress and strain remains practically unchanged in the presence of shrinkage cavities. Analysis of the position of the zones with high stress and strain sheds light on the grating bar failure by cracking in the course of operation. The presence of shrinkage cavities in the metal is found to be a major cause of the buckling, cracking, and fracture of 40Kh24N12SL steel grating bars in roasting cars. Simulation of the operating conditions permits explanation of the defect formation in the grating bars in accordance with observational data.

Metal products obtained from rolled blanks by cold upsetting are used in every branch of manufacturing. The quality of such components is assessed in terms of the required chemical composition and the plasticity, the consistency of the mechanical characteristics over the whole length, and the lack of internal and surface defects. If such metal components are to be competitive, all the steps in the production chain must be optimized: from smelting of the steel to cold upsetting of the product. In attempting to minimize costs and ensure the required quality, it is important to ensure safety and to decrease energy and labor costs in manufacturing. In this chain, the preparation of the material for cold bulk stamping is a key step. The high-strength fasteners obtained by cold upsetting are most often made of chrome steel. Recently, alternative boron-bearing steels have been actively introduced. However, their thermal hardening in quenching is unstable because boron oxides and nitrides may be formed, with decrease in their hardenability. In addition, chrome steels are 12–16% cheaper, as a rule. Also, since foreign supplies of boron steels are associated with additional costs, fasteners made of boron steels are even more expensive. That is a further impetus to using chrome steels. In the present work, we obtain standard mechanical characteristics and failure criteria for 40Kh steel components patented in a saltpeter bath at different temperatures, with subsequent drawing. The optimal preparation of the rolled steel in terms of its structural and mechanical characteristics after cold bulk stamping is determined: patenting (in a saltpeter bath at 400°C) and drawing (with 5–10% reduction). Such treatment yields products of the required quality and is preferable to the existing technology.

A method of continuous deformational nanostructuring of wire is described. In the method, a continuously moving wire is subjected simultaneously to tensile deformation in drawing, flexural deformation on passing through a roller system, and torsional deformation. This combination permits wide variation in its mechanical properties, ensuring both high strength and plasticity. The benefits of such deformation are the use of a tool already employed in the production of metal components; compatibility with the speeds of coarse and moderate wire drawing; and simplicity of the equipment. Laboratory apparatus for this method is described. Carbon steel 50 wire is selected for investigation, since it in great demand. The chemical composition and mechanical properties of the wire in the initial state are described. Experiments are conducted to investigate the effectiveness of the proposed differential nanostructuring in producing ultrafine-grain structure in the wire. The deformation conditions of the wire are described, as well as the drawing process. The transverse and longitudinal microstructure of the carbon steel 50 wire at the surface and in the center after different types of deformational treatment is investigated. In the experiments, the influence of the type of deformational treatment on the microstructure of the steel and its anisotropy over the wire cross section is established. The compliance of the wire’s mechanical properties with current standards is verified. After all types of treatment, its mechanical properties are consistent with State Standard GOST 17305–91. Metallographic data and mechanical test results after combined deformational treatment indicate that such combinations of deformation provide a promising approach to creating ultrafine-grain structure in carbon wire.

Methods of specifying the boundary conditions in the secondary-cooling zone of the continuous-casting machine are compared in simulating slab solidification. Experimental data are used to assess the correctness of the models. The results of simulation are different when using the mean heat-transfer coefficient for the section of the continuous-casting machine and the local heat-transfer coefficients for the zones with and without coolant. The modeling results are compared with experimental data for the surface temperature of the continuous-cast ingot at the center of its broad face.

Ninefold drawing of pearlitic steel wire is investigated. On the basis of multiscale computer models, the behavior of pearlite colonies at the surface of the wire and in its central layer is analyzed. The key factors are the orientation of the cementite lamellae relative to the drawing axis, the interlamellae distance, and the shape of the cementite inclusions. On the basis of finite-element models, the laws governing the reorientation of the pearlite colonies, change in shape and size of the cementite lamellae, and localization of the deformation in the ferrite are determined. The model results are verified by means of metallographic results and industrial experiments.

A method of microdiffraction analysis is developed in order to determine the defect structure of pearlitic steels during cold plastic deformation. The total reduction in the drawing of C86D steel coil is shown to affect the azimuthal blurring of the subreflexes in the microdiffraction pattern and the distortion of the plates in the pearlite colony.