Electron Microscope Studies of the 01Cr17Ni13Mo3 Austenitic Steel Structure after Cold Rolling Combined with Hydrogen Alloying with Varying Degrees of Deformation

In this paper, we consider the effect of cold rolling and hydrogen alloying on the formation of twin boundaries of the corrosion resistance of austenitic steel 01Cr17Ni13Mo3. Using the method of transmission electronic microscopy, microdiffraction patterns were obtained. The analysis of microdiffraction patterns indicates the formation of a developed grain-subgrain structure with small-angle and large-angle misorientation. The structure has a high dislocation density, deformation twins and localized shift bands. It was established that plastic deformation by flat rolling to ε = 90 % at room temperature does not contribute to the appearance of a noticeable amount of α' and ε-martensite. At the temperature of liquid nitrogen, the samples were found to form a small fraction of the α'-martensite phase. Such a small amount of martensite can contribute to steel strengthening, and a decrease in the rolling temperature will lead to an increase in the strength properties of steel. It was detected that the density of twin boundaries under the decrease in the rolling temperature but with the same intensity of hydrogen saturation is significantly higher. A noticeable reduction in the width of the twin lamellas was revealed.

Effect of Microstructure Evolution and Corrosion Behavior on Phase Transformation of Nanocrystalline SUS304 Prepared by Dry Ice Shot Peening

Microstructure and corrosion behavior of nanocrystalline SUS304 by dry ice shot peening has been investigated in detail in term of phase transformation. SUS304 as metastable austenitic stainless has excellent corrosion resistance and induced martensite by shot peening process. However, the SUS304 has quite low strength which is difficult to wear as metallic component. The dry ice shot peening process was carried out on SUS304 surface for one and three hours. The microstructure was observed by transmission electron microscope (TEM) and scanning electron microscope (SEM) equipped with electron back-scattered diffraction (EBSD). The phase transformation was analyzed by X-ray diffraction (XRD). The corrosion testing was carried out in 3.5% NaCl solution. The result indicated that the grain size of SUS304 surface was finer by deformation due to dry ice shot peened process. The hardness was improved properly by the increasing the shot peened time, and the corrosion resistance was increased. The XRD results showed that three hours shot peening process induced martensite phase of SUS304 by 15 m thickness. It can be summarized that the dry ice shot peening can be induced phase transformation due to high deformation on the SUS304 surface

Investigation on the microstructure and mechanical properties of Ti6Al4V titanium alloy electron beam welding joint

Electron beam welding (EBW) is a fusion joining process particularly suitable for welding titanium plates. In the present work, 2.5 mm thickness Ti6Al4V titanium alloy plates were butt-welded together with backing plates by EBW. The detailed procedures of experiments were used to investigate the microstructure and mechanical properties of welded joints. The optimum welding speed was determined by microstructure examinations, microhardness tests, X-Ray diffraction tests, shear punch tests (SPT) and stress simulation calculations. The results showed that all microstructure of welded metal (WM) was martensite phase under the different welding speeds. In the heat-affected zone (HAZ), the martensite phase gradually evolved to be small and equiaxed. It can be seen that the microstructure of each region in welded joints did not change significantly. When the welding speed is between 8 mm/s and 14 mm/s, it can be seen from the macroscopic appearance of the joints that there was no utterly fused penetration between the butt plate and substrate. Finite element simulation was carried out for the no-penetration depth under different welding conditions, and it was found that the stress suffered by the small no-penetration depth was the smallest. Using different welding parameters shows that the engineering stress in WM was higher than other areas, and BM was the lowest. As welding speed increases from 8 mm/s to 14 mm/s, the variation of microhardness distribution was not evident.

Влияние микротрещин на коэффициент Пуассона при пластическом деформировании аустенитной стали

We researched the influence of damage accumulation on the Poisson's ratio measured by echo-pulse acoustic method during plastic deformation of 12Kh18N10T steel. On the basis of the obtained experimental data we calculated the partial contributions to the change in the Poisson's ratio of damage accumulation and separation of the strain induced martensite phase. The characteristics of stable cracks forming near strain martensite particles at small degrees of plastic strain have been analyzed by computer simulation. The theoretical dependence of the change in the Poisson's ratio due to crack formation during plastic deformation has been constructed. A good agreement between the experimental data and theoretical calculations has been obtained.

Pengaruh Media Arang Kayu Bakau Mangrove Dan Arang Kayu Asam Pada Proses Perlakuan Carburizing Terhadap Sifat Mekanik Baja Karbon ST-37

In the military field, tank is armored fighting vehicles that move using chain-shaped wheels. The tread of the tank chain is a component to tread and move so that it requires tougher properties on the surface and has ductile and tough properties on the inside and is more resistant to wear on the surface. The development of tank chain production materials is necessary for the independence of national defense and security as well as reducing dependence on imports. Imported tank chain hardness value 28 HRC or 286 HV. In this research, the objective of this research is to increase the surface hardness of the steel by carburizing the initial material, especially the low carbon steel ST-37. The carburizing treatment process is a method of adding carbon content in steel using solid media. The carbon media used were mangrove charcoal and tamarind wood charcoal using calcium carbonate (CaCO3) catalyst at a constant heating temperature of 900ºC, variations in holding time of 30 minutes, 60 minutes and 90 minutes, cooled rapidly with water media. Then performed an analysis of the effect of the type of wood charcoal on the mechanical properties of carbon steel ST-37. The results obtained will be applied to the tank chain tread production process. The results of the micro structure of martensite and the highest hardness value were found in the holding time of 60 minutes of mangrove charcoal media with the microstructure results of 63.8% martensite, 36.2% bainite and a hardness value of 453.1 HV. The highest toughness value is found in the holding time of 60 minutes of tamarind wood charcoal media with an impact price (HI) of 0.4345 J/mm2. The difference between the impact test results of tamarind charcoal media with mangroves is not too significant. The higher the martensite phase, the higher the hardness value. However, there is also a bainite phase which can increase the toughness of the steel which will be used as a tread chain production material.

IDENTIFICATION OF BAINITE IN A MULTI-PHASE MICROSTRUCTURE OF AN AUSTEMPERED STEEL ALLOY: A METALLOGRAPHY APPROACH

IDENTIFICATION OF BAINITE IN A MULTI-PHASE MICROSTRUCTURE OF AN AUSTEMPERED STEEL ALLOY: A METALLOGRAPHY APPROACH. Structural characterization of a multi-phase steel has become an exciting issue in various studies to date. This relates to the difficulty in distinguishing phases with similar morphology, i.e. bainite and martensite, through chemical etching. This study discusses a method to observe bainite phase through a metallographic approach on FeNi steel using color etching. Variations in the use of etching in this research include 2% nital, 4% picral, and 15% sodium metabisulphite (SMB). First, the samples were austenized then austempered at either 400 °C or 500 °C, for 60 min followed by quenching in either water or brine solution. Based on optical microscope observations, SMB color etching provides more explicit information on the visualization of bainite and martensite phases because they have different color appearances. The bainite phase is shown in bluish color, while the martensite phase is shown in brownish color. Furthermore, the influence of variation in austempering temperature and quench media on microstructure morphology was also discussed. In addition, the calculation of the lattice parameters of the X-Ray Diffraction (XRD) pattern was also carried out in this study to identify the crystal structure formed.

Assessment of SMA Electrical Resistance Change during Cyclic Stretching with Small Elongation

In this article, changes in NiTi alloy (Flexinol) electrical resistance during cyclic stretching with small elongation were investigated. A dedicated test stand consisting of motorized vertical test stand, force gauge, and electric resistance measuring device with an accuracy of 0.006 Ω was developed. A dedicated control algorithm was developed using LabVIEW software. Changes in electrical resistance were investigated for the 0.1 mm Flexinol wire with length of 120 mm. Testing was performed in the elongation range between 0.25% and 1.5% in martensite phase. Tested samples were subjected to 30 stretching cycles with a movement speed of 10 mm/min. Obtained results show that the cyclic stretching of Flexinol wire reduces its electrical resistance with each stretching cycle. Moreover, it was noted that changes in Flexinol electrical resistance during cycling stretching depend on the assumed elongation and number of the already performed stretching cycles. The observed electrical resistance change decreases with each stretching cycle. Thus, the observed changes are greater during the first stretching cycles. For elongations exceeding 1%, the Flexinol electrical resistance in the first stretching cycle increases. In each subsequent cycle, electrical resistance decreases, as in the case of the smallest value of assumed elongation. In almost all tested cases (except in the case with 1.5% of assumed elongation), Flexinol electrical resistance after 30 stretching cycles was smaller than before the test.

Microstructural Tailoring and Enhancement in Compressive Properties of Additive Manufactured Ti-6Al-4V Alloy through Heat Treatment

Among laser additive manufacturing, selective laser melting (SLM) is one of the most popular methods to produce 3D printing products. The SLM process creates a product by selectively dissolving a layer of powder. However, due to the layerwise printing of metal powders, the initial microstructure is fully acicular α′-martensitic, and mechanical properties of the resultant product are often compromised. In this study, Ti-6Al-4V alloy was prepared using SLM method. The effect of heat treatment was carried out on as-built SLM Ti-6Al-4V alloy from 650–1000 °C to study respective changes in the morphology of α/α′-martensite and mechanical properties. The phase transition temperature was also analyzed through differential thermal analysis (DTA), and the microstructural studies were undertaken by optical microscopy (OM) and scanning electron microscopy (SEM). The mechanical properties were assessed by microhardness and compressive tests before and after heat treatment. The results showed that heat treated samples resulted in a reduction in interior defects and pores and turned the morphology of the α′-martensite into a lamellar (α + β) structure. The strength was significantly reduced after heat treatment, but the elongation was improved due to the reduction in columnar α′-martensite phase. An optimum set of strength and elongation was found at 900 °C.

Effect of Tension-Compression Asymmetry Response on the Bending of Prismatic Martensitic SMA Beams: Analytical and Experimental Study

This paper aims to analytically derive bending equations, as well as semi-analytically predict the deflection of prismatic SMA beams in the martensite phase. To this end, we are required to employ a simplified one-dimensional parametric model considering asymmetric response in tension and compression for martensitic beams. The model takes into account the different material parameters in martensite twined and detwinned phases as well as elastic modulus depending on the progress of the detwinning process. In addition, the model considers the diverse slope of loading and unloading in martensite detwinned phases favored by tension and compression. To acquire general bending equations, we first solve the pure bending problem of a prismatic SMA beam. Three different phases are assumed in the unloading procedure and the effect of neutral fiber distance from the centerline is also considered during this stage. Then according to the pure bending solution and employing semi-analytical methods, general bending equations of an SMA beam are derived. Polynomial approximation functions are utilized to obtain the beam deflection–length relationship. To validate the attained analytical expressions, several three- and four-point bending tests were conducted for rectangular and circular SMA beams. Experimental data confirm the reasonable accuracy of the analytical results. This work may be envisaged to go deep enough in investigating the response of SMA beams under an arbitrary transverse loading and stress distribution during loading and unloading, as well as findings may be applicable to a good prediction of bending behavior.