Strength and fracture mechanism during torsion of ultrafine-grained austenitic steel for medical applications

The article considers evaluation of torsional strength and fracture of austenitic corrosion-resistant steel 08Kh18N9 with an ultrafine-grained (UFG) and coarse-grained (CG) structure, widely used in medicine for the production of plates, screws, rods for bone osteosynthesis and other medical products. The structure of the CG steel was studied using an Axiovert 40 MAT metallographic microscope, and the fine structure of the UFG steel was investigated with a JEM-2100 transmission electron microscope. Torsion tests of the cylindrical samples with a diameter of 10 mm were carried out at a temperature of 20 °C on MK-50 installation. JEOL JCM-6000 scanning electron microscope was used for the microfractographic studies of fracture surfaces. The analysis of the “Torque - torsion angle” diagrams showed that the torsional ultimate strength (τt) and yield strength (τ0.3) of UFG steel increase by 1.3 - 3.8 times, and the relative shear (g) decreases by 2.4 times in comparison with CG steel. High values of torsional strength properties of UFG steel make it possible to provide high torque without destroying the product. Consequently UFG steel 08Kh18N9 in comparison with CG steel is a more promising material for the manufacture of medical screws and other medical products that experience significant loads during the torsion process. Three areas were identified on the surface of all fractures: fibrous central part, transitional (middle) part, and a relatively smooth peripheral part. Fracture begins with the formation of shear pits in the middle and peripheral parts, which, with further rotation of the sample, are completely rubbed out (in case CG steel), or remain (in case of UFG steel). Final failure occurs under the action of normal stresses in the central part of the sample.

Naturally Occurring Exudates Gums as Ecofriendly Inhibitors for Mild Steel Corrosion in Acidic Medium

The corrosion inhibition potentials of gum exudates from Daniella oliveri (DO) and Commiphora Africana (CA) for the corrosion of mild steel in H2 SO4 have been studied using weight loss and thermometric methods at 303 and 333K. Results show that the exudates gum actually reduced the rates of corrosion of mild steel. Increase in the concentrations of the exudate’s gums increased their percentage inhibition efficiencies. Corrosion rate was found to increase with increase in temperature in the presence and absence of the gum exudates, though the corrosion rate was slower in the presence of the exudates gums. Both DO and CA exudates gums were found to obey Temkin and Langmuir adsorption models at all concentrations and temperatures studied. Physical adsorption mechanism was proposed from the adsorption parameters. Kinetic and thermodynamic parameters revealed that the adsorption process is spontaneous, exothermic and no significant difference was found between the inhibition efficiencies of DO and CA.

Low-carbon cast microalloyed steel intercritically heat-treated at different temperatures: microstructure and mechanical properties

In this study, dual-phase (DP, ferrite + martensite) microstructures were obtained by performing intercritical heat treatments (IHT) at 750 and 800 °C followed by quenching. Decreasing the IHT temperature from 800 to 750 °C leads to: (i) a decrease in the volume fraction of austenite (martensite after quenching) from 0.68 to 0.36; (ii) ~ 100 °C decrease in martensite start temperature (Ms), mainly due to the higher carbon content of austenite and its smaller grains at 750 °C; (iii) a reduction in the block size of martensite from 1.9 to 1.2 μm as measured by EBSD. Having a higher carbon content and a finer block size, the localized microhardness of martensite islands increases from 380 HV (800 °C) to 504 HV (750 °C). Moreover, despite the different volume fractions of martensite obtained in DP microstructures, the hardness of the steels remained unchanged by changing the IHT temperature (~ 234 to 238 HV). Applying lower IHT temperature (lower fraction of martensite), the impact energy even decreased from 12 to 9 J due to the brittleness of the martensite phase. The results of the tensile tests indicate that by increasing the IHT temperature, the yield and ultimate tensile strengths of the DP steel increase from 493 to 770 MPa, and from 908 to 1080 MPa, respectively, while the total elongation decreases from 9.8 to 4.5%. In contrast to the normalized sample, formation of martensite in the DP steels could eliminate the yield point phenomenon in the tensile curves, as it generates free dislocations in adjacent ferrite.

Effect of Niobium on Inclusions in Fe-Mn-C-Al Twinning-Induced Plasticity Steel

The effect of Nb addition on the composition, morphology, quantity, and size of inclusions in Fe-Mn-C-Al steel was studied by SEM, EDS, and thermodynamic analysis. The research shows that the number of inclusions in Fe-Mn-C-Al high manganese steel decreases obviously after adding 0.04% element Nb, and some inclusions in the steel evolve into complex niobium inclusions. When the niobium content increases to 0.08%, the influence of niobium on inclusions in steel becomes more obvious. The precipitation temperature of inclusions in Fe-Mn-C-Al steel was analyzed by thermodynamics. The results show that the nucleation core of the composite inclusions is AlN, and then NbC and MnS precipitate locally on its surface. With the increase of Nb, the amount and volume fraction of NbC inclusions precipitated in steel increase.

Increasing in effi ciency of steel refi ning process by using production waste

The results of the possibility for using of spent ANF-6-1 fl ux for electroslag remelting and breakage of spent silicon carbide abrasive wheels in the smelting of 20GFL steel are presented. Noticeable advantage of the experimental smelting technology is shown. Saving of expensive materials, reduction of harmful impurities in the metal and increase in the desulfurization rate from 0.0004 to 0.0007 %/min are noted. The use of spent ANF6-1 fl ux for electroslag remelting made it possible to reduce the duration of melting, the consumption of slagforming materials and reducing agents. There is also decrease in electricity consumption by 11 kW/h per ton of liquid steel. Increase in the plastic characteristics and impact toughness of 20GFL steel is shown when using the experimental melting technology in comparison with the current one. At the same time, the strength characteristics of steel remained at the same level. The economic effect at using of secondary materials in the smelting of 20GFL cold-resistant steel is 430...450 rubles per ton of liquid steel.

ANALISIS PENGARUH PARAMETER PENGELASAN GTAW PADA STAINLESS STEEL AISI 304 TERHADAP SIFAT MEKANIS DAN STRUKTUR MIKRO

Stainless steel common worn in industry because it has the mechanical properties of a strong, the physical properties of a good, can be recycled without reducing the quality of its constituent compound, decorative and easily cleared, resistant to corrosion, capable of preventing contamination so that the use of stainless steel increase significantly. The use of stainless steel can not be separated from the process of welding, hence writer do research by varying discharge a stream of gas (13,17,21 liter per minute), current (70,130,180 ampere) And types of electrodes (EWLa-1.5, EWTh-2, EWCe-2) With the design Taguchi L9. The purpose of research to know the influence of parameter against the force pull, violence and structure micro, using of GTAW welding with Taguchi methods. The results of tensile test: yield stress dust the highest to parameter stream of gas 17 liters per minutes, the current 70 ampere, electrodes EWLa-1.5 gold with the 387 MPa, maximum stress to the flow of gas 21 liters per minutes, the current 70 ampere, electrodes EWLa-1.5 gold with the 648 MPa and strain to the low of gas 17 liters per minutes, the current 70 ampere, electrodes EWTh-2 red with the 62,2 %. The Rockwell hardness regional of weld to gas flow is 17 liters per minutes, the current 130 ampere, electrodes EWCe-2 grey the hardness poin is 74,2 HRb. Regional HAZ to the gas flow is17 liters per minutes, the current 180 ampere, electrodes EWLa-1.5 gold of 77,3 HRb. Best parameter with the taguchi method to tensile streng of gas flow 21 liter per minutes, the current 70 ampere and types of electrodes EWLa-1.5. Against rockwell hardness test (HRb) found in a stream of gas 17 liter per minutes, the current 130 ampere and types of electrodes EWCe-2.The phase that is formed before welding at micro structure is the phase austenite and the crom, nickel through welding there are adding the phase carbide crom, only the size of the widening weld and haz different.

Mechanical Characterization of Zirconia Ceramic Composite

In this day and age, zirconia ceramics are used widely in the medical field as biomaterials for the replacement of damaged body parts. This is because zirconia is one of the closest replacements for bone tissue. However, there were a few cases regarding the failure of zirconia ceramic hip transplants. To overcome this issue, composite materials are being studied as they are able to combine different properties which are not present in a material. This study of Y-TZP/stainless steel 316 composite is carried out with the idea of providing a solution for failure of zirconia implants and also an improvement in biomaterials which will benefit the biomedical world. The study aims to determine the effects on how the increasing of stainless-steel content in the composite will affect the relative density, Vickers hardness, fracture toughness and ageing resistance of the Y-TZP/stainless steel 316 composite. To carry out the research, the composite samples were prepared by mixing the powder of each samples according to their determined content with ethanol. After the powders were mixed, the powders were then pressed, followed by undergoing a Cold Isostatic Press process (CIP) and then it underwent sintering at its determined temperature. After sintering, the samples underwent grinding and polishing before being ready for testing. The outcomes of the research showed that as the sintering temperature and the content of stainless-steel increase in the composite, the fracture toughness and ageing resistance improved while the Vickers hardness and relative density decreased.

Micromechanical Finite Element Analysis of the Effects of Martensite Particle Size and Ferrite Grain Boundaries on the Overall Mechanical Behavior of Dual Phase Steel

This paper focuses on micromechanical finite element (FE) modeling of the effects of size and morphology (particularly elongation or aspect ratio (AR) along the loading direction) of martensite particles and the ferrite grains on the overall mechanical behavior of dual-phase (DP) steels. To capture the size-effect of the martensite particles and ferrite grains, the core and mantle approach is adapted in which a thin interphase of geometrically necessary dislocations (GNDs) is embedded at the martensite–ferrite boundaries. It is shown that as the martensite particles size decreases or their aspect ratio increases, both the strength and ductility of DP steel increase simultaneously. On the other hand, as the ferrite grain size decreases or its aspect ratio increases, the overall strength increases on the expense of the ductility. The conclusions from this study can be used in guiding the microstructural design of DP steels.

ABOUT THE NEW INTERSTATE STANDARD GOST 34028-2016 "STEEL FOR THE REINFORCEMENT FOR CONCRETE "

Currently rebar for reinforced concrete structures is the most popular type of building purpose steel. Increase consumer properties of reinforcing bar is possible with close collaboration of metallurgists and builders. The results of paper of the reinforcing bar in weldability, endurance and stress relaxation in accordance with the requirements of the project of a new GOST 34028-2016 "Steel for the reinforcement for concrete."

ABOUT THE NEW INTERSTATE STANDARD GOST 34028-2016 "STEEL FOR THE REINFORCEMENT FOR CONCRETE "

Currently rebar for reinforced concrete structures is the most popular type of building purpose steel. Increase consumer properties of reinforcing bar is possible with close collaboration of metallurgists and builders. The results of paper of the reinforcing bar in weldability, endurance and stress relaxation in accordance with the requirements of the project of a new GOST 34028-2016 "Steel for the reinforcement for concrete."