Bainitic Transformation in High-Speed Steels

The investigation on the structure formation in the bainitic area for high-speed steel HS18-0-1 is performed. The austempering is carried out at 270 °С after austenitizing at 1280 °С following by isothermal retention in the area of high resistance of the undercooled austenite(500÷650°С). The kinetic of the bainitic transformation, the obtained structure by means of optical metallography (OM), transmission electron microscope (TEM), X-ray analysis and hardness measurement by Rockwell method are studied. The influence of the preliminary destabilisation of the undercooled austenite at 560 °C and 650 °C on the characteristics of the austenite-to-bainitе transformation in steel HS18-0-1 is established

TRIBOLOGICAL PROPERTIES AND MICROSTRUCTURE OF ELECTROLESS NICKEL COATINGS REINFORCED WITH NANOPARTICLES

Composite nickel coatings composed of Ni; Ni + TiN are studied. The method for elecrtroless nickel deposition EFFTOM-NICKEL with TiN nanosized strengthening particles (50nm) is applied. The coatings are deposited on austempered ductile iron (ADI) samples. The composition of cast iron samples is: Fe-3,63C-2,59Si-0,30Mn-0,010S-0,034P-0,53Cu wt. %. The samples are put under isothermal hardening at 900oС for an hour and isothermal retention at 290 oС for 2 hours with the aim to receive a lower bainite structure. The wear resistance experimental testing is carried out using Taber-Abraser test machine by disk to disk classical method. The microstructure observations of the coatings and padding are performed using an optical microscope GX41 OLIMPUS also the coatings’ microhardness by Knoop Method is examined. The wear resistance, microstructure, thickness and microhardness of the as plated and thermally processed at 290oС for 6 hours coatings are defined

STRUCTURE AND MECHANICAL PROPERTIES OF SPHEROIDAL GRAPHITE CAST IRON WITH NANOSIZED ADDITIVES

The microstructure and properties of spheroidal graphite cast irons and austempered ductile irons with nanosized additives of titanium carbonitride and titanium nitride (TiCN+TiN), titanium nitride TiN and cubic boron nitride cBN are investigated. The microstructure of the patterns is observed by optical metallography, quantity metallographic analysis, X-Ray analysis, SEM analysis and EDX analysis. Hardness measurement, impact strength and abrasion wear test on fixed abrasive are performed. The influence of the nanosized additives on the microstructure, mechanical and tribological properties of the cast irons are examined

MICROSTRUCTURE AND PROPERTIES OF HIGH CHROMIUM WHITE CAST IRONS ALLOYED WITH BORON

The microstructure and mechanical properties of high chromium white cast iron with composition: 2,6÷3,4% C; 0,9÷1,1% Si; 0,8÷1,1% Mn; 1,0÷1,3% Mo; 12,3÷13,4% Cr, additionally doped with boron in an amount of 0,18% to 1,25% is investigated. The microstructure of six compositions of white cast irons is studied by means of an optical metallographic analysis - one without boron, and the others contain 0,18%; 0,23%; 0,59%; 0,96% and 1,25% boron. A test is performed to determine: hardness by the Rockwell method; microhardness; bending strength and impact toughness. It was found that at a boron content of 0,18%; 0,23% and 0,59%, the structure of white cast irons is subeutectic, with impact toughness in the range of 1,80÷1,52 J/cm2; with a boron content of 0,96%, the structure of white cast iron is close to the eutectic, with impact toughness 0,98 J/cm2 ; at a boron content of 1,25% the structure of white cast iron is supereutectic and the impact toughness decreases to 0,68 J/cm2. With a change in the boron content from 0,8% to 1,25%, the amount of carbide phase in the structure of white cast iron increases, which leads to an increase in hardness from 53 to 59 HRC. The highest bending strength (Rmi=660,85 MPa) was obtained in white cast irons with a boron content of 0,23%.

EFFECT OF BORON ON THE WEAR BEHAVIOR OF HIGH CHROMIUM WHITE CAST IRONS

The wear behavior of high chromium white cast irons with composition: 2,6÷3,4% C; 0,9÷1,1% Si; 0,8÷1,1% Mn; 1,0÷1,3% Mo; 12,3÷13,4% Cr and 0,18 ÷ 1,25% B is investigated. The microstructure and tribological characteristics of six compositions of high chromium white cast irons (one without boron and with 0,18; 0,23; 0,59; 0,96; 1,25% boron) are studied.After casting, heat treatment was carried out, including quenching at 9500C and tempering at 2350C for 1 h. The influence of the heating temperature in the interval 850÷11000С, 25 min on the Rockwell hardness and the microstructure are studied.The wear resistance during abrasive wear for samples after casting and after heat treatment is investigated as measured loss of mass in terms of dry friction under load of 1,5 kg during 10 min. The lowest mass loss during abrasive wear test in dry conditions friction is defined for cast irons alloyed with 0,18 % boron - ∆ m = 0,1469 g after casting and ∆ m = 0,0022 g after heat treatment. The highest mass loss is determined during abrasive testing of alloyed cast irons with 0,96 and 1,25% boron. The alloyed cast irons with 0,18 % boron show highest wear resistance.

INVESTIGATION ON TRIBOLOGICAL BEHAVIOR OF DUCTILE CAST IRONS WITH NANOSIZED PARTICLES

The work in this study is focused on investigation of the tribological behavior of ductile cast iron with nanosized particles: titanium nitride TiN; titanium nitride 30% + titanium carbonitride 70% (30%TiN+70%TiCN). The ductile cast iron composition is: Fe-3,55C-2,67Si-0,31Mn-0,009S-0,027P-0,040Cu-0,025Cr-0,08Ni-0,06Mg wt%. Before the addition to the melt nanosized particles were coated with nickel by the electroless nickel deposition method EFFTOMNICKEL .The nickel coating on the nanosized particles ensures their wetting in the melt as well as their uniform distribution into the cast. The optical and quantity metallographic observations and wear test are performed to study the influence of the nanoparticle additives on the cast iron tribological properties. It is observed that the quantity proportion changes between pearlite, ferrite and graphite phase in the cast iron structure. The graphite shape is retained the same, but the nanosized additives decrease the average diameter of the graphite spheres Dmid and increase the quantity of the graphite phase in the structure of ductile cast irons. The cast iron wear resistance in the presence of nanosized additives of (TiN+TiCN) and TiN increases to 55–69% in comparison to wear resistance of the cast iron without nanoparticles

Microstructure and Tribological Properties of Spheroidal Graphite Cast Irons with Nanoadditives

In this paper metallographic, mechanical and tribological tests of spheroidal graphite cast iron with applied nanosized additives of titanium nitride + titanium carbonitride (TiN + TiCN), titanium nitride TiN and cubic boron nitride cBN are perfomed. With the aim to achieve upper bainite structure, samples of spheroidal graphite cast iron are put under austhempering at the following conditions: heating at 900 °С, 1 h and isothermal retention at 380 °С, 2 h. In order to achieve the wear resistance, the resulting structure of the upper bainite has similar properties as martensitic structure, but with improved toughness. By X-ray analysis before and after the wear resistance test, the share of retained austenite was reduced in samples with applied nanosized additives compared to the samples of spheroidal graphite cast iron that were tested without the application of nanosized additives. Based on the analysis of the test results it was concluded that the samples with applied nanosized additives increased wear resistance compared to the samples that were tested without the application of nanosized additives

Critical current anisotropy in Nd-1111 single crystals and the influence of neutron irradiation

We report on angle-resolved magnetization measurements on NdFeAsO0.65F0.35 (Nd-1111) single crystals. The field dependence of the critical current density, Jc, is non-monotonic in these crystals at all orientations and temperatures due to the fishtail effect, which strongly influences the angular dependence of Jc. The currents decrease as the field is tilted from the crystallographic c-axis at low fields, but increase at high fields. A peak occurs in the angular dependence of Jc at intermediate fields. The critical currents are significantly enhanced after irradiation with fast neutrons and the fishtail disappears. The different current anisotropies at low and high fields, however, persist. We discuss the data in the framework of the anisotropic scaling approach and propose a transition from dominant pinning by large defects of low density at low fields to pinning by small defects of high density at high fields in the pristine crystal. Strong pinning dominates at all fields after the irradiation, and the angular dependence of Jc can be described via anisotropic scaling only after an appropriate extension to this pinning regime.ISSN:0953-2048ISSN:1361-666

Prognostic value of matrix metalloproteinases in oral squamous cell carcinoma

The aim of this study was to investigate whether there is a correlation between the expressions of four matrix metalloproteinases (MMPs): MMP-2, MMP-7, MMP-9 and MMP-13, and the TNM (tumour-node-metastasis) stages of oral squamous cell carcinoma (OSCC); and to explore the implication of these MMPs in OSCC dissemination. Samples from 61 patients diagnosed with oropharyngeal tumour were studied by immunohistochemistry against MMP-2, MMP-7, MMP-9 and MMP-13. The assessment of immunoreactivity was semi-quantitative. The results showed that MMP-2 and MMP-9 had similar expression patterns in the tumour cells with no changes in the immunoreactivity during tumour progression. MMP-9 always had the highest expression, whereas that of MMP-2 was moderate. MMP-7 showed a significant decrease in expression levels during tumour evolution. MMP-13 had constant expression levels within stage T2 and T3, but showed a remarkable decline in immunoreactivity in stage T4. No significant differences in the MMPs immunoreactivity between tumour cells and stroma were observed. Although strong evidence for the application of MMPs as reliable predictive markers for node metastasis was not acquired, we believe that combining patients' MMPs expression intensity and clinical features may improve the diagnosis and prognosis. Strong evidence for the application of MMPs as reliable predictive markers for node metastasis was not acquired. Application of MMPs as prognostic indicators for the malignancy potential of OSCC might be considered in every case of tumour examination. We believe that combining patients' MMPs expression intensity and clinical features may improve the process of making diagnosis and prognosis