Leposava Sidjanin

Austempering study of unalloyed and alloyed ductile irons

Abstract Austempered ductile iron (ADI) proved to be an advanced material as it possesses remarkable combination of high strength, ductility and toughness with good wear resistance and machinability. These properties can be achieved upon adequate heat treatment which yields optimum microstructure for a given chemical composition. In the present paper, an investigation has been conducted on unalloyed ADI and alloyed with 0·47%Cu and 1·6%Cu + 1·5%Ni, austempered at 350°C for the time up to the 6 h. The microstructure and fracture mode developed throughout these treatments have been studied by means of light, transmission and scanning electron microscopy, as well as X-ray diffraction. It was shown that the strength, elongation and impact energy strongly depend on amount of ausferritic ferrite and stable, high carbon enriched retained, reacted austenite. Based on the results, optimal processing windows for alloyed ductile irons used, have been established. In addition, for alloyed ADIs with maximum amount of reacted, retained austenite, transition temperature was also obtained.

Transition temperature and fracture mode of as‐castand austempered ductile iron

The ductile to brittle transition temperature is a very important criterion that is used for selection of materials in some applications, especially in low‐temperature conditions. For that reason, in this paper transition temperature of as‐cast and austempered copper and copper–nickel alloyed ductile iron (DI) in the temperature interval from −196 to +150°C have been investigated. The microstructures of DIs and ADIs were examined by light microscope, whereas the fractured surfaces were observed by scanning electron microscope. The ADI materials have higher impact energies compared with DIs in an as−cast condition. In addition, the transition curves for ADIs are shifted towards lower temperatures. The fracture mode of Dls is influenced by a dominantly pearlitic matrix, exhibiting mostly brittle fracture through all temperatures of testing. By contrast, with decrease of temperature, the fracture mode for ADI materials changes gradually from fully ductile to fully brittle.

Investigation of chip formation during milling

Abstract Metal cutting process is actually a process of chip formation. Most of the information, for evaluation of the cutting process, such as surface finish, cutting temperature, tool life and cutting forces are closely related to the chip geometry. This paper shows that the influence of discontinuities in microstructure plays an important role in cutting. The quick-stop technique of tool in machining, light microscope and SEM were used to study chip formation and surface integrity association with voids and crack formation and its propagation mechanism.

The influence of honing process parameters on surface quality, productivity, cutting angle and coefficients of friction

Purpose – The purpose of this paper is to explore the influence of tool kinematics parameters on surface roughness, productivity and cutting angle for grey cast iron cylinder liners machined by normal honing.Design/methodology/approach – For experimental investigation, a long stroke honing system was used. Diamond and SiC tools were used, for pre‐ and finishing, respectively. The values of cutting parameters were varied within the following limits: cutting speed vs=0.931‐1.11 m/s; specific pressure of pre‐honing process pd=1.0‐1.4 N/mm2 and specific pressure of finishing honing process pz=0.2‐0.5 N/mm2. The analysis of dispersion was conducted for determining the mathematical model for cutting parameter influence on surface roughness and productivity.Findings – Dispersion analysis proved that the most influential parameters on maximum roughness depth are cutting speed for D181 tool and specific pressure of finishing honing for D151 tool. The most influential parameter on productivity in the honing process...

Modification of cellulose and rutile welding electrode coating by infiltrated TiO2 nanoparticles

In this paper, a novel method of infiltration of TiO2 nanoparticles into the coating of the cellulose and rutile shielded metal arc welding electrode is shown. Tensile properties and strength of weld metals were correlated to the chemical composition of the weld metals, ferrite type, and non-metallic inclusion type, size and composition. As infiltration time is increased in the cellulose electrodes, the non-metallic inclusion count increases and their size decreases. They act as inoculants and lead to the replacement of Widmanstaetten with the finegrained acicular ferrite which increases the mechanical properties of the welds. The modification of rutile electrodes with low and medium infiltration time also refines the microstructure and increases the mechanical properties. Specimens welded with rutile electrodes infiltrated at maximum duration exhibited the lowest mechanical properties due to the relatively large non-metallic inclusions that act as void nucleation sites and the appearance of large grain allotriomorphic ferrite in the weld metal.

Austempering kinetics of Cu-Ni alloyed austempered Ductile Iron

The aim of the paper was to investigate the effect of austempering parameters (time and temperature) on the microstructure and mechanical properties of ADI alloyed with 1.5% Cu and 1.6% Ni (in wt.%) in order to establish the optimal processing window. It was shown that the strength, elongation and impact energy strongly depend on the amounts of ausferritic ferrite and retained austenite. A processing window was established according to the results of the kinetics of the isothermal transformation. The results show that the processing window for ADI alloyed with Cu and Ni at 350 °C was relatively wide, while the processing window for the isothermal transformation at 400 °C becomes narrower and shifted to the left. The processing window of ADI austempered at 300 °C is also narrower, but shifted to the right towards the longer times compared to the processing window of ADI austempered at 350 °C.

The influence of tool kinematics on surface texture, productivity, power and torque of normal honing

Purpose – In this paper, the influence of cutting regimes on surface texture and productivity of cylinder liner is shown, obtained by normal honing. Furthermore, normal honing power and torque is discussed. The paper aims to discuss these issues. Design/methodology/approach – Normal honing was done on grey cast iron cylinder liners. Both pre- and finishing honing were done by mechanical means, to achieve the required level of surface texture quality, traditionally achieved by a combination of electrochemical pre-honing and mechanical finishing honing. To determine the most influential parameter on normal honing, statistical mathematical model was devised. Surface texture was controlled by light microscope and scanning electron microscope. Findings – Mathematical model describing the influence of cutting speed, feed rate and depth of cut has shown that the most influential parameter on maximum peak height, productivity and specific volume productivity was shown. The most influential parameter has shown to ...

The influence of torsional and tensile pre-straining on the validity of ductile fracture criteria

Continuous loading and smooth strain paths are usually used to obtain data for empirical ductile fracture criteria or to verify such criteria. It is of interest to understand whether or not these ductile fracture criteria are valid for discontinuous paths. To this end, an experimental program is carried out and its results are combined with two conventional empirical ductile fracture criteria. It is shown that the criteria are not applicable for discontinuous loading paths. Based on the experimental results obtained and experimental results available in the literature it is hypothesized that a measure of rotation of the principal stress (or principal strain rate) axes relative to the material affects the initiation of ductile fracture.

Mechanical finishing honing: cutting regimes and surface texture

Purpose – The aim of this paper was to confirm the hypothesis that it is possible to conduct normal honing by mechanical method, providing the prescribed quality of cylinder liners. For this, cutting parameter optimization is needed.Design/methodology/approach – Normal honing was performed on grey cast iron with lamellar graphite and mostly pearlitic microstructure of metal matrix. Cutting speed, feed rate and specific pressure during metalworking were varied and accordingly, a mathematical model for processing of results by the least squares method was proposed. Surface texture was controlled by scanning electron microscope.Findings – A mathematical model describing the influence of cutting speed, feed rate and specific pressure during metalworking was devised. At the same time, surface texture was adequate, with geometrically appropriate crosshatch pattern, without standing‐out material and mashed graphite lamellas.Originality/value – It was found that normal honing may be done by mechanical means, prov...

Microstructure and cavitation behaviour of alloyed austempered ductile irons

ABSTRACT In this paper, the study of cavitation behaviour of austempered ductile iron (ADI) alloyed with copper, as well as copper and nickel with a fully ausferritic microstructure, is presented. The ADI materials used were austenitized at 900 °C and austempered at 350 °C having an ausferrite microstructure with 16 and 19% of austenite, respectively. The experimental investigations were conducted using the ultrasonically induced cavitation test method. The results show that the cavitation damage was initiated at graphite nodules, as well as in the interface between a graphite nodule and an ausferrite matrix. The cavitation rate revealed that the ADI material alloyed with Cu + Ni austempered at 350 °C/3 h has a higher cavitation resistance in water than ADI alloyed with Cu. An increased cavitation resistance of the ADI material alloyed with Cu and Ni is due to the matrix hardening by stress assisted phase transformation of austenite into the martensite (SATRAM) phenomenon.