Papers by Keyword: Austenite

Abstract: The article considers the technology for producing GX120Mn13 steel with high manganese content altered by a special modifier in order to improve the constructional durability of the manufactured parts. The ultra-dispersed powder of refractory metal oxides is used for the modification process. The samples are produced in the series of casting and tested mechanically. The structural research demonstrates the improvement of the steel microstructure and its mechanical characteristics. It has also revealed that the size of an austenite grain and nonmetallic inclusions on grain boundaries are reduced, and sulphide inclusions are partially dissolved, which has a positive impact on the operation characteristics of the steel.

Abstract: Aspect ratio is a key factor to calculate stress intensity factor (SIF) K using fracture mechanics. Cracks are approximated to be semi-circle or semi-ellipse in simple calculation, however, their empirical shapes are changed by stress concentration. In this study, in order to calculate K simply and precisely, a new method to predict fatigue crack initiation stress, σ_w1 of austenitic stainless steel with modified aspect ratio is discussed. The new method succeeded to predict σ_w1 within 20% error from empirical values using average austenite grain sizes.

Abstract: The characterization of steel microstructures is an important tool for metallurgists as mechanical properties are controlled by microstructural parameters such as grain size, phase balance and precipitates. This paper describes a model of the phase transformation of tool steel CSN 41 9436. Each of the experimental data was observed by electromagnetic sensor. The mathematic model was developed for an optimizing of tool steel heat treatment. The model was developed from one experiment and next experiments were for an evaluation of the model. A model can be satisfactory used for graphical form of the austenite phase transformation.

Abstract: Seven-pass strip rolling simulations were carried out on a 0.06%C and a 0.09%C-0.036%Nb steel. The rolling loads (mean flow stresses or MFS’s) did not increase as the temperature decreased during the simulation. This is ascribed to the occurrence of dynamic transformation. The simulation results are compared to the high temperature flow curves determined on eight plain C and Nb-modified steels in both compression and torsion and at a series of temperatures and strain rates. When the associated MFS’s are plotted against inverse absolute temperature in the form of Boratto diagrams, the stress drop temperatures, normally defined as the upper critical temperature applicable to rolling, A_r3*, are shown to be about 40 degrees above the paraequilibrium and about 20-30 degrees above the orthoequilibrium A_e3’s. These drops are ascribed to the dynamic transformation of austenite to ferrite, a softer phase. The characteristics of the ferrite produced dynamically are described and the transformation is shown to be displacive in nature, leading to the appearance of fine Widmanstätten plates. These plates coalesce into polygonal grains on further deformation and on holding.

Abstract: After equal channel angular pressing (ECAP) at room temperature in 08%C-18%Cr-10%Ni-Ti steel grain-subgrain structure with the size of structural elements of 100-250 nm, volume of high angle boundaries (HAB) about 59% and 38% of martensite is formed. ECAP at 400°C results in fully austenitic structure with the structural element size of 100-400 nm and volume of HAB ~54%. ECAP increases the ultimate tensile strength of 08%C-18%Cr-10%Ni-Ti steel by 1.5 - 2 times, the yield stress by 3.8 - 5.2 times, the fatigue limit - by 1.4 - 1.7 times, however the ductility is reduced. Fatigue strength is enhanced by the refinement of the structure and twinning in the austenite during ECAP and due to intensive dynamic twinning, partial martensitic transformation and increasing of the volume of HAB during cyclic deformation.

Abstract: The study proves that by introducing the iron powder to low-sulphur cast iron still before the inoculation carried out with a conventional graphitising inoculant, the mechanical properties similar to those obtained during the inoculation treatment carried out on cast iron with the recommended high sulphur content are achieved. The said operation increases the number of crystallisation nuclei for of the primary austenite dendrites. In this case, the iron particles act as substrates for the nucleation of primary austenite due to a similar crystallographic behaviour of the regular face centered cubic lattice The more numerous are the dendrites of primary austenite, the less free space is available in the interdendritic spaces for the formation of graphite eutectic grains, which makes the mechanical properties higher.

Abstract: Inoculation of casting used to improve the microstructure and the properties of the component. Depending upon the area of application, gray cast iron has different microstructure and mechanical properties. The type and amount of the inoculation result in shape and orientation differences of the flake graphite. The Linear Variable Differential Transformer (LVDT) shows a variation in displacements change during the solidification. Temperature measurement used to analyze cooling curves and microstructural analysis of sample to examine the physical differences. Thermal analysis compared with the experimental results and microstructural study for describing the variation in area fraction and shape of graphite. The experimental result indicates contraction in austenite formation region, and expansion in eutectic formation region. The effect of the inoculant and the superheat temperature shows a variation in degree of expansion/contraction and cooling rates of the experiments. The comparisons between the experimental and the theoretical results have been done. Combining the theoretical and experimental results, it resembles a difference in eutectic formation region, and it needs carful investigation in future works.

Abstract: The kinetics of austenite recrystallization was evaluated in range of typical forging temperatures (850 - 1250) °C. The steels SA-508 and 3.5Ni-1.5Cr were compared. The laboratory one step deformation was applied. The effect of selected chemical elements in evaluated steels on grain growth and recrystallization kinetics of austenite and precipitation was monitored using metallographic methods. The retarding of static recrystallization was proved and no abnormal grain coarsening at defined condition was observed.

Abstract: Duplex stainless steel is a material that attracts great interest of different branches of engineering and industry because of its combination of good structural and mechanical characteristics and high corrosion resistance. The microstructure of duplex steel presents an example of composite material with approximately equal amounts of austenite and ferrite phases. Physical and mechanical properties of these components are different so their behaviors under loading are different too. Therefore it is important to analyze the distribution of applied stress between ferrite and austenite phases of duplex steel. The analysis of stress distribution was made by X-ray diffraction technique. X-ray diffraction method allows separate measuring of stresses in each phase and determination of others mechanical characteristics as Young ́s modulus, yield stress of ferrite and austenite both in elastic and plastic region. In presented paper the samples of duplex steel after rolling were loaded by calibrated springs; using of Cr-K_α radiation allows carrying out of stress measurements in ferrite and austenite phases of duplex stainless steel.

Abstract: In this study, ductile Ni-resist alloy with a minimum 18 wt. % nickel composition was modified. Up to 12 wt. % manganese was added together with 10 wt. % nickel before undergoing the inoculation process at various percentages to investigate the effects of the alloying elements on both its microstructure and mechanical properties.. The results showed that increasing inoculation did reduce carbide formation and further led to improved tensile value and decreased hardness value. Moreover, inoculation led to a uniform distribution of free graphite. The experimental results show the inoculation process refined the modified alloyed iron microstructure and improved its mechanical properties.