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Processes forming the microstructure evolution of high-manganese austenitic steel in hot-working conditions

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Dobrzański L. A. , Borek W.

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2009

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tom Vol. 37, nr 2

397-407

EN

Purpose: The aim of the paper is to characterise the microstructure evolution of new-developed 27Mn-4Si-2Al-Nb-Ti high-manganese steel in various conditions of hot-working. Design/methodology/approach: Flow stresses during the multistage compression test were measured using the Gleeble 3800 thermo-mechanical simulator. To describe the hot-working behaviour, the steel was compressed to the various amount of deformation (4x0.29, 4x0.23 and 4x0.19). The microstructure evolution in successive stages of deformation was determined in metallographic investigations using light, scanning and electron microscopy as well as X-ray diffraction. Findings: The steel has austenite microstructure with annealing twins and some fraction of ĺ martensite plates in the initial state. The flow stresses are much higher in comparison with austenitic Cr-Ni and Cr-Mn steels and slightly higher compared to Fe-(15-25) Mn alloys. The flow stresses are in the range of 200-400 MPa for the applied conditions of hot-working. Making use of dynamic and metadynamic recrystallization, it is possible to refine the microstructure and to decrease the flow stress to 350 MPa during the last deformation at 850°C. Applying the true strains of 0.23 and 0.19 requires the microstructure refinement by static recrystallization. After the grain refinement due to recrystallization, the steel is characterised by uniform structure of ă phase without ĺ martensite plates. Research limitations/implications: To fully describe the hot-working behaviour of the new-developed steel, further investigations in wider temperature and strain rate ranges are required. Originality/value: The hot-deformation resistance and microstructure evolution in various conditions of hot-working for the new-developed high-manganese 27Mn-4Si-2Al-Nb-Ti austenitic steel were investigated.

2

TWIP mechanism in processing of high-manganese austenitic steel

80%

Dobrzański L. A. , Borek W. , Mazurkiewicz J.

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tom Vol. 71, nr 1

22--27

EN

Purpose: The aim of this paper is to determine the high-manganese austenite propensity to twinning induced by the cold working and its effect on structure and mechanical properties, and especially the strain energy per unit volume of new developed high-manganese Fe-Mn-(Al,Si) high-manganese austenitic TWIP (TWinning Induced Plasticity) steel containing about 25% Mn, 1% Si, 3% Al. Design/methodology/approach: The essence of the research concerns the analysis of the influence of microstructure evolution during cold plastic deformation. The microstructure of investigated steel was determined in metallographic investigations using light, scanning and high- resolution transmission electron microscopies (HRTEM). Findings: The activation of intensive mechanical twinning mechanisms in high-manganese austenitic steels, in order to increase strain energy, allows the formation of technological components of complex shape or permits the discharge of energy during cold plastic deformation. According to currently presented views, it is believed that the new austenitic steels with the A1 crystallographic structure containing Mn more than 25 mass.%, Si and Al can provide a significant advance, particularly in automotive applications, because practically there are no more possibilities to improve at the same time the strength and ductility of the steel with A2 crystallographic structure. Research limitations/implications: Results obtained in static conditions for new developed high-manganese austenitic steel indicate the possibility and purposefulness of their employment for constructional elements of vehicles, especially of the passenger cars to take advantage of the significant growth of their strain energy per unit volume which guarantee reserve of plasticity in the zones of controlled energy absorption during possible collision resulting from activation of twinning induced by cold working, which may lead to significant growth of the passive safety of these vehicles' passengers. Originality/value: TWIP steels show not only excellent strength, but also have excellent formability due to twinning, thereby leading to an excellent combination of strength, ductility, and formability over conventional dual-phase steels.

3

CARBIDES ANALYSIS OF THE HIGH STRENGTH AND LOW DENSITY Fe-Mn-Al-Si STEELS

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Matus K. , Borek W. , Sozańska-Jędrasik L. , Mazurkiewicz J.

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nr 1

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Carbides Analysis of the High Strength and Low Density Fe-Mn-Al-Si Steel

80%

Sozańska-Jędrasik L. , Mazurkiewicz J. , Borek W. , Matus K.

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tom Vol. 63, iss. 1

265--276

EN

The work presents the results of investigations into the structure and phase composition of newly developed high manganese steels of the X98MnAlSiNbTi24-11 and X105MnAlSi24-11 type. The average density of such steels is 6.67 g/cm3, which is 15% lower as compared to typical structural steels. An analysis of phase composition and structure allows to conclude that the investigated steels feature an austenitic γ-Fe(Mn,Al,C) structure with uniformly distributed and elongated α-Fe(Mn,Al) ferrite grains on the boundaries of austenite grains and carbides. Examinations by diffraction of back scattered electrons (EBSD) allow to conclude that high-angle boundaries dominate in such steels, having significant influence on mechanical properties. Three types of carbides with differentiated chemical composition and size were identified in steel X98MnAlSiNbTi24-11 with scanning and transmission electron microscopy. κ-(Fe,Mn)3AlC carbides, having a regular, face-centered cubic lattice (fcc), were identified in austenite. Transmission electron microscopy examinations have enabled to identify M7C3-type carbide in ferrite. Nb- and Ti-based complex carbides were identified in steel X98MnAlSiNbTi24-11, both, in ferrite and austenite. (NbTi)C2 carbide precipitates were confirmed in an X-ray qualitative phase analysis. The size of the above-mentioned carbides is within several to several dozens of μm. An X-ray qualitative phase analysis has confirmed the precipitates of M7C3 carbides in both steels.

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Mechanical Properties of High-Mn Austenitic Steel Tested under Static and Dynamic Conditions

80%

Dobrzański L. A. , Borek W. , Mazurkiewicz J.

Archives of Metallurgy and Materials

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2016

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tom Vol. 61, iss. 2A

725--730

EN

The purpose of the paper is to investigate X73MnSiAlNbTi25-1-3 high manganese austenitic steel containing 0.73% C to determine structural mechanisms decisive for increasing a reserve of cold deformation energy of such steel. The influence of a strain rate on the structure of the investigated steels and on the structural mechanisms decisive for their properties was analysed. Specialist research instrumentation was used for this purpose such as Scanning Transmission Microscopy (including EBSD examinations), conventional and high-resolution transmission electron microscopy together with diffraction examinations and metallographic examinations. It was found that the principal cause of an increased reserve of cold deformation energy of the investigated steels in dynamic conditions is the activation of mechanical twinning in the mutually intersecting systems in austenite grains and annealing twins, which are densifying when a cold deformation rate is growing, thereby confirming the basic mechanism of TWIP (TWinning Induced Plasticity).

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Influence of Isothermal Heating Time on the Disappearance of Strain Hardening in High-Manganese TRIPLEX Type Steels

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Sozańska-Jędrasik L. , Mazurkiewicz J. , Borek W.

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tom Vol. 63, iss. 4

2023--2030

EN

The paper presents the results of the effect of isothermal heating time on the disappearance of strain hardening (the softening degree) of the studied high-manganese TRIPLEX type steels at a temperature of 900 and 1000°C. In order to determine the kinetics of recrystallization of austenite plastically deformed for selected steels, hot compression tests with draft ε = 0.2 were made. The presented results reveal that the complete recrystallization of austenite needs long isothermal heating times. In industrial conditions, such long times are not used, therefore in the initial rolling passages, the time required for half recrystallization of austenite t0.5 is often used. The total disappearance of the strain hardening, completion of the recrystallization of austenite tested high-manganese X98 and X105 TRIPLEX type steels isothermal heating time requires far more than 200 s. The increase of the deformation temperature is a factor influencing the acceleration of the disappearance of strain hardening.

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Influence of Isothermal Heating Time on the Disappearance of Strain Hardeningin High-Manganese TRIPLEX Type Steels

80%

Sozańska-Jędrasik L. , Mazurkiewicz J. , Borek W.

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8

Numerical analysis of the cavitation effect occurring on the surface of steel constructional elements

80%

Linek T. , Tański T. , Borek W.

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tom Vol. 85, nr 1

24--34

EN

Purpose: The aim of the work is to present the results of own investigations concerning the geometric optimisation of constructional elements working in the environment of cavitation wear together with a computer numerical analysis. The engineering material used for constructional elements working in the environment of cavitation wear is steel, commonly used for pressure devices working at elevated temperatures, P265GH, acc. to PN-EN 10028:2010. Design/methodology/approach: SOLID EDGE ST 7 software, for synchronous designing, was used for the parametrisation of the shape, distribution, configuration and size of openings in constructional elements. Five models, with a different spacing and number of openings, were proposed for the optimisation of internal geometry of the cavitation generator and for the investigations; the models were then subjected to a numerical analysis using specialised software, ANSYS FLUENT v.16, employed for modelling the effects associated with fluid mechanics (Computational Fluid Dynamics - CFD). The data was implemented for this purpose in the software used, such as: density, yield point, tensile strength, heat conductivity coefficient for steel P265GH, material surface roughness, medium (water) flow rate, constant pressure loss of medium, pressure of steam saturation in a medium; and such data was called boundary conditions. Findings: The authors’ principal accomplishment is the optimisation of the shape, the selection of the most appropriate geometry of a constructional element generating the maximum number of cavity implosions in the environment of a flowing medium (water), with the use of computer tools dedicated to engineering design: a 3D and numerical computer analysis of fluid mechanics, CFD. Moreover, an attempt was made in this work to develop a methodology for characterisation of the phenomena accompanying the environment of cavitation wear. Practical implications: A possibility of examining the phenomena and a process of wear of a constructional element made of P265GH grade steel for pressure devices working at elevated temperatures. The demonstration and presentation of potential places, areas and sizes of erosion existing on constructional elements working in the environment of cavitation wear.

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Effect of Laser Feeding on Heat Treated Aluminium Alloy Surface Properties

61%

Labisz K. , Tański T. , Janicki D. , Borek W. , Lukaszkowicz K. , Dobrzański L. A.

Archives of Metallurgy and Materials

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2016

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tom Vol. 61, iss. 2A

741--746

EN

In this paper are presented the investigation results concerning microstructure as well as mechanical properties of the surface layer of cast aluminium-silicon-copper alloy after heat treatment alloyed and/ or remelted with SiC ceramic powder using High Power Diode Laser (HPDL). For investigation of the achieved structure following methods were used: light and scanning electron microscopy with EDS microanalysis as well as mechanical properties using Rockwell hardness tester were measured. By mind of scanning electron microscopy, using secondary electron detection was it possible to determine the distribution of ceramic SiC powder phase occurred in the alloy after laser treatment. After the laser surface treatment carried out on the previously heat treated aluminium alloys, in the structure are observed changes concerning the distribution and morphology of the alloy phases as well as the added ceramic powder, these features influence the hardness of the obtained layers. In the structure, there were discovered three zones: the remelting zone (RZ) the heat influence zone (HAZ) and transition zone, with different structure and properties. In this paper also the laser treatment conditions: the laser power and ceramic powder feed rate were investigated. The surface laser structure changes in a manner, that there zones are revealed in the form of. This carried out investigations make it possible to develop, interesting technology, which could be very attractive for different branches of industry.