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1

Effect of strain rate on hot ductility of C-Mn-B steel

Lis A., Lis J., Kolan C., Knapiński M.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 41, nr 1-2

26-33

EN

Purpose: The aim of the paper is to determine the influence of hot deformation conditions on hot ductility and ó-ĺ curves of C-Mn-B steel. Design/methodology/approach: The force – energetic parameters of hot – working were determined in hot tensile tests performed in a temperature range of 700 to 1200°C by the use of Gleeble 3800 thermo – mechanical simulator with strain rate 0.01 s-1 and 6.5 s-1 After rupture the contractions of samples were measured. Samples were taken from columnar and equiaxed grains zone of continuously cast billet. Findings: Hot ductility curves as a measure of contraction in function of temperature of deformation for given strain rate and shape of the grains were established. At strain rate 6.5 s-1 there was no minimum of hot ductility for columnar grains and for equiaxed grains minimum of hot ductility was temperature 800 – 850°C (40%). At strain rate 0.01 s-1 and equiaxed grains minimum of the hot ductility (23%) was between 800 – 900°C and for columnar grains between 850-950°C at about 40%. Minimum of the hot ductility was usually in the vicinity of Ar3 temperature. Research limitations/implications: To determine in detail the hot ductility behaviour of C-Mn-B steel, a SEM investigations of rupture should be done. Practical implications: The obtained stress-strain curves can be useful in determination of power-force parameters of hot-rolling. Originality/value: The hot ductility behaviour of new-developed low carbon steel containing Boron microaddition was investigated.

2

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

Dobrzański L. A., Borek W.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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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.

3

Electrostatic powder lubrication for hot massive forming

Gulde M.

Problemy Eksploatacji

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2005

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nr 2

75--82

EN

Growing productivity in the forging industry leads to higher quantities of waste, like lubricant residues, scales and greases. As a consequence, the financial charging for forging companies concerning waste management grows. Investigations showed that the electrostatic powder technology has the potential to lower the amount of lubricants in the process. Today, electrostatic powder lubrication is only established for extrusion moulding of aluminium by using Boron Nitride Powder. Due to high costs of BN-powder, the bad electrostatic chargeability of graphite powder must be improved. An electrostatic powder lubrication system has to be integrated in a production line in the field of hot massive forming.

PL

Rosnąca wydajność w przemyśle kuźniczym prowadzi do zwiększenia ilości odpadów, takich jak pozostałości po smarach, zgorzeliny i tłuszcze. Rezultatem tego są rosnące opłaty za zagospodarowanie odpadów ponoszone przez firmy kuźnicze. Badania wykazały, że wykorzystanie technologii proszków elektrostatycznych może obniżyć zużycie środków smarowych w procesach obróbki na gorąco. Obecnie smarowanie proszkiem elektrostatycznym jest stosowane tylko w przypadku formowania wytłocznego aluminium przy zastosowaniu proszku azotku boru. Ze względu na jego wysoką cenę dąży się do zastąpienia go grafitem. Jednak w takim wypadku należy rozwiązać problem ładowania elektrostatycznego. Umożliwi to włączenie do linii produkcyjnej obróbki na gorąco systemu smarowania grafitowym proszkiem elektrostatycznym.