Poboljšavanje svojstava brzoreznog čelika 1.3302u vrućem stanju

Laboratory investigation of hot workability of 1.3302 high speed steel was carried out and its improving was achieved. Hot compression tests for the determination of optimal soaking temperature as well as for the study of hot workability in temperature range 1150-850 ºC, strain rates range 0,001-6 s–1 and applied strain up to 0,9 were performed. Microstructure of deformed specimen was analyzed. Apparent activation energies for hot working for upper and for lower temperature range were calculated. Onsets of dynamical recrystallization for applied deformation conditions on the basis of calculated strain hardening ratewere determined. Extending of hot working temperature range at its lower limit, i.e. down to 850 ºC, by applying optimal soaking temperature was obtained.Data su laboratorijska istraživanja prerađivačkih svojstva brzoreznog čelika 1.3302 u vrućem stanju koji su doprinijeli poboljšanju tih svojstava. Izvedeni su pokusi vrućeg sabijanja za određivanje temperature zagrijavanja kao i prerađivačkih svojstva u temperaturnom rasponu 1 150-850 ºC, brzinom deformacije 0,001-6 s–1 i stupnja deformacije do 0,9. Analizirana je mikrostruktura deformiranih proba.Izračunane su prividne aktivacijske energije za vruću preradu za gornje i donje temperaturno područje. Počeci dinamičke rekristalizacije za primijenjene uvjete deformacije utvrđeni su na temelju izračuna brzine deformacijskog očvršćavanja. Primjenjujući optimalno temperaturu zagrijavanja dobiveno je povećanje vrućeg radnog temperaturnog raspona na svojoj donjoj granici, odnosno do 850 ºC

Increasing of hot workability of 1.3302HIGH speed steel

Laboratory investigation of hot workability of 1.3302 high speed steel was carried out and its improving was achieved. Hot compression tests for the determination of optimal soaking temperature as well as for the study of hot workability in temperature range 1150-850 ºC, strain rates range 0,001-6 s<sup>–1/sup> and applied strain up to 0,9 were performed. Microstructure of deformed specimen was analyzed. Apparent activation energies for hot working for upper and for lower temperature range were calculated. Onsets of dynamical recrystallization for applied deformation conditions on the basis of calculated strain hardening ratewere determined. Extending of hot working temperature range at its lower limit, i.e. down to 850 ºC, by applying optimal soaking temperature was obtained

Primjena novo razvijenih testova sa grijanjem i unutarnjim hlađenjem uzoraka od alatnog čelika za različite primjene

In this study two new tests were developed, i.e., with continuous internal water cooling as well as discontinuous internal water and air cooling. It was proved that the first type of testing is appropriate for simulating the time course of the temperature at a selected depth of a thermally loaded, hot-working die surface layer, i.e., the temperature field on the die surface layer. The second type of testing is appropriate for a study of the thermal fatigue resistance of a tool material.U ovom istraživanju razvijeni su dva nova testa, tj. test sa kontinuiranom unutarnjim vodenim hlađenjem, kao i test sa diskontinuiranom unutarnjim vodenim i zračnim hlađenjem. Dokazano je da je prvi tip ispitivanja primjeran za simulaciju vremenske raspodjele temperature na odabranoj dubini termalno opterećene površine alata za vruću preradu. Druga vrsta ispitivanja je prikladno za proučavanje otpora termalnog zamora alatnog materijala

Predmnijevanje napona naprezanja kod vrućeg sabijanja čelika s CAE NN i hiperboličnom - sinusoidnom jednadžbom

Hot compression experiments are carried out on steel workpieces by means of Gleeble 1500 thermo mechanical simulator in wide range of temperatures 800 °C - 1200 °C with strain rates 0,1 s-1, 1,0 s-1 and 8,0 s-1and true strains of 0,0 to 0,5. Hot flow curves were estimated by means of the CAE neural networks. The methods of constant smoothness parameter and non-constant (ellipsoidal) smoothness parameter were applied. The use of the latter proved more exact (up to 3,4 %) and simpler if we compare it with the existing data for the flow curve prediction of tool steel by BP NN (up to 7 %), as the proposed method yields better results. The activation energy and other parameters in hyperbolic-sine equation were calculated according to the method proposed by McQueen et al. and according to the method recently proposed by Kugler et al. The latter yields better results at predicting the maximum values of hot flow curves.Pomoću termomehaničkog simulatora Gleeble 1500 izvedeni su vrući pokusi sabijanja čeličnih proba u temperaturnom rasponu 800 °C - 1200 °C, brzinom deformacije 0,1 s-1, 1,0 s-1 i 8,0 s-1 i stupnja defor-macije od 0,0 do 0,5. Naprezanja materijala određena su pomoću CAE neuralnih mreža. Rabljene su metode stalnog i nestalnog (elipsoidnog) parametra glatkoće. Upotreba zadnjih pokazala se za točniju (do 3,4 %) i jednostavniju ako ih se usporedi s znanima podacima krivulje naprezanja alatnog čelika metodom BP NN (do 7 %). Aktivacijska metoda i ostali parametri u hiperbolično - sinusoidnoj jednadžbi izračunani su metodom koju predlaže McQueen i ostali te novijom metodom predloženoj od Kuglera i ostalih. Ta zadnja ima bolje rezultate za predmnijevanje maksimalnih vrijednosti krivulja tečenja u vrućem

Analyses of the reasons for the decreased service time of CrN-coated die for aluminy hot extrusion – a case study

Presented study shows that considerable reserves still exist for increasing the service times (lifetimes) of CrN – coated dies for Al hot extrusion. The main reasons for the decreased service times are revealed and explained regarding the selected CrN - coated die for hot extrusion, i.e. why the service time of the coated-die is not in accordance with the wear resistance of the CrN - coating. The shaping of the bearing surface and presence of the scratches, size and amount of nonmetalic inclusions in the die steel, nodular defects in the CrN - coating, as well as thicknesses uniformity of CrN - coatings along the bearing surface, are relevant influential parameters

Predmnijevanje napona naprezanja kod vrućeg sabijanja čelika s CAE NN i hiperboličnom - sinusoidnom jednadžbom

Hot compression experiments are carried out on steel workpieces by means of Gleeble 1500 thermo mechanical simulator in wide range of temperatures 800 °C - 1200 °C with strain rates 0,1 s-1, 1,0 s-1 and 8,0 s-1and true strains of 0,0 to 0,5. Hot flow curves were estimated by means of the CAE neural networks. The methods of constant smoothness parameter and non-constant (ellipsoidal) smoothness parameter were applied. The use of the latter proved more exact (up to 3,4 %) and simpler if we compare it with the existing data for the flow curve prediction of tool steel by BP NN (up to 7 %), as the proposed method yields better results. The activation energy and other parameters in hyperbolic-sine equation were calculated according to the method proposed by McQueen et al. and according to the method recently proposed by Kugler et al. The latter yields better results at predicting the maximum values of hot flow curves.Pomoću termomehaničkog simulatora Gleeble 1500 izvedeni su vrući pokusi sabijanja čeličnih proba u temperaturnom rasponu 800 °C - 1200 °C, brzinom deformacije 0,1 s-1, 1,0 s-1 i 8,0 s-1 i stupnja defor-macije od 0,0 do 0,5. Naprezanja materijala određena su pomoću CAE neuralnih mreža. Rabljene su metode stalnog i nestalnog (elipsoidnog) parametra glatkoće. Upotreba zadnjih pokazala se za točniju (do 3,4 %) i jednostavniju ako ih se usporedi s znanima podacima krivulje naprezanja alatnog čelika metodom BP NN (do 7 %). Aktivacijska metoda i ostali parametri u hiperbolično - sinusoidnoj jednadžbi izračunani su metodom koju predlaže McQueen i ostali te novijom metodom predloženoj od Kuglera i ostalih. Ta zadnja ima bolje rezultate za predmnijevanje maksimalnih vrijednosti krivulja tečenja u vrućem

Wear Beahaviour of Nitrided Microstructures of AlSl H13 Dies for Hot Extrusion of Aluminium

Nitriding of bearing surfaces on dies (tools, AISI H13) for hot extrusion of aluminium is technologically a very sensitive process with regard to achieving a constant quality of the nitrided layers. This study was based on the analysis of microstructure on dies with intentionally prepared deep and narrow gaps which were nitrided by various manufacturers of equipment for gas and ionic nitriding. The manufacturers chose their own nitriding parameters in order to achieve an optimal wear resistant microstructure. The microstructures obtained showed differences with regard to the presence or absence of a compound layer (white layer), its thickness and its e/g\u27 phase ratio (XRD), nitriding depth and microhardness profile. The measured nitriding depths and the maximum microhardness values on nitrided surface layers were quite similar on dies of the same manufacturer, while for different manufacturers these values differed. Differences with regards to compound layer characteristics were also found on the same die. The die samples with these various nitrided microstructures were then laboratory tested for wear resistance using equipment that provides simulation of the tribological conditions during hot extrusion of aluminium. The wear testing results show differences in behaviour of the nitrided samples. The differences in the actual structures, microstructures, hardness, etc. explain the high level of scattering in die life in actual industrial applications

Implementation of newly developed tests with heated and internally cooled tool steel samples for different applications

In this study two new tests were developed, i.e., with continuous internal water cooling as well as discontinuous internal water and air cooling. It was proved that the first type of testing is appropriate for simulating the time course of the temperature at a selected depth of a thermally loaded, hot-working die surface layer, i.e., the temperature field on the die surface layer. The second type of testing is appropriate for a study of the thermal fatigue resistance of a tool material