Certain aspects of determination of continuous cooling conditions directly after forging and their applicability to industrial conditions are discussed. On example of high-pressure-pump crankshaft problems concerning realization of drop forging of microalloyed-steel forged shaft with thermomechanical treatment involving subsequent direct controlled cooling are presented.The paper is focused on determination of both forging conditions and subsequent cooling parameters, which in combination with modelling of precipitation kinetics in the analysed steel allowed accomplishment of required final mechanical properties of the forged part. For the determined conditions of thermomechanical treatment experimental trials in industrial conditions were carried out. Obtained in simulation pattern of continuous cooling was realized with a line consisting of six stages of controlled rate of stirred air flow. Satisfactory level of mechanical properties, exceeding minimum of the assumed requirements was reported, as well as uniform fine grained microstructure regardless of cross-sectional dimensions, meeting the requirements of automotive industry.Keywords: thermomechanical treatment, controlled cooling, drop forging, mechanical properties, numerical modelling, hardness, ductility Przedstawiono niektóre zagadnienia dotyczące doboru warunków kontrolowanego chłodzenia odkuwek matrycowych bezpośrednio po kuciu i ich stosowalności w warunkach przemysłowych. Na przykładzie odkuwki wału korbowego pompy wysokociśnieniowej samochodu osobowego przedstawiono próbę zastosowania obróbki cieplnoplastycznej z uwzględnieniem warunków technologicznych jej realizacji dla odkuwek ze stali z mikrododatkami.W pracy skupiono się na określeniu zarówno warunków kucia matrycowego, jak również parametrów bezpośredniego chłodzenia z temperatury kucia, co w połączeniu z modelowaniem kinetyki wydzielania pozwoliło na uzyskanie założonych finalnych własności mechanicznych odkuwki. Dla określonych drogą modelowania numerycznego warunków obróbki cieplnoplastycznej przeprowadzono weryfikację doświadczalną w warunkach przemysłowych, przy wykorzystaniu specjalnej linii do ciągłego chłodzenia, składającej się z kilku stref chłodzenia z kontrolowaną szybkością. Wykonane próby przemysłowe zapewniły uzyskanie wymaganego poziomu własności mechanicznych i plastycznych odkuwki, a tym samym potwierdziły zasadność przyjętych warunków technologicznych.
An investigation has been carried out into the effects of multiple additions of the microalloying elements It: Ti, and Nb on the austenite grain growth characteristics ofO·4C-1·6Mn (mass-%) steels. It has been shown that simultaneous additions of It: Ti, and Nb inhibit grain growth and increase the grain coarsening temperature markedly. In both Vand Ti steels, increased Nb contents refine further the austenite grain size. Using a thermodynamic model, good agreement has been obtained between the measured and calculated volume fractions of carbonitride particles at the solidus temperature, although such particles are too large for effective grain boundary pinning. Afeature of interest is that increased Nb contents in Ti-V steels decrease the size of the larger Ti rich carbonitride particles and inhibit their formation during solidification of the steel. The stability of the carbonitrides increases with increasing Ti content especially. The N dissolved in the austenite decreases with simultaneous additions ofTi, Nb, and It: which may have effects on other properties. It is concluded that increased N in the steels results in a further refinement of the austenite grain size by increasing the volume fraction of carbo nitride, and such increased N may decrease the microalloy content dissolved in the austenite to such an extent that carbo nitride particle coarsening rates are decreased and more efficient grain refinement is produced. On the basis of the results obtained, suggestions are made for the optimisation of grain boundary pinning and grain refinement.MSTj1332
To control austenite grain growth in high strength low alloy (HSLA) steels, additions of micro alloying elements showing chemical affinity for interstitial elements (C and N) are used. These elements have a significant effect on the mechanical properties of the steels. The mechanical properties of HSLA steels depend both on the amounts of the microalloying elements dissolved in the austenite and on undissolved carbonitrides. In the present work, a thermodynamic model enabling calculation of the composition of the austenite as well as the composition and quantity of the carbonitrides in HSLA steels containing up to four microalloying elements is presented. This model can be a useful tool in determining the optimum chemical compositions for steels as well as the heat treatment parameters required to maximise hardenability and to control austenite grain growth.MST/1471
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