were determined by means of light microscopy. The results show that high strength steel DOMEX 700 MC can be compatible with good weldability, as regards weld and beat affected zone (HAZ) hardness and toughness by careful selection of filler materials combination and welding parameters.

metodami mikroskopii świetlnej. Wyniki potwierdziły, iż dobór odpowiednich parametrów spawania oraz materiału elektrody podwyższa właściwości mechaniczne i udarność spoiny oraz strefy wpływu ciepła z zachowaniem wymaganych właściwości mechanicznych materiału rodzimego - stali DOMEX 700MC.

hardened steel grades, thereby reducing costs in the development stage. Other important aims are tailoring of mechanical properties with respect to alloying of the steels and reduction of weight by usage of steels with higher strength. In many cases steels are over alloyed to ascertain full hardenability. This can however increase the cost of the steel with no beneficial gain in the mechanical properties. With the help of modelling hopefully over alloying can be avoided. So, the benefit with modelling is reduced costs for material development as well as production costs with improved properties of the final products. Basis for the hardenability model is divided in three sub-models: 1. Dissolution of particles during reheating. Alloying elements generally increase hardenability when in solution in the austenite. 2. Calculation of hardenability distance kinetically depending on the dissolution of particles. Equilibrium of elements in solution or in particles is determined with ThermoCalc with a database for HSLA steels. Multiplication factors for alloying elements based on Grossmans work are used for calculation of Ideal diameter for 50% martensite in the centre of a bar. For comparison with Jominy bars, the Ideal diameter is transformed to Jominy distance. Also boron is considered since many quenched steels contain this alloying element, having a large effect on hardenability. 3. Grain growth with consideration taken to particles and their dissolution. Larger grains increase hardenability. The hardenability model will be used specifically for steel containing less than 0.4% C. For low carbon steels modified relations should be used. Below 0.2% C alloying elements such as Cr and Mo contribute less to hardenability. Therefore other relations must be used to fully describe the influence of alloying elements on hardenability. Combination effects occur, not only due to presence of particles and their ability to dissolve during reheat. Also interaction effects such as those for Mo and Ni in low carbon steels. According to the literature a high Ni-content (>0.75 wt-%) increases the influence of Mo on hardenability. In general the influence of individual alloying elements are lower than for steels with higher C-contents. The tempering model is based on experimental information from the literature. In this sense it is empirical. By combining the data from hardenability calculations using the hardenability model room temperature hardness and ultimate tensile strength after tempering in the temperature range 20-700 °C are calculated. The final properties are dependent on dissolution of alloying elements already during reheat before quench. In this paper comparisons of different alloys are given for hardening and tempering. Examples of verifications to experimental data are given both for the hardenability model as well as the tempering model. The tempering model generally functions well in comparison with experimental data. The pre-history before quench is important and affects the level of hardness and strength. In current work we try to take this into consideration by first applying the hardenability model.

obszarów zahartowanych w oparciu o kinetykę rozpuszczania cząstek i (iii) rozrost ziaren (uwzględniając wpływ rozmiaru i objętości cząstek na efekt piningu Zenera. Model hartowalności przewiduje Idealną Średnicę, odległość Jominy'ego dla 50% martenzytu oraz twardość powierzchni stali po hartowaniu. Przykłady obliczeń dla stali z SSAB Oxelósund są przedstawione w artykule i porównane z wynikami doświadczeń. W K1MAB opracowano również doświadczalny model odpuszczania, który opiera się na danych doświadczalnych zaczerpniętych z literatury. Obliczona została twardość i wytrzymałość na rozciąganie hartowanych stali, otrzymanych z Ovako Bar, po odpuszczeniu w temperaturach 150°-700°C, i wyniki porównano z pomiarami. Model odpuszczania funkcjonuje poprawnie i ogólit skano zgodność z danymi doświadczalnymi. Niemniej j historia zmian temperatury przed hartowaniem ma wpływ i powinna być uwzględniona, ponieważ rzutuje i twardość i wytrzymałość stali. Stosując razem modele hartowalności i odpuszczania można badać wpływ nierozpuszczonych cząstek na własności stali po obróbce cieplnej.

define rolling schedules combining a maximum degree of microstructural refinement with acceptably low rolling loads, good shape and surface control and high productivity. In this context, the simulation of the TMCP treatment in laboratory scale as well as the computer models for calculation of microstructure development and precipitate evolution during hot rolling are invaluable for design of rolling schedules. For good control of final microstructure, it is invaluable to have a computer model for prediction of microstructure evolution during TMCP, to enable optimal design of rolling and cooling schedules. By modelling of microstructure evolution, the steel composition and the properties of the final product can be optimised without expensive testing, so reducing the production cost of high strength steels and making them competitive in more applications. It is intended that the developed models will give steel producers essential advantages in thermo-mechanical processing, applicable to structural/microalloyed steels, so achieving optimisation of process parameters and steel chemistry. Several models based on empirical and/or semi-empirical equations describing recrystallization and recovery and have been developed around the world and applied successfully to specific steels. However, such models have limited improvement potential and typically suffer from difficulties in applicability to different steels even when these are quite similar in chemical composition. In order to gain flexibility, the models should be based on a physical description of microstructure evolution, including deformation, recovery, recrystallization, precipitation and phase transformation. Such so-called physical models should be intrinsically capable of handling multi-component systems. A brief survey is made of the models developed at the Corrosion & Metals Research Institute and used by the Swedish Steel Industry. The models can be used for predictions of recrystallization and grain growth of austenite after deformation, precipitation or dissolution of microalloying carbo-nitrides in austenite and phase transformation behaviour during accelerated cooling. The effect of TMCP- parameters, low reheating and high finish rolling temperature, as well as rolling schedules, cooling / quenching rate will be discussed with regard to the transformation characteristics as well as the strength, hardness and microstructure of structure steels.

artykułu. Symulacja TMCP w skali laboratoryjnej oraz komputerowe modelowanie w celu przewidywania rozwoju mikrostruktury i procesów wydzieleniowych podczas walcowania na gorąco są ważnym wspomaganiem projektowania technologii walcowania. W pracy przedstawiono krótki przegląd modeli opracowanych w Corrosion & Metals Research Institute i sto­sowanych przez przemysł metalurgiczny w Szwecji. Modele są stosowane do przewidywania rekrystalizacji i rozrostu ziarna austenitu po odkształceniu, procesów wydzieleniowych i rozpuszczalności węgliko-azotków w austenicie oraz przemian fazowych podczas przyspieszonego chłodzenia. Otrzymane parametry TMCP - niższe temperatury wygrzewania i wysokie temperatury końca walcowania, plany przepustów, i prędkości chłodzenia są omówione w artykule ze względu na ich wpływ na charakter przemiany fazowej oraz na mikrostrukturę i wytrzymałość wyrobów ze stali konstrukcyjnych.

related to the start and finish of these phase transformations. Attention was paid to structural effects of dynamic precipitation and resulted morphology of structural components dependent on expected localization of phase transformation. It was shown that the flow localization during hot deformation and preferred growth of the pearlite colonies at shear bands was very limited. The most characteristic feature of the microstructure observed for hot deformed samples was the development of carbides that nucleated along elongated ferrite grains.

Odkształcenia realizowano w czasie przejścia przez temperaturowy zakres przemiany fazowej. Uwagę szczególną zwrócono na obserwację mikrostruktury i morfologię składników fazowych mogących potwierdzić proces niejednorodnego wydzielania związanego z lokalizacją przemiany. Wykazano, że w warunkach dynamicznych nieciągła przemiana stali praktycznie nie charakteryzuje się skłonnością do lokalizacji spowodowanej niejednorodnością odkształcenia. Najistotniejszą cechą mikrostruktury stali po odkształceniu w zakresie przemiany jest wydzielanie węglików na granicach odkształconych ziarn ferrytu.

recrystallization and grain growth of austenite after deformation, precipitation or dissolution of microalloying carbonitride in austenite, flow stress during hot working, phase transformation behaviour during accelerated cooling as well as the final microstructure and mechanical properties. The database, which contains information about the steel behaviour for a large number of HSLA steels, is also presented. Optimisation TMCP parameters for improving the properties of steel are discussed in relation to the microstructure and mechanical properties. The effect of TMCP parameters (reheating temperature, rolling schedules and finish rolling temperature as well as accelerated control cooling) on steel properties was studied in laboratory scale.

microstructure development and precipitate evolution during hot rolling are invaluable for design of rolling schedules. TEM study of precipitate evolution regarding property enhancement TMCP and optimisation of TMCP parameters (reheating temperature, rolling schedules as well as accelerated cooling rate) are discussed in relation to the precipitation strengthening, microstructure and mechanical properties of HSLA steel, microalloyed with Ti, V, and/or Nb. Mathematical modelling of steel behaviour during thermo-mechanical treatments is of importance for correct prediction of precipitate/microstructure evolution. The models developed at the Swedish Institute for Metals Research for computer predictions of precipitation or dissolution of microalloying carbonitrides in austenite during thermal or thermo-mechanical treatment are also discussed.

wydzielania, jak również modele matematyczne dla przeliczania zmian mikrostruktury oraz ewolucji wydzieleń podczas walcowania na gorąco, są bezcenne w planowaniu parametrów procesu TMCP. Badania procesu wydzielania z użyciem TEM, dotyczące podwyższenia własności stali poprzez TMCP oraz optymalizacje parametrów tego procesu (temperatury nagrzewania, schematu walcowania i przyspieszonego chłodzenia) są dyskutowane w relacji umocnienia wydzieleniowego, mikrostruktury i własności mechanicznych stali typu HSLA, z mikrododatkami Ti, V lub Nb. Modelowanie matematyczne zachowania się stali podczas obróbki cieplno-mechanicznej jest bardzo ważne dla dokładnego przewidywania zmian wydzielania oraz mikrostruktury. Modele opracowane w Szwedzkim Instytucie Badań Metali dla przeliczania procesu wydzielania czy też rozpuszczania węglikoazotków w austenicie podczas TMCP są również dyskutowane.

and/or Nb. Computer models for calculation of microstructure evolution (grain size, grain growth, precipitation and flow stress) during heavy plate, strip and long product hot rolling are invaluable for design of TMCP-rolling schedules combining a maximum degree of microstructure refinement with acceptably low rolling loads. Intelligent design of deformation/temperature schedules aims to generate an optimal austenite microstructure and subsequently a fine ferrite/bainite conferring both taughness and strength. A comparison is made of the results of laboratory simulations with full scale industrial plate, strip and long product processing using TMCP practices obtained at various (high and low) finish rolling temperatures with and without application of accelerated cooling/direct quenching.