The article is aimed to investigate a shift of transformation temperatures of C-Mn-Al HSLA steel with different cooling rates. The transformation temperatures from austenite to ferrite have been determined by dilatometry using thermal-mechanical simulator Gleeble 1500D. To define the start and finishing temperatures of the austenite-ferrite transformation intersectional method was used. Effect of cooling rate on transformation temperature has been evaluated for 0.17, 1, 5, 10, 15, 20, 25°C.s-1. There was found out that rising the cooling rate results in moving transformation temperature range to lower temperatures. The transformation temperatures have been also compared with temperatures calculated using equations of several authors. Some of them have considered cooling rates only. Cooling rates have effect on final microstructure. The effect has been evaluated by measuring hardness (HV10) relating the cooling rates from 0.17 to 25°C.s-1. Increasing cooling rates resulted in increase of hardness. Moreover, Thermo-Calc software was used to determine the Ae3 and Ae1 equilibrium temperatures. Equilibrium transformation temperatures Ae3-Ae1 were higher than experimentally measured by dilatometric method using Gleeble 1500D.
The aim of present article was to consider the influence of annealing parameters on evolution of microstructure and mechanical properties of dual phase steel. Dual phase steel was annealed according to the three chosen cycles of annealing: into intercritical region (780°C), into austenite region (920°C) and into austenite region (920°C) by subsequently cooling into intercritical region (780°C) with the hold at the temperature of 495°C. Tensile tests of the heat-treated specimens were carried out. The obtained microstructure consists from three phases: ferritic matrix, austenite and martensite. Nanoindentation experiments were performed with the peak load of 19.62 mN for ferrite grains and 0.981 mN for austenite and martensite grains, using a Berkovich tip as an indenter. The nanohardness for ferrite and martensite was 2.5 ±1 GPa and 7.1 ±1 GPa and for austenite the nanohardness varied from 4.1 to 4.5 GPa.
The article aims to investigate the effect of different austenitization temperatures on the hot ductility of C-Mn-Al High-Strength Low-Alloy (HSLA) steel. The thermo-mechanical simulator of physical processes Gleeble 1500D was used for steel hot ductility study. Hot ductility was estimated by measuring the reduction of area after static tensile testing carried out at temperatures in the range 600 °C to 1200 °C with the step of 50 °C. Evaluation of fracture surfaces after austenitization at 1250 °C and 1350 °C with a holding time of the 30 s showed significant differences in the character of the fracture as well as in the ductility. The fracture surfaces and the microstructure near the fracture surfaces of samples at a test temperature of 1000 °C for both austenitization temperatures were analyzed by Scanning Electron Microscopy (SEM), Light Optical Microscopy (LOM), and AZtec Feature analysis (particle analysis of SEM). AlN and AlN-MnS precipitates at grain boundaries detected by the detailed metallographic analysis were identified as the main causes of plasticity trough in the evaluated steel. Moreover, using Thermo-Calc software, it was found that AlN particles precipitate from solid solution below the temperature of 1425 °C.
The article deals with the influence of annealing parameters on evolution of microstructure and mechanical properties of dual phase steel. Dual phase steel was annealed in laboratory conditions according to the three chosen cycles of annealing: into intercritical region (780• C), into austenite region (920 • C) and into austenite region (920 • C) by subsequently cooling into intercritical region (780• C) with the hold at the temperature of 495• C. Simulation of annealing regimes by thermo-mechanical simulator Gleeble was done. The obtained microstructure consists from three phases: ferritic matrix, martensite and martensite/bainite grains. For the microstructure identification the TEM and nanoindentation experiments were performed.Keywords: dual phase steel, microstructure, annealing simulation, TEM observations, nanoindentation method Praca dotyczy wpływu parametrów wyżarzania na zmiany mikrostruktury i właściwości mechaniczne stali dwufazowej C-Mn. Stal dwufazową poddano wyżarzaniu w warunkach laboratoryjnych według trzech wybranych cykli: w zakresie międzykrytycznym (780• C), w obszarze austenitu (920 • C) i w obszarze austenitu (920 • C) ze schładzaniem do zakresu między-krytycznego (780• C) przy temperaturze wytrzymania 495• C. Przeprowadzono symulację schematów wyżarzania przy użyciu symulatora obróbki cieplno-plastycznej Gleeble. Uzyskana mikrostruktura składa się z trzech faz: osnowy ferrytycznej, martenzytu oraz ziaren martenzytu/bainitu. W celu identyfikacji mikrostruktury wykonano badania metodą TEM oraz nanoindentacji.
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