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Struktura i własności mechaniczne blach grubych z niskowęglowej stali C-Mn-V-Nb po regulowanym walcowaniu

Lis A., Lis J., Kolan C.

Hutnik, Wiadomości Hutnicze

2008

Vol. 75, nr 7

362-365

W pracy przedstawiono badania struktury i własności mechanicznych blach grubych 12 mm, 25 mm, 45 mm ze stali niskowęglowej z mikrododatkami Nb i V, po procesie regulowanego walcowania. Określono wielkość ziarna austenitu uzyskiwaną w temperaturach nagrzewania. Ustalono skład fazowy mikro wy dzieleń występujących w badanej stali aż do temperatury nagrzewania 1200 °C. Po procesach walcowania określono średnicę ziarna ferrytu występującego w ferrytyczno-perlitycznej strukturze badanych blach. Szczegółową morfologię struktury opisano na podstawie obserwacji w TEM. Przeprowadzono badanie własności wytrzymałościowych i technologiczną próbę zginania. Na podstawie uzyskanej energii łamania na próbkach Charpy V w zakresie temperatur od 20 °C do -40 °C określono odporność na pękanie.

Structure and mechanical properties of heavy plates thickness 12, 25 and 40 mm after control rolling of low carbon steel microalloyed with Nb and V are presented in this paper. Austenite grain sixe was determined for reheating temperature. Phase composition of precipitates present in steel up to 1200 °C temperature was established. After rolling an average mean ferrite grain diameter was determined in ferrite-pearlite microstructure of the plates. Detailed morphology of the structure was described based on TEM observation. Investigations of the tensile properties and technological bending test were performed. Fracture toughness of the steel was determined from impact energy of Charpy V specimens at 20 °C, 0 °C, -20 °C, -40 °C.

High strength hot rolled and aged microalloyed 5% Ni steel

Lis A. K., Lis J.

Journal of Achievements in Materials and Manufacturing Engineering

2006

Vol. 18, nr 1-2

37--42

Purpose: Purpose of this paper was to give information about low temperature strength and impact CharpyV toughness of low carbon microalloyed 5%Ni bainitic steel after thermomechanical rolling (TMR) or thermomechanical controlled processing (TMCP) and ageing at different temperatures: 580°C/2 h, 640°C/1h and 680°C/1h. Design/methodology/approach: The tensile strength tests were performed at -196, -60 and 20°C and Charpy V samples were broken at -100, -80, -60, -40, -20 and 20°C temperatures. The tensile strength TS, yield strength YS, elongation A5 and reduction of area RA were established from tensile experiments. After TMCP 16 mm steel plate had YS = 730MPa, TS = 950 MPa, A5 = 22,5% and RA = 61% and impact energy > 50 J at -196°C. Findings: The best combination of mechanical properties; yield strength and Charpy V toughness was achieved for steel after TMR and ageing 580°C/ 2h; YS = 800MPa, TS = 900 MPa, A5 = 22.5%, at -1000C KVmin.= 110 J. Research limitations/implications: The precise methodology for retained austenite identification and its amount content determination in the investigated microstructures is still metallographic problem which needs to be resolved. Practical implications: The best combination of yield strength and Charpy V toughness was achieved for steel after TMR and ageing 580°C/ 2h. At liquid nitrogen temperature ultrahigh strength properties were: YS = 1140 MPa, TS = 1280 MPa, A5 = 26%, RA = 55% and KV 122 J at -100°C. Originality/value: The detailed microstructure examination of the steel with optical and mainly scanning transmission electron microscopy was needed to explain its good properties at very low temperature. TRIP effect was observed due to the presence of highly alloyed retained austenite in the microstructure. That type of steel may be used for contemporary military and structural applications working at low temperatures.