engleski

The influence of Nb content on the mechanical properties of micro alloyed low carbon steels

Niobium Nb micro-alloyed low carbon steel contains small amounts of Nb as an alloying element (0.02-0.1 wt%), which has a significant impact on many material properties. Niobium shows a strong affinity for nitrogen and carbon and causes the formation of niobium carbide and niobium nitride within the structure of the steel which improve the grain refining, retardation of recrystallization, and precipitation hardening [1- 5]. Those precipitates are dispersed in the form of small Nb (CN) precipitates, which are arranged in fine lines [1, 4]. Consequently, the toughness, yield point, and ultimate tensile strength, formability, and weldability of the micro- alloyed steel are increased with a small decrease in elongation and ductility [1- 5]. The mechanical properties of Nb micro-alloyed low carbon steel were researched in the paper. For the purpose of research the low alloyed steels with different Nb content ; 0.035 wt. %Nb and 0.06 wt. %Nb were selected. The tensile test with the combination of digital image correlation (DIC) and thermography were used to study the thermomechanical behavior of materials. The test pieces were cut from the hot rolling strips which were air cooled and thermomechanically treated. The test pieces of low carbon steel were tested for the comparison. The test pieces with the original gauge length L0 of 45 mm, original width b0 of 20 mm were prepared. The tensile test was performed in accordance with ISO 6892-1:2009 at room temperature. Two different strain rates ; 5mm/min and 20 mm/min were applied in order to research the potential of Nb micro-alloyed low carbon steels for improved energy absorption. The highest values of yield strength and tensile strength and the lowest values of elongation were measured for the test pieces with 0.06 wt. %Nb. The strength measured at different strain rates did not change for both Nb micro-alloyed steels and low carbon steel indicating that materials do not show positive strain rate sensitivity.

Nb content ; micro-alloyed low carbon steel ; mechanical properties

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