Abstract
Physicochemical characteristics of the nitrogen-alloyed steel melt of the 04Kh20N6G11M2AFB grade (nitrogen content 0.47–0.49%) are investigated by using the torsional vibration method of a crucible with metal in the atmosphere, which provides a stable nitrogen content during the experiment (80% nitrogen and 20% helium). Using the method sensitivity to the aggregate state of the tested substance, at a heating rate of 0.0033–0.0050 K/s, the liquidus temperatures are experimentally determined for the 04Kh20N6G11M2AFB steel (1660–1666 K) and low nitrogen steel ([N] = 0.063%) with the identical content of other elements (1685–1690 K). These results make it possible to recommend the value of the coefficient –60 K/% [N] for the calculated assessment of nitrogen influence on the liquidus temperature of complex and high alloy steels. The viscosity of the 04Kh20N6G11M2AFB steel melt is relatively high ((11.5 ± 0.7) ×10–7 m2/s) in comparison with the traditional austenitic steels ((8.2 ± 0.2) × 10–7 m2/s) with a relatively small partial effect of nitrogen. A significant nonequilibrium of the structural state of the 04Kh20N6G11M2AFB steel melt is revealed by the high-temperature viscometry methods. The comparative analysis of polytherms and kinematic viscosity isotherms of the 04Kh20N6G11M2AFB steel melt and its low nitrogen ([N] = 0.063%) analogue makes it possible to conclude that the nitrogen presence in concentrations close to saturation plays a decisive role in the melt nonequilibrium level and low relaxation rate. This is confirmed by the results of special experiments on saturation with nitrogen of low nitrogen steel, in which a sharp increase in nonequilibrium of the melt structural state is recorded when nitrogen concentration in metal reaches the limiting values (0.45–0.50%). There is a potential possibility to increase and stabilize the operational properties of corrosion resistant nitrogen-alloyed steels due to reducing the melt’s structural state nonequilibrium by excluding the excess of limiting values of nitrogen concentrations for the chemical composition considered.
Highlights
Using sensitivity of the method to aggregate state of the test substance, at a heating rate of 0.0033 ÷ 0.0050 K/s, the liquidus temperatures were experimentally determined for 04Kh20N6G11M2AFB steel (1660 ÷ 1666 K) and lownitrogen steel ([N] = 0.063 %) with identical content of other elements
It is shown that the viscosity of the melt of 04Kh20N6G11M2AFB steel has a relatively high level ((11.5 ± 0.7)·10–7 m2/s) in comparison with the traditional ((8.2 ± 0.2)·10–7 m2/s) austenitic steels with a relatively small partial effect of nitrogen
Comparative analysis of polytherms and isotherms of the melt kinematic viscosity for 04Kh20N6G11M2AFB steel and its low nitrogenous ([N] = 0.063 %) analogue made it possible to conclude that the presence of nitrogen at concentrations close to saturation plays a decisive role in the level of non-equilibrium of the melt and low rate of its relaxation
Summary
ИССЛЕДОВАНИЕ ФИЗИКО-ХИМИЧЕСКИХ ХАРАКТЕРИСТИК РАСПЛАВОВ КОРРОЗИОННОСТОЙКИХ СТАЛЕЙ, ЛЕГИРОВАННЫХ АЗОТОМ. Методом крутильных колебаний тигля с металлом в обеспечивающей стабильное содержание азота в металле по ходу эксперимента атмосфере (80 % азота и 20 % гелия) исследованы физико-химические характеристики расплава легированной азотом стали марки 04Х20Н6Г11М2АФБ (марочное содержание азота 0,47 – 0,49 %). Это нашло подтверждение в результате специально поставленных экспериментов по насыщению азотом низкоазотистой стали, в ходе которых зафиксировано резкое возрастание неравновесности структурного состояния расплава с достижением концентрации азота в металле предельных значений (0,45 – 0,50 %). Отмечена принципиальная возможность повышения и стабилизации эксплуатационных свойств коррозионностойких сталей, легированных азотом, за счет снижения неравновесности структурного состояния расплава путем исключения превышения предельных для рассматриваемого химического состава значений концентраций азота. Для теоретической формулировки гарантирующих заданное качество и надежность изделий условий выплавки сталей, легированных азотом, исследованы физико-химические характеристики расплава стали марки 04Х20Н6Г11М2АФБ (марочное содержание азота 0,47 – 0,49 %)
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