ИССЛЕДОВАНИЕ ВЛИЯНИЯ МИКРОЛЕГИРОВАНИЯ БОРОМ НА КОРРОЗИОННОЕ ПОВЕДЕНИЕ НИЗКОУГЛЕРОДИСТОЙ КОНСТРУКЦИОННОЙ СТАЛИ В РАЗЛИЧНОМ СТРУКТУРНОМ СОСТОЯНИИ

Abstract

The aim of the work is to study the effect of boron, structural features of the rolled steel of low-carbon steel in hot rolled and thermally hardened states on its corrosion resistance. Investigation of the corrosion resistance of hot-rolled and thermally hardened (quenching and tempering at temperatures of 200-600 jC) low-carbon steel St3sp containing 0.007% B and having no boron additives was carried out on polished samples with constant immersion in room temperature acidic medium, causing corrosion with hydrogen depolarization (1 N solution of H2SO4), and with variable immersion in aggressive media, causing corrosion with oxygen depolarization (in a 3 % NaCl solution). It was found that the atmospheric corrosion rate of hot-rolled low-carbon steel with and without boron is almost the same. It was experimentally established that samples of boron-containing steel (0.007 % B), when tested in a 1 N solution of H2SO4 and when immersed in a 3 % NaCl solution in a thermally hardened state, have a lower corrosion resistance than steel without boron: the maximum corrosion losses were samples hardened and tempered at a temperature of 300 оC. As shown by studies of microstructures using an electron microscope, when tempering 300 оC, hardened boron-containing steel is released, many relatively small inclusions of boron are released that contribute to the so-called structural corrosion. These finely divided inclusions, most of which are identified as Fe2B, are released from the supersaturated solid solution upon cooling and sharply reduce the resistance of steel to atmospheric corrosion. Thus, improving the hardenability of low-carbon steel, boron significantly reduces its corrosion resistance in aggressive environments after quenching and tempering.