Changes in Hydrogen Content During Steelmaking

Abstract

Store Steel produces steel grades for spring, forging and engineering industry applications. Steelmaking technology consists of scrap melting in Electric Arc Furnace (EAF), secondary metallurgy in Ladle Furnace (LF) and continuous casting of billets (CC). Hydrogen content during steelmaking of various steel grades and steelmaking technologies was measured. Samples of steel melt from EAF, LF and CC were collected and investigated. Sampling from Electric Arc Furnace and Ladle Furnace was carried out using vacuum pin tubes. Regular measurements of hydrogen content in steel melt were made using Hydris device. Hydrogen content results measured in tundish by Hydris device were compared with results from pin tube samples. Based on the measurement results it was established that hydrogen content during steelmaking increases. The highest values were determined in tundish during casting. Factors that influence the hydrogen content in liquid steel the most were steelmaking technology and alloying elements.Keywords: hydrogen content, pin tubes, tundish, deoxidation StalowniaŠtore Steel produkuje gatunki stali sprężynowych, stali do kucia oraz stali do innych zastosowań przemysłowych. Linia technologiczna obejmuje elektryczny piec łukowy (EAF), rafinację pozapiecową w piecu kadziowym (LF) oraz maszynę do ciągłego odlewania kęsów (COS). Badaniom poddana została zmienność zawartości wodoru w stali w zależności od gatunku stali i wybranej linii technologicznej. Zgromadzono bazę danych w postaci próbek pobieranych z pieca łukowego, pieca kadziowego oraz maszyny COS. Próbki z pieca łukowego oraz pieca kadziowego pobierano za pomocą rurek próżniowych. Przeprowadzano regularnie pomiary zawartości wodoru w stali za pomocą urządzenia Hydris. Mierzoną zawartość wodoru w kadzi pośredniej za pomocą urządzenia Hydris porównywano z zawartością wodoru w próbkach pobranych za pomocą rurek próżniowych. Bazując na opisanych pomiarach stwierdzono wzrost zawartości wodoru w stali w czasie realizowanego procesu stalowniczego. Najwyższe zawartości stwierdzono w kadzi pośredniej urządzenia COS. Czynnikami mającymi największy wpływ na zawartość wodoru w ciekłej stali była zastosowana technologia wytapiania oraz pierwiastki stopowe.

Application of Thermodynamics in Mitigating Wire Rod Chipping During Hot Rolling of Continuously Cast Steel Billets

“…Based on the plant measurements, dissolved nitrogen and hydrogen contents of steel were kept constant at 50 ppm and 5 ppm respectively in calculations. It is evident, the total gas pressure exceeded the threshold pressure ( = 1.05 atm), 7,8) significantly for higher [O] contents of liquid steel, essentially indicating very strong tendency towards formation of gas porosity during billet casting of liquid steels Therefore, present experimental observations were found to be reasonably consistent with the thermodynamic predictions. It can also be seen that steels containing above 30 ppm oxygen are quite prone to gas porosity formation.…”

“…Gas porosities are caused by the evolution and entrapment of dissolved gases during the solidification of metals and alloys. 7,8) These gases may result from several sources: (i) decrease in their solubility on cooling and liquid steel solidi- fication, (ii) reaction of dissolved oxygen and carbon to form CO and (iii) reaction of liquid metal with moisture in lime, alloy additions, ladle and tundish refractory, etc. Primary effects of gas holes and porosity are that they reduce the tensile properties of the finished steels as they act as stress concentrators.…”

“…Dissolved gases viz., hydrogen, oxygen and nitrogen, in liquid steel cause blowholes or gas pores in cast sections. 7,8) During subsequent soaking, blowholes located close to surfaces may get open up and oxidize, leading to surface defects in hot rolled wire rods. Dissolved oxygen and nitrogen contents varied from 24 to 45 ppm and 40 to 52 ppm respectively.…”

“…Value of P sup/excess has been found to be almost insignificant for industrial casting, as there is no nucleation barrier (owing to heterogeneous nucleation of gas bubbles. 7,8) Therefore, condition required for blowhole formation during billet casting:…”

“…Following reactions were considered for calculating the partial pressures of CO, N 2 and H 2 gases in the gas mixtures with progress of solidification. Amongst the above, reactions (6) to (8) are essentially deoxidation/inclusion formation reactions, whereas reactions (9) to (11) are responsible for blowhole formation during liquid steel solidification in the mold. Gradual enrichment of liquid steel with progress of solidification (i.e.…”