DETERMINATION OF NITROGEN AND CARBON INTERSTITIALLY DISSOLVED IN CONTINUOUSLY-ANNEALED STEEL SHEETS BY MEANS OF A FULLY-AUTOMATIC TORSION PENDULUM

A fully automatic torsion pendulum of the Collette type was built to test continuously annealed steels in the thickness range between 0.15 and 0.4 mm for their contents of dissolved nitrogen and carbon. The influence of composition and production conditions on unalloyed steels which had been annealed commercially and in the laboratory were investigated. With an increase in the total carbon and aluminium contents, the percentages of dissolved nitrogen and carbon decrease, whereas higher nitrogen contents resulted in an increase of the percentages dissolved. A higher coiling temperature of the hot band leads to a decrease in the dissolved nitrogen due to the formation of AIN but to an increase of the carbon dissolved. As these effects almost compensate each other, the coiling temperature is not a suitable means to influence the aging potential. During continuous annealing, temperatures of more than 750°C results in a decrease of the dissolved nitrogen, which is precipitated as AIN leaving the carbon content nearly unaffected. No major differences were observed when the material was annealed either with or without a subsequent overaging treatment. However, rapid cooling to low temperatures increased the percentages of elements dissolved.