RU2461635C1 - Method of steel out-of-furnace processing by calcium - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: steel is run from steel making unit into steel teeming ladle with feeding deoxidising agent, alloying and slag-forming calcium-bearing materials therein, to be jet degassed. Calcium-bearing material represents powder wire with combined filler consisting of mechanical mix of silicocalcium CK15 and metallic calcium in amount of 0.3-1.0 kg/t taken to get calcium content in metal equal to 0.0012-0.0040 wt %. Jet degassing is performed by argon with total flow rate of 0.2-0.5 l/(t*min) for 7 to 10 minutes.

EFFECT: maximum possible removal of nonmetallic inclusions, stabilised casting, higher quality of cast steel.

Description

The invention relates to ferrous metallurgy, in particular to methods for out-of-furnace steel processing.

There is a method of out-of-furnace steel processing in a ladle, including guidance of highly basic slag, deoxidation of steel with aluminum, purging of a metal melt with argon, and introducing calcium-containing materials into the metal [RF Patent No. 2323744, cl. C21C 7/00].

A significant disadvantage of this method of out-of-furnace steel processing is the insufficient degree of purity of the finished steel in the content of non-metallic inclusions.

As a prototype, a method of processing steel in a ladle was selected, including the release of steel from a steelmaking unit into a steel ladle, feeding deoxidizers, alloying and slag-forming materials in the form of calcium-containing materials to the ladle, purging the steel in the ladle with neutral gas [RF Patent No. 2362812, cl. C21C 7/00].

This method does not provide a sufficient degree of purity of the finished steel for the content of non-metallic inclusions for the following reasons:

1. Found in the known method, the technological method of input of calcium-containing materials does not take into account the purity of the filler of the flux-cored wires according to the content of non-metallic inclusions. The filler of the ferro-calcium flux-cored wire is a mechanical mixture consisting of granules of calcium metal (about 40%) and iron powder (about 60%), and the filler of the silico-calcium flux-cored wire is an SK30 silicocalcium alloy containing about 30% calcium, 40 ... 50% silicon, the rest is iron.

When a calculated amount of any of these calcium-containing wires is introduced into the metal, non-metallic inclusions contained in their fillers - in iron or silicocalcium powder - are introduced into the metal, which leads to additional metal contamination.

Thus, the consumption and type of calcium-containing materials do not provide the required purity of steel for the content of non-metallic inclusions.

2. Also, in the known method, the metal is not purged with inert gases after calcium is introduced into the steel, i.e. metal blowing with minimum intensity for maximum removal of non-metallic inclusions from metal to slag.

The problem solved by the invention is to increase the efficiency of the process of refining and modifying liquid steel by treating the metal with a flux-cored wire with a filler consisting of a mechanical mixture of SK15 silicocalcium and calcium metal, as well as creating rational conditions for the removal of non-metallic inclusions.

The desired technical result of the invention is the maximum possible removal of non-metallic inclusions, stabilization of the metal casting process due to the prevention of non-metallic inclusions from sticking to the stopper, improving the quality of cast steel, reducing the consumption of calcium-containing materials.

To do this, in the proposed method of out-of-furnace steel processing with calcium, which includes the release of steel from the steelmaking unit into the steel pouring ladle, feeding deoxidizers, alloying and slag-forming materials to the ladle, purging the steel in the ladle with neutral gas, unlike the closest analogue, a flux-cored wire is used with a calcium-containing material combined filler, consisting of a mechanical mixture of SK15 silicocalcium and calcium metal in an amount of 0.3 ... 1.0 kg / t based on the calculation of calcium content in m etale 0.0012 ... 0.0040%, and metal purging with argon is carried out with a total flow rate of 0.2 ... 0.5 l / (t * min) lasting 7 ... 10 minutes.

The declared type of filler cored wire and limits are selected experimentally. The type of cored wire filler is selected based on the considerations of using materials that are cleaner in content of non-metallic inclusions and to reduce the consumption of cored wire in comparison with the standard technology of using cored wires with fillers SK30 or FC40. The flux-cored wire consumption of 0.3 ... 1.0 kg / t was selected on the basis of obtaining the required calcium content in steel (0.0012 ... 0.0040%). The argon purge intensity of 0.2 ... 0.5 l / (t * min) and the purge duration of 7 ... 10 min after calcium injection were chosen to provide the most favorable conditions for the ascent of non-metallic inclusions.

The use of flux-cored wire with traditional fillers, such as ferrocalcium and silicocalcium, and a decrease in the metal purge time of less than 7 min after calcium input do not allow to provide the required technical result in terms of reducing the content of non-metallic inclusions in steel. An increase in argon purge time of more than 10 min leads to an additional decrease in the temperature of the metal and requires subsequent additional electric heating, which leads to an increase in the duration of out-of-furnace treatment. The calcium content in the metal was selected with the aim of modifying the total amount of formed aluminum oxides. A decrease in the calcium content in the metal of less than 0.0012% does not allow to achieve the required technical result in terms of modifying the aluminum oxides generated during the deoxidation process. With an increase in calcium content of more than 0.0040%, increased wear of the stoppers occurs during casting. With an increase in the argon purge intensity of more than 0.5 l / (t * min), the process of back pulling of non-metallic inclusions from slag to metal will occur, and with a decrease of less than 0.2 l / (t * min), non-metallic inclusions will not have enough inertia to float and transition to slag.

The claimed method of out-of-furnace steel processing was implemented in an oxygen-converter shop for the production of more than 50 melts of pipe steel grades.

Metal smelting was carried out in 370 tons of oxygen converters. Metal processing was carried out at the ladle furnace No. 2. After obtaining the required chemical composition, the metal was treated with cored wire with a combined filler, consisting of a mechanical mixture of SK15 silicocalcium and calcium metal in an amount of 0.3 ... 1.0 kg / t (by filler). At the end of the calcium injection, a soft metal purge was carried out with argon with an intensity of 0.2 ... 0.5 l / (t * min) lasting 7 ... 10 minutes. The calcium content in the finished metal was 0.0012 ... 0.0040%.

The proposed method of out-of-furnace steel processing allowed to reduce the consumption of calcium-containing wire, metal sorting after rolling by defect - non-metallic inclusions, to exclude oscillations of the stoppers of the intermediate ladle during continuous casting.

Claims (1)

A method of out-of-furnace treatment of steel with calcium, including the release of steel from the steelmaking unit into a steel ladle, feeding deoxidizers, alloying and slag-forming materials in the form of calcium-containing materials to the ladle, purging the steel in the ladle with neutral gas, characterized in that a flux-cored wire is used as a calcium-containing material with a combination filler, consisting of a mechanical mixture of SK15 silicocalcium and calcium metal in an amount of 0.3-1.0 kg / t based on the calculation of calcium content in m Talle 0,0012-0,0040% and purging with argon is carried out steel with a total flow rate of 0.2-0.5 liters / (m · min) 7-10 min duration.