Yurui Metallurgical Material

The Cored Wire Technology is Used in the Treatment of Molten Steel in Steel Mills

Ⅰ. Calcium Treatment of Molten Steel

1. Calcium treatment of aluminum killed steel

Calcium (mainly in the form of CaSi alloy) is used to transform the solid Al2O3 and SiO2-Al2O3 produced during aluminum deoxidation into calcium aluminate that is liquid at the casting temperature. In clean steel, these aluminates will be covered with a thin layer of calcium and manganese complex sulfides.

According to different steel grades, the amount of Ca added per ton of molten steel is 0.15-0.5kg.

The success of calcium addition is largely related to the amount of Al203 remaining in the molten steel.

2. Calcium treatment of silicon killed steel

In steel with a carbon content of 0.1% and a silicon content of 0.2%, the oxygen content is usually about 75ppm. By feeding the CaSi cored wire 0.8-1.7kg/t to the molten steel, it can be reduced to 15 -20ppm.

Since there are no wear-resistant alumina inclusions, and as long as the silicate and sulfide inclusions are non-brittle and plastic at the rolling temperature, silicon killed steel can exhibit good workability.

3. Add calcium treatment to avoid clogging of the nozzle

At the casting temperature, alumina, silica, cerium sulfur oxide, and titanium dioxide, which are solid at the casting temperature, may cause blockage of the small diameter nozzle. In the condition of aluminum killed steel, when the aluminum content of molten steel exceeds 0.01%, it will quickly cause the nozzle to block. Adding calcium-containing alloys to molten steel can solve this problem.

Depending on the number of solid inclusions in the molten steel before treatment, 0.3-1.5kg CaSi/t is usually added.

4. Calcium treatment with CaAl wire instead of CaSi wire

For low-silicon steels such as deep drawing steel, thin strip steel, and automotive steel, replacing CaSi alloy cored wire with CaAl alloy cored wire has the following advantages:

  • CaAl alloy is a silicon-free carrier;

  • Because it is alloyed, the vapor pressure of Ca is lower than that of single calcium;

  • Aluminum can be compatible with the most elements in the steel;

  • Aluminum can increase the solubility of calcium in the molten steel.

5. Calcium treatment for CaFe line production of ultra-low silicon steel

Ca30/Fe70 or Ca70/Fe30 alloy cored wire for steel making is used to add calcium to molten steel without any amount of silicon, so it is particularly suitable for deep-drawn steel, some special steels (such as calcium-containing stainless steel, calcium-containing gear steel), and steel with specific physical properties.

Ⅱ. Fine Adjustment of Alloy Composition

1. Carbon increases after the furnace

When producing low-carbon and medium-carbon steel, the average recovery rate of carbon is 68-71%; when producing alloy steel, the recovery rate of carbon reaches 83%.

2. Stainless molten steel with Titanium

When producing stainless steel such as Cr18Ni9Ti, a ferrotitanium wire is used to adjust the titanium content of molten steel, which not only has a high yield but also accurately meets the requirements of technical standards.

Ⅲ. Microalloying

1. Add Titanium to steels like 20CrMnTi

After the molten steel is deoxidized, titanium is added with a ferrotitanium shovel, and the recovery rate of titanium can reach more than 80%.

2. Add boron to 40MnB and 40MnVB containing boron steel and 303, 304, and 316 stainless steel.

After the molten steel is deoxidized and nitrogen-fixed, and then boron is added with a boron-iron wire, the boron recovery rate can be as high as 80%, and the result is stable and accurate.

3. Rare earth can purify molten steel, refine the structure of steel, and control the shape of inclusions. After the molten steel is deoxidized, the rare earth ferrosilicon wire or cerium iron wire is added to the rare earth alloy or cerium, which can stably increase the recovery rate of the rare earth or cerium.

4. Add Niobium to the steel

Compared with the impulse method, adding niobium with ferroniobium wire not only melts the alloy faster, but there is no danger that small pieces of ferroniobium will be wrapped by slag and reduce the efficiency and recovery rate of niobium.

5. Add steel to steel

The addition of barium with cored wire can increase the recovery rate and increase the stability of vanadium addition.

Ⅳ. The Revulcanization of Molten Steel

1. Use a sulfur wire or iron sulfide wire to add sulfur to molten steel to produce sulfur-containing free-cutting steel; the sulfur recovery rate can reach more than 80%, and almost no toxic SO2 is released.

2. Use a sulfur wire or iron sulfide wire to add sulfur to the stainless steel molten steel to change the appearance of vulcanized inclusions and improve machinability.

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