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Reconstruction of an Open-Hearth Plant of the Specialized Metallurgical Works

 

УДК 669.083.4
 
A.N. Smirnov, V.M. Safonov, A.Y. Tsuprun, V.N. Tiunov,
V.I. Zema, V.A. Timofeev, I.N. Salmash
RPC «Donix», JSC NKMZ, OJSC VSW, DonNTU
 
Magazine «Stal'» № 8, 2006

 

Before reconstruction the open-hearth plant of CJSC «Vyksa Steel Works» included three main 250 t open-hearth furnaces (scrap-process without oxygen), each of them was equipped with a tilting spout for tapping into two teeming ladles. According to the technology used on the plant the steel was reduced in the furnace by silicon and manganese, and the final reduction took place during tapping by ferrosilicon and complex alloy SCTA (45 % Si, 15 % Ca, 10 % Ti, 2 % Al) in each of the two ladles.

 

 

To develop the technology and to design the equipment the experts of JSC NKMZ took into account the requirements to the steel quality in the ladle as well as peculiarities and restrictions of the existing plant:

 

  • strong requirements to the chemical composition of the wheel steel, namely close carbon content limits for high-carbon steel (up to 0,03 %), low hydrogen (≤ 1,5 ppm) and total oxygen content (≤ 30 ppm) in the ingot;
  • specific quality of the intermediate product smelted in the open-hearth furnace;
  • on-line processing of all the steel smelted by two open-hearth furnaces of the plant;
  • steel tapping from the open-hearth furnace into two 105 t teeming ladles with the full cutoff of the furnace slag in one of the ladles and its overflow into the other ladle (the heat size after the reconstruction was reduced to 210 t);
  • estimation of the steel tapping regularity shows that the out-of-furnace processing, particularly the metal heating in the teeming ladle, is to be sped up in some heats of the series;
  • restrictions concerning the construction site (the equipment for out-of-furnace processing is situated at the site of the dismantled open-hearth furnace), lack of the working area and a number of «bottle-necks»;
  • the specified design and configuration of the teeming ladle;
  • reconstruction of the teeming inventory due to the for the basic lining of teeming ladles.

According to the route pattern developed for each ladle the melt can experience concurrent as well as sequential processing in the ladle-furnace facility and in the degassing plant (see Figure). Steel processing in the two ladles is ensured by the two-position ladle-furnace facility. The main design peculiarity of the two-position facility is the fixed plant for the arc heating of steel. The teeming ladles are delivered to the plant by two teeming ladle cars.

The following operations are carried out during processing:

 

  • slag skimming from the teeming ladle by the drag-type machine;
  • arc heating of the metal by the three-phase AC two-position ladle-furnace facility;
  • ladle processing of the killed steel in the chamber-type degassing plant;
  • continuous pneumatic stirring of the steel;
  • injection of reagents in the form of the wire into the metal;
  • injection of powder materials in the carrier gas stream.

Guarantee tests were carried out during the first three weeks after the start-up of the ladle-furnace facility. The parameters specified by the contract were obtained: metal heating speed - 4,34 °C/min; energy consumption - 0,47 kWt/(t · °C); graphitized electrodes consumption - 11,6 g/(kWt · hour).

Degassing in the teeming ladle immediately before the ingot casting with forced argon stirring is used to reduce the hydrogen content in the wheel steel.

A well-known method was used to estimate the indifferent gas consumption for vacuum degassing. According to the method the consumption of argon necessary for degassing and the residual pressure in the degassing chamber were determined. The quantity of argon necessary to obtain the specified degassing level after inert-gas degassing (100 Pa and lower) doesn't exceed 5 m³. The hydrogen content in the railroad wheel blanks didn't exceed 1,5 ppm, the nitrogen content made ~ 30-35 ppm.

The modern technology and equipment for out-of-furnace treatment allow to accomplish the main manufacturing operations in the teeming ladle and to reduce the average heat time by more than 20%.

 

 

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