China’s scrap, especially stainless steel scrap accumulation is very small, so the development of all or part of molten iron smelting stainless steel is the goal of China’s stainless steel plants, there are 3 factories in the world with molten iron smelting stainless steel. In 2003, TiSTEEL established a three-step production process with molten iron as the main raw material, namely, molten iron pretreatment, desilication, dephosphorization, 30tUHP electric furnace, prefusion alloy, 75TK-OBM-S converter, decarbonization, 80tVOD refining, 80tLF refining, vertical bending square slab continuous caster. Its key equipment hot metal pretreatment was introduced from Japan JFE Group Kawasaki, 75TK-B0M-S converter from Voestcom and 80tVOD from Danieli. The designed stainless steel output of this production line is 55t.
The converter smelting stainless steel has the following characteristics:
Flexible raw materials, not only can use EAF pre-fusion alloy + part of dephosphorized hot iron, but also can use all dephosphorized hot iron smelting stainless steel;
Converter furnace capacity is large, can ensure smooth operation without splashing;
The top gun with gun position control can obtain high decarbonization rate and CO post blowing operation to ensure the thermal energy needs in smelting operation;
The cooling gas flow and pressure at the bottom of the tuyere can be controlled separately to ensure the best cooling and prolong the service life of the tuyere;
Vai-con-temp continuous temperature measuring device is adopted.
Pneumatic slag stopper and IRIS slag measurement system are adopted to reduce excessive slag during steel drawing and ensure smooth OPERATION of VOD in the next process.
Adopt advanced LevelII automatic control system and software model to ensure the automatic control of stainless steel smelting in converter and improve the quality of stainless steel.
The following achievements have been achieved by mastering k-OBM-S converter stainless steel process:
The original design output of K-OBII-S is 350,000 t/a. Since it was put into production in April 2003, the production of stainless steel in that year is 260,500 t. In 2004, k-OBNI-S converter shell replacement car was installed to shorten the replacement time of the furnace shell. After the transformation, the design output of stainless steel is 550,000 t/a.
The life of furnace lining is continuously improved, from about 200 times at the beginning to nearly 700 times at present, and the life of furnace bottom is also continuously improved, from 50 times at the beginning to nearly 300 times at present.
Hydrogen discharge consumption is greatly reduced, the original design of 304 stainless steel smelting hydrogen consumption is 8m3/t, now the whole process of the bottom tuyere with N2 Ar generation, achieved obvious economic benefits.
The two-step production process of 100% dephosphorized molten iron and 100% ferrochrome smelting 400 series stainless steel in converter has been implemented, which greatly reduces the production cost.
Due to the use of dep molten iron smelting stainless steel, the content of P in steel is lower than that of stainless steel smelting with scrap steel As the main raw material, As, Su, Cu and other harmful elements in steel are also greatly reduced.
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