Corrosion mechanism and protection of BOF lining

 BOF smelting is a series of physical and chemical reaction processes under high temperature conditions. In this process, the furnace lining is corroded by a series of strong mechanical, physical and chemical effects. The main mechanism is as following,

1. Mechanical impact erosion.

The operations such as adding scrap steel and mixing molten iron directly face the large-surface furnace lining of the BOF, which produces strong impact, wear and erosion on the large-surface furnace lining, which are the main factors for the corrosion of the refractory lining of the furnace.

2. Physical effects.

During the smelting process, the airflow in the furnace scoured the furnace wall, the furnace cap and other refractory materials, the molten steel and slag melted and washed the furnace lining, and the high temperature reaction during the smelting process caused physical erosion of the furnace lining.

3. Chemical action.

The working layer of the BOF lining is generally made of magnesia-carbon bricks. The magnesia-carbon bricks contain a certain amount of graphitic carbon, which has poor wettability with the slag and can hinder the penetration of the slag into the brick body; the thermal conductivity is good and can greatly improve the thermal vibration resistance of the lining brick, so that the magnesia carbon brick lining life is longer. However, there is a strong oxidizing atmosphere in the BOF furnace. During the smelting process, high-temperature oxidizing gas will oxidize and remove part of the carbon in the brick, causing the brick structure to become loose and brittle, which will be lost and eroded by the flue gas and fluid.

Article Source: Corrosion mechanism and protection of BOF lining
Company name: Henan Xinmi Changxing Refractory Materials Co.,Ltd
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The advantages of AOD refining

 AOD refining method is the abbreviation of Argon Oxygen Decarburization. When refining stainless steel, it blows oxygen into the molten steel at standard atmospheric pressure while blowing inert gases (Ar, N2) to reduce the partial pressure of CO to achieve the effect of false vacuum, thereby reducing the carbon content to a very low level, and inhibit the oxidation of chromium in steel.

The advantages of the AOD refining method include:

Its high recovery rate of refined chromium, suitable for the production of low-carbon and ultra-low-carbon stainless steel, easy to control the S content in special steels below 0.005%;
Low requirements for raw materials, cheap high-carbon chromium can be used.
Iron can use 100% recycled scrap to produce stainless steel;
In the high-carbon zone, the blowing speed is fast and the reaction kinetic conditions are superior;
The equipment is simple, the operation is convenient, the infrastructure investment is low, and the economic benefits are significant.

Article Source:The advantages of AOD refining
Company name: Henan Xinmi Changxing Refractory Materials Co.,Ltd
Email: info@cxrefractories.com
Website:http://www.cxrefractories.com

Causes and avoiding methods of open pouring breakout

 

Reason:

(1) The head of the tundish stopper rod and the bowl of the upper water inlet are poorly baked. Because the bowl is low, the baking flame of traditional baking method can't reach the bowl, so the temperature of the bowl is 100 ~ 200℃ lower than that of other parts. The low temperature of molten steel can easily cause cold steel to pad bars and steel flow to get out of control, which leads to insufficient solidification of billet head and breakout during casting.
(2) The paper rope is loose, and molten steel leaks from its gap; Paper rope is damp, and it explodes after meeting molten steel, resulting in cracks, and molten steel leaks from the cracks.
(3) The iron scrap layer is too thin, which causes the molten steel to burn the paper rope and seep out from the gap; If the iron chip layer is too thick, the strength of the blank head will be insufficient and the blank shell will be broken; Iron filings are affected with damp, greasy or sundries, and explode or burn after encountering molten steel. The molten steel burns paper ropes and seeps out from gaps or the strength of billet head is insufficient, and the billet shell is broken.
(4) The traditional way of blocking dummy ingot is to plug the gap between dummy ingot head and crystallizer with paper rope. When molten steel arrives at the station for temperature measurement, iron nail chips with a thickness of 20 ~ 30 mm are evenly spread on the dummy ingot head, and then steel strips are placed on the iron nail chips in a cross way according to regulations. If the steel strip is not placed well, the molten steel will directly wash away the iron filings and paper ropes; If the steel strip is not melted sufficiently, the primary shell will be too thin, which will cause the shell to tear when drawing.
(5) There are the following problems in the operation: the steel flow in the casting is too large, which flushes iron chips or splashes molten steel on the crystal wall and corner joints to form steel clips; The starting speed is too fast, each time it exceeds 0.1m/min, and the primary shell can not bear its tensile force; Foreign matter enters the crystallizer and bites into the primary shell.
(6) There are the following problems in equipment: the dummy bar slides over 20mm; The mold corner gap is too large, exceeding 0.30mm .

In order to prevent steel leakage before pouring, adequate preparation and inspection should be made before pouring, with the following points to be paid attention to:

(1) Check the compaction of dummy ingot head and stacking of cold materials;
(2) Check the alignment between nozzle and crystallizer;
(3) Check whether there is cold steel on the crystallizer copper plate and whether the taper is appropriate;
(4) Check whether the secondary cooling nozzle is unblocked and intact;
(5) Understand the fluidity of molten steel, the temperature state of molten steel, the baking state of tundish nozzle, and the quality of mold powder. The upper water inlet and immersion water inlet shall be fully baked to ensure that the temperature of immersion water inlet is above 800℃ within 2.5 hours, and the temperature of upper water inlet stopper is above 1100℃.
(6) The size of injection flow and the residence time of molten steel in the mold should be determined according to the section of slab.
(7) Once the initial drawing speed is generally kept at 0.5m/min, and the growth rate is slower (0.15m/min), so as to prevent excessive fluctuation of crystallizer liquid level.

Article Source:Causes and avoiding methods of open pouring breakout
Company name: Henan Xinmi Changxing Refractory Materials Co.,Ltd
Email: info@cxrefractories.com
Website:http://www.cxrefractories.com

The advantages of AOD refining

 1. 100% waste stainless steel, or cheap high-carbon ferrochrome and scrap carbon steel can be used as ingredients to make the chromium content in the raw materials meet the requirements of the finished product specifications, which can save most of the time when the electric furnace is used to return to the oxygen blowing process. The micro-carbon ferrochrome or metallic chromium that must be added reduces the cost of raw materials. For example, after a company in the United States adopted the AOD method, the consumption of micro-carbon ferrochromium decreased from 42.75 kg/ton in electric furnace single smelting in 1968 to 4.125 kg/ton. The consumption of silicon-chromium alloy is reduced from 10.125 kg/ton to 2.625 kg/ton, and the total chromium recovery rate reaches 98%, which is more than 10% higher than that of the electric furnace return oxygen blowing method.

2. When the double method of electric furnace and AOD furnace is used to produce stainless steel, only melting and heating are carried out in the electric furnace, so the productivity can be increased by 10-15%. The melting and heating of the electric furnace takes about 2.5-3.0 hours, and the blowing cycle of the AOD furnace is about 70-90 minutes, so two electric furnaces with one AOD furnace can achieve the best match, and the output can be increased by 40-50% compared with the single-refining of the electric furnace.

3. Compared with other secondary stainless steel refining methods, the AOD method has simple equipment and small capital investment, which is about 1/3 of the VOD method.

4. The process control is relatively simple. The vacuum oxygen blowing decarburization method needs to determine the end point through gas phase analysis, and also add a deoxidizer under vacuum, while the AOD method can dilute and decarburize in the atmosphere, and can create slag, measure temperature, and sample, which is much more convenient in comparison. In addition, compared with the electric furnace return oxygen blowing method, the AOD method is easier to smelt ultra-low carbon stainless steel, and can realize process automatic control more stably.

5. The quality of stainless steel smelted by AOD method is not inferior to electric furnace single smelting, and the gas content in the steel is slightly reduced.

We Changxing Refractory Material Co.,LTD is professional manufacturer and supplier of refractory materials for more than 30 years. Our high quality refractory products are good sold to many countries say South Africa, Bangladesh, Indonesia, Malaysia, etc. Shall any interests, welcome to contact us. Our team would make best to be your reliable partner!

Article Source:The advantages of AOD refining
Company name: Henan Xinmi Changxing Refractory Materials Co.,Ltd
Email: info@cxrefractories.com
Website:http://www.cxrefractories.com

 

The difference between AOD furnace and ordinary converter

 1. AOD generally uses side and bottom combined blowing, and ordinary converters generally use top and bottom combined blowing;

2. AOD furnace also has top and bottom blowing;
3. The ordinary converter plays the role of removing carbon and adjusting other components in the process of making ordinary steel. Generally, the molten iron comes out of the converter as molten steel;
4. AOD furnace is mainly used for the continuous refining of ordinary molten steel, and is often used to smelt stainless steel and low carbon steel;
5. For the first decarburization in the converter, one of the main contradictions in stainless steel smelting is that it can decarburize while retaining chromium during further decarburization. AOD and VOD retain chromium in different ways.

We Changxing Refractory Material Co.,LTD is professional manufacturer and supplier of refractory materials for more than 30 years. Our high quality refractory products are good sold to many countries say South Africa, Bangladesh, Indonesia, Malaysia, etc. Shall any interests, welcome to contact us. Our team would make best to be your reliable partner!

Article Source:How to choose refractory bricks for industrial furnace
Company name: Henan Xinmi Changxing Refractory Materials Co.,Ltd
Email: info@cxrefractories.com
Website:http://www.cxrefractories.com

How to choose refractory bricks for industrial furnace

 How to choose refractory bricks

1.It resists high temperature and heat load, does not soften or melt. The refractory bricks are required to have a relatively high refractoriness.
2. Resistance to high temperature heat load, no shrinkage in volume and only uniform expansion. The material is required to have high volume stability, the residual shrinkage and residual expansion should be small, without crystal transformation and serious volume effect.
3. It resists the combined action of high temperature thermal load and heavy load, without losing strength, creeping and collapse. The material is required to have quite high normal temperature strength and high temperature thermal strength, high load softening temperature, and high creep resistance.
4. Resistance to rapid changes in temperature or uneven heating, cracking and no peeling. The material is required to have good thermal shock resistance.
5. It resists the chemical erosion of molten liquid, dust and gas, does not deteriorate and does not corrode. The material is required to have good slag resistance.
6. It resists the impact, impact and abrasion of flame, charge and dust, and the surface is not damaged.
7. The material is required to have high compactness and wear resistance at room temperature and high temperature.
8. It resists the influence of high-temperature vacuum operation and atmospheric changes, does not volatilize and does not damage. The material is required to have low vapor pressure and high chemical stability.
9. In addition, in order to ensure the overall quality of the structure or lining made of block refractory brick. The slag resistance and air tightness are good, and it is easy to construct. It also requires the materials to be neat in appearance, accurate in size, to ensure certain tolerances, and to eliminate impermissible defects. In order to withstand the impact and possible mechanical vibration and extrusion during transportation, the material must have a relatively high normal temperature strength. For some special requirements, sometimes the thermal conductivity and electrical conductivity are also considered.

Article Source:How to choose refractory bricks for industrial furnace
Company name: Henan Xinmi Changxing Refractory Materials Co.,Ltd
Email: info@cxrefractories.com
Website:http://www.cxrefractories.com