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Control the change of chemical composition of castings during smelting

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scan it! 控制铸件在冶炼过程中化学成分的增减变化 scan it!
发表时间:2019-09-16 14:03【 Popularity: -Published time: 2019-09-16 14:03 [Large Middle Small]

Control the change of chemical composition of castings during smelting


Nanjing Kirin Scientific Instrument Group Co., Ltd. and everyone share with Yang Qunshou's "Controlling the increase and decrease of chemical composition of castings during the smelting process". 产过程中,根据铸件物理性能的要求,正确的配料或调料,严格控制材质的各化学成分含量尤为重要。 In the production process, according to the requirements of the physical properties of the casting, the correct batching or seasoning, and strict control of the content of each chemical component of the material are particularly important.

In production practice, as a smelting technician and furnace worker, batching and seasoning should be a general technical problem that is proficient. But for the newly graduated students and most furnace workers, it is not easy to master systematically and flexibly.

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Target chemical composition

Now most of the castings, according to the requirements of their grades, have made corresponding requirements in the national standard, which can be found in the casting manual.

2.4 甚至直径φ 4.2 的中大型球磨机衬板上,降低了生产成本,取得了良好的经济效益。 However, with the advancement of science and technology, according to the service status of castings, the market needs more castings with different physical properties, and higher requirements for the comprehensive performance and quality of castings. Research institutions have also continuously developed new materials to replace the old Materials, such as the "medium-carbon multi-alloy steel" researched by Hefei Cement Research and Design Institute, have successfully replaced the original ball mill linings and high-manganese steel, and used this material to produce medium and large diameters of φ 2.4 and φ 4.2 The ball mill liner reduces production costs and achieves good economic benefits.

600 × 900 破碎机用的锤头,都是超高铬铸铁,其主要成分见表(一),这些材质的详细化学成分要求,在铸造手册中是查不到的。 In addition, if our factory produces high-chromium bimetal cylinder liners for mud pumps used in foreign oil drilling and hammers for 600 × 900 crushers in quarries , all are ultra-high-chromium cast iron. The main components are shown in Table (1) The detailed chemical composition requirements of these materials cannot be found in the foundry manual.


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  When accepting production products such as the above, if you do not fully grasp the chemical composition requirements of the casting, and you do not know the service status of the casting in detail, you should let users provide the detailed chemical composition requirements and heat treatment processes as much as possible. Of course, as a manufacturer, you must grasp the chemical composition range and physical properties required by your product in as much detail as possible. In order to produce high-quality products that customers are satisfied with.

In short, before producing the ingredients, you should know the target chemical composition of the castings to be sure. The chemical composition of the raw materials refers to the main chemical composition of the fresh iron, scrap steel, and regrind used in the furnace, and the grades or chemical composition contents of ferrosilicon and ferromanganese.


Changes in chemical composition during smelting

It will be a complicated problem to master the changing rules of the chemical composition of various charge materials during the smelting process. Different smelting equipment, such as cupola (hot and cold air) three furnaces, medium frequency induction electric furnace, etc., the chemical composition changes. Even if it is the same furnace, the chemical composition changes during the smelting process are different due to the different materials used for the furnace repair and the different operation methods. Take cupola as an example, hot air and cold air, the height of the wind pressure, the size of the eye diameter, the coke quality and the size of the block, whether the furnace lining material is acidic, neutral or alkaline, the changes in the chemical composition of the material not exactly.


1. Changes in carbon content

)炉料中含碳量高低的不同,碳量的增减率不同。 The change in carbon content can be divided into four types: ( 1 ) the carbon content in the charge is different, and the rate of increase and decrease of the carbon content is different. )炉料中硅、锰含量高低对碳量的影响。 ( 2 ) The effect of the content of silicon and manganese in the charge on the carbon content. )炉温高低和炉气氧化性强弱对碳量的影响。 ( 3 ) The effect of furnace temperature and furnace gas oxidation on the carbon content. )其它因素。 ( 4 ) Other factors.

)炉料的平均含碳愈低,碳向金属中的溶解度愈大,铁水就会发生增碳,废钢用量越大,这种现象越明显。 ( 1 ) The lower the average carbon content of the charge, the greater the solubility of carbon in the metal, and the increase in carbon in the molten iron. The greater the amount of scrap steel, the more obvious this phenomenon. 以上),铁水从焦炭中吸收碳量愈少,而碳的氧化烧损增加,铁水含碳量不仅不增加反而减少。 The higher the average carbon content in the charge (for example, above 3.6% ), the less the molten iron absorbs carbon from the coke, and the oxidative burning of carbon increases, and the carbon content of the molten iron does not increase but decreases. 时,冶炼中铁水的含碳量就基本不再变化了。 If the carbon content in the charge is as high as 3.6 to 3.8% , the carbon content of the molten iron in the smelting will basically not change.

)铁水中含硅量越高,增碳量越少,这是因为硅可以溶解于铁内,降低了碳在铁中的溶解度。 ( 2 ) The higher the silicon content in the molten iron, the less the amount of carbon increase. This is because silicon can be dissolved in iron, which reduces the solubility of carbon in iron. Manganese is the opposite. When the manganese content increases, the carbon content of molten iron increases.

)加大焦炭用量,或者使用的焦炭块度小,都会使增碳量加大,这是由于增加了铁水与焦炭的接触时间和接触面积。 ( 3 ) Increasing the amount of coke, or the smallness of the coke used, will increase the amount of carbon increase, which is due to the increase in the contact time and area of molten iron and coke. The iron material melts into iron droplets and drops. When flowing through the red hot bottom coke, the carbon in the coke will slowly dissolve into the iron droplets, which will increase the carbon content of the molten iron, which is called carbon increasing effect. This effect mainly occurs in the superheated zone and the hearth zone. The longer the contact time of molten iron with coke, the larger the contact area, and the higher the temperature, the more the molten iron will increase carbon. The cupola is equipped with a forehearth, because the molten iron can flow from the hearth into the forehearth in time, so the carbon addition is small. Ovens do not have a front hearth, and there is more chance that molten iron can only exist in the stove and come in contact with coke, so the amount of carbon increase will be greater.

Increasing the temperature in the furnace will cause the carbon to dissolve faster and more in the molten iron, which will increase the carbon significantly. Therefore, if other conditions are unchanged and a hot-air cupola is used, the temperature of the furnace will be increased to increase the amount of carbon added.

There are also factors that reduce carbon in the furnace. For example, when iron droplets are close to the air outlet, or the air volume is very high, when the air pressure is high, the oxygen in the furnace gas will oxidize the molten iron and reduce the carbon content (or decarbonization). Increasing the air volume and the temperature of the molten iron will also promote carbon increase. However, after increasing the air volume, because of the enhanced molten iron oxidation, it also promotes decarburization. However, in this state, the decarburization effect is greater than the carbon increase effect.

)除以上因素之外,还有其它具体因素也影响着碳量。 ( 4 ) In addition to the above factors, there are other specific factors that also affect the amount of carbon.

Increasing the height of the bottom coke will lengthen the overheating distance of the molten iron and increase the temperature of the molten iron, while also promoting the dissolution of carbon into the molten iron. Therefore, when the bottom coke height is too high, the amount of carbon added to cast iron is also large.

If the height of the furnace bottom is high, the distance that the molten iron drops through is short, and the molten iron flows into the front hearth in time, which reduces the contact time with coke and the carbon increase rate is small. On the contrary, the amount of carbon increase is large.

When the charge is too small and the dosage is large, the phenomenon of fast melting speed, rapid drop of molten iron, and small carbon increase is easy to occur. Along with this phenomenon, cast iron parts are also prone to white mouth defects.

When smelting in a cupola furnace, the two contradictory processes of increasing carbon and reducing carbon are carried out simultaneously. There are too many factors affecting the carbon content and it is difficult to determine precisely.

When smelting with an intermediate frequency induction electric furnace, whether it is an acid, neutral or alkaline furnace, the carbon content is burned. If the operation is improper, the carbon loss will be greater. When the furnace temperature reaches the pouring temperature, the power should be reduced in time to keep the pouring hot. With the extension of the high temperature time in the metal liquid in the furnace, the burning loss of carbon increases, and the spontaneous crystal nucleus decreases. A carburizing agent and a relay deoxidizer should be added.


2. Changes in the amount of silicon

)炉衬的属性(酸性、中性或碱性)。 The change in the amount of silicon mainly depends on two factors, ( 1 ) the properties of the furnace lining (acid, neutral or alkaline). )炉温的高低以及在炉内的停留时间。 ( 2 ) The temperature of the furnace and the residence time in the furnace.

2 )作修炉料,即用酸性炉冶炼钢铁时。 Quartz sand (SiO 2 ) is used as the furnace charge, that is, when the steel is smelted in an acid furnace. The amount of silicon burned is not obvious. If the amount of silica sand or quartz powder is small, the amount of silicon will not only decrease, but will increase.

15%计算,硅铁合金中硅的烧损率还要更高一些。 When magnesia (alkaline) or bauxite (neutral) is used to repair the furnace lining, the burning loss of silicon is large, and the burning loss rate can generally be calculated according to 10-15% . Higher.


3. Burning loss of manganese

25%计算,锰铁合金中锰的烧损率还要更高一些。 Regardless of smelting in any furnace, the amount of manganese is burned. The higher the furnace temperature, the longer the molten metal stays in the furnace, and the higher the sulfur content in the molten iron, the higher the burnout rate of manganese and the burnout rate Generally calculated at 15-25% , the burning rate of manganese in ferromanganese alloys is even higher.

In the smelting process, the loss of elements such as copper and molybdenum is very small, and the loss rate can be ignored when batching. Other elements have different degrees of loss.

Nanjing Kirin Scientific Instrument Group Co., Ltd.

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2019.09.16



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