The use of carbon additive in casting

The addition of ash iron scrap steel depends on the purity of scrap and the cool cost of the production plant. Affected by the high cost price of pig iron. Now many enterprises basically do not use pig iron, casting all the use of scrap steel plus a part of the furnace material.

And most enterprises are to control the amount of scrap steel to about 40%. From scrap steel raw materials into the ash iron casting production, carbon increase is the most serious process. Therefore, it is very important to choose to match the carbon-adding agent with the type of scrap steel. Now the quality of carbon-added agents in the market is not aligned. Good carbon enhancement agent can play a stable carbon enhancement, promote absorption effect.

However, the proportion of carbon increase depends on the composition of scrap steel.


Matters needing attention in the casting of ash iron in Ningxia carbon additive 1. The composition of carbon additive in Ningxia should be distinguished by the composition of nitrogen content. With induction furnace adding more than 60%---of scrap steel, smelting synthetic cast iron, the larger the amount of scrap added, the greater the nitrogen content of iron and steel. Because the harmful elements such as titanium, lead and antimony in synthetic cast iron iron liquid are low, low nitrogen carbon additive should be used. If the carbon additive nitrogen content is high, it is easy to make the castings appear nitrogen hole.


Generally speaking, low-end carbon additive nitrogen content is relatively high. Because the content of titanium in iron is very low, it is impossible to use Ti to consume a large amount of nitrogen, so that the casting is easy because the nitrogen content is too high to appear nitrogen hole, fractured nitrogen hole or related defects. This phenomenon, has been in the units I have worked in before, many experts in their published articles have also talked about, the quality of carbon additive is not good to bring them heavy losses, with special emphasis on synthetic cast iron smelting, the key to the use of good quality, low nitrogen content of calcined petcoke.

Many casting friends think that the carbon additive sulfur is higher, will not affect the quality of ordinary gray iron (pregnant cast iron), but the carbon additive sulfur is high, along with the nitrogen will also be very high, resulting in quality problems. 2. International carbon additive signage only high nitrogen, medium nitrogen, low nitrogen three species, carbon additive nitrogen content is a very important indicator! At present, the use of carbon additive in domestic casting has not yet established the standard, ordinary coal, there is no calcined petroleum coke content is very high, generally more than 500-4000PPM (0.05-0.40%). After high temperature calcination of petroleum coke, nitrogen content is generally less than 300PPM, but suppliers in the production of carbon additive, calcination temperature and other control measures, nitrogen content is also different, especially nitrogen content detection, many factories do not have, resulting in factory acceptance is relatively blind, just look at the graphite degree of carbon, to add carbon particles on the white paper writing , Feel comfortable, the stroke is clear or not to judge.
   
The nitrogen content of petcoke carbon additive is less than 100PPM. 3. Of course, a variety of carbon additive in the country is still gradually adapt, especially high-nitrogen carbon additive, involving casting costs, but also in a large number of use, graphite poor petcoke, fine coal and so on, these low-end products for what cast iron smelting use? Is it used for high titanium containing cast iron? Or is the molten iron in the smelting insulation, gas discharge? There is also a need for gradual gain of experience in the future. Graphite is not good carbon additive, add iron, one is low absorption rate, (only up to 40-60%), second, the absorption speed is slow, the third is the furnace to produce more slag. It is easy to make the nitrogen content of molten iron exceed the standard and produce nitrogen hole.

Sometimes there is no large number of stomata defects, of which the reason, estimated and iron in the titanium, pickaxes and other elements related, these elements and nitrogen affinity is strong, I hope you pay attention to, gradually sum up experience. 4. Carbon additive addition method, in the synthesis of cast iron, carbon additive addition is very large, in the electric furnace smelting feeding in the early or medium term can be added, and scrap steel at the same time, and with the addition of silicon carbide. It involves the addition of smelting in the later stage, play pretreatment, increase the core role of graphite, at this time must be added to the low nitrogen content of carbon additive, the amount of addition should not be too much, do not exceed 0.2%, to avoid the thickness of graphite.

Supplemental Carbon additive, the ideal iron temperature of about 1500 degrees, added to the clean liquid surface of the stripping slag, a few minutes later, the temperature is appropriate to come out, do not pay attention to the liquid surface does not absorb the residual carbon additive, because it in the molten iron shock stirring process, can also play a role in gestation.
 
5. High nitrogen content of carbon additive, in the smelting of ash iron, very easy to produce nitrogen hole defects, on the ball iron, nitrogen hole defects also appear, the probability is lower than the gray iron, estimated because the spheroidization inside the rare earth and other degasification elements play a role.

The problem of nitrogen content in gray cast iron 1. Gray iron smelting from cupola to electric furnace, non-synthetic cast iron ingredients, the same raw materials, carbon equivalent, electric furnace iron strength performance is always not as high as cupola, detailed reasons, in the metallurgical principle is different, but there is no information can be learned and introduced, but from the composition of the point of view, you can find different content of trace elements,

In particular, titanium content is different. 2. Now, domestic experts in the Foundry technology conference repeatedly talked about, in the gray iron, nitrogen as an alloying element to treat, so that we gradually realize that the impact of nitrogen alloy elements, titanium, and even zirconium, should pay attention to control.
In cast iron, with the increase of nitrogen content, the strength of cast iron increased, until the content of more than 150PPM appeared stomata, cast iron strength increased a lot.
3. Effect of nitrogen on tensile strength of gray cast iron 4. A large number of synthetic cast iron ingredients in the electric furnace smelting gray iron, to add carbon ingredients, increase the carbon content of molten iron, and bring a significant increase in the content of iron and steel, especially bad carbon additive, nitrogen content is very high, at the same time, a lot of scrap, iron and nitrogen content accumulation, It is also affecting the quality of the castings.

Many articles introduce them in solving nitrogen hole defects, add titanium or zirconium alloy, successfully overcome the nitrogen hole of gray iron castings, but from the point of view of nitrogen increase casting strength, coupled with the current large number of casting enterprises to accurately analyze the nitrogen content of iron and gas is difficult, the final control of molten iron nitrogen in the reasonable content is insufficient, there are also problems.

Ingredients of carbon-added agents 1. The nitrogen content is too high, causing the castings to produce stomata. Nitrogen increased further and fractured nitrogen holes appeared. Of course, the actual casting, smelting process will inevitably have other gases dissolved into iron, once there is hydrogen dissolved, the production of stomatal defects of the nitrogen content to be reduced. Nitrogen content is generally not required to exceed 120PPM. The higher the nitrogen content, the higher the intensity of gray iron, until the appearance of stomata, the intensity suddenly reduced.

Although the hydrogen content acts simultaneously and produces stomatal defects, its allowable content in iron is an order of magnitude lower than the nitrogen content, which mainly causes stomatal defects in gray iron, or nitrogen.

2. Foreign casting procurement customers, more than 10 years ago called for the detection of nitrogen content in gray iron, these customers now ash iron in the nitrogen content testing requirements, more frequent. 3. Nitrogen content has an impact on the performance of gray iron, but many practical conditions are difficult to explain. A. The results of oxygen nitrogen Analyzer analysis are total nitrogen content, while the effect on mechanical properties is dissolved nitrogen, the effect of combined nitrogen is small. B. Most factories test nitrogen content means do not have, occasionally cast steel plant spectrometer has nitrogen channel, can analyze nitrogen, accuracy is problematic. C. Silicon, titanium, zirconium and other trace elements of nitriding, the mechanism of the effect on the performance of gray iron, the principle is not clear. There is insufficient data accumulation and experimental research in production practice. D. Personal experience, titanium higher than 0.05% definitely significantly affects the performance of gray iron.

Zirconium is also severely affected.
Additional content: 1. Grey iron smelting from cupola to induction furnace, simple understanding is the induction furnace smelting time is relatively long, graphite crystallization core in the high temperature less and fewer, easy to form white mouth, the general explanation is that metallurgical quality is not as good as cupola.

However, in particular, there are few detailed theoretical explanations, and there are many theoretical statements on the different content of trace elements in the two smelting equipment. 2. Induction furnace smelting, pig iron and other raw materials in the various elements of burning loss is much less than cupola, that is, the retention of raw materials, especially in pig iron, the harmful elements are titanium, lead, tellurium, and so on.

In order to reduce the influence of harmful elements on iron in pig iron, the casting industry now has more synthetic cast iron process and high purity pig iron material to smelt the molten iron by cupola smelting, which has a large burn loss of various elements. 3. Induction furnace power density configuration is relatively large, to ensure that the smelting time is shortened, that is, to quickly smelting.

(Cangzhou plant 10 tons of smelting takes 3-4 hours). 4. It is strictly forbidden for the high temperature insulation time above the equilibrium temperature to be too long to reduce the reduction of graphite crystallization core at high temperature.

(Silicon dioxide microcrystalline problem). 5. If there is a need to split the molten iron several times in production, the iron is kept in the furnace for too long, then to increase the core of iron and graphite various treatment measures to do "pretreatment" of molten iron. Generally speaking, the large casting workshop, a furnace of molten iron temperature ingredients qualified, are immediately out, or a packet out, or 2-3 packets out, immediately pouring castings. And the assembly line casting workshop, if the furnace configuration is large, to be divided into several times to complete the iron. (20 tons of molten iron pouring.)

10 tons of stove divided into 4 times, waiting more than 1 hours, Southern Factory example, you can see color metallographic photos).
6. Pretreatment operations have a variety of methods: Left part of the Pig Iron, furnace (rust removal, sand removal) or 0.05%-0.1% (high impact graphite thickness) of high-quality carbon-added agents, are added in the late smelting, in order to increase the crystallization core.

7. Iron and water temperature components qualified, ready to come out, add zirconium, barium containing pretreatment agent, or add a small amount of fine particles of metallurgical silicon carbide as a pretreatment agent, and then out, the purpose is also to increase the graphite core. 8. Gray iron cylinder body, cylinder head Casting assembly line workshop, is every time from the large electric furnace out of the molten iron, immediately in the furnace to add the same grade of furnace material, reduce the temperature in the furnace below the equilibrium temperature, and so on the next package of molten iron ready for gestation, and then heat up to the specified temperature out. These same grades of furnace not only reduce the heat preservation temperature in the furnace, but also have the pretreatment effect on iron. Wan Renfang introduced, two auto foundry factory, are so operating.

Otherwise the castings are going to go wrong. 9. Introduction of plant assembly line pouring gray iron 250 cylinder body.
Metallographic photos.
Classification and physical parameters of scrap steel Scrap steel is a generic term for black metal waste in scrap metal recycling. It includes scrap steel, scrap iron, slag steel, oxidized waste and other major categories, there are carbon scrap steel, alloy scrap steel, steel chips, iron chips, oxidation chips, light materials, steel slag and other more than 10 varieties. According to different specifications and quality requirements of reasonable planning, separation of varieties, that is, easy to make full use of, but also conducive to production.
Scrap steel According to the current customary division generally has four categories of more than 10 varieties.

1, scrap steel; 2, scrap iron; 3, oxidized waste; 4, slag steel.
First, the classification of waste steel
1. Carbon Scrap Steel Plate thickness of more than 2mm, wire diameter above 4mm, single weight in more than 0.25 kg of various carbon scrap steel.
 
These include scrap steel, corner residue, steel products, cast steel parts, waste machine parts, steel farm tools, etc., must not be mixed with alloy scrap steel.
2. Alloy Scrap Steel Specification requirements are the same as carbon scrap steel, including a variety of alloy steel edge, mechanical parts, alloy steel castings and so on.
 
Alloy steel should be separated according to a variety of different steel numbers, not mixed with carbon scrap steel.
3. Lightweight material Thickness of less than 2mm of thin sheet edge material, silicon steel sheet, iron barrel, packaging iron, car cab, diameter below 4mm of waste steel wire, wire, wire rope and so on.
 
Tons of yield below 60%, converter steel production refused to eat back, generally similar to lightweight materials, packaging, pressure blocks, such as electric furnace steel production, but converter steel production should be subject to the availability of resources.
4. Steel Scrap
 
Do not mix iron chips, no impurities, no oxidation blocks, no non-ferrous metals, long and long chips separate, carbon steel chips and alloy steel chips separate.
5. Waste Gray Iron
 
Waste gray iron castings, machine bed body, low pressure valve, ingot mold, sandbox, radiator, etc., size block is not divided.
6. Waste White Iron
 
Iron pot, Ploughshare steel mill and other waste white iron castings, size blocks are not divided.
7. Recycled iron (commonly known as Earth Iron)
 
Both high sulfur iron, soil blast furnace smelting out of the compartmentalized pig iron, including soil ingots, iron slag, etc., the size of the block is not divided.
8. Fire Iron
 
After a long period of fire, surface oxidation spoilage of cast iron parts, such as stoves, cinder, smelting tanks and so on.
9. Forged Iron (Masteel)
 
A variety of fittings, wrenches, automotive rear axle and mechanical forging castings.
10. Raw Iron Chips
    Do not mix with steel chips, non-ferrous metals and other impurities, no oxidation agglomeration.
11. Oxidized Iron
 
Rolling mill in the process of rolling steel and steelmaking plant in the cleaning of ingots to fall off the iron scales, iron content reached more than 60%, no impurities, no agglomeration, no non-ferrous metals.
12. Iron Mud
 
Steelmaking plant oxygen top blowing converter blowing out of the furnace dust, grinding plant grinding down the iron mud, iron content in about 55%.
13. Steel Slag
 
The steel content requirement is above 60%, the size is not divided.
14. Primary pressure block
 
Density is greater than 1.5t/m3.
15. Level two pressure block
 
Density is greater than 1t/m3.
16. First Class raw iron scrap pressure block
 
Density is greater than 3t/m3.
17. Level two raw iron scrap pressure block
 
Density is greater than 2t/m3.
18. First-stage hot pressing block
 
Density is greater than 2t/m3, pressure block oxidation burn does not exceed 5%.
19. Level two hot pressing block
 
Density greater than 1.5t/m3, pressure block oxidation over burning no more than 1%-15%.
20. Light Hand Bundles
 
Tighten, loading and unloading car is not loose, not scattered, the size of bundles can be easily filled into the furnace to fill the beach material.

Second, the acceptance standard of furnace scrap steel
 
Furnace Carbon scrap steel includes ordinary carbon scrap steel, carbon structural steel, carbon tool steel and carbon spring steel.
1. Aggregate Scrap Steel
     Thickness of more than 2mm, the length is not limited.
2. Qualified Scrap Steel
 
Thickness of more than 2mm, length less than 700mm.
3. Concentrate Scrap Steel
 
Thickness of more than 4mm, length less than 300mm.
4. Heavy scrap Steel Thickness of more than 10mm, length less than 1000mm, width 400mm below. (Outer profile size ≦1000mmx500mmx400mm).
 
The form is lumpy, such as rail, train axle, large gear, billet, cutting head, cutting tail, steel castings large groove steel, I-steel, etc., are actually judged as heavy scrap steel, the shape of the outer profile size is determined to be super long heavy waste steel.
5. Lightweight material
 
Less than 2mm, filaments below 4mm in diameter and so on.
6. Miscellaneous Iron
 
Refers to waste pot iron, gray mouth iron, white iron, cast iron pipe fittings and so on. 7. Pressure block, fried steel and other with the converter, electric furnace steel production needs to determine the standard.

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