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How to make ingredients and the requirements of chemical composition content of raw materials

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How to make ingredients and the requirements of chemical composition content of raw materials

When selecting raw materials before batching, the quality requirements of castings should be taken into consideration, and the prices of various materials as well as the inventory should be paid attention to. The recycled materials, scrap steel and scrap iron should be used as much as possible to reduce the overstocking and production cost of castings.

In addition to the above two calculation methods for the proportioning of carbon, the calculation method for the proportion of other elements is the cumulative method.

1. Formula 1 of carbon calculation

C=1.8%+ CL 2    

Where C ——Carbon content of molten iron( %

C L - average carbon content in the charge( %

1.8% -- the (estimated) intermediate value of decarburization and Carburization in the process of preheating, melting, superheating and reduction of the burden in cupola smelting.

This formula is only applicable to the calculation of cupola carbon content, not to the calculation of electric furnace burden, and in order to make the calculation results conform to the smelting situation of the unit's equipment, 1.8% The coefficient should be selected according to the correction of multiple melting experience.

For example: HT250 The carbon content of gray cast iron is three point one 3.4% The carbon content of the new pig iron used 3.8% The carbon content of the recycled material 3.2% Carbon content of steel scrap 0.4%

Estimate the ratio and the amount of new iron added 40% , the amount of recycled material added 35% , scrap addition 25%

C=1.8%+3.8× 0.4+3.2 × 0.35+0.4 × 0.25                    2   × 100%

 =3.17%

2. Cumulative calculation method

That is to add up the amount of each charge input according to the proportion into the composition, calculate the increase and decrease rate in the smelting process, and then adjust it to the range of target composition. The calculation method is applicable to the proportioning of cupola and electric furnace.

The chemical composition content of raw materials is shown in Table 2


Table 2

Name of raw materials

Main chemical components( %

C

Si

Mn

pig iron Z18

three point five

1.6~2.0

zero point five

Recycled material

three point two

one point nine

zero point eight

steel scrap

zero point four

zero point two seven

zero point five

The raw materials mentioned above are used together with ferrosilicon seventy-five , ferromanganese sixty-five , produced in a cupola HT200 The chemical composition requirements of grade gray cast iron are shown in Table 3.

Table 3

component


content %


Brand

C

Si

Mn

P

S

HT200

3.1~3.4

1.8~2.1

0.7~0.9

<0.15

zero point one two

According to practical experience, it should be considered that the carbon increase rate is 10% The burning loss of silicon in charge is 0 15% The burning loss of silicon in ferrosilicon is 20% The burning loss of manganese in the charge is 20% The burning loss of manganese in ferromanganese is 0 25%

The material ratio after adjustment is shown in Table 4

Table 4

raw material

Dosage( %

pig iron Z18

forty-five

Recycled material

forty

steel scrap

fifteen

Cumulative substituted components:

carbon C= 3.5% × 0.45+3.2% × 0.4+0.4% × zero point one five )× one point one (carburization rate) ≈ 3.2%

silicon Si=1.8% × 0.45%+1.9% × 0.4+-0.27% × zero point one five )×( 1-0.15 )(burning rate)   1.37%

manganese Mn= 0.7%  × 0.45+0.8% × 0.4+0.5% × zero point one five )(burning rate)

     ≈ 0.568%

Of course, it is impossible for each batch to be successfully calculated at one time. It is necessary to adjust the proportion of ingredients several times to achieve the desired results, especially for those who have mastered it.

3. The third way to calculate carbon is to make equations

The advantage of the proportioning method is that after mastering the carburizing rate of cupola, it can be batched successfully at one time without several trial blending.

The chemical composition content of raw materials is shown in Table 2;

Casting material HT200 The required range of chemical components is shown in Table 3;

The carburizing rate of cupola is 0 10%

First, determine the amount of recycled material added as 40% Carbon is replaced by recycled material

3.2%× 0.4=1.28%

The total charge should be replaced with carbon (i.e. not Carburized 10% Previous quantity:

3.2% (middle line of required carbon amount) 1 + 10% (amount of carbon increase) ≈ 2.91%

Carbon should be replaced by pig iron and scrap 2.91%-1.28%=1.63%

The equation is as follows:

Let the pig iron content be   x

3.5% (carbon content of pig iron) × x+0.4% (carbon content of scrap) × [(1-40%)-x]=1.63%      x=45%

Scrap amount: (1 - forty %)- forty-five %=15%

For the above ingredients, carbon has achieved the expected purpose, but silicon and manganese still can not meet the requirements. It is necessary to add ferrosilicon and ferromanganese. The addition of ferrosilicon, ferromanganese and any other ferroalloys can be obtained by the following formula.

Supplement (%) = required % Alloy content % X yield % × 100%

What is the target line silicon content one point nine five %When silicon is substituted into the charge one point three seven %It's not good zero point five eight %It is necessary to add ferrosilicon to make up the difference, and the amount of ferrosilicon can be calculated by the above formula.

ferrosilicon 75# Supplement (%) = 0.58% 75% × zero point eight × 100%

                      ≈ 1%

The manganese content in the target line should be zero point eight %The manganese added into the furnace charge is zero point five six 8%, not so good zero point two three two It is necessary to add ferromanganese.

ferromanganese 65# Supplement (%) = 0.232% 65% × zero point seven five × 100%

                   ≈ 0.5%

In the production of ordinary cast iron or steel, After mastering the above methods, we can basically guide the production However, in the production of alloy steel, especially high alloy steel, it is also necessary to consider other components that will be substituted when ferroalloy is added in order to ensure that the material has enough alloy content, and how to reduce the production cost.

For example, when using electric furnace to produce "medium carbon multi-element alloy steel" researched by Hefei Cement Research and Design Institute.

The main chemical composition content of medium carbon multi-element alloy steel is shown in Table 1, and the common chemical composition of ferrochromium is shown in the following table:


category

Chemical composition content %

Cr

C

Si

Low carbon ferrochrome

sixty

zero point five

two

High carbon ferrochrome

sixty-two

nine point five

three

In the process of proportioning, the chromium content is taken as the middle line 5% The total amount of two types of ferrochrome in the above table should be added 8% (because the chromium content of low-carbon ferrochrome and high-carbon ferrochrome are close, so they are mixed together to calculate the addition amount), so as to approach the requirements of the central line. Since ferrochrome contains a certain amount of carbon and silicon, the addition of 8% At the same time, it will cause the increase of carbon and silicon. In addition, in order to ensure the chromium content 5% If all high carbon ferrochrome is used, the carbon content must exceed. If all low carbon ferrochrome is used and carbon is adjusted with carburizing agent, the production cost will rise because the price of low carbon ferrochrome is much higher than that of high carbon ferrochrome. In order to ensure the qualified chemical composition and reduce the production cost, low-carbon ferrochrome and high-carbon ferrochrome are used together. In the actual production, when the furnace test results come out (carbon, silicon), to quickly and correctly match the feed ratio, it is really difficult, and often prone to errors in busy, so we should constantly sum up experience, make perfect in the cooked. In order to facilitate the batching, we make a conventional ingredient list as shown in Table 5, which is convenient, fast and accurate.

Table 5

Furnace test

Ferrochrome addition( %

Amount of silicon substituted by FERROCHROME( %

Carbon( %

Low carbon ferrochrome

High carbon ferrochrome

zero point two

four

four

zero point two

zero point three

four

four

zero point two

five

three

zero point four

five

three

zero point one eight

six

two

There are two problems in using the above table( one )Why are there two proportions of high and low carbon ferrochrome in two columns? Although they are all "medium carbon multi-element alloy steel", due to the different casting to be poured, according to the different service conditions, consciously take carbon on-line or off-line. It will be discussed later in this paper. two )As long as the furnace workers pay attention to the feeding quality, the silicon content will not exceed the limit. Test the silicon content before the furnace, add the sum of the amount of silicon replaced by ferrochrome and the difference between the target silicon content and silicon content, and then add ferrosilicon to supplement.

After understanding the basic knowledge and precautions of the above ingredients, although We can guide production However, it is not enough to make the quality of the products more stable, to make the chemical composition of the casting stable in the optimal content range, so as to achieve the best match of the physical properties of the castings and make the best use of the materials, it is still not enough. We need to further understand and understand the following factors:

one )Even for the castings with the same material requirements, due to the differences of casting geometry and service conditions, one of the components should be controlled on the upper line intentionally, or a component should be controlled at the lower line.

For example, the first bin liner and the second bin liner or partition plate of the ball mill. The impact force of the first bin liner is larger than that of the second bin liner. The large diameter ball mill liner bears the big impact force, but the small diameter ball mill liner bears the small impact force. Even if the requirements are "medium carbon multi-element alloy steel" material, but in the batching operation, the carbon content of the former is removed consciously to improve its impact toughness and prevent the workpiece from fracture and failure. The carbon content of the latter should be taken as the upper line to improve its hardness and enhance its wear resistance. Due to its complex geometry, great difference in thickness, many holes and long body length, the partition board has a large stress. Although the impact load is small, its carbon content should be taken down consciously.

two )According to the service condition of the casting, what kind of casting should be taken, what kind of metallographic composition should be taken, and what kind of influence on the metallographic phase of the material? What changes can be caused to the comprehensive physical properties of materials? You should have a clear idea.

For example, the inner sleeve of high chromium bimetallic liner of mud pump used in oil field drilling and the hammer head of crusher used in quarrying plant are all made of high chromium cast iron, and their main components are shown in Table 1. Due to their different working conditions, there are certain differences in the control of their chemical composition. Such as carbon and manganese, in high chromium cast iron, the carbon content is high, the amount of carbide in the gold phase structure is more, the material is relatively hard, the wear resistance is good and the toughness is reduced. Manganese plays a role in stabilizing austenite in high chromium cast iron. We know that austenite is a soft phase with low hardness and good toughness. Only under the condition of strong impact wear can phase transformation occur, which can improve the hardness and wear resistance of high chromium cast iron. The inner sleeve of mud pump liner mainly bears sliding wear, almost no impact wear. It requires high hardness of material and relatively low toughness, so its carbon content should be controlled in the middle and upper line, while the manganese content should be controlled in the middle and lower line. The situation of crusher hammer head is different. It bears strong impact wear in work, and has high requirements for impact toughness and hardness of materials. Wear resistance and impact toughness are a pair of contradictions, and sometimes we have to consider one and lose the other. In order to achieve the best combination of impact toughness and hardness of materials, we need to clarify the relationship between many factors, so we will not discuss it here. Only for the carbon and manganese content of high chromium hammerhead, the carbon content should be appropriately taken from the middle line, while the manganese content should be taken as the upper line.    

Nanjing Qilin Scientific Instrument Group Co., Ltd

Testing Center

2020.07.13

     



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