Grey Iron Casting

Qinhuangdao Zhongwei Precision Machinery Co., Ltd. mainly produces various grades of Grey iron casting, high-quality mechanical parts such as gray iron castings, steel castings, castings of various materials and row numbers, and is a leading casting enterprise in Qinhuangdao City. Our company is equipped with advanced product manufacturing technology and testing methods, pre-furnace analyzer, post-furnace testing equipment, and spectrometer imported from Germany to more accurately analyze the chemical composition and physical properties of castings. The main products are valve castings, locomotive accessories, and various mechanical parts, which are suitable for all walks of life. Diesel engines, compressors, trains, automobiles, elevators, pumps, pump heads, valves, impellers, construction machinery, etc.

Product Dsecription

1. Implementation standards: The company strictly implements ISO9001 & TS 16949 certification.

2. Product material standards: ISO, GB, ASTM, SAE, ISO, EN, DIN, JIS, BS

3.Main processes: sand casting, silica sol investment casting, water glass investment casting,

shell casting,deburring, sand blasting, machining, heat treatment, leak testing, 

surface treatment, etc.

4. Available materials:

Gray iron: ISO standard: 100, 150, 200, 250, 300, 350

Ductile iron: ISO standard: 400-18, 450-10, 500-7, 600-3, 700-2, 800-2

— Other materials: cast iron, cast steel, cast aluminum, cast copper, alloy steel, etc. can be customized according to customer requirements.

According to the country, please check the corresponding national material grade in the table.

Country	Grey iron casting
China	-	HT350	HT300	HT250	HT200	HT150	HT100
Japan	-	FC350	FC300	FC250	FC200	FC150	FC100
U.S.	NO.60	NO.50	NO.45	NO.35	NO.30	NO.20	-
Russia	C40	C35	C30	C25	C20	C15	C10
Germany	GG40	GG35	GG30	GG25	GG20	GG15	-
Italy	-	G35	G30	G25	G20	G15	G10
France	FGL400	FGL350	FGL300	FGL250	FGL200	FGL150	-
U.K.	-	350	300	250	200	150	100
Poland	Z140	Z135	Z130	Z125	Z120	Z115	-
India	FG400	FG350	FG300	FG260	FG200	FG150	-
Romania	FC400	FC350	FC300	FC250	FC200	FC150	-
Spain	-	FG35	FG30	FG25	FG20	FG15	-
Bulgaria	FGG40	FGG35	FGG30	FGG25	FGG20	FGG15	FGG10
Australia	T400	T350	T300	T260	T220	T150	-
Sweden	O140	O135	O130	O125	O120	O115	O110
Hungary	OV40	OV35	OV30	OV25	OV20	OV15	-
Bulgaria	-	Vch35	Vch30	Vch25	Vch20	Vch15	-
(International Organization for Standardization)	-	350	300	250	200	150	100
(COPANT)	FG400	FG350	FG300	FG250	FG200	FG150	FG100
Netherlands	-	GG35	GG30	GG25	GG20	GG15	-
Luxembourg	FGG40	FGG35	FGG30	FGG25	FGG20	FGG15	-
Austria	-	GG35	GG30	GG25	GG20	GG15	-
Country	Ductile Iron casting
China	QT400-18	QT450-10	QT500-7	QT600-3	QT700-2	QT800-2	QT900-2
Japan	FCD400	FCD450	FCD500	FCD600	FCD700	FCD800	-
U.S.	60-40-18	65-45-12	70-50-05	80-60-03	100-70-03	120-90-02	-
Russia	B40	B45	B50	B60	B70	B80	B100
Germany	GGG40	-	GGG50	GGG60	GGG70	GGG80	-
Italy	GS370-17	GS400-12	GS500-7	GS600-2	GS700-2	GS800-2	-
France	FGS370-17	FGS400-12	FGS500-7	FGS600-2	FGS700-2	FGS800-2	-
U.K.	400/17	420/12	500/7	600/7	700/2	800/2	900/2
Poland	ZS3817	ZS4012	ZS4505	ZS6002	ZS7002	ZS8002	ZS9002
			5002
India	SG370/17	SG400/12	SG500/7	SG600/3	SG700/2	SG800/2	-
Romania	-	-	-	-	FGN70-3	-	-
Spain	FGE38-17	FGE42-12	FGE50-7	FGE60-2	FGE70-2	FGE80-2	-
Belgium	FNG38-17	FNG42-12	FNG50-7	FNG60-2	FNG70-2	FNG80-2	-
Australia	300-17	400-12	500-7	600-3	700-2	800-2	-
Sweden	0717-02	-	0727-02	0732-03	0737-01	0864-03	-
Hungary	GV38	GV40	GV50	GV60	GV70	-	-
Bulgaria	380-17	400-12	450-5	600-2	700-2	800-2	900-2
			500-2
(International Organization for Standardization)	400-18	450-10	500-7	600-3	700-2	800-2	900-2
(COPANT)	-	FMNP45007	FMNP55005	FMNP65003	FMNP70002	-	-
Finland	GRP400	-	GRP500	GRP600	GRP700	GRP800	-
Netherlands	GN38	GN42	GN50	GN60	GN70	-	-
Luxembourg	FNG38-17	FNG42-12	FNG50-7	FNG60-2	FNG70-2	FNG80-2	-
Austria	SG38	SG42	SG50	SG60	SG70	-	-

5. Available software: Pro/E, Auto CAD, Solidwork.

6. 2D & 3D drawings (Igs, PDF, JPEG, DWG, CAXA, UG, Stp...etc) can also be made according to samples.

7. Production process: sand casting, lost foam casting, water glass lost wax casting, silica sol investment casting, etc.

8. Product weight range: from 0.01kg to 2000kg;

Process Control

1. Process measures for producing high-strength gray iron castings

In recent years, many units have researched and developed the production methods of high-strength gray iron suitable for specific production conditions and different casting requirements (including thin-walled and high-strength gray iron castings). To sum up, there are the following four types.

(1) Strengthening inoculated cast iron:

More scrap steel is added to the charge, and high-quality casting coke is used to obtain molten iron with a discharge temperature greater than 1500 ° C and a high carbon equivalent, and high-strength gray cast iron is obtained by strengthening the inoculation with a high-efficiency inoculant. In the past, the production of inoculated cast iron relied on adding more scrap steel and reducing the carbon content to increase the strength, but this method has poor technological performance and a large tendency to white mouth, especially for thin-walled castings (minimum wall thickness 3~10mm). Modern high-strength inoculated cast iron does not use this method, but relies on high-efficiency inoculants to strengthen inoculation and improve performance. The general method is: the carbon equivalent is about 3.9~4.1%, the temperature is about 1480 °C, and the molten iron is required to be less oxidized. Si-Ca, Cr-Si-Ca, Re-Ca-Ba, Si-Ca, Si-Fe composite, Rare earth compound and other high-efficiency inoculants are used for inoculation treatment. For example, a 5-ton cupola furnace in a factory uses foundry coke, and more than 40% scrap steel is added to the charge. When the total coke ratio is 7, the molten iron temperature is 1520℃~1540℃, and the iron oxide content in the slag is low (1.8~3.0%). After inoculation treatment with special inoculant, when the carbon equivalent is 4.28%, the tensile strength of the test bar can reach 250MPa, the relative strength RG=1.28, HB229, and the pearlite content is greater than 98%. Another example is that a unit increases the superheating temperature of molten iron, and then uses Re-Ca-Ba inoculant to inoculate molten iron, and injects a batch of cylinder head castings. When the carbon equivalent is 3.9~4.05%, the tensile strength is 285~304MPa, The relative strength is RG=1.1~1.21, the graphite shape is good, and no shrinkage and water leakage are found in the hydraulic test after processing.

(2) Synthetic cast iron

The so-called synthetic cast iron process is smelting in an induction furnace. More than 50% of the scrap steel is used in the charge, and the rest is returned iron and iron filings, and the molten iron obtained by carbonization treatment. The advantages of this approach are:

①The furnace department uses a large amount of scrap steel instead of pig iron, which reduces the cost of cast iron;

②The molten iron with low phosphorus content can be obtained to reduce the influence of phosphorus content on shrinkage and leakage defects of thin-walled high-strength gray iron such as cylinder block and cylinder head;

③It can avoid the hereditary influence of pig iron. The cast iron has good graphite shape, high pearlite content and good mechanical properties. At the same equivalent, the strength can be increased by 1 to 2 grades compared with cupola cast iron.

Using the synthetic cast iron process to smelt high-strength gray cast iron to produce the cylinder block, the effect is very good. The production results show that:

①The mechanical properties of the cylinder body cast by the synthetic cast iron smelting process are high. When the carbon equivalent is 4.0%, the tensile strength is greater than 250MPa, which is one grade higher than that of cupola smelting;

②The sensitivity of molten iron section is small, and the hardness distribution of sections with different thicknesses of the cylinder block and the section of the stepped test block is uniform;

③The cast iron has low phosphorus content and less impurities, which overcomes the leakage defect of castings;

④Low cost;

⑤ The smelting process is simple and easy to hold.

(3) Low alloyed inoculated cast iron

Adjust the chemical composition of the original molten iron to achieve a higher carbon equivalent, add a small amount of chromium, copper, molybdenum and other alloying elements in the furnace (or in the bag) to obtain high-temperature low-alloyed molten iron, and then undergo inoculation treatment to obtain fine graphite and pearlescent light. The structure of high volume content and small spacing between sheets can obtain high-strength cast iron. Using this method to produce high-strength gray cast iron is widely used abroad, and the effect is relatively stable. The alloying elements are mostly Cu, Cr, Mo, Ni, etc. The biggest advantage is that the matrix structure of the thin-walled part of the cylinder block and cylinder head can obtain more than 95% pearlite, and the hardness difference is small.

Some units use 0.3~0.7%Cr to inoculate instantaneously, control the ratio of chromium/silicon, and solve the production problem of cylinder block and cylinder head.

(4) Adjusting the conventional chemical composition and proportion of cast iron to obtain high-strength, low-stress gray cast iron Under the condition that the carbon equivalent remains unchanged, appropriately increasing the Si/C ratio is one of the important ways to improve the strength and rigidity of machine tool castings.

By adjusting the chemical composition, especially changing the ratio of silicon/carbon, to make Si/C between 0.5 and 0.9, plus proper inoculation and alloying, high-strength gray iron castings with good comprehensive properties can be obtained.

The rule for the silicon/carbon ratio is:

① Under the same carbon equivalent, the Si/C ratio is high, the tensile strength can be increased by 30~60MPa, the relative strength is high, the relative hardness is low, and the elastic performance is good;

② Under the same carbon equivalent, the Si/C ratio increases, the residual stress tends to decrease, and the stress tendency is also smaller;

③ Increasing the ratio of Si/C, the tendency of white mouth is small, the sensitivity of section is small, but it has no effect on the fluidity and linear shrinkage of molten iron.

The manganese and silicon contents are adjusted so that the Mn content is 0.2-1.3% higher than the Si content, and another high-strength and low-stress cast iron is obtained. Gray cast iron contains Mn in the range of 1.5~3.0%. Increasing the Mn content, especially when the Mn content is greater than the Si content, can significantly refine the eutectic group, and it is easy to obtain D, E type graphite and fine pearlite matrix. In addition, the difference between Mn and Si and the absolute value of Mn in gray cast iron are controlled, so that the difference between Mn and Si is 0~0.5%, and Mn is greater than 2%, and different types of hardening phases can be obtained in gray cast iron. Therefore, by controlling the difference value of Mn, Si, and the absolute value of Mn, high-strength gray cast iron with high mechanical properties, uniform hardness, good compression resistance and good wear resistance can be obtained. This kind of high manganese ash casting is produced in Zhengzhou Textile Machinery Factory and three industries of machine tools, cylinder liners and hydraulic parts, and has achieved good results. Mn=1.7S+0.3% (to ensure that sulfur is completely bound by manganese).

How to reduce the shrinkage tendency of high strength gray cast iron?

High strength and shrinkage have always been a pair of contradictions. The production of high-strength castings has a large shrinkage tendency. If the shrinkage problem cannot be solved well, a large number of shrinkage waste defects will be generated. To solve the problem of material shrinkage, the general principle is to have a higher carbon-silicon equivalent. The process of high carbon silicon equivalent plus alloying is less prone to shrinkage than the low carbon silicon equivalent plus alloying process. Therefore, under the premise of selecting high carbon silicon content, a new technology to improve performance should be developed. The specific measures to reduce shrinkage can be from the following aspects to consider:

(1) The process measures to promote graphitization are the best measures to reduce the shrinkage of molten iron.

Electric furnace smelting: The application of carbonization technology is the key technology to solve the shrinkage of molten iron. Since the graphite precipitation during the solidification of the molten iron produces graphitization expansion, good graphitization will reduce the shrinkage tendency of the molten iron. Therefore, the carburizing technology is the best process.

Since the addition of a carburizer improves the graphitization ability of the molten iron, the shrinkage tendency of the molten iron is smaller when the whole scrap steel smelting process is used to add the carburizer. This is a very important concept change. The traditional concept is that adding more scrap steel will increase the shrinkage tendency of the molten iron, so we are easy to fall into a misunderstanding, not willing to use more scrap steel, but prefer to use more pig iron.

The disadvantage of multi-purpose pig iron is that there are many coarse hypereutectic graphites in pig iron. This coarse graphite is hereditary. If it is smelted at low temperature, the coarse graphite is difficult to eliminate. The coarse graphite is inherited from the liquid state to the solid state. Since the expansion effect that the graphite precipitation should produce is weakened, the shrinkage tendency during the solidification of the molten iron increases, and the coarse graphite will inevitably reduce the performance of the material. Therefore, compared with the carbonization process of scrap steel, the disadvantages of using pig iron in large quantities are:

①Low strength performance. The same ingredients have been tested for comparison, and the performance is half a row lower.

②The tendency to shrink is large. Under the same conditions, the shrinkage is larger than that of the scrap carbonization process.

For electric furnace melting, the core of carburizing technology is the use of high-quality recarburizers. Using the scrap carbonization process, the recarburizer has become the most important link in the carbonization process. The quality of the recarburizer determines the quality of the molten iron. Whether the carburizing process can obtain a good graphitization effect and reduce the shrinkage of the molten iron mainly depends on the recarburizer:

① The recarburizer must be a recarburizer that has undergone high temperature graphitization. .

Only after high-temperature graphitization can carbon atoms change from disordered arrangement to flake arrangement, and flake graphite can become the best core for graphite nucleation and promote graphitization.

②The sulfur content of good recarburizers is very low, and w(S) less than 0.03% is an important indicator.

For cupola smelting: high-temperature smelting is the most critical technical indicator, and high-temperature smelting can effectively eliminate the heritability of coarse graphite in pig iron. High temperature smelting can increase the carburization rate and reduce the amount of pig iron added in the ingredients. The carbon obtained by carburizing has better activity and has better graphitization effect than the carbon brought by adding more pig iron, which is reflected in the casting, that is, the shape of graphite is better and the distribution is more uniform. Good shape of graphite will improve the properties of the material, including cutting performance, while good graphitization effect will reduce the shrinkage tendency of molten iron.

(2) Increase the silicon content of the original molten iron and control the inoculation volume.

Part of the silicon in the gray cast iron is the silicon in the original molten iron, and part is the silicon brought in by the inoculation.

Many people like the low point of silicon in the molten iron, and then inoculate with a large amount of inoculation, which is not scientific: a large amount of inoculation is not advisable, it will increase the shrinkage tendency. The purpose of inoculation is to increase the number of crystalline cores and promote graphitization, and a small amount of inoculation (0.2% to 0.4%) can achieve this purpose. In terms of process control, the inoculation amount should be stable accordingly, and there should be no excessive changes. This requires that the amount of silicon in the original molten iron should be stable accordingly. Increasing the silicon content of the original molten iron can not only reduce the white mouth and shrinkage tendency, but also play the role of silicon solid solution strengthening matrix, but the performance does not decrease. At present, a more scientific approach is to increase the silicon content of the original iron liquid of gray cast iron, and the inoculation amount is controlled at about 0.3%, which can exert the solid solution strengthening effect of silicon, which is beneficial to improve the strength and reduce the shrinkage of the casting.

(3) The method of alloying has a great influence on the shrinkage of molten iron.

Alloying can effectively improve the properties of cast iron, and our commonly used alloying elements are chromium, molybdenum, copper, tin, and nickel.

Chromium: Chromium can effectively improve the performance of gray cast iron, and the performance will always improve with the increase of the addition amount. Chromium has a relatively large tendency to white mouth, which is the most scruples of everyone. If the amount added is too large, carbides will appear. As for how to control the upper limit of the amount of chromium, the upper limit is different for different chromium adding processes. If chromium is added to the original molten iron, the upper limit should not exceed 0.35%. Increasing the amount of chromium in the original molten iron will make the molten iron tend to be white. And the tendency to shrink is increased, which is very harmful.

Another method of adding chromium is not to increase the chromium in the original molten iron, but to add chromium into the molten iron ladle and flush it in by the punching method. This process will greatly reduce the whitening and shrinkage tendency of the molten iron, the same as the previous one. Compared with this process, with the same amount of chromium, the white mouth and shrinkage tendency will be reduced by more than half. In this way of adding chromium, the upper limit of chromium can be controlled to 0.45%.

Molybdenum: The properties of molybdenum are very similar to those of chromium and will not be described in detail. Due to the high price of molybdenum, adding molybdenum will greatly increase the cost. Therefore, molybdenum should be added as little as possible and some chromium should be added.

Adding chromium and molybdenum by punching method is an effective measure to reduce alloying shrinkage.

⑷The influence of molten iron casting temperature on shrinkage.

High temperature molten iron tends to shrink greatly, which is everyone's experience. It is very important to control the pouring temperature within a reasonable range. If the pouring temperature is 20-30°C higher than the reasonable temperature specified by the process, the shrinkage tendency will increase significantly. Pay attention to such a phenomenon in production. An electric furnace without automatic heat preservation function may increase the temperature of molten iron. The pouring temperature of the first ladle of molten iron will be lower, and then the temperature will become higher and higher. If it is not controlled, It is possible to generate shrinkage waste. In production, the first ladle of molten iron should be ironed, and the ironed ladle should be used again, and the pouring temperature of the first ladle of molten iron should be controlled at the lower limit, not at the upper limit, to prevent the temperature from rising continuously. Controlling the pouring temperature in electric furnace smelting is a key measure to prevent shrinkage waste products from castings.

⑸ The oxidation tendency of molten iron cannot be ignored: large oxidation and large shrinkage.

The high tendency of molten iron to oxidize is very harmful, and it will also increase the tendency to shrink. In order to reduce the oxidation of molten iron, cupola smelting should achieve rapid smelting. At present, the advanced electric furnace smelting technology in foreign countries can achieve rapid melting of the added iron material in a few minutes, which greatly shortens the time of the iron material in the high temperature oxidation stage, and the oxidation tendency is greatly reduced. The oxidation is further reduced, so electric furnace smelting can also produce molten iron with low oxidation and low shrinkage. As long as the pouring temperature is strictly controlled, it is also very advantageous to use the electric furnace to produce complex cylinder block and cylinder head castings.

Casting Process

1. Heat treatment: annealing, carbonization, tempering, quenching, normalizing, surface tempering

2. Processing equipment: CNC, WEDM, lathe, milling machine, drilling machine, grinder, etc.;

3. Surface treatment: powder spraying, chrome plating, painting, sandblasting, nickel plating, galvanizing, blackening, polishing, bluing, etc.

Moulds and Inspection Fixtures

1. Mold service life: usually semi-permanent. (except for lost foam)

2. Mold delivery time: 10-25 days, (according to product structure and product size).

3. Tooling and mold maintenance: Zhongwei is responsible for precision parts.

Available Materials List:

Grey iron casting and ductile iron casting

Other materials: cast iron, cast steel, cast aluminum, cast copper, alloy steel, etc. can be customized according to customer requirements.

Quality Control

1. Quality control: the defective rate is less than 0.1%.

2. Samples and trial run will be 100% inspected during production and before shipment, sample inspection for mass production according to ISDO standards or customer requirements

3. Testing equipment: flaw detection, spectrum analyzer, golden image analyzer, three-coordinate measuring machine, hardness testing equipment, tensile testing machine;

4. Provide after-sales service.

5. The quality can be traced back.

Scope of application

1. Engine parts

2. Auto parts

3. Mechanical parts

4. Railway train parts

5. Truck parts

6. Tractor accessories

7. Construction equipment

8. Agricultural equipment

9. Other industrial fields

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