It is customary to say that steel is a general term for steel and iron, but the actual steel and iron are different. The two are mainly divided by the amount of carbon. For the increase of carbon content, it is necessary to use a recarburizer, and a petroleum coke recarburizer[calcined petroleum coke & graphitized petroleum coke] is commonly used.
The carbon content classification standard for steel.
China has used the carbon content of steel as the grading standard for many years. In the national standard for casting carbon steel, regarding the steel grade, chemical composition and mechanical properties, the “ZG” in the grade indicates cast steel, and then The figure indicates the nominal value of the weight fraction of carbon in the steel, expressed in parts per million. Cast carbon steel is classified into three grades according to the phosphorus and sulfur content of its impurity elements, and the grades of grades of phosphorus and sulfur are less than 0.04% (I grade) steel; and the quality of grade II grade steel is less than 0.05%. Less than 0.06% is ordinary (III grade) steel.
1. Low carbon steel: usually C% <0.25%, called low carbon steel, low strength, good plasticity and weldability.
2, medium carbon steel: C% is 0.25 ~ 0.60%, called medium carbon steel, has higher strength, but poor plasticity and weldability.
3, high carbon steel: C%> 0.60%, called high carbon steel. Poor plasticity and weldability, but high strength and hardness after heat treatment.
More than 2% carbon is cast iron, and cast iron is mainly gray cast iron and ductile iron. Recarburizers[CPC & GPC] are often used in the smelting of cast iron.
1. Gray cast iron C%: 2.7%-3.9%. Ordinary gray cast iron is mainly cast iron in which carbon is precipitated in the form of flake graphite. Gray cast iron is widely used. In the total output of various types of cast iron, gray cast iron accounts for more than 80%.
2. Ductile iron C%: 3.5% -3.9%, ductile iron is a high-strength cast iron material, its comprehensive performance is close to steel, it is based on its excellent performance, has been successfully used for casting some force complex, strength Parts with high toughness and wear resistance. Ductile iron has rapidly developed into a cast iron material that is second only to gray cast iron and is widely used. The so-called "iron-based steel" mainly refers to ductile iron.
A ductile iron pipe is a type of cast iron that is an alloy of iron, carbon and silicon. Graphite in ductile iron exists in the form of spheres, so the mechanical properties of the material itself are better improved, with the nature of iron and the properties of steel.
Development history of ductile iron
In 1948, A. P. Ganganebin et al. pointed out that magnesium was added to cast iron, followed by ferrosilicon as an inoculant. When the residual magnesium amount was more than 0.04 wt%, spheroidal graphite was obtained. Since then, ductile iron has begun large-scale industrial production.
Development and current status of Chinese ductile iron pipe
The industry of ductile iron pipes in China started in the early 1990s with the strong support of the China Urban Water Supply Association. After nearly 20 years of practical use, its safety and practicability have been widely recognized by the water supply industry. The annual output has reached 2.2 million tons, 11 times that of 1990. Since China is a country with a lack of water resources, there are more than 600 water-scarce cities and more than 200 water-scarce cities. The water supply and water-saving business is in the ascendant, and ductile iron pipes have broad prospects for development.
Ductile iron pipe is a kind of cast iron pipe. The ductile iron pipe is mainly called centrifugal ductile iron pipe. It has the essence of iron, the performance of steel, excellent anti-corrosion performance, good ductility, good sealing effect, easy installation, mainly used for Municipalities, industrial and mining enterprises for water supply, gas transmission, oil transportation, etc., the quality requirements of the cast iron pipe spheroidization level control is 1-3 (spheroidization rate) 80%.
The recarburizer required for the smelting cast iron in the smelting process is usually a graphite recarburizer. According to the requirements of carbon and sulfur content, different carbon and sulfur content recarburizers are selected. The graphite recarburizer sulfur content provided by Foshan Jitian Foundry Co., Ltd. There are 0.3% and 0.05%, the specific indicators are as follows:
Semi-graphite petroleum coke recarburizer:
Fixed carbon (FC) /% : ≥98
Sulfur (S) /% : ≤0.3
Moisture (%) /%: ≤0.5
Ash (A)/% : ≤0.8
Volatile (V) /%: ≤0.8
Nitrogen (N) /%: ≤0.2
Particle size Remarks: 0-1mm 0-2mm 0-3mm 0.5-2mm 2-8mm 8-30mm (produced according to customer requirements)
graphitized petroleum coke recarburizer:
Fixed carbon (FC) /% : ≥98.5
Sulfur (S) /%: ≤0.05
Moisture (Mad) /% : ≤0.5
Ash (A)/%: ≤0.8
Volatile (V) /%: ≤0.8
Nitrogen (N) /%: ≤0.03
Particle size Remarks: 0-2mm 1-5mm 8-30mm (produced according to customer requirements)
In the transmission and distribution of drinking water, ductile iron pipes have achieved great success in the fields of hydraulics, foundry and metallurgy and have earned a reputation. In order to better serve the protection of drinking water resources in China, Jinhui Casting Co., Ltd. currently covers 30 kinds of spheroidal graphite iron pipes and fittings of DN80-DN2600 in China. The products strictly implement the internal standards of Jinhui Casting Pipe and comply with ISO2531. , EN545 and GB13295 standards.
Although the properties of ductile iron and steel are very different, the quenching of the two is basically the same. The only difference is that the parameters of quenching of ductile iron have little to do with their own cost, including heating temperature, holding time, The cooling rate and so on, and the key depends on the matrix structure of the workpiece. Let's take a look at the temperature setting in the quenching section: When quenching ductile iron, it is concerned with its heating problem because it has a direct effect on hardness. In order to achieve the hardness of the workpiece, its quenching temperature is generally 800-900 ° C, which will have a negative impact if it is too low or too high.
The advantage of ductile iron pipe is that it is a material between rigidity and elasticity, which is the advantage to ensure the safe transfer of industrial water. Industrial water pipelines must take into account the external loads caused by soil backfilling and transportation. Therefore, it is particularly important to select pipes with excellent mechanical properties to avoid the impact of production leakage and water stop events. The high-performance Jinhui ductile iron pipe allows the conditions for burying and backfilling to meet minimum requirements and does not require welding operations, thus achieving safety and investment savings.