The difference between pig iron and cast iron

1. Pig iron: refers to the iron-carbon alloy obtained by smelting iron ore in a blast furnace.
2. Cast iron: iron-carbon obtained by remelting new iron (the blast furnace pig iron mentioned in 1), old pig iron (referring to recycled materials, including risers, scrap cast iron blocks), low-carbon scrap steel and some required iron alloys after remelting alloy. The carbon content is above 2.11% (practical 2.8-4.3%). Low melting point, easy to cast. Also called white cast iron (the fracture is white due to eutectic cementite).
3. Wrought iron: the carbon content is less than 0.008%, that is, to the left of point Q in the iron-carbon phase diagram, the carbon is solid-dissolved in the ferrite. The strength is very low, and it is generally only used as an electromagnet core.
4. Industrial pure iron: carbon content is less than 0.0218%, that is, to the left of point P. Commonly used DT4, etc., are also magnetic materials.
I wonder if you understand? As a digression, the concepts of pig iron and wrought iron are not so strict. The definition of pig iron and wrought iron that people refer to in life is very different from the theoretical definition. It is good for everyone to understand this.

1. Casting pig iron
Pig iron is an iron-carbon alloy with a carbon content of more than 2% (2.11%). Industrial pig iron generally has a carbon content of 2.5% to 4.0%, and contains elements such as Si, Mn, S, and P. It is smelted from iron ore in a blast furnace The product.
Pig iron is divided into iron numbers according to the amount of silicon (Si), grouped according to the amount of manganese (Mn), classified according to the amount of phosphorus (P), and classified according to the amount of sulfur (S).

1) Steelmaking pig iron
The silicon content of steel-making pig iron is not more than 1.7%, and the carbon exists in the form of Fe3C. Therefore, it is hard and brittle, and the fracture is white. It is mainly used as raw material for steelmaking and malleable cast iron. See the table below for steelmaking pig iron.
Pig iron for steelmaking (according to GB717-82)
Iron Number Code L04 L08 L10

2) Cast iron
The silicon content of cast iron is 1.25~3.6%. Carbon mostly exists in the state of graphite. The fracture is gray. Soft and easy cutting processing. Mainly used to produce all kinds of cast iron raw materials such as bed, box, etc. Casting pig iron is shown in the following table:
Cast iron (according to YB/T14–91)
Grade Cast 34 Cast 30 Cast 26 Cast 22 Cast 18 Cast 14
Iron number
Code Z34 Z30 Z26 Z22 Z18 Z14

3) Pig iron for ductile casting
Nodular cast pig iron is also a kind of cast pig iron, but it is low in sulfur and phosphorus. Low sulfur makes carbon fully graphitized in iron. Low phosphorus improves the mechanical properties of pig iron; it is mainly used to produce ductile iron parts with better properties (mechanical properties). Ductile iron is shown in the following table:
Pig iron for ductile iron (according to GB1412-85)
Grade Q10 Q12 Q16
In addition, vanadium-containing pig iron and phosphorus-copper-titanium low-alloy wear-resistant pig iron for casting are also currently used. See the following two tables:
Vanadium-containing pig iron (according to GB5025-85)
Grade Vanadium 02 Vanadium 03 Vanadium 04 Vanadium 05
Iron number
Code F02 F03 F04 F05
Phosphor-copper-titanium low-alloy wear-resistant pig iron for casting (according to GB9949-88)
Iron number NMZ34 NMZ30 NMZ26 NMZ22 NMZ18 NMZ14

2. Cast iron
Cast iron is an iron-carbon alloy with a carbon content of more than 2.11%. It is obtained by remelting cast pig iron (part of steel-making pig iron) in the furnace, and adding ferroalloy, scrap steel, and reheating iron to adjust the composition. The difference with pig iron is that cast iron is secondary processing, mostly processed into cast iron parts. Iron castings have excellent castability and can be made into complex parts, and generally have good machinability. In addition, it has the characteristics of good wear resistance and shock absorption, and low price.
According to the different forms of carbon in cast iron, cast iron can usually be divided into white cast iron, gray cast iron and pitted cast iron.

1) White cast iron
The carbon in white cast iron is all in the form of infiltrated carbon (Fe3C), because the fracture is bright white. Therefore, it is called white cast iron. Because of the large amount of hard and brittle Fe3C, white cast iron has high hardness, high brittleness, and is difficult to process. Therefore, it is rarely used directly in industrial applications, and is only used for a few parts that require wear resistance without impact, such as wire drawing dies, ball mill iron balls, etc. Mostly used as billets for steelmaking and malleable cast iron.

2) Gray cast iron
Most or all of the carbon in cast iron exists as free flake graphite. The fracture is gray. It has good casting performance, good cutting processability, wear resistance, and good wear resistance. In addition, it has simple melting ingredients and low cost. It is widely used in the manufacture of structurally complex castings and wear-resistant parts. Gray cast iron is divided into ferrite-based gray cast iron, pearlite-ferrite-based gray cast iron and pearlite-based gray cast iron according to different matrix structures.
Due to the presence of flake graphite in gray cast iron, graphite is a component with low density, low strength, low hardness, plasticity and toughness tending to zero. Its existence is like a large number of small gaps in the steel matrix, which reduces the bearing area and increases the source of cracks. Therefore, gray cast iron has low strength and poor toughness and cannot be press processed. In order to improve its performance, add a small amount of ferrosilicon, calcium silicon and other inoculants in the molten iron before pouring to refine the pearlite matrix, and the graphite becomes finer and evenly distributed. The cast iron is treated by this inoculation. Inoculated cast iron

3) Malleable cast iron
Malleable cast iron is made of white cast iron blanks made of iron-carbon alloys with low carbon and silicon content, and then subjected to long-term high-temperature annealing treatment to decompose the cementite into flocculent graphite. That is, wrought iron is a kind of graphite Chemically treated white cast iron.
Malleable cast iron is divided into two categories according to the different microstructures after heat treatment; one is black-core malleable cast iron and pearlescent malleable cast iron. The structure of black-core malleable cast iron is mainly ferrite (F) basic flocculent graphite; the structure of pearlite malleable cast iron is mainly pearlite (P) matrix flocculent graphite. The other type is white-core malleable cast iron. The structure of white-core malleable cast iron is determined by the size of the section. The small section is based on ferrite, the surface area of ​​the large section is ferrite, and the core is pearlite and annealed carbon.

4) Ductile iron
Add a certain amount of spheroidizing agent (commonly used ferrosilicon, magnesium, etc.) to spheroidize the graphite in the cast iron before pouring the molten iron (spheroidal graphite iron). Because carbon (graphite) exists in the cast iron matrix in a spherical shape, it improves its splitting effect on the matrix, and the tensile strength, yield strength, plasticity, and impact toughness of ductile cast iron are greatly improved. And has the advantages of wear resistance, shock absorption, good process performance, low cost, etc., it has been widely substituted for malleable cast iron and some cast steel, forged steel parts, such as crankshafts, connecting rods, rolls, automobile rear axles, etc. According to GB1348-88 nodular cast iron grades, it is divided into single casting and attached casting test block; in addition to the above-mentioned several commonly used cast irons, there are wear-resistant white cast iron, chilled cast iron, heat-resistant cast iron, etc. Casting pig iron can change its internal structure, improve and improve its mechanical properties through forging, modification, spheroidization and other methods. Therefore, cast pig iron can be divided into white cast iron, gray cast iron, malleable cast iron, ductile cast iron and special cast iron.