Year1
- 规格：
- 齐全
- 材质：
- GCD370
Iron-carbon alloys with carbon content above. Industrial cast iron generally contains carbon. Carbon mostly exists in the form of graphite in cast iron and sometimes in the form of cementite. In addition to carbon, cast iron also contains elements such as silicon, manganese, phosphorus and sulfur. Alloy cast iron also contains elements such as nickel, chromium, molybdenum, aluminum, copper, boron and vanadium. Carbon silicon is the main element affecting the microstructure and properties of cast iron.
Cast iron can be divided into
① Gray cast iron. High carbon content (carbon mainly exists in the form of flake graphite, the fracture is gray, referred to as gray iron. Low melting point (℃), small shrinkage during solidification, compressive strength and hardness close to carbon steel, good shock absorption. Used to manufacture machine tool beds Cylinder box and other structural parts.
② White cast iron. The carbon silicon content is low. The carbon mainly exists in the form of cementite and the fracture surface is silvery white. It shrinks greatly during solidification and is prone to shrinkage cracks. It has high hardness and brittleness and cannot withstand it. Impact load. It is mostly used as the blank of malleable cast iron and the production of wear-resistant parts.
③ Malleable cast iron. After annealing the white cast iron, the graphite is distributed in a floc-like distribution, referred to as tough iron. Its structure and properties are uniform and wear-resistant. It has good plasticity and toughness. It is used to manufacture parts with complex shapes that can withstand strong dynamic loads.
④ Ductile iron. The precipitated graphite obtained after spheroidizing the molten iron of gray cast iron is in the form of spheroids, referred to as ductile iron. Than ordinary Gray cast iron has higher strength, better toughness and plasticity. It is used to manufacture internal combustion engine automobile parts and agricultural machinery.
⑤ Vermicular graphite cast iron. The precipitated graphite is obtained after creeping treatment of gray cast iron molten iron in the form of worms shape. The mechanical properties are similar to ductile iron. The casting performance is between gray cast iron and ductile iron. Used to manufacture automobile parts.
⑥Alloy cast iron. Ordinary cast iron is added with appropriate amounts of alloying elements (such as silicon, manganese, phosphorus, nickel, chromium) Molybdenum, copper, aluminum, boron, vanadium, tin, etc.) are obtained. The alloying elements change the matrix structure of cast iron and thus have corresponding heat resistance, wear resistance, corrosion resistance, low temperature resistance or non-magnetic properties. It is used to manufacture parts for mining chemical machinery, instrumentation, etc. .
Classification of cast iron
Classification method Classification name description
Fracture color classification
Gray cast iron Most or all of the carbon in this type of cast iron is in the form of free state flake graphite. The fracture surface is dark gray and has certain mechanical properties and good cutting properties. It is widely used in industry
White cast iron White cast iron is an iron-carbon alloy with no or almost no graphite in the structure. Its fracture surface is bright white. It is hard and brittle and cannot be cut. It is rarely used directly in industry to make mechanical parts. Because of its high surface hardness and wear resistance, it is also called chilled cast iron or chilled cast iron
Makou cast iron Makou Cast iron is a kind of cast iron between white cast iron and gray cast iron. Its fracture surface is gray and white pitted. Its performance is poor and rarely used
Chemical composition
Ordinary cast iron means that it does not contain any alloys Elemental cast iron such as gray cast iron, malleable cast iron, ductile iron, etc.
Alloy cast iron is a high-grade cast iron prepared by adding some alloying elements to ordinary cast iron to improve certain special properties. Such as various corrosion-resistant, heat-resistant and wear-resistant Special performance cast iron
Production method and structural properties
Ordinary gray cast iron, see gray cast iron
Breeding cast iron is a modified cast iron based on gray cast iron, also known as modified cast iron. Its strength, plasticity and The toughness is much better than that of ordinary gray cast iron, and the structure is more uniform. It is mainly used to manufacture large castings with high mechanical performance requirements and large changes in cross-sectional dimensions
Malleable cast iron Malleable cast iron is made of white cast iron with a certain composition that has been graphitized and annealed Compared with gray cast iron, it has higher toughness and is also called ductile cast iron. It cannot be forged and is commonly used to make castings that can withstand impact loads
Ductile iron is referred to as ductile iron. It is obtained by adding a certain amount of nodularizing agent and inking agent to the molten iron before casting to promote the crystallization of spheroidal graphite. Compared with steel, except for its slightly lower plastic toughness, it has almost all other properties. It is an excellent material that combines the advantages of steel and cast iron. It is widely used in mechanical engineering
Special performance cast iron This is a cast iron with certain characteristics according to its use. The difference can be divided into wear-resistant cast iron, heat-resistant cast iron, corrosion-resistant cast iron, etc. Most of them belong to alloy cast iron and are widely used in machinery manufacturing
Cast iron heat treatment process
Stress relief annealing Due to the uneven wall thickness of the casting, effective stress and structural stress will be generated during the heating, cooling and phase transformation processes. In addition, large parts are prone to residual stress after machining. All these internal stresses must be eliminated. The usual heating temperature for stress relief annealing is ℃ and the holding time is then furnace cooling (gray iron) or air cooling (ductile iron). Using this process can eliminate the internal stress of the casting without changing the cast iron structure. If the temperature exceeds ℃ or the holding time is too long, it will cause graphitization and reduce the strength and hardness of the casting.
High-temperature graphitization annealing to remove cast iron white spots
White spots often occur on the surface and thin sections of castings when they are cooled. The white structure is hard and brittle and has poor processing performance and is easy to peel off. Therefore, annealing (or normalizing) must be used to eliminate the white structure. The annealing process is to heat to ℃ and keep warm, then cool the furnace to ℃ and then leave the furnace for air cooling. During the high-temperature holding period, high-temperature cementite and eutectic cementite decompose into graphite, and during the subsequent cooling process, secondary cementite and eutectoid cementite also decompose and graphitize. Due to the decomposition of cementite, the hardness decreases and the machinability is improved.
Normalizing Iron
The purpose of normalizing ductile iron is to obtain the pearlite matrix structure and refine the uniform grain structure to improve the mechanical properties of the casting. Sometimes normalizing is also a structural preparation for surface quenching of ductile iron. Normalizing is divided into high-temperature normalizing and low-temperature normalizing. The high-temperature normalizing temperature generally does not exceed ℃, and the low-temperature normalizing temperature is generally heated to the co-folding temperature range ℃. After normalizing, four people are generally required to handle it to eliminate the internal stress generated during normalizing.
Quenching and tempering of iron
In order to improve the mechanical properties of ductile iron, castings are generally heated to above ℃ (which represents the final temperature formed during heating) and then quenched in oil to obtain a martensite structure. In order to appropriately reduce the quenching The final residual stress should generally be tempered after quenching. The low-temperature tempering structure is tempered martensite plus residual bainite plus spherical graphite. This structure has good wear resistance and is used for parts requiring high wear resistance and high strength. The medium temperature tempering temperature is ℃. The structure after tempering is tempered troostite plus spherical graphite. It is suitable for thick parts that require good wear resistance, certain stability and elasticity. Most of the relevant talents of Boyang Company are concentrated in the Steel Talent Network. The high temperature tempering temperature is ℃. The structure after tempering is tempered Soxhlet plus spherical graphite, which has a good combination of toughness and strength. The structure after tempering is ℃. The structure after tempering is tempered Soxhlet plus spherical graphite, which has a good combination of toughness and strength. Therefore, it is widely used in production.
Multi-temperature quenching of iron
After isothermal quenching, ductile iron can obtain high strength and good plasticity and toughness. The main consideration for the selection of multi-temperature quenching heating temperature is: The original structure is completely transformed without remaining and grain growth is avoided. The heating temperature is generally above ℃ and the isothermal treatment temperature is ℃ to ensure that the lower bainite structure with comprehensive mechanical properties is obtained. After isothermal quenching of rare earth magnesium aluminum ductile iron. But it should Pay attention to adding a tempering process after isothermal quenching.
Surface quenching
In order to improve the surface hardness, wear resistance and fatigue strength of some castings, surface quenching can be used. Both gray cast iron and ductile iron castings can be surface quenched. Quenching. Generally, high (medium) frequency induction heating surface quenching and electrical contact surface quenching are used. [Sales hotline Fang Yan]
Learn heat treatment
For castings that require surface wear resistance or oxidation and corrosion resistance, similar methods can be used Chemical heat treatment processes for steel such as gas soft chlorination, chlorination, boronization, sulfurization, etc.
Gray cast iron
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Ductile Iron
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