Cast iron

Cast iron production in addition to the proper choice of ingredients to be gifted to the organization, the heat treatment is further adjust and improve the matrix structure to enhance the performance of a cast iron important ways. Iron and steel heat treatment of the heat being buried in common, but also different. Cast iron heat treatment in general can not improve the original graphite in the shape and distribution. The grey cast iron, because flake graphite caused by the effects of stress concentration of iron play a leading role in the storm, the gray iron impose the enhanced effect of heat treatment are far less ductile iron and steel as significant. Guyou iron main heat treatment process for annealing, normalizing, and so on. For ductile iron, as a spherical graphite, the base of the fragmented role greatly reduced, through heat treatment will be based organizations to fully play its role, which can significantly improve the mechanical properties of the ball. Therefore, ductile iron like steel, its heat treatment process are annealed, normalizing, conditioning, multi-quenching, induction heating and hardening the surface, such as chemical heat treatment.

The cast iron heat treatment process:

1. Annealing elimination of stress due to uneven casting thickness, heating, cooling and phase transition process will produce stress and stress. Also in large parts of its processed within easy residual stress, all of which are necessary to eliminate stress. Annealing is usually to stress the heating temperature of 500 ~ 550 ?鏍╫lding time for 2 ~ 8 h, and then furnace cold (gray iron) or air-cooled (ductile iron). Using this technology can eliminate the stress of casting 90 to 95 percent, but the cast iron organization does not change. If the temperature exceeds 550 ?鏍痳 holding time is too long, it will cause graphite, to reduce the casting strength and hardness.

2. Elimination of the high-temperature casting white graphite annealing casting cooling, surface and thin cross sections, often produce white. White hard and brittle organizations, poor processing performance, easily peeling off. Annealing to be used (or normalizing) approach to the fight against white organizations. Annealing Process: heated to 550-950 ?鏍﹏sulation 2 ~ 5 h, then cold to furnace 500-550 ?鏍磑air-cooled. In high-temperature insulation, high outbound cementite and eutectic cementite divided into graphite and A, in the subsequent cooling process for the second cementite and eutectoid cementite also decomposition, in the process of graphite. As cementite of decomposition, resulting in hardness decline, thereby enhancing the cutting of.

3. Ductile iron is the iron fireballs normalizing the purpose is to be pearlite matrix organization, and refined grains, uniform organizations, to enhance the mechanical properties of casting. Sometimes the ball is normalizing iron surface hardening in the organization of preparation, normalizing at low temperature and high temperature normalizing normalizing. High-temperature normalizing temperature generally no more than 950 ~ 980 ?娆爈ow-temperature heat to a total of normalizing the general presentation of the temperature range 820 ~ 860 ?娈燗fter normalizing for the general need to deal with four to eliminate at normalizing the stress.

4. Ductile iron quenching and tempering in order to improve the mechanical properties of ductile iron, heated to Afc1 general casting more than 30 ~ 50 ?鏍ˋfc1 heating A representative of the end of a temperature), the insulation after quenching oil, be martensite . In order to appropriately lower after quenching the residual stress, the general should be quenched tempered, low-tempered organizations to increase tempering Markov for residual bainite with spherical graphite. This wear-resistance organizations, and demand for high wear resistance, high-strength parts. Tempering temperature in the temperature of 350-500 ?鏍ter tempering tempering troostite organizations to increase spherical graphite, applicable to the requirements of good wear resistance, a certain validity of the stability and flexibility in thick pieces. High-temperature tempering temperature of 500-60 D ?娆燼fter tempering tempering Soxhlet for organizations to increase spherical graphite, a good combination of strength and toughness of the comprehensive performance, wide application in production.

5. Ball and the use of multi-quenching ductile iron, such as the temperature can be quenched high-intensity, and both plastic and good toughness. Multi-quenching heating temperature of the main consideration so that the original choice of organizations of all A, non-residual F, but also to avoid A grain growth. The general Afc1 heating temperature above 30 ~ 50 ?娆爏uch as temperature temperature of 0 ~ 350 ?鏍磑 ensure access to a comprehensive mechanical properties of the bainite organizations. Mg-Al-iron, and other rare earth temperature quenched ?覡b = 1200 ~ 1400MPa, ??k = 3 ~ 3.6J/cm2, HRC = 47 ~ 51. It should be noted, such as temperature quenched with a tempering process.

6. Hardening the surface of certain items in order to improve the surface hardness, wear resistance and fatigue strength, the surface can be quenched. Ductile iron and gray iron castings to the surface can be quenched. The general high (in) frequency induction heating and hardening the surface, hardening the surface contact.

7. Chemical heat treatment requirements for wear-resistant surface or anti-oxidation, corrosion resistance of the castings, steel can be used similar to the chemical heat treatment process, such as soft chloride gas, chloride, boronizing, seepage, such as sulfur treatment.

Cast iron

Iron (Fe) accounts for more than 95% of the alloy material, while the main alloying elements are carbon (C) and silicon (Si). The amount of carbon in cast irons is 2.1 - 4%, while ferrous alloys with less carbon are denoted as carbon steel by definition. Cast irons contain appreciable amounts of silicon, normally 1 - 3%, and consequently these alloys should be considered ternary Fe-C-Si alloys.

Despite this, the principles of cast iron solidification are understood from the binary iron-carbon phase diagram, where the eutectic point lies at 1154 °C and 4.3 wt% carbon. Since cast iron has nearly this composition, its melting temperature of 1150 to 1200 °C is about 300 degrees lower than the melting point of pure iron. Cast iron tends to be brittle, unless the name of the particular alloy suggests otherwise. The color of a fracture surface can be used to identify an alloy: carbide impurities allow cracks to pass straight through, resulting in a smooth, "white" surface, while graphite flakes deflect a passing crack and initiate countless new cracks as the material breaks, resulting in a rough surface that appears grey.

With its low melting point, good fluidity, castability, excellent machinability and wear resistance, cast irons have become an engineering material with a wide range of applications, including pipes, machine and car parts.

Cast iron

Silicon is essential to making of grey cast iron as opposed to white cast iron. When silicon is alloyed with ferrite and carbon in amounts of about 2 percent, the carbide of iron becomes unstable. Silicon causes the carbon to rapidly come out of solution as graphite, leaving a matrix of relatively pure, soft iron. Weak bonding between planes of graphite lead to a high activation energy for growth in that direction, resulting in thin, round flakes. This structure has several useful properties.

The metal expands slightly on solidifying as the graphite precipitates, resulting in sharp castings. The graphite content also offers good corrosion resistance.

Graphite acts as a lubricant, improving wear resistance. The exceptionally high speed of sound in graphite gives cast iron a much higher thermal conductivity. Since ferrite is so different in this respect (having heavier atoms, bonded much less tightly) phonons tend to scatter at the interface between the two materials. In practical terms, this means that cast iron tends to “damp” mechanical vibrations (including sound), which can help machinery to run more smoothly.

All of the properties listed in the paragraph above ease the machining of grey cast iron. The sharp edges of graphite flakes also tend to concentrate stress, allowing cracks to form much more easily, so that material can be removed much more efficiently.

Easier initiation of cracks can be a drawback once an item is finished, however: grey cast iron has less tensile strength and shock resistance than steel. It is also difficult to weld.

Grey cast iron's high thermal conductivity and specific heat capacity are often exploited to make cast iron cookware and disc brake rotors.