Galvannealed or Galvanneal, Is the result from the combined process of galvanizing and annealing the steel. Galvanneal does not flake off its galvanized coatin when formed, stamped and bent. The very fine matte finish acts like a printer and easily adheres to paint and is very rust proof, only white to dark grey marks appear if it comes in contact with water. Galvanneal sheets offers good paintability, weldability, corrosion resisttance, and formability. It is extensively used in the automotive, signage, electric equipment, and other industries requiring good paintability and long reliable service life.
Galvannealed sheet is carbon steel sheet coated with zinc on both sides by the continous hot-dip process described in production methods. Immediately as the strip exits the coating bath, the molten zinc coating is subjected to an in-line heat treatment that converts the entire coating to a zinc-iron alloy.
Thursday, April 26, 2007
ANNEALING
Annealing, in metallurgy and material science, is a heat treatment wherein the microstructure of a material is altered, causing changes in its poperties such as strength and hardness. It is a process that produces equilibrium conditions by heating and maintaining at a suitable temperature and then cooling very slowly. It is used to induce softness, relieve internal stresses, refine the structure and improve the cold working properties. There are three stages in the annealing process, with the first being the recovery phase, which results in the softening of the metal through removal of crystal defects and the internal stresses which they cause. The second phase is recrystallization, where new grains nucleate and grow to replace those deformed by internal stresses. If annealing is allowed to continue once recrystallization has been completed, grain growth will occur, in which the microstructure starts to coarsen and may cause the metal to have less than satisfactory mechanical properties.
GALVANIZATION
In current use, it typically means hot dip galvanizing, a metallurgical process that is used to coat steel or iron with zinc. This is done to prevent corrosion of the ferrous item; while it is accompalished by non-electrochemical means, it serves as electrochemical purpose.
HOT DIP GALVANIZING is a form of galvanization. It is the process of coating iron or steel with a thin zinc layer, by passing the steel through a molten bath of zinc at a temperature of around 460 °C. When exposed to the atmosphere, pure zinc reacts with oxygen to form zinc oxide, which further reacts with carbon dioxide to form zinc carbonate, a dull grey, fairly strong material that stops further corrosion in many circumstances. Galvanized steel is widely used in applications where rust resistance is needed.
HOT DIP GALVANIZING is a form of galvanization. It is the process of coating iron or steel with a thin zinc layer, by passing the steel through a molten bath of zinc at a temperature of around 460 °C. When exposed to the atmosphere, pure zinc reacts with oxygen to form zinc oxide, which further reacts with carbon dioxide to form zinc carbonate, a dull grey, fairly strong material that stops further corrosion in many circumstances. Galvanized steel is widely used in applications where rust resistance is needed.
Tuesday, April 24, 2007
COLD ROLLING PROCESS
Cold rolling is a metalurgical process in which metal is passed through a pair of rollers at a temperature below its recrystallization temperature. This process hardens the metal, by compressing and stretching the metal crystals. After the rolling process, the metal is annealed by heating it above the recrystallization temperature after every few rollings, to prevent it from becoming brittle and cracking.
HOT ROLLING PROCESS
Hot rolling is primarily concerned with manipulating material shape and geometry rather than mechanical properties. This is achieved by heating a component or material to its upper critical tempearture and then applying controlled load which forms the material to a desired specification or size.
Monday, April 23, 2007
STEEL MAKING PROCESS
Steel is an alloy of iron and carbon. It is produced in two-stage process.
First, iron ore is reduced or smelted with coke and limestone in a blast furnace, producing molten iron which is either cast into pig iron or carried to the next stage as molten iron.
In the second stage, known as steel making, impurities such as sulpur, phosphorus, and excess carbon are removed and alloying elements such as manganese, nickel, chromium and vanadium added to produce the exact steel required.
First, iron ore is reduced or smelted with coke and limestone in a blast furnace, producing molten iron which is either cast into pig iron or carried to the next stage as molten iron.
In the second stage, known as steel making, impurities such as sulpur, phosphorus, and excess carbon are removed and alloying elements such as manganese, nickel, chromium and vanadium added to produce the exact steel required.
STEEL ALLOYING ELEMENTS AND RESULTANT PROPERTIES
Other materials are often added to the iron-caron mixture to tailor the resulting properties.
NICKEL AND MANGANESE
When added in steel, it add to its tensile strength and make austenite more chemically stable.
CHROMIUM
It increases the hardness and melting temperature.
VANADIUM
It also increases the hardness while reducing the effects of metal fatigue.
CHROMIUM AND NICKEL
Lare amount of chromium and nickel (often 18% and 8% respectively) are added to stainless steel so that a hard oxide forms on the metal surface to inibit corrosion.
TUNGSTEN
Tungsten interferes with the formation of cementite, allowing martensite to form with slower quench rates, resulting in high speed steel.
On the other hand Sulphur, nitrogen and phosphorusmake steel more brittle , so these comonly found elements must be removed from the ore during processing.
NICKEL AND MANGANESE
When added in steel, it add to its tensile strength and make austenite more chemically stable.
CHROMIUM
It increases the hardness and melting temperature.
VANADIUM
It also increases the hardness while reducing the effects of metal fatigue.
CHROMIUM AND NICKEL
Lare amount of chromium and nickel (often 18% and 8% respectively) are added to stainless steel so that a hard oxide forms on the metal surface to inibit corrosion.
TUNGSTEN
Tungsten interferes with the formation of cementite, allowing martensite to form with slower quench rates, resulting in high speed steel.
On the other hand Sulphur, nitrogen and phosphorusmake steel more brittle , so these comonly found elements must be removed from the ore during processing.
STEEL
Steel is an alloy element primarily made of iron, with caron conten of .02% to 1.7% by weight.
Carbon and other agent act as hardening agent, preventing the dislocations in iron atom crystal lattice fron sliding past one another.
Varying the amount of alloying elements and their distribution in the steel controls qualities such as the hardness, elasticity, ductility and tensile strength of resultant steel.
Steel with higher carbon content can be made harder and stronger than iron, but is also more brittle. The maximum solubility of carbon in iron is 1.7% by wieght at 1130 °C
Carbon and other agent act as hardening agent, preventing the dislocations in iron atom crystal lattice fron sliding past one another.
Varying the amount of alloying elements and their distribution in the steel controls qualities such as the hardness, elasticity, ductility and tensile strength of resultant steel.
Steel with higher carbon content can be made harder and stronger than iron, but is also more brittle. The maximum solubility of carbon in iron is 1.7% by wieght at 1130 °C
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