Heat Treatment Technology
1. What is Heat Treatment?
— To bring out the inherent properties of metallic materials
Heat treatment is widely used in metal products all around us and is an indispensable technology in modern industry.
Heat treatment is a technique that humanity has known since ancient times, frequently utilized by blacksmiths. It relates to everyday life, as symbolized by the familiar phrase, "Strike while the iron is hot."
Heat treatment is a manufacturing process that exposes metal to high and low temperatures to draw out its inherent properties. A metal's properties are deeply related to its crystal grain size. To achieve the desired performance, the heated metal is sometimes cooled slowly to relieve internal stress, refine the crystal grain size, and homogenize the microstructure. At other times, the metal is subjected to rapid cooling (quenching) to harden it and increase its strength.
The foundation of modern society is deeply intertwined with heat treatment. The heat treatment technology used in many products around us simultaneously plays a crucial role in guaranteeing product quality. Various steel materials are used in essential products like buildings, roads and bridges, aircraft flying in the sky, cars on the highway, and various machine tools in workshops, and everyday home appliances. These materials undergo various heat treatment techniques, including annealing, normalizing, quenching and tempering, surface hardening, and the latest process of surface modification. Depending on the purpose, heat treatment is skillfully utilized to optimize properties such as a product's strength, wear resistance, fatigue strength, and corrosion resistance.
Furthermore, there are components classified as "critical safety parts", "safety parts", and even "fatal parts" that concern human life. Heat treatment technology holds a vital position in guaranteeing the quality of these parts. Those involved in heat treatment carry out the process with the awareness that every component being treated is a "fatal part." This dedication protects quality and enhances product reliability.
2. Differences Among Iron, Steel, and Cast Iron
— The clear distinction is the Carbon Content
Iron, steel, and cast-iron exhibit diverse properties due to differences in their carbon content.
Carbon is the Most Important Alloying Element
While we commonly refer to cast iron, iron, and steel indiscriminately as "steel products", they are distinct materials. So, what is the clear difference? It is the difference in Carbon (C) content. The carbon content clearly distinguishes them: Iron < 0.02% C, Steel is between 0.02% C and 2.0% C, and Cast Iron > 2.0% C.
The state where solid carbon dissolves into solid γiron, steel, or cast iron is called a solid solution, and the process of two or more elements dissolving together to create a material is called an alloy. Carbon is one of the most important alloying elements. Differences in carbon content allow iron, steel, and cast iron to exhibit various properties, and the technology used to bring out these properties is heat treatment. The representation of the state of an iron-carbon alloy at various temperatures is called the Phase Diagram (or Equilibrium Diagram). Through heat treatment, the metal microstructure and mechanical strength can be changed in various ways.
3. How is Steel Made?
Iron Ore - (Ironmaking Process) → Pig Iron- (Steelmaking) → Steel
Iron accounts for 34.6% of the Earth's total mass. The process of manufacturing iron is called smelting.
In the smelting process, pig iron is made from iron ore in a blast furnace. This pig iron is then turned into steel in a converter and drawn out as steel products using a continuous caster.
To make pig iron:
Steelmaking involves reducing the carbon and impurities in the pig iron to make steel. Converters and electric furnaces are used as melting furnaces in this process.
4. What is the System for Naming Steel Materials?
— The symbols assigned to various steel grades have meaning
The symbols attached to all steel grades indicate the carbon content, alloying element names, or intended application.
— To bring out the inherent properties of metallic materials
Heat treatment is widely used in metal products all around us and is an indispensable technology in modern industry.
Heat treatment is a technique that humanity has known since ancient times, frequently utilized by blacksmiths. It relates to everyday life, as symbolized by the familiar phrase, "Strike while the iron is hot."
Heat treatment is a manufacturing process that exposes metal to high and low temperatures to draw out its inherent properties. A metal's properties are deeply related to its crystal grain size. To achieve the desired performance, the heated metal is sometimes cooled slowly to relieve internal stress, refine the crystal grain size, and homogenize the microstructure. At other times, the metal is subjected to rapid cooling (quenching) to harden it and increase its strength.
The foundation of modern society is deeply intertwined with heat treatment. The heat treatment technology used in many products around us simultaneously plays a crucial role in guaranteeing product quality. Various steel materials are used in essential products like buildings, roads and bridges, aircraft flying in the sky, cars on the highway, and various machine tools in workshops, and everyday home appliances. These materials undergo various heat treatment techniques, including annealing, normalizing, quenching and tempering, surface hardening, and the latest process of surface modification. Depending on the purpose, heat treatment is skillfully utilized to optimize properties such as a product's strength, wear resistance, fatigue strength, and corrosion resistance.
Furthermore, there are components classified as "critical safety parts", "safety parts", and even "fatal parts" that concern human life. Heat treatment technology holds a vital position in guaranteeing the quality of these parts. Those involved in heat treatment carry out the process with the awareness that every component being treated is a "fatal part." This dedication protects quality and enhances product reliability.
— The clear distinction is the Carbon Content
Iron, steel, and cast-iron exhibit diverse properties due to differences in their carbon content.
Carbon is the Most Important Alloying Element
While we commonly refer to cast iron, iron, and steel indiscriminately as "steel products", they are distinct materials. So, what is the clear difference? It is the difference in Carbon (C) content. The carbon content clearly distinguishes them: Iron < 0.02% C, Steel is between 0.02% C and 2.0% C, and Cast Iron > 2.0% C.
| Material | Carbon (C) Content |
|---|---|
| Iron | ~ 0.02% |
| Steel | 0.02% ~ 2.0% |
| Cast Iron | 2.0% ~ |
The state where solid carbon dissolves into solid γiron, steel, or cast iron is called a solid solution, and the process of two or more elements dissolving together to create a material is called an alloy. Carbon is one of the most important alloying elements. Differences in carbon content allow iron, steel, and cast iron to exhibit various properties, and the technology used to bring out these properties is heat treatment. The representation of the state of an iron-carbon alloy at various temperatures is called the Phase Diagram (or Equilibrium Diagram). Through heat treatment, the metal microstructure and mechanical strength can be changed in various ways.
Iron Ore - (Ironmaking Process) → Pig Iron- (Steelmaking) → Steel
Iron accounts for 34.6% of the Earth's total mass. The process of manufacturing iron is called smelting.
In the smelting process, pig iron is made from iron ore in a blast furnace. This pig iron is then turned into steel in a converter and drawn out as steel products using a continuous caster.
To make pig iron:
- Sintered ore, made by mixing powdered iron ore with lime, and coke are charged into the blast furnace.
- High-temperature air is blown into the furnace through the tuyeres, raising the internal temperature to over 2000℃.
- The coke burns, and the sintered ore melts.
- Carbon monoxide, generated by the combustion of the coke, reacts with the oxygen in the iron ore (which exists as iron oxide) at high temperatures. This reaction reduces the iron ore, resulting in molten pig iron.
- Impurities react with the limestone to form slag, which separates from the molten pig iron at the bottom of the furnace due to density differences, and both are removed separately.
Steelmaking involves reducing the carbon and impurities in the pig iron to make steel. Converters and electric furnaces are used as melting furnaces in this process.
- In a converter, oxygen is blown into the molten pig iron, which heats the iron through oxidation and removes carbon. Scrap iron is added to adjust the composition and furnace temperature. Limestone is added to react with impurities, forming slag that separates at the top of the furnace. Other elements are added to achieve the desired composition. The steel produced in the converter is drawn out by a continuous casting machine and then rolled.
- Electric furnaces include arc furnaces and high-frequency induction furnaces. They are often used to manufacture alloy steels or high-purity steels. The composition is adjusted according to the required steel grade after sufficiently separating gas and impurities from the molten steel.
— The symbols assigned to various steel grades have meaning
The symbols attached to all steel grades indicate the carbon content, alloying element names, or intended application.
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