ASTM A105N is a carbon steel material used to make forged steel pipe fittings (such as flanges, valves, joints, etc.). This is one of the common materials we provide to our customers. The N in A105N represents the state of ASTM A105 material after normalizing heat treatment. Normalizing is a common type of heat treatment.
So, what is heat treatment?
Heat Treatment Definition
Heat treatment of metals is a processing process that changes the microstructure and physical properties of metal materials through controlled heating and cooling. Heat treatment aims to improve the mechanical properties of metals (such as hardness, strength, toughness, etc.), change their physical and chemical properties (such as corrosion resistance, conductivity, machinability, etc.), and make them more suitable for specific application requirements.
Basic Process of Heat Treatment
Heat treatment usually includes the following basic steps:
STEP 1 Heating: Heating the metal material to a specific temperature, usually above its phase transformation point, to change its microstructure or dissolve alloying elements.
STEP 2 Soaking: The metal is kept at the target temperature for some time to homogenize its internal structure and ensure that the required phase transformation occurs entirely.
STEP 3 Cooling: Depending on the required properties, different cooling rates (fast cooling, slow cooling, or controlled rate cooling) are used to obtain the desired material properties.
Heat Treatment Types
Heat treatment types, including annealing, normalizing, quenching, tempering, solution annealing, stress relieving, and surface hardening, involve controlled heating and cooling processes to alter a metal’s mechanical properties, such as hardness, strength, and ductility, for specific applications.
| Heat Treatment Type | Abbreviation/Code | Heat Treatment Type | Abbreviation/Code |
| Annealing | AN | Carburizing | CARB |
| Normalizing | N or NORM | Surface Hardening | SH |
| Quenching | Q | Induction Hardening | IH |
| Tempering | T | Flame Hardening | FH |
| Quenching and Tempering | Q&T | Low-Temperature Tempering | LT |
| Solution Annealing | SA or SHT | Medium-Temperature Tempering | MT |
| Aging | AG | High-Temperature Tempering | HT |
| Stress Relieving | SR |
Annealing
Annealing is a process in which a metal material is heated to above the recrystallization temperature (usually 700°C to 900°C), held for a certain period, and then slowly cooled. Its purpose is to reduce the hardness of the material, improve plasticity and machinability, eliminate internal stress, and improve toughness. Annealing is usually applied to carbon steel (such as AISI 1018) and stainless steel (such as 304 and 316). Annealing is often used for cold-rolled steel plates, castings, and welded parts to make them easier to handle during subsequent processing.
Normalizing
Normalizing is when a metal material is heated to above the critical temperature (usually 850°C to 950°C), held for some time, and then cooled in air. The primary purpose of normalizing is to refine the grains, homogenize the structure, improve the strength and toughness of the material, and eliminate internal stress. Normalizing is commonly used for carbon steels (such as 1010 and 1020) and low alloy steels (such as 4130) and is widely used in forgings, structural parts, gears, etc., to improve their mechanical properties.
Quenching
Quenching is when a metal material is heated to an austenitizing temperature (usually 800°C to 900°C) and then rapidly cooled (such as in water, oil, or air). Its purpose is to significantly increase the hardness and strength of the material while increasing wear resistance. Common materials include carbon steel (AISI 1045) and tool steel (D2 and H13). Quenching is often used to manufacture tools, molds, bearings, and springs to enhance service life and wear resistance.
Tempering
Tempering is heating the material below the critical temperature (usually 150°C to 650°C) after quenching and slowly cooling it. Its purpose is to reduce the hardness formed after quenching, improve toughness, reduce brittleness, and eliminate internal stress. Tempering is commonly used for carbon steels (such as AISI 4140 and AISI 4340). This process is widely used for workpieces such as shafts, gears, and mechanical parts that require high strength and a certain degree of toughness.
Quenching and Tempering
Quenching and Tempering is a combined process of quenching the material first and then tempering it. Its purpose is to increase the hardness while maintaining sufficient toughness to obtain highly comprehensive mechanical properties. Commonly used for alloy steels (such as AISI 4140 and AISI 4340), typical applications of quenching and tempering include heavy-duty mechanical parts, connectors, and structural parts that require high strength and good toughness.
Solution Annealing
Solution treatment is when an alloy is heated to a specific temperature (1000°C to 1100°C for stainless steel), maintained for a certain period, and then rapidly cooled. Its purpose is to completely dissolve the alloying elements into the matrix, thereby improving the corrosion resistance and plasticity of the material. This method is commonly used for stainless steel (304 and 316) and nickel-based alloys (such as Inconel 600). Solution treatment is often used in chemical equipment, heat exchangers, aerospace parts, and other occasions that require high corrosion resistance.
Stress Relieving
Stress relief annealing is when a metal is heated to a lower temperature (550°C to 650°C), kept for some time, and then slowly cooled. It aims to eliminate internal stress introduced by welding, cold working, or casting processes to prevent deformation or cracking. It is commonly used for carbon and low-alloy steel (such as 1040 and 4140). Stress relief annealing is also used in precision mechanical parts, welded structural parts, and large castings to ensure dimensional stability and avoid cracking.
Why SSM is Your Trusted Supplier of Alloy Products
The alloys supplied by SSM include carbon steel, stainless steel, various nickel alloys, aluminum alloys, etc. Get in touch with us today for a free quote and experience the difference of partnering with true experts in metal excellence.
Heat Ttreatment Precautions
During the metal heat treatment process, it is important to note the following key issues to ensure stability:
1. Select the appropriate heat treatment temperature based on the material and mechanical properties.
2. Control heating and cooling rates to prevent stress and achieve required properties.
3. Use protective atmospheres or vacuum technology to prevent oxidation and decarburization.
4. Prevent deformation and cracking by using stress relief annealing for complex parts.
5. Consider the material’s heat treatment history to develop a suitable treatment route.
6. Set reasonable heating and holding times based on material thickness and specifications.
7. Maintain equipment and process control to ensure accuracy and stability.
8. Ensure workpiece cleanliness to avoid surface defects.
9. Load and place workpieces in the furnace to ensure uniform heating and cooling.
These measures help ensure the quality and performance of the final product meet design requirements.
FAQ
The effect of heat treatment is evaluated by mechanical property testing (such as hardness, strength, and toughness), microstructural inspection, and non-destructive testing (such as ultrasound and X-ray) of the material. In addition, the deformation caused by heat treatment can be checked by measuring the size and shape changes.
Quenching involves heating a metal to a high temperature and then rapidly cooling it to increase hardness and strength. Tempering, on the other hand, is the process of reheating the material to a lower temperature after quenching and then slowly cooling it to reduce brittleness and improve toughness. In summary, quenching increases hardness, while tempering adjusts the balance between hardness and toughness.
Solution treatment involves heating the alloy material to a specific temperature to completely dissolve the alloy elements and then cooling it rapidly to improve its corrosion resistance and plasticity.
Stress relief annealing involves heating the material to a lower temperature to eliminate internal stress caused by welding, cold working, casting, etc., thereby preventing deformation or cracking.
The main difference lies in the temperature range and purpose: solution treatment is usually used to improve corrosion resistance, and stress relief annealing is used to eliminate internal stress.
Heat treatment costs involve equipment investment, energy consumption, process time, and labor costs. Complex heat treatment processes (such as multi-step heating and cooling) increase prices. In addition, strict process control and equipment maintenance are required to ensure consistency and quality, which increases operating costs.
Different metal materials and alloys have different composition and performance requirements, so the proper heat treatment process needs to be selected. For example, carbon steel usually requires quenching and tempering to improve hardness and toughness; stainless steel may require solution treatment to enhance corrosion resistance; tool steel may require multiple heat treatments to obtain specific hardness and wear resistance.
