Common quenched and tempered steels

Quenched and tempered steels are categorized based on their hardenability into three types: low, medium, and high hardenability steels. These steels are widely used in various mechanical applications due to their ability to undergo heat treatment, which enhances their mechanical properties like strength, toughness, and wear resistance.

Quenched and Tempered Steels

1.Low Hardenability Steels

(a) Carbon Quenched and Tempered Steels

The most commonly used carbon quenched and tempered steels include grades like 30, 35, 40, 45, 50, and 55.

30 and 35 Steel: These grades have lower carbon content, which provides better plasticity and toughness with moderate strength. They are often used for forging parts and standard components.

40 and 45 Steel: These are the most commonly used grades in mechanical part manufacturing, owing to their good balance of mechanical properties.

50 and 55 Steel: These steels are selected for parts requiring higher wear resistance but not subjected to heavy loads. However, the hardenability of these steels is relatively poor; for example, 45 steel has a critical diameter of less than 20 mm when water-quenched and less than 10 mm when oil-quenched. Additionally, their tempering stability is low, which limits their use.

(b) Chromium, Manganese, Boron, and Silicon-Manganese Steels

Common steels in this category include:

Chromium Steel (e.g., 40Cr)

Manganese Steel (e.g., 45Mn2)

Silicon-Manganese Steel (e.g., 35SiMn)

Boron Steel (e.g., 40MnB)

These steels have minimal alloying elements, generally less than 2.5% by mass. They offer better hardenability than carbon steels, with maximum critical diameters of 30 to 40 mm when oil-quenched. They also exhibit higher tempering stability and reduced tendencies for quenching deformation and cracking compared to carbon steels.

2.Medium Hardenability Steels

Common medium hardenability steels include:

Chromium-Molybdenum Steel (e.g., 35CrMo, 42CrMo)

Chromium-Manganese Steel (e.g., 40CrMn)

Chromium-Nickel Steel (e.g., 40CrNi)

Chromium-Manganese-Silicon Steel (e.g., 35CrMnSi)

These steels have a critical diameter of approximately 40 to 60 mm when oil-quenched. Their higher hardenability and tempering stability make them suitable for manufacturing parts requiring high strength or those with larger cross-sections.

3.High Hardenability Steels

Common high hardenability steels include:

Chromium-Manganese-Molybdenum Steel (e.g., 40CrMnMo)

Chromium-Nickel-Molybdenum Steel (e.g., 40CrNiMoA)

These are multi-element alloy steels with critical diameters of 60 to 100 mm or more when oil-quenched. Due to their high hardenability, they are ideal for producing large cross-section parts that require high strength and toughness.

The selection of quenched and tempered steel depends on the specific requirements of the mechanical parts, such as the required strength, toughness, and wear resistance, as well as the dimensions of the parts. Understanding the characteristics of low, medium, and high hardenability steels allows engineers to choose the appropriate material for their applications, ensuring optimal performance and durability of the finished components.

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