21 Common Metal Materials Every Mechanical Engineer Should Know (Part 1)

Publish Time: 2025-10-28 Origin: Site

In the field of mechanical engineering, the selection of metal materials directly affects the performance, service life, and safety of mechanical equipment. Among numerous metal materials, there are several commonly used ones that every mechanical professional must be familiar with. This article will focus on introducing three typical metal materials, including their core characteristics and application scenarios, to provide practical references for mechanical design, manufacturing, and maintenance.

1. 45 Steel - High-Quality Carbon Structural Steel

45 Steel is the most widely used medium-carbon quenched and tempered steel in mechanical engineering, belonging to the category of high-quality carbon structural steel.

Core Characteristics

It exhibits excellent comprehensive mechanical properties, striking a good balance between strength and toughness, which makes it suitable for parts bearing moderate loads.
However, it has low hardenability. When water quenching is adopted (a heat treatment process to improve hardness), the material is prone to cracking due to uneven internal stress.
For heat treatment: Small-sized workpieces are recommended to undergo quenching and tempering treatment (to optimize comprehensive performance), while large-sized workpieces are more suitable for normalizing treatment (to refine grains and reduce internal stress, avoiding cracking).

Application Examples

It is widely used in the manufacturing of key mechanical components, such as turbine impellers, compressor pistons, shafts, gears, racks, and worms. These parts require moderate strength and good toughness to adapt to long-term mechanical operation.

2. Q235A Steel (A3 Steel) - The Most Commonly Used Carbon Structural Steel

Q235A Steel, also known as A3 Steel in traditional terms, is one of the most extensively applied carbon structural steels in industrial production due to its cost-effectiveness and stable performance.

Core Characteristics

It has high plasticity and toughness, which means it is not easy to break under external force and can undergo a certain degree of deformation, making it suitable for forming processes.
It possesses excellent weldability and cold stamping performance. It can be easily welded into various structural parts, and can also be processed into different shapes through cold stamping (such as stamping into washers or brackets).
While it has a certain level of strength to meet general load requirements, its strength is lower than that of medium-carbon steels like 45 Steel. Additionally, it has good cold bending performance, and no cracks will occur when bent at a specified angle.

Application Examples

It is commonly used in the production of parts and welded structures with general performance requirements (no high-strength demands), such as tie rods, connecting rods, pins, shafts, screws, nuts, collars, brackets, machine bases with small loads, as well as building structures (like steel frames) and bridges.

3. 40Cr Steel - The Most Widely Used Alloy Structural Steel

40Cr Steel is a representative alloy structural steel with chromium as the main alloying element. It is favored in mechanical manufacturing due to its excellent comprehensive performance after heat treatment.

Core Characteristics

After quenching and tempering treatment, it has outstanding comprehensive mechanical properties, along with good low-temperature impact toughness (it can still maintain toughness in low-temperature environments) and low notch sensitivity (not prone to stress concentration and cracking at notches).
It has good hardenability. When oil quenching is used (slower cooling rate than water quenching), it can obtain higher fatigue strength (resistant to damage under cyclic loads), which is beneficial for improving the service life of parts. However, if water quenching is adopted for complex-shaped parts, cracking may still occur due to rapid cooling.
Its cold bending plasticity is moderate. After tempering or quenching and tempering, it has good machinability (easy to be processed into precise shapes through turning, milling, etc.).
A key note: Its weldability is poor. Welding without preheating is likely to cause cracks. Therefore, the workpiece must be preheated to 100~150°C before welding.
It has strong process adaptability: In addition to being used in the quenched and tempered state, it can also be subjected to carbonitriding (to improve surface hardness and wear resistance) and high-frequency surface quenching (to enhance surface strength while keeping the core tough).

Application Examples

It is widely used in the manufacturing of important mechanical parts that bear medium to heavy loads and require high fatigue resistance, such as crankshafts, connecting rods of high-power engines, gears of heavy-duty machinery, and high-precision shafts.

Conclusion

45 Steel, Q235A Steel, and 40Cr Steel are three fundamental metal materials in mechanical engineering, each with unique performance advantages and application scopes. Mastering their characteristics and reasonable application scenarios is the basis for mechanical engineers to conduct scientific material selection, optimize product design, and ensure the reliability of mechanical equipment. In subsequent articles, we will continue to introduce more common metal materials in the mechanical field to help professionals further enrich their material knowledge reserves.

21 Common Metal Materials Every Mechanical Engineer Should Know (Part 1)

1. 45 Steel - High-Quality Carbon Structural Steel

Core Characteristics

Application Examples

2. Q235A Steel (A3 Steel) - The Most Commonly Used Carbon Structural Steel

Core Characteristics

Application Examples

3. 40Cr Steel - The Most Widely Used Alloy Structural Steel

Core Characteristics

Application Examples

Conclusion

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