How do the tensile strength and fatigue resistance of carbon steel screws compare to other fasteners made from different materials?

The tensile strength and fatigue resistance of carbon steel screws are influenced by their material properties, and when compared to screws made from other materials like stainless steel and alloy steel, there are distinct differences:

1. Tensile Strength
Tensile strength refers to the maximum stress a material can withstand while being stretched or pulled before breaking.
Carbon Steel Screws:
Tensile Strength: Carbon steel screws typically have good tensile strength, which can range widely depending on the carbon content. Low-carbon steels (e.g., AISI 1006) tend to have a tensile strength of about 350-500 MPa, while high-carbon steels (e.g., AISI 1095) can have a tensile strength of up to 850-1000 MPa or more.
Carbon steel is often heat-treated or alloyed to increase its tensile strength, but it is generally not as strong as high-strength alloy steels or some stainless steel grades.
Stainless Steel Screws:

Tensile Strength: Stainless steel screws generally have higher tensile strength than low-carbon steel, with common alloys like 304 or 316 reaching 500-800 MPa in tensile strength. Some high-strength stainless steel grades (e.g., PH 17-4) can reach up to 1000 MPa.
Stainless steel offers a balance of tensile strength and corrosion resistance, making it ideal for many applications, but it’s often not as strong as heat-treated alloy steels.
Alloy Steel Screws:

Tensile Strength: Alloy steels, such as those with high carbon content or added elements like chromium, molybdenum, or vanadium, can achieve 1000-1500 MPa or more in tensile strength. These materials are specifically engineered for high-performance applications requiring maximum strength.
Alloy steel screws often outperform both carbon and stainless steel screws in tensile strength, particularly in heavy-duty, high-stress applications.

2. Fatigue Resistance
Fatigue resistance refers to a material's ability to withstand repeated or fluctuating stress without breaking.
Carbon Steel Screws:
Fatigue Resistance: Carbon steel screws generally have moderate fatigue resistance. Their ability to withstand cyclic loading is influenced by the carbon content and heat treatment. High-carbon steel screws, while offering better tensile strength, tend to be more brittle, which can reduce their fatigue resistance.
In applications where the screws are subject to frequent or cyclic loading, carbon steel may fail sooner than higher-performance materials unless specially treated or coated to improve resistance.
Stainless Steel Screws:

Fatigue Resistance: Stainless steel screws tend to offer better fatigue resistance than carbon steel due to their toughness and ductility. The presence of chromium and other elements increases their ability to absorb stress over time. Austenitic stainless steels like 304 and 316 are particularly good at handling fatigue stress due to their work-hardenable properties.
Stainless steel screws are often chosen for applications involving frequent vibrations or cyclic loading because they perform better under such conditions compared to carbon steel.
Alloy Steel Screws:

Fatigue Resistance: Alloy steels, particularly those with higher hardness or engineered to resist fatigue, typically offer the best fatigue resistance among the three. Heat treatment processes such as tempering or quenching enhance their ability to withstand repeated loading. Alloy steels are optimized for fatigue resistance in demanding applications like aerospace, automotive, and heavy machinery.
High-strength alloys such as 4130 or 4340 are commonly used in environments with high cyclic stresses and fatigue loading, offering significantly superior fatigue resistance compared to both carbon and stainless steel.

Carbon steel screws are typically sufficient for applications with moderate load-bearing and static stress but may struggle under cyclic loading or extreme tensile stress without additional treatments.
Stainless steel screws offer better fatigue resistance and corrosion resistance but are generally not as strong as alloy steel screws.
Alloy steel screws are ideal for high-stress and fatigue-prone environments, offering superior tensile strength and fatigue resistance due to their high-performance alloy composition and heat treatments.