About Mild Steel Fastners

Mild Steel Fasteners: Comprehensive Description

Mild steel fasteners, commonly referred to as MS fasteners, are essential components in industrial, construction, automotive, and mechanical applications worldwide. Made from low-carbon steel containing between 0.05% and 0.25% carbon, these fasteners offer an ideal balance of strength, ductility, weldability, and cost-efficiency that makes them the most widely used fastening solution across multiple industries.

Material Composition and Properties

Mild steel is classified as plain carbon steel with no more than 2% carbon and no appreciable alloying elements, making it the most mass-produced steel type globally. The typical chemical composition includes carbon (0.16-0.18%), silicon (0.40% max), manganese (0.70-0.90%), sulphur (0.040% max), and phosphorus (0.040% max). This low carbon content provides exceptional ductility, allowing the material to be easily formed into various shapes without cracking, while maintaining excellent machinability and weldability.

The mechanical properties of mild steel fasteners are impressive for their price point. They exhibit tensile strength ranging from 400 to 560 N/mm, yield stress of 300-440 N/mm minimum, and elongation of 10-14% minimum. The material is strong, stiff, and magnetic, making it suitable for applications involving motors and electrical appliances. However, mild steel exhibits poor corrosion resistance and should not be used in corrosive environments without protective platings or coatings.

Grades and Classification

Mild steel fasteners are classified based on their mechanical properties and tensile strength using property class markings. Common grades include:

• Grade 4.6: 400 MPa tensile strength, suitable for light machinery and furniture

• Grade 4.8: Standard mild steel grade for general-purpose applications

• Grade 8.8: 800 MPa tensile strength, used for heavy-duty machinery and construction bolts

Grade 4.6 fasteners have a minimum tensile strength of 400 MPa and minimum yield strength of 240 MPa, making them suitable for various non-critical applications. The property class marking indicates both the tensile strength and yield ratio, helping engineers select the appropriate fastener for their specific application requirements.

Types and Applications

Mild steel fasteners come in various types including hex bolts, flange bolts, nuts, washers, studs, and rivets. The MS hex bolt features a hexagonal head designed for high-strength fastening using spanners or wrenches, making it the most common bolt type. MS flange bolts include a built-in washer-like flange beneath the head that distributes load evenly, reduces loosening, and eliminates the need for separate washers.

These fasteners are extensively used in construction for securing structural components, in machinery manufacturing for assembling mechanical parts, in automotive applications for non-critical connections, and in home improvement projects. They're particularly valuable for light to medium-duty applications where high strength is not critical but cost-efficiency is important.

Advantages and Limitations

The primary advantages of mild steel fasteners include excellent cost-efficiency, good strength-to-weight ratio, superior formability, easy fabrication, and wide thermal range resistance. MS fasteners offer higher strength and flexibility due to their mild carbon content, supporting accuracy and formability in various shapes with ease of fabrication.

The main limitation is poor corrosion resistance. However, this can be addressed through various surface treatments including galvanization, zinc plating, black oxide coating, or painting. Black mild steel studs can withstand general atmospheric corrosion for extended periods as the oxide layer prevents further oxidation and rusting.