Standard Specification for Carbon Steel Bolts, Studs, and Threaded Rod 60000 PSI Tensile Strength - PDF

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ASTM A307 is a widely used specification covering low-carbon steel bolts and studs for general-purpose applications. These fasteners are commonly found in construction, industrial machinery, piping systems, and structural connections where high-strength bolts are not necessary. ASTM A307 ensures consistency in mechanical performance and dimensional tolerances across a wide range of bolt sizes and shapes.

This article explains the scope of ASTM A307, details its grades, describes mechanical testing procedures, and outlines the equipment needed to perform these tests properly.

What Is ASTM A307?

ASTM A307 is a standard developed by ASTM International that specifies mechanical and dimensional requirements for low-carbon steel bolts, studs, and threaded rods. The specification is used in non-critical load applications where medium or high-strength bolts (such as ASTM A325 or A490) are not required.

The standard covers externally threaded fasteners up to 4 inches (100 mm) in diameter.

ASTM A307 Grades

ASTM A307 defines three primary grades:

GradeDescriptionMinimum Tensile Strength

AGeneral purpose bolts, studs, and threaded rods for use in cast iron and structural steel connections60,000 psi (414 MPa)

BBolts for flanged joints in cast iron piping and pressure systems60,000 psi (414 MPa)

C*Mechanically galvanized bolts for general-purpose use (now replaced by ASTM F3125)60,000 psi (414 MPa)

*Note: Grade C has been removed from the active standard and is now addressed in other standards like ASTM F3125.

Both Grade A and Grade B fasteners are manufactured from low-carbon steel, typically AISI 1006 to 1025.

Mechanical Requirements of ASTM A307

The critical mechanical properties that bolts must meet under ASTM A307 include:

1. Tensile Strength

The tensile strength is the maximum load a bolt can bear before fracturing when pulled in tension.

Equation:

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Tensile Strength (psi) = Maximum Load (lbf) / Cross-Sectional Area (in²)

ASTM A307 requires a minimum tensile strength of 60,000 psi for all grades.

2. Yield Strength (Optional)

Yield strength is not mandatory in ASTM A307 but may be reported when known. It marks the point of plastic deformation in the material.

3. Elongation

This is a measure of ductility and is typically required over a 2-inch gauge length. A typical minimum elongation is 18%, though this may vary with diameter and test method.

Equation:

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% Elongation = [(Final Gauge Length - Original Gauge Length) / Original Gauge Length] × 100

4. Reduction of Area

Another indicator of ductility, representing the change in cross-sectional area after fracture.

Equation:

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Reduction of Area (%) = [(Original Area - Fractured Area) / Original Area] × 100

Chemical Composition

ASTM A307 fasteners are manufactured from low-carbon steel with the following typical chemical composition ranges:

• Carbon: ≤ 0.27%

• Manganese: 0.60–0.90%

• Phosphorus: ≤ 0.04%

• Sulfur: ≤ 0.15%

The chemical analysis is conducted according to ASTM A751.

Threading and Dimensions

Threading must comply with the Unified Inch Screw Threads standard (ASME B1.1). The bolts can be either fully or partially threaded depending on the length and application.

• Coarse threads (UNC) are most commonly used.

• Dimensional tolerances must follow ASME B18.2.1 for bolts and B18.2.2 for nuts.

Required Testing Equipment for ASTM A307

Proper quality control and testing of ASTM A307 bolts require specialized equipment:

1. Universal Testing Machine (UTM)

• Purpose: Measures tensile strength, elongation, and reduction of area.

• Grip Type: Threaded or wedge grips depending on bolt geometry.

• Load Cell Range: Appropriate to expected tensile forces (typically 30 kN – 250 kN for A307 bolts).

• Extensometer (optional): Improves accuracy in measuring elongation.

2. Thread Gauge or Ring Gauge

• Purpose: Verifies pitch, diameter, and thread form compliance with ASME B1.1.

3. Micrometer and Calipers

• Purpose: Checks bolt length, head dimensions, and thread depth.

4. Hardness Tester (Optional)

• Purpose: Measures Brinell or Rockwell hardness when required for material validation.

5. Charpy Impact Tester (for optional ductility testing)

• Not required under A307 but may be used in R&D or custom specification environments.

Inspection Requirements

Typical inspections performed on ASTM A307 bolts include:

• Visual inspection for surface flaws or deformation

• Dimensional verification against ASME tolerances

• Tensile and elongation testing per ASTM A370

• Chemical composition verification via optical emission spectroscopy (OES) or spark testing

Certification documents, such as Mill Test Reports (MTRs) and Certificates of Conformance (COCs), are commonly provided to buyers for quality assurance.

Common Applications of ASTM A307 Bolts

ASTM A307 bolts are ideal for general-purpose and structural applications that do not require high strength. These include:

• Structural steel connections

• Pipe flange assemblies

• HVAC and mechanical systems

• Low-pressure tanks and vessels

• Building components and machinery mounting

Their wide availability, ease of manufacturing, and low cost make them a go-to solution for non-critical fastening needs.

Related Standards

Several standards are commonly referenced alongside ASTM A307:

• ASTM A563: Standard for carbon and alloy steel nuts used with A307 bolts

• ASME B18.2.1: Dimensional standards for bolts and screws

• ASME B1.1: Unified inch screw threads

• ASTM F3125: Covers high-strength structural bolts (replaces former A325 and A490)

• ASTM A370: Mechanical testing methods for steel products

• ASTM A751: Chemical analysis procedures for steel

Conclusion

ASTM A307 provides a reliable specification for low-carbon steel bolts used in a broad range of general-purpose applications. While not designed for high-stress environments, these bolts offer consistent performance, easy sourcing, and low-cost implementation.

Accurate testing using universal testing machines and standard inspection tools ensures compliance with ASTM A307, giving manufacturers and engineers confidence in the structural integrity of their fasteners.