JIS G 3114

JIS G 3114 — Detailed Technical Overview

Hot-Rolled Atmospheric Corrosion Resisting Steels for Welded Structure

1. Scope and Purpose

JIS G 3114is the Japanese industrial standard that specifies the requirements for hot-rolled weathering steels intended for welded structural applications.
These steels contain alloying elements such as Cu, Cr, Ni, and sometimes P, which promote the formation of a stable, adherent oxide layer that significantly improves atmospheric corrosion resistance.

The standard is used for:

• Bridges
• Building structures
• Transmission towers
• Containers
• Architectural outdoor structures
• General welded steel construction in open-air environments

The 2022 edition aligns closely with ISO 630-5 (structural steels with improved atmospheric corrosion resistance).

2. Steel Grades in JIS G 3114

The standard contains 14 grades, divided into strength classes and alloying series.

400 MPa class (SMA400 series)

• SMA400AW
• SMA400BW
• SMA400CW
• SMA400AP
• SMA400BP
• SMA400CP

490 MPa class (SMA490 series)

• SMA490AW
• SMA490BW
• SMA490CW
• SMA490AP
• SMA490BP
• SMA490CP

High-strength grade (SMA570 series)

• SMA570W
• SMA570P

The ending letter has meaning:

• A = Class A composition
• B = Class B (different chemical ranges)
• C = Class C (enhanced thickness coverage)
• W = Weathering steel for welded structure
• P = Phosphorus-enhanced type

Additional suffixes may be applied:

• N= normalized
• T= tempered
• Q= quenched and tempered
• TMC= thermomechanically controlled process (TMCP)

Example: SMA490BWN = SMA490BW, normalized.

3. Chemical Composition Requirements

Each grade has its own limits, but the standard chemical design concept is:

Typical alloying elements in JIS G 3114:

• Carbon (C):Usually ≤ 0.18%
• Silicon (Si):0.15–0.65% (varies by grade)
• Manganese (Mn):~0.90–1.40%
• Phosphorus (P):≤ 0.035%
• Sulfur (S):≤ 0.035%
• Copper (Cu):0.20–0.55%
• Chromium (Cr):0.30–1.25%
• Nickel (Ni):0.05–0.65% depending on strength class

Higher strength grades (SMA490, SMA570) tend to use higher levels of Cu, Cr, and Ni to increase corrosion resistance and mechanical performance.

4. Mechanical Properties

Mechanical properties depend on plate thickness and grade.

SMA400 Series (400 MPa class)

• Yield strength:≥ 245 MPa (thickness-dependent)
• Tensile strength:400–540 MPa
• Elongation:~18–23%
• Charpy V-notch impact:tested typically at 0 °C

SMA490 Series (490 MPa class)

• Yield strength:~325–365 MPa
• Tensile strength:490–610 MPa
• Elongation:~15–21%
• Charpy impact:0 °C standard test temperature

SMA570 Series (High-strength weathering steel)

• Yield strength:≥ 570 MPa
• Tensile strength:650–860 MPa
• Elongation:depends on thickness (~16–20%)

All grades are designed for good weldability, with controlled carbon equivalent (CE) values to minimize welding cracks.

5. Product Forms and Delivery Conditions

JIS G 3114 steels may be supplied as:

• Plates
• Sheets
• Wide flats
• Hot-rolled sections
• Steel strips

Typical thickness ranges vary by grade; some CW and CP grades allow thickness up to 100 mm.

Possible delivery conditions:

• As-rolled
• Normalized (N)
• Quenched and tempered (Q/T)
• TMCP (TMC)

6. Atmospheric Corrosion Resistance

These steels are known as weathering steels.
Their corrosion resistance is achieved by forming a dense, stable protective oxide layer after exposure to atmospheric cycles.

Benefits:

• Lower maintenance costs
• Protective rust layer eliminates the need for painting in many environments
• Excellent long-term corrosion resistance compared to ordinary carbon steel

However:

• In marine or highly polluted industrial environments, coating may still be necessary.
• Initial rust stabilization may require proper drainage and surface exposure.

7. Weldability Characteristics

JIS G 3114 steels are specifically engineered for welded structure usage.

Key points:

• Low carbon content provides excellent weldability.
• CE (carbon equivalent) is controlled to avoid cold cracking.
• Standard welding processes can be used: SMAW, GMAW, SAW, FCAW.
• Weathering steel welding consumables should be used if matching corrosion resistance is required.

8. Applications

JIS G 3114 steels are widely used in:

• Highway bridges and railway bridges
• Pedestrian bridges
• Steel frames in buildings
• Outdoor sculptures and architectural structures
• Park equipment
• Garden landscape steel
• Storage tanks and containers
• Utility poles and towers

The combination of strength and corrosion resistance makes them popular for long-service-life infrastructure.

9. Comparison with Other Standards

Typical equivalences (approximate):

• ASTM A588 / A242→ similar to SMA490 and SMA400 series
• EN 10025-5 S355J2W / S355JOW / S355K2W→ comparable to SMA400 series
• EN 10025-5 S460W→ comparable to SMA490 series
• ISO 630-5 W classes→ directly related

However, exact equivalence must always be confirmed by comparing chemical composition and mechanical requirements.

10. Summary

JIS G 3114provides a comprehensive specification for hot-rolled weathering steels used in welded structural applications.
The standard covers multiple strength levels, detailed chemical and mechanical requirements, and focuses on steels that offer:

• High corrosion resistance
• Good weldability
• Suitable mechanical performance for structural use
• Low long-term maintenance

It is one of the key standards for weathering steel in Japan and is widely used in civil engineering and architecture.