SN490(B,C) steel plates are widely used in bridge construction due to their excellent mechanical properties, weldability, and adaptability to dynamic loads and harsh environments. Below is a detailed overview of their characteristics, standards, and applications in bridge building:

1. Standard and Classification

SN490 steel plates belong to the welded structural rolled steel category specified in JIS G3106 (Japanese Industrial Standard for Carbon Steel and Low-Alloy High-Tensile Steel Plates, Sheets, and Strip for Welded Structures).

 

The "SN" prefix indicates they are designed for welded structures (S: Structural; N: Weldable).

"490" refers to the minimum tensile strength of 490 MPa, classifying them as high-tensile structural steel.

Variants SN490B and SN490C differ primarily in their impact toughness requirements, with stricter standards for SN490C.

2. Chemical Composition (Typical, % by Weight)

SN490 steel is a low-alloy steel with controlled elements to balance strength, weldability, and toughness:

 

Element	C	Si	Mn	P (Max)	S (Max)	Cu	Ni	Cr	Mo	Nb	V	Ti
Range	≤0.20	≤0.55	1.00-1.60	0.035	0.035	≤0.30	≤0.30	≤0.30	≤0.15	≤0.05	≤0.10	≤0.03

 

Low carbon content (≤0.20%) ensures good weldability, reducing the risk of cold cracking during welding.

Alloying elements like Mn, Nb, V, and Ti refine grain structure, enhancing strength and toughness without sacrificing weldability.

 

 

 

 

 

 

 

 

3. Mechanical Properties

These properties make SN490B/C suitable for bridge components subjected to static/dynamic loads (e.g., girders, piers, or connectors):

 

Property	SN490B	SN490C
Tensile Strength	490-610 MPa	490-610 MPa
Yield Strength (Min)	325 MPa	325 MPa
Elongation (Min)	17% (for thickness ≤16mm)	17% (for thickness ≤16mm)
Impact Toughness	≥27 J at 0°C (Charpy V-notch test)	≥27 J at -20°C (Charpy V-notch test)
Hardness	~160-200 HB (annealed/normalized)	~160-200 HB

4. Key Differences: SN490B vs. SN490C

The primary distinction lies in impact test temperature and toughness, critical for bridges in cold regions:

 

SN490B: Charpy impact test at 0°C, minimum absorption energy of 27 J. Suitable for mild climates or non-critical bridge components.

SN490C: Charpy impact test at -20°C, same minimum energy (27 J). Better suited for bridges in cold regions (e.g., Hokkaido, high-altitude areas) where low-temperature toughness is critical to resist brittle fracture under dynamic loads.

 

 

 

 

 

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