Q345B Q345D HIGH STRENGTH LOW ALLOY STEEL PLATES

 

 

 

 

Here's a detailed overview of Q345B and Q345D high strength low alloy steel plates, focusing on their composition, properties, differences, applications, and technical considerations:

1. Grade Classification and Core Differences

Both belong to the Q345 series (GB/T 1591 standard), with yield strength ≥345 MPa. The suffixes B/D denote quality grades distinguished by:

 

Impact Toughness: Tested at different temperatures.

Impurity Control: Lower sulfur (S) and phosphorus (P) in higher grades.

 

Property	Q345B	Q345D
Impact Test Temp	20°C (room temperature)	-20°C (low temperature)
Impact Energy (KV2)	≥34 J	≥34 J
Max S Content	≤0.045%	≤0.035%
Max P Content	≤0.045%	≤0.035%
Typical Use Case	General structures in mild climates	Cold-region structures or dynamic loads

 

Key Takeaway: Q345D offers better resistance to brittle fracture in low temperatures and cleaner metallurgy for critical applications.

2. Chemical Composition

(Typical values for thickness ≤16mm, GB/T 1591-2018)

 

Element	Q345B/Q345D (%)	Role in Steel
C	≤0.20	Balances strength and weldability (low carbon).
Si	0.25-0.55	Improves oxidation resistance and toughness.
Mn	1.00-1.60	Enhances strength via solid solution hardening.
Nb/V/Ti	0.02-0.15 (microalloying)	Refines grains for improved ductility.
S/P	≤0.045 (B), ≤0.035 (D)	Reduces embrittlement; stricter in Q345D.

 

 

 

 

 

 

 

 

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