1. Hardness under Standard Delivery Conditions

The measured hardness of A516 Grade 70 (SA516 Gr.70) steel plate in its normal delivery condition (normalized/as-rolled) ranges from approximately 130–187 HB.

2. Main Factors Affecting Hardness

2.1 Delivery Condition Factors

As-rolled: Approximately 160–180 HB, relatively high hardness.

Normalized: Approximately 130–170 HB, relatively low hardness, more uniform, and better toughness.

2.2 Material Thickness Factors

When the steel plate thickness is >40 mm, the hardness in the center is slightly higher, but still controlled within ≤200 HB.

2.3 Chemical Composition Factors

C content range: 0.27–0.31%, Mn content range: 0.85–1.20%. Within this range, higher carbon and manganese content results in higher hardness.

2.4 Welding and Heat Treatment Factors

Hardness may increase in the weld heat-affected zone (HAZ).

Post-weld heat treatment (PWHT) can effectively reduce hardness and improve toughness.

3. Engineering Significance of Hardness Control

3.1 Ensures good machinability, cold bending properties, and weldability.

3.2 Ensures good toughness, reducing the risk of brittle fracture in pressure vessels under medium and low temperature conditions.

3.3 Hardness control is a key indicator in stress corrosion cracking (SSC) testing.