Q355 Overview
Q355 steel is a low alloy, high-strength steel used in welded structures supporting stress and heavy loads. The 'Q' references the yield point, while '355' indicates its yield strength of 355 MPa. Defined under Chinese standard GB/T 1591-2018, it replaced the earlier Q345 grade and contains microalloying elements (niobium, vanadium, titanium) with a combined Nb+V+Ti limit of 0.12%, giving good weldability and low-temperature toughness.
Q355 Equivalent Materials
The European match depends on the specific grade: Q355B aligns with S355JR (both tested at +20 C), while Q355C and Q355D correspond to S355J0 and S355J2. The closest ASTM match is A572 Grade 50, though that specification lists a minimum yield of 345 MPa. The JIS match is SM490B under G3106, with SS490 also referenced.
The 2018 revision of GB/T 1591 aligned Chinese composition limits with the European standard, allowing direct substitution in many structural projects. Verify impact toughness and composition before substitution, since each standard has slightly different limits and delivery conditions.
Characteristics of Q355
Q355 is a structural steel with a yield strength of 345 MPa and tensile strength of 450 MPa. It offers excellent processing performance and compressive strength, suitable for high-pressure gas vessels under 500 liters. The material includes elements providing atmospheric corrosion resistance.
As a mild steel with lower carbon content, Q355 has a material density of 7.85 g/cm3 and comes in three quality levels: Q355B, Q355C, and Q355D. It demonstrates superior mechanical properties compared to A36 ASTM steel and exhibits great hot and cold processing capabilities.
Q355 Grade Variants
The quality levels share the same base mechanical properties but differ in impact test temperature and impurity limits.
| Property | Q355B | Q355C | Q355D |
|---|---|---|---|
| Impact Test Temp | +20 C | 0 C | -20 C |
| Max Carbon (%) | 0.24 | 0.20 | 0.20 |
| Max Phosphorus (%) | 0.035 | 0.030 | 0.025 |
| Max Sulfur (%) | 0.035 | 0.030 | 0.025 |
| Charpy V-notch (J) | >= 34 longitudinal | >= 34 longitudinal | >= 34 longitudinal |
The B grade covers general construction and bridge work. The C grade suits structures with heavy joining, where lower carbon improves heat-affected zone performance. The D grade handles outdoor and cold-region installations, with tighter impurity limits that reduce brittle fracture risk.
Uses of Q355
Q355 steel is utilized for petroleum storage tanks, high-pressure vessels, boilers, ships, power stations, and structural components requiring excellent weldability and toughness.
- Shipping containers
- Waste storage containers
- Weather containers
- Offshore containers
- Workshop containers
- Toolboxes
Q355 Physical Properties
| Property | Metric | US/Imperial |
|---|---|---|
| Density | 7.80 g/cc | 0.282 lb/in3 |
Q355 Mechanical Properties
| Property | Metric | US/Imperial |
|---|---|---|
| Hardness, Brinell | 135 | 135 |
| Hardness, Rockwell B | 74 | 74 |
| Tensile Strength, Ultimate | 450 MPa | - |
| Tensile Strength, Yield | 345 MPa | - |
| Elongation at Break | 18% | 18% |
| Bulk Modulus | 160 GPa | 23200 ksi |
| Shear Modulus | 80.0 GPa | 11600 ksi |
Q355 Chemical Composition
The composition below applies to hot-rolled plate per GB/T 1591-2018. All values are maximums.
| Element | Q355B | Q355C | Q355D |
|---|---|---|---|
| Carbon, C (%) | 0.24 | 0.20 | 0.20 |
| Silicon, Si (%) | 0.55 | 0.55 | 0.55 |
| Manganese, Mn (%) | 1.60 | 1.60 | 1.60 |
| Phosphorus, P (%) | 0.035 | 0.030 | 0.025 |
| Sulfur, S (%) | 0.035 | 0.030 | 0.025 |
| Chromium, Cr (%) | 0.30 | 0.30 | 0.30 |
| Nickel, Ni (%) | 0.30 | 0.30 | 0.30 |
| Copper, Cu (%) | 0.40 | 0.40 | 0.40 |
Lower carbon in the C and D grades improves weldability and toughness in cold conditions. Independent lab testing or spectrometer analysis on incoming Q355 material confirms the alloy composition matches the mill certificate, catching errors before production.
Frequently Asked Questions About Q355 Steel
What is the grade equivalent of Q355? Q355B matches S355JR, while Q355C and Q355D align with S355J0 and S355J2. The primary ASTM match is A572 Grade 50. Verify impact toughness before direct substitution, because each standard has slightly different composition limits and delivery conditions.
What is the difference between Q355 and S355? Q355 and S355 share the same minimum yield and similar tensile ranges. The differences are the governing standard (GB/T 1591 versus EN 10025-2), composition limits, and delivery conditions. The 2018 revision aligned Q355B with S355JR for most structural projects.
What is the difference between Q235 and Q355? Q235 steel has a minimum yield of 235 MPa, while Q355 delivers 355 MPa with better cold-weather toughness, making it preferred for machinery and bridge applications where load-bearing capacity matters. Q235 is more formable due to lower carbon and fits general work where high strength is not required.
