Q345R and Q370R are Chinese (GB standard) pressure vessel steel grades, indicating they are low-alloy steels used for boilers, tanks, and reactors, with the "Q" for yield strength, numbers for minimum MPa (345 vs 370 MPa), and "R" for pressure vessels. The main difference is strength: Q370R offers higher minimum yield strength (≥365 MPa) and tensile strength (≥570 MPa) than Q345R (≥345 MPa yield, 490-620 MPa tensile), providing better performance, while both offer good weldability and impact toughness for demanding applications.
Chemical Composition
| Element | Q345R - Typical range / role | Q370R - Typical range / role |
|---|---|---|
| C | Low carbon, controlled for welded pressure-vessel performance (e.g., ~≤0.20%) | Slightly higher or similar C control to reach higher yield; still kept low enough for weldability |
| Mn | Moderate (deoxidation, strength) | Moderate to slightly higher to assist strength and hardenability |
| Si | Small deoxidizer (≤~0.35%) | Similar to Q345R |
| P | Tight control (impurity limit) | Similar or slightly tighter control in some specs |
| S | Low sulfur for toughness | Low sulfur; controlled similarly |
| Cr, Ni, Mo | Generally minimal in Q345R; occasional small additions in special variants | May include small amounts (trace to low tenths of percent) in some manufacturers to boost hardenability and strength |
| V, Nb, Ti | Usually absent or at very low levels in basic Q345R | Q370R variants more likely to include microalloying (V, Nb, Ti) for precipitation strengthening and grain refinement |
| B, N | Not a primary alloying strategy; N controlled | N controlled; trace B occasionally used in microalloyed steels for hardenability control |
Mechanical Properties
| Property | Q345R - Typical | Q370R - Typical |
|---|---|---|
| Yield strength (MPa) | Nominal ~345 | Nominal ~370 |
| Tensile strength (MPa) | Typical range ~470–630 | Typical range ~500–700 |
| Elongation (%) | Typically ≥20 (depending on thickness) | Typically ≥17–20 (slightly lower at equal thickness) |
| Impact toughness | Specified impact energy at temperature (designed for acceptable low-temp toughness) | Targeted to match Q345R at similar test temps but sometimes requiring stricter control |
| Hardness (HB or HRC) | Moderate (consistent with ductile plate) | Slightly higher due to added strength mechanisms |
Q345R
Type: Low-alloy, high-strength steel for pressure vessels.
Yield Strength: Minimum 345 MPa.
Tensile Strength: 490-620 MPa.
Applications: Boilers, heat exchangers, chemical reactors, storage tanks.
Properties: Good weldability, impact toughness.
Q370R
Type: Higher strength pressure vessel steel.
Yield Strength: Minimum 365 MPa.
Tensile Strength: ≥570 MPa (typically 570-690 MPa).
Applications: Similar to Q345R but for more demanding conditions, including nuclear equipment.
Properties: Improved low-temperature impact toughness while meeting strength requirements.
