Steel A302-SR (Stress relieved)
Heat-treated state
ASTM A302
Condition after simulated post-weld heat treatment cycles — the basis for design values in welded, heavy-wall vessels.
Values for the SR condition
Other A302 tempers and conditions
A302 is listed in 9 conditions; see the grade overview at A302.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Grade A | Lowest-strength Mn-Mo grade; pick when 310 MPa minimum yield and easy fabrication of moderate-thickness shells is enough. | 360 | 550 | 24 | 170 HB | — |
SRThis page Stress relieved | Condition after simulated post-weld heat treatment cycles — the basis for design values in welded, heavy-wall vessels. | 375 | 565 | 25 | 170 HB | 7.9 % IACS |
As-rolled | Lowest-cost supply condition allowed for thinner plate where impact requirements are modest. | 390 | 600 | 21 | 11 HRC | 7.8 % IACS |
Normalized and tempered | Tempering after normalizing (620–660 °C) to stabilise properties and reduce residual stress before welding. | 395 | 575 | 24 | 175 HB | 7.8 % IACS |
GrB-NDefault Grade B | The workhorse A302 grade (higher Mn than A); default stock condition for boiler drums and heavy pressure-vessel shells at 345 MPa minimum yield. | 400 | 590 | 22 | 180 HB | — |
Normalized | Grain-refining normalize (~900 °C, air cool) — standard heavy-plate condition balancing strength and toughness. | 400 | 590 | 22 | 180 HB | 7.8 % IACS |
Grade C | Grade A chemistry plus 0.4–0.7 % Ni; choose when Grade A/B strength is needed with better notch toughness and section hardenability. | 405 | 590 | 23 | 185 HB | — |
Grade D | Highest-hardenability A302 grade (Grade B Mn level plus Ni); used for the thickest sections and the best low-temperature toughness, closest to A533 Type B. | 415 | 600 | 23 | 190 HB | — |
Quenched and tempered | Optional Q&T route giving the highest strength and upper-shelf toughness in very heavy sections — the practice that evolved into ASTM A533. | 480 | 640 | 21 | 17 HRC | — |
What is A302-SR?
A302-SR is A302 heat treated to SR — condition after simulated post-weld heat treatment cycles — the basis for design values in welded, heavy-wall vessels. A302-SR has a yield strength of 375 MPa (54.4 ksi) and a tensile strength of 565 MPa (81.9 ksi) — weaker than 70% of steel grades. Elongation at break is 25% and the elastic modulus is 204 GPa (29.6 Msi). A302-SR has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). GrB-N is the default condition FabDigit quotes; SR is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 160 MPa·√m (145.6 ksi·√in), better than 98% of steel grades
- High service temperature — 450°C (842 °F), better than 86% of steel grades
- Ductile — tolerates forming and impact — 25%, better than 77% of steel grades
- Readily welded — 72/100, better than 75% of steel grades
A302-SR properties
Typical room-temperature values for A302-SR; 22 are specific to this condition. Other listed values are A302 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A302-SR has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
A302-SR has a yield strength of 375 MPa (54.4 ksi) and a tensile strength of 565 MPa (81.9 ksi) — weaker than 70% of steel grades. Elongation at break is 25% and the elastic modulus is 204 GPa (29.6 Msi).
Thermal6
A302-SR is rated for continuous service to 450°C (842 °F). It conducts heat at 41 W/m·K (23.7 BTU/hr·ft·°F), worse than 62% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
A302-SR conducts electricity at 7.9 % IACS, better than 50% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of A302-SR takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 25%.
Manufacturability6
A302-SR's machinability is good (58/100, better than 75% of steel grades); weldability very good (72/100); formability good (60/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A302-SR
Is A302 easy to machine?
Machines like normalized 4130/1330 at ~60 % of AISI 1212; use rigid setups, carbide inserts at 120–180 m/min and generous coolant for heavy plate edge prep.
Can A302 be welded?
Readily welded by SAW/SMAW/GTAW with low-hydrogen Mn-Mo consumables; preheat 100–200 °C by thickness and PWHT at 595–650 °C is standard for pressure-vessel construction.
Can A302 be formed, bent or molded?
Hot-form heads and shells at 900–1000 °C followed by re-normalizing; cold rolling of shells is possible in thinner gauges with generous bend radii (≥2t).
What surface finishes work on A302?
No self-protection — blast and paint, or apply stainless/Alloy 600 weld overlay or roll-bonded cladding for wetted surfaces.
A302 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Cheat analysis maximum, all grades | ≤ 0.25 | 0.2 |
| Mn0.95–1.30 for Grades A and C; 1.15–1.50 for Grades B and D | 0.95 – 1.5 | 1.3 |
| Si | 0.15 – 0.4 | 0.25 |
| Mo | 0.45 – 0.6 | 0.52 |
| NiGrades C and D only; not specified for Grades A and B | 0.4 – 0.7 | 0.55 |
| Plow P preferred for irradiation resistance | ≤ 0.04 | 0.01 |
| S | ≤ 0.04 | 0.01 |
| Cunot specified; kept low (<0.10) in nuclear-quality plate to limit irradiation embrittlement | ≈ 0.1 | 0.1 |
| Fe | balance | — |
A302-SR — frequently asked
What is A302-SR used for?
A302-SR is typically used for nuclear reactor vessels, heavy-wall pressure vessels and boiler drums. In short: mn-Mo nuclear vessel plate; heavy-section pressure grade; weldable with mandatory PWHT.
What is the yield strength of A302-SR?
A302-SR has a typical yield strength of 375 MPa (54.4 ksi) and a tensile strength of 565 MPa (81.9 ksi) — weaker than 70% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is A302-SR easy to machine?
Reasonably — machinability is rated good (58/100, better than 75% of steel grades). Machines like normalized 4130/1330 at ~60 % of AISI 1212; use rigid setups, carbide inserts at 120–180 m/min and generous coolant for heavy plate edge prep.
Can A302-SR be welded?
Yes — weldability is rated very good (72/100). Readily welded by SAW/SMAW/GTAW with low-hydrogen Mn-Mo consumables; preheat 100–200 °C by thickness and PWHT at 595–650 °C is standard for pressure-vessel construction.
What surface finishes work on A302-SR?
No self-protection — blast and paint, or apply stainless/Alloy 600 weld overlay or roll-bonded cladding for wetted surfaces.
Can A302-SR be formed, bent or molded?
Hot-form heads and shells at 900–1000 °C followed by re-normalizing; cold rolling of shells is possible in thinner gauges with generous bend radii (≥2t).
What is the maximum service temperature of A302-SR?
A302-SR is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between A302 GrB-N and A302-QT?
GrB-N is the default condition — the workhorse A302 grade (higher Mn than A); default stock condition for boiler drums and heavy pressure-vessel shells at 345 MPa minimum yield. QT: optional Q&T route giving the highest strength and upper-shelf toughness in very heavy sections — the practice that evolved into ASTM A533. Yield strength is 400 MPa in GrB-N versus 480 MPa in QT.
Sources
- ASTM A302/A302M — Pressure Vessel Plates, Alloy Steel, Manganese-Molybdenum and Manganese-Molybdenum-Nickel — ASTM International (2017)
- ASME BPVC Section II Part A (SA-302) and Part D (allowable stresses, physical properties) — ASME (2023)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- Heavy Section Steel Technology (HSST) Program plate 02 characterization reports — Oak Ridge National Laboratory (1985)
- GB/T 713 (15MnMoR / 13MnNiMoR comparison grades) — SAC (2014)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.