Steel A387 Gr 21L Class 1 Q+T
Heat-treated state
ASTM A387 Gr 21L Class 1
Q+T = quenched and tempered
Ordered when maximum through-thickness toughness is wanted in heavy sections; still tempered back into the Class 1 strength band.
Values for the Q+T condition
Other A387 Gr 21L Class 1 tempers and conditions
A387 Gr 21L Class 1 is listed in 5 conditions; see the grade overview at A387 Gr 21L Class 1.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Alternative Class 1 heat treatment permitted by A387; softest condition, easiest cold forming and machining, lowest strength. | 235 | 440 | 31 | 128 HB | 7.8 % IACS |
Post-weld heat treated | Properties certified after the fabricator's simulated PWHT soak — the condition specified for reactor shells and heads. | 245 | 450 | 29 | 133 HB | 7.8 % IACS |
N+TDefault Normalized and tempered | Standard supply condition for A387 Gr 21L Class 1 plate: normalize ~900–940 °C, temper ≥650 °C for best toughness/HTHA resistance. | 265 | 470 | 28 | 140 HB | — |
Normalized and Tempered + step-cooled | Supplementary-requirement order where the plate is step-cooled and Charpy-tested to prove low temper-embrittlement shift (J-factor / X-bar limits) for hydroprocessing reactors. | 265 | 470 | 28 | 140 HB | 7.8 % IACS |
Q+TThis page Quenched and tempered | Ordered when maximum through-thickness toughness is wanted in heavy sections; still tempered back into the Class 1 strength band. | 350 | 520 | 25 | 160 HB | 7.7 % IACS |
What is A387 Gr 21L Class 1 Q+T?
A387 Gr 21L Class 1 Q+T is A387 Gr 21L Class 1 heat treated to Q+T — ordered when maximum through-thickness toughness is wanted in heavy sections; still tempered back into the Class 1 strength band. A387 Gr 21L Class 1 Q+T has a yield strength of 350 MPa (50.8 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 74% of steel grades. Elongation at break is 25% and the elastic modulus is 207 GPa (30 Msi). A387 Gr 21L Class 1 Q+T 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). N+T is the default condition FabDigit quotes; Q+T is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 200 MPa·√m (182 ksi·√in), better than 100% of steel grades
- High service temperature — 540°C (1,004 °F), better than 93% of steel grades
- Good corrosion resistance — 22/100, better than 90% of steel grades
- Ductile — tolerates forming and impact — 25%, better than 77% of steel grades
Limitations
- Poor heat conductor — 35 W/m·K (20.2 BTU/hr·ft·°F), worse than 75% of steel grades
A387 Gr 21L Class 1 Q+T properties
Typical room-temperature values for A387 Gr 21L Class 1 Q+T; 22 are specific to this condition. Other listed values are A387 Gr 21L Class 1 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A387 Gr 21L Class 1 Q+T 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
A387 Gr 21L Class 1 Q+T has a yield strength of 350 MPa (50.8 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 74% of steel grades. Elongation at break is 25% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
A387 Gr 21L Class 1 Q+T is rated for continuous service to 540°C (1,004 °F). It conducts heat at 35 W/m·K (20.2 BTU/hr·ft·°F), worse than 75% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
A387 Gr 21L Class 1 Q+T conducts electricity at 7.7 % IACS, worse than 65% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (22/100), better than 90% of steel grades.
Sustainability4
Producing a kilogram of A387 Gr 21L Class 1 Q+T takes about 31 MJ of energy and emits 2.3 kg of CO₂ — more than 64% of steel grades. Typical recycled content is 25%.
Manufacturability6
A387 Gr 21L Class 1 Q+T's machinability is fair (48/100, worse than 57% of steel grades); weldability good (60/100); formability fair (48/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with A387 Gr 21L Class 1 Q+T
Is A387 Gr 21L Class 1 easy to machine?
Machines like annealed low-alloy steel (~55–60 % of 1212); use rigid setups, sharp carbide and generous coolant, and rough before final PWHT to avoid distortion.
Can A387 Gr 21L Class 1 be welded?
SAW/SMAW/GTAW with matching 3Cr-1Mo (or low-C 2.25Cr-1Mo) consumables, 200–250 °C preheat/interpass, low-hydrogen practice, and mandatory PWHT ~690 °C; control weld-metal J-factor/X-bar and step-cool test for reactor service.
Can A387 Gr 21L Class 1 be formed, bent or molded?
Hot form heads and shells at 900–1000 °C followed by re-normalizing and tempering; cold forming is limited and should be followed by stress relief.
What surface finishes work on A387 Gr 21L Class 1?
Not corrosion resistant in wet service — internal surfaces are weld-overlaid with 309L/347 stainless or Alloy 625; external surfaces are shop-primed and insulated.
A387 Gr 21L Class 1 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 |
|---|---|---|
| CL grade: carbon restricted vs Gr 21 | ≤ 0.1 | 0.08 |
| Mn | 0.3 – 0.6 | 0.45 |
| Poften ≤0.008 for temper-embrittlement control | ≤ 0.04 | 0.01 |
| S | ≤ 0.03 | 0.01 |
| Sioften ≤0.10 with X-bar control | ≤ 0.5 | 0.2 |
| Cr | 2.75 – 3.25 | 3 |
| Mo | 0.9 – 1.1 | 1 |
| Fe | balance | — |
A387 Gr 21L Class 1 Q+T — frequently asked
What is A387 Gr 21L Class 1 Q+T used for?
A387 Gr 21L Class 1 Q+T is typically used for hydrocracker vessels, welded pressure vessel shells requiring PWHT control and refinery reactors. In short: low-carbon 3Cr-1Mo plate; temper-embrittlement resistant; hydroprocessing vessel grade.
What is the yield strength of A387 Gr 21L Class 1 Q+T?
A387 Gr 21L Class 1 Q+T has a typical yield strength of 350 MPa (50.8 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 74% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is A387 Gr 21L Class 1 Q+T easy to machine?
Reasonably — machinability is rated fair (48/100, worse than 57% of steel grades). Machines like annealed low-alloy steel (~55–60 % of 1212); use rigid setups, sharp carbide and generous coolant, and rough before final PWHT to avoid distortion.
Can A387 Gr 21L Class 1 Q+T be welded?
Yes — weldability is rated good (60/100). SAW/SMAW/GTAW with matching 3Cr-1Mo (or low-C 2.25Cr-1Mo) consumables, 200–250 °C preheat/interpass, low-hydrogen practice, and mandatory PWHT ~690 °C; control weld-metal J-factor/X-bar and step-cool test for reactor service.
What surface finishes work on A387 Gr 21L Class 1 Q+T?
Not corrosion resistant in wet service — internal surfaces are weld-overlaid with 309L/347 stainless or Alloy 625; external surfaces are shop-primed and insulated.
Can A387 Gr 21L Class 1 Q+T be formed, bent or molded?
Hot form heads and shells at 900–1000 °C followed by re-normalizing and tempering; cold forming is limited and should be followed by stress relief.
What is the maximum service temperature of A387 Gr 21L Class 1 Q+T?
A387 Gr 21L Class 1 Q+T is rated for continuous use to about 540°C (1,004 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between A387 Gr 21L Class 1 N+T and A387 Gr 21L Class 1-A?
N+T is the default condition — standard supply condition for A387 Gr 21L Class 1 plate: normalize ~900–940 °C, temper ≥650 °C for best toughness/HTHA resistance. A: alternative Class 1 heat treatment permitted by A387; softest condition, easiest cold forming and machining, lowest strength. Yield strength is 265 MPa in N+T versus 235 MPa in A.
Sources
- ASTM A387/A387M — Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum — ASTM International (2021)
- ASTM A20/A20M — General Requirements for Steel Plates for Pressure Vessels — ASTM International (2020)
- ASME BPVC Section II Part D — Material Properties (allowable stress, E, α, k) — ASME (2023)
- API RP 934-A — Materials and Fabrication of 2¼Cr-1Mo, 2¼Cr-1Mo-¼V, 3Cr-1Mo and 3Cr-1Mo-¼V Heavy-Wall Pressure Vessels — API (2019)
- API RP 941 — Steels for Hydrogen Service at Elevated Temperatures (Nelson curves) — API (2016)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- Mysteel / SMM (2025)
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.