Steel A387 Gr 11
ASTM A387 Gr 11 · UNS K11789
A387 Grade 11 (K11789, SCMV4) is a 1.25 % chromium, 0.5 % molybdenum low-alloy plate steel for elevated-temperature pressure vessels, boilers and piping, supplied normalized and tempered in Class 1 or Class 2, quenched and tempered, or N&T plus PWHT.
Values for the N&T condition
A387 Gr 11 tempers and conditions
A387 Gr 11 is supplied in 5 conditions, soft to hard. N&T is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
N&T Class 1 | Pick Class 1 when maximum ductility/toughness and easier forming and welding matter more than strength (415–585 MPa band). | 275 | 480 | 27 | 150 HB | — |
N&T + simulated PWHT / stress relief | Order this when the vessel sees long or multiple PWHT cycles — properties are certified after simulated post-weld heat treatment, at somewhat lower strength. | 330 | 530 | 25 | 165 HB | 8 % IACS |
N&TDefault Normalized and tempered | Default stocked condition: N&T Class 2 plate for pressure vessels needing the higher 515–690 MPa tensile band. | 355 | 560 | 23 | 175 HB | 8 % IACS |
N&T Class 2 | Explicit Class 2 order for reactor shells and hot piping designed to the higher ASME allowable stresses. | 355 | 560 | 23 | 175 HB | 8 % IACS |
Q&T Class 2 | Used on heavy-wall plate where liquid quenching plus temper is needed to meet Class 2 strength and low-temperature CVN through thickness. | 400 | 585 | 22 | 185 HB | 8 % IACS |
What is A387 Gr 11?
A387 Grade 11 (K11789, SCMV4) is a 1.25 % chromium, 0.5 % molybdenum low-alloy plate steel for elevated-temperature pressure vessels, boilers and piping, supplied normalized and tempered in Class 1 or Class 2, quenched and tempered, or N&T plus PWHT. Typical N&T properties are 355 MPa yield, 560 MPa tensile, 23 % elongation and 175 HB, with a maximum service temperature of 550 °C and moderate creep strength at that level. It is a P-No.4 material, so preheat and post-weld heat treatment are mandatory, and it has no inherent corrosion resistance in process service. A387 Grade 22 (2.25Cr-1Mo) is the next step up for higher temperature and hydrogen service. A387 Gr 11 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,450°C (2,642 °F). A387 Gr 11 has a yield strength of 355 MPa (51.5 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 73% of steel grades. Elongation at break is 23% and the elastic modulus is 207 GPa (30 Msi).
What is A387 Gr 11 used for?
- Boilers
- Pressure vessels
- Cracking tower
Advantages
- High service temperature — 550°C (1,022 °F), better than 95% of steel grades
- Tough — resists crack growth — 120 MPa·√m (109.2 ksi·√in), better than 81% of steel grades
A387 Gr 11 properties
Typical room-temperature values for A387 Gr 11-N&T; bars are the position among steel grades.
Physical3
A387 Gr 11 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,450°C (2,642 °F).
Mechanical16
A387 Gr 11 has a yield strength of 355 MPa (51.5 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 73% of steel grades. Elongation at break is 23% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
A387 Gr 11 is rated for continuous service to 550°C (1,022 °F). It conducts heat at 38 W/m·K (22 BTU/hr·ft·°F), worse than 69% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
A387 Gr 11 conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (20/100), better than 87% of steel grades.
Sustainability4
Producing a kilogram of A387 Gr 11 takes about 27 MJ of energy and emits 2.1 kg of CO₂ — less than 59% of steel grades. Typical recycled content is 25%.
Manufacturability7
A387 Gr 11's machinability is fair (50/100, worse than 53% of steel grades); weldability good (55/100); formability fair (50/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. A387 Gr 11 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with A387 Gr 11
Is A387 Gr 11 easy to machine?
Machines like normalized 4130 at roughly 55 % of AISI 1212 — rigid setups, carbide tooling and moderate speeds; the 0.5–0.8 % Si makes chips slightly abrasive.
Can A387 Gr 11 be welded?
P-No.4 material: preheat 150–250 °C, low-hydrogen B2/CM filler (E8018-B2, ER80S-B2), interpass control, and PWHT at 690–730 °C to avoid hard HAZ and hydrogen cracking.
Can A387 Gr 11 be formed, bent or molded?
Cold-form only with generous radii; heavy heads and shells are hot-formed 900–1000 °C and then re-normalized and tempered.
Manufacturability
The process limits FabDigit applies to A387 Gr 11. Every A387 Gr 11 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Fair50 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Fair50 / 100 |
|---|---|
| Weldability | Better55 / 100 |
| Bendable | Yes |
A387 Gr 11 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 | 0.05 – 0.17 | 0.12 |
| Sihigh-Si is characteristic of Gr 11 | 0.5 – 0.8 | 0.65 |
| Mn | 0.4 – 0.65 | 0.52 |
| P | ≤ 0.04 | 0.02 |
| Smax; often restricted to ≤0.010 for clean-steel reactor plate | ≤ 0.04 | 0.01 |
| Cr | 1 – 1.5 | 1.25 |
| Mo | 0.45 – 0.65 | 0.55 |
| Fe | balance |
What surface finishes work on A387 Gr 11?
Not anodizable — blast and paint, aluminize/thermal-spray for hot service, or weld-overlay/clad with 347SS or Inconel 625 where corrosive process fluids contact the surface.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel A387 Gr 11 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- K11789
- ASTM
- A387 Grade 11
- Similar grades
- SCMV4
How much does A387 Gr 11 cost?
A387 Gr 11 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
A387 Gr 11 — frequently asked
What is A387 Gr 11 used for?
A387 Gr 11 is typically used for boilers, pressure vessels and cracking tower. In short: chrome-moly pressure plate.
What is the yield strength of A387 Gr 11?
A387 Gr 11 has a typical yield strength of 355 MPa (51.5 ksi) and a tensile strength of 560 MPa (81.2 ksi) — weaker than 73% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is A387 Gr 11 easy to machine?
Reasonably — machinability is rated fair (50/100, worse than 53% of steel grades). Machines like normalized 4130 at roughly 55 % of AISI 1212 — rigid setups, carbide tooling and moderate speeds; the 0.5–0.8 % Si makes chips slightly abrasive.
Can A387 Gr 11 be welded?
Yes — weldability is rated good (55/100). P-No.4 material: preheat 150–250 °C, low-hydrogen B2/CM filler (E8018-B2, ER80S-B2), interpass control, and PWHT at 690–730 °C to avoid hard HAZ and hydrogen cracking.
What surface finishes work on A387 Gr 11?
Not anodizable — blast and paint, aluminize/thermal-spray for hot service, or weld-overlay/clad with 347SS or Inconel 625 where corrosive process fluids contact the surface.
Can A387 Gr 11 be formed, bent or molded?
Cold-form only with generous radii; heavy heads and shells are hot-formed 900–1000 °C and then re-normalized and tempered.
What is the maximum service temperature of A387 Gr 11?
A387 Gr 11 is rated for continuous use to about 550°C (1,022 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does A387 Gr 11 cost?
A387 Gr 11 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Can FabDigit make parts in A387 Gr 11?
Yes — A387 Gr 11 is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM A387/A387M — Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum — ASTM International (2021)
- ASME BPVC Section II Part A (SA-387) 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)
- API RP 941 — Steels for Hydrogen Service at Elevated Temperatures — API (2016)
- GB/T 713 (15CrMoR ) — SAC (2014)
- Mysteel / 1688 (2026)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.