Steel A387 Gr 9
ASTM A387 Gr 9 · UNS K90941
A387 Grade 9 (K90941, X11CrMo9-1, 1.7386) is a 9Cr-1Mo chromium-molybdenum plate, the plate counterpart of T9/P9 pipe, with a martensitic/ferritic structure after normalizing and tempering.
Reference datasheet — A387 Gr 9 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the CL2 condition
A387 Gr 9 tempers and conditions
A387 Gr 9 is supplied in 4 conditions, soft to hard. CL2 is the default FabDigit quotes; the values on this page are for it.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Order or re-anneal in this condition when heads/shells must be cold formed or heavily machined, then re-normalize and temper to the required class. | 270 | 450 | 28 | 150 HB | — |
Class 1 | Choose for maximum ductility/toughness and easier forming and welding where the lower 240 MPa minimum yield is adequate. | 300 | 480 | 26 | 160 HB | — |
CL2Default Class 2 | Standard stocked condition for refinery and boiler pressure parts needing the 415 MPa minimum yield and full creep credit. | 470 | 640 | 22 | 18 HRC | — |
Class 2, quenched and tempered | Use for heavy plate where liquid quenching plus tempering is needed to keep through-thickness strength and toughness at the Class 2 level. | 505 | 680 | 21 | 20 HRC | — |
What is A387 Gr 9?
A387 Grade 9 (K90941, X11CrMo9-1, 1.7386) is a 9Cr-1Mo chromium-molybdenum plate, the plate counterpart of T9/P9 pipe, with a martensitic/ferritic structure after normalizing and tempering. It carries the highest strength of the common A387 grades at 470 MPa yield, 640 MPa tensile, 22 % elongation and about 210 HB (18 HRC), with high-temperature sulfidation resistance and service to 600 °C. The trade-offs are low weldability (rated 40) requiring 200–300 °C preheat and PWHT at 730–770 °C, plus limited cold formability (40). Grade 5 is easier to weld where 5 % Cr is sufficient. A387 Gr 9 has a density of 7.78 g/cm³ (0.281 lb/in³), lighter than 91% of steel grades. It melts at 1,425°C (2,597 °F). A387 Gr 9 has a yield strength of 470 MPa (68.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — stronger than 57% of steel grades. Elongation at break is 22% and the elastic modulus is 211 GPa (30.6 Msi).
What is A387 Gr 9 used for?
- high-temperature reactor vessels
- hydrogen service equipment
- sulfidation-resistant piping components
Advantages
- High service temperature — 600°C (1,112 °F), better than 98% of steel grades
- Good corrosion resistance — 30/100, better than 95% of steel grades
Limitations
- Low electrical conductivity — 2.9 % IACS, worse than 93% of steel grades
- Poor heat conductor — 29 W/m·K (16.8 BTU/hr·ft·°F), worse than 84% of steel grades
A387 Gr 9 properties
Typical room-temperature values for A387 Gr 9-CL2; bars are the position among steel grades.
Physical3
A387 Gr 9 has a density of 7.78 g/cm³ (0.281 lb/in³), lighter than 91% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical17
A387 Gr 9 has a yield strength of 470 MPa (68.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — stronger than 57% of steel grades. Elongation at break is 22% and the elastic modulus is 211 GPa (30.6 Msi).
Thermal6
A387 Gr 9 is rated for continuous service to 600°C (1,112 °F). It conducts heat at 29 W/m·K (16.8 BTU/hr·ft·°F), worse than 84% of steel grades. Thermal expansion is 11.2 µm/m·K (6.22 µin/in·°F).
Electrical3
A387 Gr 9 conducts electricity at 2.9 % IACS, worse than 93% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (30/100), better than 95% of steel grades.
Sustainability4
Producing a kilogram of A387 Gr 9 takes about 32 MJ of energy and emits 2.4 kg of CO₂ — more than 70% of steel grades. Typical recycled content is 30%.
Manufacturability7
A387 Gr 9's machinability is fair (45/100, worse than 65% of steel grades); weldability fair (40/100); formability fair (40/100).
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 9 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with A387 Gr 9
Is A387 Gr 9 easy to machine?
Machine in the annealed or tempered condition with rigid setups, sharp carbide tooling, moderate speeds and heavy coolant; the 9%Cr matrix work-hardens and is abrasive on HSS.
Can A387 Gr 9 be welded?
Weld with matching 9Cr-1Mo consumables (E505/ER80S-B8), preheat/interpass 200–300 °C, no interruption below preheat, and mandatory PWHT at ~730–770 °C to temper the martensitic HAZ.
Can A387 Gr 9 be formed, bent or molded?
Hot form at 950–1100 °C followed by re-normalizing and tempering; cold forming is limited and should be done in the annealed state with generous bend radii.
A387 Gr 9 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 |
|---|---|---|
| C | 0.05 – 0.15 | 0.1 |
| Mn | 0.3 – 0.6 | 0.45 |
| Si | 0.25 – 1 | 0.6 |
| Cr | 8 – 10 | 9 |
| Mo | 0.9 – 1.1 | 1 |
| P | ≤ 0.03 | |
| S | ≤ 0.03 | |
| Fe | balance |
What surface finishes work on A387 Gr 9?
Not stainless — descale/pickle after heat treatment and protect with high-temperature aluminizing, thermal-spray coating or heat-resistant paint; anodizing is not applicable.
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).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel A387 Gr 9 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- K90941
- ASTM
- A387 Grade 9
- Similar grades
- X11CrMo9-11.7386
How much does A387 Gr 9 cost?
A387 Gr 9 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 9 — frequently asked
What is A387 Gr 9 used for?
A387 Gr 9 is typically used for high-temperature reactor vessels, hydrogen service equipment and sulfidation-resistant piping components. In short: highest-Cr A387 plate; strongest common A387 grade; most demanding to weld.
What is the yield strength of A387 Gr 9?
A387 Gr 9 has a typical yield strength of 470 MPa (68.2 ksi) and a tensile strength of 640 MPa (92.8 ksi) — stronger than 57% of steel grades. Strength varies by condition: see the 4 listed tempers.
Is A387 Gr 9 easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machine in the annealed or tempered condition with rigid setups, sharp carbide tooling, moderate speeds and heavy coolant; the 9%Cr matrix work-hardens and is abrasive on HSS.
Can A387 Gr 9 be welded?
With care — weldability is rated fair (40/100). Weld with matching 9Cr-1Mo consumables (E505/ER80S-B8), preheat/interpass 200–300 °C, no interruption below preheat, and mandatory PWHT at ~730–770 °C to temper the martensitic HAZ.
What surface finishes work on A387 Gr 9?
Not stainless — descale/pickle after heat treatment and protect with high-temperature aluminizing, thermal-spray coating or heat-resistant paint; anodizing is not applicable.
Can A387 Gr 9 be formed, bent or molded?
Hot form at 950–1100 °C followed by re-normalizing and tempering; cold forming is limited and should be done in the annealed state with generous bend radii.
What is the maximum service temperature of A387 Gr 9?
A387 Gr 9 is rated for continuous use to about 600°C (1,112 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between A387 Gr 9-CL2 and A387 Gr 9-ANN?
CL2 is the default condition — standard stocked condition for refinery and boiler pressure parts needing the 415 MPa minimum yield and full creep credit. ANN: order or re-anneal in this condition when heads/shells must be cold formed or heavily machined, then re-normalize and temper to the required class. Yield strength is 470 MPa in CL2 versus 270 MPa in ANN.
How much does A387 Gr 9 cost?
A387 Gr 9 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.
Sources
- ASTM A387/A387M Standard Specification for Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum — ASTM International (2021)
- ASME BPVC Section II Part D — Properties (Metric), 9Cr-1Mo materials — ASME (2023)
- EN 10028-2 / X11CrMo9-1 (1.7386) — CEN (2017)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.13C — Corrosion: Environments and Industries (refinery Cr-Mo steels) — ASM International (2006)
- API RP 941 — Steels for Hydrogen Service at Elevated Temperatures — API (2016)
- Mysteel / 1688 (9Cr1Mo) (2025)
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.