Steel A387 Gr 9-CL2
Grade · default condition
ASTM A387 Gr 9 · UNS K90941
CL2 = class 2
Standard stocked condition for refinery and boiler pressure parts needing the 415 MPa minimum yield and full creep credit.
Values for the CL2 condition
Other A387 Gr 9 tempers and conditions
A387 Gr 9 is listed in 4 conditions; see the grade overview at A387 Gr 9.
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 | — |
CL2DefaultThis page 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-CL2?
A387 Gr 9-CL2 is A387 Gr 9 in the CL2 grade — standard stocked condition for refinery and boiler pressure parts needing the 415 MPa minimum yield and full creep credit. A387 Gr 9-CL2 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). A387 Gr 9-CL2 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).
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-CL2 properties
Typical room-temperature values for A387 Gr 9-CL2; 18 are specific to this condition. Other listed values are A387 Gr 9 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
A387 Gr 9-CL2 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-CL2 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-CL2 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-CL2 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-CL2 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-CL2'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. Confirm any required mill or lot documentation when quoting.
Working with A387 Gr 9-CL2
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.
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.
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 | — |
A387 Gr 9-CL2 — frequently asked
What is A387 Gr 9-CL2 used for?
A387 Gr 9-CL2 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-CL2?
A387 Gr 9-CL2 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-CL2 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-CL2 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-CL2?
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-CL2 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-CL2?
A387 Gr 9-CL2 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.