Lincoln Chromet 92 E9015-B91 — Overview
Lincoln Chromet 92 is a low-hydrogen, low-alloy SMAW electrode classified to AWS A5.5/A5.5M E9015-B91, engineered for welding modified 9Cr-1Mo-V (Grade 91) creep-resistant steel used in the most demanding high-temperature power generation and petrochemical applications. Grade 91 (ASTM A335 P91, A182 F91, ASME P-No. 5B) has largely displaced older 9Cr-1Mo steels due to its significantly improved creep strength above 1000°F, and requires precisely matched filler metal to achieve the required mechanical properties in the as-welded-and-PWHT condition. Chromet 92 meets AWS A5.5 B91 alloy requirements with a controlled deposit chemistry including 8.0–10.5% Cr, 0.85–1.05% Mo, and critical vanadium, niobium, and nitrogen additions. DC+ only. Available at WeldingMart as an authorized Lincoln Electric distributor.
Specifications
| AWS classification | AWS A5.5/A5.5M E9015-B91 |
|---|---|
| Alloy chemistry (deposit) | 8.0–10.5% Cr, 0.85–1.05% Mo, V, Nb, N additions (nominal) |
| Coating type | Low-hydrogen, basic |
| Polarity | DC+ (DCEP) only |
| Welding positions | All positions: 1G, 2G, 3G, 4G |
| Minimum tensile strength | 90,000 psi (620 MPa) |
| Minimum yield strength | 78,000 psi (538 MPa) |
| Elongation | 14% minimum |
| Typical current range | 1/8 in: 90–140 A | 5/32 in: 115–170 A | 3/16 in: 145–215 A |
| Available diameters | 1/8, 5/32, 3/16 in |
| Manufacturer | Lincoln Electric |
| Standards compliance | AWS A5.5/A5.5M B91; ASME Section IX P-No. 5B; ASME B31.1 |
Applications & Industries
- Ultra-supercritical (USC) power plants: Main steam and hot reheat piping, headers, and thick-section pressure parts in USC boilers operating above 1050°F service temperature
- Fossil fuel power generation: Superheater and reheater tube stubs, header nozzles, and main steam system components fabricated from ASTM A335 P91 or A213 T91 tubing
- Petrochemical and refinery: High-temperature, high-pressure reactor piping and pressure vessels where Grade 91 provides superior creep resistance over P22
- Repair welding: In-service repair of Grade 91 power plant components using properly qualified WPS procedures with controlled preheat and PWHT
- HRSG (Heat Recovery Steam Generator): Duct burner and HRSG header fabrication for combined-cycle power plants
Process Technology — How to Run E9015-B91 (Grade 91)
Grade 91 welding requires strict adherence to qualified procedures. Key requirements:
- Preheat: 400–500°F (204–260°C) minimum preheat and interpass temperature. The preheat must be maintained throughout the entire weld cycle; loss of preheat risks hydrogen cracking and martensite formation without tempering.
- Interpass temperature maximum: 600°F (315°C) to control microstructure. The martensite transformation temperature (Ms) for Grade 91 is approximately 750°F — controlling interpass temperature is essential for achieving a fully martensitic microstructure before PWHT.
- Cooling to MFRT: Before PWHT, the weldment must cool below the martensite-finish temperature (~200°F / 93°C) to ensure complete martensite transformation — a critical, often-overlooked step unique to Grade 91.
- Post-Weld Heat Treatment: 1350–1400°F (732–760°C) for a minimum of 1 hour per inch of wall thickness. PWHT is mandatory — as-welded Grade 91 is not acceptable for service.
- Heat input control: Limit heat input per WPS. Excessive heat input degrades the creep properties of the HAZ (Type IV cracking zone).
- Low-hydrogen discipline: Use electrodes from sealed packaging or holding oven at 250–300°F. Maintain heated quiver during welding.
Storage & Handling
Chromet 92 is a low-hydrogen electrode. Hydrogen control is critical when welding Grade 91 alloy steel:
- Store sealed in original packaging at ambient temperature, away from moisture
- After opening: transfer to a holding oven at 250–300°F (121–149°C) immediately
- Use within 4 hours of removal from oven or recondition at 700–800°F (371–427°C) for 1 hour maximum once
- Field: use a heated quiver. Never leave Grade 91 filler metal in open air overnight
- Reconditioned electrodes must still meet AWS A5.5 diffusible hydrogen requirements — do not recondition rods that show visible coating damage
Frequently Asked Questions
- What is Grade 91 steel and why does it need a special electrode?
- Grade 91 (modified 9Cr-1Mo-V steel, ASTM A335 P91) is a creep-resistant alloy steel with additions of vanadium, niobium, and nitrogen that dramatically improve its high-temperature strength versus conventional 9Cr-1Mo. Its complex alloy chemistry requires precisely matched filler metal (E9015-B91 / E9018-B91) to achieve the required post-weld microstructure and creep properties after PWHT. Using mismatched filler metal is one of the leading causes of premature Grade 91 weld failures.
- What is the difference between Lincoln Chromet 9 and Chromet 92?
- Lincoln Chromet 9 (E8015-B8) is designed for conventional 9Cr-1Mo steel (ASTM A335 P9) without the vanadium-niobium-nitrogen additions. Chromet 92 (E9015-B91) is specifically formulated for modified 9Cr-1Mo-V Grade 91 with the controlled V, Nb, N chemistry required to match Grade 91 base metal properties. Do not substitute Chromet 9 for Grade 91 applications.
- Why do Grade 91 welds need to cool before PWHT?
- Grade 91 undergoes a martensitic transformation on cooling. The martensite-finish temperature (Mf) is approximately 200°F (93°C). The weldment must cool below this temperature before PWHT to ensure complete martensite transformation — otherwise, retained austenite can remain in the weld, and PWHT will not produce the correct tempered martensitic microstructure. This mandatory pre-PWHT cooling step is unique to Grade 91 compared to P22 and other Cr-Mo steels.
- Is PWHT mandatory for Chromet 92 welds?
- Yes, in all code-governed applications. Grade 91 in the as-welded condition has high hardness and extremely low toughness. PWHT at 1350–1400°F tempers the martensitic microstructure to achieve the creep properties for which Grade 91 is specified. ASME B31.1 and B31.3 both mandate PWHT for P-No. 5B materials.
Browse all Cr-Mo electrodes: Stick Welding Electrodes & Rods — or compare with Lincoln Chromet 9-B9 (E8015-B8) for conventional 9Cr-1Mo applications.