1. Is A387 Grade 22 Class 2 a High-Speed Steel?
No. High-speed steels (HSS) are tool steels with high tungsten, molybdenum, vanadium and carbon contents, used for cutting tools. ASTM A387 Grade 22 Class 2 is a chromium-molybdenum alloy steel for welded boilers and pressure vessels in raised-temperature service. The confusion should not influence material selection: the two families have completely different compositions, properties and applications.
2. Chemical Composition
Grade 22 is defined by its 2.25% chromium, 1% molybdenum composition. Typical limits are carbon 0.05–0.15%, manganese 0.30–0.60%, silicon 0.50% maximum, phosphorus and sulfur each 0.035% maximum, chromium 2.00–2.50% and molybdenum 0.90–1.10%. The chromium provides oxidation and corrosion resistance, and the molybdenum maintains strength and creep resistance at elevated temperatures. The heat analysis should be verified against the current edition of ASTM A387 and the mill certificate.
3. Mechanical Properties
The guaranteed values for Class 2 are a minimum yield strength of 310 MPa (45 ksi) at 0.2% offset, a tensile strength of 515–690 MPa (75–100 ksi), and elongation per the standard's gauge-length-dependent tables, with reduction of area requirements measured on round or flat specimens. Class 1, the annealed condition, has a tensile range of 415–585 MPa and a minimum yield of 205 MPa; Class 2 is specified where the higher strength is needed.
4. Applications
The correct applications of A387 Grade 22 Class 2 are in pressure vessels, boilers, heat exchangers, valves, pipe clamps, flanges and high-temperature ducting for the oil, gas, petrochemical, chemical processing and power generation industries, at service temperatures up to about 600°C. The grade is not intended for wear liners, truck bodies or general structural use; those applications call for abrasion-resistant or structural steels. The closest international equivalents are EN 10CrMo9-10 (10CrMo910) and BS 622-515B.
5. Welding Precautions
Welding of Grade 22 requires strict hydrogen control: low-hydrogen consumables such as E9018-B3 or ER90S-B3, baked electrodes, preheating to about 150–200°C for thick sections, controlled interpass temperature, stringer beads rather than weaving, and mandatory post-weld heat treatment around 700–760°C to prevent hydrogen-induced cracking and temper embrittlement. Under ASME Section IX the material is classified as P-Number 5A, the group for 2.25Cr-1Mo steels, which drives the welding procedure qualification.
Frequently Asked Questions
Is ASTM A387 Grade 22 Class 2 carbon steel? No. It is a chromium-molybdenum alloy steel, a low-alloy steel with about 2.25% chromium and 1% molybdenum added for elevated-temperature strength and corrosion resistance.
What is the tensile strength of A387 Grade 22 Class 2? 515–690 MPa (75–100 ksi), with a minimum yield strength of 310 MPa (45 ksi).
What temperature can this steel serve? It is designed for elevated-temperature service up to about 600°C, where its creep and oxidation resistance outperform carbon steel.
What is the P-number of A387 Grade 22? P-Number 5A under ASME Section IX, the group covering 2.25Cr-1Mo ferritic steels; P-Number 5B applies to higher-chromium grades such as A387 Grade 5.
What is the difference between Class 1 and Class 2? The composition is the same; Class 2 is normalized and tempered with higher guaranteed strength, while Class 1 is the annealed, lower-strength condition.
What is A387 Grade 22 Class 2 equivalent to? It is identical to ASME SA387 Grade 22 Class 2 and corresponds to EN 10CrMo9-10 and BS 622-515B.
