AL-6XN Stainless Steel Bar | UNS N08367 | 1.4563 | 6% Mo Super-Austenitic | SHUNFU METAL

AL-6XN (UNS N08367), designated as 1.4563 and X1CrNiMoCuN24-22-7 in the European system, is a super-austenitic stainless steel developed by Allegheny Ludlum (now ATI) that combines approximately 6.0–7.0% molybdenum with an exceptionally high nickel content of 23.50–25.50% — substantially richer than 254SMO (17.50–18.50% Ni). This enhanced nickel content, together with the 6% Mo and 0.18–0.25% nitrogen additions, delivers a pitting resistance equivalent number (PREN) exceeding 45 and, critically, superior resistance to chloride stress corrosion cracking — the failure mode that most often limits super-austenitic component life in hot seawater and aggressive chloride service. SHUNFU METAL, certified to ISO 9001:2015 and API Q1, produces AL-6XN bars through controlled electric arc furnace (EAF) melting with AOD refining, precisely controlling the critical nickel and molybdenum additions to deliver the enhanced corrosion resistance that defines this grade.

AL-6XN Stainless Steel Bar — Overview

AL-6XN positions itself as the higher-nickel alternative to 254SMO, sharing the same 6% molybdenum architecture but elevating nickel content by approximately 6 percentage points (23.5–25.5% vs 17.5–18.5%). This nickel enrichment provides a measurably wider window of immunity to chloride stress corrosion cracking — particularly valuable in oil and gas operations where hot seawater, produced water with high total dissolved solids, and sour well fluids combine elevated chloride concentrations with tensile stresses in welded or cold-worked components. The alloy delivers yield strength comparable to 254SMO at approximately 310 MPa (45 ksi minimum) while offering improved fabricability due to the higher nickel-stabilized austenite — reducing the risk of sigma and chi intermetallic phase formation during welding and hot working. In petroleum applications, AL-6XN has become the preferred super-austenitic for critical seawater cooling systems on offshore platforms, subsea hydraulic and chemical injection umbilicals, firewater ring mains, FGD scrubber internals, and heat exchangers where operating temperatures and chloride levels exceed the safe envelope of standard 254SMO. SHUNFU METAL supplies AL-6XN bars in the solution-annealed condition (minimum 1175°C, water quenched), with every production lot verified by in-house OES and full MTC documentation per EN 10204 Type 3.1.

AL-6XN Equivalent Grades — International Standards

Standard	Designation
ASTM A479 / A276 / A240 / A182	UNS N08367
ASME SA-479 / SA-240	SA-479 N08367 / SA-240 N08367
EN 10088-3 / DIN	1.4563 / X1CrNiMoCuN24-22-7

No direct JIS, GOST, or GB equivalents exist for AL-6XN. SHUNFU METAL supplies bars certified to ASTM A479 UNS N08367 and EN 10088-3 Grade 1.4563, with full heat traceability and API Q1 documentation as standard. ASME-certified material is available for pressure vessel and piping code construction.

AL-6XN Applications — Oil & Gas Industry

AL-6XN excels where 254SMO approaches its stress corrosion cracking limit — the additional 6% nickel provides a critical safety margin in elevated-temperature seawater, high-chloride produced water, and sour hydrocarbon streams where combined tensile stress and aggressive chemistry accelerate SCC in lower-nickel super-austenitics. SHUNFU METAL supplies AL-6XN bars to manufacturers serving the following critical applications:

Supply Range — AL-6XN Bar Dimensions

SHUNFU METAL maintains dedicated production capability for AL-6XN bars across hot-rolled, cold-finished, and forged product forms, processed through ISO 9001:2015 controlled workflows. The high nickel and molybdenum content demands precise solution annealing at minimum 1175°C followed by rapid water quenching to ensure complete dissolution of all intermetallic phases. SHUNFU METAL’s metallurgical team verifies each batch by microstructural examination and ASTM G48 pitting corrosion testing when specified:

All bars are supplied with EN 10204 Type 3.1 Mill Test Certificates documenting heat number, full chemical analysis (including nickel, molybdenum, and nitrogen), mechanical test results, solution annealing verification, grain size per ASTM E112, and dimensional compliance. Critical pitting temperature (CPT) testing per ASTM G48 Method C and intergranular corrosion testing per ASTM A262 are available for qualification to offshore project specifications.

AL-6XN Chemical Composition per ASTM A479

The AL-6XN chemistry is defined by 6.0–7.0% molybdenum combined with a distinctively high nickel content of 23.50–25.50% — the key differentiator from 254SMO. This elevated nickel level not only raises the alloy’s resistance to chloride stress corrosion cracking but also stabilizes the fully austenitic microstructure against the formation of sigma and chi intermetallic phases during welding and elevated-temperature exposure. At SHUNFU METAL, every heat is verified by in-house optical emission spectrometry (OES) against ASTM A479 UNS N08367 limits:

Composition conforms to ASTM A479 UNS N08367 and EN 10088-3 Grade 1.4563. The PREN calculated as %Cr + 3.3(%Mo) + 16(%N) = 21 + 3.3(6.5) + 16(0.215) ≈ 45.9, exceeding 254SMO (PREN ~43) and providing a measurably higher critical pitting temperature. The 23.5–25.5% nickel content — approximately 6 percentage points above 254SMO — is the primary metallurgical justification for selecting AL-6XN where chloride SCC resistance governs material selection. SHUNFU METAL’s API Q1 certified traceability links every finished bar to its original heat analysis, with nickel and molybdenum verification included on every MTC.

AL-6XN Mechanical Properties — Solution Annealed Condition

The nitrogen content (0.18–0.25%) provides solid solution strengthening, delivering a yield strength of 310 MPa minimum — comparable to 254SMO and approximately 80% higher than standard 316L. SHUNFU METAL performs in-house tensile testing (ASTM E8) and hardness testing (ASTM E18) on every production lot, with full results documented on the MTC:

Values per ASTM A479 for bar products in the solution-annealed condition (minimum 1175°C, water quenched). AL-6XN delivers marginally higher tensile and yield strength than 254SMO (690 vs 650 MPa, 310 vs 300 MPa respectively), though the practical design advantage is minor — the material selection decision between these two grades is driven by corrosion performance, not strength.

AL-6XN vs 254SMO — selection guidance: Both alloys share the 6% Mo architecture and exhibit comparable pitting resistance in standard ASTM G48 testing. The selection typically hinges on two factors: (1) when chloride stress corrosion cracking is the primary service risk — the elevated nickel content of AL-6XN provides a wider operating envelope, particularly above 60°C in neutral chloride solutions; and (2) when fabrication involves extensive welding — the higher nickel-stabilized austenite matrix of AL-6XN is more resistant to intermetallic phase formation in weld heat-affected zones, reducing the risk of localized corrosion at welds. Where neither SCC risk nor weldability is the governing factor, 254SMO provides equivalent pitting resistance at a typically lower cost.

Service temperature limits: AL-6XN is suitable for continuous service from cryogenic temperatures to approximately 450°C. Its critical pitting temperature in neutral chloride solutions typically exceeds 60°C, substantially above 316L (CPT ~15°C) and comparable to or slightly exceeding 254SMO. SHUNFU METAL’s ISO 9001:2015 accredited laboratory validates all mechanical properties on representative test specimens from each heat treatment batch, with API Q1 ensuring full material traceability from melt to end user.