Stainless Steel Grades Chart: AISI, UNS, EN & JIS Cross-Reference Guide

Written by: Emma, Technical Sales Engineer  |  Reviewed by: Ethan, Materials Engineer  |  Updated: August 2026

1. Introduction

Every buyer, engineer, and inspector who works with stainless steel eventually encounters the same problem: the same material is called different names under different international standards.

A grade you know as AISI 304 becomes UNS S30400, EN 1.4301 (X5CrNi18-10), and JIS SUS304 under other systems. While these designations are routinely cross-referenced in commercial documents, they are not automatically identical — differences in chemical composition limits, mechanical property requirements, and product form standards can exist between systems.

This guide brings all four designation systems together in a practical reference format, explains each system, walks through the five stainless steel families, and provides actionable guidance on grade selection and common procurement mistakes.

2. Complete Stainless Steel Grade Cross-Reference Table

3. Understanding the Four Major Designation Systems

3.1 AISI — American Iron and Steel Institute

The most widely recognized system in global stainless steel trade. Numbering logic:

• 200 Series: Austenitic, Mn substituted for Ni (lower cost, lower corrosion resistance)
• 300 Series: Austenitic Cr-Ni grades — 304, 316, 321, etc. (~70% of global production)
• 400 Series: Ferritic (430, 409) and martensitic (410, 420, 440) grades

Suffixes are not optional details:
L = Low carbon (≤ 0.03%, prevents sensitization during welding)
H = High carbon (creep strength above ~500°C)
N = Nitrogen addition (higher strength, higher PREN)
Ti / Nb = Stabilized grades (321 with Ti, 347 with Nb) for welded high-temperature service

3.2 UNS — Unified Numbering System

UNS provides the most precise material identification. Austenitic stainless steels use S + five digits. Unlike AISI names, UNS numbers map 1:1 to specific chemical composition ranges, making them the preferred designation for purchase orders where ambiguity must be eliminated.

3.3 EN — European Standard

European stainless steels use two identifiers: a 1.4XXX steel number and a material name that encodes composition directly. For example, X5CrNi18-10 = ~0.05% C, 18% Cr, 10% Ni.

3.4 JIS — Japanese Industrial Standards

JIS uses the SUS prefix. While SUS304 appears to map cleanly to AISI 304, the underlying JIS standard may define slightly different composition tolerances than ASTM. For projects governed by Japanese EPC contractors, verify the specific JIS standard edition.

4. Stainless Steel Family Classification

Stainless steels divide into five families based on metallurgical structure. Understanding which family a grade belongs to is the first step in predicting how it will behave in your application.

4.1 Austenitic Stainless Steel (300 Series)

Structure: Face-centered cubic (FCC). Non-magnetic in annealed condition. Cannot be hardened by heat treatment — strength comes from cold working. Accounts for roughly 70% of global production.

4.2 Ferritic Stainless Steel (400 Series)

Structure: Body-centered cubic (BCC). Magnetic. Zero or minimal nickel — cost advantage and price stability.

Key advantage: Excellent resistance to chloride stress corrosion cracking (Cl-SCC), a failure mode that affects 304/316 above 60°C with chlorides.

Limitation: Lower toughness, especially at low temperatures and in thick sections. Not suitable for cryogenic service.

4.3 Martensitic Stainless Steel

Trade-off: You gain hardness and wear resistance by heat treatment, at the cost of lower corrosion resistance (than austenitics) and more demanding welding (preheat + PWHT usually required).

4.4 Duplex Stainless Steel

Structure: ~50% austenite + 50% ferrite. Combines high strength (~2× 316L yield) + excellent Cl-SCC resistance.

2205 (UNS S32205): The workhorse duplex. PREN ~33–36. For chemical processing, offshore topsides, and pressure vessels where 316L would require uneconomically thick sections.

2507 (UNS S32750): Super duplex. PREN > 40. For seawater handling, desalination, subsea umbilicals.

Temperature window: Typically –50°C to 300°C. Not for use above 300°C (475°C embrittlement risk); verify Charpy for cryogenic applications.

4.5 Precipitation Hardening (PH) Stainless Steel

Achieves high strength through low-temperature aging — without the distortion of martensitic quenching. 17-4PH (SUS630): the most widely used PH grade, common in aerospace structural components, high-strength valves, shafts, and fittings.

5. Grade Selection Quick Reference

6. When Grade Equivalents Are Not Enough

A cross-reference chart is a useful starting point — not a substitute for a complete specification review in these situations:

• Pressure equipment governed by ASME BPVC, EN 13445, or PD 5500 — design codes mandate specific material grades with full traceability and impact testing
• Sour service (H₂S environments) — NACE MR0175 / ISO 15156 imposes hardness limits and qualification beyond standard MTC
• Welded fabrication without PWHT — carbon content differences between "equivalent" grades determine whether you get acceptable service or intergranular corrosion failure
• Severe corrosion service — PREN, critical pitting temperature (CPT), and critical crevice temperature (CCT) testing are required, not a grade-name comparison

7. Five Procurement Mistakes and How to Avoid Them

8. How to Write a Complete Stainless Steel Specification

A properly written material specification eliminates ambiguity. Include these elements in every inquiry:

9. How Shangyou Ensures Grade Accuracy

Grade identification errors in stainless steel supply can be costly — material rejection, fabrication rework, or in-service failure. Shangyou addresses this with systematic verification:

• Document verification: Every heat is matched to its mill certificate (EN 10204 3.1) before dispatch. We verify heat number traceability, full chemical composition, mechanical properties, and heat treatment records.
• PMI screening: Positive Material Identification using handheld XRF and mobile OES is available on request, cross-checking that major alloying elements (Cr, Ni, Mo) match the specified grade.
• Third-party inspection: We routinely arrange pre-shipment inspection with SGS, Bureau Veritas, TÜV, and Intertek — including dimensional verification, PMI spot checks, and documentation review.
• Technical review: Our engineering team can review your service conditions and verify that the selected grade meets your specific temperature, corrosion, and mechanical requirements.

10. Frequently Asked Questions

Q1: Are AISI 304 and EN 1.4301 exactly the same material?
They are considered equivalent for most commercial applications, but they are defined by different standards (ASTM vs. EN) which may have slightly different chemical composition limits. For general industrial use they are interchangeable; for code-governed pressure equipment, verify against the specific standard edition.

Q2: What is the UNS number for 316L, and why use it on a purchase order?
UNS S31603. Using "UNS S31603 per ASTM A240" on your PO provides an unambiguous material reference that works across countries and supplier systems. Unlike "316L" alone — which is understood but not formally defined in ASTM — the UNS number links to a specific composition range.

Q3: 304 vs. 316 — how do I decide which one to buy?
The decision hinge is chloride exposure. 316 contains 2–3% molybdenum, which significantly improves resistance to pitting and crevice corrosion in chloride environments. For coastal/marine or any chloride above ~200 ppm, 316/316L is the appropriate baseline. For indoor, mild, general industrial without chlorides, 304/304L provides adequate performance at lower cost.

Q4: What does the "L" suffix mean and when is it mandatory?
"L" = low carbon, max 0.03% (vs. 0.08% standard). It is mandatory practice for any welded fabrication without post-weld solution annealing, because lower carbon prevents chromium carbide precipitation (sensitization) in the heat-affected zone. If your component will be welded and placed in corrosive service without PWHT, specify the L grade.

Q5: Which grade for high-temperature applications above 500°C?
For welded high-temperature equipment, use stabilized grades 321 (Ti) or 347 (Nb). For maximum oxidation resistance, use 310S (up to ~1,100°C in air). If creep strength is the controlling criterion, 304H or 316H may be required by the design code instead of the low-carbon variants. The correct choice depends on temperature, atmosphere, loading type, and whether welding is involved.

Q6: Is duplex 2205 a direct upgrade from 316L?
Not in all cases. 2205 offers ~2× the yield strength of 316L plus superior Cl-SCC resistance — excellent for pressure vessels, chemical processing, and offshore applications. However, duplex has a restricted operating range (typically –50°C to 300°C), requires stricter welding control (heat input, interpass temperature), and costs more. It is an upgrade for the right application, not a universal replacement.

Q7: What's the difference between 304L and 304LN?
Both have low carbon (≤ 0.03%). 304LN adds deliberate nitrogen (0.10–0.16%), which increases yield/tensile strength above 304L and also improves pitting resistance (higher PREN). Specify 304LN when you need the weldability of 304L plus higher strength.

Q8: What is dual-certified stainless steel (304/304L or 316/316L)?
Dual-certified material meets chemistry and mechanical requirements of both standard-carbon and low-carbon grades simultaneously — carbon ≤ 0.03% (L requirement) and strength ≥ standard grade minimums. This simplifies inventory by covering both specifications with one material. However, dual certification covers chemistry and tensile properties; always verify that supplementary requirements (impact, hardness, corrosion tests) are met for your application.

Q9: Can I use a handheld XRF to confirm I received the correct grade?
XRF is a valuable screening tool: it can distinguish 304 from 316 (by detecting Mo) and austenitic from duplex grades. However, XRF cannot detect carbon — it cannot tell 304 from 304L, or 316 from 316L. It also cannot confirm heat treatment or phase balance. Use XRF as a quick field check; the MTC (EN 10204 3.1) with full laboratory chemical analysis is the definitive document.

Q10: What information needed for a fast stainless steel quotation?
Include: (1) grade and UNS number, (2) product standard, (3) product form and dimensions, (4) quantity and weight, (5) surface finish, (6) MTC type (3.1 or 3.2), (7) supplementary testing (PMI, IGC, Charpy, NACE), (8) delivery terms (FOB/CIF/CFR) and destination port, and (9) target delivery date. A complete inquiry enables a firm quotation within one business day.

Related Reading

• [304 vs 316 Stainless Steel: Differences and Applications]
• [Stainless Steel Surface Finish Guide: 2B, BA, No.4 and HL]
• [Duplex Stainless Steel 2205 vs 2507 Comparison]
• [Stainless Steel Coil Manufacturing Process Explained]