IS 6603:2001 is the Indian Standard (BIS) for stainless steel bars and flats. IS 6603 covers stainless steel bars and flats in austenitic (304, 316), martensitic (410, 420), and ferritic grades. 304 and 316 are the most commonly used grades in India for corrosion-resistant applications in food, chemical, pharmaceutical, and marine industries.
Specification for stainless steel bars and flats (round, square, hexagonal, flat) covering grades, dimensions, mechanical properties, and testing.
Key reference values — verify against the current code edition / project specification.
| Reference | Value | Clause |
|---|---|---|
| Subject | Stainless-steel bars & flats | Scope |
| Grades | Austenitic/ferritic/martensitic (e.g. 304/316/410) | Grades |
| Properties | 0.2% proof, UTS, elongation by grade/condition | Acceptance |
| Use | Corrosion-critical fixings/rebar/architectural | Application |
| Read with | IS 6911 (SS sheet) / IS 1608 (tensile) | Cross-ref |
IS 6603:2001 is the Indian Standard for Stainless Steel Bars and Flats — Specification. It is the companion specification to IS 6911:2017 (sheet/strip), covering round, square, hexagonal, and flat stainless-steel products in bar form.
Use it when: - Procuring stainless steel rod / bar for machined components — shafts, fasteners, pins, valve spindles, pump impellers - Specifying stainless reinforcement for marine concrete (in lieu of carbon steel rebar, for corrosion-critical structures) - Manufacturing stainless flats for fabrication — handrails, brackets, decorative trim, pharma equipment frames - Auditing imported stainless bar stock against IS conformance - Investigating premature corrosion of stainless components — grade verification, chemistry analysis, surface condition
Forms covered: - Round bars: diameters 3-100 mm typically (mill rolled), 1-300+ mm in cold-drawn / centerless ground - Square bars: 5-60 mm side - Hexagonal bars: 4-50 mm AF (across flats) — for fastener manufacturing - Flats: 12-300 mm wide × 3-50 mm thick
Distinct from: - IS 6911 — stainless sheet/strip (flat rolled coil) - IS 6529 — chromium-nickel stainless steel plate, sheet, strip (older spec, largely superseded) - IS 1570 — chemical composition of carbon and low-alloy steels - IS 1786 — TMT rebar (carbon, not stainless — for normal RCC work) - IS 16651 — Stainless Steel Reinforcement Bars (specialised reinforcement code)
IS 6603 covers the standard AISI-equivalent grades used in Indian engineering. Grade naming uses Indian X-prefix designation (e.g., X04Cr19Ni10 for AISI 304), with cross-reference tables in Annex A.
Common austenitic grades (most-used; non-magnetic, formable, weldable):
| Indian designation | AISI equiv | Cr | Ni | Mo | Typical use | |---|---|---|---|---|---| | X04Cr19Ni10 | 304 | 18-20 | 8-10.5 | — | General-purpose; food contact; architectural | | X02Cr19Ni10 | 304L | 18-20 | 8-12 | — | Welded fabrication (low-carbon prevents weld sensitisation) | | X04Cr18Ni10Mo3 | 316 | 16-18 | 10-14 | 2-3 | Marine, chloride-resistant | | X02Cr18Ni10Mo3 | 316L | 16-18 | 10-14 | 2-3 | Welded marine fabrication | | X07Cr19Ni10Ti | 321 | 17-19 | 9-12 | — | High-temperature service (Ti-stabilised) | | X07Cr18Ni10Cb | 347 | 17-19 | 9-13 | — | High-temperature (Nb-stabilised) |
Ferritic grades (magnetic, lower cost, less ductile): - X06Cr17 (430): kitchen utensils, decorative trim, low-corrosion applications - X10Cr13 (410): martensitic; hardenable; cutlery, fasteners
Duplex grades (premium; high strength + corrosion resistance): - X2CrNiMoN22-5-3 (2205): marine structures, chemical plants - X2CrNiMoN25-7-4 (2507) — super duplex: oil/gas, severe environment
Mechanical properties (annealed, cold-drawn condition, per IS 1608 Part 1):
| Grade | Rp0.2 min (MPa) | Rm min (MPa) | Elongation min (%) | Hardness HV max | |---|---|---|---|---| | 304 | 205 | 515 | 40 | 200 | | 304L | 170 | 485 | 40 | 200 | | 316 | 205 | 515 | 40 | 200 | | 316L | 170 | 485 | 40 | 200 | | 430 | 240 | 450 | 22 | 200 | | 410 (hardened) | 1200 | 1450 | 5 | 450 HRC | | 2205 (duplex) | 450 | 620 | 25 | 290 |
Cold-worked variants: bars supplied in 'quarter hard', 'half hard', 'three-quarter hard', 'full hard' (Clause 5.4) — increasing Rm and Rp0.2 with corresponding reduction in elongation. Standard procurement is annealed unless specified.
Surface finish (Clause 7): - Hot-rolled (HR): rough scaly surface from rolling; needs surface treatment for visible / corrosion-critical applications - Pickled (HRP): hot-rolled + acid-pickled to remove scale; matt-grey finish; ready for further machining - Cold-drawn (CD): smooth-bright finish from drawing through dies; tight dimensional tolerance - Centerless ground (CG): precision-ground OD; smooth shiny finish; for precision shafts - Polished (P): mechanically polished after grinding; mirror or No. 4 brushed finish
Dimensional tolerance (Clause 8): - HR rounds: ± 0.5 mm typical for 25-50 mm dia; tighter for smaller - CD rounds: h7 / h8 / h9 ISO tolerances; tighter than HR - CG: h6 / h7 precision class - Length: ± 25 mm on bar lengths typically; cut-to-length premium for tighter tolerance
Pickling and passivation (Clause 9): critical for service performance: - Pickling: removes oxide scale + heat-tint from heat treatment / welding using HNO₃ + HF solution - Passivation: HNO₃ alone (without HF) — strips iron contamination from surface, allows the chromium-rich passive layer to form - Both treatments mandatory for stainless components in corrosion-critical service - Inadequate passivation = embedded iron particles + corrosion initiation = premature pitting failure within months in coastal / chlorinated environments
1. Confusing 304 and 304L — almost identical except carbon content (304 = 0.08% max; 304L = 0.03% max). For welded fabrication, 304L is essential — 304 can sensitize in the HAZ (chromium carbide precipitation), causing intergranular corrosion. Many fabricators use 304 for welded handrails / brackets and have rust failure within 2-3 years.
2. Using 304 in coastal locations — chloride pitting attacks 304 within 5-15 years in coastal Mumbai/Chennai/Kochi air. Specify 316L for marine atmosphere; duplex 2205 for direct seawater immersion.
3. No pickling/passivation post-fabrication — bars cut, welded, ground, or otherwise heated produce heat-tint and embedded contaminants. Without post-fabrication passivation per ASTM A967 or pickling per IS 14237, surface integrity is compromised.
4. Galvanic coupling with carbon steel fasteners — using a stainless flat with carbon-steel bolts creates galvanic cell in damp environment. The carbon-steel bolt corrodes first, leaving rust streaks on the stainless. Always use stainless fasteners (A2 = 304 grade; A4 = 316 grade) with stainless components.
5. Spec confusion in procurement — '304 round bar 25 mm diameter' from one supplier might be 304 hot-rolled (rough finish), from another centreless-ground (smooth precision). Always specify: GRADE + FORM (round/square/flat) + SIZE + FINISH (HR/HRP/CD/CG) + CONDITION (annealed/half-hard/etc.) + TOLERANCE.
6. Cold-drawn properties assumed without verification — cold-drawn bars have higher strength but lower ductility than annealed. For applications requiring formability (bending, threading, machining heavy cuts), specify annealed condition explicitly.
7. Mistaking hex-bar for fastener material — IS 6603 hex bars are GENERAL stainless steel. Stainless fasteners require additional cold-drawing + threading per IS 6760 / ISO 3506 with specific Rm/Rp0.2 ratings (A2-70, A4-80, etc.). Don't substitute IS 6603 hex bar where a graded fastener is specified.
8. Lifting / handling damage — stainless bars contaminated by carbon-steel wire ropes, slings, or chains absorb iron particles. Use only nylon slings, stainless-strap lifters, or wood blocking. Wire-rope contamination = pitting initiation within months.
IS 6603:2001 is 24 years old and overdue for revision. Limitations of the 2001 edition: - Duplex / super-duplex grades (2205, 2507, LDX 2101) underspecified — engineers must reference EN 10088-3 for these - High-nitrogen austenitic grades (904L, 254 SMO) not included — common in modern chemical / pulp & paper industry - Free-machining grades (303, 416) underspecified
Indian market reality: - 304 / 304L round bar: ubiquitous, available from countless suppliers. Quality varies from premium (Jindal, BRG Iron & Steel, Mukand, Salem Stainless) to budget (Mumbai / Ahmedabad re-rollers). Premium ~₹250-350/kg; budget ~₹180-250/kg. - 316 / 316L round bar: less commonly stocked; ~₹350-500/kg; lead times can be 2-4 weeks for non-stocked sizes. - Duplex 2205 / super-duplex 2507: niche market; specialist suppliers (Sandvik, Outokumpu via Indian distributors); 2-4× the cost of 316L; 4-8 week lead times.
Procurement tip: for orders > 1 tonne of stainless bar, mandate Material Test Certificate (MTC) per heat with full chemistry and mechanical-property data. For projects in marine / chemical industry, additionally specify passivation certificate per IS 14237.
Counterfeit risk: Indian and imported bars marked '304' or '316' have been found, on testing, to be lower grades. The fraud occurs at the distributor / cut-and-bend level. Stainless steel grades can be verified by portable XRF analyzer (₹2-5 lakh equipment); some major contractors carry one onsite for QA.
For premium projects: source directly from BIS-licensed manufacturers with traceable heat numbers. Major Indian stainless steel manufacturers: Jindal Stainless, Mukand, BRG Iron & Steel, Salem Stainless, Saint-Gobain Stainless (in India).
| Parameter | IS Value | International | Source |
|---|---|---|---|
| 304 yield strength | Min 205 MPa | Min 205 MPa (30 ksi) | ASTM A276 |