SS 304 / 304L / 304H
Fasteners
Manufacturer India
SS 304 vs 304L vs 304H — Which Grade to Specify
304, 304L, and 304H share identical 18% Cr / 8% Ni base chemistry. The three variants differ only in carbon content range — and that carbon level governs sensitisation behaviour, weld performance, and elevated-temperature creep resistance. Always specify the correct suffix for the application.
SS 304
SS 304L
SS 304H
The 425–870°C Sensitisation Zone — Why 304L Prevents Weld Decay
Sensitisation is the most important metallurgical concept for understanding when to specify 304L instead of 304. When austenitic stainless steel is held in the temperature range of 425–870°C — either during welding, post-weld heat treatment, or service at intermediate temperatures — chromium diffuses to grain boundaries to form Cr₂₃C₆ carbides. This depletes the adjacent metal of chromium below the 10.5% minimum required for the passive Cr₂O₃ layer, leaving a chromium-depleted zone at every grain boundary throughout the microstructure.
The result is intergranular corrosion (also called weld decay, Bain corrosion, or IGA — intergranular attack) — corrosion propagates along grain boundaries, not through grain interiors. A sensitised fastener can appear completely intact externally while its interior has been completely destroyed by intergranular corrosion. The classic test for sensitisation is ASTM A262 — the oxalic acid etch screening test followed by the Strauss test.
304L solves this by limiting carbon to ≤0.030% — there is simply not enough carbon available to form Cr₂₃C₆ carbides in meaningful quantity. As the temperature zone diagram shows, 304L in welded service safely passes through the sensitisation zone without depleting grain boundary chromium. 304H deliberately uses the higher carbon range (0.04–0.10%) for a completely different reason: above ~400°C in long-term service, the carbides that form in 304H actually pin dislocation movement and resist creep — the same carbides that damage 304 in corrosive service provide a creep benefit in elevated-temperature structural service.
<425°C
RISK ZONE
425–870°C
>870°C*
304 (≤0.080% C) — sensitisation risk if welded or service dwells in the amber zone. ✗ (for wet corrosive service)
304H (0.04–0.10% C) — not for use in corrosive service above ambient. Use for creep resistance in dry elevated-temperature service only. *Above 870°C, specify SS 310S for oxidation.
304L Fastener Types — Full Range
304L (S30403) is the primary stocking grade — suitable for food, pharma, dairy, cryogenic, and welded service. Standard 304 on order for non-welded general service. 304H for elevated-temperature service. M2–M100.
Stud Bolts
Fully threaded and equal-end stud bolts in 304L (S30403) and standard 304 (S30400). ASTM A193 B8 certified. M6–M100, lengths to 3,000mm. General industrial flanges, food-grade stainless flanges, pressure vessel stainless connections, and all ASME B16.5 flanged assemblies in 304/304L where the chloride risk does not require 316L’s PRE≈24.
Hex Bolts
Full thread (DIN 933) and partial thread (DIN 931) hex bolts in 304L. M2–M100. ISO property class A2-70 (standard) and A2-80 (strain-hardened, higher strength). Food processing equipment, pharmaceutical clean-room, dairy plant, laboratory furniture, general industrial construction, architectural, and outdoor structural applications where stainless appearance and mild corrosion resistance are required.
Hex Nuts
Standard hex nuts in 304L. M2–M100. ISO A2 property class. Matched from same A276 S30403 certified bar as hex bolts for single-alloy assembly documentation. DIN 934 standard hex and heavy hex ASME B18.2.2 for ASME B16.5 stud bolt assemblies. NABL hardness testing confirming ISO A2 property class.
Washers
Plain flat (DIN 125 / ISO 7089) and small OD (DIN 433) washers in 304L. M2–M100. Spring washers DIN 127. For complete 304L assembly documentation — bolt, nut, and washer from same certified heat. Food and pharmaceutical equipment panel assemblies where all wetted-surface hardware must be 304L traced to a single material lot.
Socket Cap Screws
Hex socket cap screws in 304L. M2–M24. Clean-room panel screws, pharmaceutical equipment internal screws, laboratory instrument mounting, food contact surface fixture screws, and all confined-access hygienic applications where a socket head in 304L’s corrosion-resistant chemistry provides flush, cleanable surface profile.
Threaded Rods
Full thread and end-thread in 304L. M4–M100, lengths to 3,000mm. Ceiling hanger rods for stainless food-grade suspended services, pharmaceutical production facility structural rods, clean-room partition fixings, laboratory bench support rods, and all applications requiring non-magnetic corrosion-resistant threaded rod in 304L.
Machine Screws
Slotted, Phillips, and cross-recessed machine screws in 304L. M2–M12. Cheese head, pan head, countersunk, and raised countersunk. Laboratory equipment, pharmaceutical instruments, food-grade panel assemblies, electronic instrument housings, and all small machine screw applications requiring 304L’s non-magnetic corrosion-resistant properties and hygienic cleanable surface.
Custom 304 / 304L
Non-standard sizes, special head forms, inch UNC thread in 304L, coupling nuts, barrel nuts, t-slot nuts, and any drawing-specific 304/304L configuration. Contact sales@akbarfasteners.in with grade (304/304L/304H), dimensions, and documentation requirement.
304L vs 316L vs 316 — Chloride & Service Environment Matrix
304L and 316L are the two most common stainless steel fastener grades globally. The only difference is 2% Mo in 316L, raising PRE from 18 to 24. Know when 304L is sufficient and when 316L is required.
| Service Environment | SS 304L This Page | SS 316L | Decision |
|---|---|---|---|
| WHERE 304L IS THE CORRECT AND SUFFICIENT SPECIFICATION | |||
| Food processing equipment, dry | ✔ Correct choice | Also acceptable | 304L — lower cost, fully compliant |
| Pharmaceutical / clean-room | ✔ Correct choice | Also acceptable | 304L — meet FDA/GMP, lower cost |
| Dairy equipment, CIP washed | ✔ Correct choice | Also acceptable | 304L — industry standard |
| Cryogenic / LNG service | ✔ Excellent toughness | Also excellent | 304L — both equal, 304L lower cost |
| Architectural / indoor | ✔ Correct choice | Over-specified | 304L — 316L not needed indoors |
| General industrial (non-chloride) | ✔ Correct choice | Over-specified | 304L — sufficient PRE≈18 |
| WHERE 316L IS REQUIRED — 304L IS INSUFFICIENT | |||
| Marine atmosphere / coastal | Pitting risk (PRE≈18) | ✔ Required (PRE≈24) | 316L — upgrade mandatory |
| Chemical plant chloride process | Pitting risk | ✔ Required | 316L — minimum specification |
| Chloride-containing food (brine) | Pitting possible | ✔ Preferred | 316L — for brine, salt solutions |
| Swimming pool environment | Stress corrosion risk | ✔ Minimum | 316L or Duplex — chloride SCC risk |
SS 304 / 304L Application Areas
The global default stainless fastener for food, pharmaceutical, dairy, cryogenic, general industrial, architectural, and non-chloride process applications.
Food Processing
CIP vessel connections
Pharmaceutical
GMP clean-room hardware
Dairy & Beverage
CIP-compatible hardware
Cryogenic / LNG
no ductile-brittle transition
Architectural
façade & cladding bolts
General Industrial
stainless structural hardware
Water Treatment
non-chloride dosing systems
Nuclear / Research
reactor structural hardware
SS 304 / 304L / 304H Standards Coverage
Same ISO 9001:2015 quality system as our complete SS range. PMI XRF confirms Cr 18–20% and Ni 8–10.5% — the critical check distinguishing genuine 304L from lower-grade imposters marked as A2.
Complete Documentation Package
S30403 UNS Stated
Tensile · Hardness
Ni 8–10.5% Confirmed
Conformance
21 CFR (on request)
Related Higher-Alloy Stainless Grades
304L for general non-chloride service. 316L when chloride pitting risk exists. 321 for welded high-temperature. 904L for aggressive acids.
SS 316L Fasteners
The step up from 304L — 2% Mo raises PRE from 18 to 24 for chloride-containing environments. For coastal/marine atmosphere, chemical plant, brine systems, and pharmaceutical applications where 304L shows early pitting. The minimum requirement for ASME B16.5 stud bolt sets in chemical process service.
View SS 316L →SS 321 Fasteners
For welded service in the 425–870°C sensitisation zone where both 304L and standard 304 have limitations — Ti-stabilised 321 completely prevents sensitisation regardless of carbon content by tying carbon as TiC rather than Cr₂₃C₆. The specification for welded high-temperature stainless connections.
View SS 321 →SS 310S Fasteners
For service above 800°C where 304H’s creep benefit is insufficient and oxidation resistance is the design criterion — SS 310S (25% Cr, 20% Ni) provides the highest oxidation resistance of any standard austenitic stainless to 1040°C continuous service.
View SS 310S →Hastelloy C276 Fasteners
When both 304L and 316L fail — aggressive acid environments, concentrated chloride, mixed acids. Hastelloy C276 (PRE≈66) handles environments that destroy all stainless steel grades, including concentrated HCl and HNO₃/HCl mixed acid at elevated temperatures.
View C276 →Need SS 304 / 304L
Fasteners?
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