SS 304 / 304L / 304H Bolts Manufacturer & Exporter in India

The three grades share the same 18Cr-8Ni base composition but differ in carbon content and resulting performance. SS 304 is the general-purpose grade with carbon up to 0.08% max, suitable for most ambient and moderate-temperature applications. SS 304L limits carbon to 0.03% max to prevent sensitisation (chromium carbide precipitation) in welded assemblies – the preferred choice when bolts are incorporated into welded structures without post-weld annealing. SS 304H raises carbon to a controlled 0.04-0.10% range, which significantly improves creep and stress-rupture strength above 425°C – required by ASME Section I and Section VIII for elevated-temperature pressure vessel and boiler bolting. For ambient-temperature, non-welded applications, standard 304 is sufficient. For welded assemblies, specify 304L. For service above 425°C, specify 304H.

SS 304 bolts perform well in rural and urban atmospheric environments and resist oxidation, mild acids, and freshwater exposure. However, in marine splash zones, coastal environments with chloride-laden air, or applications involving direct seawater immersion, 304 is susceptible to pitting and crevice corrosion under bolt heads and in thread roots. For marine and coastal applications, SS 316 or 316L bolts – which contain 2-3% molybdenum – are the correct specification. If 304 bolts are already installed in a mildly corrosive environment, applying a PTFE thread sealant and using stainless steel washers to prevent crevice conditions under the head will extend service life.

For pressure vessel and piping flange bolting, SS 304 bolts are governed by ASTM A193 Grade B8 (304), B8L (304L), and B8H (304H). These specifications define tensile strength, yield strength, hardness, and heat treatment requirements for bolts used under ASME B31.3 process piping and ASME Section VIII pressure vessel codes. Bar stock used to manufacture the bolts must conform to ASTM A276 or ASTM A479. For metric bolting, EN ISO 3506-1 Class A2-70 covers 304 grade fasteners. Always confirm the applicable code with your engineering team before specifying fastener grade for pressure-retaining service.

Yes – austenitic stainless steels including 304, 304L, and 304H retain excellent toughness and ductility at cryogenic temperatures down to -196°C (liquid nitrogen temperature). Unlike ferritic and martensitic steels, austenitic grades do not undergo a ductile-to-brittle transition at low temperatures. ASTM A320 Grade B8 (304) and B8L (304L) specifically cover bolting for low-temperature and cryogenic pressure vessel service. Impact testing per ASTM A320 is required for service below -48°C. 304L is generally preferred for cryogenic bolting due to its lower carbon content and superior weld compatibility in cryogenic vessel fabrication.