S31603 Hot Rolled No. 1 Stainless Steel Plate: Properties and Applications

What S31603 Hot-Rolled No. 1 Plate Is

S31603 is the UNS designation of the extra-low-carbon molybdenum-bearing austenitic stainless steel known commercially as 316L. It is the grade most often selected for welded plate structures that must resist chlorides, dilute acids and a wide range of process chemicals. The material is supplied in the hot-rolled condition with a No. 1 finish, meaning the plate has been hot rolled, heat treated and pickled, giving the matt silver-white surface used as the starting condition for tanks, vessels and general fabrication. The "1" in No. 1 finish refers to the finishing sequence, not to a material type, so the same plate ordered with a 2B or polished finish would be the same steel with a different surface.

Standards and Delivery Condition

ASTM A240 / ASME SA-240: standard specification for chromium and chromium-nickel stainless steel plate, sheet and strip for pressure vessels and general applications.

ASTM A480 / A480M: general requirements for flat-rolled stainless plate, which control tolerances, flatness and the definitions of surface finishes.

GB/T 24511: stainless steel plate and strip for pressure equipment, the Chinese grade being 022Cr17Ni12Mo2.

GB/T 4237: hot-rolled stainless steel plate, sheet and strip for general use.

EN 10028-7 and EN 10088-2: European flat product standards; the equivalent designations are 1.4404 and, for the higher-molybdenum variant, 1.4435. JIS G4304 / G4305 cover the Japanese SUS316L grade.

No. 1 finish corresponds to the European designation 1D, hot rolled, annealed and pickled. The surface is rough and non-reflective and is normally blasted, ground or polished after fabrication where hygiene or appearance matters. Plate is supplied in the solution-annealed condition unless a different condition is agreed, and the mill certificate should state the heat treatment temperature, the heat number and the mechanical test results.

Chemical Composition of S31603 Plate

Element	C	Si	Mn	P	S	Cr	Ni	Mo	N
Specified range (wt%)	≤ 0.030	≤ 0.75	≤ 2.00	≤ 0.045	≤ 0.030	16.0–18.0	10.0–14.0	2.00–3.00	≤ 0.10

Three points matter in practice. The carbon limit of 0.030% is what makes the grade weldable in heavy sections without a post-weld solution anneal. The molybdenum range of 2.00% to 3.00% is what raises resistance to pitting and crevice corrosion in chloride-bearing media. The nickel range of 10.0% to 14.0% stabilises the austenitic structure, which is non-magnetic in the annealed condition and retains good toughness at low temperature. Note that some published data sheets quote a chromium range ending at 18.5%; that figure belongs to the European 1.4404 specification, while ASTM A240 and GB/T 24511 both specify 16.0% to 18.0% chromium for this grade.

Mechanical Properties and Elevated-Temperature Behaviour

Property	S31603 / 316L requirement	Test reference	Comparison with Type 304 hot-rolled plate
Tensile strength	≥ 485 MPa	ASTM A370; GB/T 228.1	Lower (304: ≥ 515 MPa)
Yield strength, 0.2% offset	≥ 170 MPa	ASTM A370; GB/T 228.1	Lower (304: ≥ 205 MPa)
Elongation in 50 mm	≥ 40%	ASTM A370	Same
Hardness	≤ 217 HBW	ASTM A480	Same order
Structure	Austenitic, non-magnetic when annealed	Metallographic	Same

Above room temperature S31603 holds its strength better than Type 304 in the creep range because of the molybdenum addition, and it is commonly used in continuous service up to about 800 °C in oxidising atmospheres. Long exposure in the 500 °C to 800 °C band promotes sigma phase formation and a progressive loss of toughness, so equipment that operates hot and must also withstand impact or pressure cycling should derive its allowable stress from the applicable design code rather than from a general temperature figure. At the cold end the grade remains ductile to cryogenic temperatures, which is one reason it appears in liquefied gas service.

Corrosion Performance, Fabrication and Typical Applications

The pitting resistance equivalent number, calculated as chromium plus 3.3 times molybdenum plus 16 times nitrogen, is about 24 for S31603 against roughly 18 for Type 304, which is the numerical expression of the well-known advantage of 316L in brackish water, salt spray and chloride-bearing process streams. The grade resists intergranular corrosion after welding because its carbon content stays below the sensitisation threshold, and it handles dilute sulfuric, phosphoric and acetic acids, most organic acids and many food products. It is not immune to chloride stress corrosion cracking above about 60 °C, and it should not be used for strong oxidising chlorides or hot concentrated caustic solutions without specific evaluation.

Fabrication follows normal austenitic practice. Weld with matching low-carbon consumables such as ER316L, keep heat input moderate, avoid excessive interpass temperature, and do not apply post-weld heat treatment; the plate is used in the as-welded condition and any thermal stress relief would itself risk carbide precipitation. After welding, remove heat tint and weld scale by pickling or mechanical means and passivate the surface. Bending and forming are carried out cold at around twice the thickness as a minimum inside radius for annealed plate, with trial forming for tight radii because the grade work-hardens rapidly. Typical applications include chemical reactor shells, storage tanks, heat exchanger plates, food and pharmaceutical equipment, architectural cladding, marine hardware and cryogenic vessels.

Frequently Asked Questions About S31603 Plate

Q: Is S31603 the same material as 316L?
Yes. S31603 is the UNS number for the extra-low-carbon grade sold as 316L, equivalent to Chinese 022Cr17Ni12Mo2 and European 1.4404. The numbers are different designations for the same steel.

Q: What does No. 1 finish mean on a stainless steel plate?
It means the plate has been hot rolled, annealed and pickled, producing a rough matt surface equivalent to European finish 1D. It is the standard mill condition for further fabrication, not a polished finish.

Q: Does S31603 plate need post-weld heat treatment?
No. The low carbon content allows welding without a solution anneal, and heat treatment after welding can actually cause carbide or sigma precipitation. Pickling and passivation of the weld zone are the normal finishing steps.

Q: Can S31603 be used in seawater?
It performs well in intermittent seawater contact and in flowing seawater where fouling is controlled, but it is susceptible to crevice attack and to chloride stress corrosion cracking in warm, stagnant or evaporative conditions, where duplex 2205 or a higher-alloy grade is preferred.

Q: How does S31603 differ from Type 316 plate?
Only in carbon content. Type 316 permits up to 0.08% carbon and offers slightly higher strength but a greater risk of sensitisation during welding; S31603 caps carbon at 0.030% and is therefore preferred for welded construction.