Type 304 stainless steel

Identity and related grades

Type 304 is austenitic chromium-nickel stainless steel, UNS S30400. Type 304L is UNS S30403. Alleima lists both identities for its low-carbon 3R12 seamless tube product. Alleima 3R12, standards and nominal composition.

The carbon comparison comes from Cleveland-Cliffs, product description and composition, page 2. The 304H identity and purpose come from Alleima 5R10, standards and description. The first row's qualification is synthesis.

Atlas calls 304 "18/8" and compares it with EN 1.4301 and JIS SUS304, but explicitly calls its comparisons approximate rather than contractual equivalents. Its January 2011 flat-product table gives 304H carbon as 0.04% to 0.10% and requires ASTM grain size No. 7 or coarser. Synthesis. An "H" designation is therefore more than a claim that ordinary 304 tolerates heat. Atlas, grade data sheet, pages 1 and 2.

Composition evidence has a specification basis

The following table compares Atlas's supplier compilation of flat-product specification limits with Cleveland-Cliffs producer information. Values are mass percent, with "maximum" distinct from a range.

Sources are Atlas, page 2 and Cleveland-Cliffs, page 2. Synthesis. These tables establish source-specific values. Neither establishes the acceptance limits of an unidentified lot. This research does not reconcile their differences through the full applicable standard editions.

Product form and supplied condition

ASTM A240/A240M-26 covers stainless plate, sheet, and strip for pressure vessels and general applications. Its public scope treats SI and inch-pound values as separate systems whose values may not be exact equivalents. It does not supply a universal acceptance basis for every 304 product form. ASTM, A240/A240M-26 public abstract and scope.

Seamless tube has a different product context. Alleima's 3R12 sheet lists ASTM A213, A269, and A312 and describes solution-annealed supply with either a pickled or bright-annealed surface. Those are product-specific statements, not a statement that all 304 stock has that condition. Alleima 3R12, product standards and forms of supply.

Atlas describes dual-certified 304 and 304L plate, pipe, and round bar as complying with both grades' chemical and mechanical requirements. It warns that such material may be unacceptable for high-temperature applications. Synthesis. Low carbon alone does not prove dual certification or suitability as 304H. Atlas, dual certification, page 1.

Annealing, cold work, and property values

Cleveland-Cliffs describes 304 as non-hardenable by heat treatment. Cold work increases strength and hardness, while intermediate annealing can restore ductility. Its flat-rolled product bulletin's typical room-temperature table gives 304 tensile strength of 655 MPa, 0.2% offset yield strength of 290 MPa, and elongation of 55% over 50.8 mm. The table does not specify the sample condition. These are typical values, not universal specified minima. Cleveland-Cliffs, pages 3 and 4.

Synthesis. "Cold rolled" identifies a production route, while "cold worked" can describe retained deformation that affects properties. A subsequent anneal changes that state. A property comparison needs the product form, final condition, temperature, and value basis. Strength in MPa, elongation in percent with gauge length, and hardness with its scale describe different quantities. A hardness number without a scale is incomplete.

Corrosion depends on environment and thermal history

Alleima reports pitting and crevice corrosion susceptibility for 3R12 even at relatively low chloride contents. Stress corrosion cracking can occur under tensile stress in certain solutions, particularly chlorides, above about 60°C. Synthesis. This does not establish universal safety below 60°C. Alleima 3R12, corrosion resistance.

Alleima's higher-carbon 5R10 reference warns that sensitization after improper heat treatment or welding can reduce resistance to intergranular corrosion. It distinguishes that risk from the lower-carbon 3R12 product. Alleima 5R10, intergranular corrosion.

Synthesis. A low-carbon suffix addresses a particular metallurgical risk. It does not establish resistance to every acid, chloride solution, or cleaning chemical. A chemical-resistance statement remains incomplete without concentration, temperature, exposure conditions, and the fabricated material state. An industrial-use example does not establish compatibility for an unspecified medical device or patient-contact use.

Magnetic response

Austenitic stainless steels generally have low magnetic permeability. Cold deformation can transform some austenite to ferromagnetic martensite, creating magnetic attraction at sheared edges, sharp bends, or machined regions. Composition and heat treatment also affect the response. British Stainless Steel Association, effect of cold work and heat treatment.

Synthesis. Magnetic attraction does not by itself disprove a 304 identification. Lack of attraction does not distinguish 304 from every other austenitic alloy. A specified magnetic response is a separate requirement from the grade label.

Welding and machinability boundaries

For 3R12, Alleima lists ER308L and E308L-17 filler options. For 5R10 it lists ER308H and E308H-17. The different recommendations reflect different producer products and service purposes. Alleima 3R12, welding, Alleima 5R10, welding.

ASME BPVC Section IX addresses qualification of joining procedures and personnel. Synthesis. A producer's statement of weldability or filler recommendation does not qualify a shop's procedure, welder, joint, or finished component under the applicable construction requirements. ASME BPVC.IX-2025, public description supplied through ANSI.

Coverage limit. This article establishes no universal machining speed, tool-life value, bend radius, welding heat input, or post-weld treatment requirement. The grade name does not contain those process qualifications.

Sources and review limits

Reviewed on 29 October 2026 PDT. The Atlas January 2011 two-page sheet and Cleveland-Cliffs May 2021 five-page bulletin were inspected as dated references. Alleima's 3R12 and 5R10 pages both state an update of 9 May 2025. The BSSA article does not establish a revision date. ASTM A240/A240M-26 and ASME BPVC.IX-2025 were inspected through public publisher or ANSI descriptions, not the full paid standards. These sources do not certify a particular heat, finished assembly, supplier's current stock, or customer capability.

Related reference: Grades, tempers, and conditions.