304 vs 430 – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
When engineers, procurement managers, and manufacturing planners select between stainless steel grades 304 and 430 they typically balance corrosion resistance, mechanical behavior, magnetic response, and cost. Common decision contexts include food- and medical-equipment specification (where corrosion resistance and non‑magnetism matter) versus appliance and automotive trim (where cost, formability, and magnetic response are important).
The primary differences arise from alloy strategy: grade 304 is an austenitic chromium‑nickel stainless steel optimized for corrosion resistance and toughness, while grade 430 is a ferritic chromium stainless steel with lower alloy content, magnetic response, and typically lower corrosion resistance in aggressive environments. These contrasting chemistries drive differences in microstructure, weldability, fabrication, and application selection.
1. Standards and Designations
- 304: Common designations — UNS S30400, AISI 304, EN 1.4301, JIS SUS304, GB 06Cr19Ni10. Classified as stainless steel, austenitic.
- 430: Common designations — UNS S43000, AISI 430, EN 1.4016 (or 1.4016/1.4010 variations), JIS SUS430, GB 0Cr17. Classified as stainless steel, ferritic.
Both are covered by sheet/plate/tube standards such as ASTM A240 (flat products) and various EN/JIS equivalents. They are not carbon steels, tool steels, or HSLA grades.
2. Chemical Composition and Alloying Strategy
Table shows typical composition ranges for commercial grade 304 and 430 (ranges vary by standard and product form; values are expressed in weight percent).
| Element | 304 (typical range) | 430 (typical range) |
|---|---|---|
| C | ≤ 0.08 | ≤ 0.12 |
| Mn | ≤ 2.0 | ≤ 1.0 |
| Si | ≤ 1.0 | ≤ 1.0 |
| P | ≤ 0.045 | ≤ 0.04 |
| S | ≤ 0.03 | ≤ 0.03 |
| Cr | 18.0–20.0 | 16.0–18.0 |
| Ni | 8.0–10.5 | ≤ 0.75 |
| Mo | ≈ 0 | ≈ 0 |
| V | trace / none | trace / none |
| Nb (Cb) | none (except stabilized variants) | none |
| Ti | none (except stabilized variants) | none |
| B | trace / none | trace / none |
| N | ≤ 0.11 | ≤ 0.1 (often not specified) |
Alloying strategy implications: - Chromium provides base stainless passivity for both grades; higher Cr improves oxidation and general corrosion resistance. - Nickel stabilizes austenite, increases toughness and formability, and greatly improves corrosion resistance in many environments—this is key to 304’s performance. - Low alloy content in 430 makes it less corrosion-resistant in chloride‑rich or acidic environments but provides magnetic properties and lower cost. - Absence of strong hardenability elements (Mo, V, Nb) means neither grade is strengthened by conventional quench‑and‑tempering; strengthening is primarily by cold work (for austenitic 304) or alloy/tensile states (for 430).
3. Microstructure and Heat Treatment Response
- 304: Fully austenitic (face-centered cubic, FCC) at room temperature due to sufficient nickel and balanced Cr. Austenite is stable, leading to excellent toughness and ductility over a wide temperature range. Solution annealing (typically ~1000–1100 °C followed by rapid cooling) dissolves precipitates and restores corrosion resistance after welding; cold work increases strength by strain hardening and can induce some martensitic transformation in very cold-worked conditions (in magnetic response).
- 430: Ferritic (body-centered cubic, BCC) microstructure at room temperature. Ferrite is magnetic and does not transform to martensite on quenching from high temperature in the same manner as martensitic steels. Ferritic stainless steels cannot be hardened by quench-and-temper; annealing (approximately 750–900 °C depending on spec, followed by slow furnace cooling) is used to soften and restore ductility. Cold work increases strength but reduces ductility.
Heat‑treatment response summary: - Normalizing/quenching & tempering: not applicable as strengthening routes for either grade in the way used for carbon or alloy steels. - Solution annealing is critical for 304 after high-temperature exposure to avoid chromium carbide precipitation (sensitization) and restore corrosion resistance. - 430 is susceptible to grain growth and degradation of ductility with improper welding thermal cycles; controlled anneal restores properties.
4. Mechanical Properties
Typical mechanical behavior depends on product form (sheet, plate, bar) and temper (annealed vs cold‑worked). Values below are indicative typical ranges for annealed commercial products; consult material certificates for precise design values.
| Property | 304 (annealed, typical) | 430 (annealed, typical) |
|---|---|---|
| Tensile strength (UTS) | ~520–750 MPa | ~450–620 MPa |
| Yield strength (0.2% offset) | ~200–310 MPa | ~200–350 MPa |
| Elongation (uniform/total) | ~40–60% (good ductility) | ~20–40% (lower ductility) |
| Impact toughness (ambient) | High, retains toughness at low T | Moderate; reduced at low temperatures |
| Hardness (HRB) | ~70–95 | ~60–90 |
Interpretation: - 304 generally offers higher ductility and toughness due to austenitic microstructure and nickel content. - 430 can have comparable yield strength in some tempers but typically lower elongation and toughness, especially at sub‑ambient temperatures. - Both grades increase strength with cold work; 304 work hardens more markedly which affects forming and machining.
5. Weldability
Weldability depends on composition, carbon equivalent, and microstructure sensitivity.
Key weldability indices (useful qualitatively): - International Institute of Welding carbon equivalent: $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - Pcm (general weld cracking susceptibility): $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Qualitative interpretation: - 304: Excellent weldability by common processes (GMAW, GTAW, SMAW). Low carbon variants (304L) are specified to minimize sensitization risk and avoid post‑weld intergranular corrosion. Solution annealing after heavy welding or maintaining low heat input practices reduces carbide precipitation. Austenitic microstructure resists cold cracking but work hardens near welds. - 430: Weldable with appropriate consumables and procedures, but requires care. Ferritic stainlesss have higher thermal conductivity and lower weld pool fluidity; grain growth in the heat‑affected zone and sigma phase formation at certain temperatures can reduce toughness and corrosion resistance. Preheat is generally not required but filler selection and control of heat input to avoid embrittlement and minimize distortion are important. Use of matched ferritic fillers or appropriate austenitic fillers depends on desired final properties.
No numeric CE or Pcm evaluation is given here — these formulas are used by engineers to compare cases and select preheat/postweld treatments.
6. Corrosion and Surface Protection
- Use of PREN (Pitting Resistance Equivalent Number) is common where molybdenum and nitrogen influence pitting resistance: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$
- For 304 and 430, Mo ≈ 0, and N is low, so PREN is driven largely by Cr and is modest; 304 typically performs better in many aqueous environments than 430 because of higher nickel and more stable passive film.
Practical corrosion guidance: - 304: Good general corrosion resistance (atmospheric, many foodstuffs, mild chemicals). Not recommended for continuous exposure to chloride‑rich environments (marine, de‑icing salts) without additional measures; for chloride resistance consider Mo‑bearing grades (e.g., 316) or controls on design and surface finish. After welding, solution annealing or low‑carbon grades (304L) avoids intergranular corrosion. - 430: Good atmospheric and mild chemical resistance but inferior to 304 in chloride-containing and acidic environments. Susceptible to localized corrosion (pitting) in aggressive chloride service and to stress corrosion cracking in some environments less than austenitics. - Surface protection: Both grades rely on passive chromium oxide films; mechanical polish, electropolish, or passivation treatments enhance performance. For non‑stainless steels (not these grades), conventional protection is galvanizing, painting, or coatings — not typically needed for stainless when passive integrity is maintained.
7. Fabrication, Machinability, and Formability
- Forming: 304 (austenitic) exhibits excellent formability and deep‑drawing characteristics; strong springback and work hardening must be managed. 430 (ferritic) is formable in the annealed condition but has lower ductility and more limited deep‑drawing capability.
- Machinability: 430 is often easier to machine in annealed condition than 304 because ferritic structure tends to cut more cleanly; 304 work hardens rapidly and may require intermediate anneals, sharp tooling, and higher cutting forces. Use of proper tooling materials and speeds, and cutting fluids, is essential for 304.
- Surface finishing: Both can be finished to decorative or hygienic surfaces; 304 generally achieves brighter finishes and easier polishability due to its austenitic nature.
8. Typical Applications
| 304 — Typical Uses | 430 — Typical Uses |
|---|---|
| Food processing equipment, kitchen sinks, cookware, pharmaceutical equipment | Appliance trim (dishwasher facades), oven panels, microwave interiors |
| Chemical processing components, heat exchangers (non‑chloride) | Decorative architectural trim, elevator panels where magnetism is acceptable |
| Medical instruments, surgical tools (sterilizable surfaces) | Automotive interior/exterior trim, reflector/backers where magnetic response is useful |
| Fasteners and flanges requiring corrosion resistance and toughness | Low‑cost corrosion‑resistant sheet for indoor environments |
Selection rationale: - Choose 304 when corrosion resistance, hygienic cleaning, non‑magnetic behavior, and formability are prioritized. - Choose 430 when cost, magnetic properties, and reasonable corrosion resistance in non‑aggressive atmospheres are the priority.
9. Cost and Availability
- 304 carries higher material cost due to nickel content; global nickel price volatility influences 304 pricing. Widely available in sheet, coil, plate, bar, and tubular forms.
- 430 is lower cost and plentiful for sheet and coil, commonly stocked for appliance and architectural markets. Lead times are generally shorter and price more stable because of lower nickel content.
Product form affects price (cold‑rolled vs hot‑rolled vs polished), and procurement should consider lead time, finish, and certification (e.g., mill test reports).
10. Summary and Recommendation
| Criterion | 304 | 430 |
|---|---|---|
| Weldability | Excellent (use 304L/solution anneal to avoid sensitization) | Good with precautions (control heat input and filler selection) |
| Strength–Toughness | High toughness and ductility; good strength | Adequate strength, lower toughness and ductility vs 304 |
| Cost | Higher (nickel content) | Lower (economical for many applications) |
Choose 304 if: - You need superior general corrosion resistance, hygienic and cleanable surfaces, non‑magnetic behavior, and excellent formability/toughness (e.g., food, medical, chemical environments).
Choose 430 if: - You require a lower‑cost stainless with reasonable atmospheric corrosion resistance, magnetic properties (e.g., where detection or magnetic attachment is required), and good formability for indoor and decorative applications with limited chloride exposure.
Final note: material selection must consider service environment (chlorides, temperatures), mechanical loads, fabrication route (forming, welding), surface finish, and total life‑cycle cost. For critical applications run a materials compatibility check (laboratory corrosion tests or field data) and consult updated ASTM/EN/JIS specifications for exact composition and certifiable mechanical properties.