201 vs 202 – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
Selecting between stainless steel grades 201 and 202 is a frequent procurement and design decision for engineers, manufacturing planners, and buyers balancing corrosion resistance, mechanical performance, and cost. Typical decision contexts include sheet and strip for consumer appliances, architectural trim, fasteners, and drawn components where a full 300‑series austenitic alloy may be cost-prohibitive.
The critical compositional distinction between the two grades centers on how nickel and manganese are deployed to achieve austenite stability: the two alloys use different nickel-to-manganese balances. That balance affects austenite stability, cold‑work response, corrosion resistance, and cost; consequently 201 and 202 are often compared where nickel price sensitivity and performance tradeoffs must be weighed.
1. Standards and Designations
- Common international designations:
- AISI/UNS: 201 = UNS S20100; 202 = UNS S20200.
- ASTM/ASME: Both appear in several ASTM product standards for cold‑rolled or hot‑rolled stainless strip/sheet; consult the specific product specification.
- EN / EN ISO: These grades are not 1:1 with 300‑series EN numbers but equivalents are often listed in supplier cross‑reference tables.
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JIS / GB: Regional equivalents exist; verify exact chemical limits against the local standard for procurement.
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Classification: Both 201 and 202 are austenitic stainless steels (non‑magnetic in annealed condition); they are not HSLA, carbon, or tool steels. They are part of the “200‑series” austenitics, designed as lower‑nickel alternatives to 300‑series stainless.
2. Chemical Composition and Alloying Strategy
The following table lists typical, commonly cited composition ranges. Actual limits vary by specification and mill; always verify mill certificates for procurement.
| Element | Typical range (201) | Typical range (202) |
|---|---|---|
| C | ≤ 0.15 wt% | ≤ 0.15 wt% |
| Mn | 5.5 – 7.5 wt% | 7.5 – 10.0 wt% |
| Si | ≤ 1.0 wt% | ≤ 1.0 wt% |
| P | ≤ 0.06 wt% | ≤ 0.06 wt% |
| S | ≤ 0.03 wt% | ≤ 0.03 wt% |
| Cr | 16.0 – 18.0 wt% | 17.0 – 19.0 wt% |
| Ni | 3.5 – 5.5 wt% | 4.0 – 6.0 wt% |
| Mo | typically trace / none | typically trace / none |
| V, Nb, Ti, B | typically not added | typically not added |
| N | controlled trace (varies by melt practice) | controlled trace (varies by melt practice) |
Notes: - The salient difference is in how nickel and manganese are balanced. Grade 202 typically contains higher manganese and slightly higher chromium; nickel is only marginally higher than in 201. The net effect is a lower nickel‑to‑manganese ratio in 202 compared with 201, which influences austenite stability and cold work response. - Both grades omit significant molybdenum (Mo) and microalloying elements commonly used in ferritic or martensitic stainless grades.
How the alloying strategy affects properties: - Chromium provides the passive film that gives stainless steels corrosion resistance; both grades have Cr in the mid‑teens and deliver general atmospheric and mild chemical corrosion resistance. - Nickel stabilizes the austenitic phase and improves ductility and toughness at low temperatures. - Manganese and nitrogen are used as inexpensive austenite stabilizers to reduce nickel demand. High Mn increases work‑hardening rate and can affect formability and machinability. - Absence of Mo limits resistance to chloride pitting and crevice corrosion compared with 300‑series or Mo‑bearing alloys.
3. Microstructure and Heat Treatment Response
- Microstructure (as annealed): Both 201 and 202 are primarily fully austenitic at ambient temperature when processed to specification. Small amounts of delta ferrite or other minor phases can appear depending on exact composition and thermal history, but these grades are engineered to be austenitic in the annealed condition.
- Heat treatment response:
- Austenitic stainless steels are not hardened by conventional quench-and-temper processes. Neither 201 nor 202 can be made martensitic by heat treatment.
- Solution annealing (typical anneal at about 1010–1120 °C followed by rapid cooling) restores ductility and dissolves strain‑induced phases formed during cold working.
- Cold work (rolling, drawing) is the principal way to increase strength in these alloys: work‑hardening raises yield and tensile strengths while reducing elongation and toughness.
- Thermo‑mechanical processing (controlled cold deformation + recrystallization anneal) will set grain size and texture and thus influence final formability and surface finish.
- Practical implication: Design and processing should assume properties are dominated by cold‑work and annealing history, not by quenchable hardenability.
4. Mechanical Properties
The absolute mechanical properties depend strongly on product form (cold‑rolled sheet, strip, coil, or cold‑drawn bar) and condition (fully annealed vs. various cold‑work levels). The following table summarizes comparative behavior rather than specific mill values.
| Property | 201 | 202 | Comment |
|---|---|---|---|
| Tensile strength | Comparable to 202; strong when cold‑worked | Comparable to 201; slight differences depend on cold work | Both strengthen markedly with cold work |
| Yield strength | Comparable; can be slightly higher after cold work | Comparable | Yield depends on degree of cold reduction |
| Elongation (ductility) | Good in annealed state; reduces with cold work | Good in annealed state; may be marginally higher than 201 in some batches | Ductility similar overall |
| Impact toughness | High in annealed condition; retains toughness at low temp | High in annealed condition | Austenitic matrix gives excellent toughness |
| Hardness | Low in annealed state; increases with cold work | Similar behavior | Hardness controlled by cold‑work |
Which is stronger/tougher/ductile and why: - Strength: Both grades are similar in annealed condition. Differences are mainly process-driven; because manganese and nitrogen influence work‑hardening, 201 can sometimes show a higher work‑hardened strength depending on exact compositions and cold reduction history, but this is not universal. - Toughness and ductility: Both maintain high toughness and good ductility in the annealed condition due to the austenitic matrix; differences are minor and application‑dependent.
5. Weldability
- General outlook: Austenitic 200‑series stainless steels are readily welded by common fusion and resistance welding processes. They do not harden by heat treatment, and welds remain ductile and tough.
- Influencing factors: Carbon content, manganese, nitrogen, and residual elements affect hot‑cracking susceptibility, ferrite content in the fusion zone, and post‑weld mechanical properties.
- Useful weldability indices (for qualitative interpretation):
- Carbon equivalent (IIW): $$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$
- Pcm (Pitting/cracking susceptibility index): $$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
- Interpretation (qualitative):
- Both 201 and 202 are low‑carbon and moderate‑alloyed; their $CE_{IIW}$ and $P_{cm}$ are generally low relative to high‑carbon steels, indicating good weldability.
- Higher manganese and nitrogen content (used as austenite stabilizers) can promote hot‑cracking in certain weld situations or change ferrite content in weld metal; using appropriate filler metal (often a compatible 300‑series filler) and controlling heat input mitigates defects.
- Preheat and post‑weld heat treatment are typically unnecessary for corrosion or hydrogen control, but welding of thicker sections or dissimilar metals should follow qualified procedures.
6. Corrosion and Surface Protection
- As stainless alloys with chromium ≈16–19 wt%, both grades offer general resistance to atmospheric corrosion, foodstuffs, and many mild chemicals. They are less corrosion‑resistant than 300‑series (304/316) in chloride‑containing environments.
- PREN (Pitting Resistance Equivalent Number) is used for assessing chloride pitting resistance when Mo/N and other pitting‑inhibitors are present: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$
- For 201 and 202, Mo ≈ 0 and N is low; therefore PREN values are low compared with Mo‑bearing alloys. Use PREN only when Mo and N are significant — otherwise the index shows these grades are not intended for aggressive chloride environments.
- Surface protection:
- In most applications these are used as stainless (no additional coating); for highly aggressive environments, surface protection such as passivation, electropolishing, or protective coatings may be required.
- For demanding outdoor or coastal service, consider higher‑alloy grades or protective coatings (hot‑dip galvanizing is typically not used on stainless where inherent stainless behavior is required).
7. Fabrication, Machinability, and Formability
- Forming: Both grades are formable in the annealed condition. Deep drawing and complex forming are possible but require tooling adjusted for higher work‑hardening rates when compared to 300‑series alloys.
- Machinability: 200‑series alloys generally machine less readily than free‑cutting carbon steels; their higher work‑hardening and tendency to work‑harden at the tool interface means higher cutting forces and rapid tool wear unless tooling and feeds are optimized. 202 is often considered similar to 201 in machinability; specific machinability depends on product form and temper.
- Finishing: Polishing, brushing, and surface finishing are typical; control of heat tint from welding and appropriate passivation are recommended to restore corrosion resistance after fabrication.
8. Typical Applications
| Typical uses — 201 | Typical uses — 202 |
|---|---|
| Decorative trim, architectural panels, furniture, appliance front panels where cost is critical | Appliance components, fasteners, screws, light‑duty kitchenware, automotive trim where improved drawability or regional availability is desired |
| Flatware and utensils, sinks (in budget‑sensitive products) | Tubing and wire applications in low‑corrosion environments |
| Cold‑formed parts where higher work‑hardening can be tolerated | Components requiring slightly higher resistance to mild corrosion and where 202 is more available |
Selection rationale: - Choose based on corrosion environment (mild vs. moderate), required formability (deep drawing vs. simple bending), surface finish expectations, and material cost. For heavily chloride‑exposed service choose higher‑alloy grades.
9. Cost and Availability
- Cost: Both 201 and 202 were developed to reduce nickel content and thus lower cost versus 300‑series alloys when nickel prices are high. Relative cost between 201 and 202 fluctuates with alloying element markets (Ni, Mn, Cr). Historically, 201 is often slightly cheaper than 202, but local supply and demand, and the nickel/manganese price spread, determine real procurement cost.
- Availability: 201 is widely produced and commonly available in sheet, strip, coil, and some drawn products. 202 availability varies by region and product form; in some markets it is offered as an alternative to 201 when performance or supplier preference suggests it.
10. Summary and Recommendation
Summary table (qualitative)
| Attribute | 201 | 202 |
|---|---|---|
| Weldability | Good | Good |
| Strength–Toughness balance | Comparable; high toughness; strength increases with cold work | Comparable; high toughness; similar cold‑work strengthening |
| Cost | Often lower | Often slightly higher (market dependent) |
Recommendations: - Choose 201 if: - Cost is the primary driver and service conditions are general (indoor, domestic appliances, decorative trim). - You need a cost‑effective austenitic stainless with good toughness and acceptable corrosion resistance for mild environments. - Choose 202 if: - You require marginally improved general corrosion resistance or slightly different formability characteristics offered by the altered Ni/Mn balance. - The procurement market shows favorable pricing or better availability for 202 in the required product form.
Final notes: - Both grades perform as austenitic stainless steels and are selected for cost‑sensitive, general‑service applications. The defining technical distinction is the nickel vs. manganese strategy to stabilize austenite; that compositional tuning alters work‑hardening, corrosion performance, and price sensitivity. For critical components, always specify required mill certificates, product form and temper, and validate welded assemblies with qualified procedures.