5 Martensitic Stainless Steel Grades: Hardness and Uses Compared
Choose 410 for a general-purpose starting point, 416 for easier machining, 420 for cutting and wear, and 440A or 440C when higher hardness matters. 440C offers the highest hardness capability of these five. But heat treatment, corrosion exposure, impact loads, and welding needs can change the best choice. Buy a grade and a verified condition—not a grade name alone.
Compare the five grades
How do 410, 416, 420, 440A, and 440C compare?
The main trade-off is between machining, hardness, toughness, and corrosion resistance. Increasing carbon can support higher hardness after suitable heat treatment. Adding sulfur helps machining, but brings other penalties.
HRC means Rockwell C hardness; HB means Brinell hardness. They are different test scales. The values below are published reference conditions, not a single controlled five-grade test or guaranteed maximum hardness.
| Grade | Key chemistry, by weight | Published hardness and condition | When to consider it |
|---|---|---|---|
| 410 | Carbon: ≤0.15% Chromium: 11.5–13.5% | 42 HRC in Carpenter’s bar comparison: hardened, then tempered at 204°C / 400°F. A typical result, not a delivery guarantee. [1] | Shafts, fasteners, and valve parts needing strength with moderate corrosion resistance. |
| 416 | Carbon: ≤0.15% Sulfur: ≥0.15% Chromium: 12–14% | 248–302 HB for hardened-and-tempered Condition T bar in the Atlas reference. This is a supply condition, not maximum hardening capability. Check the governing specification. [2] | Turned and threaded parts where machining time matters and exposure is mild. |
| 420 | Carbon: ≥0.15% in the cited grade sheet Chromium: 12–14% | 52 HRC in Carpenter’s bar comparison after hardening and tempering at 204°C / 400°F. Exact 420 chemistry and processing can produce other results. [1] | Cutting instruments, molds, and wear parts requiring more hardness than 410. |
| 440A | Carbon: 0.60–0.75% Chromium: 16–18% | About 56–57 HRC in Carpenter’s heat-treatment guidance, with low-temperature tempering at 148–176°C / 300–350°F after the specified hardening route. [3] | Cutlery, pivot pins, and valve components needing high hardness. |
| 440C | Carbon: 0.95–1.20% Chromium: 16–18% | Approximately 60 HRC in Carpenter’s guidance, with tempering at 149–177°C / 300–350°F after the specified hardening route. A reference result, not a guarantee for every part. [4] | Bearings and high-wear components where hardness is a leading requirement. |
Keep each value attached to its scale, product form, and condition. In particular, do not compare “302 HB” with “60 HRC” as ordinary numbers. Chemistry entries are selected identification features, not full purchase specifications. Sources: 410, 416, 420, 440A, and 440C.
The practical rule: define the required finished hardness range first. Then ask whether the grade can meet it in your part’s thickest section while still meeting toughness, corrosion, and dimensional requirements.
What makes stainless steel martensitic?
Martensitic stainless steels combine chromium for corrosion resistance with a structure that can be hardened by heat treatment. In simple terms, heating and rapid cooling change the steel’s internal structure. Tempering then adjusts the balance between hardness and resistance to cracking.
That is why a soft bar used for machining and a hardened finished blade can have the same grade name but very different properties. The grade describes the material family; the heat-treatment condition helps describe how the part will behave.
These five grades are normally magnetic. A magnet can therefore be a rough screening tool, but it cannot distinguish 410 from 420 or confirm whether a part was heat treated correctly. Use material traceability and suitable testing for identification.
For the wider family and its heat-treatment behavior, see the worldstainless martensitic stainless steel guide.
Which martensitic stainless steel grade should you choose?
Start with the failure you must prevent: wear, a chipped edge, a corroded surface, a cracked weld, or excessive manufacturing cost. “Hardest” is only the right answer when hardness addresses that failure.
410: a general-purpose starting point
Consider 410 for a shaft, fastener, or valve component that needs useful strength rather than a very hard cutting edge. It is the baseline comparison when moderate corrosion resistance is enough and the part can receive a suitable heat treatment.
Check before choosing: required core properties, service temperature, impact loading, and the condition needed for machining. A higher-hardness condition can make machining more demanding. [5]
416: easier machining, with clear limits
416’s sulfur addition forms inclusions that help machining. This makes it useful for repeated turning, drilling, and threading operations. However, the same grade choice gives up corrosion resistance and formability compared with 410.
Check before choosing: chloride exposure and any planned weld. Atlas specifically warns against marine or other chloride service. Do not choose 416 solely because the machining quote is lower. [2]
420: cutting and wear with chemistry control
420 is a candidate when 410 does not provide enough hardness or wear resistance. It appears in cutting instruments and mold-related applications, but “420” covers commercial variants with different carbon levels.
Check before choosing: the exact grade specification and supplier chemistry. A description such as “420 stainless” is not enough to predict final edge behavior, polishability, or hardness. [6]
440A: high hardness without defaulting to 440C
440A provides a higher-carbon option than the basic 410 grade. Its published hardness capability supports uses such as cutlery, pivot pins, and valve parts. It remains a moderate-corrosion-resistance material, not an automatic choice for aggressive liquids.
Check before choosing: whether the target hardness actually improves the part. Compare finished edge geometry, surface finish, and corrosion performance instead of relying on the “440” family name. [3]
440C: the highest hardness capability in this comparison
Choose 440C as a candidate for bearings, wear surfaces, or cutting components when high hardness is central to service life. Carpenter identifies roughly 60 HRC in the hardened-and-tempered condition and lists bearings and valve parts among its uses. [4]
Check before choosing: impact, corrosion, final grinding, and dimensional stability. A part that resists wear can still fail by chipping, corrosion, or an out-of-tolerance fit. “440C” also does not, by itself, certify bearing cleanliness or finished bearing quality.
Selection example: a small pump shaft. This is an illustrative decision, not a reported test. For a shaft that is turned and threaded, 416 may reduce machining effort. But if the shaft sees salty wash water, or a bracket must be welded onto it, those conditions can outweigh machining savings. Screen the service and joining route before comparing raw-material prices.
How does heat treatment change hardness and part performance?
Hardness is resistance to indentation; toughness is resistance to fracture. A high hardness reading does not prove that a part can withstand impact, resist fatigue, or survive a corrosive liquid.
A typical manufacturing route has three linked stages. The exact temperatures, hold times, and cooling method must come from a qualified route for the grade, section size, and required properties.
- Machine in a suitable starting condition. Annealing softens the material for manufacturing. Leave appropriate finishing allowance when later heat treatment may change dimensions.
- Harden and temper the part. Hardening develops the required structure; tempering reduces brittleness and adjusts properties. One furnace recipe should not be copied across all five grades.
- Finish and verify. Grinding, polishing, cleaning, and inspection must preserve the required surface and dimensions. Check hardness at an agreed location after the agreed manufacturing stage.
Carpenter’s same-table bar examples make the difference clear: annealed 410 is listed at 83 HRB, while hardened 410 tempered at 204°C is listed at 42 HRC. That is a change in condition—not a different grade. The different scales also mean these numbers should not be subtracted or compared as percentages. [1]
For acceptance, specify more than “hardness checked.” Record the test scale and method, permitted range, test location, surface preparation, sample quantity, and measurement stage. For a thick part, agree how core properties will be demonstrated; one accessible surface reading may not answer that question.
Can martensitic stainless steel rust?
Yes. “Stainless” does not mean rust-proof. The service liquid, temperature, crevices, surface finish, and heat treatment all matter. A higher chromium percentage alone is not enough to rank finished parts.
Outokumpu explains that corrosion resistance depends strongly on heat treatment and surface condition. Some tempering conditions promote carbides that reduce corrosion resistance in traditional martensitic grades. A smooth, correctly finished surface generally performs better than a rough one. [8]
| Service condition | Selection concern | Evidence to request |
|---|---|---|
| Mild, mostly dry service | Residue, rough surfaces, and trapped moisture can still cause staining. | Finished-surface requirements and a cleaning or exposure check appropriate to the part. |
| Salt, marine air, or chloride wash water | Do not assume 410–440C will work because they are stainless. 416 is especially unsuitable. | Review the actual chloride level, temperature, contact time, and crevices with the material supplier. |
| Chemical cleaning or repeated sterilization | The complete cleaning cycle can be more demanding than normal operation. | Test representative finished parts through the intended cycle, including cleaning agents, rinse, and drying. |
If pitting, red rust, or unacceptable staining appears during a representative test, reconsider the grade or process. Do not treat polishing or passivation as a way to turn an unsuitable alloy into a suitable one.
Can these grades be laser welded?
Some can be welded with a qualified procedure, but laser welding does not remove their metallurgical limits. A small weld or narrow heat-affected zone is not proof that the joint will resist cracking or keep its required properties.
- 410: a more practical candidate within this group, but the procedure must address cracking and the required final condition. [5]
- 416: Carpenter does not recommend welding this free-machining grade. Reconsider the material or joint design before treating it as a routine welding job. [9]
- 420: Carpenter describes it as seldom welded because of its air-hardening behavior. A procedure needs grade-specific engineering and verification. [6]
- 440A and 440C: worldstainless lists conventional welding recommendations for the 440 family as “not recommended.” That is a strong warning, not permission to assume a laser is an exception. [7]
For a proposed joint, provide the exact alloy, starting hardness, section thickness, joint geometry, restraint, and required final properties. The welding engineer should determine the procedure, any pre- or post-weld heat treatment, and acceptance testing. A smooth-looking bead alone is insufficient.
For the broader process context, see our stainless steel laser welding guide. Material compatibility still needs to be established for the specific martensitic grade and part.
When should you consider 304, 316, or 17-4 PH instead?
If the required service does not fit these five grades, widening the shortlist is better than forcing a hardness-based choice.
Consider 304 or 316 when corrosion and fabrication dominate
If the part primarily needs corrosion resistance, forming, or welding rather than a hardened cutting surface, review the austenitic grades. They are not direct substitutes for a heat-hardened 440C wear part. Start with the actual environment and mechanical requirements, then compare the complete design. Our 304 vs 316 identification guide helps avoid mixing up those common grades.
Consider 17-4 PH when the strength and aging route fit the part
17-4 PH is a martensitic precipitation-hardening stainless steel. Its aging treatment develops strength through precipitation, so it belongs in a different selection route from these conventional carbon-hardening grades. It should not be described simply as “not martensitic.” [8]
Evaluate the specified aging condition and its strength, toughness, and corrosion trade-offs. See our 17-4 PH H900 strength guide for that condition-specific comparison.
What should you specify before ordering martensitic stainless steel?
A useful purchase description connects the material to the finished part. Ask suppliers to quote the same requirements so that a low material price does not hide extra heat treatment, finishing, or rejected parts.
- Exact grade and product specification. Include the governing standard and revision, product form, dimensions, and material certificate. For 420, make the intended chemistry or variant clear.
- Delivery condition. State whether material must be annealed, supplied at a machinable hardness, or hardened and tempered. Separate incoming-stock requirements from final-part requirements.
- Finished properties. Define hardness range and test location. Add strength, impact, fatigue, or wear requirements where they matter; do not expect hardness alone to stand in for them.
- Manufacturing and dimensional limits. Identify welding, forming, heat treatment, grinding allowance, and final tolerances. Decide who is responsible for each stage.
- Surface and environment. Specify roughness, cleaning, passivation where applicable, and the real exposure or cleaning cycle used to verify performance.
- Acceptance and traceability. Agree the test method, sample plan, records, and treatment of nonconforming parts before production.
Bottom line: use 410 as a general-purpose reference, 416 for machining-led parts in suitable service, 420 for a step toward cutting and wear applications, and 440A or 440C for higher hardness. Confirm that the chosen heat treatment and finished part meet the job—not just the hardness column.
Technical sources
- Carpenter Technology: TRIMRITE datasheet, 2025, page 4. Separate 410/420 bar comparison and its hardness conditions; not TRIMRITE strip values.
- Atlas Steels: Grade 416 datasheet. Legacy May 2008 reference for chemistry, machining, exposure limits, and Condition T hardness. Verify the current purchase specification.
- Carpenter Technology: 440A datasheet. Composition, approximate hardness, heat treatment, and uses.
- Carpenter Technology: 440C datasheet. Chemistry, approximate hardness, tempering conditions, and wear-related applications.
- Carpenter Technology: 410 datasheet. Chemistry, workability, applications, and welding considerations.
- Carpenter Technology: 420 datasheet. Chemistry, grade variations, hardening, and welding limits.
- worldstainless / ISSF: Martensitic Stainless Steels. Material behavior and welding guidance, including Table 7.
- Outokumpu: Martensitic and precipitation-hardening grades. Corrosion, weldability, and PH classification.
- Carpenter Technology: 416 datasheet. Free-machining features and welding recommendation.
These references explain selection principles and published material examples. The governing specification, certified material, approved processing route, and finished-part tests control acceptance.