What is the machinability rating of AISI 321?

36 %, on the scale where AISI 1112 free-machining steel is 100%. Values above 100% mean the material cuts more easily than the reference steel; values below mean it is harder to cut. The rating is a comparison scale, not a physical property, so sources differ by roughly ±10%.

What cutting speed should I use for AISI 321?

Typical ranges are 180–280 SFM (55–85 m/min) for rough turning and 280–380 SFM (85–115 m/min) for finishing, with milling around 180–320 SFM. These are starting points only — the correct value depends on the insert grade and coating, the depth of cut, rigidity of the setup, coolant and the machine. Start at the low end and increase until tool life or finish degrades.

What is the equivalent of AISI 321 in other standards?

See the Equivalent Designations table above. Cross-standard correspondence is approximate: alloys within a designation are close but not guaranteed interchangeable, because each standard specifies its own composition ranges and tolerances. Verify against the specific specification before substituting.

What material group is AISI 321?

M — Stainless Steel, sub-group Austenitic, stabilised. Material groups — P, M, K, N, S and H — classify materials by machining behaviour so that insert grades can be selected by group rather than by individual alloy.

AISI 321

Machining data for AISI 321 (Stainless Steel 321) — material group, hardness, machinability rating, recommended cutting speeds and equivalent designations.

Page last changed 2026-10-19 · based on n/a — industry comparison scale, no governing standard

Quick Answer

AISI 321 has a machinability rating of 36 % and a hardness of 95 HRB. Typical roughing speed is 180–280 SFM, finishing 280–380 SFM. It belongs to material group M.

General Information

Material group	M — Stainless Steel
Sub-group	Austenitic, stabilised
Hardness	95 HRB
Tensile strength	620 MPa (90 ksi)
Machinability	36 %
Density	7.92 g/cm³
Product / heat-treatment condition	A shared condition for all properties is not recorded; see the individual property notes.

Hardness, tensile strength and machinability are compiled typical values. They are not a specification for a single product and heat-treatment condition. Where a grade also appears in the Steel Grades Chart, the two compilations have not been reconciled to a common condition.

Titanium-stabilised austenitic stainless that resists sensitisation at high service temperatures — the usual choice for exhaust components, expansion joints and heat-exchanger tubing. Machining is comparable to 304, with slightly higher tool wear from the titanium.

Cutting Speed Recommendations

Operation^[5]	Speed range (carbide)^[5]
Turning — roughing	180–280 SFM (55–85 m/min)
Turning — finishing	280–380 SFM (85–115 m/min)
Milling	180–320 SFM
Drilling (HSS)	45–65 SFM

Speeds are surface feet per minute with carbide tooling; millimetre equivalents are in brackets. These are typical catalogue ranges, not a specification. Depth of cut, feed, insert grade, coolant and machine rigidity all shift the correct value — start at the low end.

Equivalent Designations

Standard^[3]	Designation^[3]
AISI/SAE	321
UNS	S32100
DIN	1.4541 (X6CrNiTi18-10)
EN	1.4541
JIS	SUS321

Cross-standard correspondence is approximate. Verify against the governing specification before substituting one designation for another.

Chemical Composition

Element^[1]	Content (%)^[1]
C	≤0.08
Mn	≤2.00
Cr	17.0–19.0
Ni	9.0–12.0
Ti	≥5×C
Si	≤0.75
Fe	Balance

Compiled composition ranges. The original product specification and edition have not been recorded for these values; confirm the applicable grade document and product condition before treating them as acceptance limits.

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Machining Notes

What Machinability Rating Means

The rating compares how easily a material cuts against AISI 1112 free-machining steel, which is defined as 100%. It folds together chip formation, surface finish, tool wear and power consumption into one number — it is a shop-floor comparison, not a physical property.

Two consequences follow. First, ratings from different sources differ by roughly ±10%, because each was measured under different conditions. Second, a high rating does not mean the material is soft: gray cast iron rates 70% and machines easily because the graphite breaks chips, while pure copper rates only 20% and is soft but gummy.

Use the rating to compare two candidate materials, not to predict a cutting speed. For speeds, use the table above and your own tooling catalogue.

Frequently Asked Questions

What is the machinability rating of AISI 321?: 36 %, on the scale where AISI 1112 free-machining steel is 100%. Values above 100% mean the material cuts more easily than the reference steel; values below mean it is harder to cut. The rating is a comparison scale, not a physical property, so sources differ by roughly ±10%.
What cutting speed should I use for AISI 321?: Typical ranges are 180–280 SFM (55–85 m/min) for rough turning and 280–380 SFM (85–115 m/min) for finishing, with milling around 180–320 SFM. These are starting points only — the correct value depends on the insert grade and coating, the depth of cut, rigidity of the setup, coolant and the machine. Start at the low end and increase until tool life or finish degrades.
What is the equivalent of AISI 321 in other standards?: See the Equivalent Designations table above. Cross-standard correspondence is approximate: alloys within a designation are close but not guaranteed interchangeable, because each standard specifies its own composition ranges and tolerances. Verify against the specific specification before substituting.
What material group is AISI 321?: M — Stainless Steel, sub-group Austenitic, stabilised. Material groups — P, M, K, N, S and H — classify materials by machining behaviour so that insert grades can be selected by group rather than by individual alloy.

Value Sources

References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.

#	Source	Type	Revision / method
[1]	Chemical composition limits	compilation	n/a — original document, edition and applicable condition not recorded for each value
[2]	Values computed from the nominal figure	derived	Metric equivalents and any converted values are computed at build time; source values are the inch/imperial figures.
[3]	Equivalent international designations	compilation	n/a — original document, edition and applicable condition not recorded for each value
[4]	Machinability rating (AISI 1112 = 100%)	compilation	n/a — original document, edition and applicable condition not recorded for each value
[5]	Recommended cutting speed ranges	compilation	n/a — original document, edition and applicable condition not recorded for each value

Data Sources

Standard	Revision	What it covers on this page
Machinability rating, AISI 1112 = 100%	n/a — industry comparison scale, no governing standard	the machinability column
Tooling manufacturer cutting-speed recommendations	n/a — typical catalogue ranges	the cutting speed table
Grade specifications (ASTM / EN / DIN / JIS)	n/a — see the individual grade specification (ASTM, EN or DIN)	composition limits and equivalent designations

Verification scope

No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.

Cutting speeds vary with tooling and setup. The ranges shown are starting points for carbide tooling — confirm against the insert manufacturer's recommendation for the specific grade and geometry before production use.

Accuracy and use. Use the source notes and recorded verification scope above to assess each value. Calculated values follow the stated derivations; compilation values may lack a confirmed original document or product condition. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Read the source notes, calculation methods and verification scope above before reusing a value. To cite this page:

Plain text

Engineering Reference. "AISI 321 — Machining Data." https://refmanual.com/materials/aisi-321/ (accessed 2026-10-19). Data from Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale, no governing standard.

BibTeX

@misc{aisi-321,
  title        = {AISI 321 — Machining Data},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/materials/aisi-321/}},
  note         = {Accessed: 2026-10-19},
  source       = {Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale, no governing standard}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - AISI 321 — Machining Data
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/materials/aisi-321/
PY  - 2026
DA  - 2026-10-19
N1  - Source: Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale, no governing standard
ER  -