What is the machinability rating of Gray Iron Class 30?

70 %, 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 Gray Iron Class 30?

Typical ranges are 250–400 SFM (75–120 m/min) for rough turning and 350–500 SFM (105–150 m/min) for finishing, with milling around 250–450 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 Gray Iron Class 30 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 Gray Iron Class 30?

K — Cast Iron, sub-group Gray cast iron. 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.

Gray Iron Class 30

Machining data for Gray Iron Class 30 (Grey Cast Iron 30) — material group, hardness, machinability rating, recommended cutting speeds and equivalent designations.

Data verified 2026-09-29 · based on n/a — industry comparison scale, no governing standard

Quick Answer

Gray Iron Class 30 has a machinability rating of 70 % and a hardness of 187–241 HB. Typical roughing speed is 250–400 SFM, finishing 350–500 SFM. It belongs to material group K.

General Information

Material group	K — Cast Iron
Sub-group	Gray cast iron
Hardness	187–241 HB
Tensile strength	207 MPa (30 ksi)
Machinability	70 %
Density	7.20 g/cm³

Gray cast iron with a tensile strength of 30 ksi (207 MPa). The graphite flakes break chips and act as a lubricant, so it machines easily despite its hardness, but the graphite is also abrasive and the dust is a health hazard.

Cutting Speed Recommendations

Operation^[5]	Speed range (carbide)^[5]
Turning — roughing	250–400 SFM (75–120 m/min)
Turning — finishing	350–500 SFM (105–150 m/min)
Milling	250–450 SFM
Drilling (HSS)	80–120 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]
ASTM A48	Class 30
DIN	0.6030 (GG25 / GJL-250)
EN	GJL-250
JIS	FC250

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

Chemical Composition

Element^[1]	Content (%)^[1]
C	3.0–3.5
Si	1.8–2.3
Mn	0.5–0.9
P	≤0.30
S	≤0.15
Fe	Balance

Composition limits per the governing specification for this grade. Ranges shown are the specification window, not a typical analysis.

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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 Gray Iron Class 30?: 70 %, 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 Gray Iron Class 30?: Typical ranges are 250–400 SFM (75–120 m/min) for rough turning and 350–500 SFM (105–150 m/min) for finishing, with milling around 250–450 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 Gray Iron Class 30 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 Gray Iron Class 30?: K — Cast Iron, sub-group Gray cast iron. 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

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	Source	Type	Revision / method
[1]	Chemical composition limits	standard	n/a — composition limits are taken from whichever specification applies to the grade — source
[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	standard	n/a — correspondence table, not a revisioned document — source
[4]	Machinability rating (AISI 1112 = 100%)	standard	n/a — long-established industry comparison scale — source
[5]	Recommended cutting speed ranges	standard	n/a — typical catalogue ranges with no single revision — source

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

Cross-checked against:

Machinability ratings cross-checked against published machinability charts
Cutting speeds cross-checked against two tooling manufacturers' catalogues
Composition limits cross-checked against the governing ASTM and EN specifications

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. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. 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

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "Gray Iron Class 30 — Machining Data." https://refmanual.com/materials/gray-iron-class-30/ (accessed 2026-09-29). Data from Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale, no governing standard.

BibTeX

@misc{gray-iron-class-30,
  title        = {Gray Iron Class 30 — Machining Data},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/materials/gray-iron-class-30/}},
  note         = {Accessed: 2026-09-29},
  source       = {Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale, no governing standard}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Gray Iron Class 30 — Machining Data
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/materials/gray-iron-class-30/
PY  - 2026
DA  - 2026-09-29
N1  - Source: Machinability rating, AISI 1112 = 100%, n/a — industry comparison scale, no governing standard
ER  -

Each row in the tables above also has a permanent link — hover a row and use the # link to cite a single value rather than the whole page.