Carbon & alloy steel
300M Steel
Manufacturer or standards-body identification; product values do not apply to every form or condition.
Identity / state reference
What distinguishes this material
300M is a modified 4340 aerospace steel; the producer lists a remelted product route. It is not a drop-in name for ordinary 4340.
- Designation in this reference
- 300M / UNS K44220
- Forms covered by the sources
- Universal Stainless bar, RCS billet, flat bar and ingot programme.
- States to distinguish or confirm
- AOD plus VAR is a melting route, not a final heat-treatment condition; obtain the certified condition.
- Temperature and exposure
- No universal service-temperature limit or room-temperature property set is assigned. Use the cited product document and the purchase certificate.
Other search names in these sources
UNS K44220
Read the scope above: a source’s related product name is not a blanket interchangeability statement.
Property evidence for a stated condition
No condition-specific numerical table is reproduced here
The linked sources establish the identity and the stated product/state scope. Obtain the row for your actual form, section, treatment and test conditions before adopting strength, hardness or a thermal limit.
Resolve these conditions next
- What product standard, edition and complete grade are on the material certificate?
- What product form, section size and delivery/heat-treatment condition will be machined?
For machining, take the exact grade, supplied condition and measured hardness where applicable into the tool maker’s application data. A generic material-family speed is not a substitute for an operation and tool-specific recommendation.
Sources and what they establish
Reviewed 23 October 2026. A source’s publication date and the review date are different. The scope below identifies the fields checked.
Universal Stainless grade/product listings
Grade-specific manufacturing routes and product forms; exact listed grade only.
Universal Stainless grade/product listings ↗Carpenter Technology product line card
Exact alloy names and UNS identities; branded variants such as Project 70+ are not universal property data for the base grade.
Carpenter Technology product line card ↗Carpenter aerospace structural alloys
9310 carburizing steel and 300M modified-4340 structural alloy descriptions.
Carpenter aerospace structural alloys ↗Source identity, a named product example and a supplied-batch certificate are different evidence. Cross-standard similarity does not approve substitution.
Corrections from the previous article
- Remove the universal 1930 MPa strength and automatic 1.6928 equivalence; retain the 300M-specific procurement identity.
- Withdraw the legacy generic hardness (285–341 HB) and tensile-strength (1,930 MPa (280 ksi)) pair: the old page does not establish a matching product, heat treatment, section and test source.
- Remove the unsupported cutting-speed table and machinability percentage; select tooling only after the actual material condition is known.
Distinguish high-strength steel routes
Compare the maraging-steel identity and aging state with the treatment specified for 300M; do not compare strength without a common condition.