MIL-H-6875
Heat Treatment of Steel Raw Materials
Cancelled DoD process specification for the heat treatment of steel raw materials and parts — carbon, low-alloy, martensitic, precipitation-hardening and austenitic corrosion-resistant, and maraging steels — replaced by AMS-H-6875 and then by AMS 2759 with its slash sheets.
Superseded: AMS 2759. New drawings should cite the successor; existing call-outs to MIL-H-6875 remain understood.
What MIL-H-6875 specifies
MIL-H-6875 was for decades the US military and aerospace heat-treatment specification for steel and is still cited on thousands of legacy drawings. Revision H with Amendment 2 (1989) tabulates, alloy by alloy, the normalizing, annealing, austenitizing, quenching and tempering data, the hardness equivalents for each tensile-strength class (for example 180–200 ksi is about 39–43 HRC), decarburization limits, furnace temperature-uniformity and pyrometry requirements, atmosphere and salt-bath rules, straightening restrictions and hydrogen-embrittlement baking after plating. It also covers austenitic stainless annealing, martensitic and precipitation-hardening stainless hardening and ageing (H900–H1150), maraging steel and the case-hardening processes. The document was republished by SAE as AMS-H-6875 when the DoD adopted industry standards and then cancelled in favour of AMS 2759 and the AMS 2759/1–/12 slash sheets, which carry its tables forward with updated controls. Heat treaters accept a MIL-H-6875 callout by processing to the equivalent AMS 2759 slash sheet unless the contract forbids the substitution.
Tests and the drawing call-out
Tests the document imposes
- Hardness per ASTM E18 / E10 on each lot against the tensile-class hardness equivalents
- Tensile test per ASTM E8 when specified
- Decarburization depth by metallographic cross-section
- Furnace uniformity and instrumentation records (the pyrometry requirements now carried by AMS 2750)
- Hydrogen-embrittlement bake records after plating
How to cite it
Drawing call-out
HEAT TREAT PER MIL-H-6875 (SUPERSEDED — PROCESS PER AMS 2759/<SLASH SHEET>), 4340, 180–200 KSIAngle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to MIL-H-6875
| Treatment | Role | Cost |
|---|---|---|
Full annealing heats steel through its critical transformation range and then furnace-cools it slowly. | Related | $$ |
Normalizing heats steel above its critical range and cools it in air. | Related | $ |
Process annealing is a subcritical softening cycle inserted between cold-working operations. | Related | $ |
Quench and temper transforms hardenable steel to martensite and then tempers it to the required balance of strength and toughness. | Related | $$ |
Spheroidize annealing converts lamellar cementite into rounded carbide particles in a ferrite matrix. | Related | $$ |
Stress relief reduces residual stress from welding, machining, forming, casting, or additive manufacture without intentionally changing the bulk microstructure. | Related | $ |
MIL-H-6875 — frequently asked
My drawing says MIL-H-6875 — what do I order now?
The equivalent AMS 2759 slash sheet for the alloy and strength: /1 for carbon and low-alloy steel below 220 ksi, /2 at or above 220 ksi, /3 for PH and maraging steels, /4 for austenitic stainless, /5 for martensitic stainless, /7 for carburizing. Note the substitution on the purchase order so the certification cross-references both documents.
Are the temperatures and hardness bands the same?
Largely. AMS 2759 inherited MIL-H-6875's alloy tables and the tensile-to-hardness equivalents, then tightened controls on pyrometry (AMS 2750), atmospheres and quench and temper delays. Where a legacy drawing gives a value that conflicts with the slash sheet, the drawing governs unless the customer approves the change.
Was AMS-H-6875 a different document?
It was essentially the same text republished by SAE as a non-government standard when the DoD stopped maintaining MIL-H-6875, and it was later cancelled in favour of AMS 2759. A citation of AMS-H-6875 is handled the same way as MIL-H-6875.
Is MIL-H-6875 still available?
Yes; the cancelled document remains downloadable from DLA ASSIST / Quick Search and is in the public domain, which is useful for interpreting old drawings, but it must not be used as the process document for new work.
MIL-H-6875 is a work of the US Government and not subject to copyright. The authoritative copy is the DLA ASSIST database; check it for amendments issued after this page was updated. Official source ↗