Steel 300M Stress Relieved
Heat-treated state
Pick after rough machining, straightening or grinding of hardened parts to cut residual stress without losing strength.
Values for the Stress Relieved condition
Other 300M tempers and conditions
300M is listed in 9 conditions; see the grade overview at 300M.
- Annealed
- HR
- CD
- CR
- Normalized
- HIP
- As Printed
- Stress Relieved
- Q&T
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
full/spheroidize anneal (~650–680 °C soak, slow cool) for machining and inspection | Softest supply condition — pick for rough machining of forgings and billets before final quench and temper. | 700 | 1,030 | 14 | 31 HRC | — |
HRDefault Hot rolled | Pick for stock removal blanks and forging stock where the customer performs all final heat treatment. | 760 | 1,100 | 12 | 34 HRC | 8 % IACS |
Cold drawn | Pick for close-tolerance small-diameter bar to be finish heat treated; cold work is limited by the alloy's high work-hardening rate. | 950 | 1,150 | 9 | 36 HRC | 7.5 % IACS |
Cold rolled | Pick only for thin sheet/strip feedstock; heavy cold reduction of 300M is impractical and parts are heat treated after forming. | 1,000 | 1,200 | 7 | 38 HRC | 7.5 % IACS |
~900 °C air cool plus high temper for machinable, uniform structure | Pick for grain refinement of forgings/bar and a machinable intermediate state before final heat treatment. | 1,000 | 1,300 | 11 | 41 HRC | — |
Hot isostatic pressed | Pick for additively manufactured or powder 300M parts needing full density and isotropic properties before final quench and temper. | 1,150 | 1,450 | 10 | 44 HRC | 7 % IACS |
laser powder-bed fusion / DED, as-built (untempered martensite, residual stress) | Pick only for geometry trials — as-built 300M is hard, highly stressed and low in ductility, and normally must be HIP'd and Q&T'd. | 1,200 | 1,650 | 4 | 51 HRC | — |
Stress RelievedThis page sub-critical stress relief (typically at or just below the tempering temperature) | Pick after rough machining, straightening or grinding of hardened parts to cut residual stress without losing strength. | 1,600 | 1,900 | 9 | 52 HRC | 7 % IACS |
Quenched and tempered | Standard aerospace 280 ksi condition — pick for landing gear, shafts and fittings needing maximum strength with usable toughness. | 1,620 | 1,930 | 9 | 53 HRC | — |
What is 300M Stress Relieved?
300M Stress Relieved is 300M heat treated to Stress Relieved — pick after rough machining, straightening or grinding of hardened parts to cut residual stress without losing strength. 300M Stress Relieved has a yield strength of 1,600 MPa (232 ksi) and a tensile strength of 1,900 MPa (276 ksi) — stronger than 98% of steel grades. Elongation at break is 9% and the elastic modulus is 200 GPa (29 Msi). 300M Stress Relieved has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,400°C (2,552 °F). HR is the default condition FabDigit quotes; Stress Relieved is available on request or by drawing note.
Advantages
- High strength — 1,600 MPa (232 ksi), better than 98% of steel grades
- Polishes to a fine finish — 75/100, better than 94% of steel grades
Limitations
- Difficult to machine — 16/100, worse than 98% of steel grades
- Limited formability — 10/100, worse than 95% of steel grades
- Limited ductility — 9%, worse than 93% of steel grades
- Difficult to weld — 15/100, worse than 91% of steel grades
- High embodied carbon — 2.8 kg CO₂/kg, worse than 90% of steel grades
300M Stress Relieved properties
Typical room-temperature values for 300M Stress Relieved; 22 are specific to this condition. Other listed values are 300M reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
300M Stress Relieved has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical16
300M Stress Relieved has a yield strength of 1,600 MPa (232 ksi) and a tensile strength of 1,900 MPa (276 ksi) — stronger than 98% of steel grades. Elongation at break is 9% and the elastic modulus is 200 GPa (29 Msi).
Thermal6
300M Stress Relieved is rated for continuous service to 290°C (554 °F). It conducts heat at 35 W/m·K (20.2 BTU/hr·ft·°F), worse than 75% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
300M Stress Relieved conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 300M Stress Relieved takes about 40 MJ of energy and emits 2.8 kg of CO₂ — more than 91% of steel grades. Typical recycled content is 20%.
Manufacturability8
300M Stress Relieved's machinability is poor (16/100, worse than 98% of steel grades); weldability poor (15/100); formability not recommended (10/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 300M Stress Relieved
Is 300M easy to machine?
Rough machine annealed (≈300 HB) with rigid setups and carbide; at 51–55 HRC use CBN/ceramic hard turning or grinding, low stock removal and no sharp corners to avoid grinding burn and residual tensile stress.
Can 300M be welded?
Not recommended for primary structure — high hardenability and Si content make it crack-sensitive; if welded, use matching or low-hydrogen filler with 260–320 °C preheat, immediate post-weld temper and full re-heat-treatment.
Can 300M be formed, bent or molded?
Hot forge 1050–1180 °C with slow cooling and immediate anneal; cold forming is impractical, so form or bend in the annealed state only and heat treat afterwards.
What surface finishes work on 300M?
Always protect: cadmium, IVD aluminium, nickel-chrome or shot-peen-plus-primer; grind before plating, keep temper below the tempering temperature and bake 190 °C ≥8–23 h after plating to relieve hydrogen.
300M chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CAMS 6417/6419 | 0.38 – 0.43 | 0.4 |
| Siraises tempering resistance vs 4340 | 1.45 – 1.8 | 1.6 |
| Mn | 0.6 – 0.9 | 0.75 |
| Cr | 0.7 – 0.95 | 0.82 |
| Ni | 1.65 – 2 | 1.82 |
| Mo | 0.3 – 0.45 | 0.38 |
| V0.05 % min; grain refinement | 0.05 – 0.1 | 0.07 |
| Cu | ≤ 0.35 | — |
| P | ≤ 0.01 | — |
| Spremium (VIM/VAR) melting typically ≤0.005 | ≤ 0.01 | — |
| Fe | balance | — |
300M Stress Relieved — frequently asked
What is 300M Stress Relieved used for?
300M Stress Relieved is typically used for landing gear components, aircraft actuator rods and pistons, arresting-gear components, highly loaded drive shafts, torsion bars and high-strength structural fasteners. In short: extreme tensile strength.
What is the yield strength of 300M Stress Relieved?
300M Stress Relieved has a typical yield strength of 1,600 MPa (232 ksi) and a tensile strength of 1,900 MPa (276 ksi) — stronger than 98% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 300M Stress Relieved easy to machine?
Not especially — machinability is rated poor (16/100, worse than 98% of steel grades). Rough machine annealed (≈300 HB) with rigid setups and carbide; at 51–55 HRC use CBN/ceramic hard turning or grinding, low stock removal and no sharp corners to avoid grinding burn and residual tensile stress.
Can 300M Stress Relieved be welded?
Not readily — weldability is rated poor (15/100). Not recommended for primary structure — high hardenability and Si content make it crack-sensitive; if welded, use matching or low-hydrogen filler with 260–320 °C preheat, immediate post-weld temper and full re-heat-treatment.
What surface finishes work on 300M Stress Relieved?
Always protect: cadmium, IVD aluminium, nickel-chrome or shot-peen-plus-primer; grind before plating, keep temper below the tempering temperature and bake 190 °C ≥8–23 h after plating to relieve hydrogen.
Can 300M Stress Relieved be formed, bent or molded?
Hot forge 1050–1180 °C with slow cooling and immediate anneal; cold forming is impractical, so form or bend in the annealed state only and heat treat afterwards.
What is the maximum service temperature of 300M Stress Relieved?
300M Stress Relieved is rated for continuous use to about 290°C (554 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 300M-HR and 300M-HIP?
HR is the default condition — pick for stock removal blanks and forging stock where the customer performs all final heat treatment. HIP: pick for additively manufactured or powder 300M parts needing full density and isotropic properties before final quench and temper. Yield strength is 760 MPa in HR versus 1,150 MPa in HIP.
Can FabDigit make parts in 300M Stress Relieved?
Yes — 300M Stress Relieved is available for CNC machining and sheet metal; every part is priced by an engineer rather than instantly. Upload a STEP file to get a price and a DFM check.
Sources
- AMS 6417 — Steel Bars, Forgings and Tubing 0.95Cr-1.8Ni-0.35Mo-0.09V (300M), Consumable Electrode Vacuum Melted — SAE International (2020)
- AMS 6419 — Steel Bars and Forgings, Premium Quality, 300M, Heat Treated to 1930 MPa — SAE International (2019)
- MMPDS-17, Metallic Materials Properties Development and Standardization (300M section) — Battelle/FAA (2022)
- ASM Handbook Vol. 1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol. 19 — Fatigue and Fracture — ASM International (1996)
- Ultra-high-strength steel 300M bar and forging datasheet — Carpenter/Latrobe & Aubert&Duval typical data (2021)
- GB/T 6478 / 40CrNi2Si2MoVA (2015)
- 40CrNi2Si2MoVA/300M — Mysteel / 1688 (2026)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.