Steel 4340M-CR (Cold rolled)
Supply condition
AISI/SAE 4340M · UNS K44220 · AMS 6419 · also 300M
Thin strip/sheet condition for parts that will be formed then hardened; limited availability and limited cold-work capability.
Values for the CR condition
Other 4340M tempers and conditions
4340M is listed in 9 conditions; see the grade overview at 4340M.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed (AMS 6417 / spheroidize annealed bar) | Softest supply condition — pick for rough machining, deep drilling and forming before final quench and temper. | 690 | 930 | 15 | 26 HRC | 36 W/m·K |
CRThis page Cold rolled | Thin strip/sheet condition for parts that will be formed then hardened; limited availability and limited cold-work capability. | 830 | 1,000 | 9 | 30 HRC | 7 % IACS |
Cold drawn | Small-diameter annealed bar/wire cold drawn to size for tight tolerance and better surface before heat treatment; rarely stocked in this grade. | 860 | 1,030 | 10 | 31 HRC | 7 % IACS |
Normalized & Tempered | Normalize ~925 °C then temper for uniform grain and moderate hardness — a machining/stock condition and a grain-refining step before final hardening. | 965 | 1,240 | 12 | 40 HRC | — |
HRDefault Hot rolled | Mill product as rolled or forged — air-hardened martensite, too hard and brittle to machine; always annealed or normalized before use. | 1,150 | 1,550 | 6 | 47 HRC | 7 % IACS |
Q&T 1790 MPa | Slightly higher temper for parts where fracture toughness and ductility matter more than peak strength. | 1,520 | 1,790 | 11 | 51 HRC | 7 % IACS |
Quenched and tempered | The standard 300M service condition (AMS 6419): highest strength/toughness balance for landing gear, actuator rods and shafts. | 1,620 | 1,930 | 10 | 54 HRC | — |
VAR / CEVM premium-melt bar | Consumable-electrode vacuum remelted stock — choose for fatigue- and fracture-critical aerospace parts needing best transverse ductility and low inclusion count. | 1,640 | 1,930 | 12 | 54 HRC | 7 % IACS |
Q&T 2070 MPa | Maximum-strength condition for weight-critical rocket motor cases and springs; accept lower toughness and high notch sensitivity. | 1,720 | 2,070 | 8 | 56 HRC | — |
What is 4340M-CR?
4340M-CR is 4340M supplied in the CR condition — thin strip/sheet condition for parts that will be formed then hardened; limited availability and limited cold-work capability. 4340M-CR has a yield strength of 830 MPa (120 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 87% of steel grades. Elongation at break is 9% and the elastic modulus is 205 GPa (29.7 Msi). 4340M-CR has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,420°C (2,588 °F). HR is the default condition FabDigit quotes; CR is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 75/100, better than 94% of steel grades
- High strength — 830 MPa (120 ksi), better than 87% of steel grades
Limitations
- Limited ductility — 9%, worse than 93% of steel grades
- High embodied carbon — 2.6 kg CO₂/kg, worse than 87% of steel grades
- Limited service temperature — 290°C (554 °F), worse than 81% of steel grades
- Difficult to machine — 36/100, worse than 81% of steel grades
- Difficult to weld — 25/100, worse than 77% of steel grades
4340M-CR properties
Typical room-temperature values for 4340M-CR; 22 are specific to this condition. Other listed values are 4340M reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
4340M-CR has a density of 7.83 g/cm³ (0.283 lb/in³), lighter than 80% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
4340M-CR has a yield strength of 830 MPa (120 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 87% of steel grades. Elongation at break is 9% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4340M-CR is rated for continuous service to 290°C (554 °F). It conducts heat at 36 W/m·K (20.8 BTU/hr·ft·°F), worse than 73% of steel grades. Thermal expansion is 11.7 µm/m·K (6.5 µin/in·°F).
Electrical3
4340M-CR conducts electricity at 7 % IACS, worse than 74% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (14/100), better than 70% of steel grades.
Sustainability4
Producing a kilogram of 4340M-CR takes about 36 MJ of energy and emits 2.6 kg of CO₂ — more than 89% of steel grades. Typical recycled content is 25%.
Manufacturability8
4340M-CR's machinability is fair (36/100, worse than 81% of steel grades); weldability poor (25/100); formability poor (22/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 4340M-CR
Is 4340M easy to machine?
Rough machine in the annealed condition (≈40% of B1112) with carbide and rigid setups; at 52–56 HRC only hard turning with CBN, creep-feed or plunge grinding is practical — grind gently to avoid re-tempering burn and grinding cracks.
Can 4340M be welded?
Not weldable in the hardened state; if welding is unavoidable use electron-beam or GTAW with matching filler, 260–320 °C preheat/interpass, and immediately re-austenitize, quench and temper the whole part.
Can 4340M be formed, bent or molded?
Hot forge/upset at 1050–1200 °C with finish above 900 °C, then normalize and anneal; no meaningful cold forming above the annealed condition — bend and straighten only warm and re-stress-relieve.
What surface finishes work on 4340M?
Shot peen highly stressed fillets, then low-hydrogen-embrittlement cadmium or IVD aluminium plating (or HVOF WC-Co on journals) with a 190 °C/23 h bake within 4 h of plating; chrome plating requires strict bake and peening control.
4340M 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 |
|---|---|---|
| C | 0.4 – 0.46 | 0.43 |
| Sikey modification vs 4340 — raises temper resistance | 1.45 – 1.8 | 1.6 |
| Mn | 0.6 – 0.9 | 0.75 |
| Cr | 0.7 – 0.95 | 0.82 |
| Ni | 1.65 – 2 | 1.83 |
| Mo | 0.3 – 0.45 | 0.38 |
| Vgrain refinement | 0.05 – 0.1 | 0.07 |
| P | ≤ 0.01 | 0.01 |
| S | ≤ 0.01 | 0 |
| Cu | ≤ 0.35 | 0.1 |
| Fe | balance | — |
4340M-CR — frequently asked
What is 4340M-CR used for?
4340M-CR is typically used for aircraft landing gear cylinders and axles, arresting hooks, high-strength airframe fittings, rocket motor cases, torsion bars and high-strength drive shafts. In short: high-strength aerospace bar.
What is the yield strength of 4340M-CR?
4340M-CR has a typical yield strength of 830 MPa (120 ksi) and a tensile strength of 1,000 MPa (145 ksi) — stronger than 87% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 4340M-CR easy to machine?
Not especially — machinability is rated fair (36/100, worse than 81% of steel grades). Rough machine in the annealed condition (≈40% of B1112) with carbide and rigid setups; at 52–56 HRC only hard turning with CBN, creep-feed or plunge grinding is practical — grind gently to avoid re-tempering burn and grinding cracks.
Can 4340M-CR be welded?
Not readily — weldability is rated poor (25/100). Not weldable in the hardened state; if welding is unavoidable use electron-beam or GTAW with matching filler, 260–320 °C preheat/interpass, and immediately re-austenitize, quench and temper the whole part.
What surface finishes work on 4340M-CR?
Shot peen highly stressed fillets, then low-hydrogen-embrittlement cadmium or IVD aluminium plating (or HVOF WC-Co on journals) with a 190 °C/23 h bake within 4 h of plating; chrome plating requires strict bake and peening control.
Can 4340M-CR be formed, bent or molded?
Hot forge/upset at 1050–1200 °C with finish above 900 °C, then normalize and anneal; no meaningful cold forming above the annealed condition — bend and straighten only warm and re-stress-relieve.
What is the maximum service temperature of 4340M-CR?
4340M-CR 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 4340M-HR and 4340M-VAR?
HR is the default condition — mill product as rolled or forged — air-hardened martensite, too hard and brittle to machine; always annealed or normalized before use. VAR: consumable-electrode vacuum remelted stock — choose for fatigue- and fracture-critical aerospace parts needing best transverse ductility and low inclusion count. Yield strength is 1,150 MPa in HR versus 1,640 MPa in VAR.
Can FabDigit make parts in 4340M-CR?
Yes — 4340M-CR 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 6419 — Steel Bars, Forgings, Tubing 1.6Si-0.82Cr-1.8Ni-0.40Mo-0.08V, Consumable Electrode Melted, 1930 MPa — SAE International (2020)
- AMS 6417 — 300M Steel Bars and Forgings, Normalized and Tempered / Annealed — SAE International (2019)
- MMPDS-2023, Chapter 2 (Low-Alloy Ultrahigh-Strength Steels) — Battelle / FAA (2023)
- Aerospace Structural Metals Handbook — 300M — CINDAS (2015)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels and High-Performance Alloys — ASM International (1990)
- 300M (UNS K44220) alloy steel bar data — Carpenter Technology / Aubert & Duval (2022)
- 40CrNi2Si2MoVA (2015)
- 300M/40CrNi2Si2MoVA — 1688 / Mysteel (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.