Steel 4068-A (Solution annealed)
Temper · default condition
AISI/SAE 4068 · UNS G40680
Softest, most machinable and formable state — the stocking condition before hardening.
Values for the A condition
Other 4068 tempers and conditions
4068 is listed in 9 conditions; see the grade overview at 4068.
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefaultThis page Solution annealed | Softest, most machinable and formable state — the stocking condition before hardening. | 420 | 700 | 22 | 201 HB | 42 W/m·K |
Hot rolled | Mill as-rolled bar for parts that will be fully heat treated after rough machining or forging. | 520 | 880 | 14 | 25 HRC | 8 % IACS |
Normalized | Uniform fine pearlitic structure for forgings before final hardening or for moderate-strength wear parts. | 620 | 1,010 | 12 | 31 HRC | — |
Cold drawn | Cold-finished bar with tight size and better surface for machined parts that are hardened later. | 690 | 830 | 11 | 22 HRC | 8 % IACS |
Oil quenched and tempered at 650 °C | Softest Q&T condition — best ductility and machinability while keeping tempered-martensite fatigue behaviour. | 800 | 950 | 18 | 30 HRC | — |
Oil quenched and tempered at 540 °C | Balanced strength/toughness for shafts and highly loaded machine parts that must resist shock. | 1,100 | 1,250 | 13 | 39 HRC | — |
Oil quenched and tempered at 425 °C | Typical heavy-spring temper: high elastic limit with usable fatigue and set resistance. | 1,350 | 1,550 | 10 | 46 HRC | — |
Oil quenched and tempered at 315 °C | Very high strength spring/wear condition with slightly improved toughness over 205 °C temper. | 1,550 | 1,900 | 7 | 54 HRC | — |
Oil quenched and tempered at 205 °C | Maximum hardness and wear resistance for punches, blades and cutting edges; very low ductility. | 1,650 | 2,100 | 5 | 58 HRC | 35 W/m·K |
What is 4068-A?
4068-A is 4068 in the A temper — softest, most machinable and formable state — the stocking condition before hardening. 4068-A has a yield strength of 420 MPa (60.9 ksi) and a tensile strength of 700 MPa (102 ksi) — weaker than 53% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi). 4068-A has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,400°C (2,552 °F).
Advantages
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Difficult to weld — 12/100, worse than 96% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
4068-A properties
Typical room-temperature values for 4068-A; 14 are specific to this condition. Other listed values are 4068 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
4068-A has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical15
4068-A has a yield strength of 420 MPa (60.9 ksi) and a tensile strength of 700 MPa (102 ksi) — weaker than 53% of steel grades. Elongation at break is 22% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4068-A is rated for continuous service to 200°C (392 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 11.5 µm/m·K (6.39 µin/in·°F).
Electrical3
4068-A conducts electricity at 8 % IACS, better than 55% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (11/100), worse than 73% of steel grades.
Sustainability4
Producing a kilogram of 4068-A takes about 30 MJ of energy and emits 2.2 kg of CO₂ — more than 56% of steel grades. Typical recycled content is 30%.
Manufacturability7
4068-A's machinability is fair (45/100, worse than 65% of steel grades); weldability not recommended (12/100); formability poor (30/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 4068-A
Is 4068 easy to machine?
Machine in the spheroidize-annealed condition with sharp carbide or coated-carbide tooling and rigid setups; above ~45 HRC use CBN/ceramic hard turning or grinding only.
Can 4068 be welded?
Essentially unweldable in structural use (CE well above 0.9) — if unavoidable, preheat 300–400 °C, use low-hydrogen consumables and post-weld temper immediately.
Can 4068 be formed, bent or molded?
Cold forming limited to gentle bends on spheroidized stock; forge 1100–1200 °C, finish above 900 °C and slow-cool/anneal to avoid cracking, quench in oil from 800–830 °C.
What surface finishes work on 4068?
No natural corrosion resistance — apply oil, black oxide, manganese phosphate, zinc or Zn-Ni plating (bake at 190 °C for 4 h after plating to avoid hydrogen embrittlement); shot peen springs for fatigue life.
4068 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 |
|---|---|---|
| Chighest carbon of the SAE 40xx series | 0.64 – 0.72 | 0.68 |
| Mn | 0.75 – 1 | 0.88 |
| Si | 0.15 – 0.35 | 0.25 |
| Mo | 0.2 – 0.3 | 0.25 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Fe | balance | — |
4068-A — frequently asked
What is 4068-A used for?
4068-A is typically used for heavy springs, wear parts and high-strength fasteners. In short: higher carbon than 4063; hardest 40xx spring grade; grind rather than weld.
What is the yield strength of 4068-A?
4068-A has a typical yield strength of 420 MPa (60.9 ksi) and a tensile strength of 700 MPa (102 ksi) — weaker than 53% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 4068-A easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 65% of steel grades). Machine in the spheroidize-annealed condition with sharp carbide or coated-carbide tooling and rigid setups; above ~45 HRC use CBN/ceramic hard turning or grinding only.
Can 4068-A be welded?
Not readily — weldability is rated not recommended (12/100). Essentially unweldable in structural use (CE well above 0.9) — if unavoidable, preheat 300–400 °C, use low-hydrogen consumables and post-weld temper immediately.
What surface finishes work on 4068-A?
No natural corrosion resistance — apply oil, black oxide, manganese phosphate, zinc or Zn-Ni plating (bake at 190 °C for 4 h after plating to avoid hydrogen embrittlement); shot peen springs for fatigue life.
Can 4068-A be formed, bent or molded?
Cold forming limited to gentle bends on spheroidized stock; forge 1100–1200 °C, finish above 900 °C and slow-cool/anneal to avoid cracking, quench in oil from 800–830 °C.
What is the maximum service temperature of 4068-A?
4068-A is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4068-A and 4068-QT205?
A is the default condition — softest, most machinable and formable state — the stocking condition before hardening. QT205: maximum hardness and wear resistance for punches, blades and cutting edges; very low ductility. Yield strength is 420 MPa in A versus 1,650 MPa in QT205.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- SAE J1268 / ASTM A29 — Hardenability and general requirements for alloy steel bars — SAE / ASTM (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating — ASM International (1991)
- Machining Data Handbook — Metcut Research Associates (1980)
- UNS G40680 alloy steel data records — SAE/ASTM UNS Metals & Alloys (2019)
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.