Steel O6-SR (Stress relieved)
Heat-treated state
AISI/SAE O6 · UNS T31506
Intermediate condition used on large or asymmetric parts to minimise distortion during subsequent hardening.
Values for the SR condition
Other O6 tempers and conditions
O6 is listed in 6 conditions; see the grade overview at O6.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
SRThis page Stress relieved | Intermediate condition used on large or asymmetric parts to minimise distortion during subsequent hardening. | 400 | 710 | 23 | 13 HRC | 3.4 % IACS |
ANNDefault Annealed | Standard as-supplied condition for machining, turning and rough forming before hardening. | 415 | 720 | 22 | 200 HB | — |
Cold Drawn Annealed | Pick for close-tolerance drill rod / precision-ground stock that will be machined then hardened. | 550 | 780 | 14 | 17 HRC | 3.4 % IACS |
Hardened & Tempered 54–57 HRC | Choose when shock loading or heavier sections demand extra toughness at some cost in wear life. | 1,650 | 1,900 | 4 | 56 HRC | — |
Hardened & Tempered 58–61 HRC | Best general balance of wear resistance and toughness for rolls, cams, forming dies and slides. | 1,800 | 2,050 | 2 | 60 HRC | — |
Hardened & Tempered 62–65 HRC | Maximum hardness and wear/galling resistance for gauges, bushings and arbor surfaces in small sections. | 1,900 | 2,200 | 1 | 63 HRC | 30 W/m·K |
What is O6-SR?
O6-SR is O6 heat treated to SR — intermediate condition used on large or asymmetric parts to minimise distortion during subsequent hardening. O6-SR has a yield strength of 400 MPa (58 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 60% of steel grades. Elongation at break is 23% and the elastic modulus is 203 GPa (29.4 Msi). O6-SR has a density of 7.7 g/cm³ (0.278 lb/in³), lighter than 95% of steel grades. It melts at 1,290°C (2,354 °F). ANN is the default condition FabDigit quotes; SR is available on request or by drawing note.
Advantages
- Easy to machine — 62/100, better than 89% of steel grades
Limitations
- Difficult to weld — 15/100, worse than 91% of steel grades
- Low electrical conductivity — 3.4 % IACS, worse than 86% of steel grades
- Hard to polish — 45/100, worse than 84% of steel grades
- Poor heat conductor — 32 W/m·K (18.5 BTU/hr·ft·°F), worse than 82% of steel grades
- High embodied carbon — 2.5 kg CO₂/kg, worse than 82% of steel grades
O6-SR properties
Typical room-temperature values for O6-SR; 22 are specific to this condition. Other listed values are O6 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
O6-SR has a density of 7.7 g/cm³ (0.278 lb/in³), lighter than 95% of steel grades. It melts at 1,290°C (2,354 °F).
Mechanical15
O6-SR has a yield strength of 400 MPa (58 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 60% of steel grades. Elongation at break is 23% and the elastic modulus is 203 GPa (29.4 Msi).
Thermal6
O6-SR is rated for continuous service to 400°C (752 °F). It conducts heat at 32 W/m·K (18.5 BTU/hr·ft·°F), worse than 82% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
O6-SR conducts electricity at 3.4 % IACS, worse than 86% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (9/100), worse than 98% of steel grades.
Sustainability4
Producing a kilogram of O6-SR takes about 34 MJ of energy and emits 2.5 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 40%.
Manufacturability8
O6-SR's machinability is good (62/100, better than 89% of steel grades); weldability poor (15/100); formability poor (26/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with O6-SR
Is O6 easy to machine?
Best-machining O-series grade — free graphite acts as a chip breaker and lubricant; annealed stock turns, drills and taps easily with HSS or carbide, while hardened parts require grinding or CBN.
Can O6 be welded?
Not recommended structurally; if repair is unavoidable preheat to 300–370 °C, use matching or low-hydrogen filler, and temper immediately at the part's tempering temperature.
Can O6 be formed, bent or molded?
Cold forming is limited to gentle bends in the annealed state; hot work at 900–1050 °C followed by slow cooling and spheroidize anneal at 760–790 °C.
What surface finishes work on O6?
Takes a good but not mirror finish (graphite nodules pit at high polish); protect with black oxide, phosphate or light oil, and nitride or hard-chrome plate where extra wear resistance is needed.
O6 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 |
|---|---|---|
| Cpart present as free graphite | 1.25 – 1.55 | 1.45 |
| Mn | 0.3 – 1.1 | 0.8 |
| Sipromotes graphitization | 0.55 – 1.5 | 1.05 |
| Crmax per ASTM A681 | ≤ 0.3 | 0.15 |
| Mo | 0.2 – 0.3 | 0.25 |
| Ni | ≤ 0.3 | — |
| V | ≤ 0.3 | — |
| Cu | ≤ 0.25 | — |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Fe | balance | — |
O6-SR — frequently asked
What is O6-SR used for?
O6-SR is typically used for arbors, rolls, bushings and gauges. In short: best-machining O-series grade; built-in graphite lubricity; low-cost galling resistance.
What is the yield strength of O6-SR?
O6-SR has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 710 MPa (103 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 6 listed tempers.
Is O6-SR easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% of steel grades). Best-machining O-series grade — free graphite acts as a chip breaker and lubricant; annealed stock turns, drills and taps easily with HSS or carbide, while hardened parts require grinding or CBN.
Can O6-SR be welded?
Not readily — weldability is rated poor (15/100). Not recommended structurally; if repair is unavoidable preheat to 300–370 °C, use matching or low-hydrogen filler, and temper immediately at the part's tempering temperature.
What surface finishes work on O6-SR?
Takes a good but not mirror finish (graphite nodules pit at high polish); protect with black oxide, phosphate or light oil, and nitride or hard-chrome plate where extra wear resistance is needed.
Can O6-SR be formed, bent or molded?
Cold forming is limited to gentle bends in the annealed state; hot work at 900–1050 °C followed by slow cooling and spheroidize anneal at 760–790 °C.
What is the maximum service temperature of O6-SR?
O6-SR is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between O6-ANN and O6 QT-63?
ANN is the default condition — standard as-supplied condition for machining, turning and rough forming before hardening. QT-63: maximum hardness and wear/galling resistance for gauges, bushings and arbor surfaces in small sections. Yield strength is 415 MPa in ANN versus 1,900 MPa in QT-63.
Sources
- ASTM A681 — Standard Specification for Tool Steels, Alloy — ASTM International (2015)
- SAE J437/J438 — Tool and Die Steels — SAE International (2015)
- ASM Handbook Vol.1: Properties and Selection — Irons, Steels, and High-Performance Alloys (Tool Steels) — ASM International (1990)
- Tool Steels, 5th ed. (Roberts, Krauss, Kennedy) — ASM International (1998)
- Graphitic oil-hardening tool steel (O6) product data — Tool-steel producers/distributors (2023)
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.