Steel 4150-SPA (Spheroidize Annealed)
Heat-treated state
AISI/SAE 4150 · UNS G41500 · EN 1.7228, 50CrMo4
Sub-critical spheroidize cycle producing globular carbides — chosen when the bar must be cold headed, deep drawn or heavily machined before hardening.
Values for the SPA condition
Other 4150 tempers and conditions
4150 is listed in 11 conditions; see the grade overview at 4150.
Compare all 11 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Temper | Full anneal (~815–840 °C, furnace cool) — softest, most machinable condition and the usual delivery state for bar that will be hardened later. | 380 | 730 | 20 | 197 HB | — |
SPAThis page Spheroidize Annealed | Sub-critical spheroidize cycle producing globular carbides — chosen when the bar must be cold headed, deep drawn or heavily machined before hardening. | 400 | 690 | 23 | 11 HRC | 8.5 % IACS |
HRDefault Hot rolled | Standard as-rolled bar stock — cheapest starting form for parts that will be machined and then heat treated. | 520 | 860 | 16 | 21 HRC | — |
Heat Treat State | Air cooled from ~870 °C — uniform fine grain and higher strength than annealed; used to homogenize forgings before final machining or hardening. | 735 | 1,155 | 11.7 | 34 HRC | — |
Cold rolled | Cold rolled strip/flat bar — tighter thickness tolerance and smoother surface, higher strength but reduced ductility. | 760 | 950 | 9 | 28 HRC | 7.8 % IACS |
Cold drawn | Cold-drawn (usually annealed-then-drawn) bar for close size tolerance, straightness and good chip control on screw machines. | 830 | 945 | 10 | 28 HRC | 43 W/m·K |
Q&T to 28–32 HRC | Tough, readily re-machinable prehardened condition for shafts, arbors and fixtures that must not be re-heat-treated. | 860 | 965 | 18 | 30 HRC | 7.8 % IACS |
Q&T to 32–36 HRC | Common prehardened bar hardness for gears, die holders and hydraulic components needing wear resistance with machinability. | 985 | 1,100 | 16 | 34 HRC | 7.6 % IACS |
Quenched and tempered | General-purpose oil quench from ~845 °C plus ~540 °C temper — the standard commercial 'HT' condition (~302–352 HB) balancing strength and toughness. | 1,105 | 1,210 | 15 | 37 HRC | — |
Q&T to 40–44 HRC | Higher-hardness temper for wear surfaces, tool bodies and drill collars; machining now needs carbide tooling. | 1,250 | 1,380 | 12 | 42 HRC | — |
Q&T to 48–52 HRC | Low-temper, near-maximum hardness for wear parts and punches; grinding rather than turning, and notch sensitivity is high. | 1,550 | 1,720 | 10 | 50 HRC | — |
What is 4150-SPA?
4150-SPA is 4150 heat treated to SPA — sub-critical spheroidize cycle producing globular carbides — chosen when the bar must be cold headed, deep drawn or heavily machined before hardening. 4150-SPA has a yield strength of 400 MPa (58 ksi) and a tensile strength of 690 MPa (100 ksi) — weaker than 60% of steel grades. Elongation at break is 23% and the elastic modulus is 205 GPa (29.7 Msi). 4150-SPA has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F). HR is the default condition FabDigit quotes; SPA is available on request or by drawing note.
4150-SPA properties
Typical room-temperature values for 4150-SPA; 23 are specific to this condition. Other listed values are 4150 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
4150-SPA has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F).
Mechanical14
4150-SPA has a yield strength of 400 MPa (58 ksi) and a tensile strength of 690 MPa (100 ksi) — weaker than 60% of steel grades. Elongation at break is 23% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4150-SPA is rated for continuous service to 425°C (797 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
4150-SPA conducts electricity at 8.5 % IACS, better than 63% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 4150-SPA takes about 31 MJ of energy and emits 2.3 kg of CO₂ — more than 64% of steel grades. Typical recycled content is 30%.
Manufacturability8
4150-SPA's machinability is good (57/100, better than 71% of steel grades); weldability poor (30/100); formability fair (48/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 4150-SPA
Is 4150 easy to machine?
Machine in the annealed or 28–32 HRC condition with rigid setups and carbide tooling; above 40 HRC switch to hard turning inserts or grinding.
Can 4150 be welded?
Poor weldability (CE ≈ 0.95): preheat 300–400 °C, low-hydrogen consumables, and temper/stress relieve immediately after welding to avoid HAZ cracking.
Can 4150 be formed, bent or molded?
Hot forge 1100–1200 °C and normalize afterwards; cold forming is limited to the spheroidize-annealed condition with generous bend radii.
What surface finishes work on 4150?
No natural corrosion resistance — use black oxide, manganese phosphate, zinc or hard chrome plating (bake to avoid hydrogen embrittlement above 40 HRC), or nitriding for wear surfaces.
4150 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 |
|---|---|---|
| CSAE J404 / AISI 4150 | 0.48 – 0.53 | 0.5 |
| Mn | 0.75 – 1 | 0.88 |
| Si | 0.15 – 0.35 | 0.25 |
| Cr | 0.8 – 1.1 | 0.95 |
| Mo | 0.15 – 0.25 | 0.2 |
| P | ≤ 0.04 | — |
| Smax; 4150H/resulfurized variants differ | ≤ 0.04 | — |
| Fe | balance | — |
4150-SPA — frequently asked
What is 4150-SPA used for?
4150-SPA is typically used for gun barrels, axles and gears. In short: deep-hardening toughness.
What is the yield strength of 4150-SPA?
4150-SPA has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 690 MPa (100 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 11 listed tempers.
Is 4150-SPA easy to machine?
Reasonably — machinability is rated good (57/100, better than 71% of steel grades). Machine in the annealed or 28–32 HRC condition with rigid setups and carbide tooling; above 40 HRC switch to hard turning inserts or grinding.
Can 4150-SPA be welded?
Not readily — weldability is rated poor (30/100). Poor weldability (CE ≈ 0.95): preheat 300–400 °C, low-hydrogen consumables, and temper/stress relieve immediately after welding to avoid HAZ cracking.
What surface finishes work on 4150-SPA?
No natural corrosion resistance — use black oxide, manganese phosphate, zinc or hard chrome plating (bake to avoid hydrogen embrittlement above 40 HRC), or nitriding for wear surfaces.
Can 4150-SPA be formed, bent or molded?
Hot forge 1100–1200 °C and normalize afterwards; cold forming is limited to the spheroidize-annealed condition with generous bend radii.
What is the maximum service temperature of 4150-SPA?
4150-SPA is rated for continuous use to about 425°C (797 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4150-HR and 4150-CD?
HR is the default condition — standard as-rolled bar stock — cheapest starting form for parts that will be machined and then heat treated. CD: cold-drawn (usually annealed-then-drawn) bar for close size tolerance, straightness and good chip control on screw machines. Yield strength is 520 MPa in HR versus 830 MPa in CD.
Can FabDigit make parts in 4150-SPA?
Yes — 4150-SPA 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
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- EN 10083-3 — Quenched and tempered steels: alloy steels (50CrMo4, 1.7228) — CEN (2006)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- Machinery's Handbook, 31st ed. — machinability ratings and heat treating data — Industrial Press (2020)
- Alloy bar 4150 / 50CrMo4 datasheet — Böhler / Ovako / TimkenSteel (2022)
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.