Steel 4012
AISI/SAE 4012 · UNS G40120
4012 is a low-carbon molybdenum alloy steel (UNS G40120) in the SAE-AISI 40xx family, alloyed with Mo for hardenability and used mainly as a carburizing grade that gives a tough core under a moderately hard case.
Reference datasheet — 4012 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the N condition
4012 tempers and conditions
4012 is supplied in 7 conditions, soft to hard. N is the default FabDigit quotes; the values on this page are for it.
Compare all 7 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition; pick for deep machining, cold forming or before carburizing. | 295 | 440 | 32 | 126 HB | — |
Hot rolled | Cheapest stock form for parts that will be machined and then carburized. | 320 | 480 | 27 | 143 HB | 7.8 % IACS |
NDefault Normalized | Standard stock condition — uniform fine-grain structure for machining and subsequent case hardening. | 330 | 470 | 28 | 137 HB | — |
Stress relieved | Cold drawn bar with residual stress removed for dimensionally stable machining. | 420 | 520 | 20 | 156 HB | 7.7 % IACS |
Cold drawn | Tighter tolerance and better surface with a strength boost; choose for turned parts and shafts. | 470 | 550 | 16 | 163 HB | — |
Q&T | Used only where a tough medium-strength core is needed without carburizing; low carbon limits attainable hardness. | 480 | 620 | 22 | 11 HRC | 7.7 % IACS |
Carburized, quenched and tempered | Final service condition: hard wear-resistant case over a tough low-carbon core, for gears and pins. | 520 | 700 | 18 | 60 HRC | — |
What is 4012?
4012 is a low-carbon molybdenum alloy steel (UNS G40120) in the SAE-AISI 40xx family, alloyed with Mo for hardenability and used mainly as a carburizing grade that gives a tough core under a moderately hard case. In the default condition it shows about 330 MPa yield, 470 MPa tensile, 28 % elongation and 137 HB (76 HRB), and it is supplied as hot-rolled, annealed, normalized, cold-drawn and stress-relieved bar as well as carburized-and-quenched or quenched-and-tempered parts. It is readily weldable (CE approximately 0.35) but soft and gummy to cut, and has no corrosion resistance of its own, so plating or phosphating is required. Where a higher core strength is needed after carburizing, 4023 is the nearest step up. 4012 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). 4012 has a yield strength of 330 MPa (47.9 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 78% of steel grades. Elongation at break is 28% and the elastic modulus is 205 GPa (29.7 Msi).
What is 4012 used for?
- carburized gears
- small shafts
- camshafts
- pins
Advantages
- Ductile — tolerates forming and impact — 28%, better than 89% of steel grades
- Forms and bends easily — 72/100, better than 88% of steel grades
- Readily welded — 80/100, better than 79% of steel grades
Limitations
- Low strength — 330 MPa (47.9 ksi), worse than 78% of steel grades
4012 properties
Typical room-temperature values for 4012-N; bars are the position among steel grades.
Physical3
4012 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical14
4012 has a yield strength of 330 MPa (47.9 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 78% of steel grades. Elongation at break is 28% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4012 is rated for continuous service to 400°C (752 °F). It conducts heat at 44 W/m·K (25.4 BTU/hr·ft·°F), better than 57% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
4012 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 4012 takes about 29 MJ of energy and emits 2.1 kg of CO₂ — less than 53% of steel grades. Typical recycled content is 30%.
Manufacturability7
4012's machinability is good (58/100, better than 75% of steel grades); weldability very good (80/100); formability very good (72/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. 4012 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 4012
Is 4012 easy to machine?
Machines like a gummy low-carbon steel — use sharp positive-rake tooling, high speed and generous coolant; normalizing before turning improves surface finish and chip control.
Can 4012 be welded?
Readily weldable (CE ≈ 0.35) by SMAW/GMAW with low-hydrogen consumables; preheat 100–150 °C on heavy sections and never weld after carburizing.
Can 4012 be formed, bent or molded?
Good cold formability in the annealed condition (bending, upsetting, cold heading); hot forge at 1100–1200 °C and normalize afterwards.
4012 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 heat analysis | 0.09 – 0.14 | 0.12 |
| Mn | 0.75 – 1 | 0.88 |
| Si | 0.15 – 0.35 | 0.25 |
| Mo | 0.15 – 0.25 | 0.2 |
| P | ≤ 0.04 | |
| S | ≤ 0.04 | |
| Fe | balance |
What surface finishes work on 4012?
No anodizing — protect with zinc or manganese phosphate, black oxide, zinc/nickel plating or paint; carburized surfaces should be finish-ground after hardening.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 4012 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G40120
How much does 4012 cost?
4012 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
4012 — frequently asked
What is 4012 used for?
4012 is typically used for carburized gears, small shafts, camshafts and pins. In short: tough carburizing core steel; most weldable 40xx grade; low-carbon moly case grade.
What is the yield strength of 4012?
4012 has a typical yield strength of 330 MPa (47.9 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 78% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 4012 easy to machine?
Reasonably — machinability is rated good (58/100, better than 75% of steel grades). Machines like a gummy low-carbon steel — use sharp positive-rake tooling, high speed and generous coolant; normalizing before turning improves surface finish and chip control.
Can 4012 be welded?
Yes — weldability is rated very good (80/100). Readily weldable (CE ≈ 0.35) by SMAW/GMAW with low-hydrogen consumables; preheat 100–150 °C on heavy sections and never weld after carburizing.
What surface finishes work on 4012?
No anodizing — protect with zinc or manganese phosphate, black oxide, zinc/nickel plating or paint; carburized surfaces should be finish-ground after hardening.
Can 4012 be formed, bent or molded?
Good cold formability in the annealed condition (bending, upsetting, cold heading); hot forge at 1100–1200 °C and normalize afterwards.
What is the maximum service temperature of 4012?
4012 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 4012-N and 4012 CARB-QT?
N is the default condition — standard stock condition — uniform fine-grain structure for machining and subsequent case hardening. CARB-QT: final service condition: hard wear-resistant case over a tough low-carbon core, for gears and pins. Yield strength is 330 MPa in N versus 520 MPa in CARB-QT.
How much does 4012 cost?
4012 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- SAE J404 — Chemical Compositions of SAE Alloy Steels — SAE International (2021)
- SAE J1268 — Hardenability Bands for Carbon and Alloy H Steels — SAE International (2019)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought, General Requirements — ASTM International (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4A — Steel Heat Treating Fundamentals and Processes (carburizing) — ASM International (2013)
- Machinery's Handbook (machinability ratings) — Industrial Press (2020)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.