Steel 4118
AISI/SAE 4118 · UNS G41180 · EN 20CrMo
4118 (UNS G41180) is a low-carbon chromium-molybdenum case-hardening steel used for carburized parts that need a hard case over a tough core.
Reference datasheet — 4118 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 ANN condition
4118 tempers and conditions
4118 is supplied in 8 conditions, soft to hard. ANN is the default FabDigit quotes; the values on this page are for it.
Compare all 8 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize Annealed | Pick for cold heading, cold extrusion or deep-form gear blanks needing maximum ductility. | 330 | 480 | 30 | 140 HB | 7.8 % IACS |
ANNDefault Annealed | Standard stocked bar condition for machining gear blanks before carburizing. | 350 | 530 | 26 | 149 HB | — |
Hardenability-guaranteed (H-band) grade | Order the H grade when Jominy end-quench hardenability must fall inside the SAE H-band for repeatable case/core response. | 355 | 540 | 25 | 149 HB | 7.8 % IACS |
Hot rolled | Cheapest mill condition for forging or re-heat-treatment stock; scaled surface, less uniform properties. | 380 | 570 | 24 | 163 HB | 7.8 % IACS |
Normalized | Use to homogenize forgings and refine grain before carburizing; better toughness uniformity than as-rolled. | 415 | 620 | 23 | 179 HB | — |
Cold drawn | Choose for close-tolerance bright bar and small shafts/pins where extra as-machined strength helps. | 540 | 640 | 13 | 187 HB | — |
Q&T | Direct-hardened condition for shafts and fasteners that need a tough medium-strength body without a case. | 660 | 860 | 18 | 25 HRC | — |
Carburized, hardened and tempered | The service condition for gears, splines and pins: hard wear-resistant case over a tough ~28–40 HRC core. | 760 | 1,000 | 12 | 60 HRC | — |
What is 4118?
4118 (UNS G41180) is a low-carbon chromium-molybdenum case-hardening steel used for carburized parts that need a hard case over a tough core. Engineers specify it for medium-duty gears, camshafts and pins, and it is available as annealed, hot-rolled, normalized, spheroidize-annealed and cold-drawn bar, plus the 4118H hardenability-controlled variant. In the annealed condition it runs about 350 MPa yield, 530 MPa tensile, 26 % elongation and 149 HB; carburizing produces a 58–62 HRC case with cores around 25 HRC after quench and temper. Hardenability is lower than 8620, so heavier sections or higher core strength point to that grade; the steel has no corrosion resistance. 4118 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). 4118 has a yield strength of 350 MPa (50.8 ksi) and a tensile strength of 530 MPa (76.9 ksi) — weaker than 74% of steel grades. Elongation at break is 26% and the elastic modulus is 205 GPa (29.7 Msi).
What is 4118 used for?
- gears
- camshafts
- small pins
- clutch parts
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- Ductile — tolerates forming and impact — 26%, better than 82% of steel grades
- Forms and bends easily — 65/100, better than 81% of steel grades
4118 properties
Typical room-temperature values for 4118-ANN; bars are the position among steel grades.
Physical3
4118 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
4118 has a yield strength of 350 MPa (50.8 ksi) and a tensile strength of 530 MPa (76.9 ksi) — weaker than 74% of steel grades. Elongation at break is 26% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4118 is rated for continuous service to 400°C (752 °F). It conducts heat at 42 W/m·K (24.3 BTU/hr·ft·°F), worse than 56% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
4118 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 4118 takes about 24 MJ of energy and emits 1.9 kg of CO₂ — less than 97% of steel grades. Typical recycled content is 30%.
Manufacturability7
4118's machinability is good (60/100, better than 83% of steel grades); weldability good (60/100); formability good (65/100).
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. 4118 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 4118
Is 4118 easy to machine?
Machine in the annealed or normalized state (~150–180 HB) with carbide at moderate speeds; finish-machine before carburizing since the 58–62 HRC case demands grinding or hard turning with CBN.
Can 4118 be welded?
Weldable in the low-carbon condition with low-hydrogen consumables and 150–250 °C preheat plus post-weld stress relief; never weld carburized surfaces.
Can 4118 be formed, bent or molded?
Good hot forgeability at 1150–1200 °C; cold heading and cold extrusion practical after spheroidize annealing, with normalizing afterwards to refine grain.
4118 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 |
|---|---|---|
| C0.17–0.23 for 4118H | 0.18 – 0.23 | 0.2 |
| Mn | 0.7 – 0.9 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| Cr | 0.4 – 0.6 | 0.5 |
| Mo | 0.08 – 0.15 | 0.12 |
| P | ≤ 0.04 | 0.02 |
| S | ≤ 0.04 | 0.02 |
| Fe | balance |
What surface finishes work on 4118?
No anodizing (ferrous); protect with oil, black oxide, manganese phosphate, zinc plating or nitrided/carburized-and-ground surfaces, and shot-peen gear roots to boost fatigue life.
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 4118 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G41180
- EN / DIN / Werkstoff-Nr.
- 20CrMo
How much does 4118 cost?
4118 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.
4118 — frequently asked
What is 4118 used for?
4118 is typically used for gears, camshafts, small pins and clutch parts. In short: economical Cr-Mo carburizing steel; tough core, 58–62 HRC case; leaner alloy than 8620.
What is the yield strength of 4118?
4118 has a typical yield strength of 350 MPa (50.8 ksi) and a tensile strength of 530 MPa (76.9 ksi) — weaker than 74% of steel grades. Strength varies by condition: see the 8 listed tempers.
Is 4118 easy to machine?
Reasonably — machinability is rated good (60/100, better than 83% of steel grades). Machine in the annealed or normalized state (~150–180 HB) with carbide at moderate speeds; finish-machine before carburizing since the 58–62 HRC case demands grinding or hard turning with CBN.
Can 4118 be welded?
Yes — weldability is rated good (60/100). Weldable in the low-carbon condition with low-hydrogen consumables and 150–250 °C preheat plus post-weld stress relief; never weld carburized surfaces.
What surface finishes work on 4118?
No anodizing (ferrous); protect with oil, black oxide, manganese phosphate, zinc plating or nitrided/carburized-and-ground surfaces, and shot-peen gear roots to boost fatigue life.
Can 4118 be formed, bent or molded?
Good hot forgeability at 1150–1200 °C; cold heading and cold extrusion practical after spheroidize annealing, with normalizing afterwards to refine grain.
What is the maximum service temperature of 4118?
4118 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 4118-ANN and 4118-CD?
ANN is the default condition — standard stocked bar condition for machining gear blanks before carburizing. CD: choose for close-tolerance bright bar and small shafts/pins where extra as-machined strength helps. Yield strength is 350 MPa in ANN versus 540 MPa in CD.
How much does 4118 cost?
4118 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 — ASTM (2020)
- ASTM A322 — Steel Bars, Alloy, Standard Grades — ASTM (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 — ASM International (2013)
- ASM Handbook Vol.16 — Machining — ASM International (1989)
- GB/T 3077 — Alloy structural steels (20CrMo comparison) — SAC (2015)
- Mysteel / 1688 alloy structural steel bar price levels (2025)
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.