Steel 5120
AISI/SAE 5120 · UNS G51200 · JIS SCr420
5120 (UNS G51200) is a SAE-AISI low-carbon chromium case-hardening steel, equivalent to JIS SCr420 and GB 20Cr, intended for carburizing rather than through-hardening.
Values for the HR condition
5120 tempers and conditions
5120 is supplied in 7 conditions, soft to hard. HR 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 |
|---|---|---|---|---|---|---|
Annealed (soft annealed, ~870 °C furnace cool) | Softest and most machinable/formable state; use before heavy cold forming or deep drilling. | 280 | 450 | 28 | 131 HB | 7.9 % IACS |
HRDefault Hot rolled | Standard stock form for bar and billet destined for forging, machining and subsequent carburizing. | 295 | 470 | 25 | 145 HB | 7.8 % IACS |
Normalized (~900 °C, air cool) | Uniform fine-grain structure and stable machining response prior to carburizing; standard pre-treatment for forgings. | 330 | 520 | 24 | 155 HB | 7.8 % IACS |
Cold rolled | Cold-rolled strip for stamped and formed parts that will be case-hardened after forming. | 400 | 520 | 18 | 160 HB | 7.8 % IACS |
Cold drawn | Choose for close-tolerance, bright-finish bar with higher yield strength and better surface for turned parts. | 480 | 570 | 15 | 170 HB | 7.8 % IACS |
Quenched and tempered | Through-hardened low-carbon martensite for small tough parts where full case hardening is not required. | 640 | 830 | 16 | 23 HRC | — |
Carburized, quenched & low-temper (case 0.5–1.5 mm, 58–62 HRC surface) | The intended service condition: hard wear- and pitting-resistant case over a tough low-carbon core for gears, splines and pins. | 700 | 900 | 11 | 60 HRC | — |
What is 5120?
5120 (UNS G51200) is a SAE-AISI low-carbon chromium case-hardening steel, equivalent to JIS SCr420 and GB 20Cr, intended for carburizing rather than through-hardening. Engineers use it where a hard, wear-resistant case must sit on a tough core, and it is stocked as hot-rolled, cold-rolled, cold-drawn, annealed and normalized bar for gears, pins and shafts; in the as-supplied condition it gives about 295 MPa yield, 470 MPa tensile, 25 % elongation and 145 HB, with final properties set by the carburize-and-quench cycle. It has no corrosion resistance and lower hardenability than 20MnCr5 or 8620 in heavy sections, which are the usual alternatives when core strength must carry through thick parts. 5120 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F). 5120 has a yield strength of 295 MPa (42.8 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 87% of steel grades. Elongation at break is 25% and the elastic modulus is 205 GPa (29.7 Msi).
What is 5120 used for?
- Gears
- Pins
- Shafts
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 92% of steel grades
- Easy to machine — 62/100, better than 89% of steel grades
- Ductile — tolerates forming and impact — 25%, better than 77% of steel grades
Limitations
- Low strength — 295 MPa (42.8 ksi), worse than 87% of steel grades
5120 properties
Typical room-temperature values for 5120-HR; bars are the position among steel grades.
Physical3
5120 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,420°C (2,588 °F).
Mechanical16
5120 has a yield strength of 295 MPa (42.8 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 87% of steel grades. Elongation at break is 25% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
5120 is rated for continuous service to 350°C (662 °F). It conducts heat at 46 W/m·K (26.6 BTU/hr·ft·°F), better than 71% of steel grades. Thermal expansion is 11.9 µm/m·K (6.61 µin/in·°F).
Electrical3
5120 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 5120 takes about 25 MJ of energy and emits 1.9 kg of CO₂ — less than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
5120's machinability is good (62/100, better than 89% of steel grades); weldability good (60/100); formability good (58/100).
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. 5120 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 5120
Is 5120 easy to machine?
Machines well in annealed/normalized state (~65% of 1212); rough-machine before carburizing and leave grinding stock for post-hardening finishing.
Can 5120 be welded?
Weldable with low-hydrogen consumables at ~150–250 °C preheat; avoid welding carburized surfaces and stress-relieve afterwards.
Can 5120 be formed, bent or molded?
Good cold formability when annealed — used for cold-headed and stamped blanks; hot forge 1150–850 °C then normalize.
Manufacturability
The process limits FabDigit applies to 5120. Every 5120 part is priced by an engineer; design inside these and the quote comes back without a redesign loop.
CNC machining
| Machinability | Better62 / 100 |
|---|---|
| ISO material group | P.2 |
| Cutting speed (rough / finish) | 180 / 210 m/min |
| Minimum wall | 0.8 mm |
| Minimum internal radius | 1 mm |
| Drill depth limit | 5× diameter |
| Best surface (machined / polished) | Ra 1.6 / — |
| Hardenable after machining | No |
Sheet metal
| Formability | Better58 / 100 |
|---|---|
| Weldability | Better60 / 100 |
5120 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 |
|---|---|---|
| C | 0.17 – 0.22 | 0.2 |
| Mn | 0.7 – 0.9 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| Cr | 0.7 – 0.9 | 0.8 |
| P | ≤ 0.04 | |
| Smax; 5120H/resulfurized variants differ | ≤ 0.04 | |
| Fe | balance |
What surface finishes work on 5120?
No anodizing; protect with oil, phosphate, black oxide or zinc/nickel plating — bake after plating to avoid hydrogen embrittlement in hardened parts.
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).
Plating
CVD Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel 5120 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
How much does 5120 cost?
5120 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
5120 — frequently asked
What is 5120 used for?
5120 is typically used for gears, pins and shafts. In short: carburizing Cr-Mn bar.
What is the yield strength of 5120?
5120 has a typical yield strength of 295 MPa (42.8 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 87% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is 5120 easy to machine?
Reasonably — machinability is rated good (62/100, better than 89% of steel grades). Machines well in annealed/normalized state (~65% of 1212); rough-machine before carburizing and leave grinding stock for post-hardening finishing.
Can 5120 be welded?
Yes — weldability is rated good (60/100). Weldable with low-hydrogen consumables at ~150–250 °C preheat; avoid welding carburized surfaces and stress-relieve afterwards.
What surface finishes work on 5120?
No anodizing; protect with oil, phosphate, black oxide or zinc/nickel plating — bake after plating to avoid hydrogen embrittlement in hardened parts.
Can 5120 be formed, bent or molded?
Good cold formability when annealed — used for cold-headed and stamped blanks; hot forge 1150–850 °C then normalize.
What is the maximum service temperature of 5120?
5120 is rated for continuous use to about 350°C (662 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 5120-HR and 5120-CD?
HR is the default condition — standard stock form for bar and billet destined for forging, machining and subsequent carburizing. CD: choose for close-tolerance, bright-finish bar with higher yield strength and better surface for turned parts. Yield strength is 295 MPa in HR versus 480 MPa in CD.
How much does 5120 cost?
5120 is a standard-cost steel ($$), cheaper than about 71% 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.
Can FabDigit make parts in 5120?
Yes — 5120 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)
- GB/T 3077 (20Cr) — SAC (2015)
- 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)
- Machinery's Handbook, 31st ed. — 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.