Steel SUJ4
JIS SUJ4
SUJ4 is a high-carbon chromium bearing steel of the JIS G 4805 family (also designated GCr15SiMo), with silicon and molybdenum additions that give deeper hardenability and higher toughness than SUJ2.
Reference datasheet — SUJ4 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 A condition
SUJ4 tempers and conditions
SUJ4 is supplied in 7 conditions, soft to hard. A 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 |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Standard supply condition for machining rings, rollers and blanks before hardening. | 420 | 700 | 22 | 190 HB | 45 W/m·K |
Hot rolled | Cheapest mill condition for forging or ring-rolling stock; must be spheroidize annealed before machining. | 550 | 950 | 12 | 27 HRC | 3.5 % IACS |
Cold drawn | Bright-drawn bar and cold-heading wire for small rollers, pins and turned parts with good size tolerance. | 620 | 800 | 12 | 21 HRC | 3.5 % IACS |
high-temperature tempered (300–350 °C) for elevated-temperature service | Choose for bearings and rolls running up to ~250 °C, where the Mo addition preserves hardness after high tempering. | 1,650 | 1,950 | 1 | 57 HRC | 3 % IACS |
Bainite hardened | Lower-bainite treatment giving compressive surface stresses, higher toughness and better tolerance of contaminated lubrication or debris denting. | 1,750 | 2,100 | 2 | 60 HRC | 3.2 % IACS |
tempered 200–250 °C (dimensionally stabilized, S1/TS class) | Pick when the part sees 150–200 °C and dimensional stability matters more than peak hardness. | 1,800 | 2,150 | 60 HRC | 35 W/m·K | |
oil/salt quenched, tempered 150–180 °C (standard martensitic hardening) | Standard finished-bearing condition: maximum contact fatigue life and wear resistance for service below ~120 °C. | 1,900 | 2,350 | 1 | 62 HRC | 34 W/m·K |
What is SUJ4?
SUJ4 is a high-carbon chromium bearing steel of the JIS G 4805 family (also designated GCr15SiMo), with silicon and molybdenum additions that give deeper hardenability and higher toughness than SUJ2. It is specified for thicker-section rings, races and rollers that must through-harden, and is supplied as annealed, hot-rolled or cold-drawn bar and tube at about 700 MPa tensile, 22 % elongation and 190 HB before quench and temper to 55–64 HRC. At roughly 1 % carbon it is effectively unweldable and has no corrosion resistance, so parts need oil, phosphate or plating. For smaller sections SUJ2/52100 is cheaper and more widely stocked. SUJ4 has a density of 7.81 g/cm³ (0.282 lb/in³), lighter than 84% of steel grades. It melts at 1,400°C (2,552 °F). SUJ4 has a yield strength of 420 MPa (60.9 ksi) and a tensile strength of 700 MPa (102 ksi) — weaker than 53% of steel grades. Elongation at break is 22% and the elastic modulus is 208 GPa (30.2 Msi).
What is SUJ4 used for?
- Large bearing rings and races
- Heavy-duty cylindrical rollers
- Thick-section tapered roller cups and cones
- Spherical roller bearing outer rings
- Gearbox and wind turbine bearing components
- Cam followers and track rollers
- Precision spindle bearing races
Advantages
- Polishes to a fine finish — 85/100, better than 99% of steel grades
Limitations
- Difficult to weld — 10/100, worse than 99% of steel grades
- Limited service temperature — 200°C (392 °F), worse than 93% of steel grades
- Low electrical conductivity — 3.5 % IACS, worse than 86% of steel grades
- Difficult to machine — 40/100, worse than 77% of steel grades
SUJ4 properties
Typical room-temperature values for SUJ4-A; bars are the position among steel grades.
Physical3
SUJ4 has a density of 7.81 g/cm³ (0.282 lb/in³), lighter than 84% of steel grades. It melts at 1,400°C (2,552 °F).
Mechanical15
SUJ4 has a yield strength of 420 MPa (60.9 ksi) and a tensile strength of 700 MPa (102 ksi) — weaker than 53% of steel grades. Elongation at break is 22% and the elastic modulus is 208 GPa (30.2 Msi).
Thermal6
SUJ4 is rated for continuous service to 200°C (392 °F). It conducts heat at 45 W/m·K (26 BTU/hr·ft·°F), better than 66% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
SUJ4 conducts electricity at 3.5 % IACS, worse than 86% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of SUJ4 takes about 33 MJ of energy and emits 2.4 kg of CO₂ — more than 76% of steel grades. Typical recycled content is 25%.
Manufacturability7
SUJ4's machinability is fair (40/100, worse than 77% of steel grades); weldability not recommended (10/100); formability fair (35/100).
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. SUJ4 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with SUJ4
Is SUJ4 easy to machine?
Machine only in the spheroidize-annealed condition (≈40% of AISI 1212) with coated carbide and rigid setups; hardened 60+ HRC parts require grinding, honing or CBN hard turning.
Can SUJ4 be welded?
Essentially unweldable — ~1% C gives severe quench cracking; if repair is unavoidable use 300–400 °C preheat, low-hydrogen consumables and immediate post-weld temper.
Can SUJ4 be formed, bent or molded?
Hot forge/ring-roll at 1050–1100 °C (stop above ~900 °C) then spheroidize anneal at 780–800 °C with slow cooling; cold heading and cold ring rolling need fully spheroidized structure.
SUJ4 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 | 0.95 – 1.1 | 1.02 |
| Si | 0.15 – 0.35 | 0.25 |
| Mn | ≤ 0.5 | 0.35 |
| Cr | 1.3 – 1.6 | 1.45 |
| Mothe distinguishing addition vs SUJ2; raises hardenability | 0.1 – 0.25 | 0.18 |
| Pimpurity limit | ≤ 0.03 | |
| Simpurity limit | ≤ 0.03 | |
| Niresidual | ≤ 0.25 | |
| Curesidual | ≤ 0.25 | |
| Ototal oxygen, vacuum-degassed bearing quality | ≤ 0 | 8×10⁻⁴ |
| Fe | balance |
What surface finishes work on SUJ4?
Not anodizable; protect with rust-preventive oil, phosphate, black oxide or thin dense chrome, and superfinish/lap raceways to Ra ≤0.05 µm for bearing 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 SUJ4 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- Similar grades
- GCr15SiMo
How much does SUJ4 cost?
SUJ4 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.
SUJ4 — frequently asked
What is SUJ4 used for?
SUJ4 is typically used for large bearing rings and races, heavy-duty cylindrical rollers, thick-section tapered roller cups and cones, spherical roller bearing outer rings, gearbox and wind turbine bearing components and cam followers and track rollers. In short: deeper-hardening SUJ2 alternative; mo-alloyed bearing steel; for thick bearing sections.
What is the yield strength of SUJ4?
SUJ4 has a typical yield strength of 420 MPa (60.9 ksi) and a tensile strength of 700 MPa (102 ksi) — weaker than 53% of steel grades. Strength varies by condition: see the 7 listed tempers.
Is SUJ4 easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% of steel grades). Machine only in the spheroidize-annealed condition (≈40% of AISI 1212) with coated carbide and rigid setups; hardened 60+ HRC parts require grinding, honing or CBN hard turning.
Can SUJ4 be welded?
Not readily — weldability is rated not recommended (10/100). Essentially unweldable — ~1% C gives severe quench cracking; if repair is unavoidable use 300–400 °C preheat, low-hydrogen consumables and immediate post-weld temper.
What surface finishes work on SUJ4?
Not anodizable; protect with rust-preventive oil, phosphate, black oxide or thin dense chrome, and superfinish/lap raceways to Ra ≤0.05 µm for bearing life.
Can SUJ4 be formed, bent or molded?
Hot forge/ring-roll at 1050–1100 °C (stop above ~900 °C) then spheroidize anneal at 780–800 °C with slow cooling; cold heading and cold ring rolling need fully spheroidized structure.
What is the maximum service temperature of SUJ4?
SUJ4 is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between SUJ4-A and SUJ4-BH?
A is the default condition — standard supply condition for machining rings, rollers and blanks before hardening. BH: lower-bainite treatment giving compressive surface stresses, higher toughness and better tolerance of contaminated lubrication or debris denting. Yield strength is 420 MPa in A versus 1,750 MPa in BH.
How much does SUJ4 cost?
SUJ4 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.
Sources
- JIS G 4805 High carbon chromium bearing steels — JSA (2019)
- ISO 683-17 Heat-treatable steels — Ball and roller bearing steels — ISO (2014)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels (bearing steels) — ASM International (1990)
- ASM Handbook Vol.19 — Fatigue and Fracture — ASM International (1996)
- Bearing steel grades 100Cr6 / 100CrMo7 data sheets — Sanyo Special Steel / Ovako (2022)
- GCr15/GCr15SiMo — Mysteel / 1688 (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.