Steel 8642
AISI/SAE 8642 · UNS G86420
8642 is a medium-carbon nickel-chromium-molybdenum through-hardening steel (UNS G86420) carrying slightly more carbon than 8640, which raises strength after quench and tempering while retaining good hardenability in medium sections.
Reference datasheet — 8642 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 QT540 condition
8642 tempers and conditions
8642 is supplied in 13 conditions, soft to hard. QT540 is the default FabDigit quotes; the values on this page are for it.
Compare all 13 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Spheroidize annealed | Choose for cold heading, thread rolling or severe cold forming of this medium-carbon alloy. | 400 | 655 | 25 | 179 HB | 8 % IACS |
Solution annealed | Softest condition for deep machining, cold work or before final heat treatment. | 435 | 710 | 21 | 192 HB | — |
Hot rolled | Lowest-cost mill condition for parts that will be fully heat treated after rough machining. | 490 | 830 | 18 | 23 HRC | 8 % IACS |
Cold drawn | Tight tolerance, bright bar with raised yield strength for shafts machined without further heat treatment. | 690 | 800 | 12 | 21 HRC | 8 % IACS |
Normalized | Uniform fine-grain structure and moderate strength before Q&T, or for parts not needing full hardening. | 700 | 1,050 | 20 | 33 HRC | 7.9 % IACS |
Q&T | Toughest Q&T setting; pick for shock-loaded or weld-repaired parts and for easier machining. | 830 | 930 | 19 | 28 HRC | — |
Q&T to 28–32 HRC | Common purchase spec for heavy shafts where machinability and toughness matter more than peak strength. | 860 | 970 | 18 | 30 HRC | 7.9 % IACS |
QT540Default Q&T | The standard stocked condition: best strength/toughness balance for general machined power-transmission parts. | 1,020 | 1,130 | 15 | 34 HRC | — |
Induction hardened | Select when a wear-resistant 55+ HRC surface with compressive residual stress is needed on a tough Q&T core. | 1,020 | 1,130 | 13 | 56 HRC | 7.4 % IACS |
Q&T to 38–42 HRC | High-strength hardness band for gears, pins and hydraulic components; machine before final temper if possible. | 1,200 | 1,340 | 13 | 40 HRC | 7.6 % IACS |
Q&T | High-strength setting (~40–44 HRC) for heavily loaded shafts, gears and fasteners. | 1,290 | 1,430 | 12 | 43 HRC | — |
Q&T | Very high strength; falls in the temper-embrittlement range, so use only where toughness is not critical. | 1,570 | 1,720 | 10 | 49 HRC | — |
Q&T | Maximum hardness and strength for wear parts; very low ductility and notch sensitivity — avoid impact loading. | 1,720 | 1,930 | 9 | 54 HRC | — |
What is 8642?
8642 is a medium-carbon nickel-chromium-molybdenum through-hardening steel (UNS G86420) carrying slightly more carbon than 8640, which raises strength after quench and tempering while retaining good hardenability in medium sections. It is stocked as annealed, spheroidize annealed, normalized, hot-rolled and cold-drawn bar plus a range of Q&T and induction-hardened conditions; the default Q&T state is about 1020 MPa yield, 1130 MPa tensile, 15 % elongation and 320 HB (34 HRC), with service to 400 °C. Carbon equivalent near 0.8 makes welding demanding and machinability sits near 50 % of 1212; 8640 or 4140 are chosen when weldability or stock availability governs. 8642 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). 8642 has a yield strength of 1,020 MPa (148 ksi) and a tensile strength of 1,130 MPa (164 ksi) — stronger than 92% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
What is 8642 used for?
- automotive axle shafts
- gears
- high-strength studs and bolts
- machinery shafts
Advantages
- High strength — 1,020 MPa (148 ksi), better than 92% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
8642 properties
Typical room-temperature values for 8642-QT540; bars are the position among steel grades.
Physical3
8642 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
8642 has a yield strength of 1,020 MPa (148 ksi) and a tensile strength of 1,130 MPa (164 ksi) — stronger than 92% of steel grades. Elongation at break is 15% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8642 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 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
8642 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 8642 takes about 34 MJ of energy and emits 2.4 kg of CO₂ — more than 82% of steel grades. Typical recycled content is 30%.
Manufacturability7
8642's machinability is fair (50/100, worse than 53% of steel grades); weldability fair (35/100); formability poor (25/100).
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. 8642 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 8642
Is 8642 easy to machine?
Best machined at 200–300 HB (annealed/normalized or Q&T ≤32 HRC); use rigid setups, carbide inserts and generous coolant, then finish-temper to final hardness.
Can 8642 be welded?
Weldable with low-hydrogen consumables but CE ≈ 0.8 demands 200–320 °C preheat, controlled interpass and immediate post-weld temper/stress relief to avoid cold cracking.
Can 8642 be formed, bent or molded?
Cold form only in annealed or spheroidized condition; hot forge 1100–1200 °C and finish above ~870 °C, then slow cool or normalize before hardening.
8642 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 | 0.4 – 0.45 | 0.42 |
| Mn | 0.75 – 1 | 0.88 |
| Si | 0.15 – 0.35 | 0.25 |
| Ni | 0.4 – 0.7 | 0.55 |
| Cr | 0.4 – 0.6 | 0.5 |
| Mo | 0.15 – 0.25 | 0.2 |
| P | ≤ 0.04 | |
| Smax; H-grade/resulfurized variants differ | ≤ 0.04 | |
| Fe | balance |
What surface finishes work on 8642?
No anodizing — protect with phosphate + oil, black oxide, zinc or Cr plating; bake plated high-strength parts at 190–220 °C to relieve hydrogen embrittlement; polishes well after Q&T.
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 8642 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G86420
How much does 8642 cost?
8642 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.
8642 — frequently asked
What is 8642 used for?
8642 is typically used for automotive axle shafts, gears, high-strength studs and bolts and machinery shafts. In short: stronger than 8640 Q&T; good medium-section hardenability; demanding weldability.
What is the yield strength of 8642?
8642 has a typical yield strength of 1,020 MPa (148 ksi) and a tensile strength of 1,130 MPa (164 ksi) — stronger than 92% of steel grades. Strength varies by condition: see the 13 listed tempers.
Is 8642 easy to machine?
Reasonably — machinability is rated fair (50/100, worse than 53% of steel grades). Best machined at 200–300 HB (annealed/normalized or Q&T ≤32 HRC); use rigid setups, carbide inserts and generous coolant, then finish-temper to final hardness.
Can 8642 be welded?
With care — weldability is rated fair (35/100). Weldable with low-hydrogen consumables but CE ≈ 0.8 demands 200–320 °C preheat, controlled interpass and immediate post-weld temper/stress relief to avoid cold cracking.
What surface finishes work on 8642?
No anodizing — protect with phosphate + oil, black oxide, zinc or Cr plating; bake plated high-strength parts at 190–220 °C to relieve hydrogen embrittlement; polishes well after Q&T.
Can 8642 be formed, bent or molded?
Cold form only in annealed or spheroidized condition; hot forge 1100–1200 °C and finish above ~870 °C, then slow cool or normalize before hardening.
What is the maximum service temperature of 8642?
8642 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 8642-QT540 and 8642-QT205?
QT540 is the default condition — the standard stocked condition: best strength/toughness balance for general machined power-transmission parts. QT205: maximum hardness and strength for wear parts; very low ductility and notch sensitivity — avoid impact loading. Yield strength is 1,020 MPa in QT540 versus 1,720 MPa in QT205.
How much does 8642 cost?
8642 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 Alloy H-Steels — SAE International (2019)
- ASTM A29/A29M — Steel Bars, Carbon and Alloy, Hot-Wrought — ASTM (2020)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.4 — Heat Treating — ASM International (1991)
- ASM Handbook Vol.16 — Machining — ASM International (1989)
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.