Steel 8642 QT_38-42HRC
Hardness band
AISI/SAE 8642 · UNS G86420
QT_38-42HRC = q&T to 38–42 HRC
High-strength hardness band for gears, pins and hydraulic components; machine before final temper if possible.
Values for the QT_38-42HRC condition
Other 8642 tempers and conditions
8642 is listed in 13 conditions; see the grade overview at 8642.
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 |
QT_38-42HRCThis page 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 QT_38-42HRC?
8642 QT_38-42HRC is 8642 heat treated to QT_38-42HRC — high-strength hardness band for gears, pins and hydraulic components; machine before final temper if possible. 8642 QT_38-42HRC has a yield strength of 1,200 MPa (174 ksi) and a tensile strength of 1,340 MPa (194 ksi) — stronger than 94% of steel grades. Elongation at break is 13% and the elastic modulus is 205 GPa (29.7 Msi). 8642 QT_38-42HRC 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). QT540 is the default condition FabDigit quotes; QT_38-42HRC is available on request or by drawing note.
Advantages
- High strength — 1,200 MPa (174 ksi), better than 94% of steel grades
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Limited formability — 12/100, worse than 92% of steel grades
- Difficult to weld — 22/100, worse than 81% of steel grades
- Limited ductility — 13%, worse than 78% of steel grades
- Difficult to machine — 40/100, worse than 77% of steel grades
8642 QT_38-42HRC properties
Typical room-temperature values for 8642 QT_38-42HRC; 22 are specific to this condition. Other listed values are 8642 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
8642 QT_38-42HRC 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 QT_38-42HRC has a yield strength of 1,200 MPa (174 ksi) and a tensile strength of 1,340 MPa (194 ksi) — stronger than 94% of steel grades. Elongation at break is 13% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
8642 QT_38-42HRC is rated for continuous service to 350°C (662 °F). It conducts heat at 43 W/m·K (24.8 BTU/hr·ft·°F), better than 51% of steel grades. Thermal expansion is 12.3 µm/m·K (6.83 µin/in·°F).
Electrical3
8642 QT_38-42HRC conducts electricity at 7.6 % IACS, worse than 65% of steel grades.
Chemical & Environmental3
Corrosion resistance is not recommended (12/100), worse than 53% of steel grades.
Sustainability4
Producing a kilogram of 8642 QT_38-42HRC 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 QT_38-42HRC's machinability is fair (40/100, worse than 77% of steel grades); weldability poor (22/100); formability not recommended (12/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 8642 QT_38-42HRC
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.
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.
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 | — |
8642 QT_38-42HRC — frequently asked
What is 8642 QT_38-42HRC used for?
8642 QT_38-42HRC 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 QT_38-42HRC?
8642 QT_38-42HRC has a typical yield strength of 1,200 MPa (174 ksi) and a tensile strength of 1,340 MPa (194 ksi) — stronger than 94% of steel grades. Strength varies by condition: see the 13 listed tempers.
Is 8642 QT_38-42HRC easy to machine?
Not especially — machinability is rated fair (40/100, worse than 77% 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 QT_38-42HRC be welded?
Not readily — weldability is rated poor (22/100). 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 QT_38-42HRC?
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 QT_38-42HRC 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 QT_38-42HRC?
8642 QT_38-42HRC 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 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.
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. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.