Steel 4042 QT-40-45HRC
Hardness band
AISI/SAE 4042 · UNS G40420
High-strength, wear-resistant condition where notch toughness is secondary; grind rather than machine.
Values for the QT-40-45HRC condition
Other 4042 tempers and conditions
4042 is listed in 9 conditions; see the grade overview at 4042.
- A
- HR
- N
- CD
- QT-28-32HRC
- IQ
- QT-33-38HRC
- QT-40-45HRC
- QT-48-52HRC
Compare all 9 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
ADefault Solution annealed | Softest, most machinable condition; standard stock form before quench and temper. | 400 | 620 | 24 | 187 HB | — |
Hot rolled | Cheapest mill condition for parts that will be fully heat treated after rough machining. | 415 | 660 | 20 | 13 HRC | 7.8 % IACS |
Normalized | Uniform fine pearlitic structure with higher strength than annealed; good pre-machining or as-supplied condition for moderately loaded parts. | 490 | 760 | 20 | 19 HRC | 7.8 % IACS |
Cold drawn | Tight tolerance, bright bar with raised yield strength for shafting and screw-machine work without heat treatment. | 620 | 720 | 14 | 17 HRC | 7.8 % IACS |
oil quenched, high-temperature temper | Tough general-purpose condition for shafts and machined components that must still be machinable. | 830 | 960 | 18 | 30 HRC | — |
Induction Hardened | Wear-resistant hardened case on a tough tempered core for journals, splines and cam surfaces. | 860 | 1,000 | 14 | 55 HRC | 7.2 % IACS |
oil quenched, medium temper | Balanced strength/toughness for gears, pins and heavily loaded fasteners. | 1,030 | 1,140 | 15 | 36 HRC | — |
QT-40-45HRCThis page oil quenched, low temper | High-strength, wear-resistant condition where notch toughness is secondary; grind rather than machine. | 1,250 | 1,380 | 12 | 43 HRC | — |
quenched, stress-relief temper | Maximum practical hardness for this carbon level — wear surfaces, cams and small sections only. | 1,450 | 1,650 | 8 | 50 HRC | — |
What is 4042 QT-40-45HRC?
4042 QT-40-45HRC is 4042 heat treated to QT-40-45HRC — high-strength, wear-resistant condition where notch toughness is secondary; grind rather than machine. 4042 QT-40-45HRC has a yield strength of 1,250 MPa (181 ksi) and a tensile strength of 1,380 MPa (200 ksi) — stronger than 95% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi). 4042 QT-40-45HRC 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). A is the default condition FabDigit quotes; QT-40-45HRC is available on request or by drawing note.
Advantages
- High strength — 1,250 MPa (181 ksi), better than 95% of steel grades
Limitations
- Limited ductility — 12%, worse than 84% of steel grades
- Limited service temperature — 300°C (572 °F), worse than 78% of steel grades
4042 QT-40-45HRC properties
Typical room-temperature values for 4042 QT-40-45HRC; 12 are specific to this condition. Other listed values are 4042 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
4042 QT-40-45HRC 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).
Mechanical13
4042 QT-40-45HRC has a yield strength of 1,250 MPa (181 ksi) and a tensile strength of 1,380 MPa (200 ksi) — stronger than 95% of steel grades. Elongation at break is 12% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4042 QT-40-45HRC is rated for continuous service to 300°C (572 °F). It conducts heat at 42.6 W/m·K (24.6 BTU/hr·ft·°F), worse than 51% of steel grades. Thermal expansion is 12.2 µm/m·K (6.78 µin/in·°F).
Electrical3
4042 QT-40-45HRC 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 4042 QT-40-45HRC takes about 26 MJ of energy and emits 2 kg of CO₂ — less than 64% of steel grades. Typical recycled content is 30%.
Manufacturability6
4042 QT-40-45HRC's machinability is good (60/100, better than 83% of steel grades); weldability fair (40/100); formability fair (45/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 4042 QT-40-45HRC
Is 4042 easy to machine?
Best machined annealed or normalized (~65% of 1212); above 35 HRC use carbide/CBN and rigid setups, finish-grind at high hardness.
Can 4042 be welded?
CE ≈ 0.60 — preheat 200–315 °C, low-hydrogen consumables and post-weld temper below the part's tempering temperature.
Can 4042 be formed, bent or molded?
Hot forge 1100–1200 °C with slow cooling; cold forming limited to mild bends in the annealed condition.
What surface finishes work on 4042?
Bare surfaces rust quickly — specify oil, phosphate-and-oil, black oxide, zinc or chrome plating (bake to avoid hydrogen embrittlement above 1000 MPa).
4042 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 | 0.7 – 0.9 | 0.8 |
| Si | 0.15 – 0.35 | 0.25 |
| Mo | 0.2 – 0.3 | 0.25 |
| P | ≤ 0.04 | — |
| S | ≤ 0.04 | — |
| Fe | balance | — |
4042 QT-40-45HRC — frequently asked
What is 4042 QT-40-45HRC used for?
4042 QT-40-45HRC is typically used for high-strength bolts, shafts and axles. In short: higher strength than 4037; chromium-free molybdenum steel; through-hardens to 52 HRC.
What is the yield strength of 4042 QT-40-45HRC?
4042 QT-40-45HRC has a typical yield strength of 1,250 MPa (181 ksi) and a tensile strength of 1,380 MPa (200 ksi) — stronger than 95% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 4042 QT-40-45HRC easy to machine?
Reasonably — machinability is rated good (60/100, better than 83% of steel grades). Best machined annealed or normalized (~65% of 1212); above 35 HRC use carbide/CBN and rigid setups, finish-grind at high hardness.
Can 4042 QT-40-45HRC be welded?
With care — weldability is rated fair (40/100). CE ≈ 0.60 — preheat 200–315 °C, low-hydrogen consumables and post-weld temper below the part's tempering temperature.
What surface finishes work on 4042 QT-40-45HRC?
Bare surfaces rust quickly — specify oil, phosphate-and-oil, black oxide, zinc or chrome plating (bake to avoid hydrogen embrittlement above 1000 MPa).
Can 4042 QT-40-45HRC be formed, bent or molded?
Hot forge 1100–1200 °C with slow cooling; cold forming limited to mild bends in the annealed condition.
What is the maximum service temperature of 4042 QT-40-45HRC?
4042 QT-40-45HRC is rated for continuous use to about 300°C (572 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4042-A and 4042-IQ?
A is the default condition — softest, most machinable condition; standard stock form before quench and temper. IQ: wear-resistant hardened case on a tough tempered core for journals, splines and cam surfaces. Yield strength is 400 MPa in A versus 860 MPa in IQ.
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)
- Machining Data Handbook — Metcut Research Associates (1980)
- Mysteel / SMM (2025)
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.