Steel 4042
AISI/SAE 4042 · UNS G40420
4042 is a medium-carbon molybdenum alloy steel in the SAE-AISI 40xx family (UNS G40420), sitting above 4037 where higher strength and wear resistance are needed.
Reference datasheet — 4042 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
4042 tempers and conditions
4042 is supplied in 9 conditions, soft to hard. A is the default FabDigit quotes; the values on this page are for it.
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 | — |
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?
4042 is a medium-carbon molybdenum alloy steel in the SAE-AISI 40xx family (UNS G40420), sitting above 4037 where higher strength and wear resistance are needed. It is stocked as hot-rolled, annealed, normalized and cold-drawn bar and in quench-and-tempered bands from 28–32 HRC to 48–52 HRC, plus intensive-quenched stock, so one grade covers shafting and hardened fastener work. Default-condition properties are 400 MPa yield, 620 MPa tensile, 24 % elongation and 187 HB (90 HRB). It has no corrosion resistance and only moderate weldability (CE ≈ 0.60); where deeper hardenability is required, 4140 is the usual step up. 4042 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). 4042 has a yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Elongation at break is 24% and the elastic modulus is 205 GPa (29.7 Msi).
What is 4042 used for?
- high-strength bolts
- shafts
- axles
4042 properties
Typical room-temperature values for 4042-A; bars are the position among steel grades.
Physical3
4042 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 has a yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Elongation at break is 24% and the elastic modulus is 205 GPa (29.7 Msi).
Thermal6
4042 is rated for continuous service to 400°C (752 °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 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 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's machinability is good (60/100, better than 83% of steel grades); weldability fair (40/100); formability fair (45/100).
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. 4042 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with 4042
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.
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 |
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).
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 4042 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- UNS
- G40420
How much does 4042 cost?
4042 is a budget-cost steel ($), cheaper than about 90% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
4042 — frequently asked
What is 4042 used for?
4042 is typically used for high-strength bolts, shafts and axles. In short: higher strength than 4037; chromium-free molybdenum steel; through-hardens to 52 HRC.
What is the yield strength of 4042?
4042 has a typical yield strength of 400 MPa (58 ksi) and a tensile strength of 620 MPa (89.9 ksi) — weaker than 60% of steel grades. Strength varies by condition: see the 9 listed tempers.
Is 4042 easy to machine?
Reasonably — machinability is rated good (60/100, better than 83% of steel grades). Best machined annealed or normalized (~65% of 1212); above 35 HRC use carbide/CBN and rigid setups, finish-grind at high hardness.
Can 4042 be welded?
With care — weldability is rated fair (40/100). CE ≈ 0.60 — preheat 200–315 °C, low-hydrogen consumables and post-weld temper below the part's tempering temperature.
What surface finishes work on 4042?
Bare surfaces rust quickly — specify oil, phosphate-and-oil, black oxide, zinc or chrome plating (bake to avoid hydrogen embrittlement above 1000 MPa).
Can 4042 be formed, bent or molded?
Hot forge 1100–1200 °C with slow cooling; cold forming limited to mild bends in the annealed condition.
What is the maximum service temperature of 4042?
4042 is rated for continuous use to about 400°C (752 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 4042-A and 4042-IQ?
A is the default condition — softest, most machinable condition; standard stock form before quench and temper. IQ: wear-resistant hardened case on a tough tempered core for journals, splines and cam surfaces. Yield strength is 400 MPa in A versus 860 MPa in IQ.
How much does 4042 cost?
4042 is a budget-cost steel ($), 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)
- Machining Data Handbook — Metcut Research Associates (1980)
- Mysteel / SMM (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.