Steel 708M40-HR (Hot rolled)
Supply condition
BS 708M40 · AISI/SAE 4140 · EN 42CrMo4
Cheapest mill stock, bought to be heat treated by the customer after rough machining.
Values for the HR condition
Other 708M40 tempers and conditions
708M40 is listed in 13 conditions; see the grade overview at 708M40.
Compare all 13 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Softest condition for deep machining, cold forming or before final heat treatment. | 420 | 655 | 25 | 190 HB | — |
HRThis page Hot rolled | Cheapest mill stock, bought to be heat treated by the customer after rough machining. | 450 | 750 | 20 | 19 HRC | 7.8 % IACS |
Q&T condition R | Lightly tempered condition for large sections or maximum toughness/ductility. | 525 | 775 | 20 | 22 HRC | — |
Cold drawn | Close-tolerance bright bar for shafts and pins where full Q&T strength is not needed. | 620 | 760 | 14 | 20 HRC | 7.8 % IACS |
Q&T condition S | Tough medium-strength Q&T grade for heavy shafts and general engineering. | 620 | 850 | 18 | 26 HRC | — |
Normalized | Uniform fine grain structure for forgings prior to machining or hardening; moderate strength off the shelf. | 655 | 1,000 | 17 | 30 HRC | — |
TDefault Q&T condition T | The standard stock condition of 708M40 bar — best all-round strength/toughness/machinability balance. | 700 | 925 | 17 | 29 HRC | — |
Q&T (condition T/U) + gas nitrided case | Choose for wear-resistant, low-distortion surfaces (spindles, rams, gears) while keeping a tough Q&T core. | 720 | 950 | 15 | 55 HRC | — |
Q&T condition V | Use where higher yield is required and section size is modest; toughness starts to fall. | 850 | 1,075 | 13 | 34 HRC | — |
Solution heat treated (unstable) | High-strength condition for small/medium sections such as bolts, pins and torsion parts. | 930 | 1,150 | 12 | 37 HRC | — |
Q&T condition X | Very high strength Q&T for small sections; check notch sensitivity and hydrogen embrittlement risk. | 1,000 | 1,225 | 11 | 40 HRC | — |
Q&T condition Y | Near the practical strength ceiling for 708M40; only for small diameters and low-notch designs. | 1,080 | 1,300 | 10 | 42 HRC | — |
Q&T condition Z | Maximum-strength low-temper condition for small parts; low toughness, high distortion and cracking sensitivity. | 1,380 | 1,600 | 8 | 48 HRC | — |
What is 708M40-HR?
708M40-HR is 708M40 supplied in the HR condition — cheapest mill stock, bought to be heat treated by the customer after rough machining. 708M40-HR has a yield strength of 450 MPa (65.3 ksi) and a tensile strength of 750 MPa (109 ksi) — stronger than 52% of steel grades. Elongation at break is 20% and the elastic modulus is 210 GPa (30.5 Msi). 708M40-HR has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F). T is the default condition FabDigit quotes; HR is available on request or by drawing note.
Advantages
- Polishes to a fine finish — 65/100, better than 78% of steel grades
Limitations
- Low fracture toughness — 55 MPa·√m (50.1 ksi·√in), worse than 82% of steel grades
708M40-HR properties
Typical room-temperature values for 708M40-HR; 23 are specific to this condition. Other listed values are 708M40 reference data and may not represent this condition. Bars are the position among steel grades.
Physical3
708M40-HR has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,416°C (2,581 °F).
Mechanical15
708M40-HR has a yield strength of 450 MPa (65.3 ksi) and a tensile strength of 750 MPa (109 ksi) — stronger than 52% of steel grades. Elongation at break is 20% and the elastic modulus is 210 GPa (30.5 Msi).
Thermal6
708M40-HR is rated for continuous service to 350°C (662 °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
708M40-HR 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 708M40-HR takes about 29 MJ of energy and emits 2 kg of CO₂ — less than 53% of steel grades. Typical recycled content is 35%.
Manufacturability7
708M40-HR's machinability is good (57/100, better than 71% of steel grades); weldability fair (45/100); formability fair (35/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 708M40-HR
Is 708M40 easy to machine?
Machines well up to ~300 HB with carbide at 100–180 m/min; above ~40 HRC use coated carbide/CBN, rigid setups and reduced feeds — annealed or ≤277 HB stock is preferred for heavy cutting.
Can 708M40 be welded?
Weldable with care only: preheat 250–350 °C, low-hydrogen consumables, interpass control and immediate stress-relief/temper at 600–650 °C; avoid welding in the high-strength (X/Y/Z) conditions.
Can 708M40 be formed, bent or molded?
Hot forge 1100–1200 °C, finish above 900 °C and normalize afterwards; cold forming limited to annealed bar with generous bend radii.
What surface finishes work on 708M40?
No anodizing — protect by oil, phosphate, paint, zinc/hard-chrome plating, black oxide or nitriding; bake 190–220 °C after plating to avoid hydrogen embrittlement.
708M40 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 | 0.36 – 0.44 | 0.4 |
| Si | 0.1 – 0.35 | 0.25 |
| Mn | 0.65 – 1 | 0.8 |
| P | ≤ 0.04 | — |
| Smax (708A42/709M40 variants have tighter S) | ≤ 0.04 | — |
| Cr | 0.9 – 1.2 | 1.05 |
| Mo | 0.15 – 0.25 | 0.2 |
| Fe | balance | — |
708M40-HR — frequently asked
What is 708M40-HR used for?
708M40-HR is typically used for shafts, gears, fasteners and tooling. In short: benchmark Cr-Mo engineering steel; widest availability in family; Q&T to R–Z classes.
What is the yield strength of 708M40-HR?
708M40-HR has a typical yield strength of 450 MPa (65.3 ksi) and a tensile strength of 750 MPa (109 ksi) — stronger than 52% of steel grades. Strength varies by condition: see the 13 listed tempers.
Is 708M40-HR easy to machine?
Reasonably — machinability is rated good (57/100, better than 71% of steel grades). Machines well up to ~300 HB with carbide at 100–180 m/min; above ~40 HRC use coated carbide/CBN, rigid setups and reduced feeds — annealed or ≤277 HB stock is preferred for heavy cutting.
Can 708M40-HR be welded?
With care — weldability is rated fair (45/100). Weldable with care only: preheat 250–350 °C, low-hydrogen consumables, interpass control and immediate stress-relief/temper at 600–650 °C; avoid welding in the high-strength (X/Y/Z) conditions.
What surface finishes work on 708M40-HR?
No anodizing — protect by oil, phosphate, paint, zinc/hard-chrome plating, black oxide or nitriding; bake 190–220 °C after plating to avoid hydrogen embrittlement.
Can 708M40-HR be formed, bent or molded?
Hot forge 1100–1200 °C, finish above 900 °C and normalize afterwards; cold forming limited to annealed bar with generous bend radii.
What is the maximum service temperature of 708M40-HR?
708M40-HR 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 708M40-T and 708M40-Z?
T is the default condition — the standard stock condition of 708M40 bar — best all-round strength/toughness/machinability balance. Z: maximum-strength low-temper condition for small parts; low toughness, high distortion and cracking sensitivity. Yield strength is 700 MPa in T versus 1,380 MPa in Z.
Sources
- BS 970-1: Wrought steels for mechanical and allied engineering purposes — BSI (1991)
- EN 10083-3 Quenched and tempered steels — alloy steels (42CrMo4) — CEN (2006)
- ASM Handbook Vol.1: Properties and Selection: Irons, Steels and High-Performance Alloys — ASM International (1990)
- ASM Handbook Vol.19: Fatigue and Fracture — ASM International (1996)
- EN19 / 708M40 engineering steel datasheet — West Yorkshire Steel / Bohler-Uddeholm (2023)
- GB/T 3077 (42CrMo) — SAC (2015)
- 42CrMo — Mysteel / 1688 (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.