EN19 / 708M40 (Cr-Mo) — Properties, Machinability & Equivalents

Mechanical & physical properties

Property	Typical value
Density	7850 kg/m³
Yield (T)	≥650 MPa
Tensile (T)	850–1000 MPa
Elongation	~13 %
Young's E	210 GPa
Hardness	~248–302 HB (T)
CTE	~12 µm/m·K
Thermal cond.	~42 W/m·K
Max service	~500 °C (stay below tempering temp)
Poisson ν	~0.29
Shear modulus G	~81 GPa (derived)
Shear strength	≈0.6 × UTS (design convention — not test data)
Specific heat	~460–480 J/kg·K
Elec. resistivity	~0.22 µΩ·m
Melting range	~1420–1500 °C
Fatigue (indicative)	~380–500 MPa (T cond., ≈0.45–0.5 × UTS) — rotating-bend, polished specimen; indicative only, surface/size/loading factors apply

Typical values for guidance — properties vary with section size, temper and batch. Check the material certificate for certification work.

Fair

~50–55% in ‘T’ condition; carbide tooling.

Poor–Fair

Preheat + PWHT essential; low-hydrogen consumables.

Equivalents & alternatives: 708M40 (EN19); 1.7225 (42CrMo4); AISI 4140. Alt: EN24 (add Ni for toughness).

BS 970:1991 renamed the grade 709M40 (Mo 0.25–0.35 %); 708M40 has 0.15–0.25 % Mo. Both are traded as EN19.

High strength

High-tensile Ni-Cr-Mo steel — heavily loaded shafts, gears, crankshafts. Tough at high strength.

The standard high-tensile bolt class — general structural and machine fasteners. Medium-carbon (or boron) steel, quenched & tempered.

High-strength class — preloaded structural assemblies (EN 14399/HSFG type) and high-duty machine fasteners.

The socket-screw class — highest standard property class. Alloy steel, tightly controlled Q&T; usually self-colour/black.

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