Machine steels

Medium-carbon steels, plain or alloyed with Cr, Mo and Ni, that are hardened and tempered (+QT) to the strength a part needs. The guaranteed values depend on the bar size (ruling section).

Where it is used

Shafts, axles and spindles
Gears, pinions and connecting rods
High-strength bolts and studs
Hydraulic piston rods and machine parts

Strengths

Two to four times the yield strength of structural steel
Strength and toughness set by heat treatment
Surface can be induction or flame hardened

Limitations

Strength falls with section size; plain carbon grades harden only in thin bars
Welding needs preheat and care: the heat-affected zone hardens
Not a structural steel: no Eurocode design values

Typical values: 42CrMo4

EN 10083-3

Yield strength Re / Rp0.2: ≥ 900 MPa; guaranteed minimum · ≤ 16 mm · quenched and tempered (+QT); 3
Tensile strength Rm: 1 100–1 300 MPa; guaranteed range · ≤ 16 mm · quenched and tempered (+QT); 3
Elongation after fracture A: ≥ 10 %; guaranteed minimum · ≤ 16 mm · quenched and tempered (+QT); 2
Impact energy (Charpy V) KV: ≥ 30 J; guaranteed minimum · ≤ 16 mm · quenched and tempered (+QT); 1
Brinell hardness HB: ≤ 255 HB; treated for cold shearability (+S); 2

What engineers ask about machine steels

Does the size of the part matter?

Yes. EN 10083 gives quenched and tempered values by ruling section: 42CrMo4 guarantees Rp0.2 900 MPa up to 16 mm but 500 MPa at 160–250 mm, because a thick bar cools more slowly in its core.

Values by diameter on each grade

2 Sources

1
Saarstahl AG — Werkstoff-Datenblatt Saarstahl – 42CrMo4 / 42CrMoS4 (1.7225 / 1.7227) · +QT table
AuthoritativeProducerfollows DIN EN 10083Read in full · 2 Nov 2026
2
thyssenkrupp Materials Services (Technology, Innovation & Sustainability) — Werkstoffdatenblatt 42CrMo4 / 42CrMoS4, 1.7225 / 1.7227 (01.2017) · Mechanische Eigenschaften (+QT)
Established referenceDistributorfollows DIN EN 10083-3:2007-01Read in full · 2 Nov 2026

Can it be welded?

Only with care. At 0.30–0.45 % carbon the heat-affected zone and weld metal harden; preheating, keeping the interpass temperature and slow cooling are generally needed, with Mo or CrMo filler of lower carbon.

1 Sources

1
thyssenkrupp Materials Services (Technology, Innovation & Sustainability) — Werkstoffdatenblatt 42CrMo4 / 42CrMoS4, 1.7225 / 1.7227 (01.2017) · Schweißen
Established referenceDistributorfollows DIN EN 10083-3:2007-01Read in full · 2 Nov 2026

Machine steels grades

Steels for quenching and tempering (EN 10083): shafts, gears, axles and bolts, with strength by ruling section.

Standard fromAnywhere

CEN

Non-alloy steels for quenching and tempering (EN 10083-2)

C22E to C60E. Cheap and machinable, but they harden only in thin sections: the guaranteed +QT values stop at 100 mm.

Grade	Standard	Yield strength at 10 mm	Tensile strength	Evidence
C45 The everyday medium-carbon machine steel: quenched and tempered Rp0.2 490 MPa and Rm 700–850 MPa up to 16 mm, less in larger sections.	EN 10083-2	≥ 490 MPa2	700–850 MPa2	Corroborated 18 Single source 13

Alloy steels for quenching and tempering (EN 10083-3)

Cr, Mo and Ni let the steel harden through larger sections. Values are given by ruling section: the bigger the bar, the lower the strength, because its core cools more slowly.

Grade	Standard	Yield strength at 10 mm	Tensile strength	Evidence
42CrMo4 Chromium-molybdenum machine steel: quenched and tempered Rp0.2 900 MPa and Rm 1 100–1 300 MPa up to 16 mm, still 500 MPa at 250 mm.	EN 10083-3	≥ 900 MPa3	1 100–1 300 MPa3	Confirmed 2 Corroborated 24 Single source 14 Disagreements explained 1

Planned groups

34CrNiMo6, 30CrNiMo8, 51CrV4 and other EN 10083-3 grades
Case-hardening steels 16MnCr5, 20MnCr5, 18CrNiMo7-6 (EN 10084)
Free-cutting 11SMnPb30 (EN 10087); cast steel G20Mn5 (EN 10340)

Standards for machine steels

All standards for machine steels