Quenched and Tempered Steels: EN 10083 Grades, Values and How to Choose

📋 Datasheets for the grades in this guide: C45 → · 25CrMo4 → · 42CrMo4 → · 39NiCrMo3 → · 34CrNiMo6 → · 51CrV4 →

What Is Quenched and Tempered Steel?

Quenched and tempered (Q&T) steel is the class that can deliver high strength and toughness at the same time, by being quenched and then tempered at high temperature. In Europe the governing standard is EN 10083. The defining feature of the class is its carbon window: roughly 0.25–0.55% C. That band is no accident — less carbon will not harden sufficiently on quenching, while more makes the part brittle and raises the risk of quench cracking.

The microstructure of a Q&T steel is tempered martensite: the hard but brittle martensite produced by quenching is softened in a controlled way at 540–680 °C. The result is the best strength-to-toughness balance obtainable from that chemistry. This is why shafts, gears, axles, crankshafts, bolts and forged parts are made from quenched and tempered grades as a matter of course.

The standard splits in two:

• EN 10083-2 — non-alloy Q&T steels (C22…C60; C45 being by far the most common)
• EN 10083-3 — alloy Q&T steels (Cr, Cr-Mo, Ni-Cr-Mo, Cr-V)

Which Steels Are Quenched and Tempered Grades?

The six main Q&T grades in our stock programme and their characters:

Grade	W.-Nr.	AISI ≈	C (%)	Main alloy	Hardenability	Typical use	Datasheet
C45	1.0503	1045	0.42–0.50	— (non-alloy)	Low	Shafts, axles, keys, general machinery	C45
25CrMo4	1.7218	4130	0.22–0.29	Cr-Mo	Medium	Welded structures, tubing, pressure parts	25CrMo4
42CrMo4	1.7225	4140	0.38–0.45	Cr-Mo	High	Shafts, gears, high-tensile bolts	42CrMo4
39NiCrMo3	1.6510	≈ 9840	0.35–0.43	Ni-Cr-Mo	High	Medium-section shafts, fasteners	39NiCrMo3
34CrNiMo6	1.6582	≈ 4340	0.30–0.38	Ni-Cr-Mo	Very high	Heavy shafts, forgings, landing gear	34CrNiMo6
51CrV4	1.8159	6150	0.47–0.55	Cr-V	High	Springs, torsion bars, hand tools	51CrV4

ℹ️ 51CrV4 has a dual identity: it appears in EN 10083-3 as a Q&T steel and in EN 10089 as a spring steel. Its high carbon plus vanadium gives it elastic spring-back behaviour.

Chemical Composition Comparison

Element	C45	25CrMo4	42CrMo4	39NiCrMo3	34CrNiMo6	51CrV4
C	0.42–0.50	0.22–0.29	0.38–0.45	0.35–0.43	0.30–0.38	0.47–0.55
Si	≤ 0.40	≤ 0.40	≤ 0.40	≤ 0.40	≤ 0.40	≤ 0.40
Mn	0.50–0.80	0.60–0.90	0.60–0.90	0.50–0.80	0.50–0.80	0.70–1.10
Cr	≤ 0.40	0.90–1.20	0.90–1.20	0.60–1.00	1.30–1.70	0.90–1.20
Mo	≤ 0.10	0.15–0.30	0.15–0.30	0.15–0.25	0.15–0.30	—
Ni	≤ 0.40	—	—	0.70–1.00	1.30–1.70	—
V	—	—	—	—	—	0.10–0.25

The Cr/Mo/Ni figures shown for C45 are residual limits, not deliberate alloying — which is why C45 counts as non-alloy. To check an incoming mill certificate against these ranges, use our Chemical Composition tool.

Section-Dependent Mechanical Values (+QT)

A Q&T steel does not have a single strength figure — the value depends on the diameter of the part. The same grade delivers noticeably higher values at Ø30 mm than at Ø200 mm, because in a thick section the core cools more slowly and does not transform fully to martensite. EN 10083 therefore tabulates values by ruling section:

Grade	d ≤ 16 mm Re / Rm	16 < d ≤ 40 mm Re / Rm	40 < d ≤ 100 mm Re / Rm
C45	490 / 700–850	430 / 650–800	370 / 630–780
25CrMo4	700 / 900–1100	600 / 800–950	450 / 700–850
42CrMo4	900 / 1100–1300	750 / 1000–1200	650 / 900–1100
39NiCrMo3	785 / 980–1180	685 / 880–1080	590 / 780–930
34CrNiMo6	1000 / 1200–1400	900 / 1100–1300	800 / 1000–1200
51CrV4	900 / 1100–1300	800 / 1000–1200	700 / 900–1100

Re = min. yield strength (MPa) · Rm = tensile strength (MPa) · Values apply to the +QT (quenched and tempered) condition.

To read tensile strength as hardness, use our Hardness Converter — for example 900–1100 MPa corresponds to roughly 266–325 HB.

Hardenability: What the Alloy Actually Does

Alloying elements do not harden steel directly — they carry the hardness deeper into the section. Chromium, molybdenum and nickel slow the transformation rate so the core of the part can also become martensitic. This is hardenability, and it is the real criterion when choosing a Q&T grade.

The most honest evidence is the standard's own tables: EN 10083 stops each grade's table where its hardenability runs out.

• The C45 table ends at 100 mm — a non-alloy steel will not harden through beyond that.
• The 42CrMo4 and 34CrNiMo6 tables run to 250 mm — Cr-Mo and Ni-Cr-Mo additions can carry hardness that deep.

The practical rule: as the section grows, the alloy level must rise with it. Making a Ø200 mm shaft from C45 means producing a part whose core was never really quenched and tempered at all.

If you want hardenability guaranteed on the order, specify the +H (hardenability band), +HH (upper half of the band) or +HL (lower half) suffix; the supplier then commits to a Jominy end-quench curve.

Delivery Conditions: What to Put on the Specification

Naming the grade is not enough — you must also state the heat-treatment condition you expect on delivery. Left unstated, a supplier will usually ship the cheapest condition.

Code	Meaning	When to ask for it
+A	Soft (spheroidize) annealed	The part will be machined or cold formed
+N	Normalized	A uniform grain structure is wanted (common on C45, 25CrMo4)
+QT	Quenched and tempered	Final strength is to come straight from the bar
+H / +HH / +HL	Guaranteed hardenability band	You will heat treat the part yourself

A common production sequence: buy the material +A, rough machine it, then quench and temper the finished part and grind to size. That gives easy machining and final strength together. For process parameters see our Steel Heat Treatment Processes guide — austenitizing runs at 830–880 °C and tempering at 540–680 °C, while the 350–500 °C window is avoided (temper embrittlement range).

Which One Should You Choose?

Choose C45 if:

• The load is moderate and cost is the deciding factor (the most economical Q&T steel)
• The section is under Ø100 mm
• The part will be induction surface hardened

Choose 25CrMo4 if:

• The part will be welded (low carbon means little or no preheat)
• You are making thin-wall tubing or pressure components
• Detailed comparison: 4130 vs 4140

Choose 42CrMo4 if:

• You want the default alloy Q&T steel — the most widely stocked grade in the world
• Sections run up to Ø250 mm
• Nitriding or induction hardening is planned

Choose 39NiCrMo3 if:

• 42CrMo4-level strength is enough but higher toughness is wanted
• You make medium-section fasteners subject to impact

Choose 34CrNiMo6 if:

• The section is very large and uniform hardness to the core is mandatory
• The duty is in the heaviest class (energy, defence, heavy machinery, forged shafts)

Choose 51CrV4 if:

• The part must spring back elastically (springs, torsion bars, leaf springs)
• High fatigue strength and wear resistance are both required

For international equivalents (AISI, JIS, GOST, BS) use our Steel Grade Equivalent tool.

A Frequently Confused Distinction: Q&T ≠ Case Hardening

These two classes get mixed up more than any other pair at the order desk, because both are described as "hardened steel" — yet they do completely different jobs:

	Quenched and tempered steel	Case-hardening steel
Carbon	0.25–0.55%	≤ 0.20% (e.g. 16MnCr5: 0.14–0.19)
Where the hardness is	Uniform through the section	Only a hard surface case
Core	Quenched and tempered, strong	Stays soft and tough
Process	Quench + temper	Carburize → quench + low temper
Typical part	Shaft, axle, bolt, crankshaft	Gear, pin, cam, bearing surface

In short: a part that must resist impact and torsion through its whole section is a Q&T steel job; a part whose surface must resist wear while the core absorbs shock is a case-hardening steel job.

Supply from Aktif Çelik

At Aktif Çelik we stock all six of the Q&T grades above — C45, 25CrMo4, 42CrMo4, 39NiCrMo3, 34CrNiMo6 and 51CrV4 — as hot-rolled bar, bright (cold drawn) bar and forged bar across a wide diameter range. Material is delivered in +A, +N or +QT condition with 3.1 certification.

If you are unsure which grade suits your section and duty, send us the part diameter and the working load — our technical team will recommend the grade and delivery condition that match your ruling section. Contact us for cut-to-length service and mill test reports.