Quenched and tempered steels
Quenched and tempered steels are medium-carbon steels designed for quenching and tempering - hardening followed by high-temperature tempering - a treatment that delivers a balanced combination of strength and toughness. They are used for mechanical components subject to fatigue, torsion and bending: shafts, gears, pins, connecting rods, spindles. Siderticino supplies the main grades in the family - C45, 42CrMo4 and 39NiCrMo3 - in bars and plates, with custom cutting and third-party heat treatment.
01What are quenched and tempered steels
This family comprises medium-carbon steels (roughly 0.25-0.50% C) that respond optimally to quenching and tempering. Hardening produces a hard but brittle martensitic structure; the subsequent high-temperature tempering transforms it into tempered martensite, which reduces brittleness and provides the strength/toughness trade-off typical of these steels. Compared with case-hardening steels - low-carbon and hardened only at the surface - quenched and tempered steels develop uniform mechanical properties across the entire section. The family is governed by EN ISO 683 (formerly EN 10083): part 1 for non-alloy steels (such as C45), part 2 for alloy steels (such as 42CrMo4 and 39NiCrMo3).
02When to choose a quenched and tempered steel
A quenched and tempered steel is the right choice when the component must offer mechanical strength and toughness throughout the section, not only at the surface, and operates under static or cyclic loads. This applies to transmission shafts, pins, tie rods, gears and machine parts. Where instead high surface hardness with a tough core is required - typical of gears subject to heavy wear - the choice falls on case-hardening steels. The selection of the specific grade within the family then depends on the part's section size, the level of loading and the cost/performance trade-off, criteria revisited further on.
03The quenched and tempered grades in our catalogue: how to choose
The three main grades supplied by Siderticino cover increasing requirements for hardenability and toughness. The selection logic, in short: from the non-alloy grade for smaller sections, to the Cr-Mo alloy grade for strength on large sections, to the Ni-Cr-Mo alloy grade when high toughness is needed.
3.1C45: non-alloy steel
C45 (EN ISO 683-1:2018 (formerly EN 10083-2)) is the benchmark non-alloy quenched and tempered steel. It offers the best balance of machinability, availability and cost, but its hardenability is modest: quench-and-temper properties are reliably achieved only on smaller sections, while on thick sections the core strength drops off. It is the right choice for general mechanical components of small-to-medium section where high core performance is not required.
3.242CrMo4: Cr-Mo alloy steel
42CrMo4 (material no. 1.7225, EN ISO 683-2:2018 (formerly EN 10083-3)) is the most widely used alloy quenched and tempered steel, thanks to its balance of performance and cost. Chromium and molybdenum significantly increase its hardenability compared with C45, allowing large sections to be effectively quenched and tempered with good core strength. It is the standard for shafts, gears and heavily loaded components of medium and large section.
3.339NiCrMo3: Ni-Cr-Mo alloy steel
39NiCrMo3 (material no. 1.6510, EN ISO 683-2:2018 (formerly EN 10083-3)) adds nickel to the Cr-Mo base: this yields superior toughness, useful for components subject to dynamic and fatigue loads where impact resistance matters alongside static strength. Compared with 42CrMo4 it favours toughness over maximum core strength on very large sections. For more critical applications, more heavily alloyed grades are used (e.g. 34CrNiMo6).
04Comparison table for grade selection
Qualitative comparison of the three catalogue grades, intended to support the decision. For chemical composition, mechanical properties by size class and Jominy hardenability, refer to the individual technical datasheets.
| Grade | Type | Standard | Hardenability | Toughness | Typical application |
|---|---|---|---|---|---|
| C45 | Non-alloy | EN ISO 683-1:2018 (formerly EN 10083-2) | Moderate | Medium | General components, small sections |
| 42CrMo4 | Cr-Mo alloy | EN ISO 683-2:2018 (formerly EN 10083-3) | High | Good | Shafts, gears, medium-to-large sections |
| 39NiCrMo3 | Ni-Cr-Mo alloy | EN ISO 683-2:2018 (formerly EN 10083-3) | High | High | Fatigue-loaded parts where toughness matters |
05Selection criteria: section size, loading, cost
The choice of grade comes down to a few decisive factors. Component section size is the first: non-alloy steels such as C45 exhaust their hardenability on small sections, whereas Cr-Mo and Ni-Cr-Mo alloy grades retain their core properties on progressively larger sections. The type of loading steers the balance between strength and toughness: for mainly static loads 42CrMo4 is generally sufficient, while for dynamic and fatigue loads 39NiCrMo3 offers a margin of toughness. The cost/performance trade-off settles the decision: choose the least alloyed grade that meets the requirements, moving up in alloy content only when the section size or loading demands it. For sizing semi-finished products, the steel bar weight calculator is available.
06Typical applications
Quenched and tempered steels are widely used in power transmission and general engineering: drive shafts and crankshafts, gears, half-shafts, pins, connecting rods, spindles, tie rods and components subject to bending and torsion. They are found in automotive, industrial and heavy machinery, earthmoving equipment and hydraulics (rods, pistons). For components with higher structural responsibility, or for use in regulated sectors, the selection must always be verified against the specific service requirements, which may call for grades with a higher alloy content than those in this family.
07Delivery conditions, standards and certification
Siderticino supplies quenched and tempered steels as round bars, square bars, flats and plates, in forged, hot-rolled, cold-drawn, peeled and ground finishes, and in the normalised (+N), annealed (+A) and quenched and tempered (+QT) delivery conditions. The reference standards are EN ISO 683-1:2018 (formerly EN 10083-2) (non-alloy steels) and EN ISO 683-2:2018 (formerly EN 10083-3) (alloy steels) for hot-rolled products, and EN ISO 683-7:2024 (formerly EN 10277:2018) for bright (cold-finished) steel products; certification follows EN 10204, with a 2.1 certificate or, on request, 3.1. Beyond supply, we also offer custom cutting and heat treatment. To obtain an offer, you can request a quote, indicating grade, format and quantity.
08Frequently asked questions about quenched and tempered steels
8.1What is the difference between quenched and tempered steels and case-hardening steels?
Quenched and tempered steels have a medium carbon content and develop uniform mechanical properties throughout the section by means of hardening and tempering. Case-hardening steels have a low carbon content and are enriched with carbon at the surface before hardening, giving a hard surface layer over a tough core. The choice depends on the type of loading: strength throughout the section for the former, surface hardness with a tough core for the latter.
8.2C45, 42CrMo4 or 39NiCrMo3: which to choose?
In short: C45 for general components with small sections, where cost matters; 42CrMo4 when hardenability and core strength are needed on medium-to-large sections; 39NiCrMo3 when, for the same strength, higher toughness is required for dynamic and fatigue loads. The choice must always be verified against the actual section of the part and the delivery condition.
8.3How does the section of the part affect the choice of grade?
As the section increases, the cooling rate at the core during hardening decreases and the quench-and-temper properties decline. Non-alloy steels such as C45 are suitable only for small sections; larger sections require alloy steels (Cr-Mo or Ni-Cr-Mo) whose hardenability ensures uniform structures and properties even at the core. This is the main reason for moving up in alloy content.
8.4In which delivery conditions are they available?
Quenched and tempered steels are typically supplied in the quenched and tempered condition (+QT), ready for use, or in the normalised (+N) or annealed (+A) condition when it is necessary to favour machinability or to set up a subsequent treatment. The optimal condition depends on the planned machining and can be agreed at the quotation stage.
8.5What certification comes with the material?
Every supply comes with an EN 10204 type 2.1 declaration of compliance with the order and, on request, a type 3.1 inspection certificate, which provides traceability of the chemical composition and mechanical properties of the batch, required for orders that need full traceability.