Quenched and tempered steel (+QT)

What is quenching and tempering, and the delivery condition +QT?

In quenching and tempering, the steel is heated to austenitising temperature, quenched in oil, polymer or water and then tempered at approx. 540–680 °C. On drawings and 3.1 certificates the condition is stated as +QT (Quenched and Tempered). Hardening creates the strength, while the high tempering temperature restores the toughness, so the part withstands dynamic load, torsion and shock without brittle fracture. It is the opposite process to case hardening (e.g. 16MnCr5), where only the case is carburised.

• +QT = Quenched and Tempered (at the mill or at a heat treater)
• +N = Normalised (typically for non-alloy C45N when full +QT is not required)
• +A / +S = Soft annealed or stress-relief annealed for demanding machining before hardening

Grades in the group – from C45 to 42CrMo4 and 34CrNiMo6

The choice of grade is governed by the diameter of the part (the ruling section) and the mechanical requirements in the core. Non-alloy C45 / 1.0503 and C45E / 1.1191 are used when the cross-section is modest. Chromium-molybdenum steels such as 42CrMo4 / 1.7225 (plus the sulphur-alloyed free-machining variant 42CrMoS4 / 1.7227 and the leaner 25CrMo4 / 1.7218 and 34CrMo4 / 1.7220) are the workhorse of Danish machine building. As the cross-section grows and through-hardening and core toughness become critical, chromium-nickel-molybdenum steels (CrNiMo) such as 34CrNiMo6 / 1.6582 or 30CrNiMo8 / 1.6580 are chosen.

• 42CrMo4 · 1.7225 (AISI 4140 family) – Cr-Mo Q&T steel, partner stock and delivery programme typically Ø10–Ø1300 mm
• 42CrMoS4 · 1.7227 – Cr-Mo with controlled sulphur for better chip breaking in +QT
• 34CrNiMo6 · 1.6582 – Cr-Ni-Mo Q&T steel for heavy shafts and large cross-sections, delivery programme Ø20–Ø825 mm
• 30CrNiMo8 · 1.6580 – high-alloy Cr-Ni-Mo for the heaviest diameters and core requirements
• 25CrMo4 · 1.7218 and 34CrMo4 · 1.7220 – Cr-Mo with lower carbon and high toughness
• C45 · 1.0503, C45E · 1.1191 and C45N – non-alloy carbon steel for smaller cross-sections

Properties of Q&T steel and the significance of the ruling section

The mechanical properties of quenched and tempered steel (+QT) depend directly on the bar diameter at heat treatment. According to EN 10083-3, the specified minimum values for yield strength (Re) and tensile strength (Rm) fall as the cross-section increases: in 42CrMo4 +QT, Rm is for example 1000–1200 MPa at Ø16–40 mm and 800–950 MPa at Ø100–160 mm, while 34CrNiMo6 +QT holds 900–1100 MPa at Ø100–160 mm and 800–950 MPa up to Ø250 mm. The full mechanical and chemical tables are on each material page.

• 42CrMo4 +QT (EN 10083-3): Re min. 550–900 MPa · Rm 800–1300 MPa at d ≤ 160 mm
• 34CrNiMo6 +QT (EN 10083-3): Re min. 600–1000 MPa · Rm 800–1400 MPa at d ≤ 250 mm
• 30CrNiMo8 +QT (EN 10083-3): Re min. 700–1050 MPa · Rm 900–1450 MPa at d ≤ 250 mm
• C45 / C45E +QT (EN 10083-2): Re min. 430–490 MPa · Rm 650–850 MPa at d ≤ 40 mm

Typical applications – steel for shafts and machine building

Q&T round bar and forgings are used throughout the machine, energy, marine and process industries where parts are subjected to bending, torque and dynamic loading.

• Shaft steel for main shafts, drive shafts, rotor shafts and heavy pins
• Gears, gear shafts, coupling parts and transmission components
• Hydraulic cylinders, piston rods, tie rods and high-strength bolts
• Forged rings, discs, bushes and bored parts in large diameters

Dimensions and delivery forms

We supply Q&T round bar, flat bar, square bar and forgings via European partners and partner stock. For 42CrMo4 / 1.7225, partner stock and delivery programme typically cover Ø10–Ø1300 mm, and for 34CrNiMo6 / 1.6582 the delivery programme covers Ø20–Ø825 mm. The ranges are delivery possibilities, not current stock status in every diameter – availability is confirmed on enquiry. Small and medium diameters are supplied as hot-rolled, peeled or drawn bar; large diameters as forged round bar or forgings.

Cut to size, small quantities and price on request

A shaft or machine part is often a single piece – and with us you do not have to buy a whole merchant length. We cut Q&T round bar and bar steel to fixed length and supply from a single cut piece to larger series without minimum charge. The price of Q&T steel depends on grade, diameter, length, quantity and condition (+QT, +N or +A). The EN 10204 3.1 certificate is included at no charge, and cutting does not change the +QT condition on the certificate. Send sizes or a drawing and we come back quickly with price and lead time.