Specifications

Nominal composition of engineering grades

Silicon, phosphorus and sulphur limits are given in each standard. Actual values for each heat are shown on the mill test certificate.

4140, EN19, 4340 and EN24

AISI 4140 and EN19 are chromium-molybdenum steels that are the general-purpose choice for hardened and tempered parts: shafts, gears, spindles, couplings, bolts and studs, drill collars and hydraulic components. They respond well to quenching and tempering and can be surface hardened by induction or nitriding. AISI 4130, with lower carbon, has better weldability and is used for tubing, aircraft and motorsport structures and oil-field components.

AISI 4340 and EN24 add nickel, which increases hardenability and toughness so that larger sections harden through. They are used for heavily loaded shafts, crankshafts, gears, landing-gear parts and high-strength bolting where 4140 would not harden fully.

A182 F11, F22 and F91 bars

ASTM A182 grades F11 (1¼Cr-½Mo), F22 (2¼Cr-1Mo), F5 (5Cr-½Mo), F9 (9Cr-1Mo) and F91 (9Cr-1Mo-V) are used for flanges, fittings, valve parts and nozzles machined from bar for high-temperature steam and refinery piping. Bars for these parts are supplied normalised and tempered so that the finished component meets the same specification as A182 forgings. Please state whether the bar will be used for pressure parts, so that the material and certification match the design code.

Heat treatment condition

Alloy steel bars are supplied in the condition that suits the customer's process. Annealed bars are soft and easy to machine, and are hardened and tempered by the customer after rough machining. Hardened and tempered bars, often to a stated hardness or tensile range, can be machined directly into finished parts without further heat treatment. Normalised bars are used for forging stock and for A182 grades. Please give the required hardness, tensile range or condition designation with the enquiry.

Through-hardening depends on the alloy content and the bar diameter: in large diameters the core cools more slowly during quenching and reaches a lower hardness than the surface. For heavy sections that must harden through, a nickel-bearing grade such as 4340 or EN24 is chosen rather than 4140 or EN19. Hardness or tensile tests are taken at the position the standard specifies, often mid-radius, and reported on the certificate.

How we manufacture alloy steel bars

We manufacture alloy steel round bars from certified billets and bars by hot rolling or forging, followed by the specified heat treatment in controlled furnaces. Bright bars are peeled, turned or ground to a clean surface and close tolerance. Every heat-treatment batch is tested for hardness, and tensile and impact tests are carried out as the order requires. Bars are marked with grade and heat number, and ultrasonic testing is carried out on request to check for internal defects.

Ordering alloy steel round bars

Please give the grade and standard, diameter and tolerance, black or bright condition, heat treatment and hardness or tensile range, length, quantity, and any ultrasonic, impact or inspection requirement. Bars are bundled and strapped, with bright bars oiled and wrapped, and each bundle is tagged with grade, size and heat number.

Applications and related products

Alloy steel round bars are used for shafts, gears, axles, spindles, high-strength studs and bolts, hydraulic cylinder rods, drilling and oil-field tools, die and tool holders, and flanges and fittings for high-temperature piping. Matching products include alloy steel fasteners, alloy steel flanges, alloy steel pipe fittings, alloy steel pipes and tubes and alloy steel plates. Other bar materials are on the round bars, rods and wires page, and grade guidance on the alloy steel page.