GlossaryKind of term: Manufacturing termAlloy steel
What is alloy steel?
Alloy steel is steel in which alloying elements such as chromium, molybdenum or nickel exceed defined limits, added for strength, toughness or hardenability.
One element above its limit value is enough; besides chromium, molybdenum and nickel, manganese and vanadium count too. On the shop floor the term usually means low-alloy engineering steel: quench and temper steels such as 42CrMo4 for shafts and gears, case hardening steels such as 16MnCr5 and nitriding steels. The term also covers tool steels such as 1.2312 and 1.2343 for mould parts. The alloying mainly raises hardenability: the depth to which the steel hardens on quenching, and so the section over which it reaches the required strength after tempering.
What does the standard say about alloy steel?
EN 10020 divides steel into three classes: non-alloy steel, stainless steel and other alloy steel, based on limit values per element. Under that classification stainless forms a class of its own, even though it carries more alloy. Grades and delivery conditions are set in product standards such as EN ISO 683-2 for quench and temper steels, EN ISO 683-3 for case hardening steels and EN ISO 4957 for tool steels. The delivery condition, such as soft annealed (+A), quenched and tempered (+QT) or treated to a ferrite-pearlite structure (+FP), belongs with the specification.
How does alloy steel behave in the shop?
Quench and temper steel in +QT can be machined straight to size. It is heavier going than carbon steel, but without the work hardening and long chips of austenitic stainless. If the part is hardened, case hardened, nitrided or induction hardened after machining, the route changes: a heat treatment, usually subcontracted, with the heat treater's lead time, allowance left on the dimensions that are finished after hardening, and often a finishing operation such as grinding or hard turning in a setup of its own. Whether finishing is needed depends on process, distortion and tolerance: nitriding distorts little and is often applied without finishing afterwards, while through hardening and case hardening distort more. Costing that chain as one machining line misses the allowance, the waiting time and any second setup.
What is alloy steel often confused with?
Alloy steel is not the same as stainless steel: stainless is high-alloy, chosen for corrosion resistance, and sits in its own class in EN 10020. And hardening is not stress relieving: stress relieving lowers residual stress without making the steel hard, whereas hardening and tempering give strength and wear resistance and can cause distortion.
How do you see alloy steel in Blake?
A heat treatment such as hardening or nitriding goes into the estimate as its own line, taken from your subcontract library; if the price is missing, that line stays open. Material, machining and finishing are also kept apart in the cost breakdown, and the total is labelled as an estimate. More on estimating.
Frequently asked questions
What does hardening after machining change in the route?
A heat treatment is added, usually subcontracted, with the heat treater's price and lead time. Roughing leaves allowance on the dimensions still to be finished, and grinding or hard turning in a separate setup often follows.
Is stainless steel an alloy steel too?
Chemically, yes: it contains a lot of chromium and often nickel and molybdenum. EN 10020, however, places stainless steel in its own class beside other alloy steels, and in everyday use the term usually refers to low-alloy quench and temper or case hardening steel.