Group
Spring steel – flat, round and square bar
Spring steel is the family that has to bend and come back. It differs from a shaft steel in what is demanded of it: not a core hardness in a heavy cross-section, but a spring that does not set. That is why it is bought on cross-section and condition – untreated, soft annealed or quenched and tempered – and not on a diameter alone. INDUSTRISTÅL sources from the European mills, cuts to length and ships with EN 10204/3.1 at no charge.
The family in the programme
The silicon grades 51Si7, 56Si7 and 65Si7 are the workhorses of flat spring steel. 61SiCr7 and 67SiCr5 add chromium and are used for compression springs in round. 55Cr3 is the chromium grade without silicon as the main element. 51CrV4 and 58CrV4 have vanadium, and 52CrMoV4 is the heaviest with molybdenum on top. 50Mn7 is the simplest of the family. If the spring has to stand in corrosion, 17-7PH and 301 are the way – that is the stainless side of the programme, not a Si grade with surface treatment.
DIN and EN are not the same list
This is where many purchasers stumble. EN 10089 carries 56Si7, 61SiCr7, 55Cr3, 52CrMoV4 and 51CrV4. The old DIN 17221 names 51Si7, 65Si7, 67SiCr5, 58CrV4 and 50Mn7 were not carried over to EN – they still appear on drawings and in older framework agreements, but there is no EN name to write next to them on the certificate. Two of the grades changed name without changing number: DIN 55Si7 is called 56Si7 in EN, and DIN 51CrMoV4 is called 52CrMoV4 – both under the same Werkstoffnummer. If a DIN name is on the drawing, we translate it and write the name the mill can certify on the enquiry.
Forms and dimensions
Flat spring steel is the main form: from 20 × 3 mm to 200 × 20 mm, in bars of 5 or 6 m, cut to fixed length when it has to fit. The edge is a choice – rounded edges or mill edge – and it belongs on the enquiry. In round and square the production method changes along the way: drawn in the small dimensions, rolled in the middle and forged in the heavy ones, with tolerance to DIN 671, DIN 1013 and DIN 7527. Not every grade runs in all forms, and that is why the cross-section is the first thing we ask about.
How to order it correctly
State cross-section, condition and standard. ‘51CrV4’ alone does not say whether the bar is to be untreated for hot forming, soft annealed for machining or quenched and tempered. If the spring is to be hot formed and hardened afterwards, that is a different condition from one that is to be cold bent. The hardening and tempering belong with whoever forms the spring – we supply the bar with the certificate, and we do not write a hardness the mill has not issued.
What is not spring steel
C75S is spring and strip steel in thin gauges to EN 10132 – same job, different product form. 42CrMo4 is the answer when the part is a QT shaft and not a spring; they get confused because both are hardened and tempered. And a bearing steel like 100Cr6 is through-hardened for hardness, not for spring action.
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Send your enquiry
State grade, dimensions and quantity — or attach a drawing. We reply with a quote.