The cold drawing process and what it does to the steel

The process has three main steps: descaling (mechanical or pickling), drawing through a carbide die (the cross-section is typically reduced 10–30%) and straightening/cutting. Cold deformation work-hardens the material: yield and tensile strength rise markedly while elongation and toughness drop somewhat; a stress-relief anneal removes internal stresses where needed. The dimensional accuracy (h9/h10/h11 per ISO 286) and clean surface make further machining unnecessary in many applications — automatic lathes run cold drawn bar directly. Typical uses: shaft and axle blanks, fasteners, hydraulic applications and precision machine parts. Carbon steels (C15–C45), free-cutting steels (11SMn30) and alloy grades are stocked as cold drawn; round, square and flat sections give a ready-to-size advantage in fixtures and fabrication. The h9 class is not a single number: it opens up with section size following the IT grades of ISO 286. For a drawn round bar the permitted deviation in h9 is 30 µm from 3 to 6 mm, 36 µm from 6 to 10 mm, 43 µm from 10 to 18 mm, 52 µm from 18 to 30 mm, 62 µm from 30 to 50 mm and 74 µm from 50 to 80 mm — always in the minus direction, so the nominal size is the upper limit. A Ø20 h9 bar therefore lies between 19.948 and 20.000 mm. Classes h10 and h11 widen that band; below h9 you move to ground bar. The three profile families answer different needs: round for shafts, axles and turned blanks; square for keys, tool holders and indexed parts; flat for base plates, spacers and platens, where a ready-to-size section removes a milling operation outright. On the grade side, carbon steels (C15–C45) cover general engineering, alloy quenched-and-tempered grades (42CrMo4) handle loaded parts, and free-cutting steels (11SMn30, 11SMnPb30) serve high-volume work on automatic lathes — the latter are almost always supplied cold drawn anyway, because surface finish and sectional consistency directly govern tool life.