Heat Treatment

Surface Hardening Treatments

Carbonitriding

Heat to 870 oC - 880 oC in a gaseous media consisting of carbon monoxide/hydrocarbon plus ammonia, hold for sufficient time to develop the required case depth, carbon and nitrogen content, followed by quenching in oil or water as required. Typical case hardness achieved up to Rc 60.Tempering immediately while still hand warm at 150 oC - 200 oC will reduce stresses and improve the toughness of the case.

Carburizing

Pack, salt or gas carburise at 880 oC - 920 oC, holding for sufficient time to develop the required case depth and carbon content, followed by a suitable heat treatment cycle to optimise case and/or core properties.Typical case hardness achieved up to Rc 63.

Case Hardening

Water quench from 760 oC - 780 oC.

or Core Refining

Oil quench from 870 oC - 880 oC prior to water quench as above.Tempering immediately following water quench at 150 oC - 200 oC will reduce stresses and improve toughness of case.

High or Medium Frequency Induction Hardening

The black hot rolled surface on 20MnV6 Hollow Bar will first require to be machined sufficiently to remove any de-carburised layer otherwise less than satisfactory results will likely be obtained. The feed material can be either in the as supplied condition or pre hardened and tempered for higher core strength.Heat to the austenitic temperature range (870 oC - 925 oC), and required case depth, quench immediately in oil or water as required. Typical case hardness achieved up to Rc 48.Tempering immediately at 150 oC - 200 oC will reduce stress and improve the toughness of the case.

Nitriding

20MnV6 either in the as supplied condition, or pre-hardened and tempered for higher core strength will respond successfully to nitriding due to the vanadium content. Typical case hardness achieved up to Rc 55.Nitriding is carried out at 490 oC - 530 oC followed by slow cooling (no quench) reducing the problem of distortion.Parts can therefore be machined to near final size, leaving a grinding tolerance only.If pre-hardened and tempered feedstock is used always ensure that the tempering temperature employed is at least 15oC above the nitriding temperature.

Hardening

Heat to 870 oC - 925 oC as required, hold until the temperature is uniform throughout the section, soak 10 - 15 minutes per 25mm of section and quench in oil or water as required.Temper immediately while still hand warm.

Tempering

Re heat to 500 oC - 600 oC as required, hold until temperature is uniform throughout the section, soak for 1 hour per 25mm of section. Cool in still air.

Normalizing

Heat to 900 oC - 925 oC, hold until temperature is uniform throughout the section, soak for 30 minutes and cool in still air.

Stress Relieving Following Welding

Heat the weld area to 550 oC - 650 oC, soak for 30 minutes and cool in still air or furnace.

Notes on Heat Treatment

Heating temperatures, rates of heating, cooling and soaking times will vary due to factors such as work piece size/shape, also furnace type employed, quenching medium and workpiece transfer facilities etc.Please consult your heat treater for best results.

Machining

20MnV6 has excellent machinability due to the silicon - calcium treatment and precise control of the sulphur content resulting in an excellent break-up of swarf, increasing feeds and speeds plus an increase in tool life for all machining operations.