The nitriding process, first developed in the early 1900s, continues to play an important role in the manufacture of aircraft, bearings, automotive components, textile machinery, and turbine generation systems.

Gas nitriding is a case hardening process in which nascent nitrogen diffuses into the surface of special alloy steel components to create a hard, nitrided surface. It is predominantly used on steel. Typical applications include gears, crankshafts, camshafts, cam followers, valve parts, extruder screws, die-casting tools, forging dies, extrusion dies, injectors and plastic-mould tools.

Plasma nitriding, also known as ion nitriding, plasma ion nitriding or glow-discharge nitriding, is a modern case hardening process that is slowly replacing gas nitriding. Plasma nitriding can be performed with higher efficiency than gas nitriding in a broad temperature range, from 260?C to more than 600?C.

In both the cases of gas nitriding and plasma ion nitriding, there is always a requirement to prevent nitriding at the selective areas of the same component and leave them soft. This process is termed 'selective nitriding'. The areas of components on which nitriding is to be prevented are typically internally threaded areas and those areas that need to be machined after nitriding. The most economical method of achieving selective nitriding is to coat the area with a stop-off paste.

An Indian firm, Steel Plant Specialities, has developed stop-off pastes for conventional gas nitriding and plasma ion nitriding, ESPON-ANT and ESPON-ION, respectively. Both products are non-hazardous, non-toxic and eco-friendly. Results of these products as confirmed by regular users are provided below:

Grade of Steel: H-13 Hot Die Steel

Most of the nitriding units in India are satisfied with ESPON selective gas nitriding and plasma nitriding stop-off pastes.

For further information contact: Steel Plant Specialities, 211 Raikar Chambers, Govandi East, Mumbai 400 088. Tel: 022-67978060. Fax: 91-22-25552459. Email: info@steelplantspecialities.com