Liquid Nitriding

Liquid Nitriding

Liquid nitriding or nitriding in a molten salt bath employs the same temperature range as gas nitriding, which is 510 to 580°C. The case hardening medium is a molten, nitrogen-bearing, fused-salt bath containing either cyanides or cyanates.

Unlike liquid carburising and cyaniding, which employ baths of similar compositions, liquid nitriding is a sub-critical case hardening process. Thus, processing of finished parts is possible because dimensional stability can be maintained. Also, liquid nitriding adds more nitrogen and less carbon to ferrous materials than that obtained through higher-temperature diffusion treatments. The degree to which steel properties are affected by liquid nitriding may vary with the process used and the chemical control maintained.

process

Salt bath Nitrocarburising (Tufftriding) is characterised by a higher temperature ie: 580oC for short periods, usually 90 minutes while bubbling air into the bath at a fixed rate. This creates a set of circumstances whereby both carbon and nitrogen are diffused into the surface layers. Liquid Nitriding is done at a lower temperature typically 520oC and for longer periods which can be 12-15 hours.

MTE has 2 Liquid Nitriding salt baths with the following dimensions…

  • N1 – 700mm x 1300mm
  • N2 – 600mm x 1100mm

Our salt is of a high quality and imported from HEF Durferrit in Germany.

Benefits

Salt bath nitriding/nitrocarburising provide design and manufacturing engineers an opportunity to improve their products’ wear resistance characteristic. Wear tests consistently confirm the superior wear resistance of salt bath nitrided/nitrocarburised parts over traditional or induction hardened or hard chrome-plated surfaces. On thinner material components the improvement in the fatigue strength properties may allow for the engineer to design even lighter-weight parts. Improved corrosion protection can also be achieved on steel, cast iron, and sintered metal parts. Salt spray test results per ASTM B 117 and DIN 50021 show improved benefits from the salt bath nitriding/nitrocarburising process over competing processes.

Application

Liquid nitriding processes are used primarily to improve wear resistance of surfaces and to increase the endurance limit in fatigue. For many steels, resistance to corrosion is improved. These processes are not suitable for many applications requiring deep cases and hardened cores, but they have successfully replaced other types of heat treatment on a performance or economic basis.

In general, the uses of liquid nitriding and gas nitriding are similar and sometimes identical. Gas nitriding may be preferred in applications where deeper case depths are required. Both processes, however, provide the same advantages: improved wear resistance and anti-galling properties, increased fatigue resistance, and less distortion than other case-hardening processes employed through heating at higher temperatures. Depending on the components’ application, salt bath nitriding/nitrocarburising is used as an alternative to other surface engineering processes such as case hardening, galvanic processing such as hard chrome plating, and other coatings. There are many applications for hydraulic parts, transmission applications, and consumer goods. Salt bath nitriding/nitrocarburising can be applied on a multitude of materials such as unalloyed steels, low alloy steels, high alloy steels, cast iron, ductile iron, and sintered metals. Salt bath nitriding can be applied to stainless steels which greatly increases surface hardness but at the expense of some of its corrosion resistance as the Chrome content in the surface layers is reduced due to the formation of Chrome nitride.