Gas nitriding is emerging as the significant surface hardening process for today's and future industry, constituting a viable alternative to the well-established carburising process. Most gears, shafts, hubs, pins and other parts are carburised in mass production to various case depths with accurate carbon potantial control. Yet, carburising is handicapped by several disadvantages. Below table compares certain important features of the two process.
|
FEATURE COMPARED |
CARBURISING |
NITRIDING |
|
Material compatibility |
Limited selection of steel types |
Wide variety of steel grades, including austenitic stainless, maraging and precipitation – hardening range |
|
Typical treatment temperature |
850 – 950°C |
460-600°C |
|
Accompanying heat treatment |
Requires hardening and tempering (optionally: sub-zero treatment) |
No additional treatment required |
|
Finish Machining |
Often requires costly grinding |
In most cases, does NOT require finish grinding |
|
Distortion |
May be substantial |
Due to lower heat treatment temperature and absence of transformation in bulk material, distortion minimum to nil |
|
Surface cleanliness |
In most cases requires washing to remove quenching oil |
After nitriding, surface ready for shipping |
|
Surface hardness |
60 – 65 HRC |
Depending on steel grade, may reach 70 HRC |
|
Corrosion resistance |
High carbon concentrations are conductive to stress corrosion cracking |
Compund layer enhances corrosion resistance (with the exception of stainless steels) |
