The purpose of this Section is to establish methods for specifying
carbonitrided gearing. the information in carburizing will generally
apply to carbonitriding, with noted exceptions.
Typically carbonitriding is carried out at lower temperatures, 1550-1650_F
(843-899_C), and for shorter times than gas carburizing. Shallower case
depths are generally specified for carbonitriding than is usual for
production carburizing. Its effect on steel is similar to liquid
cyaniding and has replaced cyaniding because of cyanide disposal
problems. Normally 2.5 to 5 percent anhydrous ammonia is added to the
carburizing atmosphere when carbonitriding. Specified case depths are
usually from 0.003 to 0.030 inch (0.076 to 0.76 mm) maximum.
Applications (Advantages and Limitations).
Use of carbonitriding is more restricted than carburizing. It is limited
to shallower cases for finer pitch gearing since the process must be
conducted at lower temperatures than carburizing. Deep case depths
require prohibitive time cycles. One of the advantages of carbonitriding
is better case hardenability in lower alloy or plain carbon steels. The
case has better wear and temper resistance than a straight carburized
case. Carbonitriding can be used to minimize distortion in
gearing because lower austenitizing and quenching temperatures can be
used along with less severe
quench techniques and still achieve hardness. These facts, along with
lower alloy steels, result in the lower core hardness mentioned
previously, thus reducing tooth growth and distortion. However, if
higher core hardness and deeper case depths are required for bending
carbonitriding may not be applicable.
Typically carbon and low alloy steels such as 1018, 1022, 1117, 4022,
4118 and 8620 steels are used for carbonitriding.
- Specification and Inspection.
Case depth, microstructure, hardness, etc.
for carbonitrided parts can all be specified and evaluated as prescribed
in the section for carburized gearing. Case depth is
specified andmeasured as effective or total, depending upon application.
Cases shallower than 0.010 inch (0.25 mm) are generally specified as
total case depth. The advantages and limitations as described herein
should be fully understood before specifying carbonitriding for
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