CARBURIZING & CARBONITRIDING

A TRADITIONAL SURFACE HARDENING TREATMENT

WITH MODERN PROCESS CONTROLS

WHAT IS IT? HOW IS IT DONE?

General Description of Carburizing & Carbonitriding Equipment & Process
Carburizing is a process of controlled diffusion of carbon into Solid, molten salt and gaseous carbon-carrying medium may
the surface of a component, followed by quenching and be employed, however, the first two are now rarely used.
tempering, with the objective of increasing the component’s Nitrex offers gas carburizing in computer controlled integral
surface hardness. The process is generally applicable to low quench and pit gas carburizing furnaces. A full range of case
carbon and low alloy steels. There are two carburizing depths if feasible with an economically derived limit of
process types available commercially – vacuum carburizing approximately 0.250” (6.4 mm). In addition, Nitrex offers
and conventional carburizing. The former is described in a vacuum carburizing which is described in a separate
separate brochure, and conventional carburizing is company publication.
discussed here.
The sequence of operations is as follows :
In this thermal process ferrous alloys are heated to above
• parts are appropriately fixtured, loaded into the furnace,
their transformation temperature and exposed to carbon rich
and the process is initiated
atmosphere. Processing temperatures in conventional
carburizing typically are in the 1450°F - 1900°F (790°C - • computers and/or process controllers are programmed to
1040°C) range. The diffusion of carbon into the part and the conduct the process automatically,
subsequent quench leads to a part with a hard, wear • at the end of the process the load is either direct
resistant surface and a tough, shock resistant core. quenched (in an integral quench furnace) or soft cased
and quenched in another furnace, for grain and case
Carbonitriding is a process similar to carburizing except that refinement,
ammonia is added to the carburizing atmosphere, which • subsequently the parts can be tempered, or cryogenically
produces an effect of supplementary nitrogen diffusion into
treated (for maximum case properties) and tempered.
the component and results in a higher surface hardness.
Note: carbonitriding is sometimes confused with nitrocarburizing. Please
read the descriptions of both processes to avoid misunderstandings.
Nitrocarburizing is described in a separate brochure.

Carbonitrided Thrust Washers,

1004 Steel

Loading a Carburizing Furnace

WHY CARBURIZING OR CARBONITRIDING?
Reasons to Use this Type of Process
The reasons to use this process in preference of any other
heat treating method are as follows:
ALTERNATIVES
• high surface hardness with a tough, durable core, What Alternatives May Be Considered and Why
• case depths up to 0.250” are achievable, Designers will normally consider one of the following options:
• ability to use inexpensive steels and still produce
• vacuum carburizing (described in a separate brochure) for
components with hard surface properties,
better control of properties and distortion,
• generally used for parts subjected to cyclical loading,
• nitriding of prehardened materials, generally for more
• cost effective for parts where some distortion is refined applications.
acceptable,
• selective carburizing – utilized when only specific areas of
• carbonitriding is used for applications where slightly higher the component need to be hardened.
surface hardness levels are required.

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 CARBURIZING & CARBONITRIDING
CAPABILITIES, PROCESS CONTROL & RESULTS

HOW IS IT CONTROLLED? WHAT CAN BE TREATED?

Characteristics Controlled in Carburizing / Carbonitriding Materials and Applications Suitable for Carburizing or
In our carburizing the following aspects of the process and Carbonitriding
the results are controlled: The process is particularly suited to low or medium-carbon
• carbon potential: Nitrex computers control the gas mix in steels, and selected alloyed steels. Typical applications
real time throughout the entire process, include: gears, bearings, ball screws, sleeves, races, rollers,
• temperature: the same computer controls the bushings, pinions, shafts, pins, and ball joints.
temperature which affects the case depth, part distortion
Carburized Forged Component
and case properties,
(Rail Car Coupling), 8620 Steel
• quench medium and its temperature dictates core, part
distortion and surface hardness,
• tempering temperature reduces the case hardness to the
specification requirement level.
An appropriate gas mix and flow are critical to the process.
Our equipment is capable of controlling the relative carbon
percent within less than 5% of the desired target.

Microstructure of Carbonitrided Thrust Washers

Hardness Profile of Carburized

Rail Car Coupling

Hardness Profile of
Carbonitrided Thrust
Washers
WHY NITREX?
Reasons for Selecting Nitrex to Be Your Subcontractor
Carburizing and carbonitriding are high temperature
processes where process control is critical to ensure the
optimal results with minimum distortion. Our processing
capabilities, computer controls and the team of engineers
with a significant amount of experience with the process,
provide you – the customer – with the best possible results
tailored to your specific applications. We offer various
versions of the carburizng / carbonitriding process:
conventional, deep case and vacuum carburizing (described
in a separate brochure).

Nitrex Inc. Nitrex Inc. Nitrex Inc. Nitrex Inc. Nitrex Inc.
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Tel: 630-851-5880 317-346-7700 517-676-6370 702-399-1554 408-275-0330
Fax: 630-851-0733 317-346-7704 517-676-6427 702-639-3819 408-279-1982
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