Gas carburizing is a surface hardening treatment that produces a strong, wear-resistant layer (case) on the metal surface. The part is heated in a neutral (endothermic) atmosphere, then a controlled carbon-rich atmosphere is introduced. As the part is held at temperature, carbon dissolves into the metal surface. After the process is complete, the part is quenched and tempered.

Gas carburizing is ideal for improving the surface hardness and wear resistance of mild or low alloy steels. Parts suitable for this type of surface hardening include pins, rings, gears, sprockets, worm gears, arbors, bushings, and wear plates.

Carbonitriding is a modified form of gas carburizing. A nitrogen source (ammonia), is added to the carbon-rich gas, so that carbon and nitrogen both diffuse into the surface of the steel. Carbonitriding is suitable for plain, low carbon steels that would not achieve a uniform case hardness under standard gas carburizing.

Carbonitriding is ideal for producing a thin, high hardness case that gives the part improved wear resistance, strength, and increased resistance to softening at elevated temperatures. However, if high bearing loads are anticipated, carburizing is more suitable than carbonitriding.

For both carburizing and carbonitriding, the optimum case depth will depend on the intended duty. If a harder, deeper case is required, a part can be carburized, followed by carbonitriding.

Thermex will meet your precise carburizing/carbonitriding specifications, or recommend the optimal process or combination of processes based on the metal composition and intended use of the part.

Successful carburizing and carbonitriding both demand a precise control of the treatment process. Thermex operates under an ISO 9001:2000 Registered Quality Management System. Process quality control measures include:

• monitoring and tight control of furnace temperature, time, atmospheric composition and gas circulation. Furnaces are controlled by digital process controllers to ensure reproducible results. Systems are automatically controlled to precise dew point levels. Carbon levels are precisely controlled for effective carbon transfer and process reproducibility, without sooting of parts.
• full control of the post-treatment cooling process, with choice of air, oil, or water quench
• inclusion of test coupons of matching material with all carburizing & carbonitriding loads. Coupons can then be used for metallurgical analysis in Thermex’s in-house metals testing laboratory. Random microhardness case depth surveys ensure that process specifications are being met.
• temperature uniformity surveys of furnaces
• daily accuracy checks of all hardness testers

Contact Thermex for more information on our carburizing and carbonitriding services.