The carbonitriding process enhances parts with a hard, wear resistant surface. Desired part case depths are designed by product engineers, and controlled by several heat treat process variables.
A part’s carbonitrided surface is produced by diffusing carbon and nitrogen into the surface of the heated part via carbon and nitrogen rich carrier gasses. Carbon is derived from endothermic gas and natural gas, nitrogen is derived from ammonia gas additions to the furnace atmosphere. The five main carbonitride process variables are temperature, time at temperature, carbon potential of the atmosphere gasses, ammonia volume, and part loading density.
Temperature control instrumentation reviews furnace temperatures and adjusts burner output appropriately. Time at temperature is controlled on continuous belt furnaces by establishing belt speeds, usually in inches per minute. In row-furnaces, time at temperature is described as “minutes per cycle”, in batch furnaces as “hours per event.” Carbon potential, usually described as % carbon, is a measure of the furnace atmosphere’s capability to provide nascent carbon to the heated surface of the work piece. It is controlled via oxygen sensing probes placed at designated locations within the furnace; the sensors provide feedback to a system which varies the input of natural gas and air to the furnace in order to balance the process gas appropriately. Established nitrogen flows are controlled through flow meters.
Part loading density is designed by IST. Each individual part number’s furnace loading is specified on work instructions; output is monitored and recorded from lot to lot. Belt furnace loading is defined as pound per hour; batch and row furnace loading is defined as pounds per basket layer, the number of layers per basket, and, the number of baskets per load. Additionally, some parts may require stacking or racking in special or common fixtures that enable parts to be oriented relatively the same throughout the furnace load in order to achieve close tolerance dimensional results or, to minimize part contact during the heat treat process.
All of these variables, and others, are tightly controlled in order to achieve high Ppk and Cpk values from lot to lot.
After the designated carbonitride process, parts are quenched into furnace-integral, temperature controlled and agitation controlled oil baths. Quenching in oil after carbonitriding fully hardens the parts, tempering is usually specified by the customer after quenching to relieve stresses in the part from the heat treat process or, to reduce part surface hardness.
IST’s metallurgical lab facility evaluates the case depth and hardness of each heat treat load, and certifies results.
Controlled Atmosphere Gas Carbonitriding Capabilities
0.05 mm – 1.25 mm
Case Depth Range Capability
0.05 mm minimum
Part Length Range
0.25 mm to 762 mm
Batch – load size: 36″ x 72″ x 36″
Continuous Mesh Belt Systems
Data log heat treat attributes
Integral oil quench, or slow cool in protective atmosphere
Integral pre and post-washing systems
Integral tempering systems
Nine-position Continuous Row – load size 36″ x 36″ x 30″ high
Customer Process Specifications
Allison Transmission TPS-301
Borg Warner 1000-447-232-D
Chrysler PS-8, PS-6333, MS-4515, MS-5001
Dana FW-247, SHAES174
Ford W-HTX, W-HT4-2, WD951
Harley Davidson ES805-41100
Mazda MES GA 221J
SFS 000034, 35, 36, 37 38, 39, 000093
Specialty Engine Components SEC-4000
TRW TPS-H-20, 187
To attain operational excellence, IST fosters employee development by diversifying employee’s capabilities, enhancing skill sets and creating a climate for action. Cross-trained employees understand all aspects of the heat treat process, and our customer’s needs. Certified employees are capable of receiving, heat treating, inspecting and shipping.
Technology and Knowledge Management
To best manage our customer’s needs, IST continually refines the knowledge management process and improves information technology resources. We utilize best practices to facilitate the transfer of knowledge to all levels of the organization; employees understand our customer’s requirements and act in their best interests.