This glossary contains the 40 most commonly used terms in controlled atmosphere heat treatment, giving Chinese and English names and one-sentence definitions. It can be used as a unified reference when reading other articles in this knowledge base, writing process documents, and communicating with overseas customers.
- Unified terminology is the basis for process documentation, audits and cross-team communication
- Each term is given Chinese, English and one-sentence definitions
- For relevant principles, please link to the corresponding special article.
- Suitable for new employee training and external technical exchanges
Atmosphere and chemistry
| Chinese | English | Definition |
|---|---|---|
| Carbon potential | Carbon Potential (CP) | The carbon content (%) on the iron surface when the atmosphere is in equilibrium with pure iron at a certain temperature |
| carbon activity | Carbon Activity (aC) | Thermodynamic quantity characterizing carbon transfer capacity, basis for calculation of carbon potential |
| Nitriding potential | Nitriding Potential (Kn) | Kn = p(NH₃) / p(H₂)^1.5, which measures the nitriding ability of the atmosphere |
| Dew point | Dew Point | The temperature at which water vapor in a gas begins to condense, reflecting the water content |
| endothermic atmosphere | Endothermic Atmosphere (Endo / RX) | CO/H₂/N₂ gas produced by endothermic cracking of air and gas on the catalyst |
| exothermic atmosphere | Exothermic Atmosphere (Exo) | N₂-based gas produced by partial combustion of gas |
| carrier gas | Carrier Gas | The basic gas that constitutes the main body of the furnace atmosphere |
| Enriched gas | Enriching Gas | Hydrocarbons used to increase carbon potential, such as natural gas and propane |
| dilution air | Dilution Air | A small amount of air introduced when lowering the carbon potential |
| dissociated ammonia | Dissociated Ammonia | 75% H₂ + 25% N₂ mixture |
| Decomposition rate | Dissociation Rate | The proportion of ammonia decomposed in the furnace, one of the nitriding control parameters |
| carbon black | Sooting | The carbon potential of the atmosphere exceeds saturation, causing free carbon to precipitate. |
| Burn charcoal | Burn-out | Blow in air to burn off carbon deposits on the catalyst or probe |
Craftsmanship
| Chinese | English | Definition |
|---|---|---|
| Carburizing | Carburizing | Infiltrating carbon into the steel surface and then quenching it |
| Carbonitriding | Carbonitriding | Infiltrate carbon and nitrogen at the same time, the temperature is lower than carburizing |
| Nitriding / Nitriding | Nitriding | Nitrogen infiltration into the surface at approximately 500–580 °C |
| Nitrocarburizing / Nitrocarburizing | Ferritic Nitrocarburizing (FNC) | Infiltrate nitrogen and carbon simultaneously in the ferrite state |
| Strong penetration-diffusion | Boost-Diffuse | Carburizing process of first strong carburizing with high carbon potential and then diffusion with low carbon potential |
| Effective hardened layer depth | Effective Case Depth (ECD) | Distance from surface to specified hardness (usually 550 HV) |
| Compound layer / white bright layer | Compound Layer / White Layer | ε or γ′ iron nitride layer on nitrided surface |
| diffusion layer | Diffusion Zone | Nitrogen solid solution and precipitation strengthening area under the compound layer |
| spheroidizing annealing | Spheroidize Annealing | Spheroidizing carbides to improve cold formability |
| bright annealing | Bright Annealing | Annealed in a protective atmosphere, the surface is not oxidized |
| Tempering | Tempering | After quenching, heat below the phase transition temperature to adjust properties. |
Measurement and control
| Chinese | English | Definition |
|---|---|---|
| Oxygen probe | Oxygen Probe | Zirconia sensor that outputs a mV signal related to oxygen partial pressure |
| hydrogen probe | Hydrogen Probe | Measures the H₂ partial pressure in the atmosphere and is used to calculate Kn |
| process factor | Process Factor (PF) | Coefficient for correcting the deviation between the controller’s carbon potential and the actual carbon potential |
| alloy factor | Alloy Factor | Coefficient for correcting the effect of alloying elements on surface carbon content |
| Three gas analyzer | 3-Gas Analyzer | Analyzer for infrared measurement of CO, CO₂, CH₄ |
| Fixed carbon sheet | Shim Stock | After the thin steel sheet is carburized in the furnace, the carbon content is measured to verify the carbon potential. |
| hot wire resistance method | Hot Wire / Resistance Method | Determining carbon potential through wire resistance changes |
| closed loop control | Closed-loop Control | Automatically adjusts the actuator based on measured values |
Quality system
| Chinese | English | Definition |
|---|---|---|
| CQI-9 | Heat Treat System Assessment | Heat treatment system evaluation requirements issued by AIAG |
| AMS2750 | Pyrometry | Specification for high temperature measurement of aviation heat treatment |
| Furnace temperature uniformity test | Temperature Uniformity Survey (TUS) | Measure the temperature distribution in the effective heating zone |
| System accuracy test | System Accuracy Test (SAT) | Compare the deviation of the control system to a reference measurement |
| special process | Special Process | A process in which the results cannot be fully verified by follow-up inspections |
| process control plan | Control Plan | Documentation specifying key parameters, monitoring methods and response plans |
Frequently asked questions
Should the unit of carbon potential be written as "%" or "%C"?
Both are common and have the same meaning, referring to mass percentage. Internal corporate documents should be written in a unified way.
What is the unit of Kn?
Kn is calculated from partial pressure, and the unit is bar^-0.5 (or atm^-0.5). In actual use, only the numerical value is often written, but the pressure unit should be stated in the file.
What is the difference between TUS and SAT?
TUS checks whether the temperature is uniform at various points in the furnace; SAT checks the deviation between the control/recording system reading and the calibrated reference thermocouple, both are requirements of CQI-9 and AMS2750.