KEVOS® MAKEOS · Materials
Carburizing Case Depth Plan (Total Case for a Ground Effective Case, Time at Temperature, Furnace Cost)
How deep must a part be carburized so that, after grinding, the effective case it needs remains, how long does that take at temperature, and is the case sensible for the section?
Plan for gas or pack carburizing: the total case depth needed for a finished effective case after grinding stock is removed and the effective case is converted to total case with your ratio, the time at temperature from the parabolic growth of case depth with the square root of time and the case depth factor for the temperature, the total furnace cycle with the heating, diffusion and quench time you enter, the cost per part for a furnace rate and load, and the total case as a share of the half-section against your limit.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Part | ||
| Effective case required after grinding | mm | Effective case depth the drawing requires on the finished part, measured to the hardness the drawing specifies. |
| Grinding stock on diameter | mm | Material removed on the diameter by grinding after heat treatment (half of it comes off each side). |
| Effective case as a share of total case | Effective case depth as a share of the total case depth for this steel and process, from the heat treater's records. | |
| Smallest section thickness or diameter | mm | Thinnest wall or smallest diameter of the carburized section. |
| Largest total case as a share of the half-section | Largest share of the half-section the total case may occupy before the core is too small, from your design practice. | |
| Process | ||
| Case depth factor at the carburizing temperature | mm/√h | Case depth factor: total case depth reached after one hour at the carburizing temperature, from the heat treater for this steel, atmosphere and temperature. |
| Heating, diffusion and quench time per cycle | h | Time per cycle outside the carburizing time itself: heating up, diffusion, cooling to the hardening temperature and quench. |
| Furnace cost rate | A$/h | Cost of an hour of furnace time, including labour and atmosphere. |
| Parts per furnace load | Number of parts in one furnace load. | |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
Part
What this means: Effective case required after grinding
- What it is
- The effective case depth the drawing requires on the finished part, measured down to the hardness that defines it.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 20 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.8 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The total case and the time at temperature rise with it.
- Get it right
- Check the drawing states the hardness that defines effective case and whether it applies after grinding.
What this means: Grinding stock on diameter
- What it is
- The material removed from the diameter by grinding after heat treatment; half of it comes off each side and takes case with it.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0 mm to 10 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.3 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the case that must be put in before grinding.
- Get it right
- Keep it to the least that cleans up distortion; every tenth on diameter costs furnace time.
What this means: Effective case as a share of total case
- What it is
- The effective case depth as a share of the total case depth for this steel and process.
- Units and format
- Enter a plain number with no unit. The form accepts 0.1 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.7 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A lower ratio means a deeper total case and longer time.
- Get it right
- Take it from the heat treater's records or sectioned test pieces for the same steel.
What this means: Smallest section thickness or diameter
- What it is
- The thinnest wall or smallest diameter of the section being carburized.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 12 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A thinner section makes the case a larger share of it.
- Get it right
- Use the thinnest section that is carburized, such as a gear tooth or a thin flange.
What this means: Largest total case as a share of the half-secti…
- What it is
- Units and format
- Enter a plain number with no unit. The form accepts 0.01 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.25 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only moves the section pass line.
- Get it right
- Use your design practice for the part; teeth and thin sections need the most care.
Process
What this means: Case depth factor at the carburizing temperature
- What it is
- The case depth factor: the total case depth reached after one hour at the carburizing temperature, which sets how fast the case grows.
- Units and format
- Enter a number in mm/√h: mm/√h. The form accepts 0.01 mm/√h to 5 mm/√h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.6 mm/√h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Time at temperature falls with the square of the factor.
- Get it right
- Get it from the heat treater for this steel, temperature and atmosphere; it rises steeply with temperature.
What this means: Heating, diffusion and quench time per cycle
- What it is
- The time each cycle spends heating up, diffusing, cooling to the hardening temperature and quenching, outside the carburizing time itself.
- Units and format
- Enter a number in h: hours. The form accepts 0 h to 200 h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3 h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Adds directly to the cycle and the cost.
- Get it right
- Take it from the heat treater's cycle sheet for this load.
What this means: Furnace cost rate
- What it is
- The cost of one hour of furnace time, including atmosphere, energy and labour.
- Units and format
- Enter a number in A$/h: A$/h. The form accepts 0 A$/h to 100000 A$/h. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 85 A$/h as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Cost per part rises in proportion.
- Get it right
- Use the heat treater's charge-out rate or your own costing.
What this means: Parts per furnace load
- What it is
- The number of parts carburized together in one furnace load.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 1000000. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 120 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More parts per load lower the cost per part.
- Get it right
- Count only parts with the same case requirement; mixed loads are set by the deepest case.
Method and formulas
- Case removed by grinding = stock ÷ 2; effective case before grinding = required + stock ÷ 2; total case = effective ÷ ratio.
- Case depth grows with the square root of time: d = K √t, so the time at temperature t = (d ÷ K)².
- Cycle = t + heating, diffusion and quench time; cost per part = cycle × rate ÷ parts per load.
- Case share = total case ÷ (section ÷ 2), against your limit.
- Example: 0.8 mm effective after grinding needs 1.3571 mm total case, 5.1162 h at temperature and a 8.1162 h cycle, A$5.749 a part.
Limitations
- The parabolic law with a constant factor is an approximation for a constant temperature and carbon potential; boost-diffuse cycles and alloy steels follow their own curves.
- Grinding is taken as removing stock evenly; distortion makes the removal uneven, so allow extra where it matters.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Specify the carburizing case depth for a part that is ground after hardening
- Estimate time at temperature and furnace cost
- Check that the case is not too deep for a thin section
Who it is for
- Heat treaters
- Mechanical and process engineers
- Purchasing and quality staff
What you get
- Case removed by grinding and total case needed
- Time at temperature and total cycle
- Cost per part
- Case as a share of the half-section
Interpreting the result
- Because depth grows only with the square root of time, doubling the case takes four times as long; grinding stock is expensive in furnace time.
- A case that is too deep for the section leaves too little tough core and can make thin sections brittle.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 467–470, 484–487. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These KEVOS® Library readings explain the method this tool uses, with worked examples.
Method explained here · KEVOS® original book
Carburising the shaft: boost, diffuse and harden
What it covers: Design DS-40's carburising cycle with a high-carbon boost and a diffusion stage, compare it with a constant-carbon cycle, mask areas that must stay soft, and see what an over-long boost does to edges.
Method explained here · Library collection
Heat treatment and surface hardening explained for designers and buyers
In Machine Elements and Mechanical Design
What it covers: A drawing that just says "harden" invites cracked, distorted or soft parts. How heat treatment works, which process suits which part, and how to specify and verify the result.
KEVOS® tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.