Evidence
Validation chain
Steel
Boost
Diffusion
HPGQ
Profile
Required technical closure
| Item | Required definition | Test data |
|---|---|---|
| Steel | grade, heat, chemistry, prior condition, hardenability | material certificate and initial hardness/microstructure |
| Case-depth target | effective case depth, surface carbon, hardness requirement | specification and measurement method |
| Boost stage | gas pulse, pressure, temperature, duration, surface carbon input | recipe log and carbon profile |
| Diffusion stage | temperature and time for carbon redistribution | profile fit and hardness profile |
| HPGQ | gas pressure, cooling rate, load geometry and distortion criterion | cooling record, hardness and dimensional check |
| Repeatability | load size, fixture, furnace zone and batch history | repeat run or comparable batch record |
Model boundary
Initial condition: C(x,0) = C0
Surface boundary: -D·∂C/∂x |x=0 = JC(t)
Core boundary: ∂C/∂x |x=L = 0 or C(L,t) ≈ C0
Calibration target: Cmodel(x) → Cmeasured(x)
Surface boundary: -D·∂C/∂x |x=0 = JC(t)
Core boundary: ∂C/∂x |x=L = 0 or C(L,t) ≈ C0
Calibration target: Cmodel(x) → Cmeasured(x)
Acceptance matrix
| Result | Accept | Reject / repeat |
|---|---|---|
| Carbon profile | matches target case depth and surface carbon range | missing profile, excessive surface carbon, shallow/deep case |
| Hardness profile | consistent with case-depth target and steel response | hardness drop, brittle layer, inconsistent gradient |
| Microstructure | acceptable martensite/carbide state for application | carbide network, abnormal retained austenite, grain-growth concern |
| Distortion | within drawing/process allowance | HPGQ or fixturing not controlled |
| Repeatability | same route works for comparable load | single coupon result used for different component class |
Application link
Engineering practice
Scientific depth: LPC transfer
| Variable | Scientific role | Measured record | Risk if missing |
|---|---|---|---|
| Surface carbon flux J(t) | Defines boost-stage boundary condition. | Carbon profile after calibrated cycle. | Recipe transfer without actual carbon uptake. |
| D(T,C) | Controls diffusion rate and concentration dependence. | Temperature log, steel grade, profile fit. | Wrong case-depth prediction. |
| Load / fixture geometry | Controls thermal lag and gas access. | Load map, thermocouple record, coupon placement. | Nominal cycle differs from part response. |
| HPGQ route | Controls final hardness and distortion. | Quench pressure, cooling path, hardness profile. | Correct carbon profile but wrong final function. |
Basis
- Record
- Carbon profile, hardness profile, thermal log, load geometry and quench record.
- Interpretation
- Boost-diffusion sequence and transfer boundary between recipe name and actual case response.
- Project use
- Acceptance depends on steel grade, target case depth, load, furnace, quench route and measured profile.