Repeat GOES laser treatment starts from the stress, domain and coating state left by the first pass. Compare same-line and offset passes against that reference to measure the value of the extra exposure. [1]
Retain a first-pass reference
Inspect and magnetically test material after the first pass before allocating matched specimens to further treatment. Record the first-pass track positions and the measured response, including any coating disturbance. If only specimens with unusually poor first-pass performance are reprocessed, compare them with equally poor retained controls; otherwise selection bias can make the second pass appear more effective than it is.
| State | Second exposure | Question addressed |
|---|---|---|
| Untreated reference | None | Starting material condition |
| First pass retained | None | Benefit and damage already present |
| Second pass on registered lines | Same-line treatment | Effect of reheating the existing track |
| Second pass between lines | Defined offset | Effect of adding a different track distribution |
| Handling control | Second transport cycle without laser output | Changes introduced by handling rather than treatment |
Measure the response to the second stress pattern
Incident energy from two exposures can be summed as an energy account. Residual stress and magnetic benefit cannot be summed in the same way. The second thermal cycle may redistribute or relax existing stresses while introducing new strains. A same-line pass and an offset pass also produce different spatial histories even when their total incident energies are equal.
Keep the interval between passes, strip temperature and pass order in the record. Distinguish a nominal second-pass command from the measured registration: positioning scatter can turn an intended same-line comparison into partial overlap. Surface inspection should include both the original and newly exposed regions.
Measure the incremental result
Compare second-pass loss and excitation with the retained first-pass state at the same induction and frequency. An improvement relative to untreated steel is insufficient if the first pass already provided that improvement. Examine whether any incremental gain is distinguishable from specimen and measurement variation.
Use the coating assessment and, where justified, a suitable stress or domain investigation to explain the result. Published laser work establishes that treatment conditions affect domains, stress and magnetic behaviour, but it does not validate this particular two-pass route. [1]
Use the 23ZH90 catalogue comparison of ≤0.90 W/kg at 1.7 T, 50 Hz [2]. Assume the trial adopts that same preparation/test basis and target. Fictional first-pass, registered-repeat and offset-repeat losses are 0.88, 0.91 and 0.87 W/kg. The same-line repeat misses 0.90; the offset result meets it but improves the first pass by only 0.01 W/kg. With assumed paired expanded uncertainty ±0.015 W/kg, that incremental benefit is unresolved. Retain the single-pass process and repeat the offset comparison with adequate discrimination and coating checks. Equal incident energy does not establish equal residual state or justify the second pass.
Pass registration, focus, pulse/scan timing and post-treatment cutting determine the second exposure. Retain the first-pass state and a single-pass reference rather than rebuilding the comparison from separate unpaired coils.
Approve repeat treatment on the finished material’s magnetic response after cutting and assembly, with surface and handling condition verified. Add the second pass when its measured gain is resolved against the first-pass reference.
References
- P. Rauscher et al., The influence of laser scribing on magnetic domain formation in grain oriented electrical steel visualized by directional neutron dark-field imaging, Scientific Reports 6, 38307, 2016, Table 1. DOI: 10.1038/srep38307.
- Nippon Steel Corporation, Grain-Oriented Electrical Steel Sheets, catalogue D004je, April 2020, specification and typical-property tables.