Cold-Working Stress Field
Definition
Residual plastic deformation and elevated dislocation density in a metal lattice created by stamping; persists below the visible surface even after surface removal and is the physical basis for serial number restoration.
- Cause
- Metal stamping
- Nature
- Residual plastic deformation, elevated dislocation density
- Depth
- Persists below the surface after removal
- Application
- Basis of serial number restoration
Common questions
How does the cold-working stress field allow a ground-off serial number to be restored?+
Stamping deforms the metal lattice deeper than the visible characters, so even after the number is filed or ground away, the disturbed grain structure remains beneath the surface and can be revealed chemically, since it etches at a different rate than the undisturbed surrounding metal.
Which restoration methods rely on this stress field?+
Acid etching, Fry's reagent, and magnetic particle or electrochemical restoration methods all exploit the same underlying principle, that the cold-worked region beneath the stamped digits reacts differently from unworked metal, though the specific reagent choice depends on the metal alloy involved.
Related terms
- ASTM E2885-13
- ASTM International standard practice for restoration of obliterated vehicle identification numbers; the reference protocol for VIN casework in US and internationally aligned...
- Backscattered Electron (BSE) Imaging
- An SEM imaging mode sensitive to atomic number and crystallographic texture; can reveal grain-boundary elongation patterns in the sub-surface cold-worked zone after...
- Davis Reagent
- Variant etchant for steel using cupric ammonium chloride (Cu(NH4)2Cl4) in dilute HCl. Slower acting than Fry's, sometimes preferred when contrast on Fry's...
- Electrolytic Etching
- Electrochemical alternative to chemical etchants. The part is the anode in an electrolyte bath; controlled current selectively dissolves the strained metal at...
- Fry's Reagent
- Classical etchant for plain carbon and low-alloy steel: 40 g cupric chloride (CuCl2) + 90 mL concentrated HCl + 100 mL water....
- INTERPOL iARMS
- INTERPOL's Illicit Arms Records and tracing Management System. Multilateral database enabling law enforcement in INTERPOL member countries to trace recovered or seized...
- Magnetic Particle Inspection (MPI)
- A non-destructive testing method that reveals magnetic-domain contrast between cold-worked and unstressed zones in ferromagnetic metals using a ferrofluid under UV illumination;...
- Neutron-Induced X-Ray Fluorescence (NIXRF)
- A synchrotron-based method using neutrons to probe deep obliterations; can detect digit geometry buried several millimetres beneath a machined surface, entirely non-destructively.
- Profilometry
- White-light interferometry or confocal laser scanning to detect nanometre-scale height differences on a metal surface; can reveal topographic ghost images of obliterated...
- Turner's Reagent
- A ferric chloride solution used to etch copper, brass, and cuprous alloy substrates; the high-potential Fe3+ ion preferentially oxidises the cold-worked zone.
- Ultrasonic Cavitation
- High-frequency pressure waves that collapse cavitation bubbles preferentially at high-energy surface zones; an alternative physical restoration method for stainless-steel and titanium substrates.