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Restoration of Obliterated Numbers on 40NiCrMo4 Steel by Etching Method: Metallurgical and Statistical Approaches
Author(s) -
Fortini Annalisa,
Merlin Mattia,
Soffritti Chiara,
Garagnani Gian L.
Publication year - 2016
Publication title -
journal of forensic sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.715
H-Index - 96
eISSN - 1556-4029
pISSN - 0022-1198
DOI - 10.1111/1556-4029.12849
Subject(s) - etching (microfabrication) , reagent , statistical analysis , isotropic etching , materials science , metallurgy , mineralogy , geology , chemistry , mathematics , composite material , statistics , layer (electronics)
The restoration of obliterated serial numbers is a problem of common occurrence in the forensic field. Among several restoration techniques, chemical etching is the most frequently used. The present research is aimed at studying the restoration of serial numbers, stamped on 40NiCrMo4 steel plates, by means of chemical etching. Microstructural characterization was firstly carried out to study the plastically deformed regions surrounding the marks. The obliteration was performed by controlled removals of material at increasing depths of erasure, and five etching reagents were considered to analyze their sensitivity and effectiveness. Experimental results revealed that Fry's reagent was the most sensitive, able to restore erased marks up to 60 μm under the depth of the imprint. The reagent comprising 25 mL HNO 3 and 75 mL H 2 O provided good results, recovering the major numbers of characters. A descriptive statistical analysis was conducted to study the operator's influence on the recovered marks’ identification.