Detection of vehicle identification number tampering through the hardening zone/Deteccao de adulteracao do numero de identificacao veicular atraves da zona de encruamento/Deteccion de manipulacion del numero de identificacion del vehiculo a traves de la zona de endurecimiento

In order to increase the success of law enforcement officers in forensic examinations of stSeeking to increase the success of public security agents in examinations carried out on stolen vehicles that have a tampered identification number, the extent of the plastically deformed zone caused by the marking of the character on specimens marked with 2, 3 and 5 tons of force was analyzed. Optical microscopy and plane grinding techniques were used to determine the depth of the marking. Then, the Vickers microhardness test and optical microscopy were used to measure the hardening zone, considering that this zone is directly affected at the time of removal during the crime. The results indicate that there is a relationship between increasing the marking force and increasing the depth of the hardening zone, in addition to both techniques proving to be efficient for measuring such regions. The depth of 0.200 mm recommended by the ABNT standard was reached when a force of 2 tons was used, which generated a hardening layer of approximately 0.7 mm. The results demonstrated that if the marking depth was increased to 0.7mm, a hardened zone of 1.2mm would be generated, making its removal very difficult. It is necessary to intensify studies in the area with a view to improving and proving results and consequently increasing success in forensic examinations. Keywords: Adulteration. Stamping. Hardening. Expertise. Vehicles. Buscando aumentar o sucesso dos agentes de seguranca publica nas pericias realizadas em veiculos furtados que apresentam o numero de identificacao adulterado, foi analisado a extensao da zona deformada plasticamente causada pela marcacao do caractere em corpos de prova marcados com 2,3 e 5 toneladas de forca. Foi utilizado a tecnica de microscopia otica e retifica plana para determinar a profundidade da marcacao. Em seguida foi utilizado o ensaio de microdureza Vickers e microscopia otica para a medicao da zona de encruamento tendo em vista que tal zona e diretamente afetada no momento da remocao no ato do crime. Os resultados apontam que existe uma relacao ao aumentar a forca de marcacao com o aumento da profundidade da zona de encruamento, alem de ambas as tecnicas se mostrarem eficientes para a medicao de tais regioes. A profundidade de 0,200mm recomendada pela norma ABNT foi atingida quando se utilizou uma forca de 2 toneladas, o que gerou uma camada de encruamento de aproximadamente 0,7mm. Os resultados demostraram que caso a profundidade de marcacao