Cromização em caixa do aço ferramenta AISI M2 utilizando irradiação por micro-ondas como fonte de aquecimento
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Data
2023-03-03
Autores
Takahashi, Luciana
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Universidade Estadual Paulista (Unesp)
Resumo
Aços ferramenta possuem um vasto campo de aplicação na indústria metal-mecânica, vinculada a confecção de ferramentas de usinagem, matrizes para estampagem profunda, entre outras. Para aumentar a vida útil dessas ferramentas podem ser aplicados revestimentos endurecidos, entre eles a formação de revestimento rico em cromo por meio de tratamentos eletroquímicos que industrialmente usam o cromo hexavalente - uma substância altamente poluente e carcinogênica. A técnica de cromização em caixa é um tratamento realizado em altas temperaturas, mas que tem a vantagem de usar cromo metálico que torna o processo mais limpo e sustentável. No presente trabalho peças do aço ferramenta AISI M2 foram cromizadas em caixa com uma mistura de pós composta por cromo metálico ou ferro-cromo em pó, um ativador (NH4Cl) e um composto inerte (Al2O3). Para o tratamento termoquímico construiu-se um aparato que permitiu o uso da técnica do aquecimento híbrido por irradiação com micro-ondas, quando temperaturas iguais ou superiores a 1000°C foram mantidas durante 1 hora. Os revestimentos foram examinados por microscopia óptica (MO) e eletrônica de varredura (MEV), além de análises por espectroscopia de energia dispersiva de elétrons (EDS), difração de Raios-X (DRX) e microdureza Vickers. Os resultados mostraram que as regiões externas das camadas são compostas preponderantemente por duros carbonitretos de cromo. A fonte de cromo usada na cromização em caixa mostrou afetar a qualidade da camada, sendo que as amostras preparadas com ferro-cromo apresentaram revestimentos com espessura mais uniforme e maior dureza que aquelas preparadas com cromo metálico. As camadas formadas usando ferro-cromo obtiveram espessuras entre 5,4 e 6,9μm e dureza média 3,5 vezes superiores à dureza do substrato, enquanto as amostras preparadas com cromo metálico mostraram camadas com espessuras entre 6,5 e 7,8μm e dureza média 2,5 vezes à dureza do substrato.
Tool steels have a vast field of application in the metal-mechanic industry, linked to the manufacture of machining tools, dies for deep drawing, among others applications. To improve the life of these tools hardened coatings can be applied on their surface, including formation of chromium-rich hard coating through electrochemical treatments that industrially use hexavalent chromium - a highly polluting and carcinogenic substance. Pack chromizing is a surface treatment carried out at high temperatures and has the advantage of using metallic chromium, which makes the processing cleaner and more sustainable. In the present work, AISI M2 tool steel samples were pack chromizing using a mixture composed by metallic chromium or iron-chromium powder, an activator (NH4Cl) and an inert compound (Al2O3). For the thermochemical treatment, an apparatus was built that allowed the use of the microwave hybrid heating (MHH), when temperature equal to or greater than 1000°C were maintained for 1 hour. Coatings were examined by optical (OM) and scanning electron (SEM) microscopy, in addition to energy dispersive electron spectroscopy (EDS), X-ray diffraction (XRD) and Vickers microhardness analyses. The results showed that outer regions of the coatings are predominantly composed by hard chromium carbonitrides. The source of chromium used in pack chromizing has showed to affect the formed coatings, with samples prepared with iron-chromium powder presenting more uniform thickness and higher hardness than those prepared with metallic chromium powder. Coatings formed using iron-chromium have attained thicknesses between 5.4 and 6.9μm and hardness 3.5 times higher than the substrate, while samples prepared with metallic chromium have presented hardened coatings with 6.5 to 7.8μm thicknesses and hardness 2.5 times superior of the substrate.
Tool steels have a vast field of application in the metal-mechanic industry, linked to the manufacture of machining tools, dies for deep drawing, among others applications. To improve the life of these tools hardened coatings can be applied on their surface, including formation of chromium-rich hard coating through electrochemical treatments that industrially use hexavalent chromium - a highly polluting and carcinogenic substance. Pack chromizing is a surface treatment carried out at high temperatures and has the advantage of using metallic chromium, which makes the processing cleaner and more sustainable. In the present work, AISI M2 tool steel samples were pack chromizing using a mixture composed by metallic chromium or iron-chromium powder, an activator (NH4Cl) and an inert compound (Al2O3). For the thermochemical treatment, an apparatus was built that allowed the use of the microwave hybrid heating (MHH), when temperature equal to or greater than 1000°C were maintained for 1 hour. Coatings were examined by optical (OM) and scanning electron (SEM) microscopy, in addition to energy dispersive electron spectroscopy (EDS), X-ray diffraction (XRD) and Vickers microhardness analyses. The results showed that outer regions of the coatings are predominantly composed by hard chromium carbonitrides. The source of chromium used in pack chromizing has showed to affect the formed coatings, with samples prepared with iron-chromium powder presenting more uniform thickness and higher hardness than those prepared with metallic chromium powder. Coatings formed using iron-chromium have attained thicknesses between 5.4 and 6.9μm and hardness 3.5 times higher than the substrate, while samples prepared with metallic chromium have presented hardened coatings with 6.5 to 7.8μm thicknesses and hardness 2.5 times superior of the substrate.
Descrição
Palavras-chave
Cromização em caixa, Micro-ondas, Aquecimento híbrido por micro-ondas, Pack chromizing, Microwave, Microwave hybrid heating