Title

MINIMIZAÇÃO DE TRATAMENTO TÉRMICO USANDO RESFRIAMENTO CONTROLADO

A STUDY ON THE DIRECT CONTROLLED COOLING OF HOT FORGED STEEL GEARS

Authorship

Yamakami, Wyser José; Button, Sérgio Tonini; Caminaga, Célio

Yamakami, Wyser José

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Button, Sérgio Tonini

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Caminaga, Célio

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DOI

10.5151/2594-5327-0173

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Abstract

Este trabalho visa estudar a viabilidade da substituição da normalização de um determinado aço, realizada a 950 °C por 2 horas, necessária antes da usinagem, pelo resfriamento controlado do mesmo a uma temperatura e por um tempo determinados, imediatamente após o seu forjamento a quente, de forma a reduzir o tempo e custos do processo produtivo. Para isso, o resfriamento controlado deve permitir a formação de uma microestrutura com as mesmas características e dureza especificadas para o aço normalizado. Corpos de prova (CDPs) desse aço foram aquecidos a 1050

In order to reduce the lead times and costs related to manufacturing processes, this work presents a study on substituting the normalizing of a carburizing steel at 950 °C for two hours, previous to finish machining, for direct controlled cooling at a constant temperature for different cooling times, immediately after hot forging. It is desired that the resultant microstructure from the controlled cooling present the same micro constituents and hardness specified for the normalized condition. Workpieces were heated to 1050 °C, hot drop forged in a hydraulic press and immediately cooled in a furnace at 600 °C for 20 and 30 minutes. The workpieces cooling curves inside the furnace were recorded with a digital data acquisition system. Samples of these workpieces were analyzed with optical microscopy and hardness tests to compare their results to those verified in normalized hot forged gears. The microstructures obtained for workpíeces cooled for 20 and 30 minutes were similar and compound by pearlite and ferrite homogeneously distributed, with a mean hardness of 170 and 175 HB respectively, and attended the specifications for the normalized steel. A eutectoid reaction at 650 °C was evident in the cooling curve. Therefore the results of this work showed that is possible to substitute the normalizing heat treatment for a direct controlled cooling with a significant reduction in production times and costs.

Keywords

Forjamento; Tratamento térmico; Resfriamento; Microestrutura.

Forging; Heat treatment; Direct cooling; Microstructure.