Microstructure and Mechanical Properties of Manganese Bronze Submitted to Cold Work and Subsequent Heat Treatment

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Applied Sciences (Switzerland)
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Lobo F.G.
Huang H.P.
Santos V.T.D.
Silva M.R.D.
Santos G.A.D.
Couto A.A.
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© 2022 by the authors.Featured Application: Manganese bronzes are applied in marine environments, for example, gate valve stems due to their characteristics of high mechanical strength and corrosion resistance. Each element present in the chemical composition of the alloy contributes to the properties required in this application, such as: lead contributes to machinability, iron improves tensile strength, tin increases corrosion resistance and manganese contributes to elastic properties. The study of the increase in mechanical properties is crucial for a better understanding of alloy hardening, as well as for the optimization of properties and manufacturing processes. The present study evaluated the influences of different temperatures during heat treatment on the microstructure and mechanical properties of the manganese bronze alloy. During heating, there was a decrease of stored energy in the form of crystal defects due to the mechanisms of rearrangement and the annihilation of dislocations, followed by nucleation and grain growth. Initially, the samples were drawn using 34% cold work. Then, the specimens were heat-treated for one hour with different temperatures ranging from 200 to 750 °C, increasing by 50 °C for each sample. The chemical composition characterization was determined by X-ray fluorescence spectrometry (XRF). The mechanical property characterization involved the Vickers hardness, tensile strength, yield strength, and elongation. For the microstructural analysis of the samples, optical microscopy and scanning electron microscopy were used. The results showed an increase of elongation and decrease of the Vickers hardness and tensile and yield strengths with the increasing annealing temperature. The Hollomon model was used to investigate the strain-hardening behavior in all specimens. The (n) strain-hardening coefficient and the (K) strength coefficient were calculated, and the correlation with the increase of temperature occurred with the increase of n and variation of K after the recrystallization temperature.
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