Application of Microalloyed Steels to Achieve High Toughness in Hot Forged Components without Further Heat Treatments

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Abstract

<div class="htmlview paragraph">Automotive parts produced by cold or hot forging steel bars are often heat treated after forging to reduce their grain size and obtain improvements in mechanical properties such as tensile, impact and fatigue properties. If heat treatments after forging can be eliminated, savings in energy and handling costs could be realised.</div> <div class="htmlview paragraph">Although rolling and cold drawing without additional heat treatments have been already used, hot forged components have not except a few applications because of low toughness properties when heat treating after forging is omitted. Tests in our laboratory have shown that the toughness and other mechanical properties of hot forged parts can be significantly improved without the use of post heat treatments. Results were as follows: <ol class="list nostyle"> <li class="list-item"><span class="li-label">1.</span> <div class="htmlview paragraph">High strength and high toughness are obtained by decreasing carbon contents, increasing manganese, adding both of microalloying elements (V, Ti).</div></li> <li class="list-item"><span class="li-label">2.</span> <div class="htmlview paragraph">Nitrogen (N) addition may be required but the amount depends on V and Ti contents present. The fatigue properties are affected by the presence of nitride precipitates.</div></li> <li class="list-item"><span class="li-label">3.</span> <div class="htmlview paragraph">Forging temperature and cooling rates after forging must be controlled to insure uniform properties throughout the finished component.</div></li> </ol></div> <div class="htmlview paragraph">By using the compositional and forging controls, automotive parts that were hot forged and air cooled had properties equivalent to those of the previous parts that were hot forged and subsequently heat treated.</div>

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