Analysis of Precipitation Phase of Alloy1.4957 Heat-Resistant Steel for Gasoline Turbocharger

Recently, strengthened environmental regulations have required the downsizing of gasoline engines, and as a result, demand for turbochargers has rapidly increased. The vane turbocharger controls flow gases toward turbine, it is manufactured by powder metallurgy due to its complex shape. Gasoline engines high exhaust gas temperature (~1000<sup>o</sup>C), thus, Alloy1.4957 (GX15CrNiCo21-20-20) containing large amounts Cr, Ni, Co used. In this study, powders were sintered hot isostatic pressing (HIP), then homogenized thermally exposed temperatures. Then, microstructural analysis was conducted observe changes that occurred each process. M<sub>6</sub>X carbonitride Si, called Cr<sub>3</sub>Ni<sub>2</sub>SiX, observed be main precipitate phase in alloy. general, known Cr<sub>3</sub>Ni<sub>2</sub>SiX only rarely heat-resistant steel. However, Alloy1.4957, amount precipitated or dissolved depending on process, probably Si N content Alloy1.4957. addition Cr<sub>23</sub>C<sub>6</sub> NbX observed. during homogenization but NbX, which thermal stability, retained fine size process provided nucleation site exposure.