Failure analysis of H13 steel die for high pressure die casting Al alloy

•Erosion region was observed close to runner system.•A large number of thermal fatigue cracking were found.•A tension residual stress up to 555 MPa was observed at the surface of the die.•Some fatal long cracks around the inserts/hole and corners, is correlated with high local stress.•A soften layer with ~0.5 mm in depth was formed via microstructural evolution induced by thermal cycling. High pressure die casting (HPDC) die is operated at severe conditions such as high pressure, high temperature and corrosion, which limit its service life. Analysis of failure mechanism of the die is beneficial to guide die design and choose of materials so as to improve the die life. A failed H13 steel die which was used to manufacture a 5G component via Al alloy HPDC, has been investigated using a complementary range of techniques such as X-ray diffractometer (XRD), Optical microscopy (OM), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM). The results show that erosion and cracking are two main failure modes. Furthermore, the fatal cracking occurs around fillet radius and hole/insert, which is correlated with high local stresses.