Heat treatment conditions to prevent failure in die cast X38CrMoV5 steel parts

• Heat treatment is not able to remove the dendritic microstructure or porosity.
• Microporosity is the main cause of cleavage fracture of these.
• To avoid cleavage fracture of the parts a KIc value of 50 MPa m1/2 was reached.
• The largest micropores (200 mm), will cause cleavage fracture.

The usual mechanical properties of martensitic steels are strongly linked to the complex microstructure obtained after their heat treatment, which is generally performed to achieve good hardness and/or tensile strength with acceptable ductility. In the present work, X38CrMoV5-1 (AISI H11-1) steel, classed as a hot-work tool steel with many applications, has been studied from the viewpoint of phase transformations and heat treatment. Parts are often manufactured by die-casting followed by quenching and tempering and the microstructure is highly sensitive to the process. Microstructural defects can lead to early failure of many parts at the service temperature as a consequence of the casting process and heat treatment conditions. The authors have used dilatometry and differential thermal analysis (DTA) techniques to study phase transformation during cooling and have determined CCT diagram. Heat treatment is not able to remove the casting dendritic microstructure or porosity, thus increasing the likelihood of brittle fracture, but it can prevent catastrophic failure in service conditions.