What are molds made from?

Most injection molds are machined from pre-hardened “tool steel” or Stainless Steel.  Depending upon part size and configuration, the cavity area may be Tool Steel inserted into a mold base.  Transfer and Compression molds can be pre-hardened but are sometimes made at a lower cost from E-45 or J-45 steel, depending upon anticipated production volume.  Prototype molds are normally E-45 or J-45 Steel.