A gate valve requires (at least) two end connectors.
If the end connectors are flanged or threaded, then the material must be at least 60K for 5000psi equipment per API 6A 21st Edition Table 7. If the end connector is an "Other End Connector" per section 14.9, then Table 7 allows the material to be PMR (per manufacturer's requirement), so 36K material could be acceptable if it meets the design requirements of 5.1.3 and is per the manufacturer's requirements.