An industry-wide interest has arisen with regards to the properties and capabilities of investment cast PH 13-8Mo corrosion resistant steel. Specifically of interest are the structural applications in the aerospace industry for this product heat treated to the H1000 condition. The objective of this AMEC cooperative test program was to generate and compile useful data for aerospace structural evaluation of investment cast PH 13-8Mo heat treated to H1000. The focus of the test program was the determination of overall mechanical properties, fatigue, fracture toughness, and crack growth data along with basic microstructural evaluation of the investment cast material. Additional objectives included the evaluation of mechanical property variations between cast and machined tensile specimens and evaluation of microstructural constituents. All testing was performed to determine the suitability of PH 13-8Mo, H1000 investment castings for use in the aerospace industry. AIR4394A has been declared "STABILIZED" by AMS Committee B. This document will no longer be updated and may no longer represent standard industry practice. This document was stabilized because it contains mature technology that is not expected to change and thus no further revisions are anticipated. NOTE: This document was issued in 1991 and has never been revised. Users of this document should refer to the cognizant engineering organization for disposition of any issues with reports/certifications to this specification; including exceptions listed on the certification. In many cases, the purchaser may represent a sub tier supplier and not the cognizant engineering organization.