Conversion from STEP to Nastran is not supported yet :(

STEP or "Standard for the Exchange of Product model data" is also referred as ISO 10303. STEP has been initially designed with the idea to supersede the IGES format (which was the first broadly used vendor-neutral CAD file format). However even today both formats co-exist and data in IGES and STEP represent lion share of all CAD files.

Typically, STEP can be used to exchange data between CAD, CAM, CAE, PDM/enterprise data modeling and other CAx systems. STEP addresses product data from mechanical and electrical design, geometric dimensioning and tolerancing, analysis and manufacturing, as well as additional information specific to various industries such as automotive, aerospace, building construction, ship, oil and gas, process plants and others.

STEP is developed and maintained by the ISO technical committee. There are also various technical groups that define usage conventions and recommended practices to ensure better interoperability between software applications. In CAD world, the most prominent group is www.cax-if.org that unites software vendors and industrial users.

ISO10303 is very extremely large and complex and is structured in multiple layers, for example, from physical file format definition (Part 21) to geometrical/topological definitions (Part 42), up to Application Protocols (AP’s) defining higher-level industry use cases. CAD Exchanger supports AP203, A214 and AP242, which are most commonly used AP's.

MSC Nastran is a multidisciplinary structural analysis application used by engineers to perform static, dynamic, and thermal analysis across the linear and nonlinear domains, complemented with automated structural optimization and award winning embedded fatigue analysis technologies, all enabled by high performance computing.

Engineers use MSC Nastran to ensure structural systems have the necessary strength, stiffness, and life to preclude failure (excess stresses, resonance, buckling, or detrimental deformations) that may compromise structural function and safety. MSC Nastran is also used to improve the economy and passenger comfort of structural designs