I3Dfun can open and display STEP files.
Also it can store/delete/rename/manage STEP files.
Tutorial:
1, you can press the button of "+ create document", it will create a sample file and display it.
2, you also can open an attachment from you email account. And open a file from a cloud storage app.
3, you can drag one finger to rotate the model, drag two fingers in the same direction to pan, pinch two fingers to zoom in or out.
4, Close the file by the button of "Close the file". note: "AR3D" would do nothing.
5,There is no requirement to sign-in. And it is a free App.