How to Decode ASTM Standard?

I don't think so; so far as I know, all the numbers are arbitrary (or almost so).

There must be some logic. As far as I understand in ASTM A 743, A indicate Ferrous material, if after ASTM there is letter B, it indicate non ferrous material it means there is a definite rule of de-coding ?

No. you cannot. ASTM standards with an A prefix generally cover carbon, alloy and stainless steels, as well as ferrous castings and coatings of all types and forms but otherwise the prefix has no significance and one must refer to the individual standard for details.

ASTM standards consist of (and are published) in 16 Sections, composed of various numbers of volumes. Section 00 is an index but section 1 is titled Iron and Steel Products and is composed of 8 Volumes; 01.01 Steel-Piping, Tubing, Fittings, 01.02 Ferrous Castings; Ferroalloys, Volume 01.03 Steel- Plates, Sheet, Strip, Wire, Stainless Steel Bar, etc.

ASTM standards can be purchased individually, by volume, by section, or by set at www.astm.org.

Here is a link to the new ASTM Unified Numbering System for Metals and alloys.