Threaded Flanges are used for special circumstances with their main advantage being that they can be attached to the pipe without welding. However, a seal weld can also be used in conjunction with the threaded connection. 
Although available in most sizes and pressure ratings, screwed fittings today are used almost exclusively in smaller pipe sizes. 
A threaded flange or fitting is not suitable for a pipe system with thin wall thickness, because cutting thread on a pipe is not possible. Thus, thicker wall thickness must be chosen. 
ASME B31.3 Piping Guide says:                                          
Where steel pipe is threaded and used for steam service above 250 psi or for water service above 100 psi with water temperatures above 220° F, the pipe shall be seamless and have a thickness at least equal to schedule 80 of ASME B36.10.

All Domestic Threaded Flanges are made with material forged and machined in USA.

Size & Dimension table for Flanges

A105 - The standard forged carbon steel piping components for ambient and high temperature / pressure systems

SS304 - A common standard for stainless steel due to its malleability, high corrosive resistance weld-ability  

SS316 - A molybdenum stainless steel that provides excellent tensile, creep and stress-rupture strengths at elevated temperatures

Material Description for Flanges