Your question is to broad and does not have a simple answer. The term hot working refers to forming of metals above their recrystallization temperature.
The hot working temperature of metals is specific to the material classification (type and alloy content), and can vary from 1700 deg F up to 1900 deg F. For example, the P-No ranges you are interested in contain various alloys like carbon steel, low alloy steel, martensitic stainless steel and ferritic stainless steel.
Your best bet is to pick one alloy in each material classification and search the internet for technical information. The key word(s) I would recommend to use is formability or hot forming.
ASME B31.3 part 332.2 defines cold bending of ferritic materials at a temperature below the transformation range and hot bending at a temperature above the transformation range.
ASME B31.1 129.3.1 defines hot bending aa being done above the lower critical temperature - 100 F. Cold bending is performed at a temperature below the lower critical temperature-100 F. The lower critical temperatures for P-1 thru P-5B are provided in Table 129.3.2.
