If so, can the tags be read immediately after being exposed to such high heat?
The answer to your first question is "yes," but the answer to the second is "it depends." Technologies ROI (TROI) has designed two new passive UHF RFID tags—the Armored 400c and the CUBE 400c—which can withstand temperatures of up to 400 degrees Celsius (752 degrees Fahrenheit). These tags are compliant with the ISO 18000-6C (-63) standard, have 128 bits of Electronic Product Code (EPC) memory, and feature 2, 4 or 8 kilobytes of user memory. They have a read range of 3 to 6 feet (0.9 to 1.8 meters) under real-world conditions.
These new tags are made of steel and can be welded to steel objects exposed to high temperature. They have an operating range from -50 degrees Celsius (-58 degrees Fahrenheit) to more than 400 degrees Celsius (752 degrees Fahrenheit), and can withstand 400 degrees Celsius for up to one hour.
I believe these are the only tags on the market that can withstand 400 degrees Celsius. TROI is working on a tag that can withstand exposure to more than 535 degrees (1,000 degrees Fahrenheit).
The second part of your question is a little more complicated. When a a transponder is exposed to such high heat for a period of time, the chip within the tag will eventually heat up. If the chip gets to 85 degrees Celsius (185 degrees Fahrenheit), it goes to sleep and cannot be read. So, if a TROI tag is exposed to high heat for a short period of time, you will likely be able to read the tag immediately. If the tag is exposed to, say, 350 degree Celsius heat for an hour, the cool-down time until the tag can be read may be a few minutes. It's rarely more than 10 minutes, according to TROI founder Pat King, even though you cannot touch the tag.
—Mark Roberti, Founder and Editor, RFID Journal