Thanks for posting your question. The installation torque for this sclampis 35 inch-pounds of torque. It appears you may be over tightening. These clamps are sold by the millions for use in OEM automotive and plumbing applications. If you believe that you have not over tightened the clamp, please reach out to Ideal Clamp Products at 800-251-3200 and ask for customer service. Ideal Customer Service
Yes, these clamps are made from 100% stainless steel, including the screw and housing.
Should be SAE 52
Maximum operating limit for 304 Stainless steel is 1650 deg F however I’m not sure if there are any carbon steel materials in the mechanism which would limit the temperature to 750 deg F.