GR 91 is a grade of steel that is commonly used in high-temperature applications, such as power generation and petrochemical plants. Here are some key properties and characteristics of GR 91 steel: - GR 91 is a chromium-molybdenum alloy steel - It has a high tensile strength of 92-122 ksi (635-841 MPa) - It has a high yield strength of 81-103 ksi (558-713 MPa) - It has good resistance to high-temperature creep and stress rupture - It has good weldability and is suitable for welding with common welding processes - It is often used in applications such as: - Power generation equipment (e.g. boilers, turbines) - Petrochemical plants - Refining and gas processing plants - High-temperature heat exchangers GR 91 steel is known for its excellent high-temperature properties, making it a popular choice for applications where high strength and resistance to creep and stress rupture are critical. Note: The "GR" in GR 91 stands for "Grade", and the number "91" indicates the grade level. The exact composition and properties of GR 91 steel may vary depending on the specific standard or specification (e.g. ASME, ASTM, etc.) being followed.