Thermomechanical coupling model for TC4 bar heating was established based on the Abaqus finite element simulation software. TC4 alloy bars with different diameters and 0.2 mm glass coating on the surface were directly heated into the furnace at 945 ℃ and analyzed. The results indicate that the maximum equivalent stress suffered by the bar during heating is increased with the increase of diameter

which is located at the bottom of the bar（the contact part with the furnace）. When the diameter of the bar is more than 40 mm

the maximum equivalent stress suffered by the bar during the heating process is greater than the yield strength at the corresponding temperature. The maximum principal stress suffered by the bar during heating is increased with the increase of diameter. Temperatures where the different diameters bearing the maximum principal stress height are all about 35 ℃. When the diameter of the bar is 100 mm

the maximum principal stress is 198.2 MPa

and the safety factor for brittle cracking is 4.8

while that of the remaining diameters are all greater than 4.8. TC4 alloy bars with a diameter of ≤40 mm are coated with 0.2 mm glass on the surface. When heated directly into the furnace at 945 ℃

the shortest holding time can be calculated.