TZM Alloy Slab Hot Rolled Cogging Process

At 1250 ~ 1350 ℃, proceeding hot rolled process on TZM alloy slab found under the process TZM alloy has lower yields, mainly due to the hot-rolled stratified, splitting and other defects. From this we will know that hot rolling process has a greater impact on the quality of TZM alloy slab. The experiment found that using low-temperature hot-rolled technology to produce TZM alloy has good performance and high yield.

Low temperature hot rolled temperature at 850 ~ 1000 ℃, the second pass deformation higher than 25%, the blank denser than 9.6g/cm can produce the best performance TZM alloy.

Low-temperature hot-rolled cogging process has three advantages:
1. Obtaining a fine grain structure so it can improve the dispersion of the second phase of impurities, changing the composition and morphology of the second phase, to improve process performance;
2. Promoting the formation of sub-structure, improving the dislocation density can achieve deformation strengthening, improving the strength of the alloy;
3. Deeping deformation and increasing the uniformity of deformation can reduce delamination and cracks.

The following main analyze the splittings influence of second pass deformation on TZM hot-rolled slab. When the second pass deformation is higher than 25%, the deformation of the slab is deeper, and it can reduce the effect of the middle metal tensioning stress. When the slab after first rolling the surface of the metal layer has already happen plastic deformation, and the middle metal didn’t happen plastic deformation, so it is still in the state of powder sintering. The middle metal surface suffers metal tensile stress.

Therefore, the amount of deformation of the second pass should higher than 25%, so that deformations will deeper. If the amount of deformation of the second pass is not large, the deformation is not deeper, than the middle metal will suffer two times tensile stress effect. When the tensile stress is large enough to destroy the inter-crystal bonding force, so the intergranular fracture will occurs, leading to macroscopic wall crack.

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