naked eye

optical microscope

metallurgical microscope

X-ray techniques

naked eye

optical microscope

metallurgical microscope

none of these

naked eye

optical microscope

metallurgical microscope

X-ray techniques

there is no change in grain size

the average grain size is a minimum

the grain size increases very rapidly

the grain size first increases and then decreases very rapidly.

there is no change in grain size

the average grain size is a minimum

the grain size increases very rapidly

the grain size first increases and then decreases very rapidly.