Who can tell me the principle of thermal correction of welded parts and which part to heat, whether this correction method is harmful to base metal and how to avoid it?

Flame correction is often used for deformed weldments of sheet metal, and most of them are stress-free workpieces.

Welding process is often used for structural parts to avoid deformation of weldments, and those with serious deformation will be rejected.

Your question is about heat treatment. The book you need to read is made of metal. You can finish it in one morning.

There is a picture in it, which systematically introduces the metallographic structure changes you mentioned.

I found a blog for you, searching for metal materials and heat treatment. Take a look.

/blog/static/119246027200981211023241/

I also tried random search. I don't know him. You want to be a professional. Don't blame me if you don't understand. . .