Are all the header tags(h1-h6) bold by default?

Question

do we again need to use <b> tags in this case?

Answer 1

No you don't need to use bold <b></b> in header tags
header tags depends upon the size you decided[h1-h6]. you can try <b> in header tags just for fun or just for your own clarification . 😊😊😂

Answer 2

h1 is the biggest one and h6 is the smallest one. You can try typing them in text editor to see what happens.