After forging steel turns brownish red in some places where it was heated. Is it because of steel type or I did something wrong?.
Nope - very normal, if you wanted to keep a nice “steel” color you can use bees wax (more traditional) or clear coat it.
If you take a wire wheel to it, it will shine up real nice. What a lot of smiths do after forging is either pickle the steel (put it in vinegar) to clean up the scale or brush it all up, then clear coat or wax it afterwards to weather proof it.
Thanks for the information.