Controlling temperature of soldering iron
My answer is based on this:

I plan to rectify the mains with rectifiers and then feed it into pwm circuit (I plan in using 555 circuit to make it simple ) and mosfet .

This is a circuit I've worked with that is uses a MOSFET to control a high voltage DC motor. You'll have to work out the values of the components based on what you have or can obtain, but this is a starting point for you. There will be several components you won't need such as DC3, D6, and D31, perhaps more.
I suggest being careful you are driving the MOSFET properly. Also, D5 is a flyback diode and will be critical in protecting the MOSFET from damage. High voltage DC like this is dangerous so please be careful. If you are new to circuit design, I'd suggest going with the lighting dimmer switch idea others have suggested.