The areas most affected by corrosive ammunition are:
Barrel, chamber, gas piston, gas cylinder tube, gas chamber, bolt face. There is no need to disassemble your bolt after firing.
WD 40 is used to displace water. It is a poor lubricant and will not stop corrosion. If you have exposed the bolt to water, it may be of some use. If using boiling water to clean out corrosive salts, try not getting everywhere. It will start to rust the metal under the wood (like the hand guard around the gas cylinder tube) and areas you can't dry and oil. Ammonia (like in Windex) works well and is easy to clean up. No funnels, etc and hot water splashing about. Remember, water and firearms is not a good mix.
After cleaning, stick with an appropriate firearm oil. I prefer Break free CLP. It is mil spec and used by both the Canadian and US military as their primary weapon lubricant.