Carbon steel has many traits. Depending on what you use it for, some of those traits may be good and some bad in your view.
One trait of carbon steel is that it takes and holds a good edge. For knives, we usually think that that trait is good.
Another trait of carbon steel is that it can become magnatized. For knives, we usually think that this trait is bad.
If the magnetic field is very light, try dropping the knife onto a hard surface. Obviously, you risk damage to the knife. But, the impact will often break the magnatism. This is why you occationally see mechanics deliberatly drop their tools. A magnetic screwdriver can be a wonderful aide, but a slightly magnetic screwdriver that isn't supposed to be can be very annoying. Magnetic pliers are the worst; you set the part exactly where it should be, everything is perfect, but as you move the pliers out of the way, the part comes with them.
If the magnetic field a little heavier, try wrapping an extension cord around your knive (carefully so as not to cut into the cord, of course). Plug in a couple of hundred watts of table lamps via that cord, and let it run for a few hours. The alternating electrical current in the cord produces an alternating magnetic field that should erase the magnatization of your knife.
If that fails, machine shops use a lot of carbon steel tools and they usually don't want them magnatized. So, they fight this problem all the time. Most have a big electromagnetic degauser device. For a very nominal fee, often nothing, they'll be happy to run your knife through it. It only takes a few seconds.
The other place to turn for help is a TV Repair shop. TV picture tubes use electromagnetic fields to deflect a beam of electrons and draw the picture onto the phosphorus screen. That's all very technical, but the bottom line is that external magnetic fields can screw up your picture. Sometimes, the metal structures within the set become magnatized and cause distortions. So, most TV Repair shops have a big degausing coil setup.
