Flatten with a grinder and then pound again some more. Try to keep it even and overlap the impact marks. Buy or make a flat blunt tool that resembles a planishing hammer and start pounding away on it. Too bad you cant just let the train reharden it for you. The problem with work hardening is that to do it yourself requires a lot of WORK. The manganese steels respond to work hardening. The bottom plate which has now become the top face to do all your work on is. Now that you have weld fabricated your dream anvil customized to your exact dimensions and shape, it is time to do one more thing. As was stated earlier, different rails = different chemistry and I am trying to be as generic as possible. Worst case scenario is that there could be a catastrophic failure (big crack!) and ruin all the hard work invested up to that point. With rail track having a medium (0.60- 0.82%) carbon content, attempts to quench harden either results in little to no gain OR too much and makes the face susceptible to cracking and chipping. Manganese steels (some recipes receive little to NO benefit from attempting to quench harden due to low carbon content).

Top side is quench hardened at the mill, but is still not as hard as when after it has been in service. It is true that the flat bottom is softer than the top. OK now for the techno mumbo jumbo part, but I'll keep it simple, brief and low keyed. Note: if you have a 110V unit, this will take a LONG time and will be very difficult to get a solid weld. You can also use an equivalent Flux cored wire in the largest size your wire feeder can handle. I recommend the 309 because of the high nickel will reduce the tendency for cracking. My preferred weld metals for this are plain old E7018, or if money is no object use E309-15 stainless steel stick rod. Weld these in place as you see fit for your own personal design or as close to a traditional shape as you like. Now, with the left over length of track, cut off a small piece for a table and a larger piece for the face. Trim to basic overall length and shape a horn and scallop as recommended in step B. Start off with a much longer piece of track than needed. Carve a pointed horn, grind the hell out of it all to remove the torch cut nicks and grooves with the top flattened, scallop out the front and rear, then scallop out the base pate and you will have a reasonably respectable looking ASO (anvil shaped object). C) Attack it with an oxy-acetylene cutting torch. B) Weld the rounded parts with a medium soft hardfacing welding rod (stick or wire) and grind off until flat and smooth. A) Leave it as is, mount onto a log (maybe drive a few large nails or spikes to keep it in place) and start pounding away. After a bit of train traffic, the tops become much harder. When rails come from the mill, they are differentially Q&T'd on the tops only. These are different than what the buckets themselves are made of (T-1). Motor grader cutting edges, drowser bars on the cheeks of dozers are also examples of really high strength/wear steels. These manganese steel recipes are designed for impact and wear resistance. But the mill has chemists and knows what they are doing with zillions of $$$ worth of hi-tech equipment to do it with. So, Rail steel is similar to T-1 and AR steels. 5) Yep, the bottom side is softer than the (worn) top side. 4) Unfortunately, they can be a labor of love and time consuming to build. Plus, it's a gonna takes you a one BIG azzed fire to do the job properly. By Q&T, there is the possibility to make it too Brittle. 3) Yes it can be quenched and tempered, but NOT recommended. Typically it is a medium carbon (0.80 max) and Manganese (1.20) steel. 2) All rails are not created equal and are often a proprietary recipe from the owner. 1) IMO they make awesome anvils and can be fabricated to YOUR specific size, weight and configuration. I see a lot of questions and myths about anvils made from Railroad Track. Something I wrote for a Newbie's Blacksmithing forum.

Railway track anvil weight