From a post on the Blacksmiths Junkyard 1997.
QUALITY OF OLD ANVILS: Those familiar with anvils can tell a good one at a distance. If an anvil is old and has been used a lot but not abused it will show its age by the thousands of little dings in its surface. Even the hardest of anvil faces will show use. This well used look indicates that the anvil has stood up to years of pounding and has taken it in stride. If the anvil is sway backed or the horn or heal droops the anvil has been abused, is of poor quality or has been used for too heavy of survice. It is not unusual to see chisel marks on the horn and table. There should not be any on the horn but is is easy enough to clean them up. On your Swedish cast steel anvils is is not unusual to see significant chipping along the edges of the face. This is more common on the side away from the smith or tward him if he had a striker helping him. Almost all good quality anvils eventually end up with some chipping along the edges.
Test the anvil's ring. Almost all good anvils will ring like a bell under the right conditions. First the anvil must be free to move. It can not be bolted or clamped down. There can not be anything sitting on it (not even a hardy in the hardy hole). It should be sitting upright on a hard flat surface. If you can, slip a piece of wood under the anvil. Then with a hammer give the face a little tap near the center. The hammer should have a crowned semi flat face without sharp corners. The anvil should ring and the hammer rebound with almost as much energy as you put into it. If you could not hear the ring (too much Rock & Roll), give the side of the horn or heal a tap (sideways). That should produce a clear bell like tone. If not, hit it harder. Don't be timid. This is an ANVIL you are hitting and when you are using it you will SMACK the H*** out of it! Its not proper etiquette to strike the face of someone else's anvil. They don't know if you know the difference between striking the face of an anvil with the flat of the hammer or the corner. So ask if they mind if you "ring" their anvil. I'm generaly testing anvils at auctions and don't want to atract too much attention ringing the anvil so I do it quietly.
Good hard anvils ring brightly. The larger the anvil the lower the pitch especially when struck from the side. The harder the anvil the higher the pitch. Small anvils tend to be harder than large anvils due to the inability to quickly quench a large anvil. Cast iron anvils, poorly heat treated anvils and cracked anvils do not ring. Really bad cast iron anvils have no rebound.
So, the anvil rings but looks like heck. If there are a few square inches of flat face and the horn isn't broken off buy it but pay less than $1/lb (US). IF the anvil looks great AND rings like a bell, buy it, pay what you have to get it (within reason). If the anvil looks like new, makes a dull thud when you hit it and has no rebound then let someone else have it. This is a door stop.
VALUE OF ANVILS: New anvils suitable for Blacksmithing sell for around $7/lb (US). Small used anvils in the 100 pound range have been selling for $1/lb since the 1950's. Larger anvils suitable for general shop work (150 to 250 pounds) sell for more per pound but $2 to $3/lb seems to be mormal. Considering the cost of new anvils, used anvils have been a bargain for a long time. Meanwhile there are fewer manufacturers and less new anvils sold. Old Hay-Buddens, Peter Wrights and Kolhswas are as good as or better than new and have been selling for considerably less for a long time. I do not see how this trend can last.
On the other hand, I've been given anvils (never when you need one), I've paid 25c for small anvils and $1.10/lb for a really nice 300 pound anvil at auction while bidding against other Blacksmiths!
MACHINING an ANVIL: IF you can machine the top of your new anvil it is much too soft. Most anvils will wreck carbide tooling. Anvils have the top surfaced and ground before hardening. It is possible to regrind an anvil but precision grinders large enough to do the job are very expensive on an hourly basis. Most of the time an anvil can be hand ground with an angle grinder (carefully) and a belt sander.
WELDING ANVIL CORNERS: It is best to leave the edges of your anvil alone unless it is completely useless. Preheating is only a small part of the problem. Good anvil faces are straight high carbon tool steel (no alloying). These steels are very temperature sensitive and will temper or soften at any temperature that produces temper colors. IF the area around your weld repair does not crack it will be soft. Any time repairs are to be made on an anvil face you should plan on re-heat treating the entire anvil.
WELDING ANVIL FACES: Anvils with wrought bodies and steel faces have the faces forge welded on. This means they have a continous weld the size of the face. Cast iron anvils with steel faces are made by a special foundry process where the face is placed in the mold and the hot iron poured to create a weld. This process probably included a flux coating of some type. Eagle anvils were made this way and a wrought horn was included as well.
It is reported that some cheap anvils had their faces brazed on. I would think that if a heavy plate were to be furnace brazed (like carbide inserts) that this would make a fair anvil.
Welding a plate around the edge to reface an anvil will produce an unsatifactory product as there will be little or no rebound. This is a common method of repair that is bound to lead to trouble later.
MORE on ANVIL REPAIRS: Unless your anvil is in really terrible condition you should leave it alone and work around the flaws. OR have an expert welder do the repairs.
The first problem is determining what kind of anvil you have. Many older anvils have a wrought iron bodies with a tool steel face welded on. The ones with faces less than 3/8" thick are not very good anvils OR belong in a museum. Those with a good heavy hard tool steel face are very good anvils. The problem is that you will probably damage the surounding face repairing a small spot. The face will crack or become softened in the weld area. Some anvils are solid cast steel while some cheap ones are cast iron OR cast iron with a thin steel face.
If your anvil has some mild pitting from rust or fatigue your best bet is to regrind the face with a belt sander or HD angle grinder. If using an angle grinder be sure you're darn good at making flat surfaces first! When roughness of anvil face is caused by fatigue there will be thousands of underlying microfine cracks near the surface. Extreame expansion and contraction caused by welding will open and extend these cracks causing more problems. Removing a small amount of the fatigued surface (1/32" or less) may increase the life of the anvil.
On the good cast steel Sweedish anvils your best bet is to grind as much as you need being careful not to overheat the face. Then be sure to radius the corners when finished. One Sweedish manufacturer recomended stress releiving a new anvil face with a small ball pean hammer. They recomended starting at the center and working toward the edges in a circular pattern taping the face at close intervals. They stressed avoiding the corners and to repeat the process several times. This is probably a good recomendation for any reground or resurfaced anvil face.
Many people claim success repairing an anvil face using Eutectic(tm) Hard Facing Rod. Generally this means a complete refacing. Eutectic provides procedures for preheat, application and heat treating. See your welding supplier for details. This is not a cheap repair. Somewhere, I read that a pattern of stainless steel weld beads will act as a cushion and help the transition from the low allow high carbon anvil face to the high alloy hard facing rod. I do know that stainless rod works well when welding high allow steels such as wrenches and sockets.
In the case of antique anvils with a very thin steel face on a wrought iron body it is probably best to remove the entire face before hard facing. Often these old anvil faces were pieced together from several pieces of tool steel and tend to come apart on these joints.
SO, live with it, work around it or grind it but make weld repair a last option.