Hand-Forging Steel.—In the main this does not differ materially from the same work in iron. Special care must be exercised to have the fire clear of sulphur, hence charcoal is the best fuel to use. In cases where the use of bituminous coal cannot be avoided, the fire should be blowed up for several minutes before putting in the steel, to drive off the sulphur.
Steel to be forged should not be heated to so high a degree as is employed for iron; for ordinary light work a little above a cherry-red is enough. It does not work well under a high degree of heat; and, to make amends, it can be worked much colder than iron. In fact, it is always best to hammer it with light blows until the red color of the heat has entirely disappeared, as this improves its texture by adding decidedly to the closeness of the grain.
Welding Steel.—The common method employed for welding iron to iron is often resorted to for welding steel to steel, but a great deal more care is necessary to success in the latter than in the former case. There must be much precision so far as relates to the rate of heat, as the margin for variation is extremely small. If the temperature is not high enough there will be no adhesion, of course; and if it attains to only a few degrees above what is actually necessary, the steel either “runs” and is ruined, or is ruined by going into an unworkable condition known as “burnt.” It sometimes becomes necessary to weld steel and iron together; this may be effected by the same process as that employed in welding steel to steel. None but workmen of thorough experience would be apt to succeed in either case, on the old plan of proceeding the same as in welding iron to iron.
But steel may be more easily welded than on the old plan by the employment of certain welding compositions. One of them consists of half a pound of saltpetre dissolved in half a pound of oil of vitriol, and afterwards added to two gallons of soft water. Heat the pieces to a cherry-red, then plunge them into this composition; after which proceed to reheat and weld in the usual way. At the welding the strokes of the hammer should be quick and light.
Another composition is made by pulverizing together ten parts of borax and one part of sal-ammoniac. Thoroughly melt the composition so made in an iron pot, then pour out upon some level surface to cool. When cooled grind to a fine powder. Heat the pieces of steel and sprinkle this welding powder over them; then return to the fire, and again heat up, and it is ready to go together under the hammer.
Some smiths claim to weld steel successfully by dusting over the heated pieces a powder composed of clear white sand, 2 lbs., and plaster of Paris, 1 lb.; then reheating and proceeding in the usual way.
In welding steel to iron the foregoing processes are employed the same as if both pieces were steel.
Tempering.—Heat the steel to a bright cherry-red, and plunge it at once into cold water. It will then be as hard as fire and water could make it, and too hard for anything except hardened bearings for machinery, or for some kind of implements necessary to be extremely hard, as tools for cutting glass, and the like. In this condition it is almost as brittle as glass itself, and hence would not stand for most of the uses to which tempered steel is applied. Its great degree of hardness must, therefore, be reduced to the proper standard, depending upon what it is to be used for. This is done by heating and closely observing the resulting colors as they appear upon the metal. If the piece under process is an edge-tool of considerable bulk, only the cutting-edge, and a little back of it, is plunged into the water at the hardening, the rest of the implement being left still hot. It is then held into the light and observed closely, when the different colors, indicating the different degrees of hardness, will be seen moving slowly, one after the other, down towards the edge, driven by the heat still left in the part of the metal not plunged. When the color wanted has reached the edge, the entire piece is plunged into the slack-tub, which stops further action of the heat, and establishes the required degree of hardness exactly where it is desired. But very light articles and implements cannot be tempered in this way, as they will not retain sufficient heat to drive the colors; it will be necessary to reheat them gradually in some way to make the colors move. Very light pieces, as drills and the like, are best tempered in a spirit or alcohol lamp; after having been hardened they should be held in the flame of the lamp a little back of the point or cutting-edge, which will enable the operator to note the movement of the colors. In this case his actions, so far as the colors are concerned, will be governed the same as in the other. Small articles to be tempered alike all over may be placed upon a bit of sheet-iron, after hardening, and the iron held over the fire of the forge, or directly over the flame of the lamp, until the required color has appeared, when they must be quickly plunged into the water. On large articles the colors will be often so strongly marked as to be readily seen on the surface of the metal, rough, just as it came from the hammer, but in small articles they will be somewhat faint; hence it is best to give small articles a slight polish before exposing them to heat for drawing the temper. Nine shades of color will present themselves one after the other as a piece of thoroughly-hardened steel is exposed to gradually-increasing heat. They are:
1. Very faint yellow, appearing at a temperature of 430° Fahrenheit. If slacked at this color, the piece will be very hard, having a temper admirably suited to drills for working in hard metals or hard stone.
2. Pale straw-color—450°. Still very hard, suitable for the faces of hammers and anvils.
3. Full yellow—470°. Shears and scissors.
4. Brown—490°. Gravers and turning-tools for hard metals; also percussion-lock gun tubes.
5. Brown, with purple spots—510°. Wood-working tools and most of the steel parts in a gun-lock with the exception of the springs; also knives of all sorts for cutting wood.
6. Purple—538°. Butcher-knives and other flesh-cutting implements.
7. Dark blue—550°. Tools requiring strong cutting-edges without extreme hardness, as case-knives.
8. Full blue—560°. Chopping-axes.
9. Grayish blue, verging on black—600°. Springs, saws, swords, and the like.
Various other methods of tempering steel are sometimes recommended, as with oils, tallow, lead, mercury and divers solutions; but since the matter-of-fact gunsmith will find use for none of them, it is not deemed proper to encumber this book with anything further on the subject of tempering. It might be well to state, however, that the hardest degree to which steel can be brought is secured by heating the piece to a light yellow and instantly plunging it into cold mercury.
To Restore “Burnt” Steel.—Pulverize together two parts horn or hoof filings; one part sal ammoniac; one part charcoal, and one part common soda. When thoroughly ground together, work in tallow enough to make a kind of wax or paste. Bring the damaged steel to a bright cherry-red heat, and then cover with the paste, leaving it to cool gradually. The process may be repeated several times with profit if considered necessary. While a piece of badly-burnt steel may not be entirely restored by this process, it can be much improved. Entire restoration is scarcely possible.
Annealing Steel.—Heat the steel to a cherry-red in a charcoal fire, the last thing to be done before quitting work at the forge for the day or night; then smother the fire down with a thick layer of ashes or sawdust, leaving the steel in, just as heated. Let so remain until the fire is all out, and the steel entirely cool, which will require several hours. Some smiths use a piece of gas-pipe in which to heat small steel articles for annealing, claiming that it is very advantageous. They put the piece into the pipe and heat to a cherry red, looking in occasionally to ascertain when it has attained to that temperature; then they cover the fire, pipe and all, and leave it to cool as in the other case.
To Blue Steel.—Polish the article to be blued, then place it upon a strip of sheet iron and heat slowly over a forge fire or lamp, until the desired blue color appears. Let cool, and the color will remain permanent.
To Remove Blue Color from Steel.—Immerse for a few minutes in a liquid composed of equal parts muriatic acid and oil of vitriol. Rinse in pure water and rub dry with chamois skin or some kind of soft cloth.
Tempering Knife Blades.—To heat the blades lay them in a clear charcoal fire, with the cutting edge downwards, and heat very slowly. It is not particular if the back of the blade, which is uppermost, is so very hot or not. Harden in clean luke-warm water. If many blades are to be hardened at once, lay a number in the fire and remove one at a time as they are properly heated. To temper, brighten one side on a grindstone or emery wheel so that the temper color can be seen, and lay the blades in the fire, or on an iron plate heated over the fire, with the backs down and the cutting edges uppermost. On the plate place wood ashes or fine sand to help keep the blades in proper position, and also facilitate even drawing. When the proper color is seen on the brightened portion of the cutting edge, remove and cool in cold water.
When an extra tough blade is wanted, after it is hardened, handle it so that it will not draw any lower after removing from the fire, and let it cool without putting in water.
Long blades, when they are being drawn, can be straightened, if necessary, by putting them between two pins in the anvil or pins fixed in an iron block and bending between these until straight, wetting the blade with a cloth or sponge saturated with water, when the blade is thus straightened. Surprising as it may seem, when hardened steel is being drawn, it can be bent to quite an extent, and when cooled will remain as bent. File makers straighten files in this manner. Sword blades and blades of butchers’ knives undergo the same process of manipulation to be made straight.
The Lead Bath for Tempering.—Among the many secrets of tempering is the employment of the lead bath, which is simply a quantity of molten lead, contained in a suitable receptacle and kept hot over a fire. The uses of this bath are many. For instance, if it be desired to heat an article that is thick in one portion and thin in another, every one who has had experience in such work knows how difficult it is to heat the thick portion without overheating the thin part. If the lead bath be made and kept at a red heat, no matter how thick the article may be, provided sufficient time be given, both the thick and thin parts will be evenly and equally heated, and at the same time get no hotter than the bath in which they are immersed.
For heating thin cutting blades, springs, surgical instruments, softening the tangs of tools, etc., this bath is unequaled.
If a portion of an article be required to be left soft, as the end of a spring that is to be bent or riveted, the entire may be tempered, and the end to be soft may be safely drawn in the lead bath to the lowest point that steel can be annealed without disturbing in the least the temper of the part not plunged in the bath. Springs, or articles made of spring brass, may be treated in the same manner. One great advantage in using the lead bath is that there is no risk of breakage or shrinkage of the metal at the water line, as is often the case when tempered by the method of heating and chilling in cold water.
As lead slowly oxidizes at a red heat, two methods may be used to prevent it. One is to cover the surface of the lead with a layer of fine charcoal or even wood ashes. Another and a better plan, when the work will admit of its use, is to float on the top of the lead a thin iron plate, fitting the vessel in which the lead is contained, but having a hole in the centre or on one side, as most convenient, and large enough to readily admit the articles to be tempered or softened.
Test for Good Steel.—Break the bar of steel and observe the grain, which in good steel should be fine and present a silvery look, with sometimes an exfoliated or leaf-like appearance. One of the best tests of steel is to make a cold chisel from the bar to be tested, and when carefully tempered (be careful not to overheat), try it upon a piece of wrought iron bar. The blows given will pretty correctly tell its tenacity and capability of holding temper. Remember the temper you gave it, and if it proves tough and serviceable, take this temper as a guide and temper other tools in like manner. Inferior steel is easily broken, and the fracture presents a dull, even appearance, which may very appropriately be termed a lifeless look.
Etching on Steel.—Make an etching solution by pulverizing together sulphate of copper, one ounce; alum, one-quarter ounce, and common salt, one-half teaspoonful. Add one gill strong vinegar and twenty drops nitric acid. Stir till thoroughly dissolved. Polish up the metal to be etched, and then cover its polished surface with a thin coating of bees-wax. This can be accomplished with neatness by simply heating the metal till the wax flows evenly over its surface. Now draw upon the wax, cutting cleanly through to the steel the figure you wish to etch; then cover the figure so prepared with the etching solution, and let stand for a short time, depending upon the depth of cut desired. Finally rinse off with clear water, and then remove the bees-wax. It will be found that the solution has cut into the surface of the steel wherever exposed, leaving untouched all parts covered by the wax.
Very good etching can be done by applying, on the foregoing plan, nitric acid alone. Etching offers a good method of cutting a man’s name on his gun or pistol. It works on silver or brass the same.