The Working of Steel Part 24

DRAWING THE TEMPER.--As in cooling, some parts of these tools will require more drawing than others, but, on the whole, they must be drawn more than water hardening tools for the same purpose or to about 500F. all over, so that a good file will just "touch"

the cutting or working parts.

BARIUM CHLORIDE PROCESS.--This is a process developed for treating certain cla.s.ses of tools, such as taps, forming tools, etc. It is being successfully used in many large plants. Briefly the treatment is as follows:

In this treatment the tools are first preheated to a red heat, but small tools may be immersed without preheating. The barium chloride bath is kept at a temperature of from 2,000 to 2,100F., and tools are held in it long enough to reach the same temperature.

They are then dipped in oil. The barium chloride which adheres to the tools is brushed off, leaving the tools as dean as before heating.

A CHROMIUM-COBALT STEEL

The Latrobe Steel Company make a high-speed steel without tungsten, its red-hardness properties depending on chromium and cobalt instead of tungsten. It is known as P. R. K-33 steel. It does not require the high temperature of the tungsten steels, hardening at 1,830 to 1,850F. instead of 2,200 or even higher, as with the tungsten.

This steel is forged at 1,900 to 2,000F. and must not be worked at a lower temperature than 1,600F. It requires soaking in the fire more than the tungsten steels. It can be normalized by heating slowly and thoroughly to 1,475F., holding this for from 10 to 20 min. according to the size of the piece and cooling in the open air, protected from drafts.

A peculiarity of this steel is that it becomes non-magnetic at or above 1,960F. and the magnetic quality is not restored by cooling.

Normalizing as above, however, restores the magnetic qualities. This enables the user to detect any tools which have been overheated, with a horseshoe magnet.

It is sometimes advantageous to dip tools, before heating for hardening, in ordinary fuel or quenching oil. The oil leaves a thin film of carbon which tends to prevent decarbonization, giving a very hard surface.

For other makes of high-speed steel used in lathe and planer tools the makers recommend that the tools be cut from the bar with a hack saw or else heated and cut with a chisel. The heating should be very slow until the steel reaches a red after which it can be heated more rapidly and should only be forged at a high heat. It can be forged at very high heats but care should be taken not to forge at a low heat. The heating should be uniform and penetrate clear to the center of the bar before forging is begun. Reheat as often as necessary to forge at the proper heat.

After forging cool in lime before attempting to harden. Do not attempt to harden with the forging heat as was sometimes done with the carbon tools.

For hardening forged tools, heat slowly up to a bright red and then rapidly until the point of the tool is almost at a melting heat. Cool in a blast of cold, dry air. For large sizes of steel, cool in linseed oil or in fish oil as is most convenient. If the tools are to be used for finis.h.i.+ng cuts heat to a bright yellow and quench in oil. Grind for use on a sand wheel or grindstone in preference to an emery or an artificial abrasive wheel.

For hardening milling and similar cutters, preheat to a bright red, place the cutter on a round bar of suitable size, and revolve it quickly over a very hot fire. Heat as high as possible without melting the points of the teeth and cool in a cold blast of dry air or in fish oil.

Light fragile cutters, twist drills, taps and formed cutters may be heated almost white and then dipped in fish oil for hardening.

Where possible it is better to give an even higher heat and cool in the blast of cold, dry air as previously recommended.

SUGGESTIONS FOR HANDLING HIGH-SPEED STEELS

The following suggestions for handling high-speed steels are given by a maker whose steel is probably typical of a number of different makes, so that they will be found useful in other cases as well.

These include hints as to forging as well as hardening, together with a list of "dont's" which are often very useful. This applies to forging, hardening of lathe, slotting, planing and all similar tools.

[Ill.u.s.tration: FIG. 84.--All-steel, 5/8 in. square, 1/2 X 1 in., and larger is usually mild finished, and can be cut in a hack saw.

If cut off hot, be sure to heat the b.u.t.t end slowly and thoroughly in a clean fire. Rapid and insufficient heating invariably cracks the steel. If you want to stamp the end with the name of the steel, it is necessary that this is done at a good high orange color heat, as it is otherwise apt to split the steel. (Take your time, do not hurry.)]

HARDENING HIGH-SPEED STEEL

In forging use c.o.ke for fuel in the forge. Heat steel slowly and thoroughly to a lemon heat. Do not forge at a lower heat. Do not let the steel cool below a bright cherry red while forging. After the tool is dressed, reheat to forging heat to remove the forging strain, and lay on the floor until cold. Then have the tool rough ground on a dry emery wheel.

[Ill.u.s.tration: FIG. 85.--Be sure to have a full yellow heat at the dotted line. Remember this is a boring mill tool and will stand out in the tool-post, and if you do not have a high thorough lemon heat, your tool will snap off at the dotted line. (Ninety-five per cent of all tools which break, have been forged at too low a heat or at a heat not thorough to the center.)]

[Ill.u.s.tration: FIG. 86.--Keep your high lemon forging heat up.

If you forge under a steam hammer, take light blows. Do not jam your tool into shape. Put frequently back into the fire. Never let the high lemon color go down and beyond the dotted line.]

For built-up and bent tools special care should be taken that the forging heat does not go below a bright cherry. For tools 3/4 by 1-1/2 or larger where there is a big strain in forging, such as bending at angles of about 45 deg. and building the tools up, they should be heated to at least 1,700F. Slowly and without much blast.

For a 3/4 by 1-1/2 tool it should take about 10 min. with the correct blast in a c.o.ke fire. Larger tools in proportion. They can then be bent readily, but no attempt should be made to forge the steel further without reheating to maintain the bright cherry red. This is essential, as otherwise the tools crack in hardening or while in use.

[Ill.u.s.tration: FIG. 87.--Be sure that the tool is absolutely straight at the bottom, so as to lie flat in the tool-post.]

[Ill.u.s.tration: FIG. 88.--This is the finished forged tool, and let this grow cold by itself, the slower the better. It is well to cool the tool slowly in hot ashes, to remove all forging strain.

You can now grind the tool dry on a sharp emery wheel. The more you now finish the tool in grinding, the less there is to come off after hardening.]

In hardening place the tool in a c.o.ke fire (hollow fire if possible) with a slow blast and heat gradually up to a white welding heat on the nose of the tool. Then dip the white hot part only into thin oil or hold in a strong cold air blast. When hardening in oil do not hold the tool in one place but keep it moving so that it cools as quickly as possible. It is not necessary to draw the temper after hardening these tools.

[Ill.u.s.tration: FIG. 89.--This tool is ground, ready for hardening.

Never harden from the forging heat.]

[Ill.u.s.tration: FIG. 90.--Heat the nose of the tool only up to dotted line, very slowly and thoroughly to an absolutely white welding heat, so that it shows a trifle fused around the edges, and be very sure that this fusing has gone thoroughly through the nose, otherwise the fusing effect will be taken off after the second grinding. Note the difference of the nose between this and Fig. 86.]

[Ill.u.s.tration: FIG. 91.--Shows unnecessary roasting and drossing.

Such hardening requires a great amount of grinding and is not good.

After hardening grind carefully on a wet emery wheel, and be sure that the wheel is sharp with a plentiful supply of water. Do not force the grinding, otherwise the cold water striking the steel heated up by friction, will crack the nose. Be sure that the grinding wheel is sharp.]

In grinding all tools should be ground as lightly as possible on a soft wet sandstone or on a wet emery wheel, and care should be taken not to create any surface cracks, which are invariably the result of grinding too forcibly. The foregoing ill.u.s.trations, Figs.

84 to 91, with their captions, will be found helpful.

Special points of caution to be observed when hardening high-speed steel.

DON'T use a green coal fire; use c.o.ke, or build a hollow fire.

DON'T have the bed of the fire free from coal.

DON'T hurry the heating for forging. The heating has to be done very slowly and the forging heat has to be kept very high (a full lemon color) heat and the tool has to be continually brought back into the fire to keep the high heat up. When customers complain about seams and cracks, in 9 cases out of 10, this has been caused by too low a forging heat, and when the blacksmith complains about tools cracking, it is necessary to read this paragraph to him.

DON'T try to jam the tool into shape under a steam hammer with one or two blows; take easy blows and keep the heat high.

DON'T have the tool curved at the bottom; it must lie perfectly flat in the tool post.

DON'T harden from your forging heat; let the tool grow cold or fairly cold. After forging you can rough grind the tool dry, but not too forcibly.

DON'T, for hardening, get more than the nose white hot.

DON'T get the white heat on the surface only.

DON'T hurry your heating for hardening; let the heat soak thoroughly through the nose of the tool.

DON'T melt the nose of the tool.

DON'T, as a rule, dip the nose into water; this should be done only for extremely hard material. It is dangerous to put the nose into water for fear of cracking and when you do put the nose into water put just 1/2 in. only of the extreme white hot part into the water and don't keep it too long in the water; just a few seconds, and then harden in oil. We do not recommend water hardening.

DON'T grind too forcibly.

DON'T grind dry after hardening.

DON'T discolor the steel in grinding.

DON'T give too much clearance on tools for cutting cast iron.