The Working of Steel Part 23

Some very adverse criticism may be heard on this point, but experience has proved that such tools will stand up very nicely and be perfectly free from scales or pipes. Where packing cannot be done, milling cutters, and tools to be hardened all over, can be placed in m.u.f.fled furnace, brought to 2,220 and quenched in oil. All such tools, however, must be preheated slowly to 1,400 to 1,500 then placed in a high-speed furnace and brought up quickly. Do not soak high-speed steel at high heats. Quench in oil.

We must bear in mind that the heating furnace is likely to expand tools, therefore provision must be made to leave extra stock to take care of such expansion. Tools with shanks such as counter bores, taps, reamers, drills, etc., should be heated no further than they are wanted hard, and quench in oil. If a forge is not at hand and heating must be done, use a m.u.f.fle furnace and cover small shanks with a paste from fire clay or ground asbestos. Hollow mills, spring threading dies, and large cutting tools with small shanks should have the holes thoroughly packed or covered with asbestos cement as far as they are wanted soft.

CUTTING-OFF STEEL FROM BAR

To cut a piece from an annealed bar, cut off with a hack saw, milling cutter or circular saw. Cut clear through the bar; do not nick or break. To cut a piece from an unannealed bar, cut right off with an abrasive saw; do not nick or break. If of large cross-section, cut off hot with a chisel by first slowly and uniformly heating the bar, at the point to be cut, to a good lemon heat, 1,800 to 1,850F. and cut right off while hot; do not nick or break. Allow the tool length and bar to cool before reheating for forging.

LATHE AND PLANER TOOLS

FORGING.--Gently warm the steel to remove any chill, is particularly desirable in the winter, then heat slowly and carefully to a scaling heat, that is a lemon heat (1,800 to 2,000F.), and forge uniformly.

Reheat the tool for further forging directly the steel begins to stiffen under the hammer. Under no circ.u.mstances forge the steel when the temperature falls below a dark lemon to an orange color about 1,700F. Reheat as often as is necessary to finish forging the tool to shape. Allow the tool to cool after forging by burying the tool in dry ashes or lime. Do not place on the damp ground or in a draught of air.

The heating for forging should be done preferably in a pipe or m.u.f.fle furnace but if this is not convenient use a good clean fire with plenty of fuel between the blast pipe and the tool. Never allow the tool to soak after the desired forging heat has been reached. Do not heat the tool further back than is necessary to shape the tool, but give the tool sufficient heat. See that the back of the tool is flatly dressed to provide proper support under the nose of the tool.

HARDENING HIGH-SPEED STEEL.--Slowly reheat the cutting edge of the tool to a cherry red, 1,400F., then force the blast so as to raise the temperature quickly to a full white heat, 2,200 to 2,250F., that is, until the tool starts to sweat at the cutting face. Cool the point of the tool in a dry air blast or preferably in oil, further cool in oil keeping the tool moving until the tool has become black hot.

To remove hardening strains reheat the tool to from 500 to 1,100F.

Cool in oil or atmosphere. This second heat treatment adds to the toughness of the tool and therefore to its life.

GRINDING TOOLS.--Grind tools to remove all scale. Use a quick-cutting, dry, abrasive wheel. If using a wet wheel, be sure to use plenty of water. Do not under any circ.u.mstances force the tool against the wheel so as to draw the color, as this is likely to set up checks on the surface of the tool to its detriment.

FOR MILLING CUTTERS AND FORMED TOOLS

FORGING.--Forge as before.--ANNEALING.--Place the steel in a pipe, box or m.u.f.fle. Arrange the steel so as to allow at least 1 in.

of packing, consisting of dry powder ashes, powdered charcoal, mica, etc., between the pieces and the walls of the box or pipe.

If using a pipe close the ends. Heat slowly and uniformly to a cherry red, 1,375 to 1,450F. according to size. Hold the steel at this temperature until the heat has thoroughly saturated through the metal, then allow the m.u.f.fle box and tools to cool very slowly in a dying furnace or remove the m.u.f.fle with its charge and bury in hot ashes or lime. The slower the cooling the softer the steel.

The heating requires from 2 to 10 hr. depending upon the size of the piece.

HARDENING AND TEMPERING.--It is preferable to use two furnaces when hardening milling cutters and special shape tools. One furnace should be maintained at a uniform temperature from 1,375 to 1,450F.

while the other should be maintained at about 2,250F. Keep the tool to be hardened in the low temperature furnace until the tool has attained the full heat of this furnace. A short time should be allowed so as to be a.s.sured that the center of the tool is as hot as the outside. Then quickly remove the tool from this preheating furnace to the full heat furnace. Keep the tool in this furnace only as long as is necessary for the tool to attain the full temperature of this furnace. Then quickly remove and quench in oil or in a dry air blast. Remove before the tool is entirely cold and draw the temper in an oil bath by raising the temperature of the oil to from 500 to 750F. and allow this tool to remain, at this temperature, in the bath for at least 30 min., insuring uniformity of temper; then cool in the bath, atmosphere or oil.

If higher drawing temperatures are desired than those possible with oil, a salt bath can be used. A very excellent bath is made by mixing two parts by weight of crude pota.s.sium nitrate and three parts crude sodium nitrate. These will melt at about 450F. and can be used up to 1,000F. Before heating the steel in the salt bath, slowly preheat, preferably in oil. Reheating the hardened high-speed steel to 1,000F. will materially increase the life of lathe tools, but milling and form cutters, taps, dies, etc., should not be reheated higher than 500 to 650F., unless extreme hardness is required, when 1,100 to 1,000F., will give the hardest edge.

INSTRUCTIONS FOR WORKING HIGH-SPEED STEEL

Owing to the wide variations in the composition of high-speed steels by various makers, it is always advisable to follow the directions of each when using his brand of steel. In the absence of specific directions the following general suggestions from several makers will be found helpful.

The Ludlum Steel Company recommend the following:

CUTTING-OFF.--To cut a piece from an annealed bar, cut off with a hack saw, milling cutter or circular saw. Cut clear through the bar; do not nick or break. To cut a piece from an unannealed bar, cut right off with an abrasive saw; do not nick or break. If of large cross-section, cut off hot with a chisel by first slowly and uniformly heating the bar, at the point to be cut, to a good lemon heat, 1,800-1,850F. and cut right off while hot; do not nick or break. Allow the tool length and bar to cool before reheating for forging.

LATHE AND PLANER TOOLS

TO FORGE.--Gently warm the steel to remove any chill is particularly desirable in the winter. Then heat slowly and carefully to a scaling heat, that is a lemon heat (1,800-2,000F.), and forge uniformly.

Reheat the tool for further forging directly the steel begins to stiffen under the hammer. Under no circ.u.mstances forge the steel when the temperature falls below a dark lemon to an orange color: about 1,700F. Reheat as often as is necessary to finish forging the tool to shape. Allow the tool to cool after forging by burying the tool in dry ashes or lime. Do not place on the damp ground or in a draught of air.

The heating for forging should be done preferably in a pipe or m.u.f.fle furnace, but if this is not convenient use a good clean fire with plenty of fuel between the blast pipe and the tool. Never allow the tool to soak after the desired forging heat has been reached. Do not heat the tool further back than is necessary to shape the tool, but give the tool sufficient heat. See that the back of the tool is flatly dressed to provide proper support under the nose of the tool.

HARDENING.--Slowly reheat the cutting edge of the tool to a cherry red, 1,400F., then force the blast so as to raise the temperature quickly to a full white heat, 2,200-2,250F., that is, until the tool starts to sweat at the cutting face. Cool the point of the tool in a dry air blast or preferably in oil; further cool in oil, keeping the tool moving until the tool has become black hot.

To remove hardening strains reheat the tool to from 500 to 1,100F.

Cool in oil or atmosphere. This second heat treatment adds to the toughness of the tool and therefore to its life.

GRINDING.--Grind tools to remove all scale. Use a quick cutting, dry, abrasive wheel. If using a wet wheel, be sure to use plenty of water. Do not under any circ.u.mstances force the tool against the wheel so as to draw the color, as this is likely to set up checks on the surface of the tool to its detriment.

The Firth-Sterling Steel Company say:

INSTEAD OF PRINTING ANY RULES ON THE HARDENING AND TEMPERING OF FIRTH-STERLING STEELS WE WISH TO SAY TO OUR CUSTOMERS: TRUST THE STEEL TO THE SKILL AND THE JUDGEMENT OF YOUR TOOLSMITH AND TOOL TEMPERER.

The steel workers of today know by personal experience and by inheritance all the standard rules and theories on forging, hardening and tempering of all fine tool steels. They know the importance of slow, uniform heating, and the danger of overheating some steels, and underheating others.

The tempering of tools and dies is a science taught by heat, muscle and brains.

The tool temperer is the man to hold responsible for results. The tempering of tools has been his life work. He may find suggestions on the following pages interesting, but we are always ready to trust the treatment of our steels to the experienced man at the fire.

HEAT TREATMENT OF LATHE, PLANER AND SIMILAR TOOLS

FIRE.--For these tools a good fire is one made of hard foundry c.o.ke, broken in small pieces, in an ordinary blacksmith forge with a few bricks laid over the top to form a hollow fire. The bricks should be thoroughly heated before tools are heated. Hard coal may be used very successfully in place of hard c.o.ke and will give a higher heat. It is very easy to give Blue Chip the proper heat if care is used in making up the fire.

FORGING.--Heat slowly and uniformly to a good forging heat. Do not hammer the steel after it cools below a bright red. Avoid as much as possible heating the body of the tool, so as to retain the natural toughness in the neck of the tool.

HARDENING.--Heat the point of the tool to an extreme white heat (about 2,200F.) until the flux runs. This heat should be the highest possible short of melting the point. Care should be taken to confine the heat as near to the point as possible so as to leave the annealing and consequent toughness in the neck of the tool and where the tool is held in the tool post.

COOL in an air blast, the open air or in oil, depending upon the tools or the work they are to do.

For roughing tools temper need not be drawn except for work where the edge tends to crumble on account of being too hard.

For finis.h.i.+ng tools draw the temper to suit the purpose for which they are to be used.

GRIND thoroughly on dry wheel (or wet wheel if care is used to prevent checking).

HEAT TREATMENT OF MILLING CUTTERS, DRILLS, REAMERS, ETC.

THE FIRE.--Gas and electric furnaces designed for high heats are now made for treating high-speed steels. We recommend them for treating all kinds of Blue Chip tools and particularly the above cla.s.s. After tools reach a yellow heat in the forge fire they must not be allowed to touch the fuel or come in contact with the blast or surrounding air.

HEATING.--Tools of this kind should be heated to a mellow white heat, or as hot as possible without injuring the cutting edges (2,000 to 2,200F.). For most work the higher the heat the better the tool. Where furnaces are used, we recommend preheating the tools to a red heat in one furnace before putting them in a white hot furnace.

COOLING.--We recommend quenching all of the above tools in oil when taken from the fire. We have found fish oil, cottonseed oil, Houghton's No. 2 soluble oil and linseed oil satisfactory. The high heat is the important thing in hardening Blue Chip tools.

If a white hot tool is allowed to cool in the open air it will be hard, but the air scales the tool.

DRAWING THE TEMPER.--Tools of this cla.s.s should be drawn considerably more than water-hardening steel for the same purpose.

HEAT TREATMENT OF PUNCHES AND DIES, SHEARS, TAPS, ETC.

HEATING.--The degree to which tools of the above cla.s.ses should be heated depends upon the shape, size and use for which they are intended. Generally, they should not be heated to quite as high a heat as lathe tools or milling cutters. They should have a high heat, but not enough to make the flux run on the steel (by pyrometer 1,900 to 2,100F.).

COOLING.--Depending on the tools, some should be dipped in oil all over, some only part way, and others allowed to cool down in the air naturally, or under air blast. In cooling, the toughness is retained by allowing some parts to cool slowly and quenching parts that should be hard.