Frederick W. Taylor
(20 Mar 1856 - 21 Mar 1915)
High Speed Steel.
by H. W. RUSHMER.
from American Machinist (1903).
[p.1270] It is not my intention to present tables showing the high speeds, heavy feeds, or the amount of metal removed from certain pieces in a given time with this high-duty steel, but rather to state a few facts that have been gleaned from daily practice which may be helpful to some in gaining a higher degree of efficiency from their tools. These high records are usually tests made under favorable conditions, and are rarely maintained any length of time in daily practice. It is sufficient to say that the gains are so large in using this steel that it would show poor business tact if we did not take full advantage of it regardless of its present high price.
In 1901 patents were granted to Messrs. Taylor and White for a brand of steels alloyed with tungsten, molybdenum and chromium in certain proportions, also a special heat treatment for the same. The edge-holding power of tools made from this steel and given the special heat treatment exceeded all previous attainments to such an extent that it required the reconstruction of certain machine tools to use the steel up to its limit.
Mr. Taylor was superintendent of the Bethlehem Steel Company, and he was testing the relative merits of the standard brands of self-hardening steel when one brand failed to give results as represented.
The agent for the steel being appraised of the failure, determined to investigate the cause, and readily discovered that the heat treatments were much lower than he had recommended them to use.
By complying with the instructions the tools were forged and quenched at a much higher range of heats, which resulted in a marked increase in the efficiency of the tools. Encouraged by these results he tried other brands by heating them to this same range, but finally carried the heats to that point where the steel softens or crumbles (between 1,900 degrees and 2,000 degrees Fahr.) if touched with a rod. As all the self-hardening brands vary considerable in composition, so did his final results, but the increase in efficiency of some brands was surprising. He concluded to push his investigations a little further and see if a steel could be made that would give better results than the self-hardening when given the high-heat treatment. By enlisting the assistance of Mr. White, a chemist, they eventually produced the remarkable steel that bears their names.
It is with interest that we note the rapid trend of events; it is a trifle over two years since this remarkable steel was patented, and to-day it is scarcely heard of. Spurred on by the successes of this new rival, the leading steelmakers were soon upon its heels with a superior steel, willing to sell to all, requiring no expensive shop right to use it or the signing of a binding contract, consequently it was forced to retire before it was generally introduced.
It was well known that if tools for planers, slotters, etc., were made from the self-hardening steels of the past (Taylor-White included) there was a decided tendency of the cutting edge to crumble, especially when cutting hard, tough materials, thereby leaving a rough finish. The construction of the above-mentioned machines is such that during the time they are retrieving, the cutting edges of the tools are required to drag back over the surface just cut, then the machine being reversed, the tools suddenly enter the work at full speed and full depth cut.
Therefore it must be obvious that tools working under these conditions, and required to maintain a good cutting edge, must be of the highest quality, and not the least friable. It is under these trying conditions that this new steel has easily demonstrated superiority over those of the past. Another advance is the manufacture of twist drills from this material; the results are very encouraging for a better drill in the near future. It is true they are not equal to the carbon steel drills in strength; there is a tendency to split through the center, but if the workman exercises good judgment there will be very little trouble from this direction. Taps, milling cutters, reamers, etc., are being made and used with some success, but, like all things in their incipiency, there are some failures. There are good reasons for believing that in strengthening the teeth, improving the methods of hardening and regulating speeds and feeds to suit the new conditions, they will be a decided success. It will be observed that the cutting edge of tools made from this steel (or in fact any of the alloyed steels) soon becomes slightly rounded, and in this condition they appear to render their best service. This peculiarity makes it unsuitable for finishing tools where keen and enduring edges are required; for instance, a tool for chasing a standard tap must cut perfectly smooth and accurate the full length of the tap; if not, the tap would be worthless. This is one of the reasons why the alloyed steels are a failure for edge tools.
The process of annealing can be easily accomplished by any of the methods employed with the self-hardening brands. A sure and safe method is to pack the steel in an iron box or a piece of pipe and surrounding the steel with powdered charcoal, then well-sealing the openings with fireclay. The box or pipe is placed in the furnace, heated to a bright cherry red color for several hours, then permitted to cool down slowly; the slower the process of cooling the softer will be the steel. If properly annealed it will machine as easily as tool steel. It has superior forging properties when compared with the self-hardening steels of the past, which allows it to be forged into the difficult shapes. Furthermore, this has been quite an advantage to the steelmakers in producing a steel almost free from seams. In order to forge it successfully, it should be heated to a good lemon-color heat, taking care to heat it slowly and thoroughly in a well-burnt coke or coal fire. If heated properly, it will be in a perfect plastic condition and the steel will flow readily under the hammer. Remember it cools down much quicker than carbon steel, and when slightly cooled it becomes hard and unyielding; far more can be accomplished in a given time by frequent heating and only working it in a perfect plastic condition; furthermore, if this is observed, strains and ruptures will be avoided. It is absolutely necessary that the base of all tools should be perfectly straight, and the attention should be directed to this important part before the tools are finished. By heeding this caution it will save the loss of many valuable tools, besides the tools can be held more firmly and rigidly in the toolpost. After forging the tool it is advisable to lay it down and allow it to grow cold, then re-heating for hardening.
Probably the most interesting and important part in manipulating this new steel is the process of tempering it. To temper the steel properly it must be heated to a fusing or welding heat; the conditions required are about the same as for welding tool steel. The methods used in applying the heat are very important, regardless of the advice to the contrary. To obtain satisfactory results, it is best to build a covered fire with a liberal amount of crushed coke over the tuyere, thus avoiding an oxidizing fire. The blast must be used rather sparingly, for if time is not allowed for the steel to conduct the heat properly the point of the tool may burn off or the coke over the tuyere will burn down to such an extent that it will allow the blast to impinge too strongly against the steel, and thereby prevent the proper conditions from taking place. If the steel is heated too quickly and to the highest possible temperature, the fractured piece will show a dry, brittle, lifeless structure, proving that deterioration has taken place, consequently there will be a corresponding loss in edge-holding power. When the steel is carefully heated in a fire, as above mentioned, and a white heat has been attained, a faint fluxing will be noted; as the temperature increases innumerable minute bubbles will be observed; by prolonging the treatment the bubbles become larger and less numerous; when carried to the extreme the steel will finally soften and melt. This part of the process, for the want of a better term, has been called “sweating” from which it somewhat resembles.
The “sweating” properties are more pronounced in some brands than in others, [p.1271] besides some steelmakers recommend a longer sweating than others, but if the smith is guided by his trained judgment and observation, he will soon learn to regulate the sweating to meet the requirements. Although not generally known, these sweating properties are inherent in all steel, and some of the old self-hardening brands can be improved considerably by this treatment, providing the sweating is not carried to the extreme. The toolsmith, to be successful in his business, must have a well-trained eye; he is required to work in all degrees of light and at times it is with difficulty that he locates the proper hardening heat. The locating of these high-sweating heats will place a greater strain upon his eyes, and will make his position more difficult and important than ever.
After sweating, the tools are quenched in oil, the compressed-air jet or a strong blast. There are other methods, but they are not used to any extent. In some cases it is advisable to draw the temper, and this can be accomplished by cooling the point and drawing in the usual way, or they can be cooled in their entirety and then drawing the points by conducting the heat from the other end of the tools, and then permitting them to cool down slowly. In order to harden taps, mills, reamers, etc., successfully, they must be heated in a lead bath, and a graphite crucible is absolutely necessary, for the lead must be heated to a white heat or to the highest possible limit. The lead should be covered with powdered charcoal, to prevent it from wasting or oxidizing.
My experience with this new branch of the art is somewhat limited, but I readily discovered that when a smith’s forge is used, caution must be exercised in heating even the best graphite crucibles to this high temperature. If the blast is too strong, the crucible will melt away in spots before the lead is hot enough to meet the requirements. The tools should be previously heated in a furnace to a bright red heat, then placed in the white hot lead. After the proper heat is obtained, the tools are submerged in the oil, and when cold they are polished and drawn the same as carbon steel tools.
Some of these steels refine equally as well as carbon steel, if the sweating is not carried to the extreme, and it is necessary that tools like milling cutters, reamers, etc., be hardened from this refining heat. We have been led to believe that the steel cannot be injured by overheating, but when we see a number of tools made from the same bar of steel, and some of them giving extraordinary results and the others a complete failure, it is quite evident that the heat treatment is a point that needs the closest attention.
There are special furnaces upon the market for sweating this steel, and it is claimed they are giving good satisfaction. It will be noticed that in grinding any of the alloyed tool steels, the emery wheels become glazed very quickly. It is believed that the alloy tungsten is responsible for this sudden glazing; the little grains of emery from which the wheels are composed become dull and then coated with the tungsten; hence, the glazing. The tools are often ground upon these glazed wheels, and this inattention has caused the loss of many valuable tools, and I dare say that one-half of the tools ground on these wheels are injured to a greater or less extent. As a rule, the workman takes no account of this glazing and bears with greater pressure as the wheel fails to cut, thereby causing an intense friction; this creates unequal expansion and contraction, resulting in numerous surface checks.
This can be avoided by replacing the wheels with others that are softer and coarser, then dressing them as soon as they show the least indication of glazing, and the workman limiting the pressure according to the cutting power of the wheels. The sparks emanating from the majority of these high-speed steels when ground upon the emery wheel are of a bright orange color. The sparks emanating from the old self-hardening when ground are dark red in color. The sparks being much lighter from the high-speed steel is due to the presence of molybdenum and chromium. In one or two brands I noted the sparks were very light, and resembled the sparks emanating from machinery steel.