Tools requiring the highest accuracy can, when made from K.9 steel, be hardened and tempered to practically any extent without the least danger of variation in size or shape. In consequence this steel is recommended for dies, stay-taps, delicate broaches, milling-cutters, plugs, gauges, circular-cutters, fine press-tools and master-tools, in all instances where price or the less exacting nature of the work prohibit the use of more expensive steels. A special application, particularly successful, is for the slender hollow nut-punches used for cold nut-production.

Treatment of K.9 Tool Steel.- A few remarks on the subject of oil- and water-hardening will clear away misconceptions.

Oils in general quench slower than either water or solutions of brine. On the other hand, their rate of cooling is more constant at higher temperatures. Water is quicker in cooling the steel, but for this very reason it increases the internal strains set up in the process. There is always a danger, therefore, that thin or complicated articles will warp or vary under heat-treatment, while larger sections may crack. Water-hardening can, of course, be used fearlessly for medium-carbon tool-steels, and for small and comparatively simple sections of the higher - carbon steels.

Oil-hardening does not, as has been erroneously suggested, affect the cutting-powers of the tool, and it is recommended, whenever conditions permit, for hardening those tools in which distortion would be especially troublesome.

Treatment instructions for K.9 oil-hardening tool-steel are :-

Heat slowly and thoroughly to cherry-red heat, say, 780°-800° C. (1436°-1472° F.). Quench in oil. For threading-dies, stamping-dies, stay-taps, etc., temper to a straw colour. For punches, drills, cutting-dies, etc., temper to a dark-straw colour.

In tempering this steel remember that if the temper is let down from a light straw to a dark straw, or from a dark straw to a brown-purple, there is very little loss of hardness but a considerable gain in toughness.

For hollow cold nut punches, heat 760°-775°C. (1400°- 1425° P.). Cool in warm oil, sperm oil is the best for tool-steel quenching. Draw temper to 245° C. (470° F.) dark straw, or to suit specific condition.

For Re-Annealing When Desired

Anneal at 730° C. and allow the steel to cool slowly. It must be remembered that K.9 steel is designed to possess oil-hardening properties, and on account of its composition, to get quite the same degree of softness as in ordinary cast steel is not possible. But if it is correctly annealed, there should be no difficulty in obtaining a Brinell reading of 4.0-4.2 rn/m dia., indicating a steel which can readily be machined.

Maxnap Steel (Label : Yellow On Brown)

This special steel is unlike the steels already discussed in that its economical use is limited to a certain class of tools. It is a selected steel for a specific purpose containing a certain percentage of alloying elements. These give it a finer and denser structure, increase its durability, give it greater hardness without greatly raising the brittleness, and also increase the steel's resistance to loss of temper through heating. It is therefore to be recommended for rivet snaps used in connection with pneumatic hammers. Rapid blows tend to cause fatigue in steel, resulting in an eventual fracture, the toughness of this steel resists fatigue, and its hardness maintains its efficiency.

Treatment Of Maxnap Steel

This steel is supplied in the softened condition.

There appears to be some variation in the methods adopted for hardening snaps in various engineering shops, but the methods recommended by Edgar Allen & Co., Ltd., are embodied in the following suggestions :

Heat the cup for a distance of 1/2in. deep in a blacksmith's fire to a temperature of 850° C. (1570° F.) which is a bright cherry-red colour, and quench in water holding the cup uppermost to avoid a steam pocket forming in the recess : keep in water until cold. Another method of quenching which gives satisfactorv results is to hold the cup under a stream of water, allowing the water to run into the recess.

The shank should then be heated for a distance of 1/2in. to 850° C. and quenched in water.

It is imperative when hardening Rivet Snaps to take special precautions to avoid hardening the radius where the shank joins the head, as this portion should be kept soft and tough to avoid breakage in service.

For Re-Annealing When Desired

Anneal at 730° C. Heat up to and thoroughly soak at this temperature.

Messrs. Edgar Allen in their notes on Air Craft Steels say, " The properties of a steel of any given percentage of carbon can be profoundly altered by the addition of other elements which itensify or otherwise change the effect of the carbon dissolved in the molten iron at the outset. For example :

A plain 0-30 per cent. Carbon Steel has a tensile strength of 28/30 tons per square inch.

A Steel with 0-30 per cent. Carbon and 3-50 per cent. Nickel has a tensile strength of 35/38 tons per square inch.

A Steel with 0-30 per cent. Carbon, 3-50 per cent. Nickel, and 0-75 per cent. Chrome has a tensile strength of 50/55 tons per square inch.

Moreover, each steel is capable of playing many parts, much depending on treatments. The steel is first quenched at a fairly high temperature, and afterwards reheated to a specified lower temperature, and then allowed to cool. On the thermal degree to which this reheating is carried depends the final characteristics of the steel A high reheating gives lower tensile strength but greater toughness, and a low reheating greater strength, with some loss of toughness. Alloy steels are extremely susceptible to such treatments, and by suitable variations can be made to acquire a remarkable variety of characters. This places at the disposal of the user a corresponding rich selection of steels, made from one original material. As an example, Allen's Nickel Chrome Steel when tempered at 410° C. has a tensile strain of 86 tons per square inch, and elongation of 12 per cent. If, however, the same steel is tempered at 610° C, it has a tensile strain of 63 tons per square inch, and elongation of 21 per cent. In the former state it might be used for Motor Car Driving Shafts, and in the latter case for Crankshafts.