The steel of which all cutting tools are made depends more, for its real value, upon the degree of its temper than on the quality of the steel itself. A piece of untempered steel, even the finest grade, will under ordinary conditions not cut at all; while a piece of steel of inferior quality may be made to cut well if judiciously hardened and tempered. While the capacity of steel to cut is mainly due to the temper, the durability of the catting edge is determined by the quality of the steel and its adaptability to the kind of work upon which it is employed. Hence, it is that, for cutting tools, the best cast - steel is employed. The degree of temper is varied to accommodate the nature of the duty. The cost of steel of which a tool is made is of very little importance compared to its efficiency, because this cost is very little in comparison with that of performing the duty. For example, a steel turning - tool weighing but 2 or 3 lb. will cut off many thousand pounds of iron, the operation lasting perhaps several weeks. The speed at which this tool will cut, or, in other words, the time it will take to cut off a given amount of iron, will vary 30 or 40 Per cent. from a very slight difference in the quality of the steel of which the tool is made.

The cost of the operator's time is so much greater than that of the steel used up in a given time, as to render it, even in the case of cheap labour, always economical to employ the best steel. With a given quality, however, the efficiency depends more upon the skill employed in the forging, hardening, and tempering of the tool, as well as upon its shape.

The art of hardening and tempering steel as applied to cutting tools is much more simple than when the same operations are employed to give steel elasticity as well as durability, of form, or to give durability to pieces of slight and irregular form with sufficient hardness to withstand abrasion. The reason of this is that for tool purposes a special and uniform grade of steel is readily obtainable, which is known as tool steel. Special sizes and grades are made to suit'the manufacture of any of the ordinary forms of tools. The steel purchased under the cognomen of steel, whether crucible or otherwise, and though of the same make and brand, may vary so much as to seriously affect the degree of hardness or temper obtained by any specific process. Most of the difficulties met with are in obtaining a uniform degree of temper, or in tempering without loss from water cracks, checks, etc. These defects may arise from rigidly adhering to some special process of hardening, and can be overcome by varying the method to suit the quality of the steel. Very few, especially of American steels, are as yet sufficiently uniform to render it practicable to employ an unchangeable method of tempering, and 'to this fact is largely due the importation of particular brands of foreign - made steel.

Manufacturers of special tools, such as saws for example, find that they must either manufacture their own steel or import some well - known brand, and this in the case of most articles manufactured that require a fine and uniform degree of temper. This is not so much due to the good quality of the article, as to a precise knowledge of the process necessary to temper such steel. There is as yet no known method of practically ascertaining in workshops the quality of a piece of steel, unless it be by use. As a rule, the steel that shows a fracture of fine dull grain, the face of the fracture being comparatively level, is of better quality than that showing a coarse or granulated surface: brightness denoting hardness, and fibrosity toughness.

The soft steels, approaching more or less in their nature to wrought - iron, are exceedingly troublesome to harden and temper to a uniform degree, because of the difficulty experienced in producing them of uniform grade. Many kinds of these steels are made of so low a grade as to render it hard to determine the line of demarcation separating them from wrought - iron. With the object of having universally adopted names which should indicate the nature and the distinction between iron and steels, an International Committee was appointed at Philadelphia by the Institute of American Mining Engineers; they resolved that the following should be recommended: - (1) That all malleable compounds of iron, with its ordinary ingredients, which are aggregated from pasty masses, or from piles, or from any form of iron not in a fluid state, and which will not sensibly harden and temper, and which generally resemble what is called wrought - iron, shall be called weld - iron (Ger. Schweisseisen; Fr. fer - soude). (2) That such compounds, when they will from any cause harden and temper, and which resemble what is now called " puddled steel," shall be called weld - steel (Ger. Schweiss - stahl; Fr. acier - soude), (3) That all compounds of iron, with its ordinary ingredients, which have been cast from a fluid state into malleable masses, and which will not sensibly harden by being quenched in water while at a red heat, shall be called ingot - iron (Ger. Fluss - eisen; Fr. fer - fondu). (4) That all such compounds, when they shall from any cause so harden, shall be called ingot - steel (Ger. Fluss - stahl; Fr. acier - fondu). The main line of demarcation here laid down lies in the capability to harden.

Steel which will harden from any cause - that is to say, by heating to any temperature and using any quench-ing liquid - is termed weld - steel. That which will harden by being heated to redness and quenched in water is termed steel.