Even in ornamental iron work the lower carbon steel or soft steel has largely replaced wrought iron, due to the cheapness and the capability of the soft steel of being readily worked into various desired forms.

STEEL.

Steel, produced by a special method little used at present, was known from very old times and manufactured in Asia, where it was used especially for making high grade tools and war weapons. The Bessemer steel of to-day was invented by Bessemer in England.

Definition. Steel is iron which is malleable and which is produced by any process with fusion.

Manufacture. Steel contains less than two per cent. carbon, and can be manufactured from wrought iron by adding carbon to same, or from cast iron by removing part of the carbon. The most common processes of steel manufacture at present are as follows:

The Crucible Process. Blister steel or impure wrought iron is mixed with some flux and carbon in a closed crucible. The mixture is fused in the absence of air for several days. The best tool steel is thus obtained.

The Open Hearth Process. Pig iron is fused in a Siemens furnace with enough wrought iron scrap to reduce the percentage of carbon to any desired amount. Most of the structural steel used for buildings and bridges is manufactured by this process.

The Bessemer Process. Air is blown through molten pig iron in a Bessemer converter until all the carbon is burned out. Then the desired percentage of carbon is obtained by throwing into the converter a sufficient amount of "Spiegeleisen," an iron compound containing a large percentage of carbon. The molten steel is cast into moulds and rolled. Steel rails are largely manufactured in this way.

Properties. Steel is a malleable metal, can be forged and welded, and will stand shocks. It can be tempered and can be melted. Good steel is flexible, has a fine texture and is a durable material. The higher the percentage of carbon the greater is the ultimate strength of steel and the lower the percentage elongation. The carbon contents also affects the temper and the welding qualities of steel. A high carbon steel takes a good temper and is hardly weldable, while a low carbon steel takes no temper but welds readily.

The following table shows a comparison between several of the properties of the various grades of steel in common use and their carbon content:

High carbon steel is used in making tools and machinery. Rails and beams are generally rolled from medium steel, while the softer grades are used in making plates and rivets.

In addition to carbon, steel contains a certain amount of impurities, like manganese, phosphorus, silicon, sulphur,

etc.

Manganese. A small amount of manganese is beneficial, as it partly counteracts the bad effects of sulphur and tends to prevent hot shortness. In addition, manganese in small quantity increases malleability, elongation, toughness and tensile strength. An excess of manganese is undesirable, as it tends to make the steel cold short.

Phosphorus. This is the worst impurity that steel could contain. Even a small amount makes the steel hard and easy to break, reduces elongation and causes cold shortness.

Silicon. A very small amount of silicon makes the steel solidify on cooling without agitation, thus preventing air holes. In addition, silicon increases the hardness and the tensile strength. Steel containing more than one-half of one per cent. of silicon is brittle and unforgeable.

Sulphur. Even one-tenth of one per cent. makes the steel "red short," that is, the steel becomes brittle under the hammer or roller when hot. A small amount of manganese will partly counteract the injurious effects of sulphur.

Fracture of Steel. Low carbon steel and thoroughly annealed higher grades show a fine and silky fracture, with an angular and irregular outline, provided the breakage is produced gradually. In other cases the fracture is partly granular and partly silky, or wholly granular. In cases of sudden rupture the fracture is generally cup-shaped, with an even surface, at right angles to the length of the piece, and with a granular texture.

The color of good steel is light pearl gray.

The fracture of poor steel is dull, sandy looking and without metallic lustre. The color may be yellowish. Burned steel has a granular fracture and a whitish hue.

Nickel steel is an alloy of steel containing about three per cent. of nickel. This makes the alloy very strong. Some bars have shown an ultimate tensile strength of over 250,000 pounds per square inch, and an elastic limit of over 100,000 pounds per square inch. Nickel steel is sometimes used in bridge work. It gives a higher strength than steel per pound of metal and it materially reduces the dead weight of the structure.

Cast steel is produced from "scrap" steel made by any process, or from pig iron melted together with a certain amount of spiegeleisen, manganese, etc. The mixture is heated to about 1500° C. and then poured. Cast steel is hard and strong, but brittle when raised above a red heat. Small amounts of manganese and silicon reduce the size and number of blowholes, but render the castings more brittle.

Steel castings contain generally from 0.25 to 0.50 per cent. of carbon and have an ultimate tensile strength from 60,000 to 100,000 pounds per square inch.

Cast steel is extensively used for axle-boxes, cross-heads, base plates for machinery, and in some cases in building work for cast steel shoes or bases in place of cast iron bases. Common Defects in Steel. Blow holes or air holes are defects caused by confined air or by the escape of gases evolved during cooling. In steel ingots they occur generally near the outer surface of the same and toward the upper part of the ingot.

Pipes are cavities caused by the outside of the ingot cooling more rapidly than the inside. This defect usually occurs within conical lines in the upper third of the ingot, and is discovered in an ingot by cutting off the metal near the upper part. If an ingot having pipes is rolled into shapes, the defect will show in the surface of the rolled material as a line of cavities.

Burning occurs when a piece of steel is overheated. is indicated by small cup-like holes called "pits." If a burning piece of steel is withdrawn from the fire it will throw off an abundance of sparks.

Cinder spots result from fragments of fire brick, dirt or cinders which have been rolled into the metal.

Cracks are due to rolled out blow holes. These cracks, although small in the beginning, may be the starting points for ultimate rupture. Steel with cracks should be rejected. Laps result from careless rolling or hammering. A portion of the steel is folded over itself, while at the same time the walls are sufficiently oxidized to prevent the parts from

uniting. Laps or laminations run parallel with the length of the piece and continue for a considerable length. Laps can be easily noticed on the surface of the metal.

Seams are open and elongated blow holes which have been brought to the surface during rolling, without being closed by the rolling process. They are usually not continuous and only one to two inches long.

Snakes consist of small lines twisting in all directions, and are due to foreign substances separating two masses of pure steel.

Stars are bright spots in mid-section, which are formed when the pipe in the ingot is not completely cut away before rolling.

Cobbles are irregularities which result when one side has been heated more than the other.

Advantages. Good steel is a durable material. The low carbon varieties can be readily welded, and are fast replacing wrought iron in the manufacture of a large variety of ornamental work. Steel is slightly stronger in compression than in tension, and is malleable and ductile.

Steel wires can be made sufficiently small in diameter to be burned in the flame of an ordinary match. In general, the smaller the diameter the higher the ultimate tensile strength. Steel wire can be manufactured to stand 150 tons per square inch in tension. It is therefore used for cables in suspension bridges. Steel is more homogenous and more. reliable than either wrought or cast iron. It also has greater strength and stiffness than wrought iron, and since the price of steel is about the same as that of wrought iron, steel has practically replaced wrought iron for structural purposes. A considerable amount of steel is used for railroad rails and for bridges and buildings.

INSPECTION OF STEEL.

Testing. Following are the tests generally employed to determine the quality and other properties of steel:

I. Tensile tests are made to determine the tenacity and ductility of the metal. The tenacity is indicated by the elastic limit and the ultimate strength of the specimen. The ductility is measured by the per cent. elongation between two points marked with a pointer on the test piece before testing, and from the decrease or per cent. reduction of the cross section of the test piece.

The common shape used for sheared plates is shown in Fig. 8. The middle portion is 11⁄2 inches wide and of the same thickness as the original plate. Points are marked

every inch on the central portion with a steel pointer. The distance between two points, one on each side of the fracture and 8 inches apart, is measured after the test, and the per cent. elongation in 8 inches is thus determined by carefully measuring the dimensions of the cross-section at the point of rupture before and after the test. The reduced area is computed, and from this the per cent. reduction.

For shapes other than plates, similar test pieces are used, after same have been planed or turned parallel throughout their entire length. The elongation is measured in 8 inches of the original length.

Rivet rounds and small bars are tested of full size as rolled.

2. Cold bending. Rivet or soft steel shall bend cold 180 degrees, and close flat upon itself without showing any cracks. For plates flat pieces one inch wide and of the original thickness may be used.

3. Hot bending. A piece of medium steel is heated to a cherry red, then cooled in water at 70° F. It is then bent 180° around a rod whose diameter equals the thickness of the test piece. No cracks should result.

4. Drifting test. Drive a drift pin through a punched hole in a plate, using a sledge hammer. Notice how much the hole can be enlarged without fracturing the metal. A hole for a 3/4 inch rivet in a steel plate, and with the center of the hole not nearer to the edge of the plate than 11⁄2 inches, shall be capable of passing a drift pin 14 inches diameter without fracture.

5. Hardening test. The specimen is heated to a red heat, then plunged in water at freezing point. Then bend the bar, and compare the results with those obtained from