No definite rules can be laid down to enable the uninitiated to judge of the temper or degree of hardness of a bar of steel ; but by habit workmen soon acquire the means of distinguishing between the dif ferent degrees of hardness of two pieces of steel. This knowledge of the degree of temper is of great importance to the steel-maker; for a file, made from soft steel which would be valuable for welding purposes, would be useless in the arts ; while a coach-spring made from steel bard enough to make a file could not be applied to its intended PurPogc .A converting furnace contains generally fifteen tons of iron ; and there are some large enough to hold eighteen to twenty tons. The bar-steel, when discharged from the furnace, is partially covered with small raised portions of the metal ; and from the resemblance of these to blisters, the steel is called blistered steel. It has been found by the experiment of ',lacing a bar of Swedish and one of Staffordshire her iron in the same furnace, that the former was much blistered, while the latter had scarcely any blisters larger than a pea. At one time it was common for the steel-maker to receive orders for steel well blistered. This arose from a mistaken idea regarding the perfection of the steel ; it being supposed that the more it was blistered, the more it was carbonised, and consequently that its quality was indicated thereby; now, however, manufacturers are better informed, and steel so blistered is complained of.
Bar-steel as it comes from the converting furnace is used for various purposes without refining; those parts which are free from flaws and blisters are brukcn out and hammered or rolled to the sizes required by the manufacturer for files, edge-tools, table knives and forks, coach springs, and a great variety of common agricultural implements. It is also manufactured into what is called single and double sheer steel ; for this purpose the converted bar is selected of an equable degree of hard ness, and broken into pieces of about two feet in length ; these are taken to the forge, heated to a full cherry red, and hammered into bans two inches by three-quarters of an inch in thickness; six of these pieces are put together and kept firmly so by a hoop, which is fixed at the end of a handle, thus They are then placed in a hollow fire urged by a soft blast, and heated gradually up to a full welding heat, during which the workman covers the surface with clay beaten very fine; this runs over the surface, and to some extent prevents oxidation. When fully heated, they are placed under the hammer, carefully welded together, and drawn into a bar of about two inches square at the same heat ; the other end is then put into the fire and welded in the same way. This is termed single sheer stech It is made doable by nicking the bar in the middle and doubling it together, giving a second welding heat, and drawing it out as before to a bar of about two inches square; it is then hammered, tilted, or rolled to the size required ; by this process bar-steel becomes more homogeneous, of a finer texture, and any instrument made of it will receive and retain a finer edge ; the steel is also rendered much tou"her, which condition is supposed to arise from the abstraction of a small portion of carbon, and the mechanical elongation of the fibre by these doublings, &c.
In Sheffield, where the steel manufacture is carried on to a larger extent than in any other town in the world, many manufacturing firms confine their operations exclusively to those above described : namely, making bar steel, in elle two forms of blister and sheer, without in cluding the making of cast-steel, or the fashioning of steel goods. The sheer-hammers, employed in the production of sheer steel, are very massive machines, having iron heads of twenty cwts. or snore, faced with steel. The blows of these hammers, acting on heated bars of steel, greatly change their character; the blistered steel loses all its blisters and flaws, acquires a uniformity of character throughout, and becomes much more malleable and tenacious. According to the degree in which it is welded or sheered, so does the steel become applicable to a large number of practical purposes.
Cast Steel is the steel employed for the best goods. Cast-steel was first made by Mr. Huntsman, at Attercliff, near Sheffield, in 1770 ; since which time the manufacture of it has very mach increased. It is steadily superseding the use of bar or sheer steel, on account of the equality of its temper, and the superior quality as well as beauty of the articles which are made of it. The process adopted is that of taking bar steel converted to a certain degree of hardness and breaking it into pieces of about a pound each ; a crucible charged with these is placed in the melting-furnace, similar to that used by; brass-founders. The furnaces are 20 inches long by 16 inches wide, and 3 feet deep. The most intense heat is kept sip for two hours and a half or three hours, coke being used as fuel. When the furnace requires feeding, the workman takes the opportunity of lifting the lid of each crucible and judging how long the charge will be before it is completely melted. All the crucibles are usually ready about the same time. They arc taken out of the furnace, and the liquid steel is poured into ingots of the shape and size required : the crucibles are immediately returned into the furnace ; and ellen the contents of all have been poured into the moulds, the crucibles are again charged. They are used three times, and then rejected as useless. The ingots are taken to the forge-tilt or rolling-mill, and hammered into bars or rolled into sheets, as may be required. The celebrated scoots, or Indian steel, is cast-steel ; but it is generally so imperfect as to resemble cast-iron rather than cast-steel. It is, however, made of iron obtained, as the Swedish is, from the magnetic ore. 1Vootz is mado by the natives from malleable iron, packed in small bits with wood in crucibles, which are then covered with some green leaves and clay : about two dozen of these crucibles are packed in one furnace; they are covered with fuel, and a blast given for about two hours and a half, which terminates the operation. When the crucibles are cold, they are broken, and small cakes of steel are obtained in the form in which it comes to England.