General remarks - General appellation of "mild steel" - Influence of small percentages of carbon - Tabular statement showing the approximate percentages of carbon and approximate ultimate tensile strength of various steels - Influence of other chemical constituents - Influence of carbon - Influence of silicon - Influence of phosphorus - Influence of sulphur - Influence of copper - Influence of aluminium - Influence of arsenic - Influence of manganese - Relationship between the chemical constitution of mild steel and its ultimate resistance to tension - Proposed formulae - For acid open-hearth steel - For basic open-hearth steel - Processes of production of mild steel - The acid Bessemer - The basic Bessemer - The acid open hearth - The basic open hearth - General descriptions - Tests of open-hearth steel - Tests on mild steel angles - On mild steel tees - On mild steel flats - On mild steel channels - On mild steel rolled joists - On mild steel zeds - On mild steel trough flooring - On mild steel round bars - On mild steel rectangular bars - On mild steel plates, lengthways and cross-ways - On mild steel rivets - On mild steel for bolts and nuts - On mild steel forgings - On mild steel for special purposes - General results of mechanical tests - Chemical analyses - Comparative tests on wrought-iron bars, rectangular and round - Microscopic analyses - Remarks on the relative output of various processes of steel manufacture - Cast steel - General remarks - Advantages and disadvantages in the use of cast steel - Defects - Blow-holes - Examples of the use of cast steel - Precautions as to use of cast steel of inferior quality - Annealing of steel castings - Table of methods employed by leading steel founders - Tests and test bars - Tables of tensile and bending tests on cast-steel bars - Pawl racks - Bollards - Roller paths - Rollers - Machinery castings - Sundry castings for various purposes - Transverse strength of steel bars - Chemical analyses of cast steel - Transverse strength of cast-iron bars - Chemical analysis of cast iron.

It is the primary object of these notes to treat, as regards riveted work, of those combinations or assemblages of various rolled sections of steel which make up the constructional forms of steelwork to be dwelt upon in the pages following.

The methods by which these sections, amongst which may be enumerated plates, bars, angles, tees, joists, channels, and the like, are produced in the rolling mills from the original ingot is beyond the scope of this work. It is, however, very desirable that the student and designer of structural work should possess some elementary knowledge at least of the leading features of the chemical and physical qualities of his material as affected by the various processes of manufacture, especially as these last are frequently referred to in modern specifications for structural steelwork, and the designer may be called upon to select that process which he considers best suited for his purpose, unless, indeed, he adopts the somewhat undesirable course of ignoring all reference to methods of manufacture, and is content to accept what is offered without further inquiry.

The following elementary and necessarily imperfect outline of these subjects has been therefore prepared, rather as an incentive to the student to prosecute further inquiry than as an attempt to treat even partially of a branch of metallurgy full of detail of absorbing interest.

Before treating of the several processes of manufacture now in vogue, it is desirable to consider briefly some of those chemical constituents which go to make up that compound of iron and carbon which is denominated steel under its various sub-divisions of hard, medium, soft, or mild.

The discussions which arose in the earlier days of modern steel manufacture as to the precise nomenclature of the various grades of steel, and especially as regards that quality of the metal now used for ordinary riveted structural work, have to-day less interest.

The appellation of " mild steel" is perfectly well understood, and the limits of the chemical and physical qualities of this metal, while they are subject to a certain amount of latitude with regard to the precise purposes in view, are nevertheless practically settled by the general consent of engineers and manufacturers.

The wonderful influence of a small percentage of carbon in combination with iron will at once attract the attention of the student, and the question of carbon content must now be entered upon.

The tabular statement which follows is intended to show the gradual increase in percentage of carbon which accompanies the increasing hardness of steel ranging from the softest quality manufactured, and applicable to those purposes which require great ductility, malleability, and welding properties, to those grades of steel standing at the summit of the scale of hardness, and used only for cutting instruments of the finest temper and edge.

The student will observe that the entire range or scale of carbon content is but about 1½ per cent.

It is unnecessary, perhaps, to point out that there is no hard. and-fast boundary line to be drawn between the several groups or strata of steels. Any one group may be found to overlap its neighbour to some slight extent, but in the main the percentages here given indicate within narrow limits those which will be found in chemical analyses of the metal used for the various purposes described.

Table No. 1. Showing The Approximate Percentages Of Carbon And Approximate Ultimate Tensile Strength Of Steel Used For The Purposes Described

1 Skelton, "Economics of Iron and Steel." Also Thallner, " Tool Steel."

The above table is intended to exhibit broadly the relationship between carbon content and ultimate tensile resistance, but this relationship is not solely of this simple nature. The influence of the other chemical elements usually found in chemical analysis of mild steel, as affecting the practical working qualities and physical characteristics of the metal, must also be traced.

The following elementary remarks upon this subject are mainly based upon the work of a well-known American authority; and, except where otherwise mentioned, the passages in italics which follow are taken from the work referred to.1