New Developments in Steel
Page 65
If you've noticed an error in this article please click here to report it so we can fix it.
The Latest Progress in Metallurgy Includes the Discovery of a Process for Centrifugally Casting Highly Alloyed Steels, the Improvement of Special Steels and the Evolution of a Method of Combining Metals and Plastic Materials
T
. HE metallurgist does not stand still, and to keep pace with his progress is not easy. Ever since the publication of the first article of this series, a great deal of work has been done, and some new discoveries made, which are bound ultimately to react on the commercial-motor industry.
There is, for example, the new process for centrifugally casting highly alloyed steels, the development of which is certain to be followed closely. It is already claimed that this new process has rendered possible the cheapening of alloy-steel castings.
ImproVement in steel castings is not, however, confined to this one achievement. Recently, vanadium, formerly regarded as valuable solely as a deoxidizer in steel-casting production, and not by any means the cheapest deoxidizer, has been found to confer certain beneficial properties on castings when it is employed primarily as an alloying ingredient. It gives to steel castings increased strength and toughness, whilst producing a grain structure of harder and better character.
Developing Special Steels.
Special steels for such parts as track links, wheels, gears for heavy duty, and the like, are continually being developed. One such steel contains i per cent. of manganese ; another is a nickel-chrome material of approximately 0.45-1.75 per cent. chromium and 3-3.5 per scent: nickel.
For such components as gears, connecting rods, etc., where a type of steel better than the ordinary casehardening gear steel is required, the nickel-chrome-molybdenum steel has been greatly improved, and is particularly to be recommended wherever high surface stresses are likely to be encountered. It has only • a low percentage of carbon in its composition, so that it can be casehardened effectively, and, after such treatment, it shows a core strength of 60-90 tons per sq. in.
Yet another steel for gears, connecting rods, etc., is the 1.25-per-cent, nickel, 0.60-per-cent. chromium steel. The analysis may vary a shade according to the particular manufacturer. This type of steel affords improyed ductility, greater toughness, . better resistance, to impact shock, closer internal structure, and adaptability to heat treatment. Heat treatment of this steel is particularly important, because the yield point and impact figures are thereby improved, whilst the extent to which the steel will harden throughout minimizes those variations of strength due to varying thickness of section.
Since the discovery of the supercutting tool steels, many attempts have been made to evolve further steels even more effective. The percentages of tungsten, chromium, vanadium and cobalt have all been raised in an endeavour to find a "super-super steel."
Rare elements, such as tantalum and uranium, have been added as a means • for improvement. Carbon percentage has been raised and molybdenum has been tried in larger quantities. Nevertheless, as yet there is no sensational discovery to announce, and the high cobalt steel reMains unexcelled, except by the tungsten carbides.
An Important American Advance.
From the United States comes the announcement of an extremely interesting advance, which is nothing less than the joint fabrication of metals and plastic materials. According to accounts of this process, a metallic part, such as a stamping, can be joined with plastic materials so as to make up a complete finished pa'st, the steel or other metal being a closebonded insert in the plastic substance. The effect is obtained by allowing the stamping to fall to the bottom of a plastic mould,
The cheapening of processes in the production of tubes, cold drawn from Carbon and alloy steels, has long been a desideratum. These tubes were extremely difficult to produce by a cold-drawing operation, owing to the necessity of frequently softening the steel and pickling it (re
moving its surface scale after heating) during production.
Every such softening and pickling process involved additional cost, and inflated the price of tubes. By coating the steel with lead, however, a lubricating effect is obtained, greatly facilitating the cold-drawing work and considerably reducing the number of softenings and picklings required. The result of this process will inevitably be a cheapening of tubes.
Twist drills are frequently used in repair and production shops, and one must refer to the two great changes which have taken place, owing to metallurgical progress, in their manufacture and design.
Changes in Drill Manufacture.
Apart from the cobalt-steel special drills for work that no other drill will touch, even the standard run of drills is now being made in a high-speed steel containing 18 per cent, tungsten, whereas previously 14-per-cent. tungsten steel has been considered good enough. But this is not all.
Twist drills used always to be made of solid high-speed steel, from 'point to butt. Both cutting flutes and tang or shank were made of the same steel. Whilst high-speed steel cuts admirably, it does not meke good drill shanks, because it is not a ell suited to resist the excessive twisting stresses.
The problem has been solved by
the manufacture. of composite drills, which consist of high-speed-steel cutting portions fuse-welded on to goodquality oil-toughened steel shanks or tangs. In this way, the best material for each particular function is secured.
A German concern is reported to have put on the market a sensational new cutting alloy, made up of iron, tungsten and cobalt. This material, being free from carbon, cannot rightly be classed as steel, but is of great importance, if the claims made for it be justified. It is said to give higher performance figures than even super-high-speed steel (400 per cent. being the figure mentioned).
Tools made from it are forgeable, show no decarbonization on heat treatment, can be machined to size after a quenching process and before ageing, thereby eliminating scaling and warping. The analysis is roughly 30 per cent. cobalt with 15-20 per cent. tungsten.