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Steel MakingBessemer ProcessThe bessemer process consists of charging molten pig iron int... Mushet And Bessemer That Mushet was "used" by Ebbw Vale against Bessemer is, perh... Leeds And Northrup Optical Pyrometer The principles of this very popular method of measuring tempe... The Leeds And Northrup Potentiometer System The potentiometer pyrometer system is both flexible and subst... Steel Can Be Worked Cold As noted above, steel can be worked cold, as in the case of ... Tempering Round Dies A number of circular dies of carbon tool steel for use in too... Plant For Forging Rifle Barrels The forging of rifle barrels in large quantities and heat-tre... Classifications Of Steel Among makers and sellers, carbon tool-steels are classed by g... Pyrometers For Molten Metal Pyrometers for molten metal are connected to portable thermoc... Quenching The Work In some operations case-hardened work is quenched from the bo... Annealing To Relieve Internal Stresses Work quenched from a high temperature and not afterward tempe... Hardening High-speed Steel In forging use coke for fuel in the forge. Heat steel slowly ... Lathe And Planer Tools TO FORGE.--Gently warm the steel to remove any chill is parti... Quenching Tool Steel To secure proper hardness, the cooling of quenching of steel ... Knowing What Takes Place How are we to know if we have given a piece of steel the ver... Composition Of Transmission-gear Steel If the nickel content of this steel is eliminated, and the pe... The Influence Of Size The size of the piece influences the physical properties obta... Hardening Carbon Steel For Tools For years the toolmaker had full sway in regard to make of st... The Penetration Of Carbon Carburized mild steel is used to a great extent in the manufa... Pyrometry And Pyrometers A knowledge of the fundamental principles of pyrometry, or th... |
ChromiumCategory: ALLOYS AND THEIR EFFECT UPON STEEL Chromium when alloyed with steel, has the characteristic function of opposing the disintegration and reconstruction of cementite. This is demonstrated by the changes in the critical ranges of this alloy steel taking place slowly; in other words, it has a tendency to raise the Ac range (decalescent points) and lower the Ar range (recalescent points). Chromium steels are therefore capable of great hardness, due to the rapid cooling being able to retard the decomposition of the austenite. The great hardness of chromium steels is also due to the formation of double carbides of chromium and iron. This condition is not removed when the steel is slightly tempered or drawn. This additional hardness is also obtained without causing undue brittleness such as would be obtained by any increase of carbon. The degree of hardness of the lower-chrome steels is dependent upon the carbon content, as chromium alone will not harden iron. The toughness so noticeable in this steel is the result of the fineness of structure; in this instance, the action is similar to that of nickel, and the tensile strength and elastic limit is therefore increased without any loss of ductility. We then have the desirable condition of tough hardness, making chrome steels extremely valuable for all purposes requiring great resistance to wear, and in higher-chrome contents resistance to corrosion. All chromium-alloy steels offer great resistance to corrosion and erosion. In view of this, it is surprising that chromium steels are not more largely used for structural steel work and for all purposes where the steel has to withstand the corroding action of air and liquids. Bridges, ships, steel building, etc., would offer greater resistance to deterioration through rust if the chromium-alloy steels were employed. Prolonged heating and high temperatures have a very bad effect upon chromium steels. In this respect they differ from nickel steels, which are not so affected by prolonged heating, but chromium steels will stand higher temperatures than nickel steels when the period is short. Chromium steels, due to their admirable property of increased hardness, without the loss of ductility, make very excellent chisels and impact tools of all types, although for die blocks they do not give such good results as can be obtained from other alloy combinations. For ball bearing steels, where intense hardness with great toughness and ready recovery from temporary deflection is required, chromium as an alloy offers the best solution. Two per cent chromium steels; due to their very hard tough surface, are largely used for armor-piercing projectiles, cold rolls, crushers, drawing dies, etc. The normal structure of chromium steels, with a very low carbon content is roughly pearlitic up to 7 per cent, and martensitic from 8 to 20 per cent; therefore, the greatest application is in the pearlitic zone or the lower percentages. Next: Nickel-chromium Previous: Nickel
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