What iron is used when silicon is decreasing
About the influence of silicon on the properties of steel.
Adapted from a communication by R. A. Hadfield in The Chemical News, 1889 vol. 60 p. 273.
Hadfield extensively compiles all of the literature, briefly summarizing the more important findings on this subject, and then discusses his extensive investigations.
Alloys of silicon and iron can only be obtained in recent times. They usually have the names silicon iron and silicon mirror; In addition to the two elements mentioned, the latter product also contains manganese. In former times these alloys were thrown aside as worthless (vitreous or burnt iron). The alloys richest in silicon contain up to 20 per cent. Si. All iron containing silicon are characterized by their low carbon content, iron contains 20 per cent. Silicon only ¾ to 1½ Proc. Carbon; but even with only a small amount of silicon the content of carbon decreases so that one can substantially reduce its carbon content by fusing a high-percentage silicon iron with other iron.
Some analytical findings follow.
|Content of C||salary|
to Si *
or manganese iron
shows the increase
of C with increasing
Sets of Mn.
|shows the decrease|
of C at feed
* It is perhaps worth noting that the silicon was always found to be very evenly distributed throughout the whole mass.|45|
It can be seen from the above that the content of carbon both in combined form and as graphite decreases when silicon is added; Since the supply of silicon-containing iron gives another iron a lighter flow, one must assume that the silicon converts the combined carbon into graphite, which then separates out and leaves behind a more easily fluid, purer material. It should be particularly emphasized that these alloys are free of sulfur.
In the past it was usually assumed that a content of 0.1 to 0.2 percent. Si is still permissible for steel, but a higher content would have a decidedly harmful effect. This is not entirely true, as is shown by Hadfield's research below. However, the tensile strength of a steel decreases sharply if larger amounts of Si and C are present in the same at the same time; but this is by no means due to the presence of Si alone, since, as will be shown later, even at 1½ to 2 Proc. Content of carbon, a silicon-containing iron has a good tensile strength and can be forged, while a silicon-free iron has only low tensile strength and cannot be forged with the same carbon content.
Since other researchers have come to different results with similar alloys, Hadfield believes that he must assume that silicon may appear in various modifications in steel, so that in one case it produces flexibility and malleability, but in the other prevents it.
Hadfield, however, in no way wants to claim that silicon can take the place of carbon in steel, since the latter must always be used for hardening the same, since silicon cannot be used for hardening.
The effect of silicon on iron was as follows:
I. On wrought iron (its C content = about 0.25 percent).
If only small amounts of silicon up to 0.24 percent. contained in the iron, it did not forge well and cracked when hammered. If the silicon content increased, namely from 0.79 to 5.53 percent, the iron forged easily with a light yellow glowing heat. With an even higher content of silicon, however, the iron began to crumble when exposed to yellow glowing heat, remained crumbly even when exposed to red glowing heat and could not be improved by adding more manganese or carbon. The iron types with a high silicon content are less hard than those with a low silicon content; the former look more like cast iron.
It should be noted here that the magnetic properties of iron remain the same whether there is much or little silicon in it.
On further examination of the samples obtained it was found that the elasticity and the ductility of the iron are greatly increased if more silicon is introduced into it; however, the tensile strength of the material decreases in a much more significant manner if the silicon content is more than 1⅓ to 1¾ Proc. increases. Similar to the carbon content of iron, a sudden change in the properties of the material seems to be produced if the silicon content increases even slightly. The fracture of the samples after the ductility test was less than 2.18 Proc for iron. Si silky, but coarsely crystalline for those with a higher silicon content; Tempering and hardening in water had no influence on the structure of the iron, any more than it had any influence on the hardness and flexibility of the material.
The ductility of silicon-containing iron must be said to be good, as it can be easily drawn out into wire with a tensile strength of 64t for the square inch; this wire, too, could neither be hardened in water nor in oil.
Silicon iron was less sensitive to electricity than | 46 | good soft iron, but kept the same longer than this, but significantly less than the hard steel used to make magnets.
The flexibility of the samples with up to 2.18 Proc. Silicon was a good one; the pieces could be bent together and driven against one another without breaking; As the silicon content increased, the material could still be bent in the beginning, but broke with the slightest impact, but ultimately it could no longer be bent at all and broke immediately.
Welding together could not be achieved with any of the samples that contained silicon.
II. On cast iron.
As could be expected from the foregoing, the samples made with Si were free from honeycombs. If the material obtained looks more uniform as a result, it is in fact worsened, since at the same time the toughness and tensile strength of the material are greatly reduced by the addition of silicon. It has also been noticed that with cast iron with 13 to 15 percent. After the silicon has been poured, a strong effervescence suddenly becomes noticeable, so that the whole pour is then full of bubbles. This effervescence usually only begins when the outer parts of the casting are already beginning to set and only stops when the whole mass has set.
This cast iron has another inconvenience to be noted for the foundryman; namely, it settles much more strongly than ordinary iron.
The only thing that can be said of the appearance of the fracture in these specimens is that which has already been mentioned for wrought iron.
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