CA1036844A - Alloy additive - Google Patents

Abstract

Abstract of the Disclosure Addition agents containing controlled percentages of nickel, silicon, magnesium and iron are useful in the production of ferrous-base compositions.
particularly ductile irons.

Description

~036~44 The subject invention is addressed to ferrous metallurgy, and more particularly, to addition agents for incorporating magnesium in ferrous-base melts.
As is known, it is virtually the most conventional of metallurgical practices to innoculate or otherwise treat molten irons for purposes of deoxi-dation, desulfurization, degasification, modification of the as-cast morphological structures, etc. Magnesium has seen extensive use in this connection and has been largely used in the production of "ductile iron", i.e., cast iron in which at least part of the graphite is present in spheroidal form. This latter develop-ment, early described in U.S. Patent No. 2,485,760 to Millis, Gagnebin & Pilling, significantly closed the gap between low-cost but brittle cast irons and the more expensive but less brittle steels.
In any case, over the years research has continued in respect of the development of improved procedures for introducing magnesium into a cast iron melt owing to its high degree of reactivity and propensity toward violent reactions. Too, in recent years increased emphasis has been and continues to be given to ecological considerations, namely, smoke emissions (attributable largely to evolved magnesium oxides) . Since most approaches to the problem, as does the present, involve the production and use of addition agents, "crusha-bility" of the additive as will be explained herein, also plays an important role.
All these factors, in turn, focus attention on the economic picture.
In accordance with the present invention, it has been discovered that a hereinafter more fully described addition agent, provided that it is controlled to contain special and correlated percentages of magnesium, nickel, silicon and iron, results in a material having a unique "combination" of attributes, particularly for ductile iron production, including (i) relatively low reactivity with molten iron and thus low smoke emission, (ii) excellent magnesium recovery both in terms of preparation of the additive and in respect of the ferrous-base product produced, (iii) and good crushability such that excessive fines can be avoided, these obtaining (iv) with the simultaneous capability of using relatively low silicon levels and (v) re]atively low cost. Prior art ductile iron addition agents have possessed one or more of these characteristics but, insofar as we are aware, none has combined all of them in one additive.
Moreover, apart from ductile iron production, it is deemed that these novel addition agents also can be used in treating both wrought and cast low alloy steels, particularly in minimizing the difficulties occasioned by reason of the contaminant sulfur.
Generally speaking, the present invention contemplates addition agents containing about 3%to 5.5%magnesium, about 19%to 24%nickel, about 15%to 28%
silicon and the balance essentially iron, the iron preferably being not less than 45%. Elements such as copper and manganese are not essential. Manganese need not exceed 2 or 3% although it can be as high as 12%.
In carrying the invention into practice, should the magnesium be too low, e . g ., 2%, the addition alloy is rendered too costly since a larger alloy addition would normally be required to produce a given magnesium level in a treated iron, notwithstanding a possibly higher magnesium recovery. On the other hand, based upon prior metallurgical principles it would be expected that as the magnesium is increased greater would be the reactivity and larger would be the obnoxious emissions, (i.e., magnesium recovery and smoke genera-tion would be expected to be roughly inversely proportional), this at the expense of smaller magnesium recoveries and higher cost. This need not be the case particularly if the nickel content is correlated with the magnesium percentage.
Within the chemistry contemplated herein, nickel promotes an increase in magnesium solubility in the addition agent. And, accordingly, if sufficient nickel is present such that the magnesium is soluble or substantially so in the addition agent, less smoke emission is encountered and magnesium recovery is enhanced in treatment of, say, a ductile iron. While the magnesium level need not exceed 5 . 5%, it can be present up to 6 or 7%.

With further regard to the nickel content, it need not exceed 23.5%
although up to about 25% can be present. And while it can be as low as 15 or 16%, particularly at the lowest magnesium levels, it is deemed that a range of 19.5% to 23.5% is most advantageous .
Concerning the element silicon, it should, at least in accordance here-with, be maintained at low levels. There is no significant reason why it should exceed about 30 or 32%; however, by keeping it below this level important commer-cial advantages are derived. For example, if in the production of ductile iron large quantities of silicon had to be added in the treatment and innoculation steps, then the silicon content of the ferrous melt would have to be kept low. However, this runs counter to desired commercial practice since it demands more careful selection of a base melt charge and would ostensibly occasion undue refractory wear. Too, excessive silicon detracts from a friable addition agent and tends to promote an unwanted amount of fines during crushing. These fines must be remelted. Thus, product yield is reduced and cost increased. A silicon range of 19 or 20% to 25 or 27% is quite satisfactory. Contributing to these desiderata is a low silicon (added) to magnesium (recovered) ratio. This ratio preferably does not exceed about 12: 1 and is desirably less than about 10: 1.
The following data will help serve as illustrative of the instant invention.
A number of addition alloys, both within and without the invention, were prepared as follows: electrolytic nickel, ferromanganese (when used) and iron were melted together (about 3% carbon was added in Alloy 1 to lower the melting temperature) and small amounts of FeSi were added as required to keep the baths deoxidized and quiet. To assure complete solution of the elements the melts were heated to about 2850F. and then cooled to about 2600F.
whereupon the remainder of the silicon was added.
The baths were then cooled to a temperature (about 2350F . ) near the freezing point and the magnesium was added either in the form of pure magnesium sticks or 50 Ni-50 Mg master alloy. The alloys were cast into small truncated ~036844 - cone-shaped pig molds (1, 2 and 5 lb. sizes) and subsequently crushed to provide generally uniform equiaxed shaped pieces of roughly 1/2" to 1/4" in diameter.
Often overlooked is the magnesium recovery in simply producing the addition agent, the emphasis usually being accorded to magnesium retention in the final ferrous base melt to be produced. However, this is an important adjunct to cost and therefore "magnesium addition agent recovery" was deter-mined for most instances (Table I).
Addition alloy #1, Table I, was added to a molten ferrous base nominally of 3.4% C, 2%Si, .45%Mn, Bal. Fe, prepared using pig iron,commercial iron, ferromanganese and ferrosilicon, and heated to 2800F. The above-described magnesium addition alloy (enough to provide approximately 0.05% Mg to the bath) was placed in a cavity in the bottom of a specially lined treatment ladle (100 lb. melts treated except Alloy 1 which was 30 lbs.) and the cavity was covered in the case of Alloy 1 with a 1/8" thick steel plate wéighing 0.6 lb.
A cover of crushed FeSi (50-50) equal to about 1% by weight of the bath was used for the remaining addition agents. The iron melt was tapped into the ladle at 2800F. On the basis that smoke emissions were relatively proportional to flare, which in retrospect is seemingly reasonably true for very high nickel (93-95%) addition agents, a camera was used to photographically judge the amount of smoke emission. In this instance, during tapping into the ladle a still camera was opened and when all visible sign of reaction ceased, the shutter was closed. After the reaction, a chill slug was poured for chemical analysis of magnesium. The bath was poured into a second ladle and innoculated with 0.5%Si as standard foundry grade ferrosilicon containing about 85%Si. A
second chill slug was analyzed for magnesium.
~ecause it was thought that the flare test was not sufficiently accurate for smoke generation in the more reactive agents, a different smoke test was devised for the remaining alloys (and also a repeat of Alloy #1). A Hi-Volume Air Sampler was used to sample a portion of the smoke drawn off through an exhaust vent. The exhaust hood was placed to encompass practically ~03684~ l all the generated smoke, the exhaust being sampled at a distance 20 feet from the ladle. A fraction of the air and likely a similar proportion of the MgO smoke was drawn through the sampler by a small fan. The smoke was collected on a filter which was weighed both before and after test. The weight gain was taken as the measurement of smoke emitted. Since clogging of the filter occurred in the more reactive alloys, a correction factor,S2 = Sl(2 Fo/Fo + Fl), was used to compensate for the drop in air flow rate through the sampler. S2 represents the corrected weight gain, Sl the measured weight gain, and Fo and Fl, respec-tively, correspond to the air flow from the smoke tester before aEld after test.
Various addition agent compositions are given in Table I below together with the percent magnesium recovery in preparing the same. It will be noted that a high magnesium recovery was obtained in most instances.
However, magnesium recovery was low in respect of Alloys A, B, and C
(alloys outside the invention) due largely, it is believed, to low nickel levels.
TABLE I

% Recovery Alloy Ni Si Mg FeOther Magnesium 21.530.2 4 31.611.8Mn 93

2 22.524.6 3.35 bal . -- 67

3 21.727.0 3.81 bal . -- 76

4 23.829.2 3.4 bal. -- 68 18.224.3 3.66 bal . -- 61 6 22.121.6 3.64 bal. -- 72 7 22.130.8 4.50 bal . -- 57 8 24.416.2 3.70 bal. -- 62 9 21.617.4 4.41 bal. -- 55 24.223.0 6.41 bal . --11 24.523.4 6.24 bal . -- 78 12 24.330.1 5.10 bal . -- 85 13 20.920.2 3.04 bal.9.64Mn 63 14 19.729.9 3.85 bal . 9.60Mn 80 A 10.825.6 1.21 bal. -- 20 B 10.930.6 0.61 bal.9.27Mn 13 C 14.926.3 2.11 bal . -- 35 D 94 -- 4.5 bal.1.5C --E -- 40 5.5 bal . -- ---The data obtained using the above agents are reported in Table II, the ductile iron base melt nominally having contained about 3.6% C, 1.7% Si, 0.4% Mn, balance iron and impurities .
TABLE II
% Mg Weight Alloy Ni Si MgRecoveredSi/MgGain, S2 22 30 4 71 10.650.41 2 23 25 3.35 62 12.0 0.185 3 22 27 3.862 11.4 0.19 4 24 29 3.470 12.2 0.20 18 24 3.66 48 13.7 0.19 6 22 22 3.660 10.0 0.23 7 22 31 3.570 9.9 0.29 8 24 16 3.770 6.2 0.27 9 22 17 4.466 5.9 0.31 24 23 6.470 5.1 0.38 11 25 23 6.24 70 5.3 0.43 12 24 30 5.160 9.8 0.37 13 ---- _ _ _ _ A 11 26 1.272 29.9 0.09 C 15 26 2.166 18.6 0.14 D 94 -- 4.595 0 0.10 E -- 40 5.544 16.5 1.00 .
NOTE: The percentages of Ni, Si and Mg are rounded off in Table II.
Concerning the alloys beyond the invention, Alloys A, C, D and E, either the S2 factor, the Si/Mg ratio or cost left something to be desired. As to the alloys within the invention, a number of them had a desirably low smoke emissionfactor, S2, of not more than 0.4, a magnesium recovery of 60% or more, and a Si/Mg ratio below about 12. The photograph flare test for Alloy #l indicated the alloy to be less reactive than a number of commercially available additives,although it was difficult to quantitatively determine the result. It is considered that a higher nickel content would have proven beneficial for alloys such as Alloy #5 (Mg recovery 48%) as evident from Alloy #6 (Mg recovery 60%) . Loweringthe magnesium level of Alloy #5 would also have likely been helpful. An additionagent containing 19.5% to 23.5% nickel, 20 to 27% silicon, 4 to 5.5% magnesium is deemed particularly beneficial.

As will be understood by those skilled in the art, in referring to the iron content as constituting the ~balance~ or "initially the balance~ of the addition agents contemplated herein other constituents can be present in amounts which do not adversely affect the basic characteristics of the additives. In this connec-tion, elements such as calcium, cerium, rare earth metals, carbon, cobalt, etc., can be present though they need not exceed up to 1% calcium, up to 1% cerium, up to lQ6 of other rare earths, up to 1% carbon, up to 2% cobalt, etc. Copper, if any, preferably does not exceed about 1% or 2%, since it is a pearlite stabilizer and can deleteriously affect graphite shape.
Although the invention has been described in connection with preferred embodiments, modifications may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand.
Such are considered within the purview and scope of the invention and appended claims .

Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition of matter particularly adapted for use as an addition agent to ferrous molten baths and formed of from about, by weight percent, 3 to 5.5% magnesium, about 19 to 24% nickel, about 15 to 28% silicon and the balance essentially iron.

2. A composition of matter in accordance with claim 1 containing 19.5 to 23.5% nickel, 20 to 27% silicon, and 4 to 5.5% magnesium.

3. A composition of matter in accordance with claim 1 containing at least 45% iron.

4. A composition of matter having from, by weight percent, 16 to 25% nickel, 15 to 32% silicon, 3 to 7% magnesium and the balance essentially iron.