FR2750142A1 - Ferrosilicon alloy for dosing melts to make spheroidal graphite cast iron - Google Patents

Abstract

An alloy which is added to the melt when making spheroidal graphite cast iron comprises (wt.%) 0.005-3% rare earths, 0.005-3% bismuth, lead and/or antimony, 0.3-3%, preferably 0.5-2%, calcium, 0.3-3%, preferably 0.5-1.5%, magnesium and the balance silicon and iron in a ratio of Si to Fe of >2, preferably >2.5. The alloy may be added to the melt in the form of wire wool.

Description

Ferroalloy for the inoculation of spheroidal graphite cast irons
Field of the invention
The invention relates to a ferroalloy based on ferrosilicon for the treatment
inoculation of spheroidal graphite cast irons
State of the art
The treatment of liquid cast irons to give them a spheroidal graphite structure comprises the succession of 4 operations: carburation, desulfurization, spheroidization and inoculation. This latter operation is generally carried out using a ferrosilicon-based alloy comprising various additives. A widely used product for this purpose is the SPHERIXB alloy, marketed by the applicant and covered by French Patent No. 2511044, filed on August 4, 1981, in the name of the company NOBELBOZEL.n This is a ferrosilicon comprising from 0.005% to 3% of rare earths and from 0.005% to 3% of at least one of the bismuth, lead and / or antimome elements.

Alloys of this type contain about 1%, and always at least 0.6% of calcium; experience shows that this element improves the yield of bismuth, lead and / or antimony at the time of development of the alloy.

The use of these alloys for many years has verified their excellent inoculant capacity, but has highlighted a drawback in its preparation, resulting in additional manufacturing cost. Indeed, during storage, the product tends to disintegrate and its particle size evolves towards an increase in fines. During final packaging, a large percentage of fine-grained alloy must be removed to meet customer specifications.

Object of the invention
The invention aims to remedy this inconvenience while maintaining the good results of the alloy as an inoculant. It relates to an alloy of the type of that described in patent FR 2511044, that is to say a ferrosilicon containing (by weight) of
0.005% to 3% rare earth and 0.005% to 3% bismuth, lead and / or
antimony, as well as calcium, characterized in that its calcium content is less than 0.5%, and preferably 0.3%.

The alloy advantageously contains at least one of magnesium and aluminum elements
and / or zirconium in a total amount of between 1% and 5%.

Description of the invention
The invention is thus based on the finding, by the plaintiff, of a spontaneous degradation over time of the granulometry of inoculants bismuth, lead or antimony and the demonstration of the role of calcium in this degradation.

With a calcium content of less than 0.5%, and preferably less than 0.3%, this evolution of the particle size is virtually halted.

To ensure, despite the low calcium content, a good yield of bismuth, lead and antimony during the development of the alloy, the applicant found that it could be replaced by magnesium, in an amount at least equal to 1%, and preferably between 1.5 and 2%. On the other hand, to maintain the inoculating power of the alloy, it found that an addition of aluminum and / or zirconium between 0.5 and 5% led to good results. The addition of aluminum and / or zirconium should be greater in the absence of magnesium The inoculant capacity is measured by optical microscope by the average number of spheroids per mm2 in a cross section of a thick cast iron plate given.

Examples
Four inoculating alloys A, B, C and D of chemical composition (% by weight) were prepared as follows:

<tb><SEP> If <SEP> Ca <SEP> TR <SEP><SEP> Bi <SEP> AI <SEP> Mg <SEP> Zr <SEP> Fe
<tb> A <SEP> 71.5 <SEP> 1.52 <SEP> 0.49 <SEP> 1.02 <SEP> 0.83 <SEP><SEP><0.001<SEP> 0.005 <SEP> baL <September>
<tb> B <SEP> 72.4 <SEP> 0.11 <SEP> 0.51 <SEP> 1.03 <SEP> 0.07 <SEP><0.001<SEP> 1.54 <SEP> baL
<tb> C <SEP> 71.7 <SEP> 0.10 <SEP> 0.52 <SEP> 1.05 <SEP> 2.54 <SEP><<SEP> 0.001 <SEP> 1.42 <SEP > baL
<tb> D <SEP> 72.1 <SEP> 0.12 <SEP> 0.48 <SEP> 1.02 <SEP> 0.92 <SEP> 1.72 <SEP> 0.005 <SEP> baL
<Tb>
The alloy A corresponds to a usual composition of SPHERIXB, the alloys B, C and D are in accordance with the invention, B containing an addition of zirconium alone, C an addition of zirconium and aluminum, and D an addition of aluminum and magnesium.

The alloys are crushed into pieces of size between 2 and 7 mm and are stored for 1 month under normal storage conditions. At the end of this storage, the alloy A contains 34% of particles smaller than 2 mm and must be retaminated before use, while alloys B, C and D contain less than 3%.

A cast iron crucible, treated with 0.85 wt.% Ni-Mg alloy at 15% Mg, was inoculated at 1410 ° C with 0.7 wt.% Alloy A. The same test was The 4 crucibles were then used to cast plates 6, 12 and 24 mm thick and the average number of spheroids per mm 2 was measured on these plates by optical microscopy. , and the results were as follows:

<tb> thickness <SEP> 6mm <SEP> 12 <SEP> mm <SEP> 24 <SEP> mm
<tb><SEP> A <SEP> 390 <SEP> 180 <SEP> 150
<tb><SEP> B <SEP> 320 <SEP> 160 <SEP> 135
<tb><SEP> C <SEP> 360 <SEP> 175 <SEP> 140
<tb><SEP> D <SEP> 380 <SEP> 185 <SEP> 145
<Tb>

Claims (3)

 that its calcium content is less than 0.5% and preferably less than 0.3%.  3% bismuth, lead and / or antimony, and calcium, characterized in that  ferrosilicon and containing (by weight) 0.005% to 3% rare earth, 0.005%  1. Ferroalloy for the inoculation of spheroidal graphite cast irons based on 2. Ferroalloy according to claim 1, characterized in that it contains one at  minus magnesium, aluminum and / or zirconium elements in total  between 1% and 5%. 3. Ferroalloy according to claim 1, characterized in that its content in  magnesium is between 1.5 and 2%.