U.S. patent application number 13/329561 was filed with the patent office on 2012-04-19 for process for producton of compacted graphite iron.
This patent application is currently assigned to NOVACAST TECHNOLOGIES AB. Invention is credited to Rudolf SILLEN.
Application Number | 20120090803 13/329561 |
Document ID | / |
Family ID | 38188913 |
Filed Date | 2012-04-19 |
United States Patent
Application |
20120090803 |
Kind Code |
A1 |
SILLEN; Rudolf |
April 19, 2012 |
PROCESS FOR PRODUCTON OF COMPACTED GRAPHITE IRON
Abstract
A process for production of compacted graphite iron using
in-mould addition of a magnesium alloy is disclosed. The process is
characterised by a step of pre-treating the base iron in a ladle or
in a furnace with an alloy containing cerium and performing a
structure forming treatment in a reaction chamber in the mould
using an alloy containing magnesium and lanthanum.
Inventors: |
SILLEN; Rudolf; (Ronneby,
SE) |
Assignee: |
NOVACAST TECHNOLOGIES AB
Ronneby
SE
|
Family ID: |
38188913 |
Appl. No.: |
13/329561 |
Filed: |
December 19, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12086637 |
Sep 3, 2008 |
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PCT/SE2006/001424 |
Dec 14, 2006 |
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13329561 |
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Current U.S.
Class: |
164/57.1 |
Current CPC
Class: |
C22C 37/10 20130101;
C21C 1/105 20130101; C21C 1/08 20130101; B22D 27/20 20130101 |
Class at
Publication: |
164/57.1 |
International
Class: |
B22D 23/00 20060101
B22D023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2005 |
SE |
0502817-0 |
Claims
1. A process for production of compacted graphite iron using
in-mould addition of a magnesium alloy comprising pre-treating the
base iron in a ladle or in a furnace with an alloy containing
cerium and performing a structure forming treatment in a reaction
chamber in the mould using an alloy containing magnesium and
lanthanum.
2. The process of claim 1, wherein the base iron is pretreated with
an alloy containing cerium in order to reach cerium levels between
0.008 and 0.025% and the iron is further treated in the casting
mould using an alloy containing 3-6% magnesium and 0.5-1.5%
lanthanum.
3. The process of claim 1, wherein the minimum percentage of cerium
in the base iron is estimated as (% S-0.006)*2.9+0.01), where S is
the sulphur content in the iron before the addition of cerium.
4. The process of claim 2, wherein the minimum percentage of cerium
in the base iron is estimated as (% S-0.006)*2.9+0.01), where S is
the sulphur content in the iron before the addition of cerium.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a process for production of cast
iron with a structure predominantly consisting of compacted
graphite shapes. The process is based on a combination of
pre-treatment of a base iron and a final treatment in the
mould.
BACKGROUND ART
[0002] Compacted graphite iron is a cast iron alloy with a graphite
structure between flake type graphite shapes and spherical shapes.
The graphite shape is determined by the conditions in the liquid
iron during the solidification. Treatment of a base iron,
preferably with a carbon equivalent between 4.0 and 4.4 and with a
sulphur content below 0.02%, with a ferrosilicon alloy containing
4-10% magnesium can be used to achieve the compacted graphite
structure. The magnesium content must be kept within very narrow
limits usually within +/-0.003% and with a level of about 0.008 to
0.015% depending on conditions of the base iron and the cooling
rate in the casting to be produced. As used herein percent refers
to percent by weight. The treatment with magnesium is usually made
in a ladle. Magnesium boils at 1090.degree. C. and since the
temperature of the iron usually is higher than 1400.degree. C.
during the treatment some of the magnesium therefore vanishes as
vapour, and some combines with the sulphur, oxygen and nitrogen in
the iron. During holding of the iron before pouring further
reduction of the active magnesium content occurs. This gradual
reduction of active magnesium is called fading.
[0003] In order to avoid these problems the magnesium treatment can
be made inside each mould. That technology known as in-mould
treatment/technology is well-known for production of ductile iron.
A special version of the technology as described in WO 01/54844 A1,
is suitable for production of compacted graphite iron. The in-mould
technology is based on placing the magnesium alloy in a chamber in
the gating system in the mould. During pouring, the iron flows into
the chamber and gradually dissolves the alloy. The treated metal
then fills the casting cavity. The problems with fading of
magnesium are eliminated when using this process.
[0004] One problem is that the sulphur level in the base iron often
varies. Therefore the magnesium level must be adjusted. However,
with the in-mould treatment this is practically not possible as the
treatment chamber is the same in each mould. Another problem is
that treatment with magnesium makes the structure sensitive to
variation in cooling rate. With a high cooling rate e.g. in thin
sections of the casting the graphite shapes tend to be more
spherical. With long cooling rates i.e. in thick sections the
graphite will precipitate as flakes.
[0005] It is known that treatment alloys containing both magnesium
and cerium reduce these problems. However high levels of cerium can
increase the risk for certain casting defects such as formation of
primary carbides and shrinkages.
DESCRIPTION OF THE INVENTION
[0006] It is an object of the present invention to solve these
problems.
[0007] The invention concerns a process for production of compacted
graphite iron using in-mould addition of a magnesium alloy in
accordance with claim 1. Preferred embodiments are defined in the
dependent claims.
[0008] The amount of cerium is adjusted in relation to the sulphur
content in the base iron. The cerium level should be adjusted
according to the formula:
% Cerium=(% Sulphur-0.006)*2.9+A.
[0009] The value for A varies preferably between 0.01 and 0.03
depending on the configuration of the casting i.e. variation in
section dimensions and casting modulus. As cerium has a very high
boiling point (3470.degree. C.) and a high density (6.14
g/cm.sup.3) it does not show any fading effect. By adding cerium to
the base iron it can be properly dissolved and less magnesium alloy
has to be added in the reaction chamber in the mould as cerium also
has a structure forming effect.
[0010] The treatment alloy preferably contains 3-6% magnesium and
0.5-1.5% lanthanum. Lanthanum has a favourable effect in reducing
defects such as carbides and shrinkages in the casting. The effect
on shrinkages is highest just after treatment and therefore it is
optimal to add the lanthanum as late as possible.
[0011] The alloys used can have various compositions since the
paramount feature is the overall fraction of active metal. However,
examples of compositions for commercially available alloys
include:
[0012] For the magnesium alloy: 48% Fe, 45% Si, 5% Mg, 1.0% Al,
0.5% La and 0.5% Ca, and
[0013] for the Cerium alloy: 65% Fe, 25% Ce, 7% La, and a balance
of other rare earth elements.
[0014] According to a preferred embodiment of the invention cerium
is added to the oven or the ladle (and not as a part of the
magnesium alloy) and magnesium is added to the mould.
[0015] With the proposed process the magnesium addition can be
reduced with at least 30% compared to a normal treatment
in-the-mould without the pre-conditioning. The reduced magnesium
level in the castings has also the advantage that casting defects
such as dross and micro-shrinkage are minimized.
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