FR2466507A2 - Cast irons or steels, including stainless steels - contain small amt. of lanthanum improving their mechanical properties - Google Patents

Abstract

This is an addn to 78.10254, which described the beneficial effects of 0.0001-5 wt %, esp 0.001-0.5% La in ferrous alloys. The novelty in the present invention is the use of 0.0001-0.01% La, pref 0.001-0.01% La, and esp 0.003-0.01% La. The La is pref added to the molten iron or steel as an alloy which possibly also contains lanthanides other than La, and esp Ce, where the alloy contains 0.01-90% La. The La may also be added as a cpd., e.g. a chloride, fluoride or oxide, or their mixts with a low Ce content.

Description

 The present addition essentially relates to improvements in the process of preparing ferrous alloy to improve their mechanical properties through the use of lanthanum which is the subject of the main patent.

 It is claimed that the invention according to the main patent consists of a process for preparing a ferrous alloy characterized in that it comprises the incorporation of at least 0.0001% to 5% by weight of lanthanum to said ferrous alloy. According to a preferred feature, according to the main patent, from 0 to about 0.5% by weight of lanthanum is incorporated into the ferrous alloy.

 According to the present addition, it has now been found that in fact the preferred lanthanum-inducing range for which best practice results are obtained is to incorporate in the ferrous alloy from 0.0001% (ie 1 ppm) to about 0 , 01% (ie 100 ppm) by weight of lanthanum. Preferably, this incorporation of lanthanum is between 0.001% (ie 10 ppm) and about 0.003% (ie 30 ppm) to 0.0196 (or 100 ppm) by weight.

 In addition, it has now been discovered that lanthanum can be incorporated as an alloy with any metal capable of forming a compound homogeneous with lanthanum, that is to say having a solubility diagram with lanthanum alone or associated with other rare earths (including cerium) in the proportion of 0.01 to 90% by weight of lanthanum, provided that the lanthanum alloy has a low cerium content alone or in combination with other rare earths. Similarly, lanthanum may be incorporated as a compound such as chloride, fluoride, oxide obtained from lanthanides, or mixtures of said compounds provided that these lanthanide compounds have a low cerium content alone or in combination with other soils. rare.

It has furthermore been determined by extensive experiments that the best efficiency of lanthanum is obtained when the lanthanum / earth weight ratio.
Rare (except lanthanum) is at least greater than 2/1 or preferably greater than 10/1 and for some particular uses greater than 100/1.

 As a result, the inoculant alloys mentioned in the main patent are particularly suitable for being incorporated into the ferrous alloy during its preparation.

 Other objects, features and advantages of the present addition will appear more clearly in the light of the explanatory description which follows, made with reference to the following examples given merely by way of illustration and which can not in any way limit its scope. .

 Example 1

During the preparation of a hypereutectic cast iron at approximately 13 ° C., 0.5% by weight of inoculant alloy usually used in foundries having the following composition (A) is inoculated in a manner known per se:
Si = 75
Ca = 3;
Al = 4
Fe = the balance.

A cast iron having the composition mentioned in Table I is obtained with the physical characteristics also mentioned in Table I
By inoculating 0.5% by weight of an inoculant alloy according to the present invention, having the following composition (B)
Si = 75
Ca = 3
Al = 4
La = 0.5; or 25.10 4% by weight of lanthanum or 25 ppm, a melting is obtained having the composition and the physical characteristics also mentioned in Table I. It can be seen that the number of graphite spheroids obtained is much more numerous and the effects of quenching (zone-carburized) lower with the use of the inoculant alloy according to the present invention relative to the known inoculant alloy, and this unexpectedly.

TABLE I

Alloy <SEP> Composition <SEP> of <SEP> PROPERTIES
<tb> incipient <SEP> the <SEP> melting <SEP> obtained <SEP> G <SEP> NnA <SEP> NnL <SEP> Qg <SEP> P <SEP> + <SEP> C <SEP> C1
<tb> A <SEP> C <SEP> = <SEP> 3.92 <SEP> 0.10297 <SEP> 491.02 <SEP> 7.156 <SEP> 0.859 <SEP> 0.5598 <SEP> 0.0425
<tb> (Art <SEP> ant ~ <SEP> If <SEP> = <SEP> 2.31
<tb> laughing <SEP> Mn <SEP> = <SEP> 0
<tb><SEP> P <SEP> = <SEP> 0.025
<tb><SEP> S <SEP> = <SEP> 0.007
<tb><SEP> Ni <SEP> = <SEP> 0.73
<tb><SEP> Cr <SEP> = <SEP> 0.04
<tb><SEP> Mg <SEP> = <SEP> 0.038
<tb><SEP> C <SEP> = <SEP> 3.91
<tb><SEP> If <SEP> = <SEP> 2.26 <SEP> 0.10734 <SEP> 568.75 <SEP> 8.4375 <SEP> 0.989 <SEW> 0.4677 <SEP> 0, 0175
<tb> B <SEP> Mn <SEP> = <SEP> 0
<tb> (Invention) <SEP> P <SEP> = <SEP> 0.026
<tb><SEP> S <SEP> = <SEP> 0.008
<tb><SEP> Ni <SEP> = <SEP> 0.70
<tb><SEP> Cr <SEP> = <SEP> 0.05
<tb><SEP> Mg <SEP> = <SEP> 0.039
<tb> Note: C = Parts by volume of graphite
NnA = number of nodules / mm
NnL = number of nodules / mm Qg = quality index (distribution of modules,
ideal distribution = 1)
P + C = Perlite and cementite
C1 = Carbide, parts by volume.

 In the case of steels, lanthanum can solve the problems associated with the deoxidation of steel.

In this regard, in order to make the best use of the properties of lanthanum, it is important to deoxidize and / or desulphurize the steel in the conventional manner, for example by pre-oven deoxidation by addition of 0.8 to 1% by weight of aluminum. that is completed by pocket deoxidation using lanthanum levels in the previously mentioned ranges, that is to say in an amount advantageously between 4% and 2%, ie from 1 to 100 ppm, and preferably from 1-10 to 30 ppm.

 Thus, because of the small amount of lanthanum added, there are very few inclusions, these being well distributed and thus modifying the viscosities of the inclusions which results in a very fluid steel bath, solidification , and lastly to a very clean steel. In addition, almost complete desulfurization of steel also acts in the same direction on the flowability of steel.

 These observations are confirmed by the following example.

 Example 2

It is desired to prepare a steel having the following chemical composition
C = 0.19 - 0.24
Mn = 0.65 - 0.90
Si = 0.40 - 0.60
P = z to 0.025
S = # to 0.012
Cr = z to 0.30
Al = 0.025 - 0.040.

 For this purpose, from a steel of conventional composition, a casting of 13570 kg is carried out in a furnace to which is added 0.07% carbon and 0.15% Mn.

To achieve a refining of the oxygen content, is carried out prior to deoxidation in the oven, according to the traditional method, by addition of about 0.8% of aluminum. After the addition of the aluminum, a sample of steel is taken directly from the furnace and the following composition is obtained:
C = 0.20 Cu = 0.06
Si = 0.30 Cr - = 0.12
Mn = 0.46 Ni = 0.07
P = 0.007 Sn = 0.007
S = 0.012 Mo = 0.03
Al = 0.026 02 = 0.011
Crystallographic analysis shows that this steel contains macro-inclusions of aluminate and silicate and micro-sulfides.

 According to the present invention, after the aforementioned oxidation in the oven with aluminum, a pocket deoxidation is carried out by adding 27 kg of a silico-lanthanum alloy comprising 45% Si, 0.5% La, the rest being iron, or an addition of about 0.20% of the alloy to lanthanum which corresponds to an addition of about 3% lanthanum or about 10 ppm.

A steel sample is taken from the ladle after deoxidation with the lanthanum inoculant alloy of the present invention and a steel having the following composition is obtained.
C = 0.23 Cu = 0.06
Si = 0.51 Cr = 0.13
Mn = 0.85 Ni = 0.07
P = 0.007 Sn = 0.007
S = 0.009 Mo = 0.03
Al = 0.031 02 = 0.006
The crystallographic analysis of this steel shows that a steel having micro-inclusions of aluminate and silicate is obtained by obtaining refractory corpuscles of small average diameter of the order of 1 to 2 microns and limited number.

 Furthermore, the lanthanum according to the present invention in alloy with other metals, including with rare earths as far as the aforementioned ratio lanthanum / rare earths, allows, in the course of the kinetics of deoxidation, desulfurization , de-nitriding and dehydrogenation, to obtain the number of inclusions in the size and composition expected for the applications of the steel that one wishes to produce which constitutes a particularly remarkable industrial result.

 Thus, the addition of lanthanum, under the conditions of the present invention, makes it possible to reduce the anisotropy of the steels and thus to improve the ratio of longitudinal and transverse resilience obtained.

 It should be noted generally that lanthanum is in the ferrous alloy in the form of compounds such as oxides, and / or sulfides, and / or oxysulfides, and / or nitrides, and / or hydrides, and / or carbides forming non-interfering inclusions in ferrous alloys.

 In addition, during the development of the ferrous alloy, a significant proportion of the lanthanum compounds is removed in the slag and found in the metal or alloy about 30% of the lanthanum added.

 Example 3

Stainless steels were prepared according to the standard Type AISI 304. Tests were carried out on industrial casting greater than or equal to 10 tons. To prepare these stainless steels, was incorporated during their preparation from 1 kg to 2 kg per ton of a ferro-silico lanthanum comprising 45% by weight of silicon, 0.5% of lanthanum, the balance being constituted by iron. Before the incorporation of the alloy with lanthanum, aluminum deoxidation had previously been carried out as indicated in the preceding example.
The results of the tests showed that the steels had a very satisfactory cleanliness characterized by the presence of few globular elements as well as a slight decrease in the presence of clusters of alumina-type hard oxide.

Two test pieces A and B were also produced from this stainless steel type AISI 304, the results of which are listed in Table II below.
TABLE II

<tb> specimen <SEP> limit <SEP> Module <SEP> Load <SEP> Allon
<tb><SEP> elastic <SEP> from <SEP> YOUNG <SEP> to <SEP><SEP>
<tb><SEP> to <SEP> 0.7% (kg / mm2) <SEP><SEP> (kg / mm) <SEP> rupture
<tb><SEP> total
<tb><SEP> (section2 <SEP> ::
<tb><SEP> 126.7 <SEP> mm <SEP>) <SEP>
<tb><SEP> A <SEP> 30.8 <SEP> 19731 <SEQ> 8300 <SEQ> kg
<tb><SEP> or
<tb><SEP> 65.5 <SEP> kg / mm2 <SEP> 56, <SEP>
<tb><SEP> B <SEP> 32.0 <SEP> 18792 <SE> 8450 <SEP> kg
<tb><SEP> or
<tb><SEP> 66.7 <SEP> kg / mm <SEP> 55,
<Tb>
Similarly, resilience tests were carried out at 200 ° C after water super-quenching of the stainless steel after heating at 11000 ° C for 30 minutes. A U-cut was made on each sample to determine the resilience. These resilience tests were performed on the two samples mentioned above.
A and B for which five attempts were made on the one hand to measure the resilience in the long direction, ie in the so-called resilient rolling direction
L then the resilience in the cross direction in the same plane as the longitudinal direction called resilience
T1 and finally the resilience in the cross direction after a rotation of 900, that is to say in a plane perpendicular to the measurement plane of the resilience through T1, said resilience T2. The results are listed in Table III below.

TABLE III

<tb> samples <SEP> resilience <SEP> L <SEP> resilience <SEP> T1 <SEP> resilience <SEP> T2
<tb><SEP> Kcu
<tb><SEP> (kgm) <SEP> (4F / cm2 <SEP> (kgm) <SEP> W <SEP> cm2) <SEP>) <SEP> (kgm) <SEP> (kgm / cm <SEP >
<tb><SEP> Assay <SEP> 1 <SEP> 18.443 <SEP> 37 <SEP> 16.042 <SEP> 32 <SEP> 14.687 <SEP> 29
<tb><SEP> Assay <SEP> 2 <SEP> 16,850 <SEP> 34 <SEP> 16,581 <SEP> 33 <SEP> 14,687 <SEP> 29
<tb><SEP> A <SEP> Assay <SEP> 3 <SEP> 16.042 <SEP> 32 <SEP> 14.687 <SEP> 29 <SEP> 15.230 <SEP> 30
<tb><SEP> Assay <SEP> 4 <SEP> 17.9 * 16 <SEP> 36 <SEP> 15,772 <SEP> 32 <SEP> 16,312 <SEP> 33
<tb><SEP> Assay <SEP> 5 <SEP> 18,180 <SEP> 36 <SEP> 16,042 <SEP> 32 <SEP> 16,582 <SEP> 33
<tb><SEP> Assay <SEP> 1 <SEP> 17.916 <SEP> 36 <SEP> 16.581 <SEP> 35 <SEP> 13.872 <SEP> 28
<tb><SEP> Assay <SEP> 2 <SEP> 18,180 <SEP> 36 <SEP> 15,501 <SEP> 31 <SEP> 13,873 <SEP> 28
<tb><SEP> B <SEP> Assay <SEP> 3 <SEP> 16,581 <SEP> 33 <SEP> 14,416 <SEP> 29 <SEP> 15,501 <SEP> 31
<tb><SEP> Assay <SEP> 4 <SEP> 15,772 <SEP> 31 <SEP> 14,416 <SEP> 29 <SEP> 14,144 <SEP> 28
<tb><SEP> Assay <SEP> 5 <SEP> 17.651 <SEP> 35 <SEP> 14.687 <SEP> 29 <SEP> 14.416 <SEP> 29
<Tb>
From the above results, the average breaking load for samples A and B obtained by the process according to the present invention is 65.5 kg / mm for sample A and 66.7 kg / mm 2 for sample B.

However, the average breaking load for stainless alloy according to the AISI 304 standard varies from 50 to 68 kg / mm 2. It can therefore be concluded that the process of the present invention provides a breaking load at the top of the range of the standard.

 With regard to the elongation property, according to the standard the percentage of elongation varies between 40 and 50% while with the method of the present invention the steel obtained has a percentage of elongation for the sample A equal to , at 56.9 and for sample B 55.4, which shows that the incorporation of lanthanum makes it possible to obtain a much greater elongation with respect to the elongation usually obtained, and this unexpectedly.

 Similarly, the yield strength at 0.2% is according to the present invention equal to 30.8 kg / mm 2 (sample A) and 32.0 kg / mm 2 (sample B) which is very significantly above average a steel according to AISI 304 which is of the order of 18.2 kg / mm2.

With regard to the resilience tests listed in Table III, it can be seen that the average values k 0 obtained are practically identical whether in the long direction L, in the transverse direction T1 or T2, these values being respectively 31 -37 kgm / cm2 (L-resilience) of 29-35 kgm / cm2 (T1 resilience)) and 28-33 kgm / cm (T2 resilience) while according to the standard the mean value in the long direction or L-resilience is twist 10-12 kgm / cm2
It can therefore be seen that the incorporation of lanthanum in the aforementioned proportions makes it possible to obtain a very clear and very significant improvement in the anisotropy of the steels, quite unexpectedly with respect to the usual anisotropy of the steels.

 Of course, the invention is not limited to the embodiments described and shown which have been given by way of example. In particular, it comprises all the means constituting technical equivalents of the means described and their combinations if they are executed according to its spirit and implemented in the context of the following claims.

Claims (6)

 A process for the preparation of ferrous alloys according to any one of the claims of the main patent, characterized in that it comprises the incorporation of about 0.0001% (ie 1 ppm) to about 0.01% (either 100 ppm) by weight of lanthanum to said ferrous alloy during its incorporation.  2. Process according to claim 1, characterized in that it comprises the incorporation of approximately 0.001% (ie 10 μm) to approximately 0.003% (ie 30 ppm) to 0.01% (ie 100 ppm) by weight of lanthanum to said ferrous alloy during its elaboration.  3. Method according to claim 1 or 2, characterized in that the lanthanum is incorporated as an alloy with any metal capable of forming a compound homogeneous with lanthanum, that is to say having a solubility diagram with the lanthanum alone or in combination with other rare earths (including cerium), in a proportion of 0.01 to 90% by weight of lanthanum, provided that the lanthanum alloy has a low cerium content alone or in combination with 'other Rare earth.  4. Method according to one of claims 1 to 3, characterized in that the lanthanum is incorporated in the form of a compound such as chloride, fluoride, oxide obtained from lanthanide, or mixtures of said compounds provided that these lanthanide compounds have low cerium content alone or in combination with other rare earths.  5. Method according to claim 3 or 4, characterized in that the weight ratio lanthanum / Terres Rare (except lanthanum) in the abovementioned alloys or compounds of the abovementioned lanthanide is at least greater than 2/1 or preferably greater than 10 and more preferably greater than 100/1.  6. Ferrous alloys, characterized in that they are prepared by the process according to any one of the preceding claims.