WO2002006548A1

WO2002006548A1 - Fe-ni or fe-ni-co or fe-ni-co-cu alloy strip with improved cuttability

Info

Publication number: WO2002006548A1
Application number: PCT/FR2001/002223
Authority: WO
Inventors: Lucien Coutu; Vincent Durieux; Jérôme GIUSTI
Original assignee: Imphy Ugine Precision
Priority date: 2000-07-13
Filing date: 2001-07-10
Publication date: 2002-01-24
Also published as: EP1299568A1; FR2811684B1; JP2004517205A; US20030164211A1; AU2001277569A1; KR20030026966A; FR2811684A1

Abstract

The invention concerns a strip made of austenitic Fe-Ni alloy or Fe-Ni-Co alloy or Fe-Ni-Co-Cu alloy whereof the chemical composition of the alloy comprises, in wt. %: 30 % </= Ni </= 70 % ; 0 % </= Cu </= 20 % ; 0 % </= Mn + Cr < 5 % ; 0 % </= W +2 x Mo </= 2 % ; 0 % </= Ti + V + Nb + Al </= 1 % ; 0.0005 % </= B </= 0.007 % ; the rest being iron and impurities such as C, S, P, O and N; the chemical composition being such that Fe + Ni + Cu + Co >/= 95 %. The alloy has a cubic texture with a cubic texture coefficient Dc >/= 7. The invention also concerns a method for making a strip and a method for making a workpiece by mechanical cutting.

Description

FE-NI OR FE-NI-CO OR FE-NI-CO-CU ALLOY BAND WITH CUT-OUT

IMPROVED

The present invention relates to the manufacture of alloy parts of the Fe-Ni or Fe-Ni-Co or Fe-Ni-Co-Cu type obtained by fine mechanical cutting of blanks which may have been previously stamped. These parts are generally used in miniature electronic or electrical components.

Many small parts, such as the electron gun parts of the color display cathode ray tubes or the integrated circuit support grids or even micro motor parts, are produced by fine mechanical cutting of blanks, possibly stamped from alloy of Fe-Ni or Fe-Ni-Co type containing about 30% to 70% nickel. The quality of the cut is very important for this type of part, in particular to avoid the presence of burrs. The blanks from which the pieces are cut are taken from strips obtained by cold rolling and annealing, generally isotropic or weakly textured. In the case of flat or almost flat parts, that is to say obtained without significant plastic deformation of the blank, the strips are often used in the work-hardened state so as to have a higher hardness and a lower ductility than the strips obtained directly after annealing. This higher hardness and lower ductility favor mechanical cutting. On the contrary, when the drawing is large, the strips are used in the annealed state so as to have a high ductility and a high plastic deformation ability. In this case, the cutting operation, which is the drilling of a hole, is sometimes preceded by local hardening intended to reduce the ductility of the metal along the cutting line. However, for both poorly stamped parts and for highly stamped parts, the quality of the cut is often insufficient, which leads to a rejection of a significant proportion of cut parts.

In order to improve the quality of the cutting, it is known to add small quantities of alloying elements such as molybdenum or niobium to the alloy, or to keep very small quantities of residual elements such as carbon, sulfur, phosphorus or oxygen which can form inclusions. However, these means are insufficient and the ability to mechanically cut Fe-Ni or Fe-Ni-Co or Fe-Ni-Co-Cu is considered to be much lower, for example, than that of 305 stainless steel.

The object of the present invention is to remedy this drawback by proposing a means for improving the cuttability of alloys of the Fe-Ni or Fe-Ni-Co or Fe-Ni-Co-Cu type used in the form of thin strips for manufacturing by fine mechanical cutting of parts used in particular in electronic or electrical equipment.

To this end, the subject of the invention is a strip of Fe-Ni alloy or of Fe-Ni-Co or Fe-Ni-Co-Cu austenitic alloy in which the chemical composition of the alloy comprises, in% by weight:

30% <Ni <70% 0% <Cu + 2 x Co <20%

0% <Mn + Cr <5% 0% <W +, 2 x Mo <2% 0% <Ti + V + Nb + AI <1%

0.0005% <B <0.007% the remainder being iron and impurities such as C, S, P, O and N; the chemical composition being such that Fe + Ni + Cu + Co> 95%. In addition, the alloy has a cubic texture with a cubic texture coefficient of> 7. Preferably, separately or in combination, the boron content is between 0.0007% and 0.004%, the index De is greater than 10, the carbon content is less than or equal to 0.05%, the sulfur content is less than or equal to 0.01%, and better still less than or equal to 0.007%, the oxygen content is less than 0.005%. The invention also relates to a method for manufacturing a strip of Fe-Ni or Fe-Ni-Co or Fe-Ni-Co-Cu alloy according to which:

an alloy strip, the chemical composition of which is defined above, is produced by cold rolling, with a work hardening rate greater than 80%,

- A fine grain recrystallization annealing is carried out on the strip, - and, optionally, an additional cold rolling is carried out with a work hardening rate of less than 40%.

Finally, the invention relates to a method for manufacturing a part by mechanical cutting or by mechanical cutting and stamping, according to which a blank is taken from a strip according to the invention and is carried out on the blank at least one mechanical cutting operation and possibly at least one stamping operation, the at least one stamping operation can be performed before or after at least one mechanical cutting operation. The part is, for example, an electron gun part with an electron passage hole. The part can also be an integrated circuit support with connection tabs. The part can also be a magnetic core of micro motor or transformer. This list of applications is not exhaustive.

The invention will now be described in more detail with reference to the appended figure and illustrated by examples. The figure 1-a diagrammatically shows a section in a band in which a hole was drilled by mechanical cutting having a cutting facies corresponding to poor cuttability.

The figure 1-b, schematically represents in section a strip in which a hole was drilled by mechanical cutting having a cutting facies corresponding to an acceptable cuttability.

Figure 1-c, schematically shows in section a strip in which a hole was drilled by mechanical cutting having a cutting facies corresponding to good cutability.

The strips according to the invention are thin strips (thickness generally less than 1.5 mm) cold-rolled in an alloy of the Fe-Ni or Fe-Ni-Co or Fe-Ni- Co-Cu type known per se in their most general form. In this type of alloy, nickel, or cobalt which is a substitute for nickel, makes it possible to adjust properties such as the coefficient of thermal expansion or the magnetic permeability. The nickel content is between 30% and 70%; copper and cobalt which are optional elements have contents such that the sum Cu + 2 x Co is less than or equal to 20%. The remainder is essentially iron, impurities such as carbon, sulfur, phosphorus, oxygen and nitrogen, and, optionally, complementary alloying elements such as manganese, chromium, tungsten, molybdenum , titanium, vanadium, niobium and aluminum. However, the iron, nickel, copper and cobalt contents must be such that: Fe + Ni + Cu + Co> 95%. The contents of alloying elements must be such that: Mn + Cr <5%, W + 2 x Mo <2% and Ti + V + Nb + Al <1%. Certain impurities such as carbon, sulfur and oxygen which is in the form of inclusions, may be desirable in small quantities because they have a favorable effect on the cuttability. Nevertheless, the carbon content should preferably remain below 0.05%, the sulfur content should preferably remain below 0.01%, and better still less than 0.007%, and the oxygen content should preferably stay below 0.005%.

Furthermore, the alloy contains from 0.0005% to 0.007% of boron, and preferably from 0.0007% to 0.004%, and it has a cubic texture (001) <100>, characterized by a cubic texture index From greater than 7, and preferably greater than 10. Indeed, the inventors have found, surprisingly, that an addition of boron combined with a strongly pronounced cubic texture very significantly improves the ability to mechanically cut the alloys of Fe-Ni or Fe-Ni-Co or Fe-Ni-Co-Cu type. The cubic texture index De is the cubic / lisotropic ratio I of the maximum intensities of reflected X-radiation, measured on a pole figure (111) at a point located at 54 ° 44 'from the center of the figure and on the line at 45 ° with respect to the rolling direction for a sample of the strip to be characterized on the one hand, and for an isotropic sample on the other hand. The more or less texture character of a strip can also be evaluated in a simple but approximate manner by a drawing test, by measuring the drawing horns. This method can only be used to characterize a sufficiently ductile metal. To implement it, one can, for example, start from a disc of 60mm in diameter, stamp this disc to form a bucket of 33mm in diameter and 19mm in average height. The height difference between the highest points and the lowest points of the upper edge is then measured. If this difference in height is less than 0.3 mm, the strip is isotropic or very little textured; if this difference is greater than 1.5mm, the strip is highly textured. In order to obtain alloy strips having a marked cubic texture, the alloy is produced, it is cast and it is hot rolled in a manner known per se so as to obtain a hot strip of sufficient thickness to allow '' obtaining a cold strip having the desired thickness, by cold rolling with a reduction rate greater than 80%, and better still greater than 90%. The thickness of the hot-rolled strip can be, for example, 5 mm. Cold rolling must be carried out without intermediate annealing, but may be preceded by annealing. This is the case, in particular, when, taking into account the thickness of the hot strip and the thickness targeted for the cold strip, it is necessary to carry out several successive cold rolls. The final cold rolling (with a reduction rate higher than 80%) is followed by recrystallization annealing generally carried out in a passage oven under a protective atmosphere consisting, for example, of a mixture of hydrogen and nitrogen with a dew point below -40 ° C. The oven temperature, around 1000 ° C, should be sufficient to achieve fine grain recrystallization, but not too high to avoid unwanted giant grain secondary recrystallization. The duration of the annealing is generally of the order of a minute. Those skilled in the art know how to adapt the precise annealing conditions on a case-by-case basis in order to obtain fine-grain recrystallization while avoiding secondary recrystallization.

Optionally, and in order to increase the hardness of the strip, the recrystallization annealing can be followed by additional cold rolling with a reduction rate of less than 50%, or better still, less than 30%, so as not to degrade too much. the initial cubic texture. When the reduction rate of the additional cold rolling is less than 10%, a softened or slightly cold worked cold strip is obtained having a marked cubic texture. When the reduction rate of the additional cold rolling is greater than 10%, a cold worked strip is obtained having a marked cubic texture.

Given the thickness of the hot strip, the cold rolled strips thus obtained have a thickness generally less than 0.5 mm.

To manufacture a part in accordance with the invention, in a strip having a cubic texture index greater than 7, or better greater than 10, or better still greater than 15, a blank is cut by mechanical cutting in a manner known per se . The blank can be either the finished part which is then flat, or a blank. The blank can be shaped by stamping and then cut again by mechanical cutting. This cut can be for example a hole. This cutting operation can be preceded by local hardening.

When the part is flat or slightly deformed by stamping, that is to say when the deformation rate generated by stamping is less than 20%, the strip can be used after additional cold rolling with a reduction rate between 10% and 30% or even 50%. This is the case, for example, of flat parts for electron guns of color display cathode ray tubes, or of integrated circuit support grids (or "lead frames") comprising connection lugs, or of rotors or stators. micro electric motors.

When the part is strongly deformed, by stamping or by bending or by local thickness reduction, i.e. with deformation rates greater than 20%, the strip is used in the softened or slightly cold worked state, that is to say without additional cold rolling or with an additional cold rolling having a reduction rate of less than 10%. This is the case, for example, with certain parts of electron guns for color display cathode ray tubes.

The quality of the cut is assessed by the cut facies which has a sheared area and a torn area. The line of demarcation between these two zones must be regular and located approximately mid-thickness. There should be no burrs. Three cutting facies are shown in Figures 1a, 1b and 1c. These facies are those observed on a hole 1a, 1b and 1c, drilled by punching in a strip 2a, 2b and 2c. Only half of each hole is shown after having cut the strips along a plane passing through the axis of the holes. The walls 3a, 3b and 3c of the holes each have a sheared area 4a, 4b and 4c, and a torn off area 5a, 5b and 5c.

Figure 1a corresponds to an alloy strip having poor cuttability. The sheared zone 3a corresponds to the greater part of the thickness and ends downwards, by large burrs 6a.

FIG. 1 b corresponds to an alloy strip having just acceptable cuttability. The sheared area 3b roughly corresponds to almost half the thickness and ends at the bottom with a few burrs 6b.

Figure 1c corresponds to an alloy strip having excellent cuttability. The sheared zone 3c corresponds to approximately half of the thickness and does not include any burrs. These figures are given for information only. A person skilled in the art knows how to assess in each case the quality of the cut according to more precise criteria than what can be deduced directly from these figures.

In addition to observing these cutting facies, the quality of the cutting can also be assessed by the geometric quality of the parts obtained. When the cut is the drilling of a round hole, the assessment of the quality of the cut takes into account the more or less circular character of the hole.

In general, the observations necessary to assess the quality of the cut pieces are made with a magnification between x10 and x50. By way of examples and comparisons, hot-rolled strips 4.5 mm thick were made of FeNi42 alloy, the chemical compositions in% by weight are given in Table 1.

Table 1

The PV588 and PW075 alloys have analyzes in accordance with the invention, the PV408 alloy is given for comparison.

With these hot strips, cold strips were produced according to 6 different manufacturing ranges, marked A, B, C, D, E and F, comprising: a first cold rolling with an ECR1 hardening rate, an annealing recrystallization in a passage furnace and a second cold rolling with an ECR2 hardening rate. The ECR1 work hardening was in some cases preceded by a preliminary work hardening of the hot rolled strip followed by recrystallization annealing to adjust the thickness to the desired value. The hardening rates for each range as well as the hardnesses HV and the elongations at break A% obtained (identical for the three alloys) are given in Table 2.

Table 2

- For each of these ranges, the cubic texture indices De obtained for each of the alloys are given in Table 3.

Table 3

PV588 Dc = 1 Dc = 1 nd De = 10 De = 25 De = 7

PW075 Dc = 1 Dc = 1 De = 10 De = 25 De = 45 De = 12

These results show that to obtain a cubic texture index of greater than 10, the rate of work hardening ECR1 must be high and preferably higher than 80%, and the rate of work hardening ECR2 must not be too important. The cold-rolled strips of PV588 alloy obtained by the ranges D, E and F, as well as the PW075 alloy strips obtained by the ranges C, D, E and F correspond to the invention. The others are given for comparison.

With the 0.25 mm thick strips corresponding to the three alloys and the manufacturing range D, mechanical support parts for integrated circuits (“lead frame”) were produced. The PV588 and PW075 alloys containing boron according to the invention gave 100% of good parts. On the other hand, the PV408 alloy gave bad parts with large burrs.

With the alloy PW075 (containing boron according to the invention), three strips of thickness 0.4 mm were obtained, obtained respectively with the ranges A, B, and C, from which lots of flat parts were cut. comprising a circular hole of 0.5mm in diameter obtained by punching.

In the batch corresponding to range A (comparison), only 24% of the pieces were good and in the batch corresponding to range B (comparison), only 53% of the pieces were good. On the other hand, 100% of the pieces in the lot corresponding to the C range (invention) were good.

Claims

1 - Strip of Fe-Ni alloy or of Fe-Ni-Co alloy or of austenitic Fe-Ni-Co-Cu alloy, characterized in that the chemical composition of the alloy comprises, in% by weight:

30% <Ni <70% 0% <Cu + 2 x Co <20%

0% <Mn + Cr <5% 0% <W + 2 x Mo <2% 0% <Ti + V + Nb + AI <1%

0.0005% <B <0.007% the remainder being iron and impurities such as C, S, P, O and N, the chemical composition being such that Fe + Ni + Cu + Co> 95%, and in that the alloy has a cubic texture with a cubic texture coefficient Dc 7.

2 - Strip according to claim 1 characterized in that:

0.0007% <B <0.004%

3 - strip according to claim 1 or claim 2 characterized in that Dc> 10. 4 - strip according to any one of claims 1 to 3 characterized in that the carbon content of the alloy is less than or equal to 0 , 05%.

5 - Strip according to any one of claims 1 to 4 characterized in that the sulfur content of the alloy is less than or equal to 0.01%.

6 - Strip according to claim 5 characterized in that the sulfur content of the alloy is less than or equal to 0.007%.

7 - Strip according to any one of claims 1 to 6 characterized in that the oxygen content is less than 0.005%.

8 - Process for manufacturing a strip according to any one of claims 1 to 7 characterized in that: - an alloy strip is manufactured by cold rolling, the composition of which is defined by claims 1 to 7, with a rate of work hardening greater than 80%,

- a fine grain recrystallization annealing is carried out on the strip,

- And, optionally, an additional cold rolling is carried out with a work hardening rate of less than 40%. 9 - Process for manufacturing a part by mechanical cutting or by mechanical cutting and stamping, characterized in that:

- a blank is taken from a strip according to any one of claims 1 to 7, - and at least one mechanical cutting operation and possibly at least one stamping operation is carried out on the blank, the at least one operation d stamping can be carried out before or after at least one mechanical cutting operation.

10 - Process according to claim 9 characterized in that the part is an electron gun part with electron passage hole, or in that the part is an integrated circuit support with connection tabs, or in that the part is a magnetic core of micro motor or transformer.