FR2757541A1 - NON-ORIENT GRAIN MAGNETIC STEEL SHEET - Google Patents

Abstract

A sheet steel contains less than 0.005 wt.% carbon, less than 0.1 wt.% phosphorous, 0.2 wt.% silicon, 0.1 wt.% manganese and additional quantities of Si, Mn and aluminium defined by equations 80Mn+90Si ≥ 85 (I) and 5.38 ≤ 6Mn+13Al+12Si ≤ 16 (II). Maximum levels of Si and Mn are 0.6 wt.% and 1.3 wt.% respectively. The steel is formed into a sheet, e.g. by cold-rolling, then annealed at 800-900 degrees C, remaining below the ferrite-austenite transformation temperature to produce a structure with non-oriented grains.

Description

NON-ORIENT GRAIN MAGNETIC STEEL SHEET.

  The present invention relates to the field of steel sheets for electrical use, used in particular for the construction of transformers, motors and alternators. It relates specifically to non-grain magnetic sheets

  cold rolled oriented delivered in the finished state so called "Fully Process" sheets.

  Electrical plates are traditionally divided into

two families.

  ] o0 Cold-rolled magnetic sheets delivered in the semi-finished state, known as "Semi Process" sheets, used in low to medium power appliances (small and medium-sized electrical appliance engines, transformers, automobile alternators, for example) ) constitute the

first family.

  These sheets contain, by weight, a carbon content of between 0.03 and 0.08%, a manganese content of between 0.2 and 1.0% and a phosphorus content of between 0.01 and 0.25%. and optionally, but not necessarily, aluminum and / or silicon, the aluminum content being less than 1.0% and the silicon content being less than

0.2%.

  These sheets are manufactured by hot and cold rolling, then recrystallized annealing and passage in a skin pass

  to harden the metal by a deformation of 4 to 10%, sometimes more.

  It is in this form that the sheets are shipped to the customer, but at this stage, their magnetic properties are poor because they have

  have been degraded during hardening.

  This hardening is however necessary for the metal

  can easily be cut by the customer.

  The latter must, after cutting and shaping of the sheet, perform a heat treatment aimed firstly to decarburize the steel to a carbon content of less than 0.005%, and secondly to increase its size. of grain (operation facilitated by hardening which has been

realized in the skin pass).

  Cold-rolled magnetic sheets delivered in the so-called finished state

  "Fully Process" sheets constitute the second family.

  These sheets have the particularity of being usable by the customer directly in the delivery condition of the producer, without the need for a subsequent heat treatment to obtain the magnetic properties concerned. These sheets "Fully Process" are divided into two categories. Grain-oriented "Fully Process" plates constitute the

first category.

  They have the particularity to contain high silicon contents (of the order of 3%), and to have a very marked orientation of their texture (110-001), the direction 100 being oriented in the direction of rolling, which corresponds, in use of the sheet, to the direction in which the

magnetic field is applied.

  Silicon increases the resistivity of the sheet and thus limits

eddy current losses.

  Es1 Sheet of this type is applied in particular to the manufacture

of power transformers.

  Non-oriented grain "Fully Process" sheets constitute the

second category.

  They contain silicon in proportions that may be lower than the previous ones (0.2 to 3.0%), and also phosphorus. This last element plays the same role as silicon in the limitation of eddy current losses, and its partial substitution at

  Silicon makes it possible not to increase too much the fragility of the metal.

  The sheets of this type do not have a particular texture and are applied in particular to the manufacture of rotating machines,

  motors or alternators for example.

  This second family of sheets called "Fully Process" sheets generally contain by weight a carbon content of less than 0.005%, a manganese content of between 0.1 and 0.7%, a silicon content of greater than 0.2%, a phosphorus content of between 0.1 and 0.2%, and are manufactured as follows: - a steel having the above composition is prepared, cast and rolled in the form of sheet metal, and then the sheet metal is subjected to developed an annealing treatment, for example a continuous annealing, under a high temperature neutral atmosphere (in the range 800 to 900 C) and so as to remain below the ferrite-austenite (a-y) transformation point of the shade

of treated steel.

  As will be understood, the method of manufacturing such a sheet "Fully Process" is to obtain a carbon content of less than 0.005%, then to subject it to an annealing to give it the

magnetic properties required.

  To obtain the carbon content of less than 0.005%, it is possible either to carry out a decarburization treatment at the steelworks by the use of an apparatus for degassing vacuum-type liquid steel of the RH or DH type, or to carry out after rolling. cold a decarburizing annealing under atmosphere

  containing a mixture of oxidizing gases.

  Each of these two families of electric sheets

  have certain advantages and disadvantages.

  It is known that the magnetic characteristics of a steel sheet are obtained on the one hand by certain alloying elements, and on the other hand by the

  grain size of the metal structure.

  Indeed, certain alloying elements, such as manganese, phosphorus, silicon and aluminum, increase very strongly the

  resistivity of the metal, and thus gives it good magnetic properties.

  Similarly, the larger the grain size (to a certain upper limit), the better the characteristics

magnetic metal.

  In the case of "Semi Process" sheets, the magnetic characteristics are guaranteed by the recrystallization and grinding annealing operation carried out after cutting.

sheet metal.

  In addition to the effect of critical hardening, the transition to the skin pass makes it possible to obtain the favorable mechanical characteristics to achieve

the cutting of the sheet.

  Thus, the chemical composition of the metal, in terms of alloying elements, is relatively secondary from the point of view of mechanical characteristics and cutability, because these are provided by the operation

from hardening to skin pass.

  Thus a sheet "Semi Process" does not pose any particular problems of cutting, but it imposes an additional stage of treatment (annealing of decarburization, recrystallization and grinding of grains) and to achieve this step on cut pieces, resulting in productivity less than if this step was carried out by the producer

  during the manufacturing cycle of the sheet.

  In the case of "Fully Process" sheets, it is impossible to optimize the mechanical properties of the metal after annealing of grain magnification, otherwise its magnetic characteristics will be damaged. In this case, the chemical composition, in terms of alloying elements, is of particular importance since it strongly conditions the obtaining of the mechanical characteristics necessary for

good cutability of the sheet.

  These "Fully Process" sheets are nevertheless less difficult to cut than the "Semi Process" sheets because the ratio between the elastic limit and the breaking load Re / Rm is between 0.65 and 0.70, and

  the elongation A% is high (greater than 30).

  The object of the invention is to propose steel sheets for electrical use, for electrical appliances of low to medium power, having excellent cutability, and manufactured according to a short chain

  and economic, of the "Fully Process" type.

  For this purpose, the subject of the invention is a steel sheet for electrical use, of the type comprising less than 0.005% by weight of carbon, obtained in two stages, a first step consisting in manufacturing a sheet of steel, then a second step of subjecting said sheet to an annealing treatment at a temperature in the range 800 C to 900 C and so as to remain below the point of transformation ferrite-austenite (a -> y), characterized in that that the sheet comprises, by weight, a carbon content of less than 0.005%, a phosphorus content of less than 0.1%, a silicon content equal to 0.2%, a manganese content equal to 0.1%, and a or more elements selected from silicon, manganese and aluminum, with contents such that: Mn + 90 Si> 85 and 5.38 <6Mn + 13AI + 12Si <16 and the total silicon content is less than 0, 6% and the total manganese content is less than 1.3%,

  the rest being iron and unavoidable residual impurities.

  According to other characteristics of the invention, the content by weight of phosphorus is between 0.01% and

0.09%;

  the ratio between the total silicon content and the total manganese content is less than 0.5; the sheet comprises, by weight, a carbon content of less than or equal to 0.004%, a silicon content of between 0.25 and 0.35%, a manganese content of between 0.8 and 1.0%, a content of phosphorus between 0.05 and 0.09%, an aluminum content of between 0.08 and

  o0 and 0.12%, the remainder being iron and unavoidable residual impurities.

  The features and advantages of the invention will become apparent

  following the description which follows, given only as an example.

  The first important characteristic of the invention lies

  in limiting the phosphorus content of the steel to 0.1% by weight.

  The inventors have found that the presence of phosphorus in the steel, with a content of between 0.10 and 0.20% by weight, is detrimental to the cutability of the sheet made from such steel, and this

  independently of the mechanical characteristics.

  When cutting a blank of sheet metal by means of a device comprising a punch and a die with cutting edges, this cutting takes place in two phases: a first phase of shearing the metal, and a second phase tearing metal. The cutting edge therefore has two zones: a first shear zone located on the punch side,

  and a second broken area located on the die side.

  In the first cutting phase, the metal is sheared, and cracks in the metal at the cutting edge of the punch and the cutting edge of the die, which meet in the

  end of the cut, causing the metal to break.

  In a sheet "Fully Process" whose phosphorus content is greater than 0.10% by weight, it tends to segregate into layers, generally between one quarter and three quarters of the thickness of said sheet. These layers of phosphorus segregation are layers having a hardness greater than the rest of the sheet, and this phenomenon is detrimental to

The homogeneity of the cut.

  Cracks that begin in the metal after the first phase of cutting a blank taken from such a sheet are deflected when they encounter a layer of segregation of phosphorus and take a horizontal orientation, which affects the quality of the broken area of the cut. Indeed, this broken area of the cut is even sharper

  that the orientation of the cracks is vertical.

  The cut thus presents a broken non-homogeneous zone

with appearance of burrs.

  In addition, the horizontal orientation of the cracks often causes the detachment of certain metal particles, causing wear and tear.

abrasive cutting tools.

  It has therefore appeared important to limit the phosphorus content in steel, and the inventors have found that this phenomenon is no longer significant when this phosphorus content is less than 0.10% by weight.

weight.

  Preferably, the phosphorus content is between

0.01% and 0.09%.

  This limitation of the phosphorus content, favorable to the

  However, there are two detrimental effects of sheet metal cutting.

  On the one hand, from a mechanical characteristics point of view, phosphorus is one of the most efficient alloying elements to give the sheet a sufficient hardness, and on the other hand, the reduction of the phosphorus content leads to a degradation. magnetic characteristics, in

  particular in terms of specific total losses.

  It is therefore necessary to replace part of the phosphorus with one or more other elements which increase the characteristics

  sheet metal and its magnetic characteristics.

  The inventors have found that these elements can be

  advantageously chosen from manganese, silicon and aluminum.

  The second important characteristic of the invention is therefore that the sheet comprises, by weight, in addition to a carbon content of less than 0.005% and a phosphorus content of less than 0.1%, a silicon content equal to 0.2%, a a manganese content equal to 0.1%, and one or more elements chosen from silicon, manganese and aluminum, with contents such that: Mn + 90 Si> 85 and 5.38 <6Mn + 13Al + 12Si < 16 and the total silicon content is less than 0.6% and the total manganese content is less than 1.3%,

  the rest being iron and unavoidable residual impurities.

  We can also limit the total silicon content to 0.5% to remain in the field of so-called non-alloyed steels. Indeed, if the total silicon content is greater than 0.5%, the standards in force classify such

  steel in the category of alloy steels.

  The minimum silicon content of 0.2% is necessary

  to limit eddy current losses.

  The limitation of the total manganese content is necessary in order to ensure that the annealing carried out in the second step of the steel manufacturing process is carried out correctly, ie in the ferritic field while allowing sufficient magnification of the grains. Indeed, if the total manganese content is greater than 1.3%, the temperature of the ferrite-austenite transformation point (a -> y) is lowered and given that it is essential to carry out the annealing in the field. ferritic, the temperature of this annealing will no longer be sufficient to obtain a structure with grains large enough to give this steel the magnetic characteristics required. It is said that manganese is a

y-gene element.

  Thus, preferably, it will be chosen to replace the phosphorus by a so-called a-gene element, such as for example silicon, or several elements

at least one of which is a-gene.

  It is also important to respect the condition that 80 Mn + 90 Si> 85, because if it is not respected, the

  mechanical characteristics of the sheet obtained will be insufficient.

  Finally, it is important to respect the condition that, 38 <6 Mn + 13 AI + 12 Si <16, in order to guarantee the magnetic characteristics of the sheet, in terms of specific total losses and permeability. To obtain the carbon content of less than 0.005%, it is possible either to carry out a decarburization treatment at the steelworks by the use of an apparatus for degassing vacuum-type liquid steel of the RH or DH type, or to carry out after rolling. cold decarburizing annealing under an atmosphere containing a mixture of oxidizing gases, which can be combined with the annealing

  of recrystallization and enlargement of grains (second stage).

  The table below shows the composition of several

  embodiments of the invention, the contents being expressed in terms of

  hundred weight. Carbon steel phosphorus silicon manganese aluminum

A 0.002 0.09 0.4 0.7 0.001

B 0.002 0.05 0.3 1.2 0.001

C 0.004 0.05 0.5 0.6 0.2

D 0.004 0.01 0.01 1.2 0.3

E 0.004 0.03 0.2 1.0 0.3

  According to a preferred embodiment of the invention, the steel has an additional characteristic of limiting the ratio between the content

  n0 in total silicon and the total manganese content to 0.5.

  Indeed, if the ratio between the total silicon content and the total manganese content is greater than 0.5, the steel may pose some problems in terms of weldability, in particular in spark welding, which is detrimental to partly to the implementation of the plate i5 made of this steel, and secondly for the implementation of the method of

  continuous manufacture of a sheet metal strip made of this steel.

  Thus, the preferred embodiment of the invention consists in producing a steel sheet which comprises, by weight, a carbon content of less than or equal to 0.004%, a silicon content of between 0.25 and 0.35%, a a manganese content between 0.8 and 1.0%, a phosphorus content between 0.05 and 0.09%, an aluminum content of between 0.08 and 0.12%, the balance being iron and impurities

inevitable residuals.

  Such a sheet has the advantage of having good magnetic characteristics and of being correctly cutable and weldable

especially by spark erosion.

  Tests were carried out from a sheet according to the invention in order to show the improvement on the cutability with respect to a metal sheet.

the state of the art.

  The exact composition of the steels taken into account in these tests is mentioned in the table below, the contents being expressed

in percent weight.

  Carbon steel phosphorus silicon manganese aluminum

F 0.003 0.159 0.486 0.404 0.132

G 0.002 0.180 0.325 0.420 0.001

H 0.005 0.047 0.326 0.885 0.094

  Steels F and G correspond to a steel according to the prior art and steel H corresponds to one embodiment of the invention.

  These three steels were developed in the same way, that is,

  i to say in two steps, a first step consisting in manufacturing the steel in the form of a sheet of thickness equal to 1 mm, then a second step consisting of subjecting said sheet to an annealing treatment at a temperature taken in the range 800 C at 900 C and so as to stay below the point of

ferrite-austenite transformation.

  This annealing step was identical for these three steels and specifically constituted a continuous annealing at a temperature equal to

870 C for 2 minutes.

  The three sheets F, G and H were compared in terms of mechanical characteristics, magnetic characteristics and in terms of

cutability.

  Magnetic characteristics were measured on a single-band cell with specimens taken in the rolling direction of the sheets. The cutability was compared during cutting tests according to two criteria, the energy dissipated by friction during cutting on the one hand, and the cutting force at the end of rupture on the other hand. This last criterion makes it possible in particular to estimate the impact of segregations. The cutting was carried out using a carbide punch of diameter

  equal to 12 mm, the clearance between the punch and the die being equal to 7%.

  The following table shows the average result of these tests.

  Re Rm A% Losses at 1.5 T Induction at Criterion Strength in Fine Steel (MPa) (MPa) (W / kg) 5000A / m Breakage Wear (Tesla) J / mm) (N)

F 300 420 34 11.8 1.724 13900 2420

  G 302 422 30.8 12.0 1.722 13420 2746

H 300 415 24.5 12.2 1.722 8490 840

  From the point of view of the mechanical characteristics, it is found that the steel H of the invention has a yield strength Re and a breaking load Rm that are almost identical to those of the steels F and G of the prior art. On the other hand, the elongation A% is considerably decreased,

  less than 30, which is favorable to the cutability of the sheet of the invention.

  From the point of view of the magnetic characteristics,

  that these are almost identical in all three cases.

  Finally, it is found that the energy dissipated by friction as well as the force at the end of the rupture are considerably reduced in the case of the steel H of the invention, which shows the best cutability of this steel H according to the invention. compared to the steels F and G of the prior art. he

Claims (4)

  1 - Steel sheet for electrical use, of the type comprising less than 0.005% by weight of carbon, obtained in two steps, a first step of manufacturing in the form of sheet metal a steel, then a second step of subjecting said sheet metal an annealing treatment at a temperature in the range 800 C to 900 C and so as to remain below the point of transformation ferrite-austenite (a -> y), characterized in that it comprises by weight a carbon content less than 0.005%, a phosphorus content of less than 0.1%, a silicon content equal to 0.2%, a manganese content equal to 0.1%, and one or more elements chosen from silicon, manganese and aluminum, with contents such that: Mn + 90 Si> 85 and 5.38 <6 Mn + 13Al + 12 Si <16 and the total silicon content is less than 0.6% and the manganese content total is less than 1.3%,   the rest being iron and unavoidable residual impurities.   2 - Steel sheet according to claim 1, characterized in that   that the content by weight of phosphorus is between 0.01% and 0.09%.   3 - Steel sheet according to claims 1 or 2, characterized   in that the ratio between the total silicon content and the content of   Total manganese is less than 0.5.   4 - Steel sheet according to claims 1, 2 or 3, characterized   in that it comprises by weight a carbon content less than or equal to 0.004%, a silicon content of between 0.25 and 0.35%, a manganese content of between 0.8 and 1.0%, a phosphorus content between 0.05 and 0.09%, an aluminum content of between 0.08 and 0.12%,   the rest being iron and unavoidable residual impurities.