LU82058A1 - WELDABLE CONCRETE STEEL AND METHOD FOR PROVIDING SAME - Google Patents

Description

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The present # invention "relates to a concrete which can be melted, the carbon content of which is less than £ 0.25 * and which, without having been subjected to a subsequent treatment such as cold detonation, lead quenching, or surface income, a stretch limit ß ^ ^ * per mclc · 500 N / am2, and a tensile strength of at least 550 îf / wa2, this steel being formed concentrically by a core or core covered by a layer surface, oh the core has a complex structure containing perlite, ferrite and, where appropriate, other constituents, while the surface layer contains softened martenaite, also The invention covers a process for obtaining of such steel II concrete *

We know that steels whose chemical composition contains 0.55 to 0.45% carbon, up to 1.5 # of mengen! Ee, 0.2 to 0, can be used as high-strength concrete steels. , 3% of silicon with the usual impurities * The * obtaining of these steels is, it is true, economical, being don · »born which one takes mainly to ensure the resistance, carbon, manganese and silicon» However, the deflected posai * of deformation of these steels are relatively falblea and, in particular, they lack the ease of welding "

We know, on the other hand, weldable concrete irons having a low carbon content (0.28% maximum) with a silicon content of 0.5% and a mangenesis content of $ 1.6 maximum, as well as the usual impurities and, in addition, a copper content of at least 0.2% (see astm Description A 44 0 * 74 page 536) · These latter steels are moreover subjected to cold deformation ”These weldable steels have the significant drawback noting that they present, already after a short period of aging * j 4 K "2ement and λ of * temperatures included * between room temperature and 800 ·, a notable loss at the limit of stretching and tensile strength. However, such temperatures appear during welding or hot bending of concrete steels on construction sites.

A concrete steel having the properties stated at the beginning of this specification and not having the aforementioned drawbacks is described in the German patent specification 24 26 920 · A particular cooling process makes it possible to obtain concrete reinforcing bars comprising this steel micro-structures λ fine granulations. The periphery of the round is made of a highly softened martensite-bainite steel, while the core of the round is made of a structural steel ranging from ferrite-baXnlte to ferrite-perlite plus balnite. On the other hand, the psrlite and balnite content should preferably be higher than the ferrite content.

This latter steel has the desired weldability properties as well as a sufficiently high tensile strength and sufficiently high stretch limit values *. However, it has been found that the breaking point of this steel should be improved. It tends to present crack initiators and consequently its behavior is poor in the presence of prolonged vibrations.

This is why the invention proposes obtaining a steel retaining the favorable properties of known steel while presenting less risk of cracking, that is to say better values for the elongation at break. .

The problem thus posed is solved, in accordance with the invention, by a weldable concrete steel of the type described, the core of which is constituted by a complex structure of ^ J

// 3 perlite and ferrite exclusively, the ferrite content of which is between 20 and 60% 9 this core being in contact, direct and without an intermediate layer, with a surface layer itself constituted by pure softened aartenaite *

The steel in accordance with the invention is thus characterized by its constitution with two pure concentric layers, both entirely free of any bainite. This steel in accordance with the invention has, at the same time, good properties of weldability and the mechanical properties required by the German standards DIN-Norm 488 as well as a significantly better elongation at break, such that the aorta is significantly less sensitive to crack initiation and exhibits better behavior with regard to prolonged vibrations

According to a preferred embodiment, the concrete steel contains in its core in roughly equal proportions ferrite and perlite · It has been found that this new steel is perfectly suitable for making ribbed reinforcing bars thanks to this that the two layers follow the shape of the ribs so that the latter have the same mechanical properties as the non-corrugated bars *

In addition, it is advantageous to give the surface layer a fraction of the total cross section equal to at least 20% and preferably to 33 # ·

The new concrete steel still has the advantage of being economical and quickly obtainable on a wire rod train. The process according to the invention is characterized by the following assembly t a) concrete steel is formed on a wire rod train,

b) the rolled product is subjected, when it has left the finishing train, to vigorous cooling, preferably in J

ί 4 several stages · c) X “cooling allows 4 · to cool the external surface of the rolled product below a temperature allowing Xa formation of martensite · d) Xa cooling tat carried out with an intensity auf-fiaanta so that Xa temperature d will balance the nucleus at the outer aurfaca · will have attained before a # transformation in baXnita “farrita or porlita puiaaa aa will produce at that this temperature of equilibrium aa found near in the gamma daa temperatures where the earlier can appear possible Xa tranafornation of the austenita aa farrita at an perlita · a) when the equilibrium temperature is reached, this temperature is kept roughly constant, until Xa end of Xa transformation into perlita, after which the prodilfe laainé tat aouais at a slow final rafroldisaaaant ·

According to a · fora · of preferred execution, the woolen product is unwound iaaédiateaent after the execution of the cooling and is air-cooled on the reel. This thus ensures both the isothermal transformation sought by the invention and the income of the aartenaite in the peripheral sounds and this in an immediate and direct way, thanks to the heat of rolling, that is to say without any other measurement being necessary ·

The recommended process makes it possible to quickly and safely obtain the desired concrete steel without having to make # big invaatiaaaaanta in this affst · concrete steel · # allowed to obtain a surprising ease on a wire rod train and it is treated in such a way that it can be achieved without large investments and as soon as the steel is obtained, the properties to which we aspire for a long time.

Or uses, according to a · preferred · variant · of the process, an ordinary air with a diameter in the middle of up to 13 years · In an ordinary steel, the ion * all d has a conatituanta of alloy, that is to say Eat ··, sili-oIum, sulfur • te, "and lower" n content at 1.7 This ordinary steel "has a particularly interesting price and can be used for the preparation of l9aoior of concrete of superior quality · in accordance with the invention, ai normal cooling is applied by “when the thickness of the concrete steel is less than 13 years.

So that one does not have to resort to λ too high costs ·· for cooling, it is advantageous to use for obtaining a concrete grinder with a diameter less than or equal to 13 mm, a ordinary steel comprising micro-constituents of alloy whose content can go up to 0,06 # · One could still, according to another variant, use in the case of diameters included between our 13 and 26 mm, a steel of which the content of alloying constituents is · at tcfcl between 1.7 and 3% · For diameters greater than 25 am, it is necessary to incorporate into the steel micro-constituents of alloy whose total content can go up to 'at 0.03 # ·

These indications relating to the alloy constituents are based on the fact that the transfoxmatlon of the austenite into ferrite, pearl or balnite, is postponed over time by the use of an aoler containing components or micro-constituents of 'alllsgs.

It has been found that the process according to the invention has allowed it to be carried out in an economical manner when the first stage of cooling takes place in less than 0.2 seconds.

We are going to "describe the J

6 according to the invention and "cm process for obtaining on * · referring to doooino ol-joints ob s

Fig. 1 reproduces the photograph of a section of a concrete λ aier according to the aforementioned patent denaade 24 26 920 ·

Lee Fige · 2a to 2d reproduce dee inagea photographic enlarged 500 times of the structure presented by the usual concrete steel “as it appears on a polished sample ·

Fig · 3 reproduces the photograph of a section through a concrete mixer according to the invention ·

Figs · 4a and 4b reproduce 500 times enlarged photographic images of the two structures of concrete steel according to the invention seen on polished samples ·

Fig · 5 is a graph showing the shape of the controlled cooling according to the invention.

Fig · 6 is a table showing the rate of cooling for concrete steels of different diameters and their behavior during this cooling ·

Fig ·? is a time and {temperature graph for normal low carbon steel ·

Fig · 8 is a graphical representation in time and temperature coordinates for a special low carbon steel.

Figs · 1 and 2 represent photographs of the concrete steel defined in the German patent application 24 26 920 · It is clearly seen in Fig · 1 that this steel has at least four concentric layers as its cross section · The outer layer consists of softened martensitc-baXnite and this? layer "and adjacent · internally to an" intermediate layer of baïnite · There is then an annular layer of ferrite and baïnite while q.ue the core consists essentially of ferrite and pearl "

Cea four elementary structures are represented on the images of polished samples of Figs * 2a to 2d with an enlargement of 500 fols · The outer layer with fine tendons in aartensite and baïnite "softened" is clearly distinguished * teaent from the intermediate layer in halnite represented in Fig · 2b · A coarser larger structure is that of the adjoining layer of ferrite and baïnite as seen in fig · 2c · The structure of the core appears in fig · 2d oh the dark spots represent the pearl elements and light spots the ferrite elements ·

Figs * 3 and 4 represent images of polished samples of the concrete steel according to the invention "comprising only two layers · The peripheral layer consists of pure aartensite softened by tempering and is immediately adjacent to the layer forming the core λ pure pearl-ferrite stoeture · Ceoi is clearly seen on figa · 4a at 4b whose fig * 4a presented the outer layer in softened aartensite and fig · 4b the abrupt transition between the marteneite structure and the structure easy to distinguish in frite-per-lit ·.

The images of polished samples in fig · 4 are enlarged 300 times · The strict two-layer constitution of the soitr according to the invention ensures advantageous properties "hitherto unexpected, as explained above. -above·

We will now describe in more detail the method 8 of making the steel considered, with reference by way of example, they freeze 3 to 8 * Fig · 5 is a graph representing the cooling of a concrete steel. »Starting at 850 · on the cooling path for fear of being re-cooled by water in three stages. As soon as it has left the cooling path, the steel is drained and cooled as desired on the roll. The laminated product thus envided incurs an isothermal trensfcreation where the austenite of the nucleus is transformed into perlite and ferrite "and the energy released by the trnnsfonaation subjects the aartensite of the external oouohe to an income * We will describe more fully below phe »nomenes * The left part of fig * 5 does not cool it» slow the laniaé product while it crosses the finishing train * From the point defining the time to, the laniné product penetrates the cooling path and teeth for about 0.15 seconds in the first cooling stage · The third cooling stage takes about 0.15 seconds *

In fig * 5 is shown apart from a section of the “rolled product” subdivided to make the pace of the cooling understand, in concentric circles. The outer circle is designated by 1 and the center of the rolled product by 4 * The circle designated by 2 has a diameter substantially equal to half that of the wire and the circle designated by 5 has a diameter equal to a quarter of this diameter of the wire * The circle delimited by 1a has a radius equal to 9/11 of the radius R of the mined product and it roughly defied the limit separating the martensltlque layer from the central one forming the nucleus *

The corresponding layers designated by 1 "1a" 2 "3 and 4 show the appearance of the temperatures in the annular soaes defined by 1, 1a, 2, 3 and 4 during cooling" 9 ssment "The outside area is sine! cooled down to daaaoua from the martenite formation temperature Mg of talla so that it forms an outer layer of marteneite between the circles 1 and 1a · Since the core cools, of course, less quickly, the layer of nartanaita between circles 1 and 1a is reheated again by the heat contained in the nucleus so that, on the one hand, the martenslte undergoes an income and that on the other hand we reach an equilibrium temperature TA, This arrival at the temperature TA is equivalent to the fact that the rolled product has over its entire straight section # the mine temperature at the end of the cooling. This temperature is then maintained until the transformation of the austenite into ferrite and perlite is completed. It is then that final cooling can be carried out. It is necessary to choose the equilibrium temperature v in such a way that during the isothermal tmsforaatien which follows the balnite zone B is not started,

This plus, this temperature must be in the zone encompassing the point where the transformation of the aatenlte into ferrite can occur as soon as possible, which ensures that the austenite is transformed into ferrite and perlite as quickly as possible and does not degenerate. not in a longer-term process "FIG. 5 clearly shows that the invention makes it possible to avoid the formation of balnite by virtue of the fact that the equilibrium temperature is reached before the transformation into ferrite can be carried out and, moreover, that the isothermal transformation prevents the zona da baXaits from Itra crossed # during the cooling process »

The selected transformation curves appearing in fig, 5 correspond to the usual diagrams of transformations as a function of time and temperature s F denotes 10 the area of formation of 1 "ferrite, P that of the formation of perlite, B oelle da Xa formation of Xa baXnite at Mg Xa temperature below which begins Xa foundation of martensite "The austénlte when it has been cooled to" * daaaoua da eatta temperature at which ooamence Xa formation of martensite has transformed into martensite * Xa table da Xa fig * 6 indicates by way of example a # alXura p · * -ailfc of cooling for different steel diameters included between 5.5 and 30 mm. We start with an anteroid temperature of 850 * an assuming that it is a special ordinal steel ra, that is to say a steel where Xa summed alloy constituents did not exceed a content of 1.7% · XX thus clearly shows that the duration of the first stage of cooling never exceeded 0.2 seconds *

Whereas for a 5.5 mm dianeter a water! sufficient cooling stage, we can provide for larger diameters up to β cooling stages · All cooling is then completed after three seconds rather late · The column following those indicating Isa durations toM.es cooling indicates the time elapsing until the equilibrium temperature is obtained * law concrete steels are subdivided into three groups 1, Π, XIX according to their diameter * The first group includes thicknesses or diameters ranging from 5 , 5 to 13 mm, the second group ranging from 13 to 25 mm and the third group from 25 to 30 mm.

Inside the first group, the equilibrium temperature is reached in less than about two seconds, inside the second group as a 10-second monk and inside the third group as "less than 14 seconds". numbers have significant significance for cooling applications, as will be demonstrated below

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11 with more details.

San “1 ·“ next column ”in fig # 6 are indicated ·“ the core temperatures at the end of each stage of cooling for the “different diameters of the rolled product. The expression “core” means the diameter r m o · In addition, a last column indicates for each wire diameter the equilibrium temperature obtained #

Freezes them. 7 and ö make understand the meaning of the above subdivision into three groups of increasing diameters # Fig. 7 is a diagram of the transformations as a function of time and temperature for an ordinary steel with low carbon content, lower or equal to 0.35% · 11 is thus possible to be able after approximately 2 seconds and tint temperature of approximately 500 ·, aeeurer as soon as possible the transformation of austenite into ferrite # Next Iss teachings of the invention, the temperature equilibrium ddt be reached km moment · It follows that by using water cooling, as defined by the table in fig. # 6, ordinary aolers up to a diameter can be treated at 13 "m # The equilibra temperature has then located a little above 500e.

By way of comparison, the graph in fig. 8 corresponds to a low carbon steel where the sum of the alloy constituents is between 1.7 and 3 $ £ * fl clearly shows that the transformation of the xs ferrite auatenite can be obtained at the suryamnt moment as soon as possible, that after about 10 seconds # In addition, it should be noted that a significantly higher equilibrium temperature must be chosen, since this transformation obtained with the maximum possible speed in ferrite produced at around 700® * The addition of Alloy constituents Λ 12 can be very small! delay the time when this small transformation is made at the earliest, so that aorta is more time available to reach equilibrium temperature.

A similar result, namely a shift of the moment in the direction of the delay, where the transformation of ustenite into ferrite occurs at the earliest, can be obtained by the addition of micro-ionics killing the alloy, such as niobium , vanadium or molybdenum. Unlike the use of special steels, according to fig. 8, the transformation curves of FIG, 7 are then simply shifted by a decade to the right, without, in addition, the relative position or the shape of the transformation layers being modified.

This is why the addition of micro-alloying alloys does not modify the equilibrium temperature, unlike the addition of the other alloying constituents.

Keeping the water cooling defined by the table in fig, 6, it is necessary, to obtain a concrete steel λ with a diameter greater than or equal to 13 years, to use either a special steel where the content tdale in constituent of alloy is between 1.7 and 3, ie a steel with micro-constituents of alloy (vanadium, niobium, or molybdenum) whose content goes up to 0.06 # "

In the case of diameters greater than 25 cm, the sum of the alloying constituents must be increased in special steel above 3% · This is not generally to be recommended in such a fool that, for such diameters, it is necessary to use alone or add micro-alloy components.

Instead of modifying the contents of the alloying components of the steel, it might as well accelerate the cooling in order to reach equilibrium temperature earlier; However, such cooling would not be economical,

^ J

13

The diagrams of * fig * 7 "t 8" extract, do more, than the content of ferrite "t do perllte in 1" nucleus ost influenced by the choice do cotto temperature of equilibra.

In the examples described above, we started from a laminated product having, at the entrance to the cooler path, a tanperatura da 850 ·. We can also adaattra other taapératuras λ provided that this tanperatura is at "high enough so that the austenite is still stable all year being low enough so that the cooling of the laminated product until the tanperatura of equilibrium can s * perform without exceeding the durations imposed · Cala meant that we can, more particularly in the case of small diameters of the product, become laden with higher inlet temperatures of the rolled product entering the cooling path. However, at tefcl, the temperature of 850 · has been found to be particularly suitable for the proposed purpose.

the isothermal transformation of austenite into ferrite and perlite can be obtained by placing an oven behind the cooling path * In any case, it is much more advantageous to bring the uncut concrete steel coming from a train to wire rod on a reel as soon as it leaves the cooling path, the fact that the concrete steel remains on the reel for a long time, prevents the temperature of this steel from falling since it would rather tandanca è ramontar eoua the effect of the release of heat from the tranafermatist, and that the transfer of heat is less from a reel. Da more, a tal cooling makes possible a faster method of obtaining steel, mode already known by mine without having been f applied until now to obtain concrete steel.

w 14 LUbagtasnt dt rupturt “tt, all # · choata being equal by aillturt, dt 5 * 2 # for the concrete aolsr obtained according to bed anMgnaatnts dt Xa dtaandt dt bravtt aXXtaand 24 26 920, • t dt 10.1 # for 1 "concrete steel conforming to the invention XX your réa dtt minoration * of the container dt Xftcitr vie-à-vi" dt Xt ttadaaot to Xt cracking tt dt Xt resistant to vibration "durable",

Dana dta favorable conditions, ta ptut increase taoort appreciably auAUonganaat dt rupture dt * steel & concrete corn * siderée, L'alloagtntnt dt rupture aoytn ptut itrt located by txtaplt tatst 13 * 9% tt 17 * 4% dt ttXXt aort that on and trmm notably at * deasus dta non · # "imposed #" ta Germany tt defined by Xt DW A88-ftuillt * 1.

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Claims (7)

15 RBVaroiCATIONS 1 “Aoiar aeudabla concrete with a lower otrbont content · k 0.25 #” presenting tan · “uun further treatment tal qua deformation λ cold, quenched you lead, or returned to perfection · a # Unit # stretching β a 9 of “anointed 500 Ji / am * • t · rtilataae · k the traotioa of aoina 990 R /“ 2 eat steel, concentrically comprising my zona oantrala or nucleus formed by my complex atructura da appear # · d # farrit # "t · la eaa necessary · d * autraa oonatltuanta at my peripheral couont oontanant da lamurtenaite softened ·· being characterized by the fact that the nucleus #at conatitué axoluaivonant by a # atructura pure complex # of # appears # at farrit # oh la t # n # ur an farrit · aat oonpria # antr # 20% #t 80%, tandia qua ca nucleus a # found in contact with the coueha "uperfioidle aana none # coucha int # rnédlairat oatta coucha auparfieialla being alla- * · * · Conatitué # by da nartanaita pur # softened # by income. 2, Concrete steel “according to claim 1” characterized by the fact that the farrita and the appearance # a # find #n proportion · a little more or less equal · · in · the “on # central # or core. 3 * Aci # r to concrete "according to claim 1 or ra ~ vantion 2, characterized by 1 # because it fern # de # barra * n" rvuré # s. 4. Concrete steel "following my * any" resale! -Cation "previous ··· characterized by the fact that the fraction of the" right action "of the aoar ororaponding to the perioural layer" "perishes eat equal k at the mine 20% at aat advantageously equal to 33% · 5 »Concrete steel« following any one of the previous «claim» ·· characterized by the fact that »fear a dlanfctra equal to or less than 13 years, the summa of »Content» of 16 all 1 * 8 alloy constituents is less than or equal to 1.7% · 6 »concrete steel according to any one of claims 1 to 4» characterized in that, for an equal diameter or greater than 13 ma, the sound of the contents of all the alloy constituents is less than or equal to 1.7 # "this steel containing" more »micro-constituents of alloy whose content can reach 0.08% · 7 · A concrete steel according to any one of claims 1 to 4 "characterized by the fact that q \% fear of thicknesses or dleneters coaprls between 13 and 25 years, the sound of the contents of alloy constituents is ooapriae between 1" 7 and 3% · 8 · Steel λ concrete follow any one of claims 1 to 4 "characterized in that" for thicknesses or dleneters greater than 25 years "the content of the ring of the alloying constituents is coaprlse between 1 »7 and 3% stretched that the steel contains» in addition, an alloy micro-constituent content ranging up to 0.03% · 8 * Method of obtaining concrete steel according to any one of claims 1 to 8, characterized by all of the following points ia) the concrete steel comes from a wire rod train. b) after leaving the finishing train "the rolled product is subjected to a very intense cold, preferably in several stages. c) the cooling brings the peripheral surface of the rolled product down below the maximum temperature for forming the martenslte. d) the cooling is carried out with an intensity such that the equilibrium temperature between the core and the peripheral layer is reached before transbraatlon in balnite, ferrite or pearl can be effected »0 17 this equilibrium temperature being in the liner · at “temperatures in which we can obtain, 1” as soon as possible ”a # transformation of the ferraténito into ferrite and appears # · ·) when the temperature of equilibrium has been reached” we maintain almost constant this temperature until the end of the transformation into perlite to then subject the rolled product λ slow final cooling · 10 "Process according to claim 9, characterized in that the rolled product is rolled up on an envidolr to be subjected to cooling in the air immediately after the execution of the cooling process 11. Method according to claim 9 or claim 10 "characterized in that the first stage of cooling is completed in less than 0.2 seconds · 12 · A method according to u »any of claims • r 9 to 11» characterized in that one uses for the eonfee-tion of a concrete steel whose diameter is equal to or greater than 13 mm »a steel ordinary with a total content of alloying constituents less than or equal to 1 »7 # · 13 · Process follow any one of claims 9 to 11 "characterized in that one uses for the manufacture of a concrete steel whose diameter eat greater than or equal to 13 mt an ordinary sawmill have a content of mioro- eonstituants alloy which Aler up to 0 »0 & 14" Process follow any · any of claims f 9 to 11 * characterized by ls fact that is used "for the confee ~ Hou of a concrete steel which l 'thickness or diameter eet corn · taken between 13 and 29 mi' an epéolal steel whose total content of alloy component eet between 1.7% and 3% · r 1 # · Process according to any one of claims ': ιβ 9. il. "MrtiMae m * u mt w x, m Utnu. ^ „Making a" clor to Mtan whose 4p "i" .. ur or the dia-nktro dipaesa 29 nu "a special aolor with a content" Il micro-con * tltuant9 d * allia "· able to go; Juaqu * at 0.03 i7 d *