for the production of high quality rebars

Transcription

1 Reprnt from "MPT-Metallurgcal Plant and Technology" ssue No. 3/84, pages Nacfdruck verboten. Verlag Stahlesen mbh, Düsseldorf TEMPCORE, an economcal process for the producton of hgh qualty rebars Ing. Perre Smon, Ing. Maro Economopoulos, Dr.-Ing. Paul Nlles, Centre de Recherches Métallurgques (C.R.M.) Lège (Belgum) In the present paper, we shall frst analyse the consumer's requrements concernng the propertes of rebars; ths wll lead to the standard profle of an up-to-date concrete renforcng steel. To follow, the dfferent producton processes of hgh qualty rebars wl be revewed and the Tempcore process wl be descrbed. Fnally the economc aspects of the dfferent processes wll be analysed n detal and the savngs resultng from the mplementaton of the Tempcore process n typcal bar mlls wll be descrbed. Analyss of the consumer's requrements For many years, a strong and defnte trend towards hgh qualty rebars s observed n the market; the man concerns of the consumer are economy and safety. We shall hereunder revew the propertes requested n ths respect. Economy. Frst of all, economy mples hgh yeld strength rebars: when the guaranteed yeld strength of the rebars s rcreased, the weght of rebars to be used for a gven constructon s reduced and, consequently, the renforcng costs are cut down. Ths evoluton s álso llustrated by the tendency observed n the standards to prescrbe hgher yeld strength. The 400 MPa grade s very common whle there s already a market for the 500 MPa grade and, n some countres, for the 600 MPa grade. Addtonal cost savngs are obtaned by the use of prefabrcated renforcements: three-dmensonal renforcng structures are manufactured n workshop's and transported drectly to the buldng ste. Ths procedure asks for assemblng technques ensurng the requred dmensonal accuracy and keepng t durng several handlngs untl the fnal postonng n the constructon. In many cases, ted connectons are not strong enough whle mechancal splces are not always applcable. Weldng becomes then a must and t s well known that weldablty of rebars requres a low-carbon content (-: 0.25 % or even -: 0.22 % for the tack resstance process) and a low-carbon equvalent (-: 0.45 %) n the steels. Another mportant property s the bendablty; rebars dsplayng a good bendablty wl make possble the use of an optmum desgn and, hence, brng a further reducton of the producton costs. On the other hand, the presence of connectng renforcements requres a good rebendng ablty. In fact, some standards prescrbe that rebars have to succeed n bendng and rebendng operatons and ths on small dameter mandrels (down to 3 or 4 tmes the rebar dameter) or n cold weather ( - 20 C). P. Smon, Engneer, Rollng Mls Department, M. Economopoulos, Chef Engneer, Rollng Mls and Product Development, P. Nlles, Drector, Steel Branch, Centre de Recherches Métallurgques (C.R.M.) Lège (Belgum). Safety. For many decades, the desgn of a concrete constructon was based on a stress concept,.e. on the assumpton that the loads whch normally appear n servce nduce only elastc stresses n the renforcng steel. In such a case, the safety of a constructon can be defned n terms of a stress rato, e.g. the rato between the servce stress and the yeld stress of the rebar (fgure 1a). However, recent research work has led to the concluson that a stress based calculaton of the renforced concrete s not suffcent because, n some cases, local plastc deformatons of a gven extent have to be absorbed wthout falure of the rebars (for nstance, when tampng occurs). In such crcumstances, the safety of a concrete constructon s expressed n terms of a stran rato, e.g. the rato between the local plastc deformaton whch can occur and the unform elongaton of the rebar (fgure 1b). Such a way of desgn s now adopted n many countres; t requres ductle rebars and a guaranteed unform elongaton of up to 4 % s prescrbed for as-receved rebars and for welded rebars. Another mportant aspect for the safety of concrete constructons s to prevent the loss of ductlty after rebendng. Ths agan emphaszes the necessty of a good rebendng ablty.. From the above revew of consumer requrements, the specfcatons to be fulfled by an up-to-date concrete renforcng steel appear clearly: - hgh yeld strength, - weld ablty, - bendablty and rebendng ablty, - ductlty. aj (J Yeld stress of the rebar I ".- oj _ Servce stress n the constructon Stress concept S a f ety Servce = stress Yeld stress Fgure 1. Safety concepts (J bl Possble plastc stran n the constructon Stran concept Unform elongaton n the rebar S a f e t y Plastc = stran Unform elongaton 1

2 ,I Methods for ncreasng the yeld strength of rebars ~~L-. : I I.,(/:::\....,... \:\::::::::?:::.:: q~:..,.,; ~ 'l V--!vt: Addton of Nb, V. Twstng drawng, cold rollng u 1200 r 0_ 1000 ~ 800 ~ 600 f 1.00 ~ l T ' emperng : temperature I 1 1 I t--ms pont Tme, s TEMP CORE Fgure 3. Schematc representaton of the Tempcore process Heat treatment from the heat of rollng Fgure 2. Methods for ncreasng the yeld strength of rebars Producton of hgh qualty rebars Conventonal processes. Before descrbng the Tempcore process, we shall make a bref survey of other processes whch can be used for the producton of hgh strength weldable rebars. These methods can be classfed nto two dstnct categores (fgure 2): - rebars used n as-rolled condton after slow coolng n ar. For these bars, the yeld strength can be ncreased by modfyng the chemcal composton but the C and Mn contents have to be kept low n order to avod a sgnfcant decrease n weld ablty. The problem s solved by mcroalloyrg,.e. by addng approprate quanttes of mcroalloyng elements such as Nb or V; - rebars submtted to a stran hardenng after hot rollng, for nstance by cold deformaton. For such bars, the yeld strength can be ncreased by ncreasng the extent of ' stranng. Ths method enables the producton of hgh strength weldable rebars from low C and Mn steels. Tempcore process (prncple). The Tempcore process has been thoroughly descrbed elswhere1)2). Therefore, we shall only summarze ts prncple (fgure 3): - the rebar leavng the last stand of the hot rollng mll passes through a specal water coolng secton. The coolng effcency of ths nstallaton s such that a surface layer of the bar s quenched nto martenste, the core remanng austentc. The quenchng treatment s stopped when a determned thckness of martenste has been formed under the skn; - when the rebar leaves the drastc coolng secton, the temperature gradent establshed n ts cross secton causes heat to flow from the center to the surface. Ths ncrease of the surface layer temperature results n the self-temperng of the martenste. The name Tempcore has been chosen to lustrate the fact that the martenstc layer s TEMPered by the heat left n the CORE at the end of the quenchng stage; - fnally, durng the slow coolng of the rebar on the coolng 2 o D :: ~ e c: ~ V ~ 500 ;; mm \ mm ~ 25-28mmo \.\ ~ ~ ++). ~' \ ~'* \. ' +. \.\ + ~~.\~ "'~~.'1 +'" Temperng temperature, Fgure 4. Example of yeld strength/temperng temperature relatonshps bed, the austentc core transforms nto ferrte and perlte or nto bante, ferrte and perlte. The temperature tme hstory of the rebar s shown n fgure 3. The three stages of the Tempcore process clearly appear: - quenchng of the surface layer; - self-temperng of the martenste; - transformaton of the core. The process, properly appled, leads to an ncrease of the yeld strength of 150 to 230 MPa, dependng on the coolng ntensty. Propertes of Tempcore rebars. Fgure 4 shows an example of yeld strength/temperng temperature relatonshps for a gven chemcal composton and dfferent rebar dameters. For a gven chemcal composton, thanks to the flexblty of the Tempcore process, t s possble to cover a large range of yeld strengths by actng only on the coolng power of the quenchng nstallaton. In ths example, t appears that grades III S and IV S can be produced by usng the same chemcal composton (0.16% C and 0.70% Mn) for all dameters. Fgure 4 also confrms that, for a specfed chemcal composton and dameter, there s an unequvocal relatonshp lnkng the mechancal propertes to the temperng temperature. Ths unequvocal relatonshp s the key to the control of the Tempcore process: to acheve the requred mechancal C 4-

3 a "- ::.." "g 500 ~ Uí a a; ;; 1,00 ~ , , Water flow rate, m3 / h Quenchng tme, s 500 Table 1. Bendablty Bendng tests 180 bendng 90 bendng and rebendng after ageng 90 bendng after electrcal butt weldng 90 bendng after electrcal Typcal D values Conventonal Tempcore Ceq = 0,61 % Ceq = 0.30 % cross weldng ;: Bendablly expressed n terms of mnmum bendng dameter D (D s the rato of the mnmum possble bendng dameter to the rebar dameler) ~ Two "easy fo adjust" and / powerful confrol varables Fgure 5. On lne control of Tempcore propertes, t s suffcent to mantan the temperng temperature wthn a predetermned range. The obvous control varables are the length of the quenchng lne and the coolng water flow rate: they are easy to adjust durng rollng and they have a strong effect on the yeld strength of the rebars (fgure 5). The valdty of ths process control method s proven by experence: for the producton of a mll durng one year (about tons), the standard devaton n the yeld strength (average 480 MPa) was lower than 30 MPa, ncludng the scatter of process and chemstry. The excellent propertes of Tempcore rebars have been dscussed n many papers 3) - 7). As a consequence, n the present paper, we shall not detal ths pont but only gve a few examples. Fgure 6 llustrates the good weldablty and ductlty of Tempcore rebars, whle table 1 shows ther èxcellent bendablty. In the above examples, the Tempcore rebars have been compared to classcal as-rolled C/Mn rebars. Technology. The mplementaton of a drect heat treat-- ment n a rollng mll has to comply wth numerous, and sometmes conflctng, producton and lay-out constrants. Wthout gong nto detals, we lst some of these constrants: - low water flow rate avalablty; - necessty of rapd changes of products, grades, and sectons; - nstallaton of the quenchng lnes n dffcult areas. These constrants have been overcome by technologcal mprovements n the desgn of the coolng nstallatons; t has thus been possble for certan applcatons: Decrease n C equv, : Improved Weldabltx. Bendabltx. C + Mn / 6 (%1 0, ' OJ Improved Ductltx. Fgure 6. Weldablty and ductlty propertes of Tempcore rebars - to reduce the requred coolng water flow rate by a factor of 2 to 3; - to change producton from Tempcore to non- Tempcore products n 3 to 5 mnutes, wthout usng a crane; - to nstall quenchng lnes n areas already crowded wth other mll equpment; for example, n two strand-mlls where the fnshng mlls are not located sde by sde, the quenchng lne of one strand s located very close to some of the equpment of the other strand (shafts, gear boxes, motors, etc.) 8)., Ths clearly shows that the expanson of the Tempcore process has been supported by an mportant development work for the coolng devces proper as well as for the detaled desgn of the quenchng nstallaton tself. From a technologcal pont of vew, ts mplementaton s feasble n practcally all bar mlls. Detaled economc comparson of Tempcore wth other processes Though n total Tempcore has superor propertes to any other rebar, we shall n a frst approxmaton consder that the other processes (mcroalloyng and cold deformng) produce hgh strength rebars of acceptable propertes. In ths case, the dfferences wll only arse from the economcs. As explaned earler, for cold deformed rebars, the yeld strength s ncreased by stranng. Ths addtonal operaton of cold deformaton s expensve, the manpower costs nvolved beeng partcularly hgh n the case of small dameter bars. As a consequence, t becomes evdent that the cold deformng process s non-compettve compared to Tempcore and mcroalloyng; therefore our detaled economc comparson wll be restrcted to these two processes. A survey has been made n 4 mn-mlls n order to determne the advantages and drawbacks of both Tempcore and mcroalloyng processes. The 4 plants had all used the mc~ ' roalloyng route before mplementng the Tempcore process on ther bar mll; ths obvously gves a good bass for our comparson. All plants are usng electrc furnaces to produce contnuously cast bllets from scrap. In these mlls, the annual producton of rebars s between to tons. The rebar dameters vares from 8/12 mm to 28/40 mm, whle the mnmum guaranteed yeld strength generally ranges from 400 to 500 MPa. The followng factors have been taken nto account for the comparson of the producton costs of the Tempcore and 'mcro alloyng processes: - alloyng elements; - off-grades; - other steelmakng factors; - rollng ml operaton. 3

4 Table 2. Alloy savngs wth Tempcore Mcroalloyng**) Tempcore**) Savngs Grades W*) C Mn S V C Mn S (OMt) Fe B 400 No ,0 DIN 488-II RU No ,5 DIN 488-II RU No " 9,2, ASTM No ,1 ASTM No ,6 ASTM Yes ,7 BS 4449 Yes ,8 Fe B 400 S Yes ,4 Fe B 400 S Yes , DIN 488-II RUS Yes ,7 DIN 488-II RUS Yes ,4 DIN 488-IV RUS Yes , DIN 488-IV RUS Yes ,9 KS60S Yes ,7 KS60S Yes ,4 KS60S Yes ,3 *) Weldable accordng to the mentoned standard. **) Chemcal compostons n 10-3%. Alloyng elements. Table 2 gves typcal chemcal compostons used for dfferent rebar grades and for both processes. The savngs lsted n the last column have been based on the followng costs (end 83/begnnng 84): MN: 1,30 DM/ton for 0.1 %; - S: 2,75 DM/ton for 0.1 %; - V: 34,00 DM/ton for 0.1 %. They represent the cost to ncrease by 0.1 % the alloy content n the rebar, takng nto account the prce of the ferroalloys, the yeld of the latter and the metal losses from lqud steel to rebar. On average, the savngs n alloyng costs brought by the Tempcore process compared to mcro alloyng are: - 8,50 DM/ton for the producton of grade III RU (420 MPa) accordng to DIN 488 (In the revsed standard, due to come nto force durng 1984, ths grade wll be suppressed.); - 8,00 to 10,60 DM/ton (or 3 to 4 US$) for the producton of grade 60 accordng to ASTM 615 wth hgh carbon manganese contents; f lower carbon/manganese contents are favoured,.e. for avodng brtteness, vanadum has to be added and ths brngs the savngs to 27,50 DM/ton; - 26,00 DM/ton for the producton of grade 460 (weldable) accordng to BS 4449; - 26,00 DM/ton for the producton of grade III RUS (420 MPa) accordng to DIN 488; - 39,00 DM/ton for the producton of grade IV RUS (500 MPa) accordng to DIN 488; - 54,00 DM/ton for the producton of grade KS 60 S accordng to SIS Off-grades. We call off-grade heat, a heat whch, due to ts actual chemcal composton, s consdered unsutable for ts ntally planned destnaton. As a consequence, such a heat has to be rerouted (dverted to another product,.e. another dameter wthn the same grade or another grade) or, n some very unusual cases, scrapped. In ths regard, compared to mcroalloyng, Tempcore dsplays several advantages: - the chemcal composton range beeng smpler (no Nb or V, lower Mn content) the percentage of off-grade heats s lower; - the reroutng s smple and cheaper. Wth the mcro alloyng process, when off-grade heats are on the low sde (low C, Mn, Nb or V) a part of them has to be downgraded to 4, lower qualtes, whch can be costly. Wth the Tempcore process, most of these off-grade heats can be mantaned wthn the ntally planned grade by adjustment of the coolng power of the nstallaton. The percentage of off-grade heats, ther reducton wth the Tempcore process, and the cost of the reroutng procedure, vary largely from plant to plant, dependng on local condtons such as product mx, steelmakng plant practce, market possbltes, etc. In some plants, the utlsaton of the Tempcore process has brought a reducton of the percentage of the off-grade heats by a factor of 2 to 5. Ths, together wth the cheaper reroutng costs lnked to the flexblty of the Tempcore process, has led to savngs varyng from 1,00 to 13,00 DM/ton. For both process - Tempcore and mcro alloyng -, correct bllet analyss normally leads to a sutable product. In certan cases, t may however happen that the actual mechancal propertes of the rolled product are found outsde ntally planned specfcatons. Such an off-grade product has then to be dverted to another grade or scrapped. It has been observed that the flexblty of the Tempcore process (adjustment of the coolng power of the nstallaton) allows a better control of the yeld strength of the product than mcroalloyng; n some cases, the reducton of the percentage of off-grade products has brought addtonal savngs of 0,7 DM/ton. Electrc furnace steelmakng. It s well known that hgh carbon, slcon and manganese contents lead to brttleness, especally when the level of tramp elements s hgh. Thanks to ts low manganese content, the Tempcore process could, n prncple, accept scrap of poorer qualty,.e. wth hgher contents of resduals. However, for reasons manly lnked to relable electrc arc furnace operatons and qualty consderatons, Tempcore lcensees have not changed ther scrap buyng polcy when swtchng from mcro alloyng to Tempcore. It s nterestng to note that - the chemcal composton beng smpler and easer to reach wth the Tempcore process - the tap-to-tap tme has been reduced by 4 to 7 % n certan plants. Rollng ml operaton. Wth the Tempcore process, the same chemcal composton can be used for producng all the dameters of a gven grade. Moreover, dfferent grades (e.g.

5 I "1 grades III S and IV S accordng to DIN 488) can also be produced by usng the same chemcal composton. As a consequence, the number of steel qualtes, defned by a range of composton for each alloyng element, s strongly reduced wth respect to mcroalloyng. Moreover, as the flexblty of the Tempcore process enables an easer recovery of the off-grade heats, t s possble to process these heats faster and thus to avod an expensve stock plng. Reductons of blets stock level from to tons have been observed, whch corresponds to a reducton of ted-up captal of to DM. Takng nto account the annual rebar producton and an nterest rate of 12 % per year, ths has led to savngs rangng from 0,4 to 10,7 DM/ton. Let us also recall that hot chargng of contnuously cast bllets steadly ncreases. The effcency of mcroalloyng elements depends on the temperature evoluton of these bllets; there s no doubt that varatons n the thermal path lnked to the hot chargng practce may lead to more off-grades or to hgher alloyng costs. Studes are under way to quantfy ths factor. As far as coolng s concerned there s an advantage for mcroalloyng, as no water s needed. The operatng costs of the Tempcore process (water, energy, mantenance, wear of equpment, etc). vary from 0,50 to 1,50 DM/ton. Table 3 summarzes the resuts of our detaled economc comparson between the Tempcore and the mcrolalloyng processes; t shows n all cases a net advantage for the Tempcore route. Example of economc evaluaton Hereunder we shall make a detaled evaluaton of the economcs of the mplementaton of the Tempcore process n bar mlls whch, at the present tme, are usng the mcroallong route. Two examples pertanng to the stuatons n Europe and the U.S.A. wll be gven. Case A (Europe). Ths mll s supposed to use bllets made by the electrc furnace-contnuous castng route for the producton of tons per year. We have also supposed that t wll produce 8 to 28 mm weldable rebars of the followng grades: - 70% of grade DIN II RTS (420 MPa); - 30% of grade DIN IV RTS (500 MPa). It should be noted that: a) the III RTS grade ncludes the equvalent grades (Fe B 400, Ks 40 S, etc); b) the IV RTS grade ncludes the equvalent grades (Fe B 500, KS 50 S, etc.); c) the "extra" savngs brought by the possble producton of ' a small percentage of grade KS 60 S rebars have been dsregarded. The followng nvestment and operatng costs have been estmated for the Tempcore process: - nvestment costs: these costs vary largely from plant to plant (1 to DM), accordng to the capacty of the nstallaton, to the water system nstalled and to the possble necessty to nstall a new dvdng shear capable of cuttng the cooler and stronger Tempcore rebars. We have consdered a total nvestment cost of DM (ncludng lcense fees, coolng equpment, new dvdng shear, water system, process control equpment, mscellaneous, etc.). On the bass of 20% per year (amortzaton and nterest), ths corresponds to a cost of 8,00 DMI ton of rebar; Table 3. Producton costs (1 US$ = 2,7 DM) Tempcore-Savngs Cost factor DM/t US$/t Alloyng element 8,0 to 54,0 3,0 to 20,0 Off-grade heats 1,0 to 13,0 0,4 to 4,8 Off-grade products 0 to 0,7 0 to 0,3 Scrap qualty *) *) Tap-to-tap duraton *) *) Level of bllets stock 0,4 tò 10,7 0,15 to 4,0 Rollng costs - 0,5 to -1,5-0,2 to - 0,6 *) In favour of Tempcore but not quantfed. - operatng costs: 1,00 DM/ton; Total costs: 9,00 DM/ton. The' followng gans have been estmated compared to mcroalloyng: - alloyng elements: 29,90 DM/ton (26,00 DM/ton for the II Sand 39,00 DM/ton for the IV S: see table 2); - off-grade heats and reroutng: 4,00 DM/ton (average of the 4 plants examned); - off-grade products: t has been assumed that there was no off-grade products, for both processes; - tap-to-tap duraton: those savngs have not been credted; - level of bllets stock: t has been supposed that the amount of stock reducton was of 2 to 3 weeks of mll producton,.e. about tons. Ths corresponds to a tedup captal of DM or, for an nterest rate of 12%, to 2,3 DM/ton. Total gans: 36,20 DM/ton. These calculatons lead to the concluson that, for case A, the mplementaton of the Tempcore process brngs net savngs of 36,20-9,00 = 27,20 DM/ton or DM/year. The correspondng pay-back perod s about 15 months. Case B (U.S.A.). Ths ml s smlar to the mll of case A; t s supposed to produce tons per year of grade 60 accordng to ASTM 615. The cheapest soluton (as far as alloyng costs are concerned) for ths grade s to produce hot rolled bars wth about 0.45 % C and 1.25 % Mn, whch corresponds to a hgh carbon equvalent (about 0.65 %). As sad above, when the contents of resdual elements are hgh, ths hgh carbon equvalent can lead to brtteness, whch means a costly downgradng or scrappng of part of the producton. To avod ths rsk, t s theoretcally possble to make a scrap selecton n order to avod hgh resdual elements contents but ths s also costly and not feasble n all cases. Ths s the reason why certan mn-mlls perfer to use lower C or Mn contents and to compensate by mcro alloyng. The nvestment and operatng costs estmaton for Tempcore s the same as n case A,.e. a total of 9,00 DM or 3,33 US$ per ton. As explaned above, there are dfferent possbltes to produce the ASTM 615 grade 60 wth the conventonal process. As a consequence, the gans vary from plant to plant and s s dffcult to estmate the average savngs. Therefore we have performed the economc calculatons n two extreme cases: hgh C/Mn steel and mcroalloyed steel. 1 st hypothess: replacement of hgh C/Mn steel by Tempcore. In ths case, the alloyng savngs are of 9,00 DM or 3,33 US$ per ton (see table 2). We have consdered a gan of 4,00 DM or 1,48 US$ per ton for the off-grades. In fact, due to the brttleness problem mentoned earler, the percentage of off-grades - and partcularly the costly off-grade products s probably larger than for the 4 mn-mlls examned n 5

6 our survey and 4,00 DM/ton consttutes a bottom lmt. Wth a gan of 2,30 DM or 0,85 US$ per ton for the lower blet stock, we reach mnmum total savngs of 15,30 DM or 5,67 US$ per ton. The calculatons lead to the concluson that the mplementaton of the Tempcore process brngs net savngs of mnmum DM or US$ per year. 2 nd hypothess: replacement of mcro alloyed steel by Tempcore. In ths case, the gans have been estmated to: - alloyng elements: 27,50 DM or 10,19 US$ per ton (see table 2); - off-grade heats and reroutng: 4,00 DM or 1,48 US$ per ton; - lower blet stock: 2,30 DM or 0,85 US$ per ton. The total gans are of33,80 DM or 12,52 US$ per ton. The mplementaton of the Tempcore process brngs net savngs of DM or US$ per year. The correspondng pay-back perod s comparable to case A. The above calculatons show that, n the case of ASTM 615 grade 60, the net savngs brought by the Tempcore process lay between 6,30 and 24,80 DM per ton (2,33 to 9,19 US$ per ton). The true savngs depend on: '" OJ "- Vl c: ;: to B c: 0,8 ~ 0,6 ': 0.4 0,2 0 Current Predcted Fgure 7. Tempcore producton Table 4. Tempcore nstallatons In operaton Arbed S.A., Luxembourg Schffange plant S.A. Metallurgque et Mnere ' De Rodange-Athus, Luxembourg Rodange plant Cockerll-Sambre S.A., Belgum, Marcnelle plant Hoogovens-Ijmuden B.V. The Netherlands, Ijmuden plant Alpa, France Porchevle plant Manufer, France Montpon plant Saclor, France Homécourt plant Sheerness Steel Co. Ltd., UK Sheerness plant North Star Steel Co, USA Monroe plant (1) Under constructon or planned Sdenor, Greece Thessalonk plant Elkem a/s, Norway Chrstana plant Voest-Alpne AG, Austra Donawtz plant Broken Hl Propretary Co Ltd Australa, Port Kembla plant Broken Hl Propretary Co Ltd Australa, Newcastle plant Badsche Stahlwerke AG, Kehl plant Hoesch Hüttenwerke AG, Dortmund plant (2) Max Acher KG, Annahütte plant Esenwerk-Gesellschaft Maxmlanshütte mbh, Hadhof plant Arbed Saarstahl GmbH, Völklngen plant Yon Moos Stahl, Swtzerland Emmenbrücke plant Norsk Jernverk a/s, Norway Mo-I-Rana plant Stahl- und Walzwerke Marenhütte GmbH, Austra Graz plant Lech-Stahlwerke GmbH, Metngen plant The Tata Iron & Steel Co Ltd Inda, Jamshedpur plant Rashtrya Ispat Ngam Ltd. Inda, Vsakhapatnam plant (1) Not for rebars but for coolng plan carbon and alloy bars. (2) Producton to be dscontnued. - the actual quantty of the off-grades and ther costs; - the percentage of hgh qualty rebars produced. In fact, f the U.S.A. market follows the tendency towards hgh qualty rebars descrbed n the frst part of ths paper, ths percentage wl rapdly ncrease. Conclusons In the techncal part of ths 'paper, we have shown that the Tempcore process consstently produces hgh qualty rebars whch meet the consumer's requrements and that ts mplementaton s easy. From the economcal pont of vew, the calculatons performed n the case of typcal bar mls demonstrate the superorty of the Tempcore process. In comparson to the mcro alloyng route, the savngs are of: DM per year when producng tons per year of weldable rebars (European market); to DM per year ( to US$) when producng tons per year of ASTM grade 60 rebars (US market). Therefore, t can be concluded that Tempcore s the answer to the present and future rebar market, as well for the consumer as for the rebar producer. Ths concluson s supported by table 4 whch shows that, at the present tme, 19 nstallatons are n operaton all over the world and that 6 more nstallatons are planned or wll start operaton n the near future. Moreover, fgure 7 shows the growth of the producton of Tempcore rebars durng the recent years and the forecast for References 1) E con 0 mop 0 u 0 5, M., Y. Res pen, G. L e sse and G. Steffes: Metallurg. Rep. CRM No. 45, 1975, p ) S m 0 n, P., M. E con 0 mop 0 u 0 sand P. N I e s : Iron Steel Engneer 61 (1984) No.3. 3) D e f 0 urn y, J., and A. Bra gar d : Met~llurg. Rep. CRM No. 50, 1977, p ) R e h m, G., and D. R u ssw u r m: Metallurg. Rep. CRM No. 51, 1977, p ) R e h m, G., D. R u ssw u r m and J. D e f 0 urn y : Betonwerk u. Fertgtel-Techn. 45(1979) No.4, p ) We s e, H. : Techn. Rdsch. 1984, No. 1/2. 7) D e f 0 urn y, J., and A. Bra gar d : to be publshed. 8) Am mer n g, W. J.: MPT Metallurg. Plant & Techno!. 1984, No.1. 6