US2816052A

US2816052A - Method of manufacturing ribbed steel rods

Info

Publication number: US2816052A
Authority: US
Inventors: Hoff Hubert; Fischer Georg
Original assignee: HOESCH WESTFALENHUTTE AG
Current assignee: HOESCH WESTFALENHUTTE AG; HOESCH-WESTFALENHUTTE AG
Priority date: 1953-11-07
Filing date: 1954-11-08
Publication date: 1957-12-10
Anticipated expiration: 1974-12-10
Also published as: LU32956A1; GB793305A; US2863913A; NL91771C; FR1111878A; NL193905A; CH334032A; CH330477A; GB777497A

Description

Dnc. 10, 1957 H. HOFF Erm.V 2,816,052

" METHOD OF" MANUFACTURING RIBBED STEEL RODS 3 Sheets-Sheet 1 2 w h I m/ m M w J Lm L ,n H um .Tawl 6 1|cILm m m 6. n IMA m w H ///////////w Filed Nv. 8. 1954 H. Hor-'F :TAL

METHOD OF MANUFACTURING RIBBED STEEL RODS 3 Sheets-Sheet 3 Dec. 10, 1957 Filed Nov. 8. 1954 Nrs/vives;

Hubcr" Hof- .'Gtorg Fischer United States Patent METHOD F MANUFACTURING RIBBED STEEL RODS Hubert Hoff, Dortmund, and Georg Fischer, Schwerte,

Germany, assignors to Hoesch-Westfalenhntte Aktiengesellschaft, Dortmund, Germany Application November 8, 1954, Serial No. 467,602

Claims priority, application Germany November 7, 1953 14 Claims. (Cl. 148-12) The present invention relates to a method of manufacturing ribbed steel rods, and more particularly to a method of manufacturing ribbed steel rods used for reinforcing of concrete.

It is known that the elastic limit or yield point and the strength of steel can be increased by cold deformation, and that the breaking elongation, which is considerably reduced by cold deformation, can be improved by subsequent tempering without causing considerable reduction in the elastic limit or strength of the steel due to the tempering. However, it has been found that objects made in accordance with this process, and especially objects made of Thomas steel, show brittleness in spite of improved elongation quality wherever sharp notches or indentations cause tension peaks under conditions of stress.

For instance, concrete reinforcing ribbed steel rods of Thomas steel, manufactured as described above and belonging to group IIIb and IVb according to the German standard DIN 1045 and having the following properties:

are not usable, because breaks due to brittleness may already occur during bending and positioning of the reinforcing rods at the building location. Hot-rolled Thomas rib steel while possessing greater strength also does not have suicient tenacity.

It is also known to use steel rods formed with two longitudinal ribs or with two longitudinal ribs and interposed transversal or oblique ribs and to cold-twist these rods for use as concrete reinforcements. These twisted rods are preferably made with a pitch of -12 times the rod diameter, especially when Thomas steel is used. Increased twisting, especially reducing the pitch below 8 times the diameter of the rod causes the breaking tension to fall below permissible limits. Making of highly twisted reinforcement rods and tempering the same has not been practical, since it was not known that by doing so considerable improvements could be achieved not only in regard to the values of the breaking tension but also in regard to the ductility of the rod.

lt is an object of the present invention to provide a method for the manufacture of ribbed steel rods which overcomes all of the above-mentioned disadvantages.

It is another object of the present invention to provide a method for the manufacture of ribbed steel rods which have great ductility, high breaking elongation and are less apt to develop cracks and fissures under the strains and stresses connected with their use as concrete reinforcements.

It is still another object of the present invention to provide a method for themanufacture of highly twisted ribbed steel rods which have high breaking tension and do not show a tendency towards developing cracks and fissures.

lt is a further object of the present invention to provide a method for the manufacture of ribbed steel rods for reinforcing concrete which in addition to the aforementioned advantages have a high degree of notch impact tenacity.

Other objects and advantages of the present invention will be apparent from a further reading of the specification.

With the above objects in view the present invention mainly consists in a method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod and deforming the' same so as to reduce its dimensions in one cross-sectional direction by at least 30%, thereafter tempering the cold-rolled deformed steel rod at a temperature ranging between 450 and 600 Centigrade for at least l5 minutes, and forming ribs on the steel rod not less than 15 minutes before termination of the tempering whereby the cold-rolled deformed steel rod with the ribs thereon is tempered for at least 15 minutes at the indicated temperature.

More particularly the method of the present invention comprises the steps of cold rolling a steel rod having an oblong cross section and deforming the same so as to reduce its dimensions in one cross sectional direction by at least 30% and to form a circular cross section; forming straight longitudinal ribs on the steel rod equally spaced from each other in circumferential direction, twisting the so-formed rod lso that each of the straight longitudinal ribs is deformed into a helical rib, the distance of the thus-formed helical ribs from each other being equal to about 0.7 time the diameter of the deformed steel rod and the pitch of the heli-cal ribs being less than 6 times the diameter of the deformed steel rod, and thereafter tempering the steel rod at a temperature ranging between 450 and 600 centigrade for at lesat l5 minutes.

According to the present invention the cold rolling of Steel rods is performed in such a way as to achieve a decrease in the thicknesses of the rods equal to a deformation of at least 30% in the area between the ribs. The tempering is performed at a temperature of between 450 and 600 C. for a sufficiently long period of time so as to obtain increasing values for notch impact resistance without appreciable decrease in the elastic limit and strength of the steel rod.

The fillet-shaped area -connecting the ribs with the steel rod is in accordance with the present invention exposed to even greater deformation, preferably ranging between 30 and 60%. Due to the increased deformation recrystallization takes place in this area during tempering, and consequently stresses which otherwise might cause formation of cracks are relieved. This is achieved by forming the ribs in such a way that the cross-section of the area connecting the ribs with the steel rod forms an arc of very small radius.

The ribs may be rolled onto the rod either cold or at tempering temperatures.

The rod prior to the cold-rolling process of the present invention may have various cross-sections such as for instance oblong, rectangular or circular, and may have been produced by a hot or cold rolling process. It is then cold-rolled and deformed to the desired cross-section. For instance, a rod of square cross-section is cold-rolled into a rod of elongated rectangular cross-section or vice versa; a rod of ovall cross-section is cold-rolled into a inite range of temperature.

rod of circular cross-section, or a rod of circular crosssection is cold-rolled to a rod having a cross-section of oval shape, both having transversal ribs. The crosssection of the rod may be changed by cold-rolling in accordance with the present invention in any desired way, provided that a deformation of at least takes place during the cold-rolling. For` instance, the rod can be cold-rolled along two axes perpendicular to each other in order to achieve deformation of at least 30% and to form at the same time ribs on the surface of the rod.

It has now been found that the tenacity or ductility of cold-rolled and tempered steel, especially Thomas steel, can only then be improved without considerable loss of strength and reduction of the elastic limit or yield point, when the cold deformation exceeds a certain minimum value and when the tempering takes place within a def- For the cold-rolling, depending upon quality and condition of the material, a reduction in thickness of at least 30% is required. This minimum reduction value is not determined by the shape of the steel rod or by the required values for the yield point or tensile strength but by the tenacity and ductility required of high grade concrete reinforcing rods.

In accordance with the present invention, the tempering, following deformation of the rod in excess of the above stated minimum, has to be carried out within the temperature range of 450 to 600J centigrade, in order to achieve a considerable increase in tenacity and ductility concurrent with a high elastic limit and great strength of the steel rod.

Tempering at a temperature below 450 centigrade tends to improve only the elastic limit which has been reduced during cold deformation, however, it does not appreciably change the notch impact tenacity in stress areas such as the fillet or notch-like areas connecting the ribs with the main body of the rod.

On the other hand, if during tempering the temperature increases above a limit of from 580 to 600 centigrade, a decrease in strength occurs due to recrystallization taking1 place throughout the entire cross-section of the steel ro Above the lower limit of cold deformation and within the temperature range provided by the present invention, the notch impact tenacity increases with increasing deformation and higher tempering temperatures, whereby the elastic limit or yield point and the strength of the steel rod continue to increase with Vthe increase in'deformation causing reduction ofthe thickness of the rod in one direction. In order to achieve a high notch impact tenacity it is therefore advisable in accordance with the present invention to obtain the highest possible degree of cold deformation and to temper at high temperatures which, however, must not exceed'the upper limit of between 580 and 600 centigrade.

The usual tempering time of between 2 and 5 minutes is not suflcient to achieve the desired increase in notch impact tenacity. In accordance with the present invention the tempering process has to extend over a period of from 15 to 90 minutes.

By working in accordance with the method of the present invention as above described, especially the notch impact tenacity of cold deformed soft Thomas steel is considerably improved. By applying for instance, a very high degree of cold deformation, corresponding to a reduction in thickness of about 60%, followed by suitable tempering, for instance of one hour at 500 centigrade, it is possible to approximately regain the notch impact tenacity of the hot-rolled initial material, while at the same time increasing the elastic limit to about 2.5 times its initial value.

The process of the presentinvention is especially suitable for the manufacture of ribbed concrete reinforcing rods belonging to groups IIIb and IVbof the German standards DIN 1045 'which were described further above.

It is important in' 'thiscaseto a'chieve 'not'only an 'increase in the notch impact tenacity together with a high degree of cold deformation, but also in addition to reduce considerably the notch effect in the area connecting the ribs with the main body of the steel rod. This is done by recrystallization of the material in this area. In ordcr to achieve this result it is necessary to increase the deformation in the area connecting the ribs with the main body of the steel rod to a considerably higher value than the deformation of the remainder of the cross-section of the steel rod; so that during tempering recrystallization and relieving of stress occurs only in this particular area, while the strength of the remainder of the steel rod remains substantially unchanged at the level attained by thc cold deformation process. Due to the relieving of strain of the material in this area, a high capacity for deformation is obtained which is necessary for an effective reduction of the stress peaks. In this Way it is possible to manufacture from soft Thomas steel, for instance, crossribbed concrete reinforcing rods which conform with the German standards according to DIN 1045 for concrete reinforcements of steel of the groups Hlb and IVb and which in comparison with concrete reinforcement rods made from Thomas steel in accordance with other methods show considerably better qualities in regard to tenacity and resistance against formation of cracks, while being of equal strength.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 is a graph showing the stretch limit of steel under tempering conditions in accordance with the present invention, in relation to the degree of cold deformation;

Fig. 2 is a graph showing the impact tenacity of steel under tempering conditions in accordance with the present invention, in relation to the degree of cold deformation;

Fig. 3 is a cross-sectional view of a cylindrical steel rod prior to deformation in accordance with the present invention; f

Fig. 4 is a cross-sectional view of the steel rod shown in Fig. 3, after deformation;

Fig. 5 is a plan view of the steel rod shown in Fig. 4;

Fig. 6 is a cross-sectional view of an oval steel rod prior to deformation in accordance with the present invention;

Fig. 7 is a cross-sectional View of the steel rod shown in Fig. 6, after deformation;

Fig. 8 is a plan view of the steel rod shown in'Fig. 7;

Fig. 9 is a cross-sectional view of a steel rod provided with longitudinal ribs in accordance with the present invention; and

' Fig. 10 is a plan view of the steel rod shown in Fig. 9 after twisting of the same.

The relationship between the reduction of thickness and the elastic limit at tempering temperatures of 450 and 500 centigrade and at a tempering time of one hour is shown in Fig. 1, while Fig. 2 shows the change in the notch impact tenacity under deformation and tempering conditions identical with those of Fig. 1. The tempering time depends on the size of the cross-section of the steel rod.

As graphically illustrated in Figs. 1 and 2, the elastic limit increases with the increase in cold deformation, while the notch impact tenacity decreases upon application of a small degree of cold deformation and only starts to increase when the degree of cold deformation reaches values approaching 40%. Upon further increase in the cold deformation, up to between 50 and 60%, the notch impact tenacity shows a very high rate of increase.

"Figs 1 and 2 ygraphically illustrate why in accordance with the present invention the area connecting the ribs with the main body of the rod has to be deformed to a higher degree than the other portions of the ribbed steel rod. As shown in these figures a sufficiently high value for the elastic limit is obtained when deformation exceeds 30%, while deformation between 40 and 60% in the critical area between the ribs and the rod is needed to obtain a satisfactory increase in the impact tenacity.

This is utilized in accordance with the present invention, in regard to twisted ribbed steel rods for concrete reinforcements, and done by twisting the ribbed rods to such an extent that the pitch of the helical ribs formed from originally longitudinal ribs by twisting of the steel rod, is below six times the maximum dimension of the cross-section of the rod, preferably between two and four times the maximum dimension. If for example a ribbed rod of circular cross-section having straight longitudinal ribs equally spaced from each other in circumferential direction is used, the twisting in accordance with the present invention is to be carried out to such an extent that the pitch of the helical ribs formed thereby is smaller than six times the diameter of said rod and preferably lies between two and four times that diameter. Twisting of the steel rod to the extent indicated above and subsequent tempering for a period of between and 90 minutes, depending on the size of the cross-section of the ribbed rods, at a temperature of between 450 and 600 C. will cause the notch impact tenacity to increase again, without appreciable reduction of the high elastic limit and strength achieved by the cold twisting of the rod.

According to this process of the present invention an improvement in the mechanical characteristics of the steel rods is achieved and the desired values in respect to notch impact tenacity and elastic limit are reached.

Furthermore, a new and considerable advantage is achieved for having the helical ribs, formed from longitudinal ribs by twisting of the steel rod, arranged at such slope as to show a certain similarity with rods having transversal ribs. As it is known, transversal ribs on concrete reinforcing rods possess the extraordinary advantage of increasing the adherence of the concrete to the reinforcing rod. The steep helical ribs of conventionally twisted reinforcing rods provide a somewhat better adherence than smooth rib-less reinforcing rods. However, longitudinal forces acting on the embedded reinforcing rod create, in the case of steep helical ribs, a relatively large force component in the direction of the ribs and consequently the rod shows a certain tendency to separate from the concrete by rotation. With reduced gradient of the helical ribs this force component becomes smaller and consequently, in order to prevent movement of the reinforcing rod relative to the concrete, it is of great advantage to increase the twisting of the rod in accordance with the present invention.

Conventional reinforcing rods with transversal ribs have the ribs arranged in a distance from each other which is about equal to 0.7 times the diameter or maximum dimension of the cross-section of the reinforcing rod, in order to enforce a desirable formation of cracks in the concrete; that is to obtain as many cracks as possible, which are, consequently, of small width. The same eect can be achieved by a reinforcing rod which is strongly twisted in accordance with the present invention, if the number of longitudinal ribs which are equally spaced from each other in circumferential direction is chosen in relation to the pitch of the helical ribs obtained after twisting in such a way that the distance between adjoining ribs deformed by twisting into helical ribs, amounts to approximately 0.7 times the diameter or maximum ydimension of the cross-section of the steel rod. This is achieved by arranging, for instance, four equally spaced ribs around the circumference of the rod and twisting to an extent that the pitch of the helical ribs amounts to three times the diameter of the rod, or if, for instance, the pitch is to be four times the diameter, six ribs have "6 to be arranged around the circumference of the rod to achieve the same result.

It is advantageous to use as raw material for the forming of concrete reinforcing steel rods, in accordance with the method of the present invention, a Thomas steel which -has been produced with the addition of oxygen to the air blast. Due to the enrichment in oxygen content, the nitrogen content of the steel is reduced to values below those found in regular Thomas steel. This low nitrogen-content steel is especially suitable to withstand the high twisting operation performed in accordance with the present invention. Preferably the nitrogen content of the steel is kept below 0.012%. Obviously different types of Thomas steel in which the nitrogen content has been lowered by various processes can also be used, as well as open hearth steel.

Referring now again to the drawings, Figs. 3, 4 and 5 show a steel rod of initially circular cross-section before and after deformation in accordance with the present invention. The steel rod blank having a diameter rz as shown in Fig. 3 is deformed in the direction of diameter a to an extent exceeding 30%. As shown in Fig. 4, diameter a has been reduced to diameter a1 for the main body of the deformed steel rod, and to diameter a2 for the ribs rolled on the main body of the steel rod. In Fig. 5, b indicates the fillet area connecting the ribs with the main body of the steel rod, which area in accordance with the present invention is deformed to a degree exceeding the degree of deformation of the steel rod, preferably to a degree of between 30 and 60%, and in which area recrystallization and release of stress is achieved during the subsequent tempering process.

Figs. 6, 7 and 8 show the deformation and formation of ribs on a steel rod blank of initially oval crosssection. The original steel rod has a longest axis c and a shortest axis d as shown in Fig. 6. The rod is colddeformed so as to reduce the longest axis c to c1 for the main body of the steel rod and to c2 for the ribs rolled on the main body. This reduction in length of the longest axis of the original steel rod, as shown in Fig. 7, exceeds 30%. As shown in Fig. 8 two longitudinal ribs and a plurality of transversal ribs were rolled on the main body of the steel rod. The llet areas connecting the ribs with the main body of the rod which in accordance with the present invention have been deformed to a degree exceeding the deformation of the main body of the rod are indicated in Fig. 8 by the letter e. The difference in the degree of deformation between these areas e and the main body of the steel rod is such that upon tempering at temperatures between 450 and 600 for a period of time of l5 to 90 minutes, recrystallization takes place in the areas e only and not in the main body of the steel rod. The upper limit of tempering temperature is chosen in accordance with the degrees of deformation actually applied, but in any event not to exceed 600 C. so as to prevent recrystallization in the main body of the steel rod.

In the cross-sectional view shown in Fig. 9 of a deformed steel rod having straight longitudinal ribs equally spaced from each other in circumferential direction, the areas of greater deformation connecting the ribs with the main body of the steel rod are indicated by the letter f.

Fig. l0 shows a steel rod having helical ribs formed on its surface by the process of twisting a steel rod having longitudinal ribs equally spaced from each other in circumferential direction. lt specifically shows the relationship between the diameter g of the steel rod, the distance of adjoining helical ribs from each other, and the pitch of the helical ribs. In the illustrated embodiment shown in Fig. l0, the distance between adjoining helical ribs is equal to 0.7 times the diameter of the steel rod and the pitch of the helical ribs equals 4 times the diameter of the steel rod. The high twist of the steel rod and the consequently relatively small pitch of the ribs causes provided with transversal ribs.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that'others canby applying current knowledge readily adapt itfor various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations shouldaud are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured vby Letters Patent is:

l. A method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod consisting of Thomas steel and deforming the same so as to reduce its dimension in one cross-sectional direction by at least 40%; thereafter tempering said coldrolled deformed steel rod at a temperature ranging between 450 and 600 centigrade for at least l5 minutes, and forming ribs on said steel rod not less than 15 minutes before termination of said tempering so that said coldrolled deformed steel rod with said ribs thereon is tempered for at least 15 minutes at the indicated temperature, whereby a ribbed steel rod of high elastic` limit and high notch impact tenacity is formed.

2. A method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod and deforming the same so as to reduce its a steel rod consisting of Thomas steel and deforming the same so as to reduce its dimensions in one cross-sectional direction by at least 40%; thereafter tempering said coldrolled deformed steel rod at a temperature of approximately 500 centigrade for between l5 and 90 minutes, and forming ribs on said steel rods not less than l5 minutes before termination of said tempering-so that said cold-rolled deformed steel rod with said ribs thereon is` tempered for at least l5 minutes -at the indicated 'ternperature, whereby a ribbed steel rod of high elastic limit and high notch impact tenacity is formed.

4. A method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod consisting of Thomas steel andl deforming the same so as to reduce its dimensions in one cross-sectional direction by at least 40%; thereafter tempering said coldrolled deformed steel rod at a temperature ranging between 450 and 600 centigrade for at least 15 minutes, and forming ribs on said steel rod not less than l5 minutes before termination of said tempering, thereby deforming the area connecting said ribs with said steel rod to a degree of between 40% and 60% thus causing recrystallization and relieving of stress in said area, and tempering said cold-rolled deformed steel rod with the ribs thereon for at least l5 minutes at the indicated temperature, whereby a ribbed steel rod of high elastic limit and high notch impact tenacity is formed.

5. A method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rollingl a steel rod 'consisting of Thomas steel and deforming thev tween 450 and 600 centigrade forat least 15 minutesf forming str-aight. longitudinalribs-on said steel'rodgand' twisting the so formed 'rod so that-each of said'straight` f catedtemperature, whereby a ribbed steel rod ofhigh elastic limit and high notch impact tenacity is formed.

6. A method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod consistingv of Thomas steel and deforming the same so as'toreduce its dimensions in one cross-sectional direction by at least 40%; thereafter tempering said coldrolled deformed steel rod at a temperature ranging between 450" and 600 centigrade for at least 15 minutes, forming straight longtudinal ribs on said steel rod; and

`twisting the so formed rod so that each of said straight longitudinal ribs is deformed into a helical rib, having a pitch of less than six times the maximum dimension of the cross section of saiddeformed steel rod, not less than l5'minutes before termination of said tempering so that said cold-rolled deformed steel rod with said ribs thereon is tempered for at least 15 minutes at the indicated temperature, whereby a ribbed steel rod of high elastic limit and high notch impact tenacity is formed.

7. A method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod consisting of Thomas steel and deforming the same so as to reduce its dimensions in one cross-sectional direction by at least-40%; thereafter tempering said coldrolled deformed steel rod at a temperature ranging between 450 and 600 centigrade for at least 15 minutes, forming straight longitudinal ribs on said steel rod; and twisting the so formed rod so that each of said straight longitudinal ribs is deformed into a helical rib, having a pitch of between two and six times the maximum dimension -of the cross section of said deformed steel rod, not less than 15 minutes before termination of said tempering so that said cold-rolled deformed steel rod with said ribs thereon is ltempered for at least l5 minutes at the indicated temperature, whereby a ribbed steel rod of high elastic limit and high notch impact tenacity is formed.

8. A method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod consisting of Thomas steel and deforming the same so as to reduce its dimensions in one cross-sectional direction by at least 40%; forming straight longitudinal ribs on said steel rod equally spaced from each other in circumferential direction; twisting the so-formed rod so that each'of vsaid straight longitudinal ribs is deformed into'a helical rib the distance of the thus formed helical ribs from each other being about 0.7 times the maximum dimension'of the cross section of said deformed steel rod; and thereafter tempering said steel rod at a temperature ranging between 450 and 600 centigrade for at least 15 minutes, whereby by a ribbed steel rod of high elastic limit and high notch impact tenacity is formed.

9; A method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod consisting of Thomas steel of oblong cross section thereby deforming the same so as to reduce its dimensions in one cross-sectional direction by at least 40% and to. form a circular cross section; thereafter tempering said cold-rolled deformed steel rod at a temperature ranging between 450 and 600 centigrade for at least 15 minutes, and forming ribs on said steel rod not less than l5 minutes before termination of said temperingV so that said cold-rolled deformed steel rod with said ribs thereon is tempered for at least l5 minutes at the indicated temperature, whereby a ribbed steel rod of high elastic limit and high notch impact tenacity is formed.

10. A method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod consistingof Thomas steel and deforming the same so as to reduce-its dimensions in one cross-sectional direction byat least 40%; forming-straight longitudinal' `ribs onv said steel-rodl equally spaced `from each other ino circumferential direction; twisting the so-formed rod so that each of said straight longitudinal ribs is deformed into a helical rib, the pitch of said helical ribs being less than 6 times the maximum dimension of the cross section of said deformed steel rod; and thereafter tempering said steel rod at a temperature ranging between 450 and 600 centigrade for at least 15 minutes, whereby a ribbed steel rod of high elastic limit and high notch impact tenacity is formed.

11. A method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod consisting of Thomas steel having an oblong cross section and deforming the same so as to reduce its dimensions in one cross sectional direction by at least 40% and to form a circular cross section; forming straight longitudinal ribs on said steel rod equally spaced from each other in circumferential direction; twisting the soformed rod so that each of said straight longitudinal ribs is deformed into a helical rib, the distance of the thusformed helical ribs from each other being equal to about 0.7 times the diameter of said deformed steel rod and the pitch of said helical ribs being less than 6 times the diameter of said deformed steel rod; and thereafter tempering said steel rod at a temperature ranging between 450 and 600 centigrade for at least 15 minutes, whereby a ribbed steel rod of high elastic limit and high notch impact tenacity is formed.

12. A method of manufacuring ribbed steel rods made of Thomas steel having a nitrogen content of not more than 0.012% for reinforcing concrete comprising the steps of cold-rolling a steel rod consisting of Thomas steel having a nitrogen content of not more than 0.012% and deforming the same so as to reduce its dimensions in one cross-sectional direction by at least 40%; thereafter tempering said cold-rolled deformed steel rod at a tempcrature ranging between 450 and 600 centigrade for at least 15 minutes, and forming ribs on said steel rod not less than 15 minutes before termination of said tempering so that said cold-rolled deformed steel rod with said ribs 10 thereon is tempered for at least 15 minutes at the indicated temperature, whereby a ribbed steel rod of high elastic limit and high notch impact tenacity is formed.

13. A method of manufacuring ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod consisting of Thomas steel in two directions normal to each other and deforming the same so as to reduce its dimensions in one cross-sectional direction by at least and to form a rectangular cross-section; thereafter tempering said cold-rolled deformed steel rod at a temperature ranging between 450 and 600 centigrade for at least l5 minutes, and forming ribs on said steel rod not less than 15 minutes before termination of said tempering so that said cold-rolled deformed steel rod with said ribs thereon is tempered for at least 15 minutes at the indicated temperature, whereby a ribbed steel rod of high elastic limit and high notch impact tenacity is formed.

14. A method of manufacturing ribbed steel rods for reinforcing concrete comprising the steps of cold-rolling a steel rod consisting of Thomas steel in two directions normal to each other and deforming the same so as to reduce its dimensions in one cross-sectional direction by at least 40% and to form a rectangular cross-section; thereafter tempering said cold-rolled deformed steel rod at a temperature ranging between 450 and 600 centigrade for at least 15 minutes, and forming transversal ribs on at least two opposite surfaces of said steel rod not less than 15 minutes before termination of said tempering so that said cold-rolled deformed steel rod with said ribs thereon is tempered for at least 15 minutes at the indicated temperature, whereby a ribbed steel rod of high elastic limit and high notch impact tenacity is formed.

644,598 Great Britain Oct. 11, 1950

Claims

1. A METHOD OF MANUFACTURING RIBBED STEEL RODS FOR REINFORCING CONCRETE COMPRISING THE STEPS OF COLD-ROLLING A STEEL ROD CONSISTING OF THOMAS STEEL AND DEFORMING THE SAME SO AS TO REDUCE ITS DIMENSION IN ONE CROSS-SECTIONAL DIRECTION BY AT LEAST 40%; THEREAFTER TEMPERING SAID COLDROLLED DEFORMED STEEL ROD AT A TEMPERATURE RANGING BETWEEN 450* AND 600* CENTIGRADE FOR AT LEAST 15 MINUTES, AND FORMING RIBS ON SAID STEEL ROD NOT LESS THAN 15 MINUTES BEFORE TERMINATION OF SAID TEMPERING SO THAT SAID COLDROLLED DEFORMED STEEL ROD WITH SAID RIBS THEREON IS TEMPERED FOR AT LEAST 15 MINUTES AT THE INDICATED TEMPERATURE, WHEREBY A RIBBED STEEL ROD OF HIGH ELASTIC LIMIT AND HIGH NOTCH IMPACT TENACITY IS FORMED.