GB2289231A

GB2289231A - High-adhesion/high-strength deformed steel bar and method for manufacturing the same

Info

Publication number: GB2289231A
Application number: GB9415023A
Authority: GB
Inventors: Eiji Yamashita; Yukio Murayama
Original assignee: Neturen Co Ltd
Current assignee: Neturen Co Ltd
Priority date: 1994-05-02
Filing date: 1994-07-26
Publication date: 1995-11-15
Anticipated expiration: 2014-07-26
Also published as: CN1042748C; CN1118811A; MY116622A; GB9415023D0; KR950032655A; GB2289231B; KR0144832B1; TW281710B

Abstract

A high-adhesion/high-strength deformed steel bar, wherein the deformed bar just hot-rolled and having spiral protrusion 12 forming a knot in its outer surface for concrete reinforcement is reduced in cross section through a rounding operation e.g. drawing at such reduction rate as to permit the knot to remain after the operation, and a plurality of flutes 13 each of which is opposite in spiral direction to the knot are formed in the deformed bar. Then, the thus formed deformed bar is heat-treated through quenching and tempering operations. <IMAGE>

Description

High-Adhesion/High-Strength Deformed Steel Bar and Method for Manufacturing the same The present invention relates to a highadhesion/high-strength deformed steel bar and a method for manufacturing the same. The high-adhesion/highstrength deformed steel bar is used for concrete reinforcement in civil engineering/building works and for main- and sub-reinforcement for prestressed concrete, and is further used as earth anchors and the like, while required to be good in adhesion to concrete and subjected in use to thread-rolling operations and cross wire welding operations.

In a conventional deformed steel bar for concrete reinforcement, i.e., in a hot-rolled deformed steel bar 1 shown in Fig. 10, protrusions or knots 11 are formed in a surface of the steel bar at predetermined intervals through a hot rolling operation to improve the steel bar in adhesion to concrete.

Though the deformed steel bar just hot-rolled is good in adhesion to concrete due to its large protrusion's height, such deformed bar is poor in outof-roundness due to its hot rolling operation in which an upper and a lower roll for hot-rolling the bar require a clearance therebetween, which clearance results in a pair of longitudinal ribs 12 of the thus hot-rolled deformed bar. These ribs 12 make it difficult to apply the thread-rolling operations to end portions of the deformed bar, and also make it difficult to steadily keep welding electrodes in contact with the deformed bar in the cross wire welding operations thereof, which impairs the deformed bar in weldability. Still further, the ribs 12 of the deformed bar make it difficult to smoothly perform straightening operations of a coiled piece of the deformed bar through straightening rolls, and also make it difficult to continuously feed the deformed bar through feed rolls. Particularly, in heat-treated high-strength deformed steel bars for prestressed concrete, since the deformed bars are large in hardness, the deformed bars poor in out-of-roundness make it impossible to be treated through the threadrolling operations for forming rolled threads thereon, which requires the deformed bars to be previously machined through auxiliary thread-cutting operations before the thread-rolling operations thereof. On the other hand, in case that the deformed bars have been previously improved in out-of-roundness through skinpass rolling operations to solve the above-mentioned problems, since the deformed bars have their knots decreased in height, the deformed bars become poor in adhesion to concrete.

Consequently, it is an aim of the present invention to provide a high-adhesion/high-strength deformed steel bar and a method for manufacturing the same, which is improved in workability in secondary processing operations such thread-rolling operations and welding operations by improving in out-ofroundness of its cross section through slight wiredrawing operations to which a hot-rolled deformed steel bar having knots is subjected. It is another aim of the present invention to provide a high adhesion/high-strength deformed steel bar and a method for manufacturing the same, which is provided with a plurality of novel spiral grooves, i.e., novel flutes which improve the deformed bar in adhesion to concrete.

In order to solve the above problems, the present invention provides a high-adhesion/highstrength deformed steel bar, wherein a hot-rolled deformed steel bar or wire blank for concrete is provided with a spiral protrusion forming a knot in its outer surface, and has its cross sectional area reduced through a rounding process at a reduction rate permitting the knot to still remain; and, the blank thus subjected to the rounding process is heat-treated through quenching and tempering processes to form the high-adhesion/high-strength deformed steel bar.

Preferably, a plurality of spiral grooves, which are formed through a hot rolling process of the bar or wire blank and different in spiral direction from that of the spiral protrusion forming the knot, are formed in the bar or wire blank through the rounding process.

Preferably, the bar or wire blank comprises in weight percentage: 0.1-0.6 % of C; 0.152.00 of Si; 0.6-2.00 % of Mn; up to 0.6 % of Cr; and the remainder being iron and inevitable impurities, the bar and wire blank having a diameter of from 5 to 50 mm and having been heat-treated to have a tensile strength of at least 930 N/mm2 and a yield point of at least 785 N/mm2.

The present invention further provides a method for manufacturing a high-adhesion/highstrength deformed steel bar as defined above, wherein the bar or wire blank provided with the spiral protrusion forming the knot in its outer surface: is drawn to have its cross-sectional area reduced at the reduction rate permitting the knot to still remain; is then rapidly heated over the entire cross-sectional area thereof to a quenching temperature by means of a high-frequency induction heating means or an electriccurrent direct application means while continuously fed; is quenched to realize a hardening operation; is then rapidly heated again to a quenching temperature by means of a high-frequency induction heating means or an electric-current direct application means; and, is then quenched again to realize a tempering operation.

The present invention further provides a method for manufacturing a high- adhesion/hi gh- strength deformed steel bar as defined above, wherein: in the rounding operation, the bar or wire blank is drawn through a round die to have the crosssectional area reduced at the reduction rate permitting the knot to still remain, the round die being provided with a plurality of spiral protrusions in its inner surface, each of which protrusions has its spiral direction be opposite to that of the knot.

A preferred embodiment of the present invention will be described hereinbelow by way of example only with reference to the accompanying drawings, in which: (Fig. 1) A perspective view of the high-adhesion/high strength deformed steel bar of the embodiment of the present invention; (Fig. 2) A flowchart for showing the manufacturing process of the embodiment of the present invention; (Fig. 3) A cross-sectional view of the blank or deformed bar just hot-rolled of the embodiment of the present invention (Fig. 4) A cross-sectional view of the deformed steel bar having no flute, which is drawn through the drawing die of the embodiment of the present invention having no internal protrusion; (Fig. 5) A cross-sectional view of the deformed steel bar having the flutes, which is drawn through the drawing die of the embodiment of the present invention having the protrusions in its inner surface; (Fig. 6) A longitudinal sectional view of the test sample of the embodiment of the present invention in the concrete adhesive-strength test; (Fig. 7) A schematic diagram of the tester for performing the concrete adhesive-strength test of the embodiment of the present invention; (Fig. 8) A graph for showing the test results of the concrete adhesive-strength test of the embodiment of the present invention; (Fig. 9) A perspective view of the drawing die of the embodiment of the present invention having the spiral protrusions in its inner surface; (Fig. 10) A perspective view of the blank or deformed bar just hot-rolled; (Fig. 11) A side view of the head portion of the highadhesion/high-strength deformed steel bar of the embodiment of the present invention, the head portion being formed through the cold pressing operation of the deformed bar; and (Fig. 12) A schematic diagram of the continuous quenching/tempering plant used in the embodiment of the present invention.

In the construction of the preferred embodiment of the present invention, the reason why the concrete-reinforcing hot-rolled deformed steel bar or wire provided with the spiral protrusions in its outer surface is used is that: although the deformed bar or blank just hotrolled is poor in out-of-roundness, since such blank is already provided with the knots, it is possible to reduce the number of the following necessary processing operations of the blank to obtain the deformed bar improved in adhesion to concrete. The knots of the blank or deformed bar having been formed through the hot-rolling operations are controlled in height according to the nominal diameter of the deformed bar, original heights of the knots and the inner diameter of a drawing die. In order to improve the deformed bar in adhesion to concrete, it is desirable to perform the drawing, i.e., rounding operations of the deformed bar at minimum reduction rate in cross-sectional area so as to accomplish a necessary improvement of the deformed bar in out-ofroundness thereof. Experiments performed according to the present invention clarify the fact that the drawing or rounding operations of the deformed bar are performed preferably at such reduction rate as to permit 40 % of the original height of each of the knots to remain after such drawing or rounding operations.

In the deformed bar of the preferred embodiment of the present invention, decrease in adhesion to concrete, which is resulted from the drawing or rounding operations which reduce the height of each of the knots, is compensated for by the provisions of a plurality of spiral grooves of the outer surface of the deformed bar. As for such provisions of the spiral grooves, since it is not possible for the spiral grooves to improve the deformed bar in adhesion to concrete when the spiral grooves have the spiral direction thereof be the same as that of the knots so as to be hidden away in the bottoms of the knots, the spiral grooves of the deformed bar of the present invention have the spiral direction thereof be opposite to that of the knots to permit the spiral grooves to be synergistic with the knots in action. Further, the deformed bar of the present invention is subjected to heat-treatments such as quenching and tempering operations for improving the deformed bar in mechanical strength.

The blank of the deformed bar of the preferred embodiment of the present invention is defined in chemical composition by the following reasons. In the deformed bar of the present invention, C is in a range of from 0.1 to 0.6 wt. %, since C of less than 0/1 wt. % makes it impossible to obtain a predetermined strength of the deformed bar through the quenching operations while C of more than 0.6 wt. % makes the deformed bar poor in toughness. Si is a useful component to improve the deformed bar in high-temperature relaxation, and is in a range of from 0.15 to 2.0 wt. % in the deformed bar since Si of less than 0.15 wt. % Can not improve the deformed bar in high-temperature relaxation while Si of more than 2.0 wt. % makes the deformed bar poor in toughness. Mn is in a range of from 0.6 to 2.00 wt. % in the deformed bar to improve the same in quenching properties, sine Mn of less than 0.6 wt. % can not sufficiently improve the deformed bar in quenching properties while Mn of more than 2.00 wt. % increases the amount of retained austenite in the deformed bar after completion of the quenching operations. Cr makes it possible to improve the deformed bar in quenching properties and in resistance in tempering operations of the deformed bar. Cr of more than 0.6 wt. % in the deformed bar makes the deformed bar disadvantageous in profitability. Further, in case of the deformed bar of a small-diameter, it is possible to neglect the addition of Cr to the deformed bar in accomplishing a necessary improvement thereof.

The deformed bar of the present invention is preferably defined in diameter in a range of from 5 to 50 mm since this range of the deformed bar is widely used in concrete reinforcement. Further, the deformed bar of the present invention preferably has a tensile strength of at least 930 N/mm2 and a yield point of at least 785 N/mm2 after completion of the heat treatments thereof, since these properties are requires for prestressed concrete reinforcement.

In the method for manufacturing the deformed bar of the present invention, the rounding operations may be of any mode. However, of the rounding operations, the drawing operation using the drawing die is preferable in mass production. Particularly, a drawing die provided with a plurality of spiral protrusions in its inner surface is advantageously used in mass production to simultaneously perform the rounding operations of the deformed bar and the forming operation of the plurality of spiral grooves of the deformed bar. The deformed bar of the present invention is continuously heat-treated or quenched and tempered by means of the high-frequency induction heating means or the electric-current direct application means so as to be improved in quality in mass production in an easy manner.

A high-adhesion/high-strength deformed steel bar or wire (hereinafter simply referred to as the high-strength deformed steel bar) is produced through operations shown in Fig. 2. Namely, in the preparation operation of a blank of the hot-rolled deformed steel bar (hereinafter simply referred to as the deformed bar), the blank assuming a shape shown in Fig. 10 having been coiled is used as a starting material of the deformed bar. In a descaling operation following the above preparation operation of the blank, the blank has its superficial scales descaled through a multistage-roll straightening machine. A drawing operation following the above, in which the blank is cold-drawn through a predetermined round die, and then subjected to a quenching operation in which the thus drawn blank or deformed bar is continuously heated to a quenching temperature by means of the high-frequency induction heating means or the electric-current direct application means, and then quenched by water to perform the quenching operation of the deformed bar.

After that, in a tempering operation, the deformed bar is continuously heated again to a tempering temperature by means of the high-frequency induction heating means or the electric-current direct application means to perform the tempering operation thereof, and then quenched. In a coiling operation of the thus treated deformed bar, the deformed bar is coiled or cut in linear state to have a predetermined straight length, and subjected to a thread-cutting operation. After that, the thus processed deformed bar is inspected and shipped as a completed product.

In the embodiment of the present invention, the hot-rolled deformed steel bar assuming the shape shown in Fig. 10 is used as a starting material, i.e., blank. The blank is provided with a spiral protrusion or knot having a substantially 30-deg, right-hand helix, and is denoted by the designation "D10" in JIS 3112, a rated diameter of which blank is 9.53 mm. A chemical composition of the blank is shown in Table 1.

TABLE 1 CHEMCIAL COMPOSITION (wt %)

STANDARD CH. No LOT No C Si Mn P S Cr Ti )3 UB32B M 34848 4721 O. 33 0.24 0.72 O. 010 0.007 0.15 O. 14 + Further, the blank or deformed bar just hot-rolled and described above has a cross-sectional contour shown in Fig. 3. Namely, in Fig. 3, the bank has a barrel diameter of from 8.85 to 8.90 mm, a rib height of from 0.36 to 0.38 mm, and a knot height of from 0.58 to 0.63 mm.

This blank or deformed bar just hot-rolled was subjected to cold-drawing operations through both a round die having an inner diameter of 9.10 mm with no internal protrusion and another round die 21 shown in Fig. 9. The round die 21 has an inner diameter of 9.20 mm and is provided with six internal spiral protrusions 22 in its inner surface. Each of the protrusions 22 has a 18-deg, left-hand helix. The blank thus drawn through the round die with no internal protrusion is shown in cross section in Fig.

4, while that drawn through the round die 21 having the internal protrusions 22 is shown in Fig. 5.

Although it is preferable in improvement of adhesion to concrete to increase the helix angle of each of the protrusions 22, since a large helix angle makes it difficult to smoothly perform the drawing operations of the blank, the helix angle of 18 degrees of the blank is determined as a proper value.

Fig. 4 shows the cross-sectional view of the blank or deformed bar thus drawn through the round die with no internal protrusion. As shown in the drawing, the deformed bar thus drawn, i.e., drawn bar has: its barrel diameter be the same as that of the blank not subjected to the drawing operations; and its ribs 12 and knot 11 slightly decreased in height relative to those of the blank not subjected to the drawing operations. Namely, in the drawn bar, each of the rib 12 has a height of from 0.24 to 0.28 mm, which corresponds to a 63-78 % of its original height, and the knot 11 has a height of from 0.25 to 0.30 mm, which corresponds to a 40-52 % of its original height, so that the drawn bar is improved in out-of-roundness and in easiness in thread-rolling properties. In comparison with the blank, the drawn bar has its knot decreased in height to become poor in adhesion to concrete, test results of which will be described later.

Fig. 5 shows the cross-sectional view of the blank having been drawn through the round die having the internal protrusions. As shown in the drawing, the round die with no internal projection has the inner diameter of 9.10 mm, whereas the round die with the internal protrusions has the inner diameter of 9.20 mm. Consequently, the blank thus drawn through the round die with the internal protrusions is slightly larger in height of the ribs 12 and the knot 11 than that drawn through the round die with no internal protrusion. The former, i.e., blank drawn through the round die with the internal protrusions is further provided with six spiral grooves or flutes 13 in its outer surface, each of which flutes 13 has a 18-deg, left-hand helix with a width of 1.3 mm and a depth of 0.40 mm, as shown in the drawing. The appearance of the thus drawn blank or bar is shown in Fig. 1.

Namely, as shown in the thus drawn or fluted deformed bar 2 of Fig. 1, each of the flutes 13 in the outer surface of the deformed bar 2 is opposite in spiral direction to the knot 11 having the substantially 30deg, right-hand helix, and has the 18-deg, left-hand helix. by these spiral grooves or flutes 13, the losses in adhesion to concrete resulted from the decrease in height of the knot 11 due to the drawing operation may be compensated for.

According to a "Method of Nippon Concrete Kougaku Kyoukai (draft)", the deformed bar having been subjected to the above drawing operations was tested to determine its adhesive strength to concrete. A test sample 4 is shown in Fig. 6. As shown in the drawing, in the test sample 4: a test piece of the deformed bar 7 was disposed in the center of a concrete block 5 having 10 cubic centimeters; and, a reinforcing wire 6 having a diameter of 6 mm was disposed around the deformed bar 7 in a spirally winding manner to have a winding diameter of 8 cm and a winding pitch "a" of 4 cm (each of opposite ends of the wire 6 was wound 1.5 turns of which 0.5 turn was waste). Further, the concrete of the block 5 had a horizontal arrangement of reinforcement, and had the following quality: Age: 28 days Curing Conditions: 14-24 C in water curing; Concrete Compressive Strength: 300 Kgf/cm2 plus or minus 30 Kgf/cm2; and Slump: 8 cm plus or minus 2 cm.

The test was conducted by using a 30-ton tension tester in a manner shown in Fig. 7. In the drawing, the test sample 4 was mounted on a table 41 of a stationary portion of the tension tester through a spherical seat 42 and its mating spherical washer 43. After that, the deformed bar 7 to be tested was pulled in the direction of arrow P by means of a clamp 44, so that the deformed bar 7 was measured in slippage. The thus measured slippage was recorded by an X-Y recorder 47 through an amplifier 46 in relation to a pulling force to which the deformed bar 7 was subjected.

Test results of the above are shown in Fig. 8 and Table 2. In Fig. 8, the vertical (Y) axis indicates intensity of the pulling force (KN), and the horizontal (X) axis shows the amount of the slippage (mm). Curve A is the pulling force-slippage diagram of the blank or deformed bar just hot-rolled. Curve B is the pulling force-slippage diagram of the drawn deformed bar having no flute. Curve C is the pulling force-slippage diagram of the drawn deformed bar having the flutes. Curve D is the pulling forceslippage diagram of a comparative example or drawn bar having a diameter of 9.2 mm (10 mm in nominal) and made of Ulbon which is a registered trade mark belonging to Neturen Co.Ltd. The table 2 shows, based on the test results shown in Fig.

8, the slippages of 0.05 mm, 0.1 mm and 0.25 mm together with the mean values thereof and the maximum adhesive strength or adhesion of each of the samples.

Summarizing the above results, the following fact appears. Namely, when the deformed bar just hot-rolled is drawn to have no flute, the thus drawn deformed bar with no flute has its knot decreased in height, which causes the maximum adhesive strength 36. 8 KN of the deformed bar to decrease to 26. 5 KN a value of which is however still larger than that of the maximum adhesive strength of the comparative example made of ULBON. On the other hand, the drawn deformed bar having the flutes has the maximum adhesive strength of 34. 7 KN, and, therefore keeps the substantially same adhesive strength as that of the deformed bar just hot-rolled. Consequently, it is recognized in effect that the decrease in adhesion to concrete of the drawn deformed bar due to the decrease in height of the knot is compensated for by the flutes formed in the drawn deformed bar through the drawing operation.

TABLE 2 TEST RESULTS OF ADHESIVE STRENGTH TO CONCRETE

SLIPPAGE (mm) MAXIMUM ADHESION SAMPLES 0.05 0.10 0.25 AVERAGE SLIPPAGE (mm) MAXIMUM ADHESION 1 D10 AS ROLLED 14.7 19.2 27.5 20.5 1.54 36.8 2 D10 #9.1 # 16.2 17.4 19.5 17.7 1.82 26.5 DRAWN WITH NO GROOVES 3 D10 #9.2 # 19.2 21.8 27.4 22.8 0.95 34.7 DRAWN WITH GROOVES 4 ULBON9.2mm * (10 # # 12.7 12.4 9.6 11.6 0.02 12.8 COMPARATIVE EXAMPLE *COMPARATIVE EXAMPLE: ULBON is the registered trade mark belonging to NETUREN Co,. Ltd.

Then, the deformed bar thus drawn was heattreated through a continuous quenching/tempering plant 30 shown in Fig. 12. In Fig. 12, the drawn deformed bar W was passed through a pinch roll unit 31, a longitudinal-stage straightening roll unit 32, a cross-stage straightening roll unit 33 and a pinch roll unit 34. After that, the deformed bar W thus straightened was heated to a quenching temperature of 920 C by means of a high-frequency induction heating coil 35 for quenching use, and then quenched in a water-cooled jacket 36 to perform the quenching operation. The thus quenched deformed bar W was heated again to a tempering temperature of from 370 to 380 C by means of a high-frequency induction heating coil 37 for tempering use, and then quenched in a water-cooled jacket 38. After that, the deformed bar W was passed through a pinch roll unit 39.

Mechanical properties of the deformed bar having been heat-treated are shown in Table 3. The deformed bar is improved in mechanical properties through the heat treatment. As shown the Table 3, the deformed bars both with and without the flutes fulfill the yield point, tensile strength, breaking extension, and reduction of area of the steel bar specified in JIS G 3109.

TABLE 3 RESULTS OF MECHANICAL STRENGTH (N=5 MEAN VALUE)

HEAT TREATING OUTER ACTUAL YIELD POINT TENSILE LOAD BREAKING SAMPLES CONDITIONS DIA. CROSS LOAD ELONGATION mm SECTIONAL KN KN 80% QUENCHING TEMPERING AREA STANDARD MORE THAN 81.6 MORE THAN 90.9 VALUE (MORE THAN (MORE THAN MORE THAN 5 JISG 3109 1,275N/mm) 1,420N/mm) D10 21.9 41.9 HOT-ROLLED 10.05 71.3 (307N/mm) (588N/mm) 25.1 BLANK D10 #9.10# 920 C 380 C 9.12 63.7 87.5 93.7 8.7 DRAWN WITH (1374N/mm) (1471N/mm) NO GROOVES D10 #9.10# 920 C 370 C 9.22 62.5 87.9 93.2 7.6 DRAWN WITH (1406N/mm) (1491N/mm) GROOVES ( ) Real strength The thus completed product of the deformed bar was then thread-rolled by using RL23-type thread rolling machine of the NETUREN CO. LTD. The results thereof are shown in Table 4. In the results, the deformed bars both with and without the flutes fulfill the requirements specified in JIS B 0221.

Incidentally, though it is not possible to thread-roll the blank or deformed bar just hot rolled due to its poor out-of-roundness, the above completed product of the embodiment of the present invention was thread-rolled without involving any problems.

Then, the thus completed deformed bar was cold-pressed to form a head portion assuming a shape shown in Fig. 11 by using FP11-type cold pressing machine of the NETUREN CO. LTD . The results thereof are shown in Table 5. In the results, any one of the defor med bars both with and without the flutes showed a predetermined tensile strength, and was normally broken in its barrel portion. Consequently, it is clarified that the head portion of the thus completed deformed bar can be formed in normal conditions.

TABLE 4 RESULTS OF THREAD-ROLLING TEST (RL23-type thread rolling machine of NETUREN Co., Ltd.)

BLANK THREAD DIMENSIONS TENSILE TEST RESULTS DIA. (M10 P=1.25) N=5 MEAN VALUE mm (THREAD STRENGTH/ OUTER DIA. EFFECTIVE DIA. BLANK STRENTH) JIS B 0211 STANDARD 9.81~9.96 8.998~9.148 D10 #9.10# DRAWN WITH 9.12 9.86 9.04 86.7KN/93.7KN 92.5% NO GROOVES D10 #9.20# DRAWN WITH 9.22 9.84 9.00 85.9KN/93.2KN 92.2% GROOVES ULBON* 9.2# COMPARATIVE 9.14 9.83 9.04 85.9KN/93.8KN 91.6% EXAMPLE * ULBON: Registered Trade Mark belonging to NETUREN Co., Ltd.

TABLE 5 RESULTS OF HEAD-PORTION PRESSING TEST FP11-type pressing machine of NETUREN Co., Ltd.)

BLANK HEAD DIMENSIONS (mm) TENSILE TEST RESULTS N=5 DIA. mm OUTER DIA. THICKNESS (ROUND SUPPORT PLATEN USED) D10 #9.10# 193.7KN 293.8KN 393.6KN ALL BROKEN DRAWN WITH 9.12 16.5 7.5 493.5KN 593.7KN IN BLANK NO GROOVES PORTION D10 #9.20# 193.0KN 293.0KN 393.2KN ALL BROKEN DRAWN WITH 9.22 16.8 7.4 493.4KN 593.4KN IN BLANK GROOVES PORTION ULBON* 9.2# 193.8KN 294.0KN 393.9KN ALL BROKEN COMPARATIVE 9.14 16.7 7.5 494.2Kn 594.1KN IN BLANK EXAMPLE * ULBON: Registered Trade Mark belonging to NETUREN Co., Ltd.

Though the embodiment of the present invention is described in the above as to the deformed bar of the designation "D10" specified in JIS G 3112, it is also possible to apply the present invention to the remaining designations "D6-D51" specified in the same JIS standard number.

As described in the above, according to the present invention, it is possible to improve the hotrolled deformed bar poor in out-of-roundness by using the drawing operation since both the knot and the ribs of the deformed bar are decreased in height through the drawing operation. Consequently, even when the blank or deformed bar, which is just hot-rolled and therefore poor in out-of-roundness to require the auxiliary thread cutting operation preparatory to the thread-rolling operation, is used, it is possible for the completed product of the deformed bar of the present invention to perform its thread rolling operation in an easy manner. straightening operation of coiled one thereof, which operation is performed by passing the deformed bar through the straightening roll unit. The thus straightened piece of the deformed bar may be easily handled.

Further, preferably, by having a 40 % of the height of the spiral protrusion or knot of the blank or hot-rolled deformed bar remain in the completed product of the deformed bar of the present invention, it is possible to obtain an adhesive strength larger than that of the ULBON bar. Still further, by providing the plurality of the spiral grooves in the outer surface of the deformed bar of the present invention, it is possible to further improve the deformed bar of the present invention in adhesion to concrete, provided that the spiral grooves are opposite in spiral direction to the spiral protrusion or knot of the deformed bar.

Further, by defining the blank or deformed bar in composition so as to comprise in weight percentage: 0.1-0.6 % of C; 0.15-2.00 of Si; 0.6-2.00 of Mn; up to 0.6 % of Cr; and the remainder being iron and inevitable impurities, it is possible to easily obtain the strengths specified in the JIS standards and improve the deformed bar of the present invention in resistance to relaxation, which enhances the safety of the high-strength of the deformed steel bar of the present invention in use.

According to the method of the present invention, it is possible to arbitrarily determine the remaining height of the knot of the blank or deformed bar through the rounding operation thereof, which makes it possible to improve the high-strength deformed bar in adhesion to concrete. Further, by drawing the hot-rolled deformed bar through the round die having the plurality of the internal spiral protrusions which are opposite in spiral direction to the knot of the deformed bar, it is possible to form each of a plurality of spiral grooves in the outer surface of the deformed bar in a spiral direction opposite to the spiral direction of the knot and arbitrarily determine the groove's width and depth in the outer surface of the deformed bar, which further improves the high-strength deformed bar in adhesion to concrete. Further, by continuously heat-treating the deformed bar through the high-frequency induction heating means or the electric-current direct application means, it is possible to economically realize the mass production of the the high-strength deformed steel bar which is improved in resistance to relaxation and is uniform in quality.

Claims

CLAIMS: 1. A high-adhesion/high-strength deformed steel bar, wherein a hot-rolled deformed steel bar or wire blank for concrete is provided with a spiral protrusion forming a knot in its outer surface, and has its cross-sectional area reduced through a rounding process at a reduction rate permitting said knot to still remain; and, said blank thus subjected to said rounding process is heat-treated through quenching and tempering processes to form said high-adhesion/high-strength deformed steel bar.
2. A high-adhesion/high-strength deformed steel bar as defined in claim 1, wherein a plurality of spiral grooves, which are formed through a hot rolling process of said bar or wire blank and different in spiral direction from that of said spiral protrusion forming said knot, are formed in said bar or wire blank through said rounding process.
3. A high-adhesion/high-strength deformed steel bar as defined in claim 1 or claim 2, wherein said bar or wire blank comprises in weight percentage: 0.1-0.6 k of C; 0.15-2.00 k of Si; 0.6-2.00 W of Mn; up to 0.6 of Cr; and the remainder being iron and inevitable impurities, said bar and wire blank having a diameter of from 5 to 50 mm and having been heat-treated to have a tensile strength of at least 930 N/mm2 and a yield point of at least 785 N/mm2.
4. A method for manufacturing the high-adhesion/high-strength deformed steel bar as defined in any one of claims 1 to 3, wherein said bar or wire blank provided with said spiral protrusion forming said knot in its outer surface: is drawn to have its cross-sectional area reduced at said reduction rate permitting said knot to still remain; is then rapidly heated over the entire cross-sectional area thereof to a quenching temperature by means of a high-frequency induction heating means or an electric-current direct application means while continuously fed; is quenched to realize a hardening operation; is then rapidly heated again to a tempering temperature by means of a high-frequency induction heating means or an electriccurrent direct application means; and, is then quenched again to realize a tempering operation.
5. A method for manufacturing the high-adhesion/high-strength deformed steel bar as defined in claim 2 or claim 3, wherein in said rounding operation, said bar or wire blank is drawn through a round die to have said cross-sectional area reduced at said reduction rate permitting said knot to still remain, said round die being provided with a plurality of spiral protrusions in its inner surface, each of which protrusions has its spiral direction opposite to that of said knot.
6. A steel rod or wire provided with a spiral protrusion forming a knot in its outer surface which has been drawn and heat-treated by quenching and tempering.
7. A high-adhesion/high-strength deformed steel bar substantially as hereinbefore described with reference to the accompanying drawings.
8. A high-adhesion/high-strength deformed steel bar substantially as hereinbefore described with reference to the Examples.
9. A method of manufacturing a high-adhesion/high-strength deformed steel bar substantially as hereinbefore described with reference to the accompanying drawings.
10. A method of manufacturing a high-adhesion/high-strength deformed steel bar substantially as hereinbefore described with reference to the Examples.