JPS581016A - Production of steel bar of steel wire having superior delayed breakdown characteristic and mechanical properties for prestressed concrete - Google Patents

Abstract

PURPOSE:To improve delayed breakdown characteristics and mechanical properties by hardening and tempering a PC steel bar then applying minute bending strains-thereto. CONSTITUTION:While a PC steel bar W is conveyed with pinch rolls 1, 4, 11, it is passed through vertical stage rolls 2 for leveling and horizontal stage rolls 3 for leveling whereby it is leveled so as to maintain linearity. After this steel bar is heated to 900-1,000 deg.C hardening temps. with high frequency induction heating coils 5, it is quickly cooled and hardened with cooling water jackets 6, and in succession to these processes it is heated to tempering temps. with high frequency induction heating coils 7. Such steel bar is passed through strain applying devices 8, 9 in the state meintained at the tempering temp. whereby it is applied with about 2% min. strains in vertical and lateral directions; further it is quickly cooled in water cooling jackets 10. The PC steel bar having superior delayed breakdown characteristics and mechanical properties is produced without degrading the uniform elongation characteristics, required for PC steel bar.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing prestressed concrete steel bars or steel wires (hereinafter referred to as "prestressed concrete steel bars") that have excellent delayed fracture characteristics and mechanical properties. In recent years, the curing of concrete during the manufacture of piles or balls (hereinafter referred to as PcJ) has been improved with the aim of shortening the curing period.
High-temperature, high-pressure curing (hereinafter referred to as autoclave curing) performed at 180°C to 200°C in an atmosphere of approximately lθ atmospheric pressure has become commonplace.

However, the autoclave curing method has the disadvantage that the amount of relaxation of the steel rod in concrete increases by a considerable amount.This phenomenon is caused by time-dependent laminar deformation, i.e., creep. It is caused by deformation and is greatly influenced by temperature, initial stress, and time.

Conventionally, the methods used to reduce the amount of relaxation VN produced by autoclave curing methods include adding alloying elements to the steel bar material to achieve the effects of Kokuto strengthening and precipitation strengthening; These methods are broadly divided into methods that aim to strengthen strain aging by adding tensile processing using a hot spring, such as with a steel F wrench.

However, when the latter conventional method greatly reduces the amount of carbon dioxide, the ``uniform elongation'' of the 4IK heat-treated PC steel bar decreases, which is a serious drawback. There is.

The present invention improves rounding &
In the tempering process in the Thermo-Asahi Twin & C, which uses high-frequency induction heating and rapid cooling, the round steel bar is heated to the tempering temperature and subjected to minute distortion of 2-depth or less. It is an object of the present invention to provide a method in which the relaxation properties can be greatly improved without impairing the uniform elongation property. The delayed failure characteristic, which is a superimposed characteristic for PC steel bars, can be significantly improved compared to conventional methods.

Hereinafter, the present invention will be explained in detail with reference to FIGS. 1 to 5.

FIG. 1 shows a tenth embodiment of the present invention. W is a steel rod, and the steel rod W is fed in the direction of the arrow by feeding means 1.4.11 such as pinch rolls, for example. The above feed pass 11
In the steel bar W, a male straightening vertical corrugated roll 2. Then, after being straightened to maintain the straightness with a straightening horizontal corrugated roll 3, a hardening high-frequency induction heating coil 5, for example, 9
After being heated to a quenching temperature of 00'' to 1,000°C, it is rapidly quenched in a water cooling jacket 6.The quenched steel bar W is then heated in a high-frequency induction heating coil 7 for tempering to a normal 0@return temperature determined by the steel type. The steel rod Wti heated to the tempering temperature is immediately sent to the strain adding device 8 and then to 9 where a minute bending strain is applied.In the zero strain adding scale 8, the steel rods 81 to 84 are bent in the vertical direction and the feeding direction. A fixed p-p is installed along the upper part of the feed passage so that adjacent bars maintain a predetermined gap from each other to prevent displacement.
The movable rolls 85 to 87 are installed along the lower part of the feeding path and can be moved vertically. , 86 companies 82 and 830°87
are at intermediate positions below 88 and 8401, respectively.

A slight bending strain is applied to the steel bar WFJ in the process of passing between the fixed roll groups 81 to 84 and the upwardly displaced movable roll groups 85 to 87. In this regard, Section 111(b)K
Yotte, even KN thin K m '14 t le.

The movable roll 85 located at the lower center position between the fixed U-rules 81 and 82 is moved as shown by the dotted line in FIG. 1(b).
H■ When it is displaced upward, the steel material between the fixed rollers 81 and 82 becomes 11M10IC (the amount of upward displacement of the movable roll 86).
A bending strain that is similar to that is given.

Steel bar W between m*crawl 1 and 82 in this case
As shown in Figure 1 (c) K, the radius of the circle that is part of the circumference is R, and J is the distance ABo% between the fixed rolls 81 and 82, then R - + (R -H)"J'-2RH+H"=0 to A B x= 95 mm No. 47.5 angle]
, Hhu) R(frame) 1 1128.6 2 565.1 3 377.5 4 284.0.

Therefore, the following relationship holds true.

H (m) R (ms+) E3 1 1128.6 3.2X103 2 565.1 6.4X103 3 ・ 377.5 9JX103 4 284.0 12.6 x
10 Such a bending strain is continuously applied between the fixed portions 82 and 83 and the movable roll 86, and then between the fixed rolls 83 and 84 and the movable roll 87. A device consisting of a fixed roll group and a movable roll group having the same configuration as the strain applying device 8 is arranged at 90 degrees with respect to the strain applying device 8, and is arranged along the feed path 9. Therefore, the steel The rod is subjected to bending strain in the vertical direction by the strain applying device 8, after which a bending strain is applied in the horizontal direction by the strain applying device 9, and then it is rapidly cooled in the water cooling jacket 1'0 and sent to a predetermined position. All of the above processing,
A second embodiment of the invention is shown in the O Hz diagrams (a) and (bl) which are carried out in one continuous step as shown.

When the second embodiment is compared with the tenth embodiment, the difference is that one strain applying device 12 is used instead of the strain applying device 8.9, but the other things are the same. 012 is a rotating body, and a plurality of pieces 123 to 127 are fixed along the axial direction of the rotating body 111. Pieces 123-127
The positions of the rods are mutually displaced in the direction perpendicular to the axis, and a through hole is provided to serve as a passage for the steel rod.

121 is toward the inlet side of the rotating body 12, and 122 is (b)
These guides are respectively provided in the direction toward the exit side of the rolling body 18.

The steel rod W heated to the tempering temperature by the high-frequency induction heating coil 7 for tempering is transferred from the population 128 of the strain applying device 12 to the pieces 123 to 127 in the rotating body 12 via the guide 121 and to the strain applying device 12 via the guide 122. The water is sent to the water-cooling jacket 10 from the outlet. When the rotating body 12° is rotated at a predetermined speed, for example, in the direction of the arrow a during this feeding process, the slight bending around the entire circumference of each chest O steel bar can continuously apply strain.

Figure 3 shows an embodiment of ga of the present invention, and when compared with the rattan l and the second embodiment, the first and second embodiments are shown.
In the embodiment described above, a high frequency induction heating coil is used as the heating means for hardening, whereas a direct current supply mechanism 13 is used, and other points are the same. 131
．． 132 and IJ3.134 are a pair of feed rollers which also serve as electrodes, and are connected to a power source gK, so that the steel rod W is heated to the quenching temperature in the process of being fed between the pair of electrodes. In addition, in FIG. 3, the strain adding device is shown in FIG.
The strain adding device shown as 12 may be used, or a known inclined roll type hakama adding device may be used.

The inventor conducted various experiments to confirm the effects of the present invention. Some of them are as follows.

Experimental Example 1 1) 8w steel bar 7.4 whose chemical composition is shown in Table 1 of the test body
I used one drawn out in a different shape from wx da.

2) Experimental method Some of the specimens were treated according to the present invention according to the 2-in shown in Figure 1g1, and the others were treated using the conventional method, that is, j111.
Processing should be done on a line that does not have a distortion adding device as shown in 8. The zero heat treatment conditions were the same for both.

Quenching temperature 940℃ Tempering temperature ffi 430℃3)
The mechanical properties, delayed fracture characteristics, and axial surface residual stress of the specimens made by the method of the present invention and those made by the conventional method were determined.

(1) Mechanical properties It was as shown in Table 2.

In Table 2, the gauge length for elongation at break is 8 d, the gauge length for uniform elongation is 10 d, the room temperature relaxation value is the value for 10 hours at an initial load of 4460 kgf, and the high temperature relaxation value is: The initial load was 4.060 kgff, and 114 tests were carried out with K-pull as shown in Fig. 4 (a). 41st il
(b) shows the actual (day I).

(2) Delayed fracture test) The mechanical properties are shown in Table 2. Delayed fracture tests were conducted on specimens prepared by the method of the present invention and the conventional method.
The results were as shown in Table 3.

Table 3 Unit: Rodan ammonium (50℃) method at time ζ＼, NH45CH
A test piece is maintained at 50°C, and a constant load of 120 kgfi is applied to the test piece. In the Jig table, A to D indicate the average value of the 010 pieces, and the circles indicate the average value of the pieces.

From the above, it was confirmed that the steel bars produced by the method of the present invention have extremely superior delayed fracture characteristics compared to those produced by the conventional method.

(Surface Residual Stress in the Axial Direction Since the increase in the pressure M residual stress on the surface in the axial direction is considered to be a factor contributing to the improvement of the constriction fracture characteristics, two Each book was measured.

The results were as shown in j1411.

This is the position shown as I-m in Fixed Position Co. No. 65il.

j1411! Since the steel bar manufactured by the method of the present invention is strained during tempering,
Irrespective of the direction of strain addition, Ki is around the entire circumference, compared to conventional products, #
t shows a uniform increase in compressive residual stress. □ Experimental Example 2 1) The specimen material itself had a chemical composition shown in Table 5, which originally had good delayed fracture characteristics. The product of the present invention was manufactured according to the line shown in Figure 1, but in this experimental example, the line shown in Figure 2 (al (b) K
Although the product of the present invention is manufactured according to the line shown, the main points are different,
The rest is the same as in Experimental Example IK.

The mechanical properties of t obtained by the method of the present invention and those obtained by the conventional method are shown below.

j16 Table In addition, regarding the constriction fracture test, Korodan Ammon (80℃
) method, but none of them broke for more than 7 hours, giving good results. Experimental Example 8 1) The chemical 1j AltlK was demonstrated on specimen j1711.
109PC#I rod (9,2u) irregular rod type No. 1 was used.

Table 7 Weight - 2) Experimental method Experimental example 1 is! The product of the present invention was manufactured according to the line shown in Figure 1, but in this experimental example, the line shown in Figure 3 was used, in other words, the steel bar was heated to the quenching temperature not by a high-frequency induction heating coil but by a direct energizer #IK. ◇ 3) 1j results (1) Mechanical properties as shown in Table 8].

(2) Delayed fracture test The results of the delayed fracture test using the Rodin Ammon (50°C) method were shown in JI911.

8th Machine No. 91N Unit Time As is clear from the above, the present invention has superior delayed fracture S properties compared to the conventional method, and has improved mechanical properties, especially high humidity Laczeshi carbon properties and uniform elongation properties. It is possible to manufacture excellent round steel bars.

Experimental Example 4 Although the present invention is characterized by applying a slight bending strain to a steel bar during tempering, a rounding experiment was conducted to confirm the preferable amount of bending strain.

1) Specimen The same specimen as shown in Experimental Example 1 was used.

2) Experimental method This is exactly the same as the experimental method shown in Experimental Example 1. The amount of bending strain added during eso-tempering was greatly reduced.

3) Experimental results j1110 table shows 9.

$1 10 From the table above, it can be confirmed that the amount of strain given to the steel rod during tempering is preferably 21iIi degrees or less, since uniform elongation properties deteriorate if the strain exceeds 2 bags.

[Brief explanation of drawings]

Iris 111(a)a is a front view showing an embodiment of the present invention, FIG. cl is shown in Figure 1 (a
2E (ml is a front view showing the $2 embodiment of the present invention, Fig. 2) is a diagram for explaining the amount of strain given by the strain adding device in Figure 2 (a). A vertical sectional view showing details of the additional device, FIG. 3 is a front view showing an embodiment of the broom 3 of the present invention, and Fig. 4 (a) is an experimental example 1K of the present invention.
Fig. 4(b) is a diagram showing the experimental conditions for the experiment conditions of Fig. 4(a), and Fig. S is a diagram showing the experimental conditions of the present invention. It is a sectional view showing the measurement position of surface residual stress in the axial direction in an experimental example. 5.13... Rapid heating device for quenching, 6... Cooling device for quenching, 7... High frequency induction heating coil for tempering, 8,
12...Mold reduction device is a strain adding device, 10...Quick cooling device procedural amendment February 1986//day Director General of the Japan Patent Office Shima 1) Haruki Tono1, Indication of the case 1982 patent 111198289 No. 2, Delayed Fracture Characteristics and Mechanical Properties, Excellent 9. Method of Manufacturing Steel Bars or Steel Wires for Prestressed Concrete 3, Person Making Amendment 4, Agent 980 511m Date of Direct Order Voluntary 6, 0

Claims (1)

[Scope of Claims] l) In one continuous step, a round steel bar or steel wire that has been quenched by rapid heating and quenching is subjected to mild bending strain during tempering by high-frequency induction heating, and then immediately quenched. 9. Manufacturing method of steel rods or steel wires for prestressed man cleats, characterized in that the steel rods or wires are prestressed with excellent delayed fracture properties and mechanical properties during tempering by high-frequency induction heating. ; Manufacturing method of steel rod or steel wire for concrete.