JPS6115926B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing high-tensile steel wire rods for use in PC steel bars and the like. Conventionally, for example, JIS-G-3109 SBPD130/145
High-strength PC steel bars of grade (130 indicates yield point and 145 indicates tensile strength) are obtained by obtaining rolled material, cold drawing straightening (deformation), quenching, and then It is manufactured by tempering. This conventional method is
The target tensile strength is obtained by quenching, and therefore the manufacturing cost and manufacturing equipment required for quenching and tempering are large and large-scale. The present invention solves the above-mentioned problems all at once. By using steel with specific components and specifying rolling conditions, high-strength steel wire rods can be manufactured only by rolling without quenching. Furthermore, by applying a warm straightening method to the conventional tempering process, we have improved mechanical properties such as yield point and relaxation resistance, achieving significant rationalization and improving the properties required for PC steel bars. The purpose of this study is to obtain a high-tensile steel wire rod that satisfactorily satisfies various mechanical properties. That is, in the present invention, C: 0.10 to 0.40%, Si:
0.05~1.50%, Mn: 0.70~2.50%, Cr: 0.10~
After hot rolling, steel with a composition of 1.50%, Mo: 0.05~0.50%, balance Fe: and unavoidable impurities is immediately forcedly cooled to 500~700℃, and then continuously transferred on a conveyor in the state of supercooled austenite. The wire is rolled out into a ring shape, cooled by air blast at a cooling rate of 7°C/sec or more to make the entire wire into a martensitic structure on a conveyor, and then formed into a coil in a converging device and slowly cooled. Self-tempering is performed to obtain a high-strength, high-strength steel wire with a tensile strength of 110 Kg/mm ² or more, and then the bending of the wire is within 4 mm/1.5 m in a temperature range of 100 to 450°C. It is characterized by performing warm straightening to obtain a high-tensile steel wire having a high yield point and excellent relaxation resistance. In the present invention, the temperature is 500 to 700℃ immediately after hot rolling.
Forced cooling. In this case, the temperature at the start of blast cooling, that is, the temperature of the supercooled austenite material, was set at 500 to 700°C because theoretically it is possible to form a martensitic structure on the conveyor even if the material is cooled to 700°C or higher. However, if the cooling start temperature increases, the blast cooling time will inevitably become longer, especially at 7.
At a cooling rate of about °C/sec, there is a practical limit on the length of the conveyor, so the material enters the next focusing device before martensitic transformation is complete, resulting in a partial paynite structure, which is unsuitable for the intended purpose. .
On the other hand, the lower limit was set at 500° C. because in actual rolling operations, it is difficult and uneconomical to cool down to a temperature lower than this in a very short time immediately after rolling. Furthermore, the steel of the invention has a specific composition.
C is added to give the steel the necessary strength and hardenability, but if the C content exceeds 0.40%, the ductility and spot weldability required for a PC steel bar will significantly deteriorate, which is undesirable. If the C content is less than 0.10%, the required strength as a PC steel bar will not be achieved. Si is an element effective in improving hardenability, strength, and toughness, but if the amount of Si is less than 1.50%, it has no effect, and if the amount of Si is added more than 1.50%, the ductility deteriorates, which is not preferable. Mn is effective in improving hardenability, but if it is less than 0.70%, no improvement in hardenability can be expected, and if it is more than 2.50%, it is not economical. Like Mn, Cr improves the hardenability of steel, but if it is less than 0.10% it has no effect, and if it exceeds 1.50% it is not economical. Mo too
Like Cr, it improves the hardenability of steel, but if it is less than 0.05% it has no effect and if it is more than 0.50% it is not economical. On the other hand, the cooling rate by blast is preferably 7° C./sec or more. At a speed lower than that, a paynite structure, a ferrite structure, etc. are generated, resulting in an incompletely quenched structure and the intended purpose cannot be achieved. Next, although it is possible to obtain the target tensile strength by adopting the method described above in hot rolling, the yield point required for the PC steel bar,
Anti-relaxation properties cannot be obtained.
Therefore, in the present invention, after the wire is slowly cooled in the focusing device, warm straightening corresponding to the conventional tempering process is performed. Through this warm straightening, the bend in the wire is straightened, and the PC
A wire rod that fully satisfies the yield point and relaxation resistance characteristics required of a steel rod and is better than that obtained by conventional tempering can be obtained. This warm straightening is carried out in a temperature range of 100 to 450°C so that the bending of the wire is 4 mm or less per 1.5 m. The reason why the straightening temperature is set at 100 to 450°C is that an excellent relaxation value cannot be obtained below 100°C, and a high yield point cannot be obtained in this component system above 450°C. moreover,
PC steel bars require great straightness, for example 1.5m
Since bends of 4 mm or more cannot be used as products, the straightening effect was set to 4 mm/1.5 m or less. Next, an example of an experiment conducted by the present inventor will be shown. That is, 10 types of steel according to the present invention shown in Table 1 were used as test materials.

【table】

[Table] These steels were hot rolled to a diameter of 7.1 mm and immediately quenched to 650°C using forced water cooling equipment. In this case, in order to stably obtain 650℃ and 500℃, the rolling speed was changed from the conventional method of 45m/Sec to 35m/Sec.
It was lowered to Sec and rolled. Next, it is formed into a ring shape using a laying cone and rolled out on a conveyor.
It was moved onto the conveyor at a speed of 0.4 m/Sec. At this time, from the bottom and both sides of the conveyor,
The length of the conveyor, which was cooled by blowing air with a cooling capacity of 10° C. or more (approximately 10° C./sec), was 40 m, and the cooling time was 100 seconds. Next, it was formed into a coil shape using a convergence device and slowly cooled. The tensile properties of the wire thus obtained are shown in Table 2. Also, although the steel composition is the same, the forced cooling temperature has been changed.
The tensile properties of a wire rod according to a comparative example where the temperature was 850°C and the cooling rate was 4°C/sec are also shown.

【table】

[Table] As is clear from the above, according to the method of the present invention,
It has high tensile strength enough to be used in PC steel bars, etc.
It has also been found that a wire rod with small variations and excellent ductility can be obtained. (Furthermore, even if the steel composition is the same, changing the manufacturing conditions will result in a wire with low strength and large variations. However, as the yield point is extremely low, it is subsequently made into a coil in a converging device and gradually reduced. The cooled wire rods were warm-straightened. Five steel types, A, D, F, G, J, and I, shown in Table 1 were used as test materials, and those with a forced cooling temperature of 550°C in Table 2 were warm-straightened. The straightening temperature was
Heating was carried out at 200, 300 and 500°C using a resistance heating method. After the above-mentioned heating, straightening is performed by horizontally and vertically arranging a total of nine idle roll groups arranged in a staggered manner, and rolling down the rolls so that the wire bends within 2 mm/1.5 m. It was adjusted. The feeding speed of the wire rod was 5 m/min. Table 3 shows mechanical properties such as yield point and room temperature relaxation value of the wire thus obtained. For comparison, a comparative example using a simple low-temperature annealing method without warm straightening is also shown. Furthermore, the relaxation value applies a load of 80% of the yield load,
This is the value after 10 hours.

【table】

[Table] As is clear from Table 3, by performing warm straightening at 100 to 450℃, the yield point and relaxation value required for PC steel bars are fully satisfied, and the straightness is also good. A wire rod is obtained. Furthermore, as is clear from the above table, according to the method of the present invention, a wire rod with sufficient high tensile strength even when used as a PC steel bar, with small variations, and with excellent ductility can be obtained. becomes clear. Furthermore, even if the steel composition is the same, changing the manufacturing conditions will result in a wire rod with low strength and large variations. As described above, according to the present invention, steel of a specific composition is rolled and cooled under specific conditions, and further warm straightening is performed, so a high-strength wire rod can be obtained without quenching. It is possible to do so, and its value is extremely high.

Claims (1)

[Claims] 1 C: 0.10-0.40%, Si: 0.05-1.50%, Mn:
0.70~2.50%, Cr: 0.10~1.50%, Mo: 0.05~
After hot rolling, steel with a composition of 0.50%, the balance being Fe and unavoidable impurities is immediately forcedly cooled to 500 to 700℃ and rolled out in a continuous ring shape on a conveyor in the state of supercooled austenite. The wire is cooled by blast air at a cooling rate of 7°C/sec or more to form a martensitic structure in the entire wire on a conveyor, and then coiled in a converging device and slowly cooled to self-temper, increasing its toughness. Obtain a high-strength high-tensile steel wire rod with a tensile strength of 110 Kg/mm ² or more,
Next, the wire bends 4 times in the temperature range of 100 to 450℃.
1. A method for producing a high-tensile steel wire, which is characterized by performing warm straightening to within mm/1.5 m to obtain a high-tensile steel wire having a high yield point and excellent relaxation resistance.