JP2000297323A - Manufacture of high toughness steel wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a high toughness steel wire, in which the micro-segregation formed in a casting stage is reduced and a steel wire improved in twisting characteristic is obtained. SOLUTION: The method of manufacturing a high carbon steel wire includes a step of hot-rolling a steel wire bar to wire rod and a step of patenting this wire rod. In the course between the hot rolling step and the patenting step, soaking is performed in inert gas at 1150-1300 deg.C for 5-120 min. The micro- segregation of a solute can be sharply decreased by the application of soaking to the wire rod after rolling, and pearlitic transformation at patenting can be uniformized to a greater extent. As a result, twisting characteristic after wire drawing can be greatly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a high toughness steel wire. In particular, PC stranded wire used for prestressed concrete, piano wire, steel core aluminum stranded wire (ACS
The present invention relates to a method for producing a high toughness steel wire most suitable for a high carbon steel hardened steel wire such as R).

[0002]

2. Description of the Related Art There are the following conventional techniques for improving toughness such as twisting characteristics of steel wires.

[0003] Japanese Patent Publication No. 4-60725: Torsional characteristics are improved by applying ultrasonic vibration to a wire drawing die and making each step area reduction ratio 5-15%.

Japanese Patent Application Laid-Open No. 7-1028: Twist characteristics are improved by adjusting the residual stress on the surface side of the wire to the compression side using a double die.

[0005] Japanese Patent No. 25553612: After drawing, the bluing temperature T and the bluing time t of 430 ° C. or more are set to T (20 + lo).
gt) By setting ≧ 12700, a high toughness galvanized steel wire having excellent twisting characteristics is obtained.

JP-A-9-87803: The amount of dissolved nitrogen is 10 ppm
By performing the following, a hot-dip galvanized steel wire having high twist characteristics while suppressing strain aging during wire drawing is obtained.

JP-A-8-120407: Fine pearlite,
In a steel wire mainly containing at least one of pseudo pearlite and bainite, a high toughness steel wire free from longitudinal cracks (delamination) is obtained by controlling the carbide particle size to 10 to 50 nm.

[0008] Japanese Patent No. 2557544: By holding the slab for 3 hours to 18 hours in a temperature range of 1250 ° C to 1300 ° C,
Reduces segregation and wire drawing workability.

[0009]

However, the above technique has the following problems. Excessive bluing (the more the twisting characteristics are improved), the lower the strength. Excessive bluing breaks down the cementite in the pearlite lamellar formed as a fibrous structure by drawing, thereby improving the torsional properties but losing the strength required for the product.

[0010] In ordinary bluing, strain aging occurs and the toughness is extremely reduced. When bluing is performed to the extent conventionally performed, the material hardens due to strain aging,
The crack susceptibility increases and a vertical crack occurs.

[0011] The improvement of the torsion characteristics by wire drawing and repeated bending does not become effective as the wire diameter increases. In the case of a large diameter, delamination is more likely to occur than in the case of a small diameter, and susceptibility to vertical cracking is high at the same working ratio. for that reason,
A method used as a method for enhancing toughness with a small diameter is often not applicable to a product with a large diameter. For example, even if the residual stress is changed by ultrasonic vibration or double dies during wire drawing, it is difficult to suppress the delamination observed during the torsion test.

Even if the amount of solute N is limited, there is a limit to the suppression of strain aging during bluing. Even if the free nitrogen is reduced to 10 ppm or less, N of 10 ppm is enough for the strain aging that occurs at the initial stage of bluing, and the twisting characteristics can be improved by controlling the amount of nitrogen. Is practically impossible.

[0013] Even if the slab is soaked (homogeneously annealed), the twisting characteristics after drawing cannot be drastically improved. The center segregation at the "center" of the wire is hardly a problem in the torsion test in which a large surface plastic working is applied. Therefore, it is difficult to improve the twisting characteristics even if the center segregation is reduced by soaking the slab.

Accordingly, it is a primary object of the present invention to provide a method for producing a high toughness steel wire capable of reducing the micro-segregation formed at the casting stage and obtaining a steel wire having improved torsion characteristics.

[0015]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and a feature of the present invention is a method for producing a high-carbon steel wire including a step of hot-rolling a steel material into a wire. 1150 ° C ~ 13 in inert gas at the stage of wire rod after cold rolling
To perform soaking (homogeneous annealing) at 00 ° C for 5 to 120 minutes. This soaking is performed between the rolling step and the patenting step.

[0016] The steel material used here is expressed as C:
The one containing 0.60 to 1.1%, Si: 0.15 to 0.8%, and Mn: 0.3 to 2.0% is preferable. Also, as the inert gas, purity 99.999
% Or more and less than 99.99999% N ₂ gas is suitable.

Hereinafter, the reasons for limiting the configuration in the present invention will be described. C: Carbon is the element that has the greatest effect on controlling the strength of the steel wire, but if the C content is less than 0.6%, the strength after wire drawing is also low, so the occurrence of delamination is very problematic. Does not. Therefore, at a C concentration of 0.6% or more, the effect of suppressing delamination is significant. On the other hand, if the content of C exceeds 1.1%, the strength is at a sufficiently high level, but the decarburization during soaking becomes extremely large, which is not preferable.

Si: Si is one of the deoxidizing elements, and it is better to contain 0.15% or more in consideration of increasing the strength of the steel wire. On the other hand, if it exceeds 0.8%, decarburization during soaking is remarkably promoted like C, so that 0.8% or less is desirable.

Mn: Mn is an element necessary for increasing strength and toughness, and it is better to contain 0.3% or more. But 2.0
%, Hardenability at the time of patenting is enhanced and micro martensite is generated inside the wire.

Soaking temperature: soaking is mainly C, S
This is to promote the diffusion of i, Mn, P, and S.
If the temperature is lower than 150 ° C, it is difficult to measure the homogeneity within the operable time. On the other hand, if the temperature exceeds 1300 ° C., the uniform effect of the solute saturates, and conversely, only decarburization proceeds.

Soaking time: Like the soaking temperature, the soaking time is less than 5 minutes, it is difficult to make the solute uniform at a temperature that can be considered in actual operation, and if it exceeds 120 minutes, the result is that only decarburization proceeds. Invite.

Soaking atmosphere: Basically, soaking must be performed in an inert gas. Preferably, the purity of N ₂ is 99.999% or more and less than 99.99999%. 99.999%
If it is less than 10, the effect on decarburization cannot be ignored, while 9
If it is 9.99999% or more, the cost for gas supply becomes large.

[0023]

Embodiments of the present invention will be described below. Production of evaluation material C: 0.82% by weight, Si: 0.23%, Mn: 0.7%, the remainder is molten steel consisting of Fe and unavoidable impurities is cast into slabs by continuous casting. Soaking (retention time was 2 hours, one material only 12 hours). Thereafter, a wire rod of φ11.5 mm was manufactured by hot rolling.

A part of the material having a diameter of 11.5 mm was soaked. Soaking conditions, temperature 1150 ~
1200 ° C. and the holding time was 1-2 hours. As decarburization does not occur due to oxidation during the soaking, soaking is carried out in a non-oxidizing atmosphere (99.999% N ₂ gas), as a result, decarburization depth did not exceed 60 [mu] m.

The rods both soaked and not soaked with the wire were patented using a lead furnace. The patenting conditions were such that the gamma-formation temperature was changed from 800 ° C to 1000 ° C, and the gamma-formation holding time was 15 minutes. The lead bath temperature was changed from 460 ° C. to 620 ° C. and immersed in a lead furnace until the pearlite transformation was completed. By performing patenting, fine pearlite or partially bainite transformation was performed at some temperatures.

After pickling and film-forming these wires,
Wire drawing was performed from φ11.5mm to φ4.22mm using a continuous wire drawing machine. Further, a part of the drawn material was subjected to a bluing treatment at 380 ° C. × 3 minutes.

Twisting characteristics A tensile test and a twisting test were performed on a drawn wire material not subjected to the bluing treatment and a drawn wire material subjected to the bluing treatment.

Table 1 shows the results of these mechanical properties of the drawn wire before bluing together with the conditions of soaking and patenting, and Table 2 shows the same contents of the drawn wire after bluing.

[0029]

[Table 1]

[0030]

[Table 2]

As can be seen from both tables, the torsion characteristics before blueing are good except for No. 5. However, after bluing, all the materials that were not soaked at the wire stage had reduced torsion values and fractured with delamination (longitudinal cracks). In particular, it should be noted that even with the material (No. 7) in which the soaking in bloom was extended up to 12 hours, no noticeable improvement in the twisting characteristics was observed, and the fracture shape was a vertical crack. On the other hand, the material subjected to soaking treatment before patenting exhibited high torsion characteristics with or without bluing, and the fracture shape was normal shearing.

Structure Observation In the above test, the structure after patenting was subjected to SEM for the purpose of comparing a structure having a low torsion value and breaking with delamination with a structure having a high torsion value and breaking normally. (Scanning Electron Microscope). The points observed were the lamellar structure of the pearlite structure, the lamellar spacing (cementite / ferrite spacing) and the form of cementite in the barite. Observations revealed that the lamellar spacing between the pearlite colonies was uniform in the material showing high twist characteristics, whereas the lamellar spacing was uneven in the low twist characteristics material. .

It has also been found that so-called "pseudo pearlite", in which cementite in pearlite is fragmented, is increased in low twisting materials compared to high twisting materials.

It is considered that the uniformity of the pearlite structure is determined by the degree of microsegregation of solutes (C, Si, Mn, P and S as impurities) in the wire before patenting and the patenting conditions. That is, it is considered that the microsegregation of the solute was drastically reduced by soaking with the wire, and the pearlite transformation at the time of patenting was made more uniform. Although soaking of cast slabs can basically reduce segregation, the biggest aim is to reduce central segregation such as C segregating in the center. The center segregation at the "center" of the wire is hardly a problem in the torsion test in which a large plastic working of the surface is applied. Therefore, the soaking at the slab stage is insufficient from the viewpoint of the torsion characteristics. Soaking with the wire can promote solute uniformization throughout the wire.

[0035]

As described above, according to the method of the present invention, a substantially uniform solute distribution can be obtained, and a uniform pearlite structure can be obtained during patenting.

The soaking of the slab before rolling to make the casting structure uniform has been performed so far. However, there are disadvantages such as decarburization, so that micro segregation is further reduced. It has not been actively pursued for the purpose. Further, conventional soaking performed in the billet stage is not sufficient in terms of making the solute distribution uniform.

In the method of the present invention, by performing soaking on the wire after rolling, not only can the processing be completed in a short time, but also the uniformity can reach an unprecedented level. As a result, a more uniform pearlite structure can be obtained at the time of patenting, whereby the twisting characteristics after drawing can be dramatically improved.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C22C 38/00 301 C22C 38/00 301Y 38/04 38/04 F term (reference) 4E096 EA02 EA12 GA03 HA21 4K032 AA06 AA07 AA16 AA31 BA02 CF03 CH06 4K043 AA02 AB05 AB06 AB15 AB27 BB04 BB05 EA04 FA03 FA07 FA09 FA12 FA13

Claims (3)

[Claims] Claims 1. A step of hot rolling a steel material into a wire,
And a step of patenting the wire rod, wherein the hot rolling step and the patenting step are performed at a temperature of 1150 ° C. to 1300 ° C. and 5 to 120 ° C. in an inert gas between the hot rolling step and the patenting step. A method for producing a high toughness steel wire, characterized by performing soaking for minutes. 2. The steel material is, by weight%, C: 0.60 to 1.1%, Si:
2. The method for producing a high-carbon steel wire according to claim 1, comprising 0.15 to 0.8% and Mn: 0.3 to 2.0%. 3. The inert gas has a purity of 99.999% or more and 99.99999.
The process according to claim 1 high toughness steel wire, wherein a is N ₂ gas of less than%.