JP3305555B2 - Carbon steel wire rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire capable of obtaining excellent strength and toughness even after strong working by drawing, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Many developments have been made on the rolling and rolling of carbon steel. Its main purpose is to increase strength and toughness after wire drawing and to reduce wire drawing and wire breakage. It is known as a conventional general technique to obtain a wire by the following steps. Finish rolling (around 900 ° C) → water cooling (several seconds) → winding (around 800 ° C) → pearlite transformation by introduction into boiling water, mist, blast, salt, etc. JP-B-63-57484, JP 62-142725
And Japanese Patent Application Laid-Open No. 6-10054. However, the wire obtained by the above method is not necessarily sufficient in strength and toughness. In addition, the wires obtained by the techniques of (1) to (4) achieve high strength or high toughness, but have a tensile strength of 2200 N / mm ² or more and an elongation of 3% or more (such as a wire subjected to off-line lead patenting). 4
(After baking at 00 ° C. × 7 seconds) has not been obtained.

[0003] Further, it is necessary for the purpose of improving productivity that a large workability can be obtained without performing intermediate patenting for a wire. However, even if wire drawing with a total area reduction rate of 94% or more is performed without intermediate patenting, a wire material that can secure an elongation of 3% or more (after bluing at 400 ° C. for 7 seconds) has not been obtained. Taking bead wire as an example, such characteristics can be achieved by processing from a 4 mm wire to 0.95 mm (total area reduction rate 94.4%) or 1.2 mm from a 5 mm wire.
There is a great advantage in terms of productivity and cost reduction, such as processing up to (total area reduction rate of 94.2%) without intermediate heat treatment. Accordingly, an object of the present invention is to provide a wire rod capable of performing strong working without performing off-line lead patenting and achieving both strength and toughness after working, and a method of manufacturing the same.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a feature that the wire diameter is 5.
A carbon steel wire rod of 5 mm or less, containing 0.6 to 0.85% by weight of C and 0.05 to 0.5% by weight of Cr, having a lamella spacing of 0.11 to 0.17 μm, 1-5
% By volume. The above-mentioned wire diameter is a value selected so as to be suitable for manufacturing a bead wire or the like, and the chemical composition is considered so as not to largely deviate from the conventional carbon steel composition. The distribution of the block size of the pearlite structure in such a wire is 30 μm.
Blocks with m or more are 60% or more in area ratio, blocks with 20 μm or more are 80% or more, and the abundance ratio of ferrite lumps with a size of 20 μm ² or more is less than 3 per 400 μm ² area. . Furthermore, in the range of 50 μm from the surface of the wire in the wire section, the number of ferrite masses in contact with one colony is 3 or less, and in the same range, the area ratio of colonies in contact with two or more ferrite masses is 30% or less. There is a feature. The lamellar spacing, ferrite lump content, distribution ratio of blocks of a specific size, ferrite lump abundance, and constitutional relationship between colonies and ferrite lump in the above-mentioned wire are all limited based on tests described later.

[0005] A method for obtaining such a wire rod is C: 0.6.
A method for producing a carbon steel wire rod in which a steel material containing 0.85% by weight and Cr: 0.05-0.5% by weight is hot-rolled to a target wire diameter and cooled to room temperature.
It is characterized in that the steel material is cooled to 900 ° C. in 3 seconds to 10 seconds, the steel material is transformed into pearlite in the cooling process, and further cooled to room temperature. Here, as concrete means for transforming the steel material to pearlite,
Introducing steel into blast, mist, boiling water, lead bath, salt, and the like. By such a treatment, γ grains are reduced to 2
It can be uniformized to 0 μm or more. Further, after the pearlite transformation, it is desirable to maintain the temperature at 50 to 200 ° C. for 3 minutes or more.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION

(Test Example 1) C: 0.7%, Si: 0.2%, Mn:
Conventional rolling was performed on carbon steel containing 0.5% and Cr: 0.04% under the following conditions. Finish rolling temperature: 1000 ° C → Cooling down to 900 ° C: 0.5 seconds by water cooling → Cooling after winding: Impulse Winding is performed on the wire after rolling at various degrees of work, A steel wire obtained by performing blueing at 400 ° C. for 7 seconds was subjected to a tensile test, and the relationship between the working ratio and the elongation was examined. The relationship is shown in the graph of FIG. In the true strain, Do represents the wire diameter before processing, and D represents the wire diameter after processing.
As shown, the elongation decreases as the degree of processing increases,
It can be seen that the required characteristic elongation of 3% is satisfied at the area reduction rate of 93%, but is not sufficient at the area reduction rate of 94% or more.

Test Example 2 Carbon steels having different Cr contents shown in Table 1 were finish-rolled at different temperatures in the range of 950 to 1050 ° C., and then allowed to cool for different times to obtain a rolled material of 4 mmφ.

[0008]

[Table 1]

This rolled material is cold drawn (0.94% area reduction) to 0.95 mmφ, introduced into boiling water and transformed into pearlite, and then subjected to blueing at 420 ° C. for 7 seconds to be stretched. The test was performed. In addition, sample E (Cr: 0.
21%) could not be drawn due to the presence of martensite at the center. The relationship between the cooling time and the elongation when the finish rolling temperature is 1000 ° C. is shown in the graph of FIG. As shown in the graph, it is possible to secure elongation of 3% or more when using a steel material having a Cr content of 0.05 to 0.15% by weight and cooling to 900 ° C. for 3 seconds to 10 seconds. Understand. If the time is less than 3 seconds, elongation of the obtained wire is insufficient.
In addition, a longer production line is required to hold the wire for more than 10 seconds, and the surface decarburized layer of the wire is increased. At other finish rolling temperatures, the content of Cr is also 0.
When the cooling time was 3 to 10 seconds, the elongation was 3% or more.

(Test Example 3) Next, a rolled material finished at 1000 ° C. was 900
After cooling to ℃, it was introduced into the air or a refrigerant to transform pearlite, and the relationship between elongation and tensile strength after wire drawing was examined. The wire used was a wire that had been drawn at 4 mmφ and then subjected to bluing at 420 ° C. for 7 seconds.
After drawing at 420 mm, bluing was performed at 420 ° C. for 7 to 10 seconds. The results are shown in the graph of FIG . In the figure, the solid line graph indicates a wire rod transformed with pearlite by boiling water, the broken line graph indicates a wire rod transformed with blast by blast, □ indicates a 5 mmφ wire rod, and Δ indicates a 4 mmφ wire rod. As shown in the drawing, it can be seen that the elongation of 3% or more is maintained even when the strong processing is performed up to a true strain of about 3.8. It was also confirmed that a tensile strength of 2200 N / mm ² or more was realized.

(Test Example 4) The amount of ferrite and the lamellar spacing of the wire obtained in Test Example 2 were measured, and the relationship between the amount of elongation after wire drawing was examined. The results are shown in the graph of FIG . As shown, there is a strong correlation between the amount of ferrite, the lamella spacing, and the elongation. That is, the lamella spacing is 0.11 to 0.18 μm
It can be seen that elongation of 3% or more was obtained when the amount of ferrite was 1 to 10% by volume. The tensile strength was also measured, and it was found that the steel material having a strength of 2200 N / mm ² or more had a lamella spacing of 0.11 to 0.17 μm and a ferrite content of 1 to 5% by volume.

(Test Example 5) Further, the structure of the cross section of the wire rod obtained in Test Example 2 was examined in detail by a micrograph. The chemical composition of the steel material used was Samples A to D of Test Example 2, and the manufacturing steps of the test material and the conventional material were as follows. Test example: Finish rolling temperature 950-1050 ° C → 900 ° C
Conventional example: Finish rolling temperature 1000 ° C → Cooling to 840 ° C by water cooling for about 0.5 seconds → Winding into boiling water In the micrograph showing the structure of the wire, (A) is a conventional material, and (B) is a test material using sample C in Table 1.
As shown, in the conventional example, many ferrites (black portions) are observed in the surface layer of the wire, particularly in a range of about 50 μm from the surface. On the other hand, in the test example, ferrite was little in the surface layer as well as in the inside of the wire, and it was found that most of the structure was occupied by pearlite (gray part).

(Test Example 6) These micrographs were further enlarged with a scanning electron microscope to examine the state of blocks and colonies. As shown in the schematic diagram of FIG. 6, blocks 1 have the same crystal orientation of ferrite, and colonies 2 have the same crystal orientation of cementite. FIG. 7 shows an enlarged photograph of the tissue. Also in this figure, (A) is a comparative example, and (B) is an example. As shown in the drawing, one colony is surrounded by many ferrite clumps (black portions) in the conventional material, whereas the number is three or less in the test material. Incidentally, these ferrite lumps are considered to be pro-eutectoid ferrite precipitated when cooled after rolling.

(Test Example 7) Next, the block size of the pearlite structure was measured, the ratio of blocks having a size of 30 μm or more and 20 μm or more per unit area was determined, and the relationship between this ratio and elongation was examined. FIG. 8 shows the result. As shown in the figure, blocks having a size of 30 μm or more have an area ratio of 60% or more, and blocks having a size of 20 μm or more have an area ratio of 80%.
It can be seen that the elongation is 3% or more in the above cases.
Furthermore, the number of ferrite masses in contact with one colony and the area ratio of colonies in contact with two or more ferrite masses were determined for each test material and the conventional material, and the relationship between these and the elongation was examined. FIG. 9 shows the result. If the number of ferrite masses in contact with one colony is 3 or less, and the area ratio of colonies in contact with two or more ferrite masses is 30% or less, 3
% Elongation is obtained.

Test Example 8 Next, the structure was photographed with a scanning electron microscope, and the number of ferrite blocks existing in an area of 400 μm ² was measured. Five visual fields were measured for one sample, and the relationship between the average number and the elongation of the sample after wire drawing was examined. As shown in FIG.
When the number is less than 3%, an elongation of 3% or more is obtained.

(Test Example 9) After the wire rod of Test Example 2 was transformed into pearlite, it was held at 30 to 300 ° C. for a different time,
After that, wire drawing (4.0 → 0.95mmφ) and 400
Blueing was performed at 7 ° C. × 7 seconds, and the relationship between holding time and elongation was examined. The result is shown in FIG. 50 ~
It was confirmed that elongation of 3% or more was obtained when the temperature was maintained at 200 ° C. for 3 minutes or more. Note that the same effect is obtained even if the holding is performed during the cooling from the rolling.

[0017]

As described above, both strength and toughness can be realized by the wire of the present invention. In particular, it is possible to maintain a strength of 2200 N / mm ² or more and an elongation of 3% or more even when performing a strong working with a reduction in area of 94% or more, which is suitable for manufacturing a bead wire or the like. Further, according to the manufacturing method of the present invention, the off-line lead patenting step before or at the stage of drawing can be omitted. If this step is performed, both the above strength and toughness can be achieved. However, this step requires complicated temperature control and the like, and increases the cost. In the method of the present invention, productivity can be improved and cost can be reduced by avoiding this step.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the workability and elongation of a conventional steel material.

FIG. 2 is a graph showing the relationship between the amount of Cr and the cooling time and elongation.

FIG. 3 is a graph showing the relationship between the amount of ferrite and lamella spacing and elongation.

FIG. 4 is a graph showing the relationship between the degree of work and the elongation and tensile strength of the wire of the present invention.

FIG. 5 is a micrograph showing the structure of a steel material, where (A) is a conventional material and (B) is a test material.

FIG. 6 is a schematic diagram of a pearlite structure.

7 is a micrograph of a steel structure in which the photograph of FIG. 5 is enlarged, (A) is a conventional material, and (B) is a test material.

FIG. 8 is a graph showing the relationship between the area ratio of blocks of a specific size and elongation.

FIG. 9 is a graph showing the relationship between the constitutive relationship between colonies and ferrite and elongation.

FIG. 10 is a graph showing the relationship between the number of ferrite lumps and elongation.

FIG. 11 is a graph showing the relationship between the time maintained at a predetermined temperature after pearlite transformation and elongation.

[Explanation of symbols]

 1 block 2 colonies

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tadaaki Matsuda 1-1-1, Kunyokita, Itami-shi, Hyogo Prefecture Itami Works, Sumitomo Electric Industries, Ltd. (56) References JP-A-62-14725 (JP, A) JP-A-53-2330 (JP, A) JP-A-6-322480 (JP, A) JP-A-57-89429 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 8/06-8/08 C21D 9/52

Claims (6)

(57) [Claims] 1. A wire diameter of 5.5 mm or less, C: 0.6 to 0.85% by weight, Cr: 0.05 to 0.5.
Weight%, lamella spacing 0.11-0.17 μm, ferrite lump 1-5 volume% , balance pearlite
A carbon steel wire rod having a texture . 2. A block size distribution of 30 μm
The above blocks have an area ratio of 60% or more, the blocks having a size of 20 μm or more have a content of 80% or more, and the abundance of ferrite lumps having a size of 20 μm ² or more is 400%.
^2. The carbon steel wire according to claim 1, wherein the number is three or less per μm ² area. 3. A wire having a cross section of 50 μm from the surface of the wire.
The number of ferrite masses in contact with one colony in the range of 3 or less, and the area ratio of colonies in contact with two or more ferrite masses in the same range is 30% or less. 3. The carbon steel wire according to 1 or 2 . 4. A steel material is hot-rolled to a target wire diameter, finish rolling is performed at 950 to 1050 ° C., and is cooled to 900 ° C. within 3 seconds to 10 seconds, and the steel is subjected to pearlite transformation in a cooling process. And room temperature
Characterized by being manufactured by cooling to
The carbon steel wire according to any one of claims 1 to 3. 5. C: 0.6 to 0.85% by weight, Cr:
A method for producing a carbon steel wire rod in which a steel material containing 0.05 to 0.5% by weight is hot-rolled to a target wire diameter and cooled to room temperature, wherein finish rolling is performed at 950 to 1050 ° C. for 3 seconds or more. A method for producing a carbon steel wire, comprising cooling to 900 ° C. within 10 seconds, transforming the steel into pearlite in a cooling process, and further cooling to room temperature. 6. After transformation to pearlite, 50-200.
The method for producing a carbon steel wire according to claim 5 , wherein the carbon steel wire is held at a temperature of at least 3 minutes.