JP2986809B2 - Method for manufacturing hard steel wire rod with good wire drawing workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is advantageous for the production of a hard steel wire having excellent drawability even under severe processing conditions such as high-speed wire drawing and ultrafine wire drawing. The method is particularly suitable for application to the production of high carbon steel wires used as ultrafine wires such as tire cords and hose wires.

(Conventional technology) Conventionally, steel cords and the like used as rubber reinforcing wires are repeatedly subjected to cold drawing and patenting processes to give a workability of approximately 95% or more to form ultra-fine wires of 0.4 mmφ or less. In general, it is generally manufactured by processing and adjusting the microstructure and strength in final patenting to secure desired strength and ductility, and then twisting several of them.

By the way, recently, quality requirements for materials have become increasingly strict in various fields, and in the field of automobile tires, further strengthening of strands has been aimed at from the viewpoint of weight reduction. In particular, it is strongly required that the number of disconnections during wire drawing and twisting be small.

The main cause of disconnection occurring during the processing of these ultrafine wires is the presence of nonmetallic inclusions in the steel. In particular, it is known that the presence of hard, poorly plastic, simple oxide inclusions such as Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ , and MgO increases notch sensitivity and causes disconnection. Have been.

Therefore, in order to produce a wire with excellent drawability,
It is important to reduce the number of inclusions and to soften the inclusions unavoidably remaining by lowering the melting point.

In view of the above circumstances, as a method to reduce the softening inclusions by increasing the detergency, in JP-B-57-22969, Al ₂
A method for controlling the composition of ternary oxide inclusions of O ₃ —SiO ₂ —MnO has been proposed.

However, in the case of the above-mentioned ternary system, it is extremely difficult to stably control the composition, and it is not possible to control the form of inclusions only by controlling the composition.

(Problems to be Solved by the Invention) The present invention advantageously solves the above-mentioned problems, and controls the form of non-metallic inclusions so as to soften the inclusions and to devise a rolling process. It is an object of the present invention to propose an advantageous method of manufacturing a hard steel wire rod that can further improve the wire drawing workability.

(Means for Solving the Problems) The inventors of the present invention, after many years of research on the above-mentioned problems, controlled the composition of the oxide-based inclusions to a specific range to lower the melting point and soften the inclusions. It has been found that wire drawing workability can be further improved by combining with appropriate rolling conditions.

 Hereinafter, the details of the clarification will be described.

First, when investigating the causes of disconnection during steel cord production, the causes were mostly 10 μm
It was found that the inclusions described above were composed of Al ₂ O ₃ alone.

Table 1 shows the size of inclusions on the broken surface when a hard steel wire equivalent to SWRH 72A was machined to 0.175 mmφ, and classified and shown. The size of the harmful inclusions that cause them is almost 10 μm or more.

Therefore, the size of inclusions in hot-rolled
The method of controlling the value to m or less was studied.

First, the inclusion composition suitable for softening by lowering the melting point was examined, and it was found that the SiO ₂ —Al ₂ O ₃ —MnO—CaO 4 system was advantageous.

Next, paying attention to the SiO ₂ —Al ₂ O ₃ —MnO—CaO-based inclusions, the rolling temperature was variously changed, and the thickness change was examined at the same rolling reduction assuming slab rolling.

 The results are shown in FIG.

As is clear from the figure, it has been found that even with the same composition, the thickness can be reduced as the temperature becomes higher, and particularly at 1100 ° C. or more, the thickness can be reduced to 10 μm or less.

Of course, it was also confirmed at the same time that as the content of Al ₂ O ₃ or SiO ₂ increased, the decrease in thickness decreased.

Therefore, it has been found that controlling the processing temperature in the subsequent rolling is even more important for improving the stretchability, even with the inclusions softened at a low melting point.

 The present invention is based on the above findings.

That is, the present invention provides a method for producing a molten steel for hard steel wire containing C: 0.5 to 0.9 wt% (hereinafter referred to as “%”) by adding a CaO—SiO ₂ synthetic flux to non-metallic inclusions in the steel. Is adjusted to a composite oxide having a composition of SiO ₂ : 30-50%, MnO: 10-30%, Al ₂ O ₃ : 5-30% and CaO: 5-20%, then cast,
Then, the obtained slab is hot-rolled at a finishing temperature of 1100 ° C. or more to reduce the thickness of the composite oxide to 10 μm or less, and then continuously rolled, rapidly cooled, and wound at a temperature of 800 ° C. or more. After taking, it is cooled at a rate of 5 to 30 ° C./s to form a hard and fine pearlite structure having a uniform fineness over the entire length of the wire.

(Operation) In the present invention, the reason why the content of C in the components of the hard steel wire, particularly C is limited to the above range, is as follows.

That is, C is an indispensable component for obtaining the strength as a hard steel wire, and at least 0.5% is required for use as a wire rope or a steel cord.
However, if it is added in an excessively large amount, the drawability is significantly impaired by the pro-eutectoid cementite generated in the segregated portion, so the upper limit was set to 0.9%.

In addition, in addition to the above-mentioned C, depending on the application and the required strength, 0.
8% or less Mn, 0.4% or less Cr, 0.15% or less V, 0.50%
It goes without saying that the addition of the following alloy elements such as Ni and the reduction of the P and S contents in order to increase the cleanliness can be performed without any problem.

Next, the reason for limiting the composition of the SiO ₂ —Al ₂ O ₃ —MnO—CaO-based inclusion will be described.

SiO ₂ : 30 to 50% When the content of SiO ₂ exceeds 50%, the inclusions become hard and the stretchability deteriorates. On the other hand, when the content is less than 30%, a composite inclusion composition having plasticity cannot be obtained. %.

MnO: 10 to 35% MnO is limited to the range of 10 to 35% because inclusions are hardened at less than 10% or more than 35%.

Al ₂ O ₃ : 5 to 30% Al ₂ O ₃ needs at least 5% in order to maintain the composition balance as a composite inclusion, while if it exceeds 30%, it does not stretch even at a high temperature rolling of 1100 ° C. or more Since it becomes a hard inclusion, it was limited to the range of 5 to 30%.

CaO: 5 to 20% CaO generally becomes a spherical inclusion and hardly deforms when its content is large, but it is a composite system and in the range of 5 to 20%, it has a low melting point composition and becomes easy to stretch. Therefore, it was limited to the above range.

The composition of the nonmetallic inclusions can be adjusted by adding a CaO—SiO ₂ -based synthetic flux (for example, JP-A-60-56011).

Now, as described above, for the composite inclusions controlled to have a low melting point and a softening composition, it is a feature of the present invention to further increase the degree of elongation by controlling the rolling temperature, thereby achieving further detoxification. The slab rolling finish temperature is set to 1100 ° C. or higher where the effect of reducing the inclusion cross section is large in the above composition range. There is no particular need to set an upper limit here, but if it is too high, decarburization will be remarkable.

Subsequently, wire rod rolling is performed, and after finishing rolling, water cooling is performed to adjust the winding temperature. At this time, in order to uniformly generate fine pearlite and obtain a secondary scale having an appropriate thickness,
It is important that the winding temperature be at least 800 ° C. The range of 800 to 950 ° C. is particularly preferable in consideration of both.

Furthermore, in the subsequent cooling process, in order to impart fine pearlite having good wire drawing workability to the entire length, 5 to 30 ° C.
It is important to cool at a rate of / s. This is because if the cooling rate is less than 5 ° C / s, the pearlite structure becomes coarse and impairs the workability, whereas if the cooling rate exceeds 30 ° C / s, the workability also deteriorates due to the formation of micro-martensite. It is.

(Example) Using a 300 kg high frequency melting furnace, under an Ar atmosphere, SWR
After performing component adjustment to H 72A corresponding chemical components was adjusted composition of inclusions by the addition of CaO-SiO ₂ based synthetic flux of various compositions. Then, after casting, it was forged into a 150 mm square, and then rolled into a 5.5 mmφ wire in a conventional manner.

Table 2 also shows the results obtained by examining the inclusions at both ends of the wire thus obtained.

As is clear from the table, those having an inclusion composition satisfying the present invention have a lower penalty point than those of the comparative examples and have excellent workability.

However, in the above experiment, since the treatment was performed at normal heating and rolling temperatures, their effects are unknown.

Then, SWRH 72A equivalent material shown in Table 3 was melted in a converter, and CaO-SiO ₂ synthetic slag was added at the time of tapping, and the inclusion composition was adjusted to a range satisfying the present invention. The cast slab was rolled into a 150 mm square at two levels of finish rolling temperature of 1160 ° C. and 1020 ° C.

About the square billet thus obtained, the surface layer, 1/4
From each part of the part and the central part, a longitudinal section observation sample (25
mm square) were collected from a total of nine locations at both ends and the center in the longitudinal direction, and those having a size of 10 μm or more were observed.

 Table 4 shows the results.

As shown in the table, 10μm for 1160 ° C finished rolled material
Although there were no such inclusions, the 1020 ° C. finish rolled material as a comparative example had inclusions of 10 μm or more.

Then, these slabs were rolled under normal heating and rolling conditions to obtain a 5.5 mmφ wire, and then rapidly cooled, and both were cooled to 850 ° C.
And cooled at three levels of 3 ° C./s, 15 ° C./s and 35 ° C./s.

Table 5 shows the results of an investigation on the mechanical properties of the 5.5 mmφ wire thus obtained and the maximum thickness of the composite inclusion (per 275 mm ² ).

First, the effect of the billet rolling finishing temperature on the maximum inclusion thickness was clearly recognized. According to the method of the present invention, the thickness of the inclusions could be reduced to about 1/2 or less of the conventional method. The effect of the cooling rate was observed in the mechanical properties, and when cooled at 15 ° C / s which satisfied the present invention, good values were obtained for both strength, elongation and drawing, whereas when cooled at 3 ° C / s In the case of, the strength and drawing were extremely reduced, while at 35 ° C./s, although the strength was improved, the elongation and drawing were significantly reduced due to the formation of micro-martensite at the center of the cross section.

The above difference is attributable to the difference in the pearlite structure, and it is expected that the drawability of E2, E3, E5 and E6 obtained by the comparative method is all reduced.

Then, next, with respect to E1 of the present invention method and E4 of the comparative method, the wire drawing workability when processing into an ultrafine wire was examined.

That is, the wire drawing and the patenting process were repeated from 5.5 mmφ, the wire diameter at the time of final patenting was made uniform, and the lead patenting conditions were the same. The wire diameter during patenting was 1.25 mmφ, and the heating temperature was 950 mm.
° C and the lead bath temperature were 570 ° C. The wire drawing workability was evaluated by the frequency of occurrence of disconnection during processing.

 Table 6 shows the obtained results.

As is clear from the table, according to the present invention method, 0.14
Although no break occurred even when the wire was drawn to a fine wire of 5 mmφ, the disconnection was not recognized up to 0.20 mmφ by the comparative method, but the break was often recognized in the ultrafine wire of 0.180 mmφ or later. Was done.

Further, it was confirmed that, even when twisting was performed, the one obtained according to the method of the present invention was superior.

(Effects of the Invention) Thus, according to the present invention, the wire drawing workability of a hard steel wire can be greatly improved, and it also contributes effectively to the reduction of disconnection susceptibility due to high strength. It greatly contributes to improving the durability of steel cords and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the rolling temperature on the maximum thickness of the composite inclusion after rolling.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-142725 (JP, A) JP-A-63-192846 (JP, A) JP-A-52-70925 (JP, A) JP-A 61-142846 143511 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C21D 8/06 C21D 9/52 C21C 7/076 B22D 11/10

Claims (1)

(57) [Claims] 1. A C: Upon melting of the hard steel wire molten steel containing 0.5~0.9wt%, the addition of CaO-SiO ₂ based synthetic flux, SiO ₂ nonmetallic inclusions in steel: 30 to 50 wt %, MnO: 10~35wt%, Al 2 O 3: 5~30wt% and CaO: After adjusting the oxide of the composite system to be 5 to 20 wt% of the composition, and cast,
Then, the obtained slab is hot-rolled at a finishing temperature of 1100 ° C. or more to reduce the thickness of the composite oxide to 10 μm or less, and then continuously rolled, rapidly cooled, and wound at a temperature of 800 ° C. or more. A method for producing a hard steel wire having good drawability, characterized in that after taking, it is cooled at a rate of 5 to 30 ° C./s to have a uniform fine pearlite structure over the entire length of the wire.