JP2001032042A - Steel wire rod excellent in scale peelability at the time of mechanical descaling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel wire rod in which the subsequent wire drawability is made better by making better the scale peelability therein at the time of mechanical descaling, and the productivity can be increased. SOLUTION: This steel wire rod is subjected to mechanical descaling after hot working and is thereafter subjected to wire drawing and has a compsn. contg., by mass, 0.03 to 0.2% C, <=0.5% (not including 0%) Si, 0.05 to 1.5% Mn, <=0.1% (not including 0%) Al, <=0.2% (not including 0%) Cu and <=0.6% (not including 0%) Cr and also satisfying the inequality of 1.0<=([Cr]+[Si])/[Cu])<=10.0, where [Cr], [Si] and [Cu] respectively denote the contents (mass %) of Cr, Si and Cu.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel wire for cold forging and a hot-rolled steel wire for ordinary wire, and for example, a synthetic wire used as a material for a rhombus wire mesh for outer shelves or a simple hanger. The present invention relates to a resin-coated steel wire, a colored steel wire, a mild steel wire used as a material for nails, and the like, and more particularly to a steel wire excellent in scale releasability during mechanical descaling.

[0002]

2. Description of the Related Art For example, a coated steel wire for a simple hanger whose surface is coated with a synthetic resin such as a vinyl chloride resin is usually manufactured by the following method. That is, a steel wire having a predetermined chemical composition is hot-rolled, adjusted and cooled, and has a diameter of 5 to 5.
After about 6.5 mm, the wire is further drawn to a predetermined wire diameter, and then coated (heated at a low temperature) with a synthetic resin such as a vinyl chloride resin to obtain a coated steel wire. And, in such a steel wire, mechanical descaling is generally performed in the middle of the process,
In order to perform the subsequent wire drawing efficiently, it is required that the scale peelability at the time of mechanical descale is good.

[0003] However, the conventional steel wire material does not always have good scale peelability at the time of mechanical descaling, and the scale remains thick after the mechanical descaling. In this case, the seizure of the die is caused. In other words, when the scale remains thick on the surface of the steel wire rod, the scale is bitten into the die, and the amount of the adhered scale increases to cause seizure on the die. The occurrence of such seizure greatly reduces the productivity of the steel wire.

[0004] Such a situation is not limited to a synthetic resin-coated steel wire or a colored painted steel wire used as a material for a simple hanger or the like, but also to a general cold forging such as a mild steel wire used as a material for a nail or the like. The same applies to hot-rolled steel wire for general wire and ordinary wire.In short, in steel wire that is subjected to wire drawing after mechanical descaling, the above-mentioned seizure during wire drawing frequently occurs. are doing.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made under such a circumstance, and an object of the present invention is to improve the scale releasability at the time of mechanical descaling to improve the subsequent drawing workability. Another object of the present invention is to provide a steel wire rod capable of improving productivity.

[0006]

The steel wire of the present invention, which has achieved the above object, is a steel wire which is subjected to mechanical descaling after hot working and then to further drawing. C: 0.03 to 0.2% (meaning by mass%, the same applies hereinafter), Si: 0.5% or less (excluding 0%), M
n: 0.05 to 1.5%, Al: 0.1% or less (including 0%), Cu: 0.2% or less (excluding 0%), and Cr: 0.6 or less (0% (Not included), and has a gist in satisfying the following expression (1). 1.0 ≦ ([Cr] + [Si]) / [Cu]) ≦ 10.0 (1) where [Cr], [Si] and [Cu] are C, respectively.
Shows the contents (% by mass) of r, Si and Cu.

The steel wire of the present invention may further contain (1) B: 0.0003 to 0.008% and (2) N: 0.001 to 0.01% as other components. It is effective, and thereby, it is possible to suppress the strength variation due to the strain aging.

In order to further exert the effect of the steel wire of the present invention, (a) the total amount of scale generated by hot working is 0.20 to 0.60% based on the weight of the wire. And (b) the requirement that the center line average roughness (Ra) of the surface of the mechanically scaled steel wire rod subjected to 4% strain after hot working is 0.55 μm or less. preferable.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have studied from various angles to achieve the above object. As a result, it has been found that the above object can be achieved satisfactorily if the composition of the chemical components is properly adjusted, and the present invention has been completed. The reasons for limiting the range of the chemical composition specified in the present invention are as follows.

C: 0.03% to 0.2% C is an effective and economical element for increasing the strength of a wire rod. However, as the C content increases, the amount of work hardening during drawing and the amount of drawing are increased. The strength due to later strain aging will increase. From such a viewpoint, the wire of the present invention preferably has low carbon. However, since a certain degree of strength is required, it is necessary to be 0.03% or more. However C
If the content is excessive, particularly in the case of mild steel wire, pearlite increases and embrittles, and the ductility becomes extremely poor. Therefore, the upper limit of the C content needs to be 0.2%. Note that C
A preferred lower limit of the content is 0.04%, and a preferred upper limit is 0.18%.

Si: 0.5% or less (excluding 0%) Si is an element that is effective not only for deoxidizing steel but also as a solid solution element of ferrite and effectively acts to improve the strength of a heat-treated material. However, when the Si content is excessive, the ferrite becomes brittle and causes ductility deterioration, and it becomes difficult to perform wire drawing after mechanical descaling. From such a viewpoint, the Si content needs to be 0.5% or less, and preferably 0.35% or less. In order to exhibit the above effects, it is preferable that Si is contained at least 0.001% or more.

Mn: 0.05 to 1.5% Mn is an element necessary as a deoxidizing agent like Si, and is used to improve the hardenability of steel and improve the uniformity of the structure of the steel wire rod. It is an element that works effectively. It is also useful as a solid solution element of ferrite for improving the strength of a heat-treated material, like Si. In order to exhibit such an effect, Mn must be contained at least 0.05% in the case of low carbon steel. However, when the content of Mn is excessive, a segregated portion of Mn is formed, and a supercooled structure such as martensite or bainite is generated to deteriorate wire drawing workability. Therefore, the upper limit is set to 1.5%. There is a need. still,
A preferred lower limit of the Mn content is 0.1%, and a preferred upper limit is 1.0%.

Al: 0.1% or less (including 0%) Al effectively acts as a deoxidizing agent and also has an effect of preventing coarsening of austenite particle size and improving wire drawing workability. Further, it also has an effect of binding with N in steel to suppress strain aging. However, if the Al content is excessive, the drawability is adversely affected by an increase in nonmetallic inclusions. Therefore, the Al content needs to be 0.1% or less, and preferably 0.05% or less. Note that a preferable lower limit when Al is contained is 0.001%.

Cu: 0.2% or less (excluding 0%) Cu is an element effective for improving the corrosion resistance, and the corrosion resistance improves as the Cu content increases. Further, by containing Cu, the wire drawing workability after mechanical descaling is also improved, which is effective in preventing troubles such as image sticking of the die. However, when the Cu content is excessive, even if the mounting temperature after hot working is relatively high, 900 ° C., blisters are generated on the surface of the wire, and magnetite is generated on the steel base material under the blisters. Therefore, die burn-in occurs at the initial stage of wire drawing. Cu reacts with S to form CuS, and this C
The uS segregates at the grain boundary and causes flaws in a steel ingot, a wire rod, or the like in the wire rod manufacturing process, and causes wire breakage during wire drawing, lowering productivity. From such a viewpoint, the Cu content needs to be 0.2% or less. In order to exhibit the above-mentioned effects of Cu, the content is preferably 0.005% or more, and a preferable upper limit is about 0.15%.

Cr: 0.6% or less (excluding 0%) Cr has the effect of increasing the work hardening rate in wire drawing, and by including an appropriate amount of Cr, the strength of the wire can be increased. However, when the Cr content is excessive, the hardenability of the steel is excessively increased, and the mechanical descaling property is deteriorated. In addition, in order to exhibit the above-mentioned effect by Cr, it is necessary to use 0.1.
005% or more is preferable, and a preferable upper limit is about 0.5%.

In the present invention, the object of the present invention cannot be achieved only by limiting the composition of the chemical components as described above, and Cr, Si and Cu must satisfy the relationship of the above formula (1). Need to adjust. The reason for defining the above equation (1) is as follows.

As described above, Cr is an element that is indispensable for increasing the strength. However, if it is too much, the mechanical descaling property deteriorates. Further, Cu has an effect of improving the mechanical descaling property. However, if too much, blisters are generated on the scale and the mechanical descaling property is rather deteriorated. Further, as described above, it has been confirmed that an excessive amount of Si deteriorates the mechanical descaling property.

Therefore, the inventors of the present invention have to improve the mechanical strength by simultaneously improving the mechanical descaling property.
We considered that it would be important to suppress the total content of r, Cu and Si, and further studied. As a result, 1.0 ≦ ([Cr] + [Si]) / [C
u]) ≦ 10.0 [Formula (1)] By satisfying the relationship, the present inventors have found that a high-strength steel wire can be obtained without deteriorating the mechanical descaling property.
In the above formula (1), if the lower limit is less than 1.0, the formation of blisters cannot be suppressed, resulting in poor drawability. If the lower limit is more than 10.0, the surface of the wire after mechanical descaling will not be formed. The presence of a large amount of residual scale makes the drawing process very difficult.

The basic chemical composition of the steel wire of the present invention is as described above, and the balance is composed of Fe and unavoidable impurities.
It is also effective to contain the steel wire of the present invention in an amount of 03 to 0.008% or N: 0.001 to 0.01%, whereby the properties of the steel wire of the present invention can be further improved. The reasons for limiting the range of these elements are as follows. In addition, besides these components, the steel wire of the present invention may also contain trace components in a range that does not impair the properties thereof, and such a steel wire is also included in the technical scope of the present invention.

B: 0.0003% to 0.008% B combines with N in the steel to fix N that causes strain aging, and exerts an action of suppressing variations in the properties of the wire.
In order to exhibit such an effect, it is preferable to contain 0.0003% or more, but even if it is contained excessively, the effect is saturated and the economy is impaired, so the upper limit is made 0.008%. I do.

N: 0.001 to 0.01% N becomes a nitride such as Al and B in steel and effectively acts to prevent austenite coarsening during heating. In order to exhibit such effects, the N content is preferably set to 0.001% or more. However, when the N content is excessive, the amount of solid solution N increases, which promotes strain aging and causes variations in the characteristics of mild steel wires. Therefore, the upper limit is set to 0.01%.

In producing the steel wire of the present invention,
First, a wire rod having a diameter of about 5 to 6.5 mm is formed by hot rolling, and then the scale is removed by mechanical descaling. The roughness of the wire rod surface after hot rolling is important for the releasability of the scale. Requirements. That is, if the surface of the wire becomes rough, the amount of residual scale increases even when mechanical descaling is performed, and problems such as burning of the dies occur in the subsequent wire drawing.

However, it is difficult to directly measure the surface roughness of the wire after hot rolling, and this roughness does not change much before and after mechanical descaling. The surface roughness of the wire rod was specified. That is, in the steel wire rod of the present invention, the surface roughness of the mechanically descaled wire rod with a strain of 4% or more after hot rolling is 0.55 μm or less in center line average roughness (Ra). Then, it can be determined that the scale releasability at the time of mechanical descaling is good.

The center line average roughness (R
a) is the measured length L from the roughness curve in the direction of its center line.
, And the center line of the extracted part is the X axis,
When the direction of the vertical magnification is represented by the Y axis and the roughness curve is represented by y = f (X), the value obtained by the following equation (2) is represented by micrometers (μm).

[0025]

(Equation 1)

When scale is removed by pickling, it is sufficient that rust does not occur during transportation or the like, so it is not necessary to pay particular attention to the scale adhesion amount. However, if the residual scale on the surface of the steel wire after the scale removal by the mechanical descaler decreases, the subsequent wire drawing becomes relatively easy, but the yield decreases because the scale amount increases. Therefore, in the steel wire of the present invention, it is preferable that the total amount of scale generated by hot rolling is 0.60% or less based on the weight of the wire in consideration of the yield.

On the other hand, when the amount of scale adhesion on the surface of the rolled steel wire is reduced, the scale peeling effect due to mechanical descaling is reduced, and the amount of residual scale after mechanical descaling is rather increased. Troubles such as image sticking occur, and the wire drawing property is remarkably deteriorated. This limit scale amount is generally about 0.45%. However, in the case of the steel wire of the present invention having the above-mentioned composition, even when the scale amount is 0.20% with respect to the wire weight, a sound scale peeling state is achieved. Therefore, in the steel wire of the present invention, it is preferable that the total amount of scale generated by hot rolling is 0.20% or more based on the weight of the wire.

The above-described surface roughness of the wire and the amount of attached scale are problematic when the scale is removed by mechanical descaling, as described above. It is not an element. In the steel wire rod of the present invention,
It can be obtained by hot-rolling a steel wire satisfying the requirements of the chemical composition as described above, and then adjusting and cooling the steel wire, and is usually obtained as having a diameter in the range of about 5.0 to 6.4 mm. Is very excellent in the drawability after mechanical descaling.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples do not limit the present invention. It is within the technical scope of the invention.

[0030]

EXAMPLES Various steel materials having the chemical composition shown in Table 1 below were melted in a vacuum melting furnace, and the wire diameter was 5.5 m by hot rolling.
m of steel wire rods were produced. At this time, the mounting temperature at the time of rolling is changed in the range of 700 to 950 ° C., and 800 to 950 ° C.
The cooling rate of the wire rod to 500 ° C is 1 ° C / sec to 30 ° C.
C / sec.

[0031]

[Table 1]

Each of the obtained steel wires is mechanically descaled by mechanical descaling, and the center line average roughness (R) of the wire surface after the scale is peeled off.
a) and the amount of scale remaining on the surface of the steel wire rod were measured. Further, the steel wire rod was subjected to a wire drawing process up to a wire diameter of 2.2 mm, and when the drawing speed was gradually increased, the drawability was determined by finding a limit wire drawing speed at which seizure occurs on a die. evaluated.

At this time, the number of the drawing dies was set to 7, and the temperature of the wire was maintained at 120 ° C. or lower by cooling the wire at any die exit. The center line average roughness (Ra) of the surface of the steel wire is 4% for the hot rolled wire.
And after descaling by applying a tensile strain of. These results are collectively shown in Table 2 below.

[0034]

[Table 2]

From these results, the following can be considered.
First, the wire rod No. 1 to 4 are examples satisfying all of the requirements defined in the present invention.
By containing r and controlling the value of ([Cu] + [Si]) / Cu within the range of 1.0 to 10.0, the surface roughness is small, the scale releasability is improved, and burn-in is caused. It can be seen that the limit speed has increased accordingly.

On the other hand, the wire rod No. Nos. 5 to 13 lack any of the requirements specified in the present invention, so that good characteristics are not exhibited. First, the wire rod No. In the case of wire No. 5, the C content was too large, and the strength variation due to strain aging after drawing was large. In the case of No. 6, since the Si content was too large, the drawability was reduced, and breakage occurred during drawing. In addition, the wire rod No. In seven,
Since the Mn content was too large, a supercooled structure was formed and the wire was broken during drawing.

The wire rod No. 8 (([Cr] +
Although the value of [Si]) / [Cu] is in the range of 1.0 to 10.0, blisters are generated because the Cu content exceeds 0.2%. And because of this blister generation, the residual scale is not so much,
The limit seizure drawing speed is poor.

The wire No. In the case of No. 9, the wire rod surface roughness (Ra) was very poor at 0.75 μm or more due to the addition of Cr, but the amount of residual scale after mechanical descaling also increased accordingly, and the seizing limit speed was 300 m / m. min or less.

The wire No. In samples 10 and 11, the balance between the Cu content and the ([Cr] + [Si]) content was lost, and blisters were generated on the scale. As a result, sub-scales were generated, resulting in extreme drawability. It got worse.

The wire rod No. In the case of 12, 13, the surface roughness of the wire rod is very poor at 0.75 μm or more in Ra, and accordingly, the amount of residual scale after mechanical descaling increases, and the seizure limit speed becomes very low at 300 m / min or less. ing.

[0041]

The present invention is constituted as described above. By appropriately adjusting the chemical composition and improving the scale releasability at the time of mechanical descaling, the subsequent drawing workability is improved. A steel wire rod that can increase productivity was realized.

Claims (5)

[Claims] 1. A steel wire rod which is subjected to mechanical descaling after hot working and then further to wire drawing, wherein C: 0.03 to 0.2% (meaning by mass%, the same applies hereinafter). , Si: 0.5% or less (excluding 0%), Mn:
0.05-1.5%, Al: 0.1% or less (including 0%), Cu: 0.2% or less (excluding 0%) and C
r: a steel wire excellent in scale releasability at the time of mechanical descaling, which contains 0.6 or less (not including 0%) and satisfies the following expression (1). 1.0 ≦ ([Cr] + [Si]) / [Cu]) ≦ 10.0 (1) where [Cr], [Si] and [Cu] are C, respectively.
Shows the contents (% by mass) of r, Si and Cu. 2. B: 0.0003 as another component
The steel wire according to claim 1, wherein the steel wire contains about 0.008%. 3. The composition further comprises N: 0.001 to 0.001.
The steel wire according to claim 1, which contains 0.01%. 4. The total amount of scale generated during hot working is 0.20 to 0.60% based on the weight of the wire.
4. The steel wire according to any one of claims 1 to 3. 5. The center line average roughness (Ra) of a surface of a steel wire rod subjected to mechanical deformation by applying a strain of 4% or more after hot working is 0.55 μm or less.
The steel wire according to any one of the above.