JPH05117763A - Manufacture of carbon steel wire rod for cold heading and cold forming excellent in mechanical descaling property - Google Patents

Abstract

PURPOSE:To provide the method for manufacturing carbon steel wire rod for cold heading and cold forming excellent in mechanical descaling properties and to form scales good in mechanical descaling properties by controlling the coiling temp. and cooling rate after the rolling of the wire rod. CONSTITUTION:This method is the method for manufacturing carbon steel wire rod for cold heading and cold forming excellent in mechanical descaling properties in which a slab having a compsn. contg., by weight, <=0.15% C, <=0.5% Mn, <=0.04% Si and 0.01 to 0.08% Al and the balance Fe with inevitable impurities is heated to the range of 900 to 1100 deg.C and is thereafter rolled at >=60m/sec finish rolling rate and 950 to 1100 deg.C finishing temp. into wire rod, and the obtd. wire rod is coiled in the range of 850 to 930 deg.C, is then cooled in such a manner that the primary cooling rate from 850 to 600 deg.C is regulated to the range of 0.5 to 2 deg.C/sec and the secondary cooling rate from 600 to 350 deg.C is regulated to 10 to 25 deg.C/sec.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a carbon steel wire rod for cold heading having excellent mechanical descaling properties.

[0002]

2. Description of the Related Art Carbon steel wire rod for cold heading is JIS G350
It is a steel wire rod with the chemical composition specified in 7. After hot-rolling the wire rod, it is air-cooled or air-blast cooled to be a wire rod, and then pickled or mechanically descaled to remove scale adhering to the steel surface After drawing steel wire by wire drawing,
By cold forging with a double header or a multi-stage former, bolts, parts, etc. are formed into shapes according to their final use.

As described above, the scale removal of the steel wire rod includes the pickling method and the mechanical descaling method. The pickling method is widely adopted because it can sufficiently remove the scale, but the use of acid may cause problems such as pollution. Therefore, there is a demand to adopt the mechanical descaling method.

Mechanical descaling is a method of removing the scale by bending the wire rod with multiple rolls, and the factors that control the mechanical descaling are the texture of the scale, the density, the structure, the cracks in the scale, and the thickness of the scale. Etc. In order to produce a wire with good mechanical descaling, the wire is rolled up at a high temperature after rolling to promote the generation of FeO composition scale, and then the cooling rate is increased to increase the F
It is necessary to prevent the generation of scale of e ₃ O ₄ composition.

In the method of manufacturing a wire rod disclosed in Japanese Patent Laid-Open No. 52-33818, the wire rod is cooled at a Stelmore line after rolling at a rate of 6 ° C./sec for the purpose of improving scale releasability. However, when the cooling rate is increased, the austenite-ferrite transformation rate increases, and the fineness of the ferrite grain size increases the tensile strength of the wire.

When the tensile strength of the carbon steel wire rod for cold heading is increased, the deformation resistance of the workpiece is remarkably increased, the life of the tool is shortened, and the operating rate of the forging machine and eventually the production capacity are reduced.

[0007]

SUMMARY OF THE INVENTION According to the present invention, the mechanical temperature is controlled by controlling the winding temperature after wire rod rolling and the primary cooling rate up to 850 to 600 ° C and the secondary cooling rate up to 600 to 350 ° C. An object of the present invention is to provide a method for producing a carbon steel wire rod for cold heading, which produces a scale with good descaling property and has a low tensile strength.

That is, by winding the wire after rolling at a high temperature, a scale having a good FeO composition is produced, and the primary cooling rate from 850 to 600 ° C. is kept low to reduce the tensile strength. Peel off, 600-3
By increasing the secondary cooling rate up to 50 ° C., it is possible to prevent the generation of scale with poor peelability. As a result, a carbon steel wire rod for cold heading having excellent mechanical descaling properties and low tensile strength can be obtained.

[0009]

The gist of the present invention is that C: 0.15 wt% or less, Mn: 0.5 wt% or less, Si: 0.04 wt% or less, Al: 0.01-0.
After heating a steel slab containing 08 wt% and the balance consisting of Fe and unavoidable impurities to a range of 900 to 1100 ° C, the finishing rolling speed is 60 m / sec or more, and the finishing temperature is 950 to 1100 ° C. Rolled into a wire rod, the obtained wire rod is wound in the range of 850 to 930 ° C., and then 850
Primary cooling rate up to ~ 600 ℃ 0.5 ~ 2 ℃ / sec
, The secondary cooling rate from 600 to 350 ° C is 10
It is a method for producing a carbon steel wire rod for cold heading having excellent mechanical descaling characteristics, which is characterized by cooling in the range of 25 ° C./sec.

[0010]

The reason for limiting the carbon steel wire rod for cold heading in the present invention will be described. C is a basic element that controls the strength and ductility of steel, and the lower the carbon content, the softer it becomes and the more the ductility improves. The upper limit of the amount of C was set to 0.15 wt% which is the limit that does not deteriorate workability.

Si is an element that increases the strength of steel,
In addition to the element that reduces ductility by working, when a small amount of Si is added as in the carbon steel wire rod for cold heading, it is a component that controls the amount of scale formation and mechanical descaling property. As the amount of Si increases, the amount of scale formation decreases, and the mechanical descaling property tends to deteriorate. Therefore, making the scale thickness and peeling property uniform is effective for improving the mechanical descaling property. Therefore, the upper limit of the Si amount is 0.04
It was set to wt%.

[0012] Mn is a deoxidizing element and an element that forms a solid solution in steel to strengthen the steel, and its lower content is desirable for lowering work hardening. The upper limit of the amount of Mn was set to 0.5 wt% as a limit that does not deteriorate workability. Al is known as a deoxidizing element of steel, and is an element that combines with N in steel to prevent coarsening of austenite crystal grains. However, if a large amount of Al is added, it becomes difficult to keep the amount of Si in steel low, and further, Al itself deteriorates the mechanical descaling property a little, so a lower amount is desirable. Therefore, the upper limit of the amount of Al is 0.08 wt%, which is the limit that does not deteriorate the mechanical descaling property, while the lower limit is not particularly limited, but is 0.01 as the limit of deoxidation.
It was set to wt%.

The heating temperature in the wire rod rolling causes the components of the steel slab to form a solid solution and affects the temperature of the steel material during rolling. The lower limit of the heating temperature is 900 ° C in order to ensure that the steel slab uniformly forms a solid solution above the austenitizing temperature, and the steel material temperature during rolling is kept above the A ₁ transformation point, and the upper limit is to keep the decarburized layer low And 1100 ° C. The finishing temperature of wire rolling has a great influence on the austenite grain size of the structure. In the finish rolling process of the wire rod, the temperature of the steel rod rises due to the heat generated during processing. The lower limit of the finishing temperature was set to 950 ° C. to obtain coarse austenite crystal grains, and the upper limit was set to 1100 ° C. due to the restrictions on the wire rod rolling equipment.

The winding temperature in the wire rolling is an important factor that determines the scale composition to be produced. The present inventors experimentally determined this. As shown in FIGS. 1 and 2, it can be seen that as the winding temperature rises, the amount of scale formation increases and the mechanical descaling property improves. The lower limit of the winding temperature was set to 850 ° C. and the upper limit was set to 930 ° C. due to the limitation of the cooling equipment in order to generate a scale having good peelability.

The primary cooling rate from 850 to 600 ° C. in the wire rolling determines the ferrite grain size during the austenite-ferrite transformation. By keeping it low, the grain size becomes coarse and the tensile strength of the wire can be reduced. it can. The upper limit of 1 cooling rate was set to 2 ° C./sec in order to obtain a ferrite grain structure for obtaining workability, and the lower limit was set to 0.5 ° C./sec due to restrictions of rolling equipment.

The secondary cooling rate from 600 to 350 ° C. determines the rate of the FeO → Fe + Fe ₃ O ₄ reaction, and the lower limit is to prevent the formation of a scale with poor mechanical descaling of the Fe ₃ O ₄ composition. The upper limit is 10 ° C / sec, and the upper limit is 25 ° C due to restrictions of cooling equipment.
/ Sec.

[0017]

Example: Low carbon steel was melted in a 250 ton converter, decarburized and components were adjusted using a degassing facility, and 300 × 500 mm ingots were cast by a continuous casting facility.
Steel pieces with mm square cross section were manufactured. Table 1 shows the chemical composition of the sample steel.

In Table 1, A to D are examples of the steels of the present invention, and E to G are examples of comparative steels. The amount of C in E steel is the upper limit of the present invention, and that of F steel is M
The n amount is the upper limit of the present invention, the G steel is the Si amount exceeding the upper limit of the present invention, and the H steel is the example in which the Al amount is above the upper limit. These test steels were cast into 300 × 500 mm slabs by a continuous casting facility, and slab-rolling was performed to produce slabs with 122 mm square cross section.

These slabs were manufactured into billets by slab-rolling, then rolled into wire rods having a diameter of 5.5 mm under the wire rod rolling conditions shown in Table 2 and subjected to Stelmore cooling. The workability during cold forging was determined by a cold upsetting test. As shown in FIG. 3, the test die had a concentric groove with a groove depth of 0.4 mm and a pitch of 0.7 mm formed on the tool surface. This is intended to completely restrain the composition flow on the upper and lower surfaces of the sample. The contact surface was made of cemented carbide.

The height-diameter ratio h ₀ / D ₀ of the test piece was fixed at 1.5, and a depth of 0.4 was measured along the surface of the cut piece.
mm finishing V-groove with a rounded radius of 0.15 mm at the groove bottom and a groove angle of 120 degrees is used as a test piece, and this test die is compressed in the axial direction and has an outer diameter of 60 mm and a length of 60 mm. The test was performed by using a pair of upper and lower carved V-grooves with a valley opening angle of 120 degrees in a concentric multiple annular array with a radial pitch of 0.7 mm in a region of an end face diameter of 40 mm in contact with the test piece. A compressive load was applied to one piece at a compressive strain rate of 3.3 × 10 ⁻³ sec ⁻¹ to visually determine the occurrence of cracks, and as a limit compression rate (%), ε _hc = (h ₀ −h _c ) / h ₀ × 100 ε _hc : Limit upsetting rate h ₀ : Original height of test piece h _c : It was determined by calculating the value of the height of the test piece when cracking occurred.

The tensile test was carried out by using the JISZ2201 No. 2 test piece according to the method described in JISZ2241. The mechanical descaling property was evaluated by removing the scale by the reverse bending method and then displaying the percentage of the scale amount with respect to the sample weight. The characteristic values thus obtained are also shown in Table 2.

No. 5 to No. 13 are comparative steels. No. 5
Since the heating temperature was too low, the finish rolling temperature decreased, the ferrite crystal grains became finer, the strength increased, and the workability decreased. In No. 6, since the finish rolling temperature was too low, the ferrite crystal grains became fine and the strength increased and the workability deteriorated.

In No. 7, since the winding temperature was too low, the scale peeling deteriorated and the mechanical descaling property deteriorated. In No. 8, since the primary cooling rate was too fast, the ferrite crystal grains became finer, the strength increased, and the workability deteriorated.
No. 9 has a poor peeling property because the secondary cooling rate is too slow.
e ₃ O ₄ was generated, and the mechanical descaling property deteriorated.

In No. 10, the workability was deteriorated because the C content was too high. In No. 11, the tensile strength increased because the Mn content was too high. In No. 12, since the amount of Si was too high, the amount of scale formation decreased, and the mechanical descaling property deteriorated. In No. 13, the mechanical descaling property was deteriorated because the Al content was too high.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

As described above, the wire manufactured according to the method of the present invention has a mechanical descaling property further improved as compared with the conventional method, which facilitates the scale removal performed in the wire drawing pretreatment. It is possible to manufacture a carbon steel wire rod for cold heading, which can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a winding temperature after rolling a wire rod and an amount of scale formation.

FIG. 2 is a diagram showing a relationship between a winding temperature after wire rod rolling and a residual scale amount after mechanical descaling.

FIG. 3 is a side sectional view of a compression tool in a cold upsetting test for determining workability during cold forging.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshitaka Nishikawa 1 Kimitsu, Kimitsu City, Chiba Shin Nippon Steel Co., Ltd. Inside the Kimitsu Works

Claims (1)

[Claims] 1. C: 0.15 wt% or less, Mn: 0.5
wt% or less, Si: 0.04 wt% or less, Al: 0.0
After heating a steel slab containing 1 to 0.08 wt% and the balance being Fe and unavoidable impurities in the range of 900 to 1100 ° C., the finish rolling speed is 60 m / sec or more,
Roll to a wire at a finishing temperature of 950 to 1100 ° C,
The obtained wire is wound in the range of 850 to 930 ° C., and then the primary cooling rate from 850 to 600 ° C. is 0.5 to 2 ° C.
/ Sec, a secondary cooling rate from 600 to 350 ° C is cooled within a range of 10 to 25 ° C / sec, and a method for producing a carbon steel wire rod for cold heading having excellent mechanical descaling properties.