JP2984886B2 - Bainite wire or steel wire for wire drawing and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bainite wire or steel wire for wire drawing and a method for producing the same. In the present invention, the wire rod as a product means a wire rod which is subjected to direct heat treatment after rolling a steel slab into a wire rod and used for wire drawing, and the steel wire as a product is before drawing or after hot rolling, A steel wire that has been subjected to a heat treatment to be subjected to wire drawing, and a steel wire that has been subjected to a primary drawing by cold working after hot rolling and then subjected to a heat treatment for a secondary drawing.

[0002]

2. Description of the Related Art Generally, a wire or a steel wire is drawn according to the use of various end products. Before the wire drawing, the wire or the steel wire is in a state suitable for wire drawing. It is necessary to keep. Conventionally, for high-carbon steel wire or steel wire, a unique heat treatment called patenting, which is a unique heat treatment called patenting, is required before the wire drawing process, because the structure must be a mixed structure of uniform and fine pearlite and a small amount of proeutectoid ferrite. Will be applied. This is a heat treatment method in which a wire or a steel wire is heated to an austenitizing temperature and then cooled at an appropriate cooling rate to complete the pearlite transformation to form a mixed structure of fine pearlite and a small amount of proeutectoid ferrite.

In the method of manufacturing a wire described in Japanese Patent Publication No. 60-56215, a wire having an austenitizing temperature is immersed in a molten salt, and a cooling rate between 800 and 600 ° C.
A heat treatment method of forming a mixed structure of fine pearlite and a small amount of proeutectoid ferrite at 100 ° C./sec is performed. However, in the pearlite structure, deterioration of ductility at a high area reduction rate in the wire drawing process and generation of cracks in a twist test (hereinafter referred to as delamination) are problems.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a bainite wire or a steel wire which does not cause the above-mentioned problems in the wire drawing process and which is excellent in wire drawability, and a method for producing the same. I do.

[0005]

The above object of the present invention is to provide:
According to the present invention, a bainite structure containing a specific amount of C, Mn, Si and optionally Cr, having a chemical composition in which the upper limit of the amount of P and S is limited, and having a specified tensile strength and a specified drawing value. The problem is solved by providing a wire rod or a steel wire.

Another object of the present invention is to increase the cooling speed to the nose position in the TTT diagram in cooling the wire after hot rolling or in heat treatment of the steel wire after heating to the austenitizing temperature. An object is to solve the problem by providing a bainite wire or steel wire obtained by preventing the formation of a structure and then isothermally maintaining the temperature at 350 to 500 ° C. In other words, after rolling the wire or heating the steel wire, 1100-755 ° C
From the above temperature range to a temperature range of 350 to 500 ° C. at a cooling rate of 60 to 300 ° C./sec, and holding at this temperature for a certain period of time to suppress the generation of micro-martensite structure. A wire or a steel wire having an excellent bainite structure can be obtained, and thus a wire or a steel wire having excellent drawability even at a high area reduction rate can be obtained.

That is, the gist of the present invention is as follows. (1) C: 0.80 to 0.90%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00% by weight%, P: 0.02% or less, S: limited to 0.01% or less, Al: limited to 0.003% or less, the balance consisting of Fe and unavoidable impurities;
A bainite wire or a steel wire for wire drawing, having a tensile strength and a drawing value defined by the following formulas (1) and (2).

TS ≦ 85 × (C) +60 (1) RA ≧ −0.875 × (TS) +158 (2) where C: carbon content (wt%) TS: tensile strength (kgf / mm) ² ) RA: drawing (%) (2) Cr: 0.10-1.
2. The bainite wire rod or the steel wire for wire drawing according to the above item 1, wherein the steel wire contains 00%.

(3) The upper bainite structure has an area ratio of 8
3. The bainite wire or steel wire for wire drawing according to the above 1 or 2, wherein the bainite wire or the wire has a microstructure of 0% or more and Hv of 450 or less. (4) C: 0.80 to 0.90%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00% by weight%, P: 0.02% or less, S: 0.01% or less, Al: 0.003% or less, rolled into a wire using a slab composed of the balance Fe and unavoidable impurities, and the wire after completion of hot rolling is reduced to 11%.
60-300 ° C / sec from the temperature range of 00-755 ° C
A method for producing a bainite wire rod for wire drawing, wherein the wire is cooled to a temperature in the range of 350 to 500 ° C. at a cooling rate of not less than 350 seconds and maintained for at least Y seconds defined by the following formula (3).

Y = exp (19.83−0.0329 × T) (3) T: heat treatment temperature (° C.) (5) The starting steel slab is used as an alloy component, and Cr: 0.
5. The method for producing a bainite wire rod for wire drawing according to the above item 4, which contains 10 to 1.00%.

(6) C: 0.80 to 0.90%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00% by weight, P: 0.02 % Or less, S: 0.01% or less, Al: 0.003% or less, and after heating a steel wire having a composition consisting of a balance of Fe and unavoidable impurities to a temperature range of 1100 to 755 ° C, 350-50 at a cooling rate of 300 ° C / sec
A method for producing a bainite steel wire for wire drawing, characterized in that the bainite steel wire is cooled to a temperature range of 0 ° C. and maintained in this temperature range for a time period Y seconds or more defined by the following formula (3).

Y = exp (19.83−0.0329 × T) (3) T: heat treatment temperature (° C.) (7) The starting steel wire is used as an alloy component, and
7. The method for producing a bainite steel wire for wire drawing according to the above item 6, containing 10 to 1.00%.

[0013]

The reasons for limiting the constituent elements of the present invention will be described.
The reasons for limiting the chemical compositions of the starting billet and the steel wire are as follows. Since the primary drawability significantly decreases when the amount of C added is less than 0.80 wt%, the lower limit is set to 0.80w.
The content is set to t%, but if added in excess of 0.90 wt%, center segregation occurs, so the upper limit was set to 0.90 wt%.

[0014] Si is added as a deoxidizing agent in an amount of 0.10 wt% or more. Si is an element that strengthens the solid solution of the steel and is an element that can reduce the relaxation loss of the steel wire. However, if it is added in excess of 1.50 wt%, the amount of scale generated is reduced, the mechanical descaling property is deteriorated, and the bond lubricity of the wire is slightly reduced. Therefore, the upper limit is set to 1.50 wt%.

Mn is added as a deoxidizing agent in an amount of 0.10% by weight or more. Further, Mn is an element for solid solution strengthening of steel, but when the amount of addition is increased, segregation tends to occur in the center of the wire, and the segregated portion improves the hardenability and shifts the transformation end time to a longer time side. Since the untransformed portion becomes martensite and leads to breakage during wire drawing, the upper limit of the amount added is 1.00.
wt%.

In the case of the hypereutectoid steel as in the present invention, a cementite network is apt to be generated in the structure after patenting, and a cementite thick one is liable to precipitate. In order to achieve high strength and high ductility in the steel of the present invention, it is necessary to eliminate cementite networks and thick cementite. Cr suppresses the appearance of such an abnormal portion of cementite, and has an effect of further reducing pearlite. Therefore, it is desirable to add Cr as necessary.
Therefore, the lower limit is set to 0.10 wt% at which the effect can be expected. However, the addition of a large amount increases the dislocation density in the ferrite after the heat treatment, and significantly impairs the ductility of the ultrafine wire after the drawing. Therefore, the upper limit is set to 1.00 wt% which does not impair ductility.

Since P and S precipitate at the grain boundaries and deteriorate the properties of steel, they must be kept as low as possible. The upper limit of P is 0.02 wt%, and the upper limit of S is 0.01 w
t%. Al is a cause of reducing the ductility of ultrafine wires.
The ₂ O _3, Al ₂ O _3, such as MgO-Al ₂ O ₃ is present in the non-ductile inclusions mainly. Therefore, in the present invention, in order to avoid a decrease in ductility due to non-ductile inclusions, Al
The content is set to 0.003 wt% or less.

Next, rolling conditions and heat treatment conditions for obtaining the bainite wire and the steel wire of the present invention will be described. Cooling start temperature or steel wire heating temperature after wire rod rolling is 755 to 1
The reason why the temperature is limited to 100 ° C. is that 755 ° C. is the lower limit of the austenite transformation point, whereas if it exceeds 1100 ° C., abnormal growth of austenite grains occurs.

After the cooling of the wire or the steel wire is started, 350 to 5
The cooling rate to the constant temperature holding temperature range of 00 ° C is 60 to 300
The reason why the temperature was limited to 60 ° C./sec is that 60 ° C./sec is the lower limit of the critical cooling rate for forming the upper bainite structure, while
This is because 0 ° C./sec is the upper limit of the cooling rate that is industrially possible. The reason for setting the constant temperature after cooling to be 350 to 500 ° C. is that 350 ° C. is the lower limit temperature for the formation of the upper bainite structure, and 500 ° C. is the upper limit temperature for the formation of the upper bainite structure.

The time required to maintain a constant temperature in the temperature range of 300 to 500 ° C. can be obtained from the transformation end line of the TTT diagram. If the immersion time in the cooling bath is insufficient, martensite is generated. It may cause disconnection during wire drawing. Therefore, it is necessary to keep the time longer than the transformation end time.
The lower limit of the time for maintaining the temperature in the temperature range of 500 ° C. is as follows (3).
The time determined by the equation was Y seconds.

Y = exp (19.83−0.0329 × T) ─ (3) where T: heat treatment temperature (° C.) Next, the reasons for limiting the characteristics of the wire and the steel wire of the product of the present invention will be described. Since the tensile strength strongly depends on the C content, it is given in relation to the C content as in the equation (1). A wire or steel wire having a bainite structure has a lower precipitation strength than a conventional wire or steel wire having a pearlite structure because the precipitation of cementite is coarser in the same composition. In the wire drawing process, the lower the initial tensile strength, the better the wire drawability, and the wire drawing can be performed up to a high area reduction rate. Therefore, as a limit that does not deteriorate wire drawing workability, the tensile strength is limited as in Expression (1). If the upper limit is exceeded, the wire drawing processability will be degraded, leading to disconnection and delamination during wire drawing.

The drawing value is an important factor indicating the ease of processing during wire drawing. Even with the same tensile strength, the higher the drawing value, the lower the work hardening rate during wire drawing, and the wire drawing can be performed to a high area reduction rate. A wire having a bainite structure has a coarser cementite precipitate than a wire having a conventional pearlite structure, and therefore has a higher aperture value even at the same tensile strength. Therefore, the aperture value is limited as in Expression (2) as a limit that does not deteriorate the drawing limit. If the lower limit is not reached, the drawability deteriorates, leading to disconnection and delamination during drawing.

The wire or steel wire having a bainite structure of the present invention has a tensile strength and a drawing value defined as described above, and also has an upper bainite structure having an area ratio of 8%.
By having a microstructure of 0% or more and Hv of 450 or less, the wire drawing workability is further improved.

[0024]

【Example】

Example 1 Table 1 shows the chemical components of the test steel. A to D in Table 1 are examples of the steel of the present invention, and E and F are examples of comparative steels. Steel E has a C content exceeding the upper limit, and steel F has a Mn content exceeding the upper limit.

These test steels were converted into 30
0 × 500mm slab and 122
A slab having a cross section of mm square was manufactured. After producing these billets by billet rolling into billets, they were rolled into wires having the diameters shown in Table 2,
DLP (Direct Lead Patentin
g) Cooling was performed. These wires were drawn to 1.00 mmφ at an average area reduction rate of 17%, and a tensile test and a twist test were performed.

The tensile test was carried out using a No. 2 test piece of JISZ2201 according to the method described in JISZ2241. In the torsion test, after cutting to a test piece length of 100d + 100, the test piece was rotated at a distance between chucks of 100d and a rotation speed of 10rpm until it was broken. d represents the diameter of the steel wire. The characteristic values thus obtained are also shown in Table 2.

No. 5-No. 10 is a comparative example. N
o. In No. 5, pearlite was generated because the cooling rate was too slow, the wire drawing workability was reduced, and the wire was broken during the wire drawing. N
o. In No. 6, pearlite was generated because the isothermal transformation temperature was too high, the wire drawing workability was reduced, and the wire was broken during drawing.

No. In No. 7, martensite was generated because the isothermal transformation time was short, wire drawing workability was deteriorated, and wire breakage occurred during wire drawing. No. In No. 8, since the cooling start temperature was too low, no bainite structure was formed, the wire drawing workability was reduced, and the wire was broken during drawing.

No. In No. 9, pearlite was generated due to an excessively high C content, and wire drawing workability was reduced. No. 10 is M
Since the amount of n was too high, micro-martensite was generated along with the center segregation, and the wire drawing workability was reduced.

[0030]

[Table 1]

[0031]

[Table 2]

Example 2 Table 3 shows the chemical composition of the test steel wire. In Table 3, A to D are examples of the present invention, and E and F are comparative examples. E steel has a C content exceeding the upper limit,
Steel F has an Mn content exceeding the upper limit. These steel wires were austenitized under the conditions shown in Table 4, heat-treated, drawn to 1.00 mmφ with an average area reduction of 17%, and subjected to a tensile test and a twist test.

The tensile test was performed using a No. 2 test piece of JISZ2201 according to the method described in JISZ2241. In the torsion test, after cutting to a test piece length of 100d + 100, the test piece was rotated at a distance between chucks of 100d and a rotation speed of 10rpm until it was broken. d represents the diameter of the steel wire. The characteristic values thus obtained are also shown in Table 4.

No. 1 to No. No. 4 is an example of the present invention, and satisfies all the heat treatment conditions of the present invention. Therefore, even after 1.0 mmφ after drawing, it is possible to draw without delamination. No. 5-No. 10 is a comparative example. No. In No. 5, pearlite was generated because the cooling rate was too slow, the wire drawing workability was reduced, and the wire was broken during the wire drawing.

No. In No. 6, pearlite was generated because the isothermal transformation temperature was too high, the wire drawing workability was reduced, and the wire was broken during the wire drawing. No. In No. 7, martensite was generated because the isothermal transformation time was short, and the wire drawing workability was reduced, and the wire was broken during drawing. No. In No. 8, since the heating temperature was too low, the bainite structure ratio became zero, the wire drawing workability was reduced, and the wire was broken during the wire drawing.

No. In No. 9, since the C content was too high, pearlite was generated and the wire drawing workability was reduced. No. 10 is Mn
The pearlite was formed because the amount was too high, and the drawability was lowered because the aperture value was low.

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

As described above, the wire or the steel wire manufactured according to the present invention can be drawn to a much higher area reduction ratio than the conventional method, and the delamination resistance is improved. Therefore, according to the present invention, it is possible to provide a bainite wire or a steel wire having excellent drawability.

[Brief description of the drawings]

FIG. 1 is a view showing a heat treatment pattern of the present invention.

Continuation of the front page (72) Inventor Seiji Nishida 1 Kimitsu, Kimitsu City, Chiba Prefecture Inside of Nippon Steel Corporation Kimitsu Works (56) References JP-A-5-117762 (JP, A) JP-A-5-117 117764 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 38/00-38/18 C21D 8/06-9/52

Claims (7)

(57) [Claims] 1. Content of C: 0.80 to 0.90%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00% by weight, P: 0.02% S: 0.01% or less, Al: 0.003% or less, with the balance being Fe and unavoidable impurities,
A bainite wire or a steel wire for wire drawing, having a tensile strength and a drawing value defined by the following formulas (1) and (2). TS ≦ 85 × (C) +60 (1) RA ≧ −0.875 × (TS) +158 (2) where C: carbon content (wt%) TS: tensile strength (kgf / mm ² ) RA : Aperture (%) 2. The alloy composition further contains Cr: 0.10
The bainite wire or the steel wire for wire drawing according to claim 1, which contains 1.00% to 1.00%. 3. The bainite wire or steel wire for wire drawing according to claim 1, wherein the upper bainite structure has a microstructure having an area ratio of 80% or more and an Hv of 450 or less. 4. C: 0.80 to 0.90%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00% by weight, P: 0.02% In the following, S is limited to 0.01% or less and Al: 0.003% or less, and is rolled into a wire by using a steel slab composed of a balance of Fe and unavoidable impurities.
60-300 ° C / sec from the temperature range of 00-755 ° C
A method for producing a bainite wire rod for wire drawing, wherein the wire is cooled to a temperature in the range of 350 to 500 ° C. at a cooling rate of not less than 350 seconds and maintained for at least Y seconds defined by the following formula (3). Y = exp (19.83−0.0329 × T) (3) T: heat treatment temperature (° C.) 5. The starting billet as an alloying component, further comprising C
The method for producing a bainite wire rod for wire drawing according to claim 4, comprising r: 0.10 to 1.00%. 6. The composition contains C: 0.80 to 0.90%, Si: 0.10 to 1.50%, Mn: 0.10 to 1.00% by weight, and P: 0.02%. S: 0.01% or less, Al: 0.003% or less, and after heating a steel wire having a composition comprising the balance of Fe and unavoidable impurities to a temperature range of 1100 to 755 ° C, 60 to 300 350-50 at a cooling rate of ° C / sec
A method for producing a bainite steel wire for wire drawing, characterized in that the bainite steel wire is cooled to a temperature range of 0 ° C. and maintained in this temperature range for a time period Y seconds or more defined by the following formula (3). Y = exp (19.83−0.0329 × T) (3) T: heat treatment temperature (° C.) 7. The starting steel wire as an alloying component, further comprising C
The method for producing a bainite steel wire for wire drawing according to claim 6, comprising r: 0.10 to 1.00%.