JP2017190515A - Steel wire and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel wire that can absorb a large amount of energy until its rupture.SOLUTION: A steel wire has a chemical component of, in mass%, C: 0.05-0.25%, Si: 0.3-1.0%, Mn: 0.10-3.00%, S: 0.005-0.015%, N: 0.005-0.013%, and Al: 0.005% or less, with the balance being Fe and unavoidable impurities. A crystal grain size of ferrite in the steel wire cross section is 9 μm or less. The steel wire contains residual austenite of 8% or more in cross sectional area. The steel wire has an absorption energy of 1300 J/cmor more per unit area until its rupture.SELECTED DRAWING: None

Description

  The present invention relates to a steel wire exhibiting large absorbed energy and a method for producing the same.

  A rockfall protection net is used to prevent rockfalls from entering the roads and tracks that are in contact with cliffs and cuts. A rockfall protection net is required to absorb the kinetic energy of the rockfall and receive the rockfall and to stop the rockfall.

  The amount of energy absorbed until the steel wire used in the rockfall protection net is broken is roughly proportional to the tensile strength and elongation. If the elongation does not change, the absorbed energy of the steel wire increases as the tensile strength increases, and if the tensile strength does not change, the elongation increases. However, normally, when the tensile strength is increased, the elongation is reduced more than the rate of increase of the tensile strength, so the absorbed energy is reduced. For this reason, steel wires for rockfall protection nets have been frequently used for soft wires with large elongation. If the tensile strength can be increased without decreasing the elongation, the energy absorbed by the rock fall protection net will increase dramatically.

  A method of utilizing retained austenite is known as a method for increasing the tensile strength without reducing the elongation of the steel material. That is, in this process, retained austenite is transformed into martensite one after another in the course of elongation (deformation) (processing-induced transformation), and the fragile portion that is the starting point of fracture is strengthened to ensure elongation.

  As a technique related to rock fall protection using residual austenite, there is a technique of Patent Document 1. The technique described in Patent Document 1 is a technique that absorbs energy with a rope that supports rockfall prevention facilities such as a rockfall protection fence and a rockfall protection net.

JP 2007-191774 A

  However, even when rock fall prevention equipment such as a rock fall protection net is produced by a method utilizing conventional retained austenite, such as Patent Document 1, the magnitude of fall rock energy that can be received is still insufficient. In order to receive larger rockfall energy, it is necessary to increase the energy absorption capacity of the steel wire that can be used for the rockfall prevention equipment itself such as the rockfall protection net.

  Therefore, there is a demand for a steel wire that can absorb a large amount of energy before it breaks.

The gist of the present invention is as follows:
(1) In mass%,
C: 0.05 to 0.25%
Si: 0.3 to 1.0%,
Mn: 0.10 to 3.00%,
S: 0.005-0.015%,
N: 0.005 to 0.013%, and Al: 0.005% or less of chemical components,
The balance is a steel wire made of Fe and inevitable impurities,
The ferrite grain size in the steel wire cross section is 9 μm or less,
Including residual austenite of 8% or more in cross-sectional area ratio,
The absorbed energy per unit area until breakage is 1300 J / cm ² or more,
A steel wire characterized by that.
(2) By mass%, Cr: 0.05 to 2.00%, Ni: 0.05 to 2.00%, Cu: 0.05 to 1.00%, Mo: 0.05 to 1.00 The steel wire as set forth in (1) above, comprising one or more of%.
(3) In mass%,
C: 0.05 to 0.25%
Si: 0.3 to 1.0%,
Mn: 0.10 to 3.00%,
S: 0.005-0.015%,
N: 0.005 to 0.013%, and Al: 0.005% or less of chemical components,
Drawing the steel material, the balance of which is Fe and inevitable impurities, giving a plastic strain of 1.0 or more,
The steel described above drawing, heating at A _C1 transformation point temperature or higher and (A _C1 transformation point temperature + A _C3 transformation temperature) / 2 or less to the heating temperature 8 ° C. / sec or more heating rate, the heating temperature Hold for 15 to 120 seconds,
The heated steel material is expressed by the formula (2) at a cooling rate of 8 ° C./second or more:
M _S (° C.) = 550−350C-40Mn-10Cu-17Ni-20Cr
-10Mo + 30Al (2)
In reference to the _{M S} transformation temperature indicated, _{(M S} transformation temperature + 50 ° C.) or less and cooled to _{(M S} transformation temperature -50 ° C.) or higher temperatures, can be held at that temperature from 50 to 320 seconds And further cooling the cooled steel material to room temperature,
A method of manufacturing a steel wire characterized by

  According to the present invention, a steel wire exhibiting large absorbed energy can be obtained.

In the present invention, by mass, C: 0.05 to 0.25%, Si: 0.3 to 1.0%, Mn: 0.10 to 3.00%, S: 0.005 to 0.015 %, N: 0.005 to 0.013%, and Al: 0.005% or less of chemical components, the balance being Fe and unavoidable impurities, and a ferrite crystal in the cross section of the steel wire Intended for a steel wire having a particle size of 9 μm or less, containing 8% or more of retained austenite in cross-sectional area ratio, and having an absorbed energy per unit area of 1300 J / cm ² or more until fracture. .

  The steel wire according to the present invention is a steel wire comprising a predetermined chemical component and the balance Fe and inevitable impurities, the ferrite crystal grain size in the cross section being 9 μm or less, and containing 8% or more of retained austenite. The steel wire according to the present invention is superior in balance between tensile strength and ductility as compared with a conventional annealed wire, and exhibits a large absorbed energy. In the present application, the absorbed energy is a value obtained by integrating the load-displacement curve in the tensile strength test of the steel wire by the displacement.

  A wire mesh for a rock fall protection net can be knitted using the steel wire according to the present invention. When a high load is applied to a specific part of a rockfall protection net provided with a wire mesh produced by using the steel wire according to the present invention, the steel wire at that part is strengthened by the formation of work-induced martensite. The deformation is dispersed in the steel wires in other parts, and the absorbed energy can be shown larger than before. In addition, since the steel wire according to the present invention exhibits a large absorbed energy, when a wire mesh for a rock fall protection net is produced using the steel wire according to the present invention, the wire mesh for the rock fall protection net can be constituted by a single wire. Therefore, a rockfall protection net can be produced at low cost. In the present application, a single wire means that it is not a stranded wire. A stranded wire is obtained by twisting a plurality of wires.

  Below, the composition of the steel wire which concerns on this invention is demonstrated. In the description of the composition below, the percentage display is mass% based on the total mass of the steel wire.

The steel wire according to the present invention is mass%,
C: 0.05 to 0.25%
Si: 0.3 to 1.0%,
Mn: 0.10 to 3.00%,
S: 0.005-0.015%,
N: 0.005 to 0.013%, and Al: 0.005% or less.

  The steel wire contains 0.05 to 0.25% C. C is an important element for the production of retained austenite. When the steel wire contains 0.05% or more of C, a sufficient amount of retained austenite can be obtained, and good elongation can be obtained. The steel wire preferably contains 0.10% or more of C. If the C content in the steel wire exceeds 0.25%, the steel wire becomes too hard and the elongation decreases, making it difficult to form into a wire mesh, so the upper limit of the C content is 0.25% or less. Preferably, the content is 0.23% or less.

  The steel wire contains 0.3 to 1.0% Si. Si is an element that promotes the concentration of C from the BCC phase (ferrite) to the untransformed FCC phase (austenite) in the transformation process, and facilitates the formation of residual austenite. When the steel wire contains 0.3% or more of Si, the generation of retained austenite can be promoted. The steel wire preferably contains 0.4% or more of Si. If the Si content in the steel wire exceeds 1.0%, a problem arises in scale peelability. Therefore, the upper limit of the Si content is 1.0% or less, preferably 0.9% or less, more preferably 0.8. 8% or less, more preferably 0.7% or less.

  The steel wire contains 0.10 to 3.00% of Mn. Mn is an element that has the effect of reducing the transformation rate of the ferrite transformation and pearlite transformation, which are diffusion transformations, and facilitating the formation of retained austenite. When the steel wire contains 0.10% or more of Mn, it is possible to suppress the coarsening of ferrite grains and to generate a sufficient amount of retained austenite. The steel wire preferably contains 0.20% or more of Mn. When the Mn content in the steel wire exceeds 3.00%, the hot ductility is lowered and the productivity is remarkably lowered. Therefore, the upper limit of the Mn content is 3.00% or less, preferably 2.50% or less. To do.

  The steel wire contains 0.005 to 0.015% S. S is an important element that forms MnS and improves the scale peelability. When the steel wire contains 0.005% or more of S, scale peelability can be improved. The steel wire preferably contains 0.008% or more of S. If the S content in the steel wire exceeds 0.015%, fracture starting from MnS becomes prominent and ductility decreases, so the upper limit of the S content is 0.015% or less, preferably 0.012%. The following. Although the steel wire according to the present invention has a high tensile strength, if a large amount of MnS is produced, the adverse effect on the tensile strength is extremely large, so the S content in the steel wire is strictly limited.

  The steel wire contains 0.005 to 0.013% N. N, like C, is an important element for the formation of retained austenite. When the steel wire contains 0.005% or more of N, the effect of generating retained austenite becomes very large. The steel wire preferably contains 0.008% or more of N. If the N content in the steel wire exceeds 0.013%, melting becomes difficult, so the upper limit of the N content is 0.013% or less, preferably 0.010%. Thus, from the viewpoint of residual austenite formation and melting, the N content in the steel wire is strictly limited.

In the steel wire according to the present invention, the Al content is preferably as low as possible, and the Al content in the steel wire is 0.005% or less, more preferably 0.003% or less. Al, like Si, can promote the concentration of C into untransformed austenite and facilitate the formation of residual austenite, but it cannot increase the absorbed energy of the steel wire. Further, Al reacts with O during smelting to produce hard Al ₂ O ₃ and causes disconnection during wire drawing, so the Al content needs to be reduced as much as possible. The steel wire according to the present invention has a high tensile strength, but the Al content in the steel wire is strictly limited because the adverse effect on the tensile strength of Al ₂ O ₃ that can be produced is extremely large.

  Preferably, the steel wire further comprises 0.05 to 2.00% Cr, 0.05 to 2.00% Ni, 0.05 to 1.00% Cu, and 0.05 to 1 type or 2 types or more are included among 1.00% Mo.

  Each of Cr, Ni, Cu, and Mo is a steel strengthening element, and is an element that facilitates the formation of retained austenite. Each of Cr, Ni, Cu, and Mo is preferably 0.05% or more, more preferably 0.2% or more, still more preferably 0.5% or more, and even more preferably 1.1% in the steel wire. It is preferable to add more. For Cr and Ni, excessive addition increases the cost, so the upper limit of the content in the steel wire is made 2.00% or less. Also for Cu and Mo, excessive addition increases the cost, so the upper limit of the content in the steel wire is made 1.00% or less.

  The balance of the steel wire is Fe and inevitable impurities.

  The crystal grain size of ferrite in the cross section of the steel wire is 9 μm or less, preferably 8 μm or less, more preferably 7 μm or less, and further preferably 6 μm or less. The lower limit of the crystal grain size of ferrite is not particularly limited, but can be about 1 μm, for example. When the crystal grain size of ferrite is in the above range, a large amount of retained austenite can be generated. Further, when the ferrite crystal grain size is in the above range, the elongation can be increased.

  The steel wire contains 8% or more, preferably 9% or more, more preferably 10% or more, and even more preferably 11% or more of retained austenite in terms of the cross-sectional area ratio. The upper limit of retained austenite is not particularly limited, but can be, for example, 30% or less. When the cross-sectional area ratio of the retained austenite is in the above range, a steel wire having excellent elongation and large absorbed energy per unit area until breakage can be obtained.

The absorbed energy per unit area until breakage of the steel wire is 1300 J / cm ² or more, preferably 1400 J / cm ² or more, more preferably 1500 J / cm ² or more, and further preferably 1600 J / cm ² or more.

  The steel wire which shows the absorption energy of the said range can be used suitably for preparation of a rock fall protection net.

  The tensile strength (TS) of the steel wire according to the present invention is preferably 500 MPa or more, more preferably 550 MPa or more, further preferably 575 MPa or more, and even more preferably 600 MPa or more.

  The elongation (EL) of the steel wire according to the present invention may be an elongation (EL) that increases the absorbed energy in balance with the tensile strength, and is preferably in the range of about 30% to 70%. it can.

The present invention also includes, in mass%, C: 0.05 to 0.25%, Si: 0.3 to 1.0%,
Mn: 0.10 to 3.00%, S: 0.005 to 0.015%, N: 0.005 to 0.013%, and Al: 0.005% or less of chemical components, with the balance being Drawing a steel material composed of Fe and inevitable impurities with a plastic strain of 1.0 or more, and drawing the drawn steel material to an _AC1 transformation point temperature or more and ( _AC1 transformation point temperature + _AC3 transformation point temperature) Heating at a heating rate of 8 ° C./second or more to a heating temperature of / 2 or less and holding at the heating temperature for 15 seconds to 120 seconds, the heated steel material is expressed at a cooling rate of 8 ° C./second or more. (2):
M _S (° C.) = 550−350C-40Mn-10Cu-17Ni-20Cr
-10Mo + 30Al (2)
In reference to the _{M S} transformation temperature indicated, _{(M S} transformation temperature + 50 ° C.) or less and cooled to _{(M S} transformation temperature -50 ° C.) or higher temperatures, can be held at that temperature from 50 to 320 seconds And a method for producing a steel wire, characterized in that the cooled steel material is further air-cooled to room temperature.

  Below, each structure of the manufacturing method of the steel wire which concerns on this invention is demonstrated.

  In mass%, C: 0.05 to 0.25%, Si: 0.3 to 1.0%, Mn: 0.10 to 3.00%, S: 0.005 to 0.015%, N: A steel material containing a chemical component of 0.005 to 0.013% and Al: 0.005% or less, with the balance being Fe and inevitable impurities is drawn to obtain a steel wire. Preferably, the steel material is drawn to a wire diameter for making a rock fall protection net. The net structure of the falling rock protection net that can be produced using the steel wire according to the present invention is preferably a rhombus metal net. The mesh size of the rockfall protection net is preferably 30 to 80 mm.

  Drawing is cold drawing and can be performed by dry drawing using a normal die, rolling using a roller, or the like.

  Next, when the drawn steel wire is heated to the ferrite-austenite two-phase region, the ferrite is recrystallized with the high dislocation density site introduced at the time of wire drawing as a nucleus.

Since the grain size at the time of recrystallization of ferrite becomes finer as the number of nuclei increases, the wire drawing strain (plastic strain) before heating is preferably higher. By setting the plastic strain before heating to 1.0 or more, coarsening of the ferrite grain size can be suppressed and the ferrite grain size can be made sufficiently fine, and retained austenite can be easily generated to improve elongation. Therefore, the lower limit of plastic strain is 1.0 or more, preferably 1.1 or more, more preferably 1.2 or more, and further preferably 1.3 or more. The plastic strain epsilon, the diameter D ₂ after the original wire diameter D ₁ and drawing before drawing, formula (1):
ε = 2 × ln (D ₁ / D ₂ ) (1)
Is calculated by

The heating temperature after the drawing, by more than A _C1 transformation point temperature, ferrite - can be austenite 2-phase region.

Further, the heating temperature after the drawing, by the (A _C1 transformation point temperature + A _C3 transformation temperature) / 2 or less, and suppress the coarsening of the ferrite grain size, and the ferrite - austenite in austenite 2-phase region The carbon concentration of the phase can be further increased. By further increasing the carbon concentration of the austenite phase, the austenite phase is stabilized, the amount of transformation from austenite to ferrite decreases during cooling, and the amount of retained austenite after cooling can be increased. On the other hand, when the heating temperature after wire drawing is higher than ( _AC1 transformation point temperature + _AC3 transformation point temperature) / 2, the amount of austenite during heating increases, but the amount of transformation from austenite to ferrite increases during cooling. Thus, the amount of retained austenite is greatly reduced.

Therefore, the heating temperature, by limiting the A _C1 transformation point temperature or higher and (A _C1 transformation point temperature + A _C3 transformation temperature) / 2 or less, it is possible to improve the elongation of the steel wire.

  When intermediate annealing is performed at the time of wire drawing, the strain is cleared at the time of annealing, so the plastic strain defined here is the wire drawing strain after the final intermediate annealing.

  Even if the plastic strain is 1.0 or more, if the rate of temperature rise is less than 8 ° C./second, the ferrite recrystallizes and coarsens during the temperature rise, and the retained austenite decreases and the elongation decreases. The lower limit of the temperature rate is 8 ° C./second or more, preferably 10 ° C./second, more preferably 20 ° C./second or more.

  By holding at the ferrite-austenite two-phase region temperature, carbon is concentrated in the austenite and residual austenite is easily generated. If the holding time after reaching the two-phase region temperature is less than 10 seconds, the concentration of carbon in the austenite is not sufficient and elongation decreases, so the lower limit is made 15 seconds or more, preferably 20 seconds or more. Further, if the two-phase region temperature is maintained for a long time, the ferrite grows and coarsens, and sufficient retained austenite is generated, but the elongation does not increase and as a result, the absorbed energy decreases, so the upper limit of the retention time is 120 seconds. Hereinafter, it is preferably 100 seconds or less, more preferably 90 seconds or less. This heat treatment at the two-phase region temperature results in a structure in which high carbon austenite grains are dispersed in a fine ferrite ground with low carbon.

  In the subsequent cooling process, it is necessary to cool at a cooling rate that does not cause pearlite transformation that does not contribute to the concentration of carbon in untransformed austenite as much as possible. When the cooling rate is less than 8 ° C./second, pearlite transformation occurs, the retained austenite decreases and the elongation decreases, so the lower limit of the cooling rate is 8 ° C./second or more, preferably 10 ° C./second or more, more preferably 20 ° C./second. More than a second.

  The cooling stop temperature after the heat treatment at the two-phase region temperature needs to be stopped in a temperature region where the bainite transformation occurs. By holding in this temperature range, C is discharged from bainite to retained austenite, the C concentration of retained austenite increases, and the retained austenite is stabilized.

Even at a temperature at which bainite transformation occurs, if the temperature is too high, carbide precipitates in the bainite earlier than C is discharged from the bainite to the residual austenite phase. ):
M _S (° C.) = 550−350C-40Mn-10Cu-17Ni-20Cr
-10Mo + 30Al (2)
In reference to the _{M S} transformation temperature which is calculated from the matrix average density represented, _{(M S} transformation temperature + 50 ° C.), preferably _{(M S} transformation temperature + 40 ° C.), more preferably _{(M S} transformation point Temperature + 30 ° C.). In formula (2), zero is substituted for components not included in the steel material.

In the formula (2), but M _S transformation temperature is calculated from the matrix average density, C the concentration of the residual austenite is higher than the average concentration, in M _S transformation point temperature determined by equation (2), martensite Does not generate. However, the temperature will occur martensite transformation is too low, since the elongation is lowered, the lower limit of the cooling stop temperature (M _S transformation temperature -50 ° C.), preferably (M _S transformation temperature -40 ° C.) , and more preferably _{(M S} transformation temperature -30 ° C.).

  The cooling after the heat treatment at the two-phase region temperature can be preferably performed by one or more methods selected from air cooling, forced air cooling, salt bath, and water cooling.

  The holding time at the cooling stop temperature is necessary for the concentration of C from bainite to retained austenite. If it is less than 50 seconds, the C concentration in the retained austenite does not occur sufficiently and the retained austenite is not stabilized and the elongation is lowered. Therefore, the lower limit of the holding time is set to 50 seconds or more, preferably 60 seconds or more. If the holding time exceeds 320 seconds, a sufficient amount of retained austenite cannot be ensured due to the progress of the bainite transformation, and the elongation decreases. Therefore, the upper limit of the holding time is 320 seconds or less, preferably 300 seconds or less, more preferably 240 Less than a second.

The steel wire manufactured by the above components and manufacturing method has a retained austenite amount of 8% or more and a ferrite particle size in a cross section of 9 μm or less, and the absorbed energy until breakage is 1300 J / cm ² or more. Therefore, the steel wire is preferably used for a rockfall protection net.

The steel wire manufactured according to the present invention absorbs energy of 1300 J / cm ² or more per unit area of the cross section until it breaks due to the processing-induced transformation of the retained austenite in the steel wire when the steel wire is deformed. By creating a rockfall protection net using this steel wire, it is possible to prevent large rockfalls from blocking roads and tracks.

Table 1 shows the chemical components and transformation temperatures of the prepared steels. The upper limit of the heating temperature (A _C1 transformation point temperature + A _C3 transformation point temperature) / 2 was described as “reference temperature”.

  Hot-rolled steel types 1-20 as examples and comparative examples shown in Table 1 to φ12 mm, φ7.5 mm, and φ5.5 mm under the wire drawing conditions in Table 2 (cold) dry drawing did.

The drawn steel was heat treated. Table 3 shows the heat treatment conditions. The heating temperature and the cooling stop temperature are also important heat treatment condition factors. However, since the A _C1 transformation point temperature, the A _C3 transformation point temperature, and the martensite transformation start temperature change as the components change, they are listed in Table 4.

  The steel material heated and held at a predetermined temperature was cooled to a cooling stop temperature by air cooling and forced air cooling, held for a predetermined time, and then cooled to room temperature.

  Table 4 shows various test results of steel wires manufactured under various conditions such as steel type (chemical composition), wire drawing conditions, heat treatment conditions, and cooling stop temperature. The amount of retained austenite was described as “residual γ”.

  The obtained steel wire was filled with resin and polished, and the cross section of the polished specimen was subjected to nital corrosion. A 500-fold optical micrograph was taken at the center of the cross-section subjected to the nital corrosion, and the ferrite crystal grain size of the steel wire was determined by a cutting method (JIS standard compliant: JIS G 0551). The amount of retained austenite in the steel wire was measured using an X-ray diffractometer (manufactured by Rigaku, AutoMATE M) having a collimator diameter of 1.0 mm at the center of the cross section of the test piece. Tensile strength (TS) and elongation (EL) were measured by a constant speed tension using a JIS No. 9A tensile test piece with a distance between the gauge points of 100 mm, a gap between the grips of 150 mm, and a tensile speed of 1 mm / min. Absorbed energy was obtained by using a JIS No. 9A tensile test piece and pulling and breaking at a grip portion interval of 50 mm and a tensile speed of 10 m / second, and integrating the time change of the load with the amount of movement of the crosshead.

According to the present invention, a steel wire having a ferrite crystal grain size of 9 μm or less, a retained austenite of 8% or more, and an absorption energy of 1300 J / cm ² or more was obtained.

Claims (3)

% By mass
C: 0.05 to 0.25%
Si: 0.3 to 1.0%,
Mn: 0.10 to 3.00%,
S: 0.005-0.015%,
N: 0.005 to 0.013%, and Al: 0.005% or less of chemical components,
The balance is a steel wire made of Fe and inevitable impurities,
The ferrite grain size in the steel wire cross section is 9 μm or less,
Including residual austenite of 8% or more in cross-sectional area ratio,
The absorbed energy per unit area until breakage is 1300 J / cm ² or more,
A steel wire characterized by that.   Further, by mass%, Cr: 0.05 to 2.00%, Ni: 0.05 to 2.00%, Cu: 0.05 to 1.00%, Mo: 0.05 to 1.00% The steel wire according to claim 1, wherein the steel wire contains one kind or two or more kinds. % By mass
C: 0.05 to 0.25%
Si: 0.3 to 1.0%,
Mn: 0.10 to 3.00%,
S: 0.005-0.015%,
N: 0.005 to 0.013%, and Al: 0.005% or less of chemical components,
Drawing the steel material, the balance of which is Fe and inevitable impurities, giving a plastic strain of 1.0 or more,
The steel described above drawing, heating at A _C1 transformation point temperature or higher and (A _C1 transformation point temperature + A _C3 transformation temperature) / 2 or less to the heating temperature 8 ° C. / sec or more heating rate, the heating temperature Hold for 15 to 120 seconds,
The heated steel material is expressed by the formula (2) at a cooling rate of 8 ° C./second or more:
M _S (° C.) = 550−350C-40Mn-10Cu-17Ni-20Cr
-10Mo + 30Al (2)
In reference to the _{M S} transformation temperature indicated, _{(M S} transformation temperature + 50 ° C.) or less and cooled to _{(M S} transformation temperature -50 ° C.) or higher temperatures, can be held at that temperature from 50 to 320 seconds And further cooling the cooled steel material to room temperature,
A method of manufacturing a steel wire characterized by