JP2013147705A - Ferritic stainless steel wire rod and steel wire, and method for producing them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferritic stainless steel wire that puts emphasis on economic efficiency, wherein all the necessary problems are solved to make a ferritic stainless steel wire rod and the steel wire into a product, such as a screw, while improving crevice corrosion resistance of the ferritic stainless steel wire rod and the steel wire.SOLUTION: A ferritic stainless steel wire rod contains, by mass, 0.05% or less of C, 0.01-2.0% of Si, 2.0% or less of Mn, 0.04% or less of P, 0.03% or less of S, 15.0-30.0% of Cr, and 0.025% or less of N, further one or two or more of 0.1-3.0% of Cu, 0.05-5.0% of Mo, and 0.05-5.0% of Ni, and further one or two of 0.1-0.8% of Nb and 0.05-0.5% of Ti, with the balance comprising Fe and unavoidable impurities, satisfies the following formulae (1) to (3), and has surface roughness of 15 μm or less and a drawing value of 60% or more. (1) Cr+3.3Mo≥19, (2) Ni+1.2Mo+1.8Cu≥3.0, (3) 28Ni+5Cr+24Mo+13Cu+350≥450.

Description

  The present invention relates to a ferritic stainless steel wire and a steel wire, and methods for producing them.

Conventionally, austenitic stainless steels such as SUS304 and SUSXM7 have been used for stainless steel wires and steel wires. Although these are excellent in corrosion resistance and moldability, they have a large Ni content and are expensive. From the economical point of view, ferritic stainless steel with a low Ni content is advantageous. However, ferritic stainless steel wires have a problem of low crevice corrosion resistance. In particular, even in crevice corrosion, there is a problem of flow rust in which the generated rust adheres along the flow of the liquid, and there are cases where the application is limited.
In addition, among the uses of steel wires, the following problems further existed in screw applications.
1. Low strength against torsional torque.
2. It is not easy to form the head and screw part (low cold forgeability)
3. The surface after molding is rough and lacks beauty.

Patent documents 1-5 are indicated as a prior art relevant to the above-mentioned problems 1-3. Patent Document 1 discloses an in-line heat treatment method for a ferritic stainless steel wire having a cold workability equivalent to or better than that of an off-line annealed material, but there is no recognition of the problem of surface beauty, and a means for achieving it is disclosed. It has not been. In Patent Document 2, as a method for producing a wire with less wrinkles (deep wrinkles extending in the rolling direction) that impairs the beauty of the surface, a ferrite that is subjected to heat treatment between inclined rolling and hole rolling Although a method for producing a stainless steel wire has been disclosed, wrinkle wrinkle suppression is not the subject of this case. In Patent Document 3, in order not to cause a shape defect of a cold forged product, a hot rolled material in a ferritic stainless steel wire or wire is hot-annealed at 720 to 800 ° C., and the area reduction rate is 40%. A manufacturing method for removing the anisotropy of the crystal orientation in a ferritic stainless steel wire and wire, which is characterized by performing the above wire drawing and drawing operations, has been disclosed. Drawing and drawing work is essential and takes time. In Patent Document 4, in hot rolling of ferritic stainless steel wire, the hot rolling end temperature is set to 800 to 930 ° C. by adjusting the hot rolling speed, and the ferritic stainless steel wire after hot rolling is finished. A ferritic stainless steel wire excellent in cold plastic workability and a method for producing the same are disclosed, characterized in that the grain size of the steel is a fine grain having a grain size number of 6 or more, but the hot rolling speed is adjusted. Therefore, it is not easy to control the hot rolling end temperature. In Patent Document 5, C: 0.0030 to 0.015% C, 19 to 21 in order to maintain tensile strength, crystal grain size, and corrosion resistance equivalent to those annealed in a separate process from hot rolling. % Ferritic stainless steel containing 0.1% Cr, 0.35 to 0.65% Si and 1.0 to 1.5% Mn is hot-rolled at a finishing temperature of 800 to 1000 ° C., and then the residual heat A method for producing a ferritic stainless steel hot-rolled wire rod is disclosed, which is held at 700 to 1000 ° C. for 2 to 5 minutes and then cooled and wound into a coil shape. However, no means for achieving surface aesthetics is disclosed.
As mentioned above, there is no prior art that can solve all the problems.

Japanese Examined Patent Publication No. 63-35690 Japanese Patent No. 3730762 JP 2000-336429 A JP 2002-167619 A JP 2006-57144 A

  The present invention provides a ferritic stainless steel wire that improves the crevice corrosion resistance of ferritic stainless steel wires and steel wires, solves all the problems necessary for commercialization into screws, etc., and emphasizes economy. The purpose is to do.

The present inventors have found the role of the alloy component and the alloy index of the following formulas (1) and (2), and by satisfying these, the crevice corrosion resistance of the ferritic stainless steel wire and the steel wire is remarkably increased. I found that it can be improved.
It is known that the crevice corrosion resistance of stainless steel depends on the alloy composition of the steel material. Therefore, each component steel was melted in a vacuum melting facility, formed into a plate material by hot forging, and a plate-shaped test piece was prepared by cutting and polishing. Using the test piece, a crevice corrosion test was performed by salt water spray using a multi-clevis gap forming material defined in ASTM G78 as an evaluation of crevice corrosion. According to the multi-clevis test method (ASTM G78), the occurrence of crevice corrosion (gap corrosion occurrence rate = the ratio of the number of crevice portions to the total number of crevice portions) and the progress of crevice corrosion (maximum depth of crevice corrosion portions) Can be quantitatively evaluated.
As a result of the test,
Cr + 3.3Mo ≧ 19 (1)
Regarding the progress of crevice corrosion,
Ni + 1.2Mo + 1.8Cu ≧ 3.0 (2)
It was found that the target can be achieved if the components satisfy both formulas.

In the present invention, it has further been found that a ferritic stainless steel wire suitable as a screw material can be obtained by producing in a process characterized by in-line heat treatment after hot rolling with a specific alloy component. Specifically, by obtaining the following knowledge, it was found that a ferritic stainless steel wire and steel wire suitable for screws can be obtained.
Knowledge (1): The strength against torsional torque can be remarkably improved by making the steel a component satisfying the index (Ts-cal) of the following formula (3) and controlling the heat treatment temperature.
Ts-cal. = 28Ni + 5Cr + 24Mo + 13Cu + 350 ≧ 450 (3)
Knowledge (2): By improving the manufacturing process for the wire of a specific component, it is possible to achieve the goal of ease of forming the head and the threaded portion (cold forgeability) and the beauty of the surface after forming.
That is, in the typical manufacturing process of the screw shown in FIG. 1, (1) wire rolling (hot rolling) is followed by (2) heat treatment (in-line heat treatment) without cooling to room temperature. The crystal grain size can be refined in the range of No. 5 to No. 9 in each part. Thereby, the drawing of the steel wire becomes 60% or more, and the cold forgeability is improved. Surprisingly, it has been found that the crystal grain size is adjusted by the in-line heat treatment, and the beauty of the surface can be improved.
Further, in this case, the present inventors have also found that the target can be achieved even if the processing after wire drawing (5) heat treatment and (6) skin pass wire drawing are omitted.

Specific means for solving the problems described above are as follows.

(1) By mass%, C: 0.05% or less, Si: 0.01% or more and 2.0% or less, Mn: 2.0% or less, P: 0.04% or less, S: 0.03% Hereinafter, Cr: 15.0% to 30.0%, N: 0.025% or less, Cu: 0.1% to 3.0%, Mo: 0.05% to 5. 0% or less, Ni: 0.05% or more and 1% or more of 5.0% or less, Nb: 0.1 or more and 0.8% or less, Ti: 0.05 or more and 0.5 or less % Or less, the balance consists of Fe and inevitable impurities, satisfies the following formulas (1) to (3), the surface roughness is 15 μm or less, and the aperture value is 60% or more. A ferritic stainless steel wire characterized by being.
Cr + 3.3Mo ≧ 19 (1)
Ni + 1.2Mo + 1.8Cu ≧ 3.0 (2)
28Ni + 5Cr + 24Mo + 13Cu + 350 ≧ 450 (3)
However, the element symbol in a formula means content (mass%) of the said element.

(2) By mass%, B: 0.0001 to 0.01%, Ca: 0.001 to 0.02%, Al: 0.001 to 0.5%, REM: 0.01 to 0.5 %, Mg: 0.0001 to 0.01%, V: 0.01 to 0.5%, Co: 0.01 to 0.5%, Zr: 0.01 to 0.5%, and Sn: 0 The ferritic stainless steel wire according to (1) above, containing 0.05 to 0.5%.
(3) The ferritic stainless steel wire according to (1) or (2) above, wherein the extraction residue amount of Fe is 0.1% or less by mass%.
(4) By mass%, C: 0.05% or less, Si: 0.01% or more and 2.0% or less, Mn: 2.0% or less, P: 0.04% or less, S: 0.03% Hereinafter, Cr: 15.0% to 30.0%, N: 0.025% or less, Cu: 0.1% to 3.0%, Mo: 0.05% to 5. 0% or less, Ni: 0.05% or more and 5.0% or less, or 2 or more types, Nb: 0.1% or more, 0.8% or less, Ti: 0.05% or more, 0 1 type or 2 types of 5% or less, the balance is composed of Fe and inevitable impurities, satisfies the following formulas (1) to (3), the surface roughness is 15 μm or less, and the strength is 500 N / m A ferritic stainless steel wire excellent in cold forgeability characterized by being ² or more.
Cr + 3.3Mo ≧ 19 (1)
Ni + 1.2Mo + 1.8Cu ≧ 3.0 (2)
28Ni + 5Cr + 24Mo + 13Cu + 350 ≧ 450 (3)
However, the element symbol in a formula means content (mass%) of the said element.
(5) By mass%, B: 0.0001 to 0.01%, Ca: 0.001 to 0.02%, Al: 0.001 to 0.5%, REM: 0.01 to 0.5 %, Mg: 0.0001 to 0.01%, V: 0.01 to 0.5%, Co: 0.01 to 0.5%, Zr: 0.01 to 0.5%, and Sn: 0 The ferritic stainless steel wire excellent in cold forgeability as described in said (4) containing 0.05 to 0.5% of 1 or more types.
(6) The ferritic stainless steel wire having excellent cold forgeability as described in (4) or (5) above, wherein the amount of Fe extraction residue is 0.1% or less by mass.
(7) The method for producing a ferritic stainless steel wire according to any one of (1) to (3) above, comprising an in-line heat treatment step of 900 ° C. or higher and 1100 ° C. or lower.
(8) The method for producing a ferritic stainless steel wire according to (7), wherein the cooling rate after in-line heat treatment is 5 ° C./second or more.
(9) The steel wire according to any one of (1) to (3) is drawn in a range of an area reduction of 5 to 55%, according to (4) to (6) above The manufacturing method of the ferritic stainless steel wire in any one.
(10) The method for producing a ferritic stainless steel wire according to (9) above, further comprising a step of heat-treating at 900 to 1100 ° C. after the wire drawing.
(11) The method for producing a ferritic stainless steel wire according to (10), wherein a cooling rate after the heat treatment is set to 5 ° C./second or more.

  According to the present invention, it has excellent crevice corrosion resistance, can further improve strength, cold forgeability, and surface beauty, and can be sufficiently applied to applications requiring various characteristics such as screws. Ferritic stainless steel wire and steel wire.

It is a figure which shows the typical manufacturing process processed sequentially from a wire to a screw | thread.

  Hereinafter, the present invention will be specifically described. First, the reason why the component composition of the stainless steel wire and the steel wire is limited to the above range in the present invention will be described. In the present invention,% of element content means mass% unless otherwise noted.

C: 0.05% or less C increases the strength of the ferrite structure of the matrix, and is an austenite phase and carbide forming element. The austenite phase generates a martensite structure after welding to improve the strength, and fine carbides also contribute to the improvement of strength, ensuring high-temperature strength as a steel wire. However, if it exceeds 0.05%, a Cr-deficient layer is generated around the grain boundary due to precipitation of Cr carbide. In a corrosive environment, so-called intergranular corrosion occurs because the Cr-depleted layer along the grain boundary dissolves. In addition, the ductility is deteriorated and the aperture is lowered. Therefore, the C content is limited to a range of 0.05% or less. Furthermore, in order to prevent intergranular corrosion, the C content is preferably 0.02% or less, and more preferably 0.015% or less.
Moreover, since excessive reduction causes an increase in manufacturing cost, it is preferable to set the lower limit to 0.0005%. From the viewpoint of increasing the strength, 0.001% or more is more preferable.

Si: 0.01% or more and 2.0% or less Si is an element useful for high-temperature oxidation resistance because it suppresses the progress of oxidation by forming an oxide film of SiO ₂ as a deoxidizer. When the amount exceeds 2.0%, it becomes hard and mechanical properties such as ductility deteriorate. Therefore, the Si amount is set to 2.0% or less. Further, if less than 0.01%, the deoxidation effect cannot be obtained, so 0.01% or more is contained. Preferably it is 0.1 to 1.0% of range.

Mn: 2.0% or less Mn, like C, increases the strength of the ferrite structure of the matrix, and is an austenite phase-forming element. However, if the Mn content exceeds 2.0%, inclusions remaining in the steel are present. The corrosion resistance may deteriorate due to increase. In addition, since the ductility deteriorates and the aperture is reduced, the Mn content is set to a range of 2.0% or less. Preferably it is 1.0% or less.
On the other hand, if the content is less than 0.1%, the strength of the steel wire is low, and the strength is insufficient after welding. Therefore, it is desirable to contain 0.1% or more.

P: 0.04% or less P is an element not only deteriorating mechanical properties such as ductility and toughness, but also harmful to corrosion resistance. Particularly, when P content exceeds 0.04%, its adverse effect Therefore, the P content is set to 0.04% or less.

S: 0.03% or less S combines with Mn to form MnS, which is the starting point of initial firing. S is also a harmful element that segregates at the grain boundaries and promotes embrittlement of the grain boundaries, so it is preferably reduced as much as possible. There is also an adverse effect that deteriorates ductility. In particular, when the S content exceeds 0.03%, the adverse effect becomes remarkable, so the S content is set to 0.03% or less.

Cr: 15.0% or more and 30.0% or less Cr is an important element as a corrosion resistance expression component in the present invention. The steel wire and steel wire to be used in the present invention require at least 15.0% as the Cr amount necessary for corrosion resistance. This is because when the content is less than 15.0%, it is difficult to form a strong passive film. On the other hand, if the Cr concentration exceeds 30.0%, the corrosion resistance is improved, but the amount of ferrite phase produced increases, leading to insufficient toughness and increased costs. In addition, the ductility is deteriorated and the aperture is lowered. Therefore, the Cr concentration is set to 30.0% or less. Preferably they are 15.0% or more and 25.0% or less, More preferably, they are 15.0% or more and less than 20.0%.

N: 0.025% or less N increases the strength of the ferrite structure of the matrix and further increases the strength because it is an austenite and nitride-forming element. However, the upper limit is set to 0. 0 because it deteriorates corrosion resistance and cold forgeability. 025%. Further, if it is less than 0.001%, the production of steel wire nitride is small and the effect of improving the strength cannot be obtained, so 0.001% or more is desirable.

Cu, Mo, and Ni are all elements that improve corrosion resistance, and one or more of these elements are contained in the following ranges.
Cu: 0.1% or more and 3.0% or less Cu is a useful element that improves corrosion resistance and strength. However, when the content exceeds 3.0%, not only the toughness but also the cold forgeability deteriorates. To do. Therefore, it was set to 3.0% or less. Preferably it is 2.0% or less, More preferably, it is 1.0% or less. Further, if it is less than 0.1%, it is difficult to obtain an effect of improving the corrosion resistance. Therefore, when added, the lower limit is made 0.1%. Preferably it is 0.2% or more.

Mo: 0.05% or more and 5.0% or less,
Mo increases corrosion resistance, but if it is less than 0.05%, corrosion resistance is not expressed. On the other hand, if it exceeds 5.0%, the σ phase tends to precipitate and becomes brittle, and the cold forgeability deteriorates, so the content is made 0.05 to 5.0%. Preferably, it is 0.2 to 3.0%, more preferably 0.2 to 2.5%.

Ni: 0.05% or more and 5.0% or less Ni is an effective element for improving the corrosion resistance and the strength like Cu, but when the content exceeds 5.0%, the cold forgeability deteriorates. Therefore, it was made 5.0% or less.
Further, if it is less than 0.05%, it is difficult to obtain the effect of improving the corrosion resistance and the strength, so when added, the lower limit is made 0.05%. Preferably it is 0.2% or more.

Ti and Nb are both elements that prevent intergranular corrosion, and one or two of them are contained in the following range.
Nb: 0.1% or more and 0.8% or less Solid solution Nb increases strength and forms carbonitrides, thereby suppressing the formation of Cr carbides and consequently suppressing the formation of Cr-deficient layers. It is possible to prevent field corrosion. Nb is a useful element that improves corrosion resistance, but when the content exceeds 0.8%, cold forgeability deteriorates. Therefore, it was set to 0.8% or less. Further, if it is less than 0.1%, it is difficult to obtain the effect of improving corrosion resistance, so the lower limit was made 0.1%. Preferably it is 0.3% or more.

Ti: 0.05% or more and 0.5% or less Ti forms carbides and nitrides like Nb, and thus suppresses the formation of Cr carbides, and consequently suppresses the formation of Cr-deficient layers, thus intergranular corrosion. Can be prevented.
Ti is a useful element for improving corrosion resistance, but when the content exceeds 0.50%, cold forgeability deteriorates. Therefore, it was made 0.5% or less. Moreover, since the effect of Ti cannot be expressed if it is less than 0.05%, it was made 0.05% or more.

Sn: 0.05% or more and 0.5% or less Sn is a useful element that suppresses active dissolution in an acid, and can be added as necessary. However, when the content exceeds 0.5%, the hot workability deteriorates. In addition, the ductility is deteriorated and the aperture is lowered. Therefore, it was made 0.5% or less. Moreover, since the effect of Sn cannot be expressed if it is less than 0.05%, when added, it was made 0.05% or more.

  In addition, B: 0.0001% to 0.01%, REM: 0.01% to 0.5%, Ca: 0.001% to 0.02% as hot workability improving elements I can do it. Moreover, you may add Al: 0.001% or more and 0.5% or less, and Zr: 0.01% or more and 0.5% or less as an element which improves the deoxidation effect. Further, V: 0.01% to 0.5% for improving corrosion resistance, Co: 0.01% to 0.5% for improving corrosion resistance and strength, Mg for deoxidation and refining of the structure : 0.0001% or more and 0.01% or less can be added respectively.

Next, the characteristics of the ferritic stainless steel wire of the present invention will be described. First, crevice corrosion resistance will be described. Cr + 3.3Mo in the formula (1) is an alloy index relating to the occurrence of crevice corrosion. Further, Ni + 1.2Mo + 1.8Cu in the formula (2) is an alloy index relating to the progress of crevice corrosion. These are indices found by experiments. As a result of conducting a salt spray test on crevice corrosion test pieces with multi-clevis gap forming materials of various alloy components, formula (1) is 19 or more and formula (2) is 3 It was found that flow rust due to crevice corrosion is less likely to occur when the value is greater than or equal to 0.0. The preferable ranges are 20 or more and 3.5 or more, respectively, and more preferably 21 or more and 4.0 or more.
Cr + 3.3Mo ≧ 19 (1)
Ni + 1.2Mo + 1.8Cu ≧ 3.0 (2)

Next, the strength against torsional torque will be described. According to the study by the present inventors, the strength against the torsional torque and the tensile strength are correlated, and if the tensile strength of the steel wire is 500 N / mm ² or more, the strength against the torsional torque is a sufficient value (implementation to be described later). It was found to be 3.5 N · m or more in the example. Then, when the conditions for making the tensile strength of a steel wire 500 N / mm < ² > or more were investigated, it discovered that the heat processing temperature at the time of manufacturing a steel wire and a steel wire, and a component composition influence. The component composition is found to correlate with the following index (Ts-cal), and in order to have a strength of 500 N / mm ² or more sufficient as a screw, Ts-cal. Was found to be more than 450. Ts-cal. If it is less than 450, the strength against torsional torque is insufficient. As for the heat treatment temperature, it is necessary to perform the final heat treatment at 1100 ° C. or lower. That is, in the steel wire manufacturing method described later, when heat treatment is not performed after wire drawing, an in-line heat treatment temperature when producing the steel wire material, and when heat treatment is performed after wire drawing, the temperature of the heat treatment is 1100 ° C. or lower. It is necessary to do in.
Ts-cal. = 28Ni + 5Cr + 24Mo + 13Cu + 350 ≧ 450 (3)

  Next, the reason why the surface roughness is set to 15 μm or less will be described. Surface roughness is an indicator of surface beauty. In general, the surface beauty is measured as glossiness in a steel sheet and can be quantified, but in the steel wire and the steel wire targeted by the present invention, the measurement surface has an arc shape, An accurate measurement cannot be obtained. Therefore, when steel wire samples having visually different gloss levels were compared, it was found that a surface roughness of 15 μm could be used as an index of surface beauty by using gloss criteria. A preferable range of the surface roughness is 10 μm or less. Further, the surface roughness can be reduced to 15 μm or less by controlling the diaphragm described later and controlling the manufacturing conditions described later to adjust the particle size.

  Next, the reason why the drawing of the steel wire material is limited to 60% or more will be described. When the drawing value of the steel wire is 60% or more, the workability of the steel wire after wire drawing is high and the surface roughness after forming is small, so the goals of cold forgeability and surface beauty after forming are achieved. it can. Desirably, it is 65% or more. If it is less than 60%, the workability of the steel wire after the drawing process becomes low, and the forming itself becomes difficult, for example, a large crack is generated during the forming process. The larger the aperture, the higher the workability and the more beautiful the surface after molding, so there is no upper limit for the aperture. Moreover, in order to make a diaphragm 60% or more, the above-mentioned component composition control and manufacturing conditions described later are important.

  Next, the steel wire of the present invention will be described. The steel wire of the present invention is manufactured by drawing the steel wire material described above. It can be used as a steel wire without impairing the properties as a steel wire by producing it under the conditions in the range generally used.

  Next, the manufacturing method of the steel wire material of this invention is demonstrated. The steel wire rod of the present invention can be manufactured by the process shown in FIG. That is, a wire rod rolling process, a heat treatment process, and a pickling process are included. The present invention is characterized in that the heat treatment step is performed by in-line heat treatment. That is, in the present invention, in-line heat treatment is performed at a temperature of 900 ° C. or higher and 1100 ° C. or lower after hot rolling in the wire rolling step. In the wire rolling process, since the area reduction ratio ((cross-sectional area of billet) − (cross-sectional area after hot rolling)) / (cross-sectional area of billet) is large, strain is introduced over the entire cross-section. By performing in-line heat treatment at a temperature of 900 ° C. or more and 1100 ° C. or less without cooling to room temperature following the hot rolling, the recrystallization with the strain as the nucleus is recovered before the strain introduced in the hot rolling is recovered by the residual heat. It progresses from the surface layer to the entire central part, and after the heat treatment, the microstructure of the cross section of the wire becomes a sized structure with no mixed grains, and can have a predetermined grain size (grain size number No. 5 to No. 9). Further, since the wire subjected to the predetermined in-line heat treatment has a sized structure with a small crystal grain size, the surface roughness of the wire can be small and a beautiful surface can be obtained. If the temperature is lower than 900 ° C., the recrystallization is insufficient, and the lower limit is 900 ° C. or higher, preferably higher than 950 ° C., in order to make the aperture value 60% or higher. Moreover, when it exceeds 1100 degreeC, a crystal | crystallization will become a coarse grain and a particle size number is No.2. Since it is smaller than 5, the upper limit is set to 1100 ° C. The in-line heat treatment time is desirably 2 to 10 minutes. In addition, the mixed grains referred to herein are those having a particle size number having the maximum frequency in one field of view, measured in five fields by the method defined in JIS G 0551 (2005) (steel-crystal grain size microscopic test method). It is assumed that grains having a particle size number different by 3 or more from the grains occupy an area of 20% or more, or fields having a grain size number different by 3 or more between the fields of view.

  Next, the manufacturing method of the steel wire of this invention is demonstrated. The steel wire of the present invention can be manufactured by drawing the above-described steel wire in the drawing step shown in FIG. Further, if necessary, a heat treatment step or a skin pass drawing can be introduced after the drawing step. These wire drawing conditions and heat treatment conditions may be set as appropriate within a generally used condition range. The condition range is a drawing area reduction of 5% to 55% and a heat treatment of 900 ° C. to 1100 ° C. If the treatment is performed under conditions outside this range, the properties obtained as a steel wire may be impaired.

Further, in the present invention, in the above-described production method, it is possible to further improve the drawing by suppressing the precipitation of the Lafest phase that is harmful to ductility. The amount of precipitation of the Lafes phase corresponds to the amount of Fe extraction residue of the steel wire or steel wire that can be measured by the method described later. If the amount of Fe residue is more than 0.1%, the ductility deteriorates and the drawing is reduced. Therefore, it is desirable that the amount of Fe extraction residue be 0.1% or less. More preferably, it is 0.07% or less. The smaller the surface phase, the better. The temperature can be reduced to 0% by adjusting the annealing temperature and the cooling rate.
The annealing temperature is desirably 850 ° C. or higher. In other words, if it is desired to obtain the above effect at the stage of the steel wire rod, the in-line heat treatment is necessary for the production of the steel wire rod as described above. Further, in order to obtain the above effect at the stage of steel wire, when the heat treatment step after the wire drawing step is omitted, the conditions may be the same as those of the steel wire. When the heat treatment step after the wire drawing step is performed, What is necessary is just to perform heat processing in the range of 900-1100 degreeC. The cooling rate is preferably 5 ° C./second or more. More preferably, it is 10 ° C./second or more. Accordingly, in order to obtain the above effect at the stage of the steel wire rod, the cooling rate after the in-line heat treatment may be set to 5 ° C./second or more. Further, in order to obtain the above effect at the stage of steel wire, when the heat treatment step after the wire drawing step is omitted, the conditions may be the same as those of the steel wire. When the heat treatment step after the wire drawing step is performed, The cooling rate after the heat treatment may be 5 ° C./second or more.

As shown in FIG. 1, a wire is manufactured by the process of billet (diameter 178 mm round section)-(1) wire rod rolling- (2) in-line heat treatment- (3) pickling-wire rod (diameter 5.5 mm). Steel wire is manufactured by the process of wire rod (diameter 5.5mm)-(4) wire drawing-steel wire (diameter 4mm), steel wire-(7) cold forging-(8) rolling (screw)-screw Screws were manufactured in the product process. The screw was a tapped pin truss screw with a cross hole (nominal diameter: 4 mm).
Table 1 shows the chemical components of the stainless steel wire and steel wire of the present invention and comparative steel.

結晶粒度番号は、王水にてエッチングを行い、ＪＩＳ Ｇ ０５５１（２００５)（鋼-結晶粒度の顕微鏡試験方法）で規定される方法にて測定した。
鋼線材、鋼線の引張強度及び絞りについてはＪＩＳ Ｚ ２２４１（金属材料引張試験方法）に準拠して実施した。
捩りトルクの測定については、ＪＩＳ Ｂ １０５４（１９８５)（ステンレス鋼製耐食ねじ部品の機械的性質）のねじり強さ試験に準拠して実施した。
冷間鍛造性については、各サンプルのサイズを揃えて１０個を同一ねじ形状に冷間鍛造を行い、１０個全てをねじ形状に成形できたものを合格、１０個中１個でも加工中に破損が生じ、ねじ形状に成形できなかったものを不合格とした。
表面粗さは、ＪＩＳ Ｂ ０６３３（２００１)に準拠し、基準長さ２．５ｍｍの条件にて測定した。表面の美麗さは表面粗さで評価し、評価長さ４ｍｍのＰｔ（断面曲線の最大断面高さ）が１５μｍ以下を合格とした。
表１Ｎｏ.１〜Ｎｏ.２３に、本発明の線材を示す。また、表２Ｎｏ.１〜Ｎｏ.２３に本発明の鋼線を示す。

The crystal grain size number was measured by a method prescribed in JIS G 0551 (2005) (steel-crystal grain size microscopic test method) after etching with aqua regia.
The tensile strength and drawing of the steel wire and the steel wire were performed in accordance with JIS Z 2241 (metal material tensile test method).
The torsion torque was measured according to the torsional strength test of JIS B 1054 (1985) (mechanical properties of stainless steel corrosion resistant screw parts).
For cold forgeability, 10 samples were made in the same screw shape with the same size of each sample, and all 10 pieces were passed into the screw shape. Those that were damaged and could not be formed into a screw shape were rejected.
The surface roughness was measured in accordance with JIS B 0633 (2001) under the condition of a reference length of 2.5 mm. The beauty of the surface was evaluated by surface roughness, and an evaluation length of 4 mm Pt (maximum cross-sectional height of the cross-sectional curve) was 15 μm or less.
Table 1 No. 1 to No. 23 show the wires of the present invention. Moreover, the steel wire of this invention is shown to Table 2 No.1-No.23.

Table 3 shows the area reduction ratio in wire drawing ((area of cross section before drawing−area of cross section after drawing) / area of cross section before drawing × 100 (%)) and after the drawing process of FIG. 1 (5). The steel wire when the heat treatment temperature is changed during the heat treatment is shown in Table 3 No. 44-No. 46 shows the steel wire of the present invention. All the steel wires are good in evaluating cold forgeability, surface beauty, and flow rust generation by a salt spray test.
Table 1 No. 24 to No. 43, Table 2 No. 24 to No. 43, and Table 3 No. 4 47-No. 49 shows a comparative example.
The comparative example at the time of having remove | deviated from the component range prescribed | regulated to Table 1 and Table 2 No.24-No.37 is shown.
Table 1 and Table 2 No. 38 to No. 43 include strength index, corrosion occurrence index, corrosion progress index, in-line heat treatment temperature, variation in crystal grain size (size / mixed grain), crystal grain number, and specified range of squeezing A comparative example is shown when exceeding. Among these, the wire is inferior in the evaluation of one or more of the strength, surface roughness, Fe residue amount of the wire. In steel wires, the strength, surface roughness, Fe residue amount, torsional torque, cold forgeability, and flow rust generation by salt spray tests are inferior in the evaluation or a plurality of evaluations.
Table 3 No. 47-No. 49 shows a comparative example of the steel wire when the heat treatment temperature after drawing is out of the specified range. These steel wires are inferior in any one or more evaluations of the amount of Fe residue, torsion torque, surface roughness, cold forgeability.

  As is clear from the above embodiments, the present invention not only supplies high-quality screws, but also has excellent crevice corrosion resistance even in loose gaps in overlapping portions such as wires. The present invention can be widely applied to products having equal overlapping portions. Since it is a ferritic stainless steel wire, the amount of alloy can be reduced and it is extremely useful in terms of economy.

Claims (11)

% By mass
C: 0.05% or less,
Si: 0.01% or more and 2.0% or less,
Mn: 2.0% or less,
P: 0.04% or less,
S: 0.03% or less,
Cr: 15.0% or more and 30.0% or less,
N: 0.025% or less,
Furthermore,
Cu: 0.1% or more and 3.0% or less Mo: 0.05% or more and 5.0% or less Ni: 0.05% or more and 5.0% or less
Furthermore,
Nb: 0.1% or more and 0.8% or less Ti: 0.05% or more and 0.5% or less containing one or two kinds, the balance is made of Fe and inevitable impurities,
A ferritic stainless steel wire material satisfying the following formulas (1) to (3), having a surface roughness of 15 μm or less and a drawing value of 60% or more.
Cr + 3.3Mo ≧ 19 (1)
Ni + 1.2Mo + 1.8Cu ≧ 3.0 (2)
28Ni + 5Cr + 24Mo + 13Cu + 350 ≧ 450 (3)
However, the element symbol in a formula means content (mass%) of the said element. Further, B: 0.0001 to 0.01%, Ca: 0.001 to 0.02%, Al: 0.001 to 0.5%, REM: 0.01 to 0.5%, Mg : 0.0001 to 0.01%, V: 0.01 to 0.5%, Co: 0.01 to 0.5%, Zr: 0.01 to 0.5%, and Sn: 0.05 to The ferritic stainless steel wire according to claim 1 containing 0.5% to 1 or more kinds.   The ferritic stainless steel wire according to claim 1 or 2, wherein the amount of Fe extraction residue is 0.1% or less in terms of mass%. % By mass
C: 0.05% or less,
Si: 0.01% or more and 2.0% or less,
Mn: 2.0% or less,
P: 0.04% or less,
S: 0.03% or less,
Cr: 15.0% or more and 30.0% or less,
N: 0.025% or less,
Furthermore,
Cu: 0.1% or more and 3.0% or less Mo: 0.05% or more and 5.0% or less Ni: 0.05% or more and 5.0% or less
Furthermore,
Nb: 0.1% or more and 0.8% or less Ti: 0.05% or more and 0.5% or less containing one or two kinds, the balance is made of Fe and inevitable impurities,
A ferritic stainless steel wire excellent in cold forgeability satisfying the following formulas (1) to (3), having a surface roughness of 15 μm or less and a strength of 500 N / m ² or more.
Cr + 3.3Mo ≧ 19 (1)
Ni + 1.2Mo + 1.8Cu ≧ 3.0 (2)
28Ni + 5Cr + 24Mo + 13Cu + 350 ≧ 450 (3)
However, the element symbol in a formula means content (mass%) of the said element. Further, B: 0.0001 to 0.01%, Ca: 0.001 to 0.02%, Al: 0.001 to 0.5%, REM: 0.01 to 0.5%, Mg : 0.0001 to 0.01%, V: 0.01 to 0.5%, Co: 0.01 to 0.5%, Zr: 0.01 to 0.5%, and Sn: 0.05 to The ferritic stainless steel wire excellent in cold forgeability according to claim 4 containing 0.5% to 1 or more types.   The ferritic stainless steel wire excellent in cold forgeability according to claim 4 or 5, wherein the extraction residue amount of Fe is 0.1% or less in terms of mass%.   The method for producing a ferritic stainless steel wire according to any one of claims 1 to 3, further comprising an in-line heat treatment step of 900 ° C or higher and 1100 ° C or lower.   The method for producing a ferritic stainless steel wire according to claim 7, wherein a cooling rate after in-line heat treatment is set to 5 ° C / second or more.   The steel wire rod according to any one of claims 1 to 3, wherein the steel wire rod is drawn in a range of a surface area reduction rate of 5 to 55%, according to any one of claims 4 to 6. Manufacturing method of ferritic stainless steel wire.   The method for producing a ferritic stainless steel wire according to claim 9, further comprising a step of heat-treating at 900 to 1100 ° C. after the wire drawing.   The method for producing a ferritic stainless steel wire according to claim 10, wherein a cooling rate after the heat treatment is set to 5 ° C / second or more.

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