TWI394848B - Two-phase stainless steel wire rod, steel wire, bolt and manufacturing method thereof - Google Patents

Description

Duplex stainless steel wire, steel wire and screw and manufacturing method thereof Field of invention

The present invention relates to a duplex stainless steel wire excellent in cold forgeability, and can provide, for example, a high-strength screw having corrosion resistance equivalent to SUS304.

The present invention relates to a soft duplex stainless steel wire having excellent cold workability, and is provided with a bolt, a pin, a wire mesh, a wire, a wire, a spring, etc., which are inexpensively provided with corrosion resistance equivalent to SUS304 and SUS316. A strong cold-worked member, and a soft duplex stainless steel wire excellent in cold workability of magnetization.

This application claims priority based on Japanese Patent Application No. 2007-264992, issued Oct. 10, 2007, and Japanese Patent Application No. 2007-264993, filed on Oct. 10, 2007. this.

Background of the invention

Up to now, SUS304 wire has been widely used for high-strength, high-corrosion-resistant screws having a strength of 700 N/mm ² . In recent years, in the field of cars, home appliances, and the like, the screw is required to be further increased in strength (light weight). Further, since the SUS304 screw is expensive because it contains a large amount of expensive Ni raw material, it is also strongly required to be reduced in cost.

Heretofore, the high-strength of the screw is associated with a SUS630 screw of a granulated iron-based stainless steel (for example, Patent Document 1).

However, although the SUS630 screw is excellent in strength, it has insufficient corrosion resistance and is inferior in cold forgeability, so that the manufacturing cost is greatly increased, and the use is extremely limited.

Further, there has been proposed a high-strength screw made of 麻田散铁-based stainless steel of about 13% Cr which is excellent in manufacturability and low in cost (Patent Document 2). However, corrosion resistance is not sufficient and its use is limited.

Further, a high-strength screw made of a high (C+N) amount of Vostian iron-based stainless steel has been proposed (Patent Document 3). However, due to the poor cold forging property, the manufacturing cost is greatly increased and is not accepted by the market.

On the other hand, in recent years, there has been proposed an inexpensive Ni-based duplex stainless steel which is used for high-priced Ni (Patent Documents 4 to 6).

However, the conventional duplex stainless steel has poor cold forgeability and high manufacturing cost, and the duplex stainless steel screw is no longer present in the market.

As described above, in the stainless steel wire for stainless steel screws and screws, there are no products having high corrosion resistance, high strength, high cold forgeability, and low cost.

For products such as bolts, pins, wire mesh, and metal wires that require corrosion resistance, use Worstian iron-based stainless steel wire materials such as SUS304 and SUSXM7, and manufacture by forced cold processing such as drawing or cold forging or bending. . In the cold working of the wire, unlike the pressability of the steel sheet which requires high tensile properties of the material, soft and high tensile fracture elongation characteristics are required (high ductility characteristics are not required). The so-called soft, tensile strength wire of the system and requires 700N / mm ² or less, is suitably 650N / mm ² or less.

However, the Worthfield iron-based stainless steel product adds a high price of Ni, so there are still disadvantages of high product prices despite the low-cost process.

In addition, the Inversity Iron-based stainless steel is non-magnetic, and it is not able to be attached to the tool during the locking operation of the fastener, resulting in poor workability, and the wire mesh, the screen (especially the conveyor belt for food, etc.) are mixed into the food due to the material falling off. In the case of the inside, there is an inconvenience caused by the non-magnetic property due to the inability to detect the incorporation by the magnetic sensor.

Regarding a product requiring magnetic properties and corrosion resistance, a ferrite-based iron-based stainless steel wire made of a ferrite-grained stainless steel wire material and having a low C and N and added with Nb has been proposed (Patent Documents 7 to 9).

However, not only the corrosion resistance of the cold-worked product is insufficient, but also the surface flaw is generated when the high-Cr line material is rolled, and the manufacturing cost is increased.

On the other hand, in recent years, a duplex stainless steel having a low cost of Ni has been proposed (Patent Documents 10 to 12).

Patent Document 10 describes a high-strength duplex stainless steel having a low Ni-based and excellent Young's modulus of 0.04% or more of nitrogen having improved strength. However, in order to increase the strength, Si is added in an amount of more than 1%, nitrogen is added in an amount of 0.04% or more, and in the examples, high-strength steel exceeding 80 kg/mm ² is described, and there is no consideration of soft and high tensile fracture and elongation characteristics. The cold workability of the wire is not good.

Patent Document 11 describes a duplex stainless steel having a low Ni-based and containing 0.05% or more of nitrogen corrosion resistance and good weldability. However, there is no description about cold workability, and the ideal range of nitrogen for improving strength is 0.06% to 0.12%. In the examples, steel containing less than 0.13% of nitrogen (low Si steel) is described, and there is no so-called soft and high-strength. Considering the tensile and elongation characteristics, the cold workability of the wire is actually poor.

Patent Document 12 describes a high-strength duplex stainless steel which is low in Ni and contains 0.05% or more of nitrogen and has excellent relaxation properties. However, in the examples, steel containing 0.13% or more of nitrogen having high strength is described, and there is no consideration of soft and high tensile fracture elongation characteristics. Actually, the cold workability of the wire is not good.

Patent Document 13 describes a duplex stainless steel which is low in Ni and contains 0.05% or more of nitrogen and is excellent in ductility and deep extensibility. However, in the examples, it is described that steel having a strength-enhancing nitrogen content of 0.08% or more which is improved in stretching and improving the deep extensibility of the steel sheet has no consideration of soft and high tensile fracture elongation characteristics, and in fact, the cold workability of the wire is not good.

In the above-mentioned stainless steel, there has been no disclosure of softness and high elongation at break which are required for cold workability of a wire rod, and it is low in cost and exhibits high corrosion resistance and magnetization.

[Patent Document 1] Japanese Patent Laid-Open Publication No. Hei 9-314276

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2005-179718

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2006-274295

[Patent Document 4] International Patent Publication No. WO2005/073422

Patent Document 5: Japanese Patent No. 3271262

[Patent Document 6] Specification of EP0337846

[Patent Document 7] Japanese Patent No. 2906445

[Patent Document 8] Japanese Patent No. 2817266

[Patent Document 9] Japanese Patent Laid-Open Publication No. 2006-16665

[Patent Document 10] Japanese Patent Laid-Open Publication No. 62-47461

[Patent Document 11] Japanese Patent Laid-Open Publication No. 61-56267

[Patent Document 12] Japanese Patent Laid-Open Publication No. 2-350940

[Patent Document 13] Japanese Patent Laid-Open Publication No. 2006-169622

The object of the present invention is to provide a low-strength, high-strength, high-corrosion-resistant screw for Worthite iron, fat-grained iron-based dual-phase steel wire, steel wire and screw, and a manufacturing method thereof, and by controlling the low price The structure, composition and material of the corrosion-resistant duplex stainless steel wire give high strength to cold forging and screw products.

An object of the present invention is to provide a duplex stainless steel wire which is excellent in cold workability and corrosion resistance and which is magnetically affordable, and can greatly reduce the manufacturing cost of a cold-processed product of a conventional Worthfield iron-based stainless steel wire and impart magnetization. .

In order to solve the above problems, the inventors of the present invention found that high-corrosion-resistant duplex stainless steel is used to reduce the high-priced Ni content, and the composition is stabilized (low M value) by the composition adjustment. The volume fraction of the phase is controlled to be high, and the tensile strength of the wire and the steel wire is optimized by heat treatment and drawing, and the cold forgeability and the high strength of the screw product can be coexisted at a low price.

Further, the inventors of the present invention found that based on the high corrosion-resistant duplex stainless steel having a magnetic ferrite phase iron phase and a Worthfield iron phase, the Ni is reduced in price and the structure is controlled by composition adjustment (M value control). The work hardening is suppressed by low (C+N), whereby the cold workability which is remarkably improved can be imparted by the low-corrosion, high-corrosion-resistant duplex stainless steel wire.

The present invention has been completed based on the above findings, and the gist thereof is as follows.

That is, the first aspect of the present invention is a Worthite iron, fat iron-based dual-phase steel wire, which is contained in mass%:

C: 0.005% to 0.05%;

Si: 0.1% to 1.0%;

Mn: 0.1% to 10.0%;

Ni: 1.0% to 6.0%;

Cr: 19.0% to 30.0%;

Cu: 0.05% to 3.0%; and

N: 0.005% to 0.20%;

Further, the residual portion is composed of Fe and substantially unavoidable impurities, and C+N is 0.20% or less, the M value of the formula (a) is 60 or less, and the F value of the formula (b) is 45 to 85, and tensile strength is obtained. 550N/mm ² ~ 750N/mm ² ;

M=551-462(C+N)-9.2Si-8.1Mn-29(Ni+Cu)-13.7Cr-18.5Mo (a)

F = 5.6Cr-7.1Ni + 2.4Mo + 15Si - 3.1Mn - 300C - 134N - 26.6 ... (b).

In the second aspect of the present invention, it is also possible to add Mo: 1.0% or less in mass% in the first aspect.

In the third aspect of the present invention, it is also possible to add B: 0.01% or less in mass% in the first aspect.

In the fourth aspect of the present invention, at least one of Al: 0.1% or less, Mg: 0.01% or less, and Ca: 0.01% or less may be added in the first aspect.

According to a fifth aspect of the present invention, the first aspect may include one or more of Nb: 1.0% or less, Ti: 0.5% or less, V: 1.0% or less, and Zr: 1.0% or less in mass%. .

A sixth aspect of the present invention is a Worstian iron, fat iron-based dual-phase steel wire, which is composed of any one of the first to fifth aspects described above, and has a tensile strength of 700 N/mm ^{2 .} ~1000N/mm ^{2 of} them.

The seventh aspect of the present invention is a high-strength, high-corrosion-resistant screw which is composed of any of the first to fifth aspects described above and has a tensile strength of 700 N/mm ² to 1200 N/mm ² . .

The eighth aspect of the present invention is a method for manufacturing a high-strength, high-corrosion-resistant screw, which is composed of any of the first to fifth aspects described above, and has a tensile strength of 700 N/mm ² to 1000 N. /mm ² of the Worthfield iron and fat iron-based duplex steel wire, which is subjected to aging heat treatment at 300 ° C to 600 ° C for 1 minute to 100 minutes after cold screw forming.

The ninth aspect of the present invention is a magnetized soft duplex stainless steel wire which is contained in mass%:

C: 0.005% to 0.05%;

Si: 0.1% to 1.0%;

Mn: 0.1% to 10.0%;

Ni: 1.6% to 6.0%;

Cr: 19.0% to 30.0%;

Cu: 0.05% to 3.0%; and

N: 0.005% or more and less than 0.06%;

Further, the residue is composed of Fe and substantially unavoidable impurities, and C+N is 0.09% or less, the M value of the formula (a) is 60 or less, the tensile strength is 700 N/mm ² or less, and the tensile fracture extension is More than 70%;

M = 551-462 (C + N) - 9.2 Si - 8.1 Mn-29 (Ni + Cu) -13.7 Cr - 18.5 Mo (a).

In the tenth aspect of the present invention, it is also possible to add Mo: 3.0% or less in mass% in the ninth aspect.

In the eleventh aspect of the present invention, it is also possible to add B: 0.01% or less in mass% in the ninth aspect.

In the twelfth aspect of the present invention, one or more of Al: 0.1% or less, Mg: 0.01% or less, and Ca: 0.01% or less may be added in the ninth aspect.

The thirteenth aspect of the present invention may be added to the ninth aspect in which one or more of Nb: 1.0% or less, Ti: 0.5% or less, V: 1.0% or less, and Zr: 1.0% or less in mass%. .

The duplex stainless steel wire for high-strength and high-corrosion-resistant screws excellent in cold forgeability of the present invention not only contains high-priced Ni but ensures excellent cold forgeability, and can impart high corrosion resistance and high equivalent to SUS304 or higher. Strength, but can provide high-strength, high-corrosion-resistant screws at low cost.

The soft duplex stainless steel wire having excellent cold workability of the present invention is excellent in cold workability and magnetizability, and is equivalent to corrosion resistance of Worthite iron-based stainless steel such as SUS304 or SUS316. Therefore, it is possible to provide an excellent effect of providing a highly corrosion-resistant product having magnetization at a low price.

Simple illustration

Figure 1 is a graph showing the relationship between the F value and the volume fraction of the ferrite phase of the wire product.

Fig. 2 is a graph showing the relationship between the processing ratio (%) of the steel wire (15% drawn wire) corresponding to the F value and the compressive deformation stress (N/mm ² ).

The best form for implementing the invention

The reasons for limitation regarding the first to eighth aspects of the present invention are explained.

In order to ensure the strength of the screw product, it contains C 0.005% or more. However, when the content exceeds 0.05%, Cr carbonitride is formed, and not only corrosion resistance is deteriorated, but also cold forgeability is deteriorated, so it is limited to 0.05% or less. It should be 0.03% or less.

In order to ensure the strength of the screw product by solid solution hardening and age hardening, N 0.005% or more is contained. However, if it contains more than 0.20%, cold forgeability will be remarkably deteriorated. Therefore, the upper limit is made 0.20%. A preferred range is less than 0.05%.

For the reason of the above-mentioned cold forgeability, C+N is limited to 0.20% or less. It should be 0.10% or less.

In order to deoxidize, Si is contained in an amount of 0.1% or more. However, if it contains more than 1.0%, cold forgeability will deteriorate. Therefore, the upper limit is 1.0%. A preferred range is from 0.2% to 0.6%.

For the deoxidation and adjustment to obtain a stable Wolster iron structure, it contains Mn 0.1% or more. However, when the content exceeds 10.0%, the rust resistance and the ferrite iron volume fraction are decreased, the tensile strength is increased, and the cold forgeability is deteriorated. Therefore, the upper limit is limited to 10.0%. A preferred range is from 0.5% to 5.0%.

In order to stabilize the Worth Iron Organization and ensure cold forgeability, Ni is contained at least 1.0%. However, if the longitudinal or contains more than 6.0%, the effect is saturated, and conversely, the volume fraction of the ferrite-grained iron phase becomes 45% or less, not only the cold forgeability (tool life) is deteriorated, but also the economy is poor due to the high price of the Ni system. . Therefore the upper limit is limited to 6.0%. A preferred range is more than 3.0% of 5.0% or less.

In order to ensure corrosion resistance and increase the volume fraction of the ferrite grain iron phase, the Worstian iron structure is stabilized and the cold forgeability is ensured, and the Cr content is 19.0% or more. However, if the longitudinal or contains more than 30.0%, the effect is saturated, and conversely, the volume fraction of the ferrite iron phase will exceed 85%, so the strength of the screw product is lowered. Therefore, the upper limit is limited to 30.0%. A preferred range is 22.0% to 26.0%.

Cu is effective in stabilizing the Worthite iron structure, suppressing work hardening and improving cold forgeability, and in the aging treatment after cold forging, promoting age hardening of the ferrite grain iron phase and increasing the strength of the screw product. . Therefore, it contains 0.05% or more. However, when the content exceeds 3.0%, the solid solution limit of Cu is exceeded and the thermal manufacturability of the material is remarkably deteriorated, so the upper limit is made 3.0%. A preferred range is 0.2% or more and less than 1.0%.

The M value of the following formula (a) is helpful for the stability of the iron phase of the Vostian. It is described in Iron and Steel, 63 (1977), page 772. Once the M value is increased, the system will produce a hard Processing induced the iron phase of the field. For the cold forging of duplex stainless steel, if the M value exceeds 60, the cold forging will produce a hard process to induce the iron phase of the granules, and the cold forgeability will be significantly deteriorated (the tool life is inferior, resulting in cold forging rupture). Therefore, the M value is limited to 60 or less. A preferred range is 40 or less.

M=551-462(C+N)-9.2Si-8.1Mn-29(Ni+Cu)-13.7Cr-18.5Mo (a)

The F value of the following formula (b) is helpful for the volume fraction of the ferrite grain iron phase. It is an index described in Japanese Patent Laid-Open No. 7-74416, and once the F value is increased, the ferrite grain iron phase will increase. . Figure 1 is a plot of the F value and the volume fraction of the ferrite phase of the duplex stainless steel wire product. When the F value is 45 or more, the volume fraction of the ferrite grain iron phase becomes 45 vol.% or more, indicating high endurance and low work hardening characteristics (Fig. 2), and the strength of the product (tensile strength of the screw shaft portion) can be obtained. The strength is increased to 700 N/mm ² to 1200 N/mm ² , and the cold forgeability of the head can be ensured. Therefore, the F value is limited to 45 or more. As shown by the relationship between the machining rate (%) and the compressive deformation stress (N/mm ² ) corresponding to the F value in Fig. ² , when the F value is less than 45, the work hardening becomes large, and the cold forgeability (forging fracture, tool damage) Increase and deteriorate. On the other hand, if the F value exceeds 85, the soft ferrite iron phase will exceed 85%, and the strength of the Wostian iron phase will decrease, so the strength of the screw product will decrease. Therefore, the upper limit is 85. A preferred range is from 50 to 80.

F=5.6Cr-7.1Ni+2.4Mo+15Si-3.1Mn-300C-134N-26.6 ...(b)

The tensile strength of the wire is greatly beneficial to the cold forging system. When the tensile strength of the wire is less than 550 N/mm ² , the strength of the cold forged part such as a screw is low, and the value as a high-strength product is low. Therefore, the lower limit is limited to 550 N/mm ² . On the other hand, when the tensile strength of the wire exceeds 750 N/mm ² , the cold forgeability is remarkably deteriorated (tool life is deteriorated, and cold forging fracture occurs). Therefore, the upper limit is made 750 N/mm ² . A preferred range is from 600 N/mm ² to 700 N/mm ² .

Mo is an element effective for improving corrosion resistance, and it is possible to stably obtain an effect by adding 0.1% or more. However, when the content exceeds 1.0%, not only the cost of the material increases, but also the material hardens and the cold forgeability deteriorates. Therefore, the upper limit is limited to 1.0%. A preferred range is 0.2% or more and less than 0.5%.

The B system is an element effective for improving hot workability, and the addition of 0.001% or more can stably obtain the effect. However, when it contains more than 0.01%, boride is also produced, and corrosion resistance and cold forgeability are deteriorated. Therefore, the upper limit is limited to 0.01%. A preferred range is from 0.002% to 0.006%.

Since Al, Mg, and Ca are effective for the deoxidation system, it is possible to stably obtain the effect by adding Al: 0.005% or more, Mg: 0.001% or more, and Ca: 0.001% or more. However, when each contains more than 0.1% of Al, Mg: 0.01%, and Ca: 0.01%, the effect is also saturated, and conversely, a rough oxide (intermediate) is generated, and cold forge fracture occurs. Therefore, the upper limit is made Al: 0.1%, Mg: 0.01%, and Ca: 0.01%. A preferred range includes Al: 0.1% to 0.06%, Mg: 0.002% to 0.005%, and Ca: 0.002% to 0.005%.

Nb, Ti, V, and Zr are effective for suppressing the formation of Cr carbonitride and ensuring corrosion resistance, and adding Nb: 0.05% or more, Ti: 0.02% or more, V: 0.05%, and Zr: 0.05% or more. One type or more is stable in efficacy. However, when the content exceeds Nb: 1.0%, Ti: 0.5%, V: 1.0%, and Zr: 1.0%, the effect is also saturated, and conversely, coarse precipitates are generated, and cold forge fracture occurs. Therefore, the upper limit of each element is specified. A preferred range is one or more of Nb: 0.1% to 0.6%, Ti: 0.05% to 0.5%, V: 0.1% to 0.6%, and Zr: 0.1% to 0.6%.

Usually, as an unavoidable impurity, the steel system contains oxygen in the process, and in the aspect of the invention, it is preferably 0.01% or less of oxygen as an unavoidable impurity.

The wire is drawn by wire drawing to form a drawn steel wire, and the tensile strength of the steel wire is helpful for the cold forging property and the strength of the screw product. When the tensile strength of the steel wire is less than 700 N/mm ² , the screw product is The strength is lowered, and the value as a high-strength product is lowered. Therefore, the lower limit is limited to 700 N/mm ² . On the other hand, if the tensile strength of the steel wire exceeds 1000 N/mm ² , the cold forgeability is remarkably deteriorated (tool life is deteriorated, and cold forging fracture occurs). Therefore, the upper limit is made 1000N/mm ² . A preferred range is 750 N/mm ² to 900 N/mm ² .

The tensile strength of the high-strength screw of the present invention is increased in strength when subjected to wire drawing processing and aging heat treatment after cold forging. At this time, if the tensile strength of the screw product is less than 700 N/mm ² , the value as a high-strength screw product is low. On the other hand, if the tensile strength of the screw product is 1200 N/mm ² or more, the cold forging cost is remarkably deteriorated due to cold forging cracking or tool damage or the like. Therefore, the upper limit of the tensile strength of the screw product is 1200 N/mm ² . A preferred range in which economic effects can be exhibited is 800 N/mm ² to 1000 N/mm ² .

After the steel wire of the present invention is formed into a screw by cold forging, in order to effectively increase the tensile strength of the screw product, it is effective to perform a heat aging treatment at 300 ° C or higher for one minute or longer. On the other hand, if it exceeds 600 ° C, it will age and the tensile strength of the screw product will decrease. Therefore, the upper limit is 600 °C. A preferred temperature range is from 400 ° C to 550 ° C. Further, if the holding time exceeds 100 minutes, not only the effect of age hardening is saturated, but also the tensile strength of the screw product is lowered due to overaging. Therefore, the upper limit of the holding time is 100 minutes. A preferred retention time range is from 5 minutes to 60 minutes.

The reasons for limitation regarding the ninth to thirteenth aspects of the present invention are explained.

To ensure the strength of the steel, the C system is added in an amount of 0.005% or more. However, when the addition exceeds 0.05%, not only the cold workability is deteriorated, but also Cr carbide is produced and the corrosion resistance is also deteriorated. Therefore, the upper limit is made 0.05% or less. A preferred range is from 0.01% to 0.03%.

In order to ensure the strength of the cold-worked part by solid solution hardening, the N system is added in an amount of 0.005% or more. However, when it exceeds 0.06% or more, the tensile strength will increase and the cold workability will deteriorate. Therefore, the upper limit is made less than 0.06%. The general duplex stainless steel is used to reduce the use of high-priced alloying elements, and is added with more than 0.06% of N. However, the aspect of the steel is controlled by the balance of the structure and composition, and the N content is suppressed to a lower level. It is soft and features a significant increase in the cold workability of the wire. A preferred range is 0.02% or more and less than 0.05%.

For the reason of the above cold workability, the C+N system is limited to 0.09% or less. Preferably, it is 0.07% or less.

In order to deoxidize, the Si system is added in an amount of 0.1% or more. However, if it is added more than 1.0%, it will be hardened and the cold workability will deteriorate. Therefore, the upper limit is made 1.0%. A preferred range is from 0.2% to 0.6%.

For deoxidation and as a two-phase structure for obtaining ferrite iron + Worthite iron, and further adjusting the stability of the Worthite iron structure, the Mn system is added by 0.1% or more. However, when the addition exceeds 10.0%, the cold workability deteriorates due to an increase in corrosion resistance and strength. Therefore, the upper limit is limited to 10.0% or more. A preferred range is from 0.5% to 5.0%.

In order to lower the M value and obtain the dual phase structure of the ferrite iron + Worthite iron, the Worstian iron structure is stabilized and the cold workability is ensured, and the Ni system is added 1.6%. However, even if it is added more than 6.0%, not only is the effect saturated, but the price of Ni is high and the economy is inferior. Therefore, the upper limit is limited to 6.0%. A preferred range is from 2.0% to 5.0%.

In order to ensure corrosion resistance and obtain a two-phase structure of ferrite iron + Worthite iron, and further stabilize the Worth iron structure and ensure cold workability, the Cr system is added by 19.0% or more. However, even if it is added more than 30.0%, not only the effect is saturated, but the cold workability is rather deteriorated. Therefore, the upper limit is limited to 30.0%. A preferred range is from 20.0% to 26.0%.

In order to reduce the M value and obtain the dual phase structure of the ferrite iron + Worthite iron, and further stabilize the Worth iron structure, inhibit work hardening and improve cold workability, it contains 0.05% or more of Cu. However, if it is more than 3.0%, the solid solution limit of Cu is exceeded and the thermal manufacturability of the material is remarkably deteriorated, so the upper limit is made 3.0%. A preferred range is less than 1.0%.

The M value of the following formula (a) is helpful for the stability of the iron phase of the Vostian. It is described in Iron and Steel, 63 (1977), page 772. Once the M value is increased, it will produce a hard Processing induced the iron phase of the field. In the case of cold forging of duplex stainless steel, if the M value exceeds 60, a hard process is formed during cold working to induce a loose iron phase in the field, and the cold workability is remarkably deteriorated. Therefore, the M value is limited to 60 or less. A preferred range is 40 or less.

M=551-462(C+N)-9.2Si-8.1Mn-29(Ni+Cu)-13.7Cr-18.5Mo (a)

The tensile strength of the wire is greatly beneficial to the cold workability of the wire, and if the tensile strength of the wire exceeds 700 N/mm ² , the cold workability is remarkably deteriorated. Therefore, the upper limit is limited to 700 N/mm ² . On the other hand, when the tensile strength of the wire is less than 500 N/mm ² , the strength of the cold-worked product is too low, and the value as a product is lowered. Therefore, the lower limit should be 500 N/mm ² . A preferred range is from 500 N/mm ² to 650 N/mm ² .

The tensile fracture extension of the wire rod is greatly beneficial to the cold workability of the wire rod, and when the tensile fracture elongation of the wire rod is less than 70%, the cold workability such as cold drawing processing and cold forgeability is deteriorated. Therefore, it is limited to 70% or more. A preferred range is 75% or more.

The magnetization is a function that is not required for the Worthfield iron-based stainless steel, and the magnetization is industrially characterized by the following functions, that is, the workability of the magnetic tool can be improved by the magnetization of the magnetic tool when the fastener is locked. When a wire mesh or a screen (especially a conveyor belt for food, etc.) is mixed with food due to falling off of a material, a magnetic sensor can be used to prevent mixing. Therefore, the present invention limits magnetization. Preferably, the relative magnetic permeability is 3.0 or more.

Mo is an element effective for improving corrosion resistance, and can be stably obtained by adding 0.1% or more. However, when the addition exceeds 3%, not only the material is hardened, but the σ phase is precipitated and the cold workability is remarkably deteriorated. Therefore, the upper limit is limited to 3%. A preferred range is from 0.3% to 1.0%.

The B system is an element effective for improving hot workability, and the effect can be stably obtained by adding 0.001% or more. However, when added more than 0.01%, boride is also generated, and corrosion resistance and cold workability are deteriorated. Therefore, the upper limit is limited to 0.01%. A preferred range is from 0.002% to 0.006%.

Since Al, Mg, and Ca are effective for the deoxidation system, the effect can be stably obtained by adding Al: 0.005% or more, Mg: 0.001% or more, and Ca: 0.001% or more. However, when the content exceeds Al: 0.1%, Mg: 0.01%, and Ca: 0.01%, the effect is also saturated, and conversely, a rough oxide (intermediate) is generated, and cold workability is deteriorated. Therefore, the upper limit is made Al: 0.1%, Mg: 0.01%, and Ca: 0.01%. A preferred range includes Al: 0.008% to 0.06%, Mg: 0.001% to 0.005%, and Ca: 0.001% to 0.005%.

Nb, Ti, V, and Zr are effective for suppressing the formation of Cr carbonitride and ensuring corrosion resistance, and adding Nb: 0.01% or more, Ti: 0.01% or more, V: 0.01% or more, and Zr: 0.01% or more. More than one type, the effect can be stably obtained. However, when the content exceeds Nb: 1.0%, Ti: 0.5%, V: 1.0%, and Zr: 1.0%, the effect is also saturated, and conversely, coarse precipitates are generated, and cold workability is deteriorated. Therefore, the upper limit of each element is specified. A preferred range is one or more of Nb: 0.05% to 0.6%, Ti: 0.05% to 0.5%, V: 0.1% to 0.6%, and Zr: 0.05% to 0.6%.

Usually, as an unavoidable impurity, the steel system contains oxygen in the process, and in the aspect of the invention, it is preferably 0.01% or less of oxygen as an unavoidable impurity.

[Example 1]

The following describes the first embodiment of the present invention.

The chemical compositions of the steel of Example 1 are shown in Tables 1 to 4.

The steel of the chemical composition is melted in a vacuum melting furnace of 300 kg, cast into a cast piece of ψ180 mm, and hot-rolled the slab by ψ5.5 mm to ψ6.5 mm, and the hot rolling is finished at 1050 ° C. Then, it was kept in a continuous heat treatment at 1050 ° C for five minutes and subjected to water-cooling dissolution treatment, after which it was pickled and made into a wire product. Thereafter, an oxalic acid film treatment was carried out, and the wire was processed by a cold drawing to ψ 5.2 mm to prepare a steel wire for cold forging.

Thereafter, about 5,000 pieces of hexagonal screws were processed by cold forging and rolling. Further, some of them are subjected to an aging treatment at 300 ° C to 650 ° C for 3 minutes to 200 minutes. Thereafter, the hexagonal screw product is made of all the screws by barrel polishing and washing.

The evaluation was carried out on the tensile strength of the steel wire, the volume fraction of the iron phase of the steel wire, the cold forgeability (with or without cracking, the presence or absence of tool damage), the tensile strength and corrosion resistance of the screw product. The evaluation results are shown in Tables 5 to 8.

The mechanical properties were evaluated by tensile strength and fracture elongation in a tensile test of JIS Z 2241. The full scope of the wire-based embodiment of the present invention to ^{650N / mm 2 ~ 1000N / mm} 2 , the screw-based embodiment of the present invention is the article on all 700N / mm ² ~ 1200N / mm ² range, the excellent performance of a high strength.

The volume fraction of the iron phase of the steel wire is the longitudinal section of the mirror-polished steel wire, and the ferrite phase is colored by the Murakami reagent, and the volume fraction is obtained by calculating the area ratio by image analysis. The iron fraction of the steel wire system of the present invention is in the range of 45 vol.% to 85 vol.%.

Cold forging is performed by 5,000 forgings on a hexagonal head by a three-stage upsetting machine, and is evaluated for the presence or absence of forging fracture and tool damage. The tool life was evaluated as ○ when no tool damage occurred, and the tool life was evaluated as ㄨ when tool damage occurred. The wire of the example of the present invention did not undergo cold cracking, and the tool life was ○, and the cold forgeability was excellent.

The corrosion resistance of the screw product was evaluated by a salt spray test in accordance with JIS Z 2371, and a spray test was performed for every ten screws for 100 hours, and whether it was rusted or not. In the case of no rust and only a slight degree of rust, the corrosion resistance was evaluated as ○, and when there was spill rust and the entire surface was rusted, the corrosion resistance was evaluated as ㄨ. The corrosion resistance of the screw product of the example of the present invention was all ○.

On the other hand, Comparative Examples No. 38 to No. 61 are inferior to the range of the present invention, and the cold forgeability, the strength of the screw product, the corrosion resistance, and the like are inferior, and the advantages of the present invention are clearly apparent.

[Example 2]

Embodiment 2 of the present invention will be described below.

The chemical composition (% by mass) of the steel (test material) used in Example 2 is shown in Tables 9 and 10.

The steel of the chemical composition is melt-cast into a 180 mm cast piece in a 150 kg vacuum melting furnace, and the cast piece is hot rolled by ψ5.5 mm, and the hot rolling is finished at 1050 ° C, and directly at 1050 The temperature was maintained at ° C for five minutes, and a continuous heat treatment of water cooling was performed, followed by pickling to form a wire. Thereafter, the cold-stretching processing was performed to 2.0 mm in a general process, and the steel wire was bent into a mesh-shaped wire mesh for a conveyor belt, thereby performing cold working.

The evaluation evaluated the tensile strength, tensile fracture elongation, cold workability, corrosion resistance, and magnetizability of the wire. The evaluation results are shown in Tables 11 and 12.

The tensile strength and tensile elongation of the wire were evaluated by tensile strength and fracture elongation in a tensile test of JIS Z 2241. Wire-based embodiment of the present invention, all of the tensile strength of ^{500N / mm 2 ~ 700N / mm} 2, breaking extension of ≧ 70% range.

The cold workability was evaluated by cold drawing processing and subsequent wire mesh workability. The cold formability in the case where the wire was not broken or broken and formed into a wire mesh was evaluated as ○, and when it was not formed into a wire mesh due to breakage or breakage, it was evaluated as ㄨ. The wire of the example of the present invention is free from breakage and breakage, and is excellent in cold workability.

Corrosion resistance After grinding the surface of the pickled wire with #500, a 100-hour spray test was carried out in accordance with the salt spray test of JIS Z 2371 to evaluate whether or not there was rust. In the case of no rust and only a slight degree of rust, the corrosion resistance was evaluated as ○, and when there was spill rust and the entire surface was rusted, the corrosion resistance was evaluated as ㄨ. The evaluation of the corrosion resistance of the steel of the present invention was all ○.

The magnetization is attached to a wire mesh and the relative magnetic permeability is measured by a ferrite meter (simple magnetic permeability meter). When the relative magnetic permeability was 3.0 or more in which the magnetization was clearly confirmed, it was evaluated as having magnetization, and when it was less than 3.0, it was evaluated as non-magnetizability.

On the other hand, Comparative Examples No. 86 to No. 107 are inferior in cold workability, corrosion resistance, cost, and magnetizability, and the advantages of the present invention are apparent.

Industry availability

As can be seen from the above examples, the high corrosion-resistant duplex stainless steel wire of the present invention which does not contain high-priced Ni has excellent cold forgeability, and can provide high strength of the screw product, and provides high strength and high cost at low cost. Corrosion-resistant screws, and thus nuts, are also suitable and are extremely useful in the industry.

According to the above embodiments, it is possible to produce a soft and magnetically priced, inexpensive duplex stainless steel wire, which provides remarkably excellent cold workability, and can be given a Worstian iron-based stainless steel such as SUS304 or SUS316. It is corrosion-resistant and can provide low-corrosion, high-corrosion-resistant cold-worked products such as screws, pins, wire mesh, metal wires, ropes, springs, etc., which are extremely useful in the industry.

Figure 1 is a graph showing the relationship between the F value and the volume fraction of the ferrite phase of the wire product.

Fig. 2 is a graph showing the relationship between the processing ratio (%) of the steel wire (15% drawn wire) corresponding to the F value and the compressive deformation stress (N/mm ² ).

Claims (14)

A Worstian iron and a ferrite iron-based dual-phase steel wire for high-strength, high-corrosion-resistant screws excellent in cold forgeability, which are contained in mass%: C: 0.005% to 0.05%; Si: 0.1% to 1.0% Mn: 0.1% to 10.0%; Ni: 1.0% to 6.0%; Cr: 19.0% to 30.0%; Cu: 0.05% to 3.0%; and N: 0.005% to 0.20%; and the residue is Fe and substantially The inevitable impurity is composed, and C+N is 0.20% or less, the M value of the formula (a) is 60 or less, the F value of the formula (b) is 45 to 85, and the tensile strength is 550 N/mm ² to 750 N/ Mm ² ;M=551-462(C+N)-9.2Si-8.1Mn-29(Ni+Cu)-13.7Cr-18.5Mo (a)F=5.6Cr-7.1Ni+2.4Mo+15Si -3.1Mn-300C-134N-26.6 (b). For example, the Worthite iron and the ferrite-grained iron-phase duplex steel wire for high-strength and high-corrosion-resistant screws excellent in cold forgeability according to the first aspect of the patent application include Mo: 1.0% or less in mass%. For example, the Worthite iron and the ferrite-grained iron-phase duplex steel wire for high-strength and high-corrosion-resistant screws excellent in cold forgeability according to the second paragraph of the patent application are contained in a mass% of B: 0.01% or less. For example, in the high-strength and high-corrosion-resistant high-strength, high-corrosion-resistant screw, the Worthite iron and the ferrite-grained dual-phase steel wire, which are excellent in cold forgeability according to any one of claims 1 to 3, which are contained in mass%: Al: 0.1% or less; Mg: 0.01% or less; and Ca: 0.01% or less. For example, the Worthite iron and the ferrite-grained iron-phase dual-phase steel wire for high-strength and high-corrosion-resistant screws excellent in cold forgeability in the second paragraph of the patent application include Nb: 1.0% or less in mass%; Ti: 0.5% or less; V: 1.0% or less: and Zr: 1.0% or less. For example, the Worthite iron and the ferrite-coated iron-phase duplex steel wire for high-strength and high-corrosion-resistant screws excellent in cold forgeability in the fourth paragraph of the patent application are contained in mass%: Nb: 1.0% or less; Ti: 0.5% or less; V: 1.0% or less: and Zr: 1.0% or less. A Worthite iron and a ferrite-granular dual-phase steel wire for a high-strength, high-corrosion-resistant screw having excellent cold forgeability, which has the chemical composition described in any one of claims 1 to 6, and a tensile strength of ^{700N / mm 2 ~ 1000N / mm} 2. A highly corrosion-resistant screw having the chemical composition described in any one of claims 1 to 6, and having a tensile strength of 700 N/mm ² to 1200 N/mm ² . The method of manufacturing a high resistance to corrosion of the screw, which has a patent based on a range of chemical in any one of claims 1 to 6 of the composition, and a tensile strength of ^{700N / mm 2 ~ 1000N / mm} 2 of the austenite, The ferrite-iron-based duplex steel wire is subjected to an aging heat treatment at 300 ° C to 600 ° C for 1 minute to 100 minutes after cold screw forming. A soft, dual-phase stainless steel wire having excellent cold workability, which contains, by mass%: C: 0.005% to 0.05%; Si: 0.1% to 1.0%; Mn: 0.1% to 10.0%; Ni: 1.6% ～6.0%; Cr: 19.0% to 30.0%; Cu: 0.05% to 3.0%; and N: 0.005% or more and less than 0.06%; and the residue is composed of Fe and substantially unavoidable impurities, and C+N is 0.09% or less, the M value of the formula (a) is 60 or less, the tensile strength is 700 N/mm ² or less, and the tensile fracture elongation is 70% or more; M=551-462 (C+N)-9.2Si-8.1 Mn-29(Ni+Cu)-13.7Cr-18.5Mo (a). The soft duplex stainless steel wire having excellent magnetization properties, which is excellent in cold workability according to claim 10, contains Mo: 3.0% or less by mass%. The soft duplex stainless steel wire having magnetization excellent in cold workability according to the tenth or eleventh aspect of the patent application is contained in a mass% of B: 0.01% or less. The soft duplex stainless steel wire having excellent magnetization properties, which is excellent in cold workability according to claim 10 or 11, is contained in mass%: Al: 0.1% or less; Mg: 0.01% or less; and Ca: 0.01% or less. One or more of them. The soft duplex stainless steel wire having excellent magnetization properties, which is excellent in cold workability according to claim 10 or 11, is contained in mass%: Nb: 1.0% or less; Ti: 0.5% or less; V: 1.0% or less; Zr: one or more of 1.0% or less.