CN101815803B - Duplex stainless steel wire material, steel wire, bolt, and method for production of the bolt - Google Patents

Abstract

The high-strength, high-corrosion-resistant austenitic-ferritic two-phase steel wire for bolts of the present invention, with excellent cold forging properties, contains, by mass %: C: 0.005-0.05%, Si: 0.1-1.0%, Mn: 0.1-10.0%, Ni: 1.0-6.0%, Cr: 19.0-30.0%, Cu: 0.05-3.0%, N: 0.005-0.20%, with the balance consisting of Fe and substantially unavoidable impurities. The C+N content is less than 0.20%, the M value in formula (a) is less than 60, the F value in formula (b) is 45-85, and the tensile strength is 550-750 N/ ^mm² . 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).

Description

Duplex stainless steel wire rod, steel wire and bolt and manufacturing method thereof

technical field

The present invention relates to a duplex stainless steel wire rod excellent in cold forgeability, and provides, for example, a high-strength bolt having corrosion resistance equivalent to that of SUS304 at low cost.

The present invention relates to a soft duplex stainless steel wire material with magnetizability and excellent cold workability, and more specifically to screws, pins, metal meshes, steel wires, steel cables, springs, etc., which can be provided at low cost and have corrosion resistance equivalent to, for example, SUS304 and SUS316 Soft duplex stainless steel wire material with strong cold workability and excellent cold workability with magnetization imparted at the same time.

This application claims priority based on Japanese Patent Application No. 2007-264992 filed in Japan on October 10, 2007, and Japanese Patent Application No. 2007-264993 filed in Japan on October 10, 2007, the contents of which are incorporated herein by reference.

Background technique

So far, SUS304 wire rods have been widely used as high-strength, high-corrosion-resistant bolts with a strength of 700N/mm Class ² . However, in recent years, there has been a further demand for higher strength (weight reduction) of bolts mainly in fields such as automobiles and home appliances. In addition, since SUS304 bolts are expensive because they contain a lot of expensive Ni raw materials, cost reduction is strongly demanded.

Up to now, the high strength of bolts has been dealt with, for example, by SUS630 bolts of martensitic stainless steel (for example, Patent Document 1).

However, although SUS630 bolts are excellent in strength, not only are they not good in corrosion resistance, but also their cold forgeability is significantly deteriorated, so that the manufacturing cost is greatly increased, and their use is greatly restricted.

In addition, an inexpensive high-strength bolt made of about 13% Cr-based martensitic stainless steel with excellent manufacturability has also been proposed (Patent Document 2). However, the corrosion resistance is not very good, and its use is limited.

In addition, a high-strength bolt made of austenitic stainless steel with a high (C+N) content has been proposed (Patent Document 3). However, the production cost is greatly increased due to the poor cold forgeability, and thus has not been accepted by the market.

On the other hand, in recent years, low-Ni-based low-cost duplex stainless steels that suppress the use of expensive Ni have been proposed (Patent Documents 4 to 6).

However, conventional duplex stainless steels have poor cold forgeability and high manufacturing costs, so bolts made of duplex stainless steels have not appeared on the market.

As mentioned above, among conventional stainless steel bolts and stainless steel wire rods for bolts, there has not been a product that combines high corrosion resistance, high strength, high cold forgeability, and low cost.

Products such as screws, pins, metal meshes, and steel wires that require corrosion resistance are manufactured using austenitic stainless steel wires such as SUS304, SUSXM7, etc., by drawing or cold forging, bending, and other strong cold processing. In the cold working of wire rods, unlike the press formability of steel sheets that require high elongation properties of the material, softness and high tensile fracture shrinkage properties are required (high elongation properties are not required). The so-called softness is required to be 700 N/mm ² or less, preferably 650 N/mm ² or less in terms of the tensile strength of the wire rod.

However, since a large amount of expensive Ni is added as a product of austenitic stainless steel, the product price is high although the manufacturing process is cheap.

In addition, austenitic stainless steel has no magnetism, so it cannot be attached to the tool during the fastener connection operation, which makes the workability poor. When it passes through the metal mesh or the mesh (especially the conveyor belt for food, etc.), the material falls off and mixes When it is in food, it is not possible to check for contamination with a magnetic sensor, which is inconvenient because it is not magnetic.

For products requiring magnetic properties and corrosion resistance, ferritic stainless steel wire materials made of ferritic stainless steel wire rods, low in C and N, and added with Nb have been proposed (Patent Documents 7 to 9).

However, not only the corrosion resistance of cold-worked products is insufficient, but also in the case of a high-Cr system, the production cost increases due to surface defects during wire rolling.

On the other hand, in recent years, various inexpensive duplex stainless steels with reduced Ni have been proposed (Patent Documents 10 to 12).

Patent Document 10 describes a high-strength duplex stainless steel that is low in Ni, contains 0.04% or more of strength-enhancing nitrogen, and is excellent in Young's modulus. However, in order to improve the strength, more than 1% of Si and more than 0.04% of nitrogen were added, and the high strength of more than 80kg/ ^mm2 was described in the examples, but the characteristics of softness and high tensile fracture shrinkage were not considered. The cold workability of wire rods is substantially difficult.

Patent Document 11 describes a low-Ni-based duplex stainless steel that contains 0.05% or more of nitrogen and has corrosion resistance and good weldability. However, there is no description on cold workability, and the preferred range of nitrogen to increase strength is 0.06 to 0.12%, and steel (low Si steel) containing 0.13% or more nitrogen is described in the examples, and soft and high tensile fractures are not considered. Shrinkage rate characteristics and cold workability of wire rods are substantially difficult.

Patent Document 12 describes a high-strength duplex stainless steel that is low in Ni, contains 0.05% or more of nitrogen, and has excellent relaxation properties. However, steels containing 0.13% or more of nitrogen to increase strength are described in Examples, but the properties of softness and high tensile fracture shrinkage are not considered, and cold workability of wire rods is substantially difficult.

Patent Document 13 describes a duplex stainless steel that is low in Ni, contains 0.05% or more of nitrogen, and is excellent in ductility and deep drawability. However, in the examples, the steel containing 0.08% or more of nitrogen to improve the strength is described in order to improve the deep drawability of the steel sheet by improving the ductility. Cold workability is difficult.

As mentioned above, among conventional stainless steels, there is no stainless steel that has softness and high fracture shrinkage characteristics required for cold workability of wire rods, is inexpensive, and exhibits high corrosion resistance and magnetizability.

Patent Document 1: Japanese Patent Application Laid-Open No. 9-314276

Patent Document 2: Japanese Patent Laid-Open No. 2005-179718

Patent Document 3: Japanese Patent Laid-Open No. 2006-274295

Patent Document 4: International Publication No. WO2005/073422

Patent Document 5: Japanese Patent No. 3271262

Patent Document 6: Specification No. EP0337846

Patent Document 7: Japanese Patent No. 2906445

Patent Document 8: Japanese Patent No. 2817266

Patent Document 9: Japanese Patent Laid-Open No. 2006-16665

Patent Document 10: Japanese Patent Laid-Open No. 62-47461

Patent Document 11: Japanese Patent Laid-Open No. 61-56267

Patent Document 12: Japanese Patent Application Laid-Open No. 2-305940

Patent Document 13: Japanese Patent Laid-Open No. 2006-169622

Contents of the invention

The purpose of the present invention is to provide cheap high-strength, high-corrosion-resistant austenitic-ferritic dual-phase steel wire rods, steel wires and bolts and manufacturing methods thereof. The structure, composition, and material are controlled to give cold forgeability and high strength of bolt products.

The object of the present invention is to provide an inexpensive duplex stainless steel wire material having excellent cold workability and corrosion resistance and magnetic properties, which can significantly reduce the production cost of cold-worked products of conventional austenitic stainless steel wire materials and impart magnetizability. .

The inventors of the present invention conducted various researches to solve the above-mentioned problems, and as a result, they found that while reducing the expensive Ni content in high-corrosion-resistant duplex stainless steel, the composition was adjusted to stabilize the structure (low M value), and the ferrite The volume fraction of the phase is controlled at a high level, and the tensile strength of the wire rod and steel wire is optimized by heat treatment and wire drawing, and cold forging and high strength of bolt products can be achieved at low cost.

In addition, the inventors of the present invention found that by using a highly corrosion-resistant duplex stainless steel having a magnetic ferrite phase + austenite phase as a basis, while reducing expensive Ni and controlling the structure through compositional adjustment (M value control), In addition, work hardening is suppressed by reducing (C+N), and extremely excellent cold workability can be imparted to an inexpensive high-corrosion-resistant duplex stainless steel wire rod.

This invention was completed based on the said knowledge, and the point which makes it the summary is as follows.

That is to say, the first aspect of the present invention is an austenite-ferritic dual-phase steel wire rod, wherein,

In mass%, it contains:

C: 0.005～0.05%,

Si: 0.1 to 1.0%,

Mn: 0.1～10.0%,

Ni: 1.0 to 6.0%,

Cr: 19.0～30.0%,

Cu: 0.05～3.0%,

N: 0.005～0.20%,

The balance is composed of Fe and virtually unavoidable impurities, C+N is 0.20% or less, the M value of formula (a) is 60 or less, the F value of formula (b) is 45-85, and the tensile strength is 550-85. 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 addition to the first aspect, the second aspect of the present invention may further contain Mo: 1.0% or less in mass %.

In the third aspect of the present invention, in addition to the first aspect, B: 0.01% or less may be further contained in mass %.

The fourth aspect of the present invention is based on the first aspect, and may further contain one or more of the following elements in mass %:

Al: 0.1% or less,

Mg: 0.01% or less,

Ca: 0.01% or less.

The fifth aspect of the present invention is based on the first aspect, and may further contain one or more of the following elements in mass %:

Nb: 1.0% or less,

Ti: 0.5% or less,

V: 1.0% or less,

Zr: 1.0% or less.

A sixth aspect of the present invention is an austenitic-ferritic dual-phase steel wire including any one of the above-mentioned first to fifth aspects and having a tensile strength of 700 to 1000 N/mm ² .

A seventh aspect of the present invention is a high-strength, high-corrosion-resistant bolt including any one of the above-mentioned first to fifth aspects, and having a tensile strength of 700 to 1200 N/mm ² .

The eighth form of the present invention is to wire-cool an austenite-ferritic dual-phase steel containing any one of the above-mentioned first form to the fifth form and having a tensile strength of 700-1000 N/mm ² A method for manufacturing high-strength, high-corrosion-resistant bolts that are subjected to aging heat treatment at 300-600°C for 1-100 minutes after being formed into bolts.

The ninth aspect of the present invention is a soft duplex stainless steel wire with magnetizability, wherein,

In mass%, it contains:

C: 0.005～0.05%,

Si: 0.1 to 1.0%,

Mn: 0.1～10.0%,

Ni: 1.6～6.0%,

Cr: 19.0～30.0%,

Cu: 0.05～3.0%,

N: more than 0.005% and less than 0.06%,

The balance is composed of Fe and virtually unavoidable impurities, C+N is 0.09% or less, the M value of the formula (a) is 60 or less, the tensile strength is 700N/ ^mm2 or less, and the tensile shrinkage at break is 70% above.

M=551-462(C+N)-9.2Si-8.1Mn-29(Ni+Cu)

-13.7Cr-18.5Mo (a)

In a tenth aspect of the present invention, in addition to the ninth aspect, Mo: 3.0% or less is further contained in mass %.

In an eleventh aspect of the present invention, in addition to the ninth aspect, B: 0.01% or less is further contained in mass %.

A twelfth aspect of the present invention is based on the ninth aspect, further containing one or more of the following elements in mass %:

Al: 0.1% or less,

Mg: 0.01% or less,

Ca: 0.01% or less.

The thirteenth aspect of the present invention is based on the ninth aspect, and further contains one or more of the following elements in mass %:

Nb: 1.0% or less,

Ti: 0.5% or less,

V: 1.0% or less,

Zr: 1.0% or less.

The high-strength, high-corrosion-resistant duplex stainless steel wire rod for bolts with excellent cold forgeability of the present invention can ensure excellent cold forgeability even though it does not contain much expensive Ni, and can impart high corrosion resistance equivalent to or higher than that of SUS304 And high strength, it has the effect of providing high-strength, high-corrosion-resistant bolts at low cost.

The soft duplex stainless steel wire material with excellent cold workability of the present invention can impart extremely excellent cold workability, magnetizability, and corrosion resistance equivalent to those of austenitic stainless steels such as SUS304 and SUS316, even though it does not contain much expensive Ni. It has the remarkable effect of being able to provide highly corrosion-resistant products with magnetizability at low cost.

Description of drawings

Fig. 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 working ratio (%) and the compressive deformation stress (N/mm ² ) of the steel wire (15% drawn wire) corresponding to the F value.

Detailed ways

Next, reasons for limiting the first to eighth aspects of the present invention will be described.

In order to ensure the strength of bolt products, C is contained at least 0.005%. However, if the content exceeds 0.05%, not only the corrosion resistance will be deteriorated due to the formation of Cr carbonitrides, but also the cold forgeability will be deteriorated, so it is limited to 0.05% or less. Preferably it is 0.03% or less.

In order to ensure the strength of bolt products through solid solution strengthening and age hardening, N is contained in an amount of 0.005% or more. However, if the content exceeds 0.20%, the cold forgeability will deteriorate significantly, so the upper limit is made 0.20%. A preferred range is below 0.05%.

From the above-mentioned reason of cold forgeability, C+N is limited to 0.20% or less. Preferably it is 0.10% or less.

For deoxidation, 0.1% or more of Si is contained. However, if the content exceeds 1.0%, the cold forgeability will deteriorate. Therefore, the upper limit is made 1.0%. The preferred range is 0.2 to 0.6%.

0.1% or more of Mn is contained as an adjustment for deoxidation and for obtaining a stable austenite structure. However, if the content exceeds 10.0%, the rust resistance and ferrite volume fraction will decrease, the tensile strength will increase, and the cold forgeability will deteriorate. Therefore, the upper limit is made 10.0%. A preferable range is 0.5 to 5.0%.

In order to stabilize the austenite structure and ensure cold forgeability, 1.0% or more of Ni is contained. However, even if it is contained in excess of 6.0%, the effect is saturated, and conversely, if the volume fraction of the ferrite phase is reduced to 45% or less, not only the cold forgeability (tool life) is deteriorated, but also the economic efficiency is deteriorated due to the high price of Ni. Therefore, the upper limit is limited to 6.0%. A preferable range is more than 3.0% and 5.0% or less.

In order to ensure the corrosion resistance, increase the volume fraction of the ferrite phase, and stabilize the austenite structure to ensure cold forgeability, 19.0% or more of Cr is contained. However, even if it is contained in excess of 30.0%, the effect is saturated, and on the contrary, the volume fraction of the ferrite phase exceeds 85%, so that the strength of the bolt product decreases. Therefore, the upper limit is made 30.0%. The preferred range is 22.0 to 26.0%.

Cu is effective for stabilizing the austenite structure, suppressing work hardening, improving cold forgeability, and promoting age hardening of the ferrite phase during aging treatment after cold forging to increase the strength of bolt products. Therefore, 0.05% or more is contained. However, if it is contained in excess of 3.0%, the solid solubility of Cu will be exceeded, and the thermal manufacturability of the raw material will be remarkably deteriorated, so the upper limit is made 3.0%. A preferable range is 0.2% or more and less than 1.0%.

The M value of the following formula (a) contributes to the stability of the austenite phase, and is an index described in "Iron and Steel", 63 (1977), page 772. If the M value increases, hard machining will occur. induced martensitic phase. During cold forging of duplex stainless steel, if the M value exceeds 60, a hard working-induced martensite phase is formed during cold forging, resulting in marked deterioration of cold forgeability (deterioration of tool life, occurrence of cold forging cracks). Therefore, the M value is set to be 60 or less. A preferable 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) contributes to the volume fraction of the ferrite phase and is an index described in Japanese Patent Publication No. 7-74416, and as the F value increases, the ferrite phase increases. Fig. 1 shows the investigation results of the F value and the volume fraction of the ferrite phase of the duplex stainless steel wire products. If the F value reaches more than 45, the volume fraction of the ferrite phase will reach more than 45vol.%, showing high endurance and low work hardening characteristics (Figure 2), which can increase the strength of the product (the tensile strength of the bolt shaft) ) is high-strength to 700-1200N/mm ² , and the cold forgeability of the head can be ensured. Therefore, the F value is limited to 45 or more. The relationship between the processing rate (%) and the compressive deformation stress (N/mm ² ) corresponding to the F value in Fig. 2 shows that when the F value is lower than 45, the work hardening is large and the cold forgeability (forging cracks, tool damage) is large Amplitude deterioration. On the other hand, if the F value exceeds 85, the soft ferrite phase exceeds 85%, and the high-strength austenite phase decreases, so the strength of the bolt product decreases instead. Therefore, the upper limit is set at 85. The preferred range is 50-80.

F＝5.6Cr-7.1Ni+2.4Mo+15Si-3.1Mn-300C

-134N-26.6 (b)

The tensile strength of the wire rod greatly contributes to cold forgeability, and when the tensile strength of the wire rod is less than 550N/ ^mm2 , the strength of cold-forged parts such as bolts is low, and the value as a high-strength product decreases. Therefore, the lower limit is made 550 N/mm ² . On the other hand, if the tensile strength of the wire rod exceeds 750 N/mm ² , cold forgeability deteriorates significantly (tool life deteriorates, cold forging cracks occur). Therefore, the upper limit is made 750 N/mm ² . A preferable range is 600 to 700 N/mm ² .

Mo is an element effective for improving corrosion resistance, and the effect can be obtained stably by adding 0.1% or more. However, if the content exceeds 1.0%, not only the cost of the material will increase, but also the material will harden and the cold forgeability will deteriorate. Therefore, the upper limit is limited to 1.0%. A preferable range is 0.2% or more and less than 0.5%.

B is an element effective in improving hot workability, and the effect can be obtained stably by adding 0.001% or more. However, if it is contained in excess of 0.01%, borides are formed to degrade corrosion resistance and cold forgeability. Therefore, the upper limit is limited to 0.01%. A preferable range is 0.002% to 0.006%.

Al, Mg, and Ca are effective for deoxidation. Therefore, by adding one or more of Al: 0.005% or more, Mg: 0.001% or more, and Ca: 0.001% or more, the effect can be stably obtained. However, even if Al exceeds 0.1%, Mg exceeds 0.01%, and Ca exceeds 0.01%, the effect is saturated, and coarse oxides (inclusions) are generated conversely to cause cold forgeability cracks. Therefore, the upper limits are set to Al: 0.1%, Mg: 0.01%, and Ca: 0.01%, respectively. A preferable range is to contain one or more of Al: 0.01% 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 carbonitrides and ensuring corrosion resistance. The effect can be obtained stably by using more than one kind. However, even if Nb exceeds 1.0%, Ti exceeds 0.5%, V exceeds 1.0%, and Zr exceeds 1.0%, the effect is saturated, and coarse precipitates and cold forgeable cracks occur on the contrary. Therefore, the upper limit of each element is specified. A preferable range is to contain 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, steel contains oxygen as an unavoidable impurity in the manufacturing process, but in the case of the present invention, it is preferable to regulate oxygen as an unavoidable impurity to 0.01% or less.

Although the wire rod is drawn to form a drawn steel wire, the tensile strength of the steel wire is very helpful to the cold forgeability and the strength of the bolt product. When the tensile strength of the steel wire is lower than 700N/ ^mm2 , the strength of the bolt product Low, the value as a high-strength product decreases. Therefore, the lower limit is made 700 N/mm ² . On the other hand, if the tensile strength of the steel wire exceeds 1000 N/mm ² , cold forgeability deteriorates significantly (tool life deteriorates, cold forging cracks occur). Therefore, the upper limit is made 1000 N/mm ² . A preferable range is 750 to 900 N/mm ² .

The tensile strength of the high-strength bolt of the present invention is increased by wire drawing and aging heat treatment after cold forging. At this time, when the tensile strength of the bolt product is less than 700N/ ^mm2 , the value as a high-strength bolt product is low. On the other hand, if the tensile strength of the bolt product reaches 1200N/mm2 ^or more, cold forging cracks occur And tool damage, etc., the cost of cold forging is significantly deteriorated. Therefore, the upper limit of the tensile strength of the bolt product is defined as 1200 N/mm ² . The preferable range to exhibit the effect economically is 800 to 1000 N/mm ² .

After forming the steel wire of the present invention into a bolt by cold forging, in order to effectively increase the tensile strength of the bolt product, it is effective to perform aging heat treatment at 300° C. or higher for 1 minute or more. On the other hand, if it exceeds 600°C, it will become over-aged, so the tensile strength of the bolt product will decrease. Therefore, the upper limit is made 600°C. The preferred temperature range is 400-550°C. In addition, if the holding time exceeds 100 minutes, not only the effect of age hardening is saturated, but also the tensile strength of the bolt product decreases due to overaging in some cases. Therefore, the upper limit of the retention time is set to 100 minutes. The preferred holding time ranges from 5 to 60 minutes.

Next, reasons for limiting the ninth to thirteenth aspects of the present invention will be described.

In order to ensure the strength of steel, 0.005% or more of C is added. However, if the addition exceeds 0.05%, not only the cold workability but also the corrosion resistance due to the formation of Cr carbides will be deteriorated. Therefore, the upper limit is made 0.05% or less. A preferable range is 0.01 to 0.03%.

In order to ensure the strength of cold-worked parts through solid solution strengthening, 0.005% or more of N is added. However, when 0.06% or more is added, the tensile strength increases and the cold workability deteriorates. Therefore, the upper limit is made less than 0.06%. In ordinary duplex stainless steel, 0.06% or more of N is added in order to reduce the use of expensive alloy elements, but in the case of the steel of the present invention, it is characterized in that the N content is kept low by controlling the structure and composition balance. Level, thereby dramatically improving the cold workability of the wire rod in a soft state. A preferable range is 0.02% or more and less than 0.05%.

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

For deoxidation, 0.1% or more of Si is added. However, if added over 1.0%, cold workability will deteriorate due to hardening. Therefore, the upper limit is made 1.0%. The preferred range is 0.2 to 0.6%.

0.1% or more of Mn is added as an adjustment for deoxidation and for obtaining a two-phase structure of ferrite+austenite and stabilizing the austenite structure. However, if adding more than 10.0%, cold workability will deteriorate due to an increase in corrosion resistance and strength. Therefore, the upper limit is limited to 10.0%. A preferable range is 0.5 to 5.0%.

1.6% of Ni is added in order to obtain a two-phase structure of ferrite+austenite by lowering the M value and to stabilize the austenite structure to ensure cold workability. However, even if it is added in excess of 6.0%, the effect is saturated, and since Ni is an expensive element, the economical efficiency is deteriorated. Therefore, the upper limit is limited to 6.0%. A preferable range is 2.0 to 5.0%.

19.0% or more of Cr is added in order to secure corrosion resistance, obtain a dual-phase structure of ferrite+austenite, and stabilize the austenite structure to ensure cold workability. However, even if it is added in excess of 30.0%, the effect is saturated, and cold workability deteriorates conversely. Therefore, the upper limit is made 30.0%. A preferable range is 20.0 to 26.0%.

Cu is contained in an amount of 0.05% or more in order to reduce the M value to obtain a two-phase structure of ferrite+austenite, stabilize the austenite structure, suppress work hardening, and improve cold workability. However, if the content exceeds 3.0%, the solid solubility of Cu will be exceeded, and the thermal manufacturability of the raw material will be significantly 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) contributes to the stability of the austenite phase, and is an index described in "Iron and Steel", 63 (1977), page 772. If the M value increases, hard machining will occur. induced martensitic phase. In cold forging of duplex stainless steel, if the M value exceeds 60, a hard working-induced martensite phase is formed during cold working, and the cold workability is significantly deteriorated. Therefore, the M value is set to be 60 or less. A preferable 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 rod greatly contributes to the cold workability of the wire rod, and if the tensile strength of the wire rod exceeds 700 N/mm ² , the cold workability is significantly reduced. Therefore, the upper limit is made 700 N/mm ² . On the other hand, when the tensile strength of the wire rod is less than 500 N/mm ² , the strength of the cold-worked product is too low, and the value as a product decreases. Therefore, it is preferable to set the lower limit to 500 N/mm ² . A preferable range is 500 to 650 N/mm ² .

The tensile fracture shrinkage of the wire rod greatly contributes to the cold workability of the wire rod, and when the tensile fracture shrinkage of the wire rod is less than 70%, the cold workability such as cold drawing and cold forgeability deteriorates. Therefore, the upper limit is made 70% or more. A preferable range is 75% or more.

Magnetization is a function that does not exist in austenitic stainless steel. When fasteners are connected, the magnetization of magnetic tools is used to improve workability. When passing through metal meshes and sieve holes (especially conveyor belts for food, etc.), materials are generated In the case of falling off and mixing in food, use a magnetic sensor to prevent mixing, etc., and the function of magnetizability is very large in industry. Therefore, the magnetizability is limited in the present invention. It is preferably 3.0 or more in terms of specific magnetic permeability.

Mo is an element effective in improving corrosion resistance, and the effect can be obtained stably by adding 0.1% or more. However, if the addition exceeds 3%, not only the material will harden but also the σ phase will be precipitated, so that the cold workability will significantly deteriorate. Therefore, the upper limit is limited to 3%. A preferable range is 0.3 to 1.0%.

B is an element effective in improving hot workability, and the effect can be obtained stably by adding 0.001% or more. However, if added in excess of 0.01%, borides are formed to degrade corrosion resistance and cold workability. Therefore, the upper limit is made 0.01%. A preferable range is 0.002% to 0.006%.

Al, Mg, and Ca are effective for deoxidation. Therefore, by adding one or more of Al: 0.005% or more, Mg: 0.001% or more, and Ca: 0.001% or more, the effect can be stably obtained. However, even if Al exceeds 0.1%, Mg exceeds 0.01%, and Ca exceeds 0.01%, the effect is saturated, and coarse oxides (inclusions) are generated conversely, deteriorating cold workability. Therefore, the upper limits are set to Al: 0.1%, Mg: 0.01%, and Ca: 0.01%, respectively. A preferable range is to contain one or more of 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 carbonitrides and ensuring corrosion resistance. The effect can be obtained stably by using more than one kind. However, even if Nb exceeds 1.0%, Ti exceeds 0.5%, V exceeds 1.0%, and Zr exceeds 1.0%, the effect is saturated, and coarse precipitates are formed on the contrary, deteriorating cold workability. Therefore, the upper limit of each element is specified. A preferable range is to contain 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, steel contains oxygen as an unavoidable impurity in the manufacturing process, but in the case of the present invention, it is preferable to regulate oxygen as an unavoidable impurity to 0.01% or less.

Example 1

Embodiment 1 of the present invention will be described below.

Tables 1 to 4 show the chemical composition of the steel of Example 1.

Melt the steel with the above chemical composition in a 300kg vacuum melting furnace, cast it into a 180mm slab, and roll the slab to 5.5~6.5mm by wire rod hot rolling, finish the hot rolling at 1050°C, and then pass the on-line heat treatment The solution treatment was carried out by holding at 1050° C. for 5 minutes and cooling in water, and thereafter, pickling was carried out to obtain a wire product. Then, oxalic acid film treatment is performed, and light cold drawing is processed to φ5.2mm, and it is finished into a steel wire for cold forging.

Then, about 5,000 hexagon bolts are processed by cold forging and rolling. Then, an aging treatment is performed at 300 to 650° C. and held for 3 to 200 minutes on a part thereof. Then, all the bolts are finished into hexagonal bolt products by barrel grinding and cleaning.

The evaluation is performed on the tensile strength of the steel wire, the volume fraction of the ferrite phase of the steel wire, the cold forgeability (with or without cracks, the presence or absence of tool defects), the tensile strength and corrosion resistance of bolt products . The evaluation results are shown in Tables 5-8.

The mechanical properties were evaluated by tensile strength and shrinkage at break in a tensile test according to JIS Z 2241. In the steel wires of the examples of the present invention, all are in the range of 650 to 1000 N/mm ² , and in the bolt products of the examples of the present invention, all are in the range of 700 to 1200 N/mm ² , showing excellent high strength.

The volume fraction of the ferrite phase in the steel wire was obtained by mirror-polishing the longitudinal section of the steel wire, coloring the ferrite phase with Murakami's reagent, and calculating the area fraction by image analysis. The ferrite fraction of the steel wires of the examples of the present invention is in the range of 45 to 85 vol.%.

Regarding cold forgeability, 5000 hexagonal heads were produced by forging with a three-stage upsetting machine, and the presence or absence of forging cracks and tool damage were evaluated. The tool life was rated as ○ when tool damage did not occur, and the tool life was rated as tool life × when tool damage occurred. The wire rod of the example of the present invention did not generate cold cracks, had a tool life of ◯, and was excellent in cold forgeability.

Regarding the corrosion resistance of bolt products, according to the salt spray test of JIS Z 2371, a spray test was carried out on 10 bolt products for 100 hours each to evaluate whether rust occurred. The corrosion resistance was evaluated as ◯ as long as there was no rust or only a little rust, and the corrosion resistance was evaluated as × when flow rust occurred or overall rust occurred. The rust resistance of the bolt products of the examples of the present invention was all ◯.

On the other hand, Comparative Examples Nos. 38 to 61 were outside the range of the present invention, and the cold forgeability, the strength of the bolt product, the corrosion resistance, etc. deteriorated, and the advantages of the present invention were obvious.

Example 2

Embodiment 2 of the present invention will be described below.

Tables 9 and 10 show the chemical composition (mass) of the steel (test material) used in Example 2.

Melt the steel with the above chemical composition in a 150kg vacuum melting furnace, cast it into a 180mm slab, and roll the slab to 5.5mm by wire rod hot rolling, and finish the hot rolling at 1050°C. In this state, it is carried out at 1050 ℃ for 5 minutes, water-cooled continuous heat treatment, and then pickled to make a wire. Then, the steel wire is cold-drawn to φ2.0 mm by a normal process, and the steel wire is cold-worked into a mesh-like metal mesh for a conveyor belt by bending.

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

Table 11

Table 12

The tensile strength and shrinkage at break of the wire rod were evaluated in accordance with the tensile strength and shrinkage at break in the tensile test of JIS Z 2241. In the wire rods of the examples of the present invention, the overall tensile strength was 500 to 700 N/mm ² , and the shrinkage at break was in the range of ≥70%.

Cold workability was evaluated based on cold drawing and subsequent metal mesh workability. The cold formability when formed into a metal mesh without wire breakage or breakage was evaluated as ◯, and when the metal mesh could not be formed due to wire breakage or breakage was evaluated as ×. In the wire rods of the examples of the present invention, there was no wire breakage or breakage, and the cold workability was excellent.

Regarding the corrosion resistance, after polishing the surface layer of the pickled wire rod with #500, a 100-hour spray test was carried out in accordance with the salt spray test of JIS Z2371, and whether rust occurred was evaluated. As long as there is no rust or only a little rust, the corrosion resistance is evaluated as ◯, and the corrosion resistance is evaluated as x when flow rust occurs or overall rust occurs. All the rust resistances of the examples of the present invention were ◯.

Regarding the magnetizability, the specific magnetic permeability was measured with a ferrite meter (simple magnetic permeability meter) using a metal mesh. When the specific magnetic permeability is 3.0 or more at which magnetization can be clearly confirmed, it is evaluated as having magnetization, and when it is less than 3.0, it is evaluated as non-magnetization.

On the other hand, Comparative Examples Nos. 86 to 107 were outside the scope of the present invention, and deteriorated in terms of cold workability, corrosion resistance, cost, magnetizability, etc., and the advantages of the present invention were obvious.

The above examples show that the high corrosion-resistant duplex stainless steel wire of the present invention that does not contain expensive Ni has excellent cold forgeability, and can increase the strength of bolt products, and can provide high-strength, Highly corrosion-resistant bolts, moreover, can also be used in nuts, which are very useful in industry.

The above examples show that according to the present invention, a soft, magnetizable and inexpensive duplex stainless steel wire can be produced, and can impart very excellent cold workability and corrosion resistance equivalent to austenitic stainless steels such as SUS304 and SUS316. , It is very useful in industry to provide low-cost and highly corrosion-resistant cold-worked products with magnetizability such as screws, pins, metal mesh, steel wires, steel cables, and springs.

Claims (19)

1. the HS of an excellent in cold forging property, high anti-corrosion bolt are the two-phase steel wire rod with austenite-ferrite, and it contains in quality %:

C：0.005～0.05％、

Si：0.1～1.0％、

Mn：0.1～10.0％、

Ni：1.0～6.0％、

Cr：19.0～30.0％、

Cu：0.05～3.0％、

N：0.005～0.20％，

Surplus by Fe and in fact unavoidable impurities constitute, C+N is below 0.20%, the M value of formula (a) is below 60, the F value of formula (b) is 45～85, tensile strength is 550～750N/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)。

2. the HS of excellent in cold forging property according to claim 1, high anti-corrosion bolt are the two-phase steel wire rod with austenite-ferrite, wherein, in quality % contain below the Mo:1.0%, in below the B:0.01% one or both.

3. the HS of excellent in cold forging property according to claim 1, high anti-corrosion bolt are the two-phase steel wire rod with austenite-ferrite, wherein, in quality % contain in the following element more than a kind:

Below the Al:0.1%,

Below the Mg:0.01%,

Below the Ca:0.01%.

4. the HS of excellent in cold forging property according to claim 1, high anti-corrosion bolt are the two-phase steel wire rod with austenite-ferrite, wherein, in quality % contain below the Mo:1.0%, in below the B:0.01% one or both;

Also contain in the following element more than a kind:

Below the Al:0.1%,

Below the Mg:0.01%,

Below the Ca:0.01%.

5. the HS of excellent in cold forging property according to claim 1, high anti-corrosion bolt are the two-phase steel wire rod with austenite-ferrite, wherein, in quality % contain in the following element more than a kind:

Below the Nb:1.0%,

Below the Ti:0.5%,

Below the V:1.0%,

Below the Zr:1.0%.

6. the HS of excellent in cold forging property according to claim 1, high anti-corrosion bolt are the two-phase steel wire rod with austenite-ferrite, wherein, in quality % contain below the Mo:1.0%, in below the B:0.01% one or both;

Also contain in the following element more than a kind:

Below the Nb:1.0%,

Below the Ti:0.5%,

Below the V:1.0%,

Below the Zr:1.0%.

7. the HS of excellent in cold forging property according to claim 1, high anti-corrosion bolt are the two-phase steel wire rod with austenite-ferrite, wherein, in quality % contain below the Al:0.1%, in below the Mg:0.01%, below the Ca:0.01% more than a kind;

Also contain in the following element more than a kind:

Below the Nb:1.0%,

Below the Ti:0.5%,

Below the V:1.0%,

Below the Zr:1.0%.

8. the HS of excellent in cold forging property according to claim 1, high anti-corrosion bolt are the two-phase steel wire rod with austenite-ferrite, wherein, in quality % contain below the Mo:1.0%, in below the B:0.01% one or both;

Also contain below the Al:0.1%, in below the Mg:0.01%, below the Ca:0.01% more than a kind;

Also contain in the following element more than a kind:

Below the Nb:1.0%,

Below the Ti:0.5%,

Below the V:1.0%,

Below the Zr:1.0%.

9. the HS of an excellent in cold forging property, high anti-corrosion bolt are the two-phase steel wire with austenite-ferrite, and it has the chemical constitution of each record in the claim 1～8, and tensile strength is 700～1000N/mm ²

10. a HS, high anti-corrosion bolt, it has the chemical constitution of each record in the claim 1～8, and tensile strength is 700～1200N/mm ²

11. the method for manufacture of a HS, high anti-corrosion bolt, wherein, the chemical constitution that will have each record in the claim 1～8, tensile strength is 700～1000N/mm ²Austenite-ferrite be after the cold-forming of two-phase steel wire becomes bolt, 300～600 ℃ of timeliness thermal treatments of implementing down 1～100 minute.

12. the soft two phase stainless steel wire rod with magnetizability that cold-workability is good, it contains in quality %:

C：0.005～0.05％、

Si：0.1～1.0％、

Mn：0.1～10.0％、

Ni：1.6～6.0％、

Cr：19.0～30.0%

Cu：0.05～3.0％、

N:0.005% is above and be lower than 0.06%,

Surplus by Fe and in fact unavoidable impurities constitute, C+N is below 0.09%, the M value of formula (a) is below 60, tensile strength is 500～700N/mm ², the tension fracture shrinking percentage is more than 70%,

M＝551-462(C+N)-9.2Si-8.1Mn-29(Ni+Cu)

-13.7Cr-18.5Mo (a)。

13. the soft two phase stainless steel wire rod that cold-workability according to claim 12 is good with magnetizability, wherein, in quality % contain below the Mo:3.0%, in below the B:0.01% one or both.

14. the soft two phase stainless steel wire rod that cold-workability according to claim 12 is good with magnetizability, wherein, in quality % contain in the following element more than a kind:

Below the Al:0.1%,

Below the Mg:0.01%,

Below the Ca:0.01%.

15. the soft two phase stainless steel wire rod that cold-workability according to claim 12 is good with magnetizability, wherein, in quality % contain below the Mo:3.0%, in below the B:0.01% one or both;

Also contain in the following element more than a kind:

Below the Al:0.1%,

Below the Mg:0.01%,

Below the Ca:0.01%.

16. the soft two phase stainless steel wire rod that cold-workability according to claim 12 is good with magnetizability, wherein, in quality % contain in the following element more than a kind:

Below the Nb:1.0%,

Below the Ti:0.5%,

Below the V:1.0%,

Below the Zr:1.0%.

17. the soft two phase stainless steel wire rod that cold-workability according to claim 12 is good with magnetizability, wherein, in quality % contain below the Mo:3.0%, in below the B:0.01% one or both;

Also contain in the following element more than a kind:

Below the Nb:1.0%,

Below the Ti:0.5%,

Below the V:1.0%,

Below the Zr:1.0%.

18. the soft two phase stainless steel wire rod that cold-workability according to claim 12 is good with magnetizability, wherein, in quality % contain below the Al:0.1%, in below the Mg:0.01%, below the Ca:0.01% more than a kind;

Also contain in the following element more than a kind:

Below the Nb:1.0%,

Below the Ti:0.5%,

Below the V:1.0%,

Below the Zr:1.0%.

19. the soft two phase stainless steel wire rod that cold-workability according to claim 12 is good with magnetizability, wherein, in quality % contain below the Mo:3.0%, in below the B:0.01% one or both;

Also contain below the Al:0.1%, in below the Mg:0.01%, below the Ca:0.01% more than a kind;

Also contain in the following element more than a kind:

Below the Nb:1.0%,

Below the Ti:0.5%,

Below the V:1.0%,

Below the Zr:1.0%.

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