JPH07316744A - Martensitic stainless steel wire rod excellent in cold workability and its production - Google Patents

Abstract

PURPOSE:To produce a high strength and high toughness martensitic stainless steel wire rod excellent in cold workability by specifying its compsn. constituted of Cr, Ni, C, N, Al, Si, Mn, S, O, Nb, V, Ti and Fe. CONSTITUTION:This martensitic stainless steel wire rod a compsn. contg., by weight, 11.0 to 16.0% Cr, 1.0 to 4.0% Ni, 0.13 to 0.30% C, 0.06 to 0.13% N, 0.01 to 0.10% Al, 0.1 to 0.5% Si, 0.1 to 2.0% Mn, <=0.005% S, <=0.005% O, <=0.01% Nb, <=0.1% V, <=0.01% Ti, and the balance substantial Fe with inevitable impurities, and in which X expressed by the formula (X=280Al-560N-290 C-600S1/2-12000-6Si-2.4Ni+207) is regulated to >=60%. This wire rod has a tempered martensitic structure, and in which tensile strength is regulated to <=100kgf/mm<2> and limit cold rolling ratio to >=60%. The wire rod can be obtd. by subjecting a stainless steel slab having the same compsn. to wire rod rolling and thereafter executing specified annealing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire material for improving cold formability of screws, bolts, nails, springs and the like of martensitic stainless steel which is difficult to cold work and a method for producing the wire material.

[0002]

2. Description of the Related Art In recent years, martensitic stainless steel wire rods have been widely used in construction / construction materials, vehicles and the like. Among the stainless steel products of this type, SUS41 is used for applications requiring high strength, high rust resistance, high toughness, etc.
Martensitic stainless steel wire rods in which alloy elements such as Ni, C, N, and Mo are positively added to a martensitic stainless steel such as 0 or SUS420J1 have been used.

Martensitic stainless steels for construction and building materials are soft annealed and then cold-formed into products such as screws, bolts, nails and springs, which are then quenched and tempered to obtain high strength and high toughness. Characterized. For this reason,
For these product processing wire rods, the compression processing rate is 60
It is required that a high cold working rate of not less than 10% is possible without cracking.

Conventionally, the softening heat treatment method for martensitic stainless steel is (a) complete annealing by ferrite transformation, (b) low temperature annealing in which heating is performed immediately below the A _c1 point and then cooling,
(C) After the ferrite transformation, an annealing method such as a constant temperature annealing is performed in which the material is cooled to just below the A _c1 point, held and further cooled. However, Ni, C, N, and other alloying elements such as Mo are positively added, and the hardening / tempering hardness of the product is H.
Martensitic stainless steel wire rods with a v of 500 or more and an impact value of 20 J / cm ² or more are difficult to soften because of the formation of fine carbonitrides during the softening heat treatment and have poor cold workability.
There has been a problem that processing cracks occur during product molding.

[0005]

DISCLOSURE OF THE INVENTION According to the present invention, the quenching / tempering hardness of the product is Hv of 500 or more and the impact value is 20 J /.
By improving the cold workability of martensitic stainless steel wire rods with a cm ² or more, it is possible to stably provide martensitic stainless steel wire rods with a high cold working rate of 60% or more with a high working strength. -The purpose is to enable the production of processed products such as high toughness screws, nails and springs.

[0006]

The present invention has been made by obtaining the following findings as a result of various studies on a method for improving the cold workability of a martensitic stainless steel wire rod. That is, the inventors
And Cr: 11.0 to 16.0%, Ni: 1.0 to 4.
0%, C: 0.13 to 0.30%, N: 0.06 to 0.
13%, Al: 0.01 to 0.10%, Si: 0.1
0.5%, Mn: 0.1 to 2.0%, S: 0.005%
Below, O: 0.005% or less, Nb: 0.01% or less,
V: 0.1% or less, Ti: 0.01% or less, the balance substantially consisting of Fe and inevitable impurities, and the value of X represented by the formula (1) is 60% or more. After rolling the slab into a wire rod and cooling it to room temperature, A _c1 to (A _c1 + A _c3 ).
Compressed by performing the first annealing in the temperature range of / 2 and further performing the second annealing treatment at the temperature of A _c1 or less under the condition that the LMP value represented by the formula (2) satisfies 17.0 or more. It was found that a martensitic stainless steel wire rod capable of high cold working with a working rate of 60% or more can be obtained.

X = 280Al-560N-290C-600√S-1200O-6Si-5Ni + 207 (1) Formula LMP = (T + 273) × (20 + logt) × 10 ⁻³ (2) Formula T: Heating temperature (° C.) , T: heating time (h) Furthermore, the above wire rod is subjected to high cold working and is subjected to quenching and tempering to obtain martensite having a complicated shape, hardness of Hv of 500 or more, and impact value of 20 J / cm ² or more. It has been found that a stainless steel product can be obtained.

[0008]

The reason for limiting the scope of the present invention will be described below. First,
The reasons for limiting the components described in claim 1 will be described. Cr is a martensitic stainless steel for imparting rust resistance 1
1.0% or more was added. However, if it exceeds 16.0%, a martensite structure cannot be obtained, and hardness cannot be 500 or more in Hv. Therefore, the range of Cr is 11.0 to 1
It was limited to 6.0%. Desirably 11.0 to 14.0%
Is good.

Ni is added in an amount of 1.0% or more in order to impart the toughness of the quenched and tempered product to an impact value of 20 J / cm ² or more. However, when Ni exceeds 4.0%, A _c1 becomes low, the annealing temperature becomes low, and it becomes difficult to soften, so that cold workability cannot be secured. Therefore, Ni
Was limited to 4.0%. Desirably 1.0-3.
0% is good.

C is added to 0.13% or more in order to make the hardness of the quenched and tempered product Hv of 500 or more. However, if C exceeds 0.30%, coarse carbides are often formed during softening annealing, and cold workability cannot be ensured.
Carbides are also formed during quenching, which deteriorates the toughness and rust resistance of the product. Therefore, the upper limit of C is limited to 0.30%. Desirably, 0.13 to 0.20% is good.

N suppresses the formation of coarse carbides during softening annealing, ensures cold workability, and also ensures the rust resistance of the base metal.
In addition, 0.06% or more is added in order to make the hardness of the quenched and tempered product Hv of 500 or more. However, if N is 0.
If it exceeds 13%, not only blowholes are formed, but also nitrides are formed, which causes resistance to temper softening and deteriorates cold workability. In addition, the rust resistance of the product deteriorates. Therefore, N
Was limited to 0.13%. Desirably 0.06 ~
0.11% is good.

Al reduces the solid solution N by forming AlN and suppresses the generation of fine nitrides during softening annealing, thus facilitating softening and improving cold workability. Also, Al
Is a strong deoxidizer, it can reduce O and improve cold workability. Further, Al deoxidation promotes the reduction of S and improves the cold workability. Therefore, 0.01% or more of Al is added. However, even if Al exceeds 0.10%, the effect is saturated, so the upper limit was limited to 0.10%. From an economical point of view, 0.01 to 0.05% is preferable.

Si is an element that easily forms a carbonitride that becomes a softening resistance during softening annealing, deteriorates the cold workability, and is effective as a deoxidizing material, so that 0.1 to 0.
The range was limited to 5%. It is preferably 0.4% or less. Mn is added at 0.1% or more for deoxidation. However, even if it exceeds 2.0%, not only the effect will be saturated,
Since the rust resistance is deteriorated, the range of Mn is 0.1 to 0.1%.
It was limited to 2.0%.

S and O deteriorate cold workability in martensitic stainless steel. For this reason, in order to carry out cold working at a compression working rate of 60% or more without cracking, each is limited to 0.005% or less. Desirably, S is 0.003% or less and O is 0.004% or less. N
b, V, and Ti are contained in a steel material such as scrap and form fine carbonitrides, which causes softening resistance and deteriorates cold workability. Therefore, Nb is limited to 0.01% or less, V is limited to 0.1% or less, and Ti is limited to 0.01% or less. Desirably, Nb is 0.008% or less, V is 0.08% or less, and Ti is 0.008% or less.

The expression (1) is obtained as a result of investigating the influence of each element on the cold workability of the base material after annealing, and shows the element which has an influence on the cold workability and its influence degree. It is a thing. If the value of X is less than 60 (%), the processing rate is 60
Since cracking occurs during cold working exceeding%, this value is limited to 60% or more. Next, the reasons for limitation of the softening annealing method according to claim 3 will be described.

In order to improve the cold workability of the above-mentioned martensitic stainless steel wire rod, it is necessary to lower the strength and ductility by softening annealing, and the heat treatment according to claim 3 of the present invention is performed. . In the first annealing in claim 3 of the present invention, the martensitic stainless steel is _subjected to A _c1 to (A
By annealing in the temperature range of _c1 + A _c3 ) / 2,
As shown in (1), a carbonitride is precipitated from the tempered martensite structure and at the same time, an austenite phase is generated. 2 of tempered martensite and austenite
By forming a phase structure, atomic diffusion is promoted, the boundary between tempered martensite and austenite region becomes a low dislocation density region, and hardness is reduced. However, if the first annealing temperature is lower than A _c1 , atomic diffusion is not promoted and the hardness does not decrease so much. Conversely, the first annealing temperature is (A _c1 +
If it is higher than A _c3 ) / 2, the amount of austenite increases, and the hardness increases due to quenching during cooling. Therefore, the first annealing temperature range is limited to A _c1 to (A _c1 + A _c3 ) / 2. It is desirable to anneal for 1 hour or more within this limited temperature range.

After that, the martensite structure annealed by the first annealing is annealed a second time at a temperature of A _c1 or less. However, when the second annealing temperature exceeds A _c1 , an austenite structure appears, and the hardness increases due to quenching during cooling. Therefore, the second annealing temperature is limited to A _c1 or less. At this time, in order to sufficiently soften the martensite structure at a temperature of A _c1 or less, the Larson-Miller parameter (LM), which is an index of diffusion represented by temperature and time, is used.
It is necessary that the value of P) is 17.0 or more. Therefore, the second annealing condition was limited to a temperature of A _c1 or less and an LMP value of 17.0 or more. Desirably, the LMP value is 18.0 or more.

[0018]

EXAMPLES Tables 1 and 2 (continued from Table 1) show the components of the tested materials. Tables 3 and 4 (continued from Table 3-
1), Table 5 (continued-2 in Table 3), Table 6 (continued-3 in Table 3), Table 7 (continued-4 in Table 3), and Table 8 (continued-5 in Table 3). Manufacturing conditions and evaluation results are shown.

In these examples, melting and hot wire rolling were performed in the usual stainless steel wire manufacturing process. After that, a part of the hot-rolled material was subjected to normal low-temperature annealing in which it was annealed just under A _c1 for 4 hours. The remaining hot rolled material is A _c1
To A _c3 in a temperature range of 0.5 to 5 hours, followed by annealing at a temperature of around A _c1 for 0.5 to 6 hours. Then, a part of the test piece was processed, and the cold workability was evaluated by a compression test. The remaining wire rod after softening annealing is 110
Quenching was performed at 0 ° C., and tempering was performed at 200 ° C. for 30 minutes to obtain a martensite structure. Then, hardness, rust resistance, and toughness were evaluated as properties of the product after quenching and tempering.

The cold workability was evaluated by performing a compression test on a cylindrical sample of φ5 × 7.5 mm, and the compression rate at which cracks occurred was evaluated as the critical cold workability. When the workability was 60% or more, the cold workability was rated as ◯, and when cracked, was rated as x. The cold workability of the examples of the present invention is ◯. The hardness was measured according to JIS Z2244 by measuring the center hardness of the longitudinal section of the wire. The product hardness after quenching and tempering of the inventive example was 500 or more in Hv.

In the rust resistance evaluation test, a surface layer of a wire having a size of φ5 × 100 mm was ground by # 500 according to JISZ2371, and was sprayed with salt water for 100 hours. The rust resistance was evaluated as ◯ when no rust was formed and as x when rusted. The rust resistance of the product of the present invention after quenching and tempering was ◯. JIS toughness
From 2202, a U-notch test piece having a size of φ5 × 55 mm and a depth of 1 mm was used to perform a test at room temperature, and the impact value at that time was evaluated. The impact value of the product of the present invention after quenching and tempering was 20 J / cm ² or more.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

[Table 5]

[0027]

[Table 6]

[0028]

[Table 7]

[0029]

[Table 8]

The test steels A to E and S to W are 2Ni-0.16.
Each Cr that contributes to rust resistance with C-0.1N as a basic component
Al amount (%) that contributes to cold workability with respect to the amount (%),
The effects of the present invention were confirmed by changing the Si content (%), the S content (%), the O content (%), and the softening and annealing conditions after the wire rod rolling to investigate the influence on each characteristic. Test Steel A to E
In, the effect of the present invention can be confirmed.

In particular, the invention sample No. 1 having a Cr content of 11.0 to 14.0%. Nos. 1, 2, and 8 of the present invention No. 1 having a Cr content of more than 14.0%. Hardness of 9 and 10 after quenching and tempering is Hv
Is less than 530, whereas it is 530 or more, and the effect is remarkable. In particular, the present invention example No. in which the S amount is 0.003% or less. No. 2 of the invention example No. 2 in which the amount of S exceeds 0.003%. The marginal cold working rate of No. 8 is 68%, whereas it is 68%, and the effect is remarkable.

In particular, the invention sample No. 1 having an O content of 0.004% or less. No. 9 of the present invention has an O content of more than 0.004%. 1
The limit cold working rate of 0 is 68%, while it is 68%, and the effect is remarkable. In particular, the invention sample No. 1 having the first heat treatment time of 1 hour or more. No. 2 of the invention example No. 2 in which the first heat treatment time was less than 1 hour. The limit working rate of No. 3 is 68%, while the limit working rate is 63%, and the effect is remarkable.

Particularly, the LMP of the second heat treatment condition is 1
The present invention example No. of 7.0 or more. No. 2 of the invention example No. 2 having LMP of less than 17.0 under the second heat treatment condition. The limit working rate of No. 4 is 68%, while it is 61%, and the effect is remarkable. Comparative Example No. No. 5 has a high softening hardness because the first annealing temperature exceeds (A _c1 + A _c3 ) / 2,
Poor cold workability.

Comparative Example No. No. 6 has a second annealing temperature of A _c1
Therefore, the softening hardness is high and the cold workability is poor.
Comparative Example No. Since No. 7 is an ordinary low temperature annealing, it has a high softening hardness and is inferior in cold workability. Comparative Example No. Since No. 11 has a high S content and a high O content, the value of X is less than 60, and the cold workability is poor.

Comparative Example No. Since No. 12 has a high Si amount and a low Al amount, the value of X is less than 60, and the cold workability is poor. Comparative Example No. No. 13 has an X value of less than 60 and is inferior in cold workability. Comparative Example No. Since 14 has a high Cr content,
Martensite structure is not obtained and the product hardness after quenching and tempering is inferior.

Comparative Example No. Since No. 15 has a low Cr content, the rust resistance of the product after quenching and tempering is poor. Steels F to K,
X to Z and AA to AC are 13.2Cr-0.16C-0.
With respect to each Ni amount (%) which contributes to toughness with 1N as a basic component and Mn amount (%) which is a deoxidizing element, Al amount (%), Si amount (%), S which contribute to cold workability, amount(%),
The effect of the present invention was confirmed by changing the O content (%) and the softening / annealing conditions and investigating the influence on each property. The effects of the present invention can be confirmed in the test steels F to K.

Particularly, the present invention sample N containing 3.0% or less of Ni
o. Nos. 16 to 18, 21, and 22 of the present invention example No. having a Ni content of more than 3.0%. The limit cold working ratio of No. 23 is 62%, whereas it is 64 to 70%, and the effect is remarkable. In particular, the present invention example No. having a Si content of 0.4% or less. 17
Inventive Example No. 1 having a Si content of more than 0.4%. The limit cold working rate of 16 is 70%, while the limit is 64%, and the effect is remarkable.

In particular, the invention sample No. 1 having an Al content of 0.05% or less. No. 18 of the present invention has an Al content of more than 0.05%.
The limit cold working rate of 23 is 66%, while 65%
The effect of Al is saturated at more than 0.05%. Comparative Example No. Since No. 19 has the first annealing temperature lower than A _c1 , the softening hardness is high and the cold workability is poor.

Comparative Example No. Since No. 20 is a normal low temperature annealing, the softening hardness is high and the cold workability is poor. Comparative Example No.
Since No. 21 has a high Mn content, the rust resistance of the product after quenching and tempering is inferior. Comparative Example No. No. 24 has a high Si content and a low Al content, and thus is inferior in cold workability.

Comparative Example No. Since No. 25 has a high S content, cold workability is poor. Comparative Example No. 27 has a high Si content and is Al
Since the amount is low, cold workability is poor. Comparative Example No. Although No. 28 satisfies the cold workability, the toughness of the product characteristics after quenching and tempering is inferior because the Ni content is low. No. 29
On the contrary, since the amount of Ni is high, the material strength is high and the cold workability is poor.

The test steels L to O and AD to AH are 14Cr-
With respect to each C amount (%) and each N amount (%) contributing to quenching hardness with 2.5Ni as a basic component, Al amount (%), Si amount (%), which contributes to cold workability, The effect of the present invention was confirmed by changing the S content (%), the O content (%) and the softening / annealing condition and investigating the influence on each property. The effects of the present invention can be confirmed in the test steels L to O.

In particular, the C content is 0.20% or less, and the N content is 0.
Inventive Example No. 11 and below 31 and 32 have a C content of 0.2
Inventive Example No. of more than 0%. The limit cold working rate of 35 is 62
% Of the present invention, and the N content exceeds 0.11%. While the limit cold working rate of 30 is 63%, it is 70% or more,
The effect is remarkable. Comparative Example No. No. 33 is the second annealing condition: LMP is less than 17.0, so the softening hardness is high and the cold workability is poor.

Comparative Example No. Since No. 34 is a normal low temperature annealing, it has a high softening hardness and is inferior in cold workability. Comparative Example No.
Since 36 has a high Si content and a low Al content, cold workability is poor. Comparative Example No. Since 37 has a low C content, it is inferior in product hardness after quenching and tempering. Comparative Example No. No. 38, which has a low N content, is inferior in product hardness after quenching and tempering.

Comparative Example No. Since No. 39 has a large amount of C, a large amount of coarse carbide is precipitated, resulting in poor cold workability as well as poor rust resistance and toughness of the product after quenching and tempering. No. 40
Has a large amount of N, so that it precipitates a lot of fine nitrides that become a softening resistance, which is not only inferior in cold workability but also produces blowholes during casting, which is inferior in manufacturability, and also produces Cr nitrides. Poor rust resistance of the product after tempering.

The test steels H, P to R, and Al to AK have a value of 13.5.
Cr-2.5Ni-0.16C-0.1N as a basic component and Nb amount (%) and V amount (%) that contribute to microcarbonitrides
The effect of the present invention was confirmed by changing the Ti content (%) and the effect on each characteristic. Applicable steel H, P
From ~ R, the effect of the present invention can be confirmed. In particular, the present invention example No. having Nb content of 0.008% or less, V content of 0.08% or less, and Ti content of 0.008% or less. No. 18 of the present invention having an Nb content of more than 0.008%. No. 41 of the present invention having a limit cold working ratio of 63% and a V content of more than 0.08%. No. 43 of the present invention having a critical cold workability of 61% and a Ti content of more than 0.008%. The limit cold working rate of 45 is 63%, whereas it is 65%, and the effect is remarkable.

Comparative Example No. No. 42 has a high Nb content (%) and thus is inferior in cold workability. Comparative Example No. Since 44 has a high V content (%), it is inferior in cold workability. Comparative Example No. Since 46 has a high Ti content (%), it is inferior in cold workability. As shown in the above examples, the superiority of the present invention for the purpose of high cold working of martensitic stainless steel wire is obvious.

[0047]

Industrial Applicability According to the present invention, it is possible to provide a martensitic stainless steel wire rod having excellent cold workability, which brings about a remarkable industrial effect.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a generation state of a low dislocation density region accompanied by atomic diffusion due to a two-phase structure.

Claims (3)

[Claims] 1. Cr: 11.0 to 16.0% by weight, Ni: 1.0 to 4.0%, C: 0.13 to 0.30%, N: 0.06 to 0.13. %, Al: 0.01 to 0.10%, Si: 0.1 to 0.5%, Mn: 0.1 to 2.0%, S: 0.005% or less, O: 0.005% or less , Nb: 0.01% or less, V: 0.1% or less, Ti: 0.01% or less, and the balance substantially consisting of Fe and inevitable impurities, and represented by the formula (1). A martensitic stainless steel wire rod having excellent cold workability, wherein the value of X is 60% or more. X = 280Al-560N-290C-600√S-1200O-6Si-2.4Ni + 207 (1) Formula 2. The composition according to claim 1, which has a tempered martensite structure and a tensile strength of 100 kgf / mm.
A martensitic stainless steel wire rod having excellent cold workability, which is characterized by having a limit cold workability of ² or less and 60% or more. 3. A martensitic stainless steel slab of the composition according to claim 1 is wire-rolled and cooled to room temperature, and then A
_The first annealing is performed in the temperature range of _c1 to (A _c1 + A _c3 ) / 2, and the LMP represented by the formula (2) at a temperature of A _c1 or less.
The method for producing a martensitic stainless steel wire rod having excellent cold workability, which comprises performing a second annealing treatment under the condition that the value of is 17.0 or more. LMP = (T + 273) × (20 + logt) × 10 ⁻³ (2) Formula T: heating temperature (° C.), t: heating time (h)