CN113631733A

CN113631733A - Bar-shaped steel

Info

Publication number: CN113631733A
Application number: CN202080023939.3A
Authority: CN
Inventors: 山先祥太; 高野光司; 吉泽明展; 森田博树
Original assignee: Nippon Steel and Sumikin Stainless Steel Corp
Current assignee: Nippon Steel Stainless Steel Corp
Priority date: 2019-03-27
Filing date: 2020-03-25
Publication date: 2021-11-09
Also published as: JP7077477B2; EP3950970A1; US20220170125A1; MX395077B; MX2021011568A; JPWO2020196595A1; EP3950970A4; WO2020196595A1

Abstract

一种棒状钢材，其是沿一个方向延伸的棒状钢材，所述棒状钢材的化学组成以质量％计为C：0.001～0.20％、Si：0.01～3.0％、Mn：0.01～2.0％、Ni：0.01～5.0％、Cr：7.0～35.0％、Mo：0.01～5.0％、Cu：0.01～3.0％、N：0.001～0.10％、Nb：0.2～2.0％、任意元素、剩余部分：Fe及不可避免的杂质，轧制方向的晶体取向RD//<100>分率(<100>取向与轧制方向的角度差为20°以下的结晶的面积比率)为0.5以下。A rod-shaped steel material, which is a rod-shaped steel material extending in one direction, the chemical composition of the rod-shaped steel material in mass % is C: 0.001-0.20%, Si: 0.01-3.0%, Mn: 0.01-2.0%, Ni: 0.01 to 5.0%, Cr: 7.0 to 35.0%, Mo: 0.01 to 5.0%, Cu: 0.01 to 3.0%, N: 0.001 to 0.10%, Nb: 0.2 to 2.0%, arbitrary elements, remainder: Fe and unavoidable The RD//<100> fraction of the crystal orientation in the rolling direction (the area ratio of crystals whose angle difference between the <100> orientation and the rolling direction is 20° or less) is 0.5 or less.

Description

Bar-shaped steel

Technical Field

The present invention relates to a bar-shaped steel material.

Background

Conventionally, high-purity ferritic stainless steel has been used as a cold forging member in some cases as a wire rod having a small diameter. However, there are cases where the large-diameter wire rod, the steel bar, or the like is restricted. The reason for this is that the coarse wire rod or steel bar of the high purity ferritic stainless steel has a reduced toughness due to the presence of coarse unrecrystallized grains or the like in the steel structure, and promotes brittle fracture during cold forging.

Patent documents 1 to 6 disclose steel wire rods and the like, which have improved properties by appropriately controlling chemical compositions, production conditions, and the like.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2015-224358

Patent document 2: japanese patent laid-open publication No. 2013-147705

Patent document 3: international publication No. 2014/157231

Patent document 4: japanese laid-open patent publication No. 2002-254103

Patent document 5: japanese patent laid-open publication No. 2005-226147

Patent document 6: japanese patent laid-open publication No. 2005-313207

Patent document 7: japanese laid-open patent publication No. H05-329510

Disclosure of Invention

Problems to be solved by the invention

However, there has been no technique for improving toughness by controlling the chemical composition, metal structure, and the like of a bar-shaped steel.

In view of the above circumstances, an object of the present invention is to solve the above problems and provide a rod-shaped steel material having excellent toughness.

Means for solving the problems

The present invention has been made to solve the above problems, and the gist thereof is the following rod-shaped steel material.

(1) A rod-shaped steel material extending in one direction, the chemical composition of the rod-shaped steel material being, in mass%:

C：0.001～0.09％、

Si：0.01～3.0％、

Mn：0.01～2.0％、

Ni：0.01～5.0％、

Cr：7.0～35.0％、

Mo：0.01～5.0％、

Cu：0.01～3.0％、

N：0.001～0.10％、

Nb：0.2～2.0％、

Ti：0～2.0％、

V：0～2.0％、

B：0～0.1％、

Al：0～5.0％、

W：0～2.5％、

Ga：0～0.05％、

Co：0～2.5％、

Sn：0～2.5％、

Ta：0～2.5％、

Ca：0～0.05％、

Mg：0～0.012％、

Zr：0～0.012％、

REM：0～0.05％、

the rest is as follows: fe and inevitable impurities, and the balance of Fe,

the crystal orientation RD// <100> fraction in the rolling direction is 0.5 or less.

The crystal orientation RD// <100> fraction in the rolling direction means the area ratio of crystals having an angular difference between the <100> orientation and the rolling direction of 20 DEG or less.

(2) The rod-shaped steel material according to the present invention further contains one or more elements selected from the following elements in terms of mass%:

Ti：0.001～2.0％、

V：0.001～2.0％

B：0.0001～0.1％

Al：0.001～5.0％、

W：0.05～2.5％、

Ga：0.0004～0.05％、

Co：0.05～2.5％、

sn: 0.01 to 2.5%, and

Ta：0.01～2.5％。

(3) the rod-shaped steel material according to the present invention further contains one or more elements selected from the following elements in terms of mass%:

Ca：0.0002～0.05％、

Mg：0.0002～0.012％、

zr: 0.0002 to 0.012%, and

REM：0.0002～0.05％。

(4) a bar-shaped steel material extending in one direction, the chemical composition of the bar-shaped steel material being the chemical composition of the present invention in mass%,

the transition temperature is 200 ℃ or lower.

(5) The rod-shaped steel material according to the present invention has a transformation temperature of 200 ℃ or lower.

(6) According to the present invention, the rod-shaped steel material has a circular cross-sectional shape,

the diameter of the circle is 15.0 to 200 mm.

The steel rod of the present invention includes steel wire rods, steel wires, and steel rods.

According to the present invention, a rod-shaped steel material having excellent toughness can be obtained.

Detailed Description

The present inventors have conducted various studies to obtain a rod-shaped steel material having excellent toughness. As a result, the following findings (a) to (c) were obtained.

(a) For example, in a rod-shaped steel material such as a high-purity ferritic stainless steel wire rod, since transformation from δ ferrite to austenite does not occur, the microstructure tends to be coarse. As for the toughness of the steel material, brittle fracture occurs due to such a coarse metal structure. In a ferritic stainless steel wire rod, a large-diameter rod-shaped steel material tends to have a significantly large and coarse metal structure and to have a reduced toughness.

(b) In order to improve the toughness of the large-diameter bar-shaped steel material, it is effective to appropriately control the RD// <100> fraction in the metal structure.

(c) In order to control the RD// <100> fraction, it is preferable to adjust the chemical composition and the conditions during production, specifically, the temperature, time, working ratio during rolling, roll diameter during rough rolling, and the like.

The present invention has been made based on the above findings. A preferred embodiment of the present invention will be described in detail. In the following description, a preferred embodiment of the present invention will be described as the present invention. Hereinafter, each element of the present invention will be described in detail.

1. Crystal orientation RD// <100> fraction in rolling direction

In the rod-shaped steel material of the present invention, the crystal orientation in the Rolling Direction (RD) is controlled. Specifically, the crystal orientation RD// <100> fraction (area ratio) (hereinafter simply referred to as "RD// <100> fraction") in the rolling direction is preferably set to 0.5 or less. This is because if the RD// <100> fraction exceeds 0.5, brittle fracture is promoted and toughness is lowered. The RD// <100> fraction is more preferably set to 0.40 or less, and still more preferably set to 0.35 or less.

The RD// <100> fraction is calculated using the following procedure. Specifically, the RD// <100> fraction is measured in an L-section of the steel material (a section parallel to the rolling direction (longitudinal direction) of the steel material and including the center of the steel material) with 200-fold visual field or more at the surface layer portion, the central portion, and the 1/4-depth position portion existing between the surface layer portion and the central portion. Then, the crystal orientation of each crystal grain in the observation field was analyzed by using FE-SEM/EBSD. The crystal plane in the RD direction was analyzed with the rolling direction RD set, and the <100> orientation component was shown only in the portion where the gap (clearance) was within 20 °, and the RD// <100> fraction was measured. The surface portion is a position having a depth of 1mm from the surface in the center axis direction. That is, the crystal orientation RD// <100> fraction in the rolling direction means the area ratio of crystals having an angular difference between the <100> orientation and the rolling direction of 20 ° or less.

2. Chemical composition

The reasons for limiting the elements are as follows. In the following description, "%" as to the content means "% by mass".

C：0.001～0.09％

C, the strength of the steel is improved. Therefore, the C content is set to 0.001% or more, preferably 0.002% or more. However, if C is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. Therefore, the C content is set to 0.09% or less. The C content is preferably 0.05% or less, more preferably 0.03% or less, and still more preferably 0.02% or less.

Si：0.01～3.0％

Si is contained as a deoxidizing element, and the high-temperature oxidation characteristics are improved. Therefore, the Si content is set to 0.01% or more, preferably 0.05% or more. However, if Si is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. Therefore, the Si content is set to 3.0% or less. The Si content is preferably 2.0% or less, more preferably 1.0% or less, and still more preferably 0.5% or less.

Mn：0.01～2.0％

Mn improves the strength of the steel. Therefore, the Mn content is set to 0.01% or more, preferably 0.05% or more. However, if Mn is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. Further, the corrosion resistance may be lowered. Therefore, the Mn content is set to 2.0% or less. The Mn content is preferably 1.0% or less, more preferably 0.8% or less, and still more preferably 0.5% or less.

Ni：0.01～5.0％

Ni improves the toughness of the steel. Therefore, the Ni content is set to 0.01% or more, preferably 0.05% or more. However, if Ni is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. Therefore, the Ni content is set to 5.0% or less. The Ni content is preferably set to 2.0% or less, more preferably 1.0% or less, and still more preferably 0.5% or less.

Cr：7.0～35.0％

Cr improves corrosion resistance. Therefore, the Cr content is set to 7.0% or more. The Cr content is preferably 10.0% or more, and more preferably 15.0% or more. However, if Cr is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. The Cr content is set to 35.0% or less. The Cr content is preferably 27.0% or less, more preferably 25.0% or less, and still more preferably 21.0% or less.

Mo：0.01～5.0％

Mo improves corrosion resistance. Therefore, the Mo content is set to 0.01% or more. However, if Mo is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. Therefore, the Mo content is set to 5.0% or less. The Mo content is preferably 2.0% or less, more preferably 1.0% or less, and still more preferably 0.5% or less.

Cu：0.01～3.0％

Cu improves corrosion resistance. Therefore, the Cu content is set to 0.01% or more, preferably 0.30% or more. However, if Cu is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. Therefore, the Cu content is set to 3.0% or less. The Cu content is preferably 2.0% or less, more preferably 1.0% or less, and still more preferably 0.5% or less.

N：0.001～0.10％

N improves the strength of the steel. Therefore, the N content is set to 0.001% or more, preferably 0.004% or more. However, if N is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. Therefore, the N content is set to 0.10% or less. The N content is preferably set to 0.05% or less, more preferably 0.03% or less, and still more preferably 0.02% or less.

Nb：0.2～2.0％

Nb has an effect of improving the strength of the steel. Further, Nb forms carbonitride, and therefore suppresses the formation of Cr carbide and the formation of a Cr-deficient layer. As a result, Nb has an effect of preventing grain boundary corrosion. That is, Nb is an element effective for improving corrosion resistance, and therefore, 0.2% or more, preferably 0.3% or more is added. However, if Nb is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. In addition, the toughness is reduced by coarse carbonitrides. Therefore, the Nb content is set to 2.0% or less. The Nb content is preferably set to 1.0% or less, more preferably 0.8% or less.

The rod-shaped steel material of the present invention may contain, in addition to the above elements, one or more elements selected from Ti, V, B, Al, W, Ga, Co, Sn, and Ta as necessary.

Ti：0～2.0％

Ti has an effect of improving the strength of the steel. Further, since Ti forms carbonitride, generation of Cr carbide is suppressed, and generation of a Cr-deficient layer is suppressed. As a result, the effect of preventing grain boundary corrosion is obtained. That is, Ti has an effect of improving corrosion resistance, and therefore, it may be contained as necessary.

However, if Ti is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. In addition, the toughness is reduced by coarse carbonitrides. Therefore, the Ti content is set to 2.0% or less. The Ti content is preferably 1.0% or less, more preferably 0.5% or less, and still more preferably 0.05% or less. On the other hand, in order to obtain the above effects, the Ti content is preferably set to 0.001% or more.

V：0～2.0％

V has an effect of improving corrosion resistance, and therefore may be contained as needed. However, if V is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. In addition, the toughness is reduced by coarse carbonitrides. Therefore, the V content is set to 2.0% or less. The V content is preferably set to 1.0% or less, more preferably 0.5% or less, and still more preferably 0.1% or less. On the other hand, in order to obtain the above effects, the V content is preferably set to 0.001% or more.

B：0～0.1％

B has the effect of improving hot workability and corrosion resistance. Therefore, it may be contained as necessary. However, if B is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. Therefore, the B content is set to 0.1% or less. The B content is preferably set to 0.02% or less, more preferably 0.01% or less. On the other hand, in order to obtain the above effects, the content of B is preferably set to 0.0001% or more.

Al：0～5.0％

Al may be contained as necessary because it has an effect of promoting deoxidation and improving the level of cleanliness of inclusions. However, if Al is contained excessively, the effect is saturated, and the RD// <100> fraction increases. As a result, toughness is reduced. In addition, toughness is reduced by coarse inclusions. Therefore, the Al content is set to 5.0% or less. The Al content is preferably set to 1.0% or less, more preferably 0.1% or less, and still more preferably 0.01% or less. On the other hand, in order to obtain the above effects, the Al content is preferably set to 0.001% or more.

W：0～2.5％

W may be contained as necessary because it has an effect of improving corrosion resistance. However, if W is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. In addition, the toughness is reduced by coarse carbonitrides. Therefore, the W content is set to 2.5% or less. The W content is preferably set to 2.0% or less, more preferably 1.5% or less. On the other hand, in order to obtain the above effects, the W content is preferably set to 0.05% or more, and more preferably 0.10% or more.

Ga：0～0.05％

Since Ga has an effect of improving corrosion resistance, Ga may be contained as needed. However, if Ga is excessively contained, hot workability is degraded. Therefore, the Ga content is set to 0.05% or less. On the other hand, in order to obtain the above effects, the Ga content is preferably set to 0.0004% or more.

Co：0～2.5％

Co may be contained as necessary because it has an effect of improving the strength of the steel material. However, if Co is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. Therefore, the Co content is set to 2.5% or less. The Co content is preferably set to 1.0% or less, more preferably 0.8% or less. On the other hand, in order to obtain the above effects, the Co content is preferably set to 0.05% or more, and more preferably 0.10% or more.

Sn：0～2.5％

Sn may be contained as necessary because it has an effect of improving corrosion resistance. However, if Sn is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. Further, the grain boundary segregation of Sn lowers the toughness. Therefore, the Sn content is set to 2.5% or less. The Sn content is more preferably 1.0% or less, and still more preferably 0.2% or less. On the other hand, in order to obtain the above effects, the Sn content is preferably set to 0.01% or more, and more preferably 0.05% or more.

Ta：0～2.5％

Ta has an effect of improving corrosion resistance, and therefore may be contained as necessary. However, if Ta is contained excessively, the RD// <100> fraction increases. As a result, toughness is reduced. Therefore, the Ta content is set to 2.5% or less. The Ta content is preferably set to 1.5% or less, more preferably 0.9% or less. On the other hand, in order to obtain the above effects, the Ta content is preferably set to 0.01% or more, more preferably 0.04% or more, and still more preferably 0.08% or more.

The rod-shaped steel material of the present invention may contain, in addition to the above elements, one or more elements selected from Ca, Mg, Zr, and REM as necessary.

Ca：0～0.05％

Mg：0～0.012％

Zr：0～0.012％

REM：0～0.05％

Ca. Mg, Zr and REM may be contained as needed because they are deoxidized. However, if these elements are contained excessively, the RD/< 100> fraction increases. As a result, toughness is reduced. In addition, toughness is reduced by coarse inclusions. Therefore, Ca: 0.05% or less, Mg: 0.012% or less, Zr: 0.012% or less, REM: less than 0.05%. The Ca content is preferably 0.010% or less, more preferably 0.005% or less. Mg is preferably set to 0.010% or less, more preferably 0.005% or less. Zr is preferably 0.010% or less, more preferably 0.005% or less. REM is preferably set to 0.010% or less.

On the other hand, in order to obtain the above effects, it is preferable to set Ca: 0.0002% or more, Mg: 0.0002% or more, Zr: 0.0002% or more, REM: 0.0002% or more. The Ca content is more preferably 0.0004% or more, and still more preferably 0.001% or more. The Mg content is preferably 0.0004% or more, and more preferably 0.001% or more. The Zr content is more preferably 0.0004% or more, and still more preferably 0.001% or more. The REM content is more preferably 0.0004% or more, and still more preferably 0.001% or more.

REM is a general term of 15 elements of lanthanoid elements plus 17 elements of Y and Sc. More than 1 of these 17 elements may be contained in the steel, and the REM content means the total content of these elements.

In the chemical composition of the steel sheet of the present invention, the balance is Fe and inevitable impurities. The "unavoidable impurities" herein mean components mixed by raw materials such as ores and scrap irons and various factors in the production process in the industrial production of steel sheets, and are contained within a range not adversely affecting the present invention.

Examples of the inevitable impurities include S, P, O, Zn, Bi, Pb, Se, Sb, H, and Te. Unavoidable impurities are preferably reduced, and when contained, Zn, Bi, Pb, Se, and H are preferably set to 0.01% or less. Sb and Te are preferably 0.05% or less.

3. Shape and size

As described above, the sectional shape of the surface perpendicular to the longitudinal direction of the rod-shaped steel material of the present invention is not particularly limited. For example, the cross-section is not limited to a generally circular shape. The steel sheet may contain a special-shaped material in addition to flat steel and square steel having a rectangular cross section.

In the case where the rod-shaped steel material of the present invention is a round steel, that is, in the case where the cross section is a circle, the diameter of the cross section is preferably set to be in the range of 15.0 to 200 mm. If the diameter of the cross section is less than 15.0mm, the diameter of the cross section cannot be adjusted to the size of a large-sized part which is currently required, and therefore, the diameter of the cross section is preferably set to 15.0mm or more, preferably 20.0mm or more, and more preferably 30.0mm or more.

However, if the diameter of the above cross section exceeds 200mm, the RD/< 100> fraction increases. As a result, toughness is reduced. Therefore, the diameter of the cross section is preferably set to 200mm or less. The diameter of the cross section is more preferably 150mm or less, still more preferably 100mm or less, and particularly preferably 70mm or less.

4. Evaluation of Properties

The toughness of the bar-shaped steel material of the present invention was evaluated by using the toughness-brittleness transition temperature obtained by the charpy impact test. When the transition temperature is 200 ℃ or lower, the toughness is judged to be good. The toughness is preferably 150 ℃ or lower, more preferably 100 ℃ or lower, still more preferably 80 ℃ or lower, and yet more preferably 30 ℃ or lower. From the viewpoint of the components involved in texture control and the cost due to production restrictions, the lower limit of the transition temperature is preferably set to-150 ℃.

5. Manufacturing method

A preferred method for producing the rod-shaped steel material of the present invention will be described. In the following description, a steel wire rod having a circular cross section will be described as an example. The rod-shaped steel material of the present invention can obtain its effects as long as it has the above-described configuration regardless of the production method, and for example, the rod-shaped steel material of the present invention can be stably obtained by the following production method.

In the rod-shaped steel material of the present invention, it is preferable that the steel having the above chemical composition is melted, a cast slab having a predetermined diameter is cast, and then hot or warm wire rod rolling is performed. After that, it is preferable to perform solution treatment and acid washing as appropriate as necessary.

5-1. heating step

The heating temperature of the cast slab is related to the processing temperature, and contributes to the cumulative strain and recrystallization behavior of the steel. Furthermore, the RD// <100> fraction was changed, depending on the toughness. Therefore, it is preferable to perform melting and heat the cast slab at a temperature of 450 to 1300 ℃. If the heating temperature of the cast slab is too low, the bar-shaped steel becomes brittle. Therefore, the heating temperature of the cast slab is preferably set to 450 ℃ or higher, more preferably 700 ℃ or higher, and still more preferably 800 ℃ or higher.

However, if the heating temperature of the cast slab is too high, the RD/< 100> fraction increases. As a result, toughness is reduced. Therefore, the heating temperature of the cast slab is preferably 1300 ℃ or lower, more preferably 1200 ℃ or lower, and still more preferably 1100 ℃ or lower.

5-2. skew rolling process

The heated cast slab is preferably hot worked by skew rolling. The hot working is not limited to the skew rolling, and any method may be used as long as it follows the same hot working process, and for example, even in the case of cogging (break down), the same hot working process may be used.

As disclosed in patent document 7, for example, in skew rolling, 3 work rolls are arranged on a roll shaft that is tilted while being twisted in the same direction around a material to be rolled, and each work roll revolves while rotating around the material to be rolled, so that the material to be rolled is rolled in a spiral shape while advancing.

The reduction of area of the skew rolling will cause a change in RD// <100> fraction. Therefore, the reduction of area has an influence on toughness. If the reduction of area is set to less than 20.0%, the RD/< 100> fraction increases. As a result, toughness is reduced. Therefore, the reduction of area is preferably set to 20.0% or more, more preferably 40.0% or more, still more preferably 50.0% or more, and still more preferably 80.0% or more.

The working temperature during skew rolling (the temperature of the steel after skew rolling) changes the RD// <100> fraction. In this way, since the working temperature in the skew rolling affects the toughness, the working temperature is preferably set in the range of 450 to 1200 ℃. If the rolling temperature is lower than 450 ℃, the steel becomes brittle. Therefore, the working temperature in the skew rolling is preferably set to 450 ℃ or higher, and more preferably set to 700 ℃ or higher. However, if the working temperature in the skew rolling exceeds 1200 ℃, the RD/< 100> fraction increases. As a result, toughness is reduced. Therefore, the working temperature in the skew rolling is preferably set to 1200 ℃ or lower, more preferably 1100 ℃ or lower, and still more preferably 1000 ℃ or lower.

After the skew rolling is completed, the steel material is preferably subjected to intermediate annealing. The time from the completion of skew rolling to the start of intermediate annealing changes the RD// <100> fraction. Therefore, the time from the completion of the skew rolling to the start of the intermediate annealing affects the toughness. The time from the completion of the skew rolling to the start of the intermediate annealing is preferably set to a range of 0.01 to 100 seconds.

If the time from the completion of the skew rolling to the start of the intermediate annealing is less than 0.01s, the RD/< 100> fraction increases in the manufacturing process described later. As a result, toughness is reduced. Therefore, the time from the completion of the skew rolling to the time of the intermediate annealing is preferably set to 0.01s or more, more preferably 0.1s or more, and still more preferably 1s or more.

However, if the time from the completion of the skew rolling to the start of the intermediate annealing exceeds 100s, the RD/< 100> fraction increases. As a result, toughness is reduced. Therefore, the time from the completion of the skew rolling to the start of the intermediate annealing is preferably set to 100 seconds or less, more preferably 50 seconds or less, and still more preferably 10 seconds or less.

5-3 intermediate annealing process

The subsequent intermediate annealing step is performed to recrystallize the coarse solidification structure formed during casting. In the intermediate annealing step, annealing is preferably performed at a temperature of 700 to 1300 ℃. When the steel material is recrystallized in the intermediate annealing step, the RD/< 100> fraction is reduced. As a result, toughness is improved. If the temperature in the intermediate annealing step (hereinafter referred to as "intermediate annealing temperature") is less than 700 ℃, the RD/< 100> fraction increases. As a result, toughness is reduced. Therefore, the intermediate annealing temperature is preferably set to 700 ℃ or higher, and more preferably set to 800 ℃ or higher.

However, if the interanneal temperature exceeds 1300 ℃, the RD/< 100> fraction increases. As a result, toughness is reduced. Therefore, the intermediate annealing temperature is preferably set to 1300 ℃ or lower, more preferably set to 1200 ℃ or lower, and still more preferably set to 1100 ℃ or lower.

The annealing time in the intermediate annealing (hereinafter referred to as "intermediate annealing time") is preferably set to a range of 1 to 480 min. If the interannealing time is less than 1min, the RD/< 100> fraction increases. As a result, toughness is reduced. Therefore, the intermediate annealing time is preferably set to 1min or more, and more preferably set to 30min or more.

However, if the interannealing time exceeds 480min, the RD/< 100> fraction increases. As a result, toughness is reduced. Therefore, the intermediate annealing time is preferably set to 480min or less, and more preferably set to 180min or less.

5-4 of total reduction of area

The rolling is performed by a skew rolling mill, a roughing mill, an intermediate rolling mill, a finishing mill, or the like. The total reduction of area by rolling including the above-described skew rolling is a reduction of area until all processing is completed. The total reduction of area will vary the RD// <100> fraction. As a result, the overall reduction of area has an effect on toughness. If the total reduction of area is less than 30.0%, the RD/< 100> fraction increases. As a result, toughness is reduced. Therefore, the total reduction of area is preferably set to 30.0% or more, more preferably 50.0% or more, still more preferably 80.0% or more, and still more preferably 90.0% or more.

5-5 roll diameter of roughing mill

The roll diameter of the roughing mill affects the hot worked structure, and particularly, is related to RD// <100> fraction, so the roll diameter of the roughing mill is preferably set to 200 to 2500 mm. When the roll diameter of the roughing mill is less than 200mm, shear deformation is promoted in the steel material, and the RD/< 100> fraction increases due to orientation other than RD/< 110> which is the preferred orientation of the deformed texture forming the BCC crystal structure. The plane perpendicular to the <100> orientation is a cleaved plane, and thus the toughness decreases due to an increase in the RD// <100> fraction. Therefore, the roll diameter of the roughing mill is set to 200mm or more. Preferably 400mm or more. On the other hand, if the roll diameter of the roughing mill exceeds 2500mm, the rolling mill becomes large, which is not economical. Therefore, the roll diameter of the roughing mill is set to 2500mm or less. Preferably 2000mm or less, and more preferably 1500mm or less.

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples.

Example 1

Steels having chemical compositions shown in tables 1 and 2 were melted. In the melting of steel, the inexpensive melting process of stainless steel, i.e., AOD melting, was assumed, and the steel was melted in a 100kg vacuum melting furnace and cast into a cast slab having a diameter of 180 mm. Then, a rod-shaped steel material having a diameter of 47.0mm was produced under the following production conditions. In the tables below, numerical values that deviate from the scope of the present invention are underlined.

The following conditions were used. Specifically, the cast slab was heated at a heating temperature of 1030 ℃ to perform skew rolling at a reduction of area of 80.0% and a working temperature of 805 ℃, and then, intermediate annealing was performed at an annealing temperature of 960 ℃ for 3.5 min. In this case, the time from the skew rolling to the intermediate annealing was set to 5.4 seconds. Thereafter, rolling is performed. In this case, the roll diameter of rough rolling was set to 940mm, the rolling temperature was set to 750 ℃, the rolling completion temperature was set to 730 ℃, and the time between passes was set to 0.5 s. The total reduction of area was 93.2%, and the steel was cooled at a cooling rate after rolling of 11 ℃/s, and final annealing was carried out at a final annealing temperature of 750 ℃ for a final annealing time of 0.8min and at a cooling rate of 14 ℃/s.

[ Table 1]

[ Table 2]

For the resulting steel wire rods, the RD// <100> fractions and the transformation temperatures were determined. The results are summarized in tables 3 and 4 below. These measurements were performed according to the following procedures.

The RD// <100> fraction was measured in L-section of the steel material at 200-fold visual field or more in the surface layer portion, the central portion, and the 1/4-depth position portion existing between the surface layer portion and the central portion. Then, the crystal orientation of each crystal grain in the observation field was analyzed by using FE-SEM/EBSD. The crystal plane in the RD direction was analyzed with the rolling direction RD set, and only the portion with a gap of 20 ° or less showed the orientation component of <001> and the RD/< 100> fraction was measured.

The transition temperature was set to the ductile-brittle transition temperature in the Charpy impact test of JIS Z2242. The test piece for the charpy impact test was set as a standard test piece, the longitudinal direction of the test piece was set as the rolling direction of the bar-shaped steel, and the notch of the test piece was set as a U-shaped notch. In addition, the ductile-brittle transition temperature uses an energy transition temperature. When the transition temperature is 200 ℃ or lower, the toughness is judged to be good.

[ Table 3]

[ Table 4]

No.1 to 37 satisfy the requirements of the present invention, and have good toughness. On the other hand, Nos. 38 to 52, which do not satisfy the requirements of the present invention, have poor toughness or poor corrosion resistance.

Example 2

Next, steel grades O and V of table 1 were melted by the same method as described above, and billets having various diameters were cast. Thereafter, the cast slab was heated at a heating temperature of 1053 ℃ to carry out cross rolling with a reduction of area of 63.2% and with a working temperature in the cross rolling set to 948 ℃, and then annealed at an annealing temperature of 1032 ℃ for an annealing time of 1.6 min. In this case, the time from the skew rolling to the annealing was set to 3 seconds. Thereafter, rolling is performed. In this case, the rough rolling diameter was 880mm, the rolling temperature was 940 ℃, the rolling finishing temperature was 835 ℃ and the time between passes was 6 seconds. The total reduction of area by rolling was set to 83.0%. Further, the steel sheet was cooled at a cooling rate after rolling at 12 ℃/s, annealed at a final annealing temperature of 1040 ℃ for a final annealing time of 1.4min, and cooled at a cooling rate of 12 ℃/s. The RD/< 100> fraction and the transformation temperature of the obtained steel bar were measured by the above-mentioned methods. The results are summarized in table 5 below. Similarly to example 1, when the transition temperature was 200 ℃ or lower, the toughness was judged to be good.

[ Table 5]

No.53 to 75 satisfy the requirements of the present invention, and have good toughness.

Example 3

Using steel grades Q shown in Table 1, rod-shaped steel materials having a diameter of 15mm were produced from casting slabs having various diameters under the conditions shown in tables 6 and 7. For the produced rod-shaped steel material, the RD// <100> fraction and the transformation temperature were measured by the methods described above. The results are summarized in tables 6 and 7 below. Similarly to example 1, when the transition temperature was 200 ℃ or lower, the toughness was judged to be good.

Nos. 76 to 95 satisfy the requirements of the present invention, and therefore exhibit good toughness. On the other hand, Nos. 96 to 108 did not satisfy the preferable production conditions of the present invention, and had poor toughness.

Industrial applicability

According to the present invention, a rod-shaped steel material having excellent toughness can be obtained, and the present invention is extremely useful industrially.

Claims

1. A rod-shaped steel material extending in one direction, the chemical composition of the rod-shaped steel material being, in mass%:

C：0.001～0.09％、

Si：0.01～3.0％、

Mn：0.01～2.0％、

Ni：0.01～5.0％、

Cr：7.0～35.0％、

Mo：0.01～5.0％、

Cu：0.01～3.0％、

N：0.001～0.10％、

Nb：0.2～2.0％、

Ti：0～2.0％、

V：0～2.0％、

B：0～0.1％、

Al：0～5.0％、

W：0～2.5％、

Ga：0～0.05％、

Co：0～2.5％、

Sn：0～2.5％、

Ta：0～2.5％、

Ca：0～0.05％、

Mg：0～0.012％、

Zr：0～0.012％、

REM：0～0.05％、

the rest is as follows: fe and inevitable impurities, and the balance of Fe,

the crystal orientation RD// <100> fraction in the rolling direction is 0.5 or less,

2. The rod-shaped steel material according to claim 1, wherein the chemical composition further contains one or more elements selected from the group consisting of:

Ti：0.001～2.0％、

V：0.001～2.0％

B：0.0001～0.1％

Al：0.001～5.0％、

W：0.05～2.5％、

Ga：0.0004～0.05％、

Co：0.05～2.5％、

sn: 0.01 to 2.5%, and

Ta：0.01～2.5％。

3. the rod-shaped steel material according to claim 1 or claim 2, wherein the chemical composition further contains one or more elements selected from the group consisting of:

Ca：0.0002～0.05％、

Mg：0.0002～0.012％、

zr: 0.0002 to 0.012%, and

REM：0.0002～0.05％。

4. a steel bar extending in one direction, the steel bar having a chemical composition in mass% according to any one of claims 1 to 3,

the transition temperature is 200 ℃ or lower.

5. The rod-shaped steel material according to any one of claims 1 to 3, wherein the transition temperature is 200 ℃ or lower.

6. The steel rod according to any one of claims 1 to 5, wherein the steel rod has a circular cross-sectional shape,

the diameter of the circle is 15.0-200 mm.