JP2014009378A - Steel member and method for producing steel member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel member having excellent rust generation resistance, and a method for producing a steel member having rust generation resistance.SOLUTION: The steel member 1 used in an in-chamber environment is made of a steel material having a componential composition comprising, by mass, 0.005 or more to 0.050% or lower of C, 0.10 or more to 1.00% or lower of Si, 0.1 or more to lower than 3.0% of Mn, 0.030% or lower of P, 0.0050% or lower of S, 5.0 or more to 9.0% or lower of Cr, 0.05% or lower of Al and 0.020% or lower of N, and the balance comprising Fe and inevitable impurities, and has a smooth region formed on the surface of the steel material, satisfying either or both of (a) and (b) shown in the following:(a) a roughness parameter Ra is 0.6 or lower; and (b) the ratio occupied by the region having a brightness distribution of 128 or lower in the region of a brightness distribution of 0 to 255 per the unit area of 1.5 mmof an image taken by the irradiation of light from a direction tilted by 20±5 degrees to a direction vertical to the surface is 20% or lower.

Description

  The present invention relates to a steel member used in an indoor environment having excellent hot workability and rust resistance and a method for producing the same.

In the case where corrosion resistance is required in a part used in an indoor environment such as a machine tool or industrial machine part, stainless steel such as SUS304 or SUS316L is generally used as a material for the part.
However, since stainless steel is expensive, it is considered to replace it with a cheaper corrosion-resistant steel material in various applications that require corrosion resistance. In recent years, steel materials have been proposed that can provide good corrosion resistance without containing a large amount of Cr as in stainless steel (see, for example, Patent Document 1). The corrosion-resistant steel material proposed by Patent Document 1 contains 4 to 9% Cr and Al: 0.1 to 5%, and is a corrosion-resistant steel material excellent in bare rust resistance.

JP 2008-127653 A

However, the conventional corrosion resistant steel material containing 4 to 9% Cr and Al: 0.1 to 5% has insufficient hot workability, and an edge crack occurs at the end in the width direction during hot rolling. There was a case.
The present invention has been made in view of the above circumstances, and is a steel member having a Cr content lower than that of stainless steel, and is used in an indoor environment and has excellent hot workability and rust resistance. It aims at providing a steel member and its manufacturing method.

The present inventor has intensively studied to solve the above problems.
As a result, in order to obtain a steel member having excellent hot workability and rust resistance, the component composition of the steel material is set to Cr: 5.0% or more and 9.0% or less, and Mn: 0.0. It was found that rust resistance is ensured by setting it to 1% or more and less than 3.0%, and hot workability needs to be improved by limiting it to Al: 0.05% or less.

  It was also found that the surface must be smooth to prevent rusting sufficiently. In order to smooth the surface, it is necessary to reduce the roughness parameter Ra or to control the shape of the unevenness. By smoothing the surface of the steel member having a component composition of Cr: 5.0% or more and 9.0% or less, Al: 0.05% or less, and Mn: 0.1% or more and less than 3.0%, The reason why the rust resistance is improved is not necessarily clear, but is considered to be due to the form of the oxide film formed on the surface. That is, by reducing the roughness parameter Ra of the steel member with the optimized component composition or controlling the shape of the irregularities, a continuous oxide film is formed on the surface, and rust resistance is improved. It is thought to do.

The present inventor conducted further earnest studies, and on the surface of the steel member, (a) the roughness parameter Ra was set to 0.6 or less, and (b) inclined by 20 ± 5 degrees with respect to the direction perpendicular to the surface. Any one of the ratio of the area having the luminance distribution 128 or less to the area of the luminance distribution 0 to 255 per unit area 1.5 mm ^{2 of the} image taken by irradiating light from the direction is set to 20% or less. Or we have found that it is necessary to satisfy both. If either one or both of the above (a) and (b) is satisfied, the unevenness that is likely to be the starting point of rusting will be sufficiently small, and the surface is sufficiently resistant as a steel member used in an indoor environment. Rust is obtained.

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

(1) A steel member used in an indoor environment, in mass%,
C: 0.005% to 0.050%,
Si: 0.10% or more and 1.00% or less,
Mn: 0.1% or more and less than 3.0%,
P: 0.030% or less,
S: 0.0050% or less,
Cr: 5.0% or more and 9.0% or less,
Al: 0.05% or less,
N: 0.020% or less, the balance is made of steel having a component composition consisting of Fe and inevitable impurities,
A steel member characterized in that a smooth region that satisfies one or both of the following (a) and (b) is formed on the surface of a steel material.
(A) The roughness parameter Ra is 0.6 or less.
(B) A luminance distribution of 128 or less in a region of luminance distribution 0 to 255 per unit area 1.5 mm ^{2 of} an image taken by irradiating light from a direction inclined by 20 ± 5 degrees with respect to a direction perpendicular to the surface The proportion of the area is 20% or less.

(2) In the steel material surface, a vacuum exposure region exposed to a vacuum space is formed, and a roughness parameter Ra of the vacuum exposure region is 0.1 or less. The steel member as described.
(3) The steel material further contains one or two of Cu: 0.05% to 0.50% and Ni: 0.05% to 0.50% by mass%. The steel member according to (1) or (2).

(4) The steel material is further in mass%, Mo: 0.01% to 0.20%, V: 0.005% to 0.050%, Nb: 0.005% to 0.050% (1) to (3), wherein Ti: 0.005% or more and 0.030% or less, Sn: 0.01% or more and 0.30% or less, or one or more of Ti The steel member as described in any one.
(5) The steel material is further in mass%, Ca: 0.0005% to 0.010%, Mg: 0.0005% to 0.010%, REM: 0.001% to 0.010% The steel member as described in any one of (1)-(4) characterized by containing the following 1 type, or 2 or more types.

(6) (1) A method for producing a steel member comprising a steel material having the component composition according to any one of (3) to (5),
Any one of a mechanical cutting process, a mechanical grinding process, a mechanical polishing process, and a blasting process for projecting spherical particles having a Mohs hardness of 5.5 to 7.5 according to a 15-step evaluation for minerals on a steel surface. Or the manufacturing method of the steel member characterized by including the surface treatment process which performs two or more processes.

(7) The surface treatment step for the region exposed to the vacuum space in the steel material surface includes a vacuum exposed surface treatment step in which mechanical polishing is performed using a 300th or higher abrasive. The manufacturing method of the steel member of description.
(8) The method for producing a steel member according to (6) or (7), wherein the spherical particles are glass beads.

The steel member of the present invention is made of a steel material having a predetermined component composition. On the surface of the steel material, (a) the roughness parameter Ra of the one surface side surface is 0.6 or less, and (b) the direction perpendicular to the one surface surface. The ratio of the area having the luminance distribution of 128 or less out of the area of the luminance distribution from 0 to 255 per unit area of 1.5 mm ^{2 of the} image taken by irradiating light from the direction inclined by 20 ± 5 degrees is 20% or less. Since a smooth region satisfying one or both of them is formed, it has excellent hot workability and rust resistance.

Fig.1 (a) is the schematic sectional drawing which showed an example of the steel member of this invention, and FIG.1 (b) is the schematic sectional drawing which showed the other example of the steel member of this invention. FIG. 2 is an example of an image of the surface of a steel material that has been subjected to mechanical cutting. FIG. 3 is an example of an image of the surface of a steel material subjected to mechanical polishing. FIG. 4 is an example of an image of the surface of a steel material that has been subjected to glass bead blasting. FIG. 5 is an example of an image of the surface of a steel material from which black skin has been removed by pickling. FIG. 6 is an example of an image of the surface of a steel material that has been subjected to ceramic blasting.

(First embodiment)
"Steel materials"
Fig.1 (a) is the schematic sectional drawing which showed an example of the steel member of this invention.
A steel member 1 of the present embodiment shown in FIG. 1A is a steel plate and is used in a room environment as a part of a machine tool or an industrial machine.
As shown in FIG. 1 (a), the steel member of the present invention may be a steel plate, a steel pipe, a part obtained by processing a steel plate or a steel pipe, and any shape. It may be. The steel member of the present invention may be obtained by welding a plurality of parts.

  In addition, the steel member of this invention may be used in air-conditioning environment, such as a member of the vacuum vessel (chamber) of a vacuum device, for example. When the steel member 1 is used in an air-conditioning environment, excellent rust resistance is obtained over a longer period.

In the present invention, the “indoor environment” is surrounded by a roof and walls and is not exposed to wind and rain, but is exposed to the atmosphere, and is not adjusted for temperature and humidity and is not cleaned of air. Means the environment. In an indoor environment, salt may accumulate on the surface of the steel member 1 due to sweating or the arrival of sea salt particles, which may lead to a corrosive environment.
In the present invention, “air-conditioning environment” means an environment in which the temperature and humidity are controlled by the air-conditioning equipment. Moreover, it is preferable that the air-conditioning environment in the present invention is an environment in which the temperature is kept within a range of 10 to 35 ° C. and the humidity is kept within a range of 80% or less. .

The steel member 1 shown to Fig.1 (a) consists of steel materials which have the predetermined component composition mentioned later. Further, in the steel member 1, both the one surface side surface 11 and the other surface side surface 12 are regions exposed to the atmosphere during use, and satisfy either or both of the following (a) and (b). It is a smooth area.
(A) The roughness parameter Ra is 0.6 or less.
(B) A luminance distribution of 128 or less in a region of luminance distribution 0 to 255 per unit area 1.5 mm ^{2 of} an image taken by irradiating light from a direction inclined by 20 ± 5 degrees with respect to a direction perpendicular to the surface The ratio occupied by the area (hereinafter sometimes referred to as “shadow area ratio”) is 20% or less.

  The roughness parameter Ra in the present invention means arithmetic average roughness (JIS B0601-1994). Further, in the present invention, the surface roughness parameter Ra was averaged by summing up absolute values of deviations from the average line to the measurement curve from the roughness parameter measurement results using an evaluation length standard value of 4.0 mm as an example. Value is expressed in units of μm.

The shadow area ratio is the luminance of the area from the luminance distribution 0 to 255 per unit area 1.5 mm ^{2 of the} image taken by irradiating light from the direction inclined by 20 ± 5 degrees with respect to the direction perpendicular to the surface. It means the ratio of the area of distribution 128 or less. In the present invention, the unit area for calculating the shadow area ratio is set to 1 mm ² or more in order to reduce the variation of the shadow area ratio. In addition, when the cutting line is formed on the surface, the light used for calculating the shadow area ratio is irradiated from a direction orthogonal to the cutting line in plan view.

The method for measuring the shadow area ratio will be described more specifically.
FIG. 2 shows the surface of a steel material that has been machine-cut by milling, and FIG. 3 shows the surface of a steel material that has been mechanically polished using an 80th abrasive. FIG. 4 shows a blast treatment in which spherical particles (glass beads) having a Mohs hardness of 5.5 to 7.5 according to a 15-step evaluation for minerals are projected using compressed air for 1 to 5 minutes after removing the black skin. It is the surface of the steel material which performed. FIG. 5 is an image of the surface of a steel plate that has been subjected to pickling and alkali neutralization to remove the black skin, and FIG. 6 is based on a 15-step evaluation for minerals after the removal of the black skin. It is the surface of the steel material which performed the blast process which projects the particle | grains (ceramics) whose Mohs hardness is 12 using compressed air for 1 to 5 minutes. In addition, the blast process which projects ceramics, such as an alumina and SiC, is called a ceramic blast process. FIG. 6 shows an example in which alumina is projected.

2 to 6 show luminance distributions obtained by dividing the photographing luminance per unit area of 1.5 mm ² from 0 to 255 in an image photographed by irradiating light from a direction inclined by 20 degrees with respect to a direction perpendicular to the surface. The luminance area with a luminance distribution of 128 or less and the luminance area with a luminance distribution of more than 128 are separated from each other, and the area of the luminance with a value of 128 or less is extracted. The area of each visual field in FIGS. 2 to 6 corresponds to 1.5 mm ² .

  In the images shown in FIGS. 2 to 6, the shadow area ratio is obtained by dividing the area of the white portion by the entire area and evaluating the area ratio as a percentage. The shadow area ratio of the steel shown in FIG. 2 is 15%, the shadow area ratio of the steel shown in FIG. 3 is 4%, and the shadow area ratio of the steel shown in FIG. 4 is 12%. Moreover, the shadow area ratio of the steel shown in FIG. 5 is 7%, and the shadow area ratio of the steel shown in FIG. 6 is 29%.

In the steel material shown in FIG. 6, since the Mohs hardness of the particles used for the blast treatment is large, the shadow area ratio exceeds 20% by the ceramic blast treatment. The upper limit of the Mohs hardness of the particles used for the blast treatment needs to be 7.5 or less.
Moreover, as shown in FIG. 5, although the shadow area ratio of the steel plate which performed the pickling process and the alkali neutralization process is 20% or less, it will rust if an alkali neutralization process is not performed immediately after a pickling process. . For this reason, it is necessary to shorten the time from pickling to alkali neutralization. In the case where the steel member is large, it is difficult to sufficiently shorten the time from the pickling treatment to the alkali neutralization treatment. Therefore, the pickling treatment is not preferable as a normal pressure exposed surface treatment step described later.

  The one surface 11 and the other surface 12 of the steel member 1 shown in FIG. 1A have a roughness parameter Ra of 0.6 or less and / or a shadow area ratio of 20% or less. The occurrence of rust on the surface 11 and the other surface 12 is sufficiently prevented. When the roughness parameter Ra of the one-side surface 11 and the other-side surface 12 exceeds 0.6 and the shadow area ratio exceeds 20%, the one-side surface 11 and others that are exposed to the atmosphere during use Rust resistance of the surface-side surface 12 becomes insufficient, and rusting is likely to occur on the one-side surface 11 and the other-side surface 12.

  Next, the component composition of the steel material which comprises the steel member 1 is demonstrated. The steel material used for the steel member 1 in this invention contains the following each element by the following content, and the remainder has a component composition which consists of Fe and an unavoidable impurity. In the following description, “%” means “% by mass” unless otherwise specified.

“C: 0.005% to 0.050%”
C is an element that improves the strength of the steel material and needs to be contained by 0.005% or more. However, when there is too much content of C, a carbide | carbonized_material will be formed and corrosion resistance will be inhibited. For this reason, the upper limit of C content is made 0.050%. In consideration of the balance between strength, ductility, and weldability, 0.005 to 0.030% is preferable. Furthermore, if considering the production stability, 0.010% or more and 0.020% or less is preferable.

“Si: 0.10% to 1.00%”
It is effective to contain Si as a deoxidizer and a strengthening element. When the Si content is less than 0.10%, a sufficient deoxidation effect cannot be obtained. On the other hand, when the Si content exceeds 1.00%, the effects as a deoxidizer and a strengthening element are saturated. Therefore, the content of Si contained in the steel material is limited to 0.10% or more and 1.00% or less. Moreover, in order to raise the intensity | strength of steel materials, it is preferable to add Si 0.15% or more, and addition of 0.18% or more is more preferable. On the other hand, in order to ensure ductility, the upper limit of the Si content is preferably 0.80% or less, and more preferably 0.50% or less.

“Mn: 0.1% or more and less than 3.0”
Mn is an element that improves the toughness of the weld and improves the strength, and is added in an amount of 0.1% or more. Further, Mn acts as an austenite forming element and has an effect of suppressing the formation of coarse ferrite, so 0.2% or more is preferably added. In addition, when Cr, which is a ferrite forming element, is contained in a large amount and a ferrite single phase structure is formed, cracking of a slab may occur and productivity may be reduced. Therefore, Mn may be contained in an amount of 0.5% or more. preferable. However, if Mn is contained in an amount of 3.0% or more, the ductility of the base material is remarkably lowered, so the Mn content is less than 3.0%. If Mn is contained in excess of 1.6%, inclusions serving as starting points of corrosion are formed, and corrosion resistance may be lowered. Therefore, the Mn content is preferably 1.6% or less. More preferably, the Mn content is 1.0% or less. Furthermore, considering the strength, workability, and corrosion resistance of the steel material, the Mn content is preferably 0.6% or more and 0.9% or less.

“P: 0.030% or less”
When P is present in a large amount, there is a concern that the ductility is lowered and the productivity is lowered. Therefore, it is desirable that the content of P contained in the steel material is small, and the P content is 0.030% or less.

“S: 0.0050% or less”
When S is present in a large amount, the pitting corrosion resistance is lowered. Therefore, the content of S contained in the steel material is desirably small, and the S content is set to 0.0050% or less. In consideration of the balance between pitting corrosion resistance and manufacturability, 0.0030% or less is preferable.

“Cr: 5.0% to 9.0%”
Cr needs to contain 5.0% or more in order to ensure corrosion resistance. However, even if Cr is contained exceeding 9.0%, not only the cost is increased, but also ductility is impaired. Therefore, the content of Cr contained in the steel material is set to 9.0% or less. In consideration of manufacturability, weldability, and workability of the steel material, 5.5% or more and 8.0% or less are preferable. Furthermore, if considering the balance with economy, 6.5% or more and 7.5% or less are preferable.

"Al: 0.05% or less"
Al is preferably contained as a deoxidizer in an amount of 0.01% or more, and more preferably 0.02% or more. However, when Al is contained in excess of 0.05%, ductility decreases due to the increase of inclusions, or hot workability decreases, and an edge crack occurs at the end in the width direction during hot rolling. Cause it. Therefore, the upper limit of the content of Al contained in the steel material is limited to 0.05% or less. Furthermore, in consideration of workability and production stability, the upper limit of the Al content is preferably 0.03% or less.

“N: 0.020% or less”
N, when added in a large amount, inhibits ductility and corrosion resistance due to formation of nitrides and the like. For this reason, content of N contained in steel materials shall be 0.020% or less. In consideration of corrosion resistance, economy, and workability, it is preferably 0.015% or less.

Furthermore, in the present invention, the following elements can be selected and added.
“Cu: 0.05 to 0.50%, Ni: 0.05 to 0.50%”
Both Cu and Ni are effective in improving strength and suppressing ferrite formation. Furthermore, Ni has an effect of improving ductility and toughness. In order to obtain these effects, it is preferable to contain 0.05% or more of Cu and / or Ni. However, Cu and Ni both cause embrittlement when contained over 0.50%. For this reason, it is preferable that both content of Cu and Ni contained in steel materials is 0.05 to 0.50%. Furthermore, considering corrosion resistance, manufacturability, and workability for both Cu and Ni, the content is preferably set to 0.10 to 0.30%.

“Mo: 0.01% or more and 0.20% or less”
Mo is an element in which the effect of suppressing the occurrence and growth of pitting corrosion is observed when contained in a steel material containing Cr and Al by 0.01% or more. However, when Mo is contained exceeding 0.20%, the above effect is saturated and toughness is reduced. Therefore, the content of Mo contained in the steel material is preferably 0.01% or more and 0.20% or less. Furthermore, considering the balance of corrosion resistance, manufacturability, and workability, it is preferably 0.05% or more and 0.10% or less.

“V: 0.005% to 0.050%”
V, like Nb, is an element that improves strength without impairing corrosion resistance. The said effect is recognized by making V contain 0.005% or more. However, when V is contained in a large amount, ductility is inhibited as is well known. Therefore, the content of V contained in the steel material is preferably 0.005% or more and 0.050% or less.

“Nb: 0.005% or more and 0.050% or less”
Nb is an element that improves strength and toughness without impairing corrosion resistance. The said effect is recognized by containing Nb 0.005% or more, but if it exceeds 0.050%, the effect is saturated. Therefore, the content of Nb contained in the steel material is preferably 0.005% or more and 0.050% or less.

“Ti: 0.005% to 0.030%”
Ti is an element that contributes to refinement of the crystal grain size at high temperature through the formation of nitrides, and is an element that contributes to improvement of ductility without impairing corrosion resistance. The said effect is recognized by containing Ti 0.005% or more. However, if Ti is contained in an amount exceeding 0.030%, a large amount of carbide is precipitated, and ductility is adversely affected. Therefore, the content of Ti contained in the steel material is preferably 0.005% or more and 0.030% or less.

“Sn: 0.01% or more and 0.30% or less”
Sn is an element that improves corrosion resistance by being added in combination with Cr, and it is preferable to contain 0.01% or more of Sn. However, when Sn exceeding 0.30% is contained, hot workability is lowered, which may cause surface defects. Therefore, the content of Sn contained in the steel material is preferably 0.01% or more and 0.30% or less. More preferably, the Sn content is 0.03% or more, and more preferably 0.05% or more.

“Ca: 0.0005% to 0.010%, Mg: 0.0005% to 0.010%”
Ca and Mg are elements that can improve corrosion resistance in steels containing Cr and Al. The said effect is recognized by containing 0.0005% or more of Ca and / or Mg. However, when the content of Ca and / or Mg exceeds 0.010%, not only the effect is saturated, but also a tendency for ductility and toughness to decrease is revealed. Therefore, it is preferable that the content of Ca and Mg contained in the steel material is 0.0005% or more and 0.010% or less.

“REM (rare earth element): 0.001% to 0.010%”
Rare earth elements (REM) are elements that can improve ductility without impairing corrosion resistance. In order to acquire the said effect, it is preferable to make content of REM 0.001% or more. However, if the content of REM is large, the above effect is inhibited. Therefore, the REM (rare earth element) content contained in the steel material is preferably 0.001% or more and 0.010% or less.

"Method of manufacturing steel members"
In the present embodiment, as an example of the method for manufacturing a steel member of the present invention, a method for manufacturing the steel member 1 shown in FIG. 1A will be described as an example. Normally, the steel member of the present invention is manufactured under an indoor environment. The method for producing a steel member of the present invention includes a surface treatment step of performing any one or more of a mechanical cutting step, a mechanical grinding step, a mechanical polishing step, and a blasting step on the steel material surface. Is the method.

  In order to manufacture the steel member 1 shown in FIG. 1A, first, a steel plate having the above-described component composition is prepared. The steel sheet is manufactured by heating a steel slab having the above-described composition of the steel material, followed by hot rolling, and performing a heat treatment process such as quenching, tempering, or normalizing as necessary. Steel slabs used for the production of steel sheets are manufactured by processes such as continuous casting and ingot-making / bundling after components are adjusted and melted by a converter or electric furnace.

  In addition, when the steel member of the present invention is a tubular part made of a steel material having the above-described predetermined component composition and surface state, the component composition of the steel material described above is used instead of the steel plate having the component composition of the steel material described above. A steel pipe having The steel pipe can be manufactured by heating a steel slab having the above-described composition of the steel material, followed by hot rolling, and performing a heat treatment step such as quenching, tempering or normalizing as necessary.

Since a black skin is usually formed on the surface of the steel plate and / or steel pipe thus obtained, any one of mechanical cutting, mechanical grinding, and pickling is performed to remove the black skin.
In order to increase productivity when removing the black skin, it is preferable to perform pickling. In the pickling in the present invention, the method using a pickling solution composed of nitric acid and hydrofluoric acid used in SUS304 or the like has a too high dissolution rate. As pickling of the steel plate and / or steel pipe in the present invention, for example, the surface is degreased and washed with an alkaline solution, then dipped in a pickling solution such as hydrochloric acid for several hours to remove the black skin, and then washed with an alkaline solution. It is preferable to use a method of sum processing.

  Next, in this embodiment, the shape processing process of the steel member 1 is performed. In the shape processing step, first, the steel plate and / or the steel pipe is cut into a predetermined shape so as to have a shape corresponding to the steel member 1, and bending or welding is performed as necessary. In addition, when welding is performed in the shape processing step, it is preferable to perform a stress removal step such as heat treatment in order to remove stress such as welding strain loaded on the steel member 1 as necessary.

Next, in this embodiment, precision shape processing is performed, and the shape of the member formed by the shape processing step is set to the shape of the steel member 1 shown in FIG. By this, it becomes the steel member 1 which consists of steel materials which have the component composition mentioned above. In addition, you may abbreviate | omit precision shape processing, when the shape of the steel member 1 can be formed with sufficient dimensional accuracy by a shape processing process. Moreover, you may perform precision shape processing after the surface treatment process demonstrated below.
In addition, since the steel material having the above-described component composition is extremely susceptible to rusting when wet treatment such as electrolytic polishing or pickling is performed, the surface treatment process is performed by dry machining such as mechanical cutting, mechanical grinding, mechanical polishing, and blasting. By processing.

Next, in this embodiment, a surface treatment process is performed on the one-side surface 11 and the other-side surface 12. The one surface side surface 11 and the other surface side surface 12 are regions exposed to the atmosphere during use on the surface of the steel member 1.
In the surface treatment process, the Mohs hardness by the 15-step evaluation for minerals is 5.5 to 7.5 by mechanical cutting, mechanical grinding, mechanical polishing, and the other surface 12 respectively. 5. Any one or two or more of the blasting process which projects the spherical particle which is 5 is performed. By performing the surface treatment step, the entire surface of the one surface 11 and the other surface 12 of the steel member 1 shown in FIG. 1A has a surface roughness parameter Ra of 0.6 or less and / or a shadow region. A smooth region having a ratio of 20% or less is obtained.

Specific examples of the step of machining the one surface 11 and the other surface 12 of the steel member 1 include a method of cutting the surface using a machine tool such as a milling machine. For example, when cutting is performed using a milling cutter, the roughness parameter Ra can be reduced by increasing the number of revolutions and decreasing the feed rate.
Specific examples of the step of mechanically grinding the one-side surface 11 and the other-side surface 12 include a method of grinding the surface using a machine tool such as a grindstone or a grinder. In order to reduce the roughness parameter Ra, it is preferable to use a surface grinder.
By mechanically cutting or grinding the one-side surface 11 and the other-side surface 12, the roughness parameter Ra of the one-side surface 11 and the other-side surface 12 can be made 0.6 or less easily and efficiently. .

The step of mechanically polishing the one-side surface 11 and the other-side surface 12 includes a method of polishing the surface using an abrasive. The count of the abrasive may be adjusted as appropriate while measuring the roughness parameter.
Moreover, when the blast process which projects the spherical particle whose Mohs hardness by the 15-step evaluation for minerals to 5.5-7.5 is performed to the one surface side surface 11 and the other surface side surface 12, the one surface side surface 11 and others Regardless of the shape of the surface-side surface 12, the shadow area ratio between the one-side surface 11 and the other-side surface 12 can be reduced to 20% or less.

  The Mohs hardness of the spherical particles used in the blasting process affects the time required for the blasting process and the shadow area ratio of the outer surface after the blasting process. When the Mohs hardness of the spherical particles is 5.5 or more, the time required for the blasting process can be shortened, and the productivity can be increased. In addition, if the Mohs hardness of the spherical particles used for the blasting process is too high, the impact on the one-side surface 11 and the other-side surface 12 due to the blasting process becomes too strong, and the shadows on the one-side surface 11 and the other-side surface 12 appear. The area ratio may increase. When the Mohs hardness of the spherical particles is 7.5 or less, the shadow area ratio between the one-side surface 11 and the other-side surface 12 can be made sufficiently small.

  The spherical particles used in the blast treatment are preferably glass beads. When the spherical particles are glass beads, even if glass beads remain on the one-side surface 11 and the other-side surface 12, it is difficult to cause rust on the one-side surface 11 and the other-side surface 12, which is preferable. The blasting process for projecting glass beads is referred to as glass bead blasting process. As the surface treatment step, an embodiment in which glass bead blasting is performed after cutting with a milling cutter is optimal.

  In the present embodiment, the surface treatment process is any one or two of a process of mechanically cutting the one surface 11 and the other surface 12, a machine grinding process, a machine polishing process, and a blast treatment process. It is preferable to include a step of performing citric acid treatment on the one-side surface 11 and the other-side surface 12 after performing the above steps. As a result, the one surface side surface 11 and the other surface side surface 12 which are smooth regions formed by the surface treatment process become smoother, and the shadow region ratio between the one surface side surface 11 and the other surface side surface 12 is further increased. It becomes small, and the rust-proof property of the one surface side surface 11 and the other surface side surface 12 can be improved further.

Moreover, in this embodiment, although the surface treatment process was performed in this order after the shaping process of the steel member 1, it is not limited to this order, and the surface treatment process is performed before the shaping process. May be. However, when heat treatment for removing welding distortion is performed in the shape processing step, an oxide film is generated depending on the atmosphere of the heat treatment. Therefore, it is preferable to perform a surface treatment step after the shape processing step.
Moreover, the surface treatment process performed with respect to the one surface side surface 11 in this embodiment and the surface treatment process performed with respect to the other surface side surface 12 may be the same, and may differ.

  The steel member 1 of the present embodiment is made of a steel material having a predetermined component composition, and has a roughness parameter Ra of 0.6 or less and / or a surface shadow on the one surface side surface 11 and the other surface side surface 12 which are steel material surfaces. Since a smooth region having a region ratio of 20% or less is formed, excellent hot workability and rust resistance can be obtained.

(Second Embodiment)
"Steel materials"
FIG.1 (b) is the schematic sectional drawing which showed the other example of the steel member of this invention. The steel member 10 of the present embodiment shown in FIG. 1B is different from the steel member 1 of the first embodiment shown in FIG. 1A in that the steel member 10 of the present embodiment is a member of a vacuum apparatus. It is used in an air-conditioning environment such as in a clean room, and the other surface side surface 12a shown in FIG. 1 (b) of the steel material surface is a vacuum exposure region exposed to the vacuum space. Therefore, in the present embodiment, a configuration different from that of the first embodiment will be described, and description of the same configuration as that of the first embodiment will be omitted.

In the steel member 10 of the present embodiment, the roughness parameter Ra of the other surface 12a is 0.1 or less.
In the case where the steel member 10 is used in an air-conditioned environment as a member of a vacuum device, it is necessary to suppress gas emission from the other surface 12a that is a vacuum exposure region exposed to the vacuum space. In the present embodiment, since the roughness parameter Ra of the other surface 12a is 0.1 or less, the amount of gas released from the other surface 12a is sufficiently small. The roughness parameter Ra of the other surface 12a is preferably 0.07 or less in order to further reduce the amount of gas released.

  When the roughness parameter Ra of the other surface 12a exceeds 0.1, when the other surface 12a of the steel member 10 of the present embodiment is disposed so as to be exposed to the vacuum space of the vacuum device, the other surface The amount of gas released from 12a cannot be reduced sufficiently, making it difficult to reduce the pressure in the vacuum space, and the vacuum degree of the vacuum device may be insufficient. Note that when the roughness parameter Ra of the other surface 12a is less than 0.03, the productivity is lowered. Therefore, the roughness parameter Ra is preferably 0.03 or more.

  Moreover, also in the steel member 10 of this embodiment, like the steel member 1 of 1st Embodiment, the one surface side surface 11 is made into the area | region exposed to air | atmosphere at the time of use, and the roughness parameter Ra is 0.6. And / or a smooth region having a shadow region ratio of 20% or less.

"Method of manufacturing steel members"
When manufacturing the steel member 10 of the present embodiment, for example, the first is that the surface treatment process for the other surface 12a includes a vacuum exposed surface treatment process that mechanically polishes using a 300th or higher abrasive. It can be manufactured in the same manner as the embodiment.
In addition, the surface treatment process for the other surface 12a may be only a vacuum exposure surface treatment process in which polishing is performed using a 300th or higher abrasive, but in order to improve productivity, the vacuum exposure surface treatment process is performed. Prior to the above, a mechanical cutting process, a mechanical grinding process, a mechanical polishing process using a 200th or lower abrasive, and a blast projecting spherical particles having a Mohs hardness of 5.5 to 7.5 according to a 15-step evaluation for minerals It is preferable to perform any one or two or more of the processing steps.

  In this embodiment, by performing the vacuum exposed surface processing step, the roughness parameter of the other surface 12a shown in FIG. Further, in the vacuum exposed surface treatment step, the other surface 12a is easily polished with a 300 to 800 abrasive so that the roughness parameter Ra of the other surface 12a is 0.03 or more and 0.0. 1 or less.

  Moreover, it is preferable that a vacuum exposure surface treatment process is a process including the process of carrying out the citric-acid process of the other surface side surface 12a after the process of grind | polishing the other surface side surface 12a using the 300th or more abrasive | polishing agent. . In this case, it is possible to remove the processing edge formed by polishing the other surface 12a with 300 or more abrasives by citric acid treatment. As a result, the other surface 12a, which is the region exposed to the vacuum space, becomes even smoother, and the roughness parameter Ra of the other surface 12a becomes even smaller. As a result, the amount of gas released from the other surface 12a can be further reduced.

  In addition, although the vacuum exposure surface treatment process with respect to the other surface 12a may be performed after performing the surface treatment process with respect to the one surface 11, it may be performed before performing the surface treatment with respect to the one surface 11. Further, the vacuum exposed surface treatment step may be performed before the shape processing step or after the shape processing step. However, when heat treatment for removing welding distortion is performed in the shape processing step, an oxide film is generated depending on the heat treatment atmosphere. Therefore, it is preferable to perform a vacuum exposed surface treatment step after the shape processing step.

  The steel member 10 of the present embodiment is made of a steel material having a predetermined component composition, and the one-side surface 11 that is an area exposed to the atmosphere during use has a roughness parameter Ra of 0.6 or less and / or a shadow of the surface. The area ratio is 20% or less, and the other surface side surface 12a, which is an area exposed to the vacuum space, has a roughness parameter Ra of 0.1 or less. While interworkability and rust resistance are obtained, the amount of gas released from the other surface 12a is sufficiently small. Therefore, the steel member 10 of this embodiment can be used suitably as a member of a vacuum apparatus.

In the steel member of the present invention, the smooth area where the roughness parameter Ra is 0.6 or less and / or the shadow area ratio of the surface is 20% or less is as in the steel member 1 shown in FIG. It may be both surfaces of the steel member 1 or may be one surface of the steel member 10 as in the steel member 10 shown in FIG. 1 (b), or one surface or both surfaces of the steel member. Part.
Further, when the steel member is formed with a vacuum exposed region exposed to the vacuum space on the surface of the steel material, the vacuum exposed region is the steel member 10 like the steel member 10 shown in FIG. One surface of the steel member may be used, or a part of one surface or both surfaces of the steel member may be used.

Hereinafter, the effect of the present invention will be described in detail with reference to examples.
"Example 1"
Steels having the composition of test examples 1 to 38 in Table 1 and Table 2 were melted and cast, and the obtained steel pieces were heated to 1200 ° C, and the total rolling reduction was 90% and finishing temperature was 800 ° C in 6 passes. A steel plate having a thickness of 3 mm was manufactured by hot rolling under the conditions described above, and the hot workability was evaluated.
Hot workability was evaluated by the following method. That is, the state of the edge cracking at the end of the steel plate was confirmed, and the case where the length of the largest edge cracking portion in the width direction was less than 5 mm was “◯”, and the case where the length was 5 mm or more was “x”.
The evaluation results of hot workability are shown in Tables 1 and 2.

As shown in Tables 1 and 2, in Test Examples 1 to 22, 29, 30, 32, and 33, which are examples of the present invention, all the hot workability evaluations were “◯”.
In contrast, in Test Examples 36 to 38 in which the Al content exceeds 0.05% and the component composition is outside the scope of the present invention, the evaluation result of hot workability was “x”.

Next, steel having the composition of Test Examples 1 to 35 in Table 1 and Table 2 in which the evaluation of hot workability was “◯” was melted and cast, and the obtained steel slab was hot rolled. A steel plate having a thickness of 10 mm was manufactured and subjected to a bending test.
As a bending test, a 90 ° bending test was performed in accordance with JIS Z 2248.
As a result of the bending test, the bent part was visually observed or a penetrant flaw detection test was performed, and “O” indicates that no crack occurred, and “X” indicates that the crack occurred.
The evaluation results of the bending test are shown in Tables 1 and 2.

As shown in Tables 1 and 2, in Test Examples 1 to 22, 29, 30, 32, and 33 which are examples of the present invention, all the evaluations of the bending test were “◯”.
On the other hand, in Test Examples 25 to 27 whose component composition is outside the range of the present invention, the result of the bending test was “x”.

"Example 2"
The steel pieces obtained by melting and casting steels having the composition compositions of Test Examples 1 to 24 and 28 to 35 in Table 1 and Table 2 in which the hot workability and the bending test were evaluated as “◯” were obtained. A steel sheet having a thickness of 10 mm was manufactured by hot rolling. Test pieces each having a length of 200 mm, a width of 150 mm, and a thickness of 10 mm were collected from the obtained steel plate. Thereafter, the test piece was pickled to remove the black skin formed on the surface. The pickling was performed by a method of neutralizing the surface after washing the surface with hydrochloric acid. Next, as shown in Tables 3 and 4, some test pieces were annealed to simulate removal of weld distortion. The annealing temperature was 550 ° C. and the holding time was 40 minutes.

Next, the surface treatment process was given to the one surface side surface of the test piece of Test Examples 1-24 and 28-35.
As shown in Tables 3 and 4, the surface treatment process for the surface on one side is any one or more of a mechanical cutting process, a mechanical grinding process using a milling machine, a mechanical polishing process, and a blasting process. Carried out. In addition, only the blasting process (ceramic blasting) which projects an alumina was given to the one surface side surface of the test piece of Test Examples 30, 32, 33, and 35. Moreover, the surface treatment process was not given to the one surface side surface of the test piece of Test Examples 31 and 34.

  As a blasting process shown in Tables 3 and 4, spherical particles (glass beads) having a Mohs hardness of 5.5 to 7.5 according to a 15-step evaluation for minerals are projected for 1 to 5 minutes using compressed air. “○” indicates that the glass bead blasting was performed, “X” indicates that the ceramic blasting using alumina having high Mohs hardness instead of the glass beads was indicated, and blank indicates that was not performed.

After the surface treatment step was performed on the one surface, the roughness parameter Ra and the shadow area ratio (surface state of the one surface) of the one surface were measured as shown below. The results are shown in Tables 3 and 4.
In addition, Ra is a value obtained by summing up the absolute values of deviations from the average line to the measurement curve from the roughness parameter measurement results using the evaluation length standard value of 4.0 mm as an example in accordance with JIS B0601-1994. .
Further, the shadow area ratio is the luminance distribution among the luminance distributions from 0 to 255 per unit area 1.5 mm ^{2 of the} image taken by irradiating light from the direction inclined by 20 degrees with respect to the direction perpendicular to the surface. It calculated | required by calculating the ratio for which the area | region 128 or less occupies.

As shown in Tables 3 and 4, in the test pieces of Test Examples 1 to 22, 29, 30, 32, and 33 which are examples of the present invention, the roughness parameter Ra is 0.6 or less and / or the shadow of the surface. The area ratio was 20% or less.
On the other hand, in the test pieces of Test Examples 31 and 34 that were not subjected to the surface treatment step, the roughness parameter Ra exceeded 0.6 and the shadow area ratio on the surface exceeded 20%.
Further, as a surface treatment step, the roughness parameter Ra exceeded 0.6 and the shadow area ratio of the surface exceeded 20% even in the test piece of Test Example 35 in which only the ceramic blast treatment was performed.

  Moreover, the rust resistance of the one surface side surface of the test piece of Test Examples 1-24 and 28-35 which performed the surface treatment process on the one surface side surface was evaluated by the method shown below.

  For the evaluation of rust resistance, an "indoor environment exposure test" and an "air conditioning environment exposure test" were conducted. In the indoor environment exposure test, the exposure was evaluated for 1 year in an indoor warehouse about 20 m from the coast. In the air conditioning environment exposure test, after exposure to a first atmosphere at a temperature of 25 ° C. and a humidity of 50% for 1 hour in a constant temperature and humidity chamber, a second atmosphere of a temperature of 50 ° C. and a humidity of 90% is gradually applied over 30 minutes. 720 cycles of a 3 hour / cycle corrosion test in which the sample was exposed to the second atmosphere for 1 hour and then gradually exposed to the first atmosphere for 30 minutes.

  "Indoor environment exposure test" and "Air conditioning environment exposure test" are "◎" when the rusting area is 1% or less, "○" when the rusting area is 5% or less, and "X" when the rusting area exceeds 5%. It was evaluated.

As shown in Table 3 and Table 4, in the test pieces of Test Examples 1 to 22, 29, 30, 32, and 33, which are examples of the present invention, evaluation of "indoor environment exposure test" and "air conditioning environment exposure test" Was “◎” or “◯”.
On the other hand, the test pieces 31 and 34 in which the surface treatment process was not performed and the test pieces of the test example 35 in which only the ceramic blast treatment was performed as the surface treatment process were “indoor environment exposure test” and “air conditioning environment exposure test”. Was evaluated as “×”.

"Example 3"
On the other side surface of the test pieces of Test Examples 1 to 22, 29, 30, 32, and 33 in which the evaluation of the “indoor environment exposure test” and the “air conditioning environment exposure test” was “「 ”or“ ◯ ” Processing steps were performed.
As the surface treatment process on the other side surface, as shown in Tables 5 and 6, any one or more of a mechanical cutting process, a mechanical grinding process, a mechanical polishing process, and a blasting process were performed.
As the mechanical polishing step, “○” indicates that the mechanical polishing step was performed using 300 or more abrasives, and “×” indicates that the mechanical polishing step was performed using 200 or lower polishing agents. It showed in.

  The roughness parameter Ra of the surface on the other surface side of the test pieces of Test Examples 1 to 22, 29, 30, 32, and 33 in which the surface treatment process was performed on the other surface surface was measured in the same manner as the one surface surface. . The results are shown in Tables 5 and 6.

Moreover, the gas release property in the other surface side surface of the test piece of Test Examples 1-22, 29, 30, 32, and 33 was evaluated by the method shown below.
That is, the test piece was held in a vacuum (1 × 10 ⁻⁵ Pa or less), heated to 250 ° C., and the released gas was subjected to mass spectrometry and evaluated. A quadrupole mass spectrometer was used for mass analysis. As a pretreatment for the gas release test, the test piece was ultrasonically washed in acetone to degrease the surface, kept in vacuum for 2 hours, heated at 400 ° C., cooled for 60 minutes, The sample was left in the atmosphere for 5 minutes, and the moisture absorption conditions were the same.

As for the gas release property, “◎” indicates that the amount of gas released from SUS304 steel having a surface roughness parameter Ra of 0.06 is 1.1 times or less, and “1.1” indicates that the surface release parameter Ra exceeds 1.1 times. “◯”, those exceeding 1.3 times were evaluated as “×”.
Tables 5 and 6 show the evaluation results of gas release properties.
As shown in Table 5 and Table 6, among the test pieces of Test Examples 1 to 22, 29, 30, 32, and 33, the test piece having a surface roughness parameter Ra of 0.1 or less has a gas releasing property. Evaluation was "◎" or "○".

  DESCRIPTION OF SYMBOLS 1,10 ... Steel member, 11 ... One surface side surface, 12, 12a ... Other surface side surface.

Claims (8)

It is a steel member used in an indoor environment, in mass%,
C: 0.005% to 0.050%,
Si: 0.10% or more and 1.00% or less,
Mn: 0.1% or more and less than 3.0%,
P: 0.030% or less,
S: 0.0050% or less,
Cr: 5.0% or more and 9.0% or less,
Al: 0.05% or less,
N: 0.020% or less, the balance is made of steel having a component composition consisting of Fe and inevitable impurities,
A steel member characterized in that a smooth region that satisfies one or both of the following (a) and (b) is formed on the surface of a steel material.
(A) The roughness parameter Ra is 0.6 or less.
(B) A luminance distribution of 128 or less in a region of luminance distribution 0 to 255 per unit area 1.5 mm ^{2 of} an image taken by irradiating light from a direction inclined by 20 ± 5 degrees with respect to a direction perpendicular to the surface The proportion of the area is 20% or less.   The steel according to claim 1, wherein a vacuum exposure region exposed to a vacuum space is formed on the steel material surface, and a roughness parameter Ra of the vacuum exposure region is 0.1 or less. Element. The steel material is further in mass%,
Cu: 0.05% or more and 0.50% or less,
The steel member according to claim 1 or 2, comprising Ni: 0.05% or more and 0.50% or less. The steel material is further in mass%,
Mo: 0.01% or more and 0.20% or less,
V: 0.005% or more and 0.050% or less,
Nb: 0.005% or more and 0.050% or less,
Ti: 0.005% or more and 0.030% or less,
The steel member according to any one of claims 1 to 3, comprising Sn: 0.01% or more and 0.30% or less. The steel material is further in mass%,
Ca: 0.0005% or more and 0.010% or less,
Mg: 0.0005% or more and 0.010% or less,
REM: 0.001% or more and 0.010% or less of 1 type or 2 types or more are contained, The steel member as described in any one of Claims 1-4 characterized by the above-mentioned. It is a manufacturing method of the steel member which consists of steel materials which have the ingredient composition according to any one of claims 1 and 3 to 5,
Any one of a mechanical cutting process, a mechanical grinding process, a mechanical polishing process, and a blasting process for projecting spherical particles having a Mohs hardness of 5.5 to 7.5 according to a 15-step evaluation for minerals on a steel surface. Or the manufacturing method of the steel member characterized by including the surface treatment process which performs two or more processes.   7. The steel according to claim 6, wherein the surface treatment step for the region exposed to the vacuum space in the steel material surface includes a vacuum exposed surface treatment step in which mechanical polishing is performed using a 300-th or higher abrasive. Manufacturing method of member.   The method for manufacturing a steel member according to claim 6 or 7, wherein the spherical particles are glass beads.