TWI661057B - Ma Tian San stainless steel plate and metal close pad - Google Patents

Abstract

An object of the present invention is to reduce the occurrence of anisotropic phenomena of workability or fatigue resistance due to oxide-based inclusions in a Matian-based stainless steel sheet.

In terms of mass%, the Ma Tian San stainless steel sheets are: C: 0.030 to 0.300%, Si: 0.20 to 2.50%, Mn: 0.15 to 4.00%, Ni: 0.01 to 1.00%, Cr: 11.00 to 15.00%, N: 0.001 to 0.100%, Al: 0.0001 to 0.0350%, V: 0 to 0.50%, Nb: 0 to 0.50%, Ti: 0 to 0.50%, B: 0 to 0.020%, residual Fe and unavoidable impurities, The composition of the γ max value determined by the following formula (1) is 80.0 or more, and the conversion composition of the oxide-based inclusions observed in the metal structure is Al ₂ O ₃ : 30% by mass or less, and SiO ₂ : 20 to 60 mass%, MnO: 15 to 70% by mass of Ma Tian bulk stainless steel sheet.

Description

Ma Tian San stainless steel plate and metal close pad

The present invention relates to a stainless steel sheet used for a metal adhesion pad having low anisotropy excellent in workability and fatigue characteristics, and a metal adhesion pad using the same.

Engine cylinder head gasket or exhaust pipe gasket for automobile and motorcycle trailers are exposed to the pressure fluctuation environment under the high temperature, high pressure and high vibration of the engine. Among them, the cylinder head gasket of the automobile engine needs to be pressurized at the time of compression, and in order to maintain the sealing property, it is necessary for the contact materials of both sides to be connected by a high contact pressure (surface pressure). Metal-adhesive mats used in engines or exhaust passages generally form beads of a certain height (continuous ridges) in order to ensure sufficient contact pressure. Beads are typically formed by pressure molding through beads. Therefore, in order to manufacture a material steel sheet of such a metal adhesion mat, high strength, high fatigue characteristics, and excellent workability are generally required.

In the past, many air cushions that are applied to automobile engines or their exhaust passages use work hardening type metastable austenitic stainless steel (SUS301 or the like). This type of steel is produced by cold calendering to form a granulated bulk. In an attempt to increase the intensity. However, in order to increase the strength level, it is necessary to increase the cold rolling ratio. The increase in the cold rolling ratio is responsible for the reduction of toughness, fatigue resistance, and processability. Further, a remarkable aggregate structure is developed, and the characteristics of the rolling parallel direction (L direction) and the rolling orthogonal direction (C direction) are poor, that is, the anisotropy is increased.

Further, in industrial piping and the like, there is a case where a metal adhesion pad to which coating is applied is used. In such a metal adhesion mat, in addition to workability and fatigue characteristics, coating film adhesion is also required.

On the other hand, there are Martensitic stainless steels which are materials which can be made high in strength without increasing the cold rolling ratio. In Patent Document 1, it is disclosed that the Matian powder type steel is applied to a mat.

[Previous Technical Literature] (Patent Literature)

Patent Document 1: Japanese Laid-Open Patent Publication No. 2000-109957

The raw material cost of the Ma Tian San stainless steel is cheaper than the metastable austenite stainless steel containing a large amount of high-priced Ni. Further, since it is possible to impart a high cold rolling ratio and it is not necessary to work harden, it is less likely to cause a problem that the toughness is lowered and the anisotropy from the aggregate structure is caused by work hardening. However, according to the investigation by the inventors of the present invention, even a metal-adhesive pad for forming a bead is formed using a Matian-based stainless steel plate. When evaluating performance under severe test conditions, it is known that properties which are considered to be the cause of material anisotropy can be obtained. The reason for this is considered to be that the coarse oxide-based inclusions continuously present in the rolling direction in the material (steel sheet) are degraded in workability or fatigue resistance in a specific direction.

The invention is disclosed in the Ma Tian bulk stainless steel plate, A technique resulting from a decrease in anisotropy of workability or fatigue resistance caused by oxide-based inclusions. Further, a technique for improving the adhesion of the coating film is disclosed.

The above problem is known to be solved by softening the oxide-based inclusions present in the steel sheet.

That is, the present invention provides a hot-rolled steel sheet of Ma Tian San stainless steel, expressed by mass %, which is: C: 0.030 to 0.300%, Si: 0.20 to 2.50%, Mn: 0.15 to 4.00%, Ni: 0.01 to 1.00%, Cr: 11.00 to 15.00%, N: 0.001 to 0.100%, Al: 0.0001 to 0.0350%, V: 0 to 0.50%, Nb: 0 to 0.50%, Ti: 0 to 0.50%, B: 0 to 0.020 %, the residual Fe, and the unavoidable impurities, and the steel composition having the γ max value of 80.0 or more is determined by the following formula (1), and the average composition conversion of the oxide-based inclusions observed in the metal structure is obtained. The mass ratio of Al ₂ O ₃ , SiO _{2 ,} and MnO is Al ₂ O ₃ : 30% by mass or less (for example, 1 to 30% by mass), SiO ₂ : 20 to 60% by mass, and MnO: 15 to 70% by mass. Ma Tian San stainless steel hot rolled steel sheet.

γ max=420C-11.5Si+7Mn+23Ni-11.5Cr-49(Ti+ Nb+V)-52Al+470N+189...(1)

Here, the value of the mass % of the element is substituted at the element symbol of the formula (1). Among the arbitrary added elements Ti, Ni, and V defined in the formula (1), for the element not included, 0 (zero) is substituted at the place where the element symbol is.

Among the above steel component elements, V, Nb, Ti, and B are arbitrarily added elements. The Al content of the steel component element means the total Al content. "Conversion ratio of mass ratio of Al ₂ O ₃ , SiO _{2 ,} and MnO" means that the content ratio of Al, Si, and Mn of the oxide-based inclusions is converted into a single oxide of Al ₂ O ₃ , SiO _{2 ,} and MnO, respectively. The meaning of the mass ratio.

Among the above steel compositions, it is more preferable to satisfy any of the following (A) and (B).

(A) Si+Mn≧1.30, and 0.25≦Si/Mn≦1.50

(B) Si + Mn < 1.30, and 0.40 ≦ Si / Mn ≦ 1.50

Therefore, in the places of Si and Mn of (A) and (B), the contents of Si and Mn are represented by mass%, respectively.

As a steel sheet suitable for the processing material of the metal adhesion mat, a Matian-based stainless steel cold-rolled annealed steel sheet derived from the above-described hot-rolled steel sheet can be cited. The thickness of such a steel sheet may be, for example, 0.05 to 0.5 mm, or may be controlled to 0.1 to 0.3 mm. The hardness of the plate surface (rolling surface) is, for example, 400 to 470 HV.

The present invention provides a Ma Tian San stainless steel cold-rolled annealed steel sheet, and in the above-mentioned cold-rolled annealed steel sheet, in particular, as a coating film having good adhesion, in the pickling treatment after the annealing is completed, the precipitated particles are peeled off. The pit hole having an opening diameter of 1.0 μm or more is formed, and the number density of the pits of 10/0.01 mm ² or more is obtained on the surface of the steel sheet, and the surface roughness Ra in the direction perpendicular to the rolling is 0.500 μm or less.

As the particles to be precipitated, it is mainly a carbide particle of M ₂₃ C ₆ (M is a transition metal element such as Cr). Although carbon nitrogen compounds are formed, the carbonitrides contained in the present specification are referred to as carbides. The surface roughness Ra is an arithmetic mean roughness Ra defined in JIS B0601:2013. The rolling right angle direction means that the rolling direction is a right angle direction. The opening diameter of the pothole refers to the diameter (long diameter) of the longest portion of the opening portion surrounded by the outline of the pit in the SEM (scanning electron microscope) image seen in the thickness direction of the steel sheet surface.

As a method of manufacturing a cold-rolled annealed steel sheet, x is provided. A method for producing a granulated stainless steel cold-rolled annealed steel sheet, which comprises a cold-rolled steel sheet derived from the above-mentioned hot-rolled steel sheet, in the range of 800 to 1100 ° C, in the austenite single-phase temperature region or by austenite The phase in which the bulk phase is +20% by volume or less of the ferrite phase is heated in the two-phase temperature region, and then cooled to form the austenite phase into a phase of the makita phase (the annealing step is completed). The above cooling is more preferably carried out at a condition that the average cooling rate from 800 ° C to 200 ° C is from 1 to 150 ° C / sec.

As a method of obtaining a cold-rolled steel sheet having particularly excellent coating film adhesion, there is provided a method for producing a Matian-based stainless steel cold-rolled annealed steel sheet having the following steps: a cold-rolled steel sheet derived from the above-described hot-rolled steel sheet is The oxidizing ambient gas is surrounded by a ferrite phase in the range of 800 to 1100 ° C, in the austenite single-phase temperature region or in the austenite phase + 20% by volume or less of the ferrite phase. After heating in the degree zone, the step of precipitating carbide particles by cooling (complete annealing step) after the annealing step is completed by setting the average cooling rate from 800 ° C to 200 ° C to 1 to 150 ° C / sec The steel sheet is subjected to a pickling treatment to remove the oxidized steel scale on the surface, and the carbide particles present on the surface are peeled off and a pit is formed on the surface (pickling step).

Moreover, the present invention provides a metal adhesion mat which has a metal bead which is formed by forming the cold-rolled annealed steel sheet, and has a bead which is formed by press molding, and presses the top of the bead head into the contact material. The metal mat is used. The aging treatment is carried out, for example, at 100 to 500 ° C after the beads are formed. "Bead top" means the top of the raised portion of the bead that is in contact with the other material.

According to the invention, the oxide-based inclusions present in the material are low-melting, soft, and the oxide-based inclusions are associated with the steel matrix material during the hot pressing delay and the subsequent cold pressing delay. The (substrate) is deformed to extend in the rolling direction, and it is possible to prevent the coarse particles from remaining directly in the thinned cold-rolled steel sheet. Therefore, the reduction in workability or fatigue resistance caused by the oxide-based inclusions can be remarkably improved. Conventionally, in oxide-based inclusions, coarse particles which are partially broken by hot rolling are distributed in the vicinity of the rolling direction, and the curved ridge line becomes a rolling direction to deteriorate bending workability or fatigue resistance. These are the causes of anisotropy in processability or fatigue resistance. The anisotropy can be alleviated by the cold-rolled annealed steel sheet according to the present invention, and the size can be obtained after the bead is formed. Highly accurate air cushion. Further, when the air cushion is used, since the anisotropy of the fatigue resistance is small, the relevant contact surface pressure at the top of the bead head is maintained equal. As a result, a metal adhesion pad excellent in leak resistance can be achieved. In the final pickling step, the cold-rolled annealed steel sheet having the detached pits on which the precipitated particles are dispersed on the surface is also excellent in coating film adhesion.

Fig. 1 is a graph showing the relationship between the ternary oxide composition of Al ₂ O ₃ , SiO ₂ and MnO and the ductility of oxide-based inclusions.

Fig. 2 (a) and (b) are optical micrographs of oxide-based inclusions observed in the L section.

Fig. 3 (a) to (c) are diagrams showing the shape of the vicinity of the bead portion of the fatigue test piece.

Figure 4 SEM photograph of the surface of the steel sheet.

Figure 5 SEM photograph of the surface of the steel sheet.

Figure 6 SEM photograph of the surface of the steel sheet.

[Best Mode for Carrying Out the Invention] [Oxide-based inclusions]

The inclusions present in the steel can be divided into two types: high elongation type and difficult deformation type. The former is mainly a sulfide system, and the latter is mainly an oxide system. Among them, the oxide-type inclusions which are difficult to deform are not easily stretched during the cold pressing, and remain coarse particles in the steel sheet. The coarse oxide-based inclusion particles cause deterioration in workability or fatigue resistance. through Often, in the steel making stage, refining or casting is performed to reduce the amount of inclusions (high-definition clarity) or to reduce the diameter. However, excessive high-definition clarity increases the load in the steelmaking step and results in an increase in product cost. In the present invention, as a melting technique of the Ma Tian San stainless steel which can achieve a general cleanliness level, a method of lowering the melting point and softening the oxide-based inclusions as much as possible is employed.

Actually, the oxide-based inclusions are composite oxides in which Al, Si, and Mn are considered as main components. According to the detailed review by the inventors of the present invention, it is known that the content of Al, Si, and Mn in the oxide-based inclusions is expressed as a composition of individual oxides of Al ₂ O ₃ , SiO ₂ , and MnO. In order to impart ductility, the inclusions can set an effective inclusion composition range to a specific value. This composition range is substantially the same as the composition range which becomes a lower melting point in the equilibrium state diagram of the Al ₂ O ₃ , SiO ₂ , and MnO ternary oxides.

In the first graph, the relationship between the ternary oxide composition of Al ₂ O ₃ , SiO ₂ and MnO and the ductility of the oxide-based inclusions is shown. The drawing in the figure shows the extension state of the oxide-based inclusions in the cross section (L section) of most of the stainless steels in relation to the rolling direction and the thickness direction of the cold-rolled steel sheets, and is evaluated on a certain basis. result. Specifically, the case where each of the oxide-based inclusion particles which are cold-rolled is crushed into a fracture shape and is clearly stretched in the rolling direction is represented by a symbol (extension). The coordinates of the respective graphs indicate the "average composition of oxide-based inclusions" when the content ratios of Al, Si, and Mn of the oxide-based inclusions are converted into mass ratios of Al ₂ O ₃ , SiO _{2 ,} and MnO, respectively. . The converted average composition is an oxide system in an area of Al ₂ O ₃ : 0 to 30% by mass, SiO ₂ : 20 to 60% by mass, and MnO: 15 to 70% by mass (indicated by a thick line in FIG. 1) Inclusions are malleable. As shown in the examples to be described later, the composition of the oxide-based inclusions is remarkably improved in the field of bending workability or fatigue resistance, and in particular, a metal suitable for high performance can be obtained. The material steel plate in the mat.

The composition of the oxide-based inclusions can be mainly Steel composition and steelmaking conditions are controlled. In particular, it is an effective method to sufficiently ensure the Mn content in the steel composition, to adjust the mass ratio of Si/Mn to a specific range, and to limit the Al content and the like. Further, it is also effective to use deoxidized oxygen in steel making as Si deoxidizing oxygen.

In Fig. 2, it is exemplified by pressure in hot rolled annealed steel sheets. The cold rolling was carried out at a rate of 60%, and an optical microscope image of an oxide-based inclusion of the L-section at a plate thickness of 0.8 mm was observed. Fig. 2(a) shows an example of the comparative example No. 21 and (b) which will be described later, and an invention example No. 5 which will be described later. In general, the oxide-based inclusions seen in the Ma Tian San stainless steel sheet are hard, and as shown in (a), they are not excessively broken in the steel sheet even with cold rolling. The thinner the plate thickness, the larger the ratio of the diameter of the inclusion particles in the thickness of the plate, which tends to cause deterioration of workability and fatigue resistance. On the other hand, according to the Ma Tian bulk stainless steel sheet of the present invention, the composition of the oxide-based inclusion is adjusted within a soft range, and is broken by calendering as in (b), as the metal of the steel base material flows. Extending in the direction of rolling. As the thickness of the sheet is reduced, the degree of elongation of the oxide-based inclusions is also increased, and the adverse effect on the bending workability or the fatigue resistance property becomes extremely small. Implement bead pressurization In the observation of the L-section of the steel sheet to be formed, it is preferable that the maximum diameter of the oxide-based inclusions is 5.0 μm or less in the thickness direction of the oxide-based inclusions, and more preferably 3.0 μm or less. Further, it is more effective that the maximum diameter in the thickness direction of the steel sheet can be extended to 1.0% or less of the sheet thickness.

[Steel composition]

The chemical composition (steel composition) of the steel sheet to be the object of the present invention will be described. Hereinafter, "%" in the steel composition means "quality%" unless otherwise specified.

C is an austenite-forming element and is an effective element for the strengthening of the ferrite phase and the granule phase. When the C content is too small, the above-mentioned strengthening action cannot be sufficiently exerted, and the amount of austenite generated at a temperature higher than Ac ₁ becomes a component adjustment (optimization of γ max) which is difficult to control within an appropriate range, and it is disadvantageously ensured. The amount of Ma Tian scattered. As a result of various reviews, the C content is necessarily set to 0.030% or more, and it is more preferably set to 0.060% or more. It can also be controlled in a C content of more than 0.100%. However, when the C content is excessive, the grain boundary of the Cr-based carbide is likely to be precipitated during the cooling process in the austenite formation temperature zone, and the corrosion resistance is lowered. The C content is adjusted to a range of 0.300% or less.

When steel is produced, Si is added as a deoxidizing agent. root According to the review by the inventors of the present invention, the composition of the oxide-based inclusions is controlled in the soft field, and deoxidation by Si is an extremely effective method. When the Si content is 0.20% or more, it is necessary to add Si. It is more preferable to set it to 0.30% or more. However, Si will solidify in the ferrite phase and in the field of the granules, especially for the hardening of the granules. Moderately hardened in the air cushion Although it is effective in high strength, excessive hardening becomes a cause of reducing workability or toughness. Also, excessive Si content causes high temperature cracking. The Si content is limited to the range of 2.50% or less.

Mn is an austenite-forming element that can expand at high temperatures. Austenite phase zone. Increasing the Mn content is an effective method in the increase in the volume of the Ma Tian. Further, Mn is an essential element for attempting to contribute to the softening of oxide-based inclusions. As a result of the detailed review by the inventors of the present invention, in order to sufficiently reduce the anisotropy of workability or fatigue resistance, a high-performance air cushion is realized, and an Mn content of 0.15% or more is effective, and the Mn content is ensured. More than 0.75% is more effective. When the content is lower than the Mn content, it is difficult to control the composition of the oxide-based inclusions within the above-described predetermined range, and it is not possible to stably obtain a close-up of the anisotropy. The Mn content can also be controlled in the range of more than 1.00%. However, when the Mn content is increased, the austenite phase formed at a high temperature is stabilized, and during the cooling process until the normal temperature, it is impossible to form a granule form and the austenite phase remains. As a result of various reviews, the Mn content was set to be 4.00% or less. It is preferably 3.50% or less.

In order to control the composition of the oxide-based inclusions, In the soft range, it is effective to adjust the content of Si and Mn to a balanced shape. For example, the ratio of the Si content to the mass % of the Mn content, and the mass ratio expressed by Si/Mn is preferably in the range of 0.25 to 1.50. In the case where the total content of Si and Mn is small, the Si/Mn mass ratio is more effective in such a manner that it does not become lower. Specifically, as a refining and casting method using a general stainless steel steelmaking apparatus, the composition of the oxide-based inclusions is easily controlled within the soft range, and Si and Mn are balanced. A steel composition of any of the following (A) and (B).

(A) Si+Mn≧1.30, and 0.25≦Si/Mn≦1.50

(B) Si + Mn < 1.30, and 0.40 ≦ Si / Mn ≦ 1.50

Ni is an element that generates austenite and is an effective element in sufficiently ensuring the amount of numbness. It is effective to set the Ni content to 0.01% or more. However, when Ni is too much, it tends to have a retained austenite phase, which is disadvantageous for improving strength. The Ni content is limited to 1.00% or less, and more preferably 0.65% or less.

Cr is an essential element when imparting corrosion resistance to stainless steel. In order to sufficiently ensure the amount of production of the granules, it is necessary to increase the content of elements of austenite formed by C, N, Ni, Mn, etc., corresponding to an increase in the Cr content, which causes an increase in the cost of steel. Further, the inclusion of a large amount of Cr is a cause of lowering the toughness. In the present invention, steel having a Cr content of 11.00 to 15.00% is taken as an object.

N is an austenite-forming element and is effective for strengthening the ferrite phase and the granule phase as well as C. Ensuring an N content of 0.001% or more is an effective method. Excessive N contains nitrides during cooling after annealing, which causes deterioration of corrosion resistance and fatigue resistance. The N content is limited to 0.100% or less.

Al is an element with strong deoxidation. However, according to the review by the inventors of the present invention, the deoxidation of Si is considered as the main force, and the total amount of Al in the steel is attempted to be 0.0001% or more, and Al is refined, and it is easy to form an oxide system. The composition of the inclusions is controlled within the above range. When the Al content increases, the toughness is poorly affected. The situation. The total Al content in the steel is limited to less than 0.0350%.

V, Nb, Ti, and B are effective elements for improving manufacturability, strength, fatigue resistance, and the like. One or more of these may be added as necessary. V is set to 0.50% or less, Nb is set to 0.50% or less, Ti is set to 0.50% or less, and B is set to a content range of 0.020% or less. A more effective content range is set to V: 0.01 to 0.50%, Nb: 0.01 to 0.50%, Ti: 0.01 to 0.50%, and B: 0.0005 to 0.020%.

The content of each element is adjusted so that the γ max value determined by the following formula (1) becomes 80.0 or more.

γ max=420C-11.5Si+7Mn+23Ni-11.5Cr-49(Ti+Nb+V)-52Al+470N+189...(1)

Here, the element % symbol of the formula (1) is substituted for the mass % value of the element. The above γ max is an index indicating the maximum austenite amount (% by volume) which is generated when the temperature region of the Ac ₁ point or higher is heated. Steel in which the content of each element is within the above range, when the austenite phase at a high temperature is cooled to a normal temperature, almost all of it is converted into a form of a phase of the field. Therefore, in the steel base material (substrate) of the cold-annealed annealing material to which the present invention is applied, the amount of the eccentric is almost equal to the γ max (volume %), and the residual portion is the ferrite phase. Where γ max is more than 100, the steel matrix material becomes almost 100% 麻田散组织.

When the ratio of the ferrite phase occupied in the steel substrate becomes too large, it is difficult to stably achieve high strength suitable for the metal adhesion mat. Further, the difference in strength between the ferrite phase and the ecsal phase becomes easy to be broken by the phase interface, and the anisotropy of workability and fatigue resistance becomes large. Various inspections As a result of the discussion, in the present invention, a steel composition in which γ max becomes 80.0 or more is employed.

[Production method]

Representative manufacturing methods are exemplified as follows. The steel adjusted to the above chemical composition can be melted by a usual stainless steel steel equipment to obtain a cast piece. There is no need for special handling for HD clarity. However, the deoxidation process is desirably deoxidized with Si compared to the deoxidation of Al alone. However, the content of Al is also expected to be within the above range. The cast piece can be subjected to hot rolling in the same manner as in the production of a usual makita-based stainless steel sheet to obtain a hot-rolled steel sheet. The oxide-based inclusions present in the hot-rolled steel sheet are within the above-described composition range and are softened.

After the annealing of the hot-rolled steel sheet, cold rolling is performed to reduce the sheet thickness. Intermediate annealing may be performed on the way to cold rolling as needed. The softened oxide-based inclusions are broken by pressurization under cold rolling, and extend in the rolling direction as the metal of the steel base material flows. The final product sheet thickness may be, for example, 0.05 to 0.5 mm. The final finish annealing is performed in a cold rolled steel sheet that becomes a predetermined final product sheet thickness. The completion annealing temperature is an austenite formation temperature region set to Ac ₁ or more. Specifically, in the range of 800 to 1100 ° C, in the "austenite single-phase temperature region" or the "austenite phase + 20% by volume or less of the ferrite phase, the two-phase temperature region" Heating is preferred. As long as it is within the steel composition range specified by the present invention, an austenite phase corresponding to the amount of γ max can be generated generally in a temperature range of 900 to 1050 °C. The holding time at which the annealing temperature is completed may be set to a range of 0 to 60 sec.

After the annealing is completed, the cooling process is continued to normal temperature. In the middle, the austenite phase becomes almost the full amount of the Ma Tian. Generally, the eccentric phase is that C and N are solidified under supersaturation, and hardened by intrinsic multi-indexing. The greater the cooling rate at the time of the deformation of the granules, the greater the degree of hardening, and the higher the strength. However, the haze phase generated at the time of quenching lacks toughness, and it is necessary to perform post-treatment such as temper heat treatment. According to the review by the inventors of the present invention, in order to obtain a good toughness of the Ma Tian loose structure, if it is not subjected to post-treatment such as tempering, the "austenite single-phase temperature region" or the austenite phase + 20% by volume or less After heating in the 2-phase temperature zone formed by the ferrite phase, it is effective to cool at a relatively gentle (not quenching) cooling rate. However, when the cooling rate becomes too slow, the amount of solid solution of C and N decreases, and the strength of the scattered phase of the field decreases. Further, when the amount of solidification of C and N in the austenite-forming element is decreased, the amount of formation of the ferrite phase is likely to increase, whereby the strength is also lowered. As a result of various reviews, the average cooling rate from 800 ° C to 200 ° C is preferably adjusted to a cooling rate of 1 to 150 ° C / sec. The cooling rate in this range is easily achieved by air cooling, but water cooling can also be used. In addition, it is effective to form a carbide which is a source of the pit formation which will be described later, in addition to the toughness of the relaxation of the Matian phase.

In order to improve the adhesion of the coating film, (i) finishing the annealing is in In the oxidizing atmosphere such as the atmosphere, (ii) the average cooling rate from 800 ° C to 200 ° C is set to 1 to 150 ° C / sec, (iii) the descaling is performed in the subsequent pickling, so-called The annealing and pickling step is an extremely effective method.

Oxidized steel scale is formed on the surface of the steel sheet by heating in an oxidizing atmosphere. Average cooling of steel sheets in this state from 800 ° C to 200 ° C When the speed is cooled at a cooling rate of 1 to 150 ° C / sec, the precipitation growth time of the carbide becomes considerably rich during the cooling process, and spherical carbides in the substrate (metal base material) can be obtained. Particles are in a state of dispersing tissue. When the annealed steel sheet in which the spherical carbide particles are dispersed is subjected to pickling for the purpose of removing steel scale, the spherical carbide particles existing directly under the steel scale on the surface of the steel sheet are easily removed from the scale. The surface of the steel plate peeled off. A pothole is formed by eluting a part of the spherical carbide particles in an acid to form a rounded off-sheath. This round-shaped pothole can exert an anchoring effect on the coating film and improve the coating film adhesion.

In order to form the pickling of the peeling marks of the carbide particles, the same process as the pickling of the purpose of removing the scale may be performed. For example, (a) electrolysis using a neutral salt, sulfuric acid, nitric acid or the like, (b) impregnation with a mixed acid bath of hydrofluoric acid and nitric acid, and the like, a typical pickling method. Any one of the above (a), (b), or both may be employed. When the pickling conditions are made strong, the so-called excessive pickling causes a cause of dissolution of the substrate (metal substrate) to increase the surface roughness. When it comes to coating film adhesion, it is advantageous to increase the general surface roughness. However, when the surface roughness is too large, the characteristics (processability, fatigue resistance, and sealing property) required for the material for the air cushion are lowered. Here, in the present invention, on the surface of the metal substrate having high smoothness, the above-mentioned pits (shedding marks) are expected to have the desired opposite characteristics to the air cushion material by being in a dispersed surface form. Adhesion to the coating film. Specifically, in the pickling treatment after the annealing is completed, the pores having an opening diameter of 1.0 μm or more formed by the precipitation of the particles are separated, and the number density of 10/0.01 mm ² or more is required on the surface, and calendering is desired. The surface roughness Ra in the right-angle direction is a surface morphology of 0.500 μm or less. The Ra in the direction perpendicular to the rolling is preferably from 0.200 to 0.500 μm.

The number density of the pits having an opening diameter of 1.0 μm or more formed by the dropping of the precipitated particles in the pickling treatment can be measured as follows.

[Method for measuring the number density of potholes]

In the observation area of one or two or more observations randomly determined on the surface of the steel sheet, the number of occurrences of the presence of the opening diameter of 1.0 μm or more in the observation area of the total area of 0.1 mm ² or more is calculated. Divided into the total area of the observation area, converted into the number of every 0.01 mm ² . The potholes existing on the boundary line of the set observation field are determined by the shape of the hole surrounded by the contour of the opening on the observation field side and the boundary line to determine whether or not the opening is 1.0 μm or more.

As mentioned above, the opening diameter of the pothole refers to the wheel in the pothole. The diameter (long diameter) of the longest portion of the opening surrounded by the profile, but the detachment of the spherical carbide particles, is characterized in that the opening portion of the formed pit has a circular shape. In the hole opening portion, the diameter of the longest portion of the opening measured in the direction perpendicular to the long diameter is referred to as "short diameter", and the ratio of the long diameter to the short diameter is referred to as the aspect ratio of the opening of the cavity. In the case of the pothole formed by the detachment of the spherical carbide particles, the aspect ratio of the opening portion is approximately 2.0 or less.

The pickling treatment after completion of annealing is a pit having an opening diameter of 1.0 μm or more formed by dropping of carbide particles and having an opening ratio of 2.0 or less, and having 10/0.01 mm ² or more on the surface. The number-density cold-rolled annealed steel sheet is a more suitable object in the present invention.

For reference, Fig. 4 shows a pickling material having a number of pits having a medium opening diameter of 1.0 μm or more and a number of pits of less than 10/0.01 mm ² and a surface roughness Ra of 0.110 μm in the direction perpendicular to the rolling, and Fig. 5 is a drawing. For the same pit, the number density is 10/0.01 mm ² or more, and the same surface Ra is 0.154 μm. The sixth figure is the same pit density of 10/0.01 mm ² or more. A pickled material having a surface Ra of 0.391 μm is exemplified as an SEM photograph of the surface. Any one of the directions parallel to the short side of the photo is in the direction of rolling.

The cold-rolled annealed steel sheet thus obtained can reduce the former material The material is due to the anisotropy of the coarse oxide-based inclusions continuously present in the rolling direction, and is suitable for various press processing applications including metal-bonded mats. Further, the cold-rolled annealed steel sheet in which the above-described precipitated particles are scattered on the surface is excellent in coating film adhesion. In the process of manufacturing a metal close-up pad, beads of a certain height are formed by press molding of beads. For the obtained press-processed product, aging treatment can be carried out at 100 to 500 ° C as needed.

[Examples] "Embodiment 1"

The steel of the chemical composition shown in Table 1 was melted to obtain a cast piece. Deoxidation was performed as Si deoxidation except for a part of Comparative Example (No. 21). Hot rolling was carried out in the cast piece to obtain a hot rolled steel sheet having a thickness of 3.0 mm.

[Composition analysis of oxide-based inclusions]

The sample cut out from each of the hot-rolled steel sheets was subjected to SEM observation of a cross section (L cross section) in the direction of the parallel rolling direction and the thickness direction, and 30 particles were randomly selected from the particles of the oxide-based inclusions existing in the L-section. Composition analysis was performed by EDX (energy dispersive X-ray analysis). The content ratios of Al, Si, and Mn of the respective inclusions were converted into mass ratios of the respective oxides Al ₂ O ₃ , SiO _{2 ,} and MnO, and 30 oxide-based inclusions having the mass ratio value were averaged. The average composition of the oxide-based inclusions in the steel sheet was obtained.

800 ° C × 24 h, heat of furnace cooling in each hot-rolled steel sheet After the treatment, the plate thickness is reduced by cold rolling. In the middle of cold rolling, one or more intermediate annealings of 800 ° C × soaking for 1 minute were carried out, and the cold rolled steel sheet having a final thickness of 0.2 mm was prepared, and after maintaining the soaking temperature for 60 sec at the temperature shown in Table 2 The annealing was carried out under the conditions of cooling outside the furnace to normal temperature to obtain a cold-rolled annealed steel sheet. The average cooling rate from 800 ° C to 200 ° C after completion of annealing is in the range of 1 to 150 ° C / sec. A part of the cold-rolled annealed steel sheets was further subjected to aging treatment under the conditions of maintaining soaking for 60 minutes at the temperatures shown in Table 2. These cold rolled annealed steel sheets and aging treated materials were used as test materials, and the following tests were carried out.

[hardness]

The Vickers hardness was measured at a test force of 9.8 N (hardness mark HV1) in accordance with JIS Z2244:2009 on the surface (rolling surface) of the test piece.

[bending workability]

The bending test of the V block method of JIS Z2248:2006 was carried out on the test material for the annealed steel sheet. The direction in which the longitudinal direction of the test piece is the parallel rolling direction is indicated by the L direction, and the direction perpendicular to the rolling direction is indicated by the C direction. The bending test piece in the L direction was such that the curved ridge line was in the direction perpendicular to the rolling direction, and the bending test piece in the C direction was the direction in which the curved ridge line became the parallel rolling direction. A defect such as a crack is not generated on the outer side of the curved portion, and the ratio of the minimum bending radius R to the thickness t is regarded as the "bending limit R/t". The bending test was carried out with the number of tests n = 3, and the worst of the three times was used as the result of the test. In the L direction and the C direction, the bending limit R/t is 1.5 or less, and the ratio of [the bending limit R/t value in the C direction] / [the bending limit R/t value in the L direction] is 1.3 or less. Bead pressed into The material steel plate for the metal tight gasket in the shape can be evaluated as having good bending workability.

[Fatigue resistance characteristics]

A strip sample (width: 8 mm) in which the longitudinal direction of the test material is in the L direction and the C direction is used, and the bead pressure molding is performed and the shape shown in the third (a) and (b) is small. Processing in the test piece of "Bead". The initial bead has a groove width of about 3 mm and an initial bead height of about 0.4 mm. In the initial bead portion, a compression test which is equivalent to the initial tightening of the metal-adhesive pad is applied, and a fatigue test piece having a simulated bead having a residual bead height of about 0.1 mm as shown in the third figure (c) is produced. . Further, the cross-sectional shape schematically shown in the third (b) and (c) is an exaggerated dimension in the thickness direction. Using this simulation fatigue test piece in two bead portions imparting vibratory stress fatigue test, the number of repeated ¹⁰⁷ times is obtained in the fatigue limit (fatigue limit; N / mm ^2). L direction, the fatigue limit is in the C direction 300N / mm ² or more, and the fatigue limit of the L direction and C direction difference of 30N / mm ² or less are to be evaluated as the metal forming the bead portion of the pressure pad adhesion Among them are those with excellent fatigue resistance.

The results are shown in Table 2 (a) and Table 2 (b).

An example of the present invention is a group of oxide-based inclusions. In the soft range described above, the anisotropy of the bending workability and the fatigue resistance is small, and the metal adhesion mat has suitable characteristics. When the L-section of the test material (cold-rolled annealed steel sheet) was investigated, it was found that the oxide-based inclusions were crushed by rolling and extended in the rolling direction, and the maximum diameter in the thickness direction was 2 μm or less.

On the other hand, Comparative Example No. 21 is an Al deoxidizer, No. 22 to 25 are those having a high Si/Mn ratio, and Nos. 27 and 28 are those having a low Mn content, and any of the oxide-based inclusion compositions of any of them deviate from the prescribed range of the present invention. Since these oxide-based inclusions are hard, they are continuously present in the rolling direction in the cold-rolled annealed steel sheet in the original coarse particle pattern. For this reason, in particular, the bending workability and the fatigue resistance in the °C direction are deteriorated. Although the oxide-based inclusions of No. 26 are soft, the amount of the ferrite phase is excessive due to the low γ max , and the difference in strength between the ferrite phase and the field is due to the phase difference. Cracking occurs and the anisotropy of workability and fatigue resistance characteristics is increased.

<<Example 2》

Using the steel of No. 5 in Table 1, a cold-rolled steel sheet having a final thickness of 0.2 mm was obtained in the same manner as in Example 1. Annealing was carried out in this cold rolled steel sheet under the conditions shown in Table 3. The cooling after completion of the annealing is cooled by air, and the cooling rate is controlled by adjusting the furnace temperature or the air blowing amount. The temperature change at the time of cooling was measured by mounting a thermocouple on the surface of the sample, and the average cooling rate from 800 ° C to 200 ° C was obtained from the cooling curve. After the plate temperature drops to about room temperature, the mixture is mixed at 3% by mass of hydrofluoric acid + 12% by mass of nitric acid at 60 ° C. The pickling treatment is carried out by immersion in the acid pickling solution. The pickling is terminated at a point when the oxidized steel scale can be removed, and is subjected to usual water washing as a test material (acid pickling material). It is also prepared to directly perform the finish annealing of the BA treated material in a reducing environment for comparison. The pickling material was examined for hardness and bending workability in the same manner as in Example 1. Regarding each of the test materials, the surface roughness Ra of the surface of the steel sheet in the direction perpendicular to the rolling was measured by a laser microscope. In the pickling material, the surface of the steel sheet is observed by SEM. According to the "method for measuring the number density of potholes" disclosed above, the particles are precipitated by pickling treatment, and the pits having an opening diameter of 1.0 μm or more are formed by falling off. Number density. At this time, the SEM images of the following 12 fields of view of each test material were investigated.

Applying an epoxy base to the surface of the steel sheet of each test material After the coating was baked and dried at 200 ° C for 40 seconds, the polyester-based coating material was applied thereon, and baked at 215 ° C for 50 seconds to obtain a coated steel sheet sample. The bending test specified in JIS 3320:1999 was carried out for each coated steel sheet sample. The bending test piece has a long direction as a rolling direction, a bending axis as a rolling right angle direction, and a curved outer side surface as a coating surface, and is bent at a normal temperature of 180°. In the curved ridge line after the bending test, whether or not the coating film was peeled off was observed, and the peeling of the coating film was evaluated as ○ (coating film adhesion; good), and the peeling of the coating film was evaluated as × (coating film adhesion) ; bad) way to judge.

The results of these are shown in Table 3.

The environment in which the annealing is completed is regarded as an oxidizing atmosphere (atmosphere), and the average cooling rate from 800 ° C to 200 ° C after annealing is set to 1 to 150 ° C / sec (No. 5-2, 5-3, 5- 4) The hardness has a sufficient level of strength of 400 to 470 HV, and the bending workability is also good. In addition, the number density of the pits having an opening diameter of 1.0 μm or more formed by the pickling treatment by the pickling treatment is 10 pieces/0.01 mm ² or more, and the coating film adhesion is also good. The surface roughness Ra in the direction perpendicular to the rolling direction is 0.500 μm or less, and an air cushion having high sealing property can be obtained.

In contrast, the cold after completion of annealing of No. 5-1 However, the speed is high, because the granules are excessively hardened, so the bending test cannot be bent to 180°. Further, since the precipitation growth of the carbide is insufficient, the number density of the pits having an opening diameter of 1.0 μm or more is small. No. 5-5 is an example in which the cooling rate after completion of annealing is extremely slow, and the hardness is low. Further, in the stage of pickling to remove the oxidized steel scale, the surface was excessively pickled, and the surface roughness Ra in the direction perpendicular to the rolling was increased to more than 0.500 μm. No. 5-6 is an example in which annealing is performed under a reducing atmosphere, and since the pickling is not performed, the smoothness of the surface is high and the coating film adhesion is poor.

Claims (12)

A Matian powder stainless steel hot-rolled steel sheet, expressed in mass%, having: C: 0.030 to 0.300%, Si: 0.20 to 2.50%, Mn: 0.15 to 4.00%, Ni: 0.01 to 1.00%, Cr: 11.00 to 15.00 %, N: 0.001 to 0.100%, Al: 0.0001 to 0.0350%, V: 0 to 0.50%, Nb: 0 to 0.50%, Ti: 0 to 0.50%, B: 0 to 0.020%, residual Fe, and inevitable The steel composition is determined by the following formula (1), and the average composition of the oxide-based inclusions observed in the metal structure is converted into Al ₂ O ₃ and SiO _{2 .} And the mass ratio of MnO is Al ₂ O ₃ : 30% by mass or less, SiO ₂ : 20 to 60% by mass, MnO: 15 to 70% by mass, γ max = 420C - 11.5Si + 7Mn + 23Ni - 11.5Cr - 49 (Ti+Nb+V)-52Al+470N+189 (1) Here, the content of the element expressed by mass% is substituted in the element mark of the formula (1). The granulated stainless steel hot-rolled steel sheet according to the first aspect of the invention, wherein the steel composition satisfies any one of the following (A) and (B), (A) Si + Mn ≧ 1.30, and 0.25. ≦Si/Mn≦1.50 (B)Si+Mn<1.30, and 0.40≦Si/Mn≦1.50 Here, Si in mass % is substituted for Si and Mn in (A) and (B), respectively. The content of Mn. A granitic stainless steel cold-rolled annealed steel sheet derived from the hot-rolled steel sheet according to claim 1 or 2. A type of Ma Tiansan stainless steel cold-rolled annealed steel sheet, which is derived from the application The hot-rolled steel sheet according to Item 1 or 2, wherein the sheet thickness is 0.05 to 0.5 mm. A granulated stainless steel cold-rolled annealed steel sheet is obtained from the hot-rolled steel sheet according to the first or second aspect of the patent application, wherein the hardness of the sheet surface (rolled surface) is 400 to 470 HV. A granitic stainless steel cold-rolled annealed steel sheet obtained from the hot-rolled steel sheet according to the first or second aspect of the patent application, wherein, on the surface, the pickling treatment after the annealing is completed causes the precipitated particles to fall off The number of pits having an opening diameter of 1.0 μm or more is 10/0.01 mm ² or more, and the surface roughness Ra in the direction perpendicular to the rolling is 0.500 μm or less. The granulated stainless steel cold-rolled annealed steel sheet according to the sixth aspect of the invention, wherein the precipitated particles are carbide particles. A method for producing a granulated stainless steel cold-rolled annealed steel sheet, wherein: a cold-rolled steel sheet derived from a hot-rolled steel sheet according to claim 1 or 2, in the range of 800 to 1100 ° C, in Austen The single-phase temperature region or the step of heating in the 2-phase temperature region in which the ferrite phase having an austenite phase + 20% by volume or less is heated, and the step of transforming the austenite to form a phase of the field (Complete the annealing step). A method for producing a granulated stainless steel cold-rolled annealed steel sheet, wherein: a cold-rolled steel sheet derived from a hot-rolled steel sheet according to claim 1 or 2, in the range of 800 to 1100 ° C, in Austen The single-phase temperature zone is heated from 800 ° C to 200 ° C after heating in a 2-phase temperature zone with a ferrite phase of austenite phase + 20 vol% or less. The average cooling rate is set to a cooling step of 1 to 150 ° C / sec (the annealing step is completed). A method for producing a granulated stainless steel cold-rolled annealed steel sheet, wherein the cold-rolled steel sheet derived from the hot-rolled steel sheet according to claim 1 or 2 is in an oxidizing atmosphere in a range of 800 to 1100 ° C After heating in the austenite single-phase temperature zone or in the 2-phase temperature zone in which the austenite phase + 20% by volume or less of the ferrite phase is formed, the average cooling rate from 800 ° C to 200 ° C is set to a step of cooling from 1 to 150 ° C / sec (completes the annealing step), and removing the oxidized steel scale on the surface by the pickling treatment while removing the carbide particles present on the surface while the annealing step is completed, The step of forming a pothole on the surface (pickling step). A metal adhesion mat, which is a metal adhesion mat formed by cold-rolled annealed steel sheets of a hot-rolled steel sheet according to claim 1 or 2, having beads formed by press molding. Use the top of the bead to squeeze into the other material. A metal-adhesive mat which is formed by subjecting a cold-rolled annealed steel sheet obtained from a hot-rolled steel sheet according to claim 1 or 2 to a metal-bonded mat aged at 100 to 500 ° C by adding Press-formed with beads, and the top of the bead is pressed into contact with the other material.