JP6160787B2 - Thin plate and manufacturing method thereof - Google Patents

Description

  The present invention relates to a thin plate and a manufacturing method thereof.

  A gasket used as a sealing material for automobile exhaust gas is required to have high strength. A metal gasket such as stainless steel is processed into a predetermined gasket shape by molding such as cutting (or punching), drilling, overhanging, bending, etc., using a thin plate of about 0.1 to 0.3 mm as a raw material. .

  In recent years, the exhaust gas temperature has increased to about 700 ° C. due to the improvement of fuel efficiency and the spread of turbo, and therefore, Ni-based alloys such as Inconel 718 may be used. Although Ni-based alloys are excellent in heat resistance, there is a problem that the alloy cost is high because Ni is contained in excess of 50%, and a cheaper heat-resistant alloy for gaskets is desired.

  On the other hand, SUS301 or the like is known as an austenitic stainless steel conventionally used as an exhaust manifold gasket. SUS301 is a material that uses processing-induced martensite to increase the strength. However, when exposed to a high temperature of 500 ° C. or higher, the material has a large softening allowance.

  On the other hand, as a material having particularly excellent heat resistance in stainless steel, SUH660 using precipitation strengthening by an intermetallic compound containing Ni, Ti, and Al is known. SUH660 has higher strength at high temperatures than SUS301. However, when used at a temperature in the vicinity of 700 ° C. where a Ni-based alloy is used, there is a problem that a decrease in strength, so-called “sagging” occurs.

  Under the background as described above, several studies have been made so far regarding the steel type (alloy) having higher heat resistance than SUH660.

  Patent Document 1 discloses an austenitic stainless steel in which the intermetallic compound species is controlled and the heat resistance is improved by defining the ratio of Ti and Al.

  Patent Document 2 discloses a heat resistant stainless steel in which Ni is 10 to 50% and the total addition amount of Ti, Al, and Nb is 3.0 to 7.0 wt%. Patent Document 3 discloses a technique that defines the amount of elements contained in IVa group and Va group.

  In Patent Document 4, there is a technology that considers the balance between cold workability and high temperature strength by defining Ni / Mn ratio and Ti / Al ratio with Ni: less than 15-20% for the purpose of reducing the cost of SUH660. It is disclosed.

JP-A-4-48051 JP 2000-109955 A JP-A-7-109539 JP 2012-2111385 A

  Although the technique of Patent Document 1 is higher in heat resistance than SUH660, it has a large sag at the time of use at 700 ° C. as described above, and cannot be said to have sufficient heat resistance. Although the technologies of Patent Document 2 and Patent Document 3 are high in heat resistance, they are technologies related to the production of a rod and wire, and these technologies exhibit sufficient heat resistance when manufacturing a gasket plate. I couldn't. Moreover, the workability to the gasket shape after manufacturing a thin plate was not considered, and the description which suggests an improvement in workability was not recognized. The technique of Patent Document 4 has a problem that heat resistance is not sufficient when used at 700 ° C.

  As described above, there has never been a stainless steel (alloy) thin plate that is cheaper than Ni-based alloys, has sufficient heat resistance to withstand use at 700 ° C., and has good workability. . The “workability” in the present invention means that a thin plate manufactured by cold rolling is easily formed into a gasket shape, that is, can be formed without cracking. Under such a background, an object of the present invention is to provide a thin plate that achieves both heat resistance and workability as a thin plate by defining steel components, hardness, and manufacturing method.

  In order to solve the above-mentioned problems, the present inventors investigated the influence of components, hardness, and manufacturing method on heat resistance. As a result, it has been found that a thin plate excellent in workability and heat resistance can be provided by utilizing the combination of precipitation strengthening by an intermetallic compound and dislocation strengthening by a combination of heat treatment and cold rolling. This invention is made | formed based on said knowledge, The summary is as follows.

(1) By mass%, C: 0.002 to 0.10%, Si: 0.02 to 3.0%, Mn: 0.02 to 2.0%, P: less than 0.050%, S: Less than 0.010%, Cr: 12.0 to 30.0%, Ni: more than 30.0% to less than 50.0%, N: 0.0005 to 0.020%, Al: 0.002 to 5. 0%, Ti: more than 3.0% to less than 7.5%, Nb: more than 0.5% to less than 4.0%, Mo: 0 to 4.0%, W: 0 to 4.0%, B : 0-0.01%, Ca: 0-0.002%, Mg: 0-0.002%, the balance is iron and impurities, the crystal grain size is 20.0 μm or more, and the plate A thin plate having a cross-sectional hardness in the range of ¼ to ¾ of the thickness of 400 HV or more, and a change in hardness before and after holding the cross-sectional hardness at 700 ° C. for 400 hours is 80 HV or less.

  (2) The thin plate according to (1), wherein the composition contains at least one of Mo: 0.02 to 4.0% and W: 0.02 to 4.0% by mass.

  (3) The composition contains one or more of mass%, B: 0.0002 to 0.01%, Ca: 0.0002 to 0.002%, and Mg: 0.0002 to 0.002%. The thin plate according to (1) or (2).

(4) The method according to any one of (1) to (3), comprising the following steps (A) to (F), and repeating the following steps (C) to (E) twice or more: Thin plate manufacturing method.
(A) a step of melting a steel ingot having a predetermined composition;
(B) A step of processing the steel ingot at a high temperature to form a steel plate,
(C) The process of hold | maintaining at 1030 degreeC or more and less than 1100 degreeC,
(D) The process of cooling on condition that the average cooling rate from 900 degreeC to 600 degreeC is 30 degrees C / s or more,
(E) a step of cold rolling at a rolling rate of 10 to 60%, and
(F) A step of temper rolling at a rolling rate of 10 to 60%.

  According to the present invention, it is possible to provide a thin plate excellent in workability and heat resistance by defining steel components and production conditions.

  The present invention is described in detail below. First, the reasons for limiting the constituent elements of the thin plate according to the present invention will be described. In addition, the description of% about a composition means the mass% unless there is particular notice.

<C: 0.002-0.10%>
C produces carbide and acts as a strengthening phase. If the amount of C is excessively reduced, the cost in the steelmaking stage increases, so the content is made 0.002% or more. In addition, it is preferable to set it as 0.005% or more from a viewpoint of stable manufacturability. Further, when the content of C is high, deterioration of workability and sensitization (embrittlement) due to Cr carbide precipitation are caused. For this reason, it is 0.10% or less. In the case of performing molding with a high degree of processing, the content is preferably 0.030% or less, and more preferably 0.020% or less.

<Si: 0.02-3.0%>
Si may be used as a deoxidizing element or may be positively added to improve oxidation resistance. Since extremely low Si causes an increase in cost, its content is set to 0.02% or more. From the viewpoint of deoxidation, it is preferably 0.05% or more. Moreover, since addition of a large amount causes the workability fall by hardening of a material, the content is good to set to 3.0% or less. In addition, when the degree of processing is severe, it is preferably 1.0% or less.

<Mn: 0.02 to 2.0%>
Mn may also be used as a deoxidizing element like Si. Since excessive reduction of Mn causes an increase in cost, its content is set to 0.02% or more. In addition, it is preferable to set it as 0.05% or more from the point of refining cost, More preferably, it is 0.07% or more. In addition, since a large amount of Mn causes hardening of the material, its content is set to 2.0% or less. From the viewpoint of oxidation resistance and stable productivity, it is preferably 1.5% or less.

<P: less than 0.050%>
P is an impurity. Although it may mix as an impurity element from a raw material, the content is so preferable that it is small. When P is present in a large amount, workability is deteriorated, so the content is limited to less than 0.050%. In addition, it is preferable to set it as 0.035% or less from a viewpoint of suppression of workability deterioration. The lower limit of the P content need not be determined, but excessive reduction leads to an increase in raw material and steelmaking costs. From this point, the P content may be 0.005% or more, and further 0.010%. It is good also as above.

<S: less than 0.010%>
S is an impurity. In some cases, it is mixed as an impurity element from the raw material. It is an element that degrades hot workability and corrosion resistance, and the lower the content, the better. Therefore, it is limited to less than 0.010%. Moreover, since corrosion resistance is so favorable that the content is low, Preferably it is less than 0.0030%. More preferably, it is less than 0.0010%. On the other hand, excessive reduction leads to an increase in the refining cost, so it may be 0.0002% or more.

<Cr: 12.0 to 30.0%>
Cr is an extremely important element in securing corrosion resistance and heat resistance. In order to acquire this effect, it is preferable to make it contain 12.0% or more. In addition, from a viewpoint of corrosion resistance and heat resistance, the content is preferably 14.0% or more. On the other hand, addition of a large amount causes toughness deterioration during production, so the content is made 30.0% or less. In consideration of manufacturing stability, the content is preferably 28.0% or less. More preferably, it is 26.5% or less.

<Ni: more than 30.0% to less than 50.0%>
Ni is an extremely important element for producing an intermetallic compound which is a precipitation strengthening phase and ensuring corrosion resistance and heat resistance. In addition, when added in combination with Ti and Nb described later, the workability of the thin plate is greatly affected. Since processing cracks occur when the amount of Ni is small, the content is preferably more than 30.0%. In addition, it is preferable to set it as 37.5% or more from a manufacturing stability and a heat resistant viewpoint. On the other hand, addition of a large amount leads to an increase in alloy cost and decreases the workability of the thin plate, so the content is made less than 50.0%. In consideration of manufacturing stability (prevention of hot work cracking), the content is preferably 46.0% or less.

<N: 0.0005 to 0.020%>
Since N may reduce workability due to the formation of nitrides, N is preferably low, and its content is 0.020% or less. When the degree of processing is severe, it is desirable to make it less than 0.010%. However, excessive reduction causes an increase in cost in the steelmaking stage, so the content is made 0.0005% or more. In addition, it is preferable to set it as 0.0010% or more from a viewpoint of stable manufacturability.

<Al: 0.002 to 5.0%>
Al is an element constituting an intermetallic compound and contributes to improvement in heat resistance. Therefore, in order to obtain this effect, 0.002% or more is preferably contained. In order to utilize also as a deoxidation element, it is preferable to set it as 0.005% or more. On the other hand, the addition of a large amount not only deteriorates the hot workability during production, but also produces precipitates that do not become a strengthening phase, so the content is made 5.0% or less. Considering the stability of manufacturability, it is desirable to make it less than 3.5%.

<Ti: more than 3.0% to less than 7.5%>
Ti is an element constituting an intermetallic compound that is a strengthening phase. In the present invention, Ti is added in combination with Nb to enhance heat resistance and ensure heat resistance that can withstand use at 700 ° C. In order to acquire this effect, it is preferable to contain more than 3.0%, More preferably, it is 3.5% or more, More preferably, it is 4.0%. On the other hand, the addition of a large amount reduces the hot workability and the forming workability after manufacturing the thin plate, so the content is made less than 7.5%. Considering stable manufacturability, it is preferably less than 5.5%.

<Nb: more than 0.5% to less than 4.0%>
Nb is an element effective for improving heat resistance, and is contained in an amount exceeding 0.5%. In the present invention, the combined addition with Ti has an effect of extremely improving heat resistance. In particular, the effect of suppressing sag after use at high temperatures is great. In order to acquire this effect, it is preferable to make it contain 1.5% or more. On the other hand, the addition of a large amount generates cracks during hot rolling and cold rolling and lowers the tensile elongation at break, so the content is made less than 4.0%. Considering the yield at the time of manufacture, less than 3.0% is desirable.

  The following elements are not essential additive elements, but one or more may be selected and added.

<Mo: 0 to 4.0%, W: 0 to 4.0%>
Mo and W are effective for improving heat resistance. The addition of these elements is thought to increase the strength of the precipitated phase in addition to strengthening the parent phase at high temperatures. In order to acquire this effect, it is preferable to contain 0.02% or more of any element. For the purpose of strengthening in a wide temperature range, 0.5% or more is preferably added. Moreover, since addition of a large amount induces cracks during production, the respective contents are set to 4.0% or less. Preferably it is 3.0% or less. Moreover, there is no problem even if both elements are added together.

  An impurity means the component mixed by raw materials and other factors, such as an ore and a scrap, when manufacturing steel materials industrially.

<B: 0 to 0.01%, Ca: 0 to 0.002%, Mg: 0 to 0.002%>
B, Ca, and Mg are elements that contribute to improving hot workability and formability of the thin steel sheet. In order to obtain this effect, each content is preferably 0.0002% or more. Preferably it is 0.0005% or more. Addition of a large amount not only reduces hot workability, but also tends to cause casting cracks, nozzle clogging, etc., so the contents are 0.01% or less for B and 0.002 for Ca and Mg, respectively. % Or less.

  The thin plate of the present invention satisfies the following characteristics. For example, “thin plate” in the present invention indicates that the plate thickness is 0.3 mm or less. In order to obtain this characteristic, predetermined cold rolling is performed. This condition will be described later. In the present invention, the crystal grain size is 20.0 μm or more. If the crystal grain size is less than 20.0 μm, the amount of change in hardness after holding at 700 ° C. for 400 hours becomes large, so this was made the lower limit. On the other hand, the upper limit is not particularly required from the viewpoint of heat resistance, but if it is too large, cracking during cold rolling tends to occur or cracking may occur during processing into a gasket shape. The following is preferable. Further, by satisfying this range, it is possible to satisfy an elongation value of 1.0% or more necessary for processing into a gasket shape after cold processing. In order to satisfy this crystal grain size, the heat treatment temperature and the cold rolling rate are important.

<Cross section hardness is 400HV or more>
As described above, when used as a sealing material, high material strength is required. For this reason, the cross-sectional hardness is Vickers hardness and the lower limit is 400 HV. The higher the hardness (strength) is, the better the sealing performance is. It is not necessary to specify the upper limit of the hardness, but if it is too hard, the ductility necessary for the molding process may be insufficient, so that it is 550 HV or less. Is desirable.

  The Vickers hardness is measured with a load of 4.903N (HV0.5) by a method based on JIS Z 2244. 5 points or more are measured in the range of 1/4 to 3/4 of the plate thickness, and an average value is taken as a representative value. In order to ensure hardness, it is particularly necessary to optimize the amounts of Ti and Nb in the component composition. In addition, the hardness is adjusted by cold rolling described later. In general, it is possible to increase the hardness to a certain extent only by increasing the degree of cold rolling, but as will be described later, in order to ensure the hardness after holding at 700 ° C., the components and It is necessary to adjust the hardness by combining manufacturing methods.

<Hardness change after holding at 700 ° C. for 400 hours is 80 HV or less>
The amount of change in hardness after holding at 700 ° C. for 400 hours is an index indicating heat resistance in the present invention. When considering driving an automobile, the gas temperature increases during high-speed driving, and the gasket is exposed to a temperature near 700 ° C. for a long time. In the existing technique, when used at 700 ° C., the settling is large, and the strength (hardness) after use at 700 ° C. is greatly reduced. In the present invention, “amount of change in hardness when held at 700 ° C. for 400 hours” is used as an index indicating a sag during use at 700 ° C. The reason why the holding time is limited to 400 hours is that the decrease in hardness when held at 700 ° C. is particularly because the hardness may change after 200 to 300 hours, and after 400 hours, the amount of change is small. This is because the hardness tends to gradually decrease with the passage of time. In the case of the steel according to the present invention, the amount of change exceeds 80 HV, although it depends on the chemical composition and the temper rolling ratio, etc., after about 1000 to 1500 hours have elapsed. Even if the composition is the same, as will be described later, when the heat treatment conditions, cold rolling conditions, and temper rolling conditions specified by the present invention are not satisfied, the hardness rapidly increases when the temperature is maintained at 700 ° C. May rise or fall. Therefore, the conditions of 700 ° C. and 400 hours were selected.

  For example, SUS301 cold rolled material has a hardness of 400 HV or more, but the room temperature hardness after holding at 700 ° C. for 400 hours is lower than 200 HV. That is, the hardness change amount is 200 HV or more. In the alloy thin plate of the present invention, the amount of change in hardness after holding at 700 ° C. for 400 hours is 80 HV or less. If it exceeds 80 HV, strength reduction during traveling increases, leading to fuel efficiency reduction due to deformation of members, generation of abnormal noise, and the like. The smaller the change in hardness, the smaller the settling, so 50HV or less is preferable.

  Moreover, since precipitation strengthening occurs in the present invention, depending on the component system, the hardness may increase after holding for 400 hours due to precipitation during holding at 700 ° C. In that case, although the hardness change amount which is a value obtained by subtracting the cross-sectional hardness after holding at 700 ° C. for 400 hours from the cross-sectional hardness takes a negative value, there is no problem if it is 80 HV or less as described above. The hardness is measured with a load of 4.903N (HV0.5) in accordance with JIS Z 2244, and 5 or more points are measured in the range of 1/4 to 3/4 of the plate thickness, and the average value is representative. Value.

  By prescribing the metal structure and composition such as initial strength and crystal grain size in this way, it is possible to suppress sag during use at 700 ° C. Since sag is due to tissue softening (metal structure change), a low sag rate indicates that there is little change in metal structure when held at 700 ° C. The inventors measured the hardness after adding various heat histories to the thin plate within the scope of the present invention, and further examined the difference from the hardness after holding at 700 ° C. for 400 hours, all of which are 80 HV or less. I have confirmed that. That is, if a material actually used (including a material whose previous thermal history is unknown) is subjected to heat treatment at 700 ° C. for 400 hours and the hardness change before and after is 80 HV or less, the characteristics of the present invention are obtained. Will be satisfied.

  As the metal structure that suppresses sag, the hardness, amount, ease of coarsening, degree of lattice mismatch with the parent phase, density, and the like are important control factors. Addition amount of elements (Ti, Nb, Al, Ni) constituting intermetallic compounds, heat treatment conditions, cold rolling conditions, and temper rolling conditions affect the hardness, precipitation amount, and coarseness of precipitates. Effect. It is important to sufficiently dissolve the precipitates that contribute to strengthening by the heat treatment process before the final cold rolling, and by regulating the subsequent cooling rate, the precipitation before the cold rolling is suppressed and the final control is performed. It is considered that the strain introduced by quality rolling (cold rolling) affects the number of precipitation sites (precipitation density) and the diffusion rate (easiness of coarsening) of each atom in the metal.

  Below, the manufacturing method of the thin plate of this invention is demonstrated.

  The thin plate of the present invention comprises the following steps (A) to (F) and is produced by repeating the following steps (C) to (E) twice or more.

(A) Step of melting an ingot having a predetermined composition First, an ingot having a predetermined composition is melted by casting. Casting may be either continuous casting or ingot casting.

(B) The process which makes the said steel ingot process at high temperature, and uses it as a steel plate The obtained steel ingot is made into a hot-rolled sheet by processing at high temperature, such as hot forging and hot rolling. In order to easily perform the cold rolling of the next step, a solution heat treatment may be performed before processing at a high temperature.

(C) The process of hold | maintaining at 1030 degreeC or more and less than 1100 degreeC If temperature is less than 1030 degreeC, an intermetallic compound will remain in large quantities without forming a solid solution, and in the case of intermediate annealing, it will become easy to produce a cold crack. On the other hand, in the case of final annealing, cracks during temper rolling and ductility (breaking elongation) after cold rolling are reduced, making it impossible to form into a gasket shape, or a decrease in hardness when held at 700 ° C. occurs early. It becomes easy. This is thought to be because the insoluble precipitate remains because the heat treatment temperature is low, and the coarsening of the precipitate is promoted with the insoluble precipitate as a nucleus when kept at 700 ° C. As described above, it is presumed that the hardness may suddenly increase or decrease when 200 to 300 hours have elapsed. On the other hand, if the reached temperature is too high, the crystal grain size becomes coarse, and sufficient hardness cannot be obtained even by subsequent cold rolling, so the temperature is set to less than 1100 ° C. In order to stabilize the material, the temperature is preferably less than 1080 ° C. Holding at this temperature for a long time is not preferable because crystal grain coarsening occurs, but a certain amount of holding may be performed to stabilize the material. However, the holding time is preferably 300 s or less.

(D) Step of cooling at an average cooling rate from 900 ° C. to 600 ° C. under a condition of 30 ° C./s or more. Is cooled at 30 ° C./s or more. When the cooling rate is slow, precipitation occurs during cooling, and sufficient workability cannot be obtained after cold rolling. Therefore, it is necessary to increase the cooling rate. In particular, since the temperature at which precipitation that affects the strength is likely to occur is 900 ° C. to 600 ° C., the average cooling rate in this temperature range is set to 30 ° C./s or more. When the average cooling rate is smaller than this, precipitation occurs during cooling and the strength is increased. The reason for limiting to this temperature range is that precipitates contributing to strengthening tend to precipitate. In order to take the precipitate dissolved in the heat treatment (C) to the next step without precipitating, it is necessary to secure a cooling rate in this temperature range. The average cooling rate is a value obtained by dividing the temperature difference between 900 ° C. and 600 ° C. (300 ° C.) by the time required to reach 600 ° C. from 900 ° C. The upper limit value of the average cooling rate does not need to be determined in particular, but it is not realistic because a special cooling device (function) exceeding 200 ° C./s is required in consideration of the current facility capacity. As long as the cooling rate is satisfied, there is no problem as long as the cooling method is satisfied. However, in consideration of existing facilities, a method of forcibly blowing a gas such as air, Ar, mist, water or the like is desirable.

(E) Step of cold rolling at a rolling rate of 10 to 60% Following the above heat treatment and cooling, cold rolling at a rolling rate of 10 to 60% is further performed, and the temper rolling rate performed after the final annealing is taken into consideration Finish to the finished thickness. When the rolling rate is less than 10%, productivity is deteriorated and abnormal grain growth is likely to occur. Moreover, in the case of the cold rolling rate exceeding 60%, a rolling material becomes hard and it becomes easy to generate | occur | produce a crack.

(F) Process of temper rolling at a rolling rate of 10 to 60% The temper rolling process is necessary for increasing the dislocation density and ensuring high hardness of the material. In addition, by using the alloy thin plate after introducing strain by cold rolling, the precipitation density of the intermetallic compound at the time of use is increased. In other words, cold rolling can achieve both an increase in initial strength and an increase in strength during use (effective precipitation strengthening). When the cold rolling rate is less than 10%, the initial strength is low and the sealing property is inferior. Further, when the cold rolling rate exceeds 60%, the crystal grain size becomes small, and therefore the hardness decrease after holding at 700 ° C. becomes large. Moreover, since material strength becomes high, workability (ductility) falls, and it becomes easy to produce a crack at the time of gasket processing, the preferable reduction rate of cold rolling which makes 60% an upper limit is 20% or more and 55% or less.

  The following steps (C) to (E) are repeated twice or more to finally produce a thin plate having a thickness of 0.3 mm or less after the step (F). If the steps (C) to (E) are less than twice, the increase or decrease in hardness at the time of holding becomes remarkable, so the number of times is set to two or more.

  The present invention is a technique for controlling the strength (hardness) and workability of a thin plate within a specific range by defining the composition and manufacturing conditions. It has been conventionally known that Ni, Ti, Nb, Al and the like constitute an intermetallic compound, and that the heat resistance is improved when the amount of these added is large. On the other hand, in order to ensure the workability of a thin plate in applications such as gaskets in the Ti, Nb, and Al amount ranges as in the present invention and to prevent a decrease in hardness during use, an optimal Ni, Ti, Nb, and Al range The existence of is a new finding.

  The reason why good heat resistance is obtained by repeating the steps (C) to (E) twice or more is not known in detail, but is presumed as follows. As described above, it is considered that the heat resistance in the present invention is mainly strengthened by precipitates during use. When the precipitate becomes coarse and the precipitation density decreases, the strengthening amount decreases. The steps (C) to (E) described above are intended to temporarily dissolve precipitates that contribute to strengthening and not to reprecipitate during cooling. However, coarse precipitates precipitated after hot rolling cannot be sufficiently dissolved in a short time solid solution, and on the other hand, if they are dissolved for a long time, crystal grains become extremely coarse. Therefore, it is estimated that the precipitate can be sufficiently dissolved by repeating cold rolling-annealing-cooling twice or more. In temper rolling (cold rolling), in addition to increasing the material strength, the dislocations introduced by cold rolling are used as precipitation nuclei when maintained at 700 ° C., thereby dispersing the precipitation.

  The effects of the present invention will be described with reference to examples, but the present invention is not limited to the conditions used in the following examples.

In the example, a sample was prepared by the following process.
(A) A 30 kg steel ingot having the composition (% by mass) shown in Table 1 was melted.
(B) The obtained steel ingot was made into a hot rolled sheet having a thickness of 5.0 mm by forging and hot rolling.
(C) Holding was performed at a predetermined temperature.
(D) The cooling rate from 900 ° C. to 600 ° C. was cooled at a predetermined cooling rate.
(E) Cold rolling was performed at a predetermined rolling rate.
(F) Temper rolling was performed at a predetermined rolling rate.

  In the examples, in (C) to (E), the heat treatment temperature, the cooling rate, and the rolling rate (10 to 60%) were changed, and in the present invention example, the process was repeated twice or more under the conditions specified in the present invention. Thereafter, the cold rolling rate was adjusted in order to obtain a target sheet thickness, and a final sheet thickness of 0.20 mm was finished by temper rolling. Using the obtained thin plate, cross-sectional hardness, tensile elongation, and heat resistance were evaluated. Since the present invention is considered to satisfy the hardness change even in the material after being actually used (held at a high temperature), the thermal history in the actual usage environment was simulated for some test pieces before holding at 700 ° C. A pre-heat treatment was performed.

  The cross-sectional hardness was measured at room temperature by measuring the Vickers hardness (HV0.5) at the central portion of the cross-sectional thickness by a method in accordance with JIS Z 2244. The average value measured 5 times was used.

  The crystal grain size was calculated from the cross-sectional structure. The measuring method of the crystal grain size was based on JIS G 0551.

  The tensile elongation was measured by a method based on JIS Z 2241 using a JIS No. 13 B tensile test piece. When the elongation value in the tensile test is 1.0% or more, molding into a gasket shape is possible. Therefore, a material having an elongation value of 1.0% or more was regarded as an acceptable level of formability.

  The heat resistance was judged by the cross-sectional hardness after holding at 700 ° C. for 400 hours. As described above, an average value (HV0.5) measured five times by a method according to JIS Z 2244 was used.

  Production conditions and evaluation results are shown in Tables 2 and 3.

  As can be seen from Tables 2 and 3, the alloy thin plate obtained using the steel type having a composition deviating from the composition of the present invention, and the alloy thin plate produced based on the production condition deviating from the production condition of the production method of the present invention are: Any of the cross-sectional hardness, tensile elongation, and heat resistance did not satisfy the predetermined characteristics. In the comparative example, variations in sheet thickness and cracks occurred in the subsequent cold rolling. Further, in the example that did not satisfy the final heat treatment condition, a crack occurred during the molding of the gasket. On the other hand, in the technology within the scope of the present invention, good characteristics were obtained regardless of the pre-heat treatment conditions.

  Steel type no. Nos. 15 and 16 are compositions that satisfy Patent Document 3, but they do not exhibit good characteristics unless they satisfy the manufacturing method and structure as in the present invention.

According to the present invention, a thin plate excellent in workability and heat resistance can be obtained, and can be used in all industrial fields. The thin plate of the present invention can be applied to members used at high temperatures in addition to gaskets used as sealing materials for automobile exhaust systems.

Claims (4)

% By mass
C: 0.002-0.10%,
Si: 0.02-3.0%,
Mn: 0.02 to 2.0%,
P: less than 0.050%,
S: less than 0.010%,
Cr: 12.0-30.0%,
Ni: more than 30.0% to less than 50.0%,
N: 0.0005 to 0.020%,
Al: 0.002 to 5.0%,
Ti: more than 3.0% to less than 7.5%,
Nb: more than 0.5% to less than 4.0%,
Mo: 0 to 4.0%,
W: 0 to 4.0%,
B: 0 to 0.01%
Ca: 0 to 0.002%,
Mg: 0 to 0.002%,
Having a composition where the balance is iron and impurities,
The crystal grain size is 20.0 μm or more,
The cross-sectional hardness in the range of 1/4 to 3/4 of the plate thickness is 400 HV or more,
A thin plate having a hardness change amount of about 80 HV or less before and after holding for 400 hours at 700 ° C. in cross-sectional hardness . The composition is in weight percent,
Mo: 0.02 to 4.0%, and W: 0.02 to 4.0%
The thin plate of Claim 1 containing 1 or more types of these. The composition is in weight percent,
B: 0.0002 to 0.01%
Ca: 0.0002 to 0.002%, and Mg: 0.0002 to 0.002%
The thin plate of Claim 1 or 2 containing 1 or more types of these. The method for producing a thin plate according to any one of claims 1 to 3 , comprising the following steps (A) to (F) and repeating the following steps (C) to (E) twice or more.
(A) a step of melting a steel ingot having a predetermined composition;
(B) A step of processing the steel ingot at a high temperature to form a steel plate,
(C) The process of hold | maintaining at 1030 degreeC or more and less than 1100 degreeC,
(D) The process of cooling on condition that the average cooling rate from 900 degreeC to 600 degreeC is 30 degrees C / s or more,
(E) a step of cold rolling at a rolling rate of 10 to 60%, and
(F) A step of temper rolling at a rolling rate of 10 to 60%.