JP6434059B2 - Ferritic stainless hot-rolled steel sheet and strip for automobile flanges with excellent face sealability, and methods for producing them - Google Patents

Description

  TECHNICAL FIELD The present invention mainly relates to a ferritic stainless hot-rolled steel sheet and a steel strip excellent in surface sealability used for a flange material used in an automobile exhaust system and other pipe joints, and a manufacturing method thereof. is there.

  Ferritic stainless steel is inferior in workability, toughness and high-temperature strength compared to austenitic stainless steel, but it is inexpensive because it does not contain a large amount of Ni, and its thermal expansion is small. It is used favorably for parts materials. In general, steel types such as SUH409L, SUS429, SUS430LX, SUS436J1L, SUS436J1L, and SUS444 are used as ferritic stainless steel suitable for these applications. These materials are used by being molded into pipes or the like. Parts processed into these pipes and the like are connected by a flange. A flange part is comprised by the flange member joined to the pipe. As the flange material (automobile flange material) used for the flange member, the steel plate has been mainly used because it has a large plate thickness and is inferior in corrosion resistance. In recent years, SUH409L, which is the cheapest ferritic stainless steel, has also been used.

  However, due to the need for weight reduction of the vehicle body and extension of service life, a material having excellent corrosion resistance is required even in the automotive flange material, and use of SUH409L or ferritic stainless steel having further excellent corrosion resistance has begun. Further, when used in an exhaust system, if the strength at high temperature is high, there is an effect that the plate thickness can be designed to be thin. In this respect, ferritic stainless steel is more advantageous than ordinary steel.

  Patent Document 1 also discloses that a ferritic stainless steel plate having excellent corrosion resistance and heat resistance is used for the flange.

  For automobile flange materials, thin cold-rolled steel sheets with a thickness of 3 mm or less may be used with improved rigidity by bending, etc., but thick hot-rolled steel sheets with a thickness of 5 mm or more are punched as they are. Often used.

  In particular, when used as it is, if the surface roughness on the flange surface is rough, exhaust gas may leak out. It is an important characteristic that the surface sealing property of the so-called flange member, in which exhaust gas does not leak out from the joint surface of the flange fastening portion, is good. In part processing, it has been usually practiced to improve the surface sealability by grinding the surface of the flange member, but this has been a factor in increasing the processing cost. Therefore, there has been a demand for a ferritic hot rolled steel sheet for automobile flanges that has excellent surface sealing properties that can be used without grinding.

JP 2012-140688 A

  In the ferritic stainless steel sheet described in the background art, it is usually practiced to improve the surface sealability by grinding in parts processing, but this is a factor that increases the processing cost and can be used without grinding. A ferritic hot-rolled steel sheet excellent in the above has been desired. An object of the present invention is to provide a ferritic stainless hot-rolled steel sheet and steel strip excellent in surface roughness used for automobile flanges and the like, and methods for producing them.

  The present inventors evaluated the surface sealing property of the current flange material. The flange 2 as shown in FIG. 1A is made from 12Cr-Ti steel having a thickness of 6 mm, and the flange portion 1 as shown in FIG. 1B is manufactured using the flange 2, and air is flowed instead of exhaust gas, and the flange is fastened. The amount of gas leakage at the fastening surface of the part 5 was evaluated. As a result, it was found that there is a correlation between the fastening surface surface roughness of the fastening portion 5 and the amount of gas leakage as shown in FIG. In other words, in order to prevent the exhaust gas from leaking, the arithmetic average roughness Ra defined in JIS B0601 is adopted as an evaluation index, and if the value is about 5 μm or less, it is found that it is sufficiently practical. It was. Furthermore, a component system that satisfies the properties required for a material for automobile flanges, such as corrosion resistance and strength, was examined. Furthermore, in order to realize the value of the surface roughness in the manufacturing process, it has been found that the hot-rolled sheet can be properly polished and pickled, and the invention has been completed.

  The present invention has been completed based on these findings. Means for solving the problems of the present invention, that is, the ferritic stainless steel sheet of the present invention is as follows.

In the present invention, the hot-rolled steel sheet is a concept including a so-called “cut sheet” and “steel strip”. Therefore, in the following (4) and ( 11 ), the steel strip of the hot rolled steel sheet is extracted and limited.
(1) By mass%, C: 0.03% or less, N: 0.03% or less, Si: 0.01 to 1.0%, Mn: 0.01 to 1.0%, P: 0.04 %: S: 0.01% or less, Cr: 10.0-23.0%, Al: 0.10% or less,
Furthermore, Ti: 0.5% or less and Nb: 0.5% or less are contained, and (Ti + Nb) / (C + N) is 8 or more (Ti, Nb, C, N are respective components) Content (mass%)), and the balance consists of Fe and inevitable impurities,
A ferritic stainless steel hot rolled steel sheet for automobile flanges, whose surface roughness is 3 μm or more and 5 μm or less with an arithmetic average roughness Ra as an index, and a plate thickness of 5.0 to 15.0 mm.
(2) The ferritic stainless steel hot rolled steel sheet for automobile flanges according to the present invention, wherein the Ti content is 0.05% or less.
(3) Furthermore, in mass%,
A first group consisting of one or more of Mo: 1.5% or less, Cu: 0.5% or less, Ni: 1% or less,
Sn: a second group consisting of 0.005 to 0.1%,
V: 1% or less, W: 1% or less, Co: 1% or less, B: 0.0001% or more, 0.005% or less, Ga: 0.10% or less, Zr: 0.50% or less, Ta: 0.1% or less, Sb: 0.30% or less, Mg: 0.0030% or less, Ca: 0.0030% or less, at least one of the third group consisting of any one or more of them A ferritic stainless steel hot-rolled steel sheet for automobile flanges according to the present invention, comprising a group.
(4) The ferritic stainless steel hot rolled steel sheet for automobile flanges according to the present invention, wherein the hot rolled steel sheet is a hot rolled steel strip.
(5) A flange member composed of the ferritic stainless hot-rolled steel sheet of the present invention.
(6) By mass%, C: 0.03% or less, N: 0.03% or less, Si: 0.01 to 1.0%, Mn: 0.01 to 1.0%, P: 0.04 %: S: 0.01% or less, Cr: 10.0-23.0%, Al: 0.10% or less,
Furthermore, Ti: 0.5% or less and Nb: 0.5% or less are contained, and (Ti + Nb) / (C + N) is 8 or more (Ti, Nb, C, N are respective components) Content (mass%)), and the balance consists of Fe and inevitable impurities,
The surface roughness is a method for producing a ferritic stainless steel hot rolled steel sheet for automobile flanges having an arithmetic average roughness Ra as an index of 5 μm or less and a plate thickness of 5.0 to 15.0 mm,
In the manufacturing process of a ferritic stainless steel hot-rolled steel sheet, which is performed by melting / casting-hot rolling-annealing-pickling, grinding is performed before the annealing, and the grinding -annealing-pickling step is repeated one or more times. method for producing automobile flange ferritic stainless hot-rolled steel sheet shall be the.
(7) By mass%, C: 0.03% or less, N: 0.03% or less, Si: 0.01 to 1.0%, Mn: 0.01 to 1.0%, P: 0.04 %: S: 0.01% or less, Cr: 10.0-23.0%, Al: 0.10% or less,
Furthermore, Ti: 0.5% or less and Nb: 0.5% or less are contained, and (Ti + Nb) / (C + N) is 8 or more (Ti, Nb, C, N are respective components) Content (mass%)), and the balance consists of Fe and inevitable impurities,
The surface roughness is a method for producing a ferritic stainless steel hot rolled steel sheet for automobile flanges having an arithmetic average roughness Ra as an index of 5 μm or less and a plate thickness of 5.0 to 15.0 mm,
Melting and casting - hot rolling - annealing - in the process of manufacturing the ferritic stainless steel sheet is performed with pickling method for automotive flange ferritic stainless hot-rolled steel sheet you and performing grinding after annealing.
(8) In the manufacturing process of the ferritic stainless steel plate, the pickling or annealing-pickling step is omitted, and the final step is a grinding step. Production method.
(9) The method for producing a ferritic stainless hot rolled steel sheet for automobile flanges according to the present invention, wherein the Ti content is 0.05% or less by mass%.
(10) Furthermore, by mass%, Mo: 1.5% or less, Cu: 0.5% or less, Ni: 1% or less, the first group consisting of one or more, Sn: 0.005 -0.1% second group, V: 1% or less, W: 1% or less, Co: 1% or less, B: 0.0001% or more, 0.005% or less, Ga: 0.10% or less Zr: 0.50% or less, Ta: 0.1% or less, Sb: 0.30% or less, Mg: 0.0030% or less, Ca: 0.0030% or less The method for producing a ferritic stainless hot rolled steel sheet for automobile flanges according to the present invention, comprising at least one of the third group.
(11) The method for producing a ferritic stainless hot rolled steel sheet for automobile flanges according to the present invention, wherein the hot rolled steel sheet is a hot rolled steel strip.

  ADVANTAGE OF THE INVENTION According to this invention, the ferritic stainless steel hot-rolled steel plate and steel strip for motor vehicle flanges which were excellent in the surface sealing property can be provided.

Schematic diagram of the simulated flange used in the example Schematic diagram of the simulated flange used in the example Relationship between surface roughness of flange fastening surface and gas leakage from flange

  Embodiments of the present invention will be described below.

<Ingredients>
First, the reason why the steel composition of the stainless hot-rolled steel sheet of the present embodiment is limited will be described. In addition, the description of% about a composition means the mass% unless there is particular notice.

C: 0.03% or less Since C deteriorates formability, corrosion resistance, and weldability, the smaller the content, the better. Therefore, the upper limit is made 0.03%. Moreover, if the viewpoint of corrosion resistance is emphasized, the upper limit is desirably set to 0.015%. However, excessive reduction leads to an increase in refining costs, so the lower limit is preferably 0.001%. 0.002% is more preferable.

N: 0.03% or less N, like C, deteriorates formability, corrosion resistance, and weldability, so its content is preferably as small as possible. Therefore, the upper limit is made 0.03%. In view of corrosion resistance, the upper limit is preferably 0.02%. However, excessive reduction leads to an increase in refining costs, so the lower limit is made 0.001%. 0.002% is more preferable.

Si: 0.01% to 1.0%
Si is an element useful as a deoxidizer, and is an element that improves high-temperature strength and oxidation resistance. The deoxidation effect is improved as the amount of Si is increased, and the effect is manifested at 0.01% or more, so the lower limit is made 0.01%. However, since Si hardens a steel plate, the upper limit is made 1.0%. A preferable upper limit is 0.5%.

Mn: 0.01 to 1.0%
Mn is an element added as a deoxidizer and an element contributing to an increase in high-temperature strength in the middle temperature range. The effect is manifested at 0.01% or more. On the other hand, excessive addition forms MnS and lowers the corrosion resistance, so the upper limit is made 1.0%. A preferable upper limit is 0.5%.

P: 0.04% or less P is an element having a large solid solution strengthening ability. However, since P is an element harmful to corrosion resistance, it is preferably as small as possible, and the upper limit is set to 0.04%. When better corrosion resistance is required, 0.02% or less is preferable. However, excessive reduction increases the dephosphorization load and increases the manufacturing cost, so the lower limit is preferably made 0.005%.

S: 0.01% or less S forms sulfide inclusions and degrades the general corrosion resistance (entire corrosion and pitting corrosion) of steel materials. Therefore, the upper limit of the content is preferably small. %. Preferably the upper limit is 0.0050%. Further, the smaller the S content, the better the corrosion resistance. However, since the desulfurization load increases and the production cost increases for lowering the S content, the lower limit is preferably made 0.0001%. A preferred upper limit is 0.0005%.

Cr: 10.0-23.0%
Cr is an essential element for ensuring corrosion resistance. In order to form a passive film in the assumed environment, 10.0% or more is necessary, and this is the lower limit. On the other hand, if it exceeds 23.0%, lowering of workability at low temperatures and deterioration of toughness are brought about by the effect of improving corrosion resistance, so 23% is made the upper limit. When Cr is high, the toughness is lowered, so the upper limit is more preferably 18%.

Al: 0.10% or less Al is useful as a deoxidizing element, and the effect is manifested at 0.005% or more. However, excessive addition causes a drop in room temperature ductility, so the upper limit is made 0.10%. When deoxidation is possible with other elements such as Si, Al may not be contained.

Containing one or two of Ti: 0.5% or less and Nb: 0.5% or less,
And (Ti + Nb) / (C + N) is 8 or more (Ti, Nb, C, N are respective component contents (mass%)).
Since the present invention is used as a flange material for automobiles, welding is essential. Therefore, it is necessary to be excellent in the corrosion resistance of the welded portion, particularly in the intergranular corrosion resistance. Therefore, in order to suppress the formation of Cr-based carbonitrides that lower the corrosion resistance of the welded portion, it is essential to add one or two of Nb and Ti that can fix C and N as carbonitrides. The required amount can be roughly evaluated by (Ti + Nb) / (C + N), and this value may be 8 or more in order to develop excellent intergranular corrosion resistance. However, excessive addition reduces the room temperature workability, so the upper limit of both Ti and Nb is 0.5%.

  Furthermore, since the present invention is a thick hot-rolled steel sheet, when importance is attached to toughness, it is better not to use Ti. In that case, considering impurities from the raw material, Ti may be 0.05% or less.

  Furthermore, in order to improve the corrosion resistance, the following elements may be added.

Mo: 1.5% or less Mo may be added as necessary in order to improve corrosion resistance. In order to exert these effects, the lower limit is preferably made 0.01%. Preferably it is 0.10%, More preferably, it is 0.5%. On the other hand, excessive addition reduces workability, so the upper limit is made 1.5%. Preferably it is 1.1%.

Cu: 0.5% or less Cu is an element that improves corrosion resistance. The effect is manifested at 0.05% or more. Preferably it is 0.1% or more. On the other hand, excessive addition causes abnormal oxidation during hot rolling and causes surface defects, and also reduces toughness, so the upper limit is made 0.5%. A preferable upper limit is 0.2%.

Ni: 1% or less Ni is an element effective for suppressing the progress of pitting corrosion, and the effect is stably exhibited by addition of 0.05% or more. In addition, it is effective for improving the toughness of the hot-rolled sheet. Therefore, the lower limit is made 0.05%. It is more effective at 0.10% or more. 0.15% or more is more effective. Moreover, since addition of a large amount may cause material hardening by solid solution strengthening, the upper limit is made 1.0%. In consideration of the alloy cost, the upper limit is preferably 0.30%.

Sn: 0.005-0.1%
Sn is an element effective for improving corrosion resistance and high temperature strength. In addition, there is an effect that the mechanical properties at room temperature are not greatly deteriorated. Since the effect on corrosion resistance is manifested at 0.005% or more, the lower limit is made 0.005%. Preferably, the lower limit is 0.01%. More preferably, it is 0.03%. On the other hand, if added excessively, manufacturability and weldability are remarkably deteriorated, so the upper limit is made 0.1%.

  Further, the following elements may be added.

V: 1% or less, W: 1% or less, Co: 1% or less V, W, and Co are elements that improve high-temperature strength, and can be added as necessary. In the present invention, it is preferably 0.05% or more. More preferably, it is 0.1% or more. However, excessive addition causes a drop in normal temperature ductility, so the upper limit is 1%. Preferably it is 0.5% or less.

B: 0.0001% or more and 0.005% or less B is effective in fixing N, which is harmful to workability, and improving secondary workability, and may be added. The effect is manifested by adding 0.0001% or more. However, to reduce workability, the upper limit is made 0.005%.

Furthermore, Ga, Zr, Ta, Sb, Mg, and Ca may be added as follows.
Ga may be added at 0.1% or less for improving corrosion resistance and suppressing hydrogen embrittlement. Furthermore, 0.0020% or less is preferable from the viewpoints of manufacturability and cost and from the viewpoints of ductility and toughness. From the viewpoint of sulfide and hydride formation, the lower limit is preferably 0.0002%.

  Zr and Ta are preferably added as necessary because they combine with C and N to contribute to improvement of toughness. However, Zr exceeds 0.50% and Ta exceeds 0.1%. In addition to increasing costs, Zr is 0.50% and Ta is 0.1%. To do. Furthermore, considering refining costs and manufacturability, 0.08% or less is desirable. When the addition amount is 0.01% or more, the above effect is manifested, which is preferable.

  Since Sb contributes to improvement of corrosion resistance and high temperature strength, it is preferable to add Sb as necessary. Addition of more than 0.3% may cause slab cracking during production of steel sheets and low toughness of muffler hangers, so the upper limit is set to 0.3%. Furthermore, considering refining cost and manufacturability, 0.15% or less is desirable. When the addition amount is 0.01% or more, the above effect is manifested, which is preferable.

  Mg may be added as a deoxidizing element, and is an element that contributes to improving the formability by refining the slab structure. Further, the Mg oxide becomes a precipitation site for carbonitrides such as Ti (C, N) and Nb (C, N), and has an effect of finely dispersing and depositing them. However, excessive addition leads to deterioration of weldability and corrosion resistance, so the upper limit was made 0.0030%. Considering the refining cost, 0.0010% or less is desirable. This effect is manifested at 0.0002% or more, and contributes to the improvement of toughness, so the lower limit is preferably 0.0002%. 0.0003% or more is more desirable.

  Ca may be added for desulfurization; however, addition of over 0.0030% produces coarse CaS and deteriorates toughness and corrosion resistance, so the upper limit was made 0.0030%. Furthermore, considering refining cost and manufacturability, 0.0020% or less is desirable. Since this effect is manifested at 0.0001% or more, the lower limit is preferably made 0.0001%. 0.0003% or more is more desirable.

  In addition to the elements described above, the elements of the present invention can be contained within a range not impairing the effects of the present invention. It is preferable to reduce as much as possible Zn, Bi, Pb, Se, H, etc. as well as the aforementioned P and S, which are general impurity elements. On the other hand, the content ratio of these elements is controlled to the extent that the problem of the present invention is solved, and if necessary, Zn ≦ 100 ppm, Bi ≦ 100 ppm, Pb ≦ 100 ppm, Se ≦ 100 ppm, H ≦ 100 ppm. Contains one or more. “Ppm” is based on mass.

<Surface roughness>
Since the ferritic stainless steel hot-rolled steel sheet of the present invention is used for automobile flanges, it needs to be excellent in surface roughness. A flange is used to connect pipe members such as an exhaust system. Connect the flanges together to make the flange part. In order to prevent gas leakage from the flange portion, a fastening material such as a gasket may be used, but a gasket is often not used. When no gasket is used, the face seal between the flanges is important. Therefore, until now, the surface seal part of the flange has been finished by surface grinding. However, this method requires a grinding cost. Therefore, in order to use the hot rolled steel sheet as it is, it is necessary to smooth the surface at the hot rolled steel sheet stage. As the index, the arithmetic surface roughness Ra defined in JIS B 0601 was adopted, and it was found that the value was 5 μm or less. Therefore, the upper limit of Ra of the hot-rolled steel sheet is 5 μm. The smaller this value is, the smoother it is, and 3 μm or less is preferable for further improving the surface sealing property.

<Thickness>
The hot-rolled steel sheet of the present invention has a thickness of 5 mm to 15 mm. If it is less than 5 mm, it is too thin to have sufficient rigidity and sufficient surface sealability cannot be maintained, and if it exceeds 15 mm, it becomes too heavy and becomes unsuitable as a flange material. 6 mm or more is more preferable from the relationship of surface sealing properties. From the relationship of weight, 10 mm or less is more preferable.

  Moreover, when using it as a flange with the surface of a hot-rolled steel plate, since the amount of torque which fastens a bolt for fastening changes with plate | board thickness, plate | board thickness precision is important. The tolerance range is preferably 10% or less. More preferably, it is 5% or less.

<Manufacturing method>
The ferritic stainless steel of the present invention is a hot-rolled steel sheet, and becomes a product through processes of melting, casting, hot-rolling, annealing, and pickling. There are no particular restrictions on the equipment, and conventional manufacturing equipment can be used. Usually, it is often manufactured in the form of a so-called steel strip that is very long in the rolling direction, and is wound and stored and moved in a coiled form. However, when the plate thickness is 10 mm or more, the plate is often rolled, cut, stored and moved.

  Although hot rolling is not particularly defined, the slab heating temperature is preferably 1150 ° C to 1250 ° C. The hot rolling finishing temperature is preferably 850 ° C. or higher. Furthermore, after hot rolling, it is cooled by air-water cooling or the like. When the alloy addition amount is large, if the cooling is insufficient, the variation in toughness of the hot-rolled sheet increases, but in that case, it is preferable to rapidly cool to 450 ° C. or less. This stabilizes the toughness of the hot-rolled sheet. However, since the coil winding becomes more unstable and wrinkles are more likely to occur as the cooling end temperature is lowered, the cooling end temperature is most preferably 400 ° C. or higher and 450 ° C. or lower.

  In the annealing step, the annealing temperature is preferably 900 to 1100 ° C. When the temperature is lower than 900 ° C., recrystallization is difficult, and when the temperature exceeds 1100 ° C., crystal grains tend to be coarse, which is not preferable. When Ti is not included, 1000 degreeC or more is preferable. Within this range, fine adjustment may be made by the Cr amount or the like. Moreover, about the cooling rate after annealing, in order to suppress the toughness fall by 475 brittleness, the cooling rate from 800 degreeC to 450 degreeC shall be 5 degrees C / sec or more. Preferably, it is 10 ° C./sec or more. The effect is saturated at 20 ° C./sec or more. Thereby, the dispersion | variation in toughness by manufacture can be reduced.

In order to achieve the surface roughness of the hot-rolled steel sheet of the present invention, it is important that the steel sheet is slightly ground before annealing in the steps of melting, casting, hot-rolling, annealing, and pickling. Thereby, fine wrinkles and the like are removed, and a smooth surface can be obtained after pickling. The grinding amount of one steel plate is preferably 10 μm or more and 100 μm or less. If it is less than 10 μm, there is a high possibility that wrinkles will not be removed, and if it exceeds 100 μm, there is a high possibility that the roughness will not be sufficiently good. It is preferable to perform grinding before annealing, and to perform annealing and pickling after grinding because the tendency of the roughness to be improved than after grinding is seen. Of course, grinding may be performed in any process as long as the surface roughness of the present invention can be realized.

Although the equipment for grinding is not particularly defined, those that are usually used can be used, and a grinding belt is generally used. The grinding count can be appropriately selected in view of the situation after manufacture, but # 80 or more is preferable. This is because if it is less than # 80, there is a high possibility that the surface roughness is too high to be achieved. Moreover, since it will take time for grinding when it becomes fine, # 600 or less is preferable.

  If the roughness is not sufficiently achieved, these grinding, heat treatment and pickling may be repeated. In this case, the annealing temperature after the second time is preferably lower than the first time.

  Moreover, if the roughness of the present invention can be realized, there is no problem even if the product is ground. Further, there is no problem even if the pickling process is omitted and the grinding process is the final process. That is, as long as the roughness of the present invention can be realized, the grinding process can be performed any number of times in the manufacturing process.

  The ferritic stainless steel hot-rolled steel sheet of the present invention can be particularly suitably used as a ferritic stainless steel sheet for automobile flanges.

  The flange member comprised from the ferritic stainless steel hot-rolled steel sheet of the present invention can be particularly suitably used for automobile flanges. The flange member of the present invention is joined to a pipe which is an exhaust system member of an automobile to form a flange. Thereby, the flange excellent in surface sealing property can be comprised.

  Hereinafter, 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 this example, steels having the components shown in Table 1-1 and Table 1-2 were melted to cast an ingot, heated to 1150 to 1250 ° C., and the finishing temperature was set within a range of 850 to 950 ° C. Hot rolled to about 6 mm to obtain a hot rolled steel sheet (hot rolled steel strip). The hot-rolled steel sheet was cooled to 400 to 450 ° C. by air-water cooling. Thereafter, the coil (steel strip) was divided, and one was ground by about 30 μm on both sides using a grinding belt. The coil was A, and the coil that was not ground was B. Then, it annealed at 1000-1100 degreeC, and cooled to normal temperature. At this time, the average cooling rate in the range of 800 to 450 ° C. was set to 10 ° C./s or more. Subsequently, the hot-rolled annealed plate (hot-rolled steel plate) was pickled. In addition, about Nb and Ti content of Table 1, that whose content is less than 0.01% means that the element is not positively added and means inevitable impurities. Numerical values that fall outside the scope of the present invention are underlined. The same applies to Tables 2-1, 2-2, and 3 below.

A Charpy impact test was performed on the hot-rolled annealed sheet thus obtained at 0 ° C. according to JIS Z 2242. In addition, the test piece in a present Example is a subsize test piece with the thickness of a hot-rolled annealing board having a 2 mmV notch, and the heat energy in each example is obtained by dividing the absorbed energy by the cross-sectional area (unit cm ² ). The toughness of the annealed annealed plates was compared and evaluated. The evaluation standard of toughness was an impact value at 0 ° C., 10 J / cm ² or more was good (A), and the others were “X”.

  In addition, the corrosion resistance was evaluated, a salt spray test (SST) was performed, and no failure occurred in 4 h was determined to be acceptable (A), and the others were defined as “X”.

  Furthermore, the surface roughness was measured. The arithmetic surface roughness Ra defined in JIS B 0601 was used as an index. Ten locations were selected at random from the steel sheet, the roughness Ra was measured, and the average value was used as an index.

  From this product plate (hot-rolled steel plate), a 80 mm square plate is taken as the flange 2 shown in FIG. 1A, and four φ5 mm bolt holes 6 and φ40 mm holes 7 are opened, and φ40 mm and 100 mm length ferritic stainless steel. A steel pipe 3 was welded to the flange 2 by TIG welding, and a flange portion 1 as shown in FIG. 1B was assembled using M5 bolts 4. An air flow 8 was flowed at a flow rate of 50 L / min, and a liquid leak detection liquid was applied to the fastening portion 5 between the flanges to confirm the presence or absence of a leak. When there was no leak, the surface sealability was good (A), and the others were “X”. As a result, it became clear that there was no leakage when the roughness Ra was 5 μm or less, and the roughness Ra was 5 μm or less.

  Table 2-1 and Table 2-2 summarize the results. The roughness and surface sealability of a hot-rolled annealed steel plate (hot-rolled steel plate) having a component composition to which the present invention was applied were good. Moreover, toughness and corrosion resistance were also good. On the other hand, in the comparative example which deviates from this invention, roughness and surface sealing property were not favorable, or Charpy impact value or corrosion resistance was unacceptable. Thereby, it turns out that the ferritic stainless steel plate in a comparative example is inferior as an automobile flange use.

  In this example, first, the steel No. 1 in Table 1-1 was used. 3 and steel no. Steel having the component composition shown in FIG. 10 was melted and cast into a slab. After this slab was heated to 1200 ° C., the finish temperature was set within the range of 850 to 950 ° C., and the steel sheet was hot-rolled to a plate thickness of 8 mm to obtain a hot-rolled steel plate. The hot-rolled steel sheet was cooled to 380 to 560 ° C. by air-water cooling and then wound into a coil. As shown in Table 3, hot-rolled coils (hot-rolled steel strips) were manufactured under several cooling conditions.

Thereafter, the hot-rolled coil was divided, and both surfaces of the hot-rolled coil were ground using a grinding belt while changing the thickness to be ground as shown in “Grinding amount” in Table 3. At this time, # 80 to # 600 were appropriately selected according to the grinding amount.
Thereafter, the hot rolled coil was annealed at 1000 to 1100 ° C. and cooled to room temperature. At this time, the average cooling rate in the range of 800 to 450 ° C. was set to 10 ° C./s or more. Subsequently, the hot-rolled annealed plate was pickled to obtain a product plate.

  About some Examples, after this, grinding, annealing, and pickling were repeated and it was set as the product board. The annealing temperature was decreased from 0 ° C. to 20 ° C. from the first time. The grinding amount was not changed from the first time. The number of repetitions is shown in “Polishing-annealing-pickling process (times)” in Table 3.

  Furthermore, about another one Example, the pickling process omission or the annealing-pickling process was abbreviate | omitted, and it was set as the grinding process of the last process.

A Charpy impact test was performed on the hot-rolled annealed sheet thus obtained at 0 ° C. according to JIS Z 2242. In addition, the test piece in a present Example is a subsize test piece with the thickness of a hot-rolled annealing board, and by dividing an absorbed energy by a cross-sectional area (unit cm < ² >), Toughness was compared and evaluated. The evaluation criteria of toughness are impact values at 0 ° C., 10 J / cm ² or more is good (A), 7 J / cm ² or more and less than 10 J / cm ² is “B”, and the others are “X”. It was.

  In addition, the corrosion resistance was evaluated, a salt spray test (SST) was performed, and no haze in 4 h was passed (A) for automobile flanges, and the others were “X”.

  The same surface sealability evaluation test as in Example 1 was performed. When there was no leak, the surface sealability was good (A), and the others were “X”. Furthermore, the surface roughness was measured. The arithmetic surface roughness Ra defined in JIS B 0601 was used as an index. The measuring method is the same as in Example 1. Further, as in Example 1, Ra was 5 μm or less as acceptable.

  As is apparent from Table 3, the roughness and surface sealability of the hot-rolled annealed steel plate having the component composition to which the present invention was applied were good. The toughness was also good. On the other hand, in the comparative example which deviates from the present invention, the roughness and the surface sealability were not good. Therefore, it turns out that the ferritic stainless steel plate in a comparative example is inferior as an automobile flange use.

  In Comparative Examples 3-1 and 10-1, since the cooling rate was too low, coil winding became unstable, and the surface roughness of the hot-rolled sheet was large due to increased wrinkles. -2, 3-3, and 10-2 showed that the surface roughness was reduced and improved by repeating grinding, annealing, and pickling.

  As apparent from the above description, the stainless hot-rolled steel sheet and steel strip of the present invention can be used as an automobile flange material as it is without surface grinding due to its excellent surface smoothness. Therefore, it is excellent in parts manufacturability such as a good material yield. That is, by applying the material to which the present invention is applied, particularly to an exhaust flange member of an automobile or a motorcycle, a long-life component can be manufactured at low cost, and the social contribution can be increased.

  That is, the present invention is very useful industrially.

DESCRIPTION OF SYMBOLS 1 Flange part 2 Flange 3 Pipe 4 Bolt 5 Fastening part 6 Bolt hole 7 Hole 8 Air flow

Claims (11)

% By mass
C: 0.03% or less,
N: 0.03% or less,
Si: 0.01 to 1.0%,
Mn: 0.01 to 1.0%
P: 0.04% or less,
S: 0.01% or less,
Cr: 10.0-23.0%,
Al: 0.10% or less,
further,
Containing one or two of Ti: 0.5% or less and Nb: 0.5% or less,
And (Ti + Nb) / (C + N) is 8 or more (Ti, Nb, C, N are respective component contents (mass%)), and the balance consists of Fe and inevitable impurities,
A ferritic stainless steel hot rolled steel sheet for automobile flanges, whose surface roughness is 3 μm or more and 5 μm or less with an arithmetic average roughness Ra as an index, and a plate thickness of 5.0 to 15.0 mm. % By mass
The ferritic stainless steel hot rolled steel sheet for automobile flanges according to claim 1, wherein the Ti content is 0.05% or less. Furthermore, in mass%,
A first group consisting of one or more of Mo: 1.5% or less, Cu: 0.5% or less, Ni: 1% or less,
Sn: a second group consisting of 0.005 to 0.1%,
V: 1% or less, W: 1% or less, Co: 1% or less, B: 0.0001% or more, 0.005% or less, Ga: 0.10% or less, Zr: 0.50% or less, Ta: 0.1% or less, Sb: 0.30% or less, Mg: 0.0030% or less, Ca: 0.0030% or less, at least one of the third group consisting of any one or more of them The ferritic stainless hot-rolled steel sheet for automobile flanges according to claim 1 or 2, characterized by containing a group.   The ferritic stainless steel hot rolled steel sheet for automobile flanges according to any one of claims 1 to 3, wherein the hot rolled steel sheet is a hot rolled steel strip.   The flange member comprised from the ferritic stainless steel hot-rolled steel plate of any one of the said Claims 1-3. % By mass
C: 0.03% or less,
N: 0.03% or less,
Si: 0.01 to 1.0%,
Mn: 0.01 to 1.0%
P: 0.04% or less,
S: 0.01% or less,
Cr: 10.0-23.0%,
Al: 0.10% or less,
further,
Ti: 0.5% or less and
Nb: 1 type or 2 types containing 0.5% or less,
And (Ti + Nb) / (C + N) is 8 or more (Ti, Nb, C, N are respective component contents (mass%)), and the balance consists of Fe and inevitable impurities,
The surface roughness is a method for producing a ferritic stainless steel hot rolled steel sheet for automobile flanges having an arithmetic average roughness Ra as an index of 5 μm or less and a plate thickness of 5.0 to 15.0 mm,
In the manufacturing process of a ferritic stainless steel hot-rolled steel sheet, which is performed by melting / casting-hot rolling-annealing-pickling, grinding is performed before the annealing, and the grinding -annealing-pickling step is repeated one or more times. A method for producing a ferritic stainless hot rolled steel sheet for automobile flanges. % By mass
C: 0.03% or less,
N: 0.03% or less,
Si: 0.01 to 1.0%,
Mn: 0.01 to 1.0%
P: 0.04% or less,
S: 0.01% or less,
Cr: 10.0-23.0%,
Al: 0.10% or less,
further,
Ti: 0.5% or less and
Nb: 1 type or 2 types containing 0.5% or less,
And (Ti + Nb) / (C + N) is 8 or more (Ti, Nb, C, N are respective component contents (mass%)), and the balance consists of Fe and inevitable impurities,
The surface roughness is a method for producing a ferritic stainless steel hot rolled steel sheet for automobile flanges having an arithmetic average roughness Ra as an index of 5 μm or less and a plate thickness of 5.0 to 15.0 mm,
A method for producing a ferritic stainless hot rolled steel sheet for automobile flanges, wherein grinding is performed after annealing in a manufacturing process of a ferritic stainless steel sheet that is performed by melting, casting, hot rolling, annealing, and pickling.   The ferritic stainless steel for automobile flanges according to claim 6 or 7, wherein in the manufacturing process of the ferritic stainless steel sheet, the pickling or annealing-pickling process is omitted, and the final process is a grinding process. A method for producing a hot-rolled steel sheet. % By mass
  The method for producing a ferritic stainless hot rolled steel sheet for automobile flanges according to any one of claims 6 to 8, wherein the Ti content is 0.05% or less. Furthermore, in mass%,
  A first group consisting of one or more of Mo: 1.5% or less, Cu: 0.5% or less, Ni: 1% or less,
  Sn: a second group consisting of 0.005 to 0.1%,
  V: 1% or less, W: 1% or less, Co: 1% or less, B: 0.0001% or more, 0.005% or less, Ga: 0.10% or less, Zr: 0.50% or less, Ta: 0.1% or less, Sb: 0.30% or less, Mg: 0.0030% or less, Ca: 0.0030% or less, at least one of the third group consisting of any one or more of them The manufacturing method of the ferritic stainless steel hot-rolled steel sheet for automobile flanges of any one of Claims 6-9 characterized by containing a group. Method for producing a motor vehicle flange ferritic stainless hot-rolled steel sheet according to any one of claims 6 to 10, wherein the hot-rolled steel sheet is hot rolled strip.

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