JP2010100877A - Method for manufacturing hot-rolled ferritic stainless steel sheet excellent in toughness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a hot-rolled ferritic stainless steel sheet excellent in the toughness, with high efficiency and at a low cost. <P>SOLUTION: A steel material containing, by mass, ≤0.03% C, ≤0.03% N, ≤0.05% C+N, ≤0.70% Si, ≤0.50% Mn, ≤0.04% P, ≤0.02% S, 20.5-25% Cr, 0.3-0.8% Cu, ≤1.0% Ni, 4×(C+N) to 0.4% Ti, ≤0.1% V, ≤0.5% Nb, ≤0.1% Mo, 0.02-0.08% Al and the balance Fe with inevitable impurities, is hot-rolled to form the steel sheet, and then reheated to the temperature of ≥550°C and a water-toughening treatment is applied in the method for manufacturing the hot-rolled ferritic stanless steel sheet excellent in toughness. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a ferritic stainless hot rolled steel sheet, and more particularly to a method for producing a ferritic stainless hot rolled steel sheet capable of improving productivity and expanding the production range by being excellent in toughness. .

  Stainless steel is characterized by excellent corrosion resistance. Among these, austenitic stainless steel represented by SUS304 (18% Cr-8% Ni) containing a large amount of Ni is used in a wide range of fields due to its excellent corrosion resistance. However, while this steel is excellent in corrosion resistance, it contains Ni and is very expensive and unstable in price.

  Moreover, in the ferritic stainless steel to which Ni is not added, SUS436L (18% Cr-1% Mo) to which Mo is added is known as a steel having corrosion resistance equivalent to that of SUS304. However, since this steel also contains Mo, it is a very expensive material.

  Therefore, there is a demand for the development of ferritic stainless steel that does not contain Mo and has corrosion resistance equivalent to SUS304 or SUS436L. However, SUS430J1L (19% Cr-0.5% Cu-0.4% Nb) that does not contain Mo, which is known as a high corrosion resistance ferritic stainless steel, is still inferior in corrosion resistance to SUS304 and SUS436L. .

  On the other hand, several stainless steels excellent in corrosion resistance that do not contain Ni or Mo have been proposed. For example, Patent Document 1 discloses a component composition of Cr: 9 to 30%, Cu: 0.1 to 0.6%, Ti: 5 × C to 15 × C%, and Sb: 0.02 to 0.2%. In addition, in Patent Document 2, at least one of Cr: 11 to 23%, Cu: 0.5 to 2.0%, Ti, Nb, Zr, and Ta is described in Patent Document 2. Ferritic stainless steel having a component composition of 01 to 1%, V: 0.05 to 2.0% is further disclosed in Patent Document 3, Cr: 5 to 60%, Cu: 0.15 to 3.0. %, Ti: 4 × (C + N) to 0.5%, and Nb: 0.003 to 0.020%, a stainless steel having a component composition has been proposed.

  However, in order to produce high corrosion resistance stainless steel at a low cost, it is necessary to be capable of mass production with higher efficiency in addition to not containing expensive Mo. In this respect, the stainless steels of Patent Documents 1 to 3 not only provide corrosion resistance as high as SUS304 and SUS436L, but also cannot hot-roll and cold-rolled sheets with high efficiency and continuous annealing as described below. There is a problem that productivity is inferior.

  In order to improve the corrosion resistance, it is effective to increase the amount of Cr added, but as the Cr content increases, the toughness of the hot-rolled sheet decreases. Therefore, it is necessary to pass the steel sheet as hot-rolled through a continuous annealing / pickling line (AP line) prior to cold rolling, and to perform annealing and pickling. However, if the toughness of the hot-rolled sheet is low, it may not be possible to pass through the continuous annealing / pickling line. Further, from the viewpoint of ensuring high-efficiency productivity, it is preferable that annealing can be performed even in a high-speed continuous annealing line used for annealing of cold rolled steel sheets of ordinary steel.

  In addition, ferritic stainless steel containing a large amount of Cr has a high recrystallization temperature, which makes it difficult to sufficiently recrystallize during hot rolling to refine the structure, resulting in a coarse structure. As a result, the toughness of the hot-rolled sheet may decrease. As one means for solving this problem, there is a method of promoting recrystallization by reducing impurities such as C, N, S, P, and O contained in the steel to achieve high purity. However, this method causes another problem that the solidification structure is greatly coarsened and the ridging of the cold-rolled sheet becomes large. Therefore, in order to improve the toughness by refining the hot rolled sheet structure, it is necessary to refine the solidified structure and promote recrystallization during hot rolling in order to improve ridging of the cold rolled sheet. There is.

  In order to promote recrystallization during hot rolling, it is effective to apply a strong reduction during rolling. However, since ferritic stainless steel containing a large amount of Cr has good oxidation resistance, the scale layer produced on the surface of the steel sheet is thin, causing seizure with the rolling rolls, resulting in surface scratches and so-called rough skin. There is a problem that it is easy. If the surface of the hot-rolled sheet becomes rough, it is necessary to increase the amount of dissolution in pickling, so it is necessary to reduce the pickling speed or, in severe cases, to grind the surface of the hot-rolled sheet with a grinder. As a result, productivity and economy are significantly reduced.

  As a method for refining a solidified structure, a method using various inclusions as solidification nuclei, a method using electromagnetic stirring, and the like are known. However, these methods have problems that it is necessary to add a large amount of metal elements or non-metal elements, or to control the superheat temperature (ΔT) at the time of solidification to be small, which makes stable casting difficult. .

Therefore, as a technique for solving the above problems, Patent Document 4 discloses a method for improving the toughness of a hot-rolled sheet by optimizing the addition amount of Ti, V, and B without adding Nb. .
Japanese Patent Publication No. 50-6167 Japanese Patent Publication No. 64-4576 Japanese Patent No. 3420371 JP-A-9-176801

  However, in the technique disclosed in Patent Document 4, in order to improve the toughness of the hot-rolled sheet, the steel sheet immediately after hot rolling is subjected to a water toughness (water cooling) process, and thus a dedicated facility for that purpose is required. Also, it was hard to say that it was excellent in productivity. Moreover, since the steel plate of patent document 4 requires addition of expensive Mo, it was hard to say that it was a technique advantageous also in terms of cost.

  Therefore, the present invention has been made in view of the above-described problems of the prior art, and the purpose thereof is manufacturing that can produce a ferritic stainless hot rolled steel sheet having excellent toughness with high efficiency and at low cost. To propose a method.

  In order to solve the above-described problems, the inventors have conducted intensive research on a method for producing a ferritic stainless hot-rolled steel sheet having excellent corrosion resistance and toughness without containing expensive Ni or Mo. As a result, from the viewpoint of balancing corrosion resistance and manufacturability, the Cr content in the steel is limited to a range of 20.5 to 25 mass%, carbon and nitrogen as impurity elements are reduced as much as possible, and an appropriate amount of Cu By adding Ti and Ti, excellent corrosion resistance equivalent to SUS304 and SUS436L can be obtained, and the above steel is hot-rolled and re-heated to a temperature of 550 ° C. or higher, By performing the treatment, it was found that the toughness of the hot-rolled steel sheet can be remarkably improved, and the present invention has been completed.

  That is, the present invention includes C: 0.03 mass% or less, N: 0.03 mass% or less, C + N: 0.05 mass% or less, Si: 0.70 mass% or less, Mn: 0.50 mass% or less, P: 0.00. 04 mass% or less, S: 0.02 mass% or less, Cr: 20.5 to 25 mass%, Cu: 0.3 to 0.8 mass%, Ni: 1.0 mass% or less, Ti: 4 × (C + N) to 0. 40 mass%, V: 0.1 mass% or less, Nb: 0.5 mass% or less, Mo: 0.1 mass% or less, Al: 0.02 to 0.08 mass%, with the balance being Fe and inevitable impurities A method for producing a ferritic stainless hot rolled steel sheet with excellent toughness, characterized by hot rolling a steel material into a steel sheet and then reheating to a temperature of 550 ° C. or higher and applying a water toughness treatment. It is.

  The method for producing a ferritic stainless hot rolled steel sheet according to the present invention is characterized in that the coiling temperature in the hot rolling is set to 550 ° C. or less.

  According to the present invention, a ferritic stainless hot rolled steel sheet having excellent corrosion resistance equivalent to SUS304 or SUS316L and having excellent toughness can be obtained without adding expensive Ni or Mo. Moreover, the hot-rolled steel sheet of the present invention having excellent toughness easily and efficiently performs annealing in a continuous annealing / pickling line in a hot-rolled sheet and subsequent annealing in a high-speed continuous annealing line in a cold-rolled sheet. be able to. Furthermore, according to the present invention, the range of thickness that can be annealed also expands, so the range of thickness of the cold-rolled steel sheet that can be manufactured from the hot-rolled steel sheet of the present invention is expanded, and the mechanical properties are also improved. It can also contribute to the expansion of the application range of ferritic stainless steel sheets.

  Moreover, since the stainless hot rolled steel sheet of the present invention does not contain expensive Ni or Mo, it can be manufactured at low cost. Furthermore, the stainless hot-rolled steel sheet of the present invention adds Ti, which reduces impurity elements and fixes and stabilizes C and N in the steel, so that weldability, weld zone workability, and weld zone corrosion resistance are also improved. Since it is excellent, the application range can be further expanded.

The component composition of the ferritic stainless steel of the present invention will be described.
C: 0.03 mass% or less, N: 0.03 mass% or less, C + N: 0.05 mass% or less C and N are harmful elements that reduce the toughness of hot-rolled sheets, so it is desirable to reduce them as much as possible. , N are each 0.03 mass% or less, and the total (C + N) is limited to 0.05 mass% or less. Preferably, C: 0.015 mass% or less, N: 0.015 mass% or less, and C + N: 0.03 mass% or less. In particular, when high corrosion resistance is required, it is preferable to further reduce to C: 0.010 mass% or less, N: 0.010 mass% or less, and C + N: 0.015 mass% or less.

Si: 0.70 mass% or less Si is an element added as a deoxidizer. However, if added in a large amount exceeding 0.70 mass%, the toughness of the hot-rolled sheet decreases, so Si is set to 0.70 mass% or less. Preferably, it is 0.3 mass% or less.

Mn: 0.50 mass% or less Mn is an element having a deoxidizing action. However, Mn is an element that forms sulfides in steel and significantly lowers corrosion resistance. Therefore, Mn is preferably as small as possible. However, in consideration of economics at the time of manufacture, it is set to 0.50 mass% or less. Preferably it is 0.3 mass% or less.

P: 0.04 mass% or less P is preferably as small as possible because it impairs hot workability, but is acceptable if it is 0.04 mass% or less.

S: 0.02 mass% or less Since S is a harmful element that impairs hot workability and corrosion resistance, it is desirable to reduce it as much as possible, and it is limited to 0.02 mass% or less. Preferably it is 0.005 mass% or less.

Cr: 20.5-25 mass%
Cr is the most important element for imparting sufficient corrosion resistance to the steel sheet of the present invention. In order to obtain corrosion resistance equivalent to SUS304 or SUS436L, addition of 20.5 mass% or more is necessary. On the other hand, if added over 25 mass%, the toughness of the hot-rolled sheet cannot be increased even if the water-toughening process, which is a feature of the present invention, is performed, so that it becomes difficult to continuously anneal the hot-rolled sheet. Therefore, Cr is set to a range of 20.5 to 25 mass%. In particular, when high toughness of hot-rolled sheet is required, the range of 20.5 to 21.5 mass% is preferable.

Cu: 0.3 to 0.8 mass%
Cu is an element that improves corrosion resistance, and is particularly effective in reducing crevice corrosion. In order to obtain this effect, addition of 0.3 mass% or more is necessary. On the other hand, if added over 0.8 mass%, the workability deteriorates due to hot brittleness. Therefore, Cu is set to a range of 0.3 to 0.8 mass%. Preferably it is 0.3 mass% or more and less than 0.5 mass%. Note that if high corrosion resistance is not required, Cu does not have to be added.

Ni: 1.0 mass% or less Ni is an element having an effect of preventing hot brittleness due to addition of Cu. It also has the effect of reducing crevice corrosion. However, in addition to being an expensive element, an excessive addition exceeding 1.0 mass% not only saturates the effect but also reduces hot workability. Therefore, Ni is set to 1.0 mass% or less. Preferably it is the range of 0.1-0.4 mass%.

Ti: 4 × (C + N) to 0.40 mass%
Ti is a useful element having an effect of fixing and detoxifying C and N harmful to the workability and corrosion resistance of the welded portion as TiC, TiN, and Ti (C, N). In addition, addition of Ti is necessary to prevent sensitization due to continuous annealing. In order to obtain these effects, addition of 4 × (C + N) mass% or more is necessary. On the other hand, when it adds exceeding 0.40 mass%, the toughness of a hot-rolled sheet will fall. Therefore, Ti is set to a range of 4 × (C + N) to 0.40 mass%. The range is preferably 8 × (C + N) to 0.35 mass%, and more preferably 8 × (C + N) to 0.30 mass%.

V: 0.1 mass% or less,
V, like Ti, is an element effective for fixing C and N. However, if added over 0.1 mass%, the toughness of the hot-rolled sheet decreases, so the content is made 0.1 mass% or less. Preferably, it is less than 0.05 mass%.

Nb: 0.5 mass% or less Nb is an element effective for fixing C and N, and a useful element having an effect of improving the toughness of the hot-rolled sheet by refining the crystal grains of the hot-rolled sheet It is. However, if Nb is added in excess of 0.5 mass%, the steel sheet is markedly hardened, so the addition amount is set to 0.5 mass% or less. Nb is also an element that raises the recrystallization temperature, so if added excessively, annealing will be insufficient in a high-speed continuous annealing line that anneals cold-rolled sheet of plain steel, and workability after annealing will decrease. There is. Therefore, when importance is attached to productivity, the amount of Nb added is preferably 0.01 mass% or less, and more preferably 0.005 mass% or less.

Mo: 0.1 mass% or less Mo is an element effective for improving the corrosion resistance. However, in addition to being expensive, there is a possibility that the toughness of the hot-rolled sheet is lowered and the productivity is lowered. Furthermore, since a cold-rolled annealing board is hardened and workability is reduced, it is limited to 0.1 mass% or less. Preferably, it is 0.05 mass% or less.

Al: 0.02-0.08 mass%
Al is added as a deoxidizer, but 0.02 mass% or more is necessary to obtain the effect. On the other hand, if added excessively, large Al oxide inclusions are generated and cause surface defects, so the upper limit is made 0.08 mass%.

In addition to the above essential elements, B and Zr can be added to the ferritic stainless steel of the present invention within the following ranges, if necessary.
B: 0.0002 to 0.002 mass%
B is an element effective for improving secondary work embrittlement resistance during deep drawing. The effect is acquired by addition of 0.0002 mass% or more. On the other hand, excessive addition of B reduces hot workability and deep drawability. Therefore, when adding B, it is preferable to set it as the range of 0.0002-0.002 mass%.

Zr: 0.01 to 0.5 mass%
Zr, like Ti, has the effect of detoxifying C and N and preventing intergranular corrosion from occurring in the weld. In order to acquire the effect, it is preferable to add 0.01 mass% or more. However, if added in excess of 0.5 mass%, the toughness of the hot-rolled sheet is lowered and the productivity is lowered. Moreover, when it adds excessively, there exists a possibility that the Zr type inclusion couple | bonded with C, N, or O may increase, and may increase a surface defect. Therefore, when adding Zr, it is preferable to set it as the range of 0.01-0.5 mass%.

Next, the manufacturing method of the ferritic stainless hot rolled steel sheet according to the present invention will be described.
The method of the present invention for producing a hot-rolled steel sheet having excellent toughness with high efficiency melts steel satisfying the above-described component composition, continuously casts it into a slab, and heats the slab to 1100 to 1300 ° C. It is preferable to use a method in which hot rolling is performed to form a hot rolled coil, and then the hot rolled coil is reheated to a temperature of 550 ° C. or higher and then subjected to a water toughness (water cooling) treatment. By producing by this method, it is possible to obtain a ferritic stainless hot rolled steel sheet that not only has excellent corrosion resistance but also has excellent toughness, rough skin resistance, and ridging resistance. Details will be described below.

  First, after melting steel in a generally known melting furnace such as a converter or an electric furnace, a vacuum degassing method (RH method), a VOD (Vacuum Oxygen Decarburization) method, an AOD (Argon Oxygen Decarburization) method, etc. The steel is refined by a known refining method, adjusted to the above-described component composition of the present invention, and then steel slab (steel material) through a continuous casting method or an ingot-bundling method. The manufacturing method of the slab is preferably a continuous casting method in terms of productivity and quality. Moreover, it is preferable that the thickness of a slab shall be 100 mm or more from a viewpoint of ensuring the reduction rate in the hot rough rolling mentioned later. More preferably, it is 200 mm or more.

  Subsequently, after heating the said steel slab to 1100-1300 degreeC with a heating furnace, it hot-rolls roughly and carries out hot finish rolling to make a hot-rolled steel sheet. The heating temperature of the slab is preferably high in order to prevent rough skin of the hot-rolled sheet and improve ridging resistance after cold rolling annealing, but when it exceeds 1300 ° C., dripping of the slab becomes remarkable, and crystal grains It becomes coarse and the toughness of the hot-rolled sheet decreases. On the other hand, if the heating temperature is less than 1100 ° C., the load on the rolling mill in hot rolling becomes large, the surface roughness due to seizure on the hot rolling roll becomes significant, and recrystallization during hot rolling becomes insufficient, resulting in cooling. Ridging properties after annealing are inferior.

  Next, it is preferable that the rough rolling process in the hot rolling is performed in a temperature range exceeding 1000 ° C., and rolling with a rolling reduction of 30% or more is performed at least one pass. By this strong rolling, the coarse cast structure is destroyed, the steel sheet structure is refined, and the ridging characteristics are improved. The subsequent hot finish rolling may be performed under generally known conditions, but for the reason described later, the winding temperature of the hot rolled coil is preferably 550 ° C. or lower.

Next, the water toughness process that is a feature of the present invention will be described.
As in the ferritic stainless steel of the present invention, a steel containing Cr exceeding 20 mass% is likely to cause so-called “sigma brittleness” or “475 ° C. brittleness” in the cooling process after hot rolling. The sigma brittleness is said to be caused by the precipitation of the σ phase when the steel is heated to 600 to 800 ° C., and is more likely to occur as the Cr content is higher. The 475 ° C. brittleness is caused by the fact that when heated to around 475 ° C., the steel structure undergoes two-phase separation into an α phase having a high Fe concentration (low Cr concentration) and an α ′ phase having a high Cr concentration. It is said that. Therefore, in order to prevent toughness reduction of the hot rolled sheet due to these brittlenesses, it is effective to shorten the residence time in the above temperature range after hot rolling, and the coiling temperature after hot rolling is 450 It is generally recommended to keep it below ℃. However, when the winding temperature is lowered, the load on the winder increases. For this reason, in a hot-rolled sheet having a large thickness, it is necessary to increase the winding temperature, and there is a problem that it is difficult to prevent a decrease in toughness due to sigma brittleness or 475 ° C brittleness.

In order to solve this problem, the inventors examined a method for recovering toughness while being wound around a coil. Fig. 1 shows a 21 mass% Cr-containing hot rolled steel sheet with a thickness of 4.5 mm, which is then wound around a coil at a coiling temperature of 550 ° C, and then held at a predetermined temperature of 450-800 ° C for 1 hour or longer. Thereafter, a test piece was sampled from a coil subjected to a water toughness treatment and subjected to a Charpy impact test, and the Charpy impact value at 0 ° C. was measured. From this figure, in the state of hot rolling, the Charpy impact value was about 40 J / cm ² , but when heated to a temperature of 550 ° C. or higher and subjected to water toughness treatment, the Charpy impact value was 150 J / cm ^2. It can be seen that the toughness is further improved when it is improved to cm ² or more, particularly when heated to 750 ° C. or more. Although there is no restriction | limiting in particular about the upper limit of the temperature to heat, From a viewpoint of suppressing generation | occurrence | production of the shape defect by the creep deformation during heating, it is about 950 degreeC.

  As described above, in the method for producing a ferritic stainless steel of the present invention, the toughness can be recovered by subjecting the hot-rolled coil after hot rolling to a water-tough treatment, so that the coiling temperature after hot-rolling There is no need to specifically limit. However, when higher hot rolled sheet toughness is required, the coiling temperature is preferably 550 ° C. or lower, more preferably 450 ° C. or lower.

  In addition, although heating of a hot-rolled sheet coil prior to the water toughening treatment can be performed using a batch-type heating furnace, a continuous heating furnace, or the like, in order to heat-treat the steel sheet having poor toughness while being wound around the coil. From the viewpoint that there is no concern about coil breakage or the like, it is preferable to use a batch type heating furnace. In addition, the water toughening process includes a method of immersing the entire coil in the water tank, a method of passing through the water tank in the continuous annealing line, etc. Is preferable.

Next, the subsequent process of the hot-rolled steel sheet of the present invention obtained as described above will be described.
Since the hot-rolled steel sheet of the present invention that has been subjected to water toughness is excellent in toughness, it is then subjected to annealing and pickling in a continuous annealing / pickling line (AP line), and a hot-rolled annealing sheet with high efficiency and high productivity. can do. This hot-rolled annealed sheet may be used as it is or as a material for various uses, but it can also be used as a material for cold-rolled steel sheets. In this case, for the annealing after cold rolling, an efficient annealing and pickling method is recommended in a high-speed continuous annealing line for cold rolled steel sheets of ordinary steel.

  First, a hot-rolled sheet having a thickness of 2.0 to 9.0 mm that has been hot-rolled and subjected to water toughness is subsequently annealed at a temperature of 800 to 1000 ° C. and pickled to remove the oxide scale on the surface. It is preferable to do this. When the annealing temperature of the hot-rolled sheet is less than 800 ° C., sufficient workability cannot be obtained. On the other hand, when the temperature exceeds 1000 ° C., the coarsening of crystal grains becomes remarkable and the toughness is lowered. In addition, when adding Nb 0.1 mass% or more, it is preferable that an annealing temperature shall be 900-1100 degreeC.

  Next, the hot-rolled sheet after annealing and pickling is subsequently subjected to the steps of cold rolling, finish annealing, and pickling to form a cold-rolled annealed sheet having a thickness of 0.03 to 6.0 mm. be able to. The rolling reduction of cold rolling is preferably 25% or more, more preferably 50% or more in order to ensure mechanical properties such as toughness and workability. The cold rolling may be performed once or twice or more with intermediate annealing. Further, the steps of cold rolling, finish annealing, and pickling may be repeated. Furthermore, for the above-mentioned finish annealing and pickling, a method of performing efficient cold rolling annealing and pickling in a high-speed continuous annealing line that is also used as a cold rolled steel sheet of ordinary steel is recommended. However, although productivity is lowered, it is possible to perform annealing / pickling in an ordinary stainless steel annealing / pickling line, and of course, annealing may be performed in a bright annealing line (BA line). is there. Further, after annealing and pickling, various polishing treatments and the like may be performed to finish to a predetermined surface state.

  For welding when the above-mentioned hot-rolled and cold-rolled plates are passed through the production line in each of the above processes, resistance welding such as TIG, MIG, arc welding, seam welding, spot welding, etc., laser Any ordinary welding method such as welding can be applied.

Ferritic stainless steel having the composition shown in Table 1 was melted by a converter-VOD process and cast by a continuous casting method to obtain a steel material (slab) having a thickness of 200 mm. The surface of this slab was grinder ground, reheated to a temperature of 1200 ° C., and hot-rolled to obtain a hot rolled coil having a plate thickness of 6.0 mm. The coiling temperature after hot rolling is No. About 10 steel plates, it was set as 650 degreeC, but others wound up in the range of 450-550 degreeC.
A test piece was taken from the hot rolled coil, a Charpy impact test was performed in the hot rolled state, the absorbed energy at 0 ° C. was measured, and the Charpy impact value was obtained by dividing by the cross-sectional area. / Cm ² or less.

  Next, the hot-rolled coil (test piece taken from or) was held at various temperatures listed in Table 1 for 1 to 8 hours in a batch-type heating furnace, and then immersed in a water tank provided for water toughness treatment. The Charpy impact value was determined in the same manner as described above.

The evaluation results are also shown in Table 1. From this result, No. 1 satisfying the component composition of the present invention was obtained. In steels 1 to 3 (invention steel), the toughness (Charpy impact value) after water toughness is improved to 150 J / cm ² or more, while No. 1 does not satisfy the composition of the present invention. For steels 4 and 5 (comparative steel), no improvement in toughness was observed.

  The technology of the present invention is not limited to a stainless hot-rolled steel sheet manufactured using a hot rolling mill, and can be applied to, for example, a stainless thick steel sheet manufactured using a thick-sheet rolling mill. .

It is a graph which shows the relationship between the reheating temperature in the hot rolled steel plate of 21 mass% Cr containing steel, and the toughness (Charpy impact value) after water toughness.

Claims (2)

C: 0.03 mass% or less,
N: 0.03 mass% or less,
C + N: 0.05 mass% or less,
Si: 0.70 mass% or less,
Mn: 0.50 mass% or less,
P: 0.04 mass% or less,
S: 0.02 mass% or less,
Cr: 20.5-25 mass%,
Cu: 0.3 to 0.8 mass%,
Ni: 1.0 mass% or less,
Ti: 4 × (C + N) to 0.40 mass%,
V: 0.1 mass% or less,
Nb: 0.5 mass% or less,
Mo: 0.1 mass% or less,
Al: 0.02 to 0.08 mass% is contained,
Hot-rolled ferritic stainless steel with excellent toughness characterized by hot-rolling a steel material consisting of Fe and unavoidable impurities into a steel sheet and then reheating to a temperature of 550 ° C. or higher and applying a water toughness treatment. A method of manufacturing a steel sheet. The method for producing a ferritic stainless hot-rolled steel sheet according to claim 1, wherein a coiling temperature in the hot rolling is 550 ° C or lower.

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