ES2632781T3 - Ferritic stainless steel - Google Patents

Abstract

A ferritic stainless steel having a chemical composition consisting of, in mass%, C: 0.003% or more and 0.015% or less, Si: 0.05% or more and 0.20% or less, Mn: 0, 10% or more and 0.35% or less, P: 0.06% or less, S: 0.02% or less, Cr: 17.0% or more and 19.0% or less, Ni: more than 0.10% and 0.30% or less, Ti: 0.10% or more and 0.40% or less, Nb: 0.005% or more and less than 0.050%, Mo: less than 0.20%, N : 0.005% or more and 0.015% or less, Cu: 0.30% or more and 0.50% or less, Mg: less than 0.0005%, and optionally also containing in bulk, Al: 0.02% or plus and 0.50% or less, Sb: 0.005% or more and 0.300% or less, at least one of Zr: 0.05% or more and 0.60% or less and V: 0.02% or more and 0.50% or less and the rest of the balance is Faith and unavoidable impurities.

Description

Ferrftico stainless steel 5 Technical Field

The present invention relates to a ferritic stainless steel with excellent surface quality, and excellent corrosion resistance in a part welded with an austenic stainless steel.

Prior art

10 Although, among the stainless steels, SUS304 (18% Cr - 8% Ni) (Japanese industrial standard, JIS G 4305), which is an austenic stainless steel, is widely used due to its good corrosion resistance, This type of steel is expensive due to a large amount of Ni contained therein. Therefore, stainless steel according to Patent Literature 1 was developed as a steel having a good corrosion resistance equivalent to that of SUS304.

fifteen

Patent Literature 1 describes a ferrotic stainless steel having a chemical composition consisting of, in mass%, C: 0.03% or less, Si: 1.0% or less, Mn: 0.5% or less , P: 0.04% or less, S: 0.02% or less, Al: 0.1% or less, Cr: 20.5% or more and 22.5% or less, Cu: 0.3% or more and 0.8% or less, Ni: 1.0% or less, Ti: 4 (C% + N%) or more and 0.35% or less, Nb: 0.01% or less, N: 0.03% or less, C + N: 0.05% or less and the rest is Faith and the inevitable impurities.

Ferritic stainless steels such as JIS-SUS444 and JIS-SUS430J1L are characterized by having low sensitivity to corrosion cracking under tension compared to austenophic stainless steels and not containing a large amount of Ni that is subject to large fluctuations of prices, and which are widely used as materials for parts of the car exhaust system, water tanks and building constructions.

However, since ferritic stainless steels have a lower formability, especially poor ductility, compared to austenophic stainless steels, austenphic stainless steels are used for 30 pieces that are too difficult to form with ferrolytic stainless steels. Therefore, there are many cases in which a component is formed by combining austenophic stainless steels and ferritic stainless steels. Among these cases, most of the pieces are joined by welding and, among the welding methods, TIG welding (welding with inert gas of tungsten) is mainly used. And good corrosion resistance is necessary for welding areas, as well as base steels.

35

List of citations Patent literature

PTL1: Japanese unexamined patent application with publication number 2007-77496 PTL2: Japanese unexamined patent application with publication number 8-10823 40 Documents EP0930375-A and EP2787096-A also disclose ferrotic stainless steels.

Description of the invention Technical problem

45 Ferritic stainless steel according to Patent Literature 1 has good corrosion resistance in an area welded with a stainless steel of the same type. However, there is a problem that the corrosion resistance in a welded area is lower than that of a base steel in the case in which the stainless steel is welded with a stainless steel of a different type, such as SUS304 , performing TIG welding.

50 This problem occurs as described below; C or N in a steel combine with Cr, precipitating chromium carbides such as Cr23C6 or chromium nitrides such as CrN2 at the grain boundaries in the thermal welding history. These precipitations form chromium depletion layers, in the vicinity of the grain boundaries, where the Cr content is less than that of the base steel. This phenomenon, called sensitization, causes a deterioration in corrosion resistance in grain boundaries.

55

Generally, in order to prevent deterioration of corrosion resistance in a welded area due to sensitization, the formation of chromium carbides and chromium nitrides is avoided by adding an appropriate amount of Ti to the steel and stabilizing the C and the N as titanium carbonitrides with a decreasing content of C and N in the steel. By this method, the welded area that is formed by TIG welding using the same 60 stainless steel steels according to Patent Literature 1 has a good corrosion resistance.

However, given that SUS304 has a C content of 0.04% to 0.05%, which is more than that of this ferric stainless steel sheet whose C content is approximately 0.01%, in order to prevent so

Sensitization similar by adding Ti in the event that this ferrotic stainless steel plate is welded with a high carbon stainless steel such as SUS304, it is necessary to increase the Ti content to approximately 1.0%.

5 However, in the case where the content of Ti in a ferric stainless steel is increased to approximately 1.0%, the Ti and N in molten steel react with each other to form and precipitate TiN during solidification. Since TiN has low ductility at high temperature, defects occur in a hot rolling process and surface quality deteriorates. Since the defects formed as described above are too deep to be eliminated during subsequent processes such as

10 annealed hot-rolled steel sheet, pickled hot-rolled steel sheet, cold rolled a hot rolled steel sheet, annealed cold-rolled sheet steel and pickled cold-rolled sheet steel.

The defects become superficial defects called veins caused by titanium nitrides, which results in

15 to a significant deterioration of the surface quality of the cold-rolled steel sheet, the annealed and stripped steel sheet, unless a treatment is carried out in which a thick layer is scraped off the surface of the sheet metal hot rolled steel, annealed and pickled by a grinder or similar.

In addition, although TIG welding is generally performed under conditions in which both sides, the front and

20 The rear, of the steel sheet are protected with an inert gas so that the formation of a thin oxidized layer called tempering color is avoided as much as possible. Since, in a practical process, this protective gas is not enough, there is a problem that the sensitization described above is facilitated because it is mixed with the N of the air.

25 In addition, there is also a problem in which adding a large amount of expensive Ti reduces the advantage of ferric stainless steel that does not use an expensive Ni.

The present invention has been completed in view of the situation described above, and an object of the present invention is to provide a ferric stainless steel with excellent surface quality, and resistance to

30 corrosion in a welding zone in the event that the ferritic stainless steel is welded not only with a ferrotic stainless steel but also with an austenical stainless steel.

Solution to the problem

The present inventors carried out exhaustive experiments and research not only on the

35 influence of the chemical composition of the steel on the corrosion resistance of the base steel and the welding zone, but also on the surface quality (streak defects caused by titanium nitrides) of the steel sheet to solve the problems described above, and, as a result, the following conclusions were obtained.

40 (1) Sensitization can be avoided by adjusting the content of the initial ferritic elements and making the microstructure of a weld zone with a ferritic stainless steel and an austenic stainless steel a martensite phase. This is because the limits of solubility of C and N are large in a martensite phase.

45 (2) By adding a very small amount of Nb, Nb nitrides precipitate at a temperature higher than a temperature at which Ti nitrides precipitate. In a subsequent cooling process, these Nb nitrides become nucleation sites of Ti carbonitrides. This phenomenon increases the effect of Ti to prevent sensitization.

50 (3) The crystallization temperature of the steel plate is generally raised by adding Nb. Since there is almost no negative effect that the crystallization temperature of the steel plate rises when a very small amount of Nb is added, a cheap high speed pickling process used in a carbon steel manufacturing line can be applied described in Patent Literature 2.

55 (4) Even if the N mixes with the air in a welding zone due to an incomplete supply of protective gas during welding, sensitization can be avoided by forming AlN in the welding zone in the case where that an appropriate amount of Al is added to the steel. In addition, sensitization can be avoided due to the formation of Sb and N compounds in a welding zone in the case where an appropriate amount of Sb is added to the steel.

60

(5) A grain defect caused by titanium nitrides is mainly caused by the TiN of a large size that exists in a more external layer of a steel sheet. A grain defect caused by titanium nitrides can be avoided by adjusting the Ti content.

From the findings described above, a ferrtic stainless steel can be obtained that has excellent corrosion resistance in a welding zone and excellent surface quality of a cold rolled, annealed and stripped steel sheet without having to grind the surface of a hot rolled, annealed and stripped steel sheet and is less expensive than austenophic stainless steels containing Ni.

5

The present invention has been completed on the basis of the findings described above and the present invention is as follows.

[1] Ferritic stainless steel having a chemical composition consisting of, in mass%, C: 0.003% or more and 10 0.015% or less, Si: 0.05% or more and 0.20% or less, Mn : 0.10% or more and 0.35% or less, P: 0.06% or less, S:

0.02% or less, Cr: 17.0% or more and 19.0% or less, Ni: more than 0.10% and 0.30% or less, Ti: 0.10% or more and 0, 40% or less, Nb: 0.005% or more and less than 0.050%, Mo: less than 0.20%, N: 0.005% or more and 0.015% or less, Cu: 0.30% or more and 0.50 % or less, Mg: less than 0.0005% and optionally also containing in bulk, Al: 0.02% or more and 0.50% or less, Sb: 0.005% or more and 0.300% or less, at least one of Zr: 0.05% or more and 0.60% or less and 15 V: 0.02% or more and 0.50% or less, and the rest is inevitable Fees and impurities.

[2] Ferritic stainless steel according to [1], the steel having a chemical composition containing, in mass%, Al:

0. 10% or more and 0.50% or less.

20 Advantageous Effects of the Invention

The ferrftico stainless steel can be ideally used as a material for kitchen instruments, architectural interiors, industrial machines and car parts, because ferrftico stainless steel has excellent corrosion resistance in a welded area even with an austenatic stainless steel and they have a excellent surface quality.

25

Description of the realizations

The limitations of the factors that constitute the present invention will be described below.

1. With respect to a chemical composition 30

The reason for the limitations in the chemical composition of steel according to the present invention will be described. In this case, the% used when describing a chemical composition always means mass%.

C: 0.003% or more and 0.015% or less

35 It is preferable that the C content be as small as possible, because C tends to combine with Cr to form Cr carbides, and intergranular corrosion is caused by Cr carbides that form in a heat-affected area. during welding. Therefore, the C content is limited to 0.015% or less. On the other hand, because it takes a long time to melt in the case where the C content is excessively small, the C content is limited to 0.003% or more and 0.015% or less, preferably 0.003% or 40 more and 0.012% or less from the point of view of corrosion resistance in a welding zone, more preferably 0.003% or more and 0.010% or less.

Yes: 0.05% or more and 0.20% or less

Because Si is a chemical element that is effective as a deoxidizing agent, the Si content is limited to be 0.05% or more. On the other hand, in the case where the Si content is greater than 0.30%, the high speed pickling performance in a carbon steel manufacturing line decreases, which results in a decrease in productivity . Therefore, the Si content is limited to 0.05% or more and 0.30% or less, preferably 0.05% or more and 0.20% or less.

50 Mn: 0.10% or more and 0.35% or less

Because Mn is effective for deoxidation, the content of Mn is limited to 0.10% or more. Also, since Mn is an austenite forming element, Mn promotes the formation of a martensite phase in a welding zone with an austenic stainless steel (from here, referred to as the welding zone of different steels). However, since, in the case that the content of Mn is excessively large, Mn 55 is combined with S in steel to form MnS which is a soluble sulfide, which results in a deterioration of corrosion resistance , the content of Mn is limited to 0.10% or more and 0.35% or less, preferably 0.10% or more and 0.25% or less.

P: 0.06% or less

60 In the case where the P content is greater than 0.06%, P does not only have a negative effect on corrosion resistance, but also deteriorates the formability due to the strengthening of the solid solution. Therefore, the P content is limited to 0.06% or less, preferably 0.04% or less from the viewpoint of corrosion resistance.

S: 0.02% or less

S is a chemical element that has a negative effect on corrosion resistance. In particular, in the case where S is present together with Mn, S becomes a source of splashes as a result of the formation of MnS, resulting in a deterioration in corrosion resistance. This negative effect becomes significant in the case where the S content is greater than 0.02%. Therefore, the S content is limited to 0.02% or less, preferably 0.01% or less from the viewpoint of corrosion resistance, more preferably 0.006% or less.

Cr: 17.0% or more and 19.0% or less

10 Cr is a chemical element that is essential to increase the corrosion resistance of the base of a stainless steel by forming a passivation film on the surface of the steel. A Cr content of 17.0% or more is necessary to achieve good corrosion resistance. However, in the event that the Cr content is greater than 19.0%, the deterioration of the corrosion resistance in the area welded with an SUS304 cannot be avoided, because in that part a phase of formation is not formed martensite Therefore, the content of 15 Cr is limited to 17.0% or more and 19.0% or less, preferably 17.5% or more and 18.5% or less.

Ni: more than 0.10% and 0.30% or less

Ni is a chemical element that helps improve the corrosion resistance of cracks. In addition, since Ni is an element that forms austenite like Mn, Ni promotes the formation of a martensite phase in the welding zone of different steels. However, there is a deterioration in the sensitivity to corrosion cracking under tension in the case where the Ni content is greater than 0.30%. In addition, Ni is an expensive chemical element. Therefore, the Ni content is limited to more than 0.10% and 0.30% or less, preferably 0.20% or more and 0.30% or less.

25 Ti: 0.10% or more and 0.40% or less

Ti is a chemical element that is essential to achieve good corrosion resistance in the welding zone of different steels when welding with an austenic stainless steel as described above. However, an excessive content of Ti causes an increase in the amount of precipitated TiN, which results in a significant number of vein defects caused by titanium nitrides, which makes it impossible to achieve a good surface quality for a product (cold rolled, annealed and pickled steel sheet) without performing a treatment such as grinding the surface of a hot rolled, annealed and pickled steel sheet. Therefore, the Ti content is limited to 0.10% or more and 0.40% or less, preferably 0.20% or more and 0.40% or less from the viewpoint of corrosion resistance in the welding zone of different steels.

35

Nb: 0.005% or more and less than 0.050%

The addition of small amounts of Nb is also one of the important factors for the present invention. Nb forms carbonitrides more easily than Cr and Ti. In particular, in the case of the welding zone of different steels, in the weld seam and in an area affected by heat, the formation of Nb 40 carbonitrides begins at a temperature higher than the temperature at which the Ti carbonitrides. In a subsequent cooling process, although the reason for this is not clear, the Nb carbonitrides become nucleation sites of the Ti carbonitrides. That is, since a small content of Nb accelerates the formation of Ti carbonitrides, the ability of Ti to stabilize the C and N in the weld seam and an area affected by the heat of the weld zone of different steels is it becomes stronger compared to the case in which the Nb is contained, making sensitization more effectively prevented. Therefore, the lower limit of the Nb content is limited to 0.005% or more. On the other hand, since an excessive Nb content causes an increase in the recrystallization temperature of a cold rolled steel sheet, it is necessary to anneal the high temperature steel sheet to achieve sufficient mechanical properties. This increases the thickness of an oxide layer, which is formed during the end of annealing, compared to the case where it does not contain Nb. This deteriorates the pickling behavior of a cold-rolled steel sheet in a high-speed pickling process that is used in a carbon steel manufacturing line described above, which results in a deterioration in productivity. Therefore, the Nb content is limited to 0.005% or more and less than 0.050%, more preferably 0.010% or more and less than 0.050% from the viewpoint of corrosion resistance in the welding zone of steels different.

55

Mo: less than 0.20%

Mo reinforces a passivation film and significantly improves corrosion resistance. However, since Mo is a ferrite forming element, even in the case where the Mo content is small, a martensite phase is not formed in the welding zone of different steels when welded with a stainless steel 60 austenphic This causes the welding zone of different steels to consist of a ferrite phase and cause sensitization. Therefore, the Mo content is limited to be less than 0.20%. In addition, because Mo causes deterioration of the toughness of a hot rolled steel sheet, it is preferable that the Mo content is less than 0.10%. Incidentally, the lower limit of Mo content is limited to 0%.

N: 0.005% or more and 0.015% or less

N easily combines with Cr to form Cr nitrides. It is preferable that the N content be as small as possible, since Cr nitrides produce intergranular corrosion in the event that Cr nitrides form in the area welding of different steels and in an area affected by heat when welding. In addition, it is preferable that the N content be as small as possible to decrease the amount of precipitated TiN that becomes the source of vein defects caused by titanium nitrides. However, because the casting takes a long time in the event that the N content is excessively reduced, the N content is limited to 0.005% or more and 0.015% or less, preferably 0.005% or more and 0.012% or less from the point of view of the corrosion resistance in the welding part of different steels, more preferably 0.005% or more and 0.010% or less.

Cu: 0.30% or more and 0.50% or less

Cu is a chemical element that improves corrosion resistance, in particular, in the case where a steel is placed in an aqueous solution or covered with slightly acidic water droplets. This is because the Cu that covers the surface of the base steel prevents the dissolution of the base steel after dissolving in the aqueous solution or in the water droplets. However, in the case where the Cu content is greater than 0.50%, high temperature formability deterioration occurs and surface defects are caused by gelatin-like oxides that are called red scales and that form on the hot rolled steel surface due to Cu. Therefore, the Cu content is limited to 0.30% or more and 0.50% or less, preferably 20 0.30% or more and 0.40% or less from the viewpoint of high temperature formability .

Mg: less than 0.0005%

Mg is an impurity that is mixed mainly by the bricks of the converter oven. Mg becomes the source of various types of places of inclusion and nucleation of other places of inclusion. In addition, since inclusions are less likely to dissolve, even when a treatment such as annealing is performed, Mg deteriorates the surface quality not only of hot rolled, annealed and stripped steel sheets but also of the product (sheet cold rolled steel, annealed and pickled). Therefore, the Mg content is limited to being less than 0.0005%, preferably less than 0.0003%.

Although the basic chemical composition according to the present invention is as described above and the rest consists of Fe and unavoidable impurities, Al and Sb can additionally be contained from the point of view of preventing the sensitization of the welding zone of steels. different caused by insufficient protection gas of a TIG welding. In addition, Zr and V may be contained in order to improve the corrosion resistance of the welding zone of different steels. Here, examples of acceptable unavoidable impurities 35 include Ca: 0.0020% or less, but it is not necessary to limit Ca.

At: 0.02% or more and 0.50% or less

Al is a chemical element that is particularly important in the case where a protective gas for TIG welding is not satisfactory. Generally, the back side of the steel sheet is protected with gas 40 when TIG welding is performed as described above. However, in the case where the shape of the welding zone of different steels is complicated, the shielding gas is not sufficiently effective and the N in air can be mixed in the weld bead. In this case, sensitization cannot be completely prevented only by adding Ti, if the content of C and N is greater than the solid solubility limit of the martensite phase. In this case, it is effective to add Al in advance to avoid sensitization. This is because Al stabilizes the N in the weld seam as AlN. This effect can be achieved by limiting the Al content of being 0.02% or more. However, in the case where the Al content is greater than 0.50%, non-metallic inclusions are formed in an iron, which results in the deterioration of the surface quality of the hot rolled steel sheet and the cold rolled steel sheet. Therefore, in the case where Al is contained, it is preferable that the Al content is 0.02% or more and 0.50% or less. A more preferable lower limit of Al content 50 is 0.10%, more preferably 0.15%. A more preferable upper limit of the Al content is 0.30%.

Sb: 0.005% or more and 0.30% or less

The Sb is a chemical element that is better to add in the case in which a component has a complicated form, since Sb is, like Al, effective to stabilize the mixed N from the air in the case in which a TlG welding protection gas is not efficient enough. However, in the case where the Sb content is excessively large, non-metallic inclusions are formed in a plate, which results in deterioration of the surface quality of the hot rolled steel sheet and the rolled steel sheet in cold Therefore, in the case where Sb is contained, it is preferable that the content of Sb is 0.005% or more and 0.30% or less, more preferably 0.005% or more and 0.10% or less from the point of view of the surface quality of the 60 product (cold rolled, annealed and pickled steel sheet).

Zr: 0.05% or more and 0.60% or less

Zr is a chemical element that is effective in improving corrosion resistance in the welding zone not only of the same steels but also of different steels forming, such as Ti, carbonitrides more easily than Cr. However, Zr It is more expensive than Ti and, in the case where the Zr content is excessively large, the Zr forms intermetallic compounds, which results in the deterioration of the toughness of the hot rolled steel sheet. Therefore, in the case where Zr is contained, it is preferable that the content of Zr is 0.05% or more and 0.60% or less, more preferably 0.15% or more and 0.35% or less.

V: 0.02% or more and 0.50% or less

The V is also a chemical element that is effective in improving the corrosion resistance in the welding zone not only of the same steels but also of different steels forming, such as Ti, carbonitrides more easily than Cr. However, This effect of V is less than that of Ti. In addition, the V is expensive. Therefore, in the case where this content is V, it is preferable that the content of V is 0.02% or more and 0.50% or less, more preferably 0.02% or more and 0.05% or less.

15 2. Regarding manufacturing conditions

Subsequently, the preferable method for manufacturing the steel according to the present invention will be described. Steel having a chemical composition described above is melted using a well known method, such as a converter furnace, an electric furnace or a vacuum melting furnace, and the molten steel is converted into a steel material (plate) using a continuous casting method or a casting method - ingot roughing. This steel material is heated at a temperature in the range from 1100 ° C to 1250 ° C for between 1 hour to 24 hours and, or directly without heating, hot rolled on a hot rolled steel sheet.

Although the hot rolled steel sheet is generally subjected to an annealing at a temperature in the range of 800 ° C to 1100 ° C for a duration of 1 minute to 10 minutes, this annealing can be omitted depending on the application of use. Then, after being subjected to pickling, the hot rolled steel sheet is cold rolled in a cold rolled steel sheet, and the cold rolled steel sheet is converted into a product performing an annealing finish. It is preferable that the cold rolling is carried out with a rolling reduction ratio of 50% or more from the point of view of elongation behavior, flexion behavior, press forming behavior and leveling of the shape. It is preferable that the finishing annealing of the cold-rolled steel sheet is generally performed at a temperature in the range of 800 ° C to 950 ° C in the case of No. 2B finished in accordance with JIS G 0203.

However, in the case of manufacturing a product that uses a tandem cold rolling line and a continuous annealing line with high productivity, it is more preferable that the product is manufactured in an economical process using a high pickling method. speed (see Patent Literature 2) of an annealing and pickling line for carbon steel as described above, and, in this case, it is preferable that the annealing temperature is in the range of 800 ° C to 900 ° C. In addition, in the case of a product for parts where gloss is most necessary, finishing annealing using the bright annealing method is effective. As described above, there is no problem in carrying out a treatment such as polishing after cold rolling or forming to achieve a better surface quality.

EXAMPLE 1 45

The present invention will be described in more detail with reference to the examples that follow.

Steels that have a chemical composition of examples from No. 1 to No. 6 and No. 33 and comparative examples from No. 9 to No. 12 shown in Table 1 were cast using a small vacuum melting furnace 50 with a capacity of 50 kg. The ingots of these steels were heated to a temperature of 1150 ° C in an oven under an Ar gas purge and hot rolled in hot rolled steel sheets having a thickness of 4.0 mm.

Subsequently, these hot-rolled sheets were subjected to annealing in air at a temperature of 950 ° C 55 for 1 minute, followed by a surface treatment using shot blasting with glass grains and pickling descaling in which the steel sheets were submerged in a sulfuric acid solution containing sulfuric acid in a 20% mass concentration at a temperature of 80 ° C for 120 seconds and then in a mixed acid solution containing nitric acid in a 15% mass concentration and hydrofluoric acid in a concentration of 3% by mass at a temperature of 55 ° C for 60 seconds.

60

Next, the hot-rolled steel sheets were cold-rolled on cold-rolled steel sheets with a thickness of 1.0 mm, subjected to an annealing in an air oven at a temperature of 900 ° C for 1 minute, and producing cold rolled and annealed steel sheets. These cold rolled steel sheets and

Anneal were subjected to electrolytic descaling with the steel sheet being for three times a positive electrode in a solution containing NaSO4 in a concentration of 20% by mass at a temperature of 80 ° C with a current of 3 A / Dm2 for 10 seconds , and a disentanglement in a mixed acid solution containing nitric acid in a concentration of 5% by mass and hydrofluoric acid in a concentration of 3% in 5 mass at a temperature of 55 ° C for 30 seconds in order to obtain plates Cold rolled steel, annealed and stripped.

[Table 1]

 Notes

 Examples Comparative Examples

 Chemical Composition (% by mass)

 >,,,,, Or CM o ',,,, 0.10

 N

 ,,,,,,,, 0.05,

 Sb

 . . . . . . . . . . .

 <

 00 CM O or '0.030 LO CM O or' 0.031 0.150 or CM or 'CO CM O or' 0.210 CM CO O or '0.110

 Mg

 0.0003 0.0001 CM O O O o '0.0004 0.0003 CM O O O o' 0.0004 0.0003 0.0003 CM O O O o '0.0004

 2

 0.009 00 o o o '0.012 0.009 0.007 00 O O o' 0.007 00 o o o '0.010 0.015 0.013

 Mo

 0.06 CM O or '0.10 00 or o' 0.05 0.07 0.04 0.09 or '0.13 0.06

 Nb

 O CM O or '0.030 0.040 0.040 O CM O or' 0.010 0.030 or CM O or '0.030 O CM O or' O CO 0 01

 i-

 CM CM o '0.14 0.29 0.20 0.15 0.19 0.20 0.27 0.34 0.07 0.29

 Cu

 0.36 0.35 0.33 0.41 0.40 0.34 0.37 0.41 0.34 0.38 0.32

 ! z

 0.23 0.12 O CM or 'CO CM or' 0.13 0.15 CM CM or 'or CM or' 0.17 0.21 0.24

 or

 18.8 18.4 18.3 17.3 18.4 18.2 co '16.2 19.4 18.2 18.5

 CO

 0.004 0.003 0.003 CM O O or '0.004 0.005 0.004 CM O O or' 0.003 0.004 CM O O o '

 Q_

 0.023 0.024 or CM O or '0.021 LO CM O or' CO CM O or '0.024 LO CM O or' 0.029 0.024 O CM O o '

 Mn

 0.18 0.15 LO CM or '0.21 0.13 0.19 0.15 0.19 CM CM or' 0.20 0.21

 C/)

 0.05 0.10 0.14 0.18 0.12 00 or o '0.15 or' 0.23 0.18 0.34

 or

 0.010 0.003 0.012 0.006 0.003 00 or o '0.005 0.009 0.005 0.012 0.005

 or

 - CM CO LO CO 33 CD O - CM

Nomenclature: The underline indicates a value outside the range of the present invention

First, the surface quality was evaluated by visual inspection of the steel sheets laminated in fno, annealed and stripped.

Subsequently, using the fno laminated, annealed and stripped steel sheets obtained, 5 two types of samples were prepared to assess the corrosion resistance of the base steel sheet. One was a sample in a pickled state obtained from the pickled steel sheet after descaling and another was a polished sample obtained by polishing the surface of the pickled steel sheet with a # 600 type sandpaper.

In addition, using the same steel sheets, a test was carried out on the welding zone performed by 10 TIG welding. In this test, two pieces cut from each steel sheet were welded by TIG welding and polished with a sandpaper of type # 600 to assess the corrosion resistance in the welding area of the equal steels.

In addition, using the same steel plates, a TIG welding test was carried out with a SUS304 type 15 steel as a different steel. In this test, a cut piece of each steel plate and a piece of the sheet of the SUS304 type of 1.0 mm thickness were welded by TIG welding to evaluate the corrosion resistance in the welding zone of different steels. The surface of the welding zone was polished with a sandpaper of type # 600. The welding conditions for the same steels and for different steels are described below. The welding current was controlled so that the width of the subsequent welding bead was 3 20 mm or more. The surface in the subsequent weld seam was evaluated.

Welding voltage: 10 V Welding current: 90 A to 110 A Welding speed: 600 mm / min 25 Electrode: 1.6 mm tungsten electrode

Protection gas: front weld seam side Ar 20 l / min,

Protection gas: side of the weld seam Ar 20 l / min

Using the two types of samples (the sample in a pickled state and the sample in a polished state), the zone of welding of equal steels and the zone of welding of different steels, a neutral corrosion salt spray corrosion test was carried out (CCT) in accordance with JIS H 8502 (1999). In the CCT, a cycle in which a solution containing NaCl is sprayed in a concentration of 5% by mass (35 ° C, 2 hours), drying (60 ° C, 4 hours, relative humidity: from 20% to 30 %) and humidification (40 ° C, 2 hours, relative humidity: 95% or more) were repeated in this order for 15 cycles. The results obtained are given in Table 2. Here, the standards for the evaluation of the tests will be described later.

a) The appearance of the surface after the cold rolling, annealing and pickling: evaluated by a relationship of the length of the portions in which the surface defects (scab, small holes, linear crust, veins defects caused by titanium nitrides, abnormal color of the white stripe method) were

40 found along the entire length of the sample. The appearance of the surface was evaluated as follows; Or indicates the case in which a defect ratio is less than 5%, OR indicates the case in which a defect ratio is equal to or greater than 5% and less than 10%; A indicates the case in which a defect ratio is equal to or greater than 10% and less than 20% and x indicates the case where a defect ratio is 20% or more, where O and O indicate satisfactory cases and A and x indicate unsatisfactory cases.

Four. Five

b) The resistance to corrosion by CCT of the samples in a pickled state and in a polished state with a sandpaper of type # 600: evaluated by an area in which rust was produced after the 15 cycle test. The result of the CCT was evaluated as follows; Or indicates the case in which a ratio of the oxide area is less than 10%, OR indicates the case in which a ratio of the oxide area is 10% or more and less than 20%, A indicates

50 the case in which a ratio of the oxide area is 20% or more and less than 30% and x indicates the case in which a ratio of the oxide area is 30% or more, where O and O indicate satisfactory cases and A and x indicate unsatisfactory cases.

c) The resistance to corrosion by CCT of the welding zone of equal steels: evaluated by a ratio 55 of the oxide area after 15 cycles of the CCT that was performed on the samples obtained by TIG welding a

Test the samples of the same steels and removing the tempering color of the welding zone with a sandpaper of type # 600. The results of the corrosion resistance were evaluated as follows;

Or indicates the case in which a ratio of the oxide area is less than 10%, OR indicates the case in which a ratio of the oxide area is 10% or more and less than 20%, A indicates the case in which a ratio of the area of oxide is 60 20% or more and less than 30% and x indicates the case in which a ratio of the area of oxide is 30% or more, where O and O indicate satisfactory cases and A and x indicate unsatisfactory cases.

d) The resistance to corrosion by CCT of the welding zone of different steels: evaluated by a ratio of the area of oxide after 15 cycles of the CCT that was performed on the samples obtained by TIG welding at the end of each sample and SUS304 and eliminating the tempering color of the welding zone with a sandpaper of type # 600. The results of the corrosion resistance were evaluated as follows;

5 OR indicates the case in which a ratio of the oxide area is less than 10%, OR indicates the case in which a ratio of the oxide area is 10% or more and less than 20%, A indicates the case in which a ratio of the area of oxide is 20% or more and less than 30% and x indicates the case in which a ratio of the area of oxide is 30% or more, where O and O indicate satisfactory cases and A and x indicate unsatisfactory cases.

Nomenclature: O, O; satisfactory, A, x; not satisfactory

 N °

 Surface quality of a cold rolled, annealed and pickled sheet Corrosion resistance by CCT of a cold rolled, annealed and pickled sheet (pickled state) CCT corrosion resistance of a cold rolled, annealed and pickled sheet (state polished) Corrosion resistance by CCT in a welding zone of steels of the same grade Corrosion resistance by CCT in a welding zone of steels of different grades Notes Notes

 one

 O O O O O - Examples

 2

 O O O O O -

 3

 O O O O O -

 4

 O O O O O -

 5

 O O O O O -

 6

 O O O O O -

 33

 O O O O O -

 9

 O X X X X - Comparative Examples

 10

 O o o o X -

 eleven

 O o o X X -

 12

 A A o o o Reduction of Ductility Residual scale

[Table 2]

Examples from No. 1 to No. 6 and No. 33 which have a chemical composition in the range according to the present invention were excellent in corrosion resistance and surface quality at all points evaluated. On the other hand, comparative example No. 9 that had a low Cr content of 16.2% was poor in corrosion resistance, as indicated by its large areas of oxide.

5

Comparative example No. 10 having a high Cr content of 19.4% was poor in corrosion resistance, as indicated by its large area of oxide in the welding zone of different steels. It is believed that this is because a phase of martensite is not formed in the welding zone of the different steels due to the high content of Cr which is a ferrite forming element.

10

Comparative example No. 11 having a low Ti content of 0.07% was poor in corrosion resistance, as indicated by its large area of rust in the welding zone of the different steels.

In the case of comparative example No. 12 which has a Si content and a Nb content greater than the interval according to the present invention, a certain residual scale was found on the surface of the base steel sheet and was poor in resistance to corrosion after cold rolling, annealing and pickling.

EXAMPLE 2

twenty

Steels having a chemical composition of examples No. 13-16 and 18 and the comparative examples No. 17 and 19 to No. 22 given in Table 3 were melted using a VOD (vacuum decarburization with oxygen) having a 150 tons capacity and are molded into cast iron sheets continuously. These plates were heated to a temperature of 1150 ° C and hot rolled in a hot rolled steel coil 25 having a thickness of 4.0 mm. Next, these hot rolled steel sheet coils were annealed in an atmosphere of a coke oven gas having an air ratio of 1.3 at a temperature of 950 ° C for 1 minute to 5 minutes .

These hot rolled and annealed sheet steel coils were subjected to a shot blasting with 30 iron shot blasting, peeling by pickling in which the sheet steel coils were immersed in a sulfuric acid solution containing sulfuric acid in a concentration of 20% by mass at a temperature of 80 ° C for 120 seconds and then in a mixed acid solution containing nitric acid in a 15% mass concentration and hydrofluoric acid in a 3% mass concentration at a temperature of 55 ° C for 60 seconds. And these coils of hot rolled and annealed steel sheets were cold rolled in coils of 35 cold rolled steel sheets that had a thickness of 1.0 mm, subjected to annealing in an oven in an atmosphere of a gas of Coke oven that has an air ratio of 1.3 at a temperature of 900 ° C for 2 minutes, to an electrolytic descaling with the steel plate being a positive electrode three times in a solution containing NaSO4 in a concentration of 20 % by mass at a temperature of 80 ° C with a current of 3 A / Dm2 for 10 seconds and descaling in a mixed acid solution containing nitric acid in a concentration of 5% by mass and fluoric acid in a concentration of 3% by mass at a temperature of 55 ° C for 30 seconds to obtain cold rolled, annealed and pickled steel sheets.

[Table 3]

 Notes

 Examples Comparative Examples

 Chemical Composition (% by mass)

 >,,,, 0.10,,,, OR CM o '

 N

 ,,,, zio,,,,

 Sb

           0.100

 <

 0,029 0,030 0,027 0,140 00 CM O or '0,031 LO CM O or' CO CM O or '0,032 O or CM o'

 Mg

 CM O O O o '0.0003 0.0004 0.0004 0.0003 CM O O O o' 0.0004 0.0001 0.0003 O O 0 01

 2

 CO O O or '00 o o o' 0.012 0.009 0.014 0.010 0.010 00 O O or '0.015 00 O o o'

 Mo

 0.05 0.07 0.08 zio 0.06 0.08 0.40 0.15 0.08 0.09

 Nb

 o CM O o '0.030 0.040 0.030 O CM O o' 0.030 O CM O o 'or CM O o' 0.003 0.010

 i-

 0.21 0.16 0.23 0.17 0.37 0.20 0.24 0.33 0.37 0.20

 Cu

 0.34 0.35 0.46 0.34 0.36 0.31 0.34 0.32 0.37 0.41

 left

 0.20 zio 0.19 0.15 0.23 0.24 0.18 0.23 0.20 0.14

 or

 18.6 18.4 17.9 18.5 18.3 18.2 18.2 19.5 17.8 18.4

 CO

 0.006 0.003 00 or o o '0.004 0.003 0.005 0.003 0.004 0.006 0.004

 Q_

 0.024 LO CM O or '0.023 LO CM O o' 0.019 0.030 0.023 0.029 0.021 0.019

 Mn

 0.21 0.23 0.19 CM CM or 'or CM or' 0.33 0.19 0.24 O CM or '0.23

 C/)

 0.06 or '0.13 0.10 00 CM or' 0.19 0.15 CO CM or '0.33 0.45

 or

 0.009 0.005 0.006 0.006 0.010 0.004 0.007 0.004 0.011 0.005

 or Z

 CO LO CO h- 00 CD 20 CM CM CM

Nomenclature: The underline indicates a value outside the ranges of the present invention. Example 17 is comparative.

Subsequently, samples of the base steel sheet, the weld zone of equal steels and the weld zone of different steels were prepared in similar ways to those described in example 1, and a test of corrosion corrosion was carried out by neutral salt spray according to JIS H 8502 (1999) as was done in example 1 and the corrosion resistance was evaluated. The results obtained are given in Table 4. Here, the test evaluation standards were similar to those in example 1.

Nomenclature: O, O; satisfactory, A, x; not satisfactory Example 17 is comparative.

 N °

 Surface quality of a cold rolled, annealed and pickled sheet Corrosion resistance by CCT of a cold rolled, annealed and pickled sheet (pickled state) CCT corrosion resistance of a cold rolled, annealed and pickled sheet (state polished) Corrosion resistance by CCT in a welding zone of steels of the same grade Corrosion resistance by CCT in a welding zone of steels of different grades Notes Notes

 13

 O O O O O - Examples

 14

 O O O O O -

 fifteen

 O O O O O -

 16

 O O O O O -

 17

 O O O O O -

 18

 O O O O O -

 19

 O O O O X - Comparative Examples

 twenty

 O O O O X -

 twenty-one

 X A O O or -

 22

 X X O O or -

[Table 4]

Examples from No. 13 to 16 and No. 18 that had a chemical composition in the range according to the present invention were excellent in corrosion resistance and surface quality at all points evaluated.

Comparative example No. 17 had a poorer surface quality than the examples of the invention.

5

On the other hand, since comparative example No. 19 had a Mo content of 0.40% greater than that of the range according to the present invention, and since comparative example No. 20 had a Cr content of 19.5 % greater than the range according to the present invention, both were poor in corrosion resistance, as indicated by their large area of oxidation in the welding zone of different steels. This is believed to be because a phase of martensite is not formed in the welding zone of different steels due to the large contents of Mo and Cr, which are ferrite forming elements.

Furthermore, since comparative example No. 21 had a Si content of 0.33% and an Nb content of 0.003% outside the range according to the present invention and because comparative example No. 22 had a content of 15 Si of the 0.45% and Mg content of 0.0010% greater than the range according to the present invention, some residual scale was found, and both were poor in corrosion resistance after cold rolling, annealing and pickling.

EXAMPLE 3

twenty

Steels having a chemical composition of examples from No. 23 to No. 26 and No. 28 and comparative examples from No. 29 to No. 32 given in Table 5 were cast using a small vacuum melting furnace with a capacity of 50 kg. These ingots of these steels were heated to a temperature of 1150 ° C in an oven under an Ar gas purge and hot rolled in hot rolled steel sheets having a thickness of 4.0 mm.

Then, these hot-rolled sheets were subjected to annealing in air at a temperature of 950 ° C for 1 minute, followed by a surface treatment by shot blasting with glass shot and peeling by pickling in which the steel sheets were submerged in a sulfuric acid solution containing sulfuric acid in a concentration of 20% by mass at a temperature of 80 ° C for 120 seconds and then in a mixed acid solution containing nitric acid in a concentration of 15% by mass and hydrofluoric acid in a solution with a concentration of 3% by mass at a temperature of 55 ° C for 60 seconds.

Next, the hot-rolled steel sheets were cold rolled in cold-rolled steel sheets with a thickness of 1.0 mm, subjected to annealing in a reducing atmosphere (H2: 5% by volume, N2: 95 Volume%, with a rocfo point: - 40 ° C) at a temperature of 900 ° C for 1 minute and cold rolled and annealed steel sheets were manufactured. These cold-rolled and annealed steel sheets were subjected to shelling by electrolysis (10 A / dm2 for 2 seconds) the steel sheet being a positive electrode twice in a solution containing nitric acid in a 15% mass concentration and hydrochloric acid in a concentration of 0.5% by mass at a temperature of 50 ° C in order to have cold rolled, annealed and pickled steel sheets.

[Table 5]

 Notes

 Examples Comparative Examples

 Chemical Composition (% by mass)

 >,,,, 0.40,,, or CM o '

 N

 ,,, 0.20,,,,,

 _Q tt>

       0,180 0,050

 <

 00 CM O or "0.030 0.150 0.027 0.160 0.210

 Mg

 0.0004 CM O O O o '0.0003 CM O O O o' 0.0004 0.0003 0.0001 0.0004 0.0003

 2

 0.012 00 O O o '0.007 0.010 00 o o o' 0.010 00 o o o '0.011 00 o o o'

 Mo

 o '0.07 0.09 0.13 0.05 or' 0.15 0.40 0.09

 Nb

 or CM o o '0.030 0.030 0.010 0.030 or CM O o' or CM O o 'or CM O o' 0.100

 i-

 0.23 0.16 0.17 0.20 zio 0.27 0.32 LO CM or '0.23

 Cu

 0.36 0.34 0.35 0.32 0.37 0.43 0.31 0.36 0.32

 left

 0.15 0.16 0.20 0.13 0.21 0.15 0.23 0.24 0.18

 or

 18.7 18.4 18.5 17.3 17.9 16.7 19.7 18.0 18.4

 CO

 0.004 CM O O '0.003 0.005 0.004 0.005 0.001 0.003 0.004

 Q_

 0.024 LO CM O o '0.023 0.024 0.024 0.029 0.027 0.024 CO CM O o'

 Mn

 00 CM or '0.21 0.19 0.23 0.23 or CM or' 0.24 0.21 LO CM o '

 C/)

 0.18 o '0.09 0.06 zio 0.18 0.20 0.36 0.50

 or

 0.010 0.005 0.006 0.009 0.003 0.010 0.005 0.012 0.005

 or Z

 CO CM CM LO CM CO CM 00 CM CD CM or CO CO CM CO

Nomenclature: The underline indicates a value outside the ranges of the present invention.

Subsequently, using cold-rolled, annealed and pickled steel sheets, two types 5 of samples were prepared to assess the corrosion resistance of the base steel sheet as in Example 1. One was a sample in a pickled state. obtained from a pickled steel plate after peeling and another was a polished sample obtained by polishing the surface of the pickled steel sheet with a sandpaper of type # 600.

10 In the preparation of the samples of the welding zone of equal steels and the welding zone of different steels using a SUS304 type, considering the case in which the shielding gas is not sufficiently effective during TIG welding, the test of Welding was carried out using a protective gas of Ar + 20% by volume of N2 on both sides of the front and rear weld seams.

15 The welding conditions are described below. The surface of the sides of the weld seam was evaluated.

Welding voltage: 10 V Welding current: from 90 A to 110 A 20 Welding speed: 600 mm / min

Electrode: 1.6mm tungsten electrode

Protection gas: side of the weld seam Ar + 20% by volume of N2 in 20 l / min,

Protection gas: side of the weld seam Ar + 20% by volume of N2 in 20 l / min

25 Using the two types of samples (a sample in a pickled state and a sample in a polished state), the weld zone of equal steels and the weld zone of different steels, a spray corrosion corrosion test was carried out in Neutral saline (CCT) in accordance with JIS H 8502 (1999). In the CCT, a cycle in which a solution containing NaCl is sprayed in a concentration of 5% by mass (35 ° C, 2 hours), drying (60 ° C, 4 hours, relative humidity: from 20% to 30 %) and humidification (40 ° C, 2 hours, relative humidity: 95% or more) were repeated in this order for 15 cycles. The results obtained are given in Table 6. Here, the evaluation patterns were similar to those in example 1.

Nomenclature: O, O; satisfactory, A, x; not satisfactory

 N °

 Surface quality of a cold rolled, annealed and pickled sheet Corrosion resistance by CCT of a cold rolled, annealed and pickled sheet (pickled state) CCT corrosion resistance of a cold rolled, annealed and pickled sheet (state polished) Corrosion resistance by CCT in a welding zone of steels of the same grade Corrosion resistance by CCT in a welding zone of steels of different grades Notes Notes

 2. 3

 O O O O O - Examples

 24

 O O O O O -

 25

 O O O O O -

 26

 O O O O O -

 28

 O O O O O -

 29

 O X X X X - Comparative Examples

 30

 O o o A X -

 31

 A A o o X -

 32

 X X o o X Reduction of Ductility Residual scale

[Table 6]

The examples from No. 23 to No. 28 were excellent in corrosion resistance and surface quality at all evaluation points. Examples from No. 25 to 26 and 28 to which Al, Sb Zr and V were added were significantly excellent in corrosion resistance even in the welding zone of different steels using an SUS304.

5

On the other hand, because comparative example No. 29 had a Cr content of 16.7% lower than that of the range according to the present invention, it was poor in corrosion resistance, as indicated by its large area of oxidation .

In addition, because comparative example No. 30 had a Cr content of 19.7% greater than that of the range according to the present invention, it was poor in corrosion resistance, as indicated by its large area of oxidation in The welding zone of different steels. This is because a martensite phase is not formed in the welding zone of different steels due to the high content of Cr, which is a ferrite forming element.

15 In addition, in comparative example No. 31 which had a Si content of 0.36% and a Mo content of 0.40% greater than that of the range according to the present invention, a certain residual scale was found on the surface of the base steel plate. And it was not only corrosion resistant after cold rolling, annealing and pickling, but also corrosion resistance in the welding zone of different steels using a SUS304 in which, in particular, the gas from Protection was not enough.

twenty

Furthermore, in comparative example No. 32 which had a Si content of 0.50% and an Nb content of 0.10% greater than that of the range according to the present invention, a certain residual scale was found on the surface of The base steel sheet and was poor in corrosion resistance after cold rolling, annealing and pickling.

25

As described above, it has been clarified that, in accordance with the present invention, an excellent ferritic stainless steel in corrosion resistance of the base steel sheet, corrosion resistance in the welding zone of equal steels, strength Corrosion in the welding zone of different steels using an SUS304 and the surface quality of the cold rolled, annealed and pickled sheet can be obtained without grinding the surface of hot rolled, annealed and pickled sheet steel.

Industrial Application

The ferric stainless steel according to the present invention can preferably be used as material 35 for parts that need corrosion resistance such as kitchen and household items, architectural interiors and exteriors, construction parts, the interior of an elevator and a escalator, electrical appliances and car components.

Claims (2)

1. A ferritic stainless steel having a chemical composition consisting of, in% by mass, C: 0.003% or more and 0.015% or less, If: 0.05% or more and 0.20% or less, Mn: 0.10% or more and 0.35% or less, P: 0.06% or less, S: 5 0.02% or less, Cr: 17.0% or more and 19.0% or less, Ni: more than 0.10% and 0.30% or less, Ti: 0.10% or more and 0 , 40% or less, Nb: 0.005% or more and less than 0.050%, Mo: less than 0.20%, N: 0.005% or more and 0.015% or less, Cu: 0.30% or more and 0, 50% or less, Mg: less than 0.0005%, and optionally also containing in bulk, Al: 0.02% or more and 0.50% or less, Sb: 0.005% or more and 0.300% or less, at minus one of Zr: 0.05% or more and 0.60% or less and V: 0.02% or more and 0.50% or less and the rest of the balance is Faith and unavoidable impurities. 10 2. The ferric stainless steel according to claim 1, the steel having a chemical composition containing, in mass%, Al: 0.10% or more and 0.50% or less.