JP2001152296A - Hot rolled stainless steel plate for civil engineering and building construction use, excellent in workability and weldability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot rolled martensitic stainless steel plate excellent in weldability and workability as well as in corrosion resistance and suitable for use as a steel for civil engineering and building construction. SOLUTION: The steel plate has a chemical composition containing, by mass, 10-15% Cr and also containing <=0.012% C and <=0.02% N under the condition of C+N=0.005 to 0.03% and C/N<0.6 and has a structure in which one or more kinds among carbides, nitrides and carbonitrides of <=0.3 μm average diameter are dispersed at >=0.5×106 piece/mm2 density. Moreover, it is preferable that, in the above composition, the value of Y defined by Y=Cr+Mo+1.5Si+0.5Nb+8Al-Ni-0.5Mn-30N-0.5Cu is regulated to <=10.7. Further, Ni, either or both of Cu and Mo, either or both of Ti and B, or either or both of Nb and V can be incorporated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hot-rolled stainless steel sheet, and more particularly to a hot-rolled stainless steel sheet suitable for civil engineering and building structures.

[0002]

2. Description of the Related Art Conventionally, as materials for civil engineering and building structures, ordinary steels such as SS400, high-strength steels such as SM490, and materials obtained by painting or plating such steels have been mainly used. However, in recent years, with the diversification of designs, utilization of various materials has begun to be considered. Above all, stainless steel excellent in design and corrosion resistance is an attractive material considering that almost no maintenance cost for rust is required from the viewpoint of life cycle cost (LCC). In particular, buildings constructed in coastal areas have problems such as short service life and increased maintenance costs for controlling corrosion.In promoting waterfront development, The development of stainless steel as a corrosion-resistant functional material for building structures is greatly expected.

[0003] Stainless steel is made of SUS
430, ferritic stainless steel, SUS410
Martensitic stainless steel, SUS 304
Austenitic stainless steel represented by SUS 329
SUS 630 and precipitation hardening stainless steel typified by SUS 630. Among these various stainless steels, the ones that have been studied for building structures in the past are the most used, including material strength, corrosion resistance, ease of welding, weld toughness, and general versatility. Austenitic stainless steel, SUS 304, SUS 304N, SUS 316, SU
Four types of S 329J1 are specified.

[0004] These austenitic stainless steels are:
It has properties that sufficiently satisfy the properties required for civil engineering and building materials, such as strength, corrosion resistance, fire resistance, and weld toughness. However, austenitic stainless steels contain a large amount of alloying elements such as Ni and Cr and are much more expensive than ordinary steel, cause stress corrosion cracking, and have a coefficient of thermal expansion 1.5 times that of ordinary steel. Because of its large thermal conductivity and relatively small thermal conductivity, it is easy to accumulate strain due to the thermal effect during welding, and it is difficult to apply it to members that require precision. There is a problem that the application is difficult and the application range is limited. Further, it is difficult to use steels for civil engineering and building structures in a wide range of applications only with the four types of austenitic stainless steel specified in the stainless steel standard for building structures SAS 601.

[0005] Under these circumstances, recently, as an alternative to plated or painted ordinary steel, application of martensitic stainless steel to civil engineering and construction steel materials is being studied. Martensitic stainless steel has a low Cr content of 11 to 13% compared to austenitic stainless steel and does not contain Ni, so it is much cheaper, has a low expansion and expansion coefficient, a large thermal conductivity, and Compared with ordinary steel, it has excellent corrosion resistance and high proof stress. In addition, martensitic stainless steel has sufficient oxidation resistance up to 800 ° C, and is free from σ embrittlement and 475 ° C embrittlement, which are problems with high Cr ferritic stainless steel. There is no fear of stress corrosion cracking in the presence of chlorides, which is a problem with stainless steel.

However, the general-purpose martensitic stainless steel represented by SUS410 has a high C content of about 0.08% by mass, is inferior in weld toughness and workability of the weld, and requires preheating for welding. It has drawbacks such as poor welding workability, and there remains a problem in application to members that require welding. For such a problem, for example,
In Japanese Patent Publication No. 51-13463, Cr: 10 to 18 wt% (mass
%), Ni: 0.1-3.4 wt% (mass%), Si: 1.0 wt%
(Mass%) or less, Mn: 4.0 wt% (mass%) or less, C: 0.03 wt% (mass%) or less, N: 0.02 wt%
% (Mass%) or less, a martensitic stainless steel for a welded structure has been proposed in which a massive martensite structure is generated in a heat affected zone of a weld and the performance of a weld is improved.

[0007] Japanese Patent Publication No. 57-28738 discloses that Cr: 10
~ 13.5wt% (mass%), Si: 0.5wt% (mass%) or less,
Mn: 1.0 to 3.5 wt% (mass%).
Pre-heating and post-heating before and after welding by reducing to less than 0.02wt% (mass%) and N: 0.02wt% (mass%) and strictly limiting Ni to less than 0.1wt% (mass%). There has been proposed a structural martensitic stainless steel excellent in toughness and workability of a welded portion, which does not require a steel.

[0008] JP-B-51-13463 and JP-B-57-287
With the technology described in Publication No. 38, the weld characteristics of martensitic stainless steel have been greatly improved compared to the past, and the application of martensitic stainless steel to parts that require welding, such as container materials, has greatly advanced. It was way.

[0009]

[Problems to be solved by the invention]
The martensitic stainless steel materials manufactured by the techniques described in JP-A-51-13463 and JP-B-57-28738 have sufficient properties with respect to the characteristics recently required as materials for civil engineering and building structures. It is hard to say that there is a need for further improvement in terms of economic efficiency, especially in addition to the toughness, workability, and corrosion resistance of the welded portion.

[0010] Recently, Japanese Patent Application Laid-Open No. 10-53843 discloses that
Cr: 10 to 13 wt% (mass%), Si: 1.0 wt% (mass%) or less, Mn: 1.0 wt% (mass%) or less, Ni: 0.10 to 1.0 wt%
(Mass%), and C: 0.03 wt% (mass%)
Hereinafter, N: 0.02~0.03wt% in terms of the (mass%) and significantly reduce the C, by reducing the A system and B ₁ based inclusions, excellent thickness 3.0mm below the workability and corrosion resistance A stainless steel for civil engineering is disclosed. However, the steel described in Japanese Patent Application Laid-Open No. Hei 10-53843 is an inexpensive steel material applicable as a structural member for a general house, but is mainly developed for a secondary member not subjected to welding. . Therefore, there is a problem that further improvement in weldability is required when applying a steel material manufactured by the technique described in JP-A-10-53843 to a member requiring welding.

The present invention solves the above-mentioned problems in the prior art, and is inexpensive, has excellent corrosion resistance, is suitable for steel for civil engineering and building structures used in places where welding is essential, and has good weldability and workability. An object of the present invention is to provide a hot-rolled martensitic stainless steel sheet having excellent heat resistance.

[0012]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors first focused on C and N, and applied C and N to the weld properties of martensitic stainless steel.
The effects of were separately and independently examined. Conventionally, C and N are elements that increase the susceptibility of the welded heat-affected zone to cracks and deteriorate the ductility and toughness of the welded heat-affected zone, and are known to have an adverse effect on the properties of the welded portion. Has been preferred. However, according to the study of the present inventors, as a steel material for civil engineering / building structural use, rather than reducing both C and N infinitely, the martensitic phase is more stable and obtains a desired hardness. While minimizing
The hardness, toughness, workability, etc. of the weld heat affected zone are improved in a well-balanced manner by keeping N to some extent, keeping the (C + N) amount in the required proper range, and maintaining the C / N ratio in the proper range. I knew it would be done.

Further, the present inventors have described the above (C + N)
In addition to controlling the amount and the C / N ratio within the proper range, the size of the precipitate and the dispersion density, which greatly affect the size of the austenite grains and the ferrite grains during tempering, are adjusted to the proper ranges, thereby improving the martensite content. It has been found that the toughness of the weld of site-based stainless steel is further remarkably improved. The present invention has been completed based on the above-mentioned findings and further studies.

That is, in the present invention, C: 0.01% by mass.
2% or less, N: 0.02% or less, (C + N): 0.005 to 0.
03%, contained under the condition of C / N <0.6.
%, Mn: 1.0% or less, P: 0.08% or less, S: 0.01%
Hereinafter, Cr: 10 to 15%, or further Al: 0.10% or less, having a composition consisting of the balance Fe and unavoidable impurities, and having an average diameter of 0.3 μm or less of carbides, nitrides and carbonitrides A hot-rolled stainless steel sheet for civil engineering and building structures excellent in workability and weldability, characterized in that one or more of them have a structure dispersed at a density of 0.5 × 10 ⁶ pieces / mm ² or more. Further, in the present invention, the composition is represented by the following formula (1): Y = Cr + Mo + 1.5Si + 0.5Nb + 8Al-Ni-0.5Mn-30C-30N-0.5Cu (1) Cr, Mo, Si, Nb, Al, Ni, Mn, C, N, Cu:
The content of each element (% by mass) preferably satisfies 10.7 or less in the Y value. In addition, in the present invention, in addition to the above composition, Ni: 0.1 to 0.6% by mass is further added. It is preferable that, in the present invention, in addition to each of the above-described compositions,
And preferably contains one or two kinds selected from Cu: 0.1 to 0.6% and Mo: 0.1 to 0.6%.
And preferably contains one or two kinds selected from Ti: 0.005 to 0.05% and B: 0.0005 to 0.0050%, and in the present invention, in addition to the above-mentioned respective compositions, further contains , Nb: 0.01 to 0.1%, and V: 0.01 to 0.1%.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the reasons for limiting the chemical components of a hot-rolled martensitic stainless steel sheet according to the present invention will be described. Hereinafter, mass% in the composition is simply referred to as%. C: 0.012% or less, N: 0.02% or less, and C + N: 0.
005 to 0.03%, C / N <0.6 C, N increases the hardness of the martensite phase, but increases the cracking susceptibility of the heat affected zone and deteriorates the ductility and toughness of the heat affected zone. Further, it combines with Cr in the steel to form carbonitrides, and forms a Cr-deficient phase to deteriorate corrosion resistance.
Therefore, in the present invention, the upper limit of C is 0.012% and the upper limit of N is 0.02%, and the sum of C content and N content (C + N)
Was limited to 0.03% or less. Reduction of C and N is effective for improving the properties of the welded portion and improving the workability. However, excessive reduction increases the refining load, promotes the softening of the martensite phase, and has low weld cracking susceptibility.
It becomes difficult to obtain a structure having a martensite phase of 80% or more in area ratio, and further, the formation of coarse ferrite grains deteriorates weld toughness. Therefore, the lower limit of (C + N) is set to 0.005%. Preferably, C is 0.008
%, N is 0.01 to 0.015%.

Further, the sum of the C content and the N content (C +
Even if N) is in the range of 0.005 to 0.03%, the weld properties, particularly the weld toughness and the weld bending properties, may be reduced. In the present invention, the ratio of the C content to the N content is further reduced.
Limit C / N to less than 0.6. FIG. 1 shows that (C + N) = 0.
The relationship between the C / N ratio and the absorbed energy value of the Charpy impact test (test temperature: -20 ° C.) of the heat affected zone (HAZ 2.0 mm) when the value is fixed at 02 to 0.03% is shown. The Charpy impact test specimen was a 7 mm thick sub-size.

FIG. 1 shows that when the C / N ratio is 0.6 or more, the absorbed energy of the heat affected zone decreases sharply. When C / N is 0.6 or more, the ductile-brittle transition temperature (vTre) in the Charpy impact test of the weld becomes high, and the weld toughness deteriorates. For this reason, in the present invention, C / N is set to less than 0.6. Si: 1.0% or less Si is an effective element having a deoxidizing effect. However, an excessive content causes a decrease in toughness and workability. Therefore, Si is 1.0%
Limited to the following. Preferably, the content is 0.03 to 0.5%.

Mn: 1.0% or less Mn is an element having a deoxidizing effect and stabilizing the austenite phase, and is also an effective element for suppressing the grain growth of the heat affected zone and improving the toughness of the weld zone. . However, an excessive content causes a reduction in workability and a reduction in corrosion resistance. Therefore, Mn is limited to 1.0% or less. In addition, preferably, it is 0.06 to 0.09%.

P: not more than 0.08% P is an element that degrades hot workability, workability, and toughness and is harmful to corrosion resistance. In the present invention, it is desirable to reduce P as much as possible. In particular, if the content exceeds 0.08%, the effect becomes remarkable, so P was limited to 0.08% or less. Preferably, it is at most 0.04%.

S: 0.01% or less S combines with Mn to form MnS. MnS is the starting point of the initial rust. In addition, S is a harmful element that segregates at the crystal grain boundaries and embrittles the grain boundaries. In the present invention, it is desirable to reduce S as much as possible. In particular, when the content exceeds 0.01%, the effect becomes remarkable, so S was limited to 0.01% or less.
Incidentally, the content is preferably 0.006% or less.

Cr: 10 to 15% Cr is an effective element for improving corrosion resistance. However, if the content is less than 10%, sufficient corrosion resistance cannot be secured. On the other hand, Cr is a ferrite phase stabilizing element.
Along with lowering the workability, the stability of the austenite phase is reduced, and a predetermined amount of martensite phase cannot be secured during quenching, and the strength is reduced. For this reason, in the present invention, Cr is limited to the range of 10 to 15%. In addition, from the viewpoint of achieving both corrosion resistance and workability, the content of Cr is preferably in the range of 11 to 13.5%.

Ni: 0.1 to 0.6% Ni is an element for improving ductility and toughness, and is preferably contained in an amount of 0.1% or more to improve the toughness of the heat affected zone. On the other hand, when the content exceeds 0.6%, the bending workability is deteriorated. For this reason, Ni is preferably limited to the range of 0.1 to 0.6%. One or two selected from Cu: 0.1 to 0.6% and Mo: 0.1 to 0.6%. Both Cu and Mo are effective elements for improving the corrosion resistance. One or two of them can be contained. Further, Cu, which is an austenite phase forming element, improves corrosion resistance, suppresses grain growth in the heat affected zone, and effectively acts to improve the toughness of the heat affected zone. Such effects are observed at a content of 0.1% or more, but 0.6% or more.
A content exceeding% increases the embrittlement of the steel material, particularly the susceptibility to hot cracking. For this reason, Cu is preferably set in the range of 0.1 to 0.6%.

Mo has an effect of improving corrosion resistance.
Such an effect is recognized at a content of 0.1% or more. On the other hand, when the content exceeds 0.6%, the stability of the austenite phase is reduced, and the toughness and workability are significantly reduced. For this reason, Mo is preferably limited to the range of 0.1 to 0.6%. Incidentally, from the balance between corrosion resistance and workability, it is more preferably 0.3 to 0.5%.

Ti: 0.005 to 0.05%, B: 0.0005 to 0.0050
% Or 1% or 2% Ti or B is an element effectively acting to improve hardenability, and may contain 1 or 2 types of Ti and B as needed. Ti effectively acts on improving hardenability, forms carbonitrides, suppresses grain boundary precipitation of Cr carbonitrides during welding and heat treatment, and effectively contributes to improving corrosion resistance. Such an effect is recognized at a content of 0.005% or more. On the other hand, if the content exceeds 0.05%, these effects tend to decrease. For this reason, Ti is preferably set in the range of 0.005 to 0.05%. Incidentally, more preferably 0.010 to 0.03
0%.

B effectively acts to improve hardenability,
If the content is less than 0.0005%, sufficient effects cannot be obtained.
A content exceeding 0.0050% excessively increases the hardness of the steel material,
Deteriorate workability and toughness. For this reason, B is 0.0005-0.
Preferably, it is in the range of 0050%. Note that the content is more preferably 0.0010 to 0.0030%. Nb: 0.01% to 0.1%, V: 0.01% to 0.1% One or two types selected from the group consisting of Nb and V both form carbonitrides and have the effect of refining austenite grains. It is an element that improves the workability of steel materials. If necessary, one or two of Nb and V
Species can be included. These effects are observed at a content of 0.01% or more. However, an excessive content of Nb and V exceeding 0.1% lowers the toughness and workability of the weld. For this reason, N
Both b and V are preferably limited to the range of 0.01 to 0.1%. It is more preferable that both Nb and V are in the range of 0.03 to 0.07%.

Al: 0.10% or less Al acts as a deoxidizing agent and is used in an amount of 0.1% to reduce oxygen in steel.
10% or less can be contained. If the content exceeds 0.10%, the amount of oxides increases and the workability deteriorates. In addition, it is preferably 0.02% or less. Y ≦ 10.7 Y = Cr + Mo + 1.5Si + 0.5Nb + 8Al-Ni-0.5Mn-30C-30N-0.5Cu (1) (where Cr, Mo, Si, Nb, Al, Ni, Mn , C, N, Cu:
In the present invention, in addition to the regulation of the chemical components described above, in order to improve the toughness of the welded heat-affected zone and the workability including the welded portion, the content of each element is regulated. It is preferable to introduce the Y value defined in the equation (1) and adjust the chemical components so that the Y value is 10.7 or less. C = 0.008%, N = 0.016 to 0.018
% And the toughness of the weld heat affected zone (−20 ° C. in the Charpy impact test)
FIG. 3 shows the relationship between the absorption energy at E.sub.2 and _E.sup.-20 ). FIG. 3 shows that when the Y value exceeds 10.7, the toughness of the heat affected zone is significantly reduced. In calculating the Y value by using the equation (1), it is assumed that the elements that are not contained are calculated as having a content of 0.

Remaining Fe and Inevitable Impurities The remainder other than the above chemical components are Fe and inevitable impurities. As unavoidable impurities, O: 0.010 or less is acceptable. The hot-rolled martensitic stainless steel sheet of the present invention has the above-mentioned composition, and further has one or more of carbides, nitrides and carbonitrides having an average diameter of 0.3 μm or less of 0.5 × 10 ^It has a structure dispersed at a density of ⁶ / mm ² or more.

C + N: 0.005 to 0.03% and C / N <0.
For the hot-rolled steel sheet having the composition of No. 6, the ductile-brittle transition temperature (vTre) and precipitates (carbide, nitride,
The relationship with the dispersion density of one or more of the carbonitrides was determined and is shown in FIG. The ductility of the heat affected zone
The brittle transition temperature (vTre) is 1.2 mm for each hot-rolled steel sheet.
Semi-automatic MI using 309 type welding wire of φ
Weld joints are produced by G welding, and Charpy impact test specimens (penetration notches) are sampled from the heat affected zone (2.0 mm from the bond) (cross bond) in accordance with JIS Z2204 and subjected to an impact test. It is what I asked for. The test was conducted at + 10 ° C. to −60 ° C. at 10 ° C. intervals (each temperature was repeated 5 times) to determine the ductile-brittle transition speed.

Further, a test piece was collected from each hot-rolled steel sheet,
Electrolysis in a non-aqueous solvent electrolyte of acetylacetone and tetramethylene ammonium, the surface is uniformly electroplated at 1 to 3 × 10 ⁶ ° C / m ² by the so-called SPEED method, and then, using a scanning electron microscope, magnification of 10,000 times. Were observed in each of 50 fields, and the size and dispersion density of the precipitate were measured. In addition, it was identified that the precipitate was a mixture of carbide, nitride and carbonitride. Also, using the maximum length and minimum length of each precipitate measured for each hot-rolled steel sheet, (maximum length + minimum length) /
2 was calculated first, the average was taken in one visual field, and the average was similarly calculated for 50 visual fields, and the average value was taken as the average diameter of the precipitate of the hot-rolled steel sheet.

FIG. 2 shows that C + N: 0.005 to 0.03%, C / N <0.6, and that the average diameter of the precipitates is 0.
It can be seen that the toughness of the heat-affected zone of a hot-rolled steel sheet having a diameter of 3 μm or less is markedly improved when the dispersion density of precipitates is 0.5 × 10 ⁶ / mm ² or more. On the other hand, if the average diameter of the precipitates exceeds 0.3 μm (marked with ○), the improvement in toughness of the weld heat affected zone becomes insignificant.

In view of the above, in the present invention, in order to further improve the toughness of the welded portion, the composition having the above-mentioned range of the present invention is used, and further, a carbide having an average diameter of 0.3 μm or less, One or more of nitrides and carbonitrides were dispersed and precipitated at a density of 0.5 × 10 ⁶ pieces / mm ² or more to form a structure. Next, a preferred method for producing the hot-rolled martensitic stainless steel sheet of the present invention will be described.

First, the molten steel having the above-described composition is melted in a commonly known melting furnace such as a converter or an electric furnace, and then is subjected to a known refining such as a vacuum degassing (RH method), a VOD method, and an AOD method. It is preferred that the steel material (slab) is refined by a method and then cast into a slab or the like by a continuous casting method or an ingot-making method. The slab is then heated, turned into a sheet bar by hot rough rolling, and then turned into a hot-rolled steel sheet that is subjected to hot finish rolling. The heating temperature of the hot rolling is not particularly limited, but if the heating temperature is too high, crystal grains are coarsened,
It deteriorates toughness and workability. Therefore, the heating temperature is 13
The temperature is preferably set to 00 ° C. or lower. In the hot rolling step, it is sufficient that a hot-rolled steel sheet having a desired thickness can be obtained,
Although the hot rolling conditions are not particularly limited, it is preferable that the rough rolling end temperature (RDT) be 1000 to 1150 ° C. from the viewpoint of defining the size of precipitates by controlling hot rolling temperature. The finish temperature (FDT) of the hot finish rolling is preferably 700 ° C. or more from the viewpoint of securing strength and toughness. However, when improvement of workability, ductility and surface properties is required, FD
It is preferable that T be 820 ° C. or more and 1000 ° C. or less.

After the completion of the hot finish rolling, preferably for 5.0 s
Cooling is started within 5 minutes, and the cooling rate is 600 ~
It is preferable to cool to 750 ° C, wind it up in a coil in the range of 600 to 750 ° C, and gradually cool to 200 ° C (50 ° C / h or less). Next, the rolled hot-rolled steel sheet is preferably subjected to hot-rolled sheet annealing in order to soften the martensite phase by tempering. For hot-rolled sheet annealing, annealing temperature: 600 to 780
C. and holding time: 1.0 to 25 hours are preferred from the viewpoint of improving processability and securing ductility. After the hot-rolled sheet annealing,
It is preferable from the viewpoint of softening that the temperature range from the annealing temperature to 200 ° C. is gradually cooled at 50 ° C./h or less.

After gradual cooling, the scale may be removed by pickling or the like, and the surface may be adjusted to a desired surface property by polishing or the like.

[0035]

EXAMPLE Molten steel having the composition shown in Table 1 was smelted in a converter-secondary refining process and made into a slab by a continuous casting method. After reheating these slabs to 1200 ° C, they were subjected to three passes of hot rough rolling with a final rolling reduction of 30 to 45%, followed by seven passes of hot rolling at a final finishing temperature of 860 to 960 ° C. Finish rolling,
After rolling, cooling rate: 0.1-30 ° C / s within 1-30s
After the quenching process was subjected to ℃ below the A ₁ transformation point, winding it takes to obtain a 2.0mm thick hot rolled steel sheet (steel strip). In addition, hot-rolled steel sheets (steel strips) having various thicknesses of 1.2, 3.0, and 7.0 mm were also produced for welding tests. In addition, a part was left to cool by hot finish rolling. Table 2 shows the hot rolling conditions.

These hot-rolled steel sheets were further subjected to hot-rolled sheet annealing and further pickling. The hot-rolled sheet annealing was 690
After maintaining at ℃ × 10h, slowly cool down to 200 ℃ (cooling rate: 10 ℃ /
h). Specimens were sampled from these hot-rolled steel sheets and subjected to tensile tests and impact tests to investigate the properties of the base material. Table 3 shows the results.

In addition, the size, dispersion density, and type of the precipitates precipitated in the steel sheets were examined for these hot-rolled steel sheets. The cross section of the hot-rolled steel sheet in the L direction is uniformly treated with a so-called SPEED method in which electrolysis is performed in a non-aqueous solvent electrolyte of acetylacetone and tetramethylammonium, and the surface is uniformly treated with 1 to 3
After electrolysis at × 10 ⁶ C / m ² , 50 fields were observed at 10,000 times using a scanning electron microscope, the size and number of the precipitates were measured, and the average diameter and dispersion density were determined. (Maximum length + Minimum length) / 2 was calculated from the maximum length and the minimum length of the precipitates measured in each hot-rolled steel sheet, and the calculated average diameter of the precipitates.
These precipitates were electrolyzed in a non-aqueous solvent electrolyte of acetylacetone and tetramethylammonium, and the obtained electrolytic extraction residue was analyzed and identified by X-ray diffraction. Table 3 also shows these results.

Further, for each of these various hot-rolled steel sheets, 1.2 m
m 309 type welding wire, semi-automatic M
A welded joint was prepared by IG welding, and a hardness test, an impact test, and a bending test of the welded portion were performed to evaluate the toughness and workability of the welded portion. The welding conditions were such that the atmosphere gas was 20% CO
₂ -80% Ar (flow rate: 20l / min) and then, the voltage: 25V, Current: 240 A, welding speed: the 8 mm / s, and the one-pass welding.

From these welded joints, a test piece for hardness measurement,
Sub-size Charpy impact test specimen with a thickness of 7.0 mm x width 10 mm x length 55 mm (only hot-rolled steel sheet with a thickness of 7 mm), a bending test piece in accordance with the provisions of JIS Z 2204 (1.2 mm thickness, 2.0 mm thickness, 3.0 mm
Thick, 7.0 mm thick hot-rolled steel sheet). In addition, the impact test piece was made into a notch, and was collected from the cross bond. In the bending test, the bending was performed at 180 ° with a bending radius of r = 1.0 t. Table 3 also shows these results.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

[0044]

[Table 5]

[0045]

[Table 6]

The examples of the present invention are excellent in the strength and toughness of the base material and in the hardness, toughness and bending workability of the weld.
On the other hand, in the comparative examples outside the range of the present invention, either the toughness of the welded portion or the bending workability of the welded portion is deteriorated. On the other hand, in steel sheets No. 8 and No. 9 in which (C + N), the size of the precipitates and the dispersion density are out of the range of the present invention, the workability and toughness of the welded portion are significantly deteriorated. In addition, (C + N) is within the range of the present invention, but the size and / or dispersion density of the precipitates are out of the range of the present invention.
No. 14 and No. 15 have reduced weld toughness. (C +
N), steel sheets No. 13 and No. 1 whose precipitate size and dispersion density are within the range of the present invention but whose C / N ratio is out of the range of the present invention.
4, No.15 cracked even in the bending test of 2.0mm thickness, and the toughness and workability deteriorated remarkably. Further, in steel sheets No. 1 and No. 2 in which the Y value is out of the preferred range of the present invention, the weld toughness is slightly deteriorated. Note that even if cracks occurred in the 7.0 mm thick test piece, the test piece was passed if no cracks occurred in the 3.5 mm and 2.0 mm thick test pieces.

[0047]

According to the present invention, a stainless hot-rolled steel sheet for civil engineering and building structures excellent in weldability and workability can be manufactured at low cost, and has a remarkable industrial effect. According to the present invention, the use of the hot-rolled martensitic stainless steel sheet is expanded, and when the life cycle cost is considered, there is also an effect that the industrial utility value of the hot-rolled martensitic stainless steel sheet is increased.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between weld toughness (Charpy impact test absorbed energy) and C / N ratio.

FIG. 2 is a graph showing a relationship between weld toughness (Charpy impact test transition temperature) and the average diameter and dispersion density of precipitates.

FIG. 3 is a graph showing a relationship between weld toughness (Charpy impact test absorbed energy) and Y value.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Susumu Sato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba

Claims (6)

[Claims] (C + N): 0.005 to 0.03%, C / N <0.6, and Si: 1.0% or less in terms of mass%, C: 0.012% or less, N: 0.02% or less. , Mn: 1.0% or less, P: 0.08% or less, S: 0.01% or less, Cr: 10 to 15%, having a composition of balance Fe and unavoidable impurities, and having an average diameter of 0.3 μm or less. One or more of carbides, nitrides and carbonitrides are 0.5 × 10 ⁶
A hot-rolled stainless steel sheet for civil and architectural structures having excellent workability and weldability, characterized by having a structure dispersed at a density of at least pcs / mm ² . 2. The hot-rolled stainless steel sheet for civil and building structures according to claim 1, wherein the composition satisfies a Y value defined by the following formula (1) of 10.7 or less. Note Y = Cr + Mo + 1.5Si + 0.5Nb + 8Al-Ni-0.5Mn-30 C-30 N-0.5Cu (1) where Cr, Mo, Si, Nb, Al, Ni, Mn, C, N, Cu: Content of each element (% by mass) 3. The composition according to claim 1, further comprising:
2. The method according to claim 1, wherein i: 0.1 to 0.6% is contained.
Or the stainless steel hot-rolled steel sheet for civil engineering or building structure according to 2. 4. In addition to the above composition, C
2. The composition according to claim 1, wherein one or two selected from u: 0.1 to 0.6% and Mo: 0.1 to 0.6% are contained.
4. The hot-rolled stainless steel sheet for civil engineering or building structures according to any one of the above items. 5. The composition according to claim 1, further comprising:
The stainless steel heat for civil engineering and building structures according to any one of claims 1 to 4, wherein one or two selected from i: 0.005 to 0.05% and B: 0.0005 to 0.0050% are contained. Rolled steel sheet. 6. The composition according to claim 1, further comprising:
b: 0.01 to 0.1%, V: one or two kinds selected from 0.01 to 0.1%.
6. A hot-rolled stainless steel sheet for civil engineering or building structure according to any one of the above-mentioned items.