JP3491625B2 - Fe-Cr alloy with excellent initial rust resistance, workability and weldability - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Fe-Cr alloy excellent in initial rust resistance, workability and weldability, and particularly civil engineering requiring initial rust resistance, bending workability and weld toughness. -It is suitable for use as a material for building structures.

[0002]

2. Description of the Related Art Conventional materials for civil engineering and construction have
Mainly used are plain steels such as SS400, high-strength steels such as SM490, and materials obtained by painting or plating these steel materials. However, in recent years, with the diversification of designs, the use of various materials has begun to be examined.

Among them, Fe-Cr alloys having excellent corrosion resistance and designability require almost no maintenance cost for rusting.
From the viewpoint of life cycle cost (LCC), it is an extremely attractive material. In particular, buildings constructed in coastal areas have the problems of short life and increased maintenance costs for corrosion control, and in promoting waterfront development, corrosion resistance and weldability are also high. ,
In particular, the role of Fe-Cr alloys as a corrosion-resistant functional material for civil engineering and building structures, which has excellent initial rust resistance, is highly expected.

The Fe--Cr alloy is SUS430 because of its metallic structure.
Typified by ferritic stainless steel, martensitic typified by SUS410 steel, austenitic typified by SUS 304, duplex stainless steel typified by SUS 329, and precipitation typified by SUS 630. It is roughly classified into hardened steel. Among such various Fe-Cr alloys, what has been conventionally considered as a material for civil engineering / building structures is material strength, corrosion resistance, ease of welding, weld toughness, and versatility in use. Most common is austenitic stainless steel.

Such an austenitic stainless steel is used for civil engineering such as strength, corrosion resistance, fire resistance and weld toughness.
It has properties that sufficiently satisfy the properties required for building materials. However, this austenitic stainless steel contains 1) a large amount of alloying elements such as Ni and Cr,
It is much more expensive than ordinary steel, 2) causes stress corrosion cracking, 3) has a higher coefficient of thermal expansion than ordinary steel, and has a relatively low thermal conductivity, so thermal effects during welding The strain caused by is easy to accumulate, and it is difficult to apply it to members that require high accuracy, so for general-purpose structural materials where ordinary steel or a material coated or plated on ordinary steel was used. It was difficult to apply and there was a problem that the range of application was limited.

Therefore, recently, as an alternative to plated or coated ordinary steel, a low Cr content of 15 mass% or less
The application of the alloy steel containing is being considered for civil engineering and construction materials. For example, civil engineering martensitic stainless steel
An example is application to building materials. The Fe-Cr alloy having a Cr content of 15 mass% or less is, as described above, Fe-Cr containing Ni.
-Not only is the amount of Cr less than that of Ni alloys, but also the amount of Ni is much less, so it is much cheaper, and has a smaller coefficient of thermal expansion and higher thermal conductivity, and corrosion resistance compared to ordinary steel. It has excellent characteristics and has a high yield strength. In addition, martensitic stainless steel contains 15 mass% or more.
There is no concern about σ embrittlement or 475 ° C embrittlement, which is a problem with high Cr alloys containing Cr, and there is no concern about stress corrosion cracking in a chloride environment, which is a problem with austenitic stainless steel. is there.

However, the martensitic stainless steel typified by SUS 410 has a high C content of about 0.1 mass%, and therefore has poor weld toughness and workability, and requires preheating during welding. However, since the welding workability is also inferior, there remains a problem in application to members requiring welding.

As a measure against the above problem, for example, Japanese Patent Publication No. 51
In the −13463 publication, Cr: 10-18 mass%, Ni: 0.1-3.
4 mass%, Si: 1.0 mass% or less and Mn: 4.0 mass% or less, further C: 0.030 mass% or less, N: 0.020
A martensitic stainless steel for welded structures has been proposed in which the performance of the welded portion is improved by reducing the mass% or less and generating a massive martensitic structure in the heat affected zone of the welded material.

In addition, Japanese Patent Publication No. 57-28738 discloses Cr:
l0 to 13.5 mass%, Si: 0.5 mass% or less and Mn: 1.0 to
Contains 3.5 mass%, C: 0.020 mass% or less, N:
After reducing it to 0.020 mass% or less, add 0.1 mass% of Ni.
A martensitic stainless steel for structure, which does not require preheating or postheating before and after welding and is excellent in weld toughness and workability, has been proposed by strictly limiting it to less than 10%.

However, in the technology disclosed in Japanese Patent Publication No. 51-13463 and Japanese Patent Publication No. 57-28738, no measures are taken for the following problems peculiar to civil engineering and construction structural materials. Was leaving a problem with. That is, in consideration of application to civil engineering / construction structure applications, members such as columns and beams are not exposed to a severe environment such as outer wall materials after the completion of the building. However, after being processed into structural members such as pipes and shaped steel at the factory and shipped, they may be left outdoors for a short period such as several months until the construction of the structure is completed. Therefore, improving the initial rust resistance of steel materials and suppressing the occurrence of initial rust that occurs during the construction period after shipping is not only important in terms of appearance, but also in terms of durability of the structure after completion. Is also important. When used as a civil engineering / construction structure material,
Since the requirement for surface properties is low, it is desirable from an economical point of view that it can be used as hot-rolled or as hot-rolled annealed and with the scale adhered to the surface of the steel sheet.
Further, when considering processing into shaped steels having various shapes, there is a great demand for improving the toughness of the steel sheet, particularly the elongation and bending workability of the base steel sheet and the welded portion.

To solve such a problem, Japanese Unexamined Patent Publication No. 11-302796
In the publication, C: 0.005 to 0.1 mass%, Si: 0.05 to 1.5
mass%, Mn: 0.05 to 1.5 mass%, P: 0.04 mass% or less,
S: 0.05 mass% or less, Cr: 10-15 mass%, N: 0.055 ma
ss% or less and (C + N): reduced to 0.1 mass% or less, and further contains one or two kinds of Ni and Cu in a range of 0.1 mass% or more and less than 1.0 mass% with the balance being Fe and There has been proposed a stainless hot-rolled steel strip for a building structure having excellent corrosion resistance and a method for producing the same, which has a composition of inevitable impurities.

Further, in Japanese Patent Laid-Open No. 11-302797, C:
0.005 to 0.1 mass%, Si: 0.05 to 1.5 mass%, Mn: 0.05
-1.5 mass%, P: 0.04 mass% or less, S: 0.05 mass% or less, Cr: 10-15 mass%, N: 0.055 mass% or less, and (C + N): 0.1 mass% or less, and further N
i, Cu 1 type or 2 types, 0.1 mass% or more, 1.0 mass%
The content of Fe in the balance is less than Fe, the balance is Fe and inevitable impurities, and the average Cr per 1 μm of the surface metal layer of the hot-rolled steel strip after mechanical peeling of the scale after hot-rolling.
There has been proposed a stainless hot-rolled steel strip for a building structure, which is excellent in corrosion resistance, and a method for producing the same, which comprises a content of 7 mass% or more.

However, the above-mentioned Japanese Patent Laid-Open No. 11-302796
In the technology disclosed in Japanese Patent Laid-Open No. 11-302797 and JP-A-11-302797, the toughness of steel sheet, There is no sufficient disclosure regarding the method of improving the initial rust resistance without impairing the elongation and bending workability of the base steel sheet and the welded portion, and the improvement thereof has been desired.

In addition, as a method for improving the corrosion resistance, weldability, and toughness of the welded portion of the Fe-Cr alloy, it is possible to improve the purity and, in addition to that, Nb and Ti for fixing carbon and nitrogen as carbides and nitrides. Since the addition of Al is effective, various steels produced by such means have been developed. For example, JP-A-60-13060 discloses a stainless steel whose corrosion resistance is improved by adding Nb, which is a carbon / nitrogen stabilizing element, in addition to Mo, Ni. It has been shown that the addition of Cu, Cu, etc. further improves the corrosion resistance.

However, for example, with regard to steel materials in consideration of welded structural material applications, a technique for effectively improving the initial rust resistance from shipping to construction has not been sufficiently studied, and it has not been examined before. In addition to the previously known techniques of adding alloying elements such as Cu, Ni, Mo, Ti and Nb and reducing C and N, it has been demanded to establish a further improvement method.

[0016]

DISCLOSURE OF THE INVENTION The present invention was developed in view of the above situation, and needless to say, it is excellent in weldability, corrosion resistance, and workability, and is also excellent in initial rust resistance. −
The purpose is to propose a Cr alloy.

[0017]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present inventors have conducted a detailed study on various elements. Paying particular attention to Co, V, and W, the Cr content is 15 ma
In Fe-Cr alloys with less than ss%, the effects of these elements on weldability, weld toughness, and initial rust resistance were investigated. Conventionally, Ni equivalent (for example, = Ni + 30C + 0.5 Mn) is used to reduce crack susceptibility of welds and to secure toughness, initial rust resistance, ductility and workability of steel sheets.
In addition to optimizing Cr and Cr equivalents (eg, = Cr + Mo + 1.5 Si + 0.5 Nb), adjustments of elements such as Cr, MoNi, C, N, Nb, and Ti have been mainly studied. However, with regard to Co, V, and W, the effects on the Cr equivalent and Ni equivalent, despite affecting the initial rust resistance and the stability of the ferrite phase (α phase) and austenite phase (γ phase), No detailed study on the effect of welds and scale on the initial rusting property of the base metal part to which the scale is attached has been made.

In the present invention, the effects of these elements on the phase stability are ascertained, and in particular, Co and V which affect the initial rust resistance near the welded portion and the initial rust resistance of the steel sheet with scale attached. , By examining the effect of W in detail,
The effects of these elements on toughness and initial rust resistance were quantitatively evaluated and the proper range and proper ratio of these elements were clarified.

That is, the following expression (1) X value = Cr + Mo + 1.5 Si + 0.5 Nb + 0.2 V + 0.3 W + 8 Al-Ni-0.6 Co-0.5 Mn-30C-30N-0.5 Cu --- (1) It is possible to evaluate the effect of Co, V, and W on the stabilization of the austenite phase and by extension on the toughness of the weld using the X value, and the composition of the alloy is adjusted so that this value satisfies the specified range. As a result, it has been found that the heat-affected zone of the weld has a substantially martensitic structure and the toughness of the weld is improved. Here, Cr, Mo, S in equation (1)
i, Nb, V, W, Al, Ni, Co, Mn, C, N and Cu mean the content (mass%) of each element.

FIG. 1 is an example of the experimental results that led to this finding, and shows the results of examining the relationship between the X value and the toughness of the welded portion (absorbed energy in the Charpy impact value test). As shown in the figure, by setting the X value to 11.0 or less, the weld toughness is remarkably improved.

Further, the Z value represented by the following equation (2) Z value = (Co + 1.5 V + 4.8 W) --- (2) gives the initial rust resistance of the steel sheet with the welded portion and scale attached. The effects of Co, V, and W on the alloys were investigated, and it was found that for steels whose X value shown in the above formula (1) was adjusted to a predetermined range, By adjusting the composition, it was clarified that the corrosion resistance, particularly the initial rust resistance and the workability are improved in a balanced manner without impairing the toughness of the weld. Here, Co, V and W in the formula (2) mean the contents (mass%) of each element.

FIGS. 2 and 3 are examples of the experimental results that lead to the above findings. The results of examining the relationship between the rust starting point number and the Z value in the base material steel sheet with the welded portion and scale attached are shown. , Respectively. As shown in FIGS. 2 and 3, it can be seen that when the Z value is 0.03 or more, the number of rust starting points sharply decreases and the initial rust resistance is improved.

Further, with respect to the steels adjusted to the above-mentioned components, an examination was conducted focusing on C and N for the purpose of improving the ductility and workability of the welded portion and the base steel sheet. FIG. 1 shows the relationship between the X value and the toughness of the welded portion when the C / N ratio is 0.6 or less and
The case where the / N ratio exceeds 0.6 is shown separately, but as shown in the figure, the weld toughness is superior when the C / N ratio is 0.6 or less.

Further, in FIG. 4, the transition temperature (1 / of the absorbed energy at the temperature at which the ductile fracture surface ratio becomes 100%) was obtained from the C / N ratio, the elongation of the base steel sheet and the Charpy impact value test of the welded portion. The following shows the results of an examination of the relationship with the temperature at which the absorbed energy of 2 is obtained). As is clear from the figure, by adjusting the C / N ratio to 0.6 or less, not only the weld toughness is improved, but also the ductility (elongation) of the base steel sheet is improved and the workability is also improved. I understand. Further, as described later in Examples, adjusting the C / N ratio also improves the toughness of the base steel sheet.

As described above, expensive Ni, Cu, Cr,
The toughness of the welded part is ensured without the addition of extremely large amounts of Mo, Nb and Ti, and the extreme reduction of C and N. Furthermore, the welded part and the resistance of the steel plate with scale attached It has been clarified that the initial rusting property and workability can be improved in a well-balanced manner, and this is an important essence of the present invention.

That is, the gist of the present invention is as follows. 1. C: more than 0.0025 mass%, less than 0.03 mass%, N: more than 0.0025 mass%, less than 0.03 mass%, Si: more than 0.1 mass%, less than 2.0 mass%, Mn: more than 0.1 mass%, less than 3.0 mass%, Cr: More than 8.0 mass%, less than 15 mass%, Al: less than 0.5 mass%, P: less than 0.04 mass%, S: less than 0.03 mass%, Ni: 0.01 mass% or more, less than 3.0 mass%, Co: 0.01 mass% or more, 0.5 less than mass%, V: 0.01mass% or more, 0.5 mass% and less than W: 0.001 mass% or more, and contains less than 0.05 mass%, balance being Fe and unavoidable impurities, below
Fe-Cr excellent in initial rust resistance, workability and weldability, characterized in that the X value represented by the formula (1) is 11.0 or less.
alloy. Record

2. In the above 1, further the following formula (2)
A Fe-Cr alloy excellent in initial rust resistance, workability and weldability, characterized in that the Z value shown by is satisfied with 0.03 ≦ Z value ≦ 1.5. Note Z value = (Co + 1.5 V + 4.8 W) --- (2)

3. In the above 1 or 2, further, C
Fe-Cr alloy excellent in initial rust resistance, workability and weldability, characterized in that the ratio (C / N) of C and N satisfies the range of (C / N) ≦ 0.60.

4. In the above 1, 2 or 3,
Fe excellent in initial rust resistance, workability and weldability, characterized by having a composition containing one or two selected from Cu: less than 3.0 mass% and Mo: less than 3.0 mass%
-Cr alloy.

5. In any one of the above 1 to 4, Ti: less than 0.7 mass%, Nb: less than 0.7 mass%, Ta: 0.7
Fe-Cr excellent in initial rust resistance, workability and weldability, characterized by having a composition containing one or more selected from less than mass% and less than 0.5 mass% Zr.
alloy.

6. In any one of 1 to 5 above, the composition further contains B: 0.0002 mass% or more and 0.002 mass% or less, initial rust resistance,
Fe-Cr alloy with excellent workability and weldability.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, in the present invention, the reason why the component composition of the alloy is limited to the above range will be described. C: more than 0.0025mass%, less than 0.03mass%, N: 0.0025mass
%, Less than 0.03 mass% As is conventionally known, reduction of C and N is effective for improving the toughness and workability of the weld heat affected zone and preventing weld cracks. Further, C and N not only have a great influence on the hardness of the martensite phase, but also cause the deterioration of corrosion resistance due to the formation of a Cr-deficient phase due to the precipitation of carbonitride. Was less than 0.03 mass%. However, in the composition range of the steel of the present invention, reduction of C and N is effective for improvement of weld characteristics, workability, corrosion resistance, etc., but excessive reduction not only increases refining load but also C and N. As the martensite phase softens and the toughness of the welded portion deteriorates due to the formation of coarse ferrite grains, C and N are each made to exceed 0.0025 mass%. A particularly preferred composition range is 0.005 to 0.02 mass% for both C and N.

Si: more than 0.1 mass% and less than 2.0 mass% Si is an element useful as a deoxidizer, but its content is 0.1
When mass% or less, sufficient deoxidizing effect cannot be obtained, while 2.0ma
Excessive addition of ss% or more causes deterioration of toughness and workability.
The Si content was limited to the range of more than 0.1 mass% and less than 2.0 mass%. The range of 0.03 to 0.5 mass% is particularly preferable.

Mn: more than 0.1 mass% and less than 3.0 mass% Mn is an austenite phase (γ phase) stabilizing element, and effectively contributes to the improvement of the toughness of the weld zone by making the weld heat affected zone structure a martensite structure. Further, Mn, like Si, is useful as a deoxidizing agent, so Mn is included in the range of more than 0.1 mass%. However, if added excessively, workability and corrosion resistance due to the formation of MnS will decrease, so 3.0
Limited to less than mass%. Particularly preferably more than 0.1 mass%,
It is within the range of 1.5 mass% or less.

Cr: more than 8 mass% and less than 15 mass% Cr is an element effective for improving the corrosion resistance, but if it is 8 mass% or less, it is difficult to secure sufficient corrosion resistance. Cr is a ferrite phase (α phase) stabilizing element, and addition of 15 mass% or more not only causes deterioration of workability, but also austenite phase (γ
Phase) and the martensite phase cannot be secured in a sufficient amount during welding, resulting in a decrease in strength and toughness of the welded part. Therefore, in the present invention, Cr is more than 8 mass%, 15
The content was set to be less than mass%. In addition, in terms of combining rust resistance, workability, and weldability, a particularly preferable range is
It is 9.0 to 13.5 mass%.

Al: less than 0.5 mass% Al is not only useful as a deoxidizing agent, but also contributes effectively to improving the toughness of the welded portion, but when the content is 0.5 mass% or more, inclusions increase. Since it causes deterioration of mechanical properties,
Al was limited to less than 0.5 mass%. It should be noted that this Al may not be particularly contained.

P: less than 0.04 mass% P is an element which not only deteriorates hot workability, formability and toughness but is also harmful to corrosion resistance.
The effect becomes remarkable when the content is 0.04 mass% or more, so P
Content was controlled to less than 0.04 mass%. It is more preferably 0.025 mass% or less.

S: less than 0.03 mass% S combines with Mn to form MnS and serves as an initial rust initiation point. Further, S is also a harmful element that segregates at the crystal grain boundaries and promotes grain boundary embrittlement, so it is preferable to reduce S as much as possible. Particularly, when the content is 0.03 mass% or more, the adverse effect becomes remarkable, so the content of S is set to be less than 0.03 mass%. More preferably, it is 0.006 mass% or less.

Ni: 0.01 mass% or more and less than 3.0 mass% Ni is an element that improves the ductility and toughness. In the present invention, in particular, the toughness of the heat-affected zone of the weld is improved, and therefore the rust resistance is further improved. To add. However, if the content is less than 0.01 mass%, the effect of addition is poor, while if it is 3.0 mass% or more, not only the effect is saturated, but also the disadvantage of hardening the material occurs, so the Ni content is 0.01 ma.
It was limited to the range of ss% or more and less than 3.0 mass%.

Co: 0.01 mass% or more and less than 0.5 mass%,
V: 0.01 mass% or more, less than 0.5 mass%, W: 0.001 mass
% And less than 0.05 mass% Co, V and W are particularly important elements in the present invention. The addition amount of Co, V, W is 0.01mass%, 0.01
The lower limit is mass%, 0.001mass%. This is the X value or Z
This is because, even if the values satisfy the appropriate range, if the content of each falls below the above lower limit, the effect of composite addition cannot be obtained. On the other hand, with respect to the upper limits, V and W of 0.5 mass% and 0.05 mass% or more, respectively, cause the precipitation of carbides to significantly harden the material.
It was determined to be less than 0.5 mass% and less than 0.05 mass%. Also, Co is added to 0.5 mass% or more, which causes hardening of the steel, so the Co content is limited to less than 0.5 mass%. Although there is a balance with the X value and the Z value, the preferable ranges of these elements are Co: 0.03 to 0.2 mass%, V: 0.05 to 0.2 mass%,
W: 0.005 to 0.02 mass%.

X value = Cr + Mo + 1.5 Si + 0.5 Nb + 0.2 V +
0.3 W + 8 Al-Ni-0.6 Co-0.5 Mn-30C-30N-0.5
Cu: 11.0 or less The X value is one of the most important parameters in the present invention.
The X value is an index for evaluating the influence of each element on the stability of the austenite phase, and particularly Co, which is important in the present invention,
The effects of V and W are accurately evaluated. By adjusting this value to 11.0 or less, the weld heat-affected zone has a substantially martensitic structure, and the weld toughness is improved. In addition,
When a steel plate having a plate thickness of 8.0 mm or more is also taken into consideration, the above X value is more preferably 10.7 or less in order to secure the stability of the austenite phase in the welded portion.

Z value = (Co + 1.5 V + 4.8 W): 0.03 or more and 1.5 or less Furthermore, in the present invention, by limiting the Z value in the range of 0.03 to 1.5, the combined addition of Co, V, and W results. The effect is optimized. This Z value serves as an index of the initial rust resistance of the welded part and the steel plate with scale attached. If this value is less than 0.03 or even one of these elements is missing, the welded part Sufficient initial rust resistance could not be obtained for base steel sheet with oxide scale or oxide scale, and even if the three elements were added together, if the Z value exceeded 1.5, the effect would only reach saturation. However, since the material hardens and the workability deteriorates remarkably, these three elements were made essential additions, and the Z value was limited to the range of 0.03 to 1.5. In addition,
A preferable range of Z value is 0.2 to 0.6 in consideration of workability.

Although the mechanism by which the three elements of Co, V, and W are added in a composite manner improves the initial rust resistance is not clear, it is concentrated on the steel plate surface or scale.
Co, V, and W work effectively, especially by affecting the morphology and scale structure of carbonitride, and also the diffusion of Cr,
It is considered that the initial rust resistance is improved by suppressing the formation of the Cr-free layer and densifying the scale structure.

(C / N): 0.60 or less In the present invention, in addition to the above component adjustment, the ratio of C and N is 0.60.
By the following, the ductility of the weld and the base steel sheet,
The toughness is further improved. The details of the mechanism for improving ductility and toughness by adjusting (C / N) are not clear, but (Fe, Cr) -based carbonitrides, which are thought to particularly affect elongation and bending workability, specifically ( Fe, Cr) ₂₃ C ₆ , (Fe, Cr) ₇ C ₃ , (F
e, Cr) ₃ C, (Fe, Cr) ₂ N, (Fe, Cr) N content ratios and changes in the precipitation morphology. It can be inferred that the improvement effect becomes remarkable when the number increases. Thus, in the steel sheet in which the precipitation form of carbonitride is controlled and the elongation is improved, good bendability can be obtained.

In the present invention, in addition to the above, various elements described below can be appropriately contained. Cu: less than 3.0 mass% Cu not only improves corrosion resistance, but also forms an austenite phase to suppress grain growth in the heat-affected zone of the weld and effectively contributes to improving the toughness of the weld. However, if the content is
When it is 3.0 mass% or more, the hot cracking sensitivity becomes strong and there is a risk of embrittlement, so the content was limited to less than 3.0 mass%. More preferably, it is 0.01 ma at which the effect of improving corrosion resistance becomes apparent.
It is preferable that the lower limit is ss% and the upper limit is 1.0 mass% from the viewpoint of hot cracking.

Mo: less than 3.0 mass% Mo is also an element effective in improving the corrosion resistance. However, when 3.0 mass% or more is added, the X value is increased, the stability of the austenite phase is lowered, and the toughness and workability are remarkably lowered, so the content is limited to less than 3.0 mass%. In addition,
From the viewpoint of balance between corrosion resistance and workability, 0.01 to 0.
The range of 5 mass% is preferable.

Nb: less than 0.7 mass%, Ti: less than 0.7 mass%, Ta: less than 0.7 mass%, Zr: less than 0.5 mass% Ti, Nb, Ta and Zr are all carbonitride forming elements, During the heat treatment and heat treatment, it suppresses the precipitation of Cr carbonitrides at the grain boundaries and effectively acts to improve the corrosion resistance. Ti is also an element effective in improving hardenability. However, Ti, N
When b and Ta are 0.7 mass% or more, and Zr is 0.5 mass% or more, the material is significantly hardened.
% And less than 0.5 mass%. A more preferable range is 0.001 to 0.3 mass% in each case.

B: 0.0002 mass% or more and 0.002 mass% or less B is also an element effective for improving the hardenability of steel. However, if the content is less than 0.0002 mass%, the effect of addition is poor, while if it exceeds 0.002 mass%, the material becomes hard and the toughness and workability are impaired, so 0.0002 to 0.002 ma
The range was ss%. It is preferably in the range of 0.0005 to 0.001 mass%.

Next, a preferred method for producing the Fe-Cr alloy of the present invention will be described. First, the molten steel adjusted to the above-mentioned suitable component composition is melted in a generally known melting furnace such as a converter or an electric furnace, and then vacuum degassing (RH method), VOD method, AO
It is refined by a known refining method such as Method D, and then cast into a slab or the like by a continuous casting method or an ingot-casting method to obtain a steel material. The steel material is then heated and made into a hot rolled steel sheet by a hot rolling process. The heating temperature in the hot rolling step is not particularly limited, but if the heating temperature is too high, it causes coarsening of the crystal grains and deteriorates the toughness and workability.
The temperature is preferably 00 ° C or lower. Further, in the hot rolling process, it is sufficient to obtain a hot-rolled steel sheet having a desired plate thickness, and the hot rolling conditions are not particularly limited, but the finishing temperature of hot rolling should be 700 ° C or higher for strength and toughness. Is preferable in terms of ensuring However, when workability, ductility, and even good surface properties are required, the finishing temperature in hot rolling is preferably about 820 ° C or higher and 1000 ° C or lower. The coiling temperature is 680 ℃ or less when tempering annealing is performed and 690 to 750 ℃ when annealing is omitted.
Is preferred.

After the completion of hot rolling, in the case where the structure becomes a martensite phase and is hard, it is preferable to perform hot-rolled sheet annealing in order to soften the martensite phase by tempering. This hot-rolled sheet annealing is preferably performed at an annealing temperature of 650 to 750 ° C. and a holding time of 3 to 20 hours from the viewpoint of not only softening but also improving workability and ensuring ductility. After annealing the hot-rolled sheet, it is more preferable from the viewpoint of softening that the temperature range of 600 to 730 ° C is gradually cooled at a cooling rate of 50 ° C / h or less. Also,
The steel sheet after hot rolling or after hot rolling annealing may be used as a product sheet after the scale is removed by shot blasting, pickling, etc., if necessary, or after being further adjusted to a desired surface texture by polishing or the like. If necessary, a rust preventive agent or the like can be applied. The steel sheet according to the present invention can be processed into shaped steels of various shapes by welding and bending. Further, the component steel according to the present invention, such as steel plate and shaped steel produced by hot rolling, further steel bar,
It can be applied to various steel materials that can be used in the fields of civil engineering and construction.

[0051]

EXAMPLES Molten steels having the chemical compositions shown in Tables 1, 2, 3, and 4 were melted in a converter-secondary refining process and made into slabs by a continuous casting method. These slabs are reheated to 1200 ° C and then subjected to 6 passes of rough rolling to make the final pass reduction rate of 30 to 45% of rough rolling, followed by 7 passes of final finishing temperature of 840 to 990 ° C. By finish rolling, a hot rolled steel sheet with a thickness of 4.0 mm was obtained. In addition, for the Charpy impact value test and bending test of the welded part,
Furthermore, hot-rolled steel sheets with various thicknesses of 2.0, 5.0, 8.0 and 12.0 mm were also prepared. These hot-rolled steel sheets were subjected to hot-rolled sheet annealing, descaled by shot blasting and pickling, and then subjected to tensile test, impact value test, bending test and corrosion resistance test. In addition, about one part, the corrosion resistance test was done without performing a descaling process, and the initial rust resistance in the state which the scale adhered was evaluated. The hot-rolled sheet was annealed at 670 ° C for 10 hours and then gradually cooled to 200 ° C (average cooling rate: 10 ° C / h). The tensile test piece is made from a steel plate with a plate thickness of 4.0 mm so that the tensile direction is the rolling direction.
A JIS No. 13 B test piece (JIS Z 2201) was sampled and used for the test.

Further, with respect to the steel plates having each of these plate thicknesses,
Using 1.2mmφ Y309 and Y309L type welding wire,
Welded joint is made by semi-automatic MIG welding machine and welded part
Hardness test, impact test, and bending test of the weld toughness
The workability, workability and corrosion resistance were evaluated. Welding conditions
Is atmosphere gas: 100% Ar (flow rate: 20 l / min) or
(20% CO ₂ + 80% Ar) (Flow rate: 20 l / min) or 100%
CO₂ (Flow rate: 11 l / min), voltage: 20-30V, current: 200
~ 280 A, welding speed: 1-pass welding at 1-20 mm / s
It was The welding direction is perpendicular to the rolling direction in hot rolling.
did.

Among the obtained welded joints, a hardness test piece, a sub-size Charpy impact value test piece according to JIS Z 2202 (thickness: 10 mm, width: 5.0 mm, length:
55 mm) was collected. In addition, the notch of the impact value test piece is 2 mm penetrating in the width direction of the test piece (5.0 mm: plate thickness direction of steel plate).
A V-notch was formed, and as shown in FIG. 5, it was sampled from a cross bond portion (a position where the ratio a: b of the weld metal portion and the weld heat affected zone was 1: 1 with the fusion line sandwiched therebetween). In addition, the bending test pieces were prepared by removing the surplus and root beads from the welded parts of each plate, and then the front and back bending test pieces (thickness: steel plate thickness, width: 40 m according to JIS Z 3122).
m, length: 200 mm). In addition, JIS stipulates that the thickness of the test piece shall be 10 mm when the plate thickness exceeds 10 mm, but the thickness of 12.0 mm thick material is not reduced.
The thickness of the test piece was 12.0 mm. In the bending test, the bending radius R
Is a condition that is stricter than JIS, R = 1.0 t (t: steel plate thickness), and after performing a 180 ° bending test, the surface is observed with a magnifying glass and there is crack (x) or no crack (○ )
The bending workability of the welded portion was evaluated by.

Further, as an initial rusting test, a 4.0 mass-thick steel sheet (anneal pickling material, scale adhering material and weld joint) was subjected to a spray test of 3.5 mass% NaCl (30 ° C.) for 6 hours. The sample after the test was evaluated by immersing it in a diammonium citrate solution (60 ° C.) and removing the rust by brush cleaning, and then measuring the number of rust starting points and the depth of the holes.
Regarding the welded portion, the starting point of rust generated in the weld heat affected zone was evaluated by the number of starting points per bead unit length (pieces / bead 10 cm) and its depth (maximum 10 points average). The obtained results are summarized in Tables 5, 6, 7, and 8.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

[Table 4]

[0059]

[Table 5]

[0060]

[Table 6]

[0061]

[Table 7]

[0062]

[Table 8]

As shown in Tables 5, 6 and 7, each of the invention examples satisfying the component composition range of the present invention not only has excellent tensile properties and impact toughness in the state of a hot rolled annealed sheet, but also welds. The parts also have excellent weld toughness, workability, and corrosion resistance. In particular, in the steel with the (C / N) ratio adjusted to 0.6 or less, in addition to the elongation and toughness of the base metal, the toughness and bending workability of the welded portion are higher than those when the (C / N) exceeds 0.6. , Has been improved further. Further, as shown in Table 8, in the invention examples, the number of rust starting points is small and the pit depth is small not only on the welded portion but also on the surface of the base material to which the scale is attached. It can be seen that it has rusting properties.

[0064]

As described above, according to the present invention, by optimizing the alloy components, it goes without saying that the weldability, weld zone toughness, and workability are excellent, and Fe having excellent initial rust resistance is also obtained.
-Cr alloy can be obtained. Further, according to the present invention,
The range of use of inexpensive Fe-Cr alloys, including its use as a material for civil engineering and building structures, has expanded greatly, and it can be said that its industrial utility value is extremely large when considering life cycle costs.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between an X value and a weld zone toughness (absorbed energy in a Charpy impact value test) using a (C / N) ratio as a parameter.

FIG. 2 is a graph showing the relationship between the Z value and the number of rust starting points of the welded portion.

FIG. 3 is a graph showing the relationship between the Z value and the number of rust initiation points of the base steel sheet.

FIG. 4 is a graph showing the relationship between the (C / N) ratio, the elongation of the base steel sheet, and the transition temperature in the Charpy impact value test of the welded portion.

FIG. 5 is a diagram showing a procedure for collecting impact value test pieces.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Ota 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Inside Kawasaki Steel Corporation Technical Research Institute (56) Reference JP 2001-107141 (JP, A) JP H11 -80881 (JP, A) JP-A-8-3642 (JP, A) JP-A-6-41696 (JP, A) JP-A-2001-152295 (JP, A) JP-A-2001-152296 (JP, A) (JP-A) 58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00

Claims (6)

(57) [Claims] 1. C: more than 0.0025 mass%, less than 0.03 mass%, N: more than 0.0025 mass%, less than 0.03 mass%, Si: more than 0.1 mass%, less than 2.0 mass%, Mn: more than 0.1 mass%, 3.0 mass %, Cr: more than 8.0 mass%, less than 15 mass%, Al: less than 0.5 mass%, P: less than 0.04 mass%, S: less than 0.03 mass%, Ni: 0.01 mass% or more, less than 3.0 mass%, Co: 0.01 mass% or more to less than 0.5 mass%, V: 0.01 mass% or more, 0.5 mass% and less than W: 0.001 mass% or more, and contains less than 0.05 mass%, balance being Fe and unavoidable impurities, below
Fe-Cr excellent in initial rust resistance, workability and weldability, characterized in that the X value represented by the formula (1) is 11.0 or less.
alloy. Record 2. The method according to claim 1, further comprising the following formula (2):
An Fe-Cr alloy excellent in initial rust resistance, workability and weldability, characterized by satisfying a Z value of 0.03≤Z value≤1.5. Note Z value = (Co + 1.5 V + 4.8 W) --- (2) 3. The method according to claim 1 or 2, further comprising C
Fe-Cr alloy excellent in initial rust resistance, workability and weldability, characterized in that the ratio (C / N) of C and N satisfies the range of (C / N) ≦ 0.60. 4. The method according to claim 1, 2, or 3,
Fe excellent in initial rust resistance, workability and weldability, characterized by having a composition containing one or two selected from Cu: less than 3.0 mass% and Mo: less than 3.0 mass%
-Cr alloy. 5. The method according to claim 1, further comprising one of Ti: less than 0.7 mass%, Nb: less than 0.7 mass%, Ta: less than 0.7 mass% and Zr: less than 0.5 mass%. Alternatively, a Fe-Cr alloy excellent in initial rust resistance, workability and weldability, characterized by having a composition containing two or more kinds. 6. The initial rust resistance as set forth in any one of claims 1 to 5, which further comprises B: 0.0002 mass% or more and 0.002 mass% or less.
Fe-Cr alloy with excellent workability and weldability.