JP4893866B2 - Structural stainless steel plate having excellent corrosion resistance of welded portion and method for producing the same - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a structural stainless steel plate excellent in welded portion corrosion resistance suitable as a material for body use of a freight car (rail wagon) carrying, for example, coal or iron ore, and a method for producing the same.

  Stainless steel is often used as a body material for freight cars (rail wagons) that carry coal and iron ore. Since mined coal contains a large amount of sulfur, rail wagon body materials are required to have sulfuric acid corrosion resistance, particularly intergranular corrosion resistance of welds.

  As stainless steel having both corrosion resistance and weldability, for example, Patent Document 1 discloses a Ti-containing ferritic stainless steel having excellent welded portion toughness. However, the technique of Patent Document 1 has a problem that the toughness and corrosion resistance of the welded portion are not sufficient because the component design is performed so that the structure of the welded portion becomes a ferrite phase.

  On the other hand, in Patent Document 2 and Patent Document 3, by controlling the phase fraction at high temperature, an appropriate amount of martensite phase is generated in the welded portion, thereby improving the workability and corrosion resistance of the welded portion. Technology is disclosed. Patent Document 4 discloses stainless steel suitable for a welding method using carbon dioxide gas. In addition, one of the inventors of the present invention previously proposed a structural stainless steel sheet that has improved the corrosion resistance of the welded portion by optimizing the component composition using parameters that can accurately predict the structure of the welded portion ( Patent Document 5).

JP-A-3-249150 JP 2002-167653 A JP 2009-13431 A JP 2002-30391 A JP 2009-280850 A

  However, in the techniques disclosed in these Patent Documents 2 to 5, the examination regarding the optimum component range is not always sufficient. In particular, they are hardly considered for manufacturability, and cracking at the slab stage and surface defects called hege are remarkable, and it is difficult to avoid an increase in cost due to a decrease in yield. is there.

  This invention is made | formed in view of this situation, Comprising: It aims at providing the stainless steel plate for structure which can be manufactured cheaply and highly efficiently, and was excellent in the corrosion resistance of a welding part, and its manufacturing method.

  As a result of earnest research to solve the above problems, one of the present inventors has found that if the content of chemical components, particularly Mn and Ti, and the balance of each component are adjusted to an appropriate range, Cr deficiency near the grain boundary The fact that intergranular corrosion caused by the above can be suppressed and that the weld heat-affected zone can be a structure mainly composed of martensite has been proposed, and a parameter (F value) as shown in Patent Document 5 has been proposed. . And based on these findings, the present inventors have continued detailed studies especially on manufacturability. As a result, in addition to containing an appropriate amount of Al, V, Ca and O are reduced to a predetermined range or less, As a new parameter indicating the quality of manufacturability, it has been found that by setting the FFV value to an appropriate range, slab cracks and inclusion-induced scabs (surface defects) can be significantly reduced, and the present invention is completed. It came.

That is, this invention is mass%, C: 0.01-0.03%, N: 0.01-0.03%, Si: 0.10-0.40%, Mn: 1.5-2 0.5%, P: 0.04% or less, S: 0.02% or less, Al: 0.05 to 0.15%, Cr: 10 to 13%, Ni: 0.5 to 1.0%, Ti : 4 × (C + N) (however, C and N indicate their content (mass%)) or more and 0.3% or less, V: 0.05% or less, Ca: 0.0030% or less , O: Restricted to 0.0080% or less, and further, F value and FFV value represented by the following formula satisfy F value ≦ 11, FFV value ≦ 9.0, and the balance is made of Fe and inevitable impurities The structural stainless steel plate excellent in the corrosion resistance of a welding part characterized by this is provided.
F value = Cr + 2 * Si + 4 * Ti-2 * Ni-Mn-30 * (C + N)
FFV value = Cr + 3 * Si + 16 * Ti + Mo + 2 * Al-2 * Mn-4 * (Ni + Cu) -40 * (C + N) + 20 * V
However, in these formulas, each element symbol is the content (mass%) of these elements.

  Moreover, this invention provides the structural stainless steel plate excellent in the corrosion resistance of a welding part characterized by containing Cu: 1.0% or less further by the mass% in addition to the said component.

  The present invention also provides a structural stainless steel sheet excellent in welded portion corrosion resistance, characterized by containing Mo: 1.0% or less in addition to the above components.

Moreover, this invention is a mass%, C: 0.01-0.03%, N: 0.01-0.03%, Si: 0.10-0.40%, Mn: 1.5-2 0.5%, P: 0.04% or less, S: 0.02% or less, Al: 0.05 to 0.15%, Cr: 10 to 13%, Ni: 0.5 to 1.0%, Ti : 4 × (C + N) (however, C and N indicate their content (mass%)) or more and 0.3% or less, V: 0.05% or less, Ca: 0.0030% or less , O: Restricted to 0.0080% or less, and further, F value and FFV value represented by the following formula satisfy F value ≦ 11, FFV value ≦ 9.0, and the balance is made of Fe and inevitable impurities After heating the steel slab having a composition to a temperature of 1100 to 1300 ° C., at least a rolling with a rolling reduction of 30% or more in a temperature range exceeding 1000 ° C. After performing hot rolling including hot rough rolling performed over a pass or after performing the hot rolling, annealing is performed without annealing the hot-rolled sheet or at a temperature of 600 to 1000 ° C. The present invention provides a method for producing a structural stainless steel sheet having excellent weld corrosion resistance.
F value = Cr + 2 * Si + 4 * Ti-2 * Ni-Mn-30 * (C + N)
FFV value = Cr + 3 * Si + 16 * Ti + Mo + 2 * Al-2 * Mn-4 * (Ni + Cu) -40 * (C + N) + 20 * V
However, in these formulas, each element symbol is the content (mass%) of these elements.

  Moreover, this invention provides the manufacturing method of the structural stainless steel plate excellent in the weld part corrosion resistance characterized by containing Cu: 1.0% or less further by the mass% in addition to the said component.

  Moreover, this invention provides the manufacturing method of the structural stainless steel plate excellent in the corrosion resistance of a welding part characterized by containing Mo: 1.0% or less further by the mass% in addition to the said component.

  According to the present invention, it is possible to produce a structural stainless steel plate excellent in welded portion corrosion resistance, which can be produced at low cost and with high efficiency, for example, suitable as a body use material of a freight car (rail wagon) carrying coal or iron ore. .

It is a graph which shows the relationship between a FFV value and a surface defect incidence. It is an optical microscope photograph which shows the example of observation when deep pit-like corrosion is recognized in the welding heat-affected zone of the test piece cross section after a sulfuric acid-copper sulfate corrosion test.

Hereinafter, the present invention will be described in detail.
First, the component composition of the present invention will be described. In the following description,% display is mass%.

C: 0.01-0.03%
・ N: 0.01-0.03%
C and N must each be contained in an amount of 0.01% or more in order to obtain the strength required for a structural stainless steel plate. On the other hand, when the content of C and N exceeds 0.03%, Cr carbide or Cr carbonitride tends to precipitate, and the corrosion resistance, particularly the corrosion resistance of the weld heat affected zone is lowered. Further, the weld heat affected zone is hardened and the toughness is also lowered. For this reason, the C and N contents are both in the range of 0.01 to 0.03%. More preferably, C ranges from 0.015 to 0.025%, and N ranges from 0.012 to 0.02%.

・ Si: 0.10 to 0.40%
Si is an element used as a deoxidizing agent, and it is necessary to contain 0.10% or more in order to obtain the effect. On the other hand, when the content exceeds 0.40%, the toughness of the hot-rolled steel sheet is lowered. For this reason, Si content shall be the range of 0.10-0.40%. Preferably, the lower limit is 0.20% and the upper limit is 0.30%.

・ Mn: 1.5-2.5%
Mn is an element useful as a deoxidizer and as a strengthening element for securing the necessary strength as a structural stainless steel plate, and is also an austenite stabilizing element at high temperatures. In the present invention, it is an important element for controlling the microstructure of the weld heat affected zone to a martensite structure having a desired volume ratio. In order to exert such an effect, the content is required to be 1.5% or more. On the other hand, even if the content exceeds 2.5%, not only the effect is saturated, but the content becomes excessive and the toughness is lowered, and the descaling property in the production process is lowered and the surface properties are adversely affected. In addition, the alloy cost also increases. For this reason, content of Mn shall be 1.5 to 2.5% of range. More preferably, it is 1.8 to 2.5% of range. More preferably, it is 1.85 to 2.0% of range.

-P: 0.04% or less P is preferably smaller in terms of hot workability, and the allowable upper limit of the content is 0.04%. More preferably, it is 0.035% or less.

S: 0.02% or less S is preferably smaller in terms of hot workability and corrosion resistance, and the allowable upper limit of the content is 0.02%. Preferably it is 0.005% or less.

-Al: 0.05-0.15%
Al is generally contained for deoxidation, but in the present invention, it is found that it works effectively to suppress the production of cracks, particularly at the slab stage, and exerts such a function. Therefore, an appropriate amount is included. In order to suppress the occurrence of slab cracking, it is necessary to reduce V, Ca, and O and further optimize the FFV value, as described later, in addition to Al content. The mechanism by which slab cracking is improved by the inclusion of Al is not necessarily clear, but is presumed to be due to the effects of optimizing the phase fraction and controlling the inclusion form. In order to acquire such an effect, it is necessary to contain 0.05% or more of Al. On the other hand, when the content exceeds 0.15%, a large Al-based inclusion is generated and causes surface defects. For this reason, the content of Al is set to a range of 0.05 to 0.15%. More preferably, it is 0.080 to 0.150% of range. More preferably, it is 0.085 to 0.120% of range.

・ Cr: 10-13%
Cr is an essential element for forming a passive film and ensuring the corrosion resistance, particularly the corrosion resistance of the weld heat affected zone. In order to obtain the effect, it is necessary to contain 10% or more. On the other hand, if Cr is contained in excess of 13%, not only the cost is increased, but it becomes difficult to secure a sufficient austenite phase at a high temperature in the welded portion, and the amount necessary for the welded heat affected zone after welding is increased. It becomes difficult to obtain a martensitic structure of the rate. As a result, the intergranular corrosion resistance is lowered in the weld heat affected zone. Therefore, the Cr content is in the range of 10 to 13%. Preferably, it is 10.5 to 12.5%.

Ni: 0.5-1.0%
Ni is contained in an amount of 0.5% or more for the purpose of ensuring strength and toughness. On the other hand, Ni is an expensive element, and its upper limit is set to 1.0% from the viewpoint of economy. Ni is an austenite stabilizing element at a high temperature, similar to Mn, and is useful in controlling the microstructure of the weld heat affected zone to a martensitic structure having a desired volume fraction. Since the effect can be sufficiently obtained by the addition of Mn, the Ni content is suitably in the range of 0.5 to 1.0%. More preferably, it is 0.60 to 1.0% of range. More preferably, it is 0.60 to 0.90% of range.

Ti: 4 × (C + N) or more, 0.3% or less Ti is an important element for obtaining excellent weld corrosion resistance in the present invention, and particularly improves the intergranular corrosion resistance of the weld heat affected zone. It is an essential element. Ti precipitates and fixes C and N in steel as Ti carbide, nitride, or carbonitride (hereinafter, three types of carbide, nitride, and carbonitride are collectively referred to as carbonitride). It has the effect of suppressing the formation of Cr carbonitrides and the like. In the present invention, the weld heat-affected zone of the steel sheet has a structure composed of ferrite and martensite. However, in terms of corrosion resistance, the problem is a decrease in corrosion resistance in the ferrite phase part accompanied by precipitation of carbonitrides and the like during cooling. is there. In the steel sheet according to the present invention, Cr deficiency is generated in the vicinity of the grain boundary due to precipitation of Cr carbonitride or the like in the weld heat-affected zone during welding, and particularly the intergranular corrosion resistance in the ferrite phase portion is reduced. This problem is solved by containing Ti. In order to exert such effects, the Ti content needs to be 4 × (C + N) or more (however, C and N indicate their content (mass%)). On the other hand, even if it is contained in a large amount exceeding 0.3%, the effect is not only saturated, but a large amount of Ti carbonitride is precipitated in the steel, leading to deterioration of toughness. For this reason, content of Ti shall be 4 * (C + N) or more and 0.3% or less. More preferably, it is in the range of 0.180 to 0.230%, and it is effective to reduce C and N so that the Ti content simultaneously satisfies 4 × (C + N) or more.

  In the present invention, it is important to reduce V, Ca, and O as follows in order to suppress productivity, particularly cracking at the slab stage and generation of scabs (surface defects) caused by inclusions. is there.

V: 0.05% or less V is often contained as an impurity such as Cr raw material, and may be included unintentionally, but in order to suppress the occurrence of cracks particularly in the slab stage, It is necessary to strictly control the content. From such a viewpoint, the V content needs to be 0.05% or less. A preferred range is 0.03% or less, and a more preferred range is less than 0.03%. By setting the content to 0.01% or less, a greater cracking suppression effect can be obtained, but it is economically disadvantageous because raw material selection is required.

-Ca: 0.0030% or less Ca generates inclusions having a low melting point, and causes surface defects caused by inclusions in particular. For this reason, in this invention, it is necessary to restrict | limit the content severely, and the upper limit shall be 0.0030%. The Ca content is preferably as low as possible, and is preferably 0.0010%, and more preferably 0.0002% or less, but it is economically disadvantageous because it requires selection of raw materials.

O: 0.0080% or less O is required to reduce the content in order to suppress generation of oxide inclusions and ensure high productivity, and the upper limit is set to 0.0080%. . Preferably, it is 0.0060% or less.

  Furthermore, in this invention, corrosion resistance and productivity are improved greatly by making the F value and FFV value shown below into an appropriate range.

・ F value ≦ 11
F value is expressed as Cr + 2 × Si + 4 × Ti-2 × Ni-Mn-30 × (C + N) (where each element symbol is the content (% by mass) of these elements), and the welding heat during welding It is a parameter for estimating the microstructure of the affected part, more specifically, a parameter for estimating the volume ratio of the martensite structure (remaining ratio of the ferrite structure). In a part exposed to a high temperature such as a weld heat affected zone, a part thereof is transformed into austenite (or a part thereof is δ ferrite), and this phase is transformed into martensite during the cooling process. The ratio is affected by the quantitative balance between the ferrite stabilizing element (ferrite-forming element) and the austenite stabilizing element (austenite-generating element). Elements with positive coefficients (Cr, Si, Ti) in the formula showing the F value are ferrite stabilizing elements, and elements with negative coefficients (Ni, Mn, C, N) are austenite stabilizing elements. That is, as the F value increases, the ferrite structure tends to remain (the volume ratio of the ferrite structure is large, that is, the volume ratio of the martensite structure decreases), and as the F value decreases, the ferrite structure hardly remains (the volume ratio of the ferrite structure is small). That is, the volume ratio of the martensite structure is large.

  In Patent Document 5, the relationship between the F value and the volume ratio of the martensitic structure of the weld heat affected zone is investigated, and the corrosion resistance in the vicinity of the weld heat affected zone is evaluated by a sulfuric acid-copper sulfate corrosion test. In the present invention, the F value is set to 11 or less (martensite volume ratio: 40% or more) in order to improve the corrosion resistance of the weld heat-affected zone as in the case of Patent Document 5 in the present invention. To do. The F value is preferably 10.5 or less (martensite volume ratio 60% or more), more preferably 10 or less. In addition, it is preferable that the minimum of F value shall be 5.0 or more from a viewpoint of the corrosion resistance of a welding part. A more preferable range is 6.0 or more.

-FFV value ≤ 9.0
FFV value is Cr + 3 * Si + 16 * Ti + Mo + 2 * Al-2 * Mn-4 * (Ni + Cu) -40 * (C + N) + 20 * V (however, each element symbol is content (mass%) of these elements) In the present invention, it is newly derived as an index indicating manufacturability. This FFV value takes into account the phase balance during hot rolling, and the value should be reduced after adjusting the components as described above, especially by restricting the Al content and the upper limit of V, Ca, and O. Thus, the occurrence of surface defects due to cracks and inclusions in the slab stage can be remarkably reduced. A major feature of the present invention is that it has succeeded in greatly reducing the yield drop due to the occurrence of surface defects by optimizing a new parameter that takes into account the amount of Al that was not taken into account when the F value was devised. It is. Although the mechanism for improving the manufacturability by optimizing the FFV value is not necessarily clarified, the manufacturability is remarkably improved by setting the FFV value to 9.0 or less. Therefore, the FFV value is set to 9.0. The following. Preferably it is 8.5 or less. In order to reduce the FFV value, it is effective to reduce the Cr amount or increase the C and N amounts. However, if this is done, there is a concern that the corrosion resistance may be lowered. For this reason, the lower limit of the FFV value is preferably 5.0 or more. A more preferable range is 6.0 or more.

In the steel sheet of the present invention used in the state of a hot rolled sheet or a hot rolled annealed sheet, it is important to control cracks and inclusions at the slab stage in order to reduce surface defects. The occurrence of surface defects is not only the appearance of cracks and dents that greatly reduce the yield, but it can also be the starting point of rust generation, so when shipping as a product, the target part must be cut off It is. In addition, although Mo, V, and Cu are included in the above formula of the FFV value, these may not be contained in the steel, and in the case where these are not contained, the component not contained is defined as 0%. FFV value is calculated.

FIG. 1 shows the relationship between the FFV value and the surface defect occurrence rate. It can be seen that the occurrence rate of the defects can be remarkably suppressed by setting the FFV value calculated from the length of the portion where the defects are generated to an appropriate range of 9.0 or less with respect to the total coil length.

  In the present invention, in addition to the above components, Cu and Mo can be contained in the following ranges as necessary.

Cu: 1.0% or less Cu is an element that improves corrosion resistance, and particularly an element that reduces crevice corrosion. For this reason, it can be added when high corrosion resistance is required. However, if the content exceeds 1.0%, the hot workability is deteriorated and the phase balance at high temperature is lost, making it difficult to obtain a desired structure in the weld heat affected zone. Therefore, when Cu is contained, the upper limit is made 1.0%. In order to sufficiently exhibit the effect of improving corrosion resistance, it is effective to contain 0.3% or more. A more preferable range is 0.3 to 0.5%.

Mo: 1.0% or less Mo is an element that improves corrosion resistance, and can be added when particularly high corrosion resistance is required. However, if the content exceeds 1.0%, the workability in the cold state is deteriorated, and the rough surface in the hot rolling occurs, so that the surface quality is extremely lowered. Therefore, when Mo is contained, the upper limit is made 1.0%. In order to sufficiently exhibit corrosion resistance, it is effective to contain 0.03% or more. A more preferable range is 0.1 to 1.0%.

  In the present invention, in addition to the improvement in corrosion resistance by containing 1.0% or less of Cu or Mo as described above, the conventional findings such as improvement of ductility by containing 0.005% or less of B are included. However, in this case, it is important to consider the phase balance at a high temperature. Note that Nb is a strong stabilizing element, and is not added in the present invention because it is combined with C and N to greatly collapse the phase balance. The balance other than the elements specified above is Fe and inevitable impurities.

  In the steel sheet according to the present invention, in order to improve the corrosion resistance of the weld heat affected zone, the martensite volume ratio of the weld heat affected zone becomes 40% or more by setting the F value to 11 or less. More preferably, by setting the F value to 10.5 or less, the martensite volume fraction of the weld heat affected zone becomes 60% or more. More preferably, it is 10 or less, and the martensite volume ratio in this case is 80% or more. In the steel sheet according to the present invention, the base material portion has a ferrite structure with a volume ratio of 50% or more. The remaining structure is a structure in which a martensite phase and a residual γ phase exist, particularly in a state of being hot-rolled, and partially includes carbonitride. In particular, the structure of the hot-rolled annealed sheet after being subjected to hot-rolled sheet annealing in an appropriate composition range as described later under an appropriate annealing condition has a ferrite phase structure of almost 100% in volume ratio, and the workability Very good.

Next, the manufacturing method of the stainless steel plate which concerns on this invention is demonstrated.
The method for producing the stainless steel sheet of the present invention is not particularly limited as long as it is carried out according to a conventional method, but as a method that can be produced with high efficiency, a steel slab melted in the above composition is slabd by continuous casting or the like. After that, a hot rolled coil is formed, and after annealing as necessary, descaling (shot blasting, pickling, etc.) is performed to obtain a stainless steel plate according to the present invention.

Details will be described below.
First, molten steel adjusted to the component composition of the present invention is melted in a commonly used melting furnace such as a converter or an electric furnace, and then vacuum degassing (RH method), VOD (Vacuum Oxygen Decarburization) method , Refining by a known refining method such as AOD (Argon Oxygen Decarburization) method, and then forming a steel slab (steel material) by a continuous casting method or ingot-bundling method. The casting method is preferably continuous casting from the viewpoint of productivity and quality. Further, the slab thickness is preferably set to 100 mm or more in order to secure a reduction ratio in hot rough rolling described later. A more preferable range is 200 mm or more.

  Subsequently, after heating a steel slab to the temperature of 1100-1300 degreeC, it hot-rolls to make a hot-rolled steel plate. The slab heating temperature is preferably higher in order to prevent roughing of the hot-rolled sheet, but if it exceeds 1300 ° C., the slab droops significantly, and the crystal grains become coarse and the toughness of the hot-rolled sheet decreases. On the other hand, when the heating temperature is less than 1100 ° C., the load in hot rolling becomes high, the rough surface in hot rolling becomes remarkable, recrystallization during hot rolling becomes insufficient, and the toughness of the hot rolled sheet is also lowered. .

  In the hot rough rolling step, it is preferable to perform at least one pass of rolling with a rolling reduction of 30% or more in a temperature range exceeding 1000 ° C. By this strong rolling, the crystal structure of the steel sheet is refined and the toughness is improved. After hot rough rolling, finish rolling is performed according to a conventional method.

  A hot-rolled sheet having a thickness of about 2.0 to 8.0 mm manufactured by hot rolling can be used as a structural material as it is or after pickling without annealing. The hot-rolled sheet may be pickled after annealing the hot-rolled sheet at a temperature of 600 to 1000 ° C. If the annealing temperature of the hot-rolled sheet is less than 600 ° C., the martensite phase and the residual γ phase that may exist in the hot-rolled state may remain, and the ferrite structure may be 50% by volume. Therefore, sufficient workability cannot be obtained. On the other hand, when the temperature exceeds 1000 ° C., the coarsening of crystal grains becomes remarkable and the toughness is lowered. The hot-rolled sheet is preferably annealed at a temperature of 600 to 1000 ° C. for 1 hour or longer by so-called box annealing. On the other hand, if the annealing temperature is too high, it may enter a temperature at which the γ transformation occurs. For this reason, it is necessary to adjust the composition to an appropriate range and select an appropriate temperature range according to the composition. In the composition range of the steel sheet of the present invention, when the annealing temperature is mainly 600 to 900 ° C., this temperature range is preferable because almost 100% of the volume ratio becomes a ferrite phase.

  For welding of the stainless steel plate according to the present invention, all ordinary welding methods such as arc welding including TIG and MIG, seam welding, resistance welding such as spot welding, and laser welding can be applied.

  Stainless steel having the component composition shown in Table 1 was made into a 200 mm thick slab by a converter-VOD-continuous casting method. These slabs were heated to a temperature of 1180 ° C., and then hot rolled to form a coiled hot rolled plate having a thickness of 5.0 mm. The hot rolling end temperature was 900 ° C., and the coiling temperature after hot rolling was 700 ° C. The obtained hot-rolled steel sheet was annealed at 690 ° C. for 10 hours, and then subjected to shot blasting and pickling to remove the scale.

A flat plate sample is cut out from the steel plate after scale removal, a T-shaped test body composed of a lower plate and a standing plate is assembled, and both sides of the fillet weld (gas metal arc welding, shielding gas: 98 volume% Ar-2 volume% O _2). , Flow rate: 20 liter / min), and three fillet welded test pieces were produced. MGS-309LS manufactured by Kobe Steel Co., Ltd. was used as the welding rod, and the heat input was in the range of 0.4 to 0.8 kJ / mm.

Corrosion test specimens were collected from the fillet welds of these fillet weld specimens, and the sulfuric acid-copper sulfate corrosion test (Modified Strauss test according to ASTM A262 practice E and ASTM A763 practice Z, the test solution was Cu / 6. % CuSO ₄ /0.5% H ₂ SO _4, and a test piece whose end face was polished in this boiling liquid was immersed for 20 hours), and the corrosion state in the vicinity of the weld heat affected zone was observed. Moreover, the surface state after the pickling of the hot-rolled annealed plate was observed over the entire length.

  FIG. 2 is an optical micrograph showing an observation example of a cross section of a test piece after a sulfuric acid-copper sulfate corrosion test. As shown in this photo, when grain boundary corrosion is observed in the weld heat-affected zone or when severe deep pit-like corrosion is observed, C, when slight corrosion is observed, B, when observed with an optical microscope The case where corrosion was not recognized was evaluated as A. Moreover, the surface state after the pickling of the hot-rolled annealed plate was observed over the entire length. The ratio of the length at which surface defects due to slab cracking or inclusions were observed relative to the total length was used as an index, and the ratio of defect generation was 3% or less a, 3% to 30%, b, 30% Was evaluated as c. These results are shown in Table 2.

  As a result, No. 1 which is the steel sheet of the present invention within the scope of the present invention. In 1-5, 10-13, and 15, the corrosion resistance of the welded portion was good, and the surface condition was also very good. On the other hand, No. which is a comparative steel plate whose F value deviates from the scope of the present invention. In Nos. 9 and 14, since the amount of martensite produced in the weld heat affected zone was small, the intergranular corrosion resistance was clearly inferior. Further, No. 1 is a comparative steel plate in which Si is higher than the range of the present invention and Al is lower than the range of the present invention. No. 6 and No. 6 which are comparative steel plates whose FFV values deviate from the scope of the present invention. In 7, 8, 9 and 14, in the surface observation after hot rolling annealing, many cracks due to slabs and lashes due to inclusions were observed.

  Since the steel sheet of the present invention is used in the state of a hot-rolled sheet or a hot-rolled annealed sheet, the occurrence of lashes greatly reduces the yield. This is because the shaved portion not only has a bad appearance but can also be a starting point of rust generation, and therefore, when shipped as a product, the target portion must be cut off.

Claims (6)

% By mass
C: 0.01-0.03%,
N: 0.01-0.03%,
Si: 0.10 to 0.40%,
Mn: 1.5 to 2.5%
P: 0.04% or less,
S: 0.02% or less,
Al: 0.05 to 0.15%,
Cr: 10-13%
Ni: 0.5 to 1.0%,
Ti: 4 × (C + N) (however, C and N indicate their content (mass%)) or more and 0.3% or less,
V: 0.05% or less,
Ca: 0.0030% or less,
O: Restricted to 0.0080% or less,
Furthermore, F value and FFV value represented by the following formula satisfy F value ≦ 11, FFV value ≦ 9.0, and the balance is made of Fe and inevitable impurities, and has excellent welded portion corrosion resistance Structural steel plate.
F value = Cr + 2 * Si + 4 * Ti-2 * Ni-Mn-30 * (C + N)
FFV value = Cr + 3 * Si + 16 * Ti + Mo + 2 * Al-2 * Mn-4 * (Ni + Cu) -40 * (C + N) + 20 * V
However, in these formulas, each element symbol is the content (mass%) of these elements.   A structural stainless steel plate excellent in welded portion corrosion resistance, characterized by further containing, in addition to the components of claim 1, Cu: 1.0% or less by mass%.   A structural stainless steel plate excellent in welded portion corrosion resistance, characterized by further containing, in addition to the components of claim 1 or 2, at a mass percentage of Mo: 1.0% or less. % By mass
C: 0.01-0.03%,
N: 0.01-0.03%,
Si: 0.10 to 0.40%,
Mn: 1.5 to 2.5%
P: 0.04% or less,
S: 0.02% or less,
Al: 0.05 to 0.15%,
Cr: 10-13%
Ni: 0.5 to 1.0%,
Ti: 4 × (C + N) (however, C and N indicate their content (mass%)) or more and 0.3% or less,
V: 0.05% or less,
Ca: 0.0030% or less,
O: Restricted to 0.0080% or less,
Further, a steel slab having a composition in which the F value and FFV value represented by the following formula satisfy F value ≦ 11 and FFV value ≦ 9.0, and the balance is composed of Fe and inevitable impurities, is 1100 to 1300 ° C. Then, hot rolling including hot rough rolling in which rolling at a rolling reduction of 30% or more is performed at least one pass in a temperature range exceeding 1000 ° C. or the hot rolling was performed. A method for producing a structural stainless steel sheet with excellent welded portion corrosion resistance, wherein the steel sheet is subjected to pickling after annealing at a temperature of 600 to 1000 ° C. without annealing the hot-rolled sheet.
F value = Cr + 2 * Si + 4 * Ti-2 * Ni-Mn-30 * (C + N)
FFV value = Cr + 3 * Si + 16 * Ti + Mo + 2 * Al-2 * Mn-4 * (Ni + Cu) -40 * (C + N) + 20 * V
However, in these formulas, each element symbol is the content (mass%) of these elements.   A method for producing a structural stainless steel sheet having excellent welded portion corrosion resistance, further comprising, in addition to the steel slab component of claim 4, by mass: Cu: 1.0% or less.   A method for producing a structural stainless steel sheet with excellent welded portion corrosion resistance, which further comprises Mo: 1.0% or less in addition to the components of the steel slab of claim 4 or 5.