High formability 430 stainless steel with elimination of black streaks and method of making same

Abstract

High-formability 430 stainless steel for eliminating black streaks and manufacturing method thereof, the component mass percentage of which is: C≤0.050%, Si 0.20~0.65%, Mn 0.15~0.65%, P≤0.045%, S≤0.0040%, Cr 16.0~17.5%, Ni≤0.20%, Mo≤0.15%, Cu≤0.10%, V 0.05~0.15%, N 0.050~0.090%, the balance including Fe and inevitable impurities, and meanwhile satisfying: material strengthening index Fc=1.1~1.7, Fc=28.84*N+2.09*Si+5.18*Ni+3.79*Cu-2.15; resistance to pitting corrosion equivalent PREN≥17.0, PREN=Cr+3.3Mo+16N. The application solves the problem of the "black streaks" defect specific to SUS430 material, and meets the surface aesthetic requirement of downstream finished products.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of stainless steel production, and particularly relates to high-formability 430 stainless steel for eliminating black strip and a manufacturing method thereof. BACKGROUND

[0002] SUS430 is a typical steel of 400 series stainless steel, and is extremely cost-effective without additional Ni element. The material is not only good in corrosion resistance, but also excellent in cold working performance, and is widely applied in the fields of household appliances, kitchen, catering and building decoration.

[0003] For a long time, the texture research of ferritic stainless steel has been a hotspot in the field, and the research of ferritic texture is mainly devoted to improving the forming wrinkling problem of the ferritic structure. It is generally believed that if more gamma-fiber texture can be obtained in the ferrite fiber texture, the wrinkling can be improved. In order to obtain the gamma-fiber texture, many studies have been made on aspects such as continuous casting, equiaxial crystal ratio control, continuous annealing after hot rolling and addition of Sn element.

[0004] Wrinkling is uneven concave-convex stripes in the thickness direction due to the difference in texture when the material is deformed. The wrinkling effect of ferrite leads to many other defect problems, one of which is the "black strip" defect.

[0005] The "black strip" is mainly generated in the cold rolling process. During the cold rolling deformation process, the material shows elongation in the length direction and thinning in the thickness direction, and the thickness of the ferritic stainless steel appears uneven change, and the wrinkling is inevitable. However, due to the rolling action of cold rolling, the "convex" part of the material wrinkling will be directly pressed into or pressed into the material matrix surface along the rolling direction according to the difference in softness. Generally, if the "convex" part appears serious organizational deformation, the roughness and reflectivity of the material will be seriously reduced, so that the black parallel line marks along the rolling direction are shown in the macro, that is, the "black strip".

[0006] In the stainless steel industry, the downstream cold working customers refer to the similar features in life, and call the black parallel lines on the surface of the 430 cold rolled plate as "black strip". In the 400 series literature, there is no relevant research on this kind of defect problem. The defect seriously affects the surface beauty and smoothness of the downstream product, although the defect can be eliminated by surface polishing treatment, but it increases the additional cost of downstream processing, and the processing is extremely inconvenient.

[0007] Ferritic stainless steel has great advantages in cold forming. In order to maintain good cold forming performance, 430 materials mostly need to be cover annealed to achieve full softening of the material and facilitate subsequent processing. However, according to existing research, the "black strip" of cover annealed material products is very serious, while the non-cover annealed material products have no "black strip" but poor formability. This makes it difficult to balance the surface quality and forming processing of the cold-rolled product, which is also a real problem in the current 430 downstream cold rolling process. Therefore, focusing on the industry's key and difficult points, effectively improving the "black strip" of 430 products while maintaining its unique forming performance of ferritic stainless steel is the ultimate goal and theme of the present invention.

[0008] Chinese patent CN119839096A discloses "a method for preventing surface defects of 430 stainless steel". By adjusting the side guide head pressure, adding a vertical wheel to adjust the friction mode, etc., the sparks between the side guide and the strip steel are eliminated, thereby avoiding scarring. By adjusting the heat transfer coefficient, coiling temperature precision, coiling roll gap, etc., the slip between the strip and the coiling roll during head coiling is prevented, and the roll marks or adhesion are reduced.

[0009] Chinese patent CN119259707A discloses "a hot rolling control method for improving the surface color difference defects of 430 stainless steel thick gauge cold plate". By controlling the coiling temperature, laminar cooling mode, placement time of rolling off-line, cover annealing process, etc., the color difference defects after 430 cold rolling are effectively improved. The patent research shows that the color difference is mainly caused by the difference in material recrystallization degree.

[0010] Chinese patent CN115747441A discloses "a method for improving the gold dust defects of 430 stainless steel". By limiting the C and N content, optimizing the cover annealing process, limiting the pickling acid concentration, and controlling the material surface roughness, the surface gold dust defects are improved.

[0011] The above patents all involve surface defects of 430 material. The scratch mark belongs to scratch injury defect, and the defect presents obvious local macroscopic features of foreign object contact. Although the color difference is also the visual "black and white" difference, it is still quite different from the "black stripe". In fact, after cold rolling and annealing, the appearance of the color difference of the 430 material, the macroscopically wide "black and white" feature and the obvious "black and white" boundary are greatly related to the roughness of the cold rolling roller, the contact friction between the roller and the material. The gold dust defect, commonly known as "gold powder" in the field of 400 series stainless steel, is the feature of shiny particles on the surface of the material after the 430 cold rolled annealed plate is stripped. In fact, the "gold powder" micro-morphology presents 0.01mm level of small peeling, which is mainly caused by high carbide aggregation or low ferrite recrystallization degree, so that the local area of the material has low plasticity and toughness, and the small peeling appears as a shiny particle when the material is stripped. Generally, to improve the "gold powder" defect, the material needs to be effectively covered and retreated to fully recrystallize and soften the material, and to disperse the carbide distribution. The "gold powder" defect is often found in 430 cold rolled annealed plates of hot rolled raw materials or insufficiently covered raw materials.

[0012] Although these patents have made many optimizations and improvements in the process to solve the surface defects, they do not involve the improvement of the "black stripe" of 430 material. Moreover, these patents generally focus on the adjustment of process parameters, and do not analyze and research the defect features, defect formation mechanism and reasons, and the theoretical basis for improving the defects is slightly insufficient. SUMMARY

[0013] The purpose of the present application is to provide a high-formability 430 stainless steel and a manufacturing method thereof for eliminating black stripes, which solves the problem of the unique "black stripe" defect of SUS430 material and meets the surface aesthetic requirements of downstream finished products.

[0014] To achieve the above purpose, the technical scheme of the present application is:

[0015] A high-formability 430 stainless steel for eliminating black stripes, the composition of which is as follows: C≤0.050%, Si: 0.20~0.65%, Mn: 0.15~0.65%, P≤0.045%, S≤0.0040%, Cr: 16.0~17.5%, Ni≤0.20%, Mo≤0.15%, Cu≤0.10%, V: 0.05~0.15%, N: 0.050~0.090%, the balance including Fe and unavoidable impurities, and simultaneously satisfying:

[0016] the material strengthening index Fc=1.1~1.7,

[0017] Fc = 28.84 * N + 2.09 * Si + 5.18 * Ni + 3.79 * Cu - 2.15

[0018] PREN = Cr + 3.3Mo + 16N, PREN = 17.0.

[0019] Further, the balance of the components is Fe and unavoidable impurities.

[0020] The Rockwell hardness HRB of the 430 stainless steel is 90-95, the tensile strength R m is 600-850 MPa, the yield strength R p0.2 is 450-600 MPa, and the elongation A is 12-20%.

[0021] In the component design of the 430 stainless steel, the content of each component is as follows:

[0022] C: As an austenite forming element, the content should not be too high; moreover, since C can easily combine with Fe and Cr to form carbides, the precipitation of a large amount of C can easily lead to a surrounding "Cr-poor" state, so the content of C element needs to be controlled.

[0023] Si: As a ferrite forming element, it can improve the strength of the material to a certain extent, and can improve the structure of the passivation film to improve corrosion resistance, but too high content can easily lead to a decrease in material plasticity.

[0024] Mn, Ni, Cu: These elements are beneficial to the organization of austenitization and stability, and in the ferrite structure state of SUS430, the content should not be too high. In particular, for SUS430 high-Cr materials, the content of austenite forming elements is too high, which can easily obtain austenite structure at high temperature, and the room temperature condition after rapid cooling cannot maintain the austenite form to obtain martensite, which sharply reduces the plasticity of the material. In addition, the addition of Cu can easily lead to hot working brittle cracking, and the content of Cu should not be too high.

[0025] Mo: As a ferrite forming element, although the increase in content can improve corrosion resistance, it can easily precipitate hard phases to reduce the plasticity and toughness of the material, and the alloy cost of Mo is relatively high, so the content should not be too high.

[0026] V: As a micro-alloying element, it is relatively easy to form precipitates with C and N, thereby strengthening the organizational structure. In SUS430 material, the presence of V has a certain effect on the refinement of carbide size.

[0027] N: as an austenite forming element, the general content should not be too high; and N solid solution in the matrix can easily produce a large lattice distortion, which is more obvious for the improvement of material strength. In the present application, in order to improve the "black strip", the material strength needs to be appropriately improved to resist external deformation; at the same time, the increase of N content can promote the recrystallization process of the material during hot rolling, which can refine the grain and also improve the "black strip".

[0028] In particular, the components of the present application require to meet:

[0029] Material strengthening index Fc=1.1~1.7, Fc=28.84xN+2.09xSi+5.18xNi+3.79xCu-2.15.

[0030] The present application requires that the components of the 430 stainless steel meet the material strengthening index Fc=1.1~1.7, so that the material meets the expected hot rolling performance strengthening requirements, thereby improving the overall organization resistance to external deformation during the deformation of the subsequent cold rolling material. After obtaining the expected components, the material can be uniformly thinned in the thickness direction during cold rolling, and the local large deformation along the rolling direction during cold rolling deformation can be better inhibited, thereby inhibiting the "black strip" defect.

[0031] In order to improve the material strength while ensuring certain material plasticity, the material can be optimized from the composition, so that the material itself has a certain strengthening level in composition. Under the same process conditions, the hot rolling performance can better reflect the influence of chemical elements on strength and hardness; the change range of strength or elongation and other parameters of the annealed state performance is relatively small, and the influence trend of the elements on the performance of the base material cannot be better evaluated, and the annealing treatment is equivalent to "covering" the influence of chemical elements on performance to some extent.

[0032] In terms of hot rolling hardness, hot rolling tensile strength, hot rolling yield strength and hot rolling elongation, in order to comprehensively evaluate multiple indicators (single parameter cannot accurately evaluate material properties; multiple parameters cannot be considered and balanced), the above parameters are normalized (the strengthening level is introduced into the elongation, considering the material plasticity).

[0033] Parameter P1: hardness / 90 (the index is proportional to the strength effect, and the denominator is the average number of performance parameters, and the integer is taken);

[0034] Parameter P2: tensile strength / 600 (the index is proportional to the strength effect, and the denominator is the average number of performance parameters, and the integer is taken);

[0035] Parameter P3: yield strength / 450 (the index is proportional to the strength effect, and the denominator is the average number of performance parameters, and the integer is taken);

[0036] Parameter P4: 20 / elongation after fracture (the index is inversely proportional to the strength effect, the average of the performance parameters is taken as an integer, and then two-by-two multiplication is taken to obtain the average value, the formula is as follows:

[0037] Parameter ,

[0038] Parameter ,

[0039] Parameter ,

[0040] Parameter ,

[0041] Performance comprehensive influence factor parameter ,

[0042] In the formula: HRB, Rockwell hardness; Rm, tensile strength; Rp0.2, yield strength; A, elongation after fracture.

[0043] By P IF and the linear trend relationship of related components, an approximate element calculation empirical formula is fitted:

[0044] Fc=28.84×N-9.99×C+2.09×Si+0.03×Mn+33.86×P+139.53×S-0.11×Cr+5.18×Ni-37.90×Mo+3.79×Cu-3.88×V+constant;

[0045] In the composition range of 430 stainless steel, the effects of P and S inclusions are excluded; at the same time, the coefficients <0.2 in the parameters (the element effect is low in the composition system) and the parameters with negative effects (in general, for the parameters related to strength performance, if the process conditions and phase transition degree are the same or similar, the higher the content of added alloying elements, the higher the material strength) are excluded, and the modified empirical formula is as follows:

[0046] Fc=28.84×N+2.09×Si+5.18×Ni+3.79×Cu-2.15;

[0047] Combined with the statistical distribution law of the tensile properties and hardness data in the actual production process, the control range of Fc is obtained: 1.1~1.7.

[0048] The material strengthening index Fc empirical formula is only applicable to 430 stainless steel due to the limitations of the data itself.

[0049] The material strengthening index Fc, as a parameter, can roughly determine the influence of chemical elements on the degree of material strengthening. In the field of metallic materials, the strength of a material can generally be predicted by its chemical composition, thereby evaluating whether the material performance meets the expected ideal. However, this empirical formula is only applicable to specific material systems or material states (solution or hot rolling, etc.). This evaluation method is similar to the methods used to evaluate the basic properties of materials, such as pitting corrosion equivalent PREN, martensitic transformation point Ms, and stacking fault energy SFE. Although these parameters are affected by material state and environmental factors, they do not affect the research on material performance. For example, in evaluating the corrosion resistance of materials, the material composition can generally be optimized by using the PREN value. However, this design method cannot completely predict the corrosion resistance of materials; it can only predict the trend of corrosion resistance changes. After the material is designed and manufactured, it needs to be evaluated by parameters such as the pitting corrosion rate obtained experimentally. Moreover, the pitting corrosion rate and the PREN value do not show a one-to-one direct proportional relationship; sometimes, even an abnormal trend appears. However, this does not affect or even negate the value of PREN in evaluating the corrosion resistance of materials. Strictly speaking, the introduction of any element will affect corrosion resistance, but PREN has selected parameters with obvious trends and significant impacts in its design.

[0050] The empirical formula for the material strengthening index Fc designed in this invention is similar to the parameters mentioned above, but the difference lies in that the empirical formula for the material strengthening index Fc is derived from the comprehensive performance influencing factor P. IF The formula was derived, selecting only chemical elements with significant influence, and this empirical formula is only applicable to the composition system of this invention. The empirical formula for the material strengthening index Fc is used for composition design and to evaluate the influence trend of composition on the strengthening degree of 430 stainless steel. The comprehensive performance influence factor P... IF It can provide a relatively intuitive assessment of the strengthening level of 430 stainless steel in its hot-rolled state and affect the subsequent "black rib stripe" defect; both are indispensable.

[0051] Using the empirical formula for the material strengthening index Fc, this invention preliminarily determines the material strengthening level of the 430 material system through chemical composition. Within the required range of 1.1 to 1.7, a higher index value indicates a higher material strengthening level. Under the condition of ensuring a certain degree of plasticity, compositional optimization introduces greater distortion energy into the material. This distortion energy can act as a driving force during hot rolling to promote new grain nucleation and recrystallization, thereby contributing to grain size refinement and improving the material strengthening effect. Figure 1 , Figure 2 The figure shows the EBSD morphology of the hot-rolled microstructure of 430 stainless steel before and after composition optimization. It can be seen that there are more recrystallized fine grains in the microstructure after composition optimization.

[0052] From the material strengthening index Fc empirical formula, in the 430 stainless steel, C has a relatively strong austenite forming element, but in the strengthening effect, because C is relatively easy to form carbide with Cr and Fe, and compared with the carbide of micro-alloying element, the second phase strengthening effect of the carbide is very low, so C has no greater strengthening effect in the 430 stainless steel composition range, only through the phase change to obtain martensite to improve the strength. Mn also acts as an austenite forming element, and the strengthening effect is also limited; V is a micro-alloying element, but its micro-alloying effect is still not as effective as Nb and Ti, in the 430 stainless steel, the content level may be too low, and no obvious strengthening effect is shown. In the composition, the improvement effect of N on the material is the most obvious, and the solid solution of N in ferrite structure also promotes the optimization of texture, but N has a greater negative effect on material forming processing, which can easily lead to processing cracking, so P IF In order to improve the material strengthening level and at the same time limit it to a certain extent, Ni and Cu, as austenitizing elements, have a relatively low content in the stainless steel, and can be added as a balance strategy for N element control; Si, as a ferrite forming element, can also be added as a balance strategy for N element control, but Si, as a non-metallic element, also has a negative impact on the plasticity of the material. Considering all these factors, the four main influencing elements cannot be added unlimitedly to achieve material strengthening, and their contents are limited.

[0053] The present application optimizes the composition by the material strengthening index Fc empirical formula, maximizes the strengthening effect of the chemical composition, and enables the designed material to have the potential of the expected strengthening level, thereby improving the "black strip".

[0054] Regarding the PREN value, the general stainless steel selects the formula PREN=Cr+3.3Mo, and the present inventors have found that N element has a certain influence on the passivation film and potential of the 430 stainless steel in the corrosion resistance effect, so the formula is optimized as follows: PREN=Cr+3.3Mo+16N. Among them, Cr element can improve the stability of the passivation film, Mo element can significantly improve the re-passivation ability of the material in the local area and enhance the repair of local pitting, and N element can improve the pitting potential, strengthen the passivation film and improve the morphology of carbide.

[0055] The manufacturing method of the high-formability 430 stainless steel for eliminating black strip according to the present application comprises the following steps:

[0056] 1) Smelting and casting

[0057] Smelting and continuous casting into a slab according to the composition of the stainless steel; the superheat is 20-30 DEG C, the withdrawal speed is 1.0-1.2 m / min, electromagnetic stirring is used, and the equiaxed crystal ratio of the continuous casting blank is controlled to be greater than or equal to 60%.

[0058] 2) Slab heating

[0059] The slab heating temperature is 1150-1200℃, the furnace time is 120-180min, and the entry temperature is ≤500℃;

[0060] 3) Hot rolling

[0061] The total reduction of rough rolling is ≥80%;

[0062] The entry temperature of finish rolling is 950-1050℃, the exit temperature of finish rolling is 850-1000℃, the reduction of each pass of the first two or three passes of finish rolling is 25-60%, and the strain rate of each pass is >10s -1 The reduction of each pass of the last two or three passes of finish rolling is controlled to be 5-60%, and the strain rate of each pass is >90s -1 ;

[0063] 4) Heat treatment

[0064] After hot rolling, the heat treatment is performed by using semi-covering method, the annealing temperature is 840-860℃, and the holding time is 10-15h;

[0065] 5) Cold rolling

[0066] The deformation amount of cold rolling is controlled to be ≤85%.

[0067] Preferably, in step 3), the rough rolling of hot rolling adopts 5 or 7 passes of rolling.

[0068] Preferably, in step 3), the finish rolling adopts 5-7 passes of rolling, wherein,

[0069] 5 passes of rolling, the reduction of each pass of the first, second, third pass and the fourth, fifth pass is 25-60% and 5-60% respectively, and the strain rate of each pass is >10s -1 and >90s -1 ;

[0070] 6 passes of rolling, the reduction of each pass of the first, second, third pass and the fourth, fifth, sixth pass is 25-60% and 5-60% respectively, and the strain rate of each pass is >10s -1 and >90s -1 ;

[0071] 7 passes of rolling, the reduction of each pass of the first, second, third, fourth pass and the fifth, sixth, seventh pass is 25-60% and 5-60% respectively, and the strain rate of each pass is >10s -1 and >90s -1 .

[0072] Preferably, step 5) cold rolling adopts a 20-roller mill with a work roll diameter of 65-75 mm. When a small-diameter roller mill is used, the contact arc area between the material and the roller is smaller, and the degree of deformation of the material surface along the rolling direction is also relatively small, and surface calendering coverage along the rolling direction is less likely to occur. Therefore, small-diameter roller mills are more advantageous in improving "black streaks".

[0073] In the manufacturing method of the high-formability 430 stainless steel for eliminating black streaks described in the present application:

[0074] In step 1) smelting and casting, in order to optimize the fiber texture in the cold-rolled annealed plate, the superheat of the molten steel and the continuous casting speed need to be properly controlled, and electromagnetic stirring is performed to increase the equiaxed crystal ratio of the continuous casting structure. Therefore, the superheat is controlled to be 20-30°C, the casting speed is controlled to be 1.0-1.2 m / min, and electromagnetic stirring is performed to obtain a 430 continuous casting blank with an equiaxed crystal ratio of ≥60%.

[0075] By increasing the equiaxed crystal ratio, the subsequent structure can obtain more γ-fiber texture due to the genetic characteristics of the ferrite structure, which promotes the improvement of wrinkles during subsequent cold rolling, thereby reducing the degree of local deformation of the material surface during cold rolling.

[0076] In addition, an equiaxed crystal ratio of 60% is a comprehensive consideration of site factors. On the one hand, the control of superheat and continuous casting speed is based on the requirement of balancing production efficiency and continuous casting quality; on the other hand, although larger electromagnetic stirring is more conducive to obtaining equiaxed crystals, increasing the intensity of electromagnetic stirring can easily lead to unstable situations such as continuous casting liquid surface fluctuation and white band, affecting the quality of continuous casting. Therefore, under the existing process equipment conditions, the equiaxed crystal ratio is controlled to be ≥60%. The preferred electromagnetic stirring control is: current 300-600 A, frequency 3-9 Hz.

[0077] In step 2) the heating stage of the casting blank, the heating temperature is controlled to be 1150-1200°C, and the furnace time is controlled to be 120-180 min to ensure the conditions for smooth rolling of the material, avoid excessive temperature or excessive holding time to cause material heterogeneity. The control of the inlet temperature ≤500°C can avoid the situation that the high inlet temperature of the blank causes the surface oxide scale to be difficult to fall off, affecting the subsequent surface quality.

[0078] Step 3) hot rolling rough rolling stage, total reduction rate ≥ 80%, preferably the target thickness of the steel plate is 35-45 mm. In high temperature state, the strength of the material is reduced, and the deformation of rough rolling is used to obtain the appropriate material thickness size before finish rolling. After the end of rough rolling, as the temperature decreases and the time is prolonged, the material temperature approaches the corresponding temperature of high proportion of austenite content, and the organization also begins to recrystallize, but the degree of recrystallization at this time is low. In fact, the rough rolling process of such materials is a pre-deformation process before finish rolling in addition to size control, and the control of deformation and size is also to provide distortion energy for the hot dynamic recrystallization process, while ensuring the stability of the rolling size and the surface quality of the subsequent finish rolling.

[0079] Step 3) hot rolling finish rolling stage, the overall lifting of finish rolling control is 430, which can promote the recrystallization of the material to a certain extent, and effectively improve the "black strip" defect in the subsequent process by means of refining the grain and improving the material strengthening level.

[0080] By optimizing the hot rolling process to promote the recrystallization process of the material in the hot rolling stage, the material strengthening level is further improved, which is beneficial to the subsequent improvement of the "black strip" defect.

[0081] According to the formula It can be seen that the greater the strain rate, the higher the degree of material recrystallization, and the finer the grain, and the strength will also increase accordingly. By controlling the corresponding rolling speed, reduction rate and other parameters, the strain rate comparison results before and after optimization are shown in Figure 3 After optimization, the overall strain rate of each pass is higher than that before optimization, and as expected, the recrystallization degree of the hot rolled structure will be higher, and the grain refinement degree will be higher, thereby effectively improving the "black strip" defect.

[0082] Regarding the effect of temperature on the degree of recrystallization, generally, as the temperature increases, the material structure gradually transitions from recovery to recrystallization, and the grain gradually shows a refinement trend; but when the temperature rises to a certain level, the effect of grain growth is also obvious, and the grain refinement effect embodied by recrystallization will be "covered" by grain growth and even secondary recrystallization.

[0083] The selection of the finish rolling temperature is close to the "peak" of the 430 high-temperature austenite phase region, and the existence of austenite has a relatively large promoting effect on the recrystallization of the material (in the rough rolling stage, the temperature is relatively high, and the influence on the recrystallization is relatively weak); in addition, due to the existence of the austenite and ferrite two-phase region, the uniformity of the two-phase deformation during rolling, the rolling stress, the adhesion of the roller to the surface of the material, and the change of the material roll gap caused by the temperature rise will all affect the setting of the rolling parameters. In the finish rolling stage, the temperature is maintained at a level of 850-1050 DEG C, which is in the high-temperature region existing in the austenite phase region. The overall temperature of the finish rolling is controlled in the region with a higher content of austenite, and the high-temperature deformation of the austenite is used to promote the dynamic recrystallization process in these regions, so that the degree of recrystallization of the overall ferrite is improved, and this law is obviously reflected in the EBSD results of the hot rolling structure. In the finish rolling stage, if the rolling temperature continues to rise, in addition to affecting the austenite content, the matrix ferrite structure will also appear abnormal and show a trend of poor plasticity, so the finish rolling temperature should not be too high. In addition, the finish rolling is carried out at a lower temperature (below 850 DEG C), although it can increase the recrystallization driving force in the form of increasing distortion energy, but due to the sharp increase of the rolling load, the surface of the 430 stainless steel material is prone to rust and even cracking during rolling, so the lower limit of the finish rolling temperature is also limited in the present application. After general rolling, the temperature of the steel coil is reduced in the form of laminar flow cooling to avoid the influence of high temperature on the service life of the coiling equipment when the material is coiled. Although increasing the laminar flow cooling can obtain more martensite structure and produce a strengthening effect, but the martensite itself has a large stress concentration, and the increase of its content is easy to cause the appearance of poor coil shape when the material is coiled. The large amount of martensite structure in the structure makes the requirement for the material offline heat preservation more strict, and cannot effectively guarantee the plasticity and toughness of the material. Considering comprehensively, under the condition that the hot rolling performance of the material meets the expected requirements and the production control is stable, the intensity and control mode of the laminar flow cooling after rolling are not limited.

[0084] Regarding the control of the finish rolling deformation, in the early stage of the finish rolling stage, the size of the steel plate is relatively large, the rolling speed is also relatively low, and the material reduction rate is also relatively high under the capacity of the roller, therefore, the reduction rate of each pass of the first two passes or three passes of the finish rolling control of the present application is 25-60%, the overall strain rate of the material is at a low level, and the strain rate of each pass is >10 s -1 By large deformation, the material can be closer to the target size, and the dynamic recrystallization of the material gradually occurs and proceeds, so that the dynamic recrystallization process "adapts" to the temperature conditions at this time.

[0085] In the later stage of the finishing rolling, the rolling speed is continuously increased, and the rolling reduction is reduced accordingly. The reduction of the last two or three passes is controlled at 5-60% to avoid excessive temperature rise and affect the size accuracy due to the difference in roll gap, and to reduce the contact friction between the steel material and the roll, reduce or eliminate defects such as surface peeling and rolling rust, and increase the strain rate, and the strain rate of each pass is >90s -1 , which further promotes the dynamic recrystallization process of the material. In parameter selection, only two main factors, deformation and strain rate, are selected. Deformation is easy to operate and control in parameter control; strain rate is not only related to parameters such as rolling speed, but also an important measure of recrystallization degree.

[0086] After finishing rolling, under the condition of a large level of dynamic recrystallization, the material organization continues to undergo static recrystallization process with the help of high temperature and retained deformation energy. The recrystallization process can continue, which makes more grain nucleation and growth in the organization, thereby promoting grain refinement and improving material strengthening level. Generally, for stainless steel plate rolling, the size becomes smaller and smaller in the finishing rolling stage, and the rolling speed becomes faster and faster. Due to the difference in stress degree of each pass roll, the rolling reduction of the corresponding rolling pass is reduced in turn, especially the last few passes usually use ordinary rolls, and the stress degree is relatively weak during rolling, so the reduction rate should not be too large. On the other hand, the material will be heated during the rolling process. Under the condition of faster and faster rolling speed, the reduction is reduced in turn, which can avoid the influence of high rolling temperature on the change of rolling gap parameters, and thus ensure that the target size of the material does not appear abnormal, thereby effectively guaranteeing the size accuracy of the material. In addition to small ferrite grains, there are also a small amount of martensite structures in the "black strip" structure in the hot rolling metallographic structure; after conventional composition optimization, the "black strip" structure in the metallographic structure is more, the distance between the strips is smaller, and the recrystallization degree of the organization is higher, as shown in Figure 4 、 Figure 5 .

[0087] 430 As ferritic stainless steel, the material system of Cr-Fe is more likely to react with the roller during hot rolling, resulting in surface quality problems. At higher rolling temperature, if additional deformation is added, the contact reaction between the material and the roller will be more serious, causing defects such as hot rolling surface peeling, iron oxide scale pressing and rolling rust. In the selection of finishing rolling passes, 7 finishing rolling passes or fewer finishing rolling passes control mode, the overall strain rate is higher (the finishing rolling process of 430 hot rolling production is usually 8 passes), which is more conducive to recrystallization of the material, thereby facilitating the refinement of the subsequent organizational grain and improving the material strengthening level; However, considering the rolling force bearing limit (rolling load), hot rolling surface defect control and the speed coordination of the front and rear rolling materials caused by too few passes, the present application selects "5-7 finishing rolling passes" as the most suitable. In principle, under the premise of ensuring that the blank can be successfully rolled and the surface quality of the plate is good, the higher the strain rate, the more conducive to recrystallization, thereby effectively improving the "black stripe" defect.

[0088] On the basis of ensuring that the hot rolling does not appear rolling peeling, rolling rust and other surface quality problems, and the hot rolling thickness size does not appear abnormal, the recrystallization degree of the material is improved, thereby refining the grain size of the material after cold rolling and annealing. On the one hand, by refining the grain size and promoting recrystallization, the negative effects of the α-fiber texture are "weakened" (the larger the grain size, the more obvious the size effect of the grain caused by deformation), effectively inhibiting the wrinkling effect of the ferrite structure and weakening the deformation degree of the material surface caused by the cold rolling roller; On the other hand, the grain is refined to strengthen the material, thereby improving the overall resistance of the material to external deformation and avoiding the over-softening of the region to cause the region to appear deformation along the rolling direction. Therefore, by inhibiting the wrinkling effect and improving the material strengthening degree, the "black stripe" is improved.

[0089] Step 4) Heat treatment stage, semi-covering heat treatment is adopted, annealing temperature is 840-860℃, holding time is 10-15h.

[0090] 430 ferritic stainless steel material, cover retreatment is generally selected to be carried out under the condition of being lower than and close to the phase transition temperature for a long time (20-30 hours), and the pickling white skin after annealing is processed by cold rolling, and then continuous annealing is carried out to obtain corresponding 2B, BA plate and other different surface state materials. When the ferritic structure is cold-rolled, the ferrite will not change phase, but will continuously accumulate dislocations in the ferrite in a deformed manner. Due to the equiaxed crystal and columnar crystal distribution characteristics of the continuous casting of the ferritic stainless steel, the material will obtain different orientation distribution of fiber texture after annealing. When the material deforms, the structure slip or grain size deformation will show different characteristics according to the difficulty of the slippable system. For example, the α-fiber texture slip system is single, and the grain deformation direction is single; the γ-fiber texture slip system is more, and the grain can relatively deform in more directions. Therefore, in the cold rolling process, some specific areas (such as the part of the wrinkle "protrusion") will deform more in the deformation process, not only stress concentration will occur, but also calendering coverage (such as Figure 6 ) will appear on the surface of the material, resulting in that these areas do not reflect light and appear color black, dark, that is, "black strip" defects. In the normal area, there will be no obvious calendering coverage characteristics (such as Figure 7 ) in the micro-morphology. As shown in Figure 8 , it is the macro-morphology of "black strip", which shows black strip lines along the rolling direction.

[0091] For "black strip" defects, the cold rolling and annealing "two rolling processes" can be used to improve (that is, effectively improve the deformation wrinkle effect to inhibit the occurrence of "black strip"). But this way needs to go through two times of cold rolling and annealing, the production cost is very high, which is not conducive to the efficient and high-quality production of 430 ferritic stainless steel material.

[0092] Through experimental research, it is found that the "black strip" area has more significant nuclear average orientation difference KAM value, and the "green" distribution area in the KAM diagram is more. Since the KAM value is directly related to the dislocation density of the local area, the "green" area with greater nuclear average orientation difference represents that the area has obvious stress and strain distribution characteristics, that is, the "black strip" area has more obvious stress concentration (as shown in Figure 9 ), and the normal area has weak stress and strain distribution (as shown in Figure 10 ); combined with the organization and texture characteristics of the corresponding area, it can be known that the generation of "black strip" is related to the {110}, {100} texture in the organization, and the normal area contains a considerable amount of {111} texture (as shown in Figure 11 , Figure 12It can be seen from the figure that the {110} and {100} textures are prone to deformation during cold rolling, and in fact, the size of the {110} and {100} textures in the thickness direction is prone to change during deformation. When further cold rolling, the {110} and {100} texture regions are prone to deformation along the rolling direction and cover the surface of the material. Figure 13 As shown in FIG. 6, the higher the wrinkle height, the more serious the deformation of the material surface along the rolling direction after rolling deformation. Figure 14 As shown in FIG. 6, the higher the wrinkle height, the more serious the deformation of the material surface along the rolling direction after rolling deformation. Figure 15 As shown in FIG. 6, the higher the wrinkle height, the more serious the deformation of the material surface along the rolling direction after rolling deformation. Figure 16 As shown in FIG. 6, the higher the wrinkle height, the more serious the deformation of the material surface along the rolling direction after rolling deformation.

[0093] At present, although the research on ferrite texture can effectively improve the forming wrinkle problem, even the continuous annealing treatment after hot rolling mentioned in the literature does not have a significant improvement effect in actual production. The most effective way to wrinkle is to optimize the composition rather than the process. In the early days, Japan had some related research on the addition of Sn element to ferrite, but considering that Sn is a five-harm element and a low-melting-point element, it is prone to rolling cracking during thermal deformation, which cannot guarantee the surface quality. In recent years, EBSD has made a lot of achievements in analyzing texture characteristics, but in the actual production of ferritic stainless steel, except for the "two-rolling process", no production plant can effectively improve the wrinkle problem through the cold rolling and continuous annealing process of the one-rolling process. Increasing the equiaxed crystal ratio is only a certain degree of optimization from the source of the microstructure characteristics, and cannot have a decisive effect on improving the wrinkle. Therefore, it is difficult and costly to improve the wrinkle to improve the "black stripe". Although the wrinkle effect of ferritic stainless steel is the source of the "black stripe" defect, improving the "black stripe" does not necessarily need to be achieved by improving the wrinkle.

[0094] In the production of 430 ferritic stainless steel, a annealing process is required to improve the material's subsequent plastic processing capabilities. However, the longer the annealing time, the more pronounced the texture inheritance characteristics in the microstructure become, which is detrimental to improving the "black vein stripe" defect by optimizing wrinkling. In fact, hot-rolled 430 ferritic stainless steel rarely exhibits "black vein stripes" on its surface after cold rolling annealing; however, annealed 430 ferritic stainless steel shows severe "black vein stripe" defects on its surface after cold rolling annealing. However, due to plasticity deviations, cold-rolled annealed sheets obtained from hot-rolled 430 ferritic stainless steel are prone to forming cracks during downstream processing, and their corrosion resistance is also poor due to uneven carbide distribution. Therefore, this invention selects a semi-annealing method in the annealing process, balancing material plasticity and the "black vein stripe" defect problem. In actual production, semi-annealing is also beneficial for controlling the fine and dispersed distribution of carbides, such as... Figures 17-19 As shown, the metallographic morphology of 430 ferritic stainless steel in different states shows that the carbide size is the smallest in the semi-annealed state. Carbide growth requires the consumption of Cr elements in the surrounding matrix, so controlling the carbide size is beneficial for improving the corrosion resistance of the material. By comparing the defect differences shown by whether or not the annealing process is used, it is helpful to understand the manifestation characteristics of the "black streaks" defect. Taking this detail as a "starting point," this invention provides ideas and directions for improving the "black streaks" from the aspects of composition and process.

[0095] 430 As ferritic stainless steel, the strength is low, and the half cover of the conventional composition of the cold rolled annealed plate has certain improvement on the "black strip" defect, but the defect rate is still high when the downstream customer processes. According to the above experimental results and the characteristics of the "black strip" defect of the 430 ferritic stainless steel, the "black strip" corresponds to the {110}, {100} area with high proportion in ferrite structure, and the KAM stress and strain degree is high; moreover, the micro-morphology characteristics of the "black strip" show obvious calendering deformation along the rolling direction; in addition, the cold rolled annealed plate corresponding to the hot rolled raw material shows the characteristics of no "black strip". Based on the above results and characteristics, the present application proposes an idea: it can be tried to improve the "black strip" by improving the material strength and the recrystallization degree. Because, the improvement of the material strength is beneficial to the effective resistance of the microstructure to external deformation, and the part is pressed into the material matrix surface as a whole, thereby inhibiting the local deformation of the "projection" (such as deformation along the rolling direction and pressing into the material matrix surface); on the contrary, if the material is softer, the local "projection" area is more likely to appear calendering coverage along the rolling direction, thereby causing the generation of "black strip" defects. In order to consider the forming processing of the subsequent cold rolled material and the corrosion resistance of the material, in addition to improving the texture characteristics distribution, the present application improves the material strength and promotes recrystallization from the two aspects of improving the material strength and promoting recrystallization by the above related composition optimization, hot rolling process and adjustment and improvement of the cover annealing link. Among them, the half cover annealing process plays a role in balancing the subsequent processing forming, corrosion resistance and "black strip" defect control of the material.

[0096] Step 5) cold rolling stage, the working roll diameter is 65-75mm, the single pass relative reduction of cold rolling is <20%, and the total reduction of cold rolling is ≤85%. Among them, the single pass relative reduction = (size before pass reduction-size after pass reduction) / size before pass reduction × 100%, and the total reduction = (raw material size-cold rolled product size) / raw material size × 100%.

[0097] The working roll diameter can be selected according to the site rolling pressure characteristics, equipment running speed, etc., and for improving the "black strip", a smaller working roll diameter is recommended; in the pass rolling, the closer to the last pass, the higher the strength of the material, and the greater the stress on the roll, so the roll diameter should not be too small, because from the perspective of torque stress, too small rolling diameter is not conducive to the efficient use of motor power and rolling mill pressure.

[0098] During the cold rolling stage, controlling the corresponding cold rolling parameters can improve the appearance of "black veins and streaks." Regarding controlling the cold rolling reduction rate, generally, the higher the reduction rate, the greater the degree of material deformation, and the more likely "black veins and streaks" will appear. In actual production, the larger the roll diameter, the greater the rolling force and the larger the contact area (e.g., ...). Figure 20 As shown in the diagram, the material surface is more prone to large-scale deformation, therefore a work roll diameter of 65-75mm is recommended. Based on field experience, for standard 430 stainless steel, the incidence of "black vein stripes" defects is high when the cold rolling deformation exceeds 85%. Therefore, the deformation amount can be appropriately controlled during the cold rolling process. In the initial stage of cold rolling, the material is relatively soft, so a certain reduction rate needs to be controlled to avoid excessive deformation leading to obvious rolling coverage on the material surface. In the later stage of cold rolling, the material is generally harder, making "black vein stripes" less likely to appear. Therefore, in cold rolling control, for 430 stainless steel with conventional composition and process, the reduction rate of each pass needs to be reasonably matched according to the actual situation in the initial stage of cold rolling; for 430 stainless steel with optimized composition and process, there are no particularly strict restrictions on this cold rolling process. This cold rolling control is only a supplementary and preferred step to improve the "black vein stripe" defect in 430 stainless steel.

[0099] The cold rolling process directly affects the appearance of "black streaks" in 430 stainless steel, being a key characteristic of this phenomenon. Therefore, proper control of the work roll diameter and deformation amount can effectively improve the appearance of "black streaks." When downstream cold rolling processes utilize large-diameter (approximately 210mm) mills with eight-roll eccentric mills, the contact area for material deformation is larger, making it easier for surface deformation along the rolling direction to occur. Therefore, under large-roll rolling conditions, the cold rolling reduction rate should be appropriately controlled according to the actual situation to avoid the appearance of "black streaks" due to excessive deformation or increased susceptibility to deformation along the rolling direction.

[0100] In actual production, the 430 stainless steel described in this invention, after undergoing optimized control of hot rolling, semi-annealing, and cold rolling annealing to obtain 2B plates, shows a significant reduction in surface wrinkling after 20% drawing. Figure 21 , Figure 22 As shown. Compare with EBSD orientation maps (e.g.) Figures 23-26 As shown in the figure, the optimized ferrite microstructure not only has smaller grain size but also a higher proportion of {111} texture. This indicates that the optimized 430 stainless steel not only has an optimized fiber texture and smaller variations in thickness, resulting in less wrinkling, but also, due to the increased material strength, its microstructure's ability to resist external deformation is enhanced, making it less prone to localized rolling deformation along the rolling direction during cold rolling. In the optimized 430-BA plate (after brightening treatment, surface defects are easier to observe), the "black veins" on the material surface are significantly improved, and the black rolling marks along the rolling direction are completely eliminated, as shown in the figure.Figure 27 、 Figure 28 The surface contrast effects before and after optimization are shown.

[0101] The mechanical properties and forming properties (as shown in Table 1) of the optimized 430 stainless steel 2B plate meet the use requirements of downstream customers, and the corrosion resistance (as shown in Table 2) is improved in terms of pitting corrosion rate and potential level, and the salt spray corrosion resistance of the material is significantly improved (as Figure 29 、 Figure 30 The optimized material does not appear obvious rust in the dry-wet alternating salt spray test). Corrosion resistance is a basic property of stainless steel, and the corrosion resistance is of great significance for material use and service. That is, the 430 stainless steel product after optimization of the composition and process not only effectively improves the "black strip" defect problem, but also maintains good mechanical properties, forming properties (as Figure 31 、 Figure 32 The optimized material not only does not crack at LDR2.1, but also has very light wrinkle lines after cupping).

[0102]

[0103]

[0104] Compared with the prior art, the advantages of the present application are:

[0105] The present application analyzes the distribution characteristics of the "black strip" defect by means of EBSD, and understands that the "black strip" defect is greatly related to the deformation wrinkle of ferrite, and the macroscopic morphology shows local plastic deformation along the rolling direction, and the microstructure shows that the {110} and {100} texture distributions are more. At the same time, the stress and strain concentration degree is higher, which is consistent with the degree of macroscopic plastic deformation.

[0106] According to the performance characteristics of SUS430 material, the present application provides a simple calculation method for judging the strengthening degree of SUS430 material, that is, the performance comprehensive influence factor P IF On the basis of understanding the mechanism and characteristics of the "black strip" defect, the P IFThe material strengthening index Fc index derived and its corresponding control range are used to optimize and adjust the composition, so that the material performance after hot rolling of SUS430 meets the requirements of improving "black strip" and the like; meanwhile, from the perspective of optimizing the ferrite texture characteristic distribution, recrystallization degree and improving the material strength, the "black strip" defect is further improved by controlling the continuous casting equiaxed crystal ratio, hot rolling finishing control and semi-cover heat treatment and the like. After cold rolling and continuous annealing, the material not only effectively improves the "black strip" defect problem, but also maintains good forming and mechanical properties, and the corrosion resistance is further improved. On the basis of not increasing the additional alloy cost and production cost, the related defect problem is solved more efficiently, and the basic performance of the material is not greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0107] Figure 1 SUS430 hot-rolled longitudinal section electron backscatter diffraction (EBSD) orientation map (composition before optimization);

[0108] Figure 2 SUS430 hot-rolled longitudinal section electron backscatter diffraction (EBSD) orientation map (composition after optimization);

[0109] Figure 3 SUS430 hot-rolled finishing pass strain rate comparison chart;

[0110] Figure 4 SUS430 hot-rolled metallographic picture of conventional composition (before finishing pass optimization);

[0111] Figure 5 SUS430 hot-rolled metallographic picture of conventional composition (after finishing pass optimization);

[0112] Figure 6 SUS430-BA plate surface metallographic morphology photo ("black strip" defect area);

[0113] Figure 7 SUS430-BA plate surface metallographic morphology photo (normal area);

[0114] Figure 8 SUS430-BA plate "black strip" defect macroscopic appearance photo;

[0115] Figure 9 SUS430-BA plate surface kernel average misorientation (KAM) map ("black strip" defect area);

[0116] Figure 10 SUS430-BA plate surface kernel average misorientation (KAM) map (normal area);

[0117] Figure 11SUS430-BA plate surface electron backscatter diffraction EBSD orientation map ("black streak" defect area);

[0118] Figure 12 SUS430-BA plate surface electron backscatter diffraction EBSD orientation map (normal area);

[0119] Figure 13 SUS430-BA plate surface "black streak" defect formation (original surface wrinkle height large) schematic diagram;

[0120] Figure 14 SUS430-BA plate surface "black streak" defect formation (original surface wrinkle height large) schematic diagram;

[0121] Figure 15 SUS430-BA plate surface "black streak" defect formation (original surface wrinkle height large) schematic diagram;

[0122] Figure 16 SUS430-BA plate surface "black streak" defect formation (original surface wrinkle height large) schematic diagram;

[0123] Figure 17 SUS430 cross-section metallographic morphology photograph (hot-rolled state);

[0124] Figure 18 SUS430 cross-section metallographic morphology photograph (half-cold-rolled state);

[0125] Figure 19 SUS430 cross-section metallographic morphology photograph (full-cold-rolled state);

[0126] Figure 20 SUS430 cross-section metallographic morphology photograph (full-cold-rolled state);

[0127] Figure 21 SUS430-2B plate drawing 20% wrinkle morphology photograph (before optimization, from left to right: 0°, 45°, 90°);

[0128] Figure 22 SUS430-2B plate drawing 20% wrinkle morphology photograph (after optimization, from left to right: 0°, 45°, 90°);

[0129] Figure 23 430-2B plate longitudinal cross-section thickness edge electron backscatter diffraction EBSD orientation map (before optimization);

[0130] Figure 24 430-2B plate longitudinal cross-section thickness edge electron backscatter diffraction EBSD orientation map (after optimization);

[0131] Figure 25 EBSD orientation map of the longitudinal section thickness center of the 430-2B plate (before optimization);

[0132] Figure 26 EBSD orientation map of the longitudinal section thickness center of the 430-2B plate (after optimization);

[0133] Figure 27 Comparison chart of the surface macro-morphology of the SUS430-BA plate (before optimization);

[0134] Figure 28 Comparison chart of the surface macro-morphology of the SUS430-BA plate (after optimization);

[0135] Figure 29 Comparison chart of the dry-wet alternating / 24h salt spray test of the SUS430-2B plate (before optimization);

[0136] Figure 30 Comparison chart of the dry-wet alternating / 24h salt spray test of the SUS430-2B plate (after optimization);

[0137] Figure 31 Comparison chart of the cup-punching LDR2.1 result of the SUS430-2B plate (before optimization);

[0138] Figure 32 Comparison chart of the cup-punching LDR2.1 result of the SUS430-2B plate (after optimization);

[0139] Figure 33 Surface 500 times metallographic corrosion morphology of the SUS430-2B plate (hot-rolled raw material);

[0140] Figure 34 Surface 500 times metallographic corrosion morphology of the SUS430-2B plate (half-closed-rolled raw material);

[0141] Figure 35 Surface electron probe corrosion morphology of the SUS430-2B plate (hot-rolled raw material);

[0142] Figure 36 Surface electron probe corrosion morphology of the SUS430-2B plate (half-closed-rolled raw material). DETAILED DESCRIPTION

[0143] The application will be further described below in conjunction with the embodiments and the drawings.

[0144] The components of the 430 stainless steel examples and the comparative examples of the application are shown in Table 3, and the rest of the amount includes Fe and inevitable impurities. The manufacturing process parameters of the examples and the comparative examples of the application are shown in Table 4, and the performance parameters of the examples and the comparative examples of the application are shown in Table 5.

[0145] As shown in Table 3, the material strengthening index Fc of the components of Examples 1-10 of the present application is greater than 1.1, and the calculated P IF is also greater than 1.1. According to historical data of SUS430, generally P IF is less than 1.7. If the index exceeds 1.7, it is generally the case that the elongation is less than 10%, which is generally considered as unqualified performance. There is no such data in the data.

[0146] As shown in Tables 4 and 5, the "black strip" defect of the 430 stainless steel product obtained by the manufacturing method of the present application is basically eliminated after cold rolling and continuous annealing treatment; the LDR2.1 cupping test is good, and no cracking occurs; 24h dry-wet alternating salt spray has no obvious rusting signs. The PREN value of the components in the examples is greater than 17.0, and the actual salt spray corrosion resistance effect is better than that of the comparative examples.

[0147] Comparative Example 1, the coiling temperature and coiling time are 0, i.e. the hot-rolled SUS430. Compared with the coiling raw material, the strength of the finished product obtained from the hot-rolled raw material is higher, and the organization is more resistant to external force deformation, and is not easy to appear "black strip". The LDR2.1 cupping test appears cracking, and since no coiling treatment is performed, the carbide is not fully dispersed, and the salt spray rusting is more serious. As shown in Table 6, the corrosion metallography and probe morphology of the 2B plate corresponding to the hot-rolled SUS430 and the semi-coiled SUS430 are shown. Without coiling treatment, not only the carbide is unevenly distributed, affecting corrosion resistance, but also the degree of ferrite recrystallization is low, affecting the forming performance. Figures 33-36

[0148] Comparative Example 2, although semi-coiling treatment is used, since the composition is not optimized and the finishing rolling is not optimized, the "black strip" defect appears, but the distribution ratio is low.

[0149] Comparative Example 3, semi-coiling treatment is used, although the finishing rolling is optimized, since the composition is not optimized, the "black strip" defect still appears, and the distribution degree is lower than that of Comparative Example 2.

[0150] Comparative Examples 4 and 6, full-coiling treatment is used, and the composition and rolling are not optimized, and the "black strip" defect is serious.

[0151] Comparative Example 5, full-coiling treatment is used, and the composition and rolling are not optimized, and the "black strip" defect is serious.

[0152] Comparative Example 7 is a new steel grade for continuous annealing test, the material strengthening index Fc value of the composition is -0.184, and the calculated P IF ​The value is 1.015, the composition of this steel is not applicable to the SUS430 system of the present application, even so, it can still obtain the corresponding material strengthening level through actual performance. Due to the use of continuous annealing treatment, the short annealing time makes the material strength level high, and the "black strip" does not appear during subsequent cold rolling, but the cup cracking occurs and rusts seriously.

[0153] In Comparative Example 8, the continuous casting control equiaxed crystal ratio is 52%, and compared with Comparative Example 2, the equiaxed crystal ratio is reduced, and the "black strip" ratio is increased.

[0154] From the results of the examples and comparative examples, it can be seen that the material strengthening index Fc calculated from the composition is consistent with the P IF There is a certain difference between the results. Through the results of the composition estimation, only the strengthening effect caused by the composition can be estimated. After all, Fc is derived from the empirical formula of P IF , and can only preliminarily judge the influence trend of the composition on the strengthening effect; finally, the actual hot rolling performance needs to be used to reflect the strengthening degree of the material.

[0155] The above examples are only used to illustrate the present application, and are not used as a limitation of the present application, as long as the above-described examples are changed, modified, and the formula algorithm idea is applied within the scope of the essential spirit of the present application. The application will fall within the scope of the claims of the present application.

[0156]

[0157]

[0158]

Claims

1. High-formability 430 stainless steel with eliminated black veins and streaks, its composition by mass percentage is: C：≤0.050%， Si: 0.20~0.65%, Mn: 0.15~0.65%, P：≤0.045%， S：≤0.0040%， Cr：16.0~17.5%， Ni: ≤0.20%, Mo: ≤0.15%, Cu: ≤0.10%, V：0.05~0.15%， N：0.050~0.090%， The balance is Fe and unavoidable impurities, and simultaneously satisfies: The material strengthening index Fc = 1.1~1.

7. Fc=28.84×N+2.09×Si+5.18×Ni+3.79×Cu-2.15; The pitting corrosion resistance equivalent PREN ≥ 17.0, PREN = Cr + 3.3Mo + 16N.

2. The high-formability 430 stainless steel with eliminated black vein stripes as described in claim 1, characterized in that, The Rockwell hardness HRB of the hot-rolled 430 stainless steel is 90~95, and the tensile strength R... m The yield strength is 600~850MPa, and the yield strength R is... p0.2 The strength is 450~600MPa, and the elongation after fracture (A) is 12~20%.

3. The method for manufacturing high-formability 430 stainless steel with eliminated black vein stripes as described in claim 1 or 2, characterized in that, Includes the following steps: 1) Smelting and casting The slab is smelted and continuously cast according to the composition of claim 1; the superheat is 20~30℃, the casting speed is 1.0~1.2m / min, electromagnetic stirring is used, and the equiaxed crystal ratio of the continuously cast slab is controlled to be ≥60%; 2) Heating of the billet The billet heating temperature is 1150~1200℃, the furnace time is 120~180min, and the furnace entry temperature is ≤500℃; 3) Hot rolling Total reduction rate in rough rolling ≥ 80%; Finishing mill inlet temperature: 950~1050℃, finishing mill outlet temperature: 850~1000℃; the reduction rate of each of the first two or three passes of finishing milling is 25~60%, and the strain rate of each pass is >10s. -1 The reduction rate of each of the last two or three passes of the finishing rolling process is controlled at 5-60%, and the strain rate of each pass is >90s. -1 ; 4) Heat treatment After hot rolling, heat treatment is carried out by a semi-enclosed annealing method, with an annealing temperature of 840~860℃ and a holding time of 10~15h. 5) Cold rolling Control the cold rolling deformation to ≤85%.

4. The method for manufacturing high-formability 430 stainless steel with eliminated black vein stripes as described in claim 3, characterized in that, In step 3), the hot rolling roughing process uses 5 or 7 passes.

5. The method for manufacturing high-formability 430 stainless steel with eliminated black vein stripes as described in claim 3 or 4, characterized in that, In step 3), Finishing rolling involves 5 to 7 passes, among which... Five-pass rolling, with a reduction rate of 25-60% for passes 1, 2, and 3, and a strain rate >10s for each pass. -1 The reduction rate for the 4th and 5th passes is 5-60%, and the strain rate for each pass is >90s. -1 ; Six-pass rolling, with a reduction rate of 25-60% for passes 1, 2, and 3, and a strain rate >10s for each pass. -1 The reduction rate for passes 4, 5, and 6 is 5-60%, and the strain rate for each pass is >90 s⁻¹. -1 ; The rolling process consists of 7 passes, with a reduction rate of 25-60% for passes 1, 2, 3, and 4, and a strain rate >10s for each pass. -1 The reduction rate for passes 5, 6, and 7 is 5-60%, and the strain rate for each pass is >90 s⁻¹. -1 .

6. The method for manufacturing high-formability 430 stainless steel with eliminated black vein stripes as described in claim 3, characterized in that, Step 5) Cold rolling is performed using a 20-roll mill with a work roll diameter of 65~75mm.

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