Technical field
[0001]
　The present invention relates to a method for producing a steel sheet.
BACKGROUND
[0002]
　Recently, from the viewpoint of protecting the global environment, improving automobile fuel efficiency it has been required. Also, from the viewpoint of ensuring passenger safety, it is also required improvement of the safety of vehicle in the event of a collision. To meet with these requirements, it is desirable to achieve the weight reduction and strengthening of the vehicle body at the same time, in the cold-rolled steel sheet as the automobile parts of the material, while maintaining high strength, thinning of the steel sheet It has been promoted.
[0003]
　In such a high-strength steel sheets, rust resistance is required. Therefore, the steel sheet is chemical conversion treatment after press molding, electrodeposition coating is performed. However, the chemical treatment, the lubricating oil is adhered to the surface of the steel sheet in the rust preventive oil or press molding that has been applied to ensure the rust prevention during transport, the rust-preventive oil and lubricating oil chemical reaction inhibit. Therefore, before performing the chemical conversion treatment, degrease the rust-preventive oil and lubricants.
[0004]
　In order to improve the chemical conversion treatability of the high-strength steel sheet, it is possible to Ni plating process is performed on the steel sheet. Also in the Si-containing steel sheet is not high strength, because it may be required good chemical conversion treatability, sometimes Ni plating process is performed on the steel sheet. On the other hand, when subjected to Ni plating treatment steel sheet, degreased deteriorates.
[0005]
　Previously various techniques have been proposed, both the degreasing and chemical conversion treatability is difficult. Recently, by improving the surface conditioning agent used in the chemical conversion treatment, the desired conversion coating because of easily formed, omitted techniques Ni plating process is proposed. However, omitting the Ni plating process, chemical conversion treatability is not sufficient. With such a technique, it is difficult to achieve both the chemical conversion treatability and degreasing properties.
CITATION
Patent Document
[0006]
Patent Document 1: JP-B 58-37391 Patent Publication
Patent Document 2: JP 2012-188693 Patent Publication
Patent Document 3: JP 2004-323969 Patent Publication
Patent Document 4: Japanese Patent No. 5482968 discloses
Patent Document 5: WO 2013 / 108785 Patent
Patent Document 6: JP 2008-190030 Patent Publication
Patent Document 7: JP-A 3-20485 Patent Publication
Summary of the Invention
Problems that the Invention is to Solve
[0007]
　The present invention aims to provide a method for manufacturing a steel sheet can achieve both chemical convertibility and degreasing properties.
Means for Solving the Problems
[0008]
　The present inventors have conducted extensive studies to solve the above problems. As a result, if the Si content is more than 0.4 mass%, Si oxide in cold-rolled sheet annealing is formed on the surface of the steel sheet, so clear that the Si oxide is reduced the chemical conversion treatability became. Si oxide can be removed by pickling, performing pickling Fe oxide film on the surface of the steel sheet rinsing after pickling grow to produce, also revealed that the residual. Further, as the Fe oxide film formed on the surface of the steel sheet is thick, it was found that chemical conversion treatability is deteriorated. Although it is possible to improve the chemical convertibility by Ni plating, as described above, degreasing and subjected to Ni plating is deteriorated. Thus, the result of the examination by the present inventors, Si content in the case of more than 0.4 wt%, both of chemical conversion treatability and degreasing properties revealed that difficulty.
[0009]
　Accordingly, the present inventors have conducted further intensive studies to suppress the formation of Fe oxide film in the water washing after pickling. As a result, the higher the electric conductivity of the rinsing water used in the washing, Fe oxide film grows thicker, the longer the washing time, Fe oxide film was found to grow thicker. Also, the longer the time from the end of the washing until the start of drying, Fe oxide film was found to grow thicker.
[0010]
　The present inventors have found that further intensive studies based on these findings, and conceived to aspects of the invention described below.
[0011]
　(1)
　obtaining a slab Si content is subjected to continuous casting of molten steel 0.4 wt% to 3.0 wt%,
　a step of obtaining a hot rolled steel sheet by performing hot rolling of the slab,
　the obtaining a cold-rolled steel sheet by performing cold rolling the hot-rolled steel sheet,
　and performing cold-rolled sheet annealing of the cold-rolled steel sheet,
　after it said cold-rolled sheet annealing, and performing pickling,
　the pickling after the step of performing washing with water, of
　after the washing, a step of drying
has,
　in the cold-rolled sheet annealing, the dew point and -35 ° C. or less,
　the electrical conductivity of the rinsing water used in the washing was less 5.0 mS / m,
　and in the water washing, water washing time was within 15 seconds,
　the manufacturing method of the steel sheet, which comprises initiating the drying within 60 seconds from the end of the washing.
[0012]
　(2)
　method for producing a steel sheet according to (1), wherein a Mn content of the molten steel is 0.5 mass% to 4.0 mass%.
[0013]
　(3) H
　contained in the rinse water + concentrations (mol / L) [H + ], Na + concentrations (mol / L) [Na + ], Mg 2+ concentration of (mol / L) [ mg 2+ ], K + concentrations (mol / L) [K + ], Ca 2+ concentration of the (mol / L) [Ca 2+ ], Fe 2+ concentration of (mol / L) [Fe 2+ ], Fe 3+ concentrations (mol / L) [Fe 3+ ], Cl - concentrations (mol / L) [Cl - ], NO 3 - concentration (mol / L) of [NO 3 - ], SO 4 2- concentrations (mol / L) [SO 4 2- when a] method for producing a steel sheet according to, characterized in that the expression 1 is satisfied (1) or (2).
　349.81 [H + ] Tasu50.1 [Na + ] + 53.05 × 2 [Mg 2+ ]
　Tasu73.5 [K + ] + 595 × 2 [Ca 2+ ] + 53.5 × 2 [Fe 2+ ]
　+ 68.4 × 3 [Fe 3+ ] Tasu76.35 [Cl - ] Tasu71.46 [NO 3 - ]
　+ 80.0 × 2 [SO 4 2- ] ≦ 5/100 (equation 1)
Effect of the invention
[0014]
　According to the present invention, since the excellent chemical conversion treatability can be obtained without performing Ni plating treatment, it is possible to achieve both the chemical conversion treatability and degreasing properties.
DESCRIPTION OF THE INVENTION
[0015]
　It will be described in detail embodiments of the present invention. In the method of manufacturing the steel sheet according to the present embodiment, the molten steel of the continuous casting, hot rolling, hot-rolled after pickling, cold rolling, cold-rolled sheet annealing, annealing after pickling, water washing and drying are performed. In the following description, a unit of content of each element contained in the molten steel "%" is especially meant to "mass%" unless otherwise specified.
[0016]
　First, in the continuous casting and hot rolling of the molten steel, the slabs produced Si content is subjected to continuous casting of 0.4% to 3.0% of the molten steel, heat and hot rolling of the slab.
[0017]
　Continuous casting and heating can be carried out in the general conditions. As described above, Si content in the case of more than 0.4%, Si oxide is produced to the extent that the pickling is required. Since Si content is 3.0 percent, the Si oxide in cold-rolled sheet annealing is a large amount on the surface of the steel sheet, it is impossible to sufficiently remove Si oxide be subjected to pickling, chemical conversion it is difficult to ensure the processability. Therefore, Si content is at most 3.0%.
[0018]
　In hot rolling, preferably performs finish rolling in the temperature range of 850 ℃ ~ 1000 ℃. Coiling temperature of the resulting hot rolled steel sheet is preferably in the range of 550 ℃ ~ 750 ℃.
[0019]
　After hot rolling pickling can be performed in common conditions.
[0020]
　Next, by performing the cold rolling of the obtained hot-rolled steel sheet to obtain a cold rolled steel sheet. When the rolling reduction of cold rolling attempts to less than 50%, since there may have to be kept by reducing the hot-rolled steel sheet in advance too, production efficiency is reduced. Therefore, the rolling reduction of cold rolling is preferably 50% or more. When the rolling reduction of cold rolling tries to 85 percent, it may load during cold rolling becomes extremely large. Therefore, the rolling reduction of cold rolling is preferably not more than 85%. Incidentally, the rolling rate, the thickness of the steel sheet before cold rolling h1, the thickness of the steel sheet after cold rolling is taken as h2, is a value calculated by (h1-h2) / h1.
[0021]
　Next, the cold-rolled sheet annealing the resulting cold-rolled steel sheet. Cold-rolled sheet annealing, for example, the preheating chamber, the heating chamber, Hitoshinetsushitsu, be carried out using a continuous annealing furnace comprising a cooling chamber and overaging chamber.
[0022]
　The holding temperature of the cold-rolled sheet annealing preferably a 750 ° C. or higher, preferably the retention time is 1 minute or more. Less than 750 ° C. The holding temperature at the cold-rolled sheet annealing, the retention time is less than 1 minute, it may not desired ductility other mechanical properties by recrystallization annealing can not be obtained.
[0023]
　Atmosphere of the annealing furnace, N 2 was mainly, H of 1 vol% ~ 40 vol% 2 may be added, steam can be added as needed. Atmosphere of the annealing furnace is inevitably H mixed 2 including O,
[0024]
　The -35 ° C. than the dew point of the atmospheric gas in the annealing furnace, the surface layer of the steel sheet inevitably decarburization, the mechanical properties of the steel sheet is degraded. Thus, the dew point of the atmospheric gas in the annealing furnace to -35 ° C. or less. May be in the annealing furnace is added water vapor, the amount of water vapor that time, H at -35 ° C. 2 O equilibrium vapor pressure was 3.2 × 10 -4 are atm, the atmospheric gas in the annealing furnace considering that the total pressure of the is equivalent to normal atmospheric pressure, it is about 0.03vol%. Sometimes steam is inevitably mixed into the annealing furnace, the water vapor amount at this time is about 0.02 vol.%. If water vapor is inevitably mixed, the dew point of the atmospheric gas in the annealing furnace is about -40 ° C..
[0025]
　After the cold-rolled sheet annealing, performing the pickling. By performing pickling to remove Si oxides and Mn oxides formed on the surface of the steel sheet during the cold-rolled sheet annealing. For the method of pickling, but are not particularly limited, for example, carried out by the steel sheet after the cold rolled sheet annealing, is continuously immersed while conveying in the pickling bath the pickling liquid has been filled be able to.
[0026]
　The pickling solution, is not particularly limited, and may be hydrochloric acid, a solution containing 1 wt% to 20 wt% in total of sulfuric acid or nitric acid or a combination thereof. The temperature of the pickling solution is not particularly limited as long as it is a 30 ℃ ~ 90 ℃. Immersion time for immersing the steel sheet in the pickling solution is not particularly restricted as long as it is 2 seconds to 20 seconds.
[0027]
　Then, washing the steel sheet after pickling. The method of washing is not particularly limited, for example, a steel sheet after pickling, rinsing water used in the water washing be carried out by continuously immersed while conveying in a bath filled it can.
[0028]
　In the 5.0 mS / m than the electric conductivity of the rinsing water during the washing, since the Fe oxide film tends to grow on the surface of the steel sheet can not be obtained excellent chemical conversion treatability. Therefore, the electric conductivity of the rinsing water, not more than 5.0 mS / m, preferably not more than 1.0 mS / m. Since the electric conductivity of the rinsing water can suppress the growth of lower the Fe oxide film A low, easily ensured chemical conversion treatability. On the other hand, even in theory pure water, the water H due to self-dissociation + ions and OH - ions 10 -7 exists by mol / L. Furthermore, literature (electrochemical Introduction, Yoshiharu Matsuda, Chiaki Iwakura, Maruzen, Tokyo, 1994, page 15) According to, H + ions and OH - , respectively, a molar electrical conductivity of the ion · cm 349.81S 2 / Mol, 198.3S · Cm 2 is / mol. For these reasons, the electrical conductivity of the theoretical pure water is expected to be 5.4μS / m. Thus, it is not possible to the electrical conductivity of the rinse water below 5.4μS / m. For example, in order to maintain low electrical conductivity such as less than 10 [mu] S / m is not only used ultrapure water, electrical conductivity by the carbon dioxide from the atmosphere carbonate ions are generated by dissolving in water increases also it must be prevented that. For this reason, it is necessary to manage the atmosphere, is not economical. Therefore, making the electrical conductivity of the rinse water less than 10 [mu] S / m is not preferable because the cost is excessive unnecessarily.
[0029]
　The washing time is 15 seconds, more than during the washing, since the Fe oxide film tends to grow on the surface of the steel sheet can not be obtained excellent chemical conversion treatability. Therefore, water washing time is not more than 15 seconds, preferably not more than 5 seconds. Rinsing the time is less than one second, it is impossible to remove the acid by water washing, acid remaining on the steel sheet Fe steel plate 2+ eluted ions, Fe 2+ ions thick Fe oxide film reacts with ambient oxygen to form, it becomes a cause of yellowing of the chemical conversion treatability of degradation and product appearance. Therefore, water washing time is preferably 1 second or more.
[0030]
　Si, in order to form a Si oxide on the surface of the steel sheet during the cold-rolled sheet annealing, deteriorates the chemical conversion treatability. Also the Si oxide as could be removed by pickling, also Si are dissolved in the steel sheet deteriorates the chemical conversion treatability. Chemical conversion treatability is dependent on the Si content in the steel sheet. The more Si content in the steel sheet, since the chemical conversion property is likely to deteriorate, depending on the Si content in the steel sheet, reduce the electrical conductivity of the rinse water, and, it is preferable to control short rinsing time.
[0031]
　And Si content in the steel sheet, the relationship between the electrical conductivity and washing time of the rinse water, shown in Table 1. If Si content in the steel sheet is less than 1.25% to 0.4%, the electrical conductivity of the rinse water preferably less 5.0 mS / m, preferably not more than 15 seconds rinsing time . If Si content in the steel sheet is less than or 1.25% 2.5%, the electrical conductivity of the rinse water preferably less 3.0 mS / m, preferably not more than 9 seconds rinsing time . If Si content in the steel sheet is 3.0% or less 2.5% or more, the electrical conductivity of the rinse water preferably less 1.0 mS / m, preferably not more than 3 seconds rinsing time . Thus by controlling the electric conductivity and washing time of the rinse water, it is possible to sufficiently ensure the chemical conversion treatability.
[0032]
[Table 1]

[0033]
　Rinse water used for washing, Na derived from the component of the rock in the fountainhead basin + , Mg 2+ , K + , Ca 2+ containing, mixed by performing pickling H + , Fe 2+ , Fe 3+ , Cl - , NO 3 - , SO 4 2- may contain. Electrical conductivity of the rinse water is dependent on these ion concentrations, the ion concentration (mol / L) for each ion, obtains the product of the electrical conductivity per 1 mole, of these products in each ion it can be calculated by summing the. Ie, H contained in the rinsing water + concentration of (mol / L) [H + ], Na + concentrations (mol / L) [Na + ], Mg 2+ concentration of (mol / L) [Mg 2+ ], K + Concentrations (mol / L) [K + ], Ca 2+ concentration of the (mol / L) [Ca 2+ ], Fe 2+ [Fe concentration (mol / L) of 2+ ], Fe 3+ concentration (mol / L) of [Fe 3+ ], Cl - [Cl concentration (mol / L) of - ], NO 3 - concentrations (mol / L) [NO 3 - ], SO 4 2- of concentration (mol / the L) [SO 4 2- upon and], it is preferable that formula 1 is satisfied. Document (Electrochemical Introduction, Yoshiharu Matsuda, Chiaki Iwakura, Maruzen, Tokyo, 1994, page 15) According to the electrical conductivity per 1 mol / L of each ion species, H + : 349.81 (S · Cm 2 / Mol), Na Tasu : 50.1 (S · cm 2 / mol), Mg 2+ : 53.05 × 2 (S · cm 2 / mol), K + : 73.5 (S · cm 2 / mol), Ca 2+ : 59. × 2 5 (S · cm 2 / mol), Fe 2+ : 53.5 × 2 (S · cm 2 / mol), Fe 3+ : 68.4 × 3 (S · cm 2 / mol), Cl - : 76 .35 (S · cm 2 / mol), NO 3 - : 71.46 (S · cm 2 / mol), SO 4 2- : 80.0 × 2 (S · cm 2 is / mol). Therefore, the electric conductivity of the rinsing water can be calculated by Equation 1. In addition, 1 (S · Cm 2 / Mol) are translated and 100 (mS · l / m · mol).
　349.81 [H + ] Tasu50.1 [Na + ] + 53.05 × 2 [Mg 2+ ]
　Tasu73.5 [K + ] + 595 × 2 [Ca 2+ ] + 53.5 × 2 [Fe 2+ ]
　+ 68.4 × 3 [Fe 3+ ] Tasu76.35 [Cl - ] Tasu71.46 [NO 3 - ]
　+ 80.0 × 2 [SO 4 2- ] ≦ 5/100 (equation 1)
[0034]
　Why Fe oxide film is easily formed on the surface of the steel sheet in the washing higher electric conductivity of the rinsing water is as follows. During water washing, Fe derived from the components of the steel sheet, Fe the following anode reaction 2+ eluted as ions in the rinse water.
　　￫ Fe Fe 2Tasu Tasu 2E -
[0035]
　On the other hand, it occurs following cathode reaction by atmospheric oxygen dissolved in the rinse water, OH - ions are generated.
　　1 / 2O 2 Tasu H 2 O Tasu 2E -　￫ 2OH -
[0036]
　Thereafter, Fe in rinse water 2+ and 2OH - and is bonded, iron hydroxide (Fe (OH) 2 precipitates as). H from iron hydroxide 2 oxide film of FeO is formed by O is eliminated.
　　Fe 2Tasu Tasu 2OH -　￫ Fe (OH)
　　2 Fe (OH) 2　￫ FeO Tasu H 2 O
[0037]
　In this series of reaction, when the low electrical conductivity of the rinse water was generated in the rinse water Fe 2+ ions and OH - in the vicinity of the ion, the positive charge / negative charges respectively is excessive, more than a predetermined amount of Fe 2+ ions and OH - believed to interfere with ions to generate. On the other hand, when the high electric conductivity of the rinsing water, since the rinse water contains many various cations / anions serve as carrier, Fe 2+ if ions are generated around the anions approach and, conversely OH - ions state electrically neutral is maintained by if it is generated around the cations approaches, considered above series of reactions is accelerated. From these, for the more rinsing time is increased above series of reactions is accelerated, it is estimated that Fe oxide film is easily formed on the surface of the steel sheet.
[0038]
　Steel sheet after rinsing, for example, may be pressure by wringer roll is usually made of rubber. You can scrape off the rinse water adhering to the surface of the steel sheet after rinsing. By reducing the amount of rinsing water adhering to the surface of the steel sheet after rinsing, it is possible to reduce the energy and time required for subsequent drying.
[0039]
　Next, drying the steel sheet after rinsing. The method of drying is not particularly limited, for example, set up a steel sheet after rinsing along the conveying direction, can be carried out by blowing hot air with a dryer to a steel sheet to be conveyed. Note that the drying capacity of the dryer (blower) is not particularly limited, taking into account the speed for conveying the steel sheet, it is enough thoroughly dried steel sheet.
[0040]
　Drying will start within 60 seconds from the end of the washing. The time is greater than 60 seconds from the end of the washing until the start of drying, to produce the Fe oxide film on the surface of the steel sheet, chemical conversion treatability deteriorates, the surface appearance of the steel sheet is degraded. Even if a rinse water purifier used in the washing, when the rinsing water on the surface of the steel sheet has passed a predetermined time remain attached, there is a risk that Fe oxide film is formed on the surface of the steel sheet.
[0041]
　During washing of the steel sheet, Fe from Fe derived from the components of the steel sheet 2+ and anode reactions ion is eluted into rinse water, atmospheric oxygen dissolved in the rinse water OH - is generated and a cathode reaction of generating ions. These reactions, since the traveling period from the completion of the water until the start of drying, the amount of the generated Fe oxide film is estimated to increase.
[0042]
　In this way, it is possible to produce a steel sheet according to the present embodiment. Incidentally, after drying, it may be wound steel sheet coil. Prior to winding into a coil, it may be coated rust preventive steel plate. Film formed on the surface of the steel sheet by rust preventive, to protect the surface of the steel sheet from ambient oxygen in the water and in the air, it is possible to suppress the formation of Fe oxide film. Therefore, it is possible to ensure the chemical conversion treatability of the steel sheet, it is possible to beautifully retain surface appearance of the steel sheet.
[0043]
　From the above, according to the manufacturing method of the steel sheet according to the present embodiment, since the good chemical conversion treatment can be obtained without performing Ni plating treatment, it is possible to achieve both the chemical conversion treatability and degreasing properties. Specifically, in the manufacturing method of the steel sheet according to the present embodiment, the electrical conductivity of the rinse water, washing time, and by controlling the time from washing with water until the end start drying, the surface of the steel sheet after washing during and washing completion the formation and growth of the Fe oxide film may be generated can be suppressed. Thus, it is possible to stably ensure the chemical conversion treatability of the steel sheet, it is possible to omit the Ni plating for securing chemical conversion treatability. Furthermore, in the manufacturing method of the steel sheet according to the present embodiment, by controlling the dew point of the cold-rolled sheet annealing, it is possible to suppress the deterioration of mechanical properties due to unavoidable decarburization in the surface layer of the steel sheet.
[0044]
　Steel sheet can be produced by this embodiment are varied, for example, it is possible to produce a Si-containing steel sheet according to the present embodiment is not a high-strength steel sheet and high strength.
[0045]
　When producing a high strength steel sheet, molten steel, for example, C: 0.05% ~ 0.25%, Si: 0.4% ~ 3.0%, Mn: 0.5% ~ 4.0%, Al : 0.005% ~ 0.1%, P: 0.03% or less, S: 0.02% or less, Ni, Cu, Cr or Mo: 0.0% ~ 1.0%, and, Ni, Cu the total content of Cr and Mo: 0.0% ~ 3.5% in total, B: 0.0000% ~ 0.005%, Ti, Nb or V: 0.000% ~ 0.1%, and , Ti, the total content of Nb and V: 0.0% ~ 0.20% in total, and the balance has a chemical composition represented by Fe and impurities. As the impurity, those included in raw materials such as ores and scrap, intended to be included in the manufacturing process, is exemplified.
[0046]
　(C: 0.05% ~ 0.25%)
　C is the tissue enhanced due the generation of quenching at the martensite phase, to ensure the strength of the steel sheet. The C content is less than 0.05%, does not produce sufficiently martensitic phase at normal annealing conditions, it may be difficult to secure the strength. Therefore, C content is preferably 0.05% or more. The C content of 0.25 percent, it is sometimes impossible to secure a sufficient spot weldability. Therefore, C content is preferably not more than 0.25%.
[0047]
　(Si: 0.4% ~
　3.0%) Si is while suppressing the deterioration of the ductility of the steel sheet, thereby improving the strength. In order to obtain the advantageous effects sufficiently, Si content is 0.4% or more. The Si content of 3.0 percent, it may workability during cold rolling is reduced. Therefore, Si content is at most 3.0%.
[0048]
　(Mn: 0.5% ~
　4.0%) Mn improves the hardenability of steel to ensure strength. In order to obtain the advantageous effects sufficiently, Mn content is preferably 0.5% or more. The Mn content of 4.0 percent, the workability during hot rolling is degraded, which may cause cracking of the steel in the continuous casting and hot rolling. Therefore, Mn content is preferably not more than 4.0%.
[0049]
　(Al: 0.005% ~
　0.1%) Al is a deoxidizing element of steel. Further, Al is formed of AlN to suppress grain grain refining, to suppress the coarsening of crystal grains by heat treatment, to ensure the strength of the steel sheet. The Al content is less than 0.005%, the effect is difficult to obtain. Therefore, Al content is preferably 0.005% or more. The Al content of 0.1 percent, it may weldability of the steel sheet is degraded. Therefore, Al content is preferably 0.1% or less. To hardly generated surface defects of the steel sheet by alumina clusters, Al content is more preferably at most 0.08%.
[0050]
　(P: 0.03% or less)
　P enhances the strength of steel. Therefore, it may be P is contained. Since refining cost is considerable, P content is preferably 0.001% or more, more preferably 0.005% or more. The P content of 0.03 percent, which may workability is lowered. Accordingly, P content is preferably 0.03% or less, more preferably 0.02% or less.
[0051]
　(S: 0.02% or less)
　S is in a normal steelmaking process contained in steel as an impurity. The S content of 0.02 percent, to deteriorate the workability during hot rolling of steel, also deteriorates the workability for forming the coarse MnS as the starting point of bending and hole expanding destroyed during processing Sometimes. Thus, S content is preferably 0.02% or less. The S content is less than 0.0001%, the cost is considerable, S content is preferably 0.0001% or more. To the surface defects of the steel sheet hardly occurs, S content is more preferably 0.001% or more.
[0052]
　Ni, Cu, Cr, Mo, B, Ti, Nb and V is not an essential element, a good optional elements be contained appropriately limit the predetermined amount on the steel sheet.
[0053]
　(Ni, Cu, Cr or Mo: 0.0% ~ 1.0%, and, Ni, Cu, total content of Cr and Mo:
　0.0% ~ 3.5% in total) Ni, Cu, Cr and Mo, delaying the formation of carbides, contributing to the residual austenite. In addition, to lower the martensitic transformation start temperature of austenite. Therefore, to improve the workability and fatigue strength. Accordingly, Ni, Cu, Cr or Mo may be contained. To obtain this effect sufficiently, the content of Ni, Cu, Cr or Mo is preferably 0.05% or more. Ni, Cu, the content of Cr or Mo 1.0 percent, with the effect of improving the strength is saturated, ductility is considerably deteriorated. Accordingly, the content of Ni, Cu, Cr or Mo is preferably 1.0% or less. Further, Ni, Cu, In total content of Cr and Mo of 3.5 percent, to improve more than necessary hardenability of steel, consisting mainly of ferrite, and difficult to produce a workability good steel along with the made, the cost is increased. Accordingly, the total content of Ni, Cu, Cr and Mo, preferably 3.5% or less in total.
[0054]
　(B: 0.0000% ~ 0.005%)
　B improves the hardenability of steel. Further, upon reheating for alloying treatment slows the pearlite transformation and bainite transformation. Thus, B may be contained. To obtain this effect sufficiently, B content is preferably 0.0001% or more. The B content of 0.005 percent, upon cooling from a temperature range where the two-phase of ferrite and austenite coexist, prevents ferrite sufficient area ratio grows, mainly composed of ferrite, good processability production of steel sheet becomes difficult. Therefore, B content is preferably 0.005% or less, more preferably 0.002% or less.
[0055]
　(Ti, Nb or V: 0.000% ~ 0.1%, and, Ti, the total content of Nb and V:
　total)0.0% Ti, Nb and V are carbide, nitride (or carbonitride) was formed, to strengthen the ferrite phase, thereby increasing the strength of the steel sheet. Thus, Ti, Nb or V may be contained. To obtain this effect sufficiently, the content of Ti, Nb or V is preferably 0.001% or more. Ti, the content of Nb or V 0.1 percent, not only the cost is increased, and the saturation effect of improving the strength, further, waste C unnecessarily. Accordingly, the content of Ti, Nb or V is preferably 0.1% or less. Further, Ti, the total content of Nb and V of 0.20 percent, not only the cost is increased, and the saturation effect of improving the strength, further, waste C unnecessarily. Thus, Ti, the total content of Nb and V is preferably not more than 0.20%.
[0056]
　When producing a Si-containing steel sheet is not high strength, molten steel, for example, C: 0.15% or less, Si: 0.4% ~ 1.0%, Mn: 0.6% or less, Al: 1.0% hereinafter, P: 0.100% or less, S: 0.035% or less, and the balance has a chemical composition represented by Fe and impurities. As the impurity, those included in raw materials such as ores and scrap, intended to be included in the manufacturing process, is exemplified.
[0057]
　(C: 0.15% or less)
　C is included in steel by iron ore was reduced with coke in ironmaking, is a residue that could not be removed by the primary refining of steel, the strength of the steel sheet there is to be secured. C content, referring to JIS G 3141, preferably not more than 0.15%.
[0058]
　(Si: 0.4% ~
　1.0%) Si, while suppressing the deterioration of the ductility of the steel sheet, it is possible to improve the strength. Further, Si is combined with oxygen in the steel in refining of the steel, sometimes to suppress the generation of bubbles when solidifying the ingot. In order to obtain the advantageous effects sufficiently, Si content is 0.4% or more. Upper limit of the Si content is preferably 1.0% or less.
[0059]
　(Mn: 0.6% or less)
　Mn is contained to remove S in the refining of the steel, it is possible to ensure the strength of steel. Mn content, referring to JIS G 3141, preferably not more than 0.6%.
[0060]
　(Al: 1.0% or
　less) Al is a deoxidizing element of steel. Further, Al is formed of AlN to suppress grain grain refining, to suppress the coarsening of crystal grains by heat treatment, to ensure the strength of the steel sheet. Upper limit of the Al content is preferably 1.0% or less.
[0061]
　(P: 0.100% or less)
　P is derived from iron ore, but a residue was not removed by the primary refining of steel, which may increase the strength of steel. P content in reference to JIS G 3141, preferably to 0.100% or less.
[0062]
　(S: 0.035% or less)
　S is in a normal steelmaking process contained in steel as an impurity. S content, referring to JIS G 3141, preferably not more than 0.035%.
[0063]
　If necessary, Si-containing steel sheet may contain an alloy element other than the elements not high strength.
[0064]
　Having described in detail preferred embodiments of the present invention, the present invention is not limited to such an example. It would be appreciated by those skilled in the relevant field of technology of the present invention, within the scope of the technical idea described in the claims, it is intended to cover various changes and modifications , also such modifications are intended to fall within the technical scope of the present invention.
Example
[0065]
　Next, a description will be given of an embodiment of the present invention. Conditions in examples are an example of conditions adopted for confirming the workability and effects of the present invention, the present invention is not limited to this single example of conditions. The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention, it is capable of adopting various conditions.
[0066]
　(Example 1)
　by casting the steels A ~ steel grade E shown in Table 2 to prepare a slab, subjected to hot rolling in the usual manner for each slab to obtain a hot rolled steel sheet. The resulting hot-rolled steel sheet subjected to pickling for, then subjected to cold rolling to obtain a cold-rolled steel sheet. The resulting cold-rolled steel sheet was cut to 100 mm × 50 mm. Underlined in Table 2 indicates that the value is out of range of the present invention.
[0067]
[Table 2]

[0068]
　Next, the obtained cold-rolled steel sheet was subjected cold-rolled sheet annealing under conditions shown in Tables 3 to 11, pickling, rinsing and drying successively. The cold-rolled sheet annealing, using a continuous annealing simulator, and the annealing temperature of 800 ° C.. Table 3 underlined in through Table 11 show that the number is out of range of the present invention.
[0069]
[table 3]

[0070]
[Table 4]

[0071]
[table 5]

[0072]
[Table 6]

[0073]
[Table 7]

[0074]
[Table 8]

[0075]
[Table 9]

[0076]
[Table 10]

[0077]
[Table 11]

[0078]
　Note that after the cold-rolled sheet annealing has been completed, to evaluate the presence or absence of the decarburized layer in the surface layer of the steel sheet. The obtained sample pieces were taken from the longitudinal central portion and the widthwise central portion and around, after filling the resin in its cross-section, was subjected to mechanical polishing and finishing mirror polishing. Thereafter, at 10μm intervals in the thickness direction from the outermost layer of the sample, using a micro Vickers hardness tester measures the hardness measured load as 0.01 kgf, to obtain a hardness profile. Also, the hardness of the central portion of the thickness direction was measured in the collected pieces was compared with the outermost layer hardness profile. If the at 20μm or less thickness dimension in softer than 90% of the hardness of the central region, the thickness of the decarburized layer is "Excellent (E)" as the allowable range, if 30μm or more "Worse ( It was W) ". The results are shown in Tables 3 to 11.
[0079]
　Rinse water used in the washing is to produce pure water with pure water system, by adding a predetermined amount of potassium chloride optionally in pure water to adjust the electrical conductivity. At this time, the electrical conductivity was measured by a handy type electric conductivity meter ES-51 manufactured by Horiba. Rinse water K + ion concentration and Cl - ion concentration, satisfy Equation 1 as "Excellent (E)", and to fulfill the formula 1 as "Worse (W)". Further, the dissolved oxygen amount of pure water was measured by a diaphragm electrode method was 2.4 mg / L. Table 12 shows the composition of the rinsing water, the measured value of the electrical conductivity, the calculated values of electrical conductivity by (Equation 1).
[0080]
[Table 12]

[0081]
　Water washing, each sample, after pulled out of the bath for pickling was performed continued against a predetermined time in the center of each sample immediately predetermined rinse water at a predetermined flow rate. At this time, the supply amount of the rinsing water, with Toyo pump TP-G2 manufactured by Miyake Chemical Co., was 7L / min constant. Further, water density, the test piece is 100 mm × 50 mm, for water pump is 7L / min, 23L / (s m · 2 was calculated to be). Drying for each sample was carried out by blowing hot air from the blower.
[0082]
　The obtained sample was measured thickness of the oxide film in glow discharge optical emission spectrometer (GDS). GDS was used manufactured by Rigaku Corporation GDA750. The thickness of the quantification of the oxide film, the concentration profile of each element in the depth direction from the surface layer of the sample was confirmed by GDS, oxygen concentration went Verify depth becomes half the maximum value. The size of up to the surface layer and a thickness of the oxide film from the depth position. The results are shown in Tables 3 to 11.
[0083]
　The obtained sample was subjected to evaluation of the chemical conversion treatability. On the surface of the obtained sample were generated phosphate chemical conversion film. Phosphate chemical treatment, degreasing, water washing, surface conditioning, chemical conversion treatment, again washing with water was carried out in the order of drying. Degreasing, the obtained sample, Nippon Parkerizing Co. degreasing agent FC-E2001, was performed by spraying for 2 minutes at a temperature 40 ° C.. Washing with water, the obtained samples was carried out 30 seconds spraying tap water at room temperature. Surface adjustment, in a bath of Nihon Parkerizing Co. surface conditioner PL-X, the resulting sample was performed by immersion for 30 seconds at room temperature. Chemical treatment, in a bath of 35 ° C. of Nihon Parkerizing Co. chemical conversion treatment agent PB-SX, was carried out by immersing the obtained sample for 2 minutes. Water washing again, the obtained sample, the tap water for 30 seconds spraying and then was carried out 30 seconds spraying pure water. Drying the obtained sample was performed and dried in a hot air oven. Thus for samples phosphate chemical conversion film was formed, it was evaluated chemical conversion treatability by the following procedure. A scanning electron microscope (SEM) was taken to a chemical conversion crystals on the surface of each sample. Chemical crystals are densely formed, and the long sides of crystals were evaluated as long as 2μm or 4μm or less "Excellent (E)". Chemical crystals are densely formed, and if the long side of the crystal is less 4μm super 8 [mu] m, were evaluated as "Medium (M)". Chemical crystals has not been formed densely, the long sides of or exposure of the sample itself is observed, or chemical conversion crystals even dense crystals if 8μm greater was evaluated as "Worse (W)". The results are shown in Tables 3 to 11.
[0084]
　The obtained sample was subjected to evaluation of degreasing. After the degreasing, it was visually observed by attaching the water to the sample. Sample Once you repel the water "Worse (W)", was to be repelled "Excellent (E)". The results are shown in Tables 3 to 11.
[0085]
　As shown in Table 3 to Table 11, sample No. 4, sample No. 5, sample No. 7 to Sample No. 9, sample No. 17, sample No. 23, sample No. 25, sample No. 26, sample No. 29, sample No. 31, sample No. 32, sample No. 36 to Sample No. 39, sample No. 42 to Sample No. 44, sample No. 48 to Sample No. 52, sample No. 57 to Sample No. 60, sample No. 63 to Sample No. 65, sample No. 69 to Sample No. 73, sample No. 78 to Sample No. 81, sample No. 84 to Sample No. 86, sample No. 90 to Sample No. 94, sample No. 99 to Sample No. 102, sample No. 105 to Sample No. 107, sample No. 111 to Sample No. 115, sample No. 120 to Sample No. 123, sample No. 126 to Sample No. 128, sample No. 132 to Sample No. 136, sample No. 141, sample No. 142, sample No. 144 to Sample No. 147, sample No. 150 to Sample No. 152, sample No. 156 to Sample No. 160, sample No. 165, sample No. 166, sample No. 168 to Sample No. 171, sample No. 174 to Sample No. 176, sample No. 180 to Sample No. 184, sample No. 189, sample No. 190, sample No. 192 to Sample No. 195, sample No. 198 to Sample No. 200, sample No. 204 to Sample No. 208, sample No. 213, sample No. 214, sample No. 216 to Sample No. 219, sample No. 222 to Sample No. 224, sample No. 228 to Sample No. 232, sample No. 237, sample No. 238, sample No. 240 to Sample No. 243, sample No. 246 to Sample No. 248, sample No. 252 to Sample No. 256, sample No. 261, sample No. 262, sample No. 264 to Sample No. 267, sample No. 270 to Sample No. 272, sample No. 276 to Sample No. 280, sample No. 285, sample No. 286, sample No. 288 to Sample No. 291, sample No. 294 to Sample No. 296, sample No. 300 to Sample No. 304, sample No. 30 9, sample No. 310, sample No. 312 to Sample No. 315, sample No. 318 to Sample No. 320, sample No. 324 to Sample No. 328, sample No. 333, sample No. 334, sample No. 336 to Sample No. 339, sample No. 342 to Sample No. 344, sample No. 348 to Sample No. 352, sample No. 357, sample No. 358, sample No. 360 to Sample No. 363, sample No. 366 to Sample No. 368, sample No. 372 to Sample No. 376, sample No. 381, sample No. 382, sample No. 384 to Sample No. 387, sample No. 390 to sample No. 392, sample No. 396 to Sample No. 400, sample No. 405, sample No. 406, sample No. 408 to Sample No. 411, sample No. 414 to Sample No. 416 and Sample No. 420 to Sample No. In 424, the dew point, the electric conductivity of the rinsing water, washing time, time and chemical composition from rinsing termination to the start drying because it is within the scope of the present invention, good chemical conversion treatability and degreasing properties were obtained. Sample No. 35, sample No. 56, sample No. 77, sample No. 98, sample No. 119, sample No. 140, sample No. 164, sample No. 188, sample No. 212, sample No. 236, sample No. 260, sample No. 284, sample No. 308, sample No. 332, sample No. 356, sample No. 380 and the sample No. At 404, for performing the drying without performing water washing after pickling, rust is formed thickly on the surface, it was not possible to measure the thickness of the oxide film.
[0086]
　(Test Example 1)
　determine the electric conductivity of the rinsing water disclosed in Patent Document 4, and compares it to the electric conductivity of the rinsing water used in the present invention. The most clean rinse water disclosed in Patent Document 4, Experiment No. It was reproduced one of the rinse water. Each ion concentration, Fe 2+ : 3.2 g / L,　NO 3 - : 1.1 g / L, Cl - : a 2.3 g / L. First, FeCl of 0.032 mol / L in pure water 2 and, Fe (NO of 0.009 mol / L 3 ) 2 was prepared a solution obtained by dissolving the. The resulting rinsing water, using a handy-type electric conductivity meter ES-51 manufactured by Horiba, was measured electrical conductivity. The results are shown in Table 13. Also, Table 13, was also shown ion concentration and the electric conductivity of the rinsing water used in the first embodiment.
[0087]
[Table 13]

[0088]
　As shown in Table 13, the electric conductivity of the cleanest rinse water disclosed in Patent Document 4, it was confirmed that the range of the present invention.

The scope of the claims
[Requested item 1]
　Obtaining a slab Si content is subjected to continuous casting of molten steel 0.4 wt% to 3.0 wt%,
　a step of obtaining a hot rolled steel sheet by performing hot rolling of the slab,
　the hot-rolled steel sheet obtaining a cold-rolled steel sheet subjected to cold rolling,
　and performing cold-rolled sheet annealing of the cold-rolled steel sheet,
　after said cold-rolled sheet annealing, and performing pickling,
　after the pickling, and performing water washing,
　after the washing, a step of drying
has,
　in the cold-rolled sheet annealing, the dew point and -35 ° C. or less,
　the electrical conductivity of the rinsing water used in the water washing 5. not more than 0 mS / m,
　and in the water washing, water washing time was within 15 seconds,
　the manufacturing method of the steel sheet, which comprises initiating the drying within 60 seconds from the end of the washing.
[Requested item 2]
　Method for producing a steel sheet according to claim 1, Mn content of the molten steel is characterized by a 0.5 wt% to 4.0 wt%.
[Requested item 3]
H 　contained in the rinse water + the concentration (mol / L) [H + ], Na + concentrations (mol / L) [Na + ], Mg 2+ concentration of (mol / L) [Mg 2+ ] , K + concentrations (mol / L) [K + ], Ca 2+ [Ca concentration (mol / L) of 2+ ], Fe 2+ concentration of (mol / L) [Fe 2+ ], Fe 3+ concentration of (mol / L) of [Fe 3+ ], Cl - [Cl concentration (mol / L) of - ], NO 3 - concentrations (mol / L) [NO 3 - ], SO 4 2- Concentration (mol / L) of [SO 4 2- upon with, production method of the steel sheet according to claim 1 or 2, characterized in that Formula 1 is satisfied.
　349.81 [H + ] Tasu50.1 [Na + ] + 53.05 × 2 [Mg 2+ ]
　Tasu73.5 [K + ] + 595 × 2 [Ca 2+ ] + 53.5 × 2 [Fe 2+ ]
　+ 68.4 × 3 [Fe 3+ ] Tasu76.35 [Cl - ]
　Tasu71.46 [NO 3 - ] + 80.0 × 2 [SO 4 2- ] ≦ 5/100 (equation 1)