WO2021166350A1 - 高強度溶融亜鉛めっき鋼板の製造方法 - Google Patents
高強度溶融亜鉛めっき鋼板の製造方法 Download PDFInfo
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Definitions
- the present invention relates to a method for producing a high-strength hot-dip galvanized steel sheet using a high-strength steel sheet containing Si and Mn as a base material.
- hot-dip galvanized steel sheets that can be manufactured at low cost and have excellent rustproof properties, and alloyed hot-dip galvanized steel sheets.
- Steel plate is used.
- hot-dip galvanized steel sheets are manufactured by the following methods. First, a thin steel plate obtained by hot rolling, cold rolling, or optionally heat-treating a steel slab is used as a base steel plate. The surface of the base steel sheet is cleaned by at least one pretreatment step of degreasing or pickling, or the pretreatment step is omitted and the oil on the surface of the base steel sheet is burned and removed in a preheating furnace, and then non-oxidizing.
- Recrystallization annealing is performed by heating in an atmosphere or a reducing atmosphere. Then, the steel sheet is cooled to a temperature suitable for plating in a non-oxidizing atmosphere or a reducing atmosphere, and immersed in a hot-dip zinc bath to which a trace amount of Al is added without being exposed to the atmosphere.
- the alloyed hot-dip galvanized steel sheet is manufactured by hot-dip galvanizing and then heat-treating the steel sheet in an alloying furnace to alloy the plating layer.
- Si and Mn form oxides on the outermost layer of the steel sheet in an annealed atmosphere, deteriorating the wettability between the base steel sheet and hot-dip zinc.
- the plating appearance was inferior, and there was a risk that surface defects such as non-plating would occur. It is considered that the surface defects are caused by the oxides of Si and Mn formed on the outermost layer of the steel sheet remaining at the interface between the plating layer and the base steel sheet.
- Patent Document 1 discloses a technique for performing reduction annealing after performing oxidation treatment.
- the present invention has been made in view of such a problem, and an object of the present invention is to perform hot-dip galvanizing treatment on a steel strip containing Si in a predetermined amount or more.
- the purpose is to obtain a high-strength hot-dip galvanized steel sheet having an excellent plated appearance.
- the present inventors obtained the following findings.
- a high-strength steel sheet containing Si and Mn is used as the base material, it is reduced after the oxidation treatment in order to suppress the oxidation of Si and Mn on the outermost layer of the steel sheet, which causes a decrease in the wettability of the steel sheet and hot-dip galvanized steel.
- Annealing is effective, but when Mn is excessively added to Si, the surface of the Si and Mn steel sheets can be surfaced by appropriately controlling the outlet temperature of the oxidation treatment and the dew point in the reduction annealing. It was found that a high-strength hot-dip galvanized steel sheet with excellent plating appearance can be obtained by suppressing oxidation in the steel sheet.
- the present invention is based on the above findings, and its features are as follows.
- High strength using a continuous hot-dip galvanizing apparatus having an annealing furnace in which a heating zone, a soaking zone, and a cooling zone are juxtaposed in this order, and a hot-dip galvanizing facility provided after the cooling zone.
- a method for manufacturing hot-dip galvanized steel sheets A step of transporting the steel strip inside the annealing furnace in the order of the heating zone, the soaking zone, and the cooling zone, and annealing the steel strip.
- the steel strip discharged from the cooling zone is hot-dip galvanized to obtain a high-strength hot-dip galvanized steel sheet.
- the steel strip contains Mn: 1.7% or more and 3.5% or less, and Si: 0.2% or more and 1.05% or less in mass%, and [Si] / [Mn] ⁇ 0. It has a component composition that satisfies 30 A method for producing a high-strength hot-dip galvanized steel sheet, wherein the component composition, the dew point of the atmosphere in the solitary tropics, and the outlet temperature of the heating zone satisfy the following formula (1).
- P. Dew point (° C) of the atmosphere in the tropics (however, -50 ° C ⁇ DP ⁇ -5 ° C)
- T Steel strip exit side temperature (° C.) (400 ° C. ⁇ T ⁇ 850 ° C.) of the heating zone Is.
- the heating zone is equipped with a direct-fired burner furnace divided into a front stage and a rear stage.
- the air ratio of the atmosphere in the previous stage is set to 1.0 or more and less than 1.3.
- the hydrogen concentration in the tempered tropical atmosphere is set to 5% by volume or more and 30% by volume or less, and the steel strip is in a temperature range of 700 ° C. or higher and 900 ° C. or lower for 10 seconds or more and 300 seconds or less.
- the high-strength hot-dip galvanized steel sheet is further alloyed by heating at a temperature of 460 ° C. or higher and 600 ° C. or lower for 10 seconds or longer and 60 seconds or shorter.
- composition of the components is further increased by mass%.
- C 0.8% or less
- P 0.1% or less
- S 0.03% or less
- Al 0.1% or less
- composition of the components is further increased by mass%.
- N 0.010% or less
- Cr 1.0% or less
- Cu 1.0% or less
- Ni 1.0% or less
- Mo 1.0% or less
- Nb 0.20% or less
- V 0.5% or less
- Sb 0.200% or less
- Ta 0.1% or less
- W 0.5% or less
- Zr 0.1% or less
- Sn 0.20% or less
- Ca 0.005% or less
- the present invention it is possible to obtain a high-strength hot-dip galvanized steel sheet having an excellent plating appearance even when a hot-dip galvanized steel strip containing Si in a predetermined amount or more is subjected to hot-dip galvanizing treatment. ..
- the unit of the content of each element in the steel component composition and the content of each element in the plating layer component composition are both “mass%”, and are simply indicated by “%” unless otherwise specified.
- the unit of gas concentration is “volume%”, and is simply indicated by “%” unless otherwise specified.
- the term "high strength" of a steel sheet means that the tensile strength of the steel sheet is 340 MPa or more.
- the manufacturing method of high-strength hot-dip galvanized steel sheet is High-strength hot-dip galvanizing using a continuous hot-dip galvanizing apparatus having an annealing furnace in which a heating zone, a soaking zone, and a cooling zone are juxtaposed in this order, and a hot-dip galvanizing facility provided after the cooling zone. It is a method of manufacturing steel sheets. A step of transporting the steel strip inside the annealing furnace in the order of the heating zone, the soaking zone, and the cooling zone, and annealing the steel strip. Using the hot-dip galvanizing equipment, the steel strip discharged from the cooling zone is hot-dip galvanized to obtain a high-strength hot-dip galvanized steel sheet.
- the steel strip contains Mn: 1.7% or more and 3.5% or less, and Si: 0.2% or more and 1.05% or less in mass%, and [Si] / [Mn] ⁇ 0. It has a component composition that satisfies 30 A method for producing a high-strength hot-dip galvanized steel sheet, wherein the component composition, the dew point of the atmosphere in the solitary tropics, and the outlet temperature of the heating zone satisfy the following formula (1).
- P. Dew point (° C) of the atmosphere in the tropics (however, -50 ° C ⁇ DP ⁇ -5 ° C)
- T Steel strip exit side temperature (° C.) (400 ° C. ⁇ T ⁇ 850 ° C.) of the heating zone Is.
- Mn 1.7% or more and 3.5% or less
- Mn is an element effective for increasing the strength of steel.
- the amount of Mn is set to 1.7% or more.
- the amount of Mn exceeds 3.5%, Mn-only oxide is excessively formed, and it is good even if the temperature on the steel strip side of the heating zone and the dew point of the solitary tropics are appropriately controlled based on the formula (1). The plated appearance cannot be obtained. Therefore, the amount of Mn is set to 1.7% or more and 3.5% or less.
- the amount of Mn is preferably 2.0% or more, more preferably 2.3% or more.
- the amount of Mn is preferably 3.3% or less, more preferably 3.0% or less.
- Si 0.2% or more and 1.05% or less Si is an element effective for strengthening steel to obtain a good material. If the amount of Si is less than 0.2%, it is necessary to add other expensive alloying elements in order to obtain high strength, which is economically unfavorable. Further, if the amount of Si is less than 0.2%, there is little need to apply the production method of the present invention. The reason is not always clear, but since a sufficient amount of iron oxide is produced by the oxidation treatment described below, oxidation of Si and Mn in the outermost layer of the steel sheet during reduction annealing can be suppressed, and the plating appearance is large. It can be estimated that it will not be a problem.
- the upper limit of the amount of Si is 1.05%. Therefore, the amount of Si is set to 0.3% or more and 1.05% or less.
- the amount of Si is preferably 0.3% or more, more preferably 0.4% or more.
- the amount of Si is preferably 0.9% or less, more preferably 0.7% or less.
- [Si] / [Mn] is set to 0.30 or less.
- Si / Mn is preferably 0.25 or less.
- the component composition may further optionally contain the following components.
- C 0.8% or less C improves workability by forming martensite or the like as a steel structure.
- the amount of C is preferably 0.8% or less, and more preferably 0.30% or less in order to obtain good weldability.
- the lower limit of C is not particularly limited, but in order to obtain good workability, C is preferably 0.03% or more, and more preferably 0.05% or more.
- P 0.1% or less (not including 0%) By suppressing the content of P, it is possible to prevent a decrease in weldability. Further, it is possible to prevent P from segregating at the grain boundaries and prevent deterioration of ductility, bendability, and toughness.
- the amount of P is preferably 0.1% or less in order to suppress ferrite transformation and obtain fine crystal grains.
- the lower limit of P is not particularly limited, and may be more than 0% and 0.001% or more due to restrictions in production technology.
- the amount of S is preferably 0.03% or less, and more preferably 0.02% or less.
- the amount of S is preferably 0.03% or less, and more preferably 0.02% or less.
- Al 0.1% or less Al is thermodynamically most easily oxidized, so it oxidizes before Si and Mn, suppresses the oxidation of Si and Mn on the outermost layer of the steel sheet, and oxidizes Si and Mn inside the steel sheet. Has the effect of promoting. This effect is obtained when the amount of Al is 0.01% or more. On the other hand, if the amount of Al exceeds 0.1%, the cost will increase. Therefore, when added, the amount of Al is preferably 0.1% or less.
- the lower limit of Al is not particularly limited, and can be more than 0% and 0.001% or more.
- B 0.005% or less B is an element effective for improving the hardenability of steel.
- the amount of B is preferably 0.0003% or more, and more preferably 0.0005% or more.
- the amount of B is preferably 0.005% or less. This is because by setting the amount of B to 0.005% or less, oxidation of Si in the outermost layer of the steel sheet can be suppressed and good plating adhesion can be obtained.
- Ti 0.2% or less
- the amount of Ti is preferably 0.2% or less, more preferably 0.05% or less. This is because good plating adhesion can be obtained by setting the Ti amount to 0.2% or less.
- the lower limit of Ti is not particularly limited, but it is preferably 0.005% or more in order to obtain the effect of strength adjustment.
- composition of the components is further optional, N: 0.010% or less, Cr: 1.0% or less, Cu: 1.0% or less, Ni: 1.0% or less, Mo: 1.0% or less, Nb: 0.20 or less, V: 0.5% or less, Sb: 0.200% or less, Ta: 0.1% or less, W: 0.5% or less, Zr: 0.1% or less, Sn: 0.20 It may contain one or more selected from the group consisting of% or less, Ca: 0.005% or less, Mg: 0.005% or less, and REM: 0.005% or less.
- N 0.010% or less (not including 0%)
- the N content is preferably 0.010% or less.
- N forms coarse nitrides at high temperatures such as Ti, Nb, and V, which impairs the effect of increasing the strength of the steel sheet by adding Ti, Nb, and V. Can be prevented.
- a decrease in toughness can be prevented.
- by setting the N content to 0.010% or less it is possible to prevent slab cracking and surface flaws from occurring during hot rolling.
- the content of N is more preferably 0.005% or less, further preferably 0.003% or less, and most preferably 0.002% or less.
- the lower limit of the content of N is not particularly limited, and may be more than 0% and 0.0005% or more due to restrictions in production technology.
- the amount of Cr is preferably 0.005% or more. By setting the amount of Cr to 0.005% or more, the hardenability can be improved and the balance between strength and ductility can be improved. When added, the amount of Cr is preferably 1.0% or less from the viewpoint of preventing cost increase.
- the amount of Cu is preferably 0.005% or more.
- the amount of Cu is preferably 1.0% or less from the viewpoint of preventing cost increase.
- Ni 1.0% or less
- the amount of Ni is preferably 0.005% or more.
- the amount of Ni is preferably 1.0% or less from the viewpoint of preventing cost increase.
- the amount of Mo is preferably 0.005% or more.
- the amount of Mo is preferably 0.05% or more and 1.0% or less from the viewpoint of preventing cost increase.
- Nb 0.20% or less
- the amount of Nb is preferably 0.20% or less from the viewpoint of preventing cost increase.
- V 0.5% or less
- the amount of V is preferably 0.5% or less from the viewpoint of preventing cost increase.
- Sb 0.200% or less
- Sb can be contained from the viewpoint of suppressing decarburization of the steel sheet surface in a region of several tens of microns caused by nitriding, oxidation, or oxidation of the steel sheet surface.
- Sb suppresses nitriding and oxidation of the surface of the steel sheet, thereby preventing the amount of martensite produced on the surface of the steel sheet from decreasing, and improving the fatigue characteristics and surface quality of the steel sheet.
- the amount of Sb is preferably 0.001% or more.
- the amount of Sb is preferably 0.200% or less.
- Ta 0.1% or less Ta is 0.001% or more to obtain the effect of improving strength.
- the amount of Ta is preferably 0.1% or less from the viewpoint of preventing cost increase.
- W 0.5% or less
- the amount of W is preferably 0.5% or less from the viewpoint of preventing cost increase.
- Zr 0.1% or less
- the amount of Zr is preferably 0.1% or less from the viewpoint of preventing cost increase.
- Sn 0.20% or less
- Sn is an element that suppresses denitrification, deboronization, etc., and is effective in suppressing a decrease in steel strength. In order to obtain such an effect, it is preferable that each is 0.002% or more. On the other hand, in order to obtain good impact resistance, the Sn amount is preferably 0.20% or less.
- Ca 0.005% or less Ca can control the morphology of sulfide and improve the ductility and toughness by containing 0.0005% or more. Further, from the viewpoint of obtaining good ductility, the amount of Ca is preferably 0.005% or less.
- Mg 0.005% or less
- the amount of Mg is preferably 0.005% or less from the viewpoint of preventing cost increase.
- REM 0.005% or less
- the amount of REM is preferably 0.005% or less from the viewpoint of obtaining good toughness.
- the rest other than the above can be Fe and unavoidable impurities.
- the steel strip having the above-mentioned composition is subjected to hot-dip galvanizing treatment by the method for producing a high-strength hot-dip galvanized steel sheet described later, or further alloyed to obtain a high-strength hot-dip galvanized steel sheet.
- the method for obtaining the steel strip is not particularly limited, but a steel slab having the above-mentioned composition can be hot-rolled, pickled, and then cold-rolled according to a known method to obtain a steel strip.
- the thickness of the steel strip is not particularly limited, but is usually 0.3 mm or more and 2.8 mm or less.
- a method for producing high-strength hot-dip galvanizing is continuous hot-dip galvanizing having a heating zone, a soaking zone, an annealing furnace in which a cooling zone is juxtaposed in this order, and a hot-dip galvanizing facility provided after the cooling zone.
- a method for manufacturing high-strength hot-dip galvanized steel sheets using a plating device A step of transporting the steel strip inside the annealing furnace in the order of the heating zone, the soaking zone, and the cooling zone, and annealing the steel strip.
- the steel strip discharged from the cooling zone is hot-dip galvanized to obtain a high-strength hot-dip galvanized steel sheet.
- the steel strip contains Mn: 1.7% or more and 3.5% or less, and Si: 0.2% or more and 1.05% or less in mass%, and [Si] / [Mn] ⁇ 0. It has a component composition that satisfies 30.
- This is a method for producing a high-strength hot-dip galvanized steel sheet, wherein the component composition, the dew point of the atmosphere in the solitary tropics, and the outlet temperature of the heating zone satisfy the following formula (1).
- P. Dew point (° C) of the atmosphere in the tropics (however, -50 ° C ⁇ DP ⁇ -5 ° C)
- T Steel strip exit side temperature (° C.) (400 ° C. ⁇ T ⁇ 850 ° C.) of the heating zone Is.
- a steel strip (thin steel plate) having the above-mentioned composition is obtained according to a known method.
- a steel slab is heated by slab and then hot-rolled to obtain a hot-rolled plate.
- the hot-rolled plate is pickled, and then the hot-rolled plate is cold-rolled once or two or more times with intermediate annealing sandwiched between them to obtain a steel strip to be used as a base steel plate.
- the continuous hot-dip galvanizing apparatus 100 includes an annealing furnace 20 in which heating zones 10, soaking zones 12 and cooling zones 14 and 16 are juxtaposed in this order, and a hot-dip galvanizing bath as a hot-dip galvanizing facility provided after the cooling zones 16. 22 and an alloying facility 23 provided after the hot-dip galvanizing bath 22.
- the heating zone 10 includes a first heating zone 10A and a second heating zone 10B. The tip of the snout 18 connected to the cooling zone 16 is immersed in the hot-dip galvanizing bath 22, and the annealing furnace 20 and the hot-dip galvanizing bath 22 are connected by the snout 18.
- the steel strip P is introduced into the first heating zone 10A from the steel strip introduction port at the lower part of the first heating zone 10A, and then introduced into the second heating zone 10B connected to the first heating zone 10A.
- Each band 10, 12, 14, 16 is provided with one or more hearth rolls at the top and bottom.
- the steel strip P is conveyed in the predetermined strip of the annealing furnace 20 a plurality of times in the vertical direction to form a plurality of paths.
- FIG. 1 an example of 10 passes in the solitary tropics 12, 2 passes in the first cooling zone 14, and 2 passes in the second cooling zone 16 is shown, but the number of passes is not limited to this and depends on the processing conditions. It can be set as appropriate.
- the steel strip P is turned at a right angle without being folded back, and the steel strip P is moved to the next strip. In this way, the steel strip P can be conveyed in the order of the heating zone 10, the soaking zone 12, and the cooling zones 14 and 16 inside the annealing furnace 20 to perform annealing on the steel strip P.
- the oxidation treatment applied to the steel strip P in the heating strip 10 will be described. As described above, it is effective to add Si, Mn, etc. to the steel in order to increase the strength of the steel sheet. However, in the steel strip P to which these elements are added, oxides of Si and Mn are generated on the outermost layer of the steel sheet in the annealing performed before the hot-dip galvanizing treatment, and the plating appearance is deteriorated.
- the plating appearance is improved by adjusting the annealing conditions to be performed before the hot-dip galvanizing treatment and suppressing the oxidation of Si and Mn in the outermost layer of the steel sheet. It was found that the reactivity between the plating and the steel strip P can be enhanced and the plating adhesion is improved.
- the second heating zone 10B used for the oxidation treatment into two zones, the front stage on the upstream side in the steel sheet moving direction and the rear stage on the downstream side, and control the air ratio of the atmosphere of each of the front stage and the rear stage. become.
- the oxidation treatment (pre-stage treatment) in the front stage of the second heating zone 10B and the oxidation treatment (post-stage treatment) in the latter stage of the second heating zone 10B will be described.
- the air ratio of the atmosphere in the first stage of the second heating zone 10B is 1.0 or more. It is preferably less than 3.
- the air ratio of the atmosphere in the first stage of the second heating zone 10B is more preferably 1.1 or more. Further, the air ratio of the atmosphere in the first stage of the second heating zone 10B is more preferably 1.2 or less.
- the heating temperature of the pretreatment is preferably 400 ° C. or higher in order to promote the oxidation of iron.
- the heating temperature of the pretreatment is preferably 850 ° C. or lower. This is because by setting the heating temperature of the pre-stage treatment to 850 ° C. or lower, the amount of iron oxide produced can be kept within a suitable range, and the occurrence of pickup in the next step can be prevented.
- the air ratio of the atmosphere in the latter stage of the second heating zone 10B is preferably 0.7 or more, and preferably less than 1.0.
- the heating temperature of the post-stage treatment is preferably 600 ° C. or higher.
- the heating temperature of the post-stage treatment is preferably 850 ° C. or lower. By setting the heating temperature to 850 ° C. or lower, the cost required for heating can be reduced.
- the second heating zone 10B needs to be composed of at least two or more zones.
- the atmosphere of each of the two zones may be controlled as described above.
- the second heating zone 10B is composed of three or more zones, any continuous zone can be regarded as one zone by controlling the atmosphere in the same manner. It is also possible to perform the pre-stage treatment and the post-stage treatment in separate oxidation furnaces. However, considering the industrial productivity and the implementation of the present invention by improving the current production line, it is preferable to divide the same furnace into two or more zones and control the atmosphere in each zone. As shown in FIG.
- the second heating zone 10B is divided into four groups (# 1 to # 4), and the three groups (# 1 to # 3) on the upstream side in the steel sheet moving direction are the front stages.
- the final zone (# 4) is the latter stage.
- the second heating zone 10B may be either a direct fire burner furnace (Direct Field Furnace; DFF) or a non-oxidizing furnace (Non Oxidizing Furnace; NOF).
- DFF Direct Field Furnace
- NOF Non Oxidizing Furnace
- the second heating zone 10B is an open flame burner furnace.
- DFF is often used in continuous hot-dip galvanizing lines, and the air ratio of each band can be easily controlled.
- the temperature of the steel strip can be raised quickly (the rate of temperature rise is high), so that there is an advantage that the furnace length of the heating zone 10 can be shortened and the line speed can be increased. From the viewpoint of efficiency, it is preferable to use DFF.
- DFF heats a steel sheet by mixing and burning fuel such as coke oven gas (COG), which is a by-product gas of a steel mill, and air. Therefore, if the ratio of air to fuel is increased, unburned oxygen remains in the flame, and the oxygen can promote the oxidation of the steel sheet.
- COG coke oven gas
- a plurality of burners are dispersedly arranged on the inner wall of the second heating zone 10B so as to face the steel strip P. It is preferable that a plurality of burners are divided into a plurality of groups, and the combustion rate and the air ratio can be controlled independently for each group.
- the heating burner of the second heating zone 10B is divided into four groups (# 1 to # 4), and the three groups (# 1 to # 3) on the upstream side in the steel sheet moving direction are used for the pretreatment.
- the oxidation burner and the final zone (# 4) are reduction burners used for the subsequent treatment, and the air ratio of the oxidation burner and the reduction burner can be controlled individually.
- the air ratio of the atmosphere in the front stage and the rear stage of the second heating zone 10B is a value obtained by dividing the amount of air actually introduced into each burner by the amount of air required for complete combustion of the fuel gas.
- the temperature T on the steel strip out side of the heating zone 10, that is, the steel strip out side of the second heating zone 10B is controlled so as to satisfy the following equation (1).
- C exp (T / 100) / [Si] And [Si]: Si concentration (mass%) [Mn]: Mn concentration (mass%) D. P.
- T Steel strip exit side temperature (° C.) (400 ° C. ⁇ T ⁇ 850 ° C.) of the heating zone Is.
- a radiation thermometer is used to measure the temperature T on the steel strip exit side of the heating zone 10.
- the measurement method of the radiation thermometer is a method that uses multiple reflections that are not easily affected by the surface of the steel sheet.
- the radiation thermometer is installed immediately after the second heating zone 10B (in FIG. 1, near the second hearth roll 11 from the steel strip exit side of the second heating zone 10B).
- the temperature T on the steel strip exit side of the heating zone 10 is more than 400 ° C. and lower than 850 ° C.
- the steel strip exit side temperature T is 850 ° C.
- the temperature T on the steel strip exit side of the heating zone 10 is more preferably 750 ° C. or lower, and even more preferably 700 ° C. or lower.
- the reduction annealing performed in the average tropics 12 following the oxidation treatment will be described.
- the iron oxide formed on the surface of the steel sheet by the oxidation treatment is reduced, and Si and Mn become internal oxides inside the steel strip due to the oxygen supplied from the iron oxide.
- a reduced iron layer in which iron oxide is reduced is formed on the outermost layer of the steel sheet, and Si and Mn remain inside the steel strip as internal oxides, so that oxidation of Si and Mn on the outermost layer of the steel sheet is suppressed.
- the decrease in wettability between the steel strip P and the plating is prevented.
- the present inventors suppress the formation of Si and Mn oxides on the outermost layer of the steel sheet by controlling the temperature on the steel strip exit side of the heating zone 10 and the dew point of the atmosphere of the solitary tropics 12, and improve the plating appearance. I devised a technology to improve it.
- the steel strip 15 vol% of H 2 concentration of the atmosphere in the soaking zone 12, a soaking temperature of 800 ° C., was subjected to reduction annealing by changing the dew point of the soaking zone 12.
- the steel strip was subjected to hot-dip galvanizing treatment using a hot-dip galvanizing bath having a component composition of effective Al concentration in the bath: 0.132% by mass and the balance consisting of Zn and unavoidable impurities, and then hot-dip galvanized at 530 ° C. for 20 seconds.
- the alloying treatment was carried out in (1) to obtain an alloyed high-strength hot-dip galvanized steel sheet.
- FIG. 4 shows an example of the GDS profile observed in the experiment.
- the GDS profiles of Si and Mn each had a surface enrichment peak due to surface enrichment and an internal oxidation peak due to internal oxidation.
- the surface concentration of Si and Mn was calculated for each steel sheet after reduction annealing.
- the amount of surface enrichment is defined as the integrated value of the surface enrichment peak in the GDS profile.
- FIG. 2A is a graph showing the relationship between the dew point in a tropical atmosphere and the surface concentration of Si in the comparative example.
- FIG. 2B is a graph showing the relationship between the dew point of a solitary tropical atmosphere and the amount of surface concentration of Mn in the comparative example.
- FIG. 2C is a graph showing the relationship between the dew point of the atmosphere of the solitary tropics 12 and the amount of surface concentration of Si in the invention example.
- FIG. 2D is a graph showing the relationship between the dew point of the atmosphere of the solitary tropics 12 and the amount of surface concentration of Mn in the comparative example. As can be seen from the comparison of FIGS.
- the dew point temperature of the heating zone 10 is 650 ° C. or 700 ° C.
- the surface concentration of Mn increases, and the surface concentration of Mn is such that the dew point of the atmosphere of the tropical 12 is around -20 ° C (medium dew point).
- FIG. 3 shows that for the steel grades [Si] / [Mn] ⁇ 0.30 and the steel grades [Si] / [Mn]> 0.30, the dew point of the atmosphere of the average tropical 12 is the low dew point (-35 ° C ⁇ 5 ° C). ) And the dew point (-15 ° C ⁇ 5 ° C) to explain the precipitation morphology of the oxide.
- the dew point of the atmosphere of the average tropical 12 is the low dew point (-35 ° C ⁇ 5 ° C).
- the dew point (-15 ° C ⁇ 5 ° C) to explain the precipitation morphology of the oxide.
- the steel grade of [Si] / [Mn]> 0.30 since the amount of Si is large relative to the amount of Mn, Si—Mn surface oxide is easily formed, and Si— has an effect on the appearance of plating. The influence of Mn surface oxides is dominant.
- the Si—Mn surface oxide 31 is formed on the surface of the steel sheet P, so that the plating layer 30 is not plated. However, at the dew point, internal oxidation is promoted, the formation of Si—Mn surface oxide 31 is suppressed, and an excellent plating appearance can be obtained.
- the steel type of [Si] / [Mn] ⁇ 0.30 since the amount of Si is small with respect to the amount of Mn, the composite oxide of Si—Mn is precipitated in the steel sheet as the Si—Mn internal oxide 32. The amount of Mn is small, that is, excess Mn is likely to be surface-concentrated, and Mn-only oxide is likely to be formed.
- the present inventors appropriately control the temperature on the exit side of the steel strip of the heating zone 10 and the dew point of the atmosphere of the solitary tropical region 12, and hot-dip galvanize the steel strip of [Si] / [Mn] ⁇ 0.30.
- Each high-strength hot-dip galvanized steel sheet was prepared in the same manner as in the preliminary experiment described above, except that the dew point was changed.
- the relationship between the composition, the temperature on the steel strip exit side of the heating zone 10, the dew point of the atmosphere of the solitary tropics 12, and Mn is double-returned, and the left side of the equation (1).
- the plating appearance was judged by the same criteria as in the examples described later.
- FIG. 5A shows an outline of the experimental data used for the multiple regression analysis.
- the amount of Mn surface concentration tended to increase as the dew point increased, and the plating appearance deteriorated when the amount of surface concentration was high.
- the left side of the equation (1) was compared with the plating appearance, and the threshold value of the left side of the equation (1) was obtained to obtain a good plating appearance.
- FIG. 5 (b) it was found that a good plating appearance can be obtained when the value on the left side of the formula (1) is less than 140, and the following formula (1) is derived. .. A ⁇ 50 + BC / 30 ⁇ 140 ...
- P. Dew point (° C) of the atmosphere in the tropics (however, -50 ° C ⁇ DP ⁇ -5 ° C)
- T Steel strip exit side temperature (° C.) (400 ° C. ⁇ T ⁇ 850 ° C.) of the heating zone Is.
- Dew point D. in the atmosphere of the tropical 12 P. Controls to satisfy Eq. (1).
- D. P. Is more than -50 ° C and less than -5 ° C.
- the lower the P the more the oxidation of the outermost layers of the Si and Mn steel sheets is suppressed, but on the other hand, the dehumidification cost is high. Therefore, D. P. Is over -50 ° C.
- D. P. If the temperature exceeds -5 ° C, the appearance and adhesion of the plating may deteriorate due to approaching the iron oxide region.
- the temperature should be -5 ° C or lower.
- the temperature is preferably ⁇ 30 ° C. or lower.
- D. P. Is measured at the dew point measurement port provided in the tropics.
- the dew point measurement port is arranged at a position 1 m or more away from the supply port for supplying the humidifying gas into the tropics, and at a position 1 m or more away from the inner wall position of the tropics 12 facing each supply port.
- the method of controlling the gas is not particularly limited, but a method of introducing heated steam into the tropics 12 and at least one of N 2 gas and H 2 gas humidified by bubbling or the like are introduced into the tropics 12. There are methods and so on.
- the H 2 concentration in the atmosphere of the solitary tropics 12 is preferably 5% by volume or more, and preferably 30% by volume or less. By setting the H 2 concentration in the atmosphere of the solitary tropics 12 to 5% by volume or more, the reduction of iron oxide can be further promoted and the occurrence of pickup can be further prevented.
- the H 2 concentration in the atmosphere of the solitary tropics 12 is more preferably 10% by volume or more. Further, the H 2 concentration in the atmosphere of the solitary tropics 12 is more preferably 20% by volume or less. Further, by setting the H 2 concentration in the atmosphere of the solitary tropics 12 to 30% by volume or less, the cost aspect is good. Further, it is preferable that the rest of the atmosphere of the solitary tropics 12 other than H 2 is N 2 and unavoidable impurities.
- the reduction annealing in the average tropics 12 is preferably applied to the steel strip P in a temperature range of 700 ° C. or higher, and is preferably applied to the steel strip P in a temperature range of 900 ° C. or lower.
- the reduction annealing is more preferably performed in a temperature range of 750 ° C. or higher.
- the reduction annealing is more preferably performed in a temperature range of 850 ° C. or lower. From the viewpoint of further improving the mechanical properties of the steel sheet, reduction annealing is preferably performed for 10 seconds or longer, and preferably for 300 seconds or shorter.
- the high-strength hot-dip galvanized steel sheet manufactured by the manufacturing method of this high-strength hot-dip galvanized steel sheet surely has a good plated appearance.
- each steel strip has the above-mentioned formula (1) based on the Si concentration and Mn concentration of each steel strip.
- D. P. And T are preferably managed to be controlled.
- all the steel strips satisfy the formula (1). P. By controlling and T, it is possible to obtain a high-strength hot-dip galvanized steel sheet having a stable and good plating appearance by using not only steel strips having a specific composition composition but also steel strips having various composition compositions. ..
- all the steel strips satisfy the above-mentioned formula (1) based on the Si concentration and the Mn concentration of each steel strip.
- Specific examples of managing and T to be controlled include the following. For example, when the product specifications of the steel strips that are continuously passed through are switched and the Si concentration and Mn concentration of the steel strips are changed, the changed Si concentration and Mn concentration are substituted into the equation (1), and the equation ( D. Satisfying 1). P. Alternatively, at least one of T may be determined. In addition, D. P. Since the control responsiveness of is poor, D. P.
- substituting into the equation (1) is not limited to the mode of substituting exactly into the same equation as the above (1). It also includes a mode of substituting equation (1) into a narrower range of inequalities that always satisfies. Further, in order to satisfy the equation (1) according to the state in the annealing furnace, D. P. And T are controlled as long as the equation (1) is satisfied. P. Alternatively, it includes an embodiment in which at least one of T is fixed. In this embodiment, the composition of the steel strip may be switched so as to satisfy the formula (1). Specifically, D. P.
- Mn concentration D.I. P.
- a manufacturing condition determination method may be carried out as a part of a step of the manufacturing method of a high-strength hot-dip galvanized steel sheet, or may be carried out as a single step.
- the steel strips P are cooled in the cooling zones 14 and 16.
- the steel strip P is cooled to about 480 to 530 ° C. in the first cooling zone 14 and to about 470 to 500 ° C. in the second cooling zone 16.
- the steel strip P discharged from the cooling zone 16 is hot-dip galvanized using the hot-dip galvanizing bath 22 to obtain a high-strength hot-dip galvanized steel sheet.
- the hot-dip galvanizing treatment is preferably carried out in a hot-dip galvanizing bath having an effective Al concentration in the bath: 0.095% by mass or more and 0.175% by mass or less, and the balance being Zn and unavoidable impurities.
- the effective Al concentration in the bath is a value obtained by subtracting the Fe concentration in the bath from the Al concentration in the bath.
- the effective Al concentration in the bath is preferably 0.095% by mass or more and 0.175% by mass or less.
- the effective Al concentration in the bath is more preferably 0.115% by mass or less.
- the bath temperature of the hot-dip galvanizing bath is usually in the range of 440 to 500 ° C, and the plate temperature of the steel strip P is 440 to 550 ° C. May be infiltrated into the hot-dip galvanizing bath.
- the amount of plating adhered can be adjusted by gas wiping or the like.
- the high-strength hot-dip galvanized steel sheet is further alloyed using the alloying facility 24 to alloy the high-strength hot-dip galvanized steel sheet.
- a plated steel plate may be obtained.
- the alloying treatment is preferably carried out at a temperature of 460 ° C. or higher, and preferably at a temperature of 600 ° C. or lower. By setting the alloying treatment to 460 ° C. or higher, it is possible to provide a steel sheet having excellent press formability without leaving the ⁇ phase. Further, by setting the alloying treatment to 600 ° C. or lower, the plating adhesion is good.
- the alloying time is preferably 10 s or more, and preferably 60 s or less.
- the steel slab obtained by melting the steel having the composition shown in Table 1 was made into a cold-rolled steel sheet having a plate thickness of 1.4 mm by hot rolling, pickling, and cold rolling.
- the second heating zone is a DFF type heating furnace, and as shown in FIG. 1, the second heating zone is divided into four groups (# 1 to # 4), and three groups (# 1) on the upstream side in the steel sheet moving direction.
- the first stage of the second heating zone with respect to the steel strip under the conditions shown in Table 2-1 and Table 2-2.
- the oxidation treatment was performed in the latter stage.
- the air ratio of the atmosphere in the first stage was 1.15, and the air ratio of the atmosphere in the second stage was 0.85.
- reduction annealing was performed under the conditions shown in Table 2-1 and Table 2-2.
- Reduction annealing was applied for 85 seconds. After cooling the steel strip to 440-550 ° C, hot-dip zinc was subsequently applied to the steel strip using a hot-dip galvanized bath at 460 ° C, consisting of effective Al concentration in the bath: 0.197% by mass, the balance being Zn and unavoidable impurities. After the plating treatment, the grain size was adjusted to about 50 g / m 2 by gas wiping to prepare a sample of a high-strength hot-dip galvanized steel sheet (GI).
- GI high-strength hot-dip galvanized steel sheet
- the steel strip was continuously melted using a hot-dip galvanizing bath at 460 ° C., in which the effective Al concentration in the bath: 0.132% by mass% was composed of Zn and unavoidable impurities.
- the grain size is adjusted to about 50 g / m 2 by gas wiping to obtain a high-strength hot-dip galvanized steel sheet.
- the plating appearance of the high-strength hot-dip galvanized steel sheet (GI) or alloyed high-strength hot-dip galvanized steel sheet (GA) obtained as described above was evaluated.
- the measurement method and evaluation method are shown below.
- ⁇ Plating appearance> The appearance of the surface of the steel sheet was visually observed, and those without unplated appearance defects were marked with ⁇ , those with no unplated appearance defects but with uneven appearance were marked with ⁇ , and those with non-plating were marked with ⁇ . If it is ⁇ or ⁇ , it is considered as a pass.
- Table 2-1 and Table 2-2 The results obtained from the above are shown in Table 2-1 and Table 2-2 together with the manufacturing conditions.
- the “judgment” was evaluated as ⁇ if the equation (1) was satisfied, and ⁇ if the equation (1) was not satisfied.
- the method for producing a high-strength hot-dip galvanized steel sheet of the present invention it is possible to provide a high-strength hot-dip galvanized steel sheet having an excellent plated appearance and capable of reducing the weight and increasing the strength of the automobile body itself.
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Abstract
Description
[1]加熱帯と,均熱帯と,冷却帯とがこの順に並置された焼鈍炉と,該冷却帯の後に設けられた溶融亜鉛めっき設備と,を有する連続溶融亜鉛めっき装置を用いた高強度溶融亜鉛めっき鋼板の製造方法であって,
鋼帯を前記焼鈍炉の内部で,前記加熱帯,前記均熱帯,および前記冷却帯の順に搬送して,該鋼帯に対して焼鈍を施す工程と,
前記溶融亜鉛めっき設備を用いて,前記冷却帯から排出される鋼帯に溶融亜鉛めっきを施して高強度溶融亜鉛めっき鋼板を得る工程と,
を有し,
前記鋼帯は,質量%で,Mn:1.7%以上3.5%以下,およびSi:0.2%以上1.05%以下を含有し,かつ[Si]/[Mn]≦0.30を満足する成分組成を有し,
前記成分組成,前記均熱帯内の雰囲気の露点,および前記加熱帯の出側温度が下式(1)を満足する,高強度溶融亜鉛めっき鋼板の製造方法。
A×50+B-C/30<140・・・(1)
ここで,A=[Mn]-[Si]×4
B=-0.0068×(D.P.)3-0.59×(D.P.)2-11.7×(D.P.)+120
C=exp(T/100)/[Si]
であり,
[Si]:Si濃度(質量%)
[Mn]:Mn濃度(質量%)
D.P.:前記均熱帯内の雰囲気の露点(℃)(ただし,-50℃<D.P.<-5℃)
T:前記加熱帯の鋼帯出側温度(℃)(400℃<T<850℃)
である。
前記前段の雰囲気の空気比を,1.0以上1.3未満とし,
前記後段の雰囲気の空気比を,0.7以上1.0未満とする,前記[1]に記載の高強度溶融亜鉛めっき鋼板の製造方法。
C:0.8%以下,
P:0.1%以下,
S:0.03%以下,
Al:0.1%以下,
B:0.005%以下および
Ti:0.2%以下を含有し,残部がFeおよび不可避的不純物からなる,前記[1]から[4]のいずれか1項に記載の高強度溶融亜鉛めっき鋼板の製造方法。
N:0.010%以下,
Cr:1.0%以下,
Cu:1.0%以下,
Ni:1.0%以下,
Mo:1.0%以下,
Nb:0.20%以下,
V:0.5%以下,
Sb:0.200%以下,
Ta:0.1%以下,
W:0.5%以下,
Zr:0.1%以下,
Sn:0.20%以下,
Ca:0.005%以下,
Mg:0.005%以下および
REM:0.005%以下
からなる群から選ばれる1種または2種以上を含有する,前記[1]から[5]のいずれか1項に記載の高強度溶融亜鉛めっき鋼板の製造方法。
なお,本明細書中で鋼板が「高強度」であるとは,鋼板の引張強さが340MPa以上であることを意味する。
加熱帯と,均熱帯と,冷却帯とがこの順に並置された焼鈍炉と,該冷却帯の後に設けられた溶融亜鉛めっき設備と,を有する連続溶融亜鉛めっき装置を用いた高強度溶融亜鉛めっき鋼板の製造方法であって,
鋼帯を前記焼鈍炉の内部で,前記加熱帯,前記均熱帯,および前記冷却帯の順に搬送して,該鋼帯に対して焼鈍を施す工程と,
前記溶融亜鉛めっき設備を用いて,前記冷却帯から排出される鋼帯に溶融亜鉛めっきを施して高強度溶融亜鉛めっき鋼板を得る工程と,
を有し,
前記鋼帯は,質量%で,Mn:1.7%以上3.5%以下,およびSi:0.2%以上1.05%以下を含有し,かつ[Si]/[Mn]≦0.30を満足する成分組成を有し,
前記成分組成,前記均熱帯内の雰囲気の露点,および前記加熱帯の出側温度が下式(1)を満足する,高強度溶融亜鉛めっき鋼板の製造方法。
A×50+B-C/30<140・・・(1)
ここで,A=[Mn]-[Si]×4
B=―0.0068×(D.P.)3-0.59×(D.P.)2-11.7×(D.P.)+120
C=exp(T/100)/[Si]
であり,
[Si]:Si濃度(質量%)
[Mn]:Mn濃度(質量%)
D.P.:前記均熱帯内の雰囲気の露点(℃)(ただし,-50℃<D.P.<-5℃)
T:前記加熱帯の鋼帯出側温度(℃)(400℃<T<850℃)
である。
上述したように,Mnは鋼の高強度化に有効な元素である。Mn量が1.7%未満では,以下で説明するように,Mn単独酸化物が過剰に形成されず,本発明の製造方法を適用する必要性に乏しい。そのため,Mn量は1.7%以上とする。一方,Mn量が3.5%を超えるとMn単独酸化物が過剰に形成され,式(1)に基づき加熱帯の鋼帯出側温度および均熱帯の露点を適切に制御しても,良好なめっき外観を得られない。したがって,Mn量は1.7%以上3.5%以下とする。Mn量は,好ましくは,2.0%以上,より好ましくは,2.3%以上とする。また,Mn量は,好ましくは,3.3%以下,より好ましくは,3.0%以下とする。
Siは鋼を強化して良好な材質を得るのに有効な元素である。Si量が0.2%未満では高強度を得るために他の高価な合金元素を添加することが必要になり,経済的に好ましくない。また,Si量が0.2%未満では本発明の製造方法を適用する必要性に乏しい。その理由は必ずしも明らかではないが,以下で説明する酸化処理によって十分な量の鉄酸化物が生成されるため,還元焼鈍時の鋼板最表層におけるSiおよびMnの酸化を抑制でき,めっき外観が大きな課題になることはないと推定できる。一方,後述するように[Si]/[Mn]≦0.30を満足するために,Si量の上限は1.05%とする。したがって,Si量は0.3%以上1.05%以下とする。Si量は,好ましくは,0.3%以上,より好ましくは0.4%以上とする。また,Si量は,好ましくは,0.9%以下,より好ましくは,0.7%以下とする。
ここで,[Si]:Si濃度(質量%),[Mn]:Mn濃度(質量%)である。
以下で説明するように,[Si]/[Mn]>0.30では,めっき外観に及ぼすSi-Mn表面酸化物(SiおよびMnの複合酸化物)による影響が支配的となり,式(1)に基づき加熱帯の鋼帯出側温度,および均熱帯の雰囲気の露点を制御する必要性に乏しい。これに対し,[Si]/[Mn]≦0.30においては,めっき外観に及ぼすMn単独酸化物による影響が支配的となり,式(1)に基づき加熱帯の鋼帯出側温度,および均熱帯の雰囲気の露点を制御することにより,めっき外観に優れた高強度溶融亜鉛めっき鋼板を得ることができる。したがって,[Si]/[Mn]は0.30以下とする。Si/Mnは,好ましくは,0.25以下とする。
Cは,鋼組織としてマルテンサイトなどを形成させることで加工性を向上する。Cを含有させる場合,良好な溶接性を得るため,C量は0.8%以下とすることが好ましく,0.30%以下とすることがより好ましい。Cの下限は特に限定されないが,良好な加工性を得るためにはCを0.03%以上とすることが好ましく,0.05%以上含有させることがより好ましい。
Pの含有量を抑制することで,溶接性の低下を防ぐことができる。さらにPが粒界に偏析することを防いで,延性,曲げ性,および靭性が劣化することを防ぐことができる。フェライト変態を抑制して微細な結晶粒を得るため,P量は0.1%以下とすることが好ましい。Pの下限は特に限定されず,生産技術上の制約から0%超であり得,0.001%以上であり得る。
S量は0.03%以下とすることが好ましく,0.02%以下とすることがより好ましい。S量を抑制することで,溶接性の低下を防ぐとともに,熱間時の延性の低下を防いで,熱間割れを抑制し,表面性状を著しく向上することができる。さらに,S量を抑制することで,不純物元素として粗大な硫化物を形成することにより,鋼板の延性,曲げ性,伸びフランジ性の低下を防ぐことができる。これらの問題はS量が0.030%を超えると顕著となり,Sの含有量は極力低減することが望ましい。Sの下限は特に限定されず,生産技術上の制約から0%超であり得,0.0001%以上であり得る。
Alは熱力学的に最も酸化しやすいため,SiおよびMnに先だって酸化し,SiおよびMnの鋼板最表層での酸化を抑制し,SiおよびMnの鋼板内部での酸化を促進する効果がある。この効果はAl量が0.01%以上で得られる。一方,Al量が0.1%を超えるとコストアップになる。したがって,添加する場合,Al量は0.1%以下とすることが好ましい。Alの下限は特に限定されず,0%超であり得,0.001%以上であり得る。
Bは鋼の焼入れ性を向上させるのに有効な元素である。焼入れ性を向上するためには,B量は0.0003%以上とすることが好ましく,0.0005%以上とすることがより好ましい。また,B量は0.005%以下とすることが好ましい。B量を0.005%以下とすることで,Siの鋼板最表層における酸化を抑制して,良好なめっき密着性を得ることができるためである。
Tiを添加する場合,Ti量は0.2%以下とすることが好ましく,0.05%以下とすることがより好ましい。Ti量を0.2%以下とすることで,良好なめっき密着性を得ることができるためである。またTiの下限は特に限定されないが,強度調整の効果を得るためには,0.005%以上とすることが好ましい。
Nの含有量は0.010%以下とすることが好ましい。Nの含有量を0.010%以下とすることで,NがTi,Nb,Vと高温で粗大な窒化物を形成することでTi,Nb,V添加による鋼板の高強度化の効果が損なわれることを防ぐことができる。また,Nの含有量を0.010%以下とすることで靭性の低下も防ぐことができる。さらに,Nの含有量を0.010%以下とすることで,熱間圧延中にスラブ割れ,表面疵が発生することを防ぐことができる。Nの含有量は,より好ましくは0.005%以下であり,さらに好ましくは0.003%以下であり,最も好ましくは0.002%以下である。Nの含有量の下限は特に限定されず,生産技術上の制約から0%超であり得,0.0005%以上であり得る。
Cr量は0.005%以上とすることが好ましい。Cr量を0.005%以上とすることで,焼き入れ性を向上し,強度と延性とのバランスを向上することができる。添加する場合,コストアップを防ぐ観点から,Cr量は1.0%以下とすることが好ましい。
Cu量は0.005%以上とすることが好ましい。Cu量を0.005%以上とすることで,残留γ相の形成を促進することができ,またNiおよびMoとの複合添加時においてめっき密着性を改善することができる。また,Cu量を添加する場合,コストアップを防ぐ観点から,Cu量は1.0%以下とすることが好ましい。
Ni量は0.005%以上とすることが好ましい。Ni量を0.005%以上とすることで,残留γ相の形成を促進することができ,またCuとMoとの複合添加時においてめっき密着性を改善することができる。また,Niを添加する場合,コストアップを防ぐ観点から,Ni量は1.0%以下とすることが好ましい。
Mo量は0.005%以上とすることが好ましい。Mo量を0.005%以上とすることで,強度調整の効果を得ることができ,またNb,Ni,Cuとの複合添加時においてめっき密着性を改善することができる。また,Moを添加する場合,コストアップを防ぐ観点から,Mo量は0.05%以上1.0%以下が好ましい。
Nbは,0.005%以上含有することで強度向上の効果が得られる。また,Nbを含有する場合,コストアップを防ぐ観点から,Nb量は0.20%以下とすることが好ましい。
Vは,0.005%以上含有することで強度向上の効果が得られる。また,Vを含有する場合,コストアップを防ぐ観点から,V量は0.5%以下とすることが好ましい。
Sbは鋼板表面の窒化,酸化,あるいは酸化により生じる鋼板表面の数十ミクロン領域の脱炭を抑制する観点から含有することができる。Sbは,鋼板表面の窒化および酸化を抑制することで,鋼板表面においてマルテンサイトの生成量が減少するのを防止し,鋼板の疲労特性および表面品質を改善する。このような効果を得るために,Sb量は0.001%以上とすることが好ましい。一方,良好な靭性を得るためには,Sb量は0.200%以下とすることが好ましい。
Taは,0.001%以上含有することで強度向上の効果が得られる。また,Taを含有する場合,コストアップを防ぐ観点から,Ta量は0.1%以下とすることが好ましい。
Wは,0.005%以上含有することで強度向上の効果が得られる。また,Wを含有する場合,コストアップを防ぐ観点から,W量は0.5%以下とすることが好ましい。
Zrは,0.0005%以上含有することで強度向上の効果が得られる。また,Zrを含有する場合,コストアップを防ぐ観点から,Zr量は0.1%以下とすることが好ましい。
Snは脱窒,脱硼等を抑制して,鋼の強度低下抑制に有効な元素である。こうした効果を得るにはそれぞれ0.002%以上とすることが好ましい。一方,良好な耐衝撃性を得るために,Sn量は0.20%以下とすることが好ましい。
Caは,0.0005%以上含有することで硫化物の形態を制御し,延性,靭性を向上させることができる。また,良好な延性を得る観点から,Ca量は0.005%以下とすることが好ましい。
Mgは,0.0005%以上含有することで硫化物の形態を制御し,延性,靭性を向上させることができる。また,Mgを含有する場合,コストアップを防ぐ観点から,Mg量は0.005%以下とすることが好ましい。
REMは,0.0005%以上含有することで硫化物の形態を制御し,延性,靭性を向上させることができる。また,REMを含有する場合,良好な靭性を得る観点から,REM量は0.005%以下とすることが好ましい。
鋼帯を前記焼鈍炉の内部で,前記加熱帯,前記均熱帯,および前記冷却帯の順に搬送して,該鋼帯に対して焼鈍を施す工程と,
前記溶融亜鉛めっき設備を用いて,前記冷却帯から排出される鋼帯に溶融亜鉛めっきを施して高強度溶融亜鉛めっき鋼板を得る工程と,
を有し,
前記鋼帯は,質量%で,Mn:1.7%以上3.5%以下,およびSi:0.2%以上1.05%以下を含有し,かつ[Si]/[Mn]≦0.30を満足する成分組成を有し,
前記成分組成,前記均熱帯内の雰囲気の露点,および前記加熱帯の出側温度が下式(1)を満足する,高強度溶融亜鉛めっき鋼板の製造方法である。
A×50+B-C/30<140・・・(1)
ここで,A=[Mn]-[Si]×4
B=-0.0068×(D.P.)3-0.59×(D.P.)2-11.7×(D.P.)+120
C=exp(T/100)/[Si]
であり,
[Si]:Si濃度(質量%)
[Mn]:Mn濃度(質量%)
D.P.:前記均熱帯内の雰囲気の露点(℃)(ただし,-50℃<D.P.<-5℃)
T:前記加熱帯の鋼帯出側温度(℃)(400℃<T<850℃)
である。
第2加熱帯10Bの前段においては,鋼板最表層におけるSiおよびMnの酸化を抑制し,鉄酸化物を生成させるために,積極的に酸化処理を行う。十分な量の鉄酸化物を得て最終的に美麗なめっき外観を得るためには,第2加熱帯10Bの前段の雰囲気の空気比を,1.0以上とすることが好ましく,また1.3未満とすることが好ましい。第2加熱帯10Bの前段の雰囲気の空気比は,より好ましくは,1.1以上とする。また,第2加熱帯10Bの前段の雰囲気の空気比は,より好ましくは,1.2以下とする。更に,前段処理の加熱温度は,鉄の酸化を促進させるために,400℃以上とすることが好ましい。また,前段処理の加熱温度は,850℃以下とすることが好ましい。前段処理の加熱温度を850℃以下とすることで,鉄酸化物の生成量を好適範囲内とし,次工程でピックアップが発生することを防ぐことができるためである。
ピックアップを防止して,押し疵などのない美麗なめっき外観を得るためには,一旦酸化された鉄酸化物の表層を還元することが重要である。このような還元処理を行うには,第2加熱帯10Bの後段の雰囲気の空気比を0.7以上とすることが好ましく,1.0未満とすることが好ましい。第2加熱帯10Bの後段の雰囲気の空気比を低下させることで,鉄酸化物の表層が一部還元され,次工程の還元焼鈍時に,均熱帯12のロールと鉄酸化物とが直接接触することを避け,ピックアップを防止することができる。また,後段処理の加熱温度は600℃以上とすることが好ましい。後段処理の加熱温度を600℃以上とすることで,良好に鋼板最表層を還元することができる。また,後段処理の加熱温度は850℃以下とすることが好ましい。加熱温度を850℃以下とすることで,加熱に要するコストを低減することができる。
A×50+B-C/30<140・・・(1)
ここで,A=[Mn]-[Si]×4
B=―0.0068×(D.P.)3-0.59×(D.P.)2-11.7×(D.P.)+120
C=exp(T/100)/[Si]
であり,
[Si]:Si濃度(質量%)
[Mn]:Mn濃度(質量%)
D.P.:前記均熱帯内の雰囲気の露点(℃)(ただし,-50℃<D.P.<-5℃)
T:前記加熱帯の鋼帯出側温度(℃)(400℃<T<850℃)
である。
A×50+B-C/30<140・・・(1)
ここで,A=[Mn]-[Si]×4
B=―0.0068×(D.P.)3-0.59×(D.P.)2-11.7×(D.P.)+120
C=exp(T/100)/[Si]
であり,
[Si]:Si濃度(質量%)
[Mn]:Mn濃度(質量%)
D.P.:前記均熱帯内の雰囲気の露点(℃)(ただし,-50℃<D.P.<-5℃)
T:前記加熱帯の鋼帯出側温度(℃)(400℃<T<850℃)
である。
また,後述する実施例で示すように,さまざまな鋼種について,上記式(1)が満足されていれば,良好なめっき外観を得ることができることを実証した。
均熱帯12内における還元焼鈍に次いで,冷却帯14,16で,鋼帯Pを冷却する。鋼帯Pは,第1冷却帯14では480~530℃程度にまで冷却され,第2冷却帯16では470~500℃程度にまで冷却される。
鋼板表面の外観を目視観察し,不めっきの外観不良がないものを◎,不めっきの外観不良はないが,外観ムラがあるものを〇,不めっきがあるものは×とした。なお,◎,〇であれば合格とした。
10 加熱帯
10A 第1加熱帯
10B 第2加熱帯(直火型加熱炉)
11 ハースロール
12 均熱帯
14,16 冷却帯
18 スナウト
20 焼鈍炉
22 溶融亜鉛めっき浴
23 合金化設備
P 鋼帯
30 めっき層
31 Si-Mn表面酸化物
32 Si-Mn内部酸化物
33 Mn単独酸化物
Claims (8)
- 加熱帯と,均熱帯と,冷却帯とがこの順に並置された焼鈍炉と,該冷却帯の後に設けられた溶融亜鉛めっき設備と,を有する連続溶融亜鉛めっき装置を用いた高強度溶融亜鉛めっき鋼板の製造方法であって,
鋼帯を前記焼鈍炉の内部で,前記加熱帯,前記均熱帯,および前記冷却帯の順に搬送して,該鋼帯に対して焼鈍を施す工程と,
前記溶融亜鉛めっき設備を用いて,前記冷却帯から排出される鋼帯に溶融亜鉛めっきを施して高強度溶融亜鉛めっき鋼板を得る工程と,
を有し,
前記鋼帯は,質量%で,Mn:1.7%以上3.5%以下,およびSi:0.2%以上1.05%以下を含有し,かつ[Si]/[Mn]≦0.30を満足する成分組成を有し,
前記成分組成,前記均熱帯内の雰囲気の露点,および前記加熱帯の出側温度が下式(1)を満足する,高強度溶融亜鉛めっき鋼板の製造方法。
A×50+B-C/30<140・・・(1)
ここで,A=[Mn]-[Si]×4
B=-0.0068×(D.P.)3-0.59×(D.P.)2-11.7×(D.P.)+120
C=exp(T/100)/[Si]
であり,
[Si]:Si濃度(質量%)
[Mn]:Mn濃度(質量%)
D.P.:前記均熱帯内の雰囲気の露点(℃)(ただし,-50℃<D.P.<-5℃)
T:前記加熱帯の鋼帯出側温度(℃)(400℃<T<850℃)
である。 - 前記加熱帯は,前段および後段に分かれた直火バーナ炉を備え,
前記前段の雰囲気の空気比を,1.0以上1.3未満とし,
前記後段の雰囲気の空気比を,0.7以上1.0未満とする,請求項1に記載の高強度溶融亜鉛めっき鋼板の製造方法。 - 前記均熱帯内において,該均熱帯の雰囲気の水素濃度を5体積%以上30体積%以下として,前記鋼帯に700℃以上900℃以下の温度域にて10秒以上300秒以下の還元焼鈍を施す,請求項1または2に記載の高強度溶融亜鉛めっき鋼板の製造方法。
- 前記溶融亜鉛めっきを施した後,前記高強度溶融亜鉛めっき鋼板にさらに460℃以上600℃以下の温度で10秒以上60秒以下加熱する合金化処理を施す,請求項1から3のいずれか1項に記載の高強度溶融亜鉛めっき鋼板の製造方法。
- 前記成分組成がさらに,質量%で,
C:0.8%以下,
P:0.1%以下,
S:0.03%以下,
Al:0.1%以下,
B:0.005%以下および
Ti:0.2%以下を含有し,残部がFeおよび不可避的不純物からなる,請求項1から4のいずれか1項に記載の高強度溶融亜鉛めっき鋼板の製造方法。 - 前記成分組成がさらに,質量%で,
N:0.010%以下,
Cr:1.0%以下,
Cu:1.0%以下,
Ni:1.0%以下,
Mo:1.0%以下,
Nb:0.20%以下,
V:0.5%以下,
Sb:0.200%以下,
Ta:0.1%以下,
W:0.5%以下,
Zr:0.1%以下,
Sn:0.20%以下,
Ca:0.005%以下,
Mg:0.005%以下および
REM:0.005%以下
からなる群から選ばれる1種または2種以上を含有する,請求項1から5のいずれか1項に記載の高強度溶融亜鉛めっき鋼板の製造方法。 - 前記成分組成を満たし,かつ互いに異なる成分組成を有する複数種類の鋼帯に対し,各鋼帯のSi濃度およびMn濃度に基づいて,いずれの鋼帯も前記式(1)を満足するように,前記D.P.および前記Tを制御する,請求項1から6のいずれか1項に記載の高強度溶融亜鉛めっき鋼板の製造方法。
- 前記D.P.は-30℃以下である,請求項1から7のいずれか1項に記載の高強度溶融亜鉛めっき鋼板の製造方法。
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MX2022010295A (es) | 2022-09-19 |
JP7095804B2 (ja) | 2022-07-05 |
JPWO2021166350A1 (ja) | 2021-08-26 |
KR20220123120A (ko) | 2022-09-05 |
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