US20080070060A1

US20080070060A1 - Hot-Dip Galvanized Sheet and Method for Manufacturing Same

Info

Publication number: US20080070060A1
Application number: US11/664,490
Authority: US
Inventors: Yoshitsugu Suzuki; Yusuke Fushiwaki; Masahiko Tada; Yoichi Tobiyama; Hisanori Ando; Takashi Kawano
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2004-10-07
Filing date: 2005-10-07
Publication date: 2008-03-20
Also published as: EP1806422A4; CA2582762A1; WO2006038736A1; KR20070050497A; TW200617207A; TWI311163B; KR100883245B1; EP1806422A1

Abstract

The hot-dip galvanized steel sheet has: a steel sheet containing 0.1 to 3.0% of Si by mass; a hot-dip galvanizing layer; and a segregated layer, being placed between the steel sheet and the hot-dip galvanizing layer, having a thickness in a range from 0.01 to 100 μm; containing an oxide containing Si, and being composed of at least one component selected from the group consisting of S, C, Cl, Na, K, B, P, F, and N. The hot-dip galvanized steel sheet shows beautiful surface appearance without generating non-plating portion and provides excellent plating adhesion and sliding property in spite of using a base steel sheet containing a large quantity of Si. Furthermore, the alloy hot-dip galvanized steel sheet obtained by allying the hot-dip galvanized plating also has excellent anti-powdering property.

Description

TECHNICAL FIELD

The present invention relates to a hot-dip galvanized steel sheet suitable for the fields of automobile, building materials, household electric appliances, and the like, and to a method for manufacturing thereof, specifically relates to a hot-dip galvanized steel sheet having excellent plating adhesion and sliding property manufactured from a steel containing a large quantity of Si as the base material, and further relates to an alloyed hot-dip galvanizing prepared by alloying the hot-dip galvanized steel sheet.

BACKGROUND ART

In recent years, varieties of fields including automobile, building materials, and household electric appliances adopt surface-treated steel sheets prepared by providing a base material of steel sheet with rust-preventive property. As of these, there are specifically adopted hot-dip galvanized steel sheets which are manufactured at a low cost and which show excellent rust-preventive property, and alloyed hot-dip galvanized steel sheet prepared by alloying them.
Generally the hot-dip galvanized steel sheets are manufactured by the following process. That is, a slab is hot-rolled, and further is cold-rolled and heat-treated to form a thin steel sheet. The surface of thus prepared thin steel sheet is subjected to a pretreatment to apply degreasing and/or pickling to clean the surface thereof, or is supplied to a preheating furnace, without applying the pretreatment, to remove the oil on the surface of the thin steel sheet by combustion, and then is subjected to recrystallization annealing in a non-oxidizing atmosphere or in a reducing atmosphere, thereby obtaining a substrate steel sheet for plating. After that, the substrate steel sheet is cooled to a temperature suitable for the plating in a non-oxidizing atmosphere or a reducing atmosphere, followed by immersing the substrate steel sheet in a molten zinc bath containing a trace quantity of Al, (normally about 0.1 to about 0.2% by mass), without exposing to air, thereby obtaining the hot-dip galvanized steel sheet. The alloyed hot-dip galvanized steel sheet is manufactured by succeeding heat-treatment of the hot-dip galvanized steel sheet in an alloying furnace.
To attain both the decrease in thickness (decrease in weight) and the increase in strength of the steel sheets, the substrate steel sheets in recent years are designed to increase the strength. Accordingly, there is increasing the consumption of high strength hot-dip galvanized steel sheets which also have the rust-preventive property by applying hot-dip galvanizing to the substrate steel sheets.
As a means to increase the strength of the steel sheets, a solid solution strengthening element such as Si, Mn, and P is added to the steel. Specifically, since Si provides the steel with high strength without deteriorating the ductility, the Si-containing steel sheets are expected as the promised high strength steel sheets.
However, the hot-dip galvanized steel sheets and the alloyed hot-dip galvanized steel sheets prepared from the substrates of Si-containing high strength steel sheets have problems described below.
As described above, the substrate steel sheets for hot-dip galvanizing are subjected to annealing at temperatures in an approximate range from 600° C. to 900° C. in a reducing atmosphere, followed by hot-dip galvanizing. Since, however, the Si in the steel is an element of being readily oxidized, the Si is selectively oxidized on the surface of the steel sheet to form an oxide even in a commonly applied reducing atmosphere, thereby segregating the Si oxide to the surface of the substrate steel. That type of Si oxide deteriorates the wettability with the molten zinc during the plating treatment, thus inducing the generation of non-plating portions. Consequently, increase in the Si concentration in the steel aiming to increase the strength decreases the wettability, which induces the generation of many non-plating portions. Even when the non-plating portion does not appear, there is a problem of deteriorating the plating adhesion.
Furthermore, if the Si in the steel is selectively oxidized on the surface of the steel sheet, and if the oxidized Si segregates to the surface, the Si oxide hinders the alloying reaction between Zn and Fe, thereby significantly delaying the alloying in the alloying step after the hot-dip galvanizing. As a result, the productivity is significantly deteriorated. On the other hand, if the alloying treatment is given at further high temperatures to assure the productivity, powdering caused by the excess-alloying likely occurs. As a result, it is difficult to attain both the high productivity and the good anti-powdering property at a time in the related art.
To those problems, there are proposed several means.
For example, Japanese Patent No. 2587724 proposes a method for improving the wettability with molten zinc by heating a steel sheet in an oxidizing atmosphere to form an iron oxide on the surface of the steel sheet, in advance, then by conducting reduction-annealing.
The proposed technology is to suppress the surface segregation of Si in the reduction-annealing step by forming the iron oxide on the surface of the steel sheet. As widely known, however, the oxidation rate of iron on the surface of steel sheet significantly decreases with increase in the Si concentration in the steel. For example, for a steel sheet containing 0.1% by mass or more of Si, sole oxidizing means disclosed in the patent cannot fully progress the oxidation of the iron, and it is difficult to attain a necessary quantity of iron oxide to suppress the surface segregation of Si.
As a result, the occurrence of non-plating portion during the hot-dip galvanization cannot fully be suppressed. In addition, when that hot-dip galvanizing layer is alloyed, the problem of significant delay of alloying which is expected to occur in the alloying step cannot fully be solved.
If the alloying rate is small, the alloying temperature has to be increased to keep a specified productivity in a CGL which has a limited length of the alloying furnace. If, however, the alloying is conducted at elevated temperatures, the anti-powdering property is unavoidably deteriorated.
In addition, if the suppression of surface segregation of Si in the reduction-annealing step is insufficient, the homogeneity of alloying reaction of Zn and Fe is significantly deteriorated. Consequently, the plating surface gives significant irregularities on the Zn—Fe alloy layer caused by the non-homogeneous alloying reaction, which then significantly deteriorates the sliding property in the press-forming step.
For example, according to JP-A-11-50223, (the term “JP-A” referred to herein signifies the “Unexamined Japanese Patent Publication”), sulfur or a sulfur compound is adhered to the steel sheet in a quantity ranging from 0.1 to 1000 mg/m²as S before the hot-dip plating step, then the preheating step is applied to the steel sheet in a weak oxidizing atmosphere, followed by annealing the steel sheet in a non-oxidizing atmosphere containing hydrogen.
Furthermore, JP-A-2001-279410 discloses a technology in which an ammonium salt containing S is adhered in a quantity from 0.1 to 1000 mg/m²as S to the surface of a high tensile steel sheet containing Mn, P, and Si, followed by applying heat treatment, thus letting the S component diffuse into the ground metal of the steel sheet, thereby forming a sulfur compound such as MnS, which is the product of reaction with Mn in the steel. The method suppresses the surface segregation of Mn and shuts off the diffusion passage of Si to the surface of the steel sheet owing to the existence of the sulfur-segregated layer, thereby suppressing the surface segregation of Si.
Those technologies aim to improve the wettability with the molten zinc using a sulfide layer formed on the surface of steel sheet. However, the inventors of the present invention applied these technologies to steel sheets containing a large quantity of Si, and found that the sole effect of the sulfide layer cannot fully suppress the surface segregation of Si. Consequently, similar to the above-description, these technologies could not solve the problems of the performance of plating layer. Furthermore, the preheating step given in a weak oxidizing atmosphere could not solve the problems of anti-powdering property and sliding property, similar to above, when these technologies were applied to steel sheets containing a large quantity of Si.
In addition, since these technologies are to adhere sulfur or a sulfur compound onto the surface of steel sheet before the heat treatment, the succeeding heat treatment step emits large quantities of sulfur components as corrosive gases such as sulfur dioxide and hydrogen sulfide in the heating furnace. As a result, the corrosion damage of the heating furnace body and the intrafurnace apparatuses becomes significant, which requires frequent repair and renewal of deteriorated parts, and further requires to install a desulfurization apparatus in case of venting the furnace gas to atmosphere from the point of air pollution prevention. Therefore, practical application of these technologies in manufacturing lines needs further improvement.
The present invention has been perfected to cope with the above situations, and an object of the present invention is to provide a hot-dip galvanized steel sheet that has excellent plating adhesion and sliding property to sufficiently endure as the steel sheet for automobile that requests specifically severe plating characteristics even with a substrate steel sheet containing a large quantity of Si, and to provide a method for manufacturing the hot-dip galvanized steel sheet. Another object of the present invention is to provide an alloyed hot-dip galvanized steel sheet also having excellent anti-powdering property.

DISCLOSURE OF THE INVENTION

The present invention provides a hot-dip galvanized steel sheet having: a steel sheet containing 0.1 to 3.0% of Si by mass; a hot-dip galvanizing layer; and a segregated layer, being placed between the steel sheet and the hot-dip galvanizing layer, having a thickness in a range from 0.01 to 100 μm, containing an oxide containing Si, and being composed of at least one component selected from the group consisting of S, C, Cl, Na, K, B, P, F, and N.
For the hot-dip galvanized steel sheet, the concentration of the component in the segregated layer is preferably higher than the concentration of the component in the steel sheet by 10% or more.
For these hot-dip galvanized steel sheets, the quantity of the oxide containing the Si in the segregated layer is preferably in a range from 0.01 to 1 g/m as oxygen.
For any of these hot-dip galvanized steel sheets, an Fe layer preferably exists below the hot-dip galvanizing layer.
For any of these hot-dip galvanized steel sheets, the segregated layer is preferably formed by a dispersed compound of the component and a component of the steel sheet. In particular, it is more preferable that the component is S, and that the quantity of MnS in a particle shape, having 50 nm or larger particle size as the oxide is five particles or more per 20 μm of length on an arbitrary cross section in parallel with the interface between the hot-dip galvanizing layer and the steel sheet.
For any of these hot-dip galvanized steel sheets, the hot-dip galvanizing layer is preferably an alloyed hot-dip galvanizing layer.
Furthermore, the present invention provides a method for manufacturing hot-dip galvanized steel sheet having the steps of: adhering at least one substance selected from the group consisting of S, C, Cl, Na, K, B, P, F, N, and a compound thereof onto a surface of a steel sheet containing 0.1 to 3% Si by mass; heating the steel sheet after adhering the substance thereon to form an oxide film containing 70% by mass or less of hematite; reducing the oxide film; and hot-dip galvanizing the reduced steel sheet.
For the method for manufacturing hot-dip galvanized steel sheet, the step of heating is preferably conducted in an oxidizing atmosphere for Fe at above 500° C. of the ultimate temperature of the steel sheet.
For any of the above methods for manufacturing hot-dip galvanized steel sheet, it is preferable to further apply the step of alloying after the step of hot-dip galvanizing.
The present invention provides a method for manufacturing hot-dip galvanized steel sheet having the steps of: preparing a steel sheet containing 0.1 to 3% Si by mass as the substrate; forming an oxide film containing 70% by mass or less of hematite on the surface of the substrate steel sheet before applying hot-dip galvanizing onto the surface of the steel sheet; applying reducing treatment to the steel sheet; and applying hot-dip galvanizing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating an example of depth profile of a cross section of an alloyed hot-dip galvanized steel sheet, drawn by the linear analysis of EPMA.
FIG. 2 is a graph illustrating an example of depth profile of a surface layer of an alloyed hot-dip galvanized steel sheet, drawn by GDS.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail in the following.
To solve the above problems, the inventors of the present invention carried out detail studies, and found the following. To prevent the segregation of Si in the steel to the surface thereof, a segregated layer for a specified element is formed below the hot-dip galvanizing layer, and an oxide containing Si is formed in the segregated layer, thereby drastically improving the adhesion of the hot-dip galvanizing layer even with a steel sheet containing a large quantity of Si. Furthermore, by the existence of that oxide containing Si and of that segregated layer for the specified element, the homogeneous alloying is enhanced, and the formation of irregular plating layer is suppressed to attain a smooth plating surface, thereby significantly improving the sliding property.
For a means to suppress the generation of non-plating portion and to enhance the plating adhesion and the alloying on the steel sheet containing 0.1% or more of Si by mass, the inventors of the present invention conducted detail studies, and derived a conclusion that, for a steel sheet containing a large quantity of Si, simple enhancement of oxidation to form a sufficient quantity of iron oxide cannot fully improve the wettability with molten zinc, and cannot fully suppress the generation of non-plating portion.
To this point, the inventors of the present invention gave further studies, and found that it is important to form a sufficient quantity of iron oxide and further to specify the composition of the iron oxide. That is, for a steel sheet containing a large quantity of Si, it was found that the above objects are achieved by controlling the composition of the iron oxide being formed on the surface of the steel sheet when the sheet is oxidized, thus the present invention has been perfected.
That is, the inventors of the present invention provides a method for manufacturing hot-dip galvanized steel sheet having the steps of: adhering at least one substance selected from the group consisting of S, C, Cl, Na, K, B, P, F, N, and a compound thereof onto a surface of a steel sheet containing 0.1 to 3% Si by mass; heating the steel-sheet after adhering the substance thereon to form an oxide film containing 70% by mass or less of hematite; reducing the oxide film; and hot-dip galvanizing the reduced steel sheet.
The description begins with the composition of the base sheet for plating, (substrate steel sheet), according to the present invention.
The present invention specifies the Si content in the substrate steel sheet to a range from 0.1 to 3.0% by mass because that level of Si quantity is necessary to increase the strength of the steel sheet, though a steel containing a large quantity of Si as the substrate steel sheet raises problems of plating adhesion and sliding property, and because the existence of Si in the substrate is necessary to form the above-described oxide containing Si. If the Si content in the steel is less than 0.1% by mass, the above-described oxide containing Si cannot fully be formed below the plating layer, which fails to attain the effect of the present invention.
According to the present invention, there is no specific limitation on the elements other than Si, and known component systems can be applied. Typical components are the following.
C, 0.5% by mass or less
Carbon is an element existing in steel, normally existing in a range from 0.0001 to 0.5% by mass. The present invention accepts that range of C content in the substrate steel sheet. Carbon is useful not only for the strengthening of steel but also for the structural control such as forming a residual austenite to improve the balance between strength and ductility. A preferred C content to realize these effects is 0.05% by mass or more. On the other hand, the C content of 0.25% by mass or less is preferred to also give superior weldability.
Mn: 5% by mass or less
Manganese is useful for strengthening steel, and the substrate steel sheet may contain Mn by 5% by mass or less. Specifically, the Mn content of 0.1% by mass or more, preferably 0.5% by mass or more, performs the effect significantly. Similar to Si, the Mn is an element to form an oxide film in the annealing step, and the Mn content of 3.0% by mass or less tends to improve the plating adhesion on forming the segregated layer for a specified element and on forming the oxide containing Si below the plating layer, and furthermore is preferable for assuring weldability and the balance between strength and ductility. Accordingly, the Mn content is preferably specified to 3.0% by mass or less, and more preferably in a range from 0.5 to 3.0% by mass.
Al: 5.0% by mass or less
Aluminum is an element added together with Si as a supplemental additive. A preferable content of Al is 0.01% by mass or more. On the other hand, 5.0% by mass or less of Al content tends to improve the plating adhesion on forming the segregated layer for a specified element and on forming the oxide containing Si below the plating layer, and furthermore is preferable for assuring weldability and the balance between strength and ductility. Accordingly, the Al content is preferably specified to 5.0% by mass or less, and more preferably in a range from 0.01 to 3.0% by mass.
Elements in steel other than those given above include Ti, Nb, V, Cr, S, Mo, Cu, Ni, B, Ca, N, P, and Sb. The confirmed content ranges of these elements to attain the effect of the present invention are: up to 1% by mass for Ti, up to 1% by mass for Nb, up to 1% by mass for V, up to 3% by mass for Cr, up to 0.1% by mass for S, up to 1% by mass for Mo, up to 3% by mass for Cu, up to 3% by mass for Ni, up to 0.1% by mass for B, up to 0.1% by mass for Ca, up to 0.1% by mass for N, up to 1% by mass for P, and up to 0.5% by mass for Sb.
One or more of the elements selected from the above group may be added within a range of 5% by mass or less as the sum of them. Balance is Fe and inevitable impurities.
According to the present invention, before the annealing step in the CGL (continuous galvanizing line), at least one substance selected from the group consisting of S, C, Cl, Na, K, B, P, F, N, and a compound thereof is adhered to the surface of the above steel sheet (substrate steel sheet).
Examples of those substances are:
a compound containing P, such as phosphoric acid (H₃PO₄), potassium phosphate (K₃PO₄), ammonium phosphate ((NH₄)₃PO₄), sodium phosphate (Na₃PO₄), sodium hydrogenphosphate (Na₂HPO₄), iron phosphate (FePO₄), phosphonic acid (H₃PO₃), and phosphinic acid (H₃PO₂);
a compound containing Na, such as sodium hydroxide (NaOH), sodium sulfate (Na₂SO₄), sodium sulfide (Na₂S), sodium thiosulfate (Na₂S₂O₃), sodium chloride (NaCl), sodium carbonate (Na₂CO₃), sodium citrate (Na₂C₆H₅O₇), sodium cyanate (NaCNO), sodium acetate (CH₃COONa), sodium hydrogenphosphate (Na₂HPO₄), sodium phosphate (Na₃PO₄), sodium fluoride (NaF), sodium hydrogencarbonate (NaHCO₃), sodium nitrate (NaNO₃), sodium oxalate ((COONa)₂), sodium tetraborate (Na₂B₄O₇), and sodium oxide (Na₂O);
a compound containing K, such as potassium hydroxide (KOH), potassium acetate (CH₃COOK), potassium borate (K₂B₄O₇), potassium carbonate (K₂CO₃), potassium chloride (KCl), potassium cyanate (KCNO), potassium hydrogencitrate (KH₂C₆H₅O₇), potassium fluoride (KF), potassium molybdate (K₂MoO₄), potassium nitrate (KNO₃); potassium permanganate (KMnO₄), potassium phosphate (K₃PO₄), potassium sulfate (K₂SO₄), potassium thiocyanate (KSCN), and potassium oxalate ((COOK)₂);
a compound containing Cl, such as hydrochloric acid (HCl), sodium chloride (NaCl), ammonium chloride (NH₄Cl), antimony chloride (SbCl₃), potassium chloride (KCl), iron chloride (FeCl₂, FeCl₃), titanium chloride (TiCl₄), copper chloride (CuCl), barium chloride (BaCl₂), molybdenum chloride (MoCl₅), and sodium chlorate (NaClO₃);
a compound containing S, such as sulfuric acid (H₂SO₄), sodium sulfate (Na₂SO₄), sodium sulfite (Na₂SO₃), sodium sulfide (Na₂S), ammonium sulfate ((NH₄)₂SO₄), ammonium sulfide ((NH₄)₂S), sodium thiosulfate (Na₂S₂O₃), sodium hydrogensulfate (NaHSO₄), ammonium hydrogensulfate (NH₄HSQ₄), potassium sulfate (K₂SO₄), iron sulfate (FeSO₄, Fe₂(SO₄)₃), ammonium ironsulfate (Fe(NH₄)₂(SO₄)₂, FeNH₄(SO₄)₂), barium sulfate (BaSO₄), antimony sulfate (Sb₂S₃), ironsulfate (FeS), thiourea (H₂NCSNH₂), thiourea dioxide ((NH₄)₂CSO₂), a thiophenic acid salt having SCH group, and a thiocyanic acid salt having SCN group;
a compound containing F, such as antimony fluoride (SbF₃), ammonium fluoride (NH₄F), potassium fluoride (KF), ammonium hydrogenfluoride (NH₄HF₂), hydrofluoric acid (HF), sodium fluoride (NaF), barium fluoride (BaF), and cobalt fluoride (CoF₃);
a compound containing B, such as boric acid (H₃BO₃), potassium borate (K₂B₄O₇), sodium tetraborate (Na₂B₄O₇), lead borate (Pb(BO₂)₂), and manganese borate (MnH₄(BO₃)₂); and
a compound containing C and N, such as oxalic acid, an oxalic acid salt, citric acid, a citric acid salt, nitric acid, and a nitric acid salt.
The method to adhere the above substances to the steel sheet is not specifically limited, and a method of physical adhesion of them may be applied, such as a method of immersing the steel sheet in an aqueous or organic solvent solution or suspension of the substance, a method of spraying that solution or suspension, and a method of coating thereof using a roll coater and the like. Succeeding step of drying the adhered compound does not affect the effect of the present invention. Alternatively, direct coating of the compound also provides similar effect to above.
It is possible that, before adhering the above substance, conventional pretreatment such as electrolytic degreasing and pickling is applied, at need. Even when the pretreatment is given after adhering the above substance, the effect of the present invention is attained if only the substance is adhered to the steel sheet. Furthermore, a rolling oil containing the above compound may be used to adhere the compound to the steel sheet in the rolling step.
For any of above methods, it is important to adhere the above substance to the surface of the steel sheet during oxidizing the steel sheet.
A preferable range of the coating weight of the above substance is from 0.01 to 1000 mg/m²as the sum of the substances, converted to the quantity of elements specified in the present invention, (hereinafter referred to also as the “quantity of specified element”), because that range is easy for controlling the hematite content to 70% by mass or less, and because the segregated layer is easily formed below the plating layer if the quantity of specified element is 0.01 mg/m²or more. The quantity of specified element is specified to 1000 mg/m²or less rather because of economical advantage than because of the effect of the present invention.
An applicable method for quantitatively determining the substance adhered to the steel sheet is a wet-system analysis. That is, the quantity of the adhered substance is readily determined by subtracting the quantity of specified element in the substrate steel sheet from the total amount of the specified element (including the substance) in the substrate steel sheet.
According to the present invention, an oxide film containing hematite in a quantity of 70% by mass or less is formed on the surface of the steel sheet by heating the steel sheet, on which steel sheet at least one substance selected from the group consisting of above S, C, Cl, Na, K, B, P, F, N, and a compound thereof is adhered, in advance.
For example, the oxide film is readily formed by heating the steel sheet with the adhered above substance. The difference in the oxidizing means does not affect the effect of the present invention, and any means can be adopted if only the means oxidizes the steel sheet.
The heating means is not specifically limited, and conventional heating means such as burner heating, induction heating, radiation heating, and electric heating may be applied. For example, the burner heating method can use a conventional heating furnace such as oxidizing furnace and non-oxidizing furnace.
For the case of non-oxidizing furnace, the steel sheet is readily oxidized by selecting the air-fuel ratio of the direct-firing burner to larger than 1.0, for example.
The oxidation is preferably conducted in an oxidizing atmosphere. For the cases of induction heating method, radiation heating method, and electric heating method, the steel sheet is readily oxidized by adjusting the atmosphere in the vicinity of the heating steel sheet to an oxidizing atmosphere. Although common oxidizing atmosphere is the one containing at least one of oxidizing gases such as oxygen, steam, and carbon dioxide, the atmosphere is not necessarily limited if only it oxidizes the steel sheet.
The above description gives typical examples, and any means may be applicable if only it oxidizes the steel sheet, thus the means is not specifically limited.
The description given below is the reason why the hematite content can be controlled to 70% by mass or less by adhering at least one substance selected from the group consisting of S, C, Cl, Na, K, B, P, F, N, and a compound thereof to the surface of the steel sheet.
For a steel sheet in which the Si content is high, the conventional oxidation means allows the Si in the steel to segregate to the interface between the iron oxide and the substrate steel sheet, thereby forming a layered and dense film of Si oxide. Since the layered Si oxide hinders the Fe diffusion from the substrate, the oxidation of iron at surface of the steel sheet is significantly suppressed so that there is formed an iron oxide containing a large quantity of hematite (Fe₂O₃) which is an oxide of a type of excess metallic ion (n-type).
On the other hand, if the substance is adhered to the surface of the steel sheet, the formation of Si oxide at the interface between the iron oxide and the substrate steel sheet is hindered, thereby allowing easy Fe diffusion from the substrate. As a result, the iron is easily oxidized at surface of the steel sheet, thus allowing formation of an iron oxide containing a large quantity of magnetite (Fe₃O₄) and wuestite (FeO) which are the metallic ion deficient type (p-type), thereby allowing decreasing the hematite content.
According to the present invention, when oxidation is applied to the steel sheet to which at least one substance selected from the group consisting of S, C, Cl, Na, K, B, P, F, N, and a compound thereof is adhered, the heating is preferably conducted in an oxidizing atmosphere giving an ultimate temperature of above 500° C. The ultimate temperature is determined by observing the surface of the steel sheet using, for example, a radiation thermometer or a contact thermometer. If the heating temperature is above 500° C., the hematite content in the oxide film is easily controlled to 70% by mass or smaller, and the surface segregation of Si is suppressed, thereby improving the wettability with molten zinc. Although the upper limit of the heating temperature is not specifically limited, there is an economical and practical upper limit, at or lower than the steel sheet temperature required to the succeeding reducing treatment, or, for example, in an approximate range from 750° C. to 800° C.
Generally, when the steel sheet is oxidized, an oxide film composed of wuestite (FeO), magnetite (Fe₃O₄), and hematite (Fe₂O₃) is formed. It is known that a steel sheet containing Si at or higher than 0.1% by mass results in increased content of hematite in the oxide film, (refer to, for example, Nisshin Seiko Technical Review No. 77, p. 1, (1998)). By adjusting the hematite content in the oxide film to 70% by mass or less, the wettability with molten zinc in the succeeding step is improved, and the generation of non-plating portion can be completely prevented. Furthermore, after plating, if the steel sheet and the hot-dip galvanizing layer are alloyed with each other, the alloying between the steel sheet and the zinc plating also becomes easy. If the hematite content exceeds 70% by mass, the wettability with molten zinc deteriorates, which fails to completely prevent the generation of non-plating portion. Since the quantity of hematite in the oxide film is preferably as small as possible, the hematite content of 0% by mass is naturally preferable. Ordinarily, however, a preferable range of hematite content is approximately from 10 to 70% by mass.
The mechanism of improvement in the wettability with molten zinc through the adjustment of hematite content in the oxide film on the steel sheet surface to 70% by mass or less is not fully analyzed. It is, however, presumed that the composition of the oxide film affects the behavior of segregation of Si on the surface of the steel sheet in the succeeding reducing step, and that the hematite content of 70% by mass or less results in complete prevention of surface segregation of Si, thus attaining excellent plating adhesion.
The term “oxide film” referred to herein does not limit to the above-described FeO, Fe₃O₄, and Fe₂O₃. Even when an oxide containing Si and the like which are the additives for steel exists, the effect of the present invention is not affected by the additives.
The determination of hematite content can be done by an X-ray diffractometry using a rotary vibration sample table, (Cu tube, 50 kV of tube voltage, and 250 mA of tube current). That is, the respective powder standard samples of hematite (Fe₂O₃), magnetite (Fe₃O₄), and wuestite (FeO) are prepared, and three kinds of samples each having different mixing rates (% by mass) are prepared for the X-ray diffractometry. There are determined the diffraction peak intensity (cps) of (104) plane for hematite (Fe₂O₃), (400) plane for magnetite (Fe₃O₄), and (200) plane for wuestite (FeO). From these determined diffraction peak intensities, the relation between the mixing rate (% by mass) and the diffraction peak intensity (cps) is derived to draw a working curve. Based on thus drawn working curve and from the obtained diffraction peak intensity, the hematite content (% by mass) can be determined.
The oxide film obtained by the above method is preferably an iron oxide of 0.01 to 5 g/m²as oxygen quantity. The oxygen quantity of 0.01 g/m²allows easy suppression of surface segregation of Si owing to the sufficient quantity of oxygen. On the other hand, the oxygen quantity of 5 g/m²or less allows the succeeding step to be conducted easily, and the alloying step given after the hot-dip galvanizing proceeds with enhanced alloying.
An example of the method for determining the quantity of oxygen in the oxide film is the following. That is, the determination is readily done by subtracting the quantity of oxygen in the substrate steel sheet from the total quantity of oxygen in the hot-dip galvanized steel sheet according to the present invention, using the wet-system analysis. If a working curve is drawn in advance, a simplified determination method such as fluorescent X-ray and GDS are also applicable.
According to the method to prepare an oxide film containing 70% by mass or more of hematite by adhering at least one substance selected from the group consisting of S, C, Cl, Na, K, B, P, F, N, and a compound thereof to the steel sheet, followed by oxidizing them, the substance is not emitted into the oxidizing atmosphere, thereby increasing the quantity of the substance entrapped in the oxide film or in the substrate steel sheet. Consequently, the method also provides an effect to suppress the entering of toxic gases into the heating furnace for oxidation treatment and the entering thereof from the heating furnace to the vent gas.
Then, according to the present invention, the oxide film thus formed on the surface of the steel sheet is reduced. The reducing method is not specifically limited, and a conventional method can be applied.
For example, it is a common practice that the reducing treatment is given in a reducing atmosphere containing hydrogen in an annealing furnace of radiation heating type at temperatures from about 600° C. to about 900° C. The method is, however, not specifically limited, and any method is applicable if only the method reduces the oxide layer at the surface of the steel sheet.
Furthermore, according to the present invention, the substrate steel sheet thus reduced is immersed in a plating bath to apply hot-dip galvanization. The hot-dip galvanization may be a conventional method. For example, the substrate steel sheet is cooled to a temperature suitable for the plating treatment, normally, a temperature near the temperature of the plating bath in a non-oxidizing or reducing atmosphere. The plating bath is normally prepared at approximate temperatures from 440° C. to 520° C. with the Al concentration of approximately from 0.1 to 0.2%.
Depending on the uses of the products, the plating conditions such as plating temperature and plating bath composition may be changed. The changes in the plating conditions, however, do not affect the effect of the present invention, thus these conditions are not specifically limited. For example, inclusion of elements such as Pb, Sb, Fe, Mg, Mn, Ni, Ca, Ti, V, Cr, Co, and Sn, other than Al, in the plating bath does not affect the effect of the present invention.
In addition, the method to adjust the thickness of the plating layer after plating is not specifically limited. Generally the gas-wiping method is applied. The thickness of the plating layer is adjusted by adjusting the gas pressure of gas-wiping, the distance between the wiping nozzle and the steel sheet, and the like. Although the thickness of the plating layer is not specifically limited, it is preferably adjusted to a range from about 3 to about 15 μm because 3 μm or larger thickness gives sufficient rust-preventive property, and because 15 μm or smaller thickness is advantageous in view of workability and economy.
Furthermore, according to the present invention, alloying treatment may be given after the above hot-dip galvanization treatment.
As described above, the present invention suppresses the surface segregation of Si in the annealing step, thus the present invention solves the problem of related art of significant delay of alloying even in a steel sheet containing a large quantity of Si. As a result, an alloyed hot-dip galvanized steel sheet having excellent anti-powdering property can be manufactured without deteriorating the productivity.
The alloying treatment may use any of conventional heating methods such as gas heating, induction heating, and electric heating, and the method is not specifically limited.
Consequently, the inventors of the present invention has developed a process of: adhering at least one substance selected from the group consisting of S, C, Cl, Na, K, B, P, F, N, and a compound thereof onto the surface of a substrate steel sheet containing 0.1 to 3% Si by mass; forming an oxide film by oxidizing the steel sheet in, preferably, an annealing furnace of CGL; applying reduction-annealing to the steel sheet to reduce the oxide film; and then applying hot-dip plating to the steel sheet.
According to the present invention, by adhering the substance to the substrate steel sheet before annealing the substrate steel sheet, or before oxidation thereof, a larger quantity of iron oxide film is formed than in the related art in the oxidation step even on a steel sheet containing a large quantity of Si. Consequently, generation of surface segregation of Si is effectively suppressed, which Si segregation on the surface is occurred on the surface of substrate steel sheet after succeeding reduction-annealing step in the related art. As a result, when the substrate steel sheet after reduction-annealing processed by the method of the present invention is subjected to hot-dip galvanization, a plating layer giving good surface appearance free from non-plating portion thereon is attained, and a hot-dip galvanized steel sheet having both excellent plating adhesion and sliding property is obtained.
Furthermore, if the above oxidation suppresses the surface segregation of Si, the adhered substance can enter the surface layer of the steel sheet by the heat treatment such as oxidation treatment. As a result, after the hot-dip galvanization or after the succeeding alloying treatment, there becomes existence of segregated layer containing at least one component selected from the group consisting of S, C, Cl, Na, K, B, P, F, and N below the plating layer.
The term “segregated layer” referred to herein signifies a zone in which the concentration of at least one component (hereinafter referred to also the “segregated component”) selected from the group consisting of S, C, Cl, Na, K, B, P, F, and N is 10% or higher than the concentration of the component in the substrate steel sheet.
That segregated layer is represented as a zone where the peak intensity appeared in the vicinity of interface is higher by 10% or more than the component intensity in the substrate steel sheet, which peak intensity is determined by a depth profile of the segregated component (element) in the depth direction from the surface of the plated steel sheet using GDS, or determined by a depth profile derived from the linear analysis of EPMA on a cross section of the plated steel sheet, as given in the examples.
The segregated layer is specified to the zone where the peak intensity of the segregated component appeared in the vicinity of interface is higher by 10% or more than the component intensity in the substrate steel sheet because smaller than 10% of increase in the intensity cannot fully prevent the surface segregation of Si during the reduction annealing step.
The determination of the depth profile of the segregated layer may be done by the linear analysis of cross section using GDS or EPMA, which are described above. As described below, however, the segregated layer is preferably the one in which the compound of the segregated component and the component in the substrate steel sheet is dispersed, thus the linear analysis by EPMA needs a special caution. That is, if the compound with the component in the substrate steel sheet is dispersed, the linear analysis of cross section by EPMA may analyze a portion of absence of the component. Accordingly, the linear analysis by EPMA is conducted by the following procedure. The measurement is given on arbitrary five positions on a cross section of the steel sheet to determine the thickness of a zone where the intensity of the segregated component is higher by 10% or more than the intensity of the component in the substrate steel sheet, and then the average thickness of the five observed values is calculated as the thickness of the segregated layer.
When the substance according to the present invention is adhered to the steel sheet, and is subjected to oxidation treatment, the quantity of the formed iron oxide increases, and the Si oxide is formed at interface between the iron oxide and the ground metal and/or within the ground metal. After that, the succeeding reducing treatment reduces the iron oxide to iron, thus the Si oxide remains in the ground metal. As a result, after the succeeding hot-dip galvanizing, a (reduced) iron layer exists below the plating layer, and the segregated layer containing the oxide containing Si exists below the (reduced) iron layer.
The “oxide containing Si” referred to herein essentially needs the existence of Si and oxygen. Since, however, the oxide containing Si includes the case of containing an oxide of a steel component and the case of containing double salt, complex salt, and the like of the oxide, the oxide containing Si is not limited to the Si oxide, and the kind is not the limited one. Typical “oxide containing Si” includes SiO₂, FeSiO₃, Fe₂SiO₄, MnSiO₃, and a mixture thereof.
That is, the hot-dip galvanized steel sheet according to the present invention has: a steel sheet containing 0.1 to 3.0% Si by mass; a hot-dip galvanizing layer; and a segregated layer between the steel sheet and the hot-dip galvanizing layer, containing an oxide containing Si, having a thickness in a range from 0.01 to 100 μm, and containing at least one component selected from the group consisting of S, C, Cl, Na, K, B, P, F, and N.
The mechanism that the hot-dip galvanized steel sheet according to the present invention provides excellent plating adhesion and sliding property is not fully analyzed. The inventors of the present invention, however, speculate the mechanism as follows.
As in the case of the present invention, when the segregated layer having the above component is formed on the surface of the substrate steel sheet, the compatibility between the Fe-Al intermetallic compound, formed at the interface between the zinc plating and the steel sheet, and the substrate steel sheet varies toward advantageous side for the adhesion in the hot-dip galvanizing step.
Furthermore, when the segregated layer of the component is formed on the surface of the substrate steel sheet, the component is unavoidably eluted into the plating layer in the hot-dip galvanizing step, and a part of the eluted component comes to exist in the plating layer in the vicinity of interface with the steel sheet. The mechanism presumably improves the sliding property compared with the ordinary hot-dip galvanized steel sheet which does not contain the segregated layer.
Furthermore, the mechanism of improving the plating adhesion and sliding property by the existence of an oxide containing Si in the segregated layer is speculated as follows.
When an oxide containing Si exists in the segregated layer, the shape of interface between the plating layer and the steel sheet becomes irregular to generate an anchor effect, which anchor effect improves the adhesion, and the sliding property in the working step also improves. The anchor effect is the same for both the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet.
Accordingly, when the segregated layer of the component is formed below the plating layer, and when the oxide containing Si is brought to exist in the segregated layer, the synergy effect of them drastically improves the adhesion, and also improves the sliding property.
The thickness of the segregated layer according to the present invention is required to be controlled in a range from 0.01 to 100 μm because the thickness of smaller than 0.01 μm cannot sufficiently attain the effect to improve the adhesion, and because the thickness of larger than 100 μm deteriorates the fatigue characteristics. Further preferable range of the thickness of the segregated layer is from larger than 1 μm to not larger than 50 μm.
According to the present invention, the concentration of the component in the segregated layer is preferably higher by 10% or more than the concentration of the component in the substrate steel sheet because that kind of segregated layer makes the surface segregation of Si sufficiently and easily suppress in the reduction annealing step.
That kind of segregated layer is represented as a zone where the peak intensity appeared in the vicinity of interface is higher by 10% or more than the intensity of the ground metal, determined by a depth profile drawn on a cross section of the plated steel sheet using GDS, or determined by a depth profile derived from the linear analysis of EPMA, as given in the examples.
The segregated layer is preferably formed by a dispersed compound of the segregated component and the component of the substrate steel sheet. The component in the substrate steel sheet is expected as, Fe naturally, and as Si, Mn, Ti, Nb, V, Cr, S, Mo, Cu, Ni, B, Ca, N, P, Sb, and the like. To form the segregated layer of a desired substance, the formation of a compound with the component of the substrate steel sheet is expected to more stably fix the segregated component. According to an analysis, most part of the compound exists at grain boundaries in the substrate steel sheet. Therefore, a presumable advantage of the dispersed state of the compound is that the compound plugs the passage of Si diffusion, thereby effectively suppressing the surface segregation of Si in the steel.
Furthermore, if the compound in the segregated layer is MnS, the effect of the present invention is more stably attained because, among the expected compounds, MnS is a very stable compound in the steel so that MnS is easily formed and easily controls the manufacturing conditions. To form MnS, when S is selected as the element to adhere to the steel sheet before the above-oxidation treatment, the S reacts with Mn in the steel in the surface layer of the steel sheet, (below the plating layer after the plating step), during oxidation treatment and reducing treatment, thereby segregates.
In that case, a favorable quantity of the formed compound is five or more of the MnS grains having a grain size of 50 μm or larger, in an arbitrary cross section, per 20 μm of length in parallel with the interface between the plating layer and the substrate steel sheet. The MnS referred to herein means that the main component is formed by Mn and S, and the inclusion of other element such as Fe raises no problem.
Determination and judgment of dispersion and the number of compound particles can be given by, adding to the SEM observation or the TEM observation of cross section of the plated steel sheet, using EDS, electron diffractometry (TED), and the like, at need.
The quantity of the oxide containing Si in the segregated layer is preferably adjusted in a range from 0.01 to 1 g/m²as oxygen. If the quantity of the oxide containing Si is 0.01 g/m²or more, the plating adhesion and the sliding property are significantly improved, and the quantity thereof at 1 g/m²or less is economical.
On determining the oxide, the existence of Si in the oxide can be confirmed by the EDX analysis of a sample prepared by the TEM replica method.
By alloying the above-described hot-dip galvanized steel sheet according to the present invention, there is obtained an alloyed hot-dip galvanized steel sheet which can be alloyed at a low temperature, and which provides not only excellent, plating adhesion and sliding property but also excellent anti-powdering property.
When the conventional hot-dip galvanized steel sheet is alloyed, a Γ phase having higher hardness than that of the substrate steel sheet is formed at the interface between the zinc plating and the substrate steel sheet, and the deterioration of plating adhesion is unavoidably occurs caused by the difference in the hardness between the Γ phase and the steel sheet. When, however, the hot-dip galvanized steel sheet according to the present invention is alloyed, there is existed a segregated layer of the component below the plating layer so that the mechanical characteristics in the vicinity of interface between the zinc plating layer and the substrate steel sheet, specifically the hardness of the substrate steel sheet, become close to those of the Γ phase, thereby effectively decreasing the strain applied to the interface during the deformation of the substrate steel sheet. As a result, the plating adhesion presumably improves.
Since the hot-dip galvanized steel sheet according to the present invention suppresses the surface segregation of Si in the annealing step, the alloying is available at relatively low temperatures. As a result, there is attained a merit of suppressing the formation of Γ phase which is not favorable to the plating adhesion.
Generally, the sliding property of alloyed hot-dip galvanized layer appears depending on the variations of alloying behavior. That is, as described above, the material of Si-surface-segregated material appeared on the surface of the substrate steel sheet in the annealing step delays the alloying rate because the surface-segregated material which is segregated by the selective oxidation on the surface after annealing suppresses the alloying reaction between Zn and Fe. As a result, the plating layer after completing the alloying reaction becomes the one having significantly irregular surface resulted from the interference of homogeneous reaction of Zn and Fe. In addition, the alloy crystals of Zn and Fe become coarse. Owing to the irregular surface of plating layer and to the coarse crystal grains caused by the suppression of alloying, the sliding property of the plating layer deteriorates.
The hot-dip galvanized steel sheet according to the present invention, however, contains a segregated layer having the component below the plating layer, similar to the above case of adhesion. Thus, compared with the normal cases, the surface segregation of Si in the annealing step is suppressed, and the alloying is enhanced. As a result, the reaction between Zn and Fe proceeds homogeneously, and the plating layer becomes smooth. In addition, the crystal grains become fine, thereby providing good sliding property compared with the Si-containing steel manufactured by the conventional method.
It was described above that the hot-dip galvanized steel sheet according to the present invention contains a layer of (reduced) iron below the plating layer, and further contains the segregated layer containing an oxide containing Si below the (reduced) iron layer. When, however, the hot-dip galvanized steel sheet according to the present invention is subjected to alloying treatment, naturally the alloying between the zinc plating layer and the (reduced) iron proceeds. Consequently, the obtained alloyed hot-dip galvanized steel sheet may fail to identify the iron layer below the galvanized layer. That type of alloyed hot-dip galvanized steel sheet, however, is within the range of the present invention because the steel sheet has the “segregated layer of the component containing an oxide containing Si” below the plating layer.

EXAMPLES

Example A

Electrolytic degreasing was conducted on eight types of test specimens of cold-rolled steel sheets and hot-rolled steel sheets, given in Table 1, in a solution of 5% NaOH by mass, under the condition of 5 A/dm², 80° C. for 5 seconds. Each of aqueous solutions containing the respective substances of (a) phosphoric acid (100 g/l), (b) hydrochloric acid (1 g/l), (c) sodium fluoride (2g/l), (d) sodium thiosulfate (20 g/l), (e) Potassium hydroxide (100 g/l), (f), ammonium thiocyanate (50 g/l), (g) sulfuric acid (50 g/l), (h) ammonium sulfate (30 g/l), (i) thiourea (20 g/l), (j) sodium sulfate (50 g/l), (k) iron sulfate (20 g/l), (l) sulfuric acid (10 g/l), (m) ammonium sulfate (5 g/l), (n) thiourea (1 g/l), and (o) ammonium sulfate (150 g/l), was applied onto the surface of the respective steel sheets using a bar-coater at the respective coating weights given in Table 2-1, Table 3-1, and Table 4-1. After that, the applied aqueous solution was dried in a drier.
Thus prepared test specimens were heated in a heating furnace in an oxidizing atmosphere. Once taken out specimens were treated by annealing, followed by plating in a hot-dip plating simulator. The oxidation condition and other conditions are given in Table 2-1, Table 3-1, and Table 4-1.
For comparison, annealing and plating were given to the specimen without applying heating treatment.
The heating was given in air while varying the ultimate temperature of the steel sheet. The holding time at the ultimate temperature was 1 second, and then rapid cooling was applied using nitrogen gas.
The annealing was given in an atmosphere of (10% by volume of hydrogen+nitrogen) of −35° C. of dew point, at 830° C. of the steel sheet temperature and 45 seconds of holding time.
The plating was done in a zinc plating bath containing 0.14% Al by mass (Fe-saturated) at 460° C., with an immersing sheet temperature of 460° C., and an immersing time of 1 second. The surface appearance after plating was evaluated. After the plating, the coating weight was adjusted to 45 g/m²on one side using a nitrogen gas wiper.
For thus prepared hot-dip galvanized steel sheets, the following-given procedure was applied to determine the thickness of the segregated component, and the degree of segregation, and to determine the oxide containing Si below the plating layer, and further the following-given evaluation criterion was applied to evaluate the plating appearance and the plating adhesion. The properties of segregated layer are given in Table 2-2, Table 3-2, and Table 4-2.
Furthermore, some of the plated steel sheets were subjected to alloying treatment, after the plating, in an electric heating furnace at 40° C./s of temperature-rise rate with 10 seconds of holding time, thus evaluating the alloying rate based on the alloying temperature that gives 10±0.5% by mass of the Fe content in the plating layer. The evaluation criterion is given later. Using a sample having 10±0.5% by mass of the Fe content in the plating layer, a 90° bend test was given to evaluate the anti-powdering property based on the evaluation criterion given later. Furthermore, the sliding property was evaluated based on the criterion given later.
Those evaluation results are shown in Table 2-3, Table 3-3, and Table 4-3.
As seen in Tables 2-1 to 4-3, even for the case of using a substrate steel sheet containing a large quantity of Si, prepared by adhering a compound containing at least one substance selected from the group consisting of S, C, Cl, Na, K, B, P, F, N, and a compound thereof onto the surface of steel sheet, and prepared by oxidizing the adhered substance to form an oxide film containing 70% by mass or less of hematite, and then by annealing in a reducing atmosphere, there is obtained excellent anti-powdering property and sliding property without generating non-plating portion and without significant delay of alloying. The obtained hot-dip galvanized steel sheet or alloyed hot-dip galvanized steel sheet has a segregated layer below the plating layer, and the segregated layer contains an oxide containing Si. It was confirmed that the oxide film formed after the oxidation treatment has a structure of hematite and balance of mainly magnetite and wuestite.

Example B

The plated steel sheets were prepared under the same conditions to those in Example A except that the substance was each of (o) potassium chloride (50 g/l), (p) ammonium oxalate (100 g/l), (q) sulfuric acid (50 g/l), (r) sodium hydroxide (30 g/l), and (s) sodium tetraborate (3 g/l), at the respective coating weights given in Table 5-1, and the heating condition of (0.1% by volume of oxygen+nitrogen) atmosphere. Evaluation to them was given on the same criterion to that of Example A. The properties of the segregated layer are given in Table 5-2. The evaluation of thus prepared plated steel sheets is given in Table 5-3.
As seen in Tables 5-1 to 5-3, for the case of a substrate steel sheet containing a large quantity of Si, prepared by adhering the substance onto the surface of steel sheet, and by oxidizing the adhered substance to form an oxide film containing 70% by mass or less of hematite, and then by annealing in a reducing atmosphere, there was obtained excellent anti-powdering property and sliding property without generating non-plating portion and without significant delay of alloying. The obtained hot-dip galvanized steel sheet or alloyed hot-dip galvanized steel sheet has a segregated layer below the plating layer, and the segregated layer contains an oxide containing Si. It was confirmed that the oxide film formed after oxidation treatment has a structure of hematite and balance of mainly magnetite and wuestite.

Example C

The plated steel sheets were prepared under the same conditions to those in Example A except that the substance was each of (t) antimony chloride (20 g/l), (u) ammonium sulfate (30 g/l), (v) lead chloride (1 g/l), (w) thiourea (20 g/l), and (x) sodium chloride (25 g/l), at the respective coating weights given in Table 6-1, and the heating condition of direct-firing burner at 1.15 of air/fuel ratio. Evaluation to them was given on the same criterion to that of Example A. The properties of the segregated layer are given in Table 6-2, and the evaluation results for thus prepared steel sheets are given in Table 6-3.
As seen in Tables 6-1 to 6-3, for the case of a substrate steel sheet containing a large quantity of Si, prepared by adhering the substance onto the surface of steel sheet, and by oxidizing the adhered substance to form an oxide film containing 70% by mass or less of hematite, and then by annealing in a reducing atmosphere, there was obtained excellent anti-powdering property and sliding property without generating non-plating portion and without significant delay of alloying. The obtained hot-dip galvanized steel sheet or alloyed hot-dip galvanized steel sheet has a segregated layer below the plating layer, and the segregated layer contains an oxide containing Si. It was confirmed that the oxide film formed after oxidation treatment has a structure of hematite and balance of mainly magnetite and wuestite.
The criteria for evaluating the plating quality are the following.
<Determination of the Thickness of Segregated Component and of the Degree of Segregation>
To the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet, the linear analysis of EPMA and/or the GDS measurement were given on their cross sections. Based on the drawn depth profiles (for example, FIG. 1 and FIG. 2), the thickness of segregated layer was determined as the thickness of a zone where the peak intensity of the segregated component (element) appeared in the vicinity of interface is higher by 10% or more than the intensity of the component in the ground metal portion, at a ground metal side from the interface between the plating layer and the substrate steel sheet. In addition, the increase in the peak intensity A of the component in the segregated layer to the peak intensity B of the component in the ground metal is determined as the degree of segregation. That is, [the degree of segregation (%)={(the intensity A−the intensity B)/(the intensity B)}×100%]. For the case of the degree of segregation smaller than 10%, the thickness of the zone where the intensity of the segregated component in the depth profile becomes slightly higher than the intensity B of the segregated component in the ground metal is given in the table as the thickness of the segregated layer. For the linear analysis of EPMA, the measurement was given at five arbitrary positions on a cross section of the steel sheet, and the thickness of the zone where the intensity of the segregated component is higher than the intensity of the ground metal by 10% or more was determined. The thickness of the segregated layer and the degree of segregation were derived by determining the average thickness and the average peak intensity A for the five measured values. In the GDS measurement, conversion from the sputtering time into the thickness of segregated layer was calculated on the basis of 0.04 μm/sec of the iron sputtering rate under the following GDS condition.
(EPMA Measurement Condition)
Acceleration voltage: 20 kV
Beam current: 0.05 μA
(GDS Measurement Condition)
Tube current: 30 mA
Argon gas flow volume: 400 ml
<Method for Determining the Oxide Containing Si Below the Plating Layer>
To the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet, the plating layer was removed by dissolving in an alkali solution given below. The oxide quantity was determined from the difference in the oxygen analysis result between thus prepared steel sheet and a steel sheet which was mechanically polished to 100 μm of surface irregularity on both sides thereof. The existence of Si in the oxide was confirmed by the EDX analysis on a test specimen prepared by TEM replica method.
(Alkali Solution)
NaOH: 8.2%
Triethanolamine: 2.1%
H₂O₂: 1.2%<
Plating Appearance>
Appearance of thus prepared hot-dip galvanized steel sheet was observed visually and with a (×10) magnifier. The evaluation was given as “No non-plating portion exists” for the case of absence of non-plating portion, “Slight non-plating portion exists” for the case that the (×10) magnifier-recognized fine non-plating portion, and “Non-plating portion exists” for the case that visual observation recognized non-plating portion.
◯: No non-plating portion exists.
Δ: Slight non-plating portion exists.
X: Non-plating portion exists.
<Plating Adhesion>
A ball-impact test was given to thus prepared hot-dip galvanized steel sheet to evaluate the plating separation on tape-peeling test. The test was conducted by positioning a hot-dip galvanized steel sheet on a hemispherical protrusion (½ inch of diameter), and by dropping a 2.8 kg weight onto the steel sheet from 1 m of height. After that, the tape-peeling test was given on the convex side.
◯: No plating separation occurred.
X: Plating separation occurred.
<Alloying Rate>
◯: Alloying temperature: alloying completed at 500° C. or below.
X: Alloying temperature: alloying completed at above 500° C.
<Anti-Powdering Property>
A test specimen (25 mm in width and 40 mm in length) was cut from the alloy hot-dip galvanized steel sheet, and a scotch tape (24 mm in width, manufactured by NICHIBAN CO., LTD.) was attached to the test specimen at 20 mm position in the length thereof. After bending the taping side by 90° inward, the specimen was again straightened. The scotch tape was peeled, and the quantity of Zn grains adhered to the scotch tape was counted under fluorescent X-ray. The Zn count was converted into the count per unit length of the test specimen (1 m), and the evaluation was given on the basis of the following criterion.
◯: Good (count: 1 to 5000)
X: Bad (count: more than 5000)
<Sliding Property Test>
The sliding property test was given under the following condition using a tool having a shape described below. From the ratio of the drawing-out force F to the pressing load P, the friction factor μ was derived by the following formula. The evaluation was given on the basis of the criterion described below.
μ=2P/F
Face pressure of 9.8 MPa, sliding distance of 100 mm, sliding rate of 10 mm/s, specimen width of 20 mm, mold of flat tool (shoulder radius of 5 mm, polished to #1200), contact area with specimen of 10×20 mm, oil-applying condition of NOX-RUST 550KH, 1.0 g/m².
◯: Good (μ: less than 0.12)
X: Bad (μ: 0.12 or more)

Example D

The plated steel sheet was prepared under the same condition to that of Example A. The evaluation method was almost the same to that of Example A. For the anti-powdering property, however, the evaluation criterion was changed to the following-given one for evaluating finer differences.
⊚: Excellent (count: less than 4000)
◯: Good (count: 4000 to 5000)
X: Bad (count: more than 5000)
For each of the test specimens, confirmation was given on the determination of segregated substance in the vicinity of interface with the plating layer and on the distribution thereof using SEM and TEM. The analytical samples were prepared from the test specimens by working the cross section using the focused ion beam (FIB). The SEM observation determined the size and the number of the generated compound particles of segregated component, and the TEM-EDS and the electron beam diffraction determined the compound. Regarding the evaluation of the number of compound particles, within a visual field of cross sectional observation by SEM, the number of compound particles having 50 nm or larger size existing in the vicinity of interface in a zone of 20 μm in width in parallel with the interface between the plating layer and the substrate steel sheet was counted at arbitrarily selected five positions. The average of the values of these five positions was adopted as the evaluation index.
The results are given in Table 7 together with adhered substance, oxidation treatment, and the properties of segregated layer.

As shown in Table 7, among the segregated layers formed adequately in the vicinity of the interface with the plating layer, further excellent characteristics are attained specifically bringing the segregated layer to establish a state of sufficiently dispersing the compound of the segregated component and the component in the substrate steel sheet.

TABLE 1


(mass %)

Steel	Steel
type	sheet	C	Si	Mn	P	S	Al	Other

A	Cold-rolled	0.002	0.15	1.5	0.07	0.004	0.03	—
B	steel sheet	0.1	0.25	2.0	0.05	0.002	0.70	—
C		0.5	0.5	2.0	0.01	0.003	0.04	—
D		0.002	0.75	1.5	0.06	0.007	0.04	—
E		0.1	1.0	3.5	0.01	0.003	0.05	—
F		0.003	1.1	0.3	0.05	0.008	0.02	—
G		0.15	1.5	2.5	0.01	0.003	0.03	—
H		0.1	2.9	1.5	0.01	0.003	0.03	—
I	Hot-rolled	0.15	0.3	1.5	0.03	0.005	0.05	—
J	steel sheet	0.1	2.0	1.0	0.10	0.005	0.03	—
K	Cold-rolled	0.15	0.5	2.0	0.01	0.003	0.04	Ti: 0.02
L	steel sheet	0.1	0.25	1.6	0.05	0.002	0.30	Nb: 0.03
M		0.002	0.25	1.5	0.07	0.004	0.03	V: 0.03
N		0.08	0.5	2.0	0.01	0.01	0.02	Cr: 0.1
O		0.15	1.5	2.1	0.01	0.003	0.03	Mo: 0.2
P		0.1	2.8	0.8	0.01	0.003	0.03	Cu: 0.2
Q		0.07	0.3	1.5	0.09	0.005	0.05	Ni: 0.2
R		0.18	1.5	2.5	0.01	0.003	0.3	B: 0.002
S		0.003	1.1	1.5	0.05	0.008	0.02	Ca: 0.02
T		0.003	0.8	1.9	0.01	0.008	0.02	N: 0.01
U		0.1	1.0	4.5	0.01	0.003	0.8	Sb: 0.02
V		0.2	1.9	1.2	0.10	0.005	0.03	Ti: 0.03,
								Nb: 0.04
W		0.08	0.35	2.2	0.02	0.002	0.70	Nb: 0.03,
								Mo: 0.25
X		0.1	2.9	2.5	0.06	0.003	0.03	Cu: 0.15

	TABLE 2-1


	Adhered substabce	Oxidation treatment

				Quantity of			Oxygen
				specific		UIltimate	quantity in	Hematite
	Steel		Concentrtion	element	Applied/	temperature	oxide film	content
No.	type	Kind	(g/l)	(mg/m²)	Not applied	(° C.)	(g/m²)	(%)

Example 1	A	Phosphoric	100	70	Applied	650	0.62	50
Example 2	B	acid					0.58	50
Example 3	C						0.59	55
Example 4	D						0.6	60
Example 5	G						0.55	60
Example 6	H						0.57	65
Example 7	B	Hydrochloric	1	0.1	Applied	550	0.45	0
Example 8	C	acid					0.48	0
Example 9	G						0.52	5
Example 10	H						0.45	5
Example 11	I						0.49	10
Example 12	J						0.5	10
Example 13	A	Sodium	2	1	Applied	700	0.75	0
Example 14	B	fluoride					0.71	0
Example 15	C						0.68	0
Example 16	E						0.77	0
Example 17	F						0.69	0
Example 18	H						0.69	0
Example 19	A	Sodium	20	70	Applied	600	0.55	0
Example 20	B	thiosulfate					0.52	0
Example 21	C						0.54	0
Example 22	D						0.5	0
Example 23	G						0.52	5
Example 24	H						0.53	5
Example 25	A	Potassium	100	100	Applied	600	0.51	0
Example 26	B	hydroxide					0.49	0
Example 27	C						0.48	5
Example 28	E						0.45	5
Example 29	F						0.45	10
Example 30	H						0.45	20
Comparative Example 1	B	None	None	None	Applied	600	0.18	90
Comparative Example 2	C						0.12	90
Comparative Example 3	G						0.07	90
Comparative Example 4	H						0.05	95
Comparative Example 5	I						0.2	90
Comparative Example 6	J						0.08	95
Comparative Example 7	A	Sodium	2	1	Not	—	—	—
Comparative Example 8	B	fluoride			applied		—	—
Comparative Example 9	C						—	—
Comparative Example 10	E						—	—
Comparative Example 11	F						—	—
Comparative Example 12	H						—	—
Comparative Example 13	A	Sodium	20	70	Applied	500	0.07	75
Comparative Example 14	B	thiosulfate					0.07	80
Comparative Example 15	C						0.07	80
Comparative Example 16	D						0.05	85
Comparative Example 17	G						0.06	85
Comparative Example 18	H						0.05	85
Comparative Example 19	A	Hydrochloric	1	0.1	Applied	400	0.006	80
Comparative Example 20	B	acid					0.007	80
Comparative Example 21	C						0.006	75
Comparative Example 22	D						0.006	80
Comparative Example 23	G						0.005	80
Comparative Example 24	H						0.002	75
Comparative Example 25	A	Phosphoric	100	70	Applied	400	0.01	85
Comparative Example 26	B	acic					0.02	85
Comparative Example 27	C						0.02	85
Comparative Example 28	D						0.01	85
Comparative Example 29	G						0.005	90
Comparative Example 30	H						0.005	90
Comparative Example 31	A	Ammonium	50	70	Applied	500	0.01	80
Comparative Example 32	B	thiocyanate					0.02	80
Comparative Example 33	C						0.02	80
Comparative Example 34	D						0.01	80
Comparative Example 35	G						0.005	90
Comparative Example 36	H						0.005	90

	TABLE 2-2


	Properties of segregated layer

Segregated
component	Thickenss of segregated	Degree of	Quantity of oxide
below plating	component (μm)	segregation (%)	containing Si

No.	layer	GDS	EPMA	GDS	EPMA	(g/m²)

Example 1	P	7	—	400	—	0.1
Example 2		7	—	400	—	0.1
Example 3		7	—	400	—	0.15
Example 4		7	—	400	—	0.12
Example 5		7	—	400	—	0.5
Example 6		7	—	400	—	0.7
Example 7	Cl	1.1	—	100	—	0.05
Example 8		1.2	—	100	—	0.05
Example 9		1.1	—	100	—	0.05
Example 10		1.1	—	100	—	0.05
Example 11		1.1	—	100	—	0.05
Example 12		1.1	—	100	—	0.04
Example 13	F, Na	F: 1.5, Na: 1.4	—	F: 100, Na: 100	—	0.12
Example 14		F: 1.5, Na: 1.4	—	F: 100, Na: 100	—	0.13
Example 15		F: 1.5, Na: 1.4	—	F: 100, Na: 100	—	0.12
Example 16		F: 1.5, Na: 1.4	—	F: 100, Na: 100	—	0.12
Example 17		F: 1.5, Na: 1.4	—	F: 100, Na: 100	—	0.14
Example 18		F: 1.5, Na: 1.4	—	F: 100, Na: 100	—	0.13
Example 19	S, Na	S: 3.0, Na: 2.0	—	S: 400, Na: 400	—	0.1
Example 20		S: 3.0, Na: 2.0	—	S: 400, Na: 400	—	0.15
Example 21		S: 3.0, Na: 2.0	—	S: 400, Na: 400	—	0.1
Example 22		S: 3.0, Na: 2.0	—	S: 400, Na: 400	—	0.11
Example 23		S: 3.0, Na: 2.0	—	S: 400, Na: 400	—	0.12
Example 24		S: 3.0, Na: 2.0	—	S: 400, Na: 400	—	0.1
Example 25	K	3.0	—	500	—	0.12
Example 26		3.0	—	500	—	0.13
Example 27		3.0	—	500	—	0.11
Example 28		3.0	—	500	—	0.1
Example 29		3.0	—	500	—	0.12
Example 30		3.0	—	500	—	0.13
Comparative Example 1	None	—	—	—	—	0.001
Comparative Example 2		—	—	—	—	0.001
Comparative Example 3		—	—	—	—	0.001
Comparative Example 4		—	—	—	—	0.001
Comparative Example 5		—	—	—	—	0.001
Comparative Example 6		—	—	—	—	0.001
Comparative Example 7	F, Na	(F: 0.004, Na: 0.003)	—	F: 5, Na: 5	—	0.002
Comparative Example 8		(F: 0.004, Na: 0.003)	—	F: 5, Na: 5	—	0.003
Comparative Example 9		(F: 0.004, Na: 0.003)	—	F: 5, Na: 5	—	0.002
Comparative Example 10		(F: 0.004, Na: 0.003)	—	F: 5, Na: 5	—	0.002
Comparative Example 11		(F: 0.004, Na: 0.003)	—	F: 5, Na: 5	—	0.003
Comparative Example 12		(F: 0.004, Na: 0.003)	—	F: 5, Na: 5	—	0.002
Comparative Example 13	S, Na	(S: 0.004, Na: 0.004)	—	S: 6, Na: 6	—	0.004
Comparative Example 14		(S: 0.004, Na: 0.004)	—	S: 6, Na: 6	—	0.005
Comparative Example 15		(S: 0.004, Na: 0.004)	—	S: 6, Na: 6	—	0.004
Comparative Example 16		(S: 0.004, Na: 0.004)	—	S: 6, Na: 6	—	0.003
Comparative Example 17		(S: 0.004, Na: 0.004)	—	S: 6, Na: 6	—	0.003
Comparative Example 18		(S: 0.004, Na: 0.004)	—	S: 6, Na: 6	—	0.003
Comparative Example 19	Cl	(0.003)	—	5	—	0.002
Comparative Example 20		(0.003)	—	5	—	0.003
Comparative Example 21		(0.003)	—	5	—	0.004
Comparative Example 22		(0.003)	—	5	—	0.003
Comparative Example 23		(0.003)	—	5	—	0.003
Comparative Example 24		(0.003)	—	5	—	0.004
Comparative Example 25	P	(0.004)	—	5	—	0.002
Comparative Example 26		(0.004)	—	5	—	0.004
Comparative Example 27		(0.004)	—	5	—	0.003
Comparative Example 28		(0.004)	—	5	—	0.002
Comparative Example 29		(0.004)	—	5	—	0.004
Comparative Example 30		(0.004)	—	5	—	0.003
Comparative Example 31	S, C, N	(S: 0.004, C: 0.003, N: 0.004)	—	S: 5, N5	—	0.004
Comparative Example 32		(S: 0.004, C: 0.003, N: 0.004)	—	S: 5, N5	—	0.005
Comparative Example 33		(S: 0.004, C: 0.003, N: 0.004)	—	S: 5, N5	—	0.004
Comparative Example 34		(S: 0.004, C: 0.003, N: 0.004)	—	S: 5, N5	—	0.004
Comparative Example 35		(S: 0.004, C: 0.003, N: 0.004)	—	S: 5, N5	—	0.003
Comparative Example 36		(S: 0.004, C: 0.003, N: 0.004)	—	S: 5, N5	—	0.004

	TABLE 2-3


	Plating quality

				Anti-
	Plating	Plating	Alloying	powdering	Sliding
No.	appearance	adhesion	rate	property	property

Example 1	◯	◯	◯	◯	◯
Example 2	◯	◯	◯	◯	◯
Example 3	◯	◯	◯	◯	◯
Example 4	◯	◯	◯	◯	◯
Example 5	◯	◯	◯	◯	◯
Example 6	◯	◯	◯	◯	◯
Example 7	◯	◯	◯	◯	◯
Example 8	◯	◯	◯	◯	◯
Example 9	◯	◯	◯	◯	◯
Example 10	◯	◯	◯	◯	◯
Example 11	◯	◯	◯	◯	◯
Example 12	◯	◯	◯	◯	◯
Example 13	◯	◯	◯	◯	◯
Example 14	◯	◯	◯	◯	◯
Example 15	◯	◯	◯	◯	◯
Example 16	◯	◯	◯	◯	◯
Example 17	◯	◯	◯	◯	◯
Example 18	◯	◯	◯	◯	◯
Example 19	◯	◯	◯	◯	◯
Example 20	◯	◯	◯	◯	◯
Example 21	◯	◯	◯	◯	◯
Example 22	◯	◯	◯	◯	◯
Example 23	◯	◯	◯	◯	◯
Example 24	◯	◯	◯	◯	◯
Example 25	◯	◯	◯	◯	◯
Example 26	◯	◯	◯	◯	◯
Example 27	◯	◯	◯	◯	◯
Example 28	◯	◯	◯	◯	◯
Example 29	◯	◯	◯	◯	◯
Example 30	◯	◯	◯	◯	◯
Comparative	Δ	X	X	X	X
Example 1
Comparative	X	X	X	X	X
Example 2
Comparative	X	X	X	X	X
Example 3
Comparative	X	X	X	X	X
Example 4
Comparative	Δ	X	X	X	X
Example 5
Comparative	X	X	X	X	X
Example 6
Comparative	X	X	X	X	X
Example 7
Comparative	X	X	X	X	X
Example 8
Comparative	X	X	X	X	X
Example 9
Comparative	X	X	X	X	X
Example 10
Comparative	X	X	X	X	X
Example 11
Comparative	X	X	X	X	X
Example 12
Comparative	Δ	X	X	X	X
Example 13
Comparative	Δ	X	X	X	X
Example 14
Comparative	X	X	X	X	X
Example 15
Comparative	X	X	X	X	X
Example 16
Comparative	X	X	X	X	X
Example 17
Comparative	X	X	X	X	X
Example 18
Comparative	X	X	X	X	X
Example 19
Comparative	X	X	X	X	X
Example 20
Comparative	X	X	X	X	X
Example 21
Comparative	X	X	X	X	X
Example 22
Comparative	X	X	X	X	X
Example 23
Comparative	X	X	X	X	X
Example 24
Comparative	X	X	X	X	X
Example 25
Comparative	X	X	X	X	X
Example 26
Comparative	X	X	X	X	X
Example 27
Comparative	X	X	X	X	X
Example 28
Comparative	X	X	X	X	X
Example 29
Comparative	X	X	X	X	X
Example 30
Comparative	X	X	X	X	X
Example 31
Comparative	X	X	X	X	X
Example 32
Comparative	X	X	X	X	X
Example 33
Comparative	X	X	X	X	X
Example 34
Comparative	X	X	X	X	X
Example 35
Comparative	X	X	X	X	X
Example 36

	TABLE 3-1


	Adhered substance	Oxidation treatment

				Quantity of			Quantity of
				specific		Ultimate	oxygen in	Hematite
	Steel		Concentration	element	Applied/	temperature	oxide film	content
No.	type	Kind	(g/l)	(mg/m²)	Not applied	(° C.)	(g/m²)	(%)

Example 31	A	Sulfuric	50	70	Applied	600	0.55	0
Example 32	B	acid					0.55	0
Example 33	C						0.53	5
Example 34	D						0.52	5
Example 35	G						0.61	10
Example 36	H						0.51	10
Example 37	B	Ammonium	30	100	Applied	650	0.56	0
Example 38	C	sulfate					0.61	0
Example 39	G						0.52	5
Example 40	H						0.54	5
Example 41	I						0.53	10
Example 42	J						0.51	10
Example 43	A	Thiourea	20	70	Applied	700	0.64	0
Example 44	B						0.64	0
Example 45	C						0.62	5
Example 46	E						0.71	5
Example 47	F						0.62	10
Example 48	H						0.51	10
Example 49	A	Sodium	50	70	Applied	600	0.55	0
Example 50	B	sulfide					0.51	0
Example 51	C						0.58	5
Example 52	D						0.54	5
Example 53	G						0.56	10
Example 54	H						0.51	10
Example 55	A	Iron	20	80	Applied	550	0.41	0
Example 56	B	sulfide					0.34	0
Example 57	C						0.35	5
Example 58	E						0.41	5
Example 59	F						0.38	10
Example 60	H						0.36	10
Comparative Example 37	B	None	None	None	Applied	600	0.21	90
Comparative Example 38	C						0.25	90
Comparative Example 39	G						0.18	90
Comparative Example 40	H						0.21	90
Comparative Example 41	I						0.24	95
Comparative Example 42	J						0.19	90
Comparative Example 43	A	Sulfuric	10	5	Not	—	—	—
Comparative Example 44	B	acid			applied		—	—
Comparative Example 45	C						—	—
Comparative Example 46	E						—	—
Comparative Example 47	F						—	—
Comparative Example 48	H						—	—
Comparative Example 49	A	Ammonium	5	10	Applied	400	0.006	80
Comparative Example 50	B	sulfate					0.008	84
Comparative Example 51	C						0.004	86
Comparative Example 52	D						0.006	82
Comparative Example 53	G						0.004	80
Comparative Example 54	H						0.003	86
Comparative Example 55	A	Thio urea	1	0.1	Applied	400	0.004	85
Comparative Example 56	B						0.003	90
Comparative Example 57	C						0.004	89
Comparative Example 58	D						0.006	86
Comparative Example 59	G						0.004	91
Comparative Example 60	H						0.002	90
Comparative Example 61	A	None	None	None	Applied	850	3.1	75
Comparative Example 62	B						2.9	72
Comparative Example 63	C						2.6	80
Comparative Example 64	D						2.8	85
Comparative Example 65	E						2.9	72
Comparative Example 66	F						2.8	71
Comparative Example 67	G						2.9	75
Comparative Example 68	H						2.5	86

	TABLE 3-2


	Properties of segregated layer

Segregated
component	Thickness of segregated	Degree of	Quantity of oxide
below plating	component (μm)	segregation (%)	containing Si

No.	layer	GDS	EPMA	GDS	EPMA	(g/m²)

Example 31	S	4.5	5	300	300	0.1
Example 32		4.6	5	300	300	0.1
Example 33		5.1	5	300	300	0.9
Example 34		5.1	5	300	300	0.9
Example 35		4.9	5	300	300	0.7
Example 36		5.3	5	300	300	0.7
Example 37	S	10.5	10	500	500	0.12
Example 38		10.4	10	500	500	0.12
Example 39		10.2	10	500	500	0.1
Example 40		10.1	10	500	500	0.1
Example 41		9.8	10	500	500	0.9
Example 42		10.0	10	500	500	0.9
Example 43	S	3.1	3	400	400	0.08
Example 44		3.0	3	400	400	0.08
Example 45		3.0	3	400	400	0.07
Example 46		2.8	3	400	400	0.07
Example 47		3.5	3	400	400	0.06
Example 48		3.2	3	400	400	0.06
Example 49	S	15.1	15	100	100	0.03
Example 50		14.8	15	100	100	0.03
Example 51		15.0	15	100	100	0.03
Example 52		15.8	15	100	100	0.02
Example 53		15.3	15	100	100	0.02
Example 54		15.4	15	100	100	0.02
Example 55	S	20.0	20	600	600	0.2
Example 56		20.1	20	600	600	0.2
Example 57		20.1	20	600	600	0.18
Example 58		20.4	20	600	600	0.17
Example 59		20.4	20	600	600	0.15
Example 60		19.9	20	600	600	0.15
Comparative Example 37	None	—	—	—	—	0.001
Comparative Example 38		—	—	—	—	0.001
Comparative Example 39		—	—	—	—	0.001
Comparative Example 40		—	—	—	—	0.001
Comparative Example 41		—	—	—	—	0.001
Comparative Example 42		—	—	—	—	0.001
Comparative Example 43	S	(0.006)	(0.006)	8	8	0.006
Comparative Example 44		(0.005)	(0.005)	8	8	0.005
Comparative Example 45		(0.004)	(0.004)	8	8	0.004
Comparative Example 46		(0.004)	(0.004)	8	8	0.004
Comparative Example 47		(0.003)	(0.003)	8	8	0.003
Comparative Example 48		(0.003)	(0.003)	8	8	0.003
Comparative Example 49	S	(0.005)	(0.005)	7	7	0.005
Comparative Example 50		(0.005)	(0.005)	7	7	0.005
Comparative Example 51		(0.004)	(0.004)	7	7	0.004
Comparative Example 52		(0.004)	(0.004)	7	7	0.004
Comparative Example 53		(0.003)	(0.003)	7	7	0.003
Comparative Example 54		(0.003)	(0.003)	7	7	0.003
Comparative Example 55	S	(0.005)	(0.005)	5	5	0.005
Comparative Example 56		(0.004)	(0.004)	5	5	0.004
Comparative Example 57		(0.004)	(0.004)	5	5	0.004
Comparative Example 58		(0.003)	(0.003)	5	5	0.003
Comparative Example 59		(0.003)	(0.003)	5	5	0.003
Comparative Example 60		(0.003)	(0.003)	5	5	0.003
Comparative Example 61	None	—	—	—	—	0.03
Comparative Example 62		—	—	—	—	0.03
Comparative Example 63		—	—	—	—	0.02
Comparative Example 64		—	—	—	—	0.02
Comparative Example 65		—	—	—	—	0.03
Comparative Example 66		—	—	—	—	0.02
Comparative Example 67		—	—	—	—	0.02
Comparative Example 68		—	—	—	—	0.04

	TABLE 3-3


	Properties of plating layer

				Anti-
	Plating	Plating	Alloying	powdering	Sliding
No.	appearance	adhesion	rate	property	property

Example 31	◯	◯	◯	◯	◯
Example 32	◯	◯	◯	◯	◯
Example 33	◯	◯	◯	◯	◯
Example 34	◯	◯	◯	◯	◯
Example 35	◯	◯	◯	◯	◯
Example 36	◯	◯	◯	◯	◯
Example 37	◯	◯	◯	◯	◯
Example 38	◯	◯	◯	◯	◯
Example 39	◯	◯	◯	◯	◯
Example 40	◯	◯	◯	◯	◯
Example 41	◯	◯	◯	◯	◯
Example 42	◯	◯	◯	◯	◯
Example 43	◯	◯	◯	◯	◯
Example 44	◯	◯	◯	◯	◯
Example 45	◯	◯	◯	◯	◯
Example 46	◯	◯	◯	◯	◯
Example 47	◯	◯	◯	◯	◯
Example 48	◯	◯	◯	◯	◯
Example 49	◯	◯	◯	◯	◯
Example 50	◯	◯	◯	◯	◯
Example 51	◯	◯	◯	◯	◯
Example 52	◯	◯	◯	◯	◯
Example 53	◯	◯	◯	◯	◯
Example 54	◯	◯	◯	◯	◯
Example 55	◯	◯	◯	◯	◯
Example 56	◯	◯	◯	◯	◯
Example 57	◯	◯	◯	◯	◯
Example 58	◯	◯	◯	◯	◯
Example 59	◯	◯	◯	◯	◯
Example 60	◯	◯	◯	◯	◯
Comparative	X	X	X	X	X
Example 37
Comparative	X	X	X	X	X
Example 38
Comparative	X	X	X	X	X
Example 39
Comparative	X	X	X	X	X
Example 40
Comparative	X	X	X	X	X
Example 41
Comparative	X	X	X	X	X
Example 42
Comparative	X	X	X	X	X
Example 43
Comparative	X	X	X	X	X
Example 44
Comparative	X	X	X	X	X
Example 45
Comparative	X	X	X	X	X
Example 46
Comparative	X	X	X	X	X
Example 47
Comparative	X	X	X	X	X
Example 48
Comparative	X	X	X	X	X
Example 49
Comparative	X	X	X	X	X
Example 50
Comparative	X	X	X	X	X
Example 51
Comparative	X	X	X	X	X
Example 52
Comparative	X	X	X	X	X
Example 53
Comparative	X	X	X	X	X
Example 54
Comparative	X	X	X	X	X
Example 55
Comparative	X	X	X	X	X
Example 56
Comparative	X	X	X	X	X
Example 57
Comparative	X	X	X	X	X
Example 58
Comparative	X	X	X	X	X
Example 59
Comparative	X	X	X	X	X
Example 60
Comparative	◯	X	◯	◯	X
Example 61
Comparative	◯	X	◯	◯	X
Example 62
Comparative	◯	X	◯	◯	X
Example 63
Comparative	◯	X	◯	◯	X
Example 64
Comparative	◯	X	◯	◯	X
Example 65
Comparative	◯	X	◯	◯	X
Example 66
Comparative	◯	X	◯	◯	X
Example 67
Comparative	◯	X	◯	◯	X
Example 68

	TABLE 4-1


	Adhered substance	Oxidation treatment

				Quantity of			Quantity of
				specified		Ultimate	oxygen in	Hematite
	Steel		Concentration	element	Applied/	temperature	oxide film	content
No.	type	Kind	(g/l)	(mg/m²)	Not applied	(° C.)	(g/m²)	(%)

Example 61	K	Ammonium	150	90	Applied	650	0.82	10
Example 62	L	sulfate					0.8	10
Example 63	M						0.8	15
Example 64	N						0.8	10
Example 65	O						0.77	15
Example 66	P						0.77	20
Example 67	Q						0.85	25
Example 68	R						0.82	20
Example 69	S						0.82	10
Example 70	T						0.82	15
Example 71	U						0.77	20
Example 72	V						0.79	15
Example 73	W						0.79	20
Example 74	X						0.8	20

	TABLE 4-2


	Properties of segregated layer

No.	layer	GDS	EPMA	GDS	EPMA	(g/m²)

Example 61	S	3	—	300	—	0.15
Example 62		3	—	300	—	0.15
Example 63		3	—	300	—	0.16
Example 64		3	—	300	—	0.15
Example 65		3	—	300	—	0.12
Example 66		3	—	300	—	0.1
Example 67		3	—	300	—	0.18
Example 68		3	—	300	—	0.15
Example 69		3	—	300	—	0.15
Example 70		3	—	300	—	0.15
Example 71		3	—	300	—	0.14
Example 72		3	—	300	—	0.15
Example 73		3	—	300	—	0.15
Example 74		3	—	300	—	0.15

	TABLE 4-3


	Plating quality

				Anti-
	Plating	Plating	Alloying	powdering	Sliding
No.	appearance	adhesion	rate	property	property

Example 61	◯	◯	◯	◯	◯
Example 62	◯	◯	◯	◯	◯
Example 63	◯	◯	◯	◯	◯
Example 64	◯	◯	◯	◯	◯
Example 65	◯	◯	◯	◯	◯
Example 66	◯	◯	◯	◯	◯
Example 67	◯	◯	◯	◯	◯
Example 68	◯	◯	◯	◯	◯
Example 69	◯	◯	◯	◯	◯
Example 70	◯	◯	◯	◯	◯
Example 71	◯	◯	◯	◯	◯
Example 72	◯	◯	◯	◯	◯
Example 73	◯	◯	◯	◯	◯
Example 74	◯	◯	◯	◯	◯

	TABLE 5-1


	Adhered substance	Oxidation treatment

				Quantity of			Quantity of
				speficied		Ultimate	oxygen in	Hematite
	Steel		Concentration	element	Applied/	temperature	oxide film	content
No.	type	Kind	(g/l)	(mg/m²)	Not applied	(° C.)	(g/m²)	(%)

Example 75	A	Potassium	50	100	Applied	600	0.41	0
Example 76	B	chloride					0.43	0
Example 77	C						0.39	0
Example 78	D						0.35	0
Example 79	G						0.42	0
Example 80	H						0.41	0
Example 81	B	Ammonium	100	800	Applied	550	0.39	20
Example 82	C	oxalate					0.35	25
Example 83	G						0.32	40
Example 84	H						0.36	60
Example 85	I						0.31	20
Example 86	J						0.32	55
Example 87	A	Sulfuric	50	80	Applied	550	0.42	0
Example 88	B	acid					0.43	0
Example 89	C						0.44	0
Example 90	E						0.42	0
Example 91	F						0.45	0
Example 92	H						0.41	0
Example 93	A	Sodium	30	1	Applied	600	0.51	10
Example 94	B	hydroxide					0.52	10
Example 95	C						0.53	15
Example 96	D						0.5	20
Example 97	G						0.49	30
Example 98	H						0.56	45
Example 99	A	Sodium	3	0.5	Applied	650	0.59	0
Example 100	B	tetraborate					0.58	0
Example 101	C						0.6	5
Example 102	E						0.57	5
Example 103	F						0.55	10
Example 104	H						0.6	20
Comparative Example 69	B	none	None	None	Applied	650	0.32	75
Comparative Example 70	C						0.29	75
Comparative Example 71	G						0.15	90
Comparative Example 72	H						0.12	95
Comparative Example 73	I						0.35	75
Comparative Example 74	J						0.15	95
Comparative Example 75	A	Sulfuric	50	80	Not	—	—	—
Comparative Example 76	B	acid			applied		—	—
Comparative Example 77	C						—	—
Comparative Example 78	E						—	—
Comparative Example 79	F						—	—
Comparative Example 80	H						—	—
Comparative Example 81	A	Ammonium	100	800	Applied	450	0.04	80
Comparative Example 82	B	oxalate					0.04	85
Comparative Example 83	C						0.03	85
Comparative Example 84	D						0.03	90
Comparative Example 85	G						0.02	90
Comparative Example 86	H						0.005	95

	TABLE 5-2


	Properties of segregated layer

Segregated
component	Thickness of segregated	Degree of	Quantity of oxide
below plating	component (μm)	segregtion (%)	containing Si

No.	layer	GDS	EPMA	GDS	EPMA	(g/m²)

Example 75	Cl, K	Cl: 3, K: 3	—	Cl: 300, K: 300	—	0.15
Example 76		Cl: 3, K: 3	—	Cl: 300, K: 300	—	0.14
Example 77		Cl: 3, K: 3	—	Cl: 300, K: 300	—	0.16
Example 78		Cl: 3, K: 3	—	Cl: 300, K: 300	—	0.14
Example 79		Cl: 3, K: 3	—	Cl: 300, K: 300	—	0.13
Example 80		Cl: 3, K: 3	—	Cl: 300, K: 300	—	0.13
Example 81	C, N	C: 30, N: 30	—	C: 500, N: 500	—	0.06
Example 82		C: 30, N: 30	—	C: 300, N: 300	—	0.06
Example 83		C: 30, N: 30	—	C: 300, N: 300	—	0.05
Example 84		C: 30, N: 30	—	C: 300, N: 300	—	0.07
Example 85		C: 30, N: 30	—	C: 300, N: 300	—	0.06
Example 86		C: 30, N: 30	—	C: 300, N: 300	—	0.06
Example 87	S	3	—	300	—	0.04
Example 88		3	—	300	—	0.05
Example 89		3	—	300	—	0.06
Example 90		3	—	300	—	0.04
Example 91		3	—	300	—	0.04
Example 92		3	—	300	—	0.05
Example 93	Na	2	—	100	—	0.17
Example 94		2	—	100	—	0.15
Example 95		2	—	100	—	0.16
Example 96		2	—	100	—	0.14
Example 97		2	—	100	—	0.13
Example 98		2	—	100	—	0.15
Example 99	Na, B	Na: 2, B: 2	—	Na: 100, B: 100	—	0.14
Example 100		Na: 2, B: 2	—	Na: 100, B: 100	—	0.15
Example 101		Na: 2, B: 2	—	Na: 100, B: 100	—	0.14
Example 102		Na: 2, B: 2	—	Na: 100, B: 100	—	0.16
Example 103		Na: 2, B: 2	—	Na: 100, B: 100	—	0.16
Example 104		Na: 2, B: 2	—	Na: 100, B: 100	—	0.13
Comparative Example 69	None	—	—	—	—	0.001
Comparative Example 70		—	—	—	—	0.001
Comparative Example 71		—	—	—	—	0.001
Comparative Example 72		—	—	—	—	0.001
Comparative Example 73		—	—	—	—	0.001
Comparative Example 74		—	—	—	—	0.001
Comparative Example 75	S	(0.001)	—	6	—	0.002
Comparative Example 76		(0.001)	—	6	—	0.003
Comparative Example 77		(0.001)	—	6	—	0.002
Comparative Example 78		(0.001)	—	6	—	0.002
Comparative Example 79		(0.001)	—	6	—	0.002
Comparative Example 80		(0.001)	—	6	—	0.002
Comparative Example 81	C, N	(0.004)	—	C: 6, N: 6	—	0.002
Comparative Example 82		(0.004)	—	C: 6, N: 6	—	0.002
Comparative Example 83		(0.004)	—	C: 6, N: 6	—	0.003
Comparative Example 84		(0.004)	—	C: 6, N: 6	—	0.002
Comparative Example 85		(0.004)	—	C: 6, N: 6	—	0.003
Comparative Example 86		(0.004)	—	C: 6, N: 6	—	0.002

	TABLE 5-3


	Plating quality

				Anti-
	Plating	Plating	Alloying	powdering	Sliding
No.	appearance	adhesion	rate	property	property

Example 75	◯	◯	◯	◯	◯
Example 76	◯	◯	◯	◯	◯
Example 77	◯	◯	◯	◯	◯
Example 78	◯	◯	◯	◯	◯
Example 79	◯	◯	◯	◯	◯
Example 80	◯	◯	◯	◯	◯
Example 81	◯	◯	◯	◯	◯
Example 82	◯	◯	◯	◯	◯
Example 83	◯	◯	◯	◯	◯
Example 84	◯	◯	◯	◯	◯
Example 85	◯	◯	◯	◯	◯
Example 86	◯	◯	◯	◯	◯
Example 87	◯	◯	◯	◯	◯
Example 88	◯	◯	◯	◯	◯
Example 89	◯	◯	◯	◯	◯
Example 90	◯	◯	◯	◯	◯
Example 91	◯	◯	◯	◯	◯
Example 92	◯	◯	◯	◯	◯
Example 93	◯	◯	◯	◯	◯
Example 94	◯	◯	◯	◯	◯
Example 95	◯	◯	◯	◯	◯
Example 96	◯	◯	◯	◯	◯
Example 97	◯	◯	◯	◯	◯
Example 98	◯	◯	◯	◯	◯
Example 99	◯	◯	◯	◯	◯
Example 100	◯	◯	◯	◯	◯
Example 101	◯	◯	◯	◯	◯
Example 102	◯	◯	◯	◯	◯
Example 103	◯	◯	◯	◯	◯
Example 104	◯	◯	◯	◯	◯
Comparative	Δ	X	X	X	X
Example 69
Comparative	Δ	X	X	X	X
Example 70
Comparative	X	X	X	X	X
Example 71
Comparative	X	X	X	X	X
Example 72
Comparative	X	X	X	X	X
Example 73
Comparative	X	X	X	X	X
Example 74
Comparative	X	X	X	X	X
Example 75
Comparative	X	X	X	X	X
Example 76
Comparative	X	X	X	X	X
Example 77
Comparative	X	X	X	X	X
Example 78
Comparative	X	X	X	X	X
Example 79
Comparative	X	X	X	X	X
Example 80
Comparative	X	X	X	X	X
Example 81
Comparative	X	X	X	X	X
Example 82
Comparative	X	X	X	X	X
Example 83
Comparative	X	X	X	X	X
Example 84
Comparative	X	X	X	X	X
Example 85
Comparative	X	X	X	X	X
Example 86

	TABLE 6-1


	Adhered substance	Oxidation treatment

				Quantity of			Quantity of
				specified		Ultimate	oxygen in	Hematite
	Steel		Concentration	element	Applied/	temperarture	oxide film	content
NO.	type	Kind	(g/l)	(mg/m²)	Not applied	(° C.)	(g/m²)	(%)

Example 105	A	Antimony	20	10	Applied	550	0.35	0
Example 106	B	chloride					0.39	0
Example 107	C						0.4	0
Example 108	D						0.36	0
Example 109	G						0.37	10
Example 110	H						0.39	10
Example 111	B	Ammonium	30	50	Applied	600	0.54	0
Example 112	C	sulfate					0.52	0
Example 113	G						0.49	0
Example 114	H						0.53	0
Example 115	I						0.51	0
Example 116	J						0.5	0
Example 117	A	Lead	1	1	Applied	650	0.59	45
Example 118	B	chloride					0.6	45
Example 119	C						0.62	50
Example 120	E						0.59	60
Example 121	F						0.58	65
Example 122	H						0.59	65
Example 123	A	Thiourea	20	70	Applied	600	0.56	0
Example 124	B						0.58	0
Example 125	C						0.55	0
Example 126	D						0.54	0
Example 127	G						0.58	0
Example 128	H						0.56	0
Example 129	A	Sodium	25	5	Applied	600	0.49	0
Example 130	B	chloride					0.52	0
Example 131	C						0.51	5
Example 132	E						0.49	5
Example 133	F						0.48	10
Example 134	H						0.51	20
Comparative Example 87	B	None	None	None	Applied	550	0.12	90
Comparative Example 88	C						0.03	90
Comparative Example 89	G						0.01	95
Comparative Example 90	H						0.005	95
Comparative Example 91	I						0.09	90
Comparative Example 92	J						0.01	95
Comparative Example 93	A	Sodium	25	5	Not	—	—	—
Comparative Example 94	B	chloride			applied		—	—
Comparative Example 95	C						—	—
Comparative Example 96	E						—	—
Comparative Example 97	F						—	—
Comparative Example 98	H						—	—
Comparative Example 99	A	Thiourea	20	70	Applied	450	0.05	75
Comparative Example 100	B						0.06	75
Comparative Example 101	C						0.05	80
Comparative Example 102	D						0.03	85
Comparative Example 103	G						0.02	95
Comparative Example 104	H						0.008	95

	TABLE 6-2


	Properties of segregated layer

Segregated
element	Thickness of segregated	Degree of	Quantity of oxide
below plating	component (μm)	segregation (%)	containing Si

NO.	layer	GDS	EPMA	GDS	EPMA	(g/m²)

Example 105	Cl	2	—	300	—	0.08
Example 106		2	—	300	—	0.05
Example 107		2	—	300	—	0.08
Example 108		2	—	300	—	0.07
Example 109		2	—	300	—	0.06
Example 110		2	—	300	—	0.05
Example 111	S	3	—	400	—	0.15
Example 112		3	—	400	—	0.14
Example 113		3	—	400	—	0.13
Example 114		3	—	400	—	0.14
Example 115		3	—	400	—	0.14
Example 116		3	—	400	—	0.15
Example 117	Cl	2	—	300	—	0.13
Example 118		2	—	300	—	0.12
Example 119		3	—	300	—	0.14
Example 120		2	—	300	—	0.12
Example 121		2	—	300	—	0.12
Example 122		2	—	300	—	0.13
Example 123	S	5	—	600	—	0.14
Example 124		5	—	600	—	0.15
Example 125		5	—	600	—	0.14
Example 126		5	—	600	—	0.14
Example 127		5	—	600	—	0.16
Example 128		5	—	600	—	0.14
Example 129	Na, Cl	Na: 2, Cl: 2	—	Na: 300, Cl: 300	—	0.14
Example 130		Na: 2, Cl: 2	—	Na: 300, Cl: 300	—	0.14
Example 131		Na: 2, Cl: 2	—	Na: 300, Cl: 300	—	0.14
Example 132		Na: 2, Cl: 2	—	Na: 300, Cl: 300	—	0.15
Example 133		Na: 2, Cl: 2	—	Na: 300, Cl: 300	—	0.15
Example 134		Na: 2, Cl: 2	—	Na: 300, Cl: 300	—	0.14
Comparative Example 87	—	—	—	—	—	0.002
Comparative Example 88		—	—	—	—	0.002
Comparative Example 89		—	—	—	—	0.003
Comparative Example 90		—	—	—	—	0.002
Comparative Example 91		—	—	—	—	0.002
Comparative Example 92		—	—	—	—	0.002
Comparative Example 93	Na, Cl	(Cl: 0.004, Na: 0.003)	—	Cl: 5, Na: 5	—	0.002
Comparative Example 94		(Cl: 0.004, Na: 0.003)	—	Cl: 5, Na: 5	—	0.001
Comparative Example 95		(Cl: 0.004, Na: 0.003)	—	Cl: 5, Na: 5	—	0.001
Comparative Example 96		(Cl: 0.004, Na: 0.003)	—	Cl: 5, Na: 5	—	0.002
Comparative Example 97		(Cl: 0.004, Na: 0.003)	—	Cl: 5, Na: 5	—	0.002
Comparative Example 98		(Cl: 0.004, Na: 0.003)	—	Cl: 5, Na: 5	—	0.003
Comparative Example 99	S	0.004	—	5	—	0.002
Comparative Example 100		0.004	—	5	—	0.003
Comparative Example 101		0.004	—	5	—	0.003
Comparative Example 102		0.004	—	5	—	0.002
Comparative Example 103		0.004	—	5	—	0.002
Comparative Example 104		0.004	—	5	—	0.003

	TABLE 6-3


	Plating quality

				Anti-
	Plating	Plating	Alloying	powdering	Sliding
NO.	appearance	adhesion	rate	property	property

Example 105	◯	◯	◯	◯	◯
Example 106	◯	◯	◯	◯	◯
Example 107	◯	◯	◯	◯	◯
Example 108	◯	◯	◯	◯	◯
Example 109	◯	◯	◯	◯	◯
Example 110	◯	◯	◯	◯	◯
Example 111	◯	◯	◯	◯	◯
Example 112	◯	◯	◯	◯	◯
Example 113	◯	◯	◯	◯	◯
Example 114	◯	◯	◯	◯	◯
Example 115	◯	◯	◯	◯	◯
Example 116	◯	◯	◯	◯	◯
Example 117	◯	◯	◯	◯	◯
Example 118	◯	◯	◯	◯	◯
Example 119	◯	◯	◯	◯	◯
Example 120	◯	◯	◯	◯	◯
Example 121	◯	◯	◯	◯	◯
Example 122	◯	◯	◯	◯	◯
Example 123	◯	◯	◯	◯	◯
Example 124	◯	◯	◯	◯	◯
Example 125	◯	◯	◯	◯	◯
Example 126	◯	◯	◯	◯	◯
Example 127	◯	◯	◯	◯	◯
Example 128	◯	◯	◯	◯	◯
Example 129	◯	◯	◯	◯	◯
Example 130	◯	◯	◯	◯	◯
Example 131	◯	◯	◯	◯	◯
Example 132	◯	◯	◯	◯	◯
Example 133	◯	◯	◯	◯	◯
Example 134	◯	◯	◯	◯	◯
Comparative	X	X	X	X	X
Example 87
Comparative	X	X	X	X	X
Example 88
Comparative	X	X	X	X	X
Example 89
Comparative	X	X	X	X	X
Example 90
Comparative	X	X	X	X	X
Example 91
Comparative	X	X	X	X	X
Example 92
Comparative	X	X	X	X	X
Example 93
Comparative	X	X	X	X	X
Example 94
Comparative	X	X	X	X	X
Example 95
Comparative	X	X	X	X	X
Example 96
Comparative	X	X	X	X	X
Example 97
Comparative	X	X	X	X	X
Example 98
Comparative	X	X	X	X	X
Example 99
Comparative	X	X	X	X	x
Example 100
Comparative	X	X	X	X	X
Example 101
Comparative	X	X	X	X	X
Example 102
Comparative	X	X	X	X	X
Example 103
Comparative	X	X	X	X	X
Example 104

	TABLE 7


	Adhered substance		Properties of segregated layer

Quantity of

Oxidation treatment

Segregated

Thickness of

			specified		Ultimate	component	segregated
	Steel	Concentration	element	Applied/	temperature	below plating	component (μm)

No.	type	Kind	(g/l)	(mg/m²)	Not applied	(° C.)	layer	GDS	EPMA

Example 135	G	Sulfuric	50	70	Applied	600	S	5	5
Example 136	E	acid		80		550	S	5	5
Example 137	G			30		600	S	3	3
Example 138	E			30		550	S	3	3
Example 139	G	Ammonium	30	100	Applied	650	S	10	10
Example 140	E	sulfate		80		550	S	6	6
Example 141	G			30		600	S	3	3
Example 142	E			30		550	S	3	3
Example 143	G	Thiourea	20	70	Applied	700	S	2	2
Example 144	E			70		700	S	3	3
Example 145	G			20		700	S	1	1
Example 146	E			20		700	S	1	1

Properties of segregated layer

Plating quality

	Quantity of oxide		Quantity			Anti-
	contining Si		(Number/	Plating	Plating	powdering	Sliding
No.	(g/m²)	Product	20 μm)	appearance	adhesion	property	property

Example 135	0.7	Granular	8.8	◯	◯	⊚	◯
Example 136	0.8	MnS	10.6	◯	◯	⊚	◯
Example 137	0.5		2.4	◯	◯	◯	◯
Example 138	0.4		3	◯	◯	◯	◯
Example 139	0.1	Granular	6.2	◯	◯	⊚	◯
Example 140	0.1	MnS	8	◯	◯	⊚	◯
Example 141	0.06		2.2	◯	◯	◯	◯
Example 142	0.04		2.8	◯	◯	◯	◯
Example 143	0.09	Granular	6.6	◯	◯	⊚	◯
Example 144	0.07	MnS	8.4	◯	◯	⊚	◯
Example 145	0.03		0.2	◯	◯	◯	◯
Example 146	0.02		1.2	◯	◯	◯	◯

INDUSTRIAL APPLICABILITY

The present invention provides a hot-dip galvanized steel sheet showing excellent plating adhesion and sliding property even with a substrate steel sheet containing a large quantity of Si. Furthermore, an alloyed hot-dip galvanized steel sheet obtained by alloying the hot-dip galvanized steel sheet shows also excellent anti-powdering property. Both the galvanized steel sheets are manufactured at high productivity.

Claims

1. A hot-dip galvanized steel sheet comprising: a steel sheet containing 0.1 to 3.0% Si by mass; a hot-dip galvanizing layer; a segregated layer, being placed between the steel sheet and the hot-dip galvanizing layer, having a thickness in a range from 0.01 to 100 μm; containing an oxide containing Si, and being composed of at least one component selected from the group consisting of S, C, Cl, Na, K, B, P, F, and N.

2. The hot-dip galvanized steel sheet according to claim 1, wherein the concentration of the component in the segregated layer is higher than the concentration of the component in the steel sheet by 10% or more.

3. The hot-dip galvanized steel sheet according to claim 1, wherein the quantity of the oxide containing the Si in the segregated layer is in a range from 0.01 to 1 g/m²as oxygen.

4. The hot-dip galvanized steel sheet according to claim 1, further comprising an Fe layer below the hot-dip galvanizing layer.

5. The hot-dip galvanized steel sheet according to claim 1, wherein the segregated layer is formed by a dispersed compound of the component and a component of the steel sheet.

6. The hot-dip galvanized steel sheet according to claim 5, wherein the component is S, the quantity of MnS in a particle shape having 50 nm or larger particle size as the compound is five or more particles per 20 μm of length on an arbitrary cross section in parallel with the interface between the hot-dip galvanizing layer and the steel sheet.

7. The hot-dip galvanized steel sheet according to claim 1, wherein the hot-dip galvanizing layer is an alloyed hot-dip galvanizing layer.

8. A method for manufacturing hot-dip galvanized steel sheet comprising the steps of: adhering at least one substance selected from the group consisting of S, C, Cl, Na, K, B, P, F, N, and a compound thereof onto a surface of a steel sheet containing 0.1 to 3% Si by mass; heating the steel sheet after adhering the substance thereon to form an oxide film containing 70% by mass or less of hematite on the surface of the steel sheet; reducing the oxide film; and hot-dip galvanizing the reduced steel sheet.

9. The method for manufacturing hot-dip galvanized steel sheet according to claim 8, wherein the step of heating is conducted in an oxidizing atmosphere for Fe at above 500° C. of the ultimate temperature of the steel sheet.

10. The method for manufacturing hot-dip galvanized steel sheet according to claim 8, further comprising the step of alloying after the step of hot-dip galvanizing.

11. A method for manufacturing hot-dip galvanized steel sheet comprising the steps of: preparing a steel sheet containing 0.1 to 3% Si by mass as the base material; forming an oxide film containing 70% by mass or less of hematite on a surface of the base steel sheet before applying hot-dip galvanizing on the surface of the steel sheet; applying reducing treatment to the steel sheet; and applying hot-dip galvanizing thereto.

12. The method for manufacturing hot-dip galvanized steel sheet according to claim 9, further comprising the step of alloying after the step of hot-dip galvanizing.

13. The hot-dip galvanized steel sheet according to claim 2, wherein the hot-dip galvanizing layer is an alloyed hot-dip galvanizing layer.

14. The hot-dip galvanized steel sheet according to claim 3, wherein the hot-dip galvanizing layer is an alloyed hot-dip galvanizing layer.

15. The hot-dip galvanized steel sheet according to claim 4, wherein the hot-dip galvanizing layer is an alloyed hot-dip galvanizing layer.

16. The hot-dip galvanized steel sheet according to claim 5, wherein the hot-dip galvanizing layer is an alloyed hot-dip galvanizing layer.

17. The hot-dip galvanized steel sheet according to claim 6, wherein the hot-dip galvanizing layer is an alloyed hot-dip galvanizing layer.