JPH0324255A - Hot-dip galvanized hot rolled steel plate and its production - Google Patents

Abstract

PURPOSE:To produce a high-quality hot-dip galvanized hot rolled steel plate free from deterioration in strength by forming a specific coating weight of Ni or Ni-base alloy plating on the surface of a pickled and descaled hot rolled steel plate, applying specific heat treatment to the above steel plate, and then carrying out hot-dip galvanizing. CONSTITUTION:A hot rolled steel plate is pickled and descaled and then subjected, if necessary, to grinding by 0.3-5mum. Subsequently, Ni plating or plating with Ni-base alloy containing at least one or more elements among Fe, Cr, Co, Mo, Ti, Zr, V, W, B, and P by 0.1-20wt.% is applied to the surface of the steel plate by 0.1-10g/m<2> coating weight. The above steel plate is heated in an H2-gas atmosphere of <=15% H2 gas concentration and <=-5 deg.C dew point at 450-600 deg.C maximum ultimate plate temp. Then, the steel plate is subjected to hot-dip galvanizing, and, if necessary, heating is further applied to the above steel plate in the air at 400-600 deg.C plate temp. for <=10sec heat-retaining time while the resulting galvanized film is in a molten state. By this method, the hot-dip galvanized hot rolled steel plate having uniform external appearance as well as stable grade can be obtained by means of low-temp. heating causing no deterioration in the strength of the steel plate without causing the occurrence of uncoating.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a descaled hot-rolled steel sheet, a hot-dip galvanized steel sheet, and a method for manufacturing the same by low-temperature heating. For high-tensile hot-rolled steel sheets, including steel sheets, which inevitably have different surface cleanliness depending on their breaking system,
The uniformity and adhesion of the galvanized appearance similar to ordinary steel can be achieved without unnecessarily changing the hot-dip galvanizing conditions, and the performance that hot-dip galvanized steel sheets should have can be efficiently obtained. (Prior art) Conventionally, in order to extend the lifespan or improve the design of bare steel materials, which are often used as structural members in building materials, etc., consumers have required some kind of post-treatment such as plating or painting after a certain forming process. However, there is a strong demand for surface treatment of supplied steel materials due to lower cost of steel materials due to labor saving in the process. Among these, recently there has been an increasing demand for surface treatment of thick high tensile strength hot rolled steel sheets, particularly those having a thickness of 2 to 6 m.

As a surface treatment method whose main purpose is to improve the rust prevention properties of high-strength hot-rolled steel sheets, there is the Zenzima hot-dip galvanizing method, which can easily increase the thickness from the viewpoint of productivity. (Problem to be solved by the invention) However, in this case, from the viewpoint of the material strength of the steel sheet, the maximum heating plate temperature before hot-dip galvanizing is preheated to a temperature that is slightly higher than the hot-dip galvanizing bath temperature. 600, which is one of the features of the Zenjima complete line.
The cleaning effect (sponge effect) on the steel surface due to non-oxidizing heating at high temperatures above ℃ cannot be expected, and on the contrary, it has the disadvantage that non-plating is likely to occur due to insufficient reduction in the low-temperature heating reduction process. A conventional technique that improves this problem is to apply hot-dip galvanization to a cold-rolled high-strength steel plate with a uniform appearance using conventional heating methods.
Special Publication No. 60-5641 characterized by e-plating
8 and Japanese Patent Publication No. 62-56949, which similarly features Zn pre-plating, have been proposed. However, in the former case, stable Fe plating is difficult due to Fe'+ generation due to electrolytic oxidation in the Fe pre-plating technology itself, and in the latter case, it is difficult to select Zn from the pre-plating layer during heating after pre-plating. Fe is vaporized, severely contaminated by the reducing gas and the atmosphere in the furnace, and is brittle to process.
- Due to the growth of the Zn binary alloy layer, there is a problem with operational stability under high productivity lines, and further issues remain in ensuring the appearance or adhesion of hot-dip galvanizing on an industrial level. ．． Therefore, the present invention has been developed to apply surface grinding and pre-plating system, which is different from conventional pre-plating such as Fe or Zn, to high-productivity lines, so that it can be heated at a low temperature within a range that does not impair the strength of the steel sheet. The purpose of this method is to obtain hot-dip galvanized steel sheets with stable quality and uniform appearance without the occurrence of uncoated surfaces. (Means for Solving the Problems) The hot-dip galvanized hot-rolled steel sheet of the present invention has Ni plating or Fe, Cr, Co, M
A Ni-based alloy plating layer containing 0.1 to 20 i+t% of at least one of o, Ti, Zr, V, W, B, and P is formed at 0.1 to 10 g/rrr2, and the upper layer is hot-dip galvanized. It is formed by forming layers.

The Si content of the steel plate to be plated is 0.5 to 1. Owt% hot rolled steel plate is used.

Also, a high tensile strength hot rolled steel plate is used as the steel plate to be plated.

AM content in the hot-dip galvanized layer is 0.2 to 10 wt%
．． and (as the third alloying element) at least one of Mg, Si, and Sb in an amount of 0.05 to 1. Contains Ovt%,
An alloy is used in which the total amount of Pb, Cd, Sn, etc. mixed as unavoidable impurities is less than 0.02 wt%, and the balance is Zn. In the manufacturing method of the present invention, the pickled and descaled hot-rolled S plate is ground by 0.3 to 5 μm as necessary, and N is added to the surface of the steel plate.
i plating or Fs, Cr, Co, Mo, Ti, Z
at least one of r, V, W, B, and P from 0.1 to 2
Ni-based alloy plating containing 0vt% was o. i~10g
/After forming the plate, the maximum plate temperature reached 450℃ in a N2 gas atmosphere with an H2 gas concentration of 15% or less and a dew point of -5℃ or less.
Heat in the range of ~600℃ and hot-dip galvanize. In addition, in the method of the present invention, a pickled and descaled hot rolled steel plate is subjected to heavy grinding of 0.3 to 5μ as necessary, and the surface of the steel plate is coated with Ni plating or Fe, Cr, Co, Mo, Ti, Zr,
0.1 to 20w of at least one of V, W, B, and P
0.1 to 10 g/r of N1-based alloy plating containing t%
After forming rr2, the highest plate temperature reached 450℃ in a N2 gas atmosphere with a H2 gas concentration of 15% or less and a dew point of -5℃ or less.
Hot-dip galvanizing is performed by heating in the range of ~600℃, and while the galvanized layer is in a molten state, the plate temperature is increased to 4℃ in the atmosphere.
Heat at 00 to 600℃ for 10 seconds or less. (Function) The gist of the structure of the present invention is that when applying uniform hot-dip galvanizing to the surface of a high-strength hot-rolled steel sheet without causing any uncoated appearance, a specified pretreatment is performed after descaling pickling. Or, after that, if necessary, a specific amount of surface grinding is performed, and then a specific pre-plating is applied, and the subsequent low-temperature heating conditions are specified,
Its structure is as follows. In the above structure of the present invention, the appropriate range and action and effect of the structural factors will be described below.

Regarding the amount of steel plate surface grinding before the pre-plating, the technical gist of the surface grinding in the present invention is to perform it as necessary as a pre-treatment for the pre-plating, and in order to strengthen the material strength of the steel plate, Si It simultaneously removes the surface concentration of additive elements in steel such as The purpose of this is to improve the uniformity of the appearance of hot-dip galvanizing and the adhesion of the plating.

In addition, this surface grinding method may originally be either mechanical or chemical, but from the viewpoint of productivity,
Mechanical methods such as a rebrush roll with discharged particles are preferable. The surface grinding effect is proportional to the amount of grinding, but 0.
At less than 3μ, the above-mentioned grinding effect is small, and at more than 5μ, the effect is saturated and is not economical. Therefore, it is preferably 0.5 to 3μ. Regarding the pre-plating system used in the present invention, the pre-plating system is characterized by concentration segregation of elements in the steel due to heating and their oxides 2 due to trace amounts of oxygen in the heating atmosphere, especially on the surface of high-strength hot-rolled steel sheets with increased Si and Mn levels. The main purpose of this process is to increase the surface tension of the steel sheet, prevent a significant drop in wettability for molten zinc, and improve the uniform finish of the hot-dip coating appearance by preventing the occurrence of unplated areas. It is based on the knowledge that it can be expected to have multiple effects such as improving the corrosion resistance and paintability of galvanized steel sheets, and its application is based on the following reasons.

Ni plating or Fe, Co, Cr, Ti, Zr+ v,
When Ni-based alloy plating containing at least one of the alloying elements Mo, W, P, and H is applied to the steel sheet, the content is O wt'1. Although the wettability with the hot-dip galvanizing bath has been greatly improved and it is possible to obtain a uniform hot-dip galvanized appearance, it is difficult to improve the corrosion resistance of the hot-dip galvanized steel sheet. N1
It is preferable to plate the plating layer with a Ni-based alloy. The higher the eutectoid ratio of the alloying element in the Ni plating layer, the higher the corrosion resistance. However, if the eutectoid ratio exceeds 20 wt%, N
Because the I-based alloy plating layer itself becomes hard and hair cracks occur due to internal stress, the Fe-Znz original alloy layer is caused by partial iron diffusion from the #I plate base, which occurs through the cracks at the interface with the hot-dip galvanized layer. The non-uniformity of galvanizing may lead to non-uniform appearance of hot-dip galvanizing, or may lead to cohesive failure of the pre-plated layer during severe press working, etc., which is not very preferable. For the above reasons, the content of the alloying element in the Ni-based pre-plating layer is preferably 0.5 to 10 wt%.

In addition, if the amount of the Ni-based alloy pre-plated layer with the above alloy ratio is less than 0.1 g/bo, the coating rate on the steel sheet surface will decrease, and the pinhole area and the pre-plated area will be difficult to coat during heating. Possibly due to a difference in the amount of oxides in the Fe
- Non-uniform formation of the Zn binary alloy layer, etc., impedes the uniformity of the plating appearance and goes beyond the spirit of the present invention, so this is not very preferable.

On the other hand, if the adhesion amount of the pre-plating layer exceeds 10 g/n, it is not economical to improve the plating quality of the hot-dipped steel sheet because it is saturated and the cost of pre-plating including equipment increases. Not.

From the above, the deposited amount of the Ni-based alloy pre-plating layer is preferably 0.5 to 5 g/m2.

The Ni-based alloy pre-plating layer of the present invention may be obtained by any of the known techniques such as electroplating, chemical plating, vapor deposition plating, vapor phase plating, and molten salt electrolysis. Preferably, electroplating or vapor deposition plating is used.

Regarding the heating conditions for the steel sheet before hot-dip galvanizing in the present invention, heating the steel sheet means heating the steel sheet to an extent that does not reduce the material strength of the steel sheet, suppresses surface oxidation, and does not interfere with the interfacial reaction with the hot-dip galvanizing bath. refers to the heating conditions. Therefore, in the present invention, it is necessary to control the plate temperature and heating atmosphere. If the plate temperature is less than 450°C, maintenance costs for the hot-dip galvanizing bath temperature will rise due to the lower plate temperature, it will be difficult to control the bath temperature during line acceleration/deceleration, and the operational stability of the line will be affected mainly by controlling the coating amount. It lacks reality and lacks reality. On the other hand, at temperatures exceeding 600°C, Fe spreads excessively from the steel sheet, and there is uneven formation of an overalloyed layer that is brittle to process, especially in the pinhole part of the pre-plated layer and its surroundings, resulting in poor adhesion of the hot-dip plated layer. This is not very desirable as it may lead to defects or a decrease in the initial material strength of the steel plate. Therefore, the preferred low temperature heating plate temperature in the present invention is 450
~550°C is preferable. Furthermore, as for the heating atmosphere, it is necessary to control the H2 gas concentration and dew point in the N2 gas atmosphere. The role of H2 gas in the present invention is to burn and remove adsorbed oxygen that is inevitably brought into the heating furnace from the steel plate under high productivity lines, and to prevent excessive oxidation contamination on the surface of the steel plate. Therefore, although dew point control is necessary, it is not advisable to maintain an excessive H2 gas concentration.

In this sense, it is sufficient for the H2 gas concentration in the N2 gas to be 15% or less in the low-temperature heating atmosphere of the present invention, and anything more than this will increase the processing cost and is not very economical. In particular, by applying the pre-plating, the critical activity of the steel sheet interface is expanded to the low H2 gas concentration side, and depending on the dew point, hot-dip galvanizing can be performed satisfactorily even with 0% H2 gas.

On the other hand, as mentioned above, the adsorbed oxygen generates moisture through a combustion reaction with H2, leading to an increase in the dew point in the furnace.It is necessary to prevent this from deteriorating the plating quality or equipment maintenance, and dew point control is necessary. becomes. In this sense, the dew point in the present invention is -5°C or lower, preferably -10°C or lower.

Regarding the hot-dip galvanizing bath composition in the present invention, Zn-based or Zn-Al-based alloy plating can be applied to the hot-dip galvanizing bath, and it is necessary to control the bath components with the aim of improving the corrosion resistance of the hot-dip galvanized steel sheet.

ill is Fe-Al- generated at the interface of the hot-dip galvanized layer.
F, which is brittle to process due to the formation of barrier 2 of the Zna base alloy layer.
e- It suppresses the abnormal growth of the Zn binary alloy layer and improves the adhesion of the plating layer, and at the same time electrochemically prevents the excessive anodic reaction (elution reaction) of Zn by forming a eutectic alloy with Zn-A (2). It is used for the purpose of suppressing Al to an appropriate level and thereby achieving high corrosion resistance as a hot-dip galvanized steel sheet.If Al is less than 0.2vt%, the formation of a ternary alloy layer of Fe-Al-Zn is insufficient. Fe-Zn2 by
This causes abnormal elongation of the original alloy layer, resulting in a decrease in plating adhesion. On the other hand, if Al is less than 10wt%, there will be abnormal elution of Al from the pre-plating and plating layer mentioned above, and this eluted pre-plating component will react with Al, dispersing or floating as dross (intermetallic compound) in the hot-dip galvanizing bath. This re-adheres in the hot-dip plating layer or on its surface, improving the uniformity of the plating appearance and
This is not preferable because it causes a large number of roll-induced scratches and scratches, which greatly impairs the commercial value of the hot-dip galvanized steel sheet.

A preferable Al concentration is 0.3 to 7 wt%.

The unavoidable impurities referred to in the present invention are Pb, Cd, S
n, etc., which is present in the hot-dip galvanized layer and segregates at grain boundaries, etc., and must be removed from the plating bath as much as possible to prevent delamination of the plating layer from local corrosion with Zn.

If the total amount of unavoidable impurities such as PB exceeds 0.02 wt%, this is not preferable because it promotes intergranular corrosion as described above and greatly impairs commercial value. A preferable amount of unavoidable impurities is 0.01 wt% or less.

In the hot-dip galvanizing bath applied to the present invention, one or more of Mg, Si, and Sb is used as the third alloying element. The purpose of applying this third element is
It has high corrosion resistance as a hot-dip galvanized steel sheet and improves the uniformity of the plating appearance.

If one or more of the above third elements is less than 0.05wt″1,
High corrosion resistance cannot be expected. On the other hand, if it exceeds 1.0 tit%, the excessively dispersed aluminum in the hot-dip galvanizing bath will react with Al in the bath, float to the bath surface as dross, and re-adhere to the plating layer, resulting in poor appearance. Since the galvanized layer loses its uniformity or becomes a galvanized layer that is prone to brittle fracture, it is difficult to obtain sufficient workability, and both are undesirable because they greatly impair commercial value.

Therefore, the preferred amount of the third element added is 0.1 to 0.
．． 5t% is good.

Regarding the heating conditions for the steel sheet after hot-dip galvanizing applied to the present invention, the post-heat treatment is such that the pre-plating layer or
By reacting with a certain amount of each alloy in the hot-dip galvanized layer and modifying the entire hot-dip galvanized layer into an iron-based composite dispersion type plating layer, it is possible to improve the surface treatment properties for painting, or the adhesion and corrosion resistance of top coats. The aim is to The heating atmosphere is in the air, and the heating conditions are such that the maximum plate temperature is 4.
At temperatures below 50°C, the effect of modifying the hot-dip galvanized layer due to the diffusion of iron ions as described above cannot be expected;
If the temperature exceeds 0°C, it is difficult to dramatically improve topcoating properties and post-coating corrosion resistance due to excessive diffusion of iron ions.

Therefore, the preferred maximum plate temperature is 500°C to 550°C.
℃ is better. In addition, the retention time at the highest plate temperature is 2.
If it is less than 2 seconds, a uniform diffusion layer cannot be formed over the entire hot-dip plating layer due to insufficient diffusion of iron ions, which deviates from the spirit of the present invention. On the other hand, if the time exceeds 10 seconds, the plating adhesion tends to deteriorate due to abnormal development of a hard iron-based alloy layer that is brittle to process due to excessive diffusion of iron ions, which is not so preferable. From the above, the preferred holding time is 3 to 7 seconds.

The effects of the present invention as described above will be described in more detail based on the following embodiments.

(Example) A high-strength hot-rolled steel sheet made of a certain portion of the specified steel shown in Table 2 that has been descaled by hydrochloric acid pickling is first surface-treated with a Scotch Bright roll of a predetermined amount as specified in Table 1 in a Sendzimer continuous hot-dip galvanizing line. After being ground and washed with water, pre-plating as specified in Table 1 is applied by electroplating in a sulfate-based bath (however, vapor deposition plating is used for Ti-based baths), washed with water, and once drained and dried. Thereafter, it is immediately heat-treated in the heating atmosphere and heat cycle specified in Table 1, and hot-dip galvanized as it is without being exposed to the atmosphere.

Next, the steel plate hot-dipped in a certain type of plating bath specified in Table 1 is gas wiped in the atmosphere, and the amount of zinc deposited on one side is controlled to 100 to 120 g/rrF. After this, the manufacturing process is divided into two systems depending on the required plating surface functionality, and if the requirements are for normal hot-dip galvanized steel sheets, the products are simply water-cooled and dried. In addition, if there is a demand for even higher paintability or corrosion resistance after painting, the above-mentioned coating amount controlled hot-dip plating layer is heated again in an atmospheric heating furnace to achieve a molten or semi-molten state. After being heated under the specific heating conditions shown in Table 1, the product is cooled and dried with water. The plating performance of the embodiments of the present invention thus constructed is summarized in Table 1 based on comparative examples.

[1] Regarding the surface grinding effect, examples of the present invention are shown in Nα■ to Na 7 regarding the hot-dip galvanizing property when a certain amount of Ni pre-plating is applied while changing the amount of grinding. As is clear from this, the surface grinding effect before pre-plating improves according to the amount of grinding in high Si-added steel, which is said to be the most difficult to hot-dip galvanize, and is particularly effective in improving the appearance of hot-dip galvanizing. The amount of grinding is 0.3
It turns out that μ1 or more is sufficient.

[2] Regarding the pre-plating effect of Ni-based alloy plating, the pre-treatment effect of directly pre-plating by a known method without surface grinding after descaling pickling, and the relationship between the pre-plating alloy ratio and the present invention example Nos. 8 to Nα 15 and Comparative Example NQ16, and the appropriate adhesion amount ranges are shown in Invention Examples 12 and NG17 to Na23 and Comparative Example 24. In addition, regarding the combined effect of surface grinding and pre-plating and the effect of the alloy element system of Ni-based alloy plating, present invention example Na
2 5～? Shown in Jn45.

It can be seen that in each case, within the appropriate range indicated by the present invention, there is no difference in the degree of effect even if the steel type of the original plate is different, and the effect is effectively exhibited.

[3] Regarding the low-temperature heating conditions before hot-dip plating after pretreatment, as appropriate conditions in the heating atmosphere, regarding the appropriate hydrogen gas concentration in the N2 gas atmosphere, inventive examples Nα4 and Nα46
~Shame 48, and regarding the appropriate dew point, Nn46 and N
I149~Na51 and comparative example Ha52~Ha53
This is shown in comparison. Furthermore, regarding the appropriate range of the highest plate temperature during heating, the examples of the present invention are set as Nα54 to N57, and the comparative examples are set as Nα58 to NQ.
59.

As is clear from this, the heating atmosphere that maintains the active state of the steel plate surface is at least non-oxidizing to reducing, and an oxidizing atmosphere is not preferred. Furthermore, under this atmosphere, low-temperature heating is possible without impairing hot-dip galvanizing properties without reducing the strength of the material.

[4 Bath composition of hot-dip galvanizing] Hot-dip galvanizing is applied to the surface of the steel sheet that has undergone the pretreatment of the present invention as described above.In order to achieve high corrosion resistance as a hot-dip galvanized steel sheet, Among them, regarding the effect of Al, the inventive example Ha60-NQ65 and the comparative examples Nα66 to Nα
It is shown together with 67. Moreover, regarding the effect of adding Si, Mg and Sb, the present invention example was compared to NG68 to Na75 and N
α78 to Na8l are shown together with comparative examples 76 to 77.

As is clear from this, it can be seen that the alloying elements in the hot-dip galvanizing bath according to the present invention have sufficiently achieved high corrosion resistance of the specifically pretreated steel sheet as a hot-dip galvanized steel sheet.

[5] Regarding unavoidable impurities in the hot-dip galvanizing bath In the present invention, unavoidable impurities in the bath are those that form local batteries with bulk Zn in the hot-dip galvanized layer and suppress intergranular corrosion and corrosion resistance life. It is essential to some extent, and includes Pb, Cd, Sn, etc. Regarding this appropriate range, the present invention example is NQ46, and the comparative example is NG82~
It is shown in Nα83.

As is clear from this, it can be seen that the above-mentioned disadvantages can be overcome within the scope of the present invention.

[6] About heating conditions after hot-dip galvanizing Post-heating in the present invention aims to improve the properties of the plating layer by Fe diffusion from the steel plate interface, and improves the properties of the hot-dip galvanized steel sheet, especially its phosphatability and coating properties. The aim is to improve the properties of the present invention, etc., and the results are as follows:
4 to Nα87 and Nα90 to Nα93, and comparative examples are shown in Na88 to NQ89. In addition, regarding the appropriate retention time, the present invention example is Nα85 and N094 to Nα97.
A comparative example is shown in Nch98. As is clear from this, it can be seen that within the appropriate range according to the present invention, the above-mentioned excellent coating base function is improved.

Note that the notes on Books 1 to 9 shown in Table ↓ are as follows: *1 Steel plate composition system of applied base plate (Table 2) Table 2 Properties of high tensile strength hot rolled steel sheet *2 Roll Scotch Brite for surface grinding Roll (manufactured by Sumitomo 3M Co., Ltd., fine type) used wood 3 Measurement of eutectoid rate of pre-plated alloy elements and coating amount After dissolving and peeling with aqua regia, the alloy elements in the stripping solution were IC
The alloy eutectoid ratio is obtained by dividing the measured P value into the numerator and the plating adhesion amount determined by the gravimetric method as the denominator.

*4 Uniformity of hot-dip galvanizing appearance (visual judgment) 0 smooth and uniformly glossy, 0 matte, Δ hair-like unplated appearance,
x Partial non-plating occurrence *5 Plating adhesion After 180 degree close bending and cellotaping peeling, evaluation O: No peeling at all, O: Slight spot peeling, Δ: Dot peeling, ×
Laminar exfoliation, 6 Phosphate treatment PB37SS treatment (Japan Parr Rising m>, 65°C
Evaluation based on the state of precipitation of the phosphate biofilm after spray treatment for X 10 sec: O uniform fine crystals, O uniform and slightly coarse grained crystals mixed, Δ fine grains, coarse grain mixed crystals precipitated, but some scratches occurred. ,× Coarse grained crystals and noticeable scratches.

*7 Paint adhesion After PB37SS treatment + Pn62 treatment (manufactured by Nippon Pariki Rising), apply melamine alkyd resin paint (manufactured by Kansai Paint) at 20μ and bake at 125°C for 20 minutes. After that, it was immersed in pure boiled water for 30 minutes, and 24 hours later, cellophane tape was removed (lm opening x 100 openings).
Next, evaluate by close contact.

The evaluation is expressed as the ratio of the number of squares of the remaining coating film to 100 squares.

0 100/100, 090/100, Δ70/100
, X50 or less/100*8 Unpainted corrosion resistant Cr"-Cr" based coated chromate treatment (T, Cr3
0 mg/ rrr) Afterwards, outdoor back mouth test {Evaluation based on the rusted area ratio after 1 year O white rust ≦5%, ○ white rust ≦lO%, ∆ white rust ≧50%, some red rust, × Red Rust ≧5% Book 9 Corrosion Resistance after Painting*7 After chemical conversion treatment and painting under the same conditions, crosscuts were carved on the painted surface and salt spray test (JIS Z-
2371) Evaluate the coating film blistering width from the crosscut after 7 days: 0 No blistering, 0 Blistering width ≦ 3 m, ∆ Blistering width ≦ 5
mgm, × blister width ≧ 10 nn, (Effect of the invention) As described in the above examples, according to the method of the present invention, surface grinding and/or Or, by pre-plating with a Ni-based alloy, even high SL additive steel, which was previously said to be difficult to plate, can be uniformly plated by low-temperature heat treatment in a specific atmosphere that does not affect the material strength. This is an epoch-making product that can improve the appearance and plating adhesion at the same time, and can produce high-strength hot-dip galvanized steel sheets at an industrial level that can be heated at low temperatures, which was not possible with conventional techniques.

Claims (6)

[Claims] (1) Ni plating or Fe, Cr, Co, Mo, Ti, Zr, V, W,
A Ni-based alloy plating layer containing 0.1 to 20 wt% of at least one of B and P is formed at a thickness of 0.1 to 10 g/m^2, and a hot dip galvanized layer is formed on top of the Ni-based alloy plating layer. Hot-dip galvanized hot-rolled steel sheet. (2) Si content of 0.5 to 1.0wt in the steel plate to be plated
% hot-rolled steel sheet according to claim (1). (3) The hot-dip galvanized hot-rolled steel sheet according to claim (1), characterized in that a high-tensile hot-rolled steel sheet is used as the steel sheet to be plated. (4) Al content in hot-dip galvanized layer 0.2-10
wt%, and (as the third alloying element) Mg, Si and S
Pb, Cd, and Sn containing 0.05 to 1.0 wt% of at least one of b and mixed as unavoidable impurities.
The hot-dip galvanized hot-rolled steel sheet according to claims (1) and (2), characterized in that the total amount of Zn is less than 0.02 wt% and the balance is Zn. (5) Pickled and descaled hot-rolled steel sheets are 0
．． Grind 3 to 5 μm, and plate the steel plate with Ni or Fe.
, Cr, Co, Mo, Ti, Zr, V, W, B, P containing 0.1 to 20 wt% of at least one of the following.
After forming the base alloy plating at a thickness of 0.1 to 10 g/m^2, H
_2 N_2 with a gas concentration of 15% or less and a dew point of -5℃ or less
A method for producing a hot-dip galvanized hot-rolled steel sheet, which comprises heating the hot-dip galvanized steel sheet in a gas atmosphere to a maximum temperature of 450 to 600°C. (6) Pickled and descaled hot-rolled steel sheets are 0
．． Grind 3 to 5 μm, and plate the steel plate with Ni or Fe.
, Cr, Co, Mo, Ti, Zr, V, W, B, P containing 0.1 to 20 wt% of at least one of the following.
After forming the base alloy plating at a thickness of 0.1 to 10 g/m^2, H
_2 N_2 with a gas concentration of 15% or less and a dew point of -5℃ or less
The plate is heated in a gas atmosphere to a maximum temperature of 450 to 600°C, hot dip galvanized, and while the galvanized layer is in a molten state, the plate is heated to a temperature of 400 to 600°C in the atmosphere.
A method for producing a hot-dip galvanized hot-rolled steel sheet, characterized by heating for a heat retention time of 10 seconds or less.