JPH04346626A - Manufacture of corrosion resistant hot rolled steel sheet high in productive efficiency and excellent in deep drawability - Google Patents

Abstract

PURPOSE:To manufacture a corrosion resistant hot rolled steel sheet having high drawability at high productivity by subjecting a steel in which the content of C, N, Ti and Nb is regulated to hot rolling, taking-up and descaling in specified conditions, injecting the alloy powder of Zn or the like thereon and forming a hot-dip plated layer. CONSTITUTION:In a steel for a hot rolled steel sheet contg., by weight, <=0.05% C and <=0.001% N and in which the relationship of the content of C and N and the content of either or both of Ti and Nb lies in a one shown by the inequality, hot rolling is finished at the Ar3 transformation point or above, and the sheet is taken-up at 700 to 800 deg.C. Then, after its rolling at 600 to 800 deg.C, till the steel sheet is taken-up, scales on the surface of this steel sheet are removed by dry descaling or high pressure water descaling. Then, single metal of Zn, Al, Pb, etc., or the alloy therebetween, etc., is sprayed thereon in the steel sheet temp. higher than its m.p. in the range of 30 to 200 deg.C to form a hot-dip plated layer on the required face of the steel sheet.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is for deep drawing with corrosion resistance and r average value of 1.4 or more for plating single metals such as Zn, Al, Pb, etc. or their alloys with good productivity and economically. The present invention relates to a method for manufacturing hot rolled steel sheets.

0002

[Prior Art] Conventionally, in order to plate hot-rolled steel sheets with metals such as zinc, the pickled sheets were cooled once after the hot-rolling process, and then the pickled sheets were immersed in a molten bath of metals such as zinc or alloys. The hot-dip plating method, in which the pickled plate is immersed in a solution containing the salt of the metal to be plated, and the electroplating method, in which DC electrolysis is performed, have been used.

[0003] However, these methods require pickling equipment and large-scale plating equipment, which requires a large amount of equipment cost and a vast installation space.Furthermore, hot-dip plating requires high fuel costs to heat the steel plate. Since electroplating requires electricity to perform electrolysis, improvements in economic efficiency have been desired.

[0004] As a metal plating method that compensates for these drawbacks, Japanese Patent Application Laid-Open No. 146230/1983 discloses a method in which molten metal is sprayed onto the outer surface of a rolled steel material running in a hot rolling process or a finishing line, and the surface layer of the steel material is A method of forming a uniform plating layer has been proposed. However, this method does not take into account the influence of scale formed during the hot rolling process, and when this method is implemented, the plating adhesion is poor because molten metal is sprayed over the scale. In the case of thin steel sheets that are subjected to press working or the like after manufacturing, the plating peels off after processing, resulting in poor corrosion resistance.

Furthermore, in order to overcome these problems, the type of metal to be sprayed, the temperature of the steel plate at the time of spraying, the appropriate roughness of the steel plate surface to improve adhesion, and the temperature during the hot rolling process during the spraying process. Moreover, there is no description of a desirable position on the finishing line, etc., and there is no disclosure or suggestion of specific conditions for obtaining a plating layer that guarantees practical adhesion.

Furthermore, in Japanese Patent Application Laid-Open No. 61-204332, a strain rate of 300 S-
After finishing rolling in step 1 and then winding up at 400°C or lower, recrystallization and plating are performed on a continuous hot-dip plating line. This method requires α-region rolling and a high strain rate, so the rolling load is extremely high for current continuous hot rolling lines.

On the other hand, as a method for improving the drawability of a hot-rolled steel sheet, there is a method for producing a hot-rolled steel sheet with a high r average value in which lubrication is applied during warm rolling (Japanese Patent Application Laid-open No. 3844/1984, etc.). This method uses a normal hot rolling process to improve the r average value. In this method, low-temperature heating is performed for the purpose of fixing precipitates, followed by highly lubricated rolling in the α region, followed by self-annealing or recrystallization treatment to obtain a hot-rolled steel sheet with a high r average value. In this method, the coefficient of friction cannot be sufficiently lowered unless high-concentration lubrication is applied during hot rolling, resulting in problems such as slippage during rolling.

[0008]

Problems to be Solved by the Invention The above-mentioned warm lubrication rolling method, when carried out on a finishing line that continuously manufactures steel plates, causes the following numerous problems. ■Implementation of low-temperature heating: The heating temperature in the normal hot rolling process is kept at 1100°C or higher in order to ensure the finishing temperature of the normal hot final material to be Ar3 or higher. For this reason, when a steel plate is manufactured using a heating furnace at a low temperature as in the warm lubrication rolling method, there is a loss of time required to change the set temperature between the normal heating temperature and the low temperature heating temperature, which deteriorates production efficiency.

[0009] α-region rolling: In order to lower the finishing temperature, it is necessary to adjust the time between rough rolling and finish rolling, which also causes time loss and similarly deteriorates production efficiency. ■High lubrication: In order to use highly lubricated rolling oil, when manufacturing regular products, it is necessary to change the concentration to a thinner one, and it is also necessary to remove the oil attached to the rolls.
Deteriorates workability and production efficiency.

■In the process of applying Zn plating to hot rolled steel sheets,
Because the temperature of the steel sheet drops below 100℃ due to cleaning with acid, not only is it not possible to shorten the number of days required after winding, but the heat retained in the coil cannot be used, and the heating process before plating still requires a huge amount of energy and time. Since it requires a heating furnace, the effect of reducing operating costs is low.

[0011] The present invention provides a hot-rolled steel sheet with excellent corrosion resistance, which has a plating layer with good plating adhesion made of a single metal such as zinc or an alloy thereof, on a hot-rolled steel sheet with a high r average value, which currently has a large energy loss. Our goal is to provide a highly productive and economical method of manufacturing steel plates without the above problems, and at the same time provide low-cost products, we also
The present invention provides a technology for imparting two added values, that is, a high r average value and high corrosion resistance due to a plating layer, to a hot rolled steel sheet.

0012

[Means for Solving the Problems] In order to achieve the above-mentioned problems, the present invention provides C: 0.05% or less, N: 0% by weight.
．． 01% or less, the content of C and N and the content of one or both of Ti and Nb are 0.4 (Ti/48+Nb
/93)≦C/12+N/14≦1.2(Ti/48+
Nb/93) After hot rolling is completed above the Ar3 transformation point, coiling is performed at 700 to 800°C, and then rolling is performed at 600 to 800°C. Before winding the steel plate, scale on the surface of the steel plate is removed using dry descaling or high-pressure water descaling, and then metal powder such as a single metal such as zinc, aluminum, or lead or an alloy thereof is added to the Corrosion-resistant heat is sprayed onto a required surface of a steel sheet at a steel sheet temperature higher than the melting point of the metal powder in a range of 30° C. or more and 200° C. or less to form a hot-dip coating layer on the required surface of the steel sheet. A method for producing inter-rolled steel sheets, and in weight%, C: 0.05
% or less, N: 0.01% or less, the content of C and N,
The content of one or both of Ti and Nb is 0.4 (Ti
/48+Nb/93)≦C/12+N/14≦1.2(
After hot rolling of a hot-rolled steel plate having a relationship of Ti/48+Nb/93) at Ar3 transformation point or higher,
After winding at 800°C and subsequent rolling at 600 to 800°C, scale on the surface of the steel plate is removed using dry descaling or high-pressure water descaling, and the surface is Roughness is Ra value 0
．． 5 μm or more, and then a metal powder of a single metal such as zinc, aluminum, lead, or an alloy thereof, with a particle size of 150 mesh or more, is applied to the required surface of the steel plate at a temperature of 30°C or more and 200°C or less than the melting point of the metal powder. This is a method for producing a corrosion-resistant hot-rolled steel sheet, characterized in that a hot-dip coating layer is formed on a required surface of the steel sheet by spraying at a high steel sheet temperature. In addition, the hot-rolled steel sheet referred to in the present invention refers to C, N as shown below.
, Nb, Ti, and other JIS G3
Indicates steel with P and S contents that meet the regulations of 131.

[0013]

[Operation] Improving the r average value of a corrosion-resistant hot-rolled steel sheet has many advantages, since it not only improves the material properties of the steel sheet, but also allows it to be used as a substitute for cold-rolled steel sheets for similar purposes. One of the methods, the lubrication rolling method, provides a high average value of r and also has high drawability compared to cold rolled steel sheets. However, the production of this steel plate requires low-temperature heating, α-region rolling, high-level lubrication, etc., which places a large load on conventional lines, causing a deterioration in production efficiency.

First of all, in order to solve these problems, the present inventors positioned the normal hot rolling process as a pre-process (preparation process) for producing high r average value hot-rolled steel sheets. , Examination of manufacturing methods under conditions that do not cause production problems. ■ Position α-region lubrication rolling, which has a large load, as a subsequent process, and consider production methods as a dedicated line. Examining ways to improve production efficiency and product characteristics by making the most of the differentiation between ■■ and ■. ■Furthermore, in consideration of continuity with the plating line for hot-rolled steel sheets, we have repeatedly considered a continuous line that can thermally save energy and process, and in order to operate the normal hot-rolling process without production failure, It was found that it is necessary to set the temperature in the range of 1100 to 1200° C., and to complete the finish rolling at a temperature higher than the Ar3 transformation point before winding.

[0015] Second, the inventors focused on the high steel plate temperature after hot rolling and coiling after producing a high r average value hot rolled steel plate in the hot rolling finishing process, and utilized that heat. The following experiment was conducted on the premise that a powdered plating metal was sprayed onto the steel plate and melted, and the alloy reaction observed therein was utilized to form a plating layer, and the findings described below were obtained.

[0016] The condition limitations will be described in detail below. (1) Chemical composition of steel sheet In the present invention, the chemical composition of steel sheet is limited in order to improve the hot rolling material, that is, the deep drawability (r average value). In order to improve deep drawability in the α region rolling method applied in the present invention, it is necessary to increase the crystal orientation and {111} plane strength ratio, which are effective for deep drawability, and reduce the harmful {100} plane strength ratio. Therefore, it is necessary to reduce solid solution C and N in the steel sheet before hot rolling. For this purpose, it is necessary to satisfy C≦0.05% and N≦0.01%. However, the industrially possible lower limit is approximately 10
It is about ppm. Furthermore, reducing C and N to extremely small amounts inevitably increases costs.

In order to prevent this increase in cost, in the present invention, Nb and Ti are added to fix C and N in the form of precipitates. However, since the addition of Nb and Ti also increases cost, it is necessary to balance them with the amounts of C and N. Therefore,
In the present invention, C/12+N/14≦1.2(Ti/48
+Nb/93) is used to balance the above, sufficiently fix the solid solution C and N as carbonitrides, reduce the solid solution C and N, improve the {111}/{100} ratio, and perform deep drawing. Improving sexuality.

[0018] Also, 0.4 (Ti/48+Nb/93)
Set the condition of ≦C/12+N/14, {111}/{1
This prevents excessive addition of Nb and Ti after the improvement in the 00} ratio is saturated, thereby preventing unnecessary cost increases. Also, P
, S, and Mn cause softening and deterioration of ductility if they are too large, so P≦0.03%, S≦0.035%, Mn
Let n≦0.5%.

(2) Rolling material In the conventional warm lubrication rolling method, it is better for the rolling material to precipitate carbonitrides with Ti and Nb in order to reduce solid solution C and N in the hot rolled steel sheet. It is better to heat at a low temperature to facilitate precipitation. However, in the present invention, in order to avoid the accompanying deterioration in production efficiency and aim for precipitation in the winding process, there are no limitations on the rolling material conditions, and ordinary continuous casting slabs, thin-walled continuous casting slabs, direct rolling methods, etc. are applied. is also possible.

(3) Hot rolling conditions To obtain fine-grained ferrite, the finish rolling temperature should be set at 850°C.
It is desirable to set the temperature to 950°C. The rolling reduction rate is not particularly limited, but it goes without saying that finer grains can be obtained by increasing the rolling reduction rate for the entire finishing process and the rolling reduction rate for the latter half.

(4) Winding temperature condition The most important winding temperature among the means of the present invention is 800 to 7
The temperature shall be 00°C. Conventionally, precipitation in a heating process has been used to precipitate carbonitrides before rolling. For this purpose, low-temperature heating is required, and as mentioned above, production efficiency inevitably deteriorates. In the present invention, precipitation of carbonitrides is carried out in the earliest high-temperature winding process, so low-temperature heating is unnecessary and productivity does not deteriorate.

(5) Warm rolling conditions The following warm rolling process utilizes the sensible heat of high-temperature coiling, so there is no time loss due to waiting before finishing rolling to perform α range rolling as in the past. does not occur. It is possible to perform rolling as is after winding, or it is also possible to select a coil that has reached a predetermined temperature and perform rolling.

Generally, if rolling is performed in the ferrite region in the absence of solid solution C and N in the steel sheet before rolling, the {111} plane strength, which improves the r average value, will increase. However, in normal rolling, the central phase {111} of the plate thickness develops, but the surface layer
{110} develops due to the influence of shear strain, which inhibits the improvement of the r average value. Therefore, to prevent it,
When producing a hot-rolled steel sheet with a high r average value, rolling is performed at low temperature while being lubricated.

[0024] At this time, the lower the rolling finish temperature, the greater the development of {111} in the center layer, but if it is too low, the rolling load will increase, which will impede rolling. When the rolling temperature is in the high temperature range α, recovery is rapid, accumulation of strain is reduced, and {111} plane strength is reduced. Therefore, the upper limit of the final finishing temperature was set at 800° C. in order to accumulate a large amount of strain in the α region during the finishing rolling process. From the above, the hot rolling finish rolling temperature range was set to 600 to 800°C.

The present inventors have also discovered that by plating by subsequent metal powder injection, a high r average value can be obtained without lubricating rolling in the hot rolling process. The reason for this is not clear, but it is thought that when an alloy layer is formed on the surface by thermal spray plating on the surface, the shear layer with a lot of {110}, which has a negative effect on improving the r average value, disappears. Therefore, when plating a warm rolled material, it is not necessary to lubricate it. (6) Dry descaling conditions Also, as a pretreatment for plating, if there is scale between the plating layer and the base metal, it will be easy to peel off in that area and the plating adhesion will deteriorate, so in order to prevent It is preferable to simultaneously remove the metal and optimize the roughness of the steel sheet surface in order to increase the contact area between the base steel and the plating layer and promote the alloying reaction.

High-pressure water descaling or dry descaling that does not use a liquid is good for this. Specific dry descaling methods include vacuum arc (10-4 to 10-6 Torr), plasma, and reduction reaction. , magnetic polishing (using magnetic powder of several tens of microns to several hundred microns), shot blasting, sand blasting, grit blasting, wire brush, grinder, etc. can be used alone or in combination. However, in the case of high-pressure water descaling, if water remains on the steel plate after descaling, it will promote the generation of new scale and further impede the alloying reaction during powder injection. It is necessary to drain the water sufficiently using gas.

Regarding the surface roughness of the steel plate formed during descaling, the rougher the surface roughness, the larger the surface area and the easier the alloying reaction to occur, so it is preferable for improving plating adhesion. In order to investigate the effect of the surface roughness of a steel plate on plating adhesion, Zn powder or Al powder with a particle size of 150 mesh or more was heated to a temperature 30 to 200 °C higher than the melting point of the metal on a roughness-adjusted steel plate. We conducted an experiment to spray the liquid.

Figure 1 shows an example of the results, and shows the experimental results when Zn powder was injected onto a steel plate 100°C higher than its melting point. A score of 1 (score based on ball impact test) was obtained, and sufficient plating adhesion was obtained with a score of 0.3 to 1.
2 was obtained even at 0.4 μm, and it was found that there was no problem in practical use. As for the above-mentioned BI rating, 1 indicates the best plating adhesion, and the larger the value, the worse the plating adhesion. As a corrosion-resistant hot-rolled steel sheet for processing purposes, this B
An I rating of 1 is most desirable.

[0029] In order to prevent the formation of new scale after descaling, it is necessary to inject powder immediately after descaling. It is more preferable to maintain a non-oxidizing or reducing atmosphere between descaling and powder injection, such as an inert gas atmosphere such as argon or nitrogen, a mixed atmosphere of an inert gas and hydrogen, or a hydrogen atmosphere. In this case, it goes without saying that descaling or powder injection may be carried out in a non-oxidizing or reducing atmosphere.

(7) Plating thermal spraying conditions After removing scale from hot rolled steel sheets heated to various temperatures, the inventors applied various metal powders such as pure zinc powder, pure aluminum powder, and zinc-aluminum alloy powder. A spraying experiment was conducted, and it was found that if the temperature of the steel plate was 30°C or more higher than the melting point of the metal powder to be sprayed, it was possible to form a plating layer with good adhesion. It was discovered that when the temperature exceeds ℃, an oxidized layer develops, impairing the appearance, and making it impossible to control the amount of plating.

Based on these findings, if the temperature of the steel plate to which the metal powder is injected is raised to a range of 30 to 200°C above the melting point of the powder, the heat of fusion to melt the powder and the sufficient time to cause the alloy reaction will be generated. It has been found that heat is supplied to maintain the molten state and the development of an oxidized layer can also be prevented.

[0032] Examples of metals forming a plating layer for corrosion-resistant purposes include zinc, aluminum, lead, an alloy of zinc and aluminum, and an alloy of zinc and iron with an iron content of about 5% by weight or less. The melting point of these metals is about 700℃ above 327℃.
It is in the temperature range of about ℃ or below, and is 30℃ higher than the melting point of these.
The temperature range of ~200℃ higher is the period from the end of finish rolling to the winding in the hot rolling process, and during that time, the injection position is determined to be the most productive and economical position based on the melting point of the metal used for injection. Good.

Regarding the particle size of the metal powder to be sprayed, if the powder is too large, heat conduction will be poor and it will be difficult to melt, so it is better to use a small powder as long as it does not scatter and consume and does not require a large amount of pulverization cost. In order to investigate the effect of metal powder particle size on plating adhesion, Zn powder or Al powder was heated to a temperature 30 to 200 ° C higher than the melting point of the metal and the surface roughness was adjusted to an Ra value of 0.5 μm or more. An experiment was conducted in which the liquid was sprayed onto a finished steel plate.

Figure 2 shows an example of the results, and shows the experimental results when Zn powder was injected onto a steel plate 100°C higher than its melting point. It was found that it was melted accurately and a BI rating of 1 was obtained, resulting in good plating adhesion, and that even when the mesh was 50 or more and less than 150 mesh, a BI rating of 2 was obtained, and adhesion that did not pose any practical problems could be obtained.

[0035]

[Example] Table 1 shows the chemical composition and hot rolling conditions of the test materials. Each material in Table 1 is prepared by performing warm rolling after hot rolling and winding, and placing various dry descaling devices and powder injection devices adjacent to each other between the warm rolling mill and the subsequent winding machine. During this time, various atmospheres were maintained, and after the steel plate after warm rolling was subjected to scale removal and roughness adjustment using various dry descaling devices, metal powder was injected using a powder injection device, and the sheet was wound up. Table 2 shows each condition, plating adhesion, corrosion resistance, and average r value after plating.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

As shown in Table 2, the present invention example No. 1~
In No. 14, it was possible to obtain a corrosion-resistant hot-rolled steel sheet with good plating adhesion, good corrosion resistance, and excellent deep drawability with an r average value of 1.4 or more. On the other hand, No. 1, which does not have the particle size of the powder that is a requirement of the present invention. 16. No. 1 whose surface roughness of the steel plate was off. 17. No. 1 where the lower limit temperature of the steel plate was exceeded. 18,2
1. No. 1 where the upper limit temperature of the steel plate was exceeded. Comparative Examples Nos. 19 and 23 both had poor plating adhesion, and it was not possible to obtain a corrosion-resistant hot-rolled steel sheet having the required corrosion resistance. Also, No.
22 is {111} because the warm rolling temperature is 800℃ or higher.
The development of surface strength was hindered, and No. In No. 20, because the winding temperature was low, precipitation of carbonitrides was insufficient and solid solution C, N
Because it could not be fixed, No. No. 15 satisfies the conditions such as thermal spraying, so the plating adhesion and corrosion resistance are good, but since no Ti or Nb is added, solute C and N cannot stick, so all have high r average values of 1.4 or more. was not obtained.

[0041] Note that No. 4 and 5 were manufactured under almost the same conditions, except for the use of high-quality lubricating oil, in order to examine the necessity of lubrication during rolling, and almost the same r average value was obtained. A high average value of r was obtained for the plated steel sheet even when rolled without lubrication.

[0042]

[Effects of the Invention] According to the present invention, a corrosion-resistant material having a plating layer of a single metal such as zinc, aluminum, or lead or an alloy thereof without reducing the productivity of a normal hot rolling process line and having high drawability. This makes it possible to economically produce hot-rolled steel sheets with high plating adhesion, smoothly, stably, with good plating adhesion, and with good productivity using small-scale equipment, so the industrial effect brought about in the field of art is extremely large.

[Brief explanation of drawings]

FIG. 1 is a chart showing the relationship between the surface roughness of a steel plate before being sprayed with plating metal powder in terms of Ra value and plating adhesion in terms of BI rating using two levels of powder particle size.

FIG. 2 is a chart showing the relationship between the particle size of the plating metal powder and the plating adhesion indicated by the BI rating using two levels of surface roughness Ra values.

Claims (2)

[Claims] [Claim 1] In weight%, C: 0.05% or less, N:
0.01% or less, the content of C and N and the content of one or both of Ti and Nb is 0.4 (Ti/48+Nb
/93)≦C/12+N/14≦1.2(Ti/48+
Nb/93) After completing hot rolling at the Ar3 transformation point or higher, coiling is performed at 700 to 800°C, and after rolling at 600 to 800°C, the steel plate is prepared. Before winding the steel sheet, scale on the surface of the steel sheet is removed using dry descaling or high-pressure water descaling, and then metal powder such as a single metal such as zinc, aluminum, lead, or an alloy thereof is applied to the steel sheet. Corrosion-resistant heat is sprayed onto a desired surface of the steel sheet at a temperature higher than the melting point of the metal powder in a range of 30° C. to 200° C. to form a hot-dip coating layer on the desired surface of the steel sheet. A method for producing inter-rolled steel plates. [Claim 2] Scale on the surface of the steel plate is removed using dry descaling or high-pressure water descaling, and the surface roughness is set to 0.5 μm or more in terms of Ra value, and then a single metal such as zinc, aluminum, lead, etc. A metal powder such as an alloy having a particle size of 150 mesh or more is injected onto a required surface of the steel plate at a steel plate temperature higher than the melting point of the metal powder in a range of 30°C or more and 200°C or less. The method for producing a corrosion-resistant hot-rolled steel sheet according to claim 1, further comprising forming a hot-dip plating layer.