JPH06228708A - High strength hot rolled steel plate having superior weldability and its production - Google Patents

Abstract

PURPOSE:To stably provide a high strength hot rolled steel plate having superior D.C. butt weldability and workability after welding and also having >=65kg/mm<2> tensile strength. CONSTITUTION:The hot rolled steel plate has a composition consisting of 0.06-0.12% C, <=0.3% Si, 1.0-2.0% Mn, <=0.03% P, <=0.005% S, 0.10-0.70% Cr, 0.01-0.05% Al, 0.02-0.08% Ti, 0.01-0.06% Nb, 0.0015-0.080% N, and the balance Fe with inevitable impurities and further containing one or more kinds among 0.03-0.5% Mo, 0.03-0.5% V, and 0.0002-0.0050% B or further containing one or >=2 kinds among the three consisting of a combination of 0.1-0.5% Cu and 0.1-0.5% Ni, 0.0005-0.005% Ca, and 0.005-0.015% rare earth elements. Further, as suitable manufacturing conditions, a steel slab of the above composition is hot-rolled at >=850 deg.C finishing temp., coiled at 400-550 deg.C, and then descaled.

Description

Detailed Description of the Invention

[0001]

This invention has a tensile strength of 65 kg / mm ²
The present invention relates to a hot-rolled steel sheet having the above-mentioned high strength and excellent in DC butt weldability and post-weld workability, which is suitable for manufacturing a wheel rim of an automobile, for example, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, energy conservation has been thoroughly practiced in all fields in the industrial world. For example, in the automobile industry as well, passenger cars were started in order to reduce the vehicle body weight and fuel consumption. The use of high strength steel sheets for various automobiles has become common. Along with this, there has been an increasing demand for steel sheets having higher strength and more excellent workability. Also, in the case of automobiles, weight reduction of wheels is more effective in reducing fuel consumption than body etc. Therefore, recently, research on “application of high strength hot rolled steel sheet to wheels” Is being turned around.

By the way, the wheels of the above-mentioned automobiles are usually composed of a "disk" and a "rim". Conventionally, the material applied to the rim is formed by forming a steel plate cut into a predetermined width and length into a ring shape, welding the ends, and performing roll forming in several steps. Are manufactured. In this way, the rim material undergoes large processing after being welded unlike other members, so it is important that the "weldability" and "workability after welding" are good as well as the formability. Requirements.

In addition to the conventional "flash butt welding method", a relatively new method "DC butt welding method" has recently been applied to the welding of the rim material. Moreover, the trend from the last few years is that a) the flash does not fly, so there is no deterioration of the work environment due to dust, b) there is less noise, and 3) there is no material consumption due to the flash, so the yield can be improved by about 1%. , 4) Since it is difficult to form an oxide, which is one of the causes of cracks on the weld end surface, it is necessary to reduce the amount added, so be careful with the composition elements such as Si, Al, and Ti as in the flash butt welding method. The DC butt welding method is gradually becoming the mainstream because it has advantages such as no need to pay.

However, in order to meet the recent demands,
When the DC butt welding method was used to manufacture a wheel rim made of a high-strength hot-rolled steel sheet having higher strength, the following problems were posed.

That is, various materials and techniques have been developed with the flash butt welding method applied in manufacturing wheel rims in consideration of it. Therefore, in these materials and techniques, When the DC butt welding method was used, welding defects sometimes occurred. So DC
New materials and techniques have been developed as the butt welding process has become widespread.

However, D.
C. A few years after the transition to the butt welding method, the strengthening of materials (50-60 kg of material strength) came to be called for, and the content of C, Si, and Mn in the material steel sheets increased. However, in this case, the hardness increase of the welded portion became a problem. In other words, the hardness of the weld becomes extremely high due to the increase in the amount of strengthening elements, and cracks may occur from the weld end face during the subsequent processing. It has been pointed out that stress causes concentration of stress in this softened portion when processing is performed, cracking occurs from the softened portion due to necking, and the defect rate increases. However, the "hardness increase problem at the welded part" at the material strength level at that time was limited by the C equivalent and Ti.
The problem could be solved by a method such as addition (see, for example, JP-A-61-170541, JP-A-61-264159, JP-A-61-264160).

However, in order to meet the recent required level of high strength (material strength of 65 to 80 kg), a problem that is more complicated and difficult to solve than the above problem has occurred. That is, in such a hot-rolled steel sheet that requires high strength, it is difficult to limit the C equivalent too much from the viewpoint of ensuring strength, and addition of a little Ti does not sufficiently suppress the increase in hardness of the welded portion. Absent. Moreover, simply Ti
If the addition amount of is increased, the effect is saturated, and the ductility is deteriorated due to coarsening of TiN and the moldability is likely to be deteriorated. Further, in these precipitation-strengthened high-strength steel sheets, softening occurs due to coarsening due to solid solution reprecipitation of TiC in the weld heat-affected zone slightly away from the weld end surface, and the softening amount increases as the strength increases, On the contrary, the hardness distribution becomes non-uniform. Such a phenomenon is the same as in the case of a steel plate strengthened by adding Cr or Nb.

Moreover, in this type of high-strength steel sheet containing a large amount of C, Si, and Mn so as to obtain a correspondingly high strength, it is not so much in the case of the conventional hot-rolled steel sheet having a tensile strength of 50 to 60 kg / mm ² or less. "Electrical resistance of steel sheet" and "hardenability of steel sheet", which did not pose a problem, become very serious problems.

This is because when the content of C, Si and Mn is large, the electric resistance value of the steel sheet becomes large, but when the electric resistance value becomes large, a large current must be passed during welding. As a result, the surface with a large amount of heat generation partially melts down and cannot be welded, and if the amount of current is reduced, the end face cannot be heated sufficiently, resulting in a welding defect called cold welding. The range becomes narrower and it becomes difficult to set the welding conditions. Further, when the hardenability of the steel sheet becomes high, the hardness of the welded portion becomes very high because the cooling rate in the cooling process after welding and forming the bead rim is fast, so that the workability is the same as described above. Cracks may occur from the weld end face on the way, or softening may occur in the weld heat affected zone, which is slightly away from the weld end face, and stress may concentrate in the softened portion during processing, causing cracking due to necking.

Among these, it has been found that the optimum welding condition range of the steel sheet can be covered to some extent by improving the welding condition such as "two-stage pressurization". Research is also underway.
However, it goes without saying that it is desirable to have a wide range of optimum welding conditions in terms of workability, stability of product performance, productivity, and the like.

Regarding the hardness distribution of the welded portion, both "the amount of hardness increase at the weld end surface" and "the amount of softening in the weld heat affected zone near the welded portion" are small, and the difference between the maximum hardness and the minimum hardness is as small as possible. As described above, the flat distribution is required. According to a study by the present inventors, this “difference between the maximum hardness and the minimum hardness” needs to be 40 or less in Vickers hardness (Hv), and this condition is not satisfied. During subsequent processing, "necking cracks in the softened portion" and "second cracks that split at the boundary between the softened portion and the base material" tend to occur, and the defect rate cannot be ignored.

It is known that the addition of Mo, V, etc. is effective for suppressing the softening of the weld heat affected zone in thick steel plates for pipes, etc. However, when these transformation strengthening elements are added, the C equivalent Is increased, the hardness of the welded part is extremely increased, which promotes non-uniformity in the hardness distribution of the welded part. Therefore, it is considered inappropriate to add it to the steel plate for DC butt welding.

Further, as another means for increasing the strength of the steel sheet, there is a "method of controlling the structure by controlled cooling". However, this type of steel sheet is particularly liable to cause softening in the weld heat affected zone and has a high strength. Since there is a tendency that the softening amount becomes larger as it is, it is inappropriate to adopt it as a method for strengthening steel plates for wheel rims of automobiles.

As described above, the current general "hot-rolled steel sheet having a high strength of 65 kg or more" has a very narrow range of optimum welding conditions, and the hardness distribution tends to be very uneven. Therefore, there is a problem in application as a wheel rim for automobiles.

In view of the above, the object of the present invention is to provide excellent DC butt weldability and post-weld workability, which can be sufficiently satisfied for the wheel rims of automobiles which are desired in the future. It was to establish means for stably providing high strength hot rolled steel sheet having a tensile strength of 65 kg / mm ² or more as shown.

[0014]

Means for Solving the Problems As a result of intensive studies conducted by the present inventor while carrying out a number of tests in order to achieve the above-mentioned object, as a result, "combined addition of appropriate amounts of Ti, Nb and Cr, and Mo,
By constructing a high strength hot rolled steel sheet by adding an appropriate amount of V and B, it is possible to suppress the increase in hardness of the weld zone and the softening of the heat affected zone at the same time while ensuring high strength, and the welding conditions are also It is not so narrow as to cause a problem in practical use, compared with the current 50-60 kg / mm ² grade hot-rolled steel sheet ”. And further, when manufacturing the hot rolled steel sheet,
It was also found that the performance of the steel sheet obtained by simply controlling cooling after hot rolling is slightly improved.

The present invention has been completed on the basis of the above-mentioned findings and the like. "The composition of the composition of the hot-rolled steel sheet is C: 0.06 to 0.12% (hereinafter,% representing the composition ratio is% by weight). , Si: 0.3% or less, Mn: 1.0 to 2.0%, P:
0.03% or less, S: 0.005% or less, Cr: 0.10 to 0.70%,
Al: 0.01-0.05%, Ti: 0.02-0.08%, Nb: 0.01-
0.06%, N: 0.0015 to 0.080%, Mo: 0.03 to 0.5%, V: 0.03 to 0.5%, B: 0.
0002 to 0.0050% of one or more, or Cu: 0.
1 to 0.5%, Ni: 0.1 to 0.5%, a combination of two components, Ca: 0.0005 to 0.005%, rare earth element: 0.
005 to 0.015%, including one or two or more of the three, and by adjusting the balance to consist of Fe and inevitable impurities, it has a high strength of 65 kg / mm ² or more, Moreover, it has excellent DC butt weldability and post-weld workability. "
In addition, "a steel slab having the above composition is hot-rolled at a finishing temperature of 850 ° C or higher, wound at 400 to 550 ° C, and then descaled to obtain a tensile strength of 6
It has a high strength of 5 kg / mm ² or more, and is capable of stably producing high-strength hot-rolled steel sheets with excellent DC butt weldability and post-weld workability ”. is there.

[0016]

As described above, according to the present invention, in producing a high-strength hot-rolled steel sheet, an appropriate amount of Ti is added to suppress an increase in hardness of the welded portion by the action of finely precipitated TiN, and the effect of welding heat is also exerted. In order to suppress the softening of the welded portion, one or more of Mo, V, and B are added in an appropriate amount, and Nb and Cr are added in combination with Ti to suppress the increase in hardness of the welded portion of TiN. While strengthening and maintaining up to the high Ti addition range, by offsetting the weld hardness increasing action of Mo, V, and B added to prevent softening, the hardness distribution near the weld is made uniform and flat, This is intended to obtain a DC butt weldability, a high-strength hot-rolled steel sheet having good workability after DC butt welding. Hereinafter, in the present invention, the composition of the hot-rolled steel sheet, and further the production conditions are as described above. The reason for such limitation will be described.

A) Component ratio <C> C is an essential component for ensuring the required strength of the steel sheet, and is an inexpensive element. And
If the C content is less than 0.06%, securing the strength must be supplemented by adding a large amount of other strengthening elements, which is extremely uneconomical. On the other hand, if too much C is used to secure the strength of the steel sheet and C is contained in an amount exceeding 0.12%, the pearlite portion increases, the ductility deteriorates significantly, and the toughness decreases, and further the welded portion The increase in hardness cannot be suppressed. Therefore, the C content was set to 0.06 to 0.12%, but if possible, the C content should be 0.
It is desirable to adjust it so that it does not exceed 10%.

<Si> Si is an element that oxidizes during the welding process and becomes a penetrator at the weld end face to easily cause defective welding. It is an element that should be refrained from addition when performing flash butt welding. However, DC butt welding has no such effect. Rather, it is an element to be positively added because it has a greater effect of increasing the strength without lowering the ductility as compared with other elements. However, Si has the effect of raising the electric resistance value and lowering the upper limit of the “appropriate range of welding current”, and although not as much as flash butt welding, if it is contained in a large amount, it still causes the penetrator. As a result, the defective welding rate increases.
Therefore, the Si content is set to a range of 0.3% or less at which such a problem does not become remarkable, but is preferably 0.05 to
It is good to adjust to 0.2%.

<Mn> Mn is a component necessary to fix S contained in molten steel as an unavoidable impurity to reduce its harmful effect and to secure the strength of the steel sheet as with C. 60kg / mm ² depending on the amount of the strengthening element added
To obtain the above tensile strength, it is necessary to contain 1.0% or more. However, if you rely on Mn too much,
When Mn is contained, deterioration of weldability and workability cannot be ignored, and also leads to cost increase. Therefore, the Mn content was set to 1.0 to 2.0%, but if possible, the C content should be 1.8%.
It is desirable to adjust so that it does not exceed.

<P> P is an important component that can increase the strength without significantly lowering the ductility in the case of producing a general high-strength steel plate. Is a harmful element which causes segregation at the grain boundaries during melting and solidification to cause embrittlement and cause defective welds. Therefore, in the steel sheet of the present invention, the lower the P content, the more desirable. The upper limit of "P as an unavoidable impurity" is usually set to about 0.05% in consideration of the manufacturing cost of steel, but good weldability as aimed at by the present invention is obtained. In order to secure the above, such a limit is not sufficient, and it is necessary to make it 0.03% or less. However, when the demand for low welding defect rate is more stringent, the P content is
It is desirable to keep it below 0.01%.

<S> S is an impurity element that is inevitably mixed in the steel sheet, and it is an inclusion that causes "heavy flaws in the manufacturing process" and "cracking during the forming of the base material or the welding material". Since (MnS) is increased, the S content should be as low as possible depending on the application of the steel sheet. And, in particular, it shows excellent workability after welding, for example, the wheel of an automobile.
Even if it is applied to rulim, it is necessary to regulate the S content in the steel sheet to 0.005% or less in order to keep the defect rate low.

<Cr> Cr is an element necessary to secure the strength of the steel sheet, like C and Mn, and is a component that contributes to uniform hardness distribution after welding by the combined addition of Ti and Nb. is there. Then, in order to have excellent weldability and workability as aimed at by the present invention and to obtain a tensile strength of 65 kg / mm ² or more, it is necessary to secure a Cr content of 0.10% or more. However, like Mn, Cr is an element that has a large effect of increasing the hardness of the welded part, and adding a large amount diminishes the effect of the above-described composite addition, and when the addition amount increases, the strength increasing effect saturates. As the temperature rises, the deterioration rate of ductility increases. Therefore, the upper limit of the Cr content is set to 0.70%. A particularly preferable range of Cr content is 0.30 to 0.60%.

<Al> Al is added for deoxidizing the steel and suppresses the reduction in the yield of Ti, which tends to be lost by oxidation, and the formation of non-metallic inclusions (oxides) in the steel that deteriorate ductility. It works to suppress. It also has a function of fixing N as AlN, which causes aging at room temperature and adversely affects ductility. However, if the Al content is less than 0.01%, the desired effect due to the above-mentioned action cannot be obtained, while if it exceeds 0.05%, the material cost is increased, and Al ₂ O ₃ is added.
Since the inclusions such as lead to deterioration of ductility and surface defects called hegging, the Al content was set to 0.01 to 0.05%.

<Ti> Ti increases the strength of the steel sheet by precipitating fine TiN, serves as a nucleus for the generation of ferrite grains during welding, suppresses the generation of hard phase, and suppresses softening due to grain growth. It is a component that exerts its action. However, if the content is less than 0.02%, the desired effect due to the above-mentioned action cannot be obtained, while if the Ti content becomes too large, TiN becomes coarse and the number of precipitations decreases, and conversely the above-mentioned effect is not obtained. Will be enough. And, for such a reason, in the case of adding Ti alone, its content must be suppressed to 0.04% or less, but in the case of the steel sheet of the present invention in which Nb and Cr are added in combination, its upper limit value is expanded. However, the effect continues until 0.08%. The reason for this is not clear,
It is considered that this is due to some interaction between these elements to be added in complex and the precipitates of N and C, or because of the formation of complex precipitates between these elements. Therefore, the Ti content is set to 0.02 to 0.08%, but a more preferable range is 0.03 to 0.07%.

<Nb> Nb is an ordinary high strength steel plate
It is an element added with the expectation of precipitation strengthening such as NbC.
In the present invention, Cr and Ti are added in combination in order to exert the effect of suppressing the softening of the heat-affected zone of the weld while suppressing the increase in the hardness of the weld. However, if the Nb content is less than 0.01%, the above effect cannot be obtained, while if the Nb content exceeds 0.06%, the effect begins to saturate, and the performance improvement becomes low despite the increase in material cost. , Nb content was set to 0.01 to 0.06%, but a more preferable range is 0.02 to 0.05%.

<N> N finely precipitates as TiN and NbN to increase the strength of the steel sheet, and serves as a nucleus for the generation of ferrite grains during welding, thus suppressing the formation of a hard phase and softening due to grain growth. It is a component that exerts a suppressing effect. However, if the content is less than 0.0015%, the desired effect cannot be obtained, whereas if it exceeds 0.080%, Ti, Al, and Nb cannot be fixed and the aging property of the steel sheet deteriorates. Therefore, the N content is 0.00
It was set at 15 to 0.080%.

<Mo, V, B> Usually, these elements are added to improve the strength and hardenability of steel and prevent softening of the welded portion, but even elements that have a large effect of increasing the hardness of the welded portion. Yes, for example, since a large amount of addition to a high-strength steel sheet for wheel rims may cause uneven hardness distribution,
In particular, it has hardly been added to steel plates using the DC butt welding method. However, in the steel sheet having the composition according to the present invention, the hardness increase of the welded portion is not so large even if these additions are performed, and the effect of suppressing the softening of the weld heat affected zone and the strength improving effect can be obtained without any trouble. it can. The reason for this is not clear, but it is considered to be due to the synergistic action related to the precipitates generated by the combined addition of Cr, Ti, and Nb as described above. The above effect can be obtained by adding Mo, V, or B alone or by adding two or more kinds in combination.
If the content of Mo and V is less than 0.03% and the content of B is less than 0.0002%, the effect is not remarkable, while the content of Mo and V is 0.5.
%, B, even if the content exceeds 0.0050%, the effect is saturated and the cost only increases. Therefore, the Mo content is 0.03 to 0.5% (preferable range 0.03 to 0.2%), and the V content is 0.03 to 0.5% (preferable range 0.03 to 0.2%).
About content 0.0002-0.0050% (suitable range 0.0005-
0.001%).

<Cu, Ni> Cu and Ni are components added as necessary because they have a function of improving the corrosion resistance of the steel sheet. Of these, Cu is a component that we want to use in preference to Ni because it is cheap, but when Cu is added alone,
Since it causes "checking flaws", it is necessary to add Cu in combination with Ni.
If it is less than 0.1%, the effect is not sufficient, while in any case
Since it is not necessary to contain more than 0.5%, Cu, Ni
The content was set to 0.1 to 0.5% in all cases.

<Ca, rare earth element> Ca, rare earth element (RE
In M), the sulfide-based inclusions are made spherical to make them harmless,
Since it has the effect of improving workability, especially stretch flangeability, it is a component added alone or in combination as necessary, but in the case of Ca less than 0.0005% and rare earth element
If the content is less than 0.005%, the above effect is not sufficient, while for Ca, 0.005% and for rare earth elements
Even if the content exceeds 0.015%, not only the effect is saturated, but also the oxide inclusions increase and the cleanliness of the steel deteriorates and the ductility and workability deteriorate. Therefore, the Ca content was set to 0.0005 to 0.005%, and the rare earth element content was set to 0.005 to 0.015%.

B) Manufacturing Conditions The steel sheet according to the present invention is provided with practically no problem even when manufactured according to ordinary hot rolling conditions. However, regarding the finishing temperature of hot rolling, precipitation strengthening of TiC It is preferable to set the temperature to 850 ° C. or higher because it can be used more effectively. The upper limit of the finishing temperature is not particularly limited, but about 930 ° C is sufficient.

Further, when the winding temperature is set low and a little controlled cooling is performed, the hardness distribution tends to be uniform.
This is because when the coiling temperature is set low, the reaction that the hard structure generated by cooling up to coiling softens due to the heat effect of welding, and "the solid structure does not precipitate due to cooling up to coiling and does not precipitate. It is considered that the "secondary hardening effect caused by the precipitation of Mo, V, etc." and the "hardness homogenizing effect described above" are synergistically exerted in the direction of further suppressing the hardness increase of the weld zone and the softening of the weld heat affected zone. To be

In this case, if the winding temperature exceeds 550 ° C., the above effect cannot be fully enjoyed, while 400
Even when wound at a temperature below 0 ° C, the effect is not further improved. The cooling rate from the end of hot rolling to the winding is preferably 15 ° C./s or more in average cooling rate.

Of course, even if the manufacturing conditions of the hot-rolled steel sheet excluding the conditions relating to the composition of the raw steel do not always fall within the above-mentioned range, they will pose a serious problem in practice unless they are manufactured under conditions far apart from each other. Characteristic defects do not occur, and if the above manufacturing conditions are satisfied, the characteristics will be slightly improved, uniformed,
It cannot be said that it shows a preferable range in which stabilization can be achieved.

Next, the present invention will be described with reference to examples.

Example First, steel pieces having the composition shown in Tables 1 and 2 were melted according to a conventional method.

[0035]

[Table 1]

[0036]

[Table 2]

Subsequently, after heating these steel slabs, hot rolling was performed so that the finishing temperature was between 850 and 950 ° C., and after the hot rolling was completed, the steel was water-cooled to the winding temperature shown in Table 3 and then wound. I took it. Next, 0.5 to 1% on each steel plate after winding
Tempered and then pickled with normal hydrochloric acid (descaling
) To obtain a product steel plate (2.6 mm thick).

[0038]

[Table 3]

Then, a JIS No. 5 tensile test piece was sampled from each hot-rolled steel sheet produced in this manner, and the tensile strength was measured. A roll bending test (test piece width of 160 mm) and a hardness distribution measurement (Hv5k) were carried out on a sample obtained by lab DC butt welding of these hot rolled steel plates with a small welding machine.
g) was carried out.

The results are also shown in Table 3. From the results shown in Table 3, the hot-rolled steel sheet according to the present invention is 65 kg / m.
It has a high tensile strength of m ² or more, a low bending crack length ratio of the welded portion, and a small value of ΔHv. Therefore, the hot-rolled steel sheet according to the present invention has sufficient strength, DC butt weldability, and workability after welding even as a wheel rim material for automobiles, for which the required performance has become more severe. You can confirm that. On the other hand, in the comparative steel sheet whose composition does not satisfy the conditions specified in the present invention, a high value is obtained in strength, but the characteristics in terms of DC butt weldability and workability after welding are not sufficient. .

[0041]

[Summary of Effects] As described above, according to the present invention,
It is possible to stably provide high-strength hot-rolled steel sheets having a high tensile strength of 65 kg / mm ² or more and excellent DC butt weldability and post-weld workability, and various types such as wheel rims for automobiles. An extremely useful effect in industry is brought about, such as being able to greatly contribute to the performance improvement of members.

Claims (5)

[Claims] 1. A weight ratio of C: 0.06 to 0.12%, Si: 0.3% or less, Mn: 1.0
~ 2.0%, P: 0.03% or less, S: 0.005% or less,
Cr: 0.10 to 0.70%, Al: 0.01 to 0.05%, Ti: 0.02
~ 0.08%, Nb: 0.01 ~ 0.06%, N: 0.0015 ~ 0.080%
In addition to containing Mo: 0.03 to 0.5%, V: 0.
03-0.5%, B: 0.0002-0.0050% at least, with the balance being Fe and unavoidable impurities, DC butt weldability is good and high after-weld workability. Strength hot rolled steel sheet. 2. By weight ratio, C: 0.06 to 0.12%, Si: 0.3% or less, Mn: 1.0
~ 2.0%, P: 0.03% or less, S: 0.005% or less,
Cr: 0.10 to 0.70%, Al: 0.01 to 0.05%, Ti: 0.02
~ 0.08%, Nb: 0.01 ~ 0.06%, N: 0.0015 ~ 0.080
%, Cu: 0.1 to 0.5%, Ni: 0.1 to 0.5%, and Mo: 0.03 to 0.5%, V: 0.03 to 0.5
%, B: 0.0002 to 0.0050% at least, with the balance being Fe and inevitable impurities, and high strength hot rolling with good DC butt weldability and excellent post-weld workability. steel sheet. 3. C: 0.06 to 0.12% by weight, Si: 0.3% or less, Mn: 1.0
~ 2.0%, P: 0.03% or less, S: 0.005% or less,
Cr: 0.10 to 0.70%, Al: 0.01 to 0.05%, Ti: 0.02
~ 0.08%, Nb: 0.01 ~ 0.06%, N: 0.0015 ~ 0.080%
In addition to containing Mo: 0.03 to 0.5%, V: 0.
03-0.5%, B: 0.0002-0.0050%, 1 or more, Ca: 0.0005-0.005%, rare earth element: 0.005-0.0
A high-strength hot-rolled steel sheet having good DC butt weldability and excellent post-weld workability, which is characterized by containing at least one of 15% and the balance being Fe and inevitable impurities. 4. C: 0.06 to 0.12% by weight, Si: 0.3% or less, Mn: 1.0
~ 2.0%, P: 0.03% or less, S: 0.005% or less,
Cr: 0.10 to 0.70%, Al: 0.01 to 0.05%, Ti: 0.02
~ 0.08%, Nb: 0.01 ~ 0.06%, N: 0.0015 ~ 0.080
%, Cu: 0.1 to 0.5%, Ni: 0.1 to 0.5%, and Mo: 0.03 to 0.5%, V: 0.03 to 0.5
%, B: 0.0002 to 0.0050%, one or more kinds, and Ca: 0.
0005 to 0.005%, rare earth element: 0.005 to 0.015%, including at least one kind, and the balance consisting of Fe and unavoidable impurities, good DC butt weldability and excellent post-weld workability High strength hot rolled steel sheet. 5. A steel slab having the composition as set forth in any one of claims 1 to 4 is hot-rolled at a finishing temperature of 850 ° C. or higher and 4
A method for producing a high-strength hot-rolled steel sheet having good DC butt weldability and excellent post-weld workability, which comprises descaling after winding at 00 to 550 ° C.