KR20060042036A - High strength cold rolled steel sheet and method for manufacturing the same - Google Patents

Abstract

The present invention is, in mass%, C: 0.015% or less, Si: 1.5% or less, Mn: 0.4 to 3%, P; 0.15% or less, S; 0.02% or less, sol.Al; 0.1-1%, N; 0.01% or less, Ti; It relates to a high strength cold rolled steel sheet having 0.2% or less and the balance made of Fe and unavoidable impurities, and at the same time satisfying 1≤ ([Ti] / 48) / ([C] / 12 + [N] / 14). Here, [M] represents content (mass%) of the element M. The high strength cold rolled steel sheet of the present invention has excellent deep drawing property at TS of 340 to 590 MPa, and therefore is suitable for automobile parts that are difficult to form, such as side outer panels and door inner panels.

Description

High strength cold rolled steel sheet and its manufacturing method {HIGH STRENGTH COLD ROLLED STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME}

Fig. 1 is a diagram showing the relationship between the amount of sol.Al, the r value, and TS.

Fig. 2 is a diagram showing the relationship between [Si] + 10 × [P] and the r value.

The present invention relates to a high strength cold rolled steel sheet used in automobiles, home appliances, and the like, in particular, a high strength cold rolled steel sheet having excellent deep drawing moldability having a tensile strength (TS) of 340 to 590 MPa and a method of manufacturing the same.

Conventionally, in automobile parts such as side outer panels or door inner panels, which are difficult to form, IFs having excellent deep drawing moldability with TS of about 270 MPa and r values of 1.8 to 2.0 are known. Interstitial Free Soft Cold Rolled Steel Sheets (SPC270E, F) have been used. In recent years, as the demand for automobile body weight has increased, the application of IF high strength cold rolled steel sheet having a TS of 340 to 590 MPa has been advanced. However, these parts are produced in high-strength cold-rolled steel sheets with TS of 340 to 390 MPa and r value of about 1.7, high-strength cold rolled steel of TS around 440 MPa and r value of about 1.5, and TS of about 590 MPa and r value of When forming using a high strength cold rolled steel sheet of about 1.0, since cracks are likely to occur at the drawing portion, any high strength cold rolled steel sheet has been applied only to a drawing component having a relatively low degree. Accordingly, a high strength cold rolled steel sheet having a higher r value at TS of 340 to 590 MPa is required. Specifically, an r value of TS of 340 to 400 MPa and 1.8 or more and a TS of 400 to 590 MPa and 1.6 or more, preferably 1.7 or more are desired.

Until now, as a method for increasing the r value, C or N is reduced as much as possible, and it is wound up at a temperature of 680 ° C. or higher after hot rolling using an IF steel in which Ti or Nb is added in a large amount. It is known to reduce N as much as possible, to coarsen precipitates, and to promote the formation and growth of recrystallized grains having a texture favorable for r value upon annealing. As a similar method, Japanese Patent Application Laid-Open No. Hei 6-108155 and Japanese Patent No. 3291639 reduce C and N as much as possible, form Ti (C, S) by using Ti-added IF steel to produce an r value at annealing. A method of developing advantageous aggregates is disclosed.

However, in the method disclosed in Japanese Patent Laid-Open No. 6-108155, a soft cold-rolled steel sheet having a TS of 260 to 300 MPa is used, and a high strength cold rolled steel sheet of IF having a TS of 340 MPa or more in which a large amount of P or Mn is added. When applied to, the r value decreases significantly due to the large amount of Pn (phosphorous compounds) such as Fe-Ti-P and Fe-Nb-P at the grain boundary during winding after hot rolling. do. In addition, in the method disclosed in Japanese Patent No. 3291639, a high strength cold rolled steel sheet for deep drawing having a TS of 340 MPa or more in which P is added in a large amount is proposed, but the non-uniformity in the plate thickness direction due to casting segregation of P during press forming Cracks due to tissues may occur.

On the other hand, a method of improving the r value by focusing research on the manufacturing method has also been proposed. For example, Japanese Patent Laid-Open No. Hei 7-188776 discloses a method of performing filamentous rolling while lubricating in the α region during hot rolling. Japanese Patent Laid-Open No. 9-279249 discloses a method of applying 1 to 50% of rolling in a temperature range of 550 to 750 ° C during annealing. Japanese Unexamined Patent Publication No. 2001-131643 discloses a method of controlling the amount of Si, Mn, and P of Nb and B additive steel, adding 0.3 ~ 5% rolling after pickling, cold rolling, and annealing, and then pickling again and sending it to a hot dip galvanizing line. It is.

However, none of these methods require special manufacturing processes, resulting in an increase in manufacturing cost and a decrease in productivity. That is, in the method of Japanese Patent Laid-Open No. Hei 7-188776, recrystallization annealing of hot-rolled steel sheet rolled in α region is required. In the method of Japanese Patent Laid-Open No. 9-279249, a rolling facility capable of withstanding high temperatures in an annealing furnace is required. In the method of Unexamined-Japanese-Patent No. 2001-131643, it is necessary to carry out pickling, annealing, and temper rolling twice each.

An object of the present invention is a high strength cold rolled steel sheet having a TS of 340 to 400 MPa and an r value of 1.8 or more, a TS of 400 to 590 MPa and an r value of 1.6 or more, preferably 1.7 or more, without requiring a special manufacturing process, and its It is to provide a manufacturing method.

The said objective is mass%, C: 0.015% or less, Si: 1.5% or less, Mn: 0.4-3%, P; 0.15% or less, S; 0.02% or less, sol.Al; 0.1-1%, N; 0.01% or less, Ti; 0.2% or less and the balance are made of Fe and unavoidable impurities, and at the same time achieved by a high strength cold rolled steel sheet satisfying the following formula (1).

1? ([Ti] / 48) / ([C] / 12 + [N] / 14)... (One)

Here, [M] represents content (mass%) of the element M.

In addition, the high strength cold rolled steel sheet is a steel slab having the above composition, a step of heating after the steel slab is heated to 1080 ~ 1350 ℃ to a record temperature of (Ar ₃ transformation point -20) ~ (Ar ₃ transformation point +150) ℃ The process of hot rolling to form a hot rolled steel sheet, the process of winding the hot rolled steel sheet at a coiling temperature CT (coiling temperature) that satisfies Equation (5) below, and the cold rolled hot rolled steel sheet at 50 to 90% rolling rate To form a cold rolled steel sheet and a continuous annealing of the cold rolled steel sheet at 750 to 870 ° C, or a box annealing at 600 to 750 ° C.

480 ≤ CT ≤ 580 + 0.17 / {([Ti] + 0.08 × [sol. Al]) × [P]}. (5)

Here, [M] represents content (mass%) of the element M.

The present inventors investigated the influence of various alloying elements on the r value of an IF high strength cold rolled steel sheet, and obtained the following knowledge.

I) If the amount of sol.Al is added in a larger amount than in the case of the conventional high strength cold rolled steel sheet, the r value is remarkably improved. In particular, this effect is remarkable when 0.4% or more of Mn is added.

Ii) Addition of Si and P is effective for improving r value.

Iii) P, sol.Al. A high r value is obtained by optimizing the amount of Ti and, if necessary, Nb and the coiling temperature after hot rolling.

The present invention has been made based on such knowledge, and details thereof will be described below.

1) sol. Al amount and r value

In order to investigate the relationship between the sol.Al amount and the r value, the following test was conducted.

C: 0.002%, Si: 0.25%, P: 0.08%, S: 0.007%, Nb: 0.015%, Ti: 0.03%, N: 0.002%, B: 0.001%, and the amount of sol.Al is 0.01 Steel slab with 1.2% of Mn and 0.6% to 1.8% was heated to 1250 ° C, followed by hot rolling to form a hot rolled steel sheet with a thickness of 3mm, and simulation of winding at 580 ° C for 1 hour. Simulated heat treatment was performed. The hot rolled steel sheet was cold rolled to form a cold rolled steel sheet having a thickness of 0.75 mm, followed by continuous annealing at 820 ° C. for 60 seconds to perform temper rolling with 0.7% elongation. And r value and TS were measured by the following method.

A JIS 5 test piece was taken in a rolling direction, in a 45 ° direction with respect to the rolling direction, in a 90 ° direction with respect to the rolling direction, and the r value and TS of each direction were measured and in the surface of the steel sheet represented by the following equation. The average value was calculated | required.

Mean = ([T ₀ ] +2 [T ₄₅ ] + [T ₉₀ ]) / 4

Here, [T ₀ ] in the rolling direction, [T ₄₅ ] in the 45 ° direction with respect to the rolling direction, and [T ₉₀ ] is the r value or TS in the 90 ° direction with respect to the rolling direction.

1 shows the relationship between the amount of sol.Al, the r value, and TS. In the figure, black circles are the result when the Mn amount is 1.8%, and white circles are the result when the total amount of sol.Al and Mn is 1.8%.

When the Mn amount is 1.8%, the r value becomes 1.6 or more at 0.1% or more, and is 1.7 or more at 0.2 to 0.7%, and decreases when it exceeds 0.7%. TS has a sol.Al of more than 460 MPa at 0.1% or more and sol. It increases monotonously with Al amount.

At this time. The increase in TS per 1% of sol.Al amount is 35MPa. This is almost equivalent to the solid solution strengthening ability of Mn. When the total amount of sol.Al and Mn is 1.8%, the relationship between the TS and r values is obtained when the intensity like the white circle is kept constant. From this, it can be seen that by adding sol.Al and reducing Mn, a higher r value can be obtained at the same intensity.

In addition, when sol.Al exceeds 1%, fine AlN precipitates at the austenite grain boundary during continuous casting of the slab to embrittle grain boundaries, and cracks are generated on the surface of the slab during bending correction of the slab or subsequent rough rolling. It becomes easy. As a result of such cracks on the surface of the slab, surface defects of scale property tend to occur, and the surface quality of the final product is significantly reduced.

From the above results, even if TS exceeds 400 MPa, when the amount of sol.Al is set to 0.1 to 1%, preferably 0.2 to 0.7%, a high r value of 1.6 or more, preferably 1.7 or more can be obtained.

The reason why a high r value can be obtained when the amount of sol.Al is set to 0.1 to 1% is considered to be as follows. That is, since Al is an element that raises the Ar ₃ transformation point, after the transformation from austenite to ferrite during hot rolling, the precipitation of carbides is promoted in the high temperature α region, the solid solution C decreases and the carbides coarsen. Therefore, at the time of annealing, a preferable recrystallized texture is formed for the r value, and the r value is improved. In addition, it is estimated that the change of the cold rolling structure by Al also contributes to the improvement of r value.

2) Si, P amount and r value

In order to investigate the relationship between Si and P amount and r value, C: 0.002%, Mn: 1%, S: 0.007%, sol.Al: 0.25%, Nb: 0.02%, Ti: 0.01%, N: 0.002 %, B: The same test as in the case of 1) was carried out using a steel slab made constant at 0.001%, Si amount of 0.005 to 1.5%, and P amount of 0.003 to 0.15%.

 2 shows the relationship between [Si] + 10 × [P] and the r value. In addition, the number in a figure shows Si amount.

In the present invention steel having an amount of sol.Al of 0.25%, it can be seen that a high r value of 1.7 or more is obtained when the following formula (2) is satisfied.

0.3? [Si] + 10 x [P]? (2)

Here, [M] represents content (mass%) of the element M.

However, since the amount of Si and 10xP exceeds 1.5% and the value of r is largely deteriorated, the amount of Si and P is made 1.5% or less and 0.15% or less, respectively.

In the case where hot-dip galvanizing is applied to the high-strength cold-rolled steel sheet of the present invention, these elements are likely to cause poor adhesion of plating. Therefore, the Si content is preferably 0.5% or less and the P content is 0.08% or less. In addition, since Si and P are effective elements for solid solution strengthening of ferrite, it is preferable to make Si amount 0.003% or more and P amount 0.01% or more.

3) Other ingredients

C; C combines with Ti or Nb to form carbides. If the amount exceeds 0.015%, the amount of this carbide increases and the r value is significantly lowered. Therefore, the amount of C is 0.015% or less, preferably 0.008% or less, and more preferably less than 0.004%. However, since C is TiC and NbC, it is effective to increase the strength by precipitation strengthening. Therefore, it is effective to contain at least 0.004% of TS in steel before and after 440 MPa. That is, when the amount of C is made 0.004 to 0.008% and Ti and Nb are added 1.0 or more in the atomic ratio with C, the fall of r value can be suppressed and the strength can be increased. In the case where the amount of C is less than 0.0005%, the ferrite grains coarsen at the time of annealing, so that surface peeling tends to occur at the time of press molding, so the amount of C is preferably 0.0005% or more. .

Mn: Mn is an element that increases strength by solid solution strengthening, and is indispensable for high strength cold rolled steel sheet of IF. In order to obtain TS of 340 MPa or more, the amount of Mn needs to be 0.4% or more. On the other hand, if the amount exceeds 3%, the r value is remarkably lowered, so the Mn amount is 3% or less, preferably 2% or less, and more preferably 1.5% or less.

The reason why the r value decreases when the amount of Mn increases is not necessarily clear, but it is thought that Mn interacts with the solid solution C to lower the r value. In addition, since Mn lowers the Ar ₃ transformation point, the carbide precipitated at the time of hot rolling is refined, or the precipitation of carbide is delayed to increase the solid solution C. Therefore, a preferable recrystallization texture for r value is not formed during annealing. , r value is inferred.

S: S is present in steel as a sulfide. If the amount exceeds 0.02%, ductile deterioration is caused, so the amount of S is made 0.02% or less, preferably 0.01% or less. Moreover, it is preferable to make S amount into 0.004% or more from a viewpoint of descale property.

N; When the amount of N exceeds 0.01%, fine AlN, NbN, and Nb (C, N) precipitate at the austenite grain boundary during continuous casting of the slab, embrittle the grain boundary, and at the slab surface at the time of slab casting or subsequent rough rolling Cracks are likely to occur. For this reason, N amount may be 0.01% or less. The smaller the amount of N, the better. However, in the current steelmaking technology, the limit is about 0.001%.

Ti: Ti has an effect of refining grains after hot rolling, or forming precipitates with C or N to reduce solid solution C and N to improve r value. In order to fully exhibit such an effect of Ti, it is necessary to add Ti so that following formula (1) may be satisfied.

1? ([Ti] / 48) / ([C] / 12 + [N] / 14)... (One)

Here, [M] represents content (mass%) of the element M.

However, even if the amount of Ti exceeds 0.2%, there is little increase in the r value, so the amount of Ti is made 0.2% or less. Moreover, when alloying hot dip galvanizing is performed on the high strength cold rolled steel sheet of this invention, it is preferable to make Ti amount into 0.04% or less from a viewpoint of preventing plating nonuniformity. In addition, in order to reliably obtain the high r value by Ti addition, it is preferable to make Ti amount into 0.005% or more.

The balance is Fe and unavoidable impurities.

In addition to the above components, addition of 0.002% or more of Nb is preferable for obtaining a higher r value. In this case, it is necessary to adjust the amounts of Nb, Ti, C, and N so as to satisfy the following formula (3).

 1≤ ([Nb] / 93 + [Ti] / 48) / ([C] / 12 + [N] / 14)... (3)

Here, [M] represents content (mass%) of the element M.

However, when the amount of Nb exceeds 0.02%, fine NbN and Nb (C, N) precipitate at the austenite grain boundary during continuous casting of the slab, embrittle grain boundaries, and at the slab surface during slab casting and subsequent rough rolling. Cracks are likely to occur. Therefore, Nb amount is made into 0.02% or less.

In addition, if B is added in an amount of 0.0001% or more, the secondary workability resistance is improved. However, when the amount of B exceeds 0.003%, the effect of improving secondary work brittleness is small, on the contrary, the r value is lowered and the rolling load is increased. Therefore, the amount of B is made into 0.003% or less.

In addition, Cu: 0.03 to 0.5%, Ni: 0.03 to 0.5%, Cr: 0.03 to 0.5%, Mo: 0.05 to 0.3%, in order to further increase the strength, improve the secondary processing brittleness, and improve the r value. And V: at least one element selected from 0.005 to 0.5% can be added. At this time, Cu and Cr deteriorate the surface quality, so the amount thereof is 0.5% or less. Since addition of Ni will increase cost significantly, the quantity shall be 0.5% or less. Mo is effective in increasing the strength while having a low adverse effect on the secondary workability, but the yield is increased to decrease the surface precision of the press part, so the amount is 0.3% or less. V also has a small adverse effect of secondary processing brittleness and is effective for high strength, but if it exceeds 0.5%, the cost increases significantly, so the amount is made 0.5% or less. Moreover, when Cu is added, it is preferable to contain Ni and Cu equivalent.

In order to improve the appearance of zinc plating, the adhesion of zinc plating, the fatigue properties, the toughness of the drawing part during press molding, and the like, at least one element selected from Sb: 0.002 to 0.2% and Sn: 0.002 to 0.2% is contained. It is effective to satisfy Eq. (4).

0.002 ≦ Sb + Sn / 2 ≦ 0.2... (4)

Here, [M] represents content (mass%) of the element M.

By adding Sb and Sn, surface nitriding during slab heating, coiling, annealing with an annealing furnace (BAF), a continuous annealing line (CAL), a continuous hot dip galvanizing line (CGL), and the like Oxidation is prevented and plating nonuniformity and deterioration of plating adhesiveness are improved. In addition, adhesion of zinc oxide in the zinc bath is prevented, and the appearance of plating is improved. In addition, surface oxidation is reduced in Sb and Sn to suppress deterioration of fatigue characteristics and toughness after drawing molding.

However, if the amount exceeds 0.2% for both Sb and Sn, the galvanized adhesiveness and toughness deteriorate.

4) Manufacturing method

The high strength cold rolled steel sheet of the present invention, the step of heating a steel slab having the component in the 1080 ~ 1350 ℃, a steel slab after heating to a temperature history of (Ar ₃ transformation point -20) ~ (Ar ₃ transformation point +150) ℃ A process of hot rolling to form a hot rolled steel sheet; a process of winding the hot rolled steel sheet with a coiling temperature CT that satisfies Equation (5) below when Nb is added, and when Nb is added; In the manufacturing method having a process of cold rolling the hot rolled steel sheet after winding at a reduction ratio of 50 to 90% to form a cold rolled steel sheet; Is manufactured.

480 ≦ CT ≦ 580 + 0.17 / {([TI] + 0.08 × [sol.Al]) × [P]}. (5)

480 ≤ CT ≤ 580 + 0.17 / {(0.6 × [Nb] + [Ti] + 0.08 × [sol.Al]) × [P]}. (6)

Here, [M] represents content (mass%) of the element M.

The steel slab needs to have a heating temperature SRT before hot rolling of 1080 ° C or more in order to sufficiently solidify the P-containing Fe-Ti-P and Fe-Nb-P produced in the slab. However, the surface quality deteriorates when it exceeds 1350 degreeC, and SRT needs to be 1350 degreeC or less.

In order to obtain an excellent appearance, it is preferable to sufficiently remove not only the primary scale but also the secondary scale generated during hot rolling. In hot rolling, it is also possible to perform heating by a bar heater.

Spirit temperature FDT of hot rolling, it is necessary to in order to refine the structure after hot rolling (Ar ₃ transformation point -20) ~ (Ar ₃ transformation point +150) ℃.

The winding temperature after hot rolling has a great influence on the r value of the cold rolled steel sheet of this invention which adds Al, P, Ti, and Nb as needed. This is because, in the P-added IF steel, undesirable P-types of Fe-Ti-P and Fe-Nb-P are easily formed in the r-value as described above. In general, the r value is remarkably improved when the winding temperature is set to a high temperature to coarsen the precipitate and at the same time reduce the solid solution C. However, when the coiling temperature is set to a high temperature exceeding the proper temperature, the above-mentioned P fluoride is formed, and the r value is significantly lowered.

Therefore, as a result of investigating the optimum winding temperature for various Al, P, Ti and steel to which Nb is added as needed, when the winding temperature CT is Nb free, 580 + 0.17 / {([TI] + 0.08 × [sol.Al]) × [P]}, or 580 + 0.17 / {(0.6 × [Nb] + [Ti] + 0.08 × [sol.Al]) × [P]} when Nb is added, When exceeded, it turned out that a pide produces | generates and r value falls remarkably. On the other hand, if the coiling temperature CT is lower than 480 ° C, even if P carbide is not produced, precipitation of carbides at the time of winding will be insufficient, and the r value will deteriorate. Therefore, the coiling temperature CT needs to satisfy the above formula (5) or (6).

Moreover, it is preferable to wind up in the temperature range of (upper limit -40)-(upper limit) degreeC of said Formula (5) and (6).

In hot rolling, it is necessary to make the reduction ratio 50 to 90%, preferably 65 to 80% from the viewpoint of improving the r value.

When annealing temperature AT is continuously annealed by CAL or CGL, it is necessary to set it as 750-870 degreeC. At temperatures lower than 750 ° C, recrystallization becomes insufficient, and a high r value is not obtained stably. Moreover, characteristics, such as elongation, remarkably deteriorate. At temperatures exceeding 870 ° C, the steel sheet having a large amount of Mn is annealed beyond the Ar ₃ transformation point, and the strength is extremely increased, and the elongation and n value are significantly deteriorated. In order to acquire higher r value and high elongation stably, it is preferable to anneal at the temperature of 820 degreeC or more. In the case of annealing in BAF, the annealing time is long, so the annealing temperature AT needs to be 600 to 750 ° C.

The cold-rolled steel sheet after annealing can be plated with zinc by electroplating or hot-dip plating, if necessary. Examples of the plating containing zinc include zinc plating, zinc alloyed plating, and zinc-nickel alloy plating. It is also possible to give an organic coating treatment after plating.

Example

Steel No. shown in Table 1 A-X steels were continuously cast into a slab of 230 mm thickness after solvent. After reheating the slab with the heating temperature SRT shown in Table 2, the slab was hot rolled to a plate thickness of 3.2 mm with the finishing temperature FDT shown in Table 2, and wound up with the coiling temperature CT shown in Table 2. The hot rolled sheet was cold rolled to a plate thickness of 0.8 mm and then annealed by CAL, CGL, and BAF at the annealing temperature AT shown in Table 2, and tempered by 0.8% elongation. 1 to 34 were produced. In CGL, the steel sheet after annealing was immersed in a hot dip galvanizing bath at 460 ° C, and then alloyed at 500 ° C in an in-line alloying furnace. The plating amount per side was 45 g / m ² per side.

And r value and TS were measured by the method mentioned above. In addition, surface defects were visually inspected to investigate surface quality.

The results are shown in Table 2.

In Table 1 and Table 2, [Nb] in the uppermost formula is 0 when Nb is not added.

In the steel sheets No. 1 to 24 which are examples of the present invention, an r value of TS of 340 to 400 MPa and 1.8 or more, an r value of 1.6 or more of TS of 400 to 590 MPa is obtained, and the surface quality is also good. In addition, it can be seen that the r value of the example of the present invention is remarkably high as compared with the comparative example of the same strength. In particular, the effect is remarkable when the Mn amount exceeds 1%.

On the other hand, in steel sheets Nos. 25 to 34 that are comparative examples, r values of TS of 340 to 400 MPa and 1.8 or more, and r values of TS of 400 to 590 MPa and 1.6 or more are not obtained. Steel plate No. corresponding to the conventional high strength cold rolled steel sheet with high Mn amount. The r value is low at 27, 28, and 29. In addition, in steel plate No. 30, 31, 32, 33, 34, (Nb + Ti) / (C + N) ratio, C, Si, Mn, P, sol.Al, Nb are respectively r as outside the scope of this invention. The value is low. Among them, in the steel sheet No. 30 corresponding to the conventional low carbon high strength cold rolled steel sheet in which the amount of C and the (Nb + Ti) / (C + N) ratio are not optimized and the solid solution C and Mn coexist, even if so.Al is increased. You cannot get a high r value. In addition, the steel sheet No. which Nb, Nb, and sol.Al are outside the scope of the present invention. At 31 and 34, surface quality deteriorates.

Moreover, the steel plate No. corresponded to the conventional soft cold rolled steel sheet SPC270F. Compared with 25 and steel plate No. 26 to which a large amount of sol.Al was added, it turns out that r value improvement effect is small even if sol.Al is added when Mn and P amount are low.

According to the present invention, a high strength cold rolled steel sheet having a TS of 340 to 400 MPa and an r value of 1.8 or more and a TS of 400 to 590 MPa and an r value of 1.6 or more, preferably 1.7 or more can be obtained without requiring a special manufacturing process. have. Since the high strength cold rolled steel sheet has excellent deep drawing property at TS of 340 to 590 MPa, it is suitable for automobile parts that are difficult to form, such as side outer panels and door inner panels.

Claims (13)

By mass%, C: 0.015% or less, Si: 1.5% or less, Mn: 0.4-3%, P; 0.15% or less, S; 0.02% or less, sol.Al; 0.1-1%, N; 0.01% or less, Ti; A high strength cold rolled steel sheet having 0.2% or less and the balance made of Fe and unavoidable impurities and at the same time satisfying the following formula (1); 1? ([Ti] / 48) / ([C] / 12 + [N] / 14)... (One) Here, [M] represents content (mass%) of the element M. The method of claim 1, High-strength cold rolled steel sheet, characterized in that by mass%, sol.Al: 0.2-0.7%. The method of claim 1, High strength cold rolled steel sheet characterized by satisfying the following formula (2); 0.3? [Si] + 10 x [P]? (2) Here, [M] represents content (mass%) of the element M. The method of claim 2, High strength cold rolled steel sheet characterized by satisfying the following formula (2); 0.3? [Si] + 10 x [P]? (2) Here, [M] represents content (mass%) of the element M. The method of claim 1, A high strength cold rolled steel sheet containing Nb: 0.002 to 0.02% by mass and satisfying the following formula (3); 1≤ ([Nb] / 93 + [Ti] / 48) / ([C] / 12 + [N] / 14)... (3) Here, [M] represents content (mass%) of the element M. The method of claim 4, wherein A high strength cold rolled steel sheet containing Nb: 0.002 to 0.02% by mass and satisfying the following formula (3); 1≤ ([Nb] / 93 + [Ti] / 48) / ([C] / 12 + [N] / 14)... (3) Here, [M] represents content (mass%) of the element M. The method of claim 1, A high strength cold rolled steel sheet, characterized by further comprising B: 0.0001 to 0.003% by mass. The method of claim 6, A high strength cold rolled steel sheet, characterized by further comprising B: 0.0001 to 0.003% by mass. The method of claim 1, In mass%, at least one element selected from Cu: 0.03-0.5%, Ni: 0.03-0.5%, Cr: 0.03-0.5%, Mo: 0.05-0.3%, and V: 0.005-0.5% is further added. High strength cold rolled steel sheet, characterized in that it contains. The method of claim 8, In mass%, at least one element selected from Cu: 0.03-0.5%, Ni: 0.03-0.5%, Cr: 0.03-0.5%, Mo: 0.05-0.3%, and V: 0.005-0.5% is further added. High strength cold rolled steel sheet, characterized in that it contains. The method of claim 1, A high strength cold rolled steel sheet containing at least one element selected from Sb: 0.002 to 0.2% and Sn: 0.002 to 0.2% by mass and simultaneously satisfying the following formula (4); 0.002 ≦ Sb + Sn / 2 ≦ 0.2... (4) Here, [M] represents content (mass%) of the element M. The method of claim 10, A high strength cold rolled steel sheet containing at least one element selected from Sb: 0.002 to 0.2% and Sn: 0.002 to 0.2% by mass and simultaneously satisfying the following formula (4); 0.002 ≦ Sb + Sn / 2 ≦ 0.2... (4) Here, [M] represents content (mass%) of the element M. The process of heating the steel slab which has a composition of any one of Claims 1-12 to 1080-1350 degreeC, The process of the steel slab after said heating, (Ar ₃ transformation point -20) ~ (Ar ₃ transformation point + 150) hot rolling the hot-rolled steel sheet to a temperature history of ℃ and, Winding the hot rolled steel sheet with a winding temperature CT that satisfies the following formula (5) or (6); Cold rolling the hot rolled steel sheet after the winding at a reduction ratio of 50 to 90% to form a cold rolled steel sheet, A method for producing a high strength cold rolled steel sheet having a step of continuously annealing the cold rolled steel sheet at 750 ° C. to 870 ° C. or annealing at 600 ° C. to 750 ° C .; 480 ≤ CT ≤ 580 + 0.17 / {([Ti] + 0.08 x [sol. Al]) x [P]}. (5) 480 ≤ CT ≤ 580 + 0.17 / {(0.6 × [Nb] + [Ti] + 0.08 × [sol.Al]) × [P]}. (6) Here, [M] represents content (mass%) of the element M.

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