JPH066738B2 - Method for producing high-strength unequal thickness unequal thick section steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is directed to the production of high-tension unequal-sided unequal-thickness section steel consisting of a thick-walled flange part and a thin-walled web part Regarding the method.

[Conventional technology]

As a method for manufacturing shaped steel having uneven thickness sides such as uneven thickness uneven angle chevron steel, there is a method as disclosed in JP-A-53-55458. Here, for the purpose of preventing bending during conveyance after finishing rolling, during cooling, and after cooling, facilitating short length processing, and further facilitating long cooling long processing, shapes with unequal thickness sides During hot rolling of steel, the primary forced cooling is performed so that the temperature of the thick part becomes equal to that of the thin part at the time of finish rolling, and then, within the cross section of the thick part and the thin part, to the temperature at which plastic deformation does not occur. The secondary forced cooling is performed so that the temperature becomes uniform.

[Problems to be solved by the invention]

However, according to the method as described above, the unequal thickness unequal thick section steel, which has a complicated sectional shape and is likely to cause uneven temperature in the product section, is subjected to primary forced cooling to perform thick rolling and thin rolling during finish rolling. It is very important to adjust the forced cooling by equalizing the temperatures of the two parts, and then performing the second forced cooling until the temperature at which plastic deformation does not occur and making the temperature in the cross section of the thick and thin parts uniform. It requires carefulness and is not always preferable in actual operation.

Therefore, the present inventors have conducted studies to solve the above-mentioned problems, focused on the thick portion to facilitate temperature control by cooling, and can manufacture a high-strength unequal-unequal-thickness shaped steel. Came to

[Means and Actions for Solving Problems]

The present invention is, as the first invention, C: 0.03 to 0.18%, S
i: 0.02-0.60%, Mn: 0.6-2.0%, balance Fe and unavoidable impurities in the balance are hot-rolled to produce a non-equal unequal-thickness section steel consisting of a thick flange and a thin web. In doing so, the rolling finish temperature was set from 650 ° C to the upper limit of the non-recrystallization temperature region, the flange part was forcibly cooled at the stage of rolling, and the temperature of the flange part and the web part were made almost the same after rolling. Subsequently, the flange part and the web part are both acceleratedly cooled to 450 to 600 ° C. at 5 to 50 ° C./sec and then air-cooled, which is a method for producing a high-strength unequal-thickness unequal-thickness section steel. High tension which contains V: 0.15% or less, Nb: 0.15% or less, Cu: 0.5% or less, Ni: 0.5% or less, if necessary, in the same manner as in the above first invention, and is similarly treated It is a manufacturing method of unequal thickness unequal thick section steel. Furthermore, as a third invention, in contrast to the first invention, Al: 0.
005 to 0.1%, Ti: 0.003 to 0.025%, B: 0.0010% or less, N: 0.010% or less, and a method for producing a high-strength unequal thickness unequal thick section steel. , Second,
It is a composite component system of the third invention.

The reasons for limiting the components in the present invention are described below. C has the effect of improving the strength of steel and is an inexpensive element, but if it is less than 0.03%, the desired strength cannot be obtained, while 0.18%
If it exceeds, the weldability will be significantly deteriorated.

Si has the effect of deoxidizing molten steel and imparting strength, but if it is less than 0.02%, the effect does not fully appear. On the other hand, if it exceeds 0.60%, the cleanliness of the steel deteriorates, and the weldability and toughness decrease. Mn has the effect of improving the strength and ductility of steel,
Moreover, it is an inexpensive element following C, but if it is less than 0.6%, its effect is not sufficiently exhibited. On the other hand, if it exceeds 2.0%, the weld hardening becomes remarkable.

In the second invention, Nb and V improve the strength by precipitation hardening of the carbonized product (Nb also improves toughness), but when it exceeds 0.15%, the hardening saturates. No further improvement can be expected.

Further, Cu and Ni also have an effect of improving strength (Ni also improves toughness).

Ni is an expensive element, and is 0.5% or less from the viewpoint of economy.

If the Cu content exceeds 0.5%, the weld cracking susceptibility increases, so the Cu content was set to 0.5% or less.

In the third invention, Al contributes to the improvement of the toughness of the welded portion by the deoxidizing action of molten steel and the refining action of crystal grains.

Ti has the effect of improving the toughness of the weld and suppressing the weld hardening. That is, in the welding heat affected zone, the hardening of the welding heat affected zone is suppressed by reducing the free N and preventing the γ particles from coarsening due to the pinning effect of TiN.

If it is less than 0.003%, the above effect is not sufficiently exhibited, and if it exceeds 0.025%, the toughness of the weld heat affected zone is deteriorated.

B has a function of compensating for the strength reduction of steel, but when it is contained in excess, solid solution B promotes weld hardening, so it was made 0.0010 or less.

N is an essential element for effective use of TiN,
When the content exceeds 0.010%, free N begins to exist and the toughness deteriorates, so the content was made 0.010% or less. The fourth invention is a composite component system of the second and third inventions, and the action and effect of each element are the same as those described above. Next, the reasons for limiting the rolling finish temperature, accelerated cooling temperature, and accelerated cooling rate will be described.

In the present invention, it is necessary to set the rolling finish temperature to 650 ° C. to the upper limit value of the uncrystallized temperature region (generally higher than the Ar ₃ temperature). This is due to the accelerated cooling treatment that is performed immediately after that, by which the structure of the steel is further refined into ferrite particles, and the ferrite and bainite structures that replace the ferrite and pearlite structures are formed.

In this case, the rolling finishing temperature, that is, the accelerated cooling start temperature is limited as shown in FIG. 1 because the yield point is 42 Kg steel (T.S56 to 70 Kgf / mm ² ) and the yield point is 40 Kg steel ( T.S54 ~ 65Kgf / mm ² ).

As a comparative material, a rolled material that was not subjected to accelerated cooling but treated under the same conditions was used, but it was difficult to obtain a tensile strength (TS) of 54 Kgf / mm ² or more.

In the present invention, the lower limit of the rolling finish temperature is set to 650 ° C., as shown in FIG.
This is because the TS is about the same and the effect of accelerated cooling disappears.

Further, the upper limit is set to the upper limit of the non-recrystallization temperature region. If the upper limit is exceeded, it becomes difficult to refine the structure of the steel, and it is difficult to obtain the high-tensile-strength steel targeted by the present invention. Is.

Next, in the present invention, it is necessary to forcibly cool the thick flange portion at the stage of rolling so that the temperature of the flange portion and the temperature of the web portion become substantially the same at the end of rolling.

As shown in FIG. 3, the shape of the unequal thickness unequal thickness steel targeted by the present invention is complicated. The figure shows an unequal side unequal side unequal thick angle steel 1, which is composed of a thick flange portion 2 and a thin web portion 3. If the flange portion 2 and the web portion are cooled in the same manner during rolling, the dimensions will be
With a test piece of about 400 x 100 x 13/18, a temperature difference of 70 to 90 ° C occurs between the flange and the web. Therefore, the strength level in the product cross-section is different, leading to non-uniformity. Therefore, in the present invention, the flange portion is forcibly cooled so that the flange portion and the web portion have substantially the same temperature at the end of rolling.

Further, in the present invention, the cooling stop temperature for accelerated cooling of the flange portion and the web portion needs to be 450 to 600 ° C. This is Fig. 4
As shown in (a), the elongation (EL) deteriorates significantly below 450 ° C, and the cooling strain of the product increases. If the temperature exceeds 600 ° C, the effect of accelerated cooling is small. Also, as shown in (b), TS shows a high value of about 4.0 to 9.0 Kgf / mm ² in the range of the cooling stop temperature in the range of 450 to 600 ° C, compared with the comparative material. Here, the vertical axis represents ΔTS = TS material of the present invention (accelerated cooling) -comparative material (as rolled).

The cooling rate of accelerated cooling in the present invention is 5 to 50 ° C /
Although it depends on the material, thickness, etc., the time is set to 5 seconds.
If it is less than / sec, accelerated cooling has no effect, and if it exceeds 50 ° C / sec, cooling distortion occurs and problems such as bending occur.

〔Example〕

Examples of the present invention will be shown below. FIG. 5 is an explanatory view showing a row of shaped steel rolling equipment used in the method of the present invention. Crude steel piece 4
After being heated in the heating furnace 5, rough rolling is performed by the breakdown rolling mill 6, and caliber rolling proceeds along the rolling line 12 below. That is, the rough rolling mill 7, the intermediate finishing rolling mill 8 and the finishing rolling mill 9 form the crude billet 4 into a shaped steel as shown in FIG. Here, 10 is a cooling device. Immediately after exiting the finishing mill 9 of the shaped steel, only the flange portion thereof is accelerated and cooled by the accelerated cooling device 11. On the other hand, the web portion is air-cooled. 13 is a surface temperature measuring device.

(First Experimental Example) An experimental example in which an unequal-height unequal thick angle section steel as shown in FIG. 3 is manufactured by a shaped steel rolling apparatus train as shown in FIG. 5 will be described.

In the method of the present invention, four kinds of steel as shown in Table 1 were used.
The rolling conditions are shown in Table 2 and the results are shown in Table 3. In this case, the dimensions of the material of the present invention and the comparative material were 400 × 100 × 13/18 mm.

As is clear from Table 3, in the case of the materials of the present invention, the TS specifications of the target standard were satisfied in all cases, whereas in the case of the comparative materials, satisfactory results could not be obtained.

(Second Experimental Example) Next, from the steel types used in the first experimental example, type C was selected, and the rolling finish temperature of the flange portion was set to an Ar ₃ temperature (about 760 ° C) or less by the same row of shaped steel rolling equipment. Experiments were conducted at 650 ° C or higher. The rolling conditions in that case are shown in Table 4, and the results are shown in Table 5.

In this case, the dimension of the material of the present invention was 300 × 90 × 13/17.

As is clear from Table 5, as in the first experimental example It was possible to obtain a predetermined high-strength unequal thickness unequal thickness steel.

FIG. 6 shows the tensile strength according to position of the material of the present invention and the comparative material. The material of the present invention used steel type C No. 5. Here, (a) is the case of the material of the present invention, and (b) is the case of the comparative material. (c)
The figure shows the measurement positions of unequal thickness unequal thick angle steel. (In the figure) ~;
Corresponds to)-; in (a) and (b). As is clear from this, in the material of the present invention, the difference in tensile strength depending on the positions of the flange portion and the web portion is about 1.2 Kgf / mm ² , which is considered to be homogeneous, whereas the comparative material has a level of strength. Differently, it shows that the product cross section is inhomogeneous.

Further, as shown in FIGS. 7 (a) and 7 (b), the hardness distribution in the circumferential direction of the angle steel is examined. In the case of the present invention material of FIG. Compared with the hardness Hv (10K
It can be seen that the difference in g) is small. The positions of the abscissas in FIGS. (a) and (b) are straight lines from the web end to the end of the flange portion at the position of the unequal thickness unequal thick angle steel shown by the arrow in FIG.

〔The invention's effect〕

According to the method of the present invention, it is possible to easily manufacture a high-strength unequal-thickness section steel in which the thick-walled flange section and the thin-walled web section are provided with uniform high strength and high hardness in the unequal-section unequal-thickness section steel. It is an invention that can be made and has a very high value in industry.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the rolling finish temperature (the same as the accelerated cooling start temperature) of the flange of the present invention and the tensile strength, and FIG. 2 is another rolling finish temperature of the flange of the present invention (accelerated cooling start). Diagram showing the relationship between tensile strength and temperature)
FIG. 3 is a cross-sectional view showing an example of the shaped steel according to the present invention, and FIG. 4 shows the relationship between the cooling stop temperature and the difference in elongation and tensile strength (according to the present invention material-comparative material) of the accelerated cooling of the flange portion of the present invention. FIG. 5 is an explanatory view showing a row of shaped steel rolling equipment used in the method of the present invention, FIG. 6 is a view showing tensile strength by position of the material of the present invention and a comparative material, and FIG. 7 is a material of the present invention. It is a figure which shows the hardness distribution of the circumference direction with a comparative material. DESCRIPTION OF SYMBOLS 1 ... Unequal unequal thick angle steel, 2 ... Flange part, 3 ... Web part, 4 ... Crude billet, 5 ... Heating furnace, 6 ... Breakdown rolling mill, 7 ... Rough rolling mill, 8 ... Intermediate finishing rolling mill, 9 ... Finishing rolling mill, 10 ... Cooling device, 11 ... Acceleration cooling device, 12 ... Rolling line, 13 ... Surface temperature measuring device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Mukai 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Stock Company (72) Inventor Masataka Suga 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Mari Okada, Internal Examiner of the Steel Pipe Stock Company

Claims (4)

[Claims] 1. C: 0.03 to 0.18%, Si: 0.02 to 0.60%,
Mn: 0.6 to 2.0%, the balance Fe and unavoidable impurities are hot-rolled to produce a unequal-thickness unequal-thickness section steel consisting of a thick flange portion and a thin web portion. From 650 ℃ to the upper limit of the non-recrystallization temperature range,
The flange part is forcibly cooled at the stage of rolling so that the temperature of the flange part and the web part are almost the same at the end of rolling, and then both the flange part and the web part are heated to 450 to 600 ° C.
A method for producing a high-strength unequal-thickness unequal-thickness section steel, which comprises accelerating cooling up to 50 ° C / sec and then air-cooling. 2. C: 0.03 to 0.18%, Si: 0.02 to 0.60%,
Mn: 0.6 to 2.0%, one or more of V: 0.15% or less, Nb: 0.15% or less, Cu: 0.5% or less, Ni: 0.5% or less, with the balance being Fe and unavoidable impurities steel hot The rolling finish temperature is 650 when rolling to produce unequal-thickness unequal-thickness shaped steel consisting of a thick flange portion and a thin web portion.
℃ to the upper limit of the non-recrystallization temperature range, the flange part is forcibly cooled at the stage of rolling, the temperature of the flange part and the web are almost the same at the end of rolling, and then the flange part and the web part are both A method for producing a high-strength unequal-thickness unequal-thickness section steel, which comprises performing accelerated cooling at 450 to 600 ° C at 5 to 50 ° C / sec and then performing air cooling. 3. C: 0.03 to 0.18%, Si: 0.02 to 0.60%,
Mn: 0.6 to 2.0%, Al: 0.005 to 0.1%, Ti: 0.00
Steel containing 3 to 0.025%, B: 0.0010% or less, N: 0.010% or less, the balance being Fe and unavoidable impurities is hot-rolled to obtain an unequal edge composed of a thick flange portion and a thin web portion. Rolling finish temperature is set to 650 when manufacturing equi-thick shaped steel.
℃ to the upper limit of the unrecrystallized temperature range, the flange part is forcibly cooled at the stage of rolling, the temperature of the flange part and the web part are almost the same at the end of rolling, and then the flange part and the web part are Both are accelerated cooling at 450 to 600 ° C. at 5 to 50 ° C./sec, and then air cooled, which is a method for producing a high tensile unequal thickness unequal thick section steel. 4. C: 0.03 to 0.18%, Si: 0.02 to 0.60% M
n: 0.6 to 2.0%, Al: 0.005 to 0.1%, Ti: 0.003
.About.0.025%, B: 0.0010% or less, N: 0.010% or less, further V: 0.15% or less, Nb: 0.15% or less, Cu: 0.
5% or less, Ni: 0.5% or less at least, and the balance is Fe and unavoidable impurities steel is hot-rolled to form a thick flange portion and a thin web portion. When manufacturing steel, the rolling finish temperature was set from 650 ° C to the upper limit of the unrecrystallized temperature range, the flange part was forcibly cooled during the rolling process, and the temperature of the flange part and the web were made almost the same at the end of rolling. Then, the flange part and the web part are both acceleratedly cooled to 450 to 600 ° C. at 5 to 50 ° C./sec, and then air-cooled, which is followed by air cooling.