JPS5818406B2 - Aruiha Kotaino Seizouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a low yield point hot rolled steel plate or steel strip (hereinafter simply referred to as steel plate) having a yield point of 20 Kfm2 or less.

When low-yield point hot-rolled steel sheets are used as small-diameter pipes for electrical conduits, steel furniture, and other weakly overhanging parts, they are prone to buckling when bending the pipes, ``beaks'', ``sinks'', or ``sinks'' during press working. It is a steel plate with good shape fixability that does not easily cause galling.

In addition, cold rolling is used in many applications, such as reducing the power required for cold rolling.

Conventionally, low-yield point hot-rolled steel sheets are made by melting low-carbon rimmed steel or capped steel, forming ingots, soaking, and blooming, and after cleaning the slab surface with hot and cold solvents, it is heated in a heating furnace. 1200-130
The material was heated to 0°C, and after rough rolling, the temperature was adjusted by delaying it on the finish rolling front table, and then hot finish rolling was performed at a temperature where the finish exit temperature was just below the Ar3 point, and then it was rolled at the highest possible temperature. It manufactured low yield point hot rolled steel sheets.

The above method has the disadvantage that the heating furnace consumes a large amount of fuel since it is heated at a high temperature before hot rolling, and the production cost is high.

Furthermore, when hot finish rolling is carried out at a finishing temperature of Ar 3 or lower, if the temperature difference between the longitudinal and width directions of the steel plate is large, it is difficult to stably obtain a low yield point of 20 Ky/mm2 or less in the longitudinal and width directions of the steel plate. It has disadvantages such as:

The purpose of the present invention is to provide a method for stably producing low-carbon rimmed steel or capped hot-rolled steel sheet with a low yield point of 20 Ky/mm2 or less, or a low yield point and low yield point elongation, with low smoke. It's there to do.

As a result of various studies, the present inventors found that c
0.0% or less, Mn 0.40% or less, the balance Fe and unavoidable impurities are melted, and after blooming, the surface defects of the hot steel billet are removed with a hot solvent, without being charged into a heating furnace. By immediately hot rolling (hereinafter referred to as the direct rolling method), we were able to lower the fuel consumption rate of the heating furnace and also succeeded in producing a low yield point steel sheet with excellent quality.

In addition, in hot rolling, the finish exit temperature is set to 3 points Ar or less, 80
The temperature is 0 to 860°C, and the winding temperature is 600°C or higher.

Also, if there are no flaws on the surface of the hot steel piece, there is of course no need to use a hot or cold solvent.

Furthermore, the depth of surface defects in hot steel sheets is mostly 1 mrrL or less, and if the amount of hot solvent is 0.1 to 5.0 mm, the surface condition of the steel sheet is good.

In addition, when carrying out the present invention, an intermediate heating device for lightly heating the widthwise end portions of the steel plate by gas burner heating or induction heating before hot finish rolling may be optionally provided as necessary.

In other words, if the rolling line is long and there is a large cooling difference between parts of the steel material due to high-pressure water from the cooling water and scale removal equipment, or if there are other quality requirements, only the edges of the steel plate where the temperature drop is particularly large should be lightly heated. This has the effect of making the quality of the steel material uniform in the longitudinal and width directions, but it goes without saying that the intermediate heating device is not required if this is not necessary.

In addition, by installing one or more thermometers in front of the gas burner heating device to predict the temperature difference in the length or width direction of the steel material, and heating only the parts of the steel material that need heating with gas, the temperature can be changed uniformly, and It is also effective in terms of energy conservation.

Next, the reason for the limitation in manufacturing the low yield point hot rolled steel sheet in the present invention will be further explained.

co, 10% or less, in order to increase the grain size of hot rolled steel sheets, it is necessary to lower C, and C is 0.10.
If it exceeds %, the steel plate becomes hard, the yield point becomes high, and workability such as elongation and bending becomes poor.

The lower limit can be appropriately selected depending on the decarburization ability.

Like C, Mn becomes hard when it exceeds 4o%, and it becomes hard at 20K.
It is difficult to replace hot rolled steel sheets with a low yield point of y/rnm2 or less.

The lower limit is not particularly limited, but it needs to be selected depending on the amount of S, etc., and if the amount of S is low, the Mn is also as low as possible, which is advantageous for producing a low yield point steel plate.

Finally, set the hot rolling finishing outlet temperature to 800 to 860 below Ar3 points.
C. If the temperature is less than 800.degree. C., the temperature is too low and the processed structure remains on the surface layer and widthwise edges of the hot rolled steel sheet, making the steel sheet hard and having an extremely high yield point.

On the other hand, when the temperature exceeds 860°C, the crystal grains of the steel sheet become fine-grained and it becomes difficult to reduce the yield point to 2.0 Kp/mm2 or less.

Furthermore, the reason why the winding temperature is set to 600°C or higher is that it is difficult to make the yield point 20'Kp/mm2 or less below 600°C.

Next, the invention will be explained according to an embodiment.

Example 1 The steel shown in Table 1 was melted in a 60-ton converter, and about 10 tons of steel ingots were made into hot steel billets through a blooming rolling process and hot-rolled by the usual method and the present method. , a 2.0 mm thick hot rolled steel plate was manufactured.

Table 2 shows the heating temperature and hot rolling temperature, and Table 31 shows the mechanical properties.

The customer test values are shown as a range of values at three locations in the width direction of the hot rolled steel plate: the head, center, and tail in the longitudinal direction.

In addition, in the method of the present invention, gas burner heating was also performed as temperature intermediate heating before hot finish rolling.

As is clear from Table 3, the method of the present invention has a yield point of 20 kg.
/mm2 or less, it is possible to produce a low yield point hot rolled steel sheet with a small yield point elongation, and the present invention is a practically extremely effective method in terms of energy saving and economics.

Claims (1)

[Claims] I C0.10% or less, Mn 0.40% or less, balance F
Steel consisting of E and unavoidable impurities is melted, then the surface is hot-solvented while it is in a hot billet state without forced cooling midway, and it is directly rolled without being charged into a heating furnace, and the finishing outlet temperature is lowered. Ar below 3 points 800-860℃, winding temperature 6
A method for producing a low-yield point hot-rolled steel sheet or copper strip, which is characterized by rolling at a temperature of 00°C or higher.