JPH03210901A - Rolling method of steel ingot by slight rolling-down - Google Patents

Abstract

PURPOSE:To improve productivity by rolling a steel ingot in a specified temperature range and by a specified draft at the time of the primary rolling of steel ingot. CONSTITUTION:At the time of the primary rolling of steel ingot, only the surface of material is rolled by slightly rolling down at 20-30 % draft when the temperature range of steel ingot is between the lowest temp. for recrystallization and th temp. higher than that temp. by 20 - 30 deg.C. In this way, the consumption unit of fuel with heating can be reduced, also rolling yield is improved, the limitation of assigned destination is few and productivity can be still more improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a steel ingot cast by a continuous casting method or a steel ingot method and processed into a slab, bloom, or billet by hot rolling. The present invention relates to a light reduction rolling method.

[Conventional technology]

In recent years, as the use of special steels and small lots and multiple sizes have progressed, in the rolling process, instead of rolling to the final product size, it is unavoidable for quality control and process control to perform two-heat treatment, that is, second heating. There is an increasing trend in the number of materials to be rolled that must be subjected to subsequent rolling, secondary rolling after secondary heating, and processing to produce finished products.

The general process flow when performing the above two heat treatments is as follows:
It is as shown in FIG. That is, in this flow, the steel ingot that has been subjected to secondary heating (■) is first subjected to secondary rolling (II). After performing this next rolling (n), shearing (
II) or as it is, by slow cooling (N') or cooling treatment (V) into cold pieces (■), and then again either directly, after cleaning (■), or after applying a heat insulator (■). Heating (secondary heating) (IX) 1. , and then subjected to secondary rolling (X) to obtain a finished product, which is a raw material for product rolling.

Regarding such a method, the technique disclosed in Japanese Patent Application Laid-open No. 128465/1984 is also known.

In the primary rolling in the above process flow, there is a method in which primary heating is performed at a relatively high temperature and primary rolling is performed at a high rolling reduction rate, that is, approximately 20 to 30%, and the process is held until the secondary rolling is performed. I've picked it up.

[Problem to be solved by the invention]

However, the conventional processing method described above has the following drawbacks.

■High thermal energy consumption is required for the above-mentioned primary heating (usually about 200 x 10!kcal/T is consumed).

(1)-Primary rolling: Usually, the cross-sectional area of the material is reduced because the material is first rolled to rough rolling dimensions, and there are restrictions on the applicable size when subjecting it to secondary rolling. That is, a product having a size larger than the short side dimension of the secondary rolling cross section cannot be supplied to the secondary rolling B.

■-During the next rolling, the rough rolled material is also stretched in the length direction, so if it is forced to be divided into two or three pieces due to handling constraints, this will result in a decrease in yield. .

In addition, the top and bottom crops occur at a high rate, and the yield is poor in this respect as well.

(2) Furthermore, the reduction in yield due to the necessity of performing secondary heating and secondary rolling cannot be ignored.

Therefore, the main purpose of the present invention is to provide a light reduction rolling method for steel ingots that can reduce the fuel consumption associated with heating, improve the rolling yield, have fewer restrictions on the distribution destination, and have excellent productivity. be.

[Means to solve the problem]

The above problem is that during the primary rolling of a steel ingot, when the temperature is within the range of the minimum temperature at which the steel ingot can be recrystallized and this temperature plus 20 to 30°C, only the material surface is rolled at a reduction rate of 20 to 30°C.
This can be solved by rolling with a light reduction in %.

[For production]

In the present invention, the steel material is primarily rolled at a low temperature that allows recrystallization, without heating, or with heating, so even if it is heated, the thermal energy required for heating can be reduced. Furthermore, since only the surface of the material is lightly rolled down and the deformation of the material is minimized as much as possible, the rate of occurrence of cropping is low and it is possible to prevent a decrease in yield due to multiple cuts. Moreover, since there are almost no restrictions on the distribution destination, subsequent processability is excellent, and furthermore, since secondary heating and secondary rolling are basically not performed, productivity is excellent.

[Specific structure of the invention]

The present invention will be explained in more detail below.

In the present invention, as shown in FIGS. 1 and 2, there are cases in which secondary heating is performed prior to subsequent rolling, and cases in which secondary rolling is directly performed without secondary heating.

That is, in the first example shown in Fig. 1, after the completion of casting, if the temperature drops below the recrystallization temperature of the steel ingot, the rolling start temperature will be raised to above the recrystallization temperature in a heating furnace or the like. 2
It is heated to a temperature range of 0 to 30°C or less, and rolled in that temperature range.

After rolling, an appropriate treatment method such as cooling, slow cooling, or immediate reheating preferably within 120 seconds is performed.

FIG. 2 shows a second example, in which after completion of casting, primary rolling is performed without heating when the temperature has not dropped below the recrystallization temperature of the steel ingot.

The subsequent processing can take any appropriate form as in the first example.

In the present invention, the rolling reduction ratio in the second rolling is 2
It is considered to be 0 to 30%. If it is less than 20%, the effect of refinement on the surface of the steel ingot will be low, and if it exceeds 30%, the elongation rate will increase, causing a decrease in yield.

Generally, the hot working characteristics of steel can be shown in FIG. 4, and it can be rolled in the blue brittle range of around 800°C and below 500°C.

In addition, as shown in Fig. 5, hot rolling is A at t1°C.
A material having a crystal grain size of E is cooled to a crystal grain size of E after several passes.

FIG. 6 shows the change in crystal grain size in relation to the material temperature and rolling reduction in the final bath. From this figure, it can be seen that in order to obtain the desired grain size in the conventional method, it is necessary to apply a reduction ratio of 20 to 30% in the second rolling.

Next, FIG. 7 shows the relationship with the cooling conditions after rolling.

Curve 1 shows the crystal grain size when heated to the same temperature and slowly cooled after forging, curve 2 shows the crystal grain size when heated to the temperature at each point and then slowly cooled, and curve 3 shows the crystal grain size when forged and then quickly cooled. show.

Based on the following findings, the inventor has determined that the micro-segregation countermeasure material is 1.
The material is heated to a temperature of about 150°C, and the other materials are subjected to primary rolling treatment at around the lower limit temperature at which they can be recrystallized without heating, by applying several passes or light reduction to only the surface, and using a cooling pattern as necessary. It is something to do.

〔Example〕

Next, the effects of the present invention will be clarified through examples.

(Example 1) A steel ingot having the steel components shown in Table 1 and having a recrystallization temperature of 800°C was obtained by continuous casting. The dimensions of the steel ingot are 670M in width and 600mm in thickness. Table 2 shows the casting conditions.

In addition, the steel ingots obtained by continuous casting were first rolled at a temperature of 1000°C without secondary heating to a width of 560 m.
m, and the thickness was rolled by light reduction to a thickness of 420 mm. Samples were taken at each position shown in Figure 8 of the thus obtained slab, and the metallographic structure was examined under a microscope. As the rolling temperature was in the high temperature range of 1000°C, it was found that penetration was observed on the surface. It was found that the metal structure of the metal structure was definitely refined.

(Example 2) When the relationship between the rolling temperature and the grain size of steel due to light reduction was investigated for various materials, the results shown in FIG. 3 were obtained.

(Example 3) On the other hand, when the method of the present invention was adopted for steel ingots made of various materials, the fuel consumption was 200 x 103 kcal/T in the case of no heating, in comparison with the conventional example. .

- When performing secondary heating, 100 x 103kcal/T
Reduced. In addition, the crop truncation amount was reduced by 0.2%.

The amount of scale was reduced by 0.5% in the case of no heating, and by 0.2% in the case of secondary heating.

〔Effect of the invention〕

As described above, according to the present invention, the fuel consumption rate associated with heating can be reduced, the rolling yield is improved, there are fewer restrictions on the distribution destination, and the productivity is improved.

[Brief explanation of drawings]

Figures 1 and 2 are graphs showing the light reduction rolling method according to the present invention in relation to billet temperature, Figure 3 is a correlation graph between rolling temperature and grain size, and Figure 4 is a graph showing the relationship between heating temperature and A graph showing the relationship between the ductility of steel, Figure 5 is a correlation graph between grain size and rolling temperature, Figure 6 is a correlation graph between rolling reduction, grain size and steel temperature in the final pass, and Figure 7 is a graph showing the relationship between grain size and rolling temperature. A correlation graph between temperature and grain size, FIG. 8 is a diagram showing sample collection positions in an example, and FIG. 9 is a conventional treatment flow diagram for steel ingots. Fig. 1 Fig. Fig. Fig. Time (Hrl Fig. Fig. Fig. 0C Fig. Fig. Fig. Reduction rate % Fig. Five friends C Fig.

Claims (1)

[Claims] (1) In the primary rolling of a steel ingot, when the temperature is within the temperature range between the minimum temperature at which the steel ingot can be recrystallized and this temperature plus 20 to 30°C, only the material surface is lightened at a reduction rate of 20 to 30%. A light reduction rolling method for steel ingots, characterized by rolling with reduction.