KR101281412B1 - Heating method having improved surface quality - Google Patents

Abstract

The present invention is a heating method of a wire rod for improving the surface quality when the copper (Cu) content is high when compared to the existing blast furnace material in the furnace process for hot rolling of the wire rod, more specifically, Cu and Si By controlling the content and the temperature during operation, there is provided a method of operating a furnace furnace for improving the surface quality.
To this end, the heating method of the wire rod of the present invention, by weight%, C: 0.03 to 0.5%, Si: 0.03 to 0.5%, Cu: 0.03 to 0.4%, the wire containing a balance Fe and other impurities, Cu content In the case of 0.03 to 0.2%, the temperature range during the furnace operation is 1050 to 1170 ° C, and when the Cu content is 0.2 to 0.4%, the temperature during the furnace operation and the content of Cu and Si are 460≤temperature × It is a technical subject matter to heat so that the relation of weight% of temperature x Cu / weight% of <= 2500 may be satisfied.

Description

Heating method for improving wire quality {HEATING METHOD HAVING IMPROVED SURFACE QUALITY}

The present invention relates to a heating method of wire rods for improving the surface quality when the copper (Cu) content is high when compared with conventional blast furnace materials in the furnace process for hot rolling, and more specifically, Cu and Si By controlling the content of and the temperature during operation, the present invention relates to a heating method of a wire rod, the surface quality is improved.

In order to diffuse chromium carbide, etc. in steel or improve high temperature rolling property, or to remove segregation and a large carbide from bearing steel and free cutting steel, it is necessary to heat at high temperature in a heating furnace for a long time.

However, in general, since the scale increases as the temperature is increased and the exposure time is longer, when the heating is performed at a high temperature for a long time as described above, the thickness of the scale increases.

In addition, the scale is known to decrease when the temperature and exposure time are lowered, the oxygen ratio is lowered, or a reducing atmosphere is maintained. Reducing the inside of the furnace to a reducing atmosphere is a traditional scale reduction method, but there is a problem in that fuel consumption is high because oxygen is insufficiently supplied.

As an improvement method, JP2000-399521 and JP1995-166207 used a method of lowering the fraction of oxygen and inducing a reduction reaction by supplying hydrogen and the like from the outside while maintaining the closed atmosphere of the heating furnace. However, the above patents for making a shielding device at the inlet / outlet and supplying a reducing gas have a problem that it cannot be used in an existing furnace and the device needs to be improved. There is a problem that a supply device and a line facility are required.

In recent years, in the case of bearing steel, diffusion technology has been popularized in the heating furnace, and scale loss has played an important role in improving the error rate. It is suggested to increase the rough rolling temperature by increasing the temperature of the heating furnace by reducing the high temperature rolling property as one way. As a result, high temperature operating conditions are required, and scale loss has a great influence on the error rate of bearing steel and free-cutting steel. Due to this phenomenon, the development of technology to reduce scale loss at high temperature is more important than before. It is true.

If there is an additional element, another oxide is also produced. For example, in the case of Cr used as an additional element of steel, a single layer oxide film of Cr ₂ O ₃ is formed. This oxide film has the effect of improving the corrosion resistance by acting as a protective film, but the separation of the oxide film occurs at a high temperature, and thus loses its role as a protective film. It is known that Cr oxide loses the role of the film in the heating furnace which temperature is maintained above 900-1000 degreeC.

When Cu is contained in steel, Cu becomes liquid at high temperatures and penetrates into surface cracks and austenite grain boundaries of the steel, causing brittleness of the surface, which is called hot shortness.

In order to prevent such heat resistance, the Cu content is conventionally controlled as low as possible, and in the case of a furnace operation of a material with a high Cu content, it has been avoided by avoiding the control over 1100 ° C.

The present invention is to solve the above problems, in order to be able to manage at a high temperature during the operation of the furnace even when the Cu content is relatively high, by controlling the operating conditions of the furnace according to the content of Cu, Si, descaling It provides a heating method of the wire rod after the surface quality is improved.

As a means for realizing this, the heating method of the wire rod which the surface quality which concerns on this invention is improved,

By weight, wires containing C: 0.03 to 0.5%, Si: 0.03 to 0.5%, Cu: 0.03 to 0.4%, balance Fe and other impurities, and Cu content of 0.03 to 0.2% (excluding 0.2) In the case of the furnace operation, the temperature range is 1050 to 1170 ° C., and when the Cu content is 0.2 to 0.4%, the temperature and the content of Cu and Si during the furnace operation are 460 ≦ temperature × temperature × Cu% by weight / It is a method of heating so as to satisfy the relational formula of weight% ≤ 2500 of Si.

Moreover, it is preferable that the said wire rod contains 1 or more types chosen from the group which consists of Cr: 1.5% or less (except O) and B: 0.005% or less (except O).

By using the heating method of the wire rod of the present invention, there is an effect that the occurrence of cracks due to de-spreading by the solid solution Cu is reduced by 10% or more without large modification or change of the existing heating furnace.

1 is a photograph taken at a magnification of 200 times using the surface flaw optical microscope of Comparative Example 1 (A) and Example 2 (B) of the inventive example.

Hereinafter, the present invention will be described in detail.

First, the steel composition of this invention is demonstrated. The content of each element below represents weight percent.

It is preferable to make content of carbon (C) into 0.03 to 0.5%.

The carbon diffuses into the oxide-metal interface and reacts with FeO to form CO. The presence of CO creates a void at the oxide-metal interface, reducing the adhesion of the scale. Therefore, an empty space is created. If there is an empty space but there is no crack in the scale, the generation speed of the scale is slowed. In addition, when the temperature and the carbon content is high, the gas pressure increases in the empty space, causing cracks on the scale, and the metal is directly exposed to the furnace atmosphere, thereby increasing the scale generation rate.

Since there are few wire products having a carbon content of 0.03% or less, and a product having a carbon content of 0.5% or more, there is almost no surface quality deterioration due to scale, so the present invention is applied to a wire rod having a carbon content of 0.03 to 0.5%.

The content of silicon (Si) is preferably 0.03 to 0.5%.

Si reacts with oxygen diffusing into the steel to form SiO ₂ precipitates at the oxide-metal interface. SiO ₂ particles form Fe ₂ Si ₄ (fayalite) to reduce the scaling rate. However, as Fayalite melts at 1171 ° C as the temperature increases, the protective properties disappear and the oxidation rate rapidly increases. If the Si content is less than 0.03%, the effect of Si oxides generated in the furnace on the entire scale cannot be obtained. If the content is more than 0.5%, the scaling rate decrease due to the production of Fayalite reaches saturation. In the case of cold-rolling steel, which is the main use of the steel, to which the present invention is applied, cold rolling may be degraded.

The content of copper (Cu) is preferably 0.03 to 0.4%.

Cu is similar in Ni in that it is not extracted at the oxide-metal interface, but does not cause scale sticking problems like Ni. When the concentration of Cu in the metal oxide is 8% or more, a Cu-plus phase precipitates. This phase melts at 1095 ° C. to form a layer between the metal and the oxide, causing hot shortness, resulting in surface defects. When Cu is added at less than 0.03%, surface quality deterioration hardly occurs due to the Cu content, and when Cu is added at 0.4% or more, the lower the physical properties of the product, the greater the surface quality improvement through the scale control set forth in the present invention. There is no meaning.

By controlling the content of Cu and Si so as to satisfy the relationship with the temperature as follows, it is possible to obtain the effect of improving the surface quality after descaling.

In the case where the Cu content is added in an amount of 0.03 to 0.2%, the temperature range of the furnace operation is preferably 1050 to 1170 ° C.

When the Cu content is added at 0.03 to 0.2%, it was confirmed that the surface quality deteriorates in the temperature range where Cu is not present in the liquid phase. If Cu is present in the solid phase, re-diffusion occurs in the known phase in the heating furnace, and thus the surface quality is deteriorated. That is, when the localized region of the surface is heated to about 1000 ° C., the solubility of Cu increases to about 5%. As the scale is generated, Cu concentrated on the scale and the Fe interface dissolves into Fe. Therefore, near the surface, the concentration of Cu increases compared to the inside, so that a solid solution effect occurs on the surface, and the strength increases on the surface compared to the inside of the wire. For example, the increase in Cu solubility in the ferrite phase is reported to be 12,000 psi / wt% = 83 MPa. This strength imbalance at the inside and the surface may cause processing imbalance during rolling, which may cause cracking. When the wire is further heated to 1100 ° C. or more, Cu is present in the liquid phase, and this effect is alleviated to reduce the amount of cracking.

Moreover, when Cu content is 0.2 to 0.4%, it is preferable to satisfy | fill 460 <=% of temperature x temperature xCu of weight% / Si of weight% <= 2500.

If the Cu content is 0.2 ~ 0.4%, the surface quality deteriorates as the furnace temperature increases. However, when Si content is increased, this phenomenon is alleviated. Fayalite produced by adding Si melts around 1150 ℃ and cracks are generated between scales. Prevents redness from occurring.

In the present invention, in addition to the above elements, at least one of Cr and less than 1.5% and B and less than 0.005% is preferably included.

The content of chromium (Cr) is preferably 1.5% or less.

Cr does not affect the oxidation rate when it is present as a residual element in the steel, but in stainless steel, a stable protective film Cr ₂ O ₃ is formed to increase the oxidation resistance. However, when the Cr content is added more than 1.5%, it is possible to precipitate chromium carbide inside the wire rod, which may affect the structure of the wire rod, and because it shows a different scale behavior than the above-described scale behavior, The content of Cr in the invention is preferably 1.5% or less.

The content of boron (B) is preferably 0.005% or less.

Unlike chromium, boron concentrates on the surface without forming oxides, thereby preventing the diffusion of oxygen or Fe ions, thereby reducing oxidative properties. However, when 0.005% or more is added, the physical properties of the steel are deteriorated, so it is preferable to set it to 0.005% or less.

Hereinafter, the present invention will be described in detail through examples.

[Example]

Steel grades having the composition as shown in Table 1 below were sampled and heated to the temperature of Table 1, and then the number of surface defects was examined to determine the effect of controlling the content of Cu and Si and the temperature of the heating furnace.

Cu Si Temperature (℃) Temperature × [Cu] / [Si] Preferred Temperature Range for Cu Content Surface flaw count
(number / cm) Comparative Example 1 0.09 0.05 1000 - 1050 ~ 1170 ℃ 59 Example 1 0.14 0.05 1150 - 1050 ~ 1170 ℃ 29 Example 2 0.04 0.04 1100 - 1050 ~ 1170 ℃ 23 Example 3 0.09 0.2 1130 - 1050 ~ 1170 ℃ 18 Example 4 0.1 0.2 1100 - 1050 ~ 1170 ℃ 21 Comparative Example 2 0.2 0.05 1120 4480 460 ~ 2500 ℃ 49 Example 5 0.2 0.3 1200 800 460 ~ 2500 ℃ 31 Example 6 0.3 0.2 1230 1845 460 ~ 2500 ℃ 34 Example 7 0.4 0.3 1200 1600 460 ~ 2500 ℃ 23

The number of surface flaws in Table 1 represents the number of surface flaws having a depth of 10 μm or more, regardless of the type. Comparing Comparative Example 1 and Examples 1 to 4, it can be seen that the effect of the present invention when the Cu content is 0.03 to 0.2%. In Comparative Example 1, the number of surface flaws is 59, whereas Examples 1 to 4. Although 4 was operated at a higher temperature than Comparative Example 1, it was confirmed that the number of the surface defects of 50% or less of the Comparative Example.

In addition, when comparing Comparative Example 2 and Examples 5 to 7, it can be seen that the effect of the present invention when the Cu content is 0.2 ~ 0.5%, in the case of Comparative Example 1, the number of scratches is 49, 5 to 7 had a value of 31 or less, and it was confirmed that they had a much smaller number of surface defects even though they were operated at a high temperature compared with the comparative example.

Through the results of the above embodiment, it can be seen that according to the heating method of the present invention, the occurrence of cracks due to the back diffusion of the solid solution Cu existing at the scale interface is reduced by 10% or more.

In order to better show the results, the surface of Comparative Example 1 and Example 2 is shown in Fig. 1, as can be seen in Fig. 1, when the conditions of the present invention is satisfied, the number of surface flaws is much smaller It can be seen that the quality is improved.

Claims (2)

By weight, the wire rod containing C: 0.03 to 0.5%, Si: 0.03 to 0.5%, Cu: 0.03 to 0.4%, balance Fe and other impurities is operated by heating when the Cu content is 0.03 to 0.2%. When the temperature range is 1050 to 1170 ° C and the Cu content is 0.2 to 0.4%, the temperature and the content of Cu and Si during the furnace operation are 460≤% by weight of temperature x Cu /% by weight of Si≤2500. A method of heating wire rods in which the surface quality of heating to satisfy the relational expression is improved.
The method according to claim 1,
The wire rod is a method of heating a wire rod is improved surface quality comprising at least one selected from the group consisting of Cr: 1.5% or less (excluding O) and B: 0.005% or less (excluding O).

Images