KR101907522B1 - Steel having superior crack resistance and deformation resistance - Google Patents

Abstract

The present invention relates to a steel used for a rapid cooling section roll used in a region where a steel sheet is quenched, and the present invention provides a steel material excellent in crack resistance and resistance to deformation by controlling the composition of the steel material can do.

Description

[0001] STEEL HAVING SUPERIOR CRACK RESISTANCE AND DEFORMATION RESISTANCE [0002]

The present invention relates to a steel used for a rapid cooling section roll used in an area where a steel sheet is quenched.

Generally, the cold rolling process is a process carried out in order to satisfy various conditions such as final thickness, hardness, roughness and shape control after pickling of a hot rolled material and belongs to the final stage in the production process of steel products. This is one of the most important processes for determining the quality of products.

In this cold rolling process, there is a rapid cooling zone for improving the strength of the cold-rolled steel sheet heated to a high temperature for the purpose of producing a high-strength steel sheet, and the rapid cooling zone includes a zone for rapidly cooling the cold- to be. The temperature of the cold-rolled steel sheet inserted into the rapid-cooling zone is high, and the cold-rolled steel sheet is rapidly cooled to a moderate temperature to ensure physical properties such as strength. At this time, the conveying of the cold-rolled steel sheet in the rapid cooling zone is performed by a rapid cooling section roll, which continuously contacts with the middle-temperature steel sheet, so that the lower part of the roll is maintained at a constant temperature, Is subjected to thermal shocks due to repeated heating and cooling, such as rapid cooling by scattering and dropping of cooling water periodically injected from the nozzles.

As described above, in consideration of the conditions applied to the rapid cooling zone roll, heat resistant steel excellent in thermal shock property has been used as the material of the roll. For example, a steel containing 0.05 to 0.15% of C, 19 to 22% of Cr, 31 to 35% of Ni, 0.5 to 1.5% of Nb, 1.5% or less of Mn and 1.2% (KHR32C) (non-patent reference 1), such a material has excellent properties in terms of elongation against cracking due to rapid expansion and contraction.

However, since the heat resistant steel as described above has excellent elongation, cracking can be minimized, but on the other hand, the steel has a low strength and is deformed by repeated thermal stress.

 www.kubotametal.com/alloys/heat_resist

An aspect of the present invention is to provide a steel material excellent in cracking and deformation resistance by satisfactory strength and ductility.

An aspect of the present invention is a method for producing a steel sheet comprising 0.17 to 0.25% of carbon (C), 19 to 22% of chromium (Cr), 31 to 35% of nickel (Ni) 1.5 to 2.5% of silicon (Si): 1.2% or less and sum of one or two selected from niobium (Nb) and vanadium (V), tungsten (W): 1 to 3%, rare earth (REM): 0.1 To 0.4%, yttrium (Y): 0.1 to 0.5%, balance Fe and unavoidable impurities.

According to the present invention, in addition to the components constituting the steel material applied to the conventional rapid cooling zone rolls and the like, addition of high temperature strength improving elements such as a rare earth metal and carbide forming elements can ensure high ductility while maintaining high temperature strength. It is possible to provide a steel material excellent in crack resistance and deformation resistance even under repeated thermal loads.

For the purpose of securing excellent physical properties such as strength of a cold-rolled steel sheet, a process of rapid cooling in a rapid-cooling zone during a cold rolling process is performed. At this time, a rapid cooling zone roll Is installed. In the rapid cooling zone, the heating and cooling of the cold-rolled steel sheet is repeated. As a result, the steel material for manufacturing the rapid cooling zone rolls should be a steel material capable of sufficiently absorbing the thermal shock condition.

Conventionally, heat resistant steel has been mainly used as a steel material for rapid cooling zone rolls. Such heat resistant steel has excellent elongation and cracking occurrence, but has a problem of being deformed by stress caused by repetitive heat load due to low strength.

As a result, the inventors of the present invention have made intensive studies to solve the above problems. As a result, the present inventors have found that control of additional components such as yttrium (Y) It is possible to obtain a steel material excellent in not only cracking but also deformation resistance, thereby completing the present invention.

Hereinafter, a steel material having excellent resistance to cracking and deformation resistance, which is one aspect of the present invention, will be described in detail.

The steel according to the present invention is characterized in that it comprises 0.17 to 0.25% of carbon (C), 19 to 22% of chromium (Cr), 31 to 35% of nickel (Ni) (Si): 1.2% or less, 1.5-2.5% of one or two kinds selected from niobium (Nb) and vanadium (V), 1 to 3% of tungsten (W) and 0.1 to 0.4% of rare earth (REM) , And yttrium (Y): 0.1 to 0.5%.

The content of chromium (Cr), nickel (Ni), manganese (Mn) and silicon (Si) is maintained in the range of the steel composition applied to the conventional rapid cooling zone rolls Non-Patent Document 1).

The reason for controlling the components as described above (hereinafter referred to as " weight% ") will be described in detail in the steel material as one aspect of the present invention.

C: 0.17 to 0.25%

Carbon (C) is an essential element that affects the strength improvement. If the content is less than 0.17%, the effect of improving the strength is insignificant. On the other hand, when the content exceeds 0.25%, the strength increases sufficiently, but the elongation rate is lowered, and the possibility of cracks is increased, and weldability at the time of welding with a roller shaft is poor.

Nb and V in a total amount of 1.5 to 2.5%

Niobium (Nb) and vanadium (V) combine with carbon (C) or nitrogen (N) to form carbides or nitrides. These carbides or nitrides contribute to improvement in tensile strength, yield strength and high temperature strength. Therefore, it is necessary to add one or two of these elements.

If the addition amount is less than 1.5%, the effect of improving the strength by precipitation strengthening and particle refinement is insignificant. On the other hand, if the addition amount exceeds 2.5%, the above-mentioned effect is saturated and the elongation rate is rather reduced.

W: 1 to 3%

Tungsten (W) is an element contributing to improvement of high-temperature strength together with Nb or V. When the content is less than 1%, the effect of improving tensile strength at high temperature is insignificant. On the other hand, if the content exceeds 3%, the strength improvement by W is sufficient, but the elongation rate is lowered to increase the risk of occurrence of cracks and weldability at the time of welding is also poor.

REM: 0.1 to 0.4%

Rare earth (REM) is added in order to prevent the lowering of the elongation due to the lowering of elongation according to the addition of Nb, V or W contributing to the improvement of the high-temperature strength. For this purpose, it is necessary to add rare earth to 0.1% or more, but if the content exceeds 0.4%, the strength may be excessively increased. The rare earth metals include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,

In the present invention, a commercially available rare earth metal can be used. The rare earth metal has a composition of 48 to 54% of cerium (Ce), 13 to 17% of neodymium (Nd) ): 24 to 28% and praseodymium (Pr): 13 to 17%.

In the present invention, it is preferable that the total content of the above-mentioned rare earth metals is 0.1 to 0.4%.

Y: 0.1 to 0.5%

Yttrium (Y) is an element which improves the strength without lowering the elongation due to the refinement effect of the metal crystal grains. When the content of Y is less than 0.1%, it is difficult to obtain the effect by the Y addition as described above, Is more than 0.5%, the elongation and strength are rather lowered, which is very disadvantageous in terms of cost.

The remainder is composed of Fe and unavoidable impurities.

The steel material satisfying the above-mentioned composition can secure sufficient strength and ductility, and is therefore excellent in cracking and deformation resistance.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

( Example )

Scrap and various alloying elements were dissolved in an atmospheric furnace to melt and cast a steel having the composition shown in Table 1 below. The casting temperature was set at 1550 ° C to produce a final metal cooling zone roll.

After the field tests were performed on each of the rapid cooling zone rolls prepared above, the lifetime of the rolls was evaluated based on the time when cracks or deformation of each rapid cooling zone roll occurred, and the results are shown in Table 1 below.

division C Cr Ni Mn Si Nb V W REM Y life span Conventional example 0.2 20 33 One 0.8 One 0.5 1.5 0.2 - × Inventory 1 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.1 ○ Inventory 2 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.3 ○ Inventory 3 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.5 ○ Comparative Example 1 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.05 △ Comparative Example 2 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.8 △ Comparative Example 3 0.2 20 33 One 0.8 One 0.5 1.5 0.2 0.9 △ Comparative Example 4 0.1 20 33 One 0.8 One 0.5 1.5 0.2 0.3 △ Comparative Example 5 0.2 20 33 One 0.8 One 0.5 0.5 0.2 0.3 △ Comparative Example 6 0.2 20 33 One 0.8 0.5 0.5 1.5 0.2 0.3 △ Comparative Example 7 0.2 20 33 One 0.8 One 0.5 4 0.2 0.3 △ Comparative Example 8 0.2 20 33 One 0.8 2.5 0.5 1.5 0.2 0.3 △ Comparative Example 9 0.2 20 33 One 0.8 One 0.5 1.5 0.05 0.3 △ Comparative Example 10 0.2 20 33 One 0.8 One 0.5 1.5 0.7 0.3 △

(X: poor,?: Normal,?: Excellent in the roll life evaluation)

As shown in Table 1, the rapid cooling zone rolls of Inventive Examples 1 to 3 which satisfied all of the component conditions proposed in the present invention were able to be used for a long time without deformation or cracking compared with the conventional example.

On the other hand, in Comparative Example 1, since the content of Y was too small, the effect of improving the life of the comparative example was small. In Comparative Examples 2 and 3, the amount of added Y was excessively excessive and the strength and ductility were lowered. The results were poor. Comparative Example 4 is a case where the content of C does not satisfy the range suggested by the present invention, and the effect of improving the life time is very small compared to the conventional examples. Comparative Examples 5 and 7 are examples in which the content of W is too small or too large, The effect of improving the life expectancy of the sample was very small. Also, in Comparative Examples 6 and 8, when the Nb content is too small or too large, the sum of Nb and V does not satisfy the present invention. In addition, even in the case of Comparative Examples 9 and 10 in which the REM content is less than the range suggested by the present invention, the effect of improving the service life is small compared with the conventional example.

Claims (2)

(C): 0.17 to 0.25%, chromium (Cr): 19 to 22%, nickel (Ni): 31 to 35%, manganese (Mn): 1.5% Si: 1.2% or less (excluding 0), 1.5-2.5% of a sum of one or two selected from niobium (Nb) and vanadium (V), tungsten (W) ): 0.1 to 0.4%, yttrium (Y): 0.1 to 0.5%, the balance Fe and unavoidable impurities.
The method according to claim 1,
The rare earth element (REM) is a mixture of 48 to 54% of cerium (Ce), 13 to 17% of neodymium (Nd), 24 to 28% of lanthanum (La) and 13 to 28% of praseodymium (Pr) 17%, and excellent resistance to cracking.