KR101382675B1 - Low alloy hot-rolled steel sheet having excellent wear-resistant and workability and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a low alloy hot rolled steel sheet having excellent wear resistance and workability, and a method for manufacturing the same, in one embodiment of the present invention, in terms of weight%, C: 0.3 to 0.5%, Mn: 0.5 to 2.0%, and Si: 0.05 to 0.5 Low alloy hot rolled steel sheet having excellent abrasion resistance and workability including%, P: 0.02% or less, S: 0.01% or less, balance Fe and other unavoidable impurities, and the microstructure includes pearlite and ferrite having an average grain size of 5 µm or less; It provides a manufacturing method.
According to the present invention, it is possible to provide a low alloy hot rolled steel sheet having excellent wear resistance and workability through control of alloying components and manufacturing conditions without using expensive alloying elements.

Description

LOW ALLOY HOT-ROLLED STEEL SHEET HAVING EXCELLENT WEAR-RESISTANT AND WORKABILITY AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a low alloy hot rolled steel sheet excellent in wear resistance and workability and a method of manufacturing the same.

The wear-resistant steel used for waste collection facilities and water supply facilities is mainly welded in the form of pipes. These pipe steels are required to have a resistance ratio in order to improve the workability, and at the same time wear resistance must also be secured, and thus are mainly manufactured by adding expensive alloy components.

Currently, steel with less than 0.3% carbon and expensive alloying elements is used as wear-resistant steel, but it is used only for curved pipes to reduce cost, and is coated with general carbon steel for straight pipes. to be. In addition, in case of infrastructure to be buried in the ground, high alloy steel is used even though it is expensive because of the astronomical cost problem in case of damage.

The present invention is to provide a low alloy hot rolled steel sheet having excellent wear resistance and workability without using a large amount of expensive alloying elements and a method of manufacturing the same.

One embodiment of the present invention is by weight, C: 0.3-0.5%, Mn: 0.5-2.0%, Si: 0.05-0.5%, P: 0.02% or less, S: 0.01% or less, residual Fe and other unavoidable impurities It includes, and the microstructure provides a low-alloy hot-rolled steel sheet excellent in wear resistance and workability including pearlite and ferrite having an average grain size of 5 µm or less.

Other embodiments of the invention are by weight, C: 0.3-0.5%, Mn: 0.5-2.0%, Si: 0.05-0.5%, P: 0.02% or less, S: 0.01% or less, residual Fe and other unavoidable impurities Reheating the slab comprising a 1000 ~ 1250 ℃; Hot rerolling the slab to obtain a hot rolled steel sheet at an Ar ₃ to Ar ₃ + 100 ° C. such that a total reduction ratio is 50% or more; Primary cooling the hot rolled steel sheet to 600 to 750 ° C. at a rate of 20 to 40 ° C./sec; Secondly cooling the hot-rolled hot rolled steel sheet to 580 to 630 ° C at a rate of 10 to 20 ° C / sec; And it provides a low alloy hot rolled steel sheet excellent in wear resistance and workability comprising the step of winding the hot-rolled hot rolled steel sheet.

According to the present invention, it is possible to provide a low alloy hot rolled steel sheet having excellent wear resistance and workability through control of alloying components and manufacturing conditions without using expensive alloying elements.

1 is an example of an apparatus for quantitatively measuring a wear rate.

The inventors of the present invention while researching to produce a hot rolled steel sheet having excellent wear resistance and workability without using expensive alloy elements to reduce the manufacturing cost, by controlling the microstructure through the derivation of the optimum alloying components and manufacturing conditions The present invention has been accomplished by recognizing that the goal can be achieved.

The present invention, in one embodiment, in weight%, C: 0.3-0.5%, Mn: 0.5-2.0%, Si: 0.05-0.5%, P: 0.02% or less, S: 0.01% or less, balance Fe and other unavoidable It provides a low-alloy hot rolled steel sheet having excellent wear resistance and workability, including impurities, and the microstructures include pearlite and ferrite having an average grain size of 5 µm or less. Hereinafter, the component system of the hot rolled sheet steel which concerns on one Embodiment of this invention is demonstrated.

Carbon (C): 0.3 to 0.5 wt%

C is an element that increases the hardenability of the steel material, which increases the tensile strength as well as the yield strength by increasing the perlite fraction by delaying the transformation of ferrite during cooling after hot finishing rolling. If the content of C is less than 0.3% by weight, the pearlite is insufficient to form the strength targeted by the present invention. On the other hand, when the content exceeds 0.5% by weight, the lowering of the toughness and the lowering of the weldability during electric resistance welding, the content of C is preferably in the range of 0.3 to 0.5% by weight. More preferably, it is 0.4 to 0.5% of range.

Manganese (Mn): 0.5 to 2.0 wt%

Mn is an effective element for strengthening the solid solution of steel and must be added at least 0.5% by weight to exhibit high strength with an increase in hardenability. However, when added in excess of 2.0% by weight, the segregation part is greatly developed at the center of thickness during slab casting in the steelmaking process, which is not preferable. Therefore, the content of Mn is preferably in the range of 0.5 to 2.0 wt%.

Silicon (Si): 0.05 to 0.5 wt%

Si increases the C activity of the ferrite phase and promotes ferrite stabilization, and contributes to securing strength by solid solution strengthening. In addition, Si forms a low melting point oxide such as Mn ₂ SiO ₄ during ERW welding and allows the oxide to be easily discharged during welding. If the content of Si is less than 0.05% by weight, the cost problem occurs in steelmaking, whereas in excess of 0.5% by weight, the amount of SiO2 oxide having a high melting point other than Mn ₂ SiO ₄ is increased and the toughness of the weld part is increased during electric resistance welding. Can be reduced. Therefore, the content of si preferably has a range of 0.05 to 0.5% by weight.

Phosphorus (P): 0.02 wt% or less

P is usually present as an impurity, but serves as a solid solution strengthening element to significantly increase the austenite / ferrite transformation start temperature, and is also useful for forming coarse ferrite particles. However, when the content is more than 0.02% by weight, it is difficult to ensure the effect, the content of P is preferably less than 0.02% by weight.

Sulfur (S): 0.01 wt% or less

S is an element that is easy to form coarse inclusions, and is preferably controlled as low as possible because it promotes a decrease in toughness and crack growth. Therefore, the content of S is preferably controlled to 0.01 wt% or less. The content of S is more preferably in the range of 0.005% by weight or less.

The hot rolled steel sheet proposed by the present invention can secure excellent wear resistance and workability by optimally controlling the alloy component and its composition as described above, and can further eliminate the addition of expensive alloy elements. However, V: 0.2% or less (excluding 0), Nb: 0.2% or less (excluding 0), Ti: 0.2% or less (excluding 0) and Cr: 0.2% or less (excluding 0) for a more desirable effect. It may further comprise one or more selected from the group consisting of. The elements are very useful for precipitation strengthening and grain refinement, but when the addition amount of each element exceeds 0.2%, the mechanical properties may be lowered, so the content thereof is preferably within the range of 0.2% or less. On the other hand, the above elements are expensive elements, and in the present invention, it is advantageous to add as few alloying elements as possible, so the lower the added amount, the better.

Hereinafter, an example of the manufacturing method of the hot rolled steel sheet which concerns on one Embodiment of this invention is demonstrated.

After preparing a steel slab that satisfies the proposed alloying component, it is preferable to reheat the slab to 1000 to 1250 ° C. Through the reheating process, it is possible to reduce the grain size of the austenite tissue, thereby easily achieving the grain refinement of the finally obtained microstructure. For this purpose, the reheating temperature needs to be 1000 ° C. or more, but when it exceeds 1250 ° C., the grain size of austenite may be excessively large. On the other hand, in order to easily achieve the grain size of the target final structure, it is preferable that the average grain size of the austenite after the reheating process has a range of 50 μm or less, and for this purpose, the reheating process is performed in 300 minutes or less. desirable.

The slab reheated as described above is preferably hot rolled so that the total reduction ratio is 50% or more at Ar ₃ to Ar ₃ + 100 ° C. for uniformity of the structure. When the hot rolling temperature is less than Ar ₃ ℃ it may not be easy to homogenize the structure or secure the ferrite fraction, the process may occur due to the rolling load. In the case of exceeding Ar ₃ + 100 ° C., the grain size of the ferrite structure may be coarse, thereby making it difficult to secure target mechanical properties. In order to maximize the reduction performance during the hot rolling, the reduction ratio is preferably 50% or more, and the reduction ratio can be varied depending on the thickness of the target steel sheet, and therefore the upper limit of the reduction ratio is not particularly limited.

The hot rolled steel sheet obtained through the hot rolling process as described above is preferably first cooled to 600 to 750 ° C at a rate of 20 to 40 ° C / sec. The cooling process may be performed in a run-out table (ROT) section after hot rolling, and the material deviation of the steel sheet may be reduced through the cooling process. In addition, it is possible to obtain a final structure consisting of pearlite and ferrite, thereby securing the target mechanical properties. If the cooling rate exceeds 40 ℃ / sec or the cooling stop temperature is less than 600 ℃ may not be easy to ensure the workability due to the formation of low-temperature transformation structure, such as martensite or bainite. On the contrary, when the cooling rate is less than 20 ° C / sec or the cooling stop temperature exceeds 750 ° C it may be difficult to secure the properties of the ferrite fraction compared to the pearlite.

Preferably, the first cooled hot rolled steel sheet is secondarily cooled to 580 to 630 ° C, and the second cooling is preferably performed at a rate of 10 to 20 ° C / sec. If the secondary cooling stop temperature is less than 580 ℃ or more than 630 ℃ material deviation may occur depending on the length of rolling.

Thereafter, by winding the hot-rolled hot-rolled steel sheet and air-cooled, a low-alloy hot-rolled steel sheet excellent in wear resistance and workability having a microstructure and mechanical properties as described below can be manufactured.

The hot rolled steel sheet proposed by the present invention preferably has a microstructure including pearlite and ferrite, and in particular, the average size of the ferrite grains is preferably 5 μm or less. As mentioned above, the hot rolled steel sheet of the present invention can obtain a finer structure 2 to 3 times finer than a conventional steel structure through the control of alloy composition and manufacturing conditions, thereby improving workability. On the other hand, by securing a pearlite structure as a columnar, wear resistance can also be ensured. That is, by securing a microstructure consisting of pearlite and ferrite can be improved to both excellent wear resistance and workability, and further improve the mechanical properties other than the above properties.

On the other hand, it is preferable that the pearlite and ferrite have a fraction of pearlite: 70 to 90 area% and ferrite: 10 to 30 area%, respectively. When the pearlite is less than 70 area%, it may not be easy to secure wear resistance or strength, and when the pearlite is more than 90 area%, workability may be reduced. Therefore, it is preferable that the said pearlite fraction has a range of 70-90 area%, More preferably, it has 80-90 area%. On the other hand, when the ferrite is less than 10 area%, it may not be easy to secure excellent workability, and when the ferrite is more than 30 area%, mechanical properties such as wear resistance may be lowered. Therefore, it is preferable that the said ferrite fraction has a range of 10-30 area%, More preferably, it has 10-20 area%.

Hot rolled steel proposed by the present invention can secure excellent mechanical properties of Vickers hardness: 200Hv or more, wear rate: 150 × 10 ^-13 m ³ / min or less, yield strength: 350 ~ 600MPa, tensile strength: 600MPa or more It can be preferably applied to products such as pipes or oil tube.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are merely illustrative for explaining the present invention in more detail does not limit the scope of the invention.

(Example)

After producing a slab having an alloy composition of Table 1, a hot rolled steel sheet was manufactured under the process conditions shown in Table 2. The microstructure was observed for the steel sheet thus prepared, the mechanical properties were measured, and the results are shown in Table 3 below. At this time, the wear rate was measured using the apparatus shown in FIG. 1, and the driving force transmitted by the DC motor 30 after mounting the specimen 10 on the pin 20 in the apparatus as shown in FIG. 1. The wear rate was measured by rotating the specimen 10 using. The size of the specimen used for measuring the wear rate was 30 × 30 mm, the thickness was 8 mm, and the AISI 52100 bearing ball (Hv: 845 kgf / mm ² ) was used as a pin. Applied load is 100N, wear track radius of wear specimen is 9mm, sliding speed is 10cm / s (106rpm), sliding distance is 300m (5308cycles) The test temperature was 23 ± 2 ° C. and the test humidity was 40 ± 5%.

division Chemical composition (% by weight) C Mn Si P S Ti Cr Comparative Example 1 0.25 2 0.3 0.009 0.002 0.02 - Comparative Example 2 0.25 One 0.3 0.008 0.005 0.02 0.3 Inventory 1 0.36 1.5 0.2 0.008 0.002 - 0.1 Inventive Example 2 0.41 1.5 0.2 0.007 0.002 - 0.1

division Reheating
Temperature (℃) Hot rolled
Temperature (℃) Reduction rate
(%) 1st cooling rate
(° C / sec) Primary cooling
Stop temperature (℃) 2nd cooling rate
(° C / sec) Secondary cooling
Stop temperature (℃) Comparative Example 1 1180 750 60 30 620 10 610 Comparative Example 2 1200 760 60 30 635 10 620 Inventory 1 1200 765 60 30 640 10 630 Inventive Example 2 1190 750 60 30 630 10 620

division Microstructure Mechanical properties Pearlite
Fraction
(area%) ferrite
Fraction
(area%) ferrite
Grain Average Size
(탆) Vickers
Hardness
(Hv) Wear rate
(× 10 ^-13 mm ³ / min) Seal
burglar
(TS)
(MPa) surrender
burglar
(YS)
(MPa) Comparative Example 1 40 60 10 185 340 660 530 Comparative Example 2 35 65 10 200 430 650 480 Inventory 1 75 25 5 245 135 730 410 Inventive Example 2 85 15 3 240 60 740 420

As shown in Tables 1 to 3, inventive examples 1 and 2 satisfying the alloy composition and production method proposed by the present invention, 75 to 85 area% of pearlite, 15 to 25 area% of ferrite, 3 to 5 The average size of the grain size of ferrite is secured, and through this, Vickers hardness of 240 ~ 240Hv is secured, and the wear rate is also good at 60 ~ 135 × 10 ^-13 mm ³ / min. Can be. In addition, the tensile strength is 730 ~ 740MPa, the yield strength is 410 ~ 420MPa, it can be seen that not only the strength is excellent but also the high workability.

On the other hand, Comparative Examples 1 and 2, which do not satisfy the alloy component proposed by the present invention, do not secure an appropriate microstructure fraction or grain size, and thus, it can be seen that not only wear resistance and workability but also low strength.

10: Psalms
20: counterpart
30: DC motor

Claims (7)

In weight percent, C: 0.3-0.5%, Mn: 0.5-2.0%, Si: 0.05-0.5%, P: 0.02% or less, S: 0.01% or less, balance Fe and other unavoidable impurities,
The microstructure is a low alloy hot rolled steel sheet having excellent wear resistance and workability including pearlite and ferrite having an average grain size of 5 μm or less.
The method according to claim 1,
The steel sheet is from the group consisting of V: 0.2% or less (excluding 0), Nb: 0.2% or less (excluding 0), Ti: 0.2% or less (excluding 0) and Cr: 0.2% or less (excluding 0) Low alloy hot rolled steel sheet excellent in wear resistance and workability further comprising at least one selected.
The method according to claim 1,
The low-alloy hot rolled steel sheet having excellent wear resistance and workability, wherein the perlite fraction is 70 to 90 area%, and the ferrite fraction is 10 to 30%.
The method according to claim 1,
The steel sheet is a low alloy hot-rolled steel sheet with excellent abrasion resistance and workability of Vickers hardness of 200Hv or more, wear rate of 150 × 10 ^-13 m ³ / min or less, yield strength: 350 ~ 600MPa, tensile strength: 600MPa or more.
By weight%, slab containing C: 0.3-0.5%, Mn: 0.5-2.0%, Si: 0.05-0.5%, P: 0.02% or less, S: 0.01% or less, balance Fe and other unavoidable impurities Reheating to 1250 ° C .;
Hot rerolling the slab to obtain a hot rolled steel sheet at an Ar ₃ to Ar ₃ + 100 ° C. such that a total reduction ratio is 50% or more;
Primary cooling the hot rolled steel sheet to 600 to 750 ° C. at a rate of 20 to 40 ° C./sec;
Secondly cooling the hot-rolled hot rolled steel sheet to 580 to 630 ° C at a rate of 10 to 20 ° C / sec; And
A method of manufacturing a low-alloy hot rolled steel sheet having excellent wear resistance and workability, comprising: winding the second hot-rolled steel sheet cooled to obtain a steel sheet having a microstructure including pearlite and ferrite having an average grain size of 5 µm or less.
The method of claim 5,
The slab is from a group consisting of V: 0.2% or less (excluding 0), Nb: 0.2% or less (excluding 0), Ti: 0.2% or less (excluding 0), and Cr: 0.2% or less (excluding 0) A method for producing a low alloy hot rolled steel sheet excellent in wear resistance and workability, further comprising one or more selected ones.
The method of claim 5,
The reheating step is a low alloy hot rolled steel sheet having excellent wear resistance and workability is performed in 300 minutes or less so that the average size of the austenite grain is 50㎛ or less.

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