KR101505287B1 - Steel and method for manufacturing the same - Google Patents

Abstract

A steel material having excellent mechanical properties and forging formability by increasing the section reduction ratio at the time of high temperature tensile while controlling the composition of the alloy and the process conditions to miniaturize the austenite grains and a manufacturing method thereof.
The method of manufacturing a steel material according to the present invention comprises the steps of: 0.35 to 0.40% by weight of carbon (C), 0.5 to 0.7% by weight of silicon (Si), 1.3 to 1.5% by weight of manganese (Mn) (S): 0.045 to 0.065 wt%, Ni: more than 0 wt% to 0.2 wt%, chromium (Cr): 0.1 to 0.2 wt%, molybdenum (Mo): 0 wt (Ti): more than 0 wt% to 0.01 wt%, aluminum (Al): 0.01 to 0.03 wt%, vanadium (Ti) (V) of 0.08 to 0.13 wt%, oxygen (O) of more than 0 ppm to less than 10 ppm, nitrogen (N) of 100 to 200 ppm, and balance of iron (Fe) and other unavoidable impurities, Reheating in the step; Hot rolling the reheated slab to a finish rolling temperature of 700 to 900 占 폚; And cooling the hot-rolled steel to 450 to 600 ° C.

Description

STEEL AND METHOD FOR MANUFACTURING THE SAME

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a steel material manufacturing technique, and more particularly, to a steel material for a piston having improved mechanical properties and forging formability and a manufacturing method thereof.

In recent years, along with performance enhancements in transportation equipment and heavy equipment fields, excellent mechanical properties have been required in the field of materials in these fields. Particularly, the mechanical properties of the piston, which is an engine part of the medium-term, are considered to be very important due to the environment. In particular, the piston is required to have good impact physical properties and abrasion properties, and forging ability in the manufacturing process depending on its role, which can be ensured from the physical properties of the steel material.

In connection with the present invention, Korean Patent Laid-Open Publication No. 10-2006-0071099 (Jun. 26, 2006) discloses a method of predicting yield strength and yield ratio of an electric resistance welding line pipe.

An object of the present invention is to provide a steel material having improved forging properties by controlling the alloy components and process conditions to make fine grains finer, and a method for producing the same.

According to another aspect of the present invention, there is provided a method of manufacturing a steel material, the method including the steps of: 0.35 to 0.40 wt% of carbon; 0.5 to 0.7 wt% of silicon; 1.3 to 1.5 wt% of manganese (P): more than 0 wt% to 0.03 wt% or less, S: 0.045 to 0.065 wt%, Ni: more than 0 wt% to 0.2 wt%, chromium (Cr) (Cu): more than 0 wt% to 0.25 wt%, titanium (Ti): 0 wt% to 0.01 wt%, aluminum (Al) (O): more than 0 ppm and less than 10 ppm, nitrogen (N): 100 to 200 ppm, and the balance of iron (Fe) and other elements (Al): 0.01 to 0.03 wt%, vanadium (V): 0.08 to 0.13 wt% Reheating slabs formed from unavoidable impurities at 1100 to 1200 ° C; Hot rolling the reheated slab to a finish rolling temperature of 700 to 900 占 폚; And cooling the hot-rolled steel to 450 to 600 ° C.

In order to achieve the above object, a steel material according to an embodiment of the present invention includes 0.35 to 0.40% by weight of carbon, 0.5 to 0.7% by weight of silicon, 1.3 to 1.5% by weight of manganese, (P): more than 0 wt% to 0.03 wt% or less, S: 0.045 to 0.065 wt%, Ni: more than 0 wt% to 0.2 wt%, Cr: 0.1 to 0.2 wt% (Cu): more than 0 wt% to 0.25 wt% or less, titanium (Ti): 0 wt% to 0.01 wt% or less, aluminum (Al (O): more than 0 ppm to 10 ppm, nitrogen (N): 100 to 200 ppm, and the balance of iron (Fe) and other unavoidable impurities And has a tensile strength (TS) of 850 to 1000 MPa, a yield strength (YP) of 580 MPa or more, and an elongation (EL) of 10% or more.

The steel material and the manufacturing method thereof according to the present invention can control the alloying components and process conditions to improve the austenite grain size and increase the sectional reduction rate at the time of high-temperature stretching, so that excellent mechanical properties and forging ability can be obtained.

1 is a flowchart showing a method of manufacturing a steel material according to an embodiment of the present invention.
Fig. 2 shows the crystal grains of the specimen produced according to Comparative Example 1. Fig.
Fig. 3 shows the crystal grains of the specimen produced according to Example 1. Fig.
4 is a graph showing the rate of decrease in section of the specimen according to Example 1 and Comparative Example 1 according to the temperature.
5 is a graph showing tensile properties of a specimen according to Example 1 and Comparative Example 1 according to temperature.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a steel material according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The steel material according to the present invention contains 0.35 to 0.40 wt% of carbon (C), 0.5 to 0.7 wt% of silicon (Si), 1.3 to 1.5 wt% of manganese (Mn) (Si): 0.045 to 0.065 wt%, Ni: more than 0 wt% to 0.2 wt%, chromium (Cr): 0.1 to 0.2 wt%, molybdenum (Mo): more than 0 wt% (Al): 0.01 to 0.03 wt.%, Vanadium (V): 0.06 wt.% Or less, copper (Cu): 0 wt.% To 0.25 wt.% Or less, titanium ): 0.08 to 0.13 wt%, oxygen (O): more than 0 ppm to 10 ppm, nitrogen (N): 100 to 200 ppm, and the balance of iron (Fe) and other unavoidable impurities.

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Hereinafter, the role and content of each component will be described.

Carbon (C)

Carbon (C) is added to ensure the strength of the steel.

The carbon is preferably added in an amount of 0.35 to 0.40% by weight based on the total weight of the steel material. When the addition amount of carbon (C) is less than 0.35% by weight, it may be difficult to secure strength. On the contrary, when the content of carbon (C) exceeds 0.40% by weight, the strength of the steel increases but the impact value and the weldability deteriorate.

silicon( Si )

Silicon (Si) acts as a deoxidizer, contributing to strength enhancement through solid solution strengthening.

The silicon is preferably added at a content of 0.5 to 0.7 wt% of the total weight of the steel. When the content of silicon (Si) is less than 0.5% by weight, the effect of adding silicon can not be exhibited properly. On the contrary, when the content of silicon (Si) exceeds 0.7% by weight, oxides are formed on the surface of the steel, thereby deteriorating the weldability of the steel.

manganese( Mn )

Manganese (Mn) is an element which increases the strength and toughness of steel and increases the incombustibility of steel. Addition of manganese (Mn) causes less deterioration of ductility when the strength is higher than that of carbon (C). Further, manganese (Mn) contributes to improvement of the hardenability of the steel.

The manganese is preferably added in an amount of 1.3 to 1.5% by weight based on the total weight of the steel material. When the addition amount of manganese (Mn) is less than 1.3% by weight, it is difficult to secure sufficient strength. On the other hand, when the addition amount of manganese exceeds 1.5% by weight, the amount of MnS-based nonmetal inclusions increases, which may cause defects such as cracks during welding.

Phosphorus (P), sulfur (S)

Phosphorus (P) contributes partly to strength improvement, but it is a representative element that lowers the secondary process embrittlement. Therefore, in the present invention, the content of phosphorus (P) is limited to more than 0 wt% and not more than 0.03 wt% of the total weight of the steel material.

Sulfur (S) is an impurity element present in the steel just like phosphorus (P). The sulfur (S) is an inclusion-forming element and forms a sulfide in the form of MnS or the like. These sulphides impair the impact properties of the steel for track shoes. Therefore, in the present invention, the content of sulfur (S) is limited to 0.045 to 0.065% by weight of the total weight of the steel material.

When the content of sulfur (S) exceeds 0.03% by weight of the total weight of the steel sheet, the content of sulfur (S) dissolved therein is too large, so that ductility and formability may be significantly lowered and there is a fear of heat and brittleness.

nickel( Ni )

Nickel (Ni) fine grains and solidify in the austenite and ferrite to strengthen the matrix.

The nickel is preferably added in an amount of more than 0 wt% to 0.2 wt% of the total weight of the steel material. If the addition amount of nickel is more than 0.2% by weight, there is a fear of giving rise to a hot brittleness.

chrome( Cr )

Chromium (Cr) is an element effective for improving hardenability by improving hardenability.

The chromium is preferably added in an amount of 0.1 to 0.2% by weight based on the total weight of the steel material. If the content of chromium (Cr) is less than 0.1% by weight, the addition amount is insufficient and the effect of addition can not be exhibited properly. On the contrary, when the content of chromium (Cr) exceeds 0.2% by weight, the weldability and the heat affected zone (HAZ) toughness are lowered.

molybdenum( Mo )

Molybdenum (Mo) contributes to improvement of strength and toughness, and also contributes to ensuring stable strength at room temperature or high temperature.

The molybdenum is preferably added in an amount of more than 0 wt% to 0.06 wt% of the total weight of the steel material. When the addition amount of molybdenum exceeds 0.06% by weight, the weldability is lowered, and the yield ratio is increased by precipitation of carbide.

Copper( Cu )

Copper (Cu) is an element effective for increasing the strength and improving the toughness. Copper also contributes to the hardening effect by controlling the amount of silicon with silicon (Si) and manganese (Mn).

The copper is preferably added in an amount of more than 0 wt% to 0.25 wt% of the total weight of the steel material. If the addition amount of copper exceeds 0.25% by weight, the surface properties of the steel may be deteriorated.

titanium( Ti )

Titanium (Ti) plays a role in refining the steel structure by inhibiting the growth of austenite grains by forming TiN during reheating.

The titanium is preferably added in an amount of more than 0 wt% to 0.01 wt% or less of the total weight of the steel material. When the addition amount of titanium exceeds 0.01% by weight, the TiN precipitate becomes coarse and the effect of suppressing grain growth is deteriorated.

aluminum( Al )

Aluminum (Al) acts as a deoxidizer to remove oxygen in the steel.

The aluminum is preferably added in an amount of 0.01 to 0.03% by weight based on the total weight of the steel material. When the added amount of aluminum is less than 0.01% by weight, the effect of deoxidation is insufficient. On the contrary, when the added amount of aluminum exceeds 0.03% by weight, the impact property of the steel material is deteriorated.

Vanadium (V)

Vanadium (V) acts as a pinning to the grain boundaries and contributes to the improvement of strength.

Vanadium (V) is preferably added in a content ratio of 0.08 to 0.13% by weight based on the total weight of the steel material according to the present invention. When the content of vanadium (V) is less than 0.08% by weight, it may be difficult to exhibit the above effect properly. On the contrary, when the content of vanadium (V) exceeds 0.13% by weight, the low-temperature impact toughness is deteriorated.

Oxygen (O), nitrogen (N)

Oxygen (O) and nitrogen (N) are inevitable impurities, which, when contained in large amounts, cause deterioration of the physical properties of the steel.

In the present invention, the content of oxygen and nitrogen is limited to more than 0 ppm and less than 10 ppm and 100 to 200 ppm, respectively.

Steel manufacturing method

1 is a flowchart showing a method of manufacturing a steel material according to an embodiment of the present invention.

Referring to FIG. 1, the illustrated method of manufacturing steel includes a slab reheating step (S110), a hot rolling step (S120), and a cooling step (S130).

Slab reheat step

In the slab reheating step S110, the alloy composition, that is, the carbon (C) is 0.35 to 0.40 wt%, the silicon (Si) is 0.5 to 0.7 wt%, the manganese (Mn) : More than 0 wt% to 0.03 wt% or less, sulfur (S): 0.045 to 0.065 wt%, nickel (Ni): more than 0 wt% to 0.2 wt%, chromium (Cr) Mo: not less than 0 wt% to not more than 0.06 wt%, Cu: not less than 0 wt% to not more than 0.25 wt%, Ti: not less than 0 wt% to not more than 0.01 wt% 0.03% by weight of vanadium (V), 0.08 to 0.13% by weight of oxygen (O), more than 0 ppm to 10 ppm of nitrogen (O), 100 to 200 ppm of nitrogen (N), and other inevitable impurities And re-heat the segregated components during casting.

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The reheating temperature is preferably 1100 to 1200 ° C. When the reheating temperature is less than 1100 ° C, there is a problem that the reheating temperature is low and the rolling load becomes large. On the other hand, when the reheating temperature exceeds 1200 ° C, the austenite grains are coarsened and it is difficult to secure the strength of the steel to be produced.

Hot rolling step

In the hot rolling step (S120), the reheated slab is rolled. At this time, the reheated slab can be rolled in the shape of a predetermined piston in the hot rolling step.

The finish rolling temperature during hot rolling is preferably 700 to 900 占 폚. If the finish rolling temperature is less than 700 ° C, an abnormal reverse rolling may occur and the ductility may be lowered. On the contrary, when the finish rolling temperature exceeds 900 캜, there is a problem that the strength of the produced steel is lowered.

Cooling step

In the cooling step (S130), the hot-rolled steel is cooled to the cooling end temperature. The cooling may be carried out by a water-cooling system that pours the rolled steel material or an air injection system that blows air against the surface of the rolled steel material. The cooling rate may be about 0.5 to 50 DEG C / sec, but is not limited thereto.

The cooling end temperature is preferably 450 to 600 ° C. If the cooling end temperature is less than 450 ° C, the yield strength can be increased due to the formation of fine crystal grains. On the other hand, when the cooling end temperature exceeds 600 ° C, the content of the effective titanium (Ti) for precipitating the solid carbon by the formation of the FeTiP precipitate is reduced, and the moldability may be lowered.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail with reference to preferred embodiments of the present invention. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

1. Preparation of specimens

Examples 1 to 3 and Comparative Examples 1 and 2 having the compositions shown in Tables 1 and 2 were reheated at 1200 ° C for 2 hours, hot-rolled at a finish rolling temperature of 800 ° C, / sec < / RTI > to a temperature of 500 < 0 > C to prepare respective specimens.

[Table 1] (unit:% by weight)

[Table 2] (unit:% by weight)

2. Mechanical properties

Table 3 shows the evaluation of the mechanical properties of the specimens according to Examples 1 to 3 and Comparative Examples 1 and 2.

In Table 3, the tensile strength (TS), the yield strength (YS), the elongation (EL) and the section reduction ratio were measured by a tensile test based on JIS No. 5 test specimens.

[Table 3]

(YP) of not less than 580 MPa, an elongation (EL) of not less than 10%, and a reduction ratio of the cross section: 20% or more is satisfied.

On the other hand, the specimen prepared according to Comparative Example 1 in which a small amount of vanadium (V) was added as compared with Example 1 was hardly improved in strength according to the content of vanadium (V), and yield strength (YP), elongation (EL) The target value is satisfied but the tensile strength TS is less than the target value.

The specimens prepared according to Comparative Example 2 in which manganese (Mn) and vanadium (V) were added in a small amount as compared with Example 1 had yield strength (YP) and elongation (EL) TS) and the section reduction rate are less than the target value.

FIG. 2 shows the crystal grains of the specimen prepared according to Comparative Example 1, FIG. 3 shows the crystal grains of the specimen prepared according to Example 1, and FIG. 4 shows the temperature dependency of the specimen according to Example 1 and Comparative Example 1 FIG. 5 is a graph showing tensile properties of a specimen according to Example 1 and Comparative Example 1 according to temperature. FIG.

2 and 3, the grain size of the specimen prepared according to Comparative Example 1 was 6.6 mu m and the grain size of the specimen prepared according to Example 1 was 5.9 mu m, It can be seen that the specimen has a finer crystal grain than that of the specimen prepared according to Comparative Example 1.

4 and 5, it can be seen that Example 1 has a higher value in comparison with Comparative Example 1 in both of the reduction rate and tensile strength at high temperature.

Therefore, according to the present invention, by controlling the alloying components and the process conditions to make the austenite grains finer, it is possible to form a steel having an increased section reduction ratio at high temperature. This is suitable for a steel for a piston having excellent mechanical properties and forging ability.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

S110: Slab reheating step
S120: Hot rolling step
S130: cooling step

Claims (6)

(P): not less than 0 wt% to not more than 0.03 wt%, sulfur (0.03 wt% or less), carbon (C): 0.35 to 0.40 wt% S: 0.045 to 0.065 wt%, Ni: more than 0 wt% to 0.2 wt%, Cr: 0.1 to 0.2 wt%, molybdenum: more than 0 wt% to 0.06 wt% (Cu): more than 0 wt% to 0.25 wt% or less, titanium (Ti): 0 wt% to 0.01 wt%, aluminum (Al): 0.01 to 0.03 wt%, vanadium (V): 0.08 to 0.13 wt% Reheating the slab at 1100 to 1200 占 폚, the slab being composed of oxygen (O): more than 0 ppm to less than 10 ppm, nitrogen (N): 100 to 200 ppm and the balance of iron (Fe) and other unavoidable impurities;
Hot rolling the reheated slab to a finish rolling temperature of 700 to 900 占 폚; And
And cooling the hot-rolled steel to 450 to 600 DEG C,
After the cooling step, the steel has a tensile strength (TS) of 850 to 1000 MPa, a yield strength (YP) of 580 MPa or more, an elongation (EL) of 10% Method of manufacturing steel.
delete The method according to claim 1,
The cooling
Cooling rate: 0.5 to 50 占 폚 / sec.
(P): not less than 0 wt% to not more than 0.03 wt%, sulfur (0.03 wt% or less), carbon (C): 0.35 to 0.40 wt% S: 0.045 to 0.065 wt%, Ni: more than 0 wt% to 0.2 wt%, Cr: 0.1 to 0.2 wt%, molybdenum: more than 0 wt% to 0.06 wt% (Cu): more than 0 wt% to 0.25 wt% or less, titanium (Ti): 0 wt% to 0.01 wt%, aluminum (Al): 0.01 to 0.03 wt%, vanadium (V): 0.08 to 0.13 wt% (O): from more than 0 ppm to less than 10 ppm, nitrogen (N): from 100 to 200 ppm, and the balance iron (Fe) and other inevitable impurities,
A tensile strength (TS) of 850 to 1000 MPa, a yield strength (YP) of 580 MPa or more, and an elongation (EL) of 10% or more.
delete 5. The method of claim 4,
The steel
Sectional reduction ratio: 20% or more.

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