KR101376683B1 - High~strength high~tensile steel and manufacturing method thereof - Google Patents

Abstract

High strength high tensile strength steel according to an embodiment of the present invention, carbon (C) 0.16 ~ 0.35% by weight, silicon (Si) 1.00% by weight or less, manganese (Mn) 0.75% by weight or less, nickel (Ni) 8.5 ~ 9.5% by weight, Chromium (Cr) 1.5 to 3.25 wt%, Molybdenum (Mo) 0.55 wt% or less, Tungsten (W) 0.70 to 3.25 wt%, Vanadium (V) 0.05 to 0.3 wt%, Boron (B) 0.0007 to 0.0023 wt%, Titanium (Ti) 0.04% by weight or less, niobium (Nb) 0.01 to 0.02% by weight, copper (Cu) 0.50% by weight and the remaining unavoidable impurities and iron (Fe), thereby increasing the strength of the steel without deterioration of toughness. .

Description

High strength high strength steel and its manufacturing method {HIGH ~ STRENGTH HIGH ~ TENSILE STEEL AND MANUFACTURING METHOD THEREOF}

One embodiment of the present invention relates to a method of manufacturing high strength high strength steel and high strength high strength steel with improved strength and improved mechanical properties.

High-strength high strength steel is a material mainly used in ships, marine structures, line pipes, pressure vessels, armor plates, foam materials, rocket motor cases, landing gears, and weapon systems. .

In fabricating such devices, there is increasing interest in high strength steels that are high in weight while less in weight. Soft materials used in the past have excellent workability but are weak to external impact.

In order to compensate for these disadvantages, the soft material is thickened to withstand external shocks, but the soft material is excellent in strength, but because of its heavy weight, the utility is poor.

Recently, Eglin Steel, developed by the US Air Force Research Institute and Ellwood National Forge Co., has developed high-strength high tensile strength steel with a tensile strength of 1700 MPa by reducing the content of expensive elements and controlling the composition and heat treatment process, but has a limited strength. .

The weight and size of the material is a very important design variable for all industries.

Thus, there has been a steady search for ways to reduce the size and thus the weight of materials without compromising important mechanical properties, in particular mechanical strength, toughness and ductility.

Because of this continuing demand for materials that allow the use of lightweight materials, it is necessary to secure steel alloys that provide much greater strength than conventional high strength high strength steel alloys.

However, it is well known that the toughness and ductility of steels are generally inversely related to the strength properties.

Thus, it is desired to fabricate high strength high tensile strength steels with greater strength properties without significant degradation of toughness and ductility properties.

One embodiment of the present invention is to provide a high-strength high-strength steel that is increased in strength without deterioration of toughness without undergoing post-rolling after hot rolling through the content control and addition of alloying components.

In order to achieve the above problems of the present invention, the high strength high tensile strength steel according to an embodiment of the present invention, carbon (C) 0.16 ~ 0.35% by weight, silicon (Si) 1.00% by weight or less, manganese (Mn) 0.75% by weight Nickel (Ni) 8.5 to 9.5 wt%, Chromium (Cr) 1.5 to 3.25 wt%, Molybdenum (Mo) 0.55 wt% or less, Tungsten (W) 0.70 to 3.25 wt%, Vanadium (V) 0.05 to 0.3 wt% , Boron (B) 0.0007 to 0.0023% by weight, titanium (Ti) 0.04% by weight or less, niobium (Nb) 0.01 to 0.02% by weight, copper (Cu) 0.50% by weight and residual unavoidable impurities and iron (Fe) .

According to an example related to the present invention, the matrix structure of the steel may be formed including a composite phase of ferrite, martensite, bainite and residual austenite.

In addition, in order to realize the above problems, the present invention, carbon (C) 0.16 ~ 0.35% by weight, silicon (Si) 1.00% by weight or less, manganese (Mn) 0.75% by weight or less, nickel (Ni) 8.5 ~ 9.5% by weight, Chromium (Cr) 1.5 to 3.25 wt%, Molybdenum (Mo) 0.55 wt% or less, Tungsten (W) 0.70 to 3.25 wt%, Vanadium (V) 0.05 to 0.3 wt%, Boron (B) 0.0007 to 0.0023 wt%, Titanium (Ti) 0.04% by weight or less, niobium (Nb) 0.01 to 0.02% by weight, copper (Cu) 0.50% by weight, and a steel sheet composition containing residual unavoidable impurities and iron (Fe) are dissolved and continuously cast to form a steel sheet. And it discloses a method for producing high strength high strength steel comprising the step of hot rolling the steel sheet at 900 ~ 1200 ℃ and quenching the hot rolled steel sheet.

According to an example related to the present invention, the step of quenching is performed so that the quenching process starts at 750 to 850 ° C. and proceeds at a rate of 10 to 50 ° C./sec.

According to an example related to the present invention, the step of hot rolling is carried out so that the rolling reduction per pass is 5 to 30% continuously until the end of rolling.

According to an example related to the present invention, the step of hot rolling is made such that the cumulative reduction ratio is 50% or more.

High strength high tensile strength steel according to at least one embodiment of the present invention, which is configured as described above, is a high strength high tensile strength steel which is increased in strength without deterioration of toughness without undergoing post-treatment after hot rolling through the content control and addition of alloying components to conventional steel. .

In addition, the method of manufacturing high strength high tensile strength steel according to an embodiment of the present invention can efficiently produce high strength high strength high tensile strength steel as a method of efficiently manufacturing high strength high tensile strength steel by reducing the heat treatment process.

1 is an electron micrograph of a high strength high strength steel according to an embodiment of the present invention quenched after hot rolling.
2 is a graph showing the mechanical properties of high strength high strength steel according to an embodiment of the present invention quenched after hot rolling.

Hereinafter, high strength high tensile strength steel and a method for manufacturing the same according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. The suffix "module" and " part "for the components used in the following description are given or mixed in consideration of ease of specification, and do not have their own meaning or role.

In the present specification, the same or similar reference numerals are given to different embodiments in the same or similar configurations. As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

In the high strength high tensile strength steel according to the embodiment of the present invention, in the case of the conventional high strength high tensile strength steel, a small amount of boron (B) and niobium (Nb) were added to apply direct quenching.

As a result, the conventional two-solution treatment is reduced to one-solution treatment to achieve a reduction in manufacturing cost and to improve the tensile strength to 1490 MPa.

In addition, by controlling the control rolling and direct quenching conditions, the tensile strength of 1470MPa class high strength high tensile strength steel was drawn by using the effective grain refinement and dislocation strengthening effect of martensite.

In addition, cobalt (Co), molybdenum (Mo) and nickel (Ni) are added in large amounts to structural components in the aerospace industry of 2000 MPa or higher, armor for both aircraft and ground vehicles, High strength high strength steels such as Aermet have been developed for use in machine tool elements.

High strength high tensile strength steel according to an embodiment of the present invention is a high tensile strength steel of 0.16 ~ 0.35% by weight of carbon (C), 1.00% by weight of silicon (Si), 0.75% by weight of manganese (Mn), 8.5 ~ 9.5% by weight of nickel (Ni) , Chromium (Cr) 1.5-3.25 wt%, molybdenum (Mo) 0.55 wt% or less, tungsten (W) 0.70-3.25 wt% and small amounts of alloying elements (vanadium (V) 0.05-0.3 wt%, boron (B) 0.0007 to 0.0023 wt%, titanium (Ti) 0.04 wt% or less, niobium (Nb) 0.01 to 0.02 wt%, copper (Cu) 0.50 wt% or less) and the balance of iron (Fe).

1 is an electron micrograph of a high strength high tensile strength steel according to an embodiment of the present invention quenched after hot rolling, Figure 2 is a graph showing the mechanical properties of high strength high tensile strength steel according to an embodiment of the present invention quenched after hot rolling .

Microstructures of high strength high tensile strength steels were etched using Nital and Beraha solutions and observed by light microscopy.

As shown in FIG. 1, the steel matrix comprises a composite phase of ferrite, martensite, bainite and residual austenite.

In particular, the martensite, bainite and ferrite structure and the residual austenite structure coexist at the same time and exhibit a tensile strength of 2100 MPa or more.

2 is a graph showing the mechanical properties of high strength high strength steel according to an embodiment of the present invention quenched after hot rolling.

In a preferred embodiment, C: 0.29%, Mn: 0.725%, Si: 0.93%, Ni: 8.86%, Ni: 8.86%, Cr: 2.83%, Mo: 0.36%, V: 0.064% by weight, B: 0.0023% by weight, Nb: 0.017% by weight, W: 1.25% by weight, Cu: 0.11% by weight, Ti: 0.04% by weight and residual unavoidable impurities, showing the mechanical properties of high strength high strength steels including Fe It is a graph.

As shown, the mechanical properties of the high strength high tensile strength steel were measured by Instron 4206, and it can be seen that the tensile strength is more than 2100 MPa.

Method for producing high strength high strength steel of the present invention is 0.16 ~ 0.35 wt% of carbon (C), 1.00 wt% or less of silicon (Si), 0.75 wt% or less of manganese (Mn), 8.5 ~ 9.5 wt% of nickel (Ni), chromium (Cr ) 1.5 to 3.25 wt%, molybdenum (Mo) 0.55 wt% or less, tungsten (W) 0.70 to 3.25 wt% and small amounts of alloying elements (vanadium (V) 0.05 to 0.3 wt%, boron (B) 0.0007 to 0.0023 weight %, 0.04 wt% or less of titanium (Ti), 0.01 to 0.02 wt% of niobium (Nb), 0.50 wt% or less of copper (Cu)) and the remaining amount of iron (Fe), after dissolving and continuously casting a composition of 1100 Hot rolling is carried out at ˜1300 ° C., followed by rapid cooling.

Hereinafter, the main element of the present invention and the reason for limitation of its content will be described in more detail.

Carbon: 0.16 to 0.35 wt%

In the composition of the steel sheet according to the present invention, carbon (C) is added to give strength to the material as a major reinforcing element, and depending on the content and manufacturing method, it may become a solid solution carbon inside the material structure, and bond with carbon They combine with elements with very high properties to form carbides. The carbon is used in an amount of 0.16 to 0.35% by weight. At this time, when the amount of carbon used is less than the above range, the hardenability and the strength are lowered.

silicon( Si ): 1.00 wt% or less

Silicon (Si) is a component that is added as a deoxidizer, but if its content is increased, the yield strength is increased, but it is preferable to limit it to 1.00% by weight or less because it increases the ductility to brittle transition temperature, thereby deteriorating toughness and harmful to weldability.

manganese( Mn ): 0.75% by weight or less

Manganese (Mn) improves the hardenability to increase the strength, but when excessively added, it impairs the weldability, it is preferable to limit to 0.75% by weight or less.

nickel( Ni ): 8.5-9.5 wt%

Nickel (Ni) is an essential element of high tensile steel that improves low-temperature toughness by lowering the ductile to brittle transition temperature of steel, but is preferably limited to 8.5 to 9.5% by weight due to its high price.

chrome( Cr ): 1.5 to 3.25 wt%, molybdenum ( Mo ): 0.55 wt% or less

The chromium (Cr) and molybdenum (Mo) is not only an essential element for improving the hardenability of steel, but also an element that significantly increases the strength even at high temperatures, but is known to damage weldability as the content increases. ) 1.5 to 3.25%, molybdenum (Mo) is preferably limited to 0.55% by weight.

Tungsten (W): 0.70 to 3.25 wt%

Tungsten (W) is an element that increases strength and wear resistance by precipitation of carbides, but when added over 3.25%, toughness decreases, so it is limited to 0.70 to 3.25%

Vanadium (V): 0.05-0.3 wt%

Vanadium (V), together with Cr and Mo, is an element that increases strength directly related to the increase in hardenability and the precipitation of M2C carbides, but it must be added more than 0.05% and is limited to 0.05 ~ 0.3% because it is expensive.

Boron (B): 0.0007 to 0.0023 wt%

Boron (B) is an alloying element that precipitates at grain boundaries and decreases grain boundary energy while increasing hardenability. If the content is less than 0.0007%, the effect cannot be expected, and if it is added more than 0.0023%, the weldability and hot workability are deteriorated, so it is preferable to limit the content to 0.0007% to 0.0023%.

titanium( Ti ): 0.04 wt% or less

Titanium (Ti) is a major element that plays a major role in grain refinement of steel by forming TiN and TiC precipitates during steel solidification and inhibiting grain growth during ingot heating and recrystallization during hot rolling. If the addition is excessive, the size of the precipitate becomes coarse, so that the effect of grain refining is inferior.

Niobium ( Nb ): 0.01 to 0.02 wt%

Niobium (Nb) is an element that suppresses austenite grain growth during hot rolling, increases the recrystallization temperature to increase rolling productivity during control rolling, and increases the strength by making carbides by reacting with carbon (C). It is preferable to limit the content to 0.01 to 0.02% by weight as the weldability worsens as this increases.

Copper( Cu ): 0.50 wt% or less

Copper (Cu) increases the strength by forming precipitates and improves the corrosion resistance of the steel, but when excessively added, the oxide film is severely formed on the surface of the steel sheet, so the content thereof is preferably limited to 0.50% or less.

In addition to the above components, the other components together with other unavoidable impurities are made of iron (Fe).

Here, a method of manufacturing high strength high strength steel using the material of the present invention having the composition and content as described above is as follows.

In order to manufacture the high strength high strength steel according to the present invention, first, the steel sheet composition is melted in a converter and continuously cast, followed by hot rolling at 900 to 1200 ° C., followed by quenching to form martensite structure.

Hot rolling shall be carried out at 5 to 30% per pass, with a cumulative reduction of 50% or more.

If the hot rolling temperature is less than 900 ℃ the roll force (roll force) during hot rolling is increased, the wear of the roll is large, the removal of rust is difficult to deteriorate the quality of the steel sheet surface. In addition, when the hot rolling temperature exceeds 1200 ℃ because the austenite particles are too coarse to deteriorate the properties of the steel sheet, the ingot heating temperature is preferably between 900 ~ 1200 ℃.

In particular, it is preferable to start the cooling at 750 ~ 850 ℃ in the quenching process to cool at a rate of 10 ~ 50 ℃ / sec.

This is because the faster the cooling rate is advantageous in terms of securing the martensite structure and increasing the strength of martensite due to the uncrystallized rolling, but the higher the cooling rate above 50 ℃ / sec causes severe plate deformation.

The higher the reduction rate per rolling pass has the effect of improving the strength and toughness, but more than 30% reduction causes overload of the rolling equipment and less than 5% reduction per rolling pass is difficult to expect the effect. The rolling reduction per rolling pass is preferably 5 to 30% and is continuously rolled until the end of rolling.

If the cumulative reduction ratio is 50% or less, insufficient improvement of low-temperature toughness due to insufficient refinement of the effective martensite grains transformed from austenite in the uncrystallized crystal temperature range, and the processing potential structure induced from austenite can be secured. Because you can't.

The high-strength high strength steel and the manufacturing method thereof described above are not limited to the configuration and method of the embodiments described above, but the embodiments may be selectively or partially all of the embodiments so that various modifications may be made. It may be configured in combination.

Claims (6)

Carbon (C): 0.16-0.35 wt%, Silicon (Si): more than 0 and 1.00 wt% or less, Manganese (Mn): more than 0 and 0.75 wt% or less, Nickel (Ni): 8.5 to 9.5 wt%, Chromium (Cr) : 1.5 to 3.25 wt%, molybdenum (Mo): more than 0 and 0.55 wt% or less, tungsten (W): 0.70 to 3.25 wt%, vanadium (V): 0.05 to 0.3 wt%, boron (B): 0.0007 to 0.0023 weight %, Titanium (Ti): more than 0 and 0.04% by weight or less, niobium (Nb): 0.01 to 0.02% by weight, copper (Cu): more than 0 and 0.50% by weight and less, and include residual unavoidable impurities and iron (Fe), and High strength high strength steel with a strength of 1280 MPa or more. The method of claim 1,
High-strength high tensile strength steel, characterized in that the base structure of the steel comprises a complex phase of ferrite, martensite, bainite and residual austenite. Carbon (C): 0.16-0.35 wt%, Silicon (Si): more than 0 and 1.00 wt% or less, Manganese (Mn): more than 0 and 0.75 wt% or less, Nickel (Ni): 8.5 to 9.5 wt%, Chromium (Cr) : 1.5 to 3.25 wt%, molybdenum (Mo): more than 0 and 0.55 wt% or less, tungsten (W): 0.70 to 3.25 wt%, vanadium (V): 0.05 to 0.3 wt%, boron (B): 0.0007 to 0.0023 weight %, Titanium (Ti): more than 0 and 0.04% by weight or less, niobium (Nb): 0.01 to 0.02% by weight, copper (Cu): more than 0 and 0.50% by weight or less, and a steel sheet composition containing residual unavoidable impurities and iron (Fe) Melting and continuous casting to form a steel sheet;
Rolling the steel sheet continuously at a rolling reduction ratio of 5 to 30% at 900 to 1200 ° C until the end of rolling, and hot rolling so that the cumulative reduction ratio is 70% or more; And
Method of producing a high strength high strength steel comprising the step of quenching the hot rolled steel sheet at a rate of 10 ~ 50 ℃ / sec starting cooling at 750 ~ 850 ℃. delete delete delete

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