METHOD FOR PRODUCING HIGH MANGANESE STEEL MATERIAL HAVING EXCELLENT ANTI-VIBRATION CHARACTERISTICS AND FORMABILITY, AND HIGH MANGANESE STEEL PRODUCED THEREBY

The present invention relates to a steel material used for a steel plate or the like for automobiles or construction and, more particularly, to a high manganese steel material having excellent anti-vibration characteristics and formability, which can be used where anti-vibration characteristics are required for noise reduction, and a method for producing same.

Skip to: Description  ·  Claims  · Patent History  ·  Patent History
Description
TECHNICAL FIELD

The present disclosure relates to a steel material for use in automobiles or construction steel plates, and more particularly, to a high manganese steel material having excellent anti-vibration characteristics and formability that may be used in locations in which anti-vibration characteristics for noise reduction are required, and a method of manufacturing the same.

BACKGROUND ART

Recently, noise reduction in materials such as automobile manufacturing or building materials is an issue that manufacturers should solve. In the case of automobile manufacturers, components such as engine parts and oil pans from which large amounts of noise occur are particularly required to have excellent mechanical properties and anti-vibration characteristics. In addition, in the case of building materials, as noise regulations for noise between floors have been strengthened, development of steel materials having excellent anti-vibration characteristics as floor plates of multi-story buildings including apartments is required.

Meanwhile, high manganese (Mn) vibration-proof steel is a steel grade that converts noise energy into thermal energy due to interfacial sliding of epsilon martensite in the case of external impacts, having high anti-vibration characteristics and excellent mechanical properties, and thus is suitable for use to reduce noise.

In general, anti-vibration properties of high manganese anti-vibration steel are secured by manufacturing a hot rolled or cold-rolled steel plate through a process of steelmaking-continuous casting-hot rolling or by adding a cold-rolling process thereto to prepare a hot-rolled or cold-rolled steel sheet and subsequently applying a post-heat treatment to form epsilon martensite and/or form a recrystallized structure.

Here, the post-heat treatment performed to secure the anti-vibration characteristics is a high-cost heat treatment to which a time exceeding 10 minutes, preferably, more than 60 minutes is applied at a temperature of usually 900° C. or higher, which has been a factor that inhibits generalization of high manganese anti-vibration steel.

Demand for noise reduction has continuously increased, and thus, there is a need to develop a steel material supporting compatibility between ensuring anti-vibration characteristics and excellent formability and omitting a high-cost post-heat treatment.

  • (Patent document 1) Korean Patent Registration No. 10-1736636

DISCLOSURE Technical Problem

An aspect of the present disclosure may provide a method of manufacturing a high manganese steel material having excellent anti-vibration characteristics and formability at low cost, compared to the related art, while eliminating a post-heat treatment essentially performed to improve anti-vibration characteristics, and a high manganese steel material having excellent anti-vibration characteristics manufactured thereby.

The technical problem of the present disclosure is not limited to the aforementioned matters. Additional problems of the present disclosure are described in the overall contents of the disclosure, and those of ordinary skill in the art to which the present disclosure pertains will not have any difficulty in understanding the additional problems of the present disclosure from the contents described in the disclosure of the present disclosure.

Technical Solution

According to an aspect of the present disclosure, a method of manufacturing a high manganese steel material having excellent anti-vibration characteristics and formability includes: heating a steel slab including, in percentages by weight, 0.1% or less of carbon (C), 8 to 30% of manganese (Mn), 3.0% or less of silicon (Si), 0.1% or less of phosphorus (P), 0.02% or less of sulfur (S), 0.1% or less of nitrogen (N), 1.0% or less (excluding 0%) of titanium (Ti), 0.01% or less of boron (B), the balance iron (F) and other inevitable impurities at 1,150 to 1,350° C.; finish hot-rolling the heated steel slab to manufacture a hot-rolled steel plate; and cooling the hot-rolled steel plate to 700° C. or lower, wherein the finish hot-rolling is performed at a finishing delivery temperature (FDT) (° C.) satisfying Relational Expression 1 below:


FDT(° C.)≥928+(480×C)+(450×N)+(0.9×Mn)+(65×Ti)  [Relational Expression 1]

(Here, each element represents content by weight)

According to an aspect of the present disclosure, a steel material manufactured by the aforementioned manufacturing method, having the aforementioned alloy composition, including, by area fraction, 90% or more epsilon martensite and the balance of an austenite phase as a microstructure, being a fully recrystallized structure, and having excellent, anti-vibration characteristics and formability

Advantageous Effects

According to an aspect of the present disclosure, the high manganese steel material having excellent anti-vibration characteristics and formability, even if a post-heat treatment required for improving the anti-vibration characteristics of the related art high-manganese anti-vibration steel is omitted, can be provided.

In addition, the present disclosure may provide high manganese vibration-proof steel at a relatively low cost by omitting the post-heat treatment, and thus, a technical effect may be obtained in terms of economics and the present disclosure may be generally used in fields requiring anti-vibration characteristics.

DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing a loss rate value at a strain of 900 (m/(m×10−6)) of an Inventive Steel and a Comparative Steel over an FDT (° C.) according to an exemplary embodiment in the present disclosure.

FIG. 2 is a graph showing a loss rate value at a strain of 200 to 900 (m/(m×10−6)) of the Inventive Steel and the Comparative Steel in an exemplary embodiment in the present disclosure.

FIG. 3 shows a microstructure image of the Inventive Steel according to an exemplary embodiment in the present disclosure.

FIG. 4 shows XRD measurement results of the Inventive Steel and the Comparative Steel according to an exemplary embodiment in the present disclosure.

FIG. 5 shows a method of measuring a loss rate against a strain according to a cantilever method.

 BEST MODE FOR INVENTION

The inventors of the present application found that, in order to improve anti-vibration characteristics, high-cost heat treatment (or a post-heat treatment) should be applied to the existing high manganese anti-vibration steel, which will resultantly significantly increases manufacturing costs and limits generalization.

Accordingly, the inventors studied in depth a method that may achieve both anti-vibration characteristics and excellent formability even if high-cost heat treatment is omitted. As a result, the inventors found that a fraction of epsilon martensite phase in the steel could be maximized by optimizing a manufacturing process along with the control of an alloy composition, and thus, a steel material having excellent anti-vibration characteristics and formability may be provided only with a series of hot rolling processes, and completed the present disclosure.

Hereinafter, the present disclosure will be described in detail.

According to a method of manufacturing a high manganese steel material having excellent anti-vibration characteristics and formability, a steel slab having an alloy composition described below may be prepared and hot-rolled and cooled to manufacture the high manganese steel material.

First, the reason for limiting an alloy composition to obtain a target high manganese steel material in the present disclosure will be described in detail. Here, unless otherwise specified, the content of each element means the weight content (% by weight).

Carbon (C): 0.1% or less

Carbon (C) is an element that stabilizes austenite in the steel and is advantageous to secure strength. However, if the carbon content exceeds 0.1%, the fraction of dissolved C is excessively increased, which impairs hot workability and significantly reduces anti-vibration characteristics.

Therefore, in the present disclosure, carbon (C) may be contained in an amount of 0.1% or less, and even if carbon (C) is included as 0%, it is not difficult to secure target physical properties.

Manganese (Mn): 8 to 30%

Manganese (Mn) is an essential element for stably securing austenite and epsilon martensite structures. In the present disclosure, in order to secure the epsilon martensite phase in a certain fraction or more without performing a separate heat treatment process, it is necessary to contain Mn in an amount of 8% or more. If the content exceeds 30%, manufacturing cost may increase and the content of phosphorus (P) may increase in the process of refining a large amount of Mn, causing slab cracking. In addition, as the content of Mn increases, internal grain boundary oxidation occurs excessively when the slab is heated, causing oxide defects on a steel surface and surface characteristics are also deteriorated during subsequent plating.

Therefore, in the present disclosure, Mn may be included in an amount of 8 to 30%, and more advantageously, 14 to 20%.

Silicon (Si): 3.0% or less

Silicon (Si) is an element that is solid solution strengthened and is advantageous in improving yield strength by reducing a grain size by a solid solution effect. If the content of Si increases, a silicon compound is formed on a surface of the steel sheet during hot rolling, resulting in poor pickling and surface quality of the hot-rolled steel sheet may be deteriorated. In addition, when excessively added, weldability is significantly reduced.

Accordingly, in the present disclosure, Si may be contained in an amount of 3.0% or less, and even if it is included as 0%, there is no difficulty in securing target physical properties.

Phosphorus (P): 0.1% or less and sulfur (S): 0.02% or less

Phosphorus (P) and sulfur (S) are elements that are inevitably contained in steel during production thereof, and it is advantageous for these elements to be contained as low as possible. If the content of P exceeds 0.1%, segregation may occur to reduce workability of the steel, and if the content of S exceeds 0.02%, a coarse manganese sulfide (MnS) is formed to cause a defect such as flange cracks and impair formability of the steel sheet, in particular, hole expandability of the steel sheet.

Therefore, in the present disclosure, P may be contained in an amount of 0.1% or less, and S may be contained in an amount of 0.02% or less.

Nitrogen (N): 0.1% or less

Nitrogen (N) is an element forming a nitride. If the N content exceeds 0.1%, the fraction of dissolved N may be excessively high, inhibiting hot workability and elongation and reducing anti-vibration characteristics.

Therefore, in the present disclosure, N is contained in an amount of 0.1% or less, and even if N is included as 0%, it is not difficult to secure target physical properties.

Titanium (Ti): 1.0% or less (excluding 0%)

Titanium (Ti) is an element that combines with carbon to form a carbide, and the formed carbide suppresses grain growth, which is advantageous for refining a grain size. In addition, since titanium forms a compound with C and N to obtain a scavenging effect, it is advantageous in improving anti-vibration characteristics. If the content of Ti exceeds 1.0%, excess titanium segregates to the grain boundaries to cause grain boundary embrittlement or form coarse precipitated phases to inhibit the effect of inhibiting grain growth.

Therefore, in the present disclosure, Ti may be included in an amount of 1.0% or less, and excluding 0%.

Boron (B): 0.01% or less

Boron (B) has the effect of preventing grain boundary cracking by forming a high-temperature compound at the grain boundary upon addition with Ti. However, if the content of B exceeds 0.01%, it is not preferable because it forms a boron compound and deteriorates the surface properties.

Therefore, in the present disclosure, B may be contained in an amount of 0.01% or less, and even if B is included as 0%, it is not difficult to secure target physical properties.

In the steel material containing each element with the aforementioned composition, if C and N are added in combination, the sum of their contents (C+N, wt %) is preferably 0.1% or less.

C and N are interstitial solid solution elements, and when combined with Ti and the like to form carbonitrides, vibration-proof performance may be improved, but if the sum of their contents exceeds 0.1%, the fraction of dissolved C or dissolved N may be increased to degrade hot workability and elongation and reduce anti-vibration characteristics, which are not desirable.

Therefore, when the C and N are added in combination, C and N may be contained in an amount of 0.1% or less by the sum of the contents.

Meanwhile, the steel material of the present disclosure may further include an additional element in addition to the aforementioned alloy composition to improve physical properties.

In an aspect, 0.005 to 2.0% of nickel (Ni) and 0.005 to 5.0% of chromium (Cr) may be further included.

Nickel (Ni): 0.005 to 2.0%

Nickel (Ni) is an element that effectively contributes to securing high temperature ductility. In order to obtain the aforementioned effect, Ni may be contained in an amount of 0.005% or more, and as the content increases, it is also effective in delayed fracture resistance and in preventing slab cracking. However, Ni is an expensive element and may be contained in an amount of 2.0% or less in consideration of the cost.

Chrome (Cr): 0.005 to 5.0%

Chromium (Cr) reacts with external oxygen during hot rolling or annealing to preferentially form a Cr-based oxide film (Cr2O3) with a thickness of 20 to 50 μm on the steel surface, thereby preventing Mn, Si, etc. contained in the steel from eluting to a surface layer. Accordingly, there is an effect of contributing to stabilization of the steel surface layer structure and improving plating surface characteristics. In order to obtain the aforementioned effect, Cr may be contained in an amount of 0.005% or more, but if the content exceeds 5.0%, a chromium carbide may be formed to rather workability and delayed fracture resistance characteristics, which, thus, is not desirable.

Therefore, Cr may be contained in an amount of 0.005 to 5.0% when added in the present disclosure.

In another aspect, at least one of 0.005 to 0.5% of niobium (Nb), 0.005 to 0.5% of vanadium (V), and 0.005 to 1.0% of tungsten (W) may be further included.

Niobium (Nb): 0.005 to 0.5%

Niobium (Nb) is an element that combines with carbon in the steel to form a carbide, and may obtain an effect of increasing strength or reducing a particle size. In general, since Nb forms a precipitated phase at a lower temperature than Ti, it has a large effect of precipitation strengthening due to refinement of the grain size and formation of the precipitated phase. In addition, Nb lowers the fraction of dissolved C to improve anti-vibration characteristics.

For the aforementioned effects, Nb may be contained in an amount of 0.005% or more. If the content exceeds 0.5%, excessive Nb segregates to the grain boundaries to cause grain boundary embrittlement or form coarse precipitated phases to reduce the effect of inhibiting grain growth. In addition, a rolling load may increase by delaying recrystallization during hot rolling.

Therefore, Nb may be contained in an amount of 0.005 to 0.5% when added in the present disclosure.

Vanadium (V): 0.005 to 0.5% and tungsten (W): 0.005 to 1.0%

Vanadium (V) and tungsten (W) are elements that combine with C and N to form carbonitrides. In the present disclosure, the elements forma fine precipitated phase at a low temperature, so that the precipitation strengthening effect is significant. In addition, there is an effect of improving anti-vibration characteristics by lowering the fractions of dissolved C and dissolved N.

For the aforementioned effect, each may be contained in an amount of 0.005% or more, but in the case of V exceeding 0.5% or in the case of W exceeding 1.0%, the precipitated phase may be excessively coarsened to reduce the effect of inhibiting grain growth and cause hot brittleness.

Therefore, in the present disclosure, V may be added in an amount of 0.005 to 0.5%, and W may be added in an amount of 0.005 to 1.0% when added.

The balance of the present disclosure is Fe. Since unintended impurities from raw materials or a surrounding environment may inevitably be mixed in a typical manufacturing process, the unintended impurities cannot be excluded. Since these impurities are known to anyone of ordinary skill in the manufacturing process, all contents are not specifically mentioned in the present specification.

After preparing a steel slab having an alloy composition as described above, the steel slab may be heated, and here, the steel slab may be subjected to heating in a temperature range of 1150 to 1,350° C.

If a temperature during heating of the steel slab is too low, a rolling load may be excessively applied during subsequent hot rolling, so it may be carried out at at least 1,150° C.

Meanwhile, in the present disclosure, as the austenite grain size increases, the fraction of the epsilon martensite phase into a final microstructure may increase, and thus, a higher temperature during heating is advantageous. In addition, as the heating temperature is higher, subsequent hot rolling may be performed more advantageously. However, since the present disclosure contains a large amount of Mn, if heating is performed at an excessively high temperature, internal oxidation may occur severely to degrade surface quality. Therefore, heating may be performed at 1,350° C. or lower, and more preferably, at 1,300° C. or lower.

As described above, the heated steel slab may be hot-rolled to be manufactured as a hot-rolled steel sheet. Here, it is preferable to perform finish hot rolling at a temperature (FDT (° C.)) that satisfies the following Relational Expression 1.


FDT(° C.)≥928+(480×C)+(450×N)+(0.9×Mn)+(65×Ti)  [Relational Expression 1]

(Here, each element represents a weight content)

Relational Expression 1 is an equation derived through a number of experiments, and is an important factor in manufacturing a high manganese steel material having excellent anti-vibration characteristics and formability targeted in the present disclosure.

Specifically, in the present disclosure, the growth and recrystallization of austenite grains to a sufficient size may be induced by performing finish hot rolling at a temperature exceeding the temperature at which full recrystallization occurs, from which an epsilon martensite phase may be stably secured in a follow-up cooling and/or coiling process.

If the temperature during finish hot rolling is lower than the temperature derived by Relational Expression 1, it may be difficult to induce growth and recrystallization of austenite grains, so that the epsilon martensite phase may not be sufficiently formed into a final microstructure and a non-recrystallized structure may be formed to lower the anti-vibration characteristics.

In addition, during the finish hot rolling, a total rolling reduction ratio may be 80% or more, more preferably, 90% or more. If the total rolling reduction ratio is 80% or more during the finish hot rolling, a recrystallization driving force may be sufficiently secured.

The hot-rolled steel sheet manufactured as described above may be cooled, and here, it is preferable to perform cooling to 700° C. or lower.

If an end temperature during cooling exceeds 700° C., scale may be generated excessively and an excessive process may be required to remove the scale, post-processing is interfered along with problems such as air pollution due to dust, which is thus not desirable.

In the present disclosure, cooling may be performed to room temperature, and in this case, there is an effect of securing more excellent anti-vibration characteristics compared to a high manganese anti-vibration steel manufactured by the existing post-heat treatment (see Table 3 below).

Therefore, in the present disclosure, it is preferable to terminate the cooling in a temperature range of 700° C. or lower, more preferably 500° C. or lower, and even more preferably, at room temperature to 300° C. during the cooling. As described above, as the cooling termination temperature decreases, the amount of residual austenite decreases, so it is more advantageous in securing the epsilon martensite phase in the final microstructure.

Meanwhile, cooling may be performed through normal water cooling (e.g., a cooling rate of 10° C./s or higher), and if the cooling termination temperature is room temperature to 300° C., the cooling termination temperature may be secured through rapid cooling. A cooling rate during rapid cooling is not particularly limited, but may be performed at a cooling rate of 50° C./s or more, for example, or may be performed at 200° C./s or less in consideration of equipment specifications.

Here, room temperature is not particularly limited, but refers to about 20 to 35° C.

In the present disclosure, after cooling is completed, a coiling process may be further performed at the corresponding temperature, which may be selectively performed in consideration of a thickness of a steel.

The high manganese steel material of the present disclosure obtained by completing the aforementioned cooling process includes an epsilon martensite phase with an area fraction of 90% or more and a fully recrystallized structure, that is, does not include a non-recrystallized structure, and thus, high anti-vibration characteristics and formability may be secured.

Hereinafter, a high manganese steel material having excellent anti-vibration characteristics and formability according to another aspect of the present disclosure will be described in detail.

Since the high manganese steel material of the present disclosure may be obtained by the aforementioned manufacturing process and has the aforementioned alloy composition, an alloy composition of the steel material is replaced by the previously mentioned matters.

The high manganese steel material of the present disclosure preferably includes epsilon martensite having an area fraction of 90% or more (including 100%) and the balance austenite phase in a microstructure. In particular, the present disclosure is a fully recrystallized structure that does not contain any non-recrystallized structure, thus securing excellent anti-vibration characteristics, and more preferably, the epsilon martensite phase may be included in an amount of 95% or more.

As such, the high manganese steel material of the present disclosure contains the epsilon martensite phase in a high fraction, and a residual dislocation is effectively removed by full recrystallization, whereby a rate in which the epsilon martensite phase converts impact energy into thermal energy when an external impact is applied is increased to contribute to improvement of damping performance.

Meanwhile, the high manganese steel material of the present disclosure does not include any phase other than the aforementioned phase as a microstructure. For example, the high manganese steel material of the present disclosure does not include an (α′)-martensite phase at all.

In particular, the present disclosure may form the epsilon martensite phase in a sufficient fraction and obtain excellent formability even if the high-cost heat treatment performed to manufacture the related art high manganese anti-vibration steel is omitted. Therefore, the high manganese steel material of the present disclosure will have an economically advantageous technical effect as compared to the related art high manganese anti-vibration steel.

Hereinafter, the present disclosure will be described in more detail through examples. However, it should be noted that the following examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. This is because the scope of the present disclosure is determined by matters described in the claims and matters reasonably inferred therefrom.

MODE FOR INVENTION Example

Steel slab having the alloy composition of Table 1 below was heated, hot-rolled, and cooled under the conditions shown in Table 2 to manufacture each hot-rolled steel sheet. Here, for comparison, a specific steel grade was subjected to a post-heat treatment, and the post-heat treatment was performed at 1000° C. for 30 minutes and thereafter air-cooling was performed.

TABLE 1 Relational Steel Alloy composition (wt %) Expression 1 grade C Mn N Ti Cr (FDT) 1 0.03 17.5 0.003 0.01 0.1 966 2 0.05 20 0.003 0.01 0 971 3 0.025 17 0.006 0.05 0 958

TABLE 2 Finish hot rolling Total Heating rolling Cooling Charge Target reduction Termination Application of Steel Sample Temperature time FDT FDT ratio temperature Rate post-heat grade No. (° C.) (min) (° C.) (° C.) (%) (° C.) (° C./s) treatment Classification 1 #1 1250 120 ≥966 970 92.5 700 27 Not Inventive applied Steel 1 1 #2 1250 120 ≥966 870 92.5 700 17 Not Comparative applied Steel 1 1 #3 1250 120 ≥966 860 92.5 400 46 Not Comparative applied Steel 2 1 #4 1250 120 ≥966 890 92.5 400 11 Not Comparative applied Steel 3 1 #5 1250 120 ≥966 905 92.5 30 87.5 Not Comparative applied Steel 4 2 #6 1200 120 ≥971 975 92.5 30 94.5 Not Inventive applied Steel 2 2 #7 1200 120 ≥971 980 92.5 400 58 Not Inventive applied Steel 3 2 #8 1200 120 ≥971 880 92.5 400 5 applied Comparative Steel 5 3 #9 1200 120 ≥958 966 90 30 93.6 Not Inventive applied Steel 4 3 #10 1300 120 ≥958 965 90 30 93.5 Not Inventive applied Steel 5 3 #11 1300 120 ≥958 982 90 30 95.2 Not Inventive applied Steel 6 3 #12 1200 120 ≥958 951 90 30 92.1 Not Comparative applied Steel 6 3 #13 1250 120 ≥958 923 90 400 52.3 Not Comparative applied Steel 7 3 #14 1250 120 ≥958 899 90 30 86.9 Not Comparative applied Steel 8 3 #15 1300 120 ≥958 926 90 30 89.6 Not Comparative applied Steel 9

Thereafter, mechanical properties and a microstructure of each hot-rolled steel sheet were measured and results thereof are shown in Table 3 below.

Here, for the measurement of mechanical properties, a tensile test piece of JIS No. 5 was manufactured, and then yield strength (YS), tensile strength (TS), and elongation (T-El and U-El) were measured. In addition, the microstructure was measured using X-ray diffraction (XRD), and a fraction of each phase was derived from a peak intensity of each phase.

As shown in FIG. 5, a loss rate for strain of 200 to 900 (m/(m×10−6)) was measured in a cantilever manner. Here, a loss rate value (Xn=(1/π)ln(Xn/Xn+1)) at the strain 900 (m/(m×10−6)) is shown in Table 3 below.

TABLE 3 Mechanical properties YS TS T-El U-El Microstructure (fraction %) Loss Classification (MPa) (MPa) (%) (%) α′-M Y ε-M rate Inventive 390 791 40.2 32 0 2.0 98.0 0.055 Steel 1 Comparative 630 896 31.2 16 10.5 1.5 88.0 0.013 Steel 1 Comparative 603 907 35.8 20 6.5 0.9 92.6 0.012 Steel 2 Comparative 629 905 35.8 33 6.0 2.0 92.0 0.015 Steel 3 Comparative 583 905 37.1 31 7.4 1.6 91.0 0.013 Steel 4 Inventive 404 810 52.7 50 0 1.0 99.0 0.065 Steel 2 Inventive 419 822 51.7 30 0 1.5 98.5 0.055 Steel 3 Comparative 363 779 52.5 33 0 1.0 99.0 0.058 Steel 5 Inventive 505 869 42.9 22.4 0 3.5 96.5 0.048 Steel 4 Inventive 433 838 45.2 29.1 0 1.9 98.1 0.056 Steel 5 Inventive 418 805 44.4 26.5 0 1.3 98.7 0.060 Steel 6 Comparative 912 523 26.3 22 9.4 0.9 89.7 0.010 Steel 6 Comparative 881 534 36.7 19.2 8.1 1.0 90.9 0.012 Steel 7 Comparative 892 550 38.6 19.8 6.7 0 93.3 0.014 Steel 8 Comparative 877 587 35.0 18.5 5.3 0.9 93.8 0.019 Steel 9

(In Table 3, α′-M represents an alpha′-martensite, γ represents austenite, and ε-M represents an epsilon martensite phase.)

As shown in Table 1 to Table 3, in Inventive Steels 1 to 6, satisfying the alloy composition and manufacturing conditions, on which finish hot rolling was performed at a temperature that satisfies Relational Expression 1 proposed in the present disclosure and the cooling was terminated at 700° C. or lower, all the epsilon martensite phases were 95% or more, securing excellent anti-vibration characteristics.

In addition, as the total elongation exceeds 40% in all of the Inventive Steels 1 to 6, it can be confirmed that formability is also excellent.

Thus, it can be seen that the Inventive Steels 1 to 6 have anti-vibration characteristics and formability equivalent to or higher than those of the high manganese anti-vibration steel (see Comparative Steel 5) subjected to a post-heat treatment in the related art.

Meanwhile, in the case of Comparative Steels 1 to 4 and 6 to 9 that do not satisfy the manufacturing conditions (Relational Expression 1, etc.) of the present disclosure, α′-martensite phase was formed, showing inferior anti-vibration characteristics, and a total elongation was secured to less than 40%, showing inferior formability.

FIG. 1 is a graph showing a loss rate value at a strain of 900 (m/(m×10−6)) of each sample over FDT (° C.).

As shown in FIG. 1, only Inventive Steels 1 to 6, which were subjected to finish hot rolling at a temperature that satisfies Relational Expression 1 of the present disclosure, showed a loss rate of 0.05 or more, which means that Inventive Steels 1 to 6 have the effect equal to or higher than that of Comparative Steel 5 subjected to a post-heat treatment.

FIG. 2 is a graph showing a loss rate value at a strain of 200 to 900 (m/(m×10−6)) of some samples.

As shown in FIG. 2, it can be seen that, in the case of Inventive Steels, the loss rate increases as the strain increases, and this means that Inventive Steels have an effect equal to or higher than that of Comparative Steel 5 subjected to a post-heat treatment. Meanwhile, in the case of Comparative Steels, it can be seen that a loss rate does not exceed 0.020 even if the strain is high.

FIG. 3 shows an image of a microstructure of Inventive Steel 4, and it can be seen that the microstructure is mostly formed in an epsilon martensite phase.

FIG. 4 shows XRD measurement results of Inventive Steel 6 and Comparative Steel 6.

As shown in FIG. 4, it can be seen that, in Comparative Steel 6, a peak on a′-martensite is observed, whereas in Inventive Steel 6, only peaks of the epsilon martensite phase and the austenite phase are observed and that an intensity of the epsilon martensite phase is greater.

Claims

1. A method of manufacturing a high manganese steel material having excellent anti-vibration characteristics and formability, the method comprising:

heating a steel slab including, in percentages by weight, 0.1% or less of carbon (C), 8 to 30% of manganese (Mn), 3.0% or less of silicon (Si), 0.1% or less of phosphorus, 0.02% or less of sulfur (S), 0.1% or less of nitrogen (N), 1.0% or less (excluding 0%) of titanium (Ti), 0.01% or less of boron (B), the balance iron (F) and other inevitable impurities at 1,150 to 1,350° C.;
finish hot-rolling the heated steel slab to manufacture a hot-rolled steel plate; and
cooling the hot-rolled steel plate to 700° C. or lower,
wherein the finish hot-rolling is performed at a finishing delivery temperature (FDT) (° C.) satisfying Relational Expression 1 below: FDT(° C.)≥928+(480×C)+(450×N)+(0.9×Mn)+(65×Ti)  [Relational Expression 1]
wherein each element represents content by weight.

2. The method of claim 1, wherein the finish hot-rolling is performed with a total rolling reduction ratio of 80% or more.

3. The method of claim 1, wherein the cooling is terminated at room temperature to 300° C.

4. The method of claim 1, wherein an epsilon martensite phase in an area fraction of 90% or more is included after the cooling.

5. The method of claim 1, further comprising performing coiling after the cooling.

6. The method of claim 1, wherein the steel slab further includes, in percentages by weight, one or more of 0.005 to 2.0% of nickel (Ni) and 0.005 to 5.0% of chromium (Cr).

7. The method of claim 1, wherein the steel slab further includes, in percentages by weight, one or more of 0.005 to 0.5% of niobium (Nb), 0.005 to 0.5% of vanadium (V), and 0.005 to 1.0% of tungsten (W).

8. A steel material manufactured by the manufacturing method of claim 1, comprising, in percentages by weight, 0.1% or less of carbon (C), 8 to 30% of manganese (Mn), 3.0% or less of silicon (Si), 0.1% or less of phosphorus (P), 0.02% or less of sulfur (S), 0.1% or less of nitrogen (N), 1.0% or less (excluding 0%) of titanium (Ti), 0.01% or less of boron (B), the balance iron (F), and other inevitable impurities,

wherein the steel material has a microstructure comprising an epsilon martensite phase in an area fraction of 90% or more and the rest austenite phase, being a fully recrystallized structure.

9. The steel material of claim 8, further comprising, in percentages by weight, one or more of 0.005 to 2.0% of nickel (Ni) and 0.005 to 5.0% of chromium (Cr).

10. The steel material of claim 8, further comprising, in percentages by weight, one or more of 0.005 to 0.5% of niobium (Nb), 0.005 to 0.5% of vanadium (V), and 0.005 to 1.0% of tungsten (W).

Patent History
Publication number: 20210381074
Type: Application
Filed: Dec 10, 2018
Publication Date: Dec 9, 2021
Inventors: Won-Tae Cho (Gwangyang-si, Jeollanam-do), Eung-Soo Kim (Incheon), Sung-Kyu Kim (Gwangyang-si, Jeollanam-do), Tae-Kyo Han (Gwangyang-si, Jeollanam-do)
Application Number: 17/282,481
Classifications
International Classification: C21D 9/46 (20060101); C22C 38/38 (20060101); C22C 38/28 (20060101); C22C 38/00 (20060101); C21D 8/02 (20060101); C21D 6/00 (20060101);