CN108474082B

CN108474082B - High manganese steel sheet having excellent vibration-proof properties and method for producing same

Info

Publication number: CN108474082B
Application number: CN201680075456.1A
Authority: CN
Inventors: 赵原兑; 金泰昊; 陈光根; 金泳河; 宋泰鎭
Original assignee: Posco Co Ltd
Current assignee: Posco Holdings Inc
Priority date: 2015-12-23
Filing date: 2016-12-21
Publication date: 2020-06-02
Anticipated expiration: 2036-12-21
Also published as: WO2017111473A1; EP3395978A4; EP3395978A1; KR101736636B1; EP3395978B1; US20180371586A1; JP2019504208A; CN108474082A

Abstract

The present invention relates to a high manganese steel sheet and a method for manufacturing the same, the steel sheet comprising, in weight%: c: 0 to 0.1% or less, Mn: 8-30%, P: 0.1% or less, S: 0.02% or less, N: 0.1% or less, Ti: 0 to 1.0% of Fe and inevitable impurities, and the microstructure comprises epsilon martensite and austenite, and the average grain diameter of the martensite and the austenite is less than 2 mu m.

Description

High manganese steel sheet having excellent vibration-proof properties and method for producing same

Technical Field

The present invention relates to a high manganese steel sheet having excellent vibration-proof characteristics, which can be used in a place where vibration-proof characteristics for reducing noise are required, by being manufactured as a steel sheet for automobiles or buildings.

Background

In recent years, noise reduction has been a problem that manufacturers must solve for automobile manufacturing and building materials. In particular, excellent mechanical characteristics and vibration damping characteristics are required for structural members such as an engine part and an oil pan, which generate large noise, by automobile manufacturers. In recent years, as building materials, vibration-proof steel sheets have been developed as floors for multistoried buildings including apartments due to the enhancement of the interlayer noise control.

The high manganese vibration-proof steel is a steel grade having high vibration-proof characteristics and excellent mechanical properties by converting noise energy into thermal energy by interfacial slippage of epsilon martensite upon external impact, and is therefore suitable for the purpose as described above.

Disclosure of Invention

Technical problem to be solved

The present invention aims to provide a high manganese steel sheet having excellent vibration-proof characteristics and a method for producing the same.

Technical scheme

A preferred aspect of the present invention relates to a high manganese steel sheet having excellent vibration-proof characteristics, the steel sheet comprising, in weight%: c: 0 to 0.1% or less, Mn: 8-30%, P: 0.1% or less, S: 0.02% or less, N: 0.1% or less, Ti: 0 to 1.0% of Fe and inevitable impurities, and the microstructure comprises epsilon martensite and austenite, and the average grain diameter of the martensite and the austenite is less than 2 mu m.

Further, another preferred aspect of the present invention relates to a method of manufacturing a high manganese steel sheet excellent in vibration-proof characteristics, the method comprising the steps of: heating the steel plate satisfying the composition range to a heat treatment temperature of Ac 1-Ac 3+50 ℃ at a heating rate of 0.01-200 ℃/s; maintaining the temperature for 0.01 second to 24 hours at the heat treatment temperature; and cooling to normal temperature at a cooling rate of 0.01 ℃/sec or more.

Advantageous effects

The present invention can provide a high manganese steel sheet having excellent vibration damping characteristics, and therefore can be used for structural members for automobiles, floor materials for building materials, and the like, which require noise reduction.

Drawings

FIG. 1 is a view showing the microstructure of an example in which heat treatment is performed at 600 ℃ and a comparative example in which heat treatment is performed at 700 to 1000 ℃.

Fig. 2 is a graph showing a dilatometer cycle (cycle) of the heat treatment shown in fig. 1.

Fig. 3 is a graph showing the results of measuring the Specific Damming Capacity (SDC) of the examples and comparative example (4) by the internal resistance method.

Best mode for carrying out the invention

The present invention will be described in detail below.

The present invention relates to a high manganese steel sheet having excellent vibration-proof characteristics, comprising, in weight%: c: 0 to 0.1% or less, Mn: 8-30%, P: 0.1% or less (including 0%), S: 0.02% or less (including 0%), N: 0.1% or less (including 0%), Ti: 1.0% or less (excluding 0), Fe and inevitable impurities, and a microstructure composed of [ epsilon ] martensite and austenite, wherein the average grain size of martensite and austenite is 2 [ mu ] m or less.

The reasons why the specific steel composition and the components of the steel sheet of the present invention are limited are as follows.

In the case where the amount of C added exceeds 0.1%, excessive carbide precipitates to reduce hot workability and elongation and greatly reduce vibration-proof ability, so that the amount of C added is limited to 0.1% or less.

Mn is an element necessary for stably securing an austenite structure and increasing stacking fault energy, and when the amount of Mn added is less than 8%, since martensite which impairs formability is formed, strength is increased, but ductility is drastically decreased. Further, since the stacking fault energy is lowered and a part of austenite formed is easily transformed into e martensite, the lower limit of Mn is limited to 8%. On the other hand, when the amount of Mn added exceeds 30%, the manufacturing cost increases due to a large amount of manganese, and the slab cracks due to an increase in the content of phosphorus (P) in the steel. Further, the upper limit of the amount of Mn added is limited to 30% because excessive internal grain boundary oxidation occurs when reheating a slab, thereby causing oxide defects on the surface of a steel sheet and deteriorating surface properties when hot dip galvanizing.

Phosphorus (P) and sulfur (S) are elements that are inevitably contained when manufacturing steel, and therefore the content of phosphorus (P) is preferably limited to 0.1% or less (including 0%), and the content of sulfur (S) is preferably limited to 0.02% or less (including 0%). In particular, phosphorus segregates to reduce the workability of steel, while sulfur forms coarse manganese sulfide (MnS) to cause defects such as flange cracks and reduce the hole expansibility of steel sheets, so that it is necessary to suppress the amounts of phosphorus and sulfur to the maximum.

Nitrogen (N) is an element that is inevitably contained during production, and therefore, the range of N addition is preferably limited to 0.1% or less (including 0%).

Titanium (Ti) is a strong carbide-forming element that forms carbide by bonding with carbon, and since the carbide formed at this time inhibits the growth of crystal grains, Ti is an element effective for refining the grain size. When titanium and boron are added in a combined manner, a high-temperature compound is formed in the grain boundary of the columnar crystal, and grain boundary cracking is prevented. Further, Ti is an element necessary for improving the vibration-proof capability because it forms a compound with C, N to have a removing (scutening) effect of reducing their fraction. However, when the content of Ti exceeds 1.00%, excessive titanium segregates in grain boundaries to cause grain boundary embrittlement, or precipitation phase transformation becomes too coarse to reduce the grain growth effect, so the amount of titanium added is limited to 1.0% or less.

The high manganese steel of another aspect of the present invention may further comprise, in wt%: si: 0-3%, Cr: 0.005% -5.0%, Ni: 0.005-2.0%, Nb: 0.005-0.5%, B: 0.0001-0.01%, V: 0.005-0.5% and W: 0.005-1% of one or more than two.

Silicon (Si) is a solid-solution strengthening element, and is an element that increases yield strength by reducing crystal grain size by a solid-solution effect, and silicon needs to be added in order to secure strength. However, when the amount of silicon added is increased, silicon oxide is formed on the surface of the steel sheet during hot rolling, and pickling property is deteriorated, thereby having a disadvantage of deteriorating surface quality of the steel sheet. Moreover, when a large amount of silicon is added, weldability of steel is greatly reduced. Therefore, the upper limit of the amount of silicon added may be limited to 3%.

Cr reacts with external oxygen during hot rolling or annealing to preferentially form a Cr-based oxide film (Cr) having a thickness of 20 to 50 μm on the surface of the steel sheet₂O₃) Thereby preventing Mn, Si, and the like contained in the steel from being eluted into the surface layer, contributing to stabilization of the surface layer structure, and functioning as an element for improving the plating surface characteristics.

However, the above effect is slight when the content of Cr is less than 0.005%, and chromium carbide is formed when the content of Cr exceeds 5.0%, thereby deteriorating workability and delayed fracture resistance, so the upper limit of the content of Cr may be limited to 5.0%.

Ni is an element that contributes not only to stabilization of austenite and contributes to improvement of elongation but also, in particular, effectively contributes to improvement of high-temperature ductility. Ni is a powerful element for improving high temperature toughness, and when the content of Ni is less than 0.005%, the effect on high temperature toughness is very small, and the more the amount of Ni added, the more remarkable the effect on prevention of delayed fracture resistance and slab cracking, but since the cost of the material is high, the production cost is increased, the content of Ni may be limited to 0.005 to 2.0%.

Nb is a carbide-forming element that forms carbides by bonding with carbon in steel, and in the present invention, Nb can be added for the purpose of improving strength and refining the grain size. In general, Nb forms a precipitate phase at a temperature lower than Ti, and therefore Nb is an element having a large precipitation strengthening effect by grain size refinement and precipitate phase formation, and 0.005 to 0.5% of Nb can be added. However, when the addition amount of Nb is less than 0.005%, the effect is small, while when the addition amount of Nb exceeds 0.5%, excessive Nb segregates in grain boundaries to cause grain boundary embrittlement, or precipitation phase transformation is too coarse to reduce the grain growth effect, and recrystallization is delayed in the hot rolling step to increase the rolling load, so the addition amount of Nb may be limited to 0.005 to 0.5%.

As Ti, V and W are elements that form carbonitrides in combination with C, N, V and W form fine precipitated phases at low temperatures in the present invention, and thus may have a precipitation strengthening effect, and may be important elements for ensuring austenite. However, when V and W are added in a small amount of less than 0.005%, the effect is small, and when V is added in an amount of more than 0.5% and W is added in an amount of more than 1.0%, precipitation phase is too coarsened to reduce the effect of grain growth and cause hot shortness, so the amount of V added may be limited to 0.005 to 0.5% and the amount of W added may be limited to 0.005 to 1%.

Boron (B) may be added together with Ti and form a high-temperature compound of grain boundaries, so that grain boundary cracks can be prevented. However, the addition of B in a trace amount of 0.0001% or less is not effective, and when the addition amount of B exceeds 0.01%, a boron compound is formed to deteriorate the surface characteristics, so that the range of boron may be limited to 0.0001 to 0.01%.

Next, a method for producing a high manganese steel sheet having excellent vibration-proof characteristics according to the present invention will be described.

In the method for producing a high manganese steel sheet according to the present invention, a steel having the above-described components and component ranges and having a microstructure composed of an austenite main phase is heated at a temperature rise rate of 0.01 to 200 ℃/sec, maintained at a heat treatment temperature of Ac1 to Ac3+50 ℃ for 0.01 to 24 hours, and then cooled to room temperature at a cooling rate of 0.01 ℃/sec or more.

The high manganese steel sheet may be a cold-rolled steel sheet or a hot-rolled steel sheet.

The fine structure of the high manganese steel sheet is composed of epsilon martensite and austenite.

When the temperature increase rate in the heating step exceeds 200 ℃/sec, the temperatures of Ac1 and Ac3 rise, and even if the heat treatment is performed under the condition range of the present invention, the average grain size of the microstructure exceeds 2 μm, so the upper limit of the temperature increase rate is limited to 200 ℃/sec. When the operation is performed at a temperature rise rate of 0.01 ℃/sec or less, coarse carbide is generated due to instability of the phase, and therefore, it is necessary to perform heat treatment at a rate of 0.01 ℃/sec or less.

When the heat treatment is performed at a temperature lower than Ac1, transformation does not proceed, and there is a problem that the heat treatment effect does not occur, and when the heat treatment temperature exceeds Ac3+50 ℃, there is a problem that the average grain size of the microstructure exceeds 2 μm, so the heat treatment temperature needs to be limited to Ac1 to Ac3+50 ℃.

When the heat treatment time is less than 0.01 second, the recrystallization and recovery effects are minute so that the heat treatment effect does not appear, and when the heat treatment time exceeds 24 hours, excessive oxidation is generated so that the base iron is corroded to disappear and excessive heat treatment costs are consumed, and there are problems in that the average particle size of the grown fine structure exceeds a desired average particle size.

When cooling is performed at a cooling rate of less than 0.01 ℃/sec in the cooling step, the average grain size of the microstructure increases during the cooling process, and coarse carbide particles are generated due to phase instability, so the lower limit of the cooling rate is limited to 0.01 ℃/sec. The upper limit of the cooling rate is not set, and it is advantageous to ensure the average grain size of the epsilon martensite and the microstructure as the cooling rate is higher.

Detailed Description

Hereinafter, examples of the present invention will be described in detail. The following examples are only for the understanding of the present invention and do not limit the present invention.

A cold-rolled steel sheet, which is heated at a temperature rising rate of 5 ℃/sec and maintained during a heat treatment period at a heat treatment temperature as shown in the following table 1, and then cooled to normal temperature at a cooling rate of 5 ℃/sec, comprises in wt%: c: 0.02%, Mn: 17%, N: 0.01, P: 0.008, S: 0.008%, Ti: 0.03%, Fe and inevitable impurities.

The average grain size of the microstructure and the fraction of the epsilon martensite of the steel sheet heat-treated and cooled as described above were examined, and the results are shown in table 1 and fig. 1 below.

[ Table 1]

Distinguishing	Temperature of Heat treatment (. degree.C.)	Heat treatment time (minutes)	Particle size (. mu.m)	Area fraction of epsilon martensite (%)
					Examples	600	30	1.23	6.2
Comparative example 1	700	30	2.3	3
					Comparative example 2	800	30	3.6	14.9
Comparative example 3	900	10	6.7	16.8
					Comparative example 4	1000	30	6.7	34.6

As shown in table 1 and fig. 1, comparing the examples subjected to the heat treatment at 600 ℃ with the comparative examples (1-4) subjected to the heat treatment at 700 to 1000 ℃, it can be seen that the area fraction of the epsilon martensite is lower and the particle size is larger in the comparative example (1) in which the heat treatment temperature is 700 ℃ than in the examples subjected to the heat treatment at 600 ℃.

In addition, the area fractions of epsilon martensite in comparative examples (2-4) in which the heat treatment temperatures were 800 ℃, 900 ℃ and 1000 ℃ respectively were larger than those in examples in which heat treatment was performed at 600 ℃, but the particle size in examples in which heat treatment was performed at 600 ℃ was smaller than that in comparative examples (2-4) in which heat treatment was performed at 700 to 1000 ℃.

It is also understood that the average particle size of the microstructure of the example of the present invention in which the heat treatment is performed at 600 ℃ is 2 μm or less.

Fig. 2 is a graph showing a dilatometer cycle of the heat treatment shown in fig. 1.

Ac1 and Ac3 were confirmed by fig. 2, and the examples were the results of heat treatment at Ac3+30 ℃.

Fig. 3 shows the results of measuring the Specific Damming Capacity (SDC) of the example heat-treated at 600 ℃ and the comparative example (4) heat-treated at 1000 ℃ by the coefficient of friction method.

Where SDC denotes damping performance (the property of an object to absorb vibration).

Referring to fig. 1 and 3, it can be seen that the anti-vibration steel having a microstructure of the example heat-treated at 600 ℃ had a value of 2.5 times higher SDC at normal temperature than the anti-vibration steel of comparative example (4). That is, the SDC value measured for the example heat-treated at 600 ℃ was 0.00025, and the SDC value measured for the comparative example (4) heat-treated at 1000 ℃ was 0.0001.

The area fraction of the epsilon martensite of the example in which the heat treatment is performed at 600 ℃ is relatively low, but the grain size is small, and thus the structure is fine and uniformly distributed, so that when an external impact is applied together with the epsilon martensite along with residual dislocations (dislocations) and interfaces, the ratio of energy to heat energy is increased, thereby contributing to an improvement in damping performance, and thus the anti-vibration characteristics are excellent.

Generally, when the SDC value at room temperature is 0.00015 or more, the vibration damping characteristics are considered to be excellent.

From the above results, it was found that when the heat treatment is performed according to the present invention, an average particle diameter of 2 μm or less can be secured, and excellent vibration-proof characteristics can be secured.

In the comparative examples, except for the comparative example in which heat treatment was performed at 700 ℃, although the area fraction of epsilon martensite was higher than that in the examples, the average particle size of the microstructure was large, and therefore the vibration damping performance was poor.

Claims

1. A high manganese steel sheet having excellent vibration-proof properties, comprising, in weight%: c: 0.1% or less, Mn: 8-30%, P: 0.1% or less, S: 0.02% or less, N: 0.1% or less, Ti: 0 to 1.0% of Fe and inevitable impurities, wherein the microstructure comprises epsilon martensite and austenite, the average grain diameter of the epsilon martensite and the austenite is less than 2 mu m, and the SDC value at normal temperature of the steel plate is more than 0.00015.

2. The high manganese steel sheet excellent in vibration-proofing characteristics according to claim 1, characterized by further comprising, in weight%: si: 0-3%, Cr: 0.005% -5.0%, Ni: 0.005-2.0%, Nb: 0.005-0.5%, B: 0.0001-0.01%, V: 0.005-0.5% and W: 0.005-1% of one or more than two.

3. A method for manufacturing a high manganese steel sheet having excellent vibration-proof characteristics, comprising the steps of:

heating a high manganese steel plate to a heat treatment temperature of Ac 1-Ac 3+50 ℃ at a heating rate of 0.01-200 ℃/sec, wherein the high manganese steel plate comprises the following components in percentage by weight: c: 0 to 0.1% or less, Mn: 8-30%, P: 0.1% or less, S: 0.02% or less, N: 0.1% or less, Ti: 0-1.0% of Fe and inevitable impurities;

maintaining the temperature for 0.01 second to 24 hours at the heat treatment temperature; and

cooling to normal temperature at a cooling rate of 0.01 ℃/s or more,

wherein the fine structure of the high manganese steel sheet comprises epsilon martensite and austenite, the average grain diameter of the epsilon martensite and austenite is less than 2 mu m,

wherein the normal temperature SDC value of the high manganese steel plate is more than 0.00015.

4. The method for manufacturing a high manganese steel sheet excellent in vibration-proof characteristics according to claim 3, wherein said steel sheet further comprises, in weight%: si: 0-3%, Cr: 0.005% -5.0%, Ni: 0.005-2.0%, Nb: 0.005-0.5%, B: 0.0001-0.01%, V: 0.005-0.5% and W: 0.005-1% of one or more than two.