KR20160078829A - Steel having excellent machinability and vibration damping ability and manufacturing method thereof - Google Patents

Abstract

The present invention provides steel having excellent machinability and vibration damping ability, which comprises: 0.80-1.20 wt% of C; 2.0-3.0 wt% of Si; 0.01-1.00 wt% of Mn; 0.01-0.03 wt% of Al; 0.001-0.010 wt% of Mg; an amount equal to or less than 0.030 wt% of P; an amount equal to or less than 0.030 wt% of S; 0.002-0.006 wt% of B; 0.004-0.008 wt% of N; an amount equal to or less than 0.005 wt% of O; and the remainder consisting of Fe and inevitable impurities.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a steel material having excellent machinability and vibration damping capability,

TECHNICAL FIELD The present invention relates to a steel material which can be used for an industrial machine, a machine part such as an automobile, and the like, and more particularly, to a steel material excellent in not only cutting ability but also vibration damping ability and a manufacturing method thereof.

In the case of cutting, the higher the hardness of the steel to be machined is, the larger the tool wear is, and therefore the tool life is shortened. Therefore, the lower the hardness of the steel to be machined, the better the machining. In addition, if the chip is not properly segmented during the cutting process, the generated chips are not properly discharged, which may cause breakage of the tool. Particularly, in recent years, there are many cases where cutting is performed unattended by an automatic lathe, so that the chips are complicatedly tangled and unnecessary work is required to remove them.

Therefore, there is a demand for a steel material excellent in chip processability in which the chip is divided into a proper length as well as a tool life. For this purpose, Pb, Bi, S and the like have been added to improve machinability. Since the melting point of Pb is very low at about 327 ° C, Pb distributed in the steel during melting is melted to embrittle the steel to improve the chip processability, and the molten Pb acts as a lubricant during cutting, do.

However, Pb, which is a typical cutting-improving element, is a harmful element to the human body by discharging toxic gas during cutting, which is disadvantageous in terms of recycling of steel. S, Bi, Sn, etc. have been proposed to replace these elements. However, these elements have only a small improvement in machinability, and some elements are very expensive, so they are limited to substitute elements of Pb. For example, S is effective for improving machinability. However, when a large amount of S is added, a large amount of MnS stretched in the hot working direction is formed in a large amount, causing anisotropy in mechanical properties, resulting in lowering toughness. As a result, the ends are cracked at the time of hot rolling, and in order to compensate for this, work such as finely sharpening the top end of the pencil is added to decrease the productivity.

On the other hand, the vibration damping capability refers to a characteristic of converting the vibration energy into thermal energy and damping the magnitude of the vibration itself in the material itself. In order to suppress noise in the fields of paper making, printing, textile machine parts, A material having damping ability is required. Representative metal materials used for this purpose include gray cast iron and Fe-Mn based alloys. In the case of gray cast iron, it is known that graphite dispersed as a flake on the base absorbs vibration energy, and Fe-Mn alloy has been reported to have vibration damping ability by phase transformation. However, in carbon steels which can be produced economically while being widely used, there has been little report on steels having vibration damping ability.

An aspect of the present invention is to provide a steel having excellent cutting performance as well as vibration damping ability.

An aspect of the present invention is to provide a method of manufacturing a steel material having excellent machinability and vibration damping ability.

An aspect of the present invention provides a method of manufacturing a semiconductor device, comprising: 0.80 to 1.20% of C, 2.0 to 3.0% of Si, 0.01 to 1.00% of Mn, 0.01 to 0.03% of Al, 0.001 to 0.010% By mass, S: not more than 0.030%, B: 0.002 to 0.006%, N: 0.004 to 0.008%, O: 0.005% or less, and the balance Fe and other unavoidable impurities.

In another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising, by weight%, 0.80 to 1.20% of C, 2.0 to 3.0% of Si, 0.01 to 1.00% of Mn, 0.01 to 0.03% of Al, 0.001 to 0.010% The steel containing S: not more than 0.030%, B: 0.002 to 0.006%, N: 0.004 to 0.008%, O: 0.005% or less and the balance Fe and other unavoidable impurities at a temperature of 700 to 770 캜 for 30 to 90 minutes And a step of subjecting the steel sheet to heat treatment for a predetermined period of time.

According to the present invention, it is possible to realize a steel material having excellent machinability and vibration damping ability. Therefore, when applied to a steel material used for parts such as automobiles or industrial machines, the life of cutting tools is increased to increase the efficiency of production, It is possible to reduce the generated vibration and noise.

The present invention relates to a steel having excellent machinability and vibration damping ability and a method of manufacturing the same.

In the present invention, it is intended to achieve the object of increasing the machinability by actively utilizing graphite. When graphite is dispersed and uniformly distributed on a steel base, graphite can serve as a cutting-imparting element such as Pb and Bi at the time of cutting, so graphite acts as a solid lubricant during cutting to suppress abrasion of cutting tool And also acts as a crack source, so that the chip can be short-circuited.

On the other hand, graphite not only improves machinability but also improves vibration damping ability. Vibration damping capacity refers to the characteristic of converting the vibration energy into heat energy and damping the magnitude of the vibration itself in the material itself. This is because the difference in modulus of elasticity between ferrite and graphite is so large that permanent deformation of graphite interferes with recovery of elastic deformation of ferrite and attenuates vibration.

As described above, graphite can play a role of improving machinability and vibration damping ability. However, when carbon is added to steel, graphite is precipitated in cementite, which is a metastable phase, even though graphite is stable. It is not easy to obtain and is not used for general steel materials. That is, in order to precipitate graphite, annealing for a long time is required, which not only increases the heat treatment cost but also causes decarburization of the steel during the heat treatment, which adversely affects the performance of the final part.

In order to solve this problem, in the present invention, the graphitization heat treatment time can be shortened to one hour or less by performing graphitization heat treatment in a temperature range in which graphite is most easily added by adding C and Si in an excess amount to promote graphitization Can be provided.

The steel material excellent in machinability and vibration attenuating ability in one aspect of the present invention comprises, by weight%, 0.80 to 1.20% of C, 2.0 to 3.0% of Si, 0.01 to 1.00% of Mn, 0.01 to 0.03% of Al, % Of P, 0.030% or less of P, 0.030% or less of S, 0.002 to 0.006% of B, 0.004 to 0.008% of N and 0.005% or less of O and the balance of Fe and other unavoidable impurities.

Hereinafter, the reasons for limiting the composition of the steel material will be described in detail. (All the composition of the following components means weight% unless otherwise specified.)

Carbon (C): 0.80 to 1.20%

Carbon is an element of graphite and is an essential element for forming graphite. One of the ways to graphitize graphite as soon as possible during cementation during cold rolling or during cold rolling of steel is to increase carbon activity. When the carbon content is less than 0.80%, the effect is small. When the carbon content is more than 1.20%, the effect is saturated and the hot ductility is deteriorated. Therefore, it is preferable to limit the carbon content range to 0.80 to 1.20%.

Silicon (Si): 2.0 to 3.0%

Silicon is a component necessary as a deoxidizing agent in the production of molten steel, and it is positively added since it is a graphitization-promoting element which causes carbon to be precipitated into graphite by destabilizing cementite in the steel. If the content is less than 2.0%, the effect is small. If it is added in an amount of more than 3.0%, the effect of promoting graphitization is saturated, and the brittleness caused by the increase of nonmetallic inclusions and decarburization during hot rolling can be increased. It is preferable to limit it.

Manganese (Mn): 0.01 to 1.00%

Manganese is an alloying element that increases the strength of the steel and affects the impact properties. It increases the rolling property and reduces the brittleness, but also the graphite production rate. When manganese is added at less than 0.01%, the strength strengthening effect is too weak. If the manganese is added in excess of 1.00%, the graphitization time becomes longer and the heat treatment cost increases.

Aluminum (Al): 0.01 to 0.03%

Aluminum is added as a deoxidizing element which forms an oxide by binding with oxygen and acts to promote graphitization, so that the machinability can be improved by sufficiently securing the solid solution Al. Further, Al is combined with N to form nitride (AlN), which has the effect of making crystal grains finer by grain peening effect and improving toughness of steel. In the present invention, aluminum is positively added. When the content is less than 0.01%, it is difficult to expect the addition effect. When the content is more than 0.03%, the promoting effect of graphitization is saturated and the hot deformability is remarkably decreased. %. ≪ / RTI >

Magnesium (Mg): 0.001 to 0.010%

Magnesium combines with oxygen to form oxides such as MgO. This contributes to the effect of generating graphite or BN nucleation site by homogeneous or complex inclusions with sulfide to uniformly disperse graphite. In addition, it acts to neutralize the graphite morphology so that uniform microstructure is formed. However, when the Mg content is less than 0.001%, the effect is small. When the Mg content exceeds 0.01%, steelmaking becomes difficult, so it is preferable that the Mg content is limited to the range of 0.001 to 0.010%.

Phosphorus (P): 0.030% or less

Phosphorus is an element promoting graphitization, but it increases the hardness of ferrite and is segregated in grain boundaries to lower toughness, reduce delayed fracture resistance, and promote the occurrence of surface defects. In order to prevent such side effects, the content of phosphorus is preferably limited to 0.030% or less.

Sulfur (S): not more than 0.030%

Sulfur is not only an element significantly inhibiting graphitization but also segregated in crystal grain boundaries to lower toughness and form a low melting point emulsion to inhibit hot rolling, so that the upper limit is preferably limited to 0.030%.

Boron (B): 0.002 to 0.006%

Boron is an element that is positively added because it bonds with nitrogen to form boron nitride (BN) and acts as nuclei of graphite to promote graphitization. If it is less than 0.002%, it is necessary to add 0.002% or more, and if it is added in an amount exceeding 0.006%, no further increase in effect can be expected, and at the same time, the grain boundary strength due to precipitation of boron- To lower the hot workability, it is preferable to limit the addition range to 0.002 to 0.006%.

Nitrogen (N): 0.004 to 0.008%

Nitrogen bonds with boron and aluminum to form nitrides, which serve as nuclei to promote the formation and growth of graphite. On the other hand, in order to form nitrides effective for promoting graphitization, it is necessary to add about the equivalent of boron and aluminum. However, in order to uniformly and finely disperse these nitrides, it is preferable to add a little higher than a chemical equivalent. It is also advantageous to add a little too much nitrogen because nitrogen improves chip processability by dynamic strain aging. For this reason, it is necessary to add 0.004% or more, but when it is added in excess of 0.008%, the effect is saturated, so it is preferable to be limited to 0.004% to 0.008%.

Oxygen (O): not more than 0.005%

Oxygen bonds with aluminum to form oxides. The formation of such oxides reduces the effective concentration of aluminum. As a result, the amount of AlN that is useful for the crystallization of graphite is reduced and, as a result, substantially prevents graphitization. In addition, the alumina oxide formed by the presence of a large amount of oxygen damages the cutting tool at the time of cutting, resulting in a deterioration in machinability. For this reason, it is desirable to manage as low as possible. The upper limit of 0.005% is preferably limited to 0.005% or less because the problems caused by the oxygen are not so serious.

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. The son impurities are not specifically mentioned in this specification, as they are known to anyone skilled in the art of manufacturing.

It is preferable that the microstructure of the steel material of the present invention having the above-described composition range contains at least 90% of ferrite in an area fraction. If the steel microstructure contains less than 90% of ferrite as an area fraction and the non-graphitized residual pearlite is present, the hardness is increased to increase the degree of tool wear at the time of cutting, thereby lowering machinability, , The vibration damping capability is reduced. Therefore, it is preferable that the microstructure of the steel material of the present invention contains at least 90% of ferrite in an area fraction.

Further, it is preferable that the steel material of the present invention includes black allium at an area fraction of 2 to 4%. In order to secure machinability and vibration damping ability, it is necessary to secure a certain amount of graphite or more, and preferably, when the black allied portion is 2% or more in the area fraction, the cutting ability and vibration damping ability improvement effect can be obtained. If the graphite fraction exceeds 4%, carbon should be added in an amount of more than 1.2% by weight. In this case, not only the effect of machinability and vibration damping ability is saturated but also the hot ductility is lowered, Preferably 2 to 4% of black alumina.

Here, the size of the black alliance is preferably 10 mu m or less. As the graphite is finely formed, the graphitization time is shortened and the surface roughness after cutting is improved in terms of machinability. Therefore, the size of the black allied layer is preferably as small as 10 탆 or less.

Hereinafter, the production method of the present invention will be described in detail.

The steel material excellent in machinability and vibration damping ability of the present invention can be produced by casting an ingot having the above-mentioned composition range, then performing homogenization heat treatment at 1100 to 1300 ° C for 5 to 10 hours, hot rolling at 1000 to 1100 ° C, .

In addition, the method for manufacturing a steel material excellent in machinability and vibration damping capability of the present invention includes a step of heat-treating the steel material at a temperature of 700 to 770 캜 for 30 to 90 minutes. The steel material of the present invention needs to graphitize cementite of pearlite through graphitization heat treatment. For the fastest graphitization, heat treatment is required in the temperature range corresponding to the nose in the isothermal transformation curve. The preferable range of the heat treatment temperature is about 700 to 770 ° C. Through the isothermal heat treatment for 30 to 90 minutes in this temperature range, the graphitization rate for graphitizing all the cementites in the steel can be completed. If the graphitization time is less than 30 minutes, the graphitization is not completely completed, and after the graphitization is completed, there is no significant change in the texture and physical properties. Therefore, the graphitization heat treatment for 90 minutes or more is meaningless.

Here, the graphitization ratio means the ratio of the carbon content present in the graphite state to the carbon content added to the steel. It is defined by the following relational expression 1, and 100% graphitization means that all the carbon added forms graphite (Meaning that the amount of solute carbon in the ferrite is extremely small and is not taken into consideration), and means that there is no microparticulate pearlite, that is, microstructure of ferrite and black alumina.

[Relation 1]

Graphitization rate (%) = (carbon content present in graphite state / carbon content in steel) x 100

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

( Example )

After casting with an ingot using a steel having the composition (weight%) as shown in Table 1 below, the steel was homogenized at 1250 ° C for 8 hours, hot rolled to a thickness of 25 mm and then air-cooled. In order to investigate the graphitization behavior, graphite precipitation was induced by heat treatment at constant temperature for 1 hour.

The ferrite area fraction, the graphite area fraction, the machinability (depth of tool wear) and the vibration damping ability (vibration decay rate) were investigated for the steel produced as described above, and the results are shown in Table 2 below. Here, the machinability was evaluated by the tool wear depth, and the tool wear depth was measured as follows.

After the graphitization heat treatment, the steel material machined into a 25 mm diameter bar was turned 180 times to a diameter of 15 mm and the depth of wear of the tool was measured. At this time, cutting conditions were performed using a cutting oil at a feed rate of 150 mm / min and a cutting speed of 0.05 mm / rev. The vibration damping ability was evaluated by the vibration logarithmic decay rate, and the vibration logarithmic decay rate was measured as follows.

The logarithmic decay rate of vibration is the natural logarithm of two consecutive amplitude ratios in the free vibration curve. In order to measure the logarithmic decrement of vibration, an external force capable of generating vibration was applied to the rod-shaped specimen, and then the change in amplitude was measured with time.

division C Si Mn Al Mg P S B N O Honor One 1.02 2.6 0.1 0.02 0.008 0.02 0.028 0.003 0.006 0.0050 2 0.98 2.8 0.1 0.021 0.004 0.015 0.025 0.004 0.008 0.0042 3 1.12 2.9 0.4 0.026 0.006 0.018 0.026 0.006 0.005 0.0045 4 0.93 2.7 0.7 0.028 0.003 0.025 0.022 0.004 0.004 0.0048 5 1.08 2.8 0.3 0.018 0.005 0.018 0.021 0.003 0.005 0.004 Comparative Example One 0.55 2.7 0.2 0.019 0.003 0.014 0.020 0.004 0.006 0.0046 2 1.11 1.5 0.3 0.022 0.006 0.012 0.030 0.006 0.007 0.0036 3 1.05 1.4 1.8 0.028 0.006 0.028 0.028 0.003 0.004 0.0048 4 1.01 2.7 0.2 0.021 0.007 0.03 0.025 0.004 0.006 0.0038 5 0.96 2.9 0.1 0.027 0.005 0.025 0.020 0.006 0.007 0.0045

division Configuration Graphitization rate
(%) Graphite area
Fraction (%) Graphite average size
(um) Tool wear depth
(um) Vibration algebraic rate Graphitization heat treatment temperature (캜) Honor One Ferrite + graphite 100 3.2 6 103 0.024 705 2 Ferrite + graphite 100 2.9 5 107 0.021 720 3 Ferrite + graphite 100 3.1 7 128 0.022 735 4 Ferrite + graphite 100 2.8 7 132 0.020 750 5 Ferrite + graphite 100 3.3 7 119 0.025 765 Comparative Example One Ferrite + graphite 100 1.7 6 330 0.014 750 2 Ferrite + graphite + pearlite 34.7 0.9 5 480 0.011 750 3 Ferrite + graphite + pearlite 32.3 0.7 6 320 0.009 750 4 Ferrite + graphite + pearlite 38.2 0.8 7 370 0.012 650 5 Ferrite + graphite + pearlite 41.4 0.9 6 430 0.008 600

As shown in Table 2, when the heat treatment temperature was less than 700 ° C, the graphite was not sufficiently heated for one hour in the heat treatment furnace, and sufficient amount of graphite could not be precipitated. When the heat treatment temperature exceeds 770 占 폚, graphite is redissolved and the amount of graphite is reduced.

On the other hand, as shown in Tables 1 and 2, when the addition amount of the graphitization inhibiting element such as carbon, silicon or manganese added for promoting graphitization is out of the scope of the present invention as in Comparative Examples 1 to 3, It can be confirmed that the amount of graphite can not be precipitated within 1 hour due to the delay of the speed, and that cementite which is not 100% graphitized and decomposed is also present. It can be seen that the depth of wear of the cutting tool is greater than that of the graphite fraction, which is relatively high.

The graphite fraction and the logarithmic decrement rate of vibration in Table 2 show that the logarithmic decrement rate of vibration is higher than that of the comparative example in the case of graphite fractions having higher graphite fractions, It says.

Claims (5)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet comprises, by weight, 0.80 to 1.20% of C, 2.0 to 3.0% of Si, 0.01 to 1.00% of Mn, 0.01 to 0.03% of Al, 0.001 to 0.010% of Mg, 0.002 to 0.006% of B, 0.004 to 0.008% of N, 0.005% or less of O, the balance Fe and other unavoidable impurities.
The steel material according to claim 1, wherein the microstructure of the steel material has a machinability and a vibration damping capability including ferrite of 90% or more in an area fraction.
The steel material as set forth in claim 1, wherein the steel material has a black alliance of 2 to 4% in an area fraction and is excellent in machinability and vibration damping ability.
The steel material according to claim 3, wherein the black allied layer has a size of 10 탆 or less and excellent cutting and vibration damping capability.
The steel sheet according to any one of claims 1 to 3, wherein the steel sheet comprises, by weight, 0.80 to 1.20% of C, 2.0 to 3.0% of Si, 0.01 to 1.00% of Mn, 0.01 to 0.03% of Al, 0.001 to 0.010% of Mg, Treating the steel containing 0.002 to 0.006% of B, 0.004 to 0.008% of N, 0.005 to 0.005% of O, the balance Fe and other unavoidable impurities at a temperature of 700 to 770 캜 for 30 to 90 minutes, And a method of manufacturing a steel material excellent in vibration damping capability.