KR20110133501A - Steel for machine structure excelling in machinability and strength property - Google Patents

Abstract

The present invention provides a mechanical structural steel having good machinability in a wide range of cutting speeds and also having high impact and high yield ratios, in mass%, C: 0.1% to 0.46%, and Si: 0.01% to 1.5. %, Mn: 0.05% to 2.0%, P: 0.005% to 0.2%, S: 0.001% to 0.15%, total Al: greater than 0.05% and less than 0.3%, Sb: less than 0.0150% (including O%) and total N : Mechanical structural steel with excellent machinability and strength characteristics, containing 0.0035% to 0.020%, and having a solid solution N of 0.0020% or less, the balance being made of Fe and unavoidable impurities.

Description

Machine structure steel with excellent machinability and strength characteristics {STEEL FOR MACHINE STRUCTURE EXCELLING IN MACHINABILITY AND STRENGTH PROPERTY}

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to machine structural steel subjected to cutting, and in particular, a wide range from cutting in a relatively low speed region by a high speed steel drill to cutting in a relatively high speed region such as turning in a longitudinal direction by a super-coated tool. The present invention relates to a steel for mechanical structure having excellent machinability and strength characteristics applicable to a cutting speed range.

In recent years, although the strength of steel is advanced, on the other hand, the problem that workability falls has arisen. For this reason, the demand for steel which does not reduce cutting efficiency while maintaining strength is increasing. It is known that it is effective to add machinability improvement elements, such as S, Pb, and Bi, in order to improve the machinability of steel conventionally. However, although Pb and Bi improve the machinability and are considered to have a relatively small influence on forging, it is known to reduce the strength characteristics.

Moreover, in recent years, there exists a tendency to avoid using Pb as an environmental load, and there exists a tendency to reduce the usage. In addition, S forms a soft inclusion in a cutting environment such as MnS and improves machinability, but the size of MnS is larger than that of particles such as Pb and is likely to be a stress concentration source. In particular, when stretched by forging and rolling, anisotropy is generated by MnS, and the specific direction of the steel is extremely weak. Moreover, when designing steel, such anisotropy needs to be considered. Therefore, when S is added, a technique for reducing the anisotropy is required.

As mentioned above, even if an element effective for improving machinability is added, strength characteristics are lowered, so that both strength characteristics and machinability are difficult. For this reason, technical innovation is required to make steel machinability and strength characteristics compatible.

Thus, conventionally, for example, a nitride produced by cutting heat during cutting by containing at least 0.005% by mass or more in total of one or more selected from solid solution V, solid solution Nb and solid solution Al, and containing 0.001% or more of solid solution N. Has been proposed to attach the tool to a tool to function as a tool protective film and to extend the cutting tool life (see Japanese Laid-Open Patent Publication No. 2004-107787). In addition, by defining the contents of C, Si, Mn, S and Mg, by defining the ratio between the Mg content and the S content, and by optimizing the aspect ratio (aspect ratio) and the number of sulfide inclusions in the steel, Mechanical structural strength is proposed for the purpose of improving cutting processability and mechanical properties (see Patent Publication No. 3706560). In the structural steel described in Japanese Patent No. 3706560, the content of Mg is 0.02% or less (not including O%), and the content of Al is controlled to 0.1% or less.

However, the above-mentioned prior art has a problem shown below. In other words, the steel described in JP-A-2004-107787 is estimated to not occur when the heat generation amount due to cutting is not more than a certain degree. For this reason, there exists a problem that the cutting speed which exhibits an effect is limited to a certain high speed cutting, and an effect cannot be expected in a low speed area | region. In the steel described in Japanese Patent No. 3706560, no consideration is given to the strength characteristics. In addition, since the steel described in Japanese Patent No. 3706560 does not consider the cutting tool life and yield ratio at all, there is a problem that sufficient strength characteristics cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-described problems, and an object thereof is to provide a mechanical structural steel having good machinability in a wide range of cutting speeds and having high impact characteristics and high yield ratio.

The mechanical structural steel having excellent machinability and strength characteristics according to the present invention is in mass%, C: 0.1% to 0.46%, Si: 0.01% to 1.5%, Mn: 0.05% to 2.0%, P: 0.005% to 0.2%, S: 0.001% to 0.15%, total Al: greater than 0.05% and 0.3% or less, Sb: less than 0.0150% (including 0%) and total N: 0.0035% to 0.020%, while solid solution N: 0.0020% or less It is limited to, and the balance is characterized by consisting of Fe and unavoidable impurities.

This mechanical structural steel may also contain Ca: 0.0003% to 0.0015% by mass.

Further, in mass%, one or two or more elements selected from the group consisting of Ti: 0.001% to 0.1%, Nb: 0.005% to 0.2%, W: 0.01% to 1.0%, and V: 0.01% to 1.0% It may contain.

In addition, it may contain one or two or more elements selected from the group consisting of Mg: 0.0001% to 0.0040%, Zr: 0.0003% to 0.01%, and Rem: 0.0001% to 0.015% by mass.

In addition, in mass%, Sn: 0.005% to 2.0%, Zn: 0.0005% to 0.5%, B: 0.0005% to 0.015%, Te: 0.0003% to 0.2%, Bi: 0.005% to 0.5% and Pb: 0.005% It may contain one or two or more elements selected from the group consisting of from 0.5%.

The mass may also contain one or two elements selected from the group consisting of Cr: 0.01% to 2.0% and Mo: 0.01% to 1.0%.

Moreover, it may contain 1 type or 2 types of elements chosen from the group which consists of Ni: 0.05%-2.0% and Cu: 0.01%-2.0% by mass%.

Advantageous Effects of Invention According to the present invention, it is possible to provide a mechanical structural steel having good machinability in a wide cutting speed range and having high impact characteristics and high yield ratio.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the sampling part of the test piece for Charpy impact test.

EMBODIMENT OF THE INVENTION Hereinafter, the best form for implementing this invention is demonstrated in detail.

For mechanical structural steel (hereinafter, simply referred to as mechanical structural steel) having excellent machinability and strength characteristics according to the present invention, in order to solve the above-mentioned problems, the amount of addition of Al and other nitride generating elements and N as the component composition of the steel is adjusted. At the same time, by appropriate heat treatment, it is possible to reduce the solid solution N harmful to the machinability and impact characteristics, and to secure the appropriate amount of the solid solution Al to improve the machinability by high temperature embrittlement and Sb having the matrix embrittlement effect and the high temperature embrittlement effect. By securing an appropriate amount of AlN for improving machinability by the crystal structure of cleavage, it has effective cutting performance in a wide range of cutting speeds from low speed to high speed, and increases the amount of Al added to the conventional Al-killed steel. In comparison, MnS (Type III MnS by the classification of SIMS) with small segregation and high uniform dispersibility was added. , That the machine structural steel combines high impact properties, and also by the fine precipitation of AlN and Al employed, to obtain a high yield ratio.

That is, the mechanical structural steel of the present invention is in mass%, C: 0.1% to 0.46%, Si: 0.01% to 1.5%, Mn: 0.05% to 2.0%, P: 0.005% to 0.2%, S: 0.001% to 0.15%, total Al: more than 0.05% and 0.3% or less, Sb: less than 0.0150% (including O%) and total N: 0.0035% to 0.020%, while solid solution N: 0.0020% or less, the balance is Fe And a composition consisting of unavoidable impurities.

First, each component element and its content in the steel for mechanical structures of this invention are demonstrated. In addition, in the following description, it describes only mass% in a composition.

C: 0.1% to 0.46%

C is an element which greatly affects the basic strength of steel. However, when the C content is less than 0.1%, sufficient strength cannot be obtained and other alloy elements must be added in a larger amount. On the other hand, when C content exceeds 0.46%, many hard carbides will precipitate, and machinability remarkably falls. Therefore, in this invention, C content is made into 0.1%-0.46% in order to acquire sufficient intensity | strength. The lower limit is preferably 0.2%.

Si: 0.01% to 1.5%

Si is generally added as a deoxidation element, but also has an effect of imparting ferrite strengthening and tempering softening resistance. However, when Si content is less than 0.01%, sufficient deoxidation effect cannot be acquired. On the other hand, when Si content exceeds 1.5%, material characteristics, such as embrittlement, will fall, and machinability will also deteriorate. Therefore, Si content is made into 0.01%-1.5%. The upper limit is preferably 1.0%.

Mn: 0.05% to 2.0%

Mn is an element necessary for fixing and dispersing sulfur (S) in steel with MnS, and solidifying it in a matrix to improve hardenability and to secure strength after hardening. However, when Mn content is less than 0.05%, S in steel will combine with Fe and become FeS, and steel will embrittle. On the other hand, when Mn content increases, specifically, when Mn content exceeds 2.0%, the hardness of a base material will become large, cold workability will fall, and the influence on strength and hardenability will also be saturated. Therefore, Mn content is made into 0.05%-2.0%.

P: 0.005% to 0.2%

P has the effect of making machinability favorable, but the effect cannot be acquired when P content is less than 0.005%. Moreover, when P content increases, specifically, when P content exceeds 0.2%, the hardness of a base material will become large in steel, and not only cold workability but hot workability and casting characteristics will fall. Therefore, P content is made into 0.005%-0.2%.

S: 0.001% to 0.15%

S binds with Mn and exists as an MnS inclusion. Although MnS has the effect of improving machinability, in order to remarkably obtain the effect, it is necessary to add S to 0.001% or more. On the other hand, when S content exceeds 0.15%, the impact value of steel will fall largely. Therefore, when improving machinability by S addition, S content is made into 0.001%-0.15%.

Total Al: more than 0.05% and less than 0.3%

In addition to forming an oxide, Al precipitates AlN effective for sizing and machinability, and has an effect of improving the machinability by becoming Al solid solution. In order to produce sufficient solid solution Al effective for this machinability, it is necessary to add the amount exceeding 0.05%. Al also influences the crystal form and precipitation form of MnS. In addition, when Al in an amount exceeding 0.05% is added, segregation at the slab stage is smaller than that of conventional Al-kilted steel, and MnS (Type III MnS by classification of SIMS) having high uniform dispersibility can be increased. As a result, mechanical structural steel having high impact characteristics can be obtained, and high yield ratio can be obtained by fine precipitation of AlN and solid solution Al. However, when the total Al content exceeds 0.3%, the machinability begins to decrease. Therefore, total Al content is made into 0.05% or more and 0.3% or less. The lower limit is preferably 0.08% and more preferably 0.1%.

Sb: less than 0.0150% (including O%)

Sb has an effect which embrittles ferrite moderately and improves machinability. This effect is remarkable especially when the amount of solid solution Al is large, but it does not appear when the Sb content is less than 0.0005%. On the other hand, when Sb content increases, specifically, when Sb content is 0.0150% or more, macro segregation of Sb will become excessive and an impact value will fall large. Therefore, Sb content is made into 0.0005% or more and less than 0.0150%. If high machinability is not required or if the total Al is more than 0.1%, no addition (0%) may be used.

Total N: 0.0035% to 0.020%

N exists as nitrides, such as Ti, Al, or V, in addition to solid solution N, and suppresses growth of austenite particles. However, if the total amount of N is less than 0.0035%, no remarkable effect can be obtained. On the other hand, when total N amount exceeds 0.020%, it will become the cause of the rolling defect in a rolling process. Therefore, the total amount of N is made into 0.0035%-0.020%.

Employment N: 0.0020% or less

Solid solution N hardens the steel. Particularly, in cutting, hardening is performed in the vicinity of the blade edge by dynamic strain aging, thereby reducing the tool life, and in rolling, causes a rolling defect. When the amount of solid solution N is high, specifically, when the amount of solid solution N exceeds 0.0020%, at the time of cutting, tool wear is encouraged by the increase of the cutting resistance accompanying the increase in local hardness. Therefore, the amount of solid solution N is suppressed to 0.0020% or less. By doing so, the tool friction can be improved. In addition, a large amount of solid solution N causes matrix embrittlement and impact characteristics deteriorate. When the amount of solid solution N is suppressed to 0.0020% or less, this matrix embrittlement can be improved. The amount of solid solution N referred to herein is a value obtained by subtracting the amount of N contained in nitrides such as AlN, NbN, TiN, and VN from the total amount of N. For example, the total amount of N is measured by an inert gas fusion-thermal conduction method, The amount of N in the nitride was measured by the indophenol absorbance method of the residue electrolytically extracted by the SPEED method and the 0.1 µm filter of the electrostatic potential electrolytic corrosion method using a non-aqueous solvent electrolyte. Can calculate by

 (N amount of employment) = (N amount in total)-(N amount in nitride) ... (1)

In addition, the amount of solid solution N can be suppressed low by the method shown below.

1) To suppress total N amount low within the range prescribed | regulated by this invention.

Although the definition of all N range is 0.020% or less, Preferably it is good to suppress to 0.01% or less, More preferably, it is 0.006% or less.

2) When the total amount of N is large, the amount of N compounds may be increased by adding an appropriate amount of nitride forming element Al and other nitride forming elements.

3) In order to reduce the solid solution N by fine precipitation of nitride, in view of being used as a mechanical structural steel, fine precipitation is preferable from the viewpoint of suppressing grain coarsening. In order to reduce the amount of solid solution N by fine deposition of nitride, it is essential to maintain a high temperature of complete solution by N and the amount of nitride generating elements, but considering this, 1100 ° C or higher, preferably 1200 ° C or higher, and more preferably After heat treatment for solution formation at 1250 ° C. or higher, the precipitates are subjected to heat treatment such as casting and carburizing. In particular, in the case of AlN, it is possible to increase the amount of precipitation and to reduce the solute N by correcting for a long time at around 850 ° C. The long time here refers to 0.8 hours or more, preferably 1 hour or more, and more preferably 1.2 hours or more.

Moreover, in the steel for mechanical structures of this invention, in addition to each said component, you may contain Ca.

Ca: 0.0003% to 0.0015%

Ca is a deoxidation element and produces | generates an oxide in steel. Since the total Al content in the machine structural steel of the present invention, not more than 0.05% greater than 0.3% of calcium aluminate (CaOAl ₂ O ₃₎ a are formed, the CaOAl ₂ O ₃ will be a low-melting oxide compared to the Al ₂ O _3, high-speed cutting It becomes a tool protective film at the time, and there exists an effect which improves machinability. However, when Ca content is less than 0.0003%, this machinability improvement effect is not acquired, and when Ca content exceeds 0.0015%, CaS will generate | occur | produce in steel and rather machinability will fall. Therefore, the content is made into 0.0003%-0.0015% when Ca is added.

In the mechanical structural steel of the present invention, when carbonitride is formed and high strength is required, in addition to the above components, Ti: 0.001% to 0.1%, Nb: 0.005% to 0.2%, and W: 0.01% to It may contain one or two or more elements selected from the group consisting of 1.0% and V: 0.01% to 1.0%.

Ti: 0.001% to 0.1%

Ti is an element that forms carbonitrides and contributes to suppressing or strengthening the growth of austenite particles, and is used as a sizing element for preventing coarse grains in steels requiring high strength and low deformation. In addition, Ti is also an element of deoxidation, and it has the effect of improving machinability by forming a soft oxide. However, when the Ti content is less than 0.91%, the effect does not appear, and when the Ti content is more than 0.1%, unused coarse carbonitride which causes hot cracking is precipitated, and mechanical properties are impaired. do. Therefore, when Ti is added, the content is made into 0.001%-0.1%.

Nb: 0.005% to 0.2%

An element that forms Nb or carbonitride and contributes to reinforcement of steel by secondary precipitation hardening, suppression and strengthening of austenite grain growth, and to prevent coarse grains in steels requiring high strength and low deformation. Used as elemental element. However, when the Nb content is less than 0.005%, the effect of high strength is not obtained, and when Nb is added in excess of 0.2%, unused coarse carbonitride which causes time cracking is precipitated, and mechanical properties are impaired. do. Therefore, when Nb is added, the content is made into 0.005%-0.2%.

W: 0.01% to 1.0%

W also forms carbonitrides and is an element capable of strengthening steel by secondary precipitation hardening. However, when the W content is less than 0.01%, the effect of high strength is not obtained, and when W is added above 1.0%, unused coarse carbonitride which causes hot cracking is precipitated, and mechanical properties are impaired. do. Therefore, when adding W, the content shall be 0.01%-1.0%.

V: 0.01% to 1.0%

V is also an element which forms carbonitrides and can strengthen steel by secondary precipitation hardening, and is appropriately added to steels requiring high strength. However, when the V content is less than 0.01%, the effect of high strength is not obtained, and when V is added beyond 1.0%, unused coarse carbonitride which causes hot cracking is precipitated, and mechanical properties are impaired. . Therefore, when adding V, the content shall be 0.05%-1.0%.

Further, in the structural steel of the present invention, in the case of performing sulfide form control by deoxidation adjustment, in addition to the above components, Mg: 0.0001% to 0.0040%, Zr: 0.0003% to 0.01%, and Rem: 0.0001% You may add 1 type, or 2 or more types of elements chosen from the group which consists of 0.01 to 0.015%.

Mg: 0.0001% to 0.0040%

Mg is a deoxidation element and produces | generates an oxide in steel. In the case of Al deoxidation premise, Al ₂ O _3, which is detrimental to machinability, is modified with MgO or Al ₂ O ₃ · MgO dispersed relatively softly. In addition, the oxide tends to be a nucleus of MnS, and has an effect of finely dispersing MnS. However, when the Mg content is less than 0.0001%, no effect appears. In addition, Mg produces a complex sulfide with MnS and spheroidizes MnS. However, when Mg is added in excess, specifically, when Mg content exceeds 0.0040%, MgS formation alone is promoted to degrade machinability. Therefore, when Mg is added, the content is made into 0.0001%-0.004 O%.

Zr: 0.0003% to 0.01%

Zr is a deoxidation element and produces an oxide in steel. It is thought that the oxide is ZrO ₂ , and since this ZrO ₂ becomes a precipitation nucleus of MnS, there is an effect of increasing the precipitation site of MnS and uniformly dispersing MnS. In addition, Zr has a function of dissolving MnS in solid solution to produce a complex sulfide, lowering its deformation ability, and suppressing stretching of the MnS shape during rolling and hot forging. Thus, Zr is an element effective for reducing anisotropy. Therefore, when Zr content is less than 0.0003%, a remarkable effect cannot be acquired about these. On the other hand, addition of Zr exceeding 0.01% not only results in extremely poor yields, but also produces a large amount of hard compounds such as ZrO ₂ and ZrS, but rather deteriorates mechanical properties such as machinability, impact value and fatigue properties. do. Therefore, when Zr is added, the content is made into 0.0003%-0.01%.

Rem: 0.0001% to 0.015%

Rem (rare earth element) is a deoxidation element, produces low melting oxide, suppresses nozzle clogging during casting, solid solution or bonds to MnS, lowers its deformation ability, and reduces MnS shape during rolling and hot forging. There is also a function to suppress distraction. Thus, Rem is an element effective for reducing anisotropy. However, when the Rem content is less than 0.0001% in total amount, the effect is not remarkable, and when Rem is added in excess of 0.015%, sulfides of Rem are produced in large quantities, and the machinability deteriorates. Therefore, when adding Rem, the content is made into 0.0001%-0.015%.

In the case of improving the machinability of the mechanical structural steel of the present invention, in addition to the above components, Sn: 0.005% to 2.0%, Zn: 0.0005% to 0.5%, B: 0.0005% to 0.015%, Te One or two or more elements selected from the group consisting of: 0.0003% to 0.2%, Bi: 0.005% to 0.5%, and Pb: 0.005% to 0.5% can be added.

Sn: 0.005% to 2.0%

Sn has an effect of embrittlement of ferrite to increase tool life and to improve surface roughness. However, when Sn content is less than 0.005%, the effect does not appear, and even if it adds Sn more than 2.0%, the effect is saturated. Therefore, when Sn is added, the content is made into 0.005%-2.0%.

Zn: 0.0005% to 0.5%

Zn has the effect of embrittling ferrite to increase tool life and at the same time improving surface roughness. However, when Zn content is less than 0.0005%, the effect does not appear, and even if Zn is added exceeding 0.5%, the effect is saturated. Therefore, when Zn is added, the content is made into 0.0005%-0.5%.

B: 0.0005% to 0.015%

B is effective in grain boundary strengthening and hardenability when it is in solution, and precipitates as BN when precipitated, which is effective in machinability. These effects are not remarkable when the B content is less than 0.0005%. On the other hand, even if B is added in excess of 0.015%, the effect is saturated, and since too much BN is precipitated, the mechanical properties of the steel are rather impaired. Therefore, the content is made into 0.0005%-0.015% when B is added.

Te: 0.0003% to 0.2%

Te is a machinability improving element. In addition, by producing MnTe or coexisting with MnS, there is a function of reducing the deformation ability of MnS and suppressing the stretching of the MnS shape. Thus, Te is an element effective for reducing anisotropy. However, when Te content is less than 0.0003%, an effect does not appear, and when Te content exceeds 0.2%, the effect is not only saturated but hot ductility falls and it becomes a cause of a defect. Therefore, when Te is added, the content is made into 0.0003%-0.2%.

Bi: 0.005% to 0.5%

Bi is a machinability improving element. However, when Bi content is less than 0.005%, the effect is not acquired, and even if it adds Bi over 0.5%, a machinability improvement effect is not only saturated but hot ductility falls and it becomes a cause of a defect. Therefore, when Bi is added, the content is made into 0.005%-0.5%.

Pb: 0.005% to 0.5%

Pb is a machinability improving element. However, when Pb content is less than 0.005%, the effect does not appear, and even if Pb is added exceeding 0.5%, a machinability improvement effect is not only saturated but hot ductility falls and it becomes a cause of a defect. Therefore, when Pb is added, the content is made into 0.005%-0.5%.

In addition, in the mechanical structural steel of the present invention, when the hardenability is improved or the tempering softening resistance is improved, and the strength is imparted to the steel, Cr: 0.01% to 2.0%, Mo: 0.05% to You may add 1 type or 2 types of 1.0%.

Cr: 0.01% to 2.0%

Cr is an element that improves hardenability and imparts temper softening resistance, and is added to steels requiring high strength. However, when the Cr content is less than 0.01%, no effect is obtained, and when a large amount of Cr is added, specifically, when the Cr content is more than 2.0%, Cr carbide is formed and the steel becomes brittle. Therefore, when Cr is added, the content is made into 0.01%-2.0%.

Mo: 0.05% to 1.0%

Mo is an element which gives tempering softening resistance and improves hardenability, and is added to steel which requires high strength. However, when Mo content is less than 0.05%, an effect is not acquired, and even if Mo is added exceeding 1.0%, the effect is saturated. Therefore, when Mo is added, the content is made into 0.05%-1.0%.

In addition, in the structural steel of the present invention, in the case of reinforcing ferrite, one or two kinds of Ni: 0.05% to 2.0% and Cu: 0.01% to 2.0% may be added to the above components. .

Ni: 0.05% to 2.0%

Ni is an element effective in strengthening ferrite, improving ductility, and improving hardenability and corrosion resistance. However, when Ni content is less than 0.05%, the effect does not appear, and even if it adds Ni over 2.0%, an effect is saturated from a viewpoint of a mechanical property, and machinability falls. Therefore, when Ni is added, the content is made into 0.05%-2.0%.

Cu: 0.01% to 2.0%

Cu is an element effective in enhancing ferrite and improving hardenability and corrosion resistance. However, when Cu content is less than 0.01%, the effect does not appear, and even if Cu is added more than 2.0%, an effect is saturated from a mechanical viewpoint. Therefore, when adding Cu, the content is made into 0.01%-2.0%. In addition, Cu is particularly preferable to be added at the same time as Ni deteriorates hot ductility and is likely to cause defects in rolling.

As described above, in the mechanical structural steel of the present invention, since the amount of solid solution N is reduced, the machinability and impact characteristics can be improved as compared with the conventional mechanical structural steel. In addition, by optimizing the total Al content and Sb content, an appropriate amount of solid solution Al, Sb, and AlN having an effect of improving machinability is secured, and thus effective cutting performance can be obtained for a wide range of cutting speeds from low speed to high speed. . In addition, high yield ratio can be obtained by fine precipitation of AlN and solid solution Al. Moreover, since the quantity of the element which affects precipitation of MnS is optimized, and the quantity of MnS with high uniform dispersibility is increased, the impact characteristic is also excellent.

Mechanical structural steel having excellent machinability and strength characteristics according to the present invention is forged into a columnar phase after hot forging a billet having the above-described steel composition at 1200 ° C or higher, and then solidified to 1100 ° C or higher. It can be manufactured by heat treatment, followed by heat treatment such as casting or carburizing. Particularly, in the steel containing AlN nitride, after solidification heat treatment at 1100 ° C. or more, the solid solution N is significantly reduced by correcting for a long time at least 0.8 hours, preferably at least 1 hour, more preferably at least 1.2 hours. You can get a river.

Example 1

Next, the effect of this invention is concretely demonstrated to an Example and a comparative example. In the present Example, 150 kg of the steels of the composition shown in Table 1 and Table 2 were melted by the vacuum melting furnace, hot forged under the temperature condition of 1250 degreeC, and were renewed to the columnar shape of diameter 65mm. Moreover, about each steel material of this Example and a comparative example, the machinability test, the Charpy impact test, and the tension test were implemented by the method shown below, and the characteristic was evaluated. In addition, the underlined part in Table 2 shows that it is outside the scope of the present invention.

Machinability test

The machinability test was performed for 1 hour under a temperature condition of 850 ° C. for each steel material of the Examples and Comparative Examples, which were heated to 1250 ° C. and renewed at a warm temperature. 49, no. About 50, after annealing for 0.5 hour, air-cooled heat processing was performed. Then, the test piece for machinability evaluation is cut out from each steel material after heat processing, the drill drilling test is performed on the cutting conditions shown in Table 3 as follows, and the longitudinal turning test is performed on the conditions shown in Table 4 below, The machinability of each steel material of an Example and a comparative example was evaluated. In that case, as an evaluation index, in the drill drilling test, the maximum cutting speed (VL1000) which can be cut to a cumulative hole depth of 1000 mm was adopted, and the allowable surface maximum wear width (VB_max) after 10 minutes in the longitudinal turning test was used, respectively.

Cutting condition
  Speed 10 ~ 120m / min   Feed 0.25mm / rev   Cutting Fluids Water Soluble Cutting Fluids
drill
  Drill diameter f3mm   NACHI Drill   Protrusion amount 45mm Etc   Hole depth 9mm   To tool life loss

Cutting condition   Speed 250m / min   Feed 0.3mm / rev   Cutting depth 1.5mm   Dry cutting
drill   Holder PTGNR2525M16   Tool geometry TNMG160408N-UZ   Material AC2000

Charpy Impact Test

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the sampling part of the test piece for Charpy impact test. In the Charpy impact test, first, as shown in FIG. 1, the center axis is perpendicular to the direction of extension of the steel 1 from each steel 1 heat-treated in the same method and conditions as the above-described cutting test. The circumferential material 2 of 25 mm in diameter was cut out. Next, with respect to each base material 2, the comparative example No. 1 hour under the temperature conditions of 850 degreeC. 49, no. For 50, the oil was quenched after holding for 0.5 hours, and cooled to 60 ° C. Further, tempering was carried out after holding for 30 minutes under a temperature condition of 550 ° C. Subsequently, each master material 2 was machined, the Charpy test piece 3 prescribed | regulated to JIS Z 2202 was produced, and the Charpy impact test in room temperature was performed by the method prescribed | regulated to JIS Z 2242. . In that case, the absorption energy (J / cm <^2> ) per unit area was employ | adopted as an evaluation index.

Tensile test

After the oil quenching and tempering were performed on the circumferential material 2 taken in parallel with the cross direction in the same manner as in the above-mentioned Charpy impact test, it was processed into a tensile test piece having a diameter of 8 mm in parallel and a length of 30 mm in parallel. Then, a tensile test was performed at room temperature based on the method specified in JIS Z 2241. At that time, the yield ratio (= (0.2% yield strength YP) / (tensile strength TS)) was adopted.

The results of the above test are shown in Tables 5 and 6.

No. 1 shown in Table 1, Table 2, and Table 5. 1 to No. The steel material of 42 is an Example of this invention, and No. shown in Table 2 and Table 6. 43 to No. The steel material of 51 is a comparative example of this invention. As shown in Table 5 and Table 6, Example No. 1 to No. The steels of 42 exhibited good values in all of the evaluation indexes VL1000, VB_max, impact value (absorption energy) and YP / TS (yield ratio), but in the steel of the comparative example, at least one or more of these characteristics It is inferior to the steel of this embodiment. Specifically, Comparative Example No. 43 to No. Since the total Al content is less than the scope of the present invention, the steel of 46 is inferior to the steel of the example, VL1000 and yield ratio (YP / TS) which are evaluation indexes of machinability. In addition, Comparative Example No. Since the total Al content of the steels of 47 is extremely lower than the scope of the present invention, the solid solution N content exceeds the scope of the present invention, and the machinability (VL1000, VB_max), impact value, and yield ratio (YS / TS) falls.

Comparative Example No. Since the total steel Al content exceeds the range of this invention, the steel of 48 has an increase in hardness and inferior machinability (VL1000, VB_max). Comparative Example No. 49, no. The steel of 50 has a shorter temperature holding time at 850 ° C. in which AlN tends to precipitate, compared to the steel of the embodiment, so that the amount of solid solution N exceeds the scope of the present invention, and the machinability (VL1000, VB_max) and impact value are higher than those of the steel of the embodiment. Falls. Comparative Example No. 51 to no. Since 54b steel is more than Sb content of the present invention, the impact value is inferior to the steel materials of an Example.

Example 2

In the present Example, 150 kg of the steels of the composition shown in Table 7 and Table 8 were melted by the vacuum melting furnace, and then hot forged under the temperature condition of 1250 degreeC, and were renewed to the columnar shape of diameter 65mm. And about the steel materials of this Example and a comparative example, the machinability test, the Charpy impact test, and the tension test were implemented by the method shown below, and the characteristic was evaluated. In addition, the underlined part in Table 7 and Table 8 shows that it is outside the scope of the present invention.

Machinability test

The machinability test was performed for 1 hour under a temperature condition of 850 ° C. for each steel material of the Examples and Comparative Examples, which were heated to 1250 ° C. and renewed at a warm temperature. 48, No. 49, no. 97 to No. The heat treatment was performed for 101 hours after being annealed for 0.5 hours, followed by air cooling. Then, the test piece for machinability evaluation was cut out from each steel material after heat processing, a drill drilling test is performed on the cutting conditions shown in Table 9, and a longitudinal turning test is performed on the conditions shown in Table 10, and an Example and a comparison The machinability of each steel of the example was evaluated. In that case, as an evaluation index, in the drill drilling test, the maximum cutting speed (VL1000) which can be cut to a cumulative hole depth of 1000 mm was adopted, and the allowable surface maximum wear width (VB_max) after 10 minutes in the longitudinal turning test was used, respectively.

Cutting condition
  speed   10 ~ 120m / min   transfer   0.25mm / rev   Cutting oil   Water soluble coolant
drill
  Drill diameter (Ø)   3mm   NACHI   Drill   Protrusion   45 mm Etc   Hole depth   9 mm   Tool life   To loss

Cutting condition   speed 250 m / min   transfer 0.3mm / rev   condition Dry cutting
drill   holder PTGNR2525M16   shape TNMG160408N-UZ   material AC2000

Charpy Impact Test

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the sampling part of the test piece for Charpy impact test. In the Charpy impact test, first, as shown in FIG. 1, from each steel material 1 heat-treated in the same method and conditions as the above-described cutting test, the central axis is perpendicular to the direction of extension of the steel material 1, The base material 2 of 25 mm in diameter was cut out. Next, with respect to each base material 2, the comparative example No. 1 hour under the temperature conditions of 850 degreeC. 48, No. 49, no. 97 to No. For 101, after quenching for 0.5 hour, oil was quenched to 60 ° C, and tempered to hold water for 30 minutes under a temperature of 550 ° C. Subsequently, each master material 2 was machined, the Charpy test piece 3 prescribed | regulated to JIS Z 2202 was produced, and the Charpy impact test in room temperature was performed by the method prescribed | regulated to JIS Z 2242. . In that case, the absorption energy (J / cm <2>) per unit area was employ | adopted as an evaluation index.

Tensile test

Each circumferential material 2 subjected to oil quenching and tempering under the same method and conditions as in the Charpy impact test described above is processed into a tensile test piece having a diameter of 8 mm and a length of 30 mm in parallel parts, and the method specified in JIS Z 2241. Based on the tensile test was carried out at room temperature. At that time, the yield ratio (= (0.2% yield strength YP) / (tensile strength TS)) was adopted.

The results of the above test are summarized in Tables 11 and 12.

Moreover, No. shown in Table 7 and Table 11 has shown. Steel of 1 is the embodiment of Claim 1, No. 2 to No. The steel of 42 is the embodiment of claim 2. Moreover, No. 8 and Table 12 show. 52 to no. 93 is the embodiment of claim 1. In addition, Comparative Example No. 43 to No. The steel materials of 49 satisfy | fill the prescription | regulation of Claim 2 regarding S content and Ca content, and the comparative example No. 94 to No. The steel material of 101 satisfy | fills the prescription | regulation of Claim 1 regarding S content and Ca content.

As shown in Table 11 and Table 12, Example No. 1 to No. 42 and No. 52 to no. In the steels of 93, good values were shown for all of the evaluation indices VL1000, VB_max, impact value (absorption energy), and YP / TS (yield ratio), but in the steel of the comparative example, at least one or more of these characteristics were implemented. It is inferior to polite steel. Specifically, Comparative Example No. 43 to No. In the steel material of 46, since the total Al content is less than the scope of the present invention, the machinability (VL1000) and the yield ratio (YP / TS) are inferior to the steel materials of the examples. In addition, Comparative Example No. Since the total Al content of the steels of 47 is extremely lower than the scope of the present invention, the amount of solid solution N exceeds the scope of the present invention, and the machinability (VL1000, VB_max), impact value, and yield ratio (YS / TS) falls.

Comparative Example No. 48 and No. Since the steel of 49 has a shorter temperature holding time at 850 ° C. in which AlN is more likely to precipitate than the steel of the embodiment, the amount of solid solution N exceeds the scope of the present invention, and the machinability (VL1000, VB_max) and impact value ( impact value) falls. In addition, Comparative Example No. 94 to No. Since the total Al content is less than the scope of the present invention, the steel materials of 96 are inferior in machinability (VL1000, VB_max) and yield ratio (YP / TS) than the steel materials of the examples. In addition, Comparative Example No. 97 to No. The steel of 101 has a shorter temperature holding time at 850 ° C. in which AlN is more likely to precipitate than the steel of Example, so that the amount of solid solution N exceeds the scope of the present invention, and the machinability (VL1000, VB_max) and impact value are higher than those of the steel of Example. Falls.

Industrial availability

Advantageous Effects of Invention According to the present invention, it is possible to provide a mechanical structural steel having good machinability in a wide cutting speed range and having high impact characteristics and high yield ratio.

1: steel
2: master
3: Charpy test piece

Claims (3)

In mass%,
C: 0.1% to 0.46%,
Si: 0.01% to 1.5%,
Mn: 0.05% to 2.0%,
P: 0.005% to 0.2%,
S: 0.001% to 0.15%,
Total Al: greater than 0.05% and less than 0.3%,
Sb: less than 0.0150% (including O%) and
Total N: 0.0035% to 0.020%
Employment N: limited to 0.0020% or less
Machine structural steel with excellent machinability and strength characteristics, characterized in that the balance consists of Fe and unavoidable impurities. The method of claim 1,
By mass%, Ca: 0.0003% to 0.0015%, Ti: 0.001% to 0.1%, Nb: 0.005% to 0.2%, W: 0.01% to 1.0%, V: 0.01% to 1.0%, Mg: 0.0001% to 0.0040 %, Zr: 0.0003% to 0.01%, Rem: 0.0001% to 0.015%, Sn: 0.005% to 2.0%, Zn: 0.0005% to 0.5%, B: 0.0005% to 0.015%, Te: 0.0003% to 0.2%, One of Bi: 0.005% to 0.5% and Pb: 0.005% to 0.5%, Cr: 0.01% to 2.0%, Mo: 0.01% to 1.0%, Ni: 0.05% to 2.0% and Cu: 0.01% to 2.0% Or mechanical structural steel having excellent machinability and strength characteristics, characterized by containing two or more kinds. In mass%,
C: 0.1% to 0.46%,
Si: 0.01% to 1.5%,
Mn: 0.05% to 2.0%,
P: 0.005% to 0.2%,
S: 0.001% to 0.15%,
Total Al: above 0.05%, below 0.3%,
Sb: less than 0.0150% (including O%),
Total N: 0.0035% to 0.020%, and the remainder is a solution of Fe and unavoidable impurities in solution at 1100 ℃ or more, and then corrected for 0.8 hours or more at 850 ℃, limiting the amount of solid solution N to 0.0020% or less The manufacturing method of the mechanical structural steel excellent in the machinability and strength characteristics made into.

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