KR101608087B1 - Free-cutting alloy tool steel - Google Patents

Abstract

The present invention provides a free-cutting alloy tool steel containing, in terms of mass%: C: from 0.50 to 0.90%, Si: from 0.50 to 2.20%, Mn: 0.8% or more, Mn+0.08Cr: from 1.35 to 2.05%, Ni: from 0.01 to 0.30%, Mo+0.5W: from 0.01 to 0.50%, V: from 0.01 to 0.15%, S: from 0.03 to 0.15%, with the balance being Fe and unavoidable impurities, in which the contents of Mn and Cr satisfy the following relationship: Mn/Cr: from 0.10 to 0.23, and the contents of Mo, W and Mn satisfy the following relationship: (Mo+0.5W)/Mn: 0.55 or less.

Description

{FREE-CUTTING ALLOY TOOL STEEL}

The present invention relates to a free cutting alloy tool steel. More particularly, the present invention relates to a free-cutting alloy tool steel in which deformation due to machining as well as heat treatment deformation by quenching can be prevented.

The results of the present invention include cold molds used in processes carried out by forging, continuous die presses in cold processing, and mechanical structural materials.

Examples of cold molds are block punches, button dies, pilot punches, straight punches, roading punches, drawing dies, bending punches / dies, punch type cutter / roll type cutters, A punching member / die, and a swaging die.

The mechanical structural member may include a base plate, a guide plate, a spacer, a stripper, a screw plug, a retainer, a guide bush, a dowel bush, a stripper guide, a knockout pin, A shank, a guide post, a picking key, a plastic forming tool, a screw member, a cam component, a seal plate and gauges.

The mold or structural material also includes a cold mold or mechanical structural material used for surface treatment such as CVD treatment, PVD treatment, TD treatment and surface treatment such as nitriding or shot peening.

According to the prior art, carbon tool steel, alloy tool steel to which a small amount of alloying element is added, and cold die steel to which a large amount of chromium and the like have been added have been used as tool steels.

Carbon tool steels or alloy tool steels have the disadvantage of low hardenability because a small amount of alloying elements are added.

In these tool steels, a large amount of manganese (Mn) is added for the purpose of improving the passing ability. However, although manganese is an element capable of greatly improving the hardenability, when a large amount of manganese is added, a large amount of residual austenite occurs after quenching. Therefore, the addition of manganese is naturally limited, and manganese can not be added beyond a certain amount.

For this reason, conventional tool steels such as carbon tool steels and alloy tool steels, which are mainly added with manganese to increase their hardenability, are basically insufficient in hardenability.

Accordingly, when quenching steel, rapid cooling such as water cooling or oil cooling is required. In this case, due to the difference in cooling speed during cooling between the surface of the product and the inside of the product or the wall thickness of the product, Many temperature differences occur, and many deformation (heat treatment deformation) occurs due to quenching (heat treatment).

Because of this problem, carbon tool steel or alloy tool steel can not be applied to products such as large molds, and the intended product is limited to small products having a thickness of 30 mm or less.

On the other hand, the cold-type molten steel has sufficient curing ability as many alloying elements are added.

In the cold-type molten steel, a large amount of chromium (Cr) is added as an element for improving the hardenability.

In view of the added amount of chromium, chromium is less effective in improving hardenability than manganese, but chromium can be added in a large amount. As a result, the hardenability of the cold-rolled steel is lower than that of the carbon tool steel or alloy tool steel Much higher.

Accordingly, gentle cooling with a cooling rate at the time of quenching is sufficient, and material deformation that occurs due to the heat treatment as in carbon tool steel or alloy tool steel can be prevented.

On the other hand, a large amount of carbide precipitates as a large amount of chromium is added in order to improve abrasion resitance in cold-forging steel. Therefore, when the cold molten steel is subjected to machining such as cutting and grinding, carbide stronger than the base material wears the cutting edge of the cutting tool or the grinding stone.

In this case, the greater the amount of carbide, the greater the wear of the blade or the grinding stone, and the greater the resistance of the material to working, the more difficult it is to process the material.

This means that a lot of stress is applied during machining and that there is a lot of stress left on the material after machining, and the material is totally or partially deformed.

That is, in the case of a cold-rolled steel, deformation due to heat treatment during quenching is small due to high hardenability, but when a large amount of chromium is added, a large amount of carbide precipitates, and a large amount of deformation may occur when machining proceeds have.

Furthermore, the following first, second, and third patent documents are available as prior arts for the present invention.

The first patent document discloses an invention for a "cold tool steel for a flame heat treatment", and a second patent document describes a "cold tool steel for maintaining constant styrene for heat treatment and a method for producing such a cold tool steel" And the third patent document discloses an invention for a "cold tool steel with excellent workability", but all of these inventions are different from the present invention in terms of technical ideas. Accordingly, embodiments corresponding to the field of the present invention are not found in the above disclosure data, and such disclosure data is different from the present invention.

First Patent Document: JP-A-11-131182 ("JP-A" means Unexamined Japanese Patent Publication)

Second Patent Document: JP-A-2002-167644

Third patent document: JP-A-2001-234278

In this situation, it is an object of the present invention to provide a free cutting alloy tool steel which prevents both material deformation due to heat treatment at the time of machining and material deformation during machining, and obtains hardness required as a cold mold or a mechanical structural component do.

That is, the present invention provides the following.

1. A free-cutting alloy tool steel according to the present invention,

Carbon (C): 0.50 to 0.90%,

Silicon (Si): 0.50 to 2.20%,

Manganese (Mn): 0.8% or more,

Manganese + 0.08 chromium (Cr): 1.35 to 2.05%

Nickel (Ni): 0.01 to 0.30%,

Molybdenum (Mo) +0.5 tungsten (W): 0.01 to 0.50%

0.01 to 0.15% of vanadium (V) and

Sulfur (S): 0.03 to 0.15%

It contains iron with balance the Fe and indispensable impurities,

The relationship between the amounts of manganese and chromium is,

Mn / Cr: 0.10 to 0.23, and

The amount of molybdenum, tungsten and manganese is characterized by (Mo + 0.5W) / Mn satisfying 0.55 or less (% is mass%).

2. The free-cutting alloy tool steel according to 1 above,

Calcium (Ca): 0.0001 to 0.0100%, and

Oxygen (O): 0.0100% or less (% is% by mass).

3. The free-cutting alloy tool steel according to 1 or 2,

Upon the addition of the sulfur,

Se + Te: 0.01 to 0.15% and

And Pb + 2Bi: 0.01 to 0.15% (or more, the% is in mass%).

4. The free cutting alloy tool steel according to any one of 1 to 3 above,

Nb, Ta, Ti and Zr of one or more elements of Nb + Ta + Ti + Zr: 0.01 to 0.15 mass%.

5. A free-cutting alloy tool steel according to any one of 1. to 4. above,

And is used after being fired at 1,000 to 1,050 占 폚.

The free-cutting alloy tool steel according to the present invention prevents both material deformation due to heat treatment at the time of machining and material deformation at the time of machining, and obtains hardness required as a cold mold or a mechanical structural component.

The present invention provides high hardenability of alloy tool steels due to the action of addition of manganese (Mn) and the cooperative action of addition of chromium (Cr). In addition, due to the increase of hardenability by addition of manganese It is possible to suppress the formation of carbide and improve the machinability degradation due to carbide due to the effect of decreasing the amount of chromium added because of the effect thereof. Despite the fact that the addition of manganese generally decreases the hardness in the quenching and bending conditions The hardness can be maintained due to the decrease in the amount of molybdenum (Mo) added.

In particular, as a main feature, Mn + 0.08Cr is added in an amount of 1.35 to 2.05% based on the assumption that Mn is added in an amount of 0.8% (mass%) or more, and Mn / Cr Is set to 0.10 to 0.23, and the ratio of (Mo + 0.5W) / Mn is set to 0.55 or less in order to maintain a balance of added Mn and (Mo + 0.5W) added.

The material deformation due to the heat treatment at the time of filling in the prior art cold molten steel can be suppressed by securing sufficient hardenability. In this case, the amount of the alloy to be added is preferably increased.

On the other hand, material deformation caused by machining can be suppressed by reducing the amount of carbide. That is, it is preferable that the amount of alloy added in view of material deformation caused by machining is reduced.

Such a problem is contradictory, but such a problem can be overcome by considering alloying elements added separately between carbide-forming elements and carbide-forming elements.

Examples of the main elements forming carbide are C, Cr, Mo, W and V, and it is preferable that the amount of these elements is reduced as much as possible.

On the other hand, the main examples of elements that do not contribute to the formation of carbide are Si, Mn and Ni, and accordingly, the amount of these elements is preferably increased as much as possible.

As a result, it is important to replace Cr added in a large amount in the conventional cold-rolled molten steel with Mn.

It is also important to add Mo, W, and V to a minimum.

On the other hand, since hardness of HRC 58 or more is required as a cold mold or a mechanical structural component, carbon (C) should be added in an amount of 0.50% or more.

The present invention has been developed on the basis of these ideas or findings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the relationship between the amount of chromium and the amount of manganese in an alloy tool steel according to the present invention. Fig.

In Fig. 1, the H region is an amount of Cr and Mn added in the present invention.

According to the present invention, not only the deformation due to the heat treatment at the time of compacting of the alloy tool steel but also the deformation due to the residual stress during machining can be reduced.

Further, according to the present invention, the amount of Cr, which is an expensive alloy element, is reduced to reduce the cost of the material, and also the machining is promoted to reduce the cost due to the machining, . ≪ / RTI >

According to the present invention, the machinability of the alloy tool steel can be further improved if Ca and O are included in a predetermined amount according to item 2 (item 2, see task solution).

Furthermore, when Se + Te or Pb + 2Bi is added according to item 3, the machinability can be further improved.

Further, when at least one element of Nb, Ta, Ti and Zr is added according to item 4, the amount of Cr added due to the pinning effect on the grain of the element such as carbide, nitride, The decrease in the amount of carbide due to the decrease can be compensated, and the grain can be prevented from being coarsened.

Further, in order to secure the hardenability, it is useful to increase the amount of the element dissolved at the quenching temperature.

Accordingly, the quenching temperature is preferably set to 1,000 ° C or higher (and 1,050 ° C or lower).

In addition, it is preferable to set a component system on the premise that it is used after being used at a high temperature as described above.

Quenching at this temperature has the following meaning.

Conventionally, Cr is added in a predetermined amount so that steel to be quenched at 1,000 to 1,050 占 폚 is quantitatively large as in the case of a tool steel, and a quenching furnace which is thus quenched is assumed to be quenched at such a temperature That is, the furnace which is buried at 1,000 to 1,050 캜 is generally used.

If the quench temperature is lower than this temperature, equipment for it needs to be installed, while the cost of quenching is increased.

When the appropriate quenching temperature for the material is in the range of 1,000 to 1,050 占 폚, the heat treatment furnace does not need to be newly installed, and the quenching process can be carried out at a low cost as in the prior art.

The reason for limiting each element of the invention in the present invention is explained in detail below. Furthermore, the unit of the component ratio is mass%. In the present description of the invention, all percentages defined as mass are equal to the percentages defined by weight, respectively.

Carbon (C): 0.50 to 0.90%

   Carbon is added for the required hardness, thus forming martensite upon ingress to increase hardness. At least 0.50% of the carbon must be involved in order to achieve HBR 58 hardness. On the other hand, if the amount added is too large, the amount of carbide increases proportionally. Therefore, the added amount of C needs to be 0.90% or less. From the above described point of view, the added amount of carbon is preferably 0.65 to 0.80%.

Silicon (Si): 0.50 to 2.20%,

     The silicon solid is dissolved and has an effect of increasing the hardness of martensite. Since these elements increase the hardenability without the formation of other materials, silicon is added in an amount of 0.50% or more. The added amount of silicon is set to 2.20% or less, because if the amount of silicon is too large, ferrite is formed and hardening hardness is decreased.

Manganese (Mn) ≥ 0.8%

   Manganese is an element that effectively increases the hardenability. As a substitute for Cr, Mo, W and V, 0.8% or more of manganese should be added to ensure hardenability.

Mn / Cr: 0.10 to 0.23

    It is preferable to increase the proportion of manganese in order to reduce the amount of carbide and ensure hardenability. If the ratio is lower than the lower limit, the amount of carbide is too large and the strain caused by the machining is not sufficiently reduced. On the other hand, when the above-mentioned ratio exceeds the upper limit, the amount of manganese becomes too much, and a large amount of the remaining austenite is produced, failing to secure hardness. In addition, when the ratio exceeds the upper limit, the amount of chromium is too small to have insufficient curing ability.

Manganese + 0.08 chromium (Cr): 1.35 to 2.05%

  The hardenability increases as the amount of manganese + 0.08 chrome (Cr) added increases, but when the total amount is excessively large, a large amount of residual austenite is generated and hardness is not secured. On the other hand, Insufficient curing ability occurs in small cases. Further, the coefficient of 0.08 of chromium represents the contribution ratio of chromium to the curing ability based on manganese.

Nickel (Ni): 0.01 to 0.30%,

    Nickel has the same effect as manganese. To compensate for the hardenability estimated by manganese, nickel is added in excess of 0.01%. The added amount is not more than 0.30%, because if the added amount is too large, the amount of austenite remaining increases and the hardness decreases accordingly.

Molybdenum (Mo) +0.5 tungsten (W): 0.01 to 0.50%

     Molybdenum and tungsten have the same effect. The effect of tungsten has half the effect of molybdenum, so the coefficient of tungsten is 0.5. It is desirable that elements such as molybdenum and tungsten are not added as the alloy tool steel approaches sufficient hardenability with the addition of manganese and chromium. On the other hand, the addition of these elements is necessary from the viewpoint of hardness, and these elements must be added in an amount of 0.01%. The amount of these elements to be added is 0.50% or less, which increases the amount of unnecessary carbides when the added amount is too large.

(Mo + 0.5W) / Mn? 0.55

When the addition of Mo + 0.5W is large, the following problems also arise.

In the present invention, 0.8% or more of manganese is added. When a large amount of Mo + 0.5W is added as a result of adding a large amount of manganese, the Ms point or the Mf point becomes too low and the hardness decreases in the quenching state or the soft state, and a hardness of HRC 58 or more can be obtained none. Accordingly, in order to obtain hardness of HRC 58 or higher, the present invention sets the ratio of (Mo + 0.5W) / Mn to 0.55 or lower.

2 is a graph showing the relationship between quenching / tempering hardness and (Mo + 0.5W) / Mn.

The results in Table 2 show that the elements of steel are 0.60 to 0.75% of C, 0.96 to 1.53% of Si, 0.81 to 1.53% of Mn, 6.65 to 7.95% of Cr, 0.12 to 0.21 of Mn / Mn: 0.005 to 3.11, V: 0.02 to 0.09%, and S: 0.05%, and a balance of (Mo + 0.5W) The value of (Mo + 0.5W) / Mn varies in various ways to test the effect of the elements mentioned in item 1 and (Mo + 0.5W) / Mn except Fe, i.e., (Mo + 0.5W) / Mn .

In FIG. 2, the relationship between (Mo + 0.5W) / Mn and the quenching / hardening hardness is determined in particular by the following contents.

The steel having the above composition was melted in a vacuum induction furnace to produce 50 kg of ingot. The ingot was soaked at 1,160 캜 for 10 hours, and a square of 45 mm x 45 mm x 1,500 mm And are forged in a square bar at a temperature of 900 ° C to 1,160 ° C.

In the square bar state, the tool steel is subjected to spheroidizing annealing at a cooling rate of 20 ° C / h at 900 ° C, followed by gentle cooling, and the material after the heat treatment is cut to a size of about 20 mm x 20 mm x 20 mm .

These specimens are heated at 1,030 ° C. for 30 minutes or more, quenched by oil cooling, and heated at 180 ° C. for 60 minutes or more.

After the heat treatment is finished, the scale is removed by grinding, and then the hardness of the specimen is measured.

FIG. 2 is a graph showing such hardness after sintering / sintering according to (Mo + 0.5W) / Mn.

2, the main element belongs to the right scope of the present invention, and the effect of (Mo + 0.5W) / Mn is conspicuous.

From the results shown in Fig. 2, (Mo + 0.5W) / Mn should be 0.55 or less in order to obtain a hardness of HRC 58 or higher in a cold mold or the like.

If molybdenum or tungsten is added excessively in the range of the composition ratio of the present invention, the structure of the unstrained residual austenite increases and hardness can not be obtained.

On the other hand, too much of the added molybdenum or tungsten generally causes a decrease in hardness or brittle hardness or a decrease in hardenability. On the other hand, in the present invention, the amount of added elements of C, Mn and Cr is set to be constant, so that sufficient quenching / bending hardness can be obtained.

From the viewpoint of hardenability, the necessary addition amount is also specially set as defined for Mn + 0.08Cr.

0.01 to 0.15% of vanadium (V) and

    Vanadium is an element having effects such as molybdenum and tungsten, and in the present invention, these elements are added in the range of 0.01 to 0.15%.

Sulfur (S): 0.03 to 0.15%,

    Sulfur bonds with manganese to form manganese oxide (MnS). This combination leads to an increase in cutting or grinding machinability. On the other hand, if the addition amount of these elements is less than 0.03%, the increasing effect can not be obtained. On the other hand, even if these elements are added in excess of 0.15%, the increasing effect is saturated. For this reason, the upper limit to which sulfur is added is 0.15%.

Calcium (Ca): 0.0001 to 0.0100%

    When calcium is added together with sulfur, the effect of increasing machinability increases. This is because calcium oxide protects the tool. An amount of addition of 0.0001% or more is required to form sufficient calcium oxide. Even when added in excess of 0.0100%, the effect is saturated. Therefore, 0.0100% is the upper limit.

Oxygen (O):? 0.0100%

    This is an inevitable element in steel. Oxygen is required to be 0.0100% or less in order to form calcium oxide.

Se + Te: 0.01 to 0.15%, Pb + 2Bi: 0.01 to 0.15%

   These elements are elements that increase cutting or grinding machinability. Depending on the scrap used as the raw material, these elements can be added in large quantities and thus become substitute elements of sulfur. In order to increase the machinability by the addition of these elements, the addition amount of these elements needs to be not less than the lower limit defined above. On the other hand, even when the upper limit defined above is exceeded, the effect is saturated.

Nb + Ta + Ti + Zr: 0.01 to 0.15%

   These elements have the effect of forming mode carbides or nitrides and have the effect of preventing grain coarsening at the time of ingestion and holding temperature. In the present invention, the addition of Cr, Mo, W and V is reduced as much as possible, so that the amount of carbide is reduced. As a result, coarsening of the grain occurs easily. In order to prevent grain coarsening and to suppress the reduction of toughness, these elements are added in an overall amount of 0.01% or more. On the other hand, even if the upper limit of 0.15% is added, the effect is saturated.

In this respect, for each element added to the steel of the present invention, according to the embodiment, the minimum amount present in the steel of the present invention is at least a non-zero amount, as in the example summarized in Table 1. In addition, according to another embodiment, the maximum amount present in the steel of the present invention is the maximum amount as shown in the example summarized in Table 1.

Dew point temperature: 1,000 to 1,050 ℃

    The penetration temperature of carbon tool steel or special tool steel (corresponding to SK or SKS) is less than 1,000 ° C, so that the solid solubility is low and shows low hardenability. The quenching temperature of steel for cold stamping (corresponding to SKD) is over 1,000 ℃, and the amount of solid dissolving elements increases. A quenching temperature of 1,000 DEG C or more is preferable in order to secure the hardenability. On the other hand, when it is heated above 1,050 DEG C, low toughness appears due to coarsening of the grain diameter. Therefore, a temperature not higher than the upper limit of the temperature is preferable.

Experimental Example

In Table 1, 120 kg of elements were dissolved in a vacuum induction furnace and the dissolution material was cast in a 250 mm x 450 mm case ingot. The ingot was heated and held at 1,150 to 1,200 ° C and then forged in a square 65 mm square form. After forging, spheroidizing annealing was performed to give a low hardness of less than HRC 25.

These forged materials were cut to the appropriate size required for each test. After cutting, the material was machined into specimens and heat treated at the quench / anneal temperatures shown in Table 2. The hardness after this heat treatment is also shown in Table 2 (in parentheses, hardness is indicated at the quench temperature). In addition, the test was carried out in a spheroidizing annealing condition in order to measure hardenability and drill machinability.

In addition, the measurement test of each value shown in Table 2 was carried out as follows.

(A) Hardenability

A specimen of 3 mm x 10 mm was prepared and the specimen was held at the quenching temperature for 5 minutes in Table 2 and then cooled to 100 ° C or lower at a constant cooling rate. When the cooling rate changes, the minimum limiting cooling rate for obtaining the hardness of the specimen above HRC 58 for each cooling rate is indicated by the hardenability.

Such a low limited cooling rate can be measured as having a higher hardenability.

The curing ability required for use is 15 ° C / min or less.

(B) Warpage after heat treatment

 A specimen of 20 mm x 50 mm x 100 mm was prepared and the specimen was held for 30 minutes at the quenching temperature in Table 2 and then quenched at a cooling rate for hardenability. In addition, the call was made later.

The degree of deformation of the specimen after heat treatment for the length of 100 mm was measured by a three dimensional measuring device.

The maximum height and the minimum height were measured at a length of 100 mm, and a size difference with respect to 100 mm was indicated.

Generally, in terms of accuracy, the size difference should be less than 0.1 mm. The difference in the state before the heat treatment was set to 0.020 mm (0.020%).

(C) Drilling machinability

 A specimen of 50 mm x 50 mm x 200 mm was prepared and the punching operation was carried out by steam treatment SKH51 HSS drill (6 mm).

During the operation, the punching operation was repeated with varying cutting rates under a constant dry condition of 0.15 mm / rev and a bore depth of 15 mm until the drill was damaged by melting or cracking. The cutting rate gradually decreased, and the cutting rate obtained at a depth of 70 mm or more was measured as the life of the drill.

The large cutting rate means higher drilling machinability.

(D) sex cleft (g rindabilty)

 A specimen of 20 mm x 50 mm x 200 mm was prepared and scraped by 0.5 mm from the surface of 50 mm x 200 mm by a flat grinding disk. Assuming that the working time of Comparative Example 6 was 100, the necessary time for 0.5 mm scraping was measured. When the required time was half, the grindabilty was 200. Higher values mean higher fracture.

(E) Warpage after processing

 The difference between the maximum height and the minimum height with respect to the length of 100 mm was measured by a three-dimensional measuring device after measuring the above-mentioned fracture property.

Generally, in terms of accuracy, the size difference should be less than 0.1 mm. The difference in the state before the grinding was set to 0.020 mm (0.020%).

(F) Charpy Impact Test

The specimen was tested according to the method described in JIS Z2242. A 10R notch specimen with a notch portion of 10R and a depth of 2 mm was prepared for the specimen. The test proceeded at room temperature, and the value was measured by impact value.

(G) Fatigue Test

The specimen was tested according to the method described in JIS Z2274. The specimen used was a first specimen (parallel portion: 8 mm) and the test proceeded at room temperature. The repetition of 107 cycles was measured as a fatigue limit that did not cause cracking. These measured values are shown in Table 2.

As can be seen from the results in Table 2, the comparative example 1 steel to which sulfur (S) is not added has unsatisfactory drilling machinability.

When the amount of added carbon and silicon deviates much from the range, and when a large amount of Mo, W and V is added, a large amount of carbide is generated, and a bad fracture and a large deformation are generated after machining. Further, the value in terms of Charpy impact or fatigue deteriorated due to the carbide.

In Comparative Examples 3, 4 and 5 where Mn / Cr was too low and the amount of added carbon was out of the range, a large amount of carbide was formed, and the values deteriorated similarly to Comparative Example 2.

In Comparative Examples 6, 7 and 8 where the amount of Mn / Cr is abnormally large and Mn + 0.08Cr is too small, the curing ability is insufficient. Therefore, rapid cooling is required after quenching and large deformation after heat treatment. Further, in the steels of this comparative example, the required hardness of HRC 58 or more can be obtained only when the ingot proceeds at less than 1,000 ° C.

 In Comparative Examples 9, 10 and 11 where Mn / Cr was too much, the curing ability was insufficient. Therefore, rapid cooling is required after quenching and large deformation after heat treatment.

Further, the required hardness of HRC 58 or more can be obtained when the quenching proceeds at less than 1,000 占 폚, but the required hardness can not be obtained when the quenching temperature is 1,000 to 1,050 占 폚.

Compared with these comparative steels, good results are obtained in all values in the steels according to the invention.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It is evident that various modifications and applications are possible.

The present invention is based on Japanese Patent Application No. 2008-189726, filed on July 23, 2008, and Japanese Patent Application No. 2009-091602, filed on Apr. 3, 2009, the contents of which are incorporated herein by reference .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between the amount of chromium and the amount of manganese in an alloy tool steel according to the present invention. FIG.

2 is a graph showing the influence of (Mo + 0.5W) / Mn on the hardness of the quench / blanket.

Claims (9)

Carbon (C): 0.50 to 0.90 mass%, Silicon (Si): 0.50 to 2.20% by mass, Manganese (Mn): 0.8 mass% or more, Manganese + 0.08 chromium (Cr): 1.35 to 2.05 mass% Nickel (Ni): 0.01 to 0.30% by mass, Molybdenum (Mo) +0.5 tungsten (W): 0.01 to 0.50 mass% 0.01 to 0.15% by mass of vanadium (V) and 0.03 to 0.15 mass% of sulfur (S) In free cutting alloy tool steels containing iron and unavoidable impurities as the remainder, The relationship between the amounts of manganese and chromium is as follows: Mn / Cr: 0.10 to 0.23, and Molybdenum, tungsten, and manganese satisfy an expression (Mo + 0.5W) / Mn of not more than 0.55. The method according to claim 1, Calcium (Ca): 0.0001 to 0.0100 mass%, and And oxygen (O): 0.0100 mass% or less. The method according to claim 1, In addition to sulfur, Se + Te: 0.01 to 0.15 mass% and And Pb + 2Bi: 0.01 to 0.15 mass%, based on the total weight of the free-cutting alloy tool steel. 3. The method of claim 2, In addition to sulfur, Se + Te: 0.01 to 0.15 mass% and And Pb + 2Bi: 0.01 to 0.15 mass%, based on the total weight of the free-cutting alloy tool steel. The method according to claim 1, Further comprising at least one element selected from the group consisting of Nb, Ta, Ti, and Zr in an amount of 0.01 to 0.15 mass% of Nb + Ta + Ti + Zr. 3. The method of claim 2, Further comprising at least one element selected from the group consisting of Nb, Ta, Ti, and Zr in an amount of 0.01 to 0.15 mass% of Nb + Ta + Ti + Zr. The method of claim 3, Further comprising at least one element selected from the group consisting of Nb, Ta, Ti, and Zr in an amount of 0.01 to 0.15 mass% of Nb + Ta + Ti + Zr. 5. The method of claim 4, Further comprising at least one element selected from the group consisting of Nb, Ta, Ti, and Zr in an amount of 0.01 to 0.15 mass% of Nb + Ta + Ti + Zr. 9. The method according to any one of claims 1 to 8, Is used after quenching at 1,000 to 1,050 占 폚.

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