KR100406428B1 - Co-free high speed steel having superior hardness by modifying Si content and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a high speed steel ball used as a cutting machine tool, and its object is to control the content of Si and Cu without the addition of expensive Co or rare earth elements, so that the high-speed cobalt-free tool steel having excellent Rockwell hardness and its manufacturing method In providing.

The present invention for achieving the above object, by weight ratio C: 0.75-1.1%, Si: 0.32-1.0%, Mn: 0.5% or less, Cr: 3.7-4.5%, Ni: 0.30% or less, Mo: 4.5-5.5 %, W: 5.5-6.8%, V: 1.7-2.2%, Cu: 0.6% or less, the cobalt-free high-speed coated oral with excellent hardness by Si control composed of the remaining Fe and unavoidable impurities and the steel formed as described above The technical gist of the present invention relates to a method for producing a cobalt-free high-speed tool steel having excellent hardness by Si control including homogenizing and hot working at 1100-1150 ^° C.

Description

Co-free high speed steel having excellent hardness by Si control and its manufacturing method {Co-free high speed steel having superior hardness by modifying Si content and method for manufacturing the same}

The present invention relates to a high-speed coated oral cavity used as a tool for cutting machining, and more particularly, to a cobalt-free high-speed coated oral which has improved hardness through Si content control.

In general, high-speed coated oral steel is widely used as a basic material for machining tools for machining mechanical parts due to its higher hardness than other steel grades. The most widely used M2 high speed steel is known as Rockwell hardness, with a hardness distribution of up to 63-65. By the way, since the normal hardness value needs appropriate toughness, it is necessary to secure about 64 levels stably, but it is very difficult to secure more than 64 actually.

There are two kinds of M2 high speed steels: high carbon M2 and low carbon M2 steel. Conventional M2 high speed steel is relatively easy to secure Rockwell hardness more than 64 in high carbon M2 steel, but high carbon M2 steel has relatively high content of carbon and carbide forming elements, resulting in poor hot workability. It is not suitable for mass production system for wire rod or rod production by rod rolling. Therefore, M2 high-speed steel is widely used commercially low carbon M2 steel. Therefore, securing a Rockwell hardness of 64 or higher in low carbon M2 steel is a key challenge in this technical field.

US Patent No. 3,859,081 is a method for improving the hardness of the high-speed coating oral. In this prior art, cobalt (Co) is contained 5-7% to increase the hardness of the matrix and fine secondary carbides to achieve a maximum Rockwell hardness of 66-69. This series of high-speed coated oral steel is mainly used for high quality, and there is an economic burden due to the high price of cobalt.

Another method is a method of manufacturing a high-speed coated oral tool by powder metallurgy, which is described in US Pat. No. 5,435,827. Since the powder metallurgy uses fine alloy powder particles, it is possible to suppress segregation at the center of the ingot and generation of coarse eutectic carbides, which generally occur when manufactured by casting ingots. Therefore, there is an advantage that can be manufactured high-speed coating oral with a relatively uniform metal structure, but the manufacturing cost is very expensive compared to the method using the general casting and rolling process due to the complex molding process.

Further, Japanese Laid-Open Patent Publication No. 57-198250 attempts to improve the hardness and mechanical properties by adding rare earth elements, but rare earth elements are rarely applied to actual products because they are many times more expensive than Co.

The present invention provides a high-speed tool steel having excellent Rockwell hardness and a method of manufacturing the same by controlling Si content and Cu content without addition of expensive Co or rare earth elements.

1 is a graph showing the hardness change of M2 high-speed coating oral ingot according to the Si, Cu content

2 is a graph showing the hardness change when the heat treatment is applied according to the Si content

3 is a tissue photograph showing the distribution of carbide

3 (a) is an invention

3 (b) is a conventional material

High-speed tool steel of the present invention for achieving the above object, by weight ratio of C: 0.75-1.1%, Si: 0.32-1.0%, Mn: 0.5% or less, Cr: 3.7-4.5%, Ni: 0.30% or less, Mo: 4.5-5.5%, W: 5.5-6.8%, V: 1.7-2.2%, Cu: 0.6% or less, and is composed of the remaining Fe and inevitable impurities.

In addition, the manufacturing method of the high-speed tool steel of the present invention comprises the homogenizing treatment of the steel composition as described above at 1100-1150 ^° C and hot working.

Hereinafter, the present invention will be described in detail.

The inventors of the present invention while using the low carbon-based M2 high-speed coating oral to secure the hot workability basically while improving the Rockwell hardness,

The amount of Si and the Rockwell hardness are correlated

Note that when the content of Cu exceeds the threshold, the hardness is deteriorated.

The present invention has been accomplished by discovering that a high-speed, high-speed coated steel can be produced in large quantities without using expensive Co or rare earth elements.

Typically, the carbon content is a factor determined by the contents of the carbide forming elements W, Mo, V and Cr and is divided into low carbon and high carbon based on the ratio of (W + Mo + V + Cr) / C. High carbon systems typically contain 0.95-1.10% carbon and low carbon systems contain 0.75-0.90% carbon.

In such M2 high-speed coating steel, Si is managed as a deoxidizer and its content is actively limited to 0.4% or less. When the amount of Si is 0.4% or more, it is known to reduce the known toughness.

However, according to the present invention, it has been found that not only Si acts as a deoxidizer but also increases the precipitation of fine carbides, thereby increasing the effective effect on increasing hardness. That is, as can be seen in Figure 1, it can be seen that as the amount of Si increases Rockwell hardness also increases.

In addition, the inventors have found that when Cu, which has not been actively managed until now, is lower than the threshold (about 0.6%), the amount of carbides is reduced to reduce the Rockwell hardness. This can also be confirmed in FIG. 1.

As described above, the present invention is characterized by limiting the addition amount of Si and Cu in the low carbon-based M2 high speed tool steel. The reason for the limitation of the composition range together with other additives is as follows. C is V, Cr, Mo, W When it is added to less than 0.75% as a basic component necessary to form various carbides in combination with various carbide forming elements such as, it is difficult to form a sufficient amount of carbide, and when it is added in excess of 1.1%, excess carbon remains at the base Forming an austenite phase reduces hardness. In addition, excess carbon can cause local melting during austenizing treatment by significantly lowering the solidus line. Thus, the C content is limited to 0.75-1.1%. Cr is a component that provides hardenability by controlling high temperature oxidation resistance and delaying carbide precipitation during tempering, if less than 3.7% is added. It is difficult to sufficiently achieve the role, when added in excess of 4.5%, because the residual austenite is excessive, the content thereof is preferably limited to 3.7-4.5%.

Mo and W are typically added to form M ₆ C carbide in M2 high speed steel and it is preferable to limit Mo to 4.5-5.5% and W to 5.5-6.8%. The reason is that if lower than the lower limit of each component range, excess carbon is generated to inhibit physical properties related to toughness such as hot workability, and conversely, if the upper limit of each component standard is exceeded, the lowered toughness is lowered to lower the physical properties. Generate.

V contains 1.7-2.2% for the formation of MC-type carbides, but lower than the lower limit of this component range makes it difficult to secure sufficient carbides and degrades the toughness due to excess carbon residue. On the contrary, if the upper limit is exceeded, a problem occurs that remains in the matrix and degrades the toughness of the matrix.

The Ni content limits the content to 0.3% or less because containing 0.3% or more increases the retained austenite and rapidly decreases the hardness.

Mn content, like Ni, is an austenite stabilizing element, and its content is actively limited to 0.5% or less.

It is preferable to manage Si at 0.32-1.0%.

Si is usually limited to 0.4% or less because it lowers the known toughness as a deoxidizer. However, as a result of confirming, even when the Si content is 0.32% or more, the decrease in toughness was determined to be almost insignificant. On the contrary, when the Si content was changed to 0.32%, the state was also changed, leading to more precipitation of fine carbides. Increasing Si above 0.32% resulted in an increase in hardness difference with the alloy below 0.32% by at least 0.4-0.5 by Rockwell hardness. It is desirable that the maximum content of Si does not exceed 1.0%. The reason is that the toughness of the material is slightly reduced, and the effect of adding Si is not so great at 1.0% or more. Increasing the Rockwell hardness of 0.5 is very important in toolmakers with hardness of 63.8 to 64.1 in the case of normal M2 high speed steels, up to 30% of the total manufacturing. The reason is that the pass hardness of M2 high speed steel is more than 64. Therefore, improving the overall hardness at least 0.4-0.5 is very important in the tool steel maker because all the bad treatments are judged as pass products. The achievement of the target hardness of 64 is also directly related to the life of the tool.

Cu is preferably at most 0.6%.

At present, commercial M2 high-speed oral steel does not limit the content of Cu, but in the present invention, the content is managed to 0.6% or less. The reason for this is that when the Cu content is more than 0.6%, the amount of carbides decreases, causing a decrease in Rockwell hardness by 0.3. More preferably, the Si content is 0.5-1.0%, and the Cu content is 0.3% or less. It is set to, because the reason to secure more than 64 hardness more stable.

The main alloy (ingot) of the present invention, which is formed as described above, is preferably homogenized at 1100-1150 ^o C to decompose M ₂ C process carbide into MC and M ₆ C carbide. This decomposition heat treatment has the effect of converting the jagged M ₂ C eutectic carbide into round and fine carbides. In addition, the homogenized ingot is preferably introduced at a homogenization temperature and processed into an appropriate shape. If the initial temperature of the ingot is less than 1100 ^o C, the load of the roll increases due to the temperature drop during hot rolling, and the hot workability also deteriorates. On the other hand, when the temperature of the ingot exceeds 1150 ^o C, the material is easily broken by hot brittleness.

In the present invention, an additional hardness improvement is obtained by increasing the Si content of the high speed tool steel slightly. In fact, the existing M2 high-speed steel can achieve the target Rockwell hardness of 64, while the ratio of about 90% is achieved in the case of the alloy of the present invention in which the Si content is microcontrolled. The high speed steel ball of the present invention is useful as a material for tools used to machine mechanical parts.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

Various high-speed coating oral cavity shown in Table 1 below was prepared in a 50KG grade ingot using a vacuum melting furnace.

Alloy type Chemical composition (wt.%) C Si Mn Cr Mo W V Ni Cu Fe Conventional 0.84 0.29 0.20 4.02 4.82 5.78 1.87 0.17 1.10 Balance Invention 1 0.85 0.37 0.20 4.01 4.76 5.76 1.88 0.19 0.10 Balance Invention 2 0.86 0.60 0.20 4.04 4.65 5.65 1.80 0.16 0.10 Balance Invention 3 0.87 0.96 0.20 4.08 4.80 5.74 1.88 0.17 0.10 Balance Comparative Material 1 0.86 0.29 0.20 4.05 4.55 5.58 1.75 0.20 0.11 Balance Comparative Material 2 0.86 0.29 0.21 4.02 4.77 5.73 1.84 0.15 0.20 Balance Comparative Material 3 0.84 0.29 0.20 4.01 4.75 5.71 1.89 0.16 0.58 Balance

The manufactured ingot was homogenized at 1100-1150 ^o C for 2 hours in a heat treatment furnace, and then hot rolled to about 12 mm to prepare a plate. In the present invention, the specimen was taken from the cast ingot and the rockwell hardness change of the cast material was evaluated and the results are shown in FIG. 1.

1 is a result showing the change of Si content and Rockwell hardness of the M2 ingot state using the test material shown in Table 1. In FIG. 1-3), and the change in Rockwell hardness according to Cu content is based on the conventional material and the comparative material (1-3). As shown in FIG. 1, the Rockwell hardness sharply increases at about 0.3% Si or more. After that, it is found that the Si content is gradually increased. This result proves that the Rockwell hardness increase is improved by 0.5 by the small increase of Si. On the other hand, when the Cu content is more than 0.6%, the Rockwell hardness decreases by about 0.3. This result shows that the effect of Si addition can be sufficiently obtained when the content of Cu is limited to less than 0.6%.

FIG. 2 shows a heat treatment process such as spheroidizing heat treatment, austenizing treatment and tempering treatment, which are the same as those of the actual product, using a plate material hot rolled with 12 mm of the test materials shown in Table 1. It is the result of measuring Rockwell hardness according to Si content after application. The spheroidization heat treatment was taken out after cooling at 840 ^° C. for 4.2 hours and then cooling to 660 ^° C. at a cooling rate of 21 ^° C./hr. Austenite age ranging the process was yunaeng After holding for 5 minutes at 1190 ^o C tempering process and repeat yunaeng After yunaeng and kept for 2 hours at a 535 ^o C again after holding for 2 hours at 535 ^o C Was performed. The Rockwell hardness value of 63.8 in the case of the conventional material, while the hardness increase of 64.35 to 64.90 in the present invention shows that the same occurred as in the ingot state. The effect of increasing the Rockwell hardness by 0.5-1.0 due to the addition of Si will play a decisive role in passing the Rockwell Hardness 64, the acceptance criterion in the toolmaker.

This result is also in good agreement with the result that the inventive process carbide (FIG. 3 a) shown in FIG. 3 is decomposed and heat treated by a slight increase in Si compared with the conventional material (b in FIG. 3). .

As described above, the present invention provides a high-speed coated oral material which is easy to produce wire rods and rods and improves the quality of M2 steel by securing a good hot workability with low carbon-based M2 steel and easily achieving a target Rockwell hardness value. There is a useful effect that can be done.

Claims (5)

By weight ratio C: 0.75-1.1%, Si: 0.32-1.0%, Mn: 0.5% or less, Cr: 3.7-4.5%, Ni: 0.30% or less, Mo: 4.5-5.5%, W: 5.5-6.8%, V : 1.7-2.2%, Cu: 0.6% or less, Cobalt-free high speed oral steel with excellent hardness by Si control composed of remaining Fe and unavoidable impurities. The cobalt-free high speed tool steel having excellent hardness by Si control according to claim 1, wherein the Si content is 0.5-1.0% and the Cu content is 0.3% or less. The cobalt-free high speed tool steel having excellent hardness by Si control according to claim 1, wherein the high speed tool steel has a Rockwell hardness of 64 or more. By weight ratio C: 0.75-1.1%, Si: 0.32-1.0%, Mn: 0.5% or less, Cr: 3.7-4.5%, Ni: 0.30% or less, Mo: 4.5-5.5%, W: 5.5-6.8%, V : 1.7-2.2%, Cu: 0.6% or less, high cobalt-free high hardness by Si control which includes hot-working the main alloy composed of remaining Fe and unavoidable impurities at 1100-1150 ^o C Method of manufacturing tool steel. The method of manufacturing cobalt-free high speed tool steel having excellent hardness by Si control according to claim 3, wherein the Si content is 0.5-1.0% and the Cu content is 0.3% or less.