KR100502193B1 - High speed tool steel having superior hardness and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a high-speed coated oral cavity and a method for manufacturing the same used as a tool of a cutting machine.

The high-speed coating steel is in weight%, C: 0.75 to 1.1%, Si: 0.1 to 1.0%, Mn: 0.5% or less, Cr: 3.7 to 4.5%, Ni: 0.30% or less, Co: 0.3 to 0.8%, Mo: 4.5-5.5%, W: 5.5-6.8%, V: 1.7-2.2%, Cu: 0.6% or less, remaining Fe and other unavoidable impurities. Moreover, the manufacturing method of this high speed coating steel is also provided.

This high-speed coated oral has the target hardness value while having hot workability of the M2 high-speed coated oral. Therefore, the production of wire rods and rods is easy, and the quality of M2 high-speed coated oral is improved.

Description

High speed tool steel having superior hardness and method for manufacturing the same

The present invention relates to a high-speed coated oral steel used as a tool of a cutting machine, and more particularly, to a cobalt-free high-speed coated oral which improves the hardness by adding Si while controlling the hardness according to the curing temperature. .

High-speed coating oral steel is widely used as a basic material for machining tools that machine mechanical parts due to its higher hardness than other steel grades. The most widely used high speed steel is M2 high speed steel, which has a hardness of 63-65 at Rockwell hardness. By the way, the M2 high-speed coating oral is required to secure a Rockwell hardness 64 level, but it is very difficult to actually secure a hardness of 64 or more.

M2 high speed steel can be divided into high carbon M2 high speed steel and low carbon M2 high speed steel. The high carbon-based M2 high-speed coated oral steel can stably secure Rockwell hardness of 64 or more, but there is a problem of poor hot workability due to high content of carbon and carbide forming elements, so that mass production system for producing wire rod or bar by rod rolling Is not suitable. Therefore, low carbon M2 high-speed coating oral is widely used commercially. Therefore, securing the Rockwell hardness of low carbon-based M2 high-speed steel can be more than 64 is a key task in the art.

The prior art for improving the hardness of high-speed coated oral is US Patent No. 3,859,081. The prior art is to add about 5 to 7% by weight of cobalt (Co) to increase the hardness of the matrix and the amount of fine secondary carbide, Rockwell hardness can be achieved up to 66 ~ 69 level. This series of high-speed coating oral is mainly used for high quality, and there is a problem that the economic burden due to the high price of cobalt.

Another prior art is US Pat. No. 5,435,827, which relates to a method for manufacturing a high speed steel ball by powder metallurgy. Since the powder metallurgy uses fine alloy powder particles, it is possible to generally suppress segregation and coarse eutectic carbides generated in the center of the ingot generated when the casting ingot is manufactured. Therefore, there is an advantage in that it is possible to manufacture a high-speed coated oral steel having a relatively uniform metal structure, but the manufacturing process is complicated and the manufacturing cost is too expensive compared to the method using a general casting and rolling process.

Another prior art is Japanese Patent Laid-Open No. 57-198250, which adds rare earth elements to improve hardness and mechanical properties. However, the prior art has a problem in that it is hardly applied to an actual product because a rare earth element that is several times more expensive than Co must be added.

Another prior art is Korean Patent Laid-Open Publication No. 2002-76723, which relates to improving hardness by controlling the Si content to 0.32 to 1.0% and increasing the carbide fineness and precipitation amount. However, the prior art has a hardness increase effect in the region where the curing temperature is low, but when the curing temperature is high, the hardness is no longer improved.

The present invention is to solve the problems of the prior art as described above, to control the Co content to control the hardness according to the curing temperature and at the same time to provide a cobalt-containing high-speed coating oral and improved manufacturing method by adding Si to the hardness , Its purpose is.

The present invention for achieving the above object by weight, C: 0.75 ~ 1.1%, Si: 0.1 ~ 1.0%, Mn: 0.5% or less, Cr: 3.7 ~ 4.5%, Ni: 0.30% or less, Co: 0.3 ~ 0.8%, Mo: 4.5-5.5%, W: 5.5-6.8%, V: 1.7-2.2%, Cu: 0.6% or less, including the remaining Fe and other inevitable impurities.

In addition, the manufacturing method of the high-speed coated oral cavity of the present invention comprises performing hot working by homogenizing the steel formed as described above at 1100 to 1150 ° C.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present inventors confirmed the following two facts while researching to increase the Rockwell hardness while basically securing the hot workability using the low carbon-based M2 high-speed coated steel.

(1) There is a hardness increase effect as the curing treatment temperature increases at a specific Co content.

(2) Hardness increase effect only in the region where curing temperature is low at specific Si content.

Therefore, paying attention to the above two facts, if the content of Co and Si is properly controlled, not only can a hardness increase at a high curing treatment temperature with only a small amount of Co, but also Si can be controlled simultaneously to cover the entire curing treatment temperature range. It is possible to increase the hardness and simultaneously control the hardness to the desired hardness.

The present invention is characterized in the composite control of the content of Co and Si in M2 high speed tool steel, and will be described below by dividing emphasis and manufacturing method.

[Strength]

C: 0.75 to 1.1 wt%

Carbon content in high-speed coatings is a factor determined by the contents of W, Mo, V and Cr, which are carbide forming elements, and is based on the ratio of (W + Mo + V + Cr) / C. Divided into tool steel. The high carbon-based high-speed oral cavity contains about 0.95 to 1.10% by weight of carbon, and the low carbon-based high-speed oral cavity contains about 0.75 to 0.90% by weight of carbon.

The C is a basic component necessary to form various carbides in combination with various carbide forming elements such as V, Cr, Mo, W, etc., if it is added less than 0.75% by weight, it is difficult to form a sufficient amount of carbide, and is added in excess of 1.1% by weight. Excess carbon remains at the base, forming excess austenite phase, thereby lowering the hardness. In addition, since excessive melt | dissolution can generate local melt at the time of austenizing treatment by greatly reducing a solidus line, it is preferable to limit the content to 0.75 to 1.1 weight%.

Si: 0.1-1.0 wt%

Said Si is a component added as a deoxidizer and contributes to the improvement of hardness by further increasing carbide precipitation. When the content of Si is less than 0.1% by weight, there is almost no inherent deoxidation effect of Si, and when added in excess of 1.0% by weight, the toughness of the material is not only reduced, but also the deoxidation effect is saturated, so that the content is 0.1 to 1.0. It is preferable to limit the weight percentage.

When the curing treatment temperature is low in the content range of Si, the hardness increase effect is obvious, but when the curing treatment temperature is high, the hardness increase is no longer achieved. Therefore, the content of Co together with the content of Si must be controlled in a complex manner so that the hardness increase effect is continuously observed as the curing treatment temperature increases.

Particularly, if the content of Si is controlled to 0.32 to 1.0% by weight, it can be accompanied by Si's inherent carbide deposition effect, which can be obtained at 0.32% by weight or more, and thus can maintain a higher hardness even at low curing treatment temperatures. desirable.

Mn: 0.5 wt% or less

The Mn is an austenite stabilizing element, and when added in excess of 0.5% by weight, the residual austenite is increased to drastically decrease the hardness, so that the content is preferably limited to 0.5% by weight or less.

Cr: 3.7-4.5 wt%

The Cr is a component that provides hardenability by controlling high temperature oxidation resistance and delaying carbide precipitation during tempering. When Cr is added less than 3.7% by weight, it is difficult to fully achieve these two roles. Since austenite is retained, the content is preferably limited to 3.7 to 4.5% by weight.

Ni: 0.30 wt% or less

Ni, like Mn, is an austenite stabilizing element. When Ni is added in excess of 0.30% by weight, the residual austenite is increased to rapidly decrease the hardness. Therefore, the content is preferably limited to 0.30% by weight or less.

Co: 0.3 ~ 0.8 wt%

Co is mainly added to secure heat resistance and improve the hardness of the tool according to the high-speed machining, it is known that the effect is only at least 3% by weight.

However, when the content of Co is controlled to 0.3 to 0.8% by weight, which is the scope of the present invention, the hardness increase effect appears in the region where the curing treatment temperature is high.

If the Co content is less than 0.3% by weight, there is little effect of increasing hardness regardless of the region of low or high curing temperature. If the content of Co is higher than 0.8% by weight, the stability of austenite is increased when heat treatment is performed in the region of high curing temperature. In order to reduce the hardness by retaining austenite to room temperature during rapid quenching, it is preferable to limit the content to 0.3 to 0.8% by weight.

Mo: 4.5-5.5 wt%

The Mo is a component added for the formation of M ₆ C-type carbide in M2 high-speed coating oral, and when less than 4.5 wt% is added, it generates excess carbon to inhibit physical properties related to toughness such as hot workability and exceeds 5.5 wt%. When added to reduce the known toughness to cause a problem of lowering the physical properties, it is preferable to limit the content to 4.5 to 5.5% by weight.

W: 5.5-6.8 wt%

W is added to form M ₆ C carbide in M2 high-speed coating oral, like Mo. When W is added below 5.5 wt%, excess carbon is generated to inhibit properties related to toughness such as hot workability, and 6.8 wt%. If it is added in excess of the drop in the known toughness causes a problem of lowering the physical properties, it is preferable to limit the content to 5.5 ~ 6.8% by weight.

V: 1.7-2.2 wt%

The V is added for the formation of MC-type carbide, and if it is added less than 1.7% by weight, it is difficult to secure sufficient carbides, as well as to reduce toughness due to excess carbon residue, and when added in excess of 2.2% by weight, it remains at the base. Since it lowers the toughness, it is preferable to limit the content to 1.7 to 2.2% by weight.

Cu: 0.6 wt% or less

Cu is a component mainly introduced from scraps, and when added in excess of 0.6% by weight, the fracture toughness is lowered, and therefore, the content thereof is preferably limited to 0.6% by weight or less.

In addition to the above compositions, the remainder is composed of Fe and other unavoidable impurities.

[Manufacturing method]

Homogenized treatment at 1100 ~ 1150 ℃ the steel composition as described above. The homogenization treatment has the effect of decomposing the pointed M ₂ C eutectic carbide into round and fine MC and M ₆ C carbide.

If the homogenization treatment temperature is less than 1100 ° C, the holding time required to decompose the M ₂ C process carbide into fine MC and M ₆ C carbides is long, and if it exceeds 1150 ° C, there is a problem in that it is higher than the initial input temperature of hot rolling. The homogenization treatment temperature is preferably limited to 1100 ~ 1150 ℃.

After the homogenization treatment, hot working is carried out to an appropriate shape at the same temperature. If the hot working temperature is less than 1100 ℃ not only increases the load of the roll due to the temperature drop during hot rolling but also deteriorates the hot workability, and if it exceeds 1150 ℃ causes a problem that the material is easily broken by hot brittleness, the hot It is preferable to limit processing temperature to 1100-1150 degreeC.

As described above, the present invention is to add a small amount of Co to the high-speed coating oral to obtain a continuous hardness improvement according to the curing treatment temperature. In addition, it is characteristic to obtain desired hardness through control of hardening temperature by managing Si compositely.

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

EXAMPLE

Steel having a composition as shown in Table 1 was prepared in a 50 kg ingot using a vacuum melting furnace. The prepared ingot was homogenized at 1100 to 1150 ° C. for 2 hours in a heat treatment furnace, and then hot rolled to about 12 mm to prepare a plate. Rockwell hardness was measured after applying the produced plate to the same heat treatment process as spheroidizing heat treatment, hardening treatment (austenizing treatment) and tempering treatment.

The spheroidization heat treatment was taken out after holding at 840 ° C. for 4.2 hours, cooling to 660 ° C. at a cooling rate of 21 ° C./hour.

The austenizing treatment was oil-cooled after maintaining for 5 minutes in the 1190 ~ 1220 ℃ section.

The tempering treatment was performed by repeatedly cooling the oil after maintaining the oil at 535 ° C. for 2 hours and then maintaining the oil at 535 ° C. for 2 hours.

1 is a graph showing the hardness change of the comparative material (1 to 3) and the invention material (1) according to the Co content and the curing treatment temperature. As shown in Figure 1, the comparative material (1 to 2) having a Co content of less than 0.3% by weight hardly increases in hardness depending on the curing treatment temperature. In addition, the comparative material (3) having a Co content of more than 0.8% by weight can be seen that the hardness is lowered at a curing treatment temperature of 1220 ° C even though more expensive Co is added.

However, in the case of the inventive material 1 to which 0.610% by weight of Co was added, a hardness increase of 1.0 or more appeared at a curing treatment temperature of 1220 ° C.

2 is a graph showing the hardness change of the comparative materials (1, 4 ~ 5) according to the Si content and the curing treatment temperature. As shown in FIG. 2, even when the content of Si satisfies the scope of the present invention, in the case of the comparative materials (1, 4 to 5) in which the content of Co does not satisfy the scope of the present invention, the hardness increase is low at low curing treatment temperatures. However, it can be seen that the hardness increase is no longer maintained at a curing temperature of about 1220 ° C.

Figure 3 is a graph showing the hardness change of the comparative material (1) and the invention material (2 to 3) by controlling Co and Si in combination. As shown in FIG. 3, the present invention provides a high-speed coated oral steel which continuously increases hardness as the curing temperature increases while simultaneously increasing the absolute value of hardness by controlling the Co content and the Si content as shown in FIG. 3. can do. In other words, the invention according to the present invention can not only control the hardness of the desired tool by the curing treatment temperature control, but also ensures that Rockwell hardness 64 or more, which is the acceptance criterion in the tool maker, in the entire curing treatment temperature section.

As described above, the present invention has the effect of ensuring the hot workability of the M2 high-speed coated oral and easily achieving the target hardness value, thereby facilitating the production of wire rods and rods and improving the quality of the M2 high-speed coated oral.

1 is a graph showing the hardness change of M2 high-speed coated oral according to Co content and curing treatment temperature

2 is a graph showing the hardness change of M2 high-speed coated oral according to Si content and curing treatment temperature

3 is a graph showing the hardness change of the M2 high-speed coated oral according to the addition of Co and Si composite

Claims (5)

By weight%, C: 0.75 to 1.1%, Si: 0.1 to 1.0%, Mn: 0.5% or less, Cr: 3.7 to 4.5%, Ni: 0.30% or less, Co: 0.3 to 0.8%, Mo: 4.5 to 5.5% , W: 5.5-6.8%, V: 1.7-2.2%, Cu: 0.6% or less, high hardness cobalt-containing high-speed coating oral including the composition of the remaining Fe and other unavoidable impurities. The high hardness cobalt-containing high-speed coating oral cavity according to claim 1, wherein the Si is 0.32 to 1.0 wt%. The high hardness cobalt-containing high speed steel ball according to claim 1, wherein the high speed steel ball has a Rockwell hardness of 64 or more. By weight%, C: 0.75 to 1.1%, Si: 0.1 to 1.0%, Mn: 0.5% or less, Cr: 3.7 to 4.5%, Ni: 0.30% or less, Co: 0.3 to 0.8%, Mo: 4.5 to 5.5% , Hardness cobalt comprising hot working, homogenizing at 1100 ~ 1150 ℃ for steel composed of W: 5.5 ~ 6.8%, V: 1.7 ~ 2.2%, Cu: 0.6% or less, remaining Fe and other unavoidable impurities Method for producing a high speed coating oral containing small amount. 5. The method of claim 4, wherein the Si is 0.32 to 1.0 wt%.