KR100570800B1 - Method for heat treatment of high speed steel ingot rarely compmising cobalt - Google Patents

Abstract

The present invention relates to a heat treatment method of a high-speed coated oral ingot material used as a tool of a cutting machine, and more particularly, to a heat treatment method for decomposing or miniaturizing the process carbide inherent in the high-speed coated oral ingot material.

In the present invention, 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: 0.8% or less, Mo: 4.5 to 5.5%, W: 5.5 ~ 6.8%, V: 1.7 ~ 2.2%, Cu: 0.6% or less, 1st homogenization treatment at 950-1050 ℃ for high hardness high-speed oral material composed of remaining Fe and other unavoidable impurities, 1100 Provided is a heat treatment method for process carbide decomposition and miniaturization of cobalt-free and trace-containing high-speed coating oral ingots, which is subjected to a two-stage homogenization treatment at -1150 ° C.

Description

Heat Treatment Method for Decomposition and Refinement of Process Carbide in Cobalt Trace High-Speed Coated Oral Ingot {METHOD FOR HEAT TREATMENT OF HIGH SPEED STEEL INGOT RARELY COMPMISING COBALT}

1 is a photograph showing the decomposition state of the process carbide after a single homogenization heat treatment at 1100, 1150, 1200 ℃,

Figure 2 is a photograph showing the process carbide decomposition state when a two-stage homogenization heat treatment is applied after the first homogenization treatment at 970, 1000, 1030 ℃ secondary homogenization heat treatment at 1100 ℃,

Figure 3 is a graph showing the measurement results of the cutting force of the 60 mm bar applied to a single homogenization heat treatment process and a two-stage homogenization heat treatment process.

The present invention relates to a heat treatment method of a high-speed coated oral ingot material used as a tool of a cutting machine, and more particularly, to a heat treatment method for decomposing or miniaturizing the process carbide inherent in the high-speed coated oral ingot material.

High-speed coating steel has a higher hardness than other steel grades and is widely used as a basic material for machining tools that process mechanical parts. The most widely used high speed steel is M2 high speed steel, which is Rockwell hardness up to 63-65. However, the M2 high-speed coated oral ingot material has excellent characteristics of uniform hardness distribution and mechanical machinability only when the coarse eutectic carbide, which plays a role of improving hardness and wear resistance, needs to be effectively decomposed or refined.

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 the high carbon content and the content of carbide forming elements have a problem in that it is poorly formed into a hot rolled material. There are difficulties in mass production systems. Therefore, low carbon-based M2 high-speed coating oral is currently widely used in the manufacturing industry.

Typically, the process carbide of M2 high speed steel is composed of M ₂ C carbide, these M ₂ C carbide is known to be decomposed into M ₆ C and MC carbide during homogenization heat treatment. The result is the hundreds to thousands of microns inherent in the M2 high-speed oral ingot, which is responsible for degrading coarse plate- or rod-shaped M ₂ C eutectic carbides into several microns of M ₆ C and MC carbides. This is the key to the microstructure change that enables hot rolling of high alloy-high carbon M2 high-speed oral ingots.

Therefore, M2 high-speed oral ingot materials are generally preheated at 800-900 ° C and then subjected to a single homogenization at 1100-1150 ° C. The M2 high-speed coated oral ingot material, despite the above-mentioned homogenization heat treatment, caused some of the process carbides to have insufficient carbide decomposition reactions, thereby leaving undecomposed process carbides.

Undegraded coarse eutectic carbides can cause defects in the subsequent forging or hot rolling process, resulting in product defects. In addition, these undigested coarse eutectic carbides remain in hot-rolled wires and rods, which not only deteriorate mechanical machinability significantly but also cause a decrease in the hardness uniformity of the raw materials.

Korean Unexamined Patent Publication No. 2002-76723 discloses improving hardness by controlling Si content to 0.32 to 1.0% by increasing carbide miniaturization and increasing 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.

Korean Patent Application No. 2002-82644 is a cobalt-free high-speed coating steel designed to show the effect of increasing hardness even in the general curing temperature area by controlling Si content from 0.1 to 1.0% and adding Co to 0.3-0.8%. .

However, the patents have a disadvantage in that it is difficult to effectively decompose or refine the coarse process carbide inherent in the ingot material by performing a single homogenization treatment in the temperature range of 1100-1150 ° C.

The present invention is to solve the problems of the prior art as described above, to provide a method for effectively controlling the decomposition or refinement of coarse eutectic carbide present in the high-speed coating oral cast by heat treatment control method There is this.

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: 0.8 Less than%, Mo: 4.5 to 5.5%, W: 5.5 to 6.8%, V: 1.7 to 2.2%, Cu: 0.6% or less, two-step homogenization heat treatment using high-speed coating steel composed of remaining Fe and other unavoidable impurities Provide a way to.

In the heat treatment method of the high-speed coated oral steel of the present invention, the steel prepared as described above is preheated at 800-900 ° C. for a predetermined time to ensure a uniform temperature over the entire large ingot, and the decomposition treatment of the M ₂ C eutectic carbide. In order to induce finer nucleation at the time, the first homogenization treatment at 950-1050 ° C and the second homogenization treatment at 1100-1150 ° C effectively decomposes or deforms the plate- or rod-shaped process carbide inherent in high-speed coated steel casting It comprises a heat treatment method for miniaturization.

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

The inventors of the present invention conducted the study of effectively decomposing process carbides using a low carbon-based M2 high-speed coated steel casting material, and confirmed the following facts.

(1) In the temperature range of 1100-1200 ° C, even if the holding time or the holding temperature were increased, the coarse process carbide decomposition reaction did not significantly improve and was almost similar.

(2) The residual amount of coarse undecomposed process carbides is significantly reduced by first maintaining in the temperature range of 950-1050 ° C and finally in the temperature range of 1100-1150 ° C.

Thus, with proper attention to the two facts and homogenizing heat treatment procedure, it is possible to significantly reduce the undecomposed amount of coarse eutectic carbides of hundreds to thousands of microns in size.

The present invention is characterized by a heat treatment method for effectively decomposing and miniaturizing coarse eutectic carbide inherent in M2 high-speed steel ball ingot material, and the composition limitation range and heat treatment method of the alloy to be applied will be described below.

[Scope of application of the alloy to be applied]

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 to form excess austenite phase, thereby lowering the hardness. In addition, since excessive carbon can cause local melting during austenizing treatment by greatly lowering the solidus, it is preferable to limit the content to 0.75 to 1.1% by 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.

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, and when added in excess of 4.5% by weight, Cr is excessive. 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: 0.8 wt% or less

The Co is mainly added to ensure heat resistance to withstand the temperature rise of the tool according to the high-speed machining, it is not necessary to add expensive Co because it does not affect the hardness improvement when a low curing treatment temperature is applied. However, when a high curing treatment temperature is applied, the hardness can be further improved by adding 0.3 to 0.8% by weight of Co. However, if the content exceeds 0.8% by weight, it is preferable to limit the content to 0.8% by weight or less because the stability of the austenite is increased in the region where the curing temperature is high and the austenite remains at room temperature during quenching, thereby reducing the hardness. .

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 steel, and when added less than 4.5 wt%, excessive carbon is generated to inhibit related properties such as toughness and 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 less than 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

The Cu is mainly introduced into the scrap, and when added in excess of 0.6% by weight is observed to lower the fracture toughness, it is preferable to limit the content to 0.6% by weight or less.

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

[Heat treatment method]

Homogenized treatment at 1100 ~ 1150 ℃ the steel composition as described above. The homogenization treatment is effective to decompose thin and broad coarse M ₂ C carbide into round and fine MC and M ₆ C carbides. However, such a single homogenization heat treatment has a problem of generating a large amount of undecomposed M ₂ C process carbide.

In the present invention, the steel prepared as described above is first preheated at 800-900 ° C. for a predetermined time in order to ensure a uniform temperature throughout the large ingot. Subsequently, the first homogenization treatment at 950-1050 ° C. and the second homogenization treatment at 1100-1150 ° C. in order to cause finer nucleation during decomposition of M ₂ C eutectic carbide are performed. A heat treatment is performed to effectively decompose or refine the plate- or rod-shaped process carbide, and this heat treatment method is a feature of the present invention.

The reason for the first homogenization treatment in the 950-1050 ℃ section at the homogenization treatment temperature is that it is difficult to apply practically because a large holding time is required to generate a fine decomposition carbide nucleus below 950 ℃, carbides that decompose when exceeding 1050 ℃ This is because the nucleus of? Is difficult to be formed sufficiently finely.

The second homogenization treatment temperature is 1100-1150 ℃. If the temperature is lower than 1100 ℃, the load of the roll or press hammer is increased due to the temperature drop during hot rolling or forging. Since the material easily breaks due to brittleness, the secondary homogenization temperature is preferably limited to 1100 to 1150 ° C.

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

Example 1

Four kinds of steels having the composition as shown in Table 1 were prepared in a 50 kg ingot using a vacuum melting furnace. The ingot thus prepared was preheated at 820-880 ° C. for 2 hours in a heat treatment furnace and then maintained at 1100, 1150, 1200 ° C. for 3-9 hours for a single homogenization treatment.

Figure 1 is a photograph showing the decomposition state of the process carbide when the homogenization treatment for 9 hours at 1100, 1150, 1200 ℃ after preheating using the ingot material. As can be seen in Figure 1 it can be observed that a large amount of eutectic carbide remains undecomposed.

After the preheating process using the ingot material, the decomposition state of the process carbide was observed after homogenizing treatment at 1100, 1150, and 1200 ° C. for 3 hours, respectively.

<Table 1>

division Ingredient (% by weight) C Si Mn Cu Co Cr W Mo V Ni Fe Alloy 1 0.86 0.28 0.20 0.11 0.023 4.05 5.58 4.55 1.74 0.17 Remainder Alloy 2 0.84 0.28 0.21 0.10 0.610 4.03 5.74 4.80 1.88 0.15 Remainder Alloy 3 0.85 0.37 0.20 0.10 0.021 4.01 5.76 4.76 1.88 0.19 Remainder Alloy 4 0.84 0.85 0.20 0.11 0.570 4.02 5.71 4.72 1.85 0.14 Remainder

Example 2

Four kinds of steels having the composition shown in Table 1 were prepared in a 50 kg ingot using a vacuum melting furnace. The ingot thus prepared was preheated at 820 to 880 ° C. for 2 hours in a heat treatment furnace, and then maintained at a temperature range of 970, 1000, and 1030 ° C. for two-step homogenization, and then heated to 100 ° C. per hour at 100 ° C. per hour. Finally, homogenization was performed at a temperature of &lt; RTI ID = 0.0 &gt;

Figure 2 shows the decomposition state of the process carbide in the case of homogenizing treatment after maintaining at 970, 1000 and 1030 ℃ after preheating using the ingot material and then elevated to 1100 ℃ at an elevated temperature rate of 100 ℃ per hour to be. As can be seen in FIG. 2, it can be observed that most of the coarse process carbides are well decomposed into fine carbides as compared to the case of FIG.

After the preheating process using the ingot material, and then maintained at 1000 ℃ each and finally homogenized at 1100, 1150 ℃ at an elevated temperature rate of 100 ℃ per hour, the decomposition state of the process carbide was observed very effectively as shown in FIG. Observation of the process carbide decomposition was observed.

Example 3

In Table 1, an ingot of 1 ton was manufactured using a vacuum melting furnace as alloy 2. One of the ingots prepared in this way was subjected to a single homogenization treatment at 1100-1150 ℃ after preheating at 820 ~ 880 ℃, the other is 970-1030 ℃ after preheating the ingot to 820 ~ 880 ℃ in a heat treatment furnace After the temperature was raised to a temperature range, and after performing a two-stage homogenization treatment, which was finally homogenized at a temperature of 1100-1150 ° C. at a temperature rising rate of 100 ° C. per hour, billets were prepared by 250 SQ in a hot forging process. The forged billet was further subjected to induction rolling at 130 SQ to finally produce a 60 mm rod-rolled material.

In order to evaluate the machinability, the rod-shaped rolling material was evaluated using a carbide tip of Sandvik under a cutting depth of 1 mm and a feed rate of 0.2 mm / rev.

3 is a result of evaluating the cutting force of the 60mm rod rolling material manufactured using the heat treatment conditions shown in Examples 1 and 2, respectively. The cutting force curve of the 60 mm rod manufactured using the heat treatment conditions shown in Example 1 is more severe than the cutting force curve of the 60 mm rod manufactured using the heat treatment conditions of Example 2 due to the presence of coarse carbides. Can be clearly observed. Therefore, it is shown that the two-stage homogenization heat treatment of Example 2 almost completely decomposes the process carbide more efficiently.

As described above, the present invention facilitates the production of wire rods and rods by effectively decomposing the coarse process carbides inherent in the M2 high-speed coated oral ingot, and improving the machinability while improving the machinability of the wire and the bar. There is an effect to improve the quality of.

Claims (2)

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 high speed oral material composed of remaining Fe and other unavoidable impurities is first homogenized at 950-1050 ℃, and 1100-1150 A heat treatment method for process carbide decomposition and miniaturization of cobalt traces containing high-speed coating oral ingots, characterized in that a two-stage homogenization treatment is carried out at 2 캜 for second homogenization. The method of claim 1, wherein the material is preheated at 820-880 ° C. prior to the two-stage homogenization treatment.

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