KR20160010930A - (High wear-resistant cold work tool steels with enhanced impact toughness - Google Patents

Abstract

The present invention relates to a high wear-resistant cold work tool steel with enhanced impact resistance, which also has impact resistance in order to be applied to not only a knife mold to cut a steel such as a hot coiled and a cold rolled steel coil and/or a plate; a high-strength stainless steel sheet and an iron scrap, which are steel products, but also a mold liner; a short blast liner; a special mold material; and a rolling roll. The high wear-resistant cold work tool steel of the present invention comprises: 1.8-2.4 wt% of carbon (C); 11.0-14.0 wt% of chrome (Cr); 0.5-2.5 wt% of molybdenum (Mo); 2.0-6.0 wt% of vanadium (V); 0.1-0.7 wt% of silicon (Si); 0.1-0.5 wt% of manganese (Mn); 0.1-1.0 wt% of titanium (Ti); and the remaining of iron by weight ratio and having coarse primary particles and eutectic carbides which are not decomposed during dissolution, and cooling of an alloy remained with a tempered martensite group as a primary base.

Description

[0001] The present invention relates to a high wear-resistant cold work tool steels with enhanced impact toughness,

The present invention relates to a cold tool steel, and more particularly to a cold tool steel which can be applied to a mold liner, a shot blast liner, a special mold material and a rolling roll, as well as a steel cutting knife mold such as a hot rolled or cold rolled steel plate, a high strength stainless steel plate, To a high wear-resistant cold tool steel having impact resistance.

In general, knife molds for cutting high-strength scrap metal and shot blast liners are typical materials that are required to have both high hardness, impact resistance (toughness) and abrasion resistance required in harsh environments.

However, the use of a high wear-resistant special tool material in such scrap metal cutting and shot blast liner has a fatal disadvantage that the impact resistance is low despite its excellent hardness and abrasion characteristics, resulting in a significant reduction in service life.

On the other hand, the CPM alloy improved the microstructural homogeneity and the distribution characteristics of the alloy carbide by using the pre-alloyed powders, but it is possible to improve the impact resistance at the high hardness level of 60 HRC or more. However, There were limitations to apply.

On the other hand, SKD-61, which has high heat hardness, excellent heat cracking and abrasion resistance and is mainly used as hot tool tool steel, is required to be used as a cutting tool tool material requiring both impact resistance and abrasion resistance. (54-56 HRC), especially for hardness. SKD-11, which has a hardness level of 60 HRC, has a toughness of less than about 2J (Charpy-V-notch) and can only be used as a small cutting tool material.

In particular, D7, which has a hardness level of 63 HRC, is known as a typical high abrasion-resistant special tool material which can be used under very poor wear / abrasion environment. However, development of an alloy capable of replacing it with a weak impact resistance characteristic is desperately required .

Korean Patent Publication No. 1998-0081249 (November 25, 1998)

Accordingly, it is an object of the present invention to provide a hot-rolled and cold-rolled steel plate, a high-strength steel plate, and a high-strength steel plate, which have remarkably improved abrasion resistance and impact resistance at a hardness level of 63 HRC, Abrasion resistant cold tool steel which has impact resistance so as to be applicable to mold liner, shot blast liner, special mold material and rolling roll as well as knife mold for steel cutting such as stainless steel plate and scrap steel scrap.

In order to achieve the above object, the high wear-resistant cold tool steel according to the technical idea of the present invention comprises 1.8 to 2.4% of carbon (C), 11.0 to 14.0% of chromium (Cr), 0.5 to 2.5% of molybdenum (Mo) , Vanadium (V) in an amount of 2.0 to 6.0%, silicon (Si) in an amount of 0.1 to 0.7%, manganese (Mn) in an amount of 0.1 to 0.5%, titanium in an amount of 0.1 to 1.0% And having coarse primary particles and process carbides remaining as a matrix and not decomposed upon dissolution and cooling of the alloy.

On the other hand, the high wear-resistant cold tool steel according to the present invention comprises 1.8 to 2.4% of carbon (C), 11.5 to 13.5% of chromium (Cr), 0.8 to 1.5% of molybdenum (V) 0.2 to 0.6% of silicon (Si), 0.3 to 0.5% of manganese (Mn), 0.1 to 0.7% of titanium (Ti), and the balance of iron.

The high wear-resistant cold tool steel according to the present invention is characterized by comprising 1.8 to 2.4% of carbon (C), 12.0 to 13.0% of chromium (Cr), 1.0 to 1.4% of molybdenum (Mo), 3.5 to 4.5% 0.3 to 0.5% of silicon (Si), 0.35 to 0.45% of manganese (Mn) of 0.15 to 0.55% of titanium (Ti), and the balance of iron.

Here, the present invention can be characterized in that the austenite grain size is 8 μm or less.

In addition, the high wear-resistant cold tool steel may be characterized by containing Ti and being a substitute for D7 which is a conventional high wear-resistant cold tool steel.

Also, the high wear-resistant cold tool steel may be a substitute for D7, which is a conventional high wear-resistant cold tool steel, by replacing a part of M7C3, which is a rough process carbide, with MC carbide.

The high wear resistance cold tool steel according to the present invention solves the deterioration in impact resistance at a high hardness level, which is a chronic problem of a high-carbon tool steel containing no titanium, by adding titanium, HRC), it can be applied to various products.

The present invention also provides a method for manufacturing a magnetic steel sheet which is capable of effectively reducing the grain size of a vanadium-based alloy and effectively replacing M7C3, which is a coarse process carbide, with MC to increase impact toughness up to 45% A product that can be improved can be obtained.

Furthermore, the present invention is expected to contribute to the overall performance improvement of the domestic tool industry by enabling the extension of the service life of the products required in various tool industries through the above-described effects.

1 is a graph for explaining hardness and impact toughness change of a cold tool steel according to an embodiment of the present invention;
FIG. 2 is a graph for explaining the effect of Ti addition on hardness and wear resistance characteristics in a cold tool steel according to an embodiment of the present invention
3 is a graph for explaining the effect of addition of Ti on impact resistance in cold tool steel according to an embodiment of the present invention
FIG. 4 is an optical microscope photograph showing the austenite grains in a cold tool steel according to an embodiment of the present invention.
5 is an optical microscope photograph and graph for explaining the Ti addition effect on the process carbide and the un-dissolved primary particles in the cold tool steel according to the embodiment of the present invention
6 is a graph for explaining hardness non-impact toughness change in a cold tool steel according to an embodiment of the present invention

A high wear-resistant cold tool steel according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. It is to be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing. In the accompanying drawings, the dimensions of the structures are enlarged to illustrate the present invention, and are actually shown in a smaller scale than the actual dimensions in order to understand the schematic configuration.

Also, the terms first and second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. On the other hand, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

Conventional titanium (Ti) is added in a small amount to a high alloy system for advanced structural materials to effectively control inclusions that degrade the toughness of the alloy. Also, in the case of low alloy tool steels, it is mainly added in order to effectively refine the initial grains during the high temperature austenitizing treatment in the form of fine carbides / carbonitrides.

The titanium addition effect can effectively suppress the growth of crystal grains during the austenitizing treatment of steel by precipitating thermally stable fine particles (Ti-rich carbide / carbo nitride) in the alloy during melting and cooling of the steel. Minimization of the initial austenite grains enables finer martensite packets and blocks, which are the final microstructures after transformation, to contribute to the mechanical properties of steel, particularly toughness.

In addition, in addition to vanadium (V), titanium is an important carbide-forming element for forming secondary particles of MC-type 1, and is an effective element for increasing precipitation amount, thermal stability, nucleation driving force, to be.

In the embodiment of the present invention, the austenitizing temperature for securing the basic alloy hardness is set in a high-wear-resistant cold tool steel which requires not only hardness but also impact resistance, and titanium carbide and un- And maximized the miniaturization of martensite, which is the final base structure. This is a fundamental solution to low toughness at the level of hardness, which is the problem of existing steel. It is the only way to solve the existing steel problem in terms of alloy design without introduction of expensive P / M process. And to provide a high wear resistance cold tool steel.

To this end, the high wear-resistant cold tool steel according to the embodiment of the present invention comprises 1.8 to 2.4% of carbon (C), 11.0 to 14.0% of chromium (Cr), 0.5 to 2.5% of molybdenum (Mo) 0.1 to 0.7% of silicon (Si), 0.1 to 0.5% of manganese (Mn), 0.1 to 1.0% of titanium (Ti), 0.01% or less of phosphorus (P), 0.009% or less of sulfur (S) Contains iron.

More preferably, as the weight ratio, 1.8 to 2.4% of carbon (C), 11.5 to 13.5% of chromium (Cr), 0.8 to 1.5% of molybdenum (Mo), 3.0 to 5.0% of vanadium (V) (P) of not more than 0.01%, sulfur (S) of not more than 0.009%, and the balance of iron, and most preferably, a weight ratio (Si), 0.3 to 0.5% of vanadium (V), 0.3 to 0.5% of vanadium (V), 0.3 to 0.5% of manganese (Mn) 0.15 to 0.55% of 0.35 to 0.45% titanium (Ti), 0.01% or less of phosphorus (P) and 0.009% or less of sulfur (S) as impurities,

The additional element components used in the high wear-resistant cold tool steel according to the embodiment of the present invention will be described in more detail as follows.

Carbon (C)

Carbon is dissolved in the matrix during the high-temperature heat treatment, forming martensite in the cooling process, and some of it is solidified in the matrix to improve hardenability and strength. In addition, most of them combine with the carbide forming elements of Cr, Mo, V and Ti to form process carbides and un-dissolved primary carbides, thereby contributing to improvement of wear resistance of the alloy. However, carbon content is limited to 1.8 ~ 2.4% because it may cause embrittlement of alloys when a large amount of carbon is added.

Chromium (Cr)

Chromium inhibits surface decarburization during reheating and improves hardenability and hinders generation of graphite by employing it in the base. It is also the main element of carbide, which combines with C to form M7C3 and M23C6 carbides, which improves high temperature softening resistance and abrasion resistance. Therefore, chromium was added at 11.0 ~ 14.0% in order to secure basic hardness and wear characteristics. The more suitable chromium content is 11.5 ~ 13.5%. The most suitable chromium content is 12.0 ~ 13.0%.

Molybdenum (Mo)

Molybdenum is an element which improves the incombustibility by employing it in the base and improves the secondary hardenability and the wear resistance by forming carbide such as Mo2C in? In addition, it contributes greatly to improvement of tempering resistance which suppresses decrease in hardness during tempering, and is effective in improving high temperature strength and corrosion resistance. Although molybdenum content is 0.5 ~ 2.5% because it is effective to reduce the resistance to thermal degradation in heat treatment due to occurrence of secondary hardening at lower temperature than chromium and tungsten, but to maximize secondary hardening effect of MC carbide together with vanadium and titanium, Respectively. A more suitable content of molybdenum is 0.8 to 1.5%. The most suitable molybdenum content is 1.0 to 1.4%.

Vanadium (V)

Similar to Ti, vanadium is effective in preventing coarsening of crystal grains and enhances the resistance to tempering of steel when combined with Mo. Especially, the content of vanadium was limited to 2.0 ~ 6.0% in order to precipitate carbide in a proper amount as a main alloy element forming high hardness MC carbide which is strong in affinity with carbon and effective in securing abrasion resistance. The more suitable content of vanadium is 3.0 to 5.0%. The most suitable vanadium content is 3.5 to 4.5%.

Silicon (Si)

Silicon has an effect of increasing the hardness by solid-solidifying the solid solution in the base, enhancing the incombustibility, preventing surface oxidation at high temperature, and promoting the precipitation reaction of carbide, thereby contributing to refinement of carbide. However, when Si is added excessively, the content of silicon is limited to 0.3 to 0.6% because the hot workability is lowered and the toughness after tempering and toughness are lowered. A more suitable silicon content is 0.2 to 0.6%. The most suitable silicon content is 0.3 to 0.5%.

Manganese (Mn)

Manganese is an element that improves hardenability and has the effect of inhibiting the generation of graphite when annealing high carbon steels. It also improves the cleanliness of the steel as a deoxidizing and desulfurizing agent and increases the quenching. In order to obtain such an effect, it is necessary to add 0.1 or more, and when 1.0% or more is added, the residual austenite is stabilized and toughness is lowered, so that the content of manganese is limited to 0.1 to 0.5%. A more suitable content of manganese is 0.3 to 0.5%. The most suitable content of manganese is 0.35 ~ 0.45%.

Titanium (Ti)

Fine grain size and weakness of the ingot are reversed when the quench temperature is high. It is a major alloying element that forms carbides and carbonitrides with strong deoxidation and denitrification agents. It is also included in the MC carbide together with vanadium, thereby greatly increasing the precipitation driving force.

In order to minimize the influence of impurities, the high wear-resistant cold tool steel according to the embodiment of the present invention is made into an ingot by vacuum induction melting (VIM) in the range of 1550 to 1650 ° C. using raw material of 99.9% or more of purity of the alloy element. At this time, the bubble o segregated part is cut and discarded, followed by sizing rolling by 50% or more at 1200 ° C and air cooling after forging. Thereafter, the steel sheet is subjected to austenitizing in a temperature range of 1000 to 1150 ° C, and then subjected to isothermal aging treatment at 150 to 250 ° C or 500 to 550 ° C to maximize abrasion resistance or impact toughness.

Table 1 below shows the composition of a steel ingot obtained by vacuum induction melting using a high purity alloy raw material and its composition ratio.

division C Si Mn Cr Mo V Ti Contrast river
(D7-HiCV) 2.3 0.4 0.4 12.5 1.1 4 Developed River-1
(KD7) 2.31 0.39 0.40 12.48 1.3 4.2 0.23 Developed River-2
(K2D7) 2.29 0.42 0.38 12.48 1.2 4.1 0.47

The steel ingots were heat treated at 1200 ° C for 1 hour and then subjected to sizing rolling at 900-1000 ° C to produce steels. The steel ingots were then subjected to austenitizing and air cooling at 1000 ~ 1150 ° C to evaluate the mechanical properties of the steel. Impact test specimens for isothermal aging heat treatment were taken from the manufactured plate. The hardness was measured after 5 tests from the test specimens obtained by cutting the bottom 10 mm of the wave front after the impact test. The impact toughness was the average of the Charpy impact test values measured three times from the test piece not containing the notch.

1 and 2 show changes in the hardness and impact toughness of the developed steel-1 (KD7) and steel-2 (K2D7) obtained through the austenitizing and heat treatment in comparison with the control steel (D7) .

In the case of the steel-1 (KD7) and steel-2 (K2D7) developed as the test results, it was found that the as-quenched as well as the improved wear characteristics were superior to the control steel in the heat treated condition at 150 and 500 ° C, respectively. In particular, impact toughness shows a significant increase in KD7 with titanium and increased K2D7 with higher titanium content, despite improved hardness and wear resistance (see FIG. 3).

This result is attributable to the fact that the final microstructure of the titanium-containing alloy can be miniaturized. As shown in FIG. 4, it was confirmed that about 70 to 80% of grain grains were refined in the steels developed in comparison with the control steels. It is believed that this is because coagulation and cooling of alloys by deposition of more thermally stable fine titanium carbides and carbonitrides, and effective suppression of austenitic phase growth in addition to the eutectic carbides mentioned below during high temperature reheating.

In general, the coarse grained steel is significantly degraded in impact toughness and hardness and other mechanical properties compared to steels having fine grains. Since the coarse grained steel has relatively low impact resistance, as well as wear resistance, hardness and other mechanical properties compared to steels with fine grains, the reliability of various high wear-resistant cold tool steels such as high- It is impossible to guarantee the safety of life.

On the other hand, titanium addition enables the tempering of eutectic carbides and un-dissolved primary carbides which are distributed in the alloy base in addition to grain refining effect. In general, coarse carbides in high abrasion resistance cold tool steels are the primary nucleation sites of cracks generated during the external impact of alloys, and they are therefore essential for the tempering of these alloys because they are the main determinant of the impact resistance of alloys.

The effect of titanium addition on coarse process carbides and unsolvated primary carbides can be categorized into two as shown in FIG. The first is the relative fractional change of M7C3 and MC carbides that are present in abundance in the developed steel and have a major impact on the mechanical properties of the alloy. In other words, the content of M7C3 carbide decreased from 17.9 → 14.1 → 13.2wt.% As titanium increased from 0 → 0.2 → 0.5wt.%, While MC carbide increased from 2 → 3.8 → 5wt.%. It should be noted that the total content of total carbides does not change as much as 19.9, 17.9, 18.2 wt.% In the control steel, the developed steel-1 and steel-2, respectively, but the relative content of carbide is changed. This is the result of Rietveld analysis of the XRD test results, which is consistent with the image analysis of SEM-BSE on the specimen surface.

Second, the size of the coarse M7C3 carbide is reduced. For carbides below 1 μm, the size of MC carbide increases with the addition of titanium, which is related to the increase in the overall fraction of MC carbide. Especially, the developed steel is considered to be the most vulnerable to crack formation due to external impact, and the size of the coarse process carbide (M7C3) of 1μm or less is reduced.

As a result, it can be confirmed that the titanium addition in the developed steel not only replaces the crude M7C3 content with MC, but also makes it possible to miniaturize it. Therefore, the addition of titanium in the steel which is developed in comparison with the control steel enables the overall microstructural tempering by improving the coarse carbide in addition to the grain refinement effect. As a result, as shown in FIG. 6, It was able to improve dramatically.

As described above, Table 1 (chemical composition), Figs. 1 and 2 (Ti addition effect on hardness and abrasion resistance characteristics), Fig. 3 (Ti addition effect on impact resistance characteristics), Fig. 4 (Initial austenite grains As can be seen from FIG. 5 (Ti addition effect on process carbide and un-dissolved primary particles) and FIG. 6 (hardness non-impact toughness change), about 0.2 to 0.5 wt.% Titanium was added (SKD-11, D2, etc., including SKH-51), exhibiting improved wear resistance and impact resistance at the same or superior hardness level as the steel containing no titanium.

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. It is clear that the present invention can be suitably modified and applied in the same manner. Therefore, the above description does not limit the scope of the present invention, which is defined by the limitations of the following claims.

Claims (6)

(Si), 0.1 to 0.7% of vanadium (V), 0.1 to 0.7% of vanadium (V), 0.1 to 0.7% of molybdenum (Mo) Mn, 0.1 to 0.5% of titanium (Ti) and 0.1 to 1.0% of iron, and the remaining primary iron particles are retained without decomposition upon melting and cooling of the alloy with the tempered martensite structure as a main base, High wear - resistant cold tool steel with carbide. (Si) and 0.2 to 0.6% of vanadium (V), 0.8 to 1.5% of vanadium (V), 0.2 to 0.6% of manganese (Mn) ) 0.3-0.5% titanium (Ti) 0.1-0.7% and the remainder being iron. (Si), 0.3 to 0.5% of vanadium (V), 0.3 to 0.5% of vanadium (V), 0.3 to 0.5% of manganese (Si) Mn) 0.35 to 0.45% titanium (Ti) 0.15 to 0.55% and the balance iron. 4. The method according to any one of claims 1 to 3,
Wherein the austenite grain size is less than or equal to 8 占 퐉. 5. The method of claim 4,
Wherein the high wear-resistant cold tool steel is a substitute for D7, which is a conventional high wear-resistant cold tool steel, containing Ti. The method according to claim 1,
Wherein the high wear-resistant cold tool steel is a substitute for D7, which is a conventional high wear-resistant cold tool steel, by replacing a part of M7C3, which is a coarse process carbide, with MC carbide.

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