KR20220119836A - Nb-CONTAINING HIGH STRENGTH CUTTING KNIFE TOOL STEEL FOR STEEL AND METHOD FOR PRODUCING SAME - Google Patents

Abstract

The present invention relates to high-strength tool steel, and particularly, to niobium (Nb)-containing tool steel for a knife for cutting steel with excellent wear resistance and impact resistance. The tool steel is formed with at least one among 0.25-0.65 wt% of carbon (C), 3.0-8.0 wt% of chromium (Cr), 2.0-4.0 wt% of molybdenum (Mo), 3 wt% or less (excluding 0 wt%) of nickel (Ni), 0.5-3.0 wt% of vanadium (V), 0.2-1.5 wt% of silicon (Si), 0.1-1.0 wt% manganese (Mn), and 1.0 wt% or less (excluding 0 wt%) of Nb, and contains the remaining iron (Fe) and unavoidable impurities. According to the present invention, Nb-containing tool steel for a knife for cutting steel with excellent wear resistance and impact resistance has increased impact toughness by adding Mo and Nb. In addition, coarsening of a crystal grain is suppressed, thereby providing Nb-containing tool steel for a knife for cutting steel with excellent wear resistance and impact resistance.

Description

Nb-containing tool steel for steel cutting knife and manufacturing method thereof

The technical idea of the present invention relates to 5Cr-Mo-V-based high-strength tool steel, which is a high-tensile steel cutting knife material, and a method for manufacturing the same, and more specifically, by adding Mo and Nb to increase impact toughness and suppress grain coarsening. It relates to a tool steel for a knife for cutting steel containing Nb having excellent wear resistance and impact resistance, and a method for manufacturing the same.

In general, tool steel for steel cutting knives is used for cutting high-strength scrap metal, thick plates and cold-rolled plates, and the use environment requires high hardness and impact resistance (toughness) characteristics at the same time. As materials that must be combined, high-strength scrap metal, and materials for knives for cutting thick and cold-rolled plates are representative.

However, as for the material for knives used for cutting such steel cutting products, SKT-4 is mainly used when the working pressure capacity is 800 tons or less, such as scrap cutting and high-strength hot-rolled thick plates, but low toughness in the case of large ones with more than 1000 tons And there is a problem that it cannot be used due to its hardness.

On the other hand, SKD-11 has a very high hardness of 60 HRc, but its impact toughness is less than about 2J (Charpy V-notch), so it can only be used for small knives, and its toughness is insufficient for use with large knives.

On the other hand, SKD-61, which is mainly used as tool steel for hot die due to its high red heat hardness and excellent heat cracking and abrasion resistance, has mechanical properties, In particular, it is known that the hardness is insufficient.

In order to fundamentally solve the above-mentioned problems, a small amount of titanium is added to increase the impact and abrasion resistance at the high hardness level, which is a chronic problem of the existing Cr-Mo-V-based knife steel that does not contain titanium. has been significantly improved. However, recently, in accordance with industrial needs for improvement of life and stability of steel products, high strength is rapidly progressing. development is required.

Therefore, the present invention is to provide a tool steel for steel cutting knife with an upgraded product lifespan based on impact resistance characteristics of 10J or more even at high hardness while improving the above problems.

1. Japanese Patent Laid-Open No. 62-1648535 2. Korean Patent Publication No. 10-2016-0010930

The technical problem to be achieved by the technical idea of the present invention is to provide a tool steel for steel cutting knife containing Nb having excellent wear resistance and impact resistance by adding Mo and Nb to increase impact toughness and suppress grain coarsening.

The technical problem to be achieved by the technical idea of the present invention is to increase the impact toughness by adding Mo and Nb and suppress the coarsening of grains to produce a Nb-containing tool steel for steel cutting with excellent abrasion resistance and impact resistance. is to provide

However, these tasks are exemplary, and the technical spirit of the present invention is not limited thereto.

Tool steel for steel cutting knife containing Nb having excellent wear resistance and impact resistance according to the technical idea of the present invention for achieving the above technical problem is, as a weight%, C: 0.25 to 0.65%, Cr: 3.0 to 8.0%, Mo: 2.0 ~4.0%, Ni: 3% or less (excluding 0%), V: 0.5 to 3.0%, Si: 0.2 to 1.5%, Mn: 0.1 to 1.0%, and Nb: 1.0% or less (excluding 0%) and may include the remaining Fe and unavoidable impurities.

In some embodiments of the present invention, the tool steel may include carbide particles in a tempered martensitic matrix.

In some embodiments of the present invention, in the tool steel, 0.5 to 2.5% of fine MC [M=V, Mo] type carbide having an area fraction of 100 to 200 nm may be formed.

In some embodiments of the present invention, the tool steel may have a hardness of 58 to 62 HRc and an impact toughness of 10 to 12J.

In some embodiments of the present invention, the change in impact toughness with respect to the change in hardness of the tool steel may be 0.1 to 0.2 J/HRc.

In some embodiments of the present invention, the tool steel may have an initial austenite grain size of 17 μm or less.

According to the technical idea of the present invention for achieving the above technical problem, a method for manufacturing a tool steel for steel cutting knife containing Nb having excellent wear resistance and impact resistance is as a weight%, C: 0.25 to 0.65%, Cr: 3.0 to 8.0%, Mo: 2.0 to 4.0%, Ni: 3% or less (excluding 0%), V: 0.5 to 3.0%, Si: 0.2 to 1.5%, Mn: 0.1 to 1.0%, and Nb: 1.0% or less (excluding 0%) Containing one or more, casting an ingot consisting of the remaining Fe and unavoidable impurities, homogenizing the ingot at 1150 ° C. to 1250 ° C. After performing a hot rolling (Rolling) step, 1000 to It may include an austenitizing step of maintaining at 1150° C. and then air cooling to room temperature, and a tempering step of air cooling to room temperature after maintaining at 500 to 580° C.

In some embodiments of the present invention, the rolling (Rolling) step may be more than 1000 sizing and rolling at less than 1100 ℃ 50%.

In some embodiments of the present invention, the tempering step may be repeated two or more times.

The tool steel for steel cutting knife containing Nb having excellent wear resistance and impact resistance according to the technical idea of the present invention increases impact toughness by adding Mo and Nb and suppresses coarsening of grains to cut Nb containing steel having excellent wear resistance and impact resistance We can provide tool steel for knives.

In addition, the method for manufacturing a tool steel for a knife for steel cutting containing Nb having excellent wear resistance and impact resistance according to the present invention increases impact toughness by adding Mo and Nb and suppresses coarsening of grains by adding Nb containing steel having excellent wear resistance and impact resistance Tool steel for cutting knives can be manufactured.

The above-described effects of the present invention have been described by way of example, and the scope of the present invention is not limited by these effects.

1 is a schematic diagram showing a rolling and heat treatment process of a tool steel (2.5Mo-Nb) for steel cutting knife containing Nb having excellent wear resistance and impact resistance according to an embodiment of the present invention.
2 is a graph of hardness change according to tempering time of tool steel (2.5Mo-Nb) and comparative steel for steel cutting knives containing Nb having excellent wear resistance and impact resistance according to an embodiment of the present invention.
3 is a graph showing the impact toughness according to the hardness (Hardness) of the tool steel (2.5Mo-Nb) for steel cutting knife containing Nb excellent in abrasion resistance and impact resistance manufactured according to an embodiment of the present invention and comparative steel. .
4 is a microstructure photograph of comparative steel according to the Mo content.
5 is a result of analyzing the primary carbide chemical composition of the comparative steel according to the Mo content.
6 is a photograph showing grains and average grain sizes of tool steel (2.5Mo-Nb) and comparative steel for steel cutting knives containing Nb having excellent wear resistance and impact resistance manufactured according to an embodiment of the present invention.
7 is a graph showing the results of a wear resistance test of a tool steel (2.5Mo-Nb) for steel cutting knife containing Nb having excellent wear resistance and impact resistance manufactured according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided to more completely explain the technical idea of the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, The scope of the technical idea is not limited to the following examples. Rather, these embodiments are provided so as to more fully and complete the present disclosure, and to fully convey the technical spirit of the present invention to those skilled in the art. As used herein, the term “and/or” includes any one and any combination of one or more of those listed items. The same symbols refer to the same elements from time to time. Furthermore, various elements and regions in the drawings are schematically drawn. Therefore, the technical spirit of the present invention is not limited by the relative size or spacing drawn in the accompanying drawings.

Nb-containing tool steel for steel cutting knives with excellent wear resistance and impact resistance according to the present invention as a weight%, C: 0.25 to 0.65%, Cr: 3.0 to 8.0%, Mo: 2.0 to 4.0%, Ni: 3% or less ( Excluding 0%), V: 0.5 to 3.0%, Si: 0.2 to 1.5%, Mn: 0.1 to 1.0%, and Nb: 1.0% or less (excluding 0%). may include

C is added 0.25 to 0.65 wt%, is dissolved in the matrix during high-temperature heat treatment to form martensite in the subsequent cooling process, and some is dissolved in the matrix to improve hardenability and strength. In addition, most of them combine with carbide forming elements of Cr, Mo, and V to form primary eutectic carbides and secondary precipitation carbides to improve wear resistance.

Preferably C may include 0.35 to 0.60 wt%. If it is less than 0.35 wt%, hardness and strength are low after austenitizing and tempering, and if it exceeds 0.60 wt%, embrittlement may occur. More preferably 0.40 to 0.60 wt% may be included.

Cr is added at 3.0 to 8.0 wt%, suppresses surface decarburization during reheating, and is dissolved in a matrix to improve hardenability and inhibit graphitization. In addition, as the main forming element of carbide, it combines with C to form M ₇ C ₃ and M ₂₃ C ₆ carbide, improving resistance to high temperature softening and abrasion resistance.

Preferably Cr contains 3.5 to 7.0 wt%, so that a large amount of M ₇ C ₃ carbides can be formed. When it exceeds 7.0 wt%, it causes coarsening of the carbide, thereby lowering the impact toughness. More preferably 4.0 to 6.5 wt% may be included.

Mo is added in 2.0 to 4.0wt%, it is dissolved in the matrix to improve hardenability, and during quenching, carbides such as Mo ₂ C are formed to improve secondary hardening ability and wear resistance. In addition, it contributes the most to the improvement of temper resistance, which suppresses the decrease in hardness during tempering heat treatment, and is effective in improving high-temperature strength and corrosion resistance.

Preferably, Mo includes 2.0 to 3.5 wt%, and together with V, it is possible to maximize the effect of secondary curing by MC carbide. When it exceeds 3.5 wt%, toughness and workability are reduced. More preferably, it may contain 2.0 to 3.0 wt%.

Ni is added at 4 wt% or less (excluding 0%), and in addition to the solid solution strengthening effect, the essential matrix toughness of tempered martensitic steel is secured. Preferably, Ni contains 3 wt% or less (excluding 0%), and when it exceeds 3 wt%, it is difficult to secure high strength and high hardness due to an increase in retained austenite and an increase in the degree of thermal degradation. More preferably 0.5 to 3.0 wt% may be included.

V is added at 0.5 to 3.0 wt%, and has the strongest affinity with C and forms VC carbide with high hardness to increase wear resistance and is effective in preventing coarsening of crystal grains. In addition, when combined with Mo, it serves to improve the tempering resistance of steel.

Preferably, V is added in an amount of 0.5 to 2.0 wt%, and in order to maximize the precipitation of the V-containing secondary hardening alloy carbide, it is added in consideration of the consumption of V to the primary particles remaining in the matrix without being decomposed during austenitization. If it exceeds 2.0 wt%, workability is reduced. More preferably 0.5 to 1.5 wt% may be included.

Si is added by 0.2 to 1.5 wt%, and has the effect of improving castability, increasing hardness by solid solution strengthening, preventing surface oxidation at high temperatures and promoting the precipitation reaction of alloy carbides. If it exceeds 1.5wt%, the hot workability is lowered due to graphitization, etc., and the toughness after quenching and tempering is lowered.

Mn is added 0.1~1.0wt%, improves hardenability, and inhibits graphitization during annealing of high carbon steel. In addition, as a deoxidizing and desulfurizing agent, it improves the cleanliness of steel and increases hardenability. To obtain this effect, 0.1 wt% or more is required, and when 1.0 wt% or more is added, the retained austenite is stabilized to reduce toughness.

Nb is added at 1.0 wt% or less (excluding 0%), and Nb forms carbonitrides and carbides at high temperatures, thereby inhibiting recrystallization and grain growth, as well as expanding non-recrystallized regions during hot rolling to refine final grains. It works. Since Nb has a lower carbonitride solubility than Ti, it can form a stable precipitate at a high temperature, thereby exhibiting a stronger grain refinement effect.

Preferably, Nb may include 0.005 to 0.09 wt%, and when it is excessively added in excess of 0.09 wt%, the amount and size of carbides are rather increased to reduce impact toughness. More preferably, it may contain 0.005 to 0.06w%.

As described above, the Nb-containing tool steel for steel cutting knives having excellent wear resistance and impact resistance can increase impact toughness and suppress grain coarsening by adding Mo and Nb. The tool steel contains carbide particles in a tempered martensite matrix, and fine MC [M=V, Mo]-type carbides of 100 to 200 nm are formed in an area fraction of 0.5 to 2.5%. Preferably 1.0 to 2.5% may be formed. In addition, the tool steel may have a hardness of 58 to 62 HRc and an impact toughness of 10 to 12J, a change in impact toughness with respect to a change in hardness is 0.1 to 0.2 J/HRc, and an initial austenite grain size is 17 μm or less. .

By increasing the Mo content added to the existing 5Cr-Mo-V-based knife steel with micro addition of Ti, it is possible to increase the knife performance when cutting high-strength steel materials by dramatically improving the hardness and wear resistance while maintaining the impact resistance properties of the steel. make it possible In addition, by adding Nb to solve the grain coarsening phenomenon of steel, it is possible to obtain a product with a long life even under severe conditions by improving the hardness ratio and toughness.

1 is a schematic view showing a rolling and heat treatment process of a tool steel (2.5Mo-Nb) for steel cutting knife containing excellent wear resistance and impact resistance according to an embodiment of the present invention. The method for manufacturing a tool steel for a knife for steel cutting containing Nb according to the present invention includes a casting step, a hot rolling step after homogenization, austenitizing step, and a tempering step do.

The casting step is as a weight %, C: 0.25 to 0.65%, Cr: 3.0 to 8.0%, Mo: 2.0 to 4.0%, Ni: 3% or less (excluding 0%), V: 0.5 to 3.0%, Si: 0.2 to 1.5%, Mn: 0.1 to 1.0% and Nb: including at least one of 1.0% or less (excluding 0%), and casting the remaining Fe and unavoidable impurities consisting of an ingot. The alloy element having a purity of 99.9% or more was subjected to vacuum induction melting (VIM) in the range of 1550 to 1650° C.

The homogenization step is a step of homogenizing the ingot at 1150 to 1250° C. The distribution of carbides can be improved by controlling the homogenization temperature to 1150 to 1250 °C.

The hot rolling (Rolling) step is a step of performing hot rolling (Rolling), the bubbles and segregated parts are cut and discarded, sizing rolling and forging more than 50% at more than 1000 and 1100 ° C. or less, and then air cooling to room temperature.

The austenitizing step is carried out in a temperature range of 1000 to 1150 °C. This is a process of heating the steel to a temperature of Ac3 or higher, which is the temperature at which it becomes austenitized, and then air-cooling it to room temperature.

If the alloy is tempered before being air cooled to room temperature, it will be in a hot tempered state, with a significant amount of retained austenite. Residual austenite causes dimensional change due to phase transformation during product use, so it is desirable to avoid it.

In the tempering step, it is carried out at 500 to 580° C. to maximize hardness and impact toughness. In order to reduce the amount of retained austenite, the tempering step may be repeated two or more times. After maintaining for 15 minutes to 2 hours, a tempering treatment of air cooling to room temperature was repeated twice.

The alloy structure may produce a tool steel for steel cutting knife including carbide particles on a tempered martensite matrix. Carbide particles include coarse primary particles (undissolved carbides) that remain without decomposition during melting and cooling of the alloy and fine secondary particles (secondary hardening alloy carbides) that are precipitated during heat treatment of the alloy.

Hereinafter, details of the process of the present invention will be described through Examples and Experimental Examples.

Table 1 is a table showing the composition of the tool steel (2.5Mo-Nb) and comparative steel for a knife for steel cutting containing Nb having excellent wear resistance and impact resistance according to an embodiment of the present invention.

division C Mo Cr Ni V Si Mn Ti Nb invention 2.5Mo-Nb 0.55 2.5 5.0 2.0 1.0 1.0 0.3 - 0.04 Comparative lecture 1 1.5Mo 0.55 1.5 5.0 2.0 1.0 1.0 0.3 0.02 - Comparative lecture 2 2.5Mo 0.55 2.5 5.0 2.0 1.0 1.0 0.3 0.02 -

For the comparative steel, two alloys were prepared in order to confirm the difference in mechanical properties according to the increase in the Mo content. At this time, in order to clearly clarify the Nb effect of the invention steel, Nb in the same atomic ratio as Ti was added to prepare a total of three alloys.

An ingot having a weight of about 30 kg was prepared after vacuum induction melting (VIM) in the range of 1550 to 1650° C. by basis weight of an alloy element having a purity of 99.9% or more as shown in Table 1 as a target composition.

As shown in the rolling and heat treatment process schematic diagram of Figure 1, the ingot was subjected to homogenization at 1200 ° C for 1 hour and then at 1050 ° C. The rolled steel was maintained at 1050° C. to austenitize, and then air-cooled to prepare a plate, and an impact test piece for tempering was collected from the manufactured plate. Tempering was performed in multiple steps (560° C.—Water cooling—560° C.—Water cooling) to reduce the residual austenite content.

Table 2 is a table showing measured values of hardness (HRc) and impact toughness (J) according to the composition of the tool steel according to an embodiment of the present invention.

tempering time
(min) invention Comparative lecture 1 Comparative lecture 2 2.5Mo-Nb 1.5Mo 2.5Mo Hardness (HRc) Impact toughness (J) Hardness (HRc) Impact toughness (J) Hardness (HRc) Impact toughness (J) 4(2+2) 58.6 10.78 59.2 7.84 58.9 8.75 30 (15+15) 60.9 10.29 58.5 - 61.9 8.25 90 (45+45) 59.4 - 57.4 7.84 59.85 8.75 240 (120+120) 57.6 10.78 56 9.8 57.1 10.78

The average of the values measured three times from the V-notch impact test piece was used for impact toughness, and the average of the hardness values measured five times was used after cutting the lower 10 mm of the shock wave front to obtain a hardness test piece. However, when the tempering time was 90 minutes, the impact toughness result value of the invention steel and the impact toughness result value of the comparative steel 1 when the tempering time was 30 minutes were written as "-" because the experimental results were not measured. It can be seen that the tool steel according to the present invention has a hardness of 58 to 62 HRc and an impact toughness of 10 to 12J.

2 is a graph of hardness change according to tempering time of tool steel (2.5Mo-Nb) and comparative steel for steel cutting knives containing Nb having excellent wear resistance and impact resistance according to an embodiment of the present invention. In addition, Figure 3 is a graph of the impact toughness (Toughness) according to the hardness (Hardness) of the tool steel (2.5Mo-Nb) for steel cutting knife containing Nb excellent in abrasion resistance and impact resistance manufactured according to an embodiment of the present invention and comparative steel to be.

As shown in FIG. 2, as the Mo content increases in Comparative Steels 1 and 2 and Inventive Steel (1.5wt.% → 2.5wt.%), it can be seen that the hardness value is high in the overall tempering condition. In addition, as shown in FIG. 3 , when the Mo content is increased, the hardness ratio toughness is improved, and the invention steel containing Nb exhibits the best hardness ratio toughness. From the results of the hardness ratio impact toughness, it can be confirmed that the impact toughness of the invention steel increases by about 12.9 to 22.5% at the same hardness level in the high range of 58 to 61 HRc.

Inventive steel has an impact toughness of 10J or more at a hardness of 61 HRc. Inventive steel has a small change in impact toughness with a change in hardness, with a change in impact toughness of 0.1 to 0.2 J/HRc with respect to a change in hardness. On the other hand, in Comparative Steels 1 and 2, the change in impact toughness with respect to the change in hardness is 0.5 to 0.6 J/HRc, and the change in impact toughness according to the change in hardness is large.

By increasing the Mo content added to the existing 5Cr-Mo-V knife steel with micro-addition of Ti, it can improve the hardness and wear resistance while maintaining the impact resistance characteristics, thereby increasing the knife performance when cutting high tensile steel. let there be In addition, by adding Nb to solve the grain coarsening phenomenon of steel, it is possible to obtain a product with a long life even under severe conditions by improving the hardness ratio and toughness.

Therefore, the addition of Nb can significantly improve the life of the knife, and it can be used for cutting-edge high-strength steels where the use of knives with a hardness of 61 HRc or higher is essential.

Table 3 is a table showing the phase fraction (%) of carbides and the average size (nm) of carbides according to the tool steel composition according to an embodiment of the present invention. In addition, Figure 4 is a microstructure photograph of the comparative steel according to the Mo content. The carbide phase fraction (%) was expressed in % by measuring the area of the carbide deposited on the entire matrix.

Phase fraction of carbide (%) Average size of carbides (nm) 100 ~ 200nm 200nm or more all 100 ~ 200nm 200nm or more Invention steel (2.5Mo-Nb) 2.080 0.832 2.712 130.1 331.2 Comparative steel 1 (1.5Mo) 0.146 1.452 1.598 151.8 344.5 Non-Steel 2 (2.5Mo) 0.777 1.562 2.339 126.5 326.8

In general, the hardness and impact toughness of tool steel are affected by the microstructure including precipitates (undissolved carbides). Prior to comparing the microstructures of the invention steel and the comparative steel, the phase fraction (%) of carbides and the average size (nm) of carbides according to the Mo content of the comparative steel were confirmed.

The carbide is a primary carbide, and the area fraction of the carbide means the carbide area fraction in the tempered martensite matrix.

The analysis of the phase fraction (%) of carbide of comparative steel according to Mo content was carried out by dividing the type of primary carbide into two categories (100-200 nm, more than 200 nm), and the results are as follows.

First, it was found that the amount of relatively small carbides with a size of 100 to 200 nm in Comparative Steel 2, having a high Mo content of 2.5% Mo, was approximately 5 times greater than Comparative Steel 1 having 1.5% Mo. In addition, as a result of measuring the average size of carbides in the range of 100 to 200 nm, Comparative Steel 1 containing 1.5% Mo was 151.8 nm, and Comparative Steel 2 containing 2.5% Mo was 126.5 nm. observed that

Next, as a result of comparing the relatively large amount of carbide over 200 nm, Comparative Steel 1 containing 1.5% Mo was about 1.452%, and Comparative Steel 2 containing 2.5% Mo was analyzed at a similar level as 1.562%. However, as a result of measuring the average size of carbides, Comparative Steel 1 with 1.5% Mo was 344.5 nm and Comparative Steel 2 with 2.5% Mo was 326.8 nm. did.

That is, when the Mo content of the comparative steel is increased, the fraction of carbides is relatively increased, and these carbides are uniformly dispersed in a fine form, so it is judged that it is possible to increase the hardness and improve the hardness ratio and impact toughness.

In the case of the invention steel to which Nb was added along with the increase in the Mo content, it can be seen that the phase fraction (%) of carbides was relatively increased compared to Comparative Steel 2. An increase of more than 2 times was observed (0.777%→2.080%). In addition, it was confirmed that the invention steel had an average carbide size of 130.1 nm in the range of 100 to 200 nm, and the average size of a relatively large carbide of 200 nm or more was 331.2 nm, which was larger than Comparative Steel 2. It is considered that the solubility products in the austenite matrix decreased during hot rolling or cooling due to the addition of Nb, a microalloy element, and the fraction of carbides and the average size of carbides were further increased.

Although the average size of carbides is increased compared to Comparative Steel 2, which is 2.5% Mo, the invention steel is made of fine grains (20.7 μm → 16.2 μm) by adding Nb with a quantitative increase of fine carbides in the range of 100 to 200 nm. organizational characteristics. These microstructural characteristics show that the hardness ratio impact toughness can be remarkably improved than those of Comparative Steels 1 and 2.

5 is a result of analyzing the primary carbide chemical composition of the comparative steel according to the Mo content. The composition of carbides contained in Comparative Steel 1 containing 1.5% Mo and Comparative Steel 2 containing 2.5% Mo was analyzed. Overall, the carbide is formed of MC (M=V, Mo rich) carbide having a high V or Mo content specific gravity. In addition, it can be seen that the content (wt%, atomic%) of Mo in Comparative Steel 2 containing 2.5% Mo of all carbides of 100 nm and 200 nm size is about twice or more higher. This is judged to delay the diffusion related to the growth of the carbide by increasing the weight ratio of Mo in the primary carbide when the Mo content is increased, and is predicted to form a microstructure in which the final fine carbide is distributed.

That is, it can be said that the improvement of the hardness ratio toughness according to the increase of the Mo content is due to the increase in the quantity of carbides, in particular, the increase in fine carbides of 100-200 nm (0.146→0.777%). And it is judged that this refinement is because the coarsening of the carbide is delayed according to the increase of Mo in the carbide (13→29 wt%).

Therefore, it can be said that it is essential to increase the Mo content in order to secure the excellent mechanical properties of the existing 5Cr-Mo-V(Ti)-based tool steel. However, when the Mo content is increased, the precipitation of TiC is reduced due to the increase of the primary carbide fraction, and thus the effect of refining the grains may be reduced, and the related microstructure can be confirmed through FIG. 6 .

6 is a photograph showing grains and average grain sizes of tool steel (2.5Mo-Nb) and comparative steel for steel cutting knives containing Nb having excellent wear resistance and impact resistance manufactured according to an embodiment of the present invention.

The grain size refers to the initial austenite grain size in the tempered martensite matrix structure. The average grain size evaluated by the linear intersection method was 16.2 μm, 13.2 μm, and 20.7 μm for the Inventive Steel (2.5Mo-Nb), Comparative Steel 1 (1.5Mo), and Comparative Steel 2 (2.5Mo), respectively. When the content was increased, crystal grains grew (13.2 μm → 20.7 μm), and it can be seen that the grains can be further refined (20.7 μm → 16.2 μm) in the invention steel containing Nb. When the Mo content increases, the grain size increases, but it was confirmed that the grains became finer when Nb was added except for Ti.

7 is a graph showing the results of a wear resistance test of a tool steel (2.5Mo-Nb) for steel cutting knife containing Nb having excellent wear resistance and impact resistance manufactured according to an embodiment of the present invention.

In the abrasion resistance test, the abrasion resistance of the steel was evaluated by measuring the weight before and after the wear test, that is, the amount of wear, after processing the Inventive Steel and Comparative Steel 1 according to the specimen specifications (18 × 18 mm, 25 mm or more in thickness).

First, a pin fixed at a distance of 9 mm from the center of the test piece was placed and a load was applied vertically, and then the test piece was rotated to measure the amount of wear versus the sliding distance of the test piece. At this time, a spherical alumina (Al ₂ O ₃ ) material was used for the fixing pin, and the wear resistance test was conducted under the conditions of humidity 40±10% at room temperature, load 150N, abrasion distance 600m, and speed 0.2m/s. did.

As a result of the abrasion resistance test, as shown in FIG. 7 , it was observed that the wear amount was 3.70 mg in Comparative Steel 1 with 1.5% Mo and 2.83 mg in the Invented Steel with 2.5% Mo of 2.5%-Nb. that can be checked

As described above, the tool steel for steel cutting knife containing Nb having excellent wear resistance and impact resistance according to the present invention can increase impact toughness and suppress grain coarsening by adding Mo and Nb. The tool steel contains carbide particles in a tempered martensite matrix, and fine MC [M=V, Mo]-type carbides of 100 to 200 nm are formed in an area fraction of 0.5 to 2.5%. Preferably 1 to 2.5% may be formed. In addition, the tool steel may have a hardness of 58 to 62 HRc and an impact toughness of 10 to 12J, a change in impact toughness with respect to a change in hardness is 0.1 to 0.2 J/HRc, and an initial austenite grain size is 17 μm or less. .

By increasing the Mo content added to the existing 5Cr-Mo-V knife steel with micro-addition of Ti, it can improve the hardness and wear resistance while maintaining the impact resistance characteristics, thereby increasing the knife performance when cutting high tensile steel. let there be In addition, by adding Nb to solve the grain coarsening phenomenon of steel, it is possible to obtain a product with a long life even under severe conditions by improving the hardness ratio and toughness.

Therefore, even at high hardness, the product service life is extended based on the impact resistance of more than 10J, which reduces the production cost required for the steel industry and contributes to high tensile strength of tool steel for knives, cutting 120~150kgf/mm class ² high-strength steel products. You can get knife steel that you can do.

The technical spirit of the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is the technical spirit of the present invention that various substitutions, modifications and changes are possible within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in the art to which this belongs.

Claims (9)

As weight%, C: 0.25 to 0.65%, Cr: 3.0 to 8.0%, Mo: 2.0 to 4.0%, Ni: 3% or less (excluding 0%), V: 0.5 to 3.0%, Si: 0.2 to 1.5%, Mn: 0.1 to 1.0% and Nb: 1.0% or less (excluding 0%), containing at least one of the remaining Fe and unavoidable impurities, Nb-containing steel cutting knife with excellent abrasion resistance and impact resistance, characterized in that it contains tool steel.
According to claim 1,
The tool steel is Nb-containing tool steel for steel cutting knife with excellent wear resistance and impact resistance, characterized in that it contains carbide particles in a tempered martensite matrix.
According to claim 1,
The tool steel is a tool steel for a knife for cutting steel containing Nb having excellent wear resistance and impact resistance, characterized in that 0.5 to 2.5% of fine MC [M = V, Mo] type carbides of 100 to 200 nm are formed by area fraction.
According to claim 1,
The tool steel has a hardness of 58 to 62 HRc and an impact toughness of 10 to 12J.
5. The method of claim 4,
The tool steel is Nb-containing tool steel for steel cutting knives with excellent wear resistance and impact resistance, characterized in that the change in impact toughness with respect to the change in hardness is 0.1 to 0.2 J/HRc.
According to claim 1,
The tool steel is Nb-containing tool steel for steel cutting knives with excellent wear resistance and impact resistance, characterized in that the initial austenite grain size is 17 μm or less.
As weight%, C: 0.25 to 0.65%, Cr: 3.0 to 8.0%, Mo: 2.0 to 4.0%, Ni: 3% or less (excluding 0%), V: 0.5 to 3.0%, Si: 0.2 to 1.5%, Mn: 0.1 to 1.0% and Nb: including at least one of 1.0% or less (excluding 0%), and casting an ingot consisting of the remaining Fe and unavoidable impurities;
Performing a hot rolling (Rolling) after the homogenization treatment (Homogenization) of the ingot at 1150 ℃ to 1250 ℃:
Austenitizing (Austenitizing) step of air cooling to room temperature after maintaining at 1000 to 1150 ℃; and
A method for manufacturing a tool steel for steel cutting knife containing Nb having excellent abrasion resistance and impact resistance, characterized in that it comprises the step of tempering, which is maintained at 500 to 580° C. and then air-cooled to room temperature.
8. The method of claim 7,
The rolling (Rolling) step is a method of manufacturing a tool steel for a knife for cutting steel containing Nb having excellent abrasion resistance and impact resistance, characterized in that 50% or more sizing rolling is performed at a temperature greater than 1000 and 1100° C. or less.
8. The method of claim 7,
The method for manufacturing a tool steel for a knife for steel cutting containing Nb having excellent wear resistance and impact resistance, characterized in that the tempering step is repeated two or more times.

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