KR20020001933A - A low alloyed high speed tool steel for hot and warm working having good toughness and high strength and manufacture method thereof - Google Patents

Abstract

PURPOSE: A high speed tool steel having high toughness and strength and abrasion resistance and superior high temperature characteristics and a method for manufacturing the same are provided in which superior life cycle of dies is guaranteed as a die material for plastic working and a high life cycle is secured as dies for a metallic or nonmetallic cutting knife in hot, warm and cold working so as to reduce cost of manufacture. CONSTITUTION: The low alloyed high speed tool steel for hot and warm work comprises 0.40 to 0.55 wt.% of C; 1.0 wt.% or less of Si; 0.1 to 1.0 wt.% of Mn; 0.1 to 0.5 wt.% of Ni; 2.8 to 4.8 wt.% of Cr; 1.0 to 3.0 wt.% of Mo; 0.1 to 2.0 wt.% of W (where W+1/2Mo=0.6 to 3.5 wt.%); 0.5 to 2.0 wt.% of V; 0.01 to 0.5 wt.% of Nb (where there are one or more types of V and Nb, and Nb+1/2V=0.26 to 1.5 wt.% when there are two types of V and Nb); 0.1 to 1.5 wt.% of Co; 0.01 wt.% or less of Al; 0.002 to 0.05 wt.% of N; 0.008 wt.% or less of S; 30 ppm or less of O; 0.001 to 0.25 wt.% of one or more elements of REM(rare earth metals) selected from the group consisting of Ce, La, Nd, Y and Fe, wherein REM%/S%=2 to 90, £REM%|£S%|=3x10¬-5 to 100x 10¬-5; and a balance of Fe and a small amount of impurities which can be contained during steelmaking in an electric furnace. The method for manufacturing low alloyed high speed tool steel comprises the steps of manufacturing molten steel comprising the above constituents; solidifying the molten steel in the temperature range of 1500±100 deg.C; hot working the solidified material in the temperature range of 1100±150 deg.C; spheroidizing annealing the hot worked material in the temperature range of 850±60 deg.C; and performing one or more times of quenching in the temperature range of 1000 to 1180 deg.C and tempering in the temperature range of 80 to 700 deg.C in a quenching and tempering furnace.

Description

A low alloyed high speed tool steel for hot and warm working having good toughness and high strength and manufacture method

TECHNICAL FIELD The present invention relates to a hot / warm combined low-alloy high-speed coated steel having excellent toughness and strength, and a method for manufacturing the same.

The present invention is a production of various industrial parts (forging, extrusion, pressing, cutting, casting, etc.) produced by the hot working process of more than 1100 ℃ and the hot working process of 600 ℃ to 900 ℃ range or cold processing process that requires high toughness, in particular In the mold steel used for manufacturing automotive parts, it has outstanding physical or mechanical properties compared to general-purpose tool steel (or improved tool steel) and high-speed coated oral materials used for each plastic processing process (hot, warm, cold). The present invention relates to a low alloy high-speed coated oral steel having a high toughness, high strength, high wear resistance and excellent high temperature properties, which is ensured a long life of the mold.

At present, in the manufacture of industrial parts and automotive parts consisting of hot, warm and cold plastic working processes, and combinations thereof, processing technology is becoming increasingly harsh due to high speed, automation, and shortening. As a result, thermal load, stress load and high surface pressure and friction action on the mold are increased, which leads to shortening of the mold life, leading to lower workability of the consumer and increase in manufacturing cost. Therefore, the consumer demands a higher performance mold material in terms of international competitiveness and work efficiency.

In Korea and abroad, STC1 (~ 7), STD61 (62), STD11 (12), SKH51 (55,59), etc. are representative steel grades or their modified steels are widely used for cold and warm processing die materials. STD61 (62) and their modified steels are mainly used as processing mold materials, but the customer's satisfaction with mold life is very low.

Conventionally, in the cold working process, STC1 (-7), which is a low-cost carbon steel, STD11 (12), which is a cold alloy steel, and SKH51 (55,59), which is an expensive high-alloy high-speed steel, have been used. However, due to the characteristics of the material, high hardness (HRC58 or more) and large (10 μm or more) primary process carbides are abundant and wear-resistant due to agglomeration, but lack of toughness in processing processes requiring high toughness (impact toughness of 3.0 kgfm / cm2 or less) The mold is damaged or broken prematurely, and the STD61 (62) and its improved steel are not severe in toughness, but due to the low hardness (below HRC48), the mold is prematurely worn and the workability is frequently replaced. The burden on manufacturing cost due to the rise of mold production cost was a big problem.

In addition, STD61 (62) and its improved steel were mainly used for the warm working process. However, there was a problem of frequent mold replacement due to early hardness, early softening, rapid thermal fatigue crack generation and progression of the mold due to the combination of low hardness below HRC48 and high temperature characteristics below expectations and high strength of the workpiece. Has already filed a patent application (10-1999-0013858) for a method for producing a high toughness, high strength low alloy high speed coated oral for use in a warm processing process in the range of 600 ° C to 900 ° C.

In addition, STD61 (62) and its improved steel were mainly used in the conventional hot working process, and in particular, expensive stellite and super heat resistant alloys were used in the process where extreme wear resistance was a problem at high temperatures. However, STD61 (62) and its modified steels are extremely low in consumer demand due to high temperature characteristics and low hardness, and Stellite and super heat-resistant alloys are expensive and costly to consumers. there was.

The present invention steel and its manufacturing method have been devised to solve the problems of the existing mold materials for each process, the present invention is the early wear and the lack of high temperature characteristics, the early wear in the warm that is a problem of the existing mold steel In order to solve premature failure due to lack of toughness, lack of high temperature characteristics and lack of toughness in cold, as a new alloy design and manufacturing process design, the matrix is Mo-W-based high-speed coating oral, and after hardness hardening (Quenching / Tempering) It has high abrasion resistance due to the high hardness of HRC58 and it overcomes the deterioration of toughness by enabling fine and uniform production of primary process carbides (MC, M ₂ C) by appropriate control of additive elements and developed manufacturing method. At the same time, it has better impact toughness than the existing STD61, and especially gold due to its excellent high temperature properties (strength, toughness, softening resistance and thermal fatigue crack resistance). The long life of the painter, characterized made.

According to the present invention, the hardness after temper heat treatment through new alloy design and manufacturing process design to satisfy the opposite characteristics of toughness and strength (hardness) at the same time in the mold material for hot, warm and cold plastic processing and to secure excellent high temperature characteristics In HRC56 ~ 58, impact toughness of 40kgfm / cm2 (non-notch), bending strength of 500kgf / mm2 and above, tensile strength of 250kgf / mm2 and above are ensured, especially high temperature softening resistance and high temperature fatigue fatigue cracking are double compared to STD61 (62). ~ 5 times.

In order to satisfy these characteristics, the present invention first designs a new alloy by appropriate titration of the appropriate C content and the main additive elements such as Si, Mn, Cr, Mo, V, W, Co, and Nb, and the selection of the appropriate content for each component. The base is composed of Mo-W-based low alloy high-speed coating oral component, and it is given high abrasion resistance by high hardness (HRC58 or more) after temper heat treatment, high tensile strength and bending strength by high strength, and proper control of alloying elements. High toughness is given by controlling MC, M ₂ C primary process carbide generation, which is inevitably determined during solidification of high-speed coating oral system, and excellent high temperature characteristics are also provided by appropriate content of additive elements effective for high temperature characteristics such as W and Co. It can be secured.

In addition, the process carbide generation control and destruction method developed by the combination of solidification, cracking, and hot rolling (forging) enables fine and uniform production of primary process carbides to overcome the deterioration of toughness and Excellent impact toughness can be secured

And annealing heat treatment developed for spheroidization and uniform dispersion of secondary precipitated carbide in ferritic base to give excellent processability during mold manufacturing, and tempered heat treatment condition and developed surface treatment to double the improvement of physical and mechanical properties of invention steel More excellent mold life is guaranteed by the conditions.

1A and 1B are microstructure photographs of microstructured inventive steel (hardened tissue (X 150) and (tissue tissue x 400)).

2 is a graph comparing hardness after temper heat treatment of inventive steel and conventional steel.

3 is an impact toughness evaluation graph of the hardness of the invention steel and conventional steel.

4 is a high temperature softening resistance evaluation graph of the invention steel and conventional steel.

5 is a mold shape applied to the life evaluation of the invention steel and conventional steel.

In order to achieve the above object, one embodiment of the hot and warm high-speed coated oral material of the present invention is a weight%, C 0.40 to 0.55%, Si 1.0% or less, Mn 0.1 to 1.0%, Ni 0.1 to 0.5%, Cr 2.8-4.8%, Mo 1.0-3.0%, W 0.1-2.0% (W + 1 / 2Mo = 0.6-3.5%), V 0.5-2.0%, Nb 0.01-0.5% (V, Nb is one or more types 2 Nb + 1 / 2V = 0.26-1.5%), Co 0.1-1.5%, Al 0.01% or less, N 0.002-0.05%, S 0.015% or less, O 30ppm or less, and the remaining amount is Fe and electric It is characterized by consisting of trace impurities that may be contained during steelmaking.

In addition, another embodiment of the raw material of hot and warm high-speed coating oral is weight%, C 0.40 to 0.55%, Si 1.0% or less, Mn 0.1 to 1.0%, Ni 0.1 to 0.5%, Cr 2.8 to 4.8%, Mo 1.0 -3.0%, W 0.1-2.0% (W + 1 / 2Mo = 0.6-3.5%), V 0.5-2.0%, Nb 0.01-0.5% (V and Nb are one or more types, and in the case of two types, Nb + 1 / 2 V = 0.26 to 1.5%), Co 0.1 to 1.5%, Al 0.01% or less, N 0.002 to 0.05%, S 0.008% or less, O 30 ppm or less, and rare earth metals (REM: Ce, La, Nd, Y, Fe) in the form of REM or one or more of each element in the range of 0.001 to 0.25%, at which time REM% / S% = 2 to 90, [REM%] [S%] = 3 × It satisfies 10 ^-5 ~ 100 × 10 ^-5 , the remaining amount is characterized by consisting of Fe and trace impurities that can be contained during steelmaking with electricity.

Examples of the manufacturing method of the high-speed coated oral cavity of the present invention are weight%, C 0.40 to 0.55%, Si 1.0% or less, Mn 0.1 to 1.0%, Ni 0.1 to 0.5%, Cr 2.8 to 4.8%, Mo 1.0 to 3.0% , W 0.1 to 2.0% (W + 1 / 2Mo = 0.6 to 3.5%), V 0.5 to 2.0%, Nb 0.01 to 0.5% (V and Nb are one or more types, and in the case of two types, Nb + 1 / 2V = 0.26 -1.5%), Co 0.1-1.5%, Al 0.01% or less, N 0.002-0.05%, S 0.015% or less, O 30ppm or less, and the remaining amount is made up of Fe and trace impurities that can be contained during steelmaking with electricity. Manufacturing molten steel; Solidifying the molten steel at 1500 ± 100 ° C. (ingot, continuous casting); Performing hot working by a primary process carbide destruction method developed while performing hot working (rolling, forging) at 1100 ± 150 ° C .; Performing spherical annealing at 850 ± 60 ° C .; The tempering heat treatment is characterized in that it comprises a step of performing quenching at 1000 to 1180 ℃ range and at least once at 80 to 700 ℃.

Another embodiment of the manufacturing method of the high-speed coated oral cavity of the present invention is a weight%, C 0.40 to 0.55%, Si 1.0% or less, Mn 0.1 to 1.0%, Ni 0.1 to 0.5%, Cr 2.8 to 4.8%, Mo 1.0 to 3.0 %, W 0.1-2.0% (W + 1 / 2Mo = 0.6-3.5%), V 0.5-2.0%, Nb 0.01-0.5% (V, Nb is one or more types, and in the case of two types, Nb + 1 / 2V = 0.26 to 1.5%), Co 0.1 to 1.5%, Al 0.01% or less, N 0.002 to 0.05%, S 0.008% or less, O 30 ppm or less, and rare earth metals (REM: Ce, La, Nd, Y, Fe) Is contained in the form of REM or one or more elements in a range of 0.001% to 0.25%, in which case REM% / S% = 2 to 90 and [REM%] [S%] = 3 × 10 ^{− 5 to} 100 × 10 ⁻⁵ , the remaining amount of which is a molten steel comprising Fe and trace impurities that may be contained during steel making with electricity; Solidifying the molten molten steel with ingot material or continuous casting material in the range of 1500 ± 100 ° C .; The method developed as a normal hot working (rolling, forging) and primary process carbide destruction technology of solidified ingot material or continuous casting material in the range of 1100 ± 150 ℃ (Crack treatment + hot in the range of 1100 ± 150 ℃ before hot processing) Hot working) by a suitable combination of four-element order of processing + firing reduction amount + cooling rate; And performing spheroidization annealing by austenitizing the hot worked material in the range of 850 ± 60 ° C. and continuously cooling or multistage cooling at a rate of 50 ° C. or less per hour. During temper heat treatment, quenching is controlled by continuous or multi-stage cooling after pressurization, salt bath, water cooling, oil cooling, air cooling after austenite and carbide solidifying treatment for more than 1 minute per 10mm thickness in the range of 1000 ~ 1180 ℃. It characterized in that the step of maintaining the material in the range of room temperature to 80 ℃ more than three minutes per 10mm thickness in the range of 80 ~ 700 ℃ at least one air cooling operation.

Hereinafter, the reason for adding the chemical component of the inventive steel and the component range will be represented by weight% and the reason for limitation will be described.

C: C is an element that plays a big role in determining the performance of high toughness and high strength for the purpose of the present invention steel, some of which is dissolved in the base to improve the hardness and strength, most of the Cr, Mo, W, V , By combining with the carbide forming element of Nb, to form a first process carbide and to form a secondary precipitated carbide to impart abrasion resistance, and is an essential element for obtaining secondary curing after quenching / consider heat treatment. In order to secure HRC60-65 after quenching intended by the present invention, addition of 0.40% or more is necessary. If it exceeds 0.55%, hot workability and machinability are reduced, and toughness is reduced by excessive generation of primary process carbide during solidification. As the melting point is lowered, austenite grain growth is promoted during austenitization heat treatment, and the high capacity of added W and V is reduced to promote the primary crystallization of WC and VC carbides, thereby providing abrasion resistance but adversely affecting impact toughness. It is limited to% to 0.55%.

Si: Si has the effect of increasing the hardness by solid solution at the base and strengthening of solid solution.Increasing softening resistance, inhibiting austenite grain growth, improving hardenability, preventing surface oxidation at high temperatures, and promoting precipitation of carbides to refine carbides There is a contributing effect. In addition, an appropriate Si content effectively works to obtain secondary curing after consideration even at low C, Cr, W, Mo, and V contents.

When excessively added, the machinability, hot workability, thermal conductivity and toughness are reduced, so it is limited to 1.0% or less.

Mn: Mn is an element mainly added as a deoxidizer, and it is an element that contributes to strength and hardenability by solid solution at the base, and when added below 0.1%, the above effect cannot be expected, and when added at 1.0% or more, residual austenite is stabilized to decrease toughness. It is limited to 0.1% to 1.0%.

Cr: Cr is a very important addition element in the present invention. It is an element that improves the hardening ability by forming a solid solution at the base and forms M ₇ C ₃ and M ₂₃ C ₆ in the process of consideration, thereby improving the high temperature softening resistance and abrasion resistance, and increasing the dissolution rate of W into austenite to form carbide. Suppress C 0.40% to 0.55%, when added more than 4.8%, the toughness is sharply lowered, and when 2.8% or less is added, softening resistance, hardenability and wear resistance are reduced. Therefore, it is limited to 2.8% to 4.8% in order to secure the above effects and to suppress the formation and segregation of large process carbides.

Mo, W (W + 1 / 2Mo: 0.6% to 3.5%):

Mo is employed in the base to improve the hardenability and at the same time to form a complex carbide of Mo ₂ C, M ₇ C ₃ , M ₂₃ C ₆ to improve the sour secondary curing ability and wear resistance, but the effect of improving the toughness of the base is small.

When the addition of 1.0% or less can not be expected the above effect, the austenite grain size is easy to coarse and toughness is lowered, when added more than 3.0% not only damages the hot workability, but also increases the toughness by increasing the amount of process carbides. Therefore, it is limited to 1.0% to 3.0%.

W is the most important addition element of the steel of the present invention, and it is used in the base to form high hardness WC and W ₂ C carbide when it is soured. Soor secondary hardening ability is smaller than Mo, but the effect of improving the toughness of the base is great. There is an effect to refine. Can not be expected the effect in more than 0.1% addition is added more than 2.0% for non-employment M ₆ C the formation of carbides easier quenching after the heat treatment non-employment M ₆ C carbide segregation rapidly reduced as much presence in wear resistance but the effect toughness Let's do it. Therefore, it is limited to 0.1% to 2.0%.

As such, W and Mo combine with C and Fe to form complex carbides, improve wear resistance, and partially act as effective elements to solidify at the base to impart softening resistance, while promoting the formation of large primary eutectic carbides and segregation. It is also an element that inhibits toughness by causing. Therefore, the addition method of W and Mo, which can maximize the effect of the invention, is also effective in the addition of a single addition within the limited range, but the compounding range is more important, so that the limited range is W + 1 / 2Mo = 0.6% to 3.5%.

V, Nb (Nb + 1 / 2V: 0.26%-1.5%):

V is an element that combines with C to form a hard VC carbide to increase wear resistance, solid solution at the base to increase secondary hardenability, and refine the grain to improve toughness.

It has the strongest affinity with C and forms stable carbides of higher hardness than W and Mo-based carbides. The lower limit of 0.5% or less contributes to softening resistance and abrasion resistance, and the upper limit of 2.0% or more is limited to 0.5% to 2.0% because large carbides are formed and segregated to lower toughness as unemployed carbides.

Nb is easy to combine with C, such as V, and in the present invention, hard carbide of V and complex carbide (Nb · V) C and carbonitride of (Nb) CN improve the wear resistance and inhibit austenite grain growth at high temperature. Since it is an effective element in improving toughness, it is limited to 0.01%-0.5%.

In addition, in the present invention, Nb and V are added alone, but in combination, Nb + 1 / 2V is limited to 0.26% to 1.5% in order to maximize the effect of inhibiting formation of macrocarbide.

Co: Co is the most important additive element of the present invention steel and is a complete solid solution in the base, so that it is possible to increase the quenching temperature without causing coarsening of austenite grain size. Therefore, it is effective in improving heat resistance and improving wear resistance in high-speed wear zones. It is possible to secure high impact toughness at high hardness. However, when it is a high element and excessively added, impact toughness is lowered, and in particular, since it impairs hot workability and machinability, it is limited to 0.1% to 1.5%.

Al: Al having an effect of deoxidation and grain refining is added as an initial deoxidizer for molten steel refining in the present invention. In addition, since the characteristics of the present invention have characteristics of deoxidation and desulfurization using rare earth metals, shape control of non-metallic inclusions and control of coagulation structure, the upper limit of the rare earth metal addition effect is limited to 0.01% or less.

N: N is an element effective for miniaturizing austenite grain size and suppressing coarsening of rod-shaped MC-type eutectic carbides by (Nb) CN and AlN, and is limited to 0.002% to 0.05%. When the lower limit of 0.002% or less is expected, the effect is expected. If the number is not greater than 0.05%, the possibility of coarsening of eutectic carbides and low temperature brittleness is increased.

S, O: S is not more than 0.015% to give the processability when the rare earth metal addition is not added, but when rare earth metal is added S and O prevents the sole formation of RE-oxide and RE ₂ required to maximize the rare earth metal addition effect In order to generate O ₂ S and RExSy, S is regulated to 0.008% or less and O to 30 ppm or less.

Rare earth metals (REM: Ce, La, Nd, Y, Fe): Rare earth metals improve cleanliness of invented steel, control the shape of non-metallic inclusions, and act as nucleation sites for dendritic crystallization during coagulation, minimizing dendritic crystallization and solute element segregation. In particular, for the purpose of improving the miniaturization and dispersibility of the primary eutectic carbide (MC type), it is added in the form of rare earth metal (REM) in the range of 0.0002% to 0.25%, or one or more kinds of rare earth elements are added alone. However, it is limited to REM% / S% = 2 to 90 and [REM%] [S%] = 3 × 10 ^{−5 to} 100 × 10 ⁻⁵ as compared with the final S content. If it is below the limit, it is impossible to expect the effect of shape control of non-metallic inclusions, miniaturization of MC type carbide and dispersion degree. If it is above the limit, it is impossible to see the effects of improving impact toughness, impact toughness anisotropy, cutting property, and high temperature thermal fatigue properties. Is not

The rest are trace impurities that may inevitably be contained in steelmaking with Fe.

{Example}

Table 1 shows the chemical components of the inventive and conventional steels.

Invented steels A, B, D, and E were mixed and dissolved with pure iron and scrap iron in a 60 Ton electric furnace, followed by refining and vacuum, and the weight% C 0.40 to 0.55%, Si 1.0% or less, Mn 0.1 to 1.0%, Ni 0.1 to 0.5%, Cr 2.8-4.8%, Mo 1.0-3.0%, W 0.1-2.0%, V 0.5-2.0%, Nb 0.01-0.5%, Co 0.1-1.5%, Al 0.01% or less, N 0.002-0.05%, S 0.015% or less, O 30ppm or less, wherein W + 1 / 2Mo = 0.6 to 3.5%, Nb + 1 / 2V = 0.26 to 1.5%, and the inventive steels C, F, G are the components and It contains a composition in the range of 0.001 to 0.25% of rare earth metal outside the composition range, except that it is REM% / S% = 2 to 90 and [REM%] [S%] = 3 × 10 ^-5 compared to the final S content. After satisfying ˜100 × 10 ⁻⁵ , the remaining amount was made of 2.5 ton ingot in the range of 1500 ± 20 ° C. after melting molten steel consisting of Fe and trace impurities that may be contained during steelmaking. In addition, conventional alloy steel balls (H: STD61, I: STD11) and high-speed steel balls (J: SKH51, K: SKH55) are also manufactured in the same weight and shape of ingot after molten steel in the same manner as the invention steel.

Table 1 (wt%)

division C Si Mn S Ni Cr Mo W V Nb Co Al Nppm Oppm REM Invention steel A 0.45 0.60 0.80 0.005 0.50 4.05 2,6 1.8 1.7 0.38 1.3 0.002 400 18 - B 0.49 0.10 0.40 0.01 0.35 3.80 2.0 1.2 1.0 0.17 0.7 0.004 150 15 - C 0.50 0.08 0.50 0.006 0.32 3.60 1.8 1.1 0.9 0.02 0.8 0.008 80 13 0.08 D 0.55 0.11 0.30 0.001 0.12 4.60 3.0 1.3 0.9 - 0.1 0.001 50 20 - E 0.56 0.30 0.70 0.003 0.50 3.60 3.0 1.0 1.4 - 2.0 0.010 100 18 - F 0.42 0.90 0.90 0.004 0.20 4.60 2.8 1.7 1.8 0.1 1.5 0.002 180 12 Ce 0.12 Nd 0.08 G 0.55 0.12 0.40 0.006 0.10 4.50 2.9 1.4 1.0 - 0.09 0.003 140 14 Ce 0.15 Conventional Steel H 1.50 0.40 0.40 0.007 - 12.0 1.1 - 0.3 - - 0.010 85 20 - I 0.38 1.00 0.35 0.008 - 5.30 1.1 - 1.0 - - 0.011 74 19 - J 0.85 0.30 0.25 0.005 - 4.20 5.2 6.0 2.1 - - 0.012 100 15 - K 0.90 0.32 0.28 0.005 - 4.00 5.1 6.2 2.0 - 5.1 0.010 120 15 -

The ingot of the invention steel AF is produced as a rolled material by ordinary hot rolling at 1100 ± 150 ° C. as indicated by ○ in Table 2, and the size and dispersion degree of eutectic carbide, which is one of the great features of the present invention indicated by? In order to effectively control the ingots homogenized in the range of 1180 ± 40 ° C, the first plastic processing was applied with a reduced amount of 20 ~ 80% of the target dimension, and after homogenization in the range of 1190 ± 40 ° C, in the temperature range of 1100 ± 100 ° C. Finished rolling was carried out to the target dimension ψ140mm and controlled cooling with a cooling rate of less than 50 ℃ / hour was produced as a rolled material

The rolled material is subjected to spheroidization annealing by continuous cooling or multistage cooling at a rate of 50 ° C or less per hour after austenitizing at least 10 minutes per 10 mm thickness in the range of 850 ± 50 ° C. The annealing hardness is HB180 to HB210. .

The tempered heat treatment of the inventive steel is performed by controlled cooling (salt, oil, water) by continuous or multi-stage cooling after austenitizing and carbide solidifying treatment for at least 1 minute per 10 mm thickness in the range of 1000 to 1180 ° C. At least one consideration is given to air-cooling after holding the material in the range of ℃ for 3 minutes or more per 10 mm thickness in the range of 80 to 700 ℃.

H-K, which is a conventional steel, has been subjected to hot rolling, spheroidizing annealing and temper heat treatment, commonly known as alloy steel balls and high alloy high speed steel balls.

1A and 1B show the microstructure of invention steel B, subjected to 1120 ° C. quenching and 580 ° C. in temper heat treatment conditions of the invention steel. The quenched base is a martensite containing residual austenite and has the same composition as SKH51, which is a high-speed coating oral. The hardness is similar to that of HRC64, but the primary eutectic carbide has a fine characteristic of 5 µm or less, and the austenitic grain size is ASTM method. No. 10 or more is shown. The base in the soothing state shows a sole bite having a viscosity that helps impact toughness, and coexists with fine MC type carbides and precipitated carbides of Mo ₂ C, M ₇ C ₃ , and M ₂₃ C ₆ which are useful for wear resistance. .

In Fig. 2, hardness of the inventive steels B steel and C steel and conventional steels J steel (SKH51), H steel (STD11) and I steel (STD61) after temper heat treatment was compared. Invented steel has a secondary hardening zone near 525 ° C, and its hardness is lower than that of J steel and higher than that of H and I steel.

Figure 3 is a graph of the impact toughness compared to the hardness of the invention steel C steel and B steel and conventional steel H steel, I steel, J steel, the impact toughness is remarkably excellent so that the test specimen does not break at the same hardness than the conventional steel H steel The hardness is low compared to the J steel, but the toughness is so high that it cannot be compared.

In FIG. 4, 600 ° C high temperature softening resistance of the inventive steel B steel and the conventional steel I steel is analyzed. The inventive steel maintains the hardness of HRC54 after 12 hours at the initial hardness of HRC57.6 at 600 ° C., and the conventional steel becomes HRC40 after 12 hours at the initial hardness of HRC50.

Table 2 shows the hardness, impact toughness, flexural strength, tensile strength, thermal fatigue characteristics and wear after temper heat treatment for inventive steel and conventional steel material subjected to melting, molten steel manufacturing, ingot manufacturing, hot rolling and spheroidizing annealing by the method of Examples. Compare the properties.

After temper heat treatment of the inventive steel, the hardness is HRC55 ~ 61, which is slightly lower than the J steel (SKH51) and K steel (SKH55), similar to H steel (STD11), and much higher than I steel (STD61). Accordingly, the wear resistance is also similar to that of the H steel, the J steel, and the K steel, and is twice as good as that of the H steel.

Impact toughness of the invention steel is excellent enough not to be broken in the test from 15kgfm / ㎠ due to the new alloy composition and manufacturing method, has a toughness more than 10 times better than the conventional steel, H steel, J steel, K steel.

The bending strength is 400 to 540 kgf / mm 2, which is much superior to H steel of 400 kgf / mm 2, I steel of 300 kgf / mm 2, J steel of 490 kgf / mm 2 and K steel of 380 kgf / mm 2. In addition, the 700 ° C tensile strength of the inventive steel is 80-122kgf / mm 2, superior to 64kgf / mm 2 I steel, and similar to 120kgf / mm 2 J steel.

The thermal fatigue characteristics of the invention steels from 700 ℃ to 20 ℃ are 5 times shorter and 6 times less frequently than those of H steel, which is the hot steel, from the viewpoint of thermal fatigue cracking.

In addition, in Table 2, although the invention steel has all the mechanical properties superior to the conventional steel, when the new hot rolling method, which is one of the great features of the present invention, is applied, it exhibits more excellent mechanical properties than the conventional hot rolling. .

Table 3 shows the mold types of hot forging, hot forging and extrusion and cold cutting for the inventive steel and the conventional steels H steel (STD11), I steel (STD61) and J steel (SKH51).

Hot forging die life is 4 to 6 times better than conventional steel, warm extrusion die life is 3 times better than conventional steel and warm forging die life is 4 to 5 times better than conventional steel.

In addition, cold cutting (special steel, scrap) die life is 4 to 10 times better than conventional steel.

Figure 4 shows the mold shape of automobile parts crankshaft and rear axle shaft manufacturing.

TABLE 2

division Temper Heat Treatment Condition Hardness (HRC) Impact value (kgfm / ㎠) Bending strength (kgf / ㎡) Tensile Strength of 700 ℃ (kgf / ㎡) Thermal fatigue Crack Abrasion Amount (10 ^-4 g) Hardening (℃) (℃) count Average length (㎛) Invention steel A ◎ 1050 580 55 (27) 420 80 28 85 24 1080 580 55.5 (28) 428 85 29 87 23 B ○ 1120 570 57.5 35 450 105 25 80 20 ◎ 1120 570 57.5 41 460 110 22 79 19 ◎ 1110 580 58 (26) 455 102 20 76 21 C ○ 1120 570 57.5 40 470 111 20 76 19 ◎ 1120 570 57.5 (27) 482 115 18 72 19 ◎ 1110 580 58 (30) 475 106 14 74 20 D ◎ 1130 570 60 17 500 90 30 90 17 E ○ 1140 570 60.5 15 520 122 32 94 16 F ◎ 1040 580 55 (30) 437 90 26 82 23 G ○ 1130 570 60 25 520 96 28 88 17 ◎ 1120 570 59 30 518 94 26 86 18 ◎ 1140 570 59 30 540 100 26 88 16 Conventional Steel H ○ 1050 560 58 2.2 400 - - - 18 I ○ 1030 560 52 23.0 300 64 184 400 40 J ○ 1210 580 62 2.0 490 120 - - 12 K ○ 1220 580 64 1.8 380 - - - 13

1) Hot working method: ◎ Invented steel rolled by invention method, ○ Invented steel rolled by general rolling method and conventional steel

2) Impact value: Notch (★ is not broken due to high toughness)

TABLE 3

fair Application Method Manufacture parts Temperature mold Conventional Steel Invention steel Mold life of invention lecture compared to conventional steel Hot Automotive parts press forging P.D.Gear Gears-Plain Nut Crankshaft 1200 ℃ Upper die and lower die I steel B steel 5 to 6 times Auto parts-set forging Rear axle shaft spindle 1200 ℃ Punch Die I steel C steel 4 to 6 times Special steel forging Special steel 1000 ℃ ~ 1200 ℃ Upper and Lower Anvils I refined steel A steel 4x Warm Extruded aluminum Aluminum rod 550 ℃ Extrusion tool I steel D steel 3 times Brass extrusion Brass phoenix brass tube 650 ℃ Extrusion tool I refined steel G steel 3 times Automotive parts press forging Constant velocity joint (C-V Joint) 850 ℃ Punch Die I steel C steel 4x I refined steel B steel 5 times Cold Scrap cutting knife Scrap metal cutting Room temperature Braid I steel B steel 4x I refined steel C steel 3.5 times Special Steel Cutting Knives Special Steel Cutting Room temperature Braid I steel C steel 4x H steel D steel 10 times J steel F steel 9x

From the above examples, the steel of the present invention maintains significantly lower C content and expensive W and Co content than the existing high alloy high speed steel, and appropriately inherent characteristics of alloying elements such as Si, Mn, Cr, Mo, V, and Nb. Alloys that contain one or two or more rare earth metals compared to the final S content, which helps in the design and wear resistance of the alloys, but allows the proper control of the primary process carbides produced during solidification that adversely affects mechanical properties such as impact toughness. It was produced by the hot rolling (forging) method of the invention.

The inventive steel produced by this method has the same base composition as the existing high-alloy high-speed coated steel, and the hardness and abrasion resistance of SKH51, SKH55, and STD11 are similar, and the impact toughness, bending strength, and tensile strength are remarkably improved. Compared to STD61, which is a hot work steel, it has not only impact toughness, bending strength and tensile strength but also significantly improved abrasion resistance, softening resistance and thermal fatigue characteristics. In addition, the actual mold life of the invention steel is 3 to 10 times better than the existing high alloy high speed steel, cold steel or hot steel in the hot forging, hot forging, and hot extrusion and cold cutting processes. have.

Claims (5)

As weight%, C 0.40-0.55%, Si 1.0% or less, Mn 0.1-1.0%, Ni 0.1-0.5%, Cr 2.8-4.8%, Mo 1.0-3.0%, W 0.1-2.0% (W + 1 / 2Mo = 0.6 to 3.5%), V 0.5 to 2.0%, Nb 0.01 to 0.5% (V and Nb are one or more and Nb + 1 / 2V = 0.26 to 1.5% in the case of two types), Co 0.1 to 1.5%, Al It contains 0.01% or less, N 0.002 ~ 0.05%, S 0.015% or less, O 30ppm or less, and the residual amount contains Fe and trace impurities which can be contained during steelmaking with electricity. Tool steel. As weight%, C 0.40-0.55%, Si 1.0% or less, Mn 0.1-1.0%, Ni 0.1-0.5%, Cr 2.8-4.8%, Mo 1.0-3.0%, W 0.1-2.0% (W + 1 / 2Mo = 0.6 to 3.5%), V 0.5 to 2.0%, Nb 0.01 to 0.5% (V and Nb are one or more and Nb + 1 / 2V = 0.26 to 1.5% in the case of two types), Co 0.1 to 1.5%, Al 0.01% or less, N 0.002 to 0.05%, S 0.008% or less, O 30 ppm or less, containing rare earth metals (REM: Ce, La, Nd, Y, Fe) in the form of REM or one or more of each element 0.001 to 0.25 It is contained in the range of%, and in this case, it satisfies REM% / S% = 2 to 90, [REM%] [S%] = 3 × 10 ^{-5 to} 100 × 10 ^-5 compared to the final S content, and the remaining amount is Hot and warm low-alloy high-speed coating steel containing Fe and trace impurities that may be contained during steelmaking. Preparing molten steel in the composition range of claim 1; Solidifying the molten steel at 1500 ± 100 ° C .; Performing hot working on the coagulant at 1100 ± 150 ° C .; Performing spherical annealing at 850 ± 60 ° C .; And a step of performing quenching at a temperature in the range of 1000 to 1180 ° C. and at least once at 80 to 700 ° C. as a temper heat treatment. Preparing molten steel in the composition range of claim 1; Solidifying the molten steel in a range of 1500 ± 100 ° C .; Ingots homogenized in the range of 1180 ± 40 ℃ are subjected to primary hot-firing with a rolling reduction in the range of 20 to 80% of the target dimensions, and then homogenized in the range of 1190 ± 40 ℃ and hot in the target dimensions in the temperature range of 1100 ± 100 ℃. A method of manufacturing a hot / warm combined low-alloy high-speed coated steel sheet including a step of performing finish rolling and controlling cooling at a cooling rate of 50 ° C./hour or less. The method according to claim 4, wherein after the hot working, the control-cooled material is austenitized in the range of 850 ± 60 ° C., and then spheroidized annealing is carried out by continuous cooling or multi-stage cooling at a rate of 50 ° C. or less per hour for HB. ≦ 230; During temper heat treatment, control cooling (pressurization, salt bath, water cooling, oil cooling, air cooling) by continuous or multi-stage cooling is performed after austenitizing and carbide solidifying treatment for more than 1 minute per 10mm thickness in the range of 1000 ~ 1180 ℃. To prepare a low-alloy, high-speed coating steel for both hot and warm combined use, comprising the step of maintaining the material in the range of room temperature to 80 ° C. for at least 3 minutes per 10 mm thickness in the range of 80 to 700 ° C. and performing air cooling at least once. Way.