KR101981226B1 - METHOD FOR MANUFACTURING CAST Ni-Cr-Mo STEEL HAVING HIGH STRENGTHIMPACT RESISTANCE AT LOW TEMPERATURE AND CAST Ni-Cr-Mo STEEL METHOD THEREBY - Google Patents

Abstract

(A) 0.4 to 0.5% by weight of carbon (C); 0.4 to 0.5% by weight of silicon (Si); 0.5 to 0.8 wt% manganese (Mn); 2.0 to 2.5% by weight of nickel (Ni); 2.0 to 2.5% by weight of chromium (Cr); 0.3 to 0.5% by weight of molybdenum (Mo); 0.1 to 0.2% by weight of vanadium (V), 0 to 0.05% by weight of titanium (Ti), 0 to 0.05% by weight of aluminum (Al) Not more than 0 wt% to not more than 0.005 wt% of boron (B); Casting a melt containing iron (Fe) remnants and other unavoidable impurities; (b) full annealing at 850 to 900 < 0 >C; (c) quenching at 850 to 870 캜; And (d) tempering at 500 to 550 ° C. According to the present invention, there is provided a method for producing high-strength nickel chromium molybdenum main steels, Made of Ni-Cr-Mo alloy cast steel, which is minimized in size, is annealed, quenched and annealed in sequence to produce 1300 MPa steel cast steel, which is significantly improved in strength compared to commercial Ni-Cr-Mo alloy steel castings. And the cast steel can be usefully used as a material for steel castings requiring high strength, such as an impeller blade for a sand pump.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of manufacturing a high strength nickel chromium molybdenum main steel, and a main steel material produced by the same. BACKGROUND ART < RTI ID = 0.0 >

More particularly, the present invention relates to a method for producing a high strength cast steel containing nickel (Ni), chrome (Cr) and molybdenum (Mo) as an alloying element.

Processing equipment for grinding, milling, pumping, short-blasting, and rolling rigid materials such as ores, coal, gravel, cement and hard alloy in various industries High strength, abrasion resistance, oxidation resistance, and the like.

For example, a sand pump is a device for collecting sand and soil and discharges the sand and sand sedimented by a special stirrer installed at the bottom of the impeller while stirring, so that the impeller blade for the sand pump has a high strength of 1300 MPa or more Is required.

At present, various materials are known as impeller blades for the san pump. Among them, Ni-Cr steel is solidified in ferrite to increase the strength and viscosity of the steel, But also the strength is not high and the toughness tends to be tempered. Therefore, there is a disadvantage that the carbide should not be precipitated by quenching after tempering.

The Ni-Cr-Mo steel obtained by adding Mo to Ni-Cr steel has the advantage of reducing the temperability of the Ni-Cr steel and increasing the hardenability and tempering resistance, but the strength is less than 1300 MPa.

Specifically, there are SNCM 630, SNCM 439 and SNCM 447 in the KS standard, and SNCM 445 (old SNCM 5), SNCM 439 (old SNCM 8), and SNCM 447 SNCM 9) has been established and commercialized, but the tensile strength of these steels is known to be only 1100 MPa.

Korean Patent Publication No. 10-2017-0053128 (published on May 15, 2015). Korean Patent Laid-Open No. 10-2015-0137182 (Publication date: December 09, 2015) Korean Patent Laid-Open No. 10-2011-0115588 (published on October 21, 2011).

The present invention optimizes the heat treatment conditions of an alloy steel including rare metals (Ti, Al, B, W, Nb and the like) added for high strength and hardenability improvement to obtain nickel chromium molybdenum - Cr-Mo) main steel material and a main steel material produced thereby.

(A) 0.4 to 0.5% by weight of carbon (C); 0.4 to 0.5% by weight of silicon (Si); 0.5 to 0.8 wt% manganese (Mn); 2.0 to 2.5% by weight of nickel (Ni); 2.0 to 2.5% by weight of chromium (Cr); 0.3 to 0.5% by weight of molybdenum (Mo); 0.1 to 0.2% by weight of vanadium (V), 0 to 0.05% by weight of titanium (Ti), 0 to 0.05% by weight of aluminum (Al) Not more than 0 wt% to not more than 0.005 wt% of boron (B); Casting a melt containing iron (Fe) remnants and other unavoidable impurities; (b) full annealing at 850 to 900 < 0 >C; (c) quenching at 850 to 870 캜; And (d) tempering at a temperature of 500 to 550 ° C. The present invention also provides a method of manufacturing a high strength nickel chrome molybdenum main steel material.

The molten metal also contained 0.45 wt% carbon (C); 0.47 wt% silicon (Si); 0.80 wt% manganese (Mn); 2.48 wt% nickel (Ni); 2.30 wt% chromium (Cr); 0.38 wt% molybdenum (Mo); 0.14 wt% vanadium (V), 0.01 wt% titanium (Ti), 0.03 wt% aluminum (Al); 0.002% by weight of boron (B); Iron (Fe) remnants, and other unavoidable impurities. The present invention also provides a method for producing high strength nickel chrome molybdenum main steels.

The method of manufacturing a high strength nickel chrome molybdenum master steel according to claim 1, wherein the molten metal further contains 0 wt% to 0.05 wt% of niobium (Nb), or 0 wt% to 0.005 wt% of tungsten (W) I suggest.

The molten metal also contained 0.44% by weight of carbon (C); 0.45% by weight of silicon (Si); 0.78 wt% manganese (Mn); 2.49 wt% nickel (Ni); 2.30 wt% chromium (Cr); 0.38 wt% molybdenum (Mo); 0.14 wt% vanadium (V), 0.01 wt% titanium (Ti), 0.01 wt% aluminum (Al); 0.002% by weight of boron (B); 0.01 wt% niobium (Nb); Iron (Fe) remnants, and other unavoidable impurities. The present invention also provides a method for producing high strength nickel chrome molybdenum main steels.

The molten metal also contained 0.44% by weight of carbon (C); 0.46 wt% silicon (Si); 0.80 wt% manganese (Mn); 2.47 wt% nickel (Ni); 2.30 wt% chromium (Cr); 0.38 wt% molybdenum (Mo); 0.15 wt% vanadium (V), 0.01 wt% titanium (Ti), 0.02 wt% aluminum (Al); 0.002% by weight of boron (B); 0.002 wt% tungsten (W); Iron (Fe) remnants, and other unavoidable impurities. The present invention also provides a method for producing high strength nickel chrome molybdenum main steels.

Further, the complete annealing heat treatment in the step (b) is carried out by maintaining at 890 캜 for 8 hours, followed by furnace cooling from 890 캜 to 400 캜 and air cooling from 400 캜. We propose a manufacturing method of chrome molybdenum steel.

In addition, the quenching heat treatment in the step (c) is performed by maintaining the steel at 860 ° C for 1 hour and then oil cooling. The present invention also provides a method of manufacturing the high strength nickel chrome molybdenum main steel material.

In addition, the tempering treatment in the step (d) is carried out by maintaining at 540 캜 for 8 hours and then air-cooling the nickel-chromium molybdenum main steel.

Another aspect of the present invention is to provide a high strength nickel chromium molybdenum main steel having a tensile strength of 1300 MPa or more manufactured by the above production method.

Further, in another aspect of the present invention, the present invention proposes an impeller blade for a sand pump made of the high strength nickel chrome molybdenum main steel.

According to the present invention, complete annealing, quenching and tempering heat treatment are sequentially performed under optimized heat treatment conditions for Ni-Cr-Mo alloy cast steel in which expensive rare metals added to improve mechanical properties such as strength are minimized, It is possible to produce 1300 MPa-class cast steel which is significantly improved in strength as compared with the Cr-Mo alloy cast steel, and the cast steel can be usefully used as a material for steel castings requiring high strength, such as impeller blades for sand pumps.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an optical microscope (OM) photograph of A, B, C, and D cast specimens in this embodiment.
Fig. 2 shows the results of analysis of the grain size of the castings of the A, B, C, and D cast specimens in the examples of the present invention.
Fig. 3 shows the results of analysis of the amounts of phases in A, B, C, and D casting specimens in this embodiment.
4 is a schematic diagram of a heat treatment profile of a full annealing heat treatment process according to the present embodiment.
FIG. 5 is a scanning electron microscope (SEM) photograph of a sample subjected to a full annealing heat treatment according to an embodiment of the present invention.
6 is a scanning electron microscope (SEM) photograph of a specimen of full annealing (890 ° C) and general cooling quenching (860 ° C) according to the present embodiment.
7 is a scanning electron microscope (SEM) photograph of a specimen of full annealing (890 ° C), oil quenched general quenching (860 ° C) and tempering heat treatment (540 ° C) according to the present embodiment.
FIG. 8 shows the results of measurement of tensile strength, yield strength and elongation of a specimen subjected to full annealing (890 ° C), oil quenching general quenching (860 ° C) and tempering heat treatment (540 ° C) according to the present embodiment.
9 is a graph showing the results of hardness measurement of the specimens of full annealing (890 ° C), oil quenched general quenching (860 ° C) and tempering heat treatment (540 ° C) according to the present embodiment.
10 is an optical microscope (OM) photograph of a normalized heat-treated specimen according to a comparative example.
FIG. 11 shows the results of the grain size index analysis of the normalized heat-treated specimen according to the comparative example.
12 shows the results of analysis of the amount of phase in the normalized heat-treated specimen according to the comparative example.
13 is a scanning electron microscope (SEM) photograph of a normalized heat-treated specimen according to a comparative example.
14 shows the results of EDS analysis of the normalized heat-treated specimen according to the comparative example.
Fig. 15 shows the hardness comparison results between the as-cast specimen and the normalized heat-treated specimen according to the comparative example.
16 is a schematic view of a heat treatment profile of a pulling-quenching-tempering heat treatment process according to a comparative example.
17 shows the results of measurement of tensile strength and yield strength of the specimens of the normalizing, water-cooling and oil-cooling pulling quenching and tempering heat treatment (570 ° C) according to the comparative examples.
18 is a graph showing the elongation measurement results of a specimen subjected to a normalizing-water-cooling / oil-impression-quenching-temper heat treatment (570 ° C) according to a comparative example.
19 is a graph showing the results of hardness measurement of a specimen subjected to normalizing, water cooling, and oil quenching and quenching and tempering (570 ° C) according to a comparative example.
FIG. 20 shows the tensile strength and yield strength of a specimen subjected to a normalizing, water-cooling, and heat-quenching-temper annealing (500 ° C., 360 ° C., or 280 ° C.) according to a comparative example.
21 shows the hardness measurement results of the specimens subjected to the normalizing-water-cooling / oil-cooling impression-quenching-heat treatment (500 ° C, 360 ° C or 280 ° C) according to the comparative example.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

Embodiments in accordance with the concepts of the present invention can make various changes and have various forms, so that specific embodiments are illustrated in the drawings and described in detail in this specification or application. It should be understood, however, that the embodiments according to the concepts of the present invention are not intended to be limited to any particular mode of disclosure, but rather all variations, equivalents, and alternatives falling within the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, the terms " comprises ", or " having ", or the like, specify that there is a stated feature, number, step, operation, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Hereinafter, the present invention will be described in detail.

In the present invention, rare metals (Ti, Al, B, W, Nb, etc.) are added to the Ni-Cr-Mo alloy cast steel composition in order to drastically improve the strength of the existing nickel chromium molybdenum alloy cast steel, The present invention proposes a method of manufacturing a nickel chromium molybdenum main steel having a high strength of 1300 MPa or higher without defects by optimizing a heat treatment process after casting.

To this end, the present invention relates to a composition comprising (a) 0.4 to 0.5% by weight of carbon (C); 0.4 to 0.5% by weight of silicon (Si); 0.5 to 0.8 wt% manganese (Mn); 2.0 to 2.5% by weight of nickel (Ni); 2.0 to 2.5% by weight of chromium (Cr); 0.3 to 0.5% by weight of molybdenum (Mo); 0.1 to 0.2% by weight of vanadium (V), 0 to 0.05% by weight of titanium (Ti), 0 to 0.05% by weight of aluminum (Al) Not more than 0 wt% to not more than 0.005 wt% of boron (B); Casting a melt containing iron (Fe) remnants and other unavoidable impurities; (b) full annealing at 850 to 900 < 0 >C; (c) quenching at 850 to 870 캜; And (d) tempering at 500 to 550 占 폚.

Said step (a) essentially comprises 0.4 to 0.5% by weight of carbon (C); 0.4 to 0.5% by weight of silicon (Si); 0.5 to 0.8% by weight of manganese (Mn); 2.0 to 2.5% by weight of nickel (Ni) based on SNCM grade of KS and JIS for improving the hardenability of the post casting; 2.0 to 2.5% by weight of chromium (Cr); (Ti, Al, B, W, Nb, and the like) for improving the mechanical properties such as strength and the like, containing 0.3 to 0.5% by weight of molybdenum (Mo).

Specifically, 0.4 to 0.5% by weight of carbon (C); 0.4 to 0.5% by weight of silicon (Si); 0.5 to 0.8 wt% manganese (Mn); 2.0 to 2.5% by weight of nickel (Ni); 2.0 to 2.5% by weight of chromium (Cr); 0.3 to 0.5% by weight of molybdenum (Mo); 0.1 to 0.2% by weight of vanadium (V), 0 to 0.05% by weight of titanium (Ti), 0 to 0.05% by weight of aluminum (Al) Not more than 0 wt% to not more than 0.005 wt% of boron (B); An alloy steel containing iron (Fe) remnants and other unavoidable impurities is dissolved in a melting furnace such as a high frequency induction furnace, an arc electric furnace or a vacuum induction melting furnace to form a molten metal, refining and degassing, The casting process of pouring and solidifying the casting mold is performed.

At this time, the molten metal may further include 0 wt% to 0.05 wt% of niobium (Nb), or 0 wt% to 0.005 wt% of tungsten (W).

Next, in the step (b), the casting obtained in the previous step is subjected to full annealing at 850 to 900 ° C.

The complete annealing in this step is carried out by improving the toughness before the quenching heat treatment to remove cracking factors and improving the mechanical properties. The annealing is carried out by keeping the temperature at A _c3 or higher for a certain period of time and then cooling and / (890 ° C) for 8 hours, followed by furnace cooling from 890 ° C to 400 ° C and air cooling from 400 ° C.

Next, the quenching of step (c) is carried out to secure mechanical properties such as strength and hardness of the main steel, and preferably quenched after being maintained at a temperature of 850 to 870 캜 for a certain period of time. The ferrite is not completely transformed into austenite at the temperature, quenching occurs in a state where the ferrite is not solidified, and the hardness is reduced. At a temperature higher than 870 DEG C, hardness decreases due to an increase in retained austenite content.

More preferably, the quenching heat treatment in this step may be performed by maintaining the temperature at 860 ° C for 1 hour and then oil cooling.

Next, the tempering treatment in the step (d) may be performed at a temperature exceeding 550 ° C., and the tensile strength may be lowered. When the austenite phase is precipitated through reverse transformation, the toughness may be lowered. , The balance between strength and toughness is deteriorated and toughness is lowered, and therefore, it is preferable to be performed at 500 to 550 ° C.

On the other hand, the holding time after heating in the tempering treatment in this step is determined according to the thickness of the main steel, but it is preferable to maintain the heating for 8 hours or more in order to achieve a sufficient effect.

For example, the tempering treatment in this step may be carried out by maintaining at 540 ° C for 8 hours and then air cooling.

According to the method for producing high-strength nickel-chromium molybdenum main steel according to the present invention as described above in detail, the nickel-chromium-molybdenum main steel which is optimized for the mechanical properties such as strength, Annealing, quenching and tempering are successively carried out to produce a cast steel of 1300 MPa in which the strength is remarkably improved as compared with that of a commercially available Ni-Cr-Mo alloy cast steel. The cast steel is cast steel having high strength, such as impeller blades for a sand pump Can be usefully used as a material of the substrate.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. The embodiments presented are only a concrete example of the present invention and are not provided for the purpose of limiting the scope of the present invention.

<Examples> Preparation and Characterization of Ni-Cr-Mo Main Steels Completely Annealed - Quenched - Tempered Heat Treated

1. Casting and chemical composition of test specimens

(1) Composition

 Ti, Al, B, Nb, and W were prepared so that the contents of Fe, Fe, and Fe were 2.0 to 2.5%, 2.0 to 2.5%, and 0.3 to 0.5% . The specimens A, B, C and D were cast as shown in Table 1, and specimen A was blended with an alloy composition containing 0.15% of V in the conventional product composition. Specimen B contained V, Ti, Al, Ti, Al, B, and Nb were added to specimen C, and V, Ti, Al, B, Nb, and W were added to specimen D. The chemical composition of the cast specimens corresponds to the target composition range of the alloy design and is shown in Table 1 below.

(2) Foundry equipment

 Fig. 1 shows the surface structure of the specimens A, B, C, and D cast with different compositions of the alloy components, which were etched for 30 seconds with a caustic solution prepared by mixing 90 mL of alcohol, 10 mL of hydrochloric acid, and 1 g of picric acid. The specimens of B, C, and D specimens were finer and the specimens of C specimens were finest

 (3) Crystal grain size index

The crystal grain size index of the cast specimen was calculated as shown in Fig. The grain size index of specimen A is 7.3, specimen B is 9.0, specimen C is 9.8 and specimen D is 8.5. Specimen C is the finest and specimen A is the most abundant.

(4) Amount of phase

As shown in FIG. 3, the amount of maltenite in the A specimen is the largest at 80%, while the amount of maltitol in the C specimen is the smallest at 1%, while the specimen B is 60% and the specimen C 20%. The amount of ferrite is the largest as 95% of the C specimen, and the amount of ferrite of the A specimen is the smallest at 5%, while the specimen B is 20% and the specimen D is 50%.

The amounts of carbide were 20% for D specimen, 15% for A specimen, 4% for B specimen, 1% for C specimen and 50% for D specimen, 13% for B specimen, 1% for A specimen, , And the C specimen is 0.5%. In summary, in the state of kitchen, A and B specimens showed more than 60% of maltingite, and C and D showed more than 50% of ferrite.

2. Fabrication and characterization of Ni-Cr-Mo main steels annealed - quenched - tempered annealed

In this embodiment, the casting specimen prepared in the above 1. is subjected to complete annealing in order to improve the toughness and to eliminate the cause of cracking before the quenching heat treatment is performed, and to improve the mechanical properties, and then quenching and tempering heat treatment are sequentially To produce 1300 MPa grade Ni-Cr-Mo main steel.

More specifically, as shown in Fig. 4, the complete annealing heat treatment performed in the present example is performed at 890 DEG C for 8 hours, then furnace cooling from 890 DEG C to 400 DEG C for 25 hours, (air cooling).

FIG. 5 is a scanning electron microscope (SEM) photograph of a specimen subjected to a complete annealing heat treatment, in which the matrix shows ferrite and void structure, and the process structure is very fine. In the EDS analysis, carbides were detected as M₃C or M₂₃C ₆ in the process tissues.

After the above-mentioned complete annealing heat treatment, general quenching heat treatment at 860 ° C was performed, and heat treatment was performed at 540 ° C for 8 hours to prepare Ni-Cr-Mo main steel according to the present invention.

FIG. 6 is a scanning electron microscope (SEM) photograph of a specimen of full annealing (890 ° C.) and oil-cooling general quenching (860 ° C.) according to the present embodiment, This is a scanning electron microscope (SEM) photograph of a specimen subjected to general quenching (860 ° C) and tempering (540 ° C).

FIG. 8 shows the results of measurement of tensile strength, yield strength and elongation of full annealing (890 ° C.), oil-cooling general quenching (860 ° C.) and tempering heat treatment (540 ° C.) according to the present embodiment, (890 ° C), general quenching (860 ° C), and annealing (540 ° C).

8 and 9, the tensile strengths of the specimens B, C and D (development target of 1,300 MPa or more) were 1,383 MPa, 1,457 MPa and 1,340 MPa, the yield strength (development target 1,000 MPa or more) was 1,249 MPa, 1,259 MPa, 1,251 MPa, and the elongation is 6.2 %%, 4.5%, and 4.5%. The hardness of specimens B, C and D (development target HRC 45 or more) is HRC 46, 47, 46. This annealing process is a completely annealed annealed specimen before quenching heat treatment, and both B, C and D specimens meet the development goal.

Table 2 shows the test results of tensile strength, yield strength, elongation and hardness of the specimen for the complete annealing-impression-quenching-tempering heat treatment process and tempering process conditions according to the present embodiment.

Completion judgment: O (satisfies the required mechanical properties) / X (does not meet the required mechanical properties)

<Comparative Example> Preparation and characterization of Ni-Cr-Mo main steels subjected to normalizing-quenching-temper annealing

The Ni-Cr-Mo main steels were prepared by subjecting the cast specimens prepared in the above Example 1 to normalizing-quenching-tempering heat treatment, and the characteristics of the Ni-Cr-Mo main steels were analyzed.

1. Characteristics of Casting Specimens after Normalizing Heat Treatment Process

The cast specimens prepared in the above Example 1 were heated and maintained at 900 ° C for 8 hours, and the specimens obtained through the air-cooled normalizing heat treatment were subjected to the following characteristics analysis.

(1) OM organization

FIG. 10 is a photograph of an optical microscope (OM) of a casting piece subjected to a normalizing heat treatment. Referring to FIG. 10, the grain size index after the normalizing heat treatment is finer than that of the A specimen and the grain size of the specimen B, .

(2) Crystal grain size index

The grain size of the specimens A, B, C, and D after the normalizing heat treatment was finer than that of the cast specimen as shown in FIG. 11. The crystal grain size index of the A specimen was 5.9, the grain size index of the B specimen was 6.2, The grain size index of the specimen is 6.4 and the grain size index of the D specimen is 9.0. The specimens A, B, C, and D showed finer grain sizes than the D specimens after the normalizing heat treatment due to the influence of alloying elements.

(3) the amount of phase

As shown in FIG. 12, after the normalizing heat treatment, the A specimen had a Martensite structure of 75% and a ferrite structure of 20%, and the B, C and D specimens had a maltenoid structure of less than 20% Increased to over 80%. The amount of carbide and retained austenite was less than 5% in both A, B, C and D specimens.

In the SEM image of FIG. 13 and the EDS analysis of FIG. 14, the A specimen shows a lot of maltitine texture whereas the B, C and D specimens show a lot of ferrite texture.

(5) Hardness

As shown in FIG. 15, the hardness values of the normalized heat treated specimens A, B, C, and D were more uniform and constant than those of the specimen of the kitchen state, and the hardness of the specimens was increased. In this normalizing heat treatment process, the hardness is low so that the machining is easy, but the hardness is high so that the machinability is difficult to be obtained. As a result, there is a concern about the occurrence of quench cracking in the quenching heat treatment.

2. Preparation and characterization of Ni-Cr-Mo main steels subjected to normalizing-quenching-temper annealing

Following the normalizing heat treatment process, Ni-Cr-Mo main steel with impression-quenching-tempering heat treatment (water-cooling / oil-cooling) was prepared and its properties were evaluated.

First, Ni-Cr-Mo main steels according to comparative examples were prepared by sequentially performing the impression-quenching-tempering process shown in FIG. 16 on the normalized heat-treated specimens.

(1) Normalizing - Quenching of water-cooling / oil-cooling - Mechanical properties of Ni-Cr-Mo main steel subjected to tempering (570 ℃)

The specimens A, B, C, and D, which were heat-treated at 570 ° C after being air-cooled after being maintained at 880 ° C and then cooled by water cooling and oil cooling, were heated at about 400 ° C and tensile strength and yield strength The yield strength was low as shown in Fig. 18, and the tensile strength was not measured. The tensile strength of the specimens quenched and annealed was 1,102 ~ 1,247 MPa, while the tensile strength of the specimens quenched by water cooling was 1,216 ~ 1,306 MPa, which was about 100 MPa. However, the specimens satisfying the development target of 1,300 MPa or more were not satisfied with the development target in both the cooling and the water-cooled specimens, and only the C specimen satisfied the development target with the tensile strength of 1,306 MPa.

As shown in Fig. 18, elongation rates of all specimens were 3% or less. Specimens C and B showed the highest elongation rates in the specimens C and B, respectively. Quenched cracks occurred in the water - cooled specimens and the elongation rate should be increased to obtain the measured value of yield strength.

Fig. 19 shows the results of hardness tests on specimens A, B, C, and D, which were heat-treated at 570 캜 after being kept at 880 캜, water-cooled and oil-cooled, The hardness of the specimens quenched and annealed was HRC 42 ~ 45, and the hardness of the specimens quenched in water was HRC 40 ~ 44. However, there were no development samples satisfying the development target HRC45 or higher, and all of them were below the target hardness. Among these specimens, there were no cracks in the specimens which were cooled, but most of them occurred in the specimens quenched by water cooling. At the 570 캜 tempering temperature, the desired mechanical properties could not be achieved, with the hardness being too low.

(2) Normalizing - Water quenching / Oil cooling impression quenching - Mechanical properties of Ni-Cr-Mo main steels subjected to tempering heat treatment (500 ℃, 360 ℃ or 280 ℃)

As shown in FIG. 20, the A specimen satisfied the target value of the tensile strength among the specimens tempered at -500 ° C., but the yield strength was lower than the target value. In addition, all samples of A, B, C, and D satisfied the target tensile strength, but yield strength was below the target value. The C and D specimens satisfied the target tensile strength, but yield strength was below the target value.

As shown in FIG. 21, hardness of all specimens satisfied the target hardness of target HRC45 or more in the specimens subjected to heat-quenching at -360.degree. The hardness of all specimens satisfies the target hardness of HRC45 or higher in the specimens heat treated at -280 ℃. The measured results are in the range of HRC48 ~ 50. The hardness at which the tempering temperature is to be lowered is increased and the hardness is lowered at higher tempering temperature. When the tempering temperature is higher than 550 ° C, the hardness is lower than HRC 45 as shown in FIG.

The results of test results such as tensile strength, yield strength and hardness of the specimen according to the annealing - impregnation quenching - tempering process and annealing process, heat treatment temperature, and other process conditions are summarized as follows. The conventional heat treatment method could not achieve the development target as shown in Table 3 below.

1) 900 ° C normalizing - 880 ° C water cooling impression quenching - 570 ° C tempering heat treatment process

This process is a conventional heat treatment method. In this method, all items such as tensile strength, yield strength, and hardness of developed specimens A, B, C, and D are not satisfied with the development target as well as existing materials.

2) 900 ℃ normalizing - 880 ℃ oil cooling impression quenching - 570 ℃ tempering heat treatment process

This process is a conventional heat treatment method, which is a process in which the product is cracked and the coolant is changed. In this method, all the items such as tensile strength, yield strength, and hardness of the developed specimens A, B, C, and D were not satisfied with the development targets.

3) 890 ℃ normalizing - 860 ℃ oil cooling impression quenching - 500 ℃ tempering heat treatment process

The conventional normalizing heat treatment process is the same, and the quenching temperature and tempering temperature are different. In this method, tensile strength and yield strength of A specimen were suitable, but B, C and D specimens were less than specimens A and B, C and D specimens were only hardness specimens.

4) 890 ℃ normalizing - 860 ℃ oil cooling impression quenching - 360 ℃ tempering heat treatment process

The tensile strength and hardness of A, B, C and D specimens are suitable for this method, but the yield strength is A, B, C, D specimens were all underdone.

5) 890 ℃ normalizing - 860 ℃ oil cooling impression quenching - 280 ℃ tempering heat treatment process

In this method, the tensile strength and hardness of the specimens C and D are suitable. However, the yield strengths of the specimens A, B, C, and D are all the same It was under.

Completion judgment: O (satisfies the required mechanical properties) / X (does not meet the required mechanical properties)

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood. It is therefore to be understood that the above-described embodiments are illustrative and not restrictive in every respect.

Claims (10)

(a) (i) 0.45% by weight of carbon (C); 0.47 wt% silicon (Si); 0.80 wt% manganese (Mn); 2.48 wt% nickel (Ni); 2.30 wt% chromium (Cr); 0.38 wt% molybdenum (Mo); 0.14 wt% vanadium (V); 0.01% by weight of titanium (Ti); 0.03 wt% aluminum (Al); 0.002% by weight of boron (B); A molten metal containing iron (Fe) remnants and other unavoidable impurities or
(ii) 0.44 wt% carbon (C); 0.45% by weight of silicon (Si); 0.78 wt% manganese (Mn); 2.49 wt% nickel (Ni); 2.30 wt% chromium (Cr); 0.38 wt% molybdenum (Mo); 0.14 wt% vanadium (V); 0.01% by weight of titanium (Ti); 0.01% by weight aluminum (Al); 0.002% by weight of boron (B); 0.01 wt% niobium (Nb); A molten metal containing iron (Fe) remnants and other unavoidable impurities or
(iii) 0.44 wt% carbon (C); 0.46 wt% silicon (Si); 0.80 wt% manganese (Mn); 2.47 wt% nickel (Ni); 2.30 wt% chromium (Cr); 0.38 wt% molybdenum (Mo); 0.15 wt% vanadium (V); 0.01% by weight of titanium (Ti); 0.02 wt% aluminum (Al); 0.002% by weight of boron (B); 0.002 wt% tungsten (W); Casting a melt containing iron (Fe) remnants and other unavoidable impurities;
(b) full annealing at 850 to 900 &lt; 0 &gt;C;
(c) quenching at 850 to 870 캜; And
(d) tempering at 500 to 550 ° C. delete delete delete delete The method according to claim 1,
Wherein the complete annealing heat treatment in the step (b) is carried out by maintaining at 890 캜 for 8 hours, followed by furnace cooling from 890 캜 to 400 캜 and air cooling from 400 캜. The high strength nickel chromium molybdenum Method of manufacturing main steel. The method according to claim 1,
Wherein the quenching heat treatment in the step (c) is performed by maintaining at 860 ° C for 1 hour and then oil cooling. The method according to claim 1,
Wherein the tempering treatment in step (d) is carried out by maintaining at 540 캜 for 8 hours and then air-cooling the nickel-chromium molybdenum main steel. A high strength nickel chrome molybdenum master steel having a tensile strength of 1300 MPa or more produced by the method according to any one of claims 1 to 6. An impeller blade for a sand pump comprising the high strength nickel chrome molybdenum main steel according to claim 9.

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