CN113549838A - Ultralow-oxygen-nitrogen medium-high heat-resistance hot-work die steel forging and preparation method thereof - Google Patents
Ultralow-oxygen-nitrogen medium-high heat-resistance hot-work die steel forging and preparation method thereof Download PDFInfo
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
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- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D17/00—Pressure die casting or injection die casting, i.e. casting in which the metal is forced into a mould under high pressure
- B22D17/20—Accessories: Details
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Abstract
The invention provides an ultralow oxygen nitrogen medium-high heat resistance hot work die steel forging and a preparation method thereof; the die steel forging comprises the following elements in percentage by mass except iron and inevitable impurities: 0.3 to 0.45 percent of carbon, 0.1 to 0.5 percent of silicon, 0.2 to 0.8 percent of manganese, 4.5 to 5.5 percent of chromium, 2 to 3.2 percent of molybdenum, 0.3 to 1 percent of vanadium, 0.002 to 0.02 percent of phosphorus, 0.0001 to 0.005 percent of sulfur, 0.0002 to 0.0008 percent of oxygen and 0.002 to 0.006 percent of nitrogen. The preparation method of the die steel forging adopts vacuum induction furnace smelting and/or vacuum consumable smelting, the content of harmful gases is low, the average notch impact performance KV2 is more than or equal to 15J, the average unnotched impact energy AK is more than or equal to 350J, the band grade is SA1 or SA2 or SB1 or SB2, the tissue grade is AS1 or AS2 or AS3 or AS4 or AS5 or AS6, and the grain size is more than or equal to 7. The method can meet the requirements of national key new materials on high-end hot-work die steel forgings of automobiles, replaces imports in China, solves the problem of neck clamping of the high-end hot-work die steel forgings, and has great economic and social benefits.
Description
Technical Field
The invention relates to the technical field of metallurgy and forging processing, in particular to an ultralow oxygen nitrogen medium-high heat resistance hot work die steel forging and a preparation method thereof.
Background
According to the handbook of practical mold materials and thermal treatment quick look-up published by the dynasty banger, the mechanical industry and publishing society, the commonly used hot work mold steel is generally divided into: low heat-resistant high-toughness hot-work die steel, medium heat-resistant hot-work die steel, high heat-resistant hot-work die steel, austenitic hot-work die steel, high-speed tool steel type heat-resistant steel, maraging type heat-resistant steel, precipitation hardening type hot-work die steel, and cold-hot dual-purpose base steel. The high-end hot-work die steel forging of the automobile is used as an advanced steel material, the working temperature of the die made of the forged die steel forging is generally 500-700 ℃, the die works, belongs to the high-heat-resistance hot-work die steel forging and is a key national issue, the service life of the die made of the current domestic high-heat-resistance hot-work die steel forging is only 1/2-1/5 which is imported, and particularly, the large, complex and important high-end hot-work die almost completely adopts the imported die steel forging.
The performance of domestic medium-high heat resistance hot-work die steel forgings in the aspects of heat resistance strength, wear resistance and high temperature thermal fatigue resistance is inferior to that of foreign similar products, and the specific embodiment is that the content of harmful elements is high, wherein S is more than or equal to 0.003 percent, P is more than or equal to 0.01 percent, N is more than or equal to 0.01 percent, and O is more than or equal to 0.001 percent; the segregation of steel is serious, the level of inclusions is high, the influence on performance indexes is large, the average unnotched impact energy is less than or equal to 300J, the ratio of the horizontal unnotched impact energy to the longitudinal unnotched impact energy is less than or equal to 85 percent, and the difference between the average unnotched impact energy and the horizontal unnotched impact energy is large compared with the foreign top level.
For other steel grades, for example, patent application publication No. CN109642294A, the main alloying elements of which are only Mn, and others are non-alloying elements and residual elements, classified as low alloy steel (alloying elements ≤ 5%) according to the national standard, relates to a steel sheet and a method for manufacturing the same, a steel sheet suitable for manufacturing parts of automobiles, home appliances, etc. formed by cold pressing, which is suitable for a low application temperature, not a die steel for hot work use; in this case, the mass ratio includes: 1.8 to 4 percent of manganese, 0.01 to 1 percent of chromium and 0.01 to 0.5 percent of molybdenum, which causes the technical problem of insufficient strength under high temperature condition.
Disclosure of Invention
In order to solve the problems, the working temperature of the die made of the die steel forging piece is generally 500-700 ℃, and the die belongs to medium-high heat-resistant hot work die steel. The medium heat-resistant hot-work die steel is characterized in that the carbon content is lower, the carbon content is medium carbon, the mass fraction of the medium heat-resistant hot-work die steel is 0.3-0.5%, alloy elements such as Cr, Mn, Si, Ni, W, Mo, V and the like are added to improve the performance of a die steel forging, the general mass fraction of Cr is 3-5%, the mass fraction of Mo is 1-3%, the hardenability of steel is greatly improved by Cr and Mo, M2C type carbide dispersed and separated out during martensite tempering of molybdenum can improve the high-temperature strength, the recrystallization temperature of a matrix can be improved by molybdenum, the high-temperature strength is also favorable, but the toughness is not favorable when the content is excessive, and therefore, the content of the molybdenum is adjusted to be 2.00-3.2%; when the content of silicon is more than 0.6 percent, particularly when the silicon and manganese exist in the steel at the same time, the silicon is easy to segregate, so the content of the silicon is adjusted to be 0.1 to 0.5 percent, and the V element ensures that the steel has better anti-overheating sensitivity, thereby the hot hardness and the hot strength can be improved, and the steel still has higher hardness, hot strength and wear resistance when the working temperature reaches 500-600 ℃, and the highest temperature can reach 650 ℃. High heat resistance hot work die steel: the high heat-resistant hot-work die steel forging has high content of alloy elements, the mass fraction of the alloy elements is 8-11%, and the steel has high heat resistance, namely high-temperature strength and high-temperature hardness, and can work at the high temperature of 600-700 ℃.
The invention adopts a vacuum induction furnace and/or a vacuum consumable furnace for smelting, reduces the content of harmful elements, particularly oxygen and nitrogen, in the hot-work die steel forging, and adopts a forging rather than plate rolling mode to process the die steel forging so as to improve the comprehensive performance of the die steel forging.
On one hand, the invention provides an ultralow-oxygen-nitrogen medium-high heat resistance hot work die steel forging, which comprises the following elements in percentage by mass in addition to iron and inevitable impurities: 0.3 to 0.45 percent of carbon, 0.1 to 0.5 percent of silicon, 0.2 to 0.8 percent of manganese, 4.5 to 5.5 percent of chromium, 2 to 4 percent of molybdenum, 0.3 to 1 percent of vanadium, 0.002 to 0.02 percent of phosphorus, 0.0001 to 0.005 percent of sulfur, 0.0002 to 0.0008 percent of oxygen and 0.002 to 0.006 percent of nitrogen; the average notch impact performance KV2 of the die steel forging is more than or equal to 15J, the average unnotched impact energy AK is more than or equal to 350J, the strip grade is SA1, SA2, SB1 or SB2, the tissue grade is AS1, AS2, AS3, AS4, AS5 or AS6, and the grain size is more than or equal to 7.
Wherein the organization level and the ribbon level are evaluated according to the standards of the North American die casting Association NADCA-207-.
Preferably, the mass percentage of nitrogen element in the die steel forging is 0.002-0.003%, and/or the mass percentage of oxygen element is 0.0002-0.0004%.
Preferably, the ultra-low oxygen nitrogen die steel forging further comprises the following elements in percentage by mass in addition to iron and inevitable impurities: 0.3 to 0.45 percent of carbon, 0.1 to 0.3 percent of silicon, 0.2 to 0.8 percent of manganese, 4.8 to 5.2 percent of chromium, 2 to 2.6 percent of molybdenum, 0.3 to 0.7 percent of vanadium, 0.002 to 0.015 percent of phosphorus, 0.0005 to 0.002 percent of sulfur, 0.0002 to 0.0004 percent of oxygen and 0.002 to 0.006 percent of nitrogen.
Furthermore, the average notch impact performance KV2 of the die steel forging is more than or equal to 20J, the average unnotched impact work is AK more than or equal to 380J, the band grade is SA1 or SA2 or SB1 or SB2, the tissue grade is AS1 or AS2 or AS3 or AS4, and the grain size is more than or equal to 8.
Further, nickel element, tungsten element and cobalt element can be added to improve the comprehensive performance of the die steel forging; preferably, the sum of the mass ratios of the tungsten element, the cobalt element and the nickel element is not more than 2%.
Oxygen is easy to combine with aluminum in steel to produce Al2O3Brittle non-metallic inclusions, hard and brittle, in AL2O3Stress concentration is easily formed in steel around brittle inclusions, the stress concentration is a cracking crack source of a die, the defects of die surface stripping, cracking and the like can be caused after the crack source develops in the manufactured die under the working condition of cold and hot circulation, the service life of the die is influenced, oxygen is controlled to be at an extremely low level, a die steel forging with high cleanliness is obtained, and the comprehensive performance of the die steel forging can be greatly improved. The influence of the content of oxygen element on the impact energy of the mold is shown in Table 1, in the case where the other components are substantially the same.
TABLE 1
Nitrogen is easy to combine with C to generate coarse carbonitride, the carbonitride is not easy to break in the hot working process and can crack a matrix to induce cracks, meanwhile, the large-size carbonitride has high stability and can exist in a tempered structure to cause the carbonitride segregation to cause the difference of the anisotropic properties of the alloy, so that the comprehensive properties of the material are reduced. The influence of the nitrogen content on the impact energy of the mold is shown in Table 2, in the case where the other components are substantially the same.
TABLE 2
As can be seen from the above table, the lower the contents of oxygen and nitrogen, the more beneficial the performance improvement of the die steel forging, and thus, the present invention provides the hot work die steel forging.
On the other hand, the invention provides a preparation method of the die steel forging, which comprises the following steps: smelting raw materials of iron and alloy by using a vacuum induction furnace to obtain a steel ingot; or smelting the raw material iron and the alloy by adopting a vacuum induction furnace, casting into the electrode steel bar, and carrying out vacuum consumable smelting to obtain a consumable steel ingot; and forging the steel ingot or the consumable steel ingot to obtain the die steel forging.
Preferably, the smelting temperature of the raw material iron smelted by the vacuum induction furnace is 1500-1650 ℃.
Further, the raw material iron comprises an iron alloy containing molybdenum, vanadium and chromium elements. In the iron alloy, the mass ratio of the sulfur element is not more than 0.005%, and the mass ratio of the phosphorus element is not more than 0.01%.
Furthermore, the mass ratio of sulfur in the raw material iron is not more than 0.001%, and the mass ratio of phosphorus is not more than 0.003%.
Further, the smelting conditions of the vacuum consumable smelting are as follows: the ultimate vacuum degree is less than or equal to 1.3Pa, the air leakage rate is less than or equal to 0.9Pa/min, the arcing time is 60-150min, the feeding time is 60-150min, and the melting speed is 5-15 kg/min. The electrode steel bar is scalped within 24 hours of vacuum consumable smelting, so that oxide skin is removed, and oxygen brought into the steel material is reduced.
Further, the preparation method of the ultralow oxygen nitrogen hot work die steel forging further comprises the following steps: remelting in an electroslag furnace under the condition of protective atmosphere, and performing desulfurization treatment to obtain the electrode rod for vacuum consumable smelting.
Preferably, when the electroslag furnace is used for remelting, the surface oxide layer of the electrode steel bar needs to be removed in advance, the actual melting speed fluctuates above and below the set melting speed value, and the fluctuation range is controlled within 5%. The remelting in the electroslag furnace aims at removing impurities, particularly sulfur elements, of the electrode steel bar, and 70% of the sulfur elements can be removed.
Further, the forging comprises the steps of: homogenizing, forging and upsetting, drawing and forging, stress relief annealing and superfine treatment.
The conditions for the homogenization treatment were as follows: the temperature is controlled to 1260-.
The forging upsetting operation comprises the following steps: firstly upsetting a die steel ingot with the temperature of 1160-1200 ℃ on a press along the height direction to 50-60% of the height, then axially drawing out the ingot with the height-diameter ratio of 2-2.5, returning to the furnace and heating for 2-4 hours, then upsetting for the second time and axially drawing out the ingot according to the proportion of the first upsetting, returning to the furnace and keeping the temperature for 2-4 hours, upsetting for the third time and axially drawing out the ingot according to the proportion of the first upsetting, and keeping the final forging temperature above 800 ℃ all the time.
The drawing and forging operation steps are as follows: keeping the finish forging temperature at 800-.
The stress relief annealing comprises the following operation steps: and heating the forging to 850-880 ℃, annealing and preserving heat for 12-24 hours, eliminating stress, cooling along with the furnace, and then cutting the head and the tail.
The operation steps of the ultra-fining treatment are as follows: keeping the temperature at 1020 and 1050 ℃ for 2-3 hours/100 mm, quenching the mixture to room temperature, raising the temperature to 860 ℃ for isothermal temperature of 6-10 hours/100 mm, cooling the mixture to 750 +/-10 ℃ for isothermal temperature of 2-10 hours, and then cooling the mixture to below 500 ℃ along with the furnace and discharging the mixture.
On the other hand, the invention also provides an automobile die-casting spare and accessory part die, which adopts the die steel forging provided by the invention.
In summary, the above embodiments of the present application may have one or more of the following advantages or benefits:
(1) smelting raw material iron by adopting a vacuum induction furnace and/or a vacuum consumable electrode furnace, reducing the content of harmful elements and obtaining the ultralow-oxygen-nitrogen medium-high heat-resistant hot-work die steel forging.
(2) The content of oxygen element, nitrogen element and sulphur element of the medium and high heat resistance hot work die steel forging is 0.0002-0.0008%, 0.002-0.006% and 0.0001-0.005%.
(3) The medium-high heat resistance hot work die steel forging provided by the invention is greatly improved in the aspects of high-temperature toughness, wear resistance and high-temperature fatigue performance, and is particularly reflected in that the indexes such as key impact energy, structure and the like are greatly improved.
(4) And (3) carrying out high-temperature homogenization treatment, three-upsetting three-drawing forging and superfine treatment on the die steel forging by adopting a proper forging process to obtain the die steel forging, and the die steel forging can greatly prolong the service life of the die when being applied to the production of die-casting dies of automobile parts.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a microstructure view of a die steel forging according to a first embodiment of the present invention.
FIG. 2 is a banded microstructure view of a die steel forging provided in accordance with a second embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The working temperature of the die made of the die steel forging provided by the embodiment of the invention is generally 500-700 ℃, and the die belongs to middle-high heat-resistant hot-work die steel, and the middle heat-resistant hot-work die steel is characterized in that the carbon content is middle carbon, the mass fraction of the middle heat-resistant hot-work die steel is 0.3-0.5%, alloy elements such as Cr, Mn, Si, Ni, W, Mo and V are added to improve the performance of the die steel forging, the general mass fraction of Cr is 3-5%, the mass fraction of Mo is 1-3%, the hardenability of the steel is greatly improved by Cr and Mo, M2C type carbide dispersed and precipitated during martensite tempering of molybdenum can improve the high-temperature strength, meanwhile, the recrystallization temperature of a matrix can be improved by molybdenum, the high-temperature strength is also favorable, but the toughness is not favorable when the content is too much, so that the molybdenum content is adjusted to be 2.00-3.2%; when the content of silicon is more than 0.6 percent, particularly when the silicon and manganese exist in the steel at the same time, the silicon is easy to segregate, so the content of the silicon is adjusted to be 0.1 to 0.5 percent, and the V element ensures that the steel has better anti-overheating sensitivity, thereby the hot hardness and the hot strength can be improved, and the steel still has higher hardness, hot strength and wear resistance when the working temperature reaches 500-600 ℃, and the highest temperature can reach 650 ℃. High heat resistance hot work die steel: the high heat-resistant hot-work die steel forging has high content of alloy elements, the mass fraction of the alloy elements is 8-11%, and the steel has high heat resistance, namely high-temperature strength and high-temperature hardness, and can work at the high temperature of 600-700 ℃.
[ first embodiment ] A method for manufacturing a semiconductor device
The embodiment provides a preparation method of an ultralow-oxygen-nitrogen medium-high heat resistance hot work die steel forging, which comprises the following steps:
s10: soft iron and iron alloy containing molybdenum, vanadium and chromium are put into a vacuum induction furnace for smelting, the temperature is controlled at 1500-1650 ℃, and after the smelting, the iron alloy is cast into a mould to form the electrode steel bar. Wherein the mass ratio of sulfur element in the soft iron is 0.001%, and the mass ratio of phosphorus element is 0.0025%; the mass percentage of the sulfur element in the iron alloy is 0.004%, and the mass percentage of the phosphorus element in the iron alloy is 0.008%.
S20: carrying out electroslag remelting on the electrode steel bar under a protective atmosphere, wherein the melting speed is set to 900-950kg/h, and the fluctuation range is controlled within 5 percent; 1000-1200kg of reserved electrode steel bar starts feeding, and the total feeding time is not less than 100 minutes. The electroslag remelting can filter impurities in the electrode steel bar, particularly the desulfurizing capacity can theoretically remove 70%, corresponding sulfides can be greatly reduced, and the circular electroslag remelting electrode bar with the S content of 0.0009% can be obtained.
S30: remelting in a vacuum consumable furnace, and performing vacuum consumable on the electroslag remelting electrode rod, wherein the ultimate vacuum degree is less than or equal to 1.3Pa, the gas leakage rate is less than or equal to 0.9Pa/min, the arc starting time is 120-150min, the feeding time is 70-150min, and the melting speed is 8-10 kg/min. And cooling the smelted vacuum consumable die for 2-3 hours, then keeping the temperature in a heat-preserving barrel or furnace for 72 hours to obtain a consumable steel ingot, and forging to obtain a die steel forging.
The vacuum consumable electrode can filter impurities, particularly gas, in the electrode rod, and in the embodiment, the mass ratio of the nitrogen element is 0.003%, and the mass ratio of the oxygen element is 0.0003%.
Except for iron elements, the main elements of the die steel forging provided in the embodiment have the following mass ratio: 0.38% of carbon, 0.24% of silicon, 0.37% of manganese, 4.98% of chromium, 0.20% of nickel, 2.4% of molybdenum, 0.62% of vanadium, 0.015% of copper, 0.015% of aluminum, 0.0057% of phosphorus and 0.0008% of sulfur.
Referring to fig. 1, the organization is fine and rated AS2 according to the standards of the north american die casting association NADCA-207-.
Further, the forging comprises the following steps:
s40: and (6) homogenizing. Heating the consumable steel ingot at 1260 ℃ for 25 hours to dissolve carbides contained in the consumable steel ingot to obtain a homogeneous steel ingot; specifically, the homogenization treatment may be performed in a controlled atmosphere furnace or an inert gas shielded furnace, and the time and temperature of the homogenization treatment may be specifically set according to the weight of the steel ingot with reference to table 3.
TABLE 3
Note: t is weight unit ton and h is time unit hour.
S50: and forging and upsetting. Reducing the temperature of the homogenized steel ingot to 1180 +/-20 ℃, preserving the heat for 1-2 hours, upsetting the steel ingot on a press along the height direction of the steel ingot to 1300mm, axially drawing the steel ingot to 2200mm, returning the steel ingot to the furnace for heating for 2-4 hours, performing secondary upsetting and axial drawing, returning the steel ingot to the furnace for preserving the heat for 2-4 hours, performing third upsetting and axial drawing, and keeping the finish forging temperature above 800 ℃ all the time; preferably, the initial forging temperature in the forging process is 1180 ℃, the final forging temperature is 800 ℃, and the reduction rate of all intermediate forging passes is preferably more than 20% except for initial forging and final forging finishing, so that the requirement of realizing center through forging and the requirement of uniform structure of the whole section can be met.
S60: drawing and forging. And (3) carrying out drawing and forging on the steel ingot subjected to the three-time repeated upsetting until the final size is 280 x 900 flat, keeping the final forging temperature at 800 ℃, and carrying out air cooling or air cooling after forging until the temperature is about 350 ℃ and then carrying out furnace annealing.
S70: and (5) stress relief annealing. And putting the forged finished product module into a furnace for annealing, heating to 860 +/-10 ℃, preserving heat for 20 hours, and then cooling to below 500 ℃ at the speed of 30 ℃ per hour and discharging.
S80: heating the finished product module to 1020-; and obtaining the die steel forging.
[ second embodiment ]
The embodiment provides a preparation method of an ultralow oxygen nitrogen hot work die steel forging, which comprises the following steps:
s10: soft iron and iron alloy containing molybdenum, vanadium and chromium are put into a vacuum induction furnace for smelting, the temperature is controlled at 1500-1650 ℃, and after the smelting, the iron alloy is cast into a mould to form the electrode steel bar. Wherein the mass ratio of sulfur element in the soft iron is 0.001%, and the mass ratio of phosphorus element is 0.0025%; the mass ratio of the sulfur element in the iron alloy is 0.003 percent, and the mass ratio of the phosphorus element in the iron alloy is 0.009 percent.
S20: remelting in a vacuum consumable furnace, performing vacuum consumable remelting on the electrode steel bar, wherein the ultimate vacuum degree is less than or equal to 1.3Pa, the gas leakage rate is less than or equal to 0.9Pa/min, the arcing time is 60-80min, the feeding time is 44-78min, and the melting speed is 5-7 kg/min. And cooling the smelted vacuum consumable die for 2-3 hours, then keeping the temperature in a heat-preserving barrel or furnace for 72 hours to obtain a consumable steel ingot, and forging to obtain a die steel forging.
The vacuum consumable can filter impurities, particularly gas, in the electrode rod, and in the embodiment, the mass ratio of nitrogen element is 0.004%, and the mass ratio of oxygen element is 0.0003%.
Except for iron elements, the main elements of the die steel forging provided in the embodiment have the following mass ratio: 0.38% of carbon, 0.24% of silicon, 0.37% of manganese, 4.98% of chromium, 0.20% of nickel, 2.4% of molybdenum, 0.62% of vanadium, 0.015% of copper, 0.015% of aluminum, 0.008% of phosphorus, 0.0009% of sulfur, 0.0003% of oxygen and 0.004% of nitrogen.
Referring to fig. 2, according to the standards of the north american die casting association NADCA-207-.
Further, the forging comprises the following steps:
s30: and (6) homogenizing. Heating the consumable steel ingot at 1260 ℃ for 20 hours to dissolve carbides contained in the consumable steel ingot to obtain a homogeneous steel ingot; specifically, the homogenization treatment may be performed in a controlled atmosphere furnace or an inert gas shielded furnace, and the time and temperature of the homogenization treatment may be specifically set with reference to table 1 in the second embodiment in accordance with the weight of the steel ingot.
S40: and forging and upsetting. Reducing the temperature of the homogenized steel ingot to 1180 +/-20 ℃, preserving the heat for 1-2 hours, upsetting the steel ingot on a press along the height direction of the steel ingot to 1300mm, axially drawing the steel ingot to 2200mm, returning the steel ingot to the furnace for heating for 2-4 hours, performing secondary upsetting and axial drawing, returning the steel ingot to the furnace for preserving the heat for 2-4 hours, performing third upsetting and axial drawing, and keeping the finish forging temperature above 800 ℃ all the time; preferably, the initial forging temperature in the forging process is 1200 ℃, the final forging temperature is 800 ℃, and the reduction rate of all intermediate forging passes is preferably more than 25% except for initial forging and final forging finishing, so that the requirement of realizing center complete forging and the requirement of uniform structure of the whole section can be met.
S50: drawing and forging. And (3) drawing and forging the steel ingot subjected to the three-time repeated upsetting to the final size of 100 x 700 flat, keeping the final forging temperature of 800 ℃, and performing air cooling or air cooling after forging to about 350 ℃ and then annealing in a furnace.
S60: and (5) stress relief annealing. And putting the forged finished product module into a furnace for annealing, heating to 860 +/-10 ℃, preserving heat for 14 hours, and then cooling to below 500 ℃ at the speed of 30 ℃ per hour and discharging.
S70: heating the finished product module to 1020-; and obtaining the die steel forging.
The performance of the die steel forgings provided by the first embodiment and the second embodiment is tested, and the results are shown in tables 4 and 5.
TABLE 4
TABLE 5
[ third embodiment ]
The embodiment provides a preparation method of an ultralow-oxygen-nitrogen medium-high heat resistance hot work die steel forging, which comprises the following steps:
s10: after melting soft iron and iron alloy containing molybdenum, vanadium and chromium in a vacuum induction furnace, casting the soft iron and the iron alloy into a mold to form an electrode steel bar, carrying out electroslag remelting on the electrode steel bar under the condition of protective atmosphere to obtain an electroslag steel ingot, and forging the electroslag steel ingot to obtain a mold steel forging; the forging method in this embodiment is the same as that in the first embodiment.
Wherein the mass ratio of sulfur element in the soft iron is not more than 0.001%, and the mass ratio of phosphorus element is not more than 0.003%. In the iron alloy, the mass ratio of the sulfur element is not more than 0.005%, and the mass ratio of the phosphorus element is not more than 0.01%.
The die steel forging provided by the embodiment comprises the following elements in percentage by mass: 0.39% of carbon, 0.25% of silicon, 0.38% of manganese, 5.18% of chromium, 0.10% of nickel, 2.4% of molybdenum, 0.62% of vanadium, 0.03% of titanium, 0.015% of copper, 0.015% of aluminum, 0.009% of phosphorus, 0.0009% of sulfur, 0.0004% of oxygen and 0.0046% of nitrogen.
The die steel forging provided by the embodiment has the hardness of 45HB, the unnotched impact energy of 380J, the notched impact energy of 28J, the banded grade of SB2, the structure grade of AS3 and the grain size of 8.
[ fourth example ] A
The embodiment provides a preparation method of an ultralow oxygen nitrogen hot work die steel forging, which comprises the following steps:
s10: the raw material iron and the ferroalloy containing molybdenum, vanadium and chromium are put into a vacuum induction furnace for smelting, the temperature is controlled at 1500-1650 ℃, and the molten raw material iron and the ferroalloy are cast into a mold to form a steel ingot. The steel ingot is forged to obtain a die steel forging, and the forging method of the embodiment refers to the second embodiment.
Wherein the mass ratio of sulfur element in the raw material iron is not more than 0.001%, and the mass ratio of phosphorus element is not more than 0.003%. In the iron alloy, the mass ratio of the sulfur element is not more than 0.005%, and the mass ratio of the phosphorus element is not more than 0.01%. The die steel forging provided by the embodiment comprises the following elements in percentage by mass: 0.37% of carbon, 0.4% of silicon, 0.38% of manganese, 5.1% of chromium, 0.30% of nickel, 2.5% of molybdenum, 0.65% of vanadium, 0.015% of copper, 0.015% of aluminum, 0.010% of phosphorus, 0.002% of sulfur, 0.0005% of oxygen and 0.0057% of nitrogen.
The die steel forging provided by the embodiment has the hardness of 45HB, the unnotched impact energy of 360J, the notched impact energy of 25J, the banded grade of SB2, the structure grade of AS3 and the grain size of 8.
[ fifth embodiment ]
The content of oxygen and nitrogen in the ultralow-oxygen-nitrogen medium-high-heat-resistance hot work die steel forging provided by the invention is low, for explaining the performance effect, the technical scheme provided by the first embodiment is referred to, the element content is adjusted, and under the condition that other components are basically the same, the influence of the content of oxygen on the impact energy of the die steel is shown in table 6.
TABLE 6
Oxygen is easy to combine with aluminum in steel to produce Al2O3Brittle non-metallic inclusions, hard and brittle, in AL2O3Stress concentration is easily formed in steel around brittle inclusions, the stress concentration is a cracking crack source of a die, the defects of die surface stripping, cracking and the like can be caused after the crack source develops in the manufactured die under the working condition of cold and hot circulation, the service life of the die is influenced, oxygen is controlled to be at an extremely low level, a die steel forging with high cleanliness is obtained, and the comprehensive performance of the die steel forging can be greatly improved.
The influence of the nitrogen content on the impact energy of the mold is shown in Table 7, in the case where the other components are substantially the same.
TABLE 7
Nitrogen is easy to combine with C to generate coarse carbonitride, the carbonitride is not easy to break in the hot working process and can crack a matrix to induce cracks, meanwhile, the large-size carbonitride has high stability and can exist in a tempered structure to cause the carbonitride segregation to cause the difference of the anisotropic properties of the alloy, so that the comprehensive properties of the material are reduced. As can be seen from the table, the lower the content of oxygen and nitrogen elements, the more beneficial the performance improvement of the die steel forging.
[ sixth embodiment ]
This embodiment provides a method for producing an ultra low oxygen nitrogen hot work die forging, which is based on any of the above embodiments, and further performs surface treatment on the ultra low oxygen nitrogen hot work die forging obtained by the production. The purpose of this embodiment is to further improve the high temperature strength of ultralow oxygen nitrogen hot work mould forging, high wearability.
The embodiment comprises the following steps:
s100, carrying out surface treatment on a die manufactured by a die forging obtained by forging a steel ingot or a consumable steel ingot.
Specifically, step S100 includes:
s110, polishing a die forging obtained by forging a steel ingot or a consumable steel ingot by using silicon carbide, and cleaning and drying the die forging;
s120, shot blasting is carried out on the die forging obtained in the S110 for 15min to 20min by adopting a stainless steel shot with the diameter of 0.2mm to 0.4mm under the pressure of 0.8MPa to 1.2MP, and cleaning and drying are carried out;
s130, heating and preserving the nitrified salt at the temperature of 700 ℃ for 6 to 8 hours, and then cooling to 500 ℃ at the speed of 2 to 2.5 ℃/min to obtain the nitrified salt subjected to preheating treatment;
s140, embedding the die forging obtained in the step S120 in the nitrified salt obtained in the step S130, performing nitriding treatment for 6 to 6.5 hours at the temperature of 550 to 560 ℃, and cleaning and drying.
In the above steps, the nitronium salt has the following components:
urea: 30 to 40 parts by mass;
silicon nitride: 10 to 20 parts by mass;
lithium carbonate: 10 to 15 parts by mass;
terbium nitrate: 5 to 10 parts by mass;
cerium nitrate: 5 to 10 parts by mass;
alkyl aromatic hydrocarbon sulfonates: 5 to 10 parts by mass;
amino silane: 5 to 10 parts by mass.
The nitriding treatment can cause nitrogen atoms to permeate into the surface layer of the die forging. The permeated nitrogen is combined with metal elements in the steel from the surface to the inside to form metal nitrides, and the nitrides have high hardness and thermal stability, so that the nitrided product can obtain high surface hardness, wear resistance, fatigue strength and high temperature resistance. The nitriding treatment of the present example was performed after the shot peening treatment. The shot blasting treatment can change the surface roughness of the die forging, so that the nitriding treatment effect of the die forging is effectively improved. The nitriding salt containing urea, silicon nitride, lithium carbonate, terbium nitrate and cerium nitrate provided by the embodiment can form uniform dislocation and defects on the surface of the die forging. In particular, the addition of terbium nitrate and cerium nitrate improves the surface activity of the die forging and increases a nitriding channel. According to the embodiment, the uniform nitrided layer can be formed on the surface of the die forging, so that the die forging has good surface performance.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. The ultra-low oxygen nitrogen medium-high heat resistance hot work die steel forging is characterized by comprising the following elements in percentage by mass except iron and inevitable impurities: 0.3 to 0.45 percent of carbon, 0.1 to 0.5 percent of silicon, 0.2 to 0.8 percent of manganese, 4.5 to 5.5 percent of chromium, 2 to 3.2 percent of molybdenum, 0.3 to 1 percent of vanadium, 0.002 to 0.02 percent of phosphorus, 0.0001 to 0.005 percent of sulfur, 0.0002 to 0.0008 percent of oxygen and 0.002 to 0.006 percent of nitrogen;
the average notch impact performance KV2 of the die steel forging is more than or equal to 15J,
the average unnotched impact energy AK is more than or equal to 350J,
the band classes are SA1 or SA2 or SB1 or SB2,
the organization level is AS1 or AS2 or AS3 or AS4 or AS5 or AS6,
the grain size is 7 or more.
2. The die steel forging of claim 1,
the mass ratio of the nitrogen element is 0.002-0.003 percent, and/or
The mass percentage of the oxygen element is 0.0002-0.0004%.
3. The die steel forging of claim 1,
the average notch impact performance KV2 of the die steel forging is more than or equal to 20J,
the average unnotched impact energy AK is more than or equal to 380J,
the band classes are SA1 or SA2 or SB1 or SB2,
the organization level is AS1 or AS2 or AS3 or AS4,
the grain size is more than or equal to 8.
4. The die steel forging of claim 1, further comprising nickel, tungsten, and cobalt;
the sum of the mass ratios of the nickel element, the tungsten element and the cobalt element is not more than 2%.
5. The preparation method of the ultralow-oxygen-nitrogen medium-high heat resistance hot work die steel forging as claimed in any one of claims 1 to 4, characterized by comprising the following steps of:
smelting raw materials of iron and alloy by using a vacuum induction furnace to obtain a steel ingot;
or smelting the raw material iron and the alloy by adopting a vacuum induction furnace, casting into an electrode steel bar, and carrying out vacuum consumable smelting to obtain a consumable steel ingot;
and forging the steel ingot or the consumable steel ingot to obtain the die steel forging.
6. The method according to claim 5, wherein the raw material iron contains not more than 0.001% by mass of sulfur element and not more than 0.003% by mass of phosphorus element.
7. The preparation method according to claim 5, wherein the smelting conditions of the vacuum consumable smelting are as follows: the ultimate vacuum degree is less than or equal to 1.3Pa, and the air leakage rate is less than or equal to 0.9 Pa/min.
8. The method of manufacturing according to claim 5, further comprising: remelting in an electroslag furnace under the condition of protective atmosphere, and performing desulfurization treatment.
9. The method of manufacturing according to claim 5, wherein the forging comprises the steps of: homogenizing, forging and upsetting, drawing and forging, stress relief annealing and superfine treatment.
10. An automobile die-casting part die, characterized in that the die steel according to any one of claims 1 to 4 is used.
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