AU2021366577A1 - Carburized workpiece and preparation method therefor - Google Patents
Carburized workpiece and preparation method therefor Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title description 7
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 70
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 67
- 230000007423 decrease Effects 0.000 claims abstract description 5
- 238000010791 quenching Methods 0.000 claims description 50
- 230000000171 quenching effect Effects 0.000 claims description 43
- 238000005496 tempering Methods 0.000 claims description 28
- 238000005255 carburizing Methods 0.000 claims description 20
- 239000000463 material Substances 0.000 claims description 13
- 238000000034 method Methods 0.000 claims description 12
- 238000009792 diffusion process Methods 0.000 claims description 10
- 230000003247 decreasing effect Effects 0.000 claims description 8
- 229910002651 NO3 Inorganic materials 0.000 claims description 7
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 7
- 230000001681 protective effect Effects 0.000 claims description 7
- 238000010438 heat treatment Methods 0.000 claims description 4
- 239000010410 layer Substances 0.000 abstract description 61
- 229910001566 austenite Inorganic materials 0.000 abstract description 13
- 230000000717 retained effect Effects 0.000 abstract description 13
- 238000005553 drilling Methods 0.000 abstract description 9
- 239000011435 rock Substances 0.000 abstract description 4
- 239000002344 surface layer Substances 0.000 abstract description 4
- 230000002035 prolonged effect Effects 0.000 abstract description 3
- 238000004227 thermal cracking Methods 0.000 abstract 1
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 16
- 238000005242 forging Methods 0.000 description 16
- 238000001816 cooling Methods 0.000 description 10
- 229910052757 nitrogen Inorganic materials 0.000 description 8
- 238000003754 machining Methods 0.000 description 7
- 229910045601 alloy Inorganic materials 0.000 description 6
- 239000000956 alloy Substances 0.000 description 6
- 150000003839 salts Chemical class 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical group OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000001000 micrograph Methods 0.000 description 2
- 229910000746 Structural steel Inorganic materials 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
- C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
- C23C8/20—Carburising
- C23C8/22—Carburising of ferrous surfaces
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
- C21D1/20—Isothermal quenching, e.g. bainitic hardening
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
- C21D1/607—Molten salts
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/22—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for drills; for milling cutters; for machine cutting tools
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
- C23C8/80—After-treatment
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
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Abstract
Provided is a carburized workpiece. From a surface to the inside, the carbon concentration of a carburized layer of the carburized workpiece first increases and then decreases, the surface carbon concentration of the carburized layer is not lower than 0.46%, the highest carbon concentration of the carburized layer is 0.58-0.68%, and a carburization depth reaching the highest carbon concentration is 15-50% of the total depth of the carburized layer. Compared with the prior art, by means of controlling a change curve of the carbon concentration of the carburized layer and also reducing the carbon concentration of an outer surface layer, the amount of retained austenite on the outermost layer is effectively controlled, the hardness of the outermost layer is reduced, the run-in degree of a carburized workpiece spline and a clamping drill sleeve spline is increased, and the thermal cracking phenomenon of the carburized layer under high-frequency friction is reduced, such that the probability of breakage of the carburized workpiece spline can be effectively reduced, the service life of the carburized workpiece can be greatly prolonged, and the carburized workpiece is widely used in the field of rock drilling with high-frequency high-load down-the-hole drill bits.
Description
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[0001] This application claims the priority of Chinese Patent Application No. 202011138231.0, filed with the China National Intellectual Property Administration on October 22, 2020, and titled with "CARBURIZED WORKPIECE AND PREPARATION METHOD THEREFOR", which is hereby incorporated by reference in its entirety.
[0002] The present belongs to the technical field of material and workpiece preparation, and in particular to a carburized workpiece and a preparation method therefor.
[0003] With the improvement of air compressor and rock drilling equipment technology, the output air pressure of the drilling rig is getting higher and higher, resulting in higher drilling frequency, higher impact force on the drill bit, and greater probability of breakage of drill bit spline.
[0004] Failure research shows that the crack source of the breakage on the carburized drill bit spline is caused by the secondary hardening caused by the frictional heat between the spline of the drill bit and the spline of the drive chuck. The higher the concentration of the carburized layer of the spline of the drill bit, the higher the austenite content retained in the structure, and the greater the risk of thermal crack caused by secondary hardening. However, in the field of down-the-hole drill bits, the carburizing concentration in carburized drill bits is generally controlled at a high level, and there is often much retained austenite in the carburized layer. Therefore, under the continuously increasing working air pressure, the probability of thermal crack caused by friction at the spline of the drill bit continues to increase, and the probability of breakage of the spline also continues to increase. In addition, at the beginning, since the contact between the spline of the drill bit and the spline of the drive chuck is linear contact, the surface hardness on the spline of the drill bit will be higher, thus it is more difficult for the running-in between the spline of the drill and the spline of the drive chuck, and it is easier to cause localized overload, Furthermore, the generation and propagation of thermal cracks are accelerated.
[0005] In view of this, the technical problem to be solved by the present invention is to provide a carburized workpiece and a preparation method that can effectively reduce the probability of spline breakage.
[0006] The present invention provides a carburized workpiece. The carburized layer of the carburized workpiece, from surface to inside, has a carbon concentration first increasing and then decreasing. The surface carbon concentration of the carburized layer is not lower than 0.46%, the highest carbon concentration of the carburized layer is 0. 5 8 -0. 6 8 %, and a carburization depth reaching the highest carbon concentration is 15-50% of the total depth of the carburized layer.
[0007] Preferably, the carburized depth reaching the highest hardness in the carburized layer is no more than 0.5 mm, and the hardness in the carburized layer decreases gradually after reaching the highest hardness.
[0008] Preferably, a total depth of the carburized layer is 1.6-2.2 mm; the carburized depth reaching the highest carbon concentration is 0.4-1.1 mm.
[0009] Preferably, a material of the carburized workpiece is selected from the group consisting of 18CrNi3Mo, 23CrN3iMo and 30CrNi4Mo.
[0010] The present invention further provides a method for preparing a carburized workpiece, comprising:
[0011] SI) carburizing a workpiece at a temperature of 920°C-930°C, a boost carbon potential of 1%-1.15% and a diffusion carbon potential of 0.78%-0.85%;
[0012] S2) quenching the carburized workpiece;
[0013] S3) performing high-temperature tempering on the quenched workpiece;
[0014] S4) performing isothermal salt-bath quenching treatment on the high-temperature tempered workpiece;
[0015] S5) performing low-temperature tempering on the isothermal salt-bath quenched workpiece to obtain a carburized workpiece.
[0016] Preferably, in the step Si), the boost stage is performed for 4.5-7 h; and the diffusion stage is performed for 4-6 h.
[0017] Preferably, in the step Sl), after the carburizing treatment, the workpiece is cooled to 855°C or lower with the furnace, and then cooled to room temperature by gas quenching.
[0018] Preferably, in the step S2), the quenching is performed at a temperature of 830°C-850°C and a protective carbon potential of 0.45%-0.5% for 3-5 h.
[0019] Preferably, in the step S3), the high-temperature tempering is performed at a temperature of 660°C-700°C in an inert atmosphere for 5-7 h.
[0020] Preferably, in the step S4), a salt-bath quenching in the isothermal salt-bath quenching treatment is performed at a heating temperature of 790°C-850°C for 25-90 min, and a nitrate bath isothermal quenching in the isothermal salt-bath quenching treatment is performed at a temperature of 230°C-280° for 20-70 min; in the step S5), the low-temperature tempering is performed at 180°C-230°C for 4-6 h.
[0021] The present invention provides a carburized workpiece. The carburized layer of the carburized workpiece, from surface to inside, has a carbon concentration first increasing and then decreasing, wherein the carbon concentration on the surface is no less than 0.46%, the highest carbon concentration is 0.58%-0.68 %, and a carburized depth reaching the highest carbon concentration is 15%-50% of the total depth of the carburized layer. Compared with the existing technology, by means of controlling a change curve of the carbon concentration of the carburized layer and reducing the carbon concentration of an outer surface layer, the present invention can effectively control the amount of retained austenite on the outermost layer, reduce the hardness of the outermost layer, increase the running-in degree of the spline of the carburized workpiece and the spline of the drive chuck, and reduce the thermal crack phenomenon of the carburized layer under high-frequency friction, such that the probability of breakage of the spline of the carburized workpiece can be effectively reduced, the service life of the carburized workpiece can be greatly prolonged, and the carburized workpiece is widely used in the field of rock drilling using high frequency high-load down-the-hole drill bits.
[0022] FIG. 1 shows the gradient curves of the carburizing concentration and hardness of the carburized layer of HD55A-152 drill bit obtained in the Example 1 of the present invention;
[0023] FIG. 2 shows the metallographic structure micrograph of the carburized layer of HD55A 152 drill bit obtained in Example 1 of the present invention.
[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the examples of the present invention. Apparently, the described examples are only some of the embodiments of the present invention, but not all of them. Based on the examples of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.
[0025] The present invention provides a carburized workpiece, which has a carburized layer, from surface to inside, having a carbon concentration first increasing and then decreasing, wherein the carbon concentration on the surface is not less than 0.46%, the highest carbon concentration is 0.58%-0.68 %, and a carburized depth reaching the highest carbon concentration is 15%-50% of the total depth of the carburized layer.
[0026] In the present invention, the carburized workpiece is preferably a carburized drill bit; the carburized workpiece is preferably formed by a high-strength structural steel; a material of the carburized workpiece is more preferably selected from the group consisting of 18CrNi3Mo, 23CrN3iMo and 30CrNi4Mo; the carburized drill bit has a spline shank with a diameter of preferably 50-180 mm, and an insert bit with a diameter of preferably 100-380 mm.
[0027] The surface of the carburized workpiece is a carburized layer; the carburized layer, from surface to inside, has a carbon concentration first increasing and then decreasing, i.e., the carbon concentration distribution curve is in a shape of analogous parabola. The carbon concentration on the surface of the carburized layer is preferably the concentration at 0.2 mm. The carbon concentration on the surface is preferably 0.48%-0.5%. The carbon concentration on the surface is preferably the concentration at 0.2 mm from the surface layer. The highest carbon concentration of the carburized layer is preferably 0.60%-0.68%, more preferably 0.62%-0.66%, further more preferably 0.62%-0.65%. In the carburized layer, the carburized depth reaching the highest carburizing concentration is preferably 20%-45%, more preferably 25%-40%, further more preferably 28%-38%, most preferably 29.4%-35.2% of the total depth of the carburized layer. In the present invention, the carburized depth reaching the highest carbon concentration is preferably 0.4-1.1 mm, more preferably 0.4-0.8 mm, further more preferably 0.4-0.7 mm, most preferably 0.5-0.6 mm. Atotal depth of the carburized layer is preferably1 -1.5%, more preferably1%-1.4%, further more preferably 1%-1.3%, yet further more preferably 1.1%-1.2%, most preferably 1.1% 1.15% of the diameter of the carburized workpiece. In the present invention, a total depth of the carburized layer is preferably 1.6-2.2 mm, more preferably 1.6-2 mm, further more preferably 1.6 1.8 mm, most preferably 1.7 mm.
[0028] According to the present invention, the carburized depth reaching the highest hardness in the carburized layer is preferably no more than 0.5 mm, more preferably 0.25-0.45 mm, further more preferably 0.3-0.4 mm, most preferably 0.3 mm. After reaching the highest hardness in the carburized layer, the hardness will gradually decrease. In the present invention, the hardness preferably decreases in a gradient after reaching the highest hardness in the carburized layer.
[0029] The metallographic structure of the carburized layer of the carburized workpiece provided by the present invention has almost no retained austenite in the 50-500 times microscope view.
[0030] In the present invention, by means of controlling a change curve of the carbon concentration of the carburized layer and reducing the carbon concentration of an outer surface layer, the amount of retained austenite on the outermost layer is effectively controlled, the hardness of the outermost of the drive chuck is increased, and the thermal crack phenomenon of the carburized layer under high-frequency friction is reduced, such that the probability of breakage of the spline of the carburized workpiece can be effectively reduced, the service life of the carburized workpiece can be greatly prolonged, and the carburized workpiece is widely used in high-frequency and high-load down-the-hole drill bits in the field of rock drilling.
[0031] The present invention further provides a method for preparing the above carburized workpiece, comprising: Si) carburizing a workpiece at a temperature of 920°C-930°C, a boost carbon potential of 1%-1.15% and a diffusion carbon potential of 0.78%-0.85%; S2) quenching the carburized workpiece; S3) performing high-temperature tempering on the quenched workpiece; S4) performing isothermal salt-bath quenching treatment on the high-temperature tempered workpiece; S5) performing low-temperature tempering on the isothermal salt-bath quenched workpiece to obtain a carburized workpiece.
[0032] The present invention has no special limitation on the sources of all raw materials, which can be commercially available.
[0033] In the present invention, the workpiece can be prepared according to methods well-known to those skilled in the art, preferably obtained by blanking, forging and machining; where the forging is performed at an initial forging temperature of preferably 1180°C-1250°C and a final forging temperature of preferably 870°C-890°C.
[0034] The workpiece is carburized at a temperature of preferably 922°C-928°C, more preferably 924°C-926°C, further more preferably 925°C; the boost carbon potential is preferably 1.05%-1.15%, and the boost stage is performed for preferably 4.5-7 h, more preferably 5-6 h; the diffusion carbon potential is preferably 0.78%-0.83%, and the diffusion stage is performed for preferably 4-6 h, more preferably 4.5-5 h. The carburizing agent in the carburizing treatment is preferably methanol and acetone, and the combination of the two can control the carbon potential in the carburizing process.
[0035] After the carburizing treatment, the workpiece is preferably cooled to 855°C or lower with the furnace, and then cooled to room temperature by gas quenching; where the gas quenching is performed using high-pressure nitrogen as a medium to realize rapid cooling.
[0036] The carburized workpiece is subjected to quenching treatment at a temperature of preferably 830°C-850°C and a protective carbon potential of preferably 0.45%-0.5% for preferably 3-5 h. After the quenching treatment, the workpiece is preferably cooled using a rapid-quenching cooling oil.
[0037] The quenched workpiece is subjected to high-temperature tempering at a temperature of preferably 660°C-700°C and preferably in an inert atmosphere for preferably 5-7 h; wherein the inert atmosphere is preferably nitrogen.
[0038] After the high-temperature tempering treatment, the workpiece is preferably machined to obtain a carburized workpiece of a specific size, which is then subjected to a isothermal salt-bath quenching treatment; where a salt-bath quenching in the isothermal salt-bath quenching treatment is performed at a heating temperature of preferably 790°C-850°C, more preferably 800°C-830°C for preferably 25-90 min, more preferably 35-60 min, further more preferably 40-50 min, most preferably 40-45 min; and a nitrate bath isothermal quenching in the isothermal salt-bath quenching treatment is performed at a temperature of preferably 230°C-280° for preferably 20-70 min, more preferably 30-50 min, further more preferably 30-45 min, most preferably 35-40 min.
[0039] The workpiece after isothermal salt-bath quenching treatment is subjected to low temperature tempering at a temperature of preferably 180°C-230°C for preferably 4-6 h. After the low-temperature tempering, the workpiece is preferably taken out of the furnace and air-cooled to obtain a carburized workpiece.
[0040] The present invention precisely controls the key process parameters of the heat treatment process to obtain a carburized layer with a carbon concentration showing an analogous parabolic gradient change and having no retained austenite near the surface, thereby reducing the key influencing factors of the thermal crack caused by the friction of the spline of the drill bit and promoting the matching degree of the spline and the drive chuck, and effectively reducing the probability of the breakage of the spline of the drill bit.
[0041] The selection of the temperature and carbon potential in the carburizing treatment, the selection of quenching temperature, carbon potential and cooling method, and the selection of temperature of the high-temperature tempering and protective atmosphere are the keys to obtain a carbon concentration gradient changing in an analogous parabolic curve, and are the prerequisite to effectively control the amount of retained austenite near the surface of the carburized layer. The selection of the temperature of the salt bath in the salt-bath quenching and the temperature of the nitrate bath isothermal quenching, and the selection of the temperature of the high-temperature tempering and cooling method are key measures to further effectively control the retained austenite.
[0042] In order to further illustrate the present invention, the carburized workpiece provided by the present invention and the preparation method thereof are described in detail below in conjunction with examples.
[0043] The reagents used in the following examples are all commercially available.
Example 1
[0044] 23CrNi3Mo was used as base material of the drill bit, which was subjected to blanking, forging, machining, carburizing treatment, quenching treatment, high-temperature tempering, machining, isothermal salt-bath quenching, low-temperature tempering, drilling alloy insert holes and inserting alloy inserts to prepare a HD55A-152 drillbit. The forging was performed at an initial forging temperature of 1180°C and a final forging temperature of 870°C. The carburizing was performed at a temperature of 925°C, at a boost carbon potential of 1.05% for 6 h, and at a diffusion carbon potential of 0.78% for 5 h. After cooling to 855°C with the furnace, the resulting material was cooled to room temperature by gas-quenching using the high-pressure nitrogen as a medium. The quenching was performed using a rapid-quenching cooling oil as a medium at a temperature of 850°C and a protective carbon potential of 0.45% for 3 h. The high-temperature tempering was performed at a temperature of 700°C for 5 h under nitrogen protection. The salt bath was performed at a temperature of 830°C for 40 min, and the nitrate bath isothermal quenching was performed at a temperature of 230°C for 35 min. The low-temperature tempering was performed at 180°C for 4 h. Then the material was taken out of the furnace and air-cooled.
[0045] The carburizing concentration and hardness of the carburized layer of the HD55A-152 drill bit obtained in Example 1 were analyzed to obtain carbon concentration and hardness curves. The results are shown in FIG. 1.
[0046] The HD55A-152 drill bit obtained in Example 1 was analyzed using a metallographic microscope to obtain a metallographic structure micrograph of the carburized layer, as shown in FIG. 2. It can be seen from FIG. 2 that there was almost no retained austenite in the metallographic structure in 500 times metallographic microscopic view.
[0047] The test results of the carburized layer show that the carbon concentration gradient of the carburized layer was in a shape of analogous parabola, the concentration at 0.2 mm from the surface was 0.48%, the highest carbon concentration was 0.62%, the carburized depth reaching the highest concentration was 0.6 mm, the total depth of the carburized layer was 1.7 mm, and the carburized depth reaching the highest hardness in the carburized layer was 0.3 mm, and the hardness of the carburized layer gradually decreased after reaching the highest hardness; there was almost no retained austenite in the metallographic structure in 500 times metallographic microscopic view. 50 test drill bits were tested under such working condition that the proportion of bit breakage was 20%. No breakage occurred.
Example 2
[0048] 30CrNi3Mo was used as the base material of the drill bit, which was subjected to blanking, forging, machining, carburizing treatment, quenching treatment, high-temperature tempering, machining, isothermal salt-bath quenching, low-temperature tempering, drilling alloy insert holes and inserting alloy inserts to prepare a HD55A-152 drill bit. The forging was performed at an initial forging temperature of 1180°C and a final forging temperature of 870°C. The carburizing was performed at a temperature of 925°C, at a boost carbon potential of 1.15% for 5 h and at a diffusion carbon potential of 0.80% for 4.5 h. After cooling to 855°C with the furnace, the resulting material was cooled to room temperature by gas-quenching using the high-pressure nitrogen as a medium. The quenching was performed using a rapid-quenching cooling oil as a medium at a temperature of 830°C and a protective carbon potential of 0.50% for 3 h. The high-temperature tempering was performed at a temperature of 680°C for 5 h under nitrogen protection. The salt bath was performed at a temperature of 810°C for 45 min, and the nitrate bath isothermal quenching was performed at a temperature of 260°C for 40 min. The low-temperature tempering was performed at 230°C for 4 h. Then the material was taken out of the furnace and air-cooled.
[0049] The test results of the carburized layer show that the carbon concentration gradient of the carburized layer was in a shape of analogous parabola, the concentration at 0.2 mm from the surface was 0.50%, the highest carbon concentration was 0.65%, the carburized depth reaching the highest concentration was 0.5 mm, the total depth of the carburized layer was 1.7 mm, and the carburized depth reaching the highest hardness in the carburized layer was 0.4 mm, and the hardness of the carburized layer gradually decreased after reaching the highest hardness; there was almost no retained austenite in the metallographic structure in 500 times metallographic microscopic view. 50 test drill bits were tested under such working condition that the proportion of bit breakage was 20%. No breakage occurred.
Example 3
[0050] 30CrNi4Mo was used as the base material of the drill bit, which was subjected to blanking, forging, machining, carburizing treatment, quenching treatment, high-temperature tempering, machining, isothermal salt-bath quenching, low-temperature tempering, drilling alloy insert holes and inserting alloy inserts to prepare a HD55A-152 drill bit. The forging was performed at an initial forging temperature of 1180°C and a final forging temperature of 870°C. The carburizing was performed at a temperature of 925°C, at a boost carbon potential of 1.05% for 5.5 h and at a diffusion carbon potential of 0.83% for 4.5 h. After cooling to 855°C with the furnace, the resulting material was cooled to room temperature by gas-quenching using the high-pressure nitrogen as a medium. The quenching was performed using a rapid-quenching cooling oil as a medium at a temperature of 830°C and a protective carbon potential of 0.48% for 3 h. The high-temperature tempering was performed at a temperature of 670°C for 5 h under nitrogen protection. The salt bath was performed at a temperature of 800°C for 45 min, and the nitrate bath isothermal quenching was performed at a temperature of 280°C for 40 min. The low-temperature tempering was performed at 230°C for 4 h. Then the material was taken out of the furnace and air-cooled.
[0051] The test results of the carburized layer show that the carbon concentration gradient of the carburized layer was in a shape of analogous parabola, the concentration at 0.2 mm from the surface was 0.50%, the highest carbon concentration was 0.65%, the carburized depth reaching the highest concentration was 0.5 mm, the total depth of the carburized layer was 1.7 mm, and the carburized depth reaching the highest hardness in the carburized layer was 0.35 mm, and the hardness of the carburized layer gradually decreased after reaching the highest hardness; there was almost no retained austenite in the metallographic structure in 500 times metallographic microscopic view. 50 test drill bits were tested under such working condition that the proportion of bit breakage was 20%. No breakage occurred.
Claims (10)
1. A carburized workpiece, which has a carburized layer, from surface to inside, having a carbon concentration first increasing and then decreasing, wherein the carbon concentration on the surface is not less than 0.46%, the highest carbon concentration is 0.58%-0.68 %, and a carburized depth reaching the highest carbon concentration is 15%-50% of the total depth of the carburized layer.
2. The carburized workpiece according to claim 1, wherein the carburized depth reaching the highest hardness in the carburized layer is no more than 0.5 mm, and the hardness in the carburized layer decreases gradually after reaching the highest hardness.
3. The carburized workpiece according to claim 1, wherein a total depth of the carburized layer is 1.6-2.2 mm; the carburized depth reaching the highest carbon concentration is 0.4-1.1 mm.
4. The carburized workpiece according to claim 1, wherein a material of the carburized workpiece is selected from the group consisting of 18CrNi3Mo, 23CrN3iMo and 30CrNi4Mo.
5. A method for preparing a carburized workpiece, comprising:
SI) carburizing a workpiece at a temperature of 920°C-930°C, a boost carbon potential of 1%-1.15% and a diffusion carbon potential of 0.78%-0.85%;
S2) quenching the carburized workpiece;
S3) performing high-temperature tempering on the quenched workpiece;
S4) performing isothermal salt-bath quenching treatment on the high-temperature tempered workpiece;
S5) performing low-temperature tempering on the isothermal salt-bath quenched workpiece to obtain a carburized workpiece.
6. The method according to claim 5, wherein in the step Sl), the boost stage is performed for 4.5-7 h; and the diffusion stage is performed for 4-6 h.
7. The method according to claim 5, wherein in the step S), after the carburizing treatment, the workpiece is cooled to 855°C or lower with the furnace, and then cooled to room temperature by gas quenching.
8. The method according to claim 5, wherein in the step S2), the quenching is performed at a temperature of 830°C-850°C and a protective carbon potential of 0.45%-0.5% for 3-5 h.
9. The method according to claim 5, wherein in the step S3), the high-temperature tempering is performed at a temperature of 660°C-700°C in an inert atmosphere for 5-7 h.
10. The method according to claim 5, wherein in the step S4), a salt-bath quenching in the isothermal salt-bath quenching treatment is performed at a heating temperature of 790°C-850°C for 25-90 min, and a nitrate bath isothermal quenching in the isothermal salt-bath quenching treatment is performed at a temperature of 230°C-280° for 20-70 min; in the step S5), the low temperature tempering is performed at 180°C-230°C for 4-6 h.
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