WO2022083248A1 - Carburized workpiece and preparation method therefor - Google Patents

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

A kind of carburized workpiece and preparation method thereof

This application claims the priority of the Chinese patent application filed on October 22, 2020 with the application number 202011138231.0 and the invention titled "A carburized workpiece and its preparation method", the entire contents of which are incorporated herein by reference Applying.

technical field

The invention belongs to the technical field of material and workpiece preparation, in particular to a carburized workpiece and a preparation method thereof.

Background technique

With the improvement of air compressor and rock drilling equipment technology, the output wind pressure of the drilling rig is getting higher and higher, resulting in higher and higher drilling frequency and impact force of the drill bit, and the probability of the bit spline breaking is also increasing.

The failure study shows that the crack source of the spline fracture of the carburized drill bit is the hot crack caused by the secondary hardening caused by frictional heat generation between the spline of the drill bit and the spline of the chuck. The higher the concentration of the drill spline carburized layer, the higher the retained austenite content in the structure, and the greater the risk of hot cracking caused by secondary hardening. In the field of down-the-hole drill bits, the carburizing concentration control of carburizing drill bits is generally high, and there is often a lot of retained austenite in the carburized layer. Therefore, under the continuously increasing working air pressure, the probability of frictional thermal cracking at the spline of the drill bit is high. As it continues to increase, the probability of spline breaking is also increasing. In addition, at the beginning, since the contact between the spline of the drill bit and the spline of the drill sleeve is line contact, the higher the surface hardness of the spline of the drill bit, the more difficult the running-in between the spline of the drill bit and the spline of the drill sleeve, and the easier it is to cause local overload, which in turn accelerates the growth of thermal cracks.

SUMMARY OF THE INVENTION

In view of this, the technical problem to be solved by the present invention is to provide a carburized workpiece and a preparation method thereof that can effectively reduce the probability of spline breaking.

The invention provides a carburized workpiece, the carburized layer of the carburized workpiece is from the surface to the inside, the carbon concentration first increases and then decreases, and the surface carbon concentration is not less than 0.46%, and the highest carbon concentration is 0.58% to 0.68% %, the carburizing depth that reaches the highest carbon concentration is 15% to 50% of the total depth of the carburized layer.

Preferably, the carburizing depth at which the highest hardness is reached in the carburized layer is no more than 0.5 mm, and the hardness of the carburizing layer decreases in a gradient after the highest hardness is reached.

Preferably, the total depth of the carburized layer is 1.6-2.2 mm; the carburizing depth that reaches the highest carbon concentration is 0.4-1.1 mm.

Preferably, the material of the carburized workpiece is selected from 18CrNi3Mo, 23CrN3iMo or 30CrNi4Mo.

The present invention also provides a preparation method of the carburized workpiece, comprising:

S1) Carburizing the workpiece; the temperature of the carburizing treatment is 920℃～930℃; the strong carburizing potential is 1%～1.15%; the diffusion carbon potential is 0.78%～0.85%;

S2) quenching the carburized workpiece;

S3) carry out high temperature tempering to the workpiece after quenching treatment;

S4) the workpiece after high temperature tempering is subjected to isothermal salt bath quenching treatment;

S5) low-temperature tempering is performed on the workpiece after isothermal salt bath quenching to obtain a carburized workpiece.

Preferably, in the step S1), the time of the strong infiltration stage is 4.5-7h; the time of the diffusion stage is 4-6h.

Preferably, in the step S1), after the carburizing treatment, the furnace is cooled to 855° C. or less, and the gas is quenched and cooled to room temperature.

Preferably, the temperature of the quenching treatment in the step S2) is 830°C to 850°C; the protective carbon potential is 0.45% to 0.5%; and the time of the quenching treatment is 3 to 5 hours.

Preferably, the temperature of the high-temperature tempering in the step S3) is 660°C to 700°C; the high-temperature tempering time is 5-7 hours; the high-temperature tempering is performed in an inert atmosphere.

Preferably, in the step S4), the heating temperature of the salt bath quenching in the intermediate temperature salt bath quenching treatment is 790 ° C ~ 850 ° C; the heating time of the salt bath quenching is 25 ~ 90min; the isothermal salt bath quenching treatment in the isothermal salt bath quenching treatment is isothermal quenching The temperature is 230 ℃～280 ℃; the time of isothermal quenching in nitrate bath is 20～70min; the temperature of low temperature tempering in the step S5) is 180 ℃～230 ℃; the time of low temperature tempering is 4～6h.

The invention provides a carburized workpiece, the carburized layer of the carburized workpiece is from the surface to the inside, the carbon concentration first increases and then decreases, and the surface carbon concentration is not less than 0.46%, and the highest carbon concentration is 0.58% to 0.68% %, the carburizing depth that reaches the highest carbon concentration is 15% to 50% of the total depth of the carburized layer. Compared with the prior art, the present invention effectively controls the amount of retained austenite in the outermost layer by controlling the change curve of the carbon concentration of the carburized layer, and at the same time reduces the carbon concentration of the outermost layer, and reduces the amount of residual austenite in the outermost layer. The hardness of the carburized workpiece accelerates the running-in degree of the spline of the carburized workpiece and the spline of the chuck, and reduces the thermal cracking phenomenon of the carburized layer under high-frequency friction, which can effectively reduce the probability of the spline of the carburized workpiece breaking. It greatly prolongs the service life of carburized workpieces, and has a wide range of applications in the field of high-frequency and high-load DTH drills.

Description of drawings

Fig. 1 is the carburizing concentration and the hardness gradient graph of the HD55A-152 drill bit carburizing layer obtained in the embodiment of the present invention 1;

FIG. 2 is a microscopic picture of the metallographic structure of the carburized layer of the HD55A-152 drill bit obtained in Example 1 of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The invention provides a carburized workpiece, the carburized layer of the carburized workpiece is from the surface to the inside, the carbon concentration first increases and then decreases, and the surface carbon concentration is not less than 0.46%, and the highest carbon concentration is 0.58% to 0.68% %, the carburizing depth that reaches the highest carbon concentration is 15% to 50% of the total depth of the carburized layer.

In the present invention, the carburizing workpiece is preferably a carburizing drill bit; the carburizing workpiece is preferably formed of high-strength structural steel; the material of the carburizing workpiece is more preferably 18CrNi3Mo, 23CrN3iMo or 30CrNi4Mo; The diameter of the key shank is preferably 50-180 mm, and the diameter of the big head of the insert is preferably 100-380 mm.

The surface of the carburized workpiece is a carburized layer; the carburized layer is from the surface to the inside, and the carbon concentration first increases and then decreases, that is, the carbon concentration distribution curve is parabolic; the surface carbon concentration of the carburized layer is preferably The surface carbon concentration is preferably 0.48% to 0.5%; the surface carbon concentration is preferably the concentration at 0.2 mm of the surface layer; the highest carbon concentration of the carburized layer is preferably 0.60% to 0.68%, more Preferably, it is 0.62% to 0.66%, more preferably 0.62% to 0.65%; the carburized depth of the highest carburized layer in the carburized layer is preferably 20% to 45% of the total depth of the carburized layer, more preferably 25% to 25%. 40%, more preferably 28% to 38%, most preferably 29.4% to 35.2%; in the present invention, the carburizing depth to reach the highest carbon concentration is preferably 0.4 to 1.1 mm, more preferably 0.4 to 0.8 mm, and then It is preferably 0.4-0.7mm, most preferably 0.5-0.6mm; the total depth of the carburized layer is preferably 1%-1.5% of the diameter of the carburized workpiece, more preferably 1%-1.4%, and more preferably 1% ～1.3%, more preferably 1.1%～1.2%, most preferably 1.1%～1.15%; in the present invention, the total depth of the carburized layer is preferably 1.6～2.2mm, more preferably 1.6～2mm, and then It is preferably 1.6 to 1.8 mm, and most preferably 1.7 mm.

According to the present invention, the carburizing depth that achieves the highest hardness in the carburized layer is preferably no more than 0.5 mm, more preferably 0.25-0.45 mm, still more preferably 0.3-0.4 mm, and most preferably 0.3 mm; After the highest hardness is reached in the carburized layer, the hardness will gradually decrease. In the present invention, the hardness of the carburized layer preferably decreases in a gradient after the highest hardness is reached.

The metallographic structure of the carburized layer of the carburized workpiece provided by the present invention has almost no residual austenite in the field of view of a 50-500 magnification microscope.

The present invention effectively controls the amount of residual austenite in the outermost layer by controlling the change curve of the carbon concentration of the carburized layer and at the same time reduces the carbon concentration of the outer layer, reduces the hardness of the outermost layer, and accelerates the carburizing workpiece The degree of running-in between the splines and the splines of the clamping sleeve reduces the thermal cracking phenomenon of the carburized layer under high-frequency friction, which can effectively reduce the probability of the spline fracture of the carburized workpiece, and greatly prolong the life of the carburized workpiece. It has a wide range of applications in the field of high-frequency and high-load down-the-hole drill bit rock drilling.

The present invention also provides a method for preparing the above carburized workpiece, comprising: S1) carburizing the workpiece; the temperature of the carburizing treatment is 920°C to 930°C; the strong carburizing potential is 1% to 1.15% ; Diffusion carbon potential is 0.78% to 0.85%; S2) quench the workpiece after carburizing treatment; S3) perform high temperature tempering on the workpiece after quenching treatment; S4) perform isothermal salt bath on the workpiece after high temperature tempering Quenching treatment; S5) performing low temperature tempering on the workpiece after isothermal salt bath quenching treatment to obtain a carburized workpiece.

Wherein, in the present invention, there is no special restriction on the sources of all raw materials, and they can be commercially available.

In the present invention, the workpiece can be prepared according to a method well known to those skilled in the art, preferably through blanking, die forging and machining to obtain the workpiece; the initial forging temperature in the die forging process is preferably 1180°C to 1250°C ; The final forging temperature is preferably 870 ℃ ~ 890 ℃.

Carburizing the workpiece; the temperature of the carburizing treatment is preferably 922°C to 928°C, more preferably 924°C to 926°C, and more preferably 925°C; the strong carburizing potential is preferably 1.05% to 1.15%; The time of the infiltration stage is preferably 4.5-7h, more preferably 5-6h; the carbon diffusion potential is preferably 0.78%-0.83%; the time of the diffusion stage is preferably 4-6h, more preferably 4.5-5h; the carburizing treatment When the carburizing agent is preferably methanol and acetone, the carbon potential in the carburizing process can be controlled by the combination of the two.

After the carburizing treatment, it is preferable to cool down to 855°C or less with the furnace, and cool to room temperature by gas quenching; the gas quenching uses high-pressure nitrogen as a medium, which can realize rapid cooling.

The workpiece after carburizing treatment is subjected to quenching treatment; the temperature of the quenching treatment is preferably 830°C to 850°C; the protective carbon potential is preferably 0.45% to 0.5%; the time of the quenching treatment is preferably 3 to 5h; Cooling with rapid quenching cooling oil.

The quenched workpiece is subjected to high temperature tempering; the temperature of the high temperature tempering is preferably 660°C to 700°C; the time of the high temperature tempering is preferably 5 to 7 hours; the high temperature tempering is preferably performed in an inert atmosphere; The inert atmosphere is preferably nitrogen.

After the high-temperature tempering treatment, machining is preferably performed to obtain a carburized workpiece of a specific size, and then an isothermal salt bath quenching treatment is performed; the heating temperature of the salt bath quenching in the isothermal salt bath quenching treatment is preferably 790 ℃～850 ℃. ℃, more preferably 800℃～830℃; the heating time of salt bath quenching is preferably 25～90min, more preferably 35～60min, more preferably 40～50min, most preferably 40～45min; in isothermal salt bath quenching treatment The temperature of isothermal quenching in nitrate tank is preferably 230 ℃～280 ℃; the isothermal quenching time in nitrate tank is preferably 20～70min, more preferably 30～50min, more preferably 30～45min, most preferably 35～40min.

The workpiece after isothermal salt bath quenching treatment is subjected to low-temperature tempering; the temperature of the low-temperature tempering is preferably 180° C. to 230° C.; the time of low-temperature tempering is preferably 4-6 h; A carburized workpiece is obtained.

By precisely controlling the key process parameters of the heat treatment process, the invention obtains a carburized layer with a parabolic gradient change in carbon concentration and no residual austenite near the surface, reduces the key influencing factor of the drill bit spline friction thermal cracking, and accelerates the drill bit operation During the process, the matching degree of the spline and the drill sleeve can effectively reduce the probability of the spline of the drill bit being broken.

Among them, the selection of temperature and carbon potential in the carburizing process, the selection of quenching temperature, carbon potential and cooling method, as well as the selection of high return temperature and protective atmosphere are the keys to obtain the parabolic curve change of carbon concentration gradient, which is the key to effectively control carburization The preconditions for the amount of retained austenite near the surface layer; the selection of the salt bath temperature and the isothermal temperature of the nitrate bath in the salt quenching process, as well as the selection of the temperature and cooling method in the low-return process are the key measures to further effectively control the retained austenite.

In order to further illustrate the present invention, a carburized workpiece provided by the present invention and a preparation method thereof are described in detail below with reference to the embodiments.

The reagents used in the following examples are all commercially available.

Example 1

Using 23CrNi3Mo as the base material of the drill bit, it is made by blanking, die forging, machining, carburizing treatment, quenching treatment, high return, machining, isothermal salt quenching, low temperature tempering, drilling alloy teeth holes and inserting alloy teeth. HD55A-152 drill bit. The initial forging temperature is 1180 °C; the final forging temperature is 870 °C; After cooling with the furnace to 855 ℃, the high-pressure nitrogen is used as the medium for gas quenching and cooling to room temperature; the quenching temperature is 850 ℃, the quenching treatment time is 3h, the protective carbon potential is 0.45%, and the quenching cooling medium selects rapid quenching cooling oil; the high return temperature is 700 ℃, high return time is 5h, using nitrogen protection; salt bath temperature is 830 ℃, salt bath time is 40min, nitrate tank temperature is 230 ℃, nitrate tank isothermal time 35min; low return temperature is 180 ℃, low return temperature The time is 4h, and the oven is air-cooled.

The carburized concentration and hardness of the carburized layer of the HD55A-152 drill bit obtained in Example 1 were analyzed, and the carbon concentration and hardness curves were obtained, as shown in FIG. 1 .

The HD55A-152 drill bit obtained in Example 1 was analyzed with a metallographic microscope, and the metallographic microscopic picture of its carburized layer was obtained, as shown in Figure 2. From Figure 2, it can be seen that the metallographic structure was observed under a metallographic microscope at a magnification of 500 times. Almost no retained austenite exists in the field of vision.

The test results of the carburized layer show that the carbon concentration gradient of the carburized layer is parabolic. The hardness of the carburized layer is 1.7mm; the hardness of the carburized layer is 0.3mm, and the hardness of the carburized layer decreases gradually; the metallographic structure has almost no residual austenite under the field of 500 times the metallographic microscope. 50 test bits were tested on the condition that the proportion of broken bits was 20%, and there was no case of breakage.

Example 2

Using 30CrNi3Mo as the base material of the drill bit, it is made by blanking, die forging, machining, carburizing treatment, quenching treatment, high return, machining, isothermal salt quenching, low temperature tempering, drilling alloy teeth holes and inserting alloy teeth. HD55A-152 drill bit. The initial forging temperature is 1180℃; the final forging temperature is 870℃; the carburizing temperature is 925℃; , cooled with the furnace to 855 ℃ and then quenched to room temperature with high pressure nitrogen as the medium; the quenching temperature is 830 ℃, the quenching treatment time is 3h, the protective carbon potential is 0.50%, and the quenching cooling medium selects rapid quenching cooling oil; the high return temperature is 680℃, high return time is 5h, nitrogen protection is adopted; salt bath temperature is 810℃, salt bath time is 45min, nitrate tank temperature is 260℃, nitrate tank isothermal time is 40min; low return temperature is 230℃, low return temperature The time is 4h, and the oven is air-cooled.

The test results of the carburized layer show that the carbon concentration gradient of the carburized layer is parabolic. The hardness of the carburized layer is 1.7mm; the hardness of the carburized layer is 0.4mm, and the hardness of the carburized layer decreases gradually; the metallographic structure has almost no residual austenite under the field of 500 times the metallographic microscope. 50 test bits were tested under the condition that the proportion of broken bits was 20%, and there was no case of breakage.

Example 3

Using 30CrNi4Mo as the base material of the drill bit, it is made by blanking, die forging, machining, carburizing treatment, quenching treatment, high return, machining, isothermal salt quenching, low temperature tempering, drilling alloy teeth holes and inserting alloy teeth. HD55A-152 drill bit. The initial forging temperature is 1180℃; the final forging temperature is 870℃; the carburizing temperature is 925℃; h, after cooling with the furnace to 855 °C, high-pressure nitrogen is used as the medium to quench and cool to room temperature; the quenching temperature is 830 °C, the quenching treatment time is 3h, the protective carbon potential is 0.48%, and the quenching cooling medium selects rapid quenching cooling oil; high return temperature The temperature of the salt bath is 800℃, the salt bath time is 45min, the temperature of the nitrate tank is 280℃, and the isothermal time of the nitrate tank is 40min; the low temperature is 230℃, the low temperature The return time is 4h, and the oven is air-cooled.

The test results of the carburized layer show that the carbon concentration gradient of the carburized layer is parabolic. The hardness of the carburized layer is 1.7mm; the hardness of the carburized layer is 0.35mm, and the hardness of the carburized layer decreases gradually; the metallographic structure has almost no residual austenite under the field of 500 times the metallographic microscope. 50 test bits were tested on the condition that the proportion of broken bits was 20%, and there was no case of breakage.

Claims (10)

1. A carburized workpiece is characterized in that, the carburized layer of the carburized workpiece is from the surface to the inside, the carbon concentration first increases and then decreases, and the surface carbon concentration is not less than 0.46%, and the highest carbon concentration is 0.58% to 0.68% %, the carburizing depth that reaches the highest carbon concentration is 15% to 50% of the total depth of the carburized layer.
2. The carburized workpiece according to claim 1, characterized in that the carburizing depth at which the highest hardness is reached 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, characterized in that, the total depth of the carburized layer is 1.6-2.2 mm; the carburizing depth that reaches the highest carbon concentration is 0.4-1.1 mm.
4. The carburized workpiece according to claim 1, wherein the material of the carburized workpiece is selected from 18CrNi3Mo, 23CrN3iMo or 30CrNi4Mo.
5. A method for preparing a carburized workpiece, comprising:

   S1) Carburizing the workpiece; the temperature of the carburizing treatment is 920℃～930℃; the strong carburizing potential is 1%～1.15%; the diffusion carbon potential is 0.78%～0.85%;

   S2) quenching the carburized workpiece;

   S3) carry out high temperature tempering to the workpiece after quenching treatment;

   S4) the workpiece after high temperature tempering is subjected to isothermal salt bath quenching treatment;

   S5) low-temperature tempering is performed on the workpiece after isothermal salt bath quenching to obtain a carburized workpiece.
6. The preparation method according to claim 5, characterized in that, in the step S1), the time of the strong infiltration stage is 4.5-7h; the time of the diffusion stage is 4-6h.
7. The preparation method according to claim 5, characterized in that, in the step S1), after the carburizing treatment, the furnace is cooled to less than or equal to 855°C, and the gas is quenched and cooled to room temperature.
8. The preparation method according to claim 5, wherein the temperature of the quenching treatment in the step S2) is 830°C to 850°C; the protective carbon potential is 0.45% to 0.5%; and the time of the quenching treatment is 3 to 5 hours.
9. The preparation method according to claim 5, wherein the temperature of the high-temperature tempering in the step S3) is 660°C to 700°C; the high-temperature tempering time is 5-7h; the high-temperature tempering is performed in an inert atmosphere in progress.
10. The preparation method according to claim 5, characterized in that, the heating temperature of the salt bath quenching in the intermediate temperature salt bath quenching treatment in the step S4) is 790 ℃～850 ℃; the heating time of the salt bath quenching is 25～90min; In the isothermal salt bath quenching treatment, the temperature of isothermal quenching in the nitrate bath is 230°C～280°C; the time for isothermal quenching in the nitrate bath is 20～70min; the temperature of the low temperature tempering in the step S5) is 180°C～230°C; The time of low temperature tempering is 4-6h.

Images