WO2022154105A1 - 鋼製部材の浸炭方法、鋼製部品及び浸炭剤 - Google Patents
鋼製部材の浸炭方法、鋼製部品及び浸炭剤 Download PDFInfo
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- WO2022154105A1 WO2022154105A1 PCT/JP2022/001236 JP2022001236W WO2022154105A1 WO 2022154105 A1 WO2022154105 A1 WO 2022154105A1 JP 2022001236 W JP2022001236 W JP 2022001236W WO 2022154105 A1 WO2022154105 A1 WO 2022154105A1
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- carburizing
- agent
- steel member
- carburizing agent
- steel
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Images
Classifications
-
- 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
- C23C8/60—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 solids, e.g. powders, pastes
- C23C8/62—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 solids, e.g. powders, pastes only one element being applied
- C23C8/64—Carburising
- C23C8/66—Carburising of ferrous surfaces
-
- 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
- C23C8/02—Pretreatment of the material to be coated
-
- 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
- C23C8/40—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 liquids, e.g. salt baths, liquid suspensions
- C23C8/42—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 liquids, e.g. salt baths, liquid suspensions only one element being applied
- C23C8/44—Carburising
- C23C8/46—Carburising of ferrous surfaces
Definitions
- the present invention relates to a method for carburizing steel members, steel parts and carburizing agents used for steelmaking equipment, excavation machines, wind power generators, etc.
- the hardness near the surface (for example, a depth of about 1 mm from the surface for small products) is increased to improve various characteristics such as wear resistance, slidability, and fatigue strength. Therefore, carburizing and quenching is used.
- the carburizing method is classified into solid carburizing, liquid carburizing, gas carburizing, and vacuum carburizing, all of which are treatments for invading carbon (C) from the surface of a heated component in the austenite region.
- FIG. 6 is a schematic view showing the carburizing mechanism of the gas carburizing method.
- FIG. 7 is a Fe—C binary phase diagram when the vertical axis is the temperature and the horizontal axis is the C content.
- a steel member 21 is arranged in a furnace heated to a temperature of line A 1 (727 ° C.) or higher shown in the phase diagram of FIG. 7, and CO, N 2 and H 2 are used as carrier gases.
- the gas atmosphere (carburized atmosphere) is created by flowing a heat-absorbing modified gas as the main component and further supplying a hydrocarbon gas such as propane or butane as an enriched gas.
- a hydrocarbon gas such as propane or butane as an enriched gas.
- carbon (C) can be penetrated from the surface 21a of the steel member 21.
- carbon dioxide (CO 2 ) is generated.
- Patent Document 1 discloses a carburizing method for steel parts, which can obtain a wide range of carburizing depth sufficient for rolling bearings in a shorter carburizing time.
- a carburizing agent which is a mixture of a powdered Fe-C alloy and sodium silicate that binds powders to each other, is in contact with the surface of a steel part, and the eutectic point or higher of the component part or the peritectic point. It is a method of keeping the temperature range of less than austenite for a certain period of time.
- Patent Document 2 describes carbon powder (graphite powder), carbonate (at least one selected from calcium carbonate and barium carbonate), and metal oxide (at least one selected from aluminum oxide and titanium oxide).
- a surface treatment method for spray coating a surface treatment agent containing a sodium silicate solution on the surface of a steel material is disclosed. According to this surface treatment method, selective carburizing treatment is possible by using spray coating.
- carbon dioxide gas (CO 2 ) is generated by decomposing carbonate in a high temperature environment, and this carbon dioxide gas is reacted with carbon (C) in carbon powder.
- Carbon monoxide (CO) is generated, and carbon monoxide gas is brought into contact with the steel material to cause a carburizing action.
- Patent Document 2 describes that the metal oxide has a function of diluting carbon powder and carbonate, and makes it easy to remove the carburizing agent after the carburizing treatment.
- Patent Document 2 when spray coating is used, there is a limit to the thickness of the carburizing agent that can be applied to the metal surface, and it is particularly difficult to obtain the carburizing depth required for large bearings. Become. Further, when the entire surface of the part is carburized, if spray coating is used, the amount of the carburizing agent applied becomes uneven, and a uniform carburized layer cannot be obtained. Further, calcium carbonate and barium carbonate used as carbon salts have a melting point of 800 to 850 ° C., and when treated at a eutectic point or higher, they can be melted to maintain a carburizing agent having a uniform carbon concentration. However, uneven carburizing may occur.
- the above object of the present invention is achieved by the configuration of the following [1] relating to the carburizing method of a steel member.
- the heating step is a method for carburizing a steel member, which is a step of holding the steel member in a temperature range of an austenite region having a eutectic point or more and less than a peritectic point for a certain period of time.
- preferred embodiments of the present invention relating to a carburizing method for steel members relate to the following [2] to [4].
- the Fe—C alloy powder is in a mixed state or a liquid phase state of a solid phase and a liquid phase at a temperature equal to or higher than the eutectic point, and the graphite powder is in a solid phase above the eutectic point.
- a step of bringing the carburizing agent into contact with at least a part of the surface of the steel member A method for carburizing a steel member, which comprises a heating step of invading at least a part of the surface of the steel member by heating the carburizing agent.
- the carburizing agent is a binding that binds the Fe—C alloy powder, the graphite powder of 5% by mass or more and 60% by mass or less with respect to the total mass of the carburizing agent, and the Fe—C alloy powder and the graphite powder to each other.
- the heating step is a method for carburizing a steel member, which is a step of holding the steel member in a temperature range of an austenite region having a eutectic point or more and less than a peritectic point for a certain period of time.
- preferred embodiments of the present invention relating to a carburizing method for steel members relate to the following [8] to [10].
- the Fe—C alloy powder is in a mixed state or a liquid phase state of a solid phase and a liquid phase at a temperature equal to or higher than the eutectic point, and the graphite powder is in a solid phase above the eutectic point.
- the carburizing agent is a binding that binds the Fe—C alloy powder, the graphite powder of 5% by mass or more and 60% by mass or less with respect to the total mass of the carburizing agent, and the Fe—C alloy powder and the graphite powder to each other.
- the heating temperature is in the austenite region above the eutectic point and below the peritectic point of the steel part, and is obtained by holding the steel part at the heating temperature for a certain period of time.
- a uniform carburized layer having a desired depth can be formed on the surface of a steel member in an extremely short treatment time, and the carburizing agent after carburizing can be easily removed.
- the carburizing method, the steel parts obtained by using the carburizing method, and the carburizing agent used in the carburizing method can be provided.
- FIG. 1A is a schematic view showing a carburizing method of a steel member according to an embodiment of the present invention, and is a diagram showing a state in which a carburizing agent is arranged on the surface of the steel member.
- FIG. 1B is a schematic view showing the next step of FIG. 1A, and is a diagram showing a step of carburizing the surface of a steel member.
- FIG. 2A is a schematic view showing a process after carburizing the surface of the steel member.
- FIG. 2B is a schematic view showing a step of peeling the carburizing agent from the surface of the steel part.
- FIG. 3 is a schematic view showing the shape and size of the test piece used in the examples.
- FIG. 4A shows Example No.
- FIG. 4B shows Comparative Example No. 6 is a drawing-substituting photograph showing a carburized layer after removal of a carburizing agent in the test piece of No. 6.
- FIG. 5A shows Example No. It is a drawing substitute photograph which shows the carburizing agent after removing the carburizing agent in the test piece of 2.
- FIG. 5B shows Comparative Example No. It is a drawing-substituting photograph showing the carburizing agent after removing the carburizing agent in the test piece of No. 7.
- FIG. 6 is a schematic view showing the carburizing mechanism of the gas carburizing method.
- FIG. 7 is a Fe—C binary phase diagram when the vertical axis is the temperature (° C.) and the horizontal axis is the carbon content (mass%).
- the method for carburizing a steel member according to the present embodiment is a step of bringing a carburizing agent into contact with at least a part of the surface of the steel member, and heating the steel member and the carburizing agent to cover at least a part of the surface. It has a heating step of carburizing carbon.
- the carburizing agent is a binding that binds the Fe-C alloy powder, the graphite powder of 20% by volume or more and 70% by volume or less with respect to the total volume of the carburizing agent, and the Fe-C alloy powder and the graphite powder to each other. Including agents.
- the carburizing agent is an Fe-C alloy powder, a graphite powder of 5% by mass or more and 60% by mass or less based on the total volume of the carburizing agent, and a binder that binds the Fe-C alloy powder and the graphite powder to each other. , May be included.
- the heating step is a step of holding the steel member in the temperature range of the austenite region above the eutectic point and below the peritectic point for a certain period of time.
- Sodium silicate as a binder may be in the form of a solution (aqueous solution, water glass) or in the form of powder or the like.
- 1A and 1B are schematic views showing a method of carburizing a steel member according to an embodiment of the present invention in order of steps.
- 2A and 2B are schematic views showing a process after carburizing a steel member with carbon.
- cast iron powder (Fe—C alloy powder) 2, graphite powder 3, and a sodium silicate solution (binding agent) are formed on at least a part of the surface 1a of the work (steel member) 1.
- the carburizing agent 5 containing 4 is brought into contact with it.
- the work 1 is, for example, a steel member made of hardened steel used for bearings and alloy steel for machine structure.
- the sodium silicate solution 4 or sodium silicate binds the cast iron powder 2 to each other, the graphite powder 3 to each other, and the cast iron powder 2 and the graphite powder 3 to each other by its own adhesiveness, and the cast iron powder 2 is attached to the surface 1a of the work 1.
- the graphite powder 3 are fixed. Therefore, the carburizing agent 5 is less likely to be peeled off from the surface 1a of the work 1, and the application site to the work 1 is not restricted.
- the work 1 and the carburizing agent 5 are placed in the furnace and heated in the temperature range of the austenite region above the eutectic point and below the peritectic point of the steel member which is the work, and this is heated. Hold for a certain period of time. As a result, a part of the cast iron powder 2 is melted (liquid phased), and the solid-phase cast iron powder 2, the liquid-phase cast iron portion 2a, the graphite powder 3, and the sodium silicate solution 4 or sodium silicate are mixed. It becomes a state.
- the graphite powder 3 does not melt, but the cast iron portion 2a, which has become a liquid phase, spreads and contacts the surface 1a of the work 1, so that the contact area between the carburizing agent 5 and the work 1 increases, so that the work Carbon can be uniformly penetrated from the surface 1a of No. 1, and the carbon supply rate to the work 1 can be significantly improved.
- the solid-phase cast iron powder 2 is further melted to form a mixed state of the liquid-phase cast iron portion 2a, the graphite powder 3, and the sodium silicate solution 4 or sodium silicate. Be done. Even in such a case, if sodium silicate solution 4 or sodium silicate is used in the binder, the sodium silicate functions as an antioxidant of the Fe—C alloy powder, and the Fe—C alloy powder It is possible to prevent an increase in the melting temperature of sodium.
- the work 1 and the carburizing agent 5 are cooled to an appropriate temperature.
- the cast iron portion 2a which was in the liquid phase state in FIG. 1B, becomes the cast iron body 2b in the solid phase state.
- the method of cooling the work 1 and the carburizing agent 5 is not particularly limited, and the method of cooling by leaving in a furnace (further cooling), the method of cooling by immersing in water (water cooling), or immersing in oil By doing so, a cooling method (oil cooling) or the like can be used.
- a cooling method oil cooling
- the carburizing agent 5 is peeled off from the surface 1a of the work 1.
- the carburizing agent used in the present embodiment and the temperature (heating temperature) of the heating step at the time of carburizing will be described in detail below.
- the carburizing treatment of the eutectic point or more and the peritectic point or less is possible, and within this range, the treatment time can be shortened.
- the eutectic point and peritectic point differ depending on the material (material composition), but in general, if the material is carburized, the heating temperature in the carburizing treatment is preferably 1150 ° C. or higher, preferably 1175 ° C. or higher. It is more preferable to keep the temperature at 1200 ° C. or higher.
- the heating temperature in the carburizing treatment is preferably 1300 ° C. or lower, more preferably 1275 ° C. or lower, and even more preferably 1250 ° C. or lower.
- the carburizing agent used in the carburizing method for the steel member according to the embodiment of the present invention (the carburizing agent according to the present embodiment) will be described in detail below.
- the carburizing agent according to another embodiment of the present invention is a carburizing agent that allows carbon to penetrate into at least a part of the surface by contacting and heating at least a part of the surface of the steel member. It contains a Fe—C alloy powder, a graphite powder of 5% by mass or more and 60% by mass or less based on the total mass of the carburizing agent, and a binder that binds the Fe—C alloy powder and the graphite powder to each other.
- the material of the Fe—C alloy powder used for the carburizing agent cast iron powder, carbon steel powder, tool steel powder, cast iron grid and the like can be used.
- the shape of the powder may be granular or needle-shaped.
- the amount of C in the Fe—C alloy powder serving as the carbon supply source is preferably calculated from the range of the liquid phase appearance region ( ⁇ + L) in FIG. 1 based on the heating temperature.
- the powder When the Fe-C alloy is in the form of powder, the powder has a large surface area, and depending on the atmosphere, the melting temperature rises with the decarburization of carbon in the Fe-C alloy powder, and the carburizing source is supplied in a liquid layer. There is a problem that it cannot be done. Such a problem can be solved by treating in an atmosphere of an inert gas or by mixing an antioxidant such as calcium sulfate (gypsum) with a carburizing agent. It is considered that sodium silicate itself has an antioxidant effect. Furthermore, calcium sulfate itself is considered to have an effect as a binder. When an inert gas is used, industrially, a reducing gas mainly composed of N2 gas or CO can be used.
- the content of the Fe—C alloy powder in the carburizing agent is 25% by mass or more with respect to the total mass of the carburizing agent, both carburizing property and removability of the carburizing agent can be achieved. Therefore, the content of the Fe—C alloy powder in the carburizing agent is preferably 25% by mass or more, more preferably 50% by mass or more, and 75% by mass or more with respect to the total mass of the carburizing agent. More preferably. On the other hand, when the content of the Fe—C alloy powder in the carburizing agent is 86% by mass or less with respect to the total mass of the carburizing agent, the removability of the carburizing agent tends to be good.
- the content of the Fe—C alloy powder in the carburizing agent is preferably 86% by mass or less, more preferably 84% by mass or less, and 80% by mass or less, based on the total mass of the carburizing agent. It is more preferable to have.
- the Fe—C alloy powder that can be used in this embodiment may contain elements other than Fe and C.
- the carburizing agent according to this embodiment contains graphite powder. Since the graphite powder does not melt even at a temperature above the eutectic point, it does not adhere to the work and has a certain carburizing property. A carburizing agent having both removability can be obtained. When the content of the graphite powder in the carburizing agent is less than 20% by volume with respect to the total volume of the carburizing agent, the removability of the carburizing agent after carburizing the steel part is lowered. Therefore, the content of the graphite powder in the carburizing agent is 20% by volume or more, preferably 25% by volume or more, and more preferably 30% by volume or more with respect to the total volume of the carburizing agent.
- the content of the graphite powder in the carburizing agent is less than 5% by mass with respect to the total mass of the carburizing agent, the removability of the carburizing agent after carburizing the steel part is lowered. Therefore, the content of the graphite powder in the carburizing agent is preferably 5% by mass or more, preferably 15% by mass or more, based on the total mass of the carburizing agent.
- the particle size of the graphite powder to be used the finer the particle size of the Fe-C alloy powder, the more the particles come into contact with each other without gaps, and uniform carburizing is possible, which is preferable. Specifically, those passing through a 180-mesh sieve are preferable, those passing through a 150-mesh sieve are more preferable, and those passing through a 100-mesh sieve are further preferable.
- the Fe-C alloy powder and the sodium silicate solution are kneaded and supplied to the work surface, the oxidation and decarburization of the Fe-C alloy powder itself can be further suppressed, so that the melting temperature rises. It is possible to prevent the problem that the carburizing source cannot be supplied by the liquid layer, and a more uniform carburizing layer can be obtained.
- the sodium silicate and its aqueous solution include water glass (sodium silicate aqueous solution) of Nos. 1 to 3 and sodium metasilicate as described in JIS K 1408 (1966). Nos. 1 and 2 (crystals) and the like can be used.
- the content of the binder in the carburizing agent is not particularly limited, but when sodium silicate is used as the binder, the content of the binder in the carburizing agent is 4% by mass with respect to the total mass of the carburizing agent. When it is% or more, the adhesion between the carburizing agent and the steel member can be improved.
- the content of the binder is preferably 0.1% by mass or more with respect to the mass of the cast iron powder in the carburizing agent.
- the content of the binder in the carburizing agent is 40% by mass or less with respect to the total mass of the carburizing agent, the contents of the Fe-C alloy powder and the graphite powder in the carburizing agent are sufficiently secured. Therefore, excellent carburizing property can be obtained. Therefore, the content of the binder in the carburizing agent is preferably 40% by mass or less, more preferably 25% by mass or less, and 20% by mass or less with respect to the total mass of the carburizing agent. Is even more preferable.
- the sodium silicate either a liquid one (sodium silicate solution) or a powdery one can be used, and when the sodium silicate solution is used, the above content is the sodium silicate solution with respect to the total mass of the carburizing agent. Represents the mass of.
- the particle size of the binder is similar to the particle size of Fe-C alloy powder, and the finer the particles, the closer the particles come into contact with each other, enabling uniform carburizing. It is preferable because it becomes. Specifically, those passing through a 180-mesh sieve are preferable, those passing through a 150-mesh sieve are more preferable, and those passing through a 100-mesh sieve are further preferable.
- the carburizing method according to the present embodiment using the above carburizing agent, it is possible to maintain a high state as compared with the carbon potential of gas carburizing, and it is possible to realize quick and uniform carburizing and carburizing.
- the later carburizing agent can be easily removed.
- the carburizing method according to the present embodiment is also suitable for carburizing the raceway ring and rolling element of an ultra-large roller bearing having an outer diameter of more than 1000 mm for industrial machinery, for example.
- the target steel member is not limited to such a size, and can be applied to steel members of various sizes.
- the steel part according to the present embodiment is a steel part obtained by contacting at least a part of the surface of the steel member with a carburizing agent and heating the steel part to allow carbon to penetrate into at least a part of the surface.
- the carburizing agent binds the Fe-C alloy powder, the graphite powder of 20% by volume or more and 70% by volume or less with respect to the total volume of the carburizing agent, and the Fe-C alloy powder and the graphite powder to each other.
- the heating temperature, including the coating agent is in the austenite region of the steel part having a eutectic point or more and less than a peritectic point, and is obtained by holding the steel part at the heating temperature for a certain period of time.
- the steel parts have the carburizing agent on the surface removed and have a uniform carburizing layer with a desired depth.
- the components and their contents contained in the carburizing agent for obtaining the steel parts, the heating conditions, etc. are the same as those described in the carburizing method and the carburizing agent for the steel members described above, and thus are detailed. The description is omitted.
- Carburizing agents with various volume fractions of graphite powder were prepared, and the test pieces were carburized to evaluate the surface carbon concentration and carburizing agent removability.
- a carburizing agent in which cast iron powder (Fe-C alloy powder), graphite powder, and sodium silicate (binding agent) are mixed in a volume ratio shown in Table 1 below is placed in the blind hole 11a.
- the surface of the blind hole 11a (side surface 12a and bottom surface 12b) was brought into contact with the carburizing agent.
- the carburizing treatment was carried out by holding for 5 minutes or 900 minutes in a state of being heated in a nitrogen gas atmosphere, and the mixture was cooled in the furnace.
- the temperature in the heating step is 1200 ° C., which is an intermediate temperature between the eutectic point 1147 ° C. and the peritectic point 1494 ° C. of the SCR420 steel material from the Fe—C binary phase diagram shown in FIG. And said.
- the carburizing agent arranged in the blind hole 11a of the obtained test piece 11 is removed, cut at the surface passing through the central line passing through the cylindrical axis, and the carburizing agent is observed by observing the cross-sectional macro with an actual microscope.
- the surface carbon concentration was measured by EPMA (Electron Probe Micro Analyzer).
- EPMA Electro Probe Micro Analyzer
- the center of the bottom surface of the blind hole 11a in the test piece 11 was measured, and the side surface was measured at an arbitrary position in the center of the distance from the top surface to the bottom surface.
- the surface carbon concentration those having a surface carbon concentration of 0.80% by mass or more were judged to have excellent carburizing properties.
- the removability of the carburizing agent is evaluated by a method of scraping the carburizing agent from the test piece after carburizing with a scraping rod having a spoon-shaped tip, and most of the carburizing agent can be removed by one scraping treatment. , Those that do not affect the post-process are marked with " ⁇ " (good), and those that require mechanical removal treatment because the carburizing agent remains even after multiple scraping treatments are marked with "x" (defective). ). The evaluation results are also shown in Table 1 below.
- the C concentration of the carburizing agent is a value calculated by the following formula (2).
- C concentration of carburizer (C mass in cast iron powder + C mass in graphite powder) / (mass of cast iron powder + mass of graphite powder) ... (2)
- the cast iron powder used in this example contains 3.1% by mass of C
- the graphite powder contains 100% by mass of C.
- FIG. 4A shows Example No. It is a drawing substitute photograph which shows the carburized layer after carburizing agent removal in the test piece of 2. Further, FIG. 4B shows Comparative Example No. 6 is a drawing-substituting photograph showing a carburized layer after removal of a carburizing agent in the test piece of No. 6.
- FIG. 5A shows Example No. It is a drawing substitute photograph which shows the carburizing agent after removing the carburizing agent in the test piece of 2. Further, FIG. 5B shows Comparative Example No. It is a drawing-substituting photograph showing the carburizing agent after removing the carburizing agent in the test piece of No. 7.
- Example No. No. 2 and Comparative Example No. No. 7 has the same surface carbon concentration on the bottom surface, but Example No. Regarding No. 2, the carburizing agent was excellently removed, and no carburizing agent remained on the bottom surface 12b and the side surface 12a.
- Comparative Example No. Regarding No. 7 the carburizing agent had poor removability, and the carburizing agent 15 was welded to the bottom surface 12b and the side surface 12a, and could not be removed even by using a scratching rod having a spoon-shaped tip.
- the parts indicated by arrows in FIG. 5B indicate the carburizing agent that could not be removed by welding.
- Test 2 The mass fraction of each component of the carburizing agent used in Test 1 was measured and compared with the volume fraction shown in Table 1 above.
- the test conditions and evaluation results are shown in Tables 2 and 3 below.
- the conditions and evaluation results other than the mass fraction of each component of the carburizing agent in Test 2 are the same as those shown in Table 1 above, but in order to compare with the evaluation results of Tests 3 and 4 shown below, It is also shown in Tables 2 and 3 below.
- Test 3 Using powdered sodium silicate, carburizing agents with various changes in the mass fraction of sodium silicate were prepared, and the above test pieces were carburized to evaluate the surface carbon concentration and carburizing agent removability. did. In Test 3, it was cooled (water-cooled) by immersing it in water after the heat treatment. The test method and evaluation method were the same as in Test 1 above.
- Test 4 After changing the packing condition of the carburizing agent and changing the bulk density of the carburizing agent with respect to the above test piece, a carburizing treatment was carried out to evaluate the surface carbon concentration and the carburizing agent removability. In Test 4, it was cooled (water-cooled) by immersing it in water after the heat treatment. Moreover, liquid sodium silicate was used as a binder. The test method and evaluation method were the same as in Test 1 above.
Abstract
Description
そこで、浸炭処理後の部品から、容易に除去することができる浸炭剤の開発が要求されている。
また、本発明の目的は、所望の深さで均一に表面に浸炭された鋼製部品を提供することである。
さらに、本発明の目的は、極めて短い処理時間で所望の深さの均一な浸炭層を鋼製部品の表面に形成することができるとともに、浸炭後に容易に除去することができる浸炭剤を提供することである。
前記鋼製部材と前記浸炭剤とを加熱することにより、前記表面の少なくとも一部に炭素を侵入させる加熱工程と、を有する鋼製部材の浸炭方法であって、
前記浸炭剤は、Fe-C合金粉末と、浸炭剤全体積に対して、20体積%以上、70体積%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含み、
前記加熱工程は、前記鋼製部材の共晶点以上、包晶点未満のオーステナイト域の温度範囲で一定時間保持する工程である、鋼製部材の浸炭方法。
前記浸炭剤は、Fe-C合金粉末と、浸炭剤全体積に対して、20体積%以上、70体積%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含み、
前記加熱の温度は、前記鋼製部品の共晶点以上、包晶点未満のオーステナイト域であり、前記加熱の温度で一定時間保持することにより得られる、鋼製部品。
Fe-C合金粉末と、浸炭剤全体積に対して、20体積%以上、70体積%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含む、浸炭剤。
前記鋼製部材と前記浸炭剤とを加熱することにより、前記表面の少なくとも一部に炭素を侵入させる加熱工程と、を有する鋼製部材の浸炭方法であって、
前記浸炭剤は、Fe-C合金粉末と、浸炭剤全質量に対して、5質量%以上、60質量%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含み、
前記加熱工程は、前記鋼製部材の共晶点以上、包晶点未満のオーステナイト域の温度範囲で一定時間保持する工程である、鋼製部材の浸炭方法。
前記浸炭剤は、Fe-C合金粉末と、浸炭剤全質量に対して、5質量%以上、60質量%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含み、
前記加熱の温度は、前記鋼製部品の共晶点以上、包晶点未満のオーステナイト域であり、前記加熱の温度で一定時間保持することにより得られる、鋼製部品。
Fe-C合金粉末と、浸炭剤全質量に対して、5質量%以上、60質量%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含む、浸炭剤。
本実施形態に係る鋼製部材の浸炭方法は、鋼製部材の表面の少なくとも一部に浸炭剤を接触させる工程と、鋼製部材と浸炭剤とを加熱することにより、表面の少なくとも一部に炭素を侵入させる加熱工程と、を有する。また、浸炭剤は、Fe-C合金粉末と、浸炭剤全体積に対して、20体積%以上、70体積%以下のグラファイト粉末と、Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含む。浸炭剤は、Fe-C合金粉末と、浸炭剤全体積に対して、5質量%以上、60質量%以下のグラファイト粉末と、Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含むものであってもよい。さらに、加熱工程は、鋼製部材の共晶点以上、包晶点未満のオーステナイト域の温度範囲に一定時間保持する工程である。結着剤としての珪酸ナトリウムは、溶液(水溶液、水ガラス)の形態であってもよく、粉体等の形態であってもよい。
図1A及び図1Bは、本発明の実施形態に係る鋼製部材の浸炭方法を工程順に示す模式図である。また、図2A及び図2Bは、鋼製部材に炭素を浸炭させた後の工程を示す模式図である。
珪酸ナトリウム溶液4又は珪酸ナトリウムは、自身の粘着性によって鋳鉄粉2同士、グラファイト粉末3同士、及び鋳鉄粉2とグラファイト粉末3とを互いに結着させるとともに、ワーク1の表面1aに、鋳鉄粉2とグラファイト粉末3とを固着させる。このため、浸炭剤5は、ワーク1の表面1aから剥がれにくくなり、ワーク1への適用部位に制約を生じることがない。
その後、図2Bに示すように、浸炭剤5をワーク1の表面1aから剥離する。
一般に、鋼材の表面から炭素を侵入させ、材料内部に拡散させる浸炭工程において、任意の深さ位置xにおける炭素濃度の時間的変化は、Fickの第二法則を用いた下記式(1)で表される。式(1)によれば、浸炭工程における炭素の拡散について理論的に説明できる。
C0:表面炭素濃度
D:γ-Fe中の炭素の拡散係数
t:時間
この手法によれば、ワーク表面の炭素濃度が、図7に示すFe-C 2元系状態図のJ-E線以上に浸炭され、液相が生じる課題、即ち、固溶限を超える過剰な浸炭を回避して、溶解現象のコントロールが可能となる。
すなわち、後述の浸炭剤を使用し、共晶点以上、包晶点以下の超高温域での拡散を利用することにより、大形軸受における鋼製部品の表面に、極めて短い処理時間で所望の深さの均一な浸炭層を形成することができる。
なお、浸炭剤及びワークを加熱する方法としては、炉を用いた加熱方法の他に、高周波加熱も使用することができる。
本実施形態に係る浸炭剤は、鋼製部材の表面の少なくとも一部に接触させ、加熱することにより、上記表面の少なくとも一部に炭素を侵入させる浸炭剤であって、Fe-C合金粉末と、浸炭剤全体積に対して、20体積%以上、70体積%以下のグラファイト粉末と、Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含む。
従来の鋼製部材の浸炭方法としては、例えば、珪酸ナトリウム溶液と、炭酸塩と、炭素粉末とを含み、さらに金属酸化物を含む表面処理剤を使用する方法がある。金属酸化物を添加することにより、保護層を形成できることに加えて、炭素粉末及び炭酸塩を希釈することができ、表面の浸炭処理が完成した後に、鋼材の表面から表面処理剤を除去しやすくすることができる。
これに対して、本発明では、炭酸塩や金属酸化物(酸化アルミニウム、酸化チタン)の代替の浸炭源として、Fe-C合金粉末を使用している。ワークを固相のオーステナイト域で加熱し、炭素源の1つを、固相と液相との混合状態又は液相状態からなるFe-C合金粉末とすることにより、浸炭性を向上させることができる。
なお、浸炭剤としてFe-C合金粉末を用いる場合、高温まで酸化を抑制することが重要となる。Fe-C合金を粉末の形態とした場合に、粉末は表面積が大きく、雰囲気によっては、Fe-C合金粉末中の炭素の脱炭に伴い、溶融温度が上昇し、浸炭源を液層で供給できなくなる問題がある。このような問題に対しては、不活性ガス雰囲気中で処理することや、浸炭剤に硫酸カルシウム(石膏)等の酸化防止剤を混合させることで解決できる。なお、珪酸ナトリウム自体も酸化防止効果を有すると考えられる。さらに、硫酸カルシウム自体も結着剤としての効果を有すると考えられる。
不活性ガスを使用する場合に、工業的にはN2ガスやCOを主体とする還元性の変成ガスを用いることができる。
一方、浸炭剤中のFe-C合金粉末の含有量は、浸炭剤全体積に対して、60体積%以下であると、浸炭剤の除去性が良好になる傾向にある。したがって、浸炭剤中のFe-C合金粉末の含有量は、浸炭剤全体積に対して、60体積%以下であることが好ましく、55体積%以下であることがより好ましく、50体積%以下であることがさらに好ましい。
一方、浸炭剤中のFe-C合金粉末の含有量は、浸炭剤全質量に対して、86質量%以下であると、浸炭剤の除去性が良好になる傾向にある。したがって、浸炭剤中のFe-C合金粉末の含有量は、浸炭剤全質量に対して、86質量%以下であることが好ましく、84質量%以下であることがより好ましく、80質量%以下であることがさらに好ましい。
なお、本実施形態において使用することができるFe-C合金粉末には、Fe及びC以外の元素が含まれていてもよい。
本実施形態に係る浸炭剤は、グラファイト粉末を含有する。グラファイト粉末は、共晶点以上の温度でも溶融しないため、ワークに固着せず、かつ、一定の浸炭性を有するため、浸炭剤中に適切な割合でグラファイト粉末を含有することにより、浸炭性と除去性を両立する浸炭剤を得ることができる。
浸炭剤中のグラファイト粉末の含有量が浸炭剤全体積に対して、20体積%未満であると、鋼製部品に浸炭させた後における浸炭剤の除去性が低下する。したがって、浸炭剤中のグラファイト粉末の含有量は、浸炭剤全体積に対して20体積%以上とし、25体積%以上であることが好ましく、30体積%以上であることがより好ましい。
したがって、浸炭剤中のグラファイト粉末の含有量は、浸炭剤全体積に対して70体積%以下とし、60体積%以下であることが好ましく、50体積%以下であることがより好ましく、40体積%以下であることがさらに好ましい。
本実施形態に係る浸炭剤は、結着剤を含有する。浸炭剤に結着剤が含有されていると、Fe-C合金粉末同士、グラファイト粉末同士、及びFe-C合金粉末とグラファイト粉末とを互いに結着させることができるとともに、浸炭剤と鋼製部材との密着性を向上させることができる。その結果、浸炭のムラが発生することを防止でき、均一な浸炭層を得ることができる。
なお、珪酸ナトリウムは、水溶液として使用することもできる。珪酸ナトリウム水溶液は、空気中のCO2ガスと反応して、固化する働きを有し、常温から高温まで粘性のあるガラス状を呈する。したがって、結着剤に珪酸ナトリウムが水溶液の状態で含まれていると、浸炭剤と鋼製部材との密着性をより一層向上させることができるとともに、酸素を遮断する効果も得ることができる。
また、Fe-C合金粉末と珪酸ナトリウム溶液とを混練して、ワーク表面に供給すると、Fe-C合金粉末自体の酸化・脱炭をさらに抑制することができるため、溶融温度が上昇して、浸炭源を液層で供給できなくなる問題を防止することができ、より均一な浸炭層を得ることができる。
なお、本実施形態に係る浸炭方法は、例えば、産業機械用の外径1000mmを超えるような超大形ころ軸受の軌道輪及び転動体に浸炭処理を施す場合にも好適であるが、本発明が対象とする鋼製部材はこのようなサイズに限定されるものではなく、種々のサイズの鋼製部材に対して適用することができる。
続いて、上記鋼製部材の浸炭方法により浸炭が実施された鋼製部品に関して、以下で説明する。本実施形態に係る鋼製部品は、鋼製部材の表面の少なくとも一部に浸炭剤を接触させ、加熱することにより、上記表面の少なくとも一部に炭素を侵入させて得られる鋼製部品であって、浸炭剤は、Fe-C合金粉末と、浸炭剤全体積に対して、20体積%以上、70体積%以下のグラファイト粉末と、上記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含み、加熱の温度は、鋼製部品の共晶点以上、包晶点未満のオーステナイト域であり、加熱の温度で一定時間保持することにより得られるものである。
図3は、本実施例において使用した試験片の形状及びサイズを示す模式図である。試験片(鋼製部材)11の材料としては、JIS4053(機械構造用合金鋼鋼材)のうちSCR420鋼材(炭素0.18~0.23%、中央値0.205%)を選定した。また、試験片11のサイズは、外径φが40mm、30mm又は20mmであり、高さhが17.5mm、22.5mm、25mm又は30mmであって、上面の中央に、内径が15mmであり、深さが15mmである止まり穴11aを有する円柱形状とした。
グラファイト粉末の体積分率を種々に変化させた浸炭剤を作製し、試験片に対して浸炭処理を実施して、表面炭素濃度と浸炭剤除去性を評価した。
試験方法としては、まず、止まり穴11aに、鋳鉄粉(Fe-C合金粉末)、グラファイト紛、及び珪酸ナトリウム(結着剤)を、下記表1に示す体積割合で混合した浸炭剤を配置し、止まり穴11aの表面(側面12a及び底面12b)に浸炭剤を接触させた。次に、加熱工程として、窒素ガス雰囲気中において加熱した状態で、5分又は900分保持して浸炭処理を実施し、炉内で冷却した。なお、加熱工程における温度は、図7に示すFe-C 2元系状態図より、SCR420鋼材の共晶点である1147℃と、包晶点である1494℃とのの中間温度である1200℃とした。
また、浸炭剤の除去性は、浸炭後の試験片から、先端がスプーン形状の引掻き棒で浸炭剤を掻き出す方法により評価し、1回の掻き出し処理により浸炭剤の大部分を除去することができ、後工程に影響がないものを「〇」(良好)とし、複数回の掻き出し処理を実施しても浸炭剤が残存し、機械的な除去処理が必要となったものを「×」(不良)とした。評価結果を下記表1に併せて示す。
ただし、本実施例において使用した鋳鉄粉は、Cを3.1質量%含むものであり、グラファイト粉末は、Cを100質量%含むものである。
なお、比較例No.5は、グラファイト粉末単体の浸炭性及び除去性を評価するための試験片であったため、側面の炭素濃度については測定しなかった。
なお、比較例No.7は、底面における表面炭素濃度は、1.30質量%であり、優れた浸炭性を得ることができたが、浸炭剤が溶融し、除去が困難な状態であったため、側面における表面炭素濃度は測定しなかった。
上記試験1において使用した浸炭剤の各成分の質量分率を測定し、上記表1に記載の体積分率と比較した。試験条件及び評価結果を下記表2及び3に示す。なお、試験2における浸炭剤の各成分の質量分率以外の条件および評価結果は、上記表1に示すものと同一であるが、以下に示す試験3及び試験4の評価結果と比較するため、下記表2及び3に併記した。
粉状の珪酸ナトリウムを使用し、珪酸ナトリウムの質量分率を種々に変化させた浸炭剤を作製し、上記試験片に対して浸炭処理を実施して、表面炭素濃度と浸炭剤除去性を評価した。なお、試験3においては、熱処理後に水中に浸漬することにより冷却(水冷)した。試験方法及び評価方法は、上記試験1と同様とした。
上記試験片に対して、浸炭剤の詰め込み具合を変化させて、浸炭剤の嵩密度を変化させた後、浸炭処理を実施して、表面炭素濃度と浸炭剤除去性を評価した。なお、試験4においては、熱処理後に水中に浸漬することにより冷却(水冷)した。また、結着剤として、液状の珪酸ナトリウムを使用した。試験方法及び評価方法は、上記試験1と同様とした。
2 鋳鉄粉
2b 鋳鉄部
3 グラファイト粉末
4 珪酸ナトリウム溶液
5 浸炭剤
11 試験片
13 浸炭層
15 浸炭剤
21 鋼製部材
Claims (12)
- 鋼製部材の表面の少なくとも一部に浸炭剤を接触させる工程と、
前記鋼製部材と前記浸炭剤とを加熱することにより、前記表面の少なくとも一部に炭素を侵入させる加熱工程と、を有する鋼製部材の浸炭方法であって、
前記浸炭剤は、Fe-C合金粉末と、浸炭剤全体積に対して、20体積%以上、70体積%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含み、
前記加熱工程は、前記鋼製部材の共晶点以上、包晶点未満のオーステナイト域の温度範囲で一定時間保持する工程である、鋼製部材の浸炭方法。 - 前記Fe-C合金粉末は、前記共晶点以上の温度で、固相と液相との混合状態、又は液相状態であり、前記グラファイト粉末は、前記共晶点以上で固相状態である、請求項1に記載の鋼製部材の浸炭方法。
- 前記結着剤は珪酸ナトリウム及び硫酸カルシウムの少なくとも一種を含む、請求項1又は2に記載の鋼製部材の浸炭方法。
- 前記加熱工程は、不活性ガス雰囲気中で実施される、請求項1~3のいずれか1項に記載の鋼製部材の浸炭方法。
- 鋼製部材の表面の少なくとも一部に浸炭剤を接触させ、前記鋼製部材と前記浸炭剤とを加熱する加熱工程により前記表面の少なくとも一部に炭素を侵入させることにより得られる鋼製部品であって、
前記浸炭剤は、Fe-C合金粉末と、浸炭剤全体積に対して、20体積%以上、70体積%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含み、
前記加熱の温度は、前記鋼製部品の共晶点以上、包晶点未満のオーステナイト域であり、前記加熱の温度で一定時間保持することにより得られる、鋼製部品。 - 請求項1~4のいずれか1項に記載の鋼製部材の浸炭方法に用いられる浸炭剤であって、
Fe-C合金粉末と、浸炭剤全体積に対して、20体積%以上、70体積%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含む、浸炭剤。 - 鋼製部材の表面の少なくとも一部に浸炭剤を接触させる工程と、
前記鋼製部材と前記浸炭剤とを加熱することにより、前記表面の少なくとも一部に炭素を侵入させる加熱工程と、を有する鋼製部材の浸炭方法であって、
前記浸炭剤は、Fe-C合金粉末と、浸炭剤全質量に対して、5質量%以上、60質量%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含み、
前記加熱工程は、前記鋼製部材の共晶点以上、包晶点未満のオーステナイト域の温度範囲で一定時間保持する工程である、鋼製部材の浸炭方法。 - 前記Fe-C合金粉末は、前記共晶点以上の温度で、固相と液相との混合状態、又は液相状態であり、前記グラファイト粉末は、前記共晶点以上で固相状態である、請求項7に記載の鋼製部材の浸炭方法。
- 前記結着剤は珪酸ナトリウム及び硫酸カルシウムの少なくとも一種を含む、請求項7又は8に記載の鋼製部材の浸炭方法。
- 前記加熱工程は、不活性ガス雰囲気中で実施される、請求項7~9のいずれか1項に記載の鋼製部材の浸炭方法。
- 鋼製部材の表面の少なくとも一部に浸炭剤を接触させ、前記鋼製部材と前記浸炭剤とを加熱する加熱工程により前記表面の少なくとも一部に炭素を侵入させることにより得られる鋼製部品であって、
前記浸炭剤は、Fe-C合金粉末と、浸炭剤全質量に対して、5質量%以上、60質量%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含み、
前記加熱の温度は、前記鋼製部品の共晶点以上、包晶点未満のオーステナイト域であり、前記加熱の温度で一定時間保持することにより得られる、鋼製部品。 - 請求項7~10のいずれか1項に記載の鋼製部材の浸炭方法に用いられる浸炭剤であって、
Fe-C合金粉末と、浸炭剤全質量に対して、5質量%以上、60質量%以下のグラファイト粉末と、前記Fe-C合金粉末及びグラファイト粉末を互いに結着させる結着剤と、を含む、浸炭剤。
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