Low friction coefficient duplex iron-ductile metal material and preparation method thereof

Abstract

The present invention discloses a low-friction-coefficient duplex ferro-ductile metal material, comprising the following components by mass percentage: C: 3.5% to 3.8%, Si: 2.3% to 2.8%, Mn: ≤0.6%, S: ≤0.02%, Mg: 0.02% to 0.04%, Re: 0.02% to 0.04%, with the remainder being Fe; the sum of the contents of the above raw materials is 100%. The method for preparing the low-friction-coefficient duplex ferro-ductile metal material of the present invention is characterized by selecting a material collection location, adopting a heat treatment process, and selecting heat treatment process parameters to obtain a ferrite and martensite two-phase structure with an optimal proportion and distribution; by combining the selection of the material collection location of the horizontal continuous casting profile with the subsequent heat treatment to control the matrix structure, the self-lubricating effect of the graphite nodules in the ferro-ductile metal during the friction and wear process is fully utilized, thereby solving the problems of high friction coefficient and short service life existing in the prior art.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas field fracturing equipment, and in particular relates to a low-friction-coefficient duplex iron-ductile metal material, and also relates to a preparation method of the low-friction-coefficient duplex iron-ductile metal material. Background Art

[0002] With the rapid development of the machinery manufacturing industry, the number of precision transmission components used in mechanical equipment is increasing. The precision requirements are becoming increasingly higher, and the service assembly clearance requirements are becoming increasingly smaller. Traditional grease lubrication is no longer able to meet these service conditions, and the development of solid self-lubricating materials is urgently needed. Although there are many types of solid self-lubricating materials available, such as molybdenum disulfide, tungsten disulfide, and polytetrafluoroethylene, only iron-ductile metal materials can be used alone as structural materials and meet their mechanical performance and service requirements.

[0003] Iron-ductile metals can be considered a special type of composite material, consisting of a steel-like matrix and spherical graphite. The spherical distribution of graphite within the matrix significantly reduces the graphite's ability to disrupt the matrix. Furthermore, through proper heat treatment and conditioning, the mechanical properties of iron-ductile metals can rival those of cast steel. Furthermore, the presence of graphite in the matrix imparts self-lubricating properties to iron-ductile metals.

[0004] At present, austempered iron-ductile metals are widely used. After austempering heat treatment, iron-graphite metals can obtain a composite structure with spheroidal graphite distributed in a high-carbon residual austenite and acicular ferrite as the matrix. It has certain strength, toughness and wear resistance, and can therefore be widely used in the production of wear-resistant transmission components such as bushings, gears and crankshafts. However, in actual use, it was found that while the austempered transmission components ensure high wear resistance, the overall hardness of the structure is relatively high. During the friction and wear process, the graphite is limited in spreading along the surface of the friction pair and forming a continuous lubricating film layer, resulting in a high friction coefficient. In addition, a large friction force is generated during service, causing severe vibration and severe wear of the transmission system, greatly reducing the service life of the transmission components. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a low friction coefficient duplex iron-ductile metal material, which solves the problems of high friction coefficient and short service life in the prior art.

[0006] Another object of the present invention is to provide a method for preparing a low friction coefficient duplex iron-ductile metal material.

[0007] A technical solution adopted by the present invention is that the low friction coefficient duplex iron-ductile metal material includes the following components in mass percentage: C: 3.5% to 3.8%, Si: 2.3% to 2.8%, Mn: ≤0.6%, S: ≤0.02%, Mg: 0.02% to 0.04%, Re: 0.02% to 0.04%, and the balance is Fe; the total content of the above raw materials is 100%.

[0008] Another technical solution adopted by the present invention is:

[0009] The invention relates to a method for preparing a low friction coefficient duplex iron-ductile metal material, comprising selecting a material sampling location, adopting a heat treatment process, and selecting heat treatment process parameters to obtain a ferrite and martensite two-phase structure with an optimal proportion and distribution.

[0010] The present invention is also characterized in that:

[0011] The method for preparing a low-friction-coefficient duplex iron-ductile metal material is characterized by being implemented in accordance with the following steps:

[0012] Step 1: Weigh the materials with preset components, place them in a medium frequency induction furnace and melt them into molten iron;

[0013] Step 2: Pour the molten iron prepared in step 1 into a ladle to which a spheroidizing agent and an inoculant have been added in advance, inject the resulting liquid into a preheated horizontal continuous casting furnace, and cool and solidify according to a horizontal continuous casting process to obtain a Φ180 mm cylindrical horizontal continuous casting profile;

[0014] Step 3: Select the part with high density of ductile iron to take the material;

[0015] Step 4: austenitizing the obtained material, ferrite precipitating along the interface between austenite and ductile graphite, and obtaining a matrix structure composed of ferrite and martensite, i.e., a low friction coefficient duplex iron-ductile graphite metal material.

[0016] The preset composition in step 1 is C: 3.5% to 3.8%, Si: 2.3% to 2.8%, Mn: ≤0.6%, S: ≤0.02%, P: ≤0.02%, Mg: 0.02% to 0.04%, Re: 0.02% to 0.04%, and the balance is Fe; the sum of the above raw material contents is 100%.

[0017] The total carbon equivalent of the preset composition of the material in step 1 is maintained at 4.3 wt.%.

[0018] In step 2, the graphite is spheroidized and inoculated, the spheroidizing agent is 1.0% to 1.5% by mass of the molten ferrosilicon metal liquid obtained in step 1, and the inoculant is 1.1% to 2.0% by mass of the molten rare earth magnesium metal liquid obtained in step 1;

[0019] In step 3, the graphite density of the cylindrical as-cast horizontal continuous casting profile obtained in step 2 is characterized from the core to the edge, and the part with the highest graphite density is selected for sampling, and the ductile density is not less than 300 / mm 2 .

[0020] In step 4, the material obtained in step 3 is austenitized in a muffle furnace at an austenitizing temperature of 900°C and a holding time of 90 minutes; then the material is cooled to the two-phase region α+γ and held in the furnace. The temperature range of the two-phase region α+γ is 770-850°C, and the holding time is selected as 180 minutes, so that ferrite is fully precipitated along the interface between austenite and ductile iron. After the two-phase region is held in the furnace, oil quenching is directly performed at room temperature to obtain a matrix structure composed of ferrite and martensite with appropriate ratios and distributions.

[0021] The holding temperature of the two-phase region in step 4 is preferably 800°C.

[0022] The beneficial effects of the present invention are: the present invention also has the following advantages:

[0023] 1) Since the material is taken from the edge of the cylindrical horizontal continuous casting profile, the density of ductile iron in the cast iron-ductile metal material is high (not less than 300 / mm 2 ), which laid the foundation for the formation of continuous graphite lubricating film in the subsequent friction and wear process.

[0024] (2) Since the ferrite is preferentially precipitated along the interface between spheroidal graphite and austenite during heat preservation in the two-phase region, a unique structure of soft ferrite distributed around the spheroidal graphite and hard martensite distributed between the spheroidal graphite can be obtained after heat preservation and oil quenching in the two-phase region;

[0025] (3) Due to the selection of appropriate heat treatment process parameters in step 4 of the present invention, a duplex iron-ductile metal structure with an appropriate ratio (50% ferrite + 50% martensite) and distribution is obtained. The soft ferrite phase is distributed around the ductile graphite, and the ductile graphite is easily dragged out during friction and wear to form a continuous graphite lubricating film, which significantly reduces the friction coefficient. The hard martensite phase is distributed between the ductile graphite, providing the material with a certain degree of wear resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a SEM image of the as-cast structure of the iron-ductile metal in Example 1 of the present invention;

[0027] Figure 2 This is a SEM image of the low friction coefficient duplex iron-ductile metal material prepared in Example 1 of the present invention;

[0028] Figure 3 This is a laser confocal image of the friction and wear surface in Example 1 of the present invention;

[0029] Figure 4 This is a comparison chart of the friction coefficients of the low-friction-coefficient duplex iron-ductile metal material prepared in Example 1 of the present invention and traditional iron-ductile metal under different loads. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] The low friction coefficient duplex iron-ductile metal material of the present invention comprises the following components by mass percentage: C: 3.5% to 3.8%, Si: 2.3% to 2.8%, Mn: ≤0.6%, S: ≤0.02%, Mg: 0.02% to 0.04%, Re: 0.02% to 0.04%, and the balance is Fe; the sum of the contents of the above raw materials is 100%.

[0032] The method for preparing a low-friction duplex iron-ductile metal material of the present invention comprises selecting a material source, employing a heat treatment process, and selecting heat treatment process parameters to obtain a ferrite and martensite two-phase structure with an optimal ratio and distribution. The method is specifically implemented in the following steps:

[0033] Step 1: Weigh the materials with preset components, place them in a medium frequency induction furnace and melt them into molten iron;

[0034] The preset composition is C: 3.5%~3.8%, Si: 2.3%~2.8%, Mn: ≤0.6%, S: ≤0.02%, P: ≤0.02%, Mg: 0.02%~0.04%, Re: 0.02%~0.04%, and the balance is Fe; the sum of the contents of the above raw materials is 100%; the total carbon equivalent of the preset composition of the material is maintained at 4.3wt.%.

[0035] Step 2: Pour the molten iron prepared in step 1 into a ladle to which a spheroidizing agent and an inoculant have been added in advance, inject the resulting liquid into a preheated horizontal continuous casting furnace, and cool and solidify according to a horizontal continuous casting process to obtain a Φ180 mm cylindrical horizontal continuous casting profile;

[0036] Spheroidizing and inoculating the graphite, wherein the spheroidizing agent is 1.0% to 1.5% by mass of the molten ferrosilicon metal liquid obtained in step 1, and the inoculant is 1.1% to 2.0% by mass of the molten rare earth magnesium metal liquid obtained in step 1;

[0037] Step 3: Select the part with high density of ductile iron to take the material;

[0038] Characterize the graphite density from the core to the edge of the cylindrical as-cast horizontal continuous casting profile obtained in step 2, and select the part with the highest graphite density for sampling. The ductile density is not less than 300 / mm 2 ;

[0039] Step 4: austenitizing the obtained material, ferrite precipitating along the interface between austenite and ductile graphite, and obtaining a matrix structure composed of ferrite and martensite, i.e., a low friction coefficient duplex iron-ductile graphite metal material.

[0040] The material obtained in step 3 is austenitized in a muffle furnace at an austenitizing temperature of 900° C. and a holding time of 90 min; then cooled to a two-phase region temperature (α+γ) and held in the furnace, wherein the temperature range of the two-phase region α+γ is 770-850° C. and the holding time is selected to be 180 min, so that ferrite is fully precipitated along the interface between austenite and spheroidal graphite. After the two-phase region holding is completed, oil quenching at room temperature is directly performed to obtain a matrix structure consisting of ferrite and martensite with appropriate ratios and distributions;

[0041] The dual phase region holding temperature is preferably 800°C.

[0042] The present invention provides a method for preparing a low-friction duplex ferro-ductile metal material. The friction coefficient of the ferro-ductile metal is primarily determined by two factors: the density of the graphite spheres in the structure, which is the basis for ensuring the formation of a continuous graphite film during friction and wear; and the matrix structure and distribution, which determine the ease with which a graphite lubricating film forms during friction and wear. Therefore, to obtain a low-friction ferro-ductile metal, it is necessary to control and obtain a suitable matrix structure based on a certain spheroidal graphite density to ensure the formation of a continuous graphite lubricating film during friction and wear, thereby maximizing the self-lubricating effect of the graphite in the ferro-ductile metal and reducing the friction coefficient of the transmission components during service.

[0043] Example 1

[0044] The method for preparing a low friction coefficient duplex iron-ductile metal material of the present invention is specifically implemented according to the following steps:

[0045] Step 1. Weigh the following raw materials according to mass percentage: C: 3.5%, Si: 2.3%, Mn: 0.3%, S: ≤0.02%, P: ≤0.02%, Mg: 0.02%~0.04%, Re: 0.02%~0.04%, the remainder is Fe, and the total content of the raw materials is 100%, put them into an induction medium frequency induction furnace and melt them into molten iron.

[0046] Step 2: According to the horizontal continuous casting process, the molten iron in step 1 is poured into a ladle to which 1.0% of 75# ferrosilicon nodularizer and 1.2% of rare earth magnesium inoculant are added in advance to spheroidize and inoculate the graphite. The resulting liquid is then injected into a preheated horizontal continuous casting furnace, cooled and solidified, and the cast morphology is as follows: Figure 1 As shown, a cylindrical horizontal continuous casting profile of Φ180 mm is obtained;

[0047] Step 3: Characterize the graphite density of the obtained cylindrical as-cast horizontal continuous casting profile from the core to the edge, and select the part with the highest graphite density to ensure that the ductile iron material has a ductile density of not less than 300 / mm 2 ;

[0048] Step 4: The obtained material is heated at 900℃ in a muffle furnace and kept at this temperature for 90min to austenitize, and then cooled to the two-phase zone temperature of 780℃ and kept at this temperature for 60min to allow ferrite to fully precipitate along the interface between austenite and spheroidal graphite. After the two-phase zone is kept at this temperature, it is directly oil quenched at room temperature. Figure 2 As shown, a matrix structure consisting of ferrite and martensite phases with appropriate distribution is obtained;

[0049] Step 5: Obtain a dual-phase matrix iron-ductile metal and measure the friction coefficient of the dual-phase iron-ductile metal. Figure 3 As shown in FIG, the friction coefficient of the iron-ductile metal of the present invention is generally lower than that of the traditional material; the graphite lubricating film on the wear surface is characterized, such as Figure 4 As shown, the surface is smooth.

[0050] Example 2

[0051] The method for preparing a low friction coefficient duplex iron-ductile metal material of the present invention is specifically implemented according to the following steps:

[0052] Step 1. Weigh the following raw materials according to mass percentage: C: 3.2%, Si: 2.4%, Mn: 0.4%, S: ≤0.02%, P: ≤0.02%, Mg: 0.02%~0.04%, Re: 0.02%~0.04%, the remainder is Fe, and the total content of the raw materials is 100%, put them into an induction medium frequency induction furnace and melt them into molten iron.

[0053] Step 2: According to the horizontal continuous casting process, the molten iron smelted in step 1 is poured into a ladle to which 1.2% of 75# ferrosilicon nodularizer and 1.3% of rare earth magnesium inoculant by weight of the molten iron are added in advance to spheroidize and inoculate the graphite. The resulting liquid is then injected into a preheated horizontal continuous casting furnace and cooled and solidified to obtain a Φ180 mm cylindrical horizontal continuous casting profile.

[0054] Step 3: Characterize the graphite density of the obtained cylindrical as-cast horizontal continuous casting profile from the core to the edge, and select the part with the highest graphite density to ensure that the ductile iron material has a ductile density of not less than 300 / mm 2 ;

[0055] Step 4: The obtained material is heated at 900° C. in a muffle furnace and kept at this temperature for 90 minutes for austenitization, and then cooled with the furnace to a two-phase temperature of 800° C. and kept at this temperature for 60 minutes, so that ferrite is fully precipitated along the interface between austenite and spheroidal graphite. After the two-phase temperature is kept at this temperature, oil quenching is directly performed at room temperature to obtain a matrix structure composed of ferrite and martensite with an optimal distribution;

[0056] Step 5: Obtain a dual-phase matrix structure of iron-ductile metal, measure the friction coefficient of the dual-phase iron-ductile metal, and characterize the graphite lubricating film on the worn surface.

[0057] Example 3

[0058] The method for preparing a low friction coefficient duplex iron-ductile metal material of the present invention is specifically implemented according to the following steps:

[0059] Step 1. Weigh the following raw materials according to mass percentage: C: 3.4%, Si: 2.6%, Mn: 0.3%, S: ≤0.02%, P: ≤0.02%, Mg: 0.02%~0.04%, Re: 0.02%~0.04%, the remainder is Fe, and the total content of the raw materials is 100%, put the materials into an induction medium frequency induction furnace and melt them into molten iron.

[0060] Step 2: According to the horizontal continuous casting process, the molten iron smelted in step 1 is poured into a ladle to which 1.3% of 75# ferrosilicon nodularizer and 1.5% of rare earth magnesium inoculant by weight of the molten iron are added in advance to spheroidize and inoculate the graphite. The resulting liquid is then injected into a preheated horizontal continuous casting furnace, cooled and solidified, and a Φ180 mm cylindrical horizontal continuous casting profile is obtained.

[0061] Step 3: Characterize the graphite density of the obtained cylindrical as-cast horizontal continuous casting profile from the core to the edge, and select the part with the highest graphite density to ensure that the ductile iron material has a ductile density of not less than 300 / mm 2 ;

[0062] Step 4: The obtained material is heated at 900° C. in a muffle furnace and kept at this temperature for 90 minutes for austenitization, and then cooled with the furnace to a two-phase temperature of 800° C. and kept at this temperature for 180 minutes, so that ferrite is fully precipitated along the interface between austenite and spheroidal graphite. After the two-phase temperature is kept at this temperature, oil quenching at room temperature is directly performed to obtain a two-phase matrix structure of ferrite and martensite with an appropriate proportion and distribution;

[0063] Step 5: Obtain a dual-phase matrix iron-ductile metal, measure the friction coefficient of the dual-phase iron-ductile metal, and characterize the graphite lubricating film on the worn surface.

[0064] Example 4

[0065] The method for preparing a low friction coefficient duplex iron-ductile metal material of the present invention is specifically implemented according to the following steps:

[0066] Step 1. Weigh the following raw materials according to mass percentage: C: 3.3%, Si: 2.5%, Mn: 0.5%, S: ≤0.02%, P: ≤0.02%, Mg: 0.02%~0.04%, Re: 0.02%~0.04%, the remainder is Fe, and the total content of the raw materials is 100%, put them into an induction medium frequency induction furnace and melt them into molten iron.

[0067] Step 2: According to the horizontal continuous casting process, the molten iron smelted in step 1 is poured into a ladle to which 1.3% of 75# ferrosilicon nodularizer and 1.4% of rare earth magnesium inoculant by weight of the molten iron are added in advance to spheroidize and inoculate the graphite. The resulting liquid is then injected into a preheated horizontal continuous casting furnace, cooled and solidified, and a Φ180 mm cylindrical horizontal continuous casting profile is obtained.

[0068] Step 3: Characterize the graphite density of the obtained cylindrical as-cast horizontal continuous casting profile from the core to the edge, and select the part with the highest graphite density to ensure that the ductile iron material has a ductile density of not less than 300 / mm 2 ;

[0069] Step 4: The obtained material is heated at 900° C. in a muffle furnace and kept at this temperature for 90 minutes for austenitization, and then cooled with the furnace to a two-phase temperature of 805° C. and kept at this temperature for 30 minutes, so that ferrite is fully precipitated along the interface between austenite and spheroidal graphite. After the two-phase temperature is kept at this temperature, oil quenching at room temperature is directly performed to obtain a matrix structure composed of ferrite and martensite with appropriate ratios and distributions;

[0070] Step 5: Obtain a dual-phase matrix iron-ductile metal, measure the friction coefficient of the dual-phase iron-ductile metal, and characterize the graphite lubricating film on the worn surface.

[0071] Example 5

[0072] The method for preparing a low friction coefficient duplex iron-ductile metal material of the present invention is specifically implemented according to the following steps:

[0073] Step 1. Weigh the following raw materials according to mass percentage: C: 3.5%, Si: 2.4%, Mn: 0.4%, S: ≤0.02%, P: ≤0.02%, Mg: 0.02%~0.04%, Re: 0.02%~0.04%, the remainder is Fe, and the total content of the raw materials is 100%, put the materials into an induction medium frequency induction furnace and melt them into molten iron.

[0074] Step 2: According to the horizontal continuous casting process, the molten iron smelted in step 1 is poured into a ladle to which 1.4% of 75# ferrosilicon nodularizer and 1.6% of rare earth magnesium inoculant by weight of the molten iron are added in advance to spheroidize and inoculate the graphite. The resulting liquid is then injected into a preheated horizontal continuous casting furnace, cooled and solidified, and a Φ180 mm cylindrical horizontal continuous casting profile is obtained.

[0075] Step 3: Characterize the graphite density of the obtained cylindrical as-cast horizontal continuous casting profile from the core to the edge, and select the part with the highest graphite density to ensure that the ductile iron material has a ductile density of not less than 300 / mm 2 ;

[0076] Step 4: The obtained material is heated at 900° C. in a muffle furnace and kept at this temperature for 90 minutes for austenitization, and then cooled with the furnace to a two-phase temperature of 820° C. and kept at this temperature for 30 minutes, so that ferrite is fully precipitated along the interface between austenite and spheroidal graphite. After the two-phase temperature is kept at this temperature, oil quenching at room temperature is directly performed to obtain a matrix structure composed of ferrite and martensite with appropriate ratios and distributions;

[0077] Step 5: Obtain a dual-phase matrix structure of iron-ductile metal, measure the friction coefficient of the dual-phase iron-ductile metal, and characterize the graphite lubricating film on the worn surface.

[0078] The present invention provides a method for preparing a low-friction duplex iron-ductile iron metal material. By using a suitable heat treatment process and adjusting heat treatment process parameters, a ferrite / martensite dual-phase matrix structure is introduced into the ductile iron. The two phases in this structure are distributed in a unique manner: soft-phase ferrite is distributed around the ductile iron, while hard-phase martensite is primarily distributed between the graphite nodules. During the friction and wear process, under the action of frictional forces, the graphite nodules are easily pulled out of the soft-phase ferrite and form a graphite lubricating film on the worn surface, thereby fully utilizing the self-lubricating effect of the graphite in the iron-ductile iron metal. The martensite distributed between the nodules provides wear resistance, ultimately producing an iron-ductile iron metal with an extremely low friction coefficient. This method also provides practical guidance for the application of iron-ductile iron metal in self-lubricating parts.

Claims

1. A method for preparing a low friction coefficient duplex iron-ductile metal material, characterized in that: Select the material location, heat treatment process, and heat treatment process parameters to obtain the optimal proportion and distribution of ferrite and martensite two-phase structure; Please follow the steps below to implement it: Step 1: Weigh the materials with preset components, place them in a medium frequency induction furnace and melt them into molten iron; Step 2: Pour the molten iron prepared in step 1 into a ladle to which a spheroidizing agent and an inoculant have been added in advance, inject the resulting liquid into a preheated horizontal continuous casting furnace, and cool and solidify according to a horizontal continuous casting process to obtain a Φ180 mm cylindrical horizontal continuous casting profile; Step 3: Select the part with high density of ductile iron to take the material; Step 4: austenitizing the obtained material, ferrite precipitating along the interface between austenite and ductile graphite, and obtaining a matrix structure consisting of ferrite and martensite, i.e., a low friction coefficient duplex iron-ductile graphite metal material; The preset components in step 1 are C: 3.5%~3.8%, Si: 2.3%~2.8%, Mn: ≤0.6%, S: ≤0.02%, P: ≤0.02%, Mg: 0.02%~0.04%, Re: 0.02%~0.04%, and the balance is Fe; The total carbon equivalent of the preset composition of the material in step 1 is maintained at 4.3 wt.%; In the step 2, the graphite is spheroidized and inoculated, the spheroidizing agent is 1.0% to 1.5% of the mass of the molten iron obtained in step 1, and the inoculant is 1.1% to 2.0% of the mass of the molten iron obtained in step 1; In step 3, the spheroidal graphite density of the cylindrical as-cast horizontal continuous casting profile obtained in step 2 is characterized from the core to the edge, and the part with the highest spheroidal graphite density is selected for sampling, and the spheroidal graphite density is not less than 300 / mm 2 ; In the step 4, the material obtained in step 3 is austenitized in a muffle furnace at an austenitizing temperature of 900°C and a holding time of 90 minutes; then the material is cooled with the furnace to the two-phase region α+γ for holding, the temperature range of the two-phase region α+γ is: 770-850°C, and the holding time is selected as 180 minutes, so that ferrite is fully precipitated along the interface between austenite and spheroidal graphite. After the two-phase region holding is completed, oil quenching at room temperature is directly performed to obtain a matrix structure composed of ferrite and martensite with appropriate ratios and distributions.

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