Nitriding performance and deformation prediction method of spheroidal graphite cast iron cylinder block plunger hole

Abstract

The application belongs to the technical field of preparation of plunger pump cylinder body, and particularly relates to a nodizing performance and deformation prediction method for a nodized cylinder plunger hole of a nodular cast iron cylinder body, which comprises the following steps: constructing a relationship model of nodizing time-cylindricality increment before and after nodizing treatment, and a relationship model of nodizing time-nodized layer depth; based on the relationship model of nodizing time-cylindricality increment before and after nodizing treatment and the relationship model of nodizing time-nodized layer depth, the cylindricality increment of a target nodular cast iron cylinder body before and after nodizing treatment and the nodized layer depth D under a preset nodizing time are calculated; the target nodular cast iron cylinder body is a nodular cast iron cylinder casting formed based on a sand mold casting process, and the nodular cast iron cylinder casting is sequentially subjected to stress relief annealing, rough and fine machining, and nodizing treatment. The application realizes accurate prediction and balanced control of the nodized layer depth and nodizing deformation, reduces trial and error costs, and shortens the process debugging period.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of preparation of plunger pump cylinder body, and particularly relates to a nitriding performance and deformation prediction method for a plunger hole of a nodular cast iron cylinder body. BACKGROUND

[0002] The nodular cast iron cylinder body is widely used in hydraulic plunger pumps due to its good casting performance, machining performance and vibration absorption performance. As one of the key components, the plunger hole surface of the nodular cast iron cylinder body is usually gas nitrided to form a nitriding layer, so as to enhance the hardness and wear resistance of the plunger hole surface of the cylinder body. However, due to the formation of the nitriding layer, the cylindricity of the plunger hole will change, and in severe cases, cylindricity out-of-tolerance will occur, resulting in product scrap. Industry technical personnel try to overcome it by optimizing the nitriding process, but the optimization of the conventional nitriding process is tested by physical test, which requires a large amount of time and samples, and consumes a lot of manpower and financial resources.

[0003] In addition, the nodular cast iron cylinder body is usually sand cast, and the plunger hole has high requirements for nitriding performance and nitriding deformation. When the nitriding process is designed, both deformation and nitriding performance need to be ensured, and at present, the two cannot be accurately balanced.

[0004] Therefore, in view of the above problems, the present application is proposed. SUMMARY

[0005] The main purpose of the present application is to provide a nitriding performance and deformation prediction method for a plunger hole of a nodular cast iron cylinder body. The method is for a nodular cast iron cylinder body formed by a sand casting process. By establishing a relationship model of nitriding time-nitriding layer depth and a relationship model of nitriding time-cylindricity increment before and after nitriding treatment, accurate prediction and balanced control of the nitriding layer depth and nitriding deformation are achieved, the trial and error cost is reduced, and the process debugging cycle is shortened.

[0006] The first aspect of the present application provides a nitriding performance and deformation prediction method for a plunger hole of a nodular cast iron cylinder body, which comprises the following steps: constructing a relationship model of nitriding time-cylindricity increment before and after nitriding treatment and a relationship model of nitriding time-nitriding layer depth; based on the relationship model of nitriding time-cylindricity increment before and after nitriding treatment and the relationship model of nitriding time-nitriding layer depth, calculating the cylindricity increment before and after nitriding treatment of a target nodular cast iron cylinder body under a preset nitriding time and the nitriding layer depth D; wherein the target nodular cast iron cylinder body is a nodular cast iron cylinder body casting formed based on a sand casting process, and the nodular cast iron cylinder body casting is sequentially subjected to stress relief annealing, rough machining, fine machining and nitriding treatment. In some embodiments, the relationship model of nitriding time-cylindricity increment before and after nitriding treatment is:

[0007] ​wherein, is the increment of cylindricity before and after nitriding treatment, t is the nitriding time, is 0.0002, and b is 0.0001-0.0004.

[0008] In some embodiments, the relationship model of the nitriding time-increment of cylindricity before and after nitriding treatment is: is 0.0002, and b is 0.0002.

[0009] In some embodiments, the relationship model of the nitriding time-nitriding layer depth is: wherein, D is the nitriding layer depth, t is the nitriding time, 1 is 0.007-0.009, and b1 is 0.04-0.07.

[0010] In some embodiments, the relationship model of the nitriding time-nitriding layer depth is: 1 is 0.007, and b1 is 0.07.

[0011] In some embodiments, in the metallographic structure of the spheroidal graphite cast iron cylinder block casting, the pearlite content is ≥70%, and the range difference of the pearlite content at each part of the spheroidal graphite cast iron cylinder block casting is less than 20%.

[0012] In some embodiments, in the metallographic structure of the spheroidal graphite cast iron cylinder block casting, the graphite spheroidization level is 1-3, and the graphite ball size is 5-7, and the difference of the graphite ball size level at each part of the spheroidal graphite cast iron cylinder block casting is not more than 1 level.

[0013] In some embodiments, the tensile strength of the spheroidal graphite cast iron cylinder block casting is ≥550 MPa.

[0014] In some embodiments, in the casting process of the spheroidal graphite cast iron cylinder block casting, the alloy content is controlled by an alloying method to obtain the spheroidal graphite cast iron cylinder block casting; the alloying method comprises adding Cu 0.2%-0.6% and Sn 0.020%-0.060% by mass percentage to the molten iron.

[0015] In some embodiments, the temperature of the stress relief annealing is 530°C-580°C, and the time is 2 h-5 h.

[0016] In some embodiments, after the stress relief annealing is completed, the temperature is lowered to 200°C at a cooling rate lower than 60°C / h, and then the furnace is discharged.

[0017] In some embodiments, the nitriding treatment adopts a nitrocarburizing process, including a one-stage nitriding process, wherein the temperature of the one-stage nitriding process is 540-560 DEG C, the nitriding time is 7-22 h, the nitrogen potential value is 1-3, and then the furnace is cooled to 200 DEG C and the casting is taken out for air cooling.

[0018] In some embodiments, the construction of the relationship model of the nitriding time and the increment of the cylindricity before and after the nitriding treatment, and the relationship model of the nitriding time and the nitriding layer depth comprises: obtaining the plunger hole cylindricity Y1 and Y2 of the target nodular cast iron cylinder before and after the nitriding treatment, the nitriding layer depth D obtained after the nitriding treatment, and the nitriding time; and obtaining the relationship model of the nitriding time and the increment of the cylindricity before and after the nitriding treatment, and the relationship model of the nitriding time and the nitriding layer depth through linear fitting.

[0019] Advantages of the present application:

[0020] (1) The present application innovatively establishes a linear relationship model of the nitriding time (t) and the increment of the cylindricity before and after the nitriding treatment (Y1-Y2), and a linear relationship model of the nitriding time (t) and the nitriding layer depth (D), and for the first time realizes the synchronous quantitative prediction of the nitriding layer depth and the deformation, with high prediction accuracy and shortened process debugging period.

[0021] (2) The present application strictly limits the matrix structure, graphite morphology and uniformity of the nodular cast iron cylinder casting, fundamentally ensures the stability of the material response in the nitriding process, breaks through the limitation of the traditional process which only relies on the adjustment of the nitriding parameters, and improves the model prediction accuracy.

[0022] The above description is only a summary of the technical solutions of the present application, in order to more clearly understand the technical means of the present application, the content of the specification can be implemented, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. DETAILED DESCRIPTION

[0023] The exemplary embodiments of the present application will be described in more detail hereinafter with reference to specific embodiments. It should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided so that the present application can be more thoroughly understood and the scope of the present application can be fully conveyed to those skilled in the art.

[0024] ​Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the use of the terms "including," "comprising," "having" and variations thereof herein is meant to encompass the items listed thereafter, but does not exclude additional, unrecited items.

[0025] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0026] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, or necessarily alternatives to other embodiments. It will be explicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0027] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of existence of A, existence of A and B, and existence of B. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0028] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0029] In the description of the embodiments of the present application, unless otherwise specified and limited, the technical terms "mounting", "connecting", "connecting", "fixing" and the like should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanical connection, or it can be electrical connection; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0030] The nodular cast iron cylinder body is cast by sand mold, the plunger hole has high requirements for nitriding performance and nitriding deformation, the deformation and nitriding performance need to be ensured at the same time when designing the nitriding process, and the two cannot be accurately balanced. Currently, the nitriding temperature is generally 500-590 DEG C, the nitrogen potential is 0.5-3, the thickness of the nitriding layer is 0.1-0.4 mm obtained by rapid cooling, and the roundness requirement after nitriding treatment is within 0.01 mm.

[0031] The application provides a method for predicting the nitriding performance and deformation of a plunger hole of a nodular cast iron cylinder body, and the key of the method is to construct a relationship model of nitriding time-roundness increment before and after nitriding treatment and a relationship model of nitriding time-nitriding layer depth. And the nitriding layer depth D is calculated based on the relationship model of nitriding time-roundness increment before and after nitriding treatment and the relationship model of nitriding time-nitriding layer depth.

[0032] In the embodiment of the application, for the nodular cast iron cylinder body cast by sand mold, the relationship model of nitriding time-nitriding layer depth and the relationship model of nitriding time-roundness increment before and after nitriding treatment are established, the simultaneous quantitative prediction of the nitriding layer depth and the deformation is realized for the first time, the accurate prediction and balance control of the nitriding layer depth and the nitriding deformation are realized, the trial and error cost is reduced, and the process debugging cycle is shortened.

[0033] In some embodiments, the relationship model of nitriding time-roundness increment before and after nitriding treatment is: Wherein, is the roundness increment before and after nitriding treatment, t is the nitriding time, is 0.0002, and b is 0.0001-0.0004. In this way, the roundness increment before and after nitriding treatment of the target nodular cast iron cylinder body at different times can be calculated.

[0034] In some embodiments, in the relationship model of nitriding time-roundness increment before and after nitriding treatment, is 0.0002, and b can be one of 0.0001, 0.0002, 0.0003 and 0.0004 or any numerical value meeting the above range.

[0035] In some embodiments, the relationship model of nitriding time-nitriding layer depth is: Wherein, D is the nitriding layer depth, t is the nitriding time, ​1 is 0.007~0.009, and b1 is 0.04~0.07. In this way, the nitrided layer depth D of the target nodular cast iron cylinder block at different times can be calculated.

[0036] In some embodiments, in the relationship model of nitriding time-nitrided layer depth, 1 is one of 0.007, 0.008, 0.009 or any value satisfying the above range.

[0037] In some embodiments, in the relationship model of nitriding time-nitrided layer depth, b1 is one of 0.04, 0.05, 0.06, 0.07 or any value satisfying the above range.

[0038] In some embodiments, in the metallographic structure of the nodular cast iron cylinder block casting prepared by the sand casting process, the pearlite content is ≥70%, and the pearlite content range difference at different positions of each part of the nodular cast iron cylinder block casting is less than 20%. In this way, by strictly limiting the pearlite content of the nodular cast iron cylinder block casting, the non-uniform stress in the nitriding process is reduced, and the stability of the subsequent nitriding parameters on the deformation of the plunger hole and the nitrided layer depth is improved.

[0039] In some embodiments, in the metallographic structure of the nodular cast iron cylinder block casting, the graphite spheroidization level is 1~3, and the graphite ball size is 5~7, and the graphite ball size level difference at different positions of each part of the nodular cast iron cylinder block casting is not more than 1 level.

[0040] In this way, by strictly limiting the pearlite content and graphite morphology of the nodular cast iron cylinder block casting, the homogeneous matrix structure and graphite distribution are achieved, the non-uniform stress in the nitriding process is reduced, and the stability of the subsequent nitriding parameters on the deformation of the plunger hole and the nitrided layer depth is improved.

[0041] In some embodiments, the tensile strength of the nodular cast iron cylinder block casting is ≥550 MPa.

[0042] In some embodiments, in the casting process of the nodular cast iron cylinder block casting, the alloy content is controlled by alloying to prepare the nodular cast iron cylinder block casting. In this way, by using the alloying method, the pearlite content in the metallographic structure of the nodular cast iron cylinder block casting is controlled by controlling the alloy content, the pearlite content is achieved to be more than 70%, the pearlite content difference at different positions of the nodular cast iron cylinder block casting is ≤20%; and the graphite spheroidization level is achieved to be 1~3, the graphite ball size is 5~7, and the graphite ball size difference at different positions of the nodular cast iron cylinder block casting is not more than 1 level.

[0043] Specifically, the alloying method includes adding copper (Cu) 0.2%~0.6% and tin (Sn) 0.020%~0.060% by mass percentage to the molten iron. Exemplarily, the mass percentage of Cu can be one of 0.2%, 0.3%, 0.4%, 0.5%, 0.6% or any value meeting the above range. The mass percentage of Sn can be one of 0.020%, 0.030%, 0.040%, 0.050%, 0.060% or any value meeting the above range.

[0044] In some embodiments, by adding copper (Cu) 0.2%~0.6% and tin (Sn) 0.020%~0.060% by mass percentage in the alloying process during sand casting, the chemical composition of the obtained ductile iron cylinder block casting (by mass percentage) includes: C 3.0%~3.85%, Si 2.0%~2.9%, Mn≤0.7%, S 0.008%~0.020%, P≤0.06%, Cu 0.2%~0.8%, Sn 0.020%~0.080%, Mg 0.030%~0.050%, Re 0.010%~0.030%, and the balance being Fe.

[0045] In some embodiments, the temperature of the stress relief annealing is 530℃~580℃, which can also be understood as the holding temperature of the stress relief annealing is 530℃~580℃. Exemplarily, the temperature of the stress relief annealing can be one of 530℃, 540℃, 550℃, 560℃, 570℃, 580℃ or any value meeting the above range.

[0046] In some embodiments, the time of the stress relief annealing is 2 h~5 h, which can also be understood as the holding time of the stress relief annealing is 2 h~5 h. Exemplarily, the time of the stress relief annealing can be one of 2 h, 3 h, 4 h, 5 h or any value meeting the above range.

[0047] By controlling the above stress relief annealing temperature and time, it is helpful to eliminate the residual stress of the structure, reduce the decomposition of the pearlite structure, and reduce the change of the structure.

[0048] In some embodiments, after the holding of the stress relief annealing is completed, the cooling is performed at a cooling rate lower than 60℃ / h to 200℃, and then the furnace is discharged. Exemplarily, the cooling rate can be one of 60℃ / h, 55℃ / h, 50℃ / h, 40℃ / h, 30℃ / h, 20℃ / h, 10℃ / h or any value meeting the above range.

[0049] In some embodiments, the cylinder casting obtained through the above steps is a blank, and rough machining and finish machining are required to improve the surface quality and the size and shape accuracy of the cylinder casting.

[0050] In some embodiments, the cylinder casting obtained through the above finish machining is subjected to nitriding treatment to form a nitriding layer or hardening layer on the surface of the cylinder casting.

[0051] In some embodiments, the nitriding treatment adopts nitrocarburizing process, including one-stage nitriding, and the one-stage nitriding adopts a low temperature, i.e., a temperature lower than 560°C, to improve the uniformity of the temperature field in the nitriding furnace and reduce the axial and radial deformation of the hole type part.

[0052] In some embodiments, the one-stage nitriding has a nitrogen potential (Kn) value of 1-3. For example, the one-stage nitriding can have a nitrogen potential value of one of 1, 2 and 3 or any value within the above range.

[0053] In some embodiments, the one-stage nitriding has a nitriding temperature of 540-560°C. For example, the one-stage nitriding can have a nitriding temperature of one of 540°C, 545°C, 550°C, 555°C and 560°C or any value within the above range.

[0054] In some embodiments, the one-stage nitriding has a nitriding time of 7-22 hours. For example, the nitriding time can be one of 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours and 22 hours or any value within the above range.

[0055] In some embodiments, after the one-stage nitriding, high-flow nitrogen gas is used to cool the cylinder part to below 200°C for air cooling.

[0056] In some embodiments, the nitrogen flow rate during the cooling process is 10-20 times the volume of the nitrogen furnace.

[0057] The temperature, time, nitrogen potential (Kn) value and the like of the one-stage nitriding are set in this way to improve the uniformity of the temperature field in the nitriding furnace and reduce the axial and radial deformation of the hole type part.

[0058] In the embodiments of the present application, the construction of the relationship model of the nitriding time and the cylinder degree increment before and after the nitriding treatment, and the relationship model of the nitriding time and the nitriding layer depth comprises: obtaining the plunger hole cylinder degrees Y1 and Y2 of the target nodular cast iron cylinder before and after the nitriding treatment, the nitriding layer depth D obtained after the nitriding treatment, and the nitriding time; and constructing the relationship model of the nitriding time and the cylinder degree increment before and after the nitriding treatment, and the relationship model of the nitriding time and the nitriding layer depth through linear fitting.

[0059] It is worth mentioning that the target nodular cast iron cylinder refers to the one prepared by the same preparation process, and can also be understood as the nodular cast iron cylinder obtained by sequentially performing stress relief annealing, rough and fine machining, and nitriding treatment on the nodular cast iron cylinder casting formed by the sand casting process.

[0060] Unless defined, the technical terms used in the following examples have the same meanings as generally understood by those skilled in the art to which the present application belongs. The experimental reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the raw materials, instruments and equipment used in the following examples, unless otherwise specified, can be purchased on the market or obtained by existing methods; the amount of the experimental reagents, unless otherwise specified, is the amount of reagents in conventional experimental operations; the experimental methods, unless otherwise specified, are conventional methods. It needs to be further explained that the following description is only exemplary and is not a specific limitation of the present application.

[0061] The construction methods of the relationship model of the cylindricality increment before and after nitriding and the relationship model of the nitriding time-nitriding layer depth are illustrated by the following Examples 1 to 3. The prediction method in the present application is verified by Example 4.

[0062] It needs to be explained that the relationship model of the cylindricality increment before and after nitriding and the relationship model of the nitriding time-nitriding layer depth provided in the present application are constructed based on a large amount of real experimental data, and can also be understood as the relationship model of the cylindricality increment before and after nitriding and the relationship model of the nitriding time-nitriding layer depth constructed based on a large amount of real experimental data of the nodular cast iron cylinder, which is obtained by sequentially performing stress relief annealing, rough and fine machining, and nitriding treatment on the nodular cast iron cylinder casting formed by the sand casting process, while the following is only an exemplary description of the construction method.

[0063] Example 1

[0064] A plunger pump cylinder is produced, wherein the diameter of the plunger hole is 33.5 mm and the height is 140 mm.

[0065] The preparation method of the plunger pump cylinder comprises the following steps:

[0066] 1) Adopting sand casting process and adding alloy elements Cu and Sn during casting to obtain the nodular cast iron cylinder block castings. The nodular cast iron cylinder block castings comprise the following components in mass percentage: C 3.77%, Si 2.28%, Mn 0.38%, S 0.012%, P 0.024%, Cu 0.44%, Sn 0.020%, Mg 0.042%, Re 0.010%, and the balance of Fe.

[0067] In the metallographic structure of the nodular cast iron cylinder block castings, the pearlite content is 75%, and the difference of the pearlite content at each part of the nodular cast iron cylinder block castings is 5%; the graphite spheroidization level is grade 3, the graphite ball size is grade 5, and the difference of the graphite ball size at each part of the nodular cast iron cylinder block castings is not more than 1 grade.

[0068] 2) The nodular cast iron cylinder block castings are subjected to stress relief annealing, after being kept at 530℃ for 3 h, the temperature is decreased to 200℃ at a cooling rate of 55℃ / h, and then the castings are taken out of the furnace.

[0069] 3) The nodular cast iron cylinder block castings are subjected to rough machining and finish machining, and the plunger hole cylindricity Y1 is 0.0048.

[0070] 4) The nodular cast iron cylinder block castings are subjected to nitriding treatment. The nitriding treatment adopts nitrocarburizing process, and the nitriding treatment comprises one-stage nitriding, the temperature of the one-stage nitriding is 560℃, the nitrogen potential Kn value is 2, the nitriding time is 7 h, the furnace is cooled to 200℃, and then the castings are taken out of the furnace and air-cooled.

[0071] 5) The plunger hole cylindricity Y2 and the nitriding layer depth D of the nodular cast iron cylinder block castings after the nitriding treatment are detected, and the cylindricity increment before and after the nitriding treatment is calculated.

[0072] Example 2

[0073] Example 2 is different from Example 1 only in that the nitriding time is 15 h, and the rest of the operations are the same as those in Example 1.

[0074] Example 3

[0075] Example 3 is different from Example 1 only in that the nitriding time is 22 h, and the rest of the operations are the same as those in Example 1.

[0076] Examples 1 to 3 are subjected to the detection of the nitriding layer depth D and the plunger hole cylindricity Y1 and Y2 of the nodular cast iron cylinder block castings before and after the nitriding treatment according to the same detection method, and the detection results are shown in Table 1.

[0077] Table 1

[0078] ​

[0079] The fitting is constructed by using software and based on the following formulas (1)-(2).

[0080] (1)

[0081] (2)

[0082] In the formulas (1)-(2), , b, 1, b1 are constants, is the increment of the cylindricity before and after the nitriding treatment, D is the nitriding layer depth, and t is the nitriding time.

[0083] The relationship model of the nitriding time-increment of the cylindricity before and after the nitriding treatment is constructed as follows: = 0.0002 t + 0.0002.

[0084] The relationship model of the nitriding time-nitriding layer depth is constructed as follows: D = 0.007 t + 0.07.

[0085] Example 4

[0086] A plunger pump cylinder body is produced, wherein the plunger hole diameter is 33.5 mm, and the height is 140 mm.

[0087] The preparation method of the plunger pump cylinder body comprises the following steps:

[0088] 1) A sand casting process is used, and alloying is performed by adding alloy elements Cu and Sn during the casting process to obtain a nodular cast iron cylinder body casting. The nodular cast iron cylinder body casting comprises the following components in mass percentage: C 3.77%, Si 2.28%, Mn 0.38%, S 0.012%, P 0.024%, Cu 0.44%, Sn 0.020%, Mg 0.042%, Re 0.010%, and the balance is Fe.

[0089] In the metallographic structure of the nodular cast iron cylinder body casting, the pearlite content is 75%, and the difference in the pearlite content at each part of the nodular cast iron cylinder body casting is 5%; the graphite spheroidization level is grade 3, the graphite ball size is grade 5, and the difference in the graphite ball size at each part of the nodular cast iron cylinder body casting is not more than 1 grade.

[0090] 2) The nodular cast iron cylinder body casting is subjected to stress relief annealing, and after being kept at 530℃ for 3 h, the temperature is lowered to 200℃ at a cooling rate of 55℃ / h, and then the casting is taken out of the furnace.

[0091] 3) The nodular cast iron cylinder body casting is subjected to rough machining and finishing, and the cylindricity Y1 of the plunger hole is 0.0048.

[0092] 4) The nodular cast iron cylinder block casting is subjected to nitriding treatment, wherein the nitriding treatment adopts nitrocarburizing process, the nitriding treatment comprises one-stage nitriding, the temperature of one-stage nitriding is 555 DEG C, the nitrogen potential Kn value is 2, the nitriding time is 18 h, and the furnace is cooled to 200 DEG C and then taken out for air cooling.

[0093] 5) Based on the relationship model of nitriding time-cylindricality increment before and after nitriding treatment and the relationship model of nitriding time-nitriding layer depth, the cylindricality increment of the nodular cast iron cylinder block before and after nitriding treatment under the nitriding time is calculated. And the nitriding layer depth D.

[0094] 6) The plunger hole cylindricality Y2 of the nodular cast iron cylinder block after nitriding treatment and the nitriding layer depth D are detected at the same time, and the cylindricality increment before and after nitriding treatment is calculated. The detection results are shown in Table 2.

[0095] Table 2

[0096]

[0097] It can be seen from Table 2 that the nitriding performance and deformation prediction method of the plunger hole of the nodular cast iron cylinder block can predict the nitriding layer depth D and the cylindricality increment of the nodular cast iron cylinder block prepared based on the sand casting process, the prediction accuracy is high, the synchronous quantitative prediction of the nitriding layer depth D and the cylindricality increment is realized, and the process debugging period is shortened.

[0098] The above describes only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any changes or replacements within the technical range disclosed by the present application can be easily thought by those skilled in the art, and should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.​​

Claims

1. A method for predicting the nitriding performance and deformation of plunger holes in ductile iron cylinder blocks, characterized in that, Includes the following steps: Construct a model relating nitriding time to the increase in cylindricity before and after nitriding treatment, and The relationship model between nitriding time and nitrided layer depth; the relationship model between nitriding time and cylindricity increment before and after nitriding treatment is as follows: ,in, The cylindricity increment before and after nitriding is given by t, where t is the nitriding time. The nitriding time is 0.0002, and the nitriding depth is 0.0001~0.0004; the relationship model between the nitriding time and the nitriding layer depth is as follows: Where D is the nitriding layer depth and t is the nitriding time. 1 is 0.007~0.009, b1 is 0.04~0.07; Based on the relationship model between nitriding time and the cylindricity increment before and after nitriding treatment, and the relationship model between nitriding time and nitriding layer depth, the cylindricity increment of the target ductile iron cylinder block before and after nitriding treatment at the preset nitriding time was calculated. and nitrided layer depth D; The target ductile iron cylinder block is formed by sand casting and then subjected to stress-relief annealing, rough and fine machining, and nitriding treatment. The nitriding treatment adopts a nitrocarburizing process, including a first-stage nitriding, with a temperature of 540℃~560℃, a nitriding time of 7 h~22 h, and a nitrogen potential value of 1~3. After that, it is cooled in the furnace to 200℃ and then air-cooled. In the metallographic structure of the ductile iron cylinder block casting, the pearlite content is ≥70%, and the range of pearlite content in different parts of the ductile iron cylinder block casting is less than 20%. In the metallographic structure of the ductile iron cylinder block casting, the graphite spheroidization level is 1 to 3, the graphite spheroid size is 5 to 7, and the difference in graphite spheroid size level at different parts of the ductile iron cylinder block casting does not exceed 1 level. The tensile strength of the ductile iron cylinder block casting is ≥550 MPa.

2. The method for predicting the nitriding performance and deformation of the plunger bore in a ductile iron cylinder block as described in claim 1, characterized in that, In the relationship model between nitriding time and the increase in cylindricity before and after nitriding treatment... The value of b is 0.0002.

3. The method for predicting the nitriding performance and deformation of the plunger bore in a ductile iron cylinder block as described in claim 1, characterized in that... In the relationship model between nitriding time and nitriding layer depth 1 is 0.007, b1 is 0.

07.

4. The method for predicting the nitriding performance and deformation of the plunger bore in a ductile iron cylinder block as described in claim 1, characterized in that, During the casting process of the ductile iron cylinder block casting, the alloy content is controlled by alloying to obtain the ductile iron cylinder block casting. The alloying method includes adding 0.2% to 0.6% Cu and 0.020% to 0.060% Sn by mass percentage to the molten iron.

5. The method for predicting the nitriding performance and deformation of the plunger bore in a ductile iron cylinder block as described in claim 1, characterized in that, The stress-relief annealing temperature is 530℃~580℃, and the time is 2 h~5 h; and / or, After the stress-relief annealing is completed, the temperature is reduced to 200°C at a rate of less than 60°C / h before being removed from the furnace.

6. The method for predicting the nitriding performance and deformation of the plunger bore in a ductile iron cylinder block as described in claim 1, characterized in that, The construction of the relationship model between nitriding time and the cylindricity increment before and after nitriding, and the relationship model between nitriding time and nitrided layer depth, includes: Obtain the cylindricity Y1 and Y2 of the plunger hole of the target ductile iron cylinder block before and after nitriding treatment, the nitriding layer depth D obtained after nitriding treatment, and the nitriding time; The relationship models between nitriding time and cylindricity increment before and after nitriding treatment, as well as the relationship model between nitriding time and nitrided layer depth, were obtained by linear fitting.

Images