Martensitic stainless steel and process for making a valve case for a fracturing pump hydraulic end by means thereof

Abstract

The present disclosure relates to the technical field of stainless steel materials, and particularly relates to a martensitic stainless steel and a process for preparing a fracturing pump fluid end valve box by using the same. The martensitic stainless steel comprises the following components in mass percent: C: a%, Mn: 0.30%-0.60%, Si: 0.25%-0.65%, Ni: b%, Cr: c%, Mo: 0.25%-0.45%, Nb: d%, P: e%, S: ≤0.02%; the rest is Fe and inevitable impurities; wherein a, b, c, d and e satisfy the following relationships: 1.8≤(d / a)≤4.2; 5.8≤(d / e); 2.2≤(c / b)≤3.8. The stainless steel material satisfying the above relationships can achieve a balance between tensile strength, yield strength and hardness.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of stainless steel materials, and particularly relates to a martensitic stainless steel and a process for preparing a fracturing pump fluid end valve box therefrom. BACKGROUND

[0002] The fracturing pump fluid end valve box is one of the most important components of the fracturing pump, and is mainly used in oil and gas field operations to inject a large amount of fracturing medium, including acidic liquid, proppant, etc., into the oil and gas well. The working environment of the fracturing pump fluid end valve box is harsh, and it is in a strong acidic corrosion, high pressure alternating load, high speed and high pressure erosion of solid-liquid medium. Therefore, the fracturing pump fluid end valve box is required to have excellent contact fatigue performance, wear resistance and corrosion resistance, and a long service life, so as to improve the fracturing construction efficiency.

[0003] With the development of the steel for the fracturing pump fluid end valve box, the matching of strength and toughness has become one of the important indicators for the material of the fracturing pump valve box. The matching of strength and toughness of the medium-carbon CrNiMoV steel can meet the specification requirements of the material performance in the harsh fracturing environment, but the corrosion resistance, especially the stress corrosion resistance, is poor. In the actual use process, the high stress and acidic fracturing liquid medium corrosion lead to the decrease of the service life. The precipitation hardening type stainless steel represented by 17-4PH has excellent stress corrosion resistance under the condition that the strength and toughness are the same as those of the traditional CrNiMoV steel, and has become a new generation of valve box steel that can replace the CrNiMoV steel.

[0004] The 17-4PH steel is a martensitic precipitation hardening type stainless steel containing Cu. During solid solution treatment, Cu is dissolved in the matrix, and there is a large supersaturation in the transformed martensite during cooling. In the subsequent aging, Cu-rich precipitates are precipitated to produce hardening effect. However, in the process of forging, the presence of Cu-rich precipitates easily leads to cracking of the forged piece in the processes of upsetting, lengthening and extrusion, so that the production cannot proceed normally, causing loss. The high content of Cr and Ni alloying elements in the 17-4PH steel ensures high mechanical properties and corrosion resistance. However, during high-temperature austenitizing, the high content of Cr, a ferrite forming element, causes segregation and promotes the formation of δ-ferrite, resulting in differences in the transverse and longitudinal properties of the steel.

[0005] Therefore, there is an urgent need for a new type of high-performance martensitic stainless steel without copper, so as to be better applicable to the fracturing pump fluid end valve box. SUMMARY

[0006] The present disclosure provides a martensitic stainless steel and a process for preparing a fracturing pump fluid end valve box therefrom, to solve the problems in the prior art.

[0007] According to a first aspect of the embodiments of the present disclosure, a martensitic stainless steel is provided, which comprises the following components in mass %:

[0008] C: a%, Mn: 0.30-0.60%, Si: 0.25-0.65%, Ni: b%, Cr: c%, Mo: 0.25-0.45%, Nb: d%, P: e%, S: ≤0.02%; the balance being Fe and unavoidable impurities;

[0009] wherein a, b, c, d, e satisfy the following relationships: 1.8≤(d / a)≤4.2; 5.8≤(d / e); 2.2≤(c / b)≤3.8.

[0010] In an aspect of the embodiments of the present disclosure, 0.04≤a≤0.07; 4.5≤b≤5.5; 14.5≤c≤15.5; 0.15≤d≤0.35; 0.005≤e≤0.0259.

[0011] In an aspect of the embodiments of the present disclosure, preferably, 0.04≤a≤0.06; 4.5≤b≤5.2; 14.5≤c≤15.0; 0.18≤d≤0.26; 0.0075≤e≤0.02.

[0012] In an aspect of the embodiments of the present disclosure, further preferably, 0.04≤a≤0.06; 4.5≤b≤5.2; 14.5≤c≤15.0; 0.20≤d≤0.22; 0.0090≤e≤0.015.

[0013] In an aspect of the embodiments of the present disclosure, further preferably, 0.052≤a≤0.057; 4.6≤b≤4.9; 14.7≤c≤15.0; 0.20≤d≤0.22; 0.0095≤e≤0.012.

[0014] In an aspect of the embodiments of the present disclosure, specifically, a is 0.055, b is 4.763, c is 14.82, d is 0.2102, and e is 0.0107.

[0015] In an aspect of the embodiments of the present disclosure, a, b, c, d, e satisfy the following relationships: 3.65≤(d / a)≤4.15; 12.20≤(d / e); 2.65≤(c / b)≤3.45.

[0016] In an aspect of the embodiments of the present disclosure, a, b, c, d, e satisfy the following relationships: 3.75≤(d / a)≤3.95; 16.55≤(d / e); 3.05≤(c / b)≤3.25.

[0017] In an aspect of the embodiments of the present disclosure, the martensitic stainless steel comprises the following components in mass%:

[0018] C: 0.050%-0.060%, Mn: 0.30%-0.60%, Si: 0.25%-0.65%, Ni: 4.760%-4.770%, Cr: 14.81%-14.83%, Mo: 0.25%-0.45%, Nb: 0.210%-0.220%, P: 0.009%-0.012%, S: ≤0.02%; the rest is Fe and inevitable impurities.

[0019] In one aspect of the embodiments of the present disclosure, specifically, the martensitic stainless steel comprises the following components in mass %:

[0020] C: 0.055%, Mn: 0.425%, Si: 0.372%, Ni: 4.763%, Cr: 14.82%, Mo: 0.324%, Nb: 0.2102%, P: 0.0107%, S: 0.059%; the rest is Fe and inevitable impurities.

[0021] According to a second aspect of the embodiments of the present disclosure, a process for preparing a fracturing pump fluid end valve box is provided, which is prepared by using the aforementioned martensitic stainless steel as raw material.

[0022] In one aspect of the embodiments of the present disclosure, the process comprises the following steps:

[0023] Step 1: preparing a martensitic stainless steel consumable electrode;

[0024] Step 2: obtaining a blank by an electroslag remelting process; the material of the blank is selected from the aforementioned martensitic stainless steel;

[0025] Step 3: subjecting the blank to a homogenization treatment process;

[0026] Step 4: subjecting the blank subjected to the homogenization treatment process to a multi-directional die forging forming process to obtain a workpiece rough product;

[0027] Step 5: subjecting the workpiece rough product subjected to the multi-directional die forging forming process to a heat treatment to obtain the fracturing pump fluid end valve box.

[0028] In one aspect of the embodiments of the present disclosure, step 1 comprises: raw material preparation, electric arc furnace initial smelting, LF furnace refining, RH vacuum refining, and round billet continuous casting process.

[0029] In one aspect of the embodiments of the present disclosure, step 4 comprises:

[0030] Step 4-1: after the blank subjected to the homogenization treatment process is coarsely milled, it is placed into a heating furnace and heated to 1050-1250℃, and after holding for 2-3h, descaling is completed;

[0031] Step 4-2: Put the descaled blank into a forming die, and perform extrusion forming by applying pressure in horizontal and vertical directions simultaneously in a hot state;

[0032] Step 4-3: Open the die, complete die forging, and air cool to room temperature.

[0033] In one aspect of the embodiments of the present disclosure, step 5 includes the following steps:

[0034] Step 5-1: Perform solid solution treatment on the workpiece rough product after the multi-directional die forging forming process at 1040-1050℃ for 15-16h, and air cool to room temperature;

[0035] Step 5-2: Further perform tempering treatment at 580-620℃ for 8-10h, and air cool to room temperature.

[0036] The technical solutions provided by the embodiments of the present disclosure can include the following beneficial effects:

[0037] As can be seen from the above embodiments, the present disclosure prepares a martensitic stainless steel with good tensile strength, yield strength and hardness.

[0038] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0039] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

[0040] Figure 1 is a full martensite structure image according to embodiment 1. DETAILED DESCRIPTION

[0041] The exemplary embodiments will be described in detail herein with reference to the accompanying drawings. The following description, when taken in conjunction with the drawings, relates to the preferred embodiments of the present disclosure. Unless otherwise stated, the same reference numerals in different drawings indicate the same or similar elements.

[0042] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below in conjunction with embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, not all of the embodiments. The embodiments described herein are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as a limitation of the present application.

[0043] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to create a range not expressly recited; and, any lower limit can be combined with any other lower limit, and any upper limit can be combined with any other upper limit, to create a range not expressly recited. Further, each individual disclosed point or singular value can be combined with any other point or singular value, either as a lower or upper limit, or with other lower or upper limits, to create a range not expressly recited.

[0044] In this document, the terms "comprise", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0045] In the description herein, "above", "below" include the number itself, unless otherwise indicated.

[0046] Unless otherwise defined, the terms used in the present disclosure have the same meaning as commonly understood by one of ordinary skill in the art. Unless otherwise indicated, the numerical values of the various parameters set forth in the present disclosure can be tested using various measuring methods commonly used in the art (for example, can be tested according to the methods given in the examples of the present disclosure).

[0047] The term "about" is used to describe and account for small variations. When used in connection with an event or circumstance, the term can refer to instances in which the event or circumstance occurs exactly, as well as instances in which the event or circumstance occurs approximately or nearly. For example, when used in connection with a numerical value, the term can refer to a range of variation of ±10% or less of the numerical value, such as ±5% or less, ±4% or less, ±3% or less, ±2% or less, ±1% or less, ±0.5% or less, ±0.1% or less, or ±0.05% or less. Additionally, quantities, ratios and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be understood as having been preceeded by the word "about". Unless otherwise indicated, the use of a number in a range format is intended to literally encompass each and every number falling within the range, inclusive of the recited number.

[0048] The list of items connected by “at least one of,” “at least one,” “at least one of the,” or other similar phrases can mean any combination of the listed items. For example, if A and B are listed, the phrase “at least one of A and B” means only A; only B; or A and B. In another example, if A, B, and C are listed, the phrase “at least one of A, B, and C” means A alone; B alone; C alone; A and B (excluding C); A and C (excluding B); B and C (excluding A); or A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0049] In the present disclosure, step 1 includes raw material preparation, arc furnace primary refining, LF furnace refining, RH vacuum refining, round billet continuous casting process, and continuous casting billet process. Among them, for raw material preparation, the main raw materials used in the present disclosure include waste stainless steel (40%-45% of the total mass of raw materials), carbon steel low phosphorus scrap (25%-30% of the total mass of raw materials), high-carbon chromium iron (Fe-Cr65C8, 5%-15% of the total mass of raw materials), nickel plate (2.5%-5.5% of the total mass of raw materials), ferromolybdenum (Fe-Mo60, 0.1%-0.5% of the total mass of raw materials), electrolytic manganese (0.05%-0.5% of the total mass of raw materials), ferrosilicon (Fe-Si75, 0.04%-0.5% of the total mass of raw materials), and niobium iron (Fe-Nb60, 0.1%-0.5% of the total mass of raw materials); but not limited thereto.

[0050] In the present disclosure, the electroslag remelting process itself mainly acts on the purity, uniformity of structure, and density of the steel, and generally has little effect on the chemical composition of the alloy; this means that during the electroslag remelting stage, the elemental composition of the alloy will not change significantly. However, in actual production, a small amount of burn loss may occur for certain elements (such as C, Mn, Cr, Ni, etc.) at high temperatures, especially when the protective atmosphere is not completely ideal; however, this burn loss amount is usually small. In addition, during the electroslag remelting process, sometimes a trace amount of rare earth (such as cerium) or other trace elements are added for inclusion modification; this will introduce a very small amount of new elements, but generally will not significantly change the content of the main alloying elements. Overall, the core of the electroslag remelting process is to improve the purity and uniformity of the structure of the material, rather than to change its basic chemical composition. Therefore, the elemental composition of the alloy after electroslag remelting should be basically consistent with that in the consumable electrode.

[0051] In the present disclosure, in step 1, the arc furnace primary refining, LF furnace refining, RH vacuum refining, and round billet continuous casting process are specifically:

[0052] Arc furnace smelting: The electric furnace adopts slag replacement operation, and all the oxidation slag is discharged at the end of the oxidation period to replace new slag, so as to ensure that the end point of the electric arc furnace is S<0.002% and P<0.0060%; the eccentric furnace bottom is used for tapping, and if the steel needs to be left, the left steel amount is controlled within 15%-20%.

[0053] LF furnace refining: the slag basicity of the LF refining is controlled within the range of 1.5-2.0, the calcium carbide and carbon powder are used for diffusion deoxidation in the LF refining process, and the white slag retention time is greater than 20 minutes.

[0054] RH vacuum refining: the vacuum degree is below 67 Pa, and the vacuum is maintained for 15-20 minutes; 5 minutes before the end of the vacuum refining.

[0055] Round billet continuous casting: the arc-shaped continuous casting machine is used to prepare round billets, and the round billet surface is bright after cutting to size and removing rust by surface sanding.

[0056] In the present disclosure, the CaF2 in the electroslag remelting slag is 68wt%-72wt%, and the Al2O3 is 28wt%-32wt%.

[0057] In the present disclosure, the electroslag remelting slag needs to be continuously baked at a temperature of 740℃-760℃ in a resistance furnace for more than 12 hours, and then it can be used immediately.

[0058] In the present disclosure, step 2 can include: using an electroslag remelting furnace with a nominal capacity of 10t to concentrate the group production, and the melting speed is constant and matched with the electrode size and the ingot type of the crystallizer. The remelting current and voltage are controlled at 17000-18500A and 65-70V respectively, and the melting speed is controlled at 820-960kg / h.

[0059] In the present disclosure, in step 2, in order to control the shape of inclusions and further deoxidize, a rare earth cerium salt is added every period of time during the electroslag remelting process, and the amount of rare earth is 0.05%-0.2% of the total amount of slag.

[0060] In the present disclosure, in step 2, the shrinkage is divided into three steps to reduce the current, and the shrinkage hole depth is controlled within 50mm.

[0061] In the present disclosure, after the shrinkage is completed, the mold is cooled for 2 hours, and then the homogenization treatment process is carried out: entering the annealing furnace at 860℃ for 10 hours, and then furnace cooling to ≤300℃, and then discharging from the furnace to obtain the blank.

[0062] In the present disclosure, specifically, step 4 comprises: heating the rough-milled blank to 1250℃, holding for 2h, and then removing the scale; loading the forming mold and simultaneously applying high pressure in the horizontal and vertical directions in the hot state for extrusion forming, the pressure applied in the horizontal direction being 18000MN, and the pressure applied in the vertical direction being 18000MN; then opening the mold to complete the die forging, and air cooling to room temperature.

[0063] In the present disclosure, specifically, step 5 comprises: holding the workpiece rough product after the multi-directional die forging forming process at 1050℃ for 16h for solid solution treatment, and air cooling to room temperature; and then holding at 620℃ for 10h for tempering treatment, and air cooling to room temperature.

[0064] In the present disclosure, in the design of the martensitic stainless steel, controlling the Nb / C ratio between 1.8 and 4.2 is to comprehensively consider the toughness and phosphorus segregation risk of the material. The interaction of Nb and C has a significant impact on the performance of the steel. When the Nb / C ratio is less than 6, the toughness of the steel is higher, and when the ratio is between 6 and 20, the toughness decreases. By controlling the Nb / C ratio to be between 1.8 and 4.2, preferably between 3.65 and 4.15, and more preferably between 3.75 and 3.95, sufficient NbC formation can be ensured to refine the grains and improve the toughness of the material, while reducing the segregation of phosphorus at the grain boundaries and reducing the risk of cracking. This not only improves the performance of the material, but also enhances its suitability for welding and plastic processing.

[0065] In the present disclosure, controlling the Cr / Ni ratio to be between 2.2 and 3.8, preferably between 2.65 and 3.45, and more preferably between 3.05 and 3.25, is to balance the formation of austenite and ferrite, avoid the formation of δ-ferrite, and at the same time ensure that the material has good toughness and corrosion resistance. Nickel as an austenite forming element, increasing its content can expand the austenite stable zone, reduce the solubility of C and N elements in austenite, thereby promoting the precipitation of C and N compounds, refining the grains and improving the toughness of the material. At the same time, nickel can reduce the resistance of dislocation motion in the crystal lattice, promote stress relaxation, and reduce the tendency of brittle fracture. The increase of chromium can improve the corrosion resistance of the material, but too high chromium content will lead to the formation of δ-ferrite, which will damage the toughness and ductility of the material. By controlling the Cr / Ni ratio to be between 2.2 and 3.8, preferably between 2.65 and 3.45, and more preferably between 3.05 and 3.25, the corrosion resistance can be improved while maintaining the good toughness and processing performance of the material. Outside this range, the material may be either brittle (high chromium and low nickel) or insufficient corrosion resistance (low chromium and high nickel).

[0066] In the present disclosure, the Nb / P ratio is controlled to be greater than or equal to 5.8, preferably greater than or equal to 12.2, and more preferably greater than or equal to 16.55, in order to reduce the segregation of phosphorus at the grain boundaries, thereby reducing the brittleness of the material. Phosphorus is an element that is prone to segregation at the grain boundaries, and it can form compounds with niobium at the grain boundaries, such as NbP, forming phosphorus segregation, which increases the brittleness of the steel. By maintaining a high Nb / P ratio, the phenomenon of phosphorus segregation can be effectively inhibited, thereby improving the toughness and welding performance of the material. At the same time, this also ensures the reliability and safety of the material during use, especially under working conditions that require high stress.

[0067] In the present disclosure, in general, maintaining 5.8≤(Nb / P) not only reduces the harmful effects of phosphorus, but also refines the grains, improves the toughness and plasticity of the material; maintaining 2.2≤(Cr / Ni)≤3.8 not only balances austenite and ferrite, avoids the formation of δ-ferrite, and improves the toughness and ductility of the material, and maintaining 1.8≤(Nb / C)≤4.2 can optimize the precipitation of NbC and improve the toughness; at the same time, meeting the above conditions can refine the grains, reduce the brittleness, and improve the corrosion resistance; and without adding copper, similar hardening effects can be achieved through the precipitation of NbC and grain refinement, while avoiding the brittleness risk brought by copper.

[0068] The present disclosure will be further described below in the manner of specific examples. The various chemical reagents used in the examples of the present disclosure are obtained through conventional commercial channels unless otherwise specified. The contents described below are mass contents unless otherwise specified.

[0069] Examples

[0070] Using waste stainless steel, carbon steel low phosphorus scrap, high carbon chromium iron, nickel plate, molybdenum iron, electrolytic manganese, silicon iron, and niobium iron as raw materials; the weights of electrolytic manganese, molybdenum iron, and silicon iron are controlled to be constant, and the mass contents of carbon steel low phosphorus scrap, high carbon chromium iron, nickel plate, and niobium iron are adjusted and controlled; through the processes of electric arc furnace smelting, LF furnace refining, RH vacuum refining, round billet continuous casting, and electroslag remelting (the specific steps are as described above); a series of stainless steels of Example 1 to Example 6 are prepared,

[0071] The element contents of Example 1 to Example 6 are as follows:

[0072] Example 1: C: 0.055%, Mn: 0.425%, Si: 0.372%, Ni: 4.763%, Cr: 14.82%, Mo: 0.324%, Nb: 0.2102%, P: 0.0107%, S: 0.059%; the rest is Fe and unavoidable impurities. Example 1 simultaneously satisfies 3.75≤(d / a)≤3.95; 16.55≤(d / e); 3.05≤(c / b)≤3.25.

[0073] Example 2: C: 0.030%, Mn: 0.421%, Si: 0.370%, Ni: 4.784%, Cr: 14.62%, Mo: 0.324%, Nb: 0.2217%, P: 0.0109%, S: 0.054%; the balance being Fe and unavoidable impurities. Example 2 does not satisfy 3.75 < (d / a) < 3.95 (too large), but does satisfy 16.55 < (d / e), 3.05 < (c / b) < 3.25.

[0074] Example 3: C: 0.057%, Mn: 0.423%, Si: 0.374%, Ni: 4.767%, Cr: 14.84%, Mo: 0.325%, Nb: 0.2317%, P: 0.0256%, S: 0.051%; the balance being Fe and unavoidable impurities. Example 3 does not satisfy 16.55 < (d / e) (too small), but does satisfy 3.75 < (d / a) < 3.95, 3.05 < (c / b) < 3.25.

[0075] Example 4: C: 0.057%, Mn: 0.425%, Si: 0.381%, Ni: 4.013%, Cr: 16.51%, Mo: 0.323%, Nb: 0.2110%, P: 0.0115%, S: 0.069%; the balance being Fe and unavoidable impurities. Example 4 does not satisfy 3.05 < (c / b) < 3.25 (too large), but does satisfy 16.55 < (d / e), 3.75 < (d / a) < 3.95.

[0076] Example 5: C: 0.051%, Mn: 0.423%, Si: 0.377%, Ni: 5.505%, Cr: 14.50%, Mo: 0.320%, Nb: 0.2107%, P: 0.0112%, S: 0.053%; the balance being Fe and unavoidable impurities. Example 5 does not satisfy 3.05 < (c / b) < 3.25 (too small), but does satisfy 16.55 < (d / e), 3.75 < (d / a) < 3.95.

[0077] Example 6: C: 0.073%, Mn: 0.428%, Si: 0.379%, Ni: 4.769%, Cr: 14.88%, Mo: 0.329%, Nb: 0.1811%, P: 0.0110%, S: 0.060%; the balance being Fe and unavoidable impurities. Example 6 does not satisfy 3.75 < (d / a) < 3.95 (too small), but does satisfy 16.55 < (d / e), 3.05 < (c / b) < 3.25.

[0078] Performance test:

[0079] The tensile strength, yield strength and hardness of test examples 1-6 were tested, and the results are shown in Table 1.

[0080] Table 1

[0081]

[0082] It can be seen that, while satisfying 3.75≤(d / a)≤3.95; 16.55≤(d / e); 3.05≤(c / b)≤3.25, the mechanical properties can be balanced. The martensite structure of the product of example 1 after further multi-directional die forging forming process and heat treatment is shown in Figure 1 .

[0083] Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the subject disclosure. The present disclosure is intended to cover any variations, uses or adaptive changes of the present disclosure, which follow the general principles of the present disclosure and include known or customary technical means in the art not disclosed in the present disclosure.

Claims

1. A martensitic stainless steel, characterized in that, The martensitic stainless steel comprises the following components, calculated as a percentage by mass: C: a%, Mn: 0.30%-0.60%, Si: 0.25%-0.65%, Ni: b%, Cr: c%, Mo: 0.25%-0.45%, Nb: d%, P: e%, S: ≤0.02%; the remainder is Fe and unavoidable impurities. Among them, a, b, c, d, and e satisfy the following relationship: 3.75≤(d / a)≤3.95; 16.55≤(d / e); 3.05≤(c / b)≤3.25; 0.04≤a≤0.07;4.5≤b≤5.5;14.5≤c≤15.5;0.15≤d≤0.35;0.005≤e≤0.0259; The martensitic stainless steel is prepared by the following steps: Step 1: Prepare a martensitic stainless steel consumable electrode; Step 2: Obtain a blank through an electroslag remelting process; the composition of the blank is selected from the above-mentioned martensitic stainless steel composition; Step 3: The blank is subjected to a homogenization process; Step 4: The blank that has undergone homogenization treatment is subjected to a multi-directional die forging process to obtain a rough workpiece; Step 5: The rough workpiece that has undergone multi-directional die forging is heat-treated to obtain the martensitic stainless steel.

2. The martensitic stainless steel according to claim 1, characterized in that, The martensitic stainless steel comprises the following components, calculated as a percentage by mass: C: 0.050%-0.060%, Mn: 0.30%-0.60%, Si: 0.25%-0.65%, Ni: 4.760%-4.770%, Cr: 14.81%-14.83%, Mo: 0.25%-0.45%, Nb: 0.210%-0.220%, P: 0.009%-0.012%, S: ≤0.02%; the remainder is Fe and unavoidable impurities.

3. A process for preparing a hydraulic end valve box for a fracturing pump, characterized in that, The process includes the following steps: Step 1: Prepare a martensitic stainless steel consumable electrode; Step 2: Obtain a blank through an electroslag remelting process; the composition of the blank is selected from the composition of the martensitic stainless steel described in claim 1 or 2; Step 3: The blank is subjected to a homogenization process; Step 4: The blank that has undergone homogenization treatment is subjected to a multi-directional die forging process to obtain a rough workpiece; Step 5: The rough workpiece that has undergone multi-directional die forging is heat-treated to obtain the hydraulic end valve box of the fracturing pump.

4. The process according to claim 3, characterized in that, Step 1 includes: raw material preparation, electric arc furnace primary refining, LF furnace refining, RH vacuum refining, and round billet continuous casting.

5. The process according to claim 3, characterized in that, Step 4 includes: Step 4-1: After rough milling, the blank that has undergone homogenization is placed in a heating furnace and heated to 1050℃-1250℃. After holding at this temperature for 2-3 hours, descaling is completed. Step 4-2: The descaled blank is placed into the forming mold and extruded under heat by applying pressure in both the horizontal and vertical directions. Step 4-3: Open the mold, complete the die forging, and air cool to room temperature.

6. The process according to claim 3, characterized in that, Step 5 includes the following steps: Step 5-1: The rough workpiece after the multi-directional die forging process is kept at 1040℃-1050℃ for 15-16 hours for solution treatment, and then air-cooled to room temperature. Step 5-2: Further tempering treatment is carried out by holding the temperature at 580℃-620℃ for 8-10 hours, followed by air cooling to room temperature.

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