Rolling method of CrNiMo series alloy steel and alloy steel

Abstract

The present invention particularly relates to a rolling method for CrNiMo series alloy steel and the alloy steel, belonging to the technical field of steel preparation. A rolling method for CrNiMo series alloy steel comprises the following steps: heating, rough rolling, finish rolling and cooling a steel billet with a preset chemical composition to obtain hollow steel. By precisely controlling the deformation amount range and each temperature range of rough rolling and finish rolling, precise control of rolling in the recrystallization zone is achieved, so that the hollow steel obtains uniform grain size; through the first-stage cooling and its parameter control, grain growth before phase transformation after finish rolling is inhibited; through the second-stage cooling and its parameter control, a bainite structure with higher toughness is obtained; through the third-stage cooling, the residual stress in the steel is relieved; through the combined action of the above-mentioned features, CrNiMo series alloy steel with a grain size of 15-40 μm is obtained, effectively solving the technical problem that the tissue grain uniformity of the existing low-carbon CrNiMo series alloy steel is poor.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel preparation, and particularly relates to a rolling method for CrNiMo series alloy steel and the alloy steel. Background Art

[0002] Low-carbon CrNiMo series high-strength alloy steel is widely used in the preparation of heavy-duty rock drilling tools due to its characteristics of high strength and excellent plasticity and toughness. During the working process, the rock drilling tools are subjected to high-frequency and severe impacts such as tension, compression, bending, and torsion, and are subjected to rock friction and wear as well as high-pressure water erosion and corrosion. The service conditions are very harsh, so high-quality requirements are imposed on the steel for rock drilling tools.

[0003] The fatigue life of the existing low-carbon CrNiMo series rock drilling tools is extremely unstable during actual rock drilling operations. The reason for this phenomenon is that the grain uniformity of the existing low-carbon CrNiMo series alloy steel is poor, there is a serious mixed crystal structure condition, and the grain size fluctuates between 20 μm and 100 μm. Summary of the Invention

[0004] The purpose of this application is to provide a rolling method for CrNiMo series alloy steel to solve the technical problem of poor grain uniformity of the existing low-carbon CrNiMo series alloy steel.

[0005] The embodiment of the present invention provides a rolling method for CrNiMo series alloy steel, including the following steps:

[0006] Heating, rough rolling, finish rolling and cooling a steel billet with a preset chemical composition to obtain a hollow steel;

[0007] Wherein:

[0008] The preset chemical composition includes, by mass percentage:

[0009] C: 0.19 - 0.27%, Si: 0.15 - 0.4%, Mn: 0.5 - 0.8%, P: ≤0.025%, S: ≤0.025%, Cr: 1.15 - 1.45%, Ni: 2.7 - 3.1%, Cu: ≤0.25%, Mo: 0.15 - 0.4%, and the balance is Fe and unavoidable impurities;

[0010] The total deformation amount of the rough rolling is 40 - 50%;

[0011] The starting rolling temperature of the rough rolling is 960 - 1050°C;

[0012] The total deformation amount of the finish rolling is 50 - 60%;

[0013] The final rolling temperature of the finish rolling is 900 - 1000°C;

[0014] The cooling includes first-stage cooling, second-stage cooling and third-stage cooling, where:

[0015] The end temperature of the first-stage cooling is 450 - 500 °C, and the cooling rate of the first-stage cooling ≥ 10 °C / s;

[0016] The end temperature of the second-stage cooling is 200 - 300 °C, and the cooling rate of the second-stage cooling < 1 °C / s.

[0017] Optionally, water cooling is used for the first-stage cooling, cooling bed cooling is used for the second-stage cooling, and stacking slow cooling is used for the third-stage cooling.

[0018] Optionally, the heating temperature is 1150 - 1220 °C, and the heating time is 2 - 3 h.

[0019] Optionally, the tapping temperature of the heating furnace is 1080 - 1120 °C.

[0020] Optionally, the steel billet is a round billet with a diameter of 90 mm.

[0021] Optionally, the preset chemical composition includes, by mass percentage:

[0022] C: 0.22 - 0.23%, Si: 0.25 - 0.26%, Mn: 0.65 - 0.72%, P: 0.007%, S: 0.004%, Cr: 1.21 - 1.23%, Ni: 3.02 - 3.06%, Cu: ≤ 0.25%, Mo: 0.21 - 0.23%, and the balance is Fe and unavoidable impurities.

[0023] Optionally, C: 0.23%, Si: 0.25%, Mn: 0.65%, P: 0.008%, S: 0.002%, Cr: 1.21%, Ni: 3.02%, Cu: ≤ 0.25%, Mo: 0.23%, and the balance is Fe and unavoidable impurities.

[0024] Optionally, the total reduction of rough rolling is 40%;

[0025] The starting rolling temperature of rough rolling is 965 - 1020 °C;

[0026] The total reduction of finish rolling is 50 - 60%;

[0027] The finishing rolling temperature of finish rolling is 920 - 980 °C;

[0028] The cooling includes first-stage cooling, second-stage cooling and third-stage cooling, where:

[0029] The end temperature of the first-stage cooling is 450 - 500 °C, and the cooling rate of the first-stage cooling is ≥ 10 °C / s;

[0030] The end temperature of the second-stage cooling is 200 - 300 °C, and the cooling rate of the second-stage cooling is < 1 °C / s.

[0031] Optionally, the heating temperature is 1150 - 1210 °C, the heating time is 2.2 - 3 h, and the furnace tapping temperature of the heating furnace is 1080 - 1120 °C.

[0032] Based on the same inventive concept, the embodiment of the present invention also provides a CrNiMo series alloy steel, and the rolling step of its preparation method is carried out by using any one of the above-mentioned rolling methods of CrNiMo series alloy steel.

[0033] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0034] The rolling method of the CrNiMo series alloy steel provided by the embodiment of the present invention realizes the precise control of rolling in the recrystallization zone by precisely controlling the deformation amount range and each temperature range of rough rolling and finish rolling, so that the hollow steel obtains uniform grain size; through the first-stage cooling and its parameter control, the grain growth before phase transformation after finish rolling is inhibited; through the second-stage cooling and its parameter control, a bainite structure with higher toughness is obtained; through the third-stage cooling, the residual stress in the steel is relieved; through the common cooperation of the above features, a CrNiMo series alloy steel with a grain size of 15 - 40 μm is obtained, effectively solving the technical problem of poor uniformity of the grain structure of the existing low-carbon CrNiMo series alloy steel.

[0035] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the following specifically gives the specific embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for description in the embodiments. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts.

[0037] Figure 1 is a flowchart of the method provided by the embodiment of the present invention;

[0038] Figure 2 is a grain size diagram of the CrNiMo series alloy steel provided by Comparative Example 1 of the present invention;

[0039] Figure 3 It is the grain size diagram after controlled cooling of the CrNiMo series alloy steel provided in Embodiment 1 of the present invention after rolling;

[0040] Figure 4 It is the grain size diagram of the CrNiMo series alloy steel provided in Comparative Example 1 of the present invention without controlled cooling after rolling. Specific Embodiments

[0041] The following will specifically elaborate on the present invention in combination with specific embodiments and examples, and the advantages and various effects of the present invention will be presented more clearly therefrom. Those skilled in the art should understand that these specific embodiments and examples are used to illustrate the present invention rather than limit the present invention.

[0042] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as having the meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as the general understanding of those skilled in the art to which the present invention pertains. In case of contradiction, this specification shall prevail. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. For example, room temperature may refer to the temperature within the range of 10 to 35 °C.

[0043] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0044] The technical solution of the embodiments of the present application is to solve the above technical problems, and the general idea is as follows:

[0045] According to a typical embodiment of the present invention, a rolling method for CrNiMo series alloy steel is provided, including the following steps:

[0046] A steel billet with a preset chemical composition is heated, rough rolled, finish rolled, and cooled to obtain a hollow steel;

[0047] Wherein:

[0048] The preset chemical composition includes, by mass percentage:

[0049] C: 0.19 - 0.27%, Si: 0.15 - 0.4%, Mn: 0.5 - 0.8%, P: ≤0.025%, S: ≤0.025%, Cr: 1.15 - 1.45%, Ni: 2.7 - 3.1%, Cu: ≤0.25%, Mo: 0.15 - 0.4%, and the balance is Fe and unavoidable impurities;

[0050] The total deformation amount of the rough rolling is 40 - 50%;

[0051] The starting rolling temperature of rough rolling is 960 - 1050 °C;

[0052] The total deformation of finish rolling is 50 - 60%;

[0053] The finishing rolling temperature of finish rolling is 900 - 1000 °C;

[0054] The cooling includes first-stage cooling, second-stage cooling and third-stage cooling, where:

[0055] The end temperature of the first-stage cooling is 450 - 500 °C, and the cooling rate of the first-stage cooling ≥ 10 °C / s;

[0056] The end temperature of the second-stage cooling is 200 - 300 °C, and the cooling rate of the second-stage cooling < 1 °C / s.

[0057] One or more technical solutions in the embodiments of the present invention have the following technical ideas:

[0058] In order to obtain a uniform austenite grain structure, rolling in the non-recrystallization zone at a lower temperature or rolling in the recrystallization zone at a higher temperature is usually adopted. Rolling in the non-recrystallization zone can obtain finer austenite grains compared to rolling in the recrystallization zone.

[0059] The present invention studied the austenite grain recrystallization and grain growth behaviors during the rolling process of low-carbon CrNi alloy steel through a large number of process tests with different rolling temperatures and rolling deformation amounts. The research results found that under the inherent deformation amount conditions of the existing pass mill, the non-crystallization temperature range of low-carbon CrNi alloy steel is very low. The rolling temperature range in the finish rolling stage of the existing process is actually in the partial recrystallization zone, thus resulting in a mixed grain state.

[0060] The present invention proposed a technical idea of avoiding rolling in the partial recrystallization zone and realizing rolling in the recrystallization zone to obtain a uniform grain structure by increasing the rolling temperature through a large number of experimental studies.

[0061] However, if the rolling temperature is too high, the grain size will be too large. Therefore, the lower limit temperature range of the recrystallization zone is determined as the finishing rolling temperature of finish rolling.

[0062] Furthermore, considering the recrystallization zone temperature range and the temperature drop during the rolling process, the rough rolling temperature and the heating furnace tapping temperature are determined. Finally, through the precise control of the rolling deformation amount and the rough rolling and finish rolling temperatures during rough rolling and finish rolling, controlled rolling in the complete recrystallization zone is achieved, and a uniform grain size after rolling is obtained.

[0063] The reason for controlling the end temperatures and cooling rates of the first-stage cooling and the second-stage cooling is as follows: The low-carbon CrNiMo alloy steel of the present invention is a bainite-structured steel, which is different from the ferrite-pearlite-structured steel and has a relatively low phase transformation temperature. Therefore, during the cooling holding time before phase transformation, the austenite grains will grow, and rapid cooling can inhibit grain growth.

[0064] Furthermore, the present invention has studied the grain growth behavior of the low-carbon CrNiMo alloy structural steel during the post-rolling cooling process.

[0065] The bainite phase transformation temperature range is 450 - 300 °C. The conventional process is air cooling after finish rolling. However, during the cooling process from finish rolling to before phase transformation, the grains will undergo recovery and recrystallization growth, as shown in the appendix Figure 4 ... Therefore, the rapid cooling in the first stage and the precise design of the finish cooling temperature are to inhibit the grain growth before phase transformation after finish rolling. The second-stage cooling process is the transformation process from austenite to bainite. Slow cooling on the cooling bed is beneficial to obtaining granular bainite structure with higher toughness.

[0066] Finally, the stacking slow cooling relieves the residual stress in the steel.

[0067] Appendix Figure 2 The grain size of the present invention fluctuates from 15 μm to 40 μm.

[0068] Therefore, as an alternative embodiment, the first-stage cooling adopts water cooling, the second-stage cooling adopts cooling bed cooling, and the third-stage cooling adopts stacking slow cooling.

[0069] As an alternative embodiment, the heating temperature is 1150 - 1220 °C, the heating time is 2 - 3 h, and the tapping temperature of the heating furnace is 1080 - 1120 °C.

[0070] The reason for controlling the heating furnace temperature, heating time, and tapping temperature is as follows: In the low-carbon CrNiMo alloy steel of the present invention, the contents of Cr, Ni, and Mo alloying elements are > 4%, and high-temperature long heating is required to promote the diffusion of alloying elements and reduce the influence of alloy element segregation. However, if the heating temperature is too high, due to the relatively high content of elements such as Ni, surface defects such as grain boundary oxidation and overburning are likely to occur. Therefore, it is necessary to limit the heating temperature below 1220 °C. At the same time, since this steel grade needs to be drilled and the hollow steel is rolled with a core material inserted, which belongs to double-metal composite rolling, a certain heating time is required to make the temperature difference between the inside and outside of the slab as small as possible to ensure synchronous rolling deformation. If the heating time is too long, there will be too much scale, which is not conducive to subsequent removal. Therefore, an appropriate heating time is controlled. From the perspective of rolling, double-metal rolling needs to be completed at a relatively high temperature. Therefore, the tapping temperature needs to be controlled at 1080 - 1120 °C.

[0071] As an alternative embodiment, the steel billet is a round billet with a diameter of 90 mm.

[0072] Preferably, the preset chemical composition includes, by mass percentage:

[0073] C: 0.22 - 0.23%, Si: 0.25 - 0.26%, Mn: 0.65 - 0.72%, P: 0.007%, S: 0.004%, Cr: 1.21 - 1.23%, Ni: 3.02 - 3.06%, Cu: ≤0.25%, Mo: 0.21 - 0.23%, and the balance is Fe and inevitable impurities.

[0074] Preferably, the total reduction ratio of rough rolling is 40%;

[0075] The starting rolling temperature of rough rolling is 965 - 1020 °C;

[0076] The total reduction ratio of finish rolling is 50 - 60%;

[0077] The final rolling temperature of finish rolling is 920 - 980 °C;

[0078] The cooling includes first-stage cooling, second-stage cooling, and third-stage cooling, where:

[0079] The end temperature of the first-stage cooling is 450 - 500 °C, and the cooling rate of the first-stage cooling is ≥10 °C / s;

[0080] The end temperature of the second-stage cooling is 200 - 300 °C, and the cooling rate of the second-stage cooling is <1 °C / s.

[0081] More preferably, the heating temperature is 1150 - 1210 °C, the heating time is 2.2 - 3 h, and the discharging temperature of the heating furnace is 1080 - 1120 °C.

[0082] According to another typical embodiment of the present invention, a CrNiMo series alloy steel is provided, and the rolling step of its preparation method is carried out by using any one of the above-mentioned rolling methods of CrNiMo series alloy steel.

[0083] The present application will be described in detail below in conjunction with examples, comparative examples, and experimental data.

[0084] Example 1

[0085] This example provides a rolling method for a CrNiMo series alloy steel, including the following steps:

[0086] S1. Obtain a steel billet with a preset chemical composition.

[0087] Wherein:

[0088] The billet is a round billet with a diameter of 90 mm;

[0089] The preset chemical composition includes by mass percentage:

[0090] C: 0.23%, Si: 0.25%, Mn: 0.65%, P: 0.008%, S: 0.002%, Cr: 1.21%, Cu: 0.18%, Ni: 3.02%, Mo: 0.23%, and the balance is Fe and inevitable impurities.

[0091] S2. Heat, rough roll, finish roll and cool the billet to obtain hollow steel.

[0092] Among them:

[0093] The heating temperature is 1150 °C, the heating time is 3 h, and the tapping temperature of the heating furnace is 1080 °C;

[0094] The total reduction of rough rolling is 40%;

[0095] The starting rolling temperature of rough rolling is 965 °C;

[0096] The total reduction of finish rolling is 60%;

[0097] The final rolling temperature of finish rolling is 920 °C;

[0098] Cooling includes first-stage cooling, second-stage cooling and third-stage cooling. The first-stage cooling uses water cooling, the second-stage cooling uses cooling bed cooling, and the third-stage cooling uses stacking slow cooling. Among them:

[0099] The end temperature of the first-stage cooling is 450 °C, and the cooling rate of the first-stage cooling is 11 °C / s;

[0100] The end temperature of the second-stage cooling is 225 °C, and the cooling rate of the second-stage cooling is 0.9 °C / s.

[0101] This embodiment also provides a CrNiMo series alloy steel prepared from the above hollow steel.

[0102] Example 2

[0103] This embodiment provides a rolling method for a CrNiMo series alloy steel, including the following steps:

[0104] S1. Obtain a billet with a preset chemical composition.

[0105] Among them:

[0106] The billet is a round billet with a diameter of 90 mm;

[0107] The preset chemical composition in mass percentage includes:

[0108] C: 0.22%, Si: 0.26%, Mn: 0.72%, P: 0.007%, S: 0.004%, Cr: 1.23%, Cu: 0.15%, Ni: 3.06%, Mo: 0.21%, the balance being Fe and unavoidable impurities.

[0109] S2. Heat, rough roll, finish roll and cool the steel billet to obtain hollow steel.

[0110] Among them:

[0111] The heating temperature is 1210 °C, the heating time is 2.2 h, and the tapping temperature of the heating furnace is 1120 °C;

[0112] The total reduction of rough rolling is 40%;

[0113] The starting rolling temperature of rough rolling is 1020 °C;

[0114] The total reduction of finish rolling is 50%;

[0115] The finishing rolling temperature of finish rolling is 980 °C;

[0116] Cooling includes first-stage cooling, second-stage cooling and third-stage cooling. The first-stage cooling uses water cooling, the second-stage cooling uses cooling bed cooling, and the third-stage cooling uses stacking slow cooling. Among them:

[0117] The end temperature of the first-stage cooling is 500 °C, and the cooling rate of the first-stage cooling is 12 °C / s;

[0118] The end temperature of the second-stage cooling is 275 °C, and the cooling rate of the second-stage cooling is 0.8 °C / s.

[0119] This embodiment also provides a CrNiMo series alloy steel prepared from the above hollow steel.

[0120] Example 3

[0121] This embodiment provides a rolling method for a CrNiMo series alloy steel, including the following steps:

[0122] S1. Obtain a steel billet with a preset chemical composition.

[0123] Among them:

[0124] The steel billet is a round billet, and the diameter of the steel billet is 90 mm;

[0125] The preset chemical composition in mass percentage includes:

[0126] C: 0.19%, Si: 0.36%, Mn: 0.56%, P: 0.010%, S: 0.007%, Cr: 1.42%, Cu: 0.13%; Ni: 2.96%, Mo: 0.31%, the balance being Fe and inevitable impurities.

[0127] S2. Heat the steel billet, rough roll, finish roll and cool it to obtain hollow steel.

[0128] Among them:

[0129] The heating temperature is 1220 °C, the heating time is 2.0 h, and the tapping temperature of the heating furnace is 1100 °C;

[0130] The total reduction of rough rolling is 50%;

[0131] The starting rolling temperature of rough rolling is 1050 °C;

[0132] The total reduction of finish rolling is 50%;

[0133] The final rolling temperature of finish rolling is 900 °C;

[0134] Cooling includes the first-stage cooling, the second-stage cooling and the third-stage cooling. The first-stage cooling uses water cooling, the second-stage cooling uses cooling bed cooling, and the third-stage cooling uses stacking slow cooling. Among them:

[0135] The end temperature of the first-stage cooling is 475 °C, and the cooling rate of the first-stage cooling is 10 °C / s;

[0136] The end temperature of the second-stage cooling is 300 °C, and the cooling rate of the second-stage cooling is 0.6 °C / s.

[0137] This embodiment also provides a CrNiMo series alloy steel, which is prepared from the above-mentioned hollow steel.

[0138] Comparative Example 1

[0139] A rolling method of a CrNiMo series alloy steel is provided, including the following steps:

[0140] S1. Obtain a steel billet with a preset chemical composition.

[0141] Among them:

[0142] The steel billet is a round billet, and the diameter of the steel billet is 90 mm;

[0143] The preset chemical composition includes, by mass percentage:

[0144] C: 0.25%, Si: 0.26%, Mn: 0.71%, P: 0.007%, S: 0.002%, Cr: 1.20%, Cu: 0.13%, Ni: 2.93%, Mo: 0.23%, the balance being Fe and unavoidable impurities.

[0145] S2. Heat the steel billet, rough roll, finish roll and cool it to obtain hollow steel.

[0146] Among them:

[0147] The heating temperature is 1070 - 1140 °C, the heating time is 2.5 h, and the tapping temperature of the heating furnace is 1030 °C;

[0148] The total reduction of rough rolling is 40%;

[0149] The starting rolling temperature of rough rolling is 950 °C;

[0150] The total reduction of finish rolling is 60%;

[0151] The finishing rolling temperature of finish rolling is 850 °C;

[0152] Cooling is carried out by cooling bed cooling and stacking slow cooling.

[0153] A CrNiMo series alloy steel is also provided, which is prepared from the above-mentioned hollow steel.

[0154] Comparative Example 2

[0155] A rolling method of a CrNiMo series alloy steel is provided, including the following steps:

[0156] S1. Obtain a steel billet with a preset chemical composition.

[0157] Among them:

[0158] The steel billet is a round billet with a diameter of 90 mm;

[0159] The preset chemical composition includes by mass percentage:

[0160] C: 0.20%, Si: 0.36%, Mn: 0.65%, P: 0.017%, S: 0.006%, Cr: 1.23%, Cu: 0.21%; Ni: 2.89%, Mo: 0.31%, the balance being Fe and unavoidable impurities.

[0161] S2. Heat the steel billet, rough roll, finish roll and cool it to obtain hollow steel.

[0162] Among them:

[0163] The heating temperature is 1050 - 1120 °C, the heating time is 2.5 h, and the tapping temperature of the heating furnace is 1050 °C;

[0164] The total reduction ratio of rough rolling is 40%;

[0165] The starting rolling temperature of rough rolling is 930 °C;

[0166] The total reduction ratio of finish rolling is 60%;

[0167] The finishing rolling temperature of finish rolling is 830 °C;

[0168] Cooling is carried out by cooling bed cooling and stacking slow cooling.

[0169] A CrNiMo series alloy steel is also provided, which is prepared from the above-mentioned hollow steel.

[0170] Experimental examples

[0171] The CrNiMo series alloy steels provided in Examples 1-3 and Comparative Examples 1-2 were prepared into the same brazing tools, and then physical inspections were carried out. The specific results are shown in the following table.

[0172] Grain condition Grain size range Service life Example 1 Grade 8.5 23 - 45μm 1400 meters Example 2 Grade 8.5 25 - 48μm 1300 meters Example 3 Grade 8.5 20 - 43μm 1350 meters Comparative example 1 Mixed crystal of Grade 6.0 + Grade 8.0 20 - 100μm 800 meters Comparative example 2 Mixed crystal of Grade 5.0 + Grade 8.0 25 - 100um 850 meters

[0173] As can be seen from the above table, compared with Comparative Examples 1-2, the CrNiMo series alloy steels provided in Examples 1-3 of the present application have obvious advantages in terms of service life, with a service life ≥ 1300 m, which is much higher than the maximum service life of 850 m in Comparative Examples 1-2.

[0174] Finally, it should also be noted that the term "comprises", "comprising" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method, article or apparatus comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or apparatus.

[0175] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0176] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A rolling method for CrNiMo series alloy steel, characterized in that It includes the following steps: Heating, rough rolling, finish rolling and cooling a steel billet with a preset chemical composition to obtain hollow steel; Wherein: The preset chemical composition includes, by mass percentage: C: 0.19 - 0.27%, Si: 0.15 - 0.4%, Mn: 0.5 - 0.8%, P: ≤0.025%, S: ≤0.025%, Cr: 1.15 - 1.45%, Ni: 2.7 - 3.1%, Cu: ≤0.25%, Mo: 0.15 - 0.4%, and the balance is Fe and inevitable impurities; The total reduction of the rough rolling is 40 - 50%; The starting rolling temperature of the rough rolling is 960 - 1050 °C; The total reduction of the finish rolling is 50 - 60%; The final rolling temperature of the finish rolling is 900 - 1000 °C; The cooling includes first-stage cooling, second-stage cooling and third-stage cooling, wherein: The end temperature of the first-stage cooling is 450 - 500 °C, and the cooling rate of the first-stage cooling ≥ 10 °C / s; The end temperature of the second-stage cooling is 200 - 300 °C, and the cooling rate of the second-stage cooling < 1 °C / s.

2. The rolling method of the CrNiMo series alloy steel according to claim 1, characterized in that, The first-stage cooling uses water cooling, the second-stage cooling uses cooling bed cooling, and the third-stage cooling uses stacking slow cooling.

3. The rolling method of the CrNiMo series alloy steel according to claim 1, characterized in that The heating temperature is 1150 - 1220 °C, and the heating time is 2 - 3 h.

4. The rolling method of the CrNiMo series alloy steel according to claim 3, characterized in that, The heating uses a heating furnace, and the tapping temperature of the heating furnace is 1080 - 1120 °C.

5. The rolling method of the CrNiMo series alloy steel according to claim 1, characterized in that The steel billet is a round billet, and the diameter of the steel billet is 90 mm.

6. The rolling method of the CrNiMo series alloy steel according to claim 1, characterized in that: The preset chemical composition includes, by mass percentage: C: 0.22 - 0.23%, Si: 0.25 - 0.26%, Mn: 0.65 - 0.72%, P: 0.007%, S: 0.004%, Cr: 1.21 - 1.23%, Ni: 3.02 - 3.06%, Cu: ≤0.25%, Mo: 0.21 - 0.23%, and the balance is Fe and inevitable impurities.

7. The rolling method of the CrNiMo series alloy steel according to claim 6, characterized in that: The preset chemical composition includes, by mass percentage: C: 0.23%, Si: 0.25%, Mn: 0.65%, P: 0.008%, S: 0.002%, Cr: 1.21%, Ni: 3.02%, Cu: ≤0.25%, Mo: 0.23%, and the balance is Fe and inevitable impurities.

8. The rolling method of the CrNiMo series alloy steel according to claim 6 or 7, characterized in that: The total reduction of the rough rolling is 40%; The starting rolling temperature of the rough rolling is 965 - 1020 °C; The total reduction of the finish rolling is 50 - 60%; The final rolling temperature of the finish rolling is 920 - 980 °C; The cooling includes first-stage cooling, second-stage cooling and third-stage cooling, wherein: The end temperature of the first-stage cooling is 450 - 500 °C, and the cooling rate of the first-stage cooling ≥ 10 °C / s; The end temperature of the second-stage cooling is 200 - 300 °C, and the cooling rate of the second-stage cooling is < 1 °C / s.

9. The rolling method of the CrNiMo series alloy steel according to claim 8, characterized in that, The temperature of the heating is 1150 - 1210 °C, the time of the heating is 2.2 - 3 h, the heating uses a heating furnace, and the tapping temperature of the heating furnace is 1080 - 1120 °C.

10. A CrNiMo series alloy steel, characterized in that, The rolling step of its preparation method is carried out by using the rolling method of the CrNiMo series alloy steel as described in any one of claims 1 - 9.

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