CN115807188A

CN115807188A - Low-carbon steel and preparation method thereof

Info

Publication number: CN115807188A
Application number: CN202211474322.0A
Authority: CN
Inventors: 董栓牢; 朱鹏霄; 文军
Original assignee: Xuzhou Construction Machinery Group Co Ltd XCMG
Current assignee: Xuzhou Construction Machinery Group Co Ltd XCMG
Priority date: 2022-11-23
Filing date: 2022-11-23
Publication date: 2023-03-17
Anticipated expiration: 2042-11-23
Also published as: CN115807188B

Abstract

The invention relates to low-carbon alloy steel and a preparation method thereof. The low-carbon alloy steel comprises the following chemical components: c:0.03 to 0.13%, mn:0.6 to 1.40%, si:0.15 to 0.30%, nb: 0.010-0.020%, ni:0.10 to 0.30%, ti: 0.015-0.030 percent of Cr, less than or equal to 0.25 percent of Cr, al:0.015 to 0.060%, N:0.01 to 0.02 percent of Fe, less than or equal to 0.20 percent of V, less than 0.015 percent of P, less than 0.020 percent of S, and the balance of Fe and acceptable impurities.

Description

Low-carbon steel and preparation method thereof

Technical Field

The invention belongs to the field of steel materials, and particularly relates to low-carbon steel and a preparation method thereof, in particular to low-carbon steel with improved mechanical properties and a preparation method thereof.

Background

With the vigorous development of capital construction in China, the demand of engineering machinery is greatly increased. In the using process, metal structural parts in engineering machinery such as an excavator, a bulldozer, a loader and the like bear a complex and variable periodic load and often bear impact and overload, for example, an arm frame of a crawler crane bears complex alternating stress with a stress ratio of 0.1, -0.2, -0.5, -1 and the like, the maximum impact and overload of the arm frame using Q890D as an arm frame material reaches 900MPa, the arm frame is cyclically used for 300 ten thousand times under low stress and fails, and the fracture analysis shows that the main fracture form is fatigue failure. According to statistics, 50% -90% of various mechanical failures are caused by fatigue, most of the mechanical failures are suddenly broken, and with the development of the current high speed and large-scale machine, many parts run under severe working conditions such as high temperature, high pressure and heavy load, and fatigue failure accidents are more serious. The yield strength and the tensile strength of high-strength steel such as Q355, Q460, Q550, Q890 which is commonly used at present meet the requirements of national standards, but the problem of low fatigue strength exists, the service life of the whole machine is directly influenced, and therefore, the development of steel materials with better performance is needed.

The related art improves the mechanical properties of steel by adding various alloying elements. For example, the chinese patent application (CN 103741037A) describes a high-strength fatigue-resistant steel tube material and a preparation method thereof, and the high-strength fatigue-resistant steel tube material comprises the following chemical components by mass percent: c:0.06-0.12%, si:0.1-0.3%, mn:1.0-1.5%, cr:0.8-1.2%, mo:0.4-0.8%, V:0.25-0.45%, al:0.03 to 0.06%, nb:0.02 to 0.04%, ti:0.015-0.025%, po:0.01-0.02%, N:0.005-0.01%, la:0.03-0.05%, nd:0.02-0.03%, lu:0.015-0.025%, P not more than 0.025%, S not more than 0.01%, and the rest is Fe. The steel disclosed by the invention is high in alloy element content, and the four rare earth elements are added, so that the cost of the steel is greatly increased, for example, the cost of each ton of steel is increased by 500 yuan for every 1% of V, and the cost of each ton of steel is increased by 3820 yuan, 260 yuan, 8700 yuan and 1050 yuan for every 1% of rare earth elements Po, la, nd and Lu. The preparation process adopts a heat treatment mode to improve the fatigue performance, 13 heating and cooling processes are totally adopted, the time consumed by one-time heat treatment is at least 38 hours, and the mechanical properties of the prepared high-strength fatigue-resistant steel pipe are as follows: the tensile strength is 652Mpa, the yield strength is 525Mpa, the elongation is 35.2 percent, the impact energy at 0 ℃ is 218J, the price cost of each ton of steel is more than 1000 yuan compared with the cost of the steel of the same grade, the price is higher, the performance has no prominent characteristics, and the large-scale popularization and application in practice are difficult.

Disclosure of Invention

The invention provides a low-carbon steel with innovative components and structure. The structure of the low carbon steel includes ferrite, pearlite, and cementite precipitated along grain boundaries. The low carbon steel has improved mechanical properties, such as improved strength and fatigue properties.

In some embodiments, the grains of the low carbon steel described above do not appear as mixed crystals. The grain size deviation of the surface and the core of the low-carbon steel product is lower than 0.5 grade, and the overall grain size reaches 9.0-10.5 grades.

In a first aspect, the present application provides a steel material having the following chemical composition: c:0.03 to 0.13%, mn:0.6 to 1.40%, si:0.15 to 0.30%, nb: 0.010-0.020%, ni:0.10 to 0.30%, ti: 0.015-0.030 percent of Cr, less than or equal to 0.25 percent of Cr, al:0.015 to 0.060%, N:0.01 to 0.02 percent of Fe, less than or equal to 0.20 percent of V, less than 0.015 percent of P, less than 0.020 percent of S, and the balance of Fe and acceptable impurities.

In some embodiments, the structure of the low carbon steel includes ferrite, pearlite, and cementite precipitated along grain boundaries.

In some embodiments, the ferrite in the low carbon steel is bulk ferrite.

In some embodiments, the pearlite in the low carbon steel is selected from coarse pearlite, sorbite, or a combination thereof.

In some embodiments, the low carbon steel has a ferrite content of 80% to 95% (e.g., 80%, 85%, 90%, or 95%) by volume, a pearlite content of 3% to 15% (e.g., 5%, 10%, 15%) by volume, and a cementite content of 0.5% to 3% (e.g., 1%, 2%, 3%) precipitated along grain boundaries.

The steel material is innovative in components, does not contain Po, la, nd, lu and Mo elements, greatly reduces the content of V element to be less than or equal to 0.20%, and greatly reduces the cost of the material.

In a second aspect, the present application provides a method of making a low carbon steel comprising the steps of:

s1) providing a raw material billet, wherein the raw material billet comprises the following chemical components:

c:0.03 to 0.13%, mn:0.6 to 1.40%, si:0.15 to 0.30%, nb: 0.010-0.020%, ni:0.10 to 0.30%, ti: 0.015-0.030 percent of Cr, less than or equal to 0.25 percent of Cr, al:0.015 to 0.060%, N:0.01 to 0.02 percent of Fe, less than or equal to 0.20 percent of V, less than 0.015 percent of P, less than 0.020 percent of S, and the balance of Fe and acceptable impurities;

s2) forging the raw material billet;

s3) carrying out hot rolling on the product obtained in the last step, and cooling to below 50 ℃ (for example, below room temperature) after the hot rolling to obtain a hot rolled plate;

and S4) carrying out cold rolling on the product obtained in the previous step to obtain a cold-rolled sheet.

In some embodiments, in step S1, the raw billet is an ingot.

In some embodiments, in step S1, the phase structure of the raw material billet is ferrite and pearlite. The ferrite in the raw material billet is selected from acicular ferrite and reticular ferrite.

In some embodiments, the forging in step S2 is free forging at a forging ratio of 3 to 5.

In some embodiments, in step S3, the hot rolling is performed at a temperature of 1050 to 1200 ℃.

In some embodiments, in step S3, the hot rolling is performed at 10 to 30% per pass with a total deformation of 70 to 90%.

In some embodiments, after hot rolling, a plate is obtained having a thickness of 10 to 150mm, for example 50 to 100mm.

In some embodiments, in step S3, the cooling rate is from 1 to 10 ℃/S.

In some embodiments, step S3 is cooled with a gaseous cooling medium. The gaseous cooling medium comprises air, a reducing gas or an inert gas. In some embodiments, cooling the steel in a gaseous cooling medium comprises air cooling or air cooling. Air cooling is cooling in air. Air cooling is cooling in a flowing gaseous cooling medium.

In some embodiments, the cold rolling in step S4 is performed at-20 to 30 ℃.

In some embodiments, in step S4, the cold rolling is performed at 5 to 25% per pass, with a total deformation of 50 to 95%.

In some embodiments, in step S4, a sheet is obtained after cold rolling, the sheet having a thickness of 3 to 8mm, for example 5 to 6mm.

In some embodiments, the method of manufacturing low carbon steel further includes a step S5 of shot blasting the product of the previous step.

In some embodiments, in step S5, the peening is laser peening with a laser single pulse energy of 2 to 6J.

In some embodiments, the laser peening technique is also referred to as a laser shock peening technique. Step S5 may be performed using a laser peening technique commonly used in the art. For example, any of the laser peening techniques described in (Zhoushukun, mjbeijing, national defense Industrial Press, 2020.11.) is known.

In a third aspect, the present application provides a low carbon alloy steel.

In some embodiments, the low carbon alloy steel has one or more of the following mechanical properties:

(1) The tensile strength is 736-852 MPa;

(2) The lower yield strength is 552 to 618MPa;

(3) Elongation after fracture is 32% -41%;

(4) The impact work is 229 to 247.5J;

(5) A fatigue limit strength of 536-608 MPa when the stress ratio is 0.1;

(6) The fatigue limit strength is 421 to 512MPa when the stress ratio is-1;

(7) The fatigue limit strength is 465-535 MPa when the stress ratio is-0.5;

(8) The average grain size is 9-11 grades.

Description of the terms

By "acceptable impurities" is meant impurities that are allowed to be present in the steel material by relevant international standards, national standards, industry standards, etc. in the art. In some embodiments, acceptable impurities may be considered as unavoidable impurities. In some embodiments, acceptable impurities have substantially no effect on the properties of the steel material,

ferrite is an interstitial solid solution formed by carbon dissolved in alpha-Fe and is a body-centered cubic lattice.

Pearlite is a eutectoid mixture of ferrite and cementite.

The invention has the advantages of

One or more embodiments of the invention may have one or more of the following benefits:

(1) The steel material has an innovative phase structure;

(2) Steel materials have improved mechanical properties, such as increased strength and fatigue properties;

(3) The steel material has reduced cost.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:

FIG. 1 is a metallographic photograph of a steel material according to example 1.

Detailed Description

Reference will now be made in detail to specific embodiments of the invention. Examples of specific embodiments are illustrated in the accompanying drawings. While the invention will be described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the invention to these specific embodiments. On the contrary, these embodiments are intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

Example 1

The low-carbon steel comprises the following chemical components in percentage by mass: 0.03%, mn:1.30%, si:0.20%, nb:0.020%, ni:0.25%, ti:0.025%, cr:0.20%, al:0.050%, N:0.015%, V:0, P:0.010%, S:0.15%, and the balance of Fe and inevitable impurities.

S1) smelting: smelting according to the component proportion, and continuously casting to obtain a raw material ingot;

s2) forging: carrying out free forging on the cast ingot, wherein the forging ratio is 4.5;

s3) hot rolling: hot rolling is carried out at 1180 ℃, each pass of hot rolling is carried out at 20%, the total deformation is 80%, and the hot rolling is finally cooled to room temperature at the speed of 8 ℃/s, so that the thickness of a product is 50mm;

s4) cold rolling: 15% of each cold rolling pass, 85% of total deformation and 6mm of product thickness;

s3) shot blasting: the obtained cold-rolled sheet was subjected to laser peening treatment with laser peening energy of 5J. Obtaining the low carbon steel plate with the product thickness of 6mm.

Example 2

The low-carbon steel comprises the following chemical components in percentage by mass: 0.12%, mn:0.7%, si:0.18%, nb:0.015%, ni:0.20%, ti:0.020%, cr:0.10%, al:0.020%, N:0.02%, V:0.20%, P:0.010%, S:0.010% and the balance of Fe and inevitable impurities.

s2) forging: carrying out free forging on the cast ingot, wherein the forging ratio is 3.5;

s3) hot rolling: hot rolling is carried out at the temperature of 1080 ℃, each hot rolling pass is 10 percent, the total deformation is 70 percent, and the hot rolling is finally cooled to the room temperature at the speed of 2 ℃/s, and the thickness of the product is 30mm;

s4) cold rolling: each cold rolling pass is 10%, the total deformation is 50%, and the thickness of the product is 4mm;

s3) shot blasting: the obtained cold-rolled sheet was subjected to laser peening with laser peening energy of 3J. Obtaining the low-carbon steel plate, wherein the thickness of the product is 4mm.

Example 3

The low-carbon steel comprises the following chemical components in percentage by mass: 0.07%, mn:1.0%, si:0.25%, nb:0.012%, ni:0.12%, ti:0.015%, cr:0.25%, al:0.035%, N:0.01%, V:0.10%, P:0.008%, S:0.010% and the balance of Fe and unavoidable impurities.

s2) forging: carrying out free forging on the cast ingot, wherein the forging ratio is 4;

s3) hot rolling: hot rolling is carried out at the temperature of 1120 ℃, each pass of hot rolling is 30 percent, the total deformation is 90 percent, and the hot rolling is finally cooled to the room temperature at the speed of 5 ℃/s, and the thickness of the product is 80mm;

s4) cold rolling: 20% of cold rolling in each pass, 60% of total deformation and 6mm of product thickness;

s3) shot blasting: the obtained cold-rolled sheet was subjected to laser peening treatment with laser peening energy of 6J. Obtaining the low carbon steel plate with the product thickness of 6mm.

Comparative example 1

Refer to patent application CN103741037A description [0008] - [0010 ].

The chemical composition of comparative example 1 was: c:0.07%, si:0.24%, mn:1.1%, cr:0.85%, mo:0.5%, V:0.25%, al:0.035%, nb:0.025%, ti:0.020%, po:0.015%, N:0.008%, la:0.04%, nd:0.025%, lu:0.018%, P:0.01%, S:0.008% and the balance of Fe.

The preparation method of comparative example 1, comprising the steps of:

1) Adding the prepared furnace burden into an electric arc furnace for smelting according to chemical composition requirements, and performing continuous casting to obtain a round billet;

2) Heating the prepared round billet and processing the round billet into a steel pipe;

3) Carrying out heat treatment on the prepared pipe;

4) And (3) carrying out subsequent processes such as straightening, flaw detection, marking spraying, packaging and the like on the pipe subjected to the heat treatment to obtain a finished product.

The rare earth element and the noble metal element are added in the comparative example 1, so that the cost of the steel is increased, and the preparation method 3) has the disadvantages of complex heat treatment process, long heat preservation time and complicated cooling mode, and can limit the application of the steel.

The raw material cost of comparative example 1 is 700-1200 yuan per ton more expensive than the raw material cost of example 1.

Comparative example 2

Steel plates were prepared according to the protocol of example 1.

The difference from example 1 is that the composition of the ingot in step S1 is: c:0.07%, si:0.24%, mn:1.1%, cr:0.85%, mo:0.5%, V:0.25%, al:0.035%, nb:0.025%, ti:0.020%, po:0.015%, N:0.008%, la:0.04%, nd:0.025%, lu:0.018%, P:0.01%, S:0.008% and the balance Fe.

s4) cold rolling: each cold rolling pass is 15%, the total deformation is 85%, and the thickness of the product is 6mm;

s3) shot blasting: the obtained cold-rolled sheet was subjected to laser peening with laser peening energy of 5J. Obtaining the low carbon steel plate with the product thickness of 6mm.

Assay detection

1. Tissue analysis

The microstructure of the mild steel sheet of example 1 is shown in fig. 1. As shown in fig. 1, the low carbon steel sheet of example 1 mainly has a phase structure of: ferrite + pearlite + cementite precipitated along grain boundaries. The white part is ferrite 1, the dark part is pearlite 2, and the dark small particles are cementite 3. The crystal grains of the steel plate have no mixed crystal. The integral grain size reaches 9.0-10.5 grade. The grain size deviation between the surface and the core of the steel sheet is less than 0.5 grade.

As a result of the examination, in examples 1 to 3, the volume content of ferrite was 80% to 95%, the volume content of pearlite was 3% to 15%, and the content of cementite precipitated along the grain boundaries was 0.5% to 3%.

2. Analysis of mechanical Properties

The mechanical properties of the low carbon steel sheets of examples 1 to 3 were analyzed. The tensile strength, the lower yield strength and the elongation after fracture are tested according to GB/T228.1-2021, the impact power is tested according to GB/T229-2020, the hardness is tested according to GB/T230.1-2018, the fatigue limit strength is tested according to GB/T3075-2021, the stress ratio is 0.1, the grain size is tested according to GB/T6493-2017, the grade is carried out by adopting an intercept method, the repeatability and the reproducibility of the grade result are less than +/-0.5 grade, the grain size testing position on the surface is less than 0.5mm from the surface of the sample, and the grain size testing position on the core part is the central position of the thickness of the plate. The mechanical property analysis results are shown in tables 1 and 2.

TABLE 1

TABLE 2

As shown in tables 1 and 2, the inventive low carbon steel products of the present invention have improved tensile strength, lower yield strength, elongation after fracture, impact work, fatigue limit strength; also has smaller surface grain size and core grain size; and also has a lower cost.

While the application has been described with reference to a preferred embodiment, various modifications may be made and equivalents may be substituted for elements thereof without departing from the scope of the application. In particular, the technical features mentioned in the embodiments can be combined in any way as long as there is no structural conflict. The present application is not intended to be limited to the particular embodiments disclosed herein, but rather to cover all embodiments falling within the scope of the appended claims.

Claims

1. A low-carbon alloy steel comprises the following chemical components: c:0.03 to 0.13%, mn:0.6 to 1.40%, si:0.15 to 0.30%, nb:0.010 to 0.020%, ni:0.10 to 0.30%, ti: 0.015-0.030%, cr is less than or equal to 0.25%, al:0.015 to 0.060%, N:0.01 to 0.02 percent of Fe, less than or equal to 0.20 percent of V, less than 0.015 percent of P, less than 0.020 percent of S, and the balance of Fe and acceptable impurities.

2. A method of making a low carbon steel comprising the steps of:

s2) forging the raw material billet;

3. The method of claim 2, having one or more of the following features:

(1) In the step S1, a raw material billet is an ingot;

(2) In step S1, the phase structure of the raw material billet is ferrite and pearlite.

4. The method according to claim 2, wherein the forging is free forging in step S2 at a forging ratio of 3 to 5.

5. The method according to claim 2, wherein the hot rolling is performed at 1050-1200 ℃ in step S3.

6. The method according to claim 2, wherein in step S3, the hot rolling is performed in a range of 10 to 30% per pass, and the total deformation is 70 to 90%.

7. The method according to claim 2, wherein in step S3, a plate is obtained after hot rolling, the plate having a thickness of 10 to 150mm.

8. The method according to claim 2, wherein in step S3, the cooling rate in step S3 is 1-10 ℃/S.

9. The method of claim 2, wherein the cold rolling is performed at-20 to 30 ℃ in step S4.

10. The method of claim 2, wherein in step S4, the cold rolling is performed at a rate of 5-25% per pass and a total strain is 50-95%.

11. The method according to claim 2, wherein in step S4, a sheet is obtained after cold rolling, the sheet having a thickness of 3 to 8mm.

12. The method of claim 2, the method of making a low carbon steel further comprising

And S5, performing shot blasting on the product in the last step.

13. The method according to claim 12, wherein the shot peening is laser peening, and the laser single pulse energy is 2 to 6J.

14. A low carbon alloy steel obtainable by the method of any one of claims 1 to 13.

15. The low carbon alloy steel of claim 14, comprising ferrite, pearlite, and cementite precipitating along grain boundaries.

16. The low carbon alloy steel of claim 15, the volume content of ferrite is 80% to 95%, the volume content of pearlite is 3% to 15%, and the content of cementite precipitated along grain boundaries is 0.5% to 3%. The low carbon alloy steel of claim 14, having one or more of the following mechanical properties: