CN115807188B - Low-carbon steel and preparation method thereof - Google Patents

Abstract

The invention relates to low-carbon alloy steel and a preparation method thereof. The chemical components of the low carbon alloy steel are as follows ：C：0.03～0.13％,Mn：0.6～1.40％,Si：0.15～0.30％,Nb：0.010～0.020％,Ni：0.10～0.30％,Ti：0.015～0.030％,Cr≤0.25％,Al：0.015～0.060％,N：0.01～0.02％,V≤0.20％,P＜0.015％,S＜0.020％, the balance being 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

Along with the great development of capital construction in China, the demand of engineering machinery is greatly increased. In the use process, a metal structural member in engineering machinery such as an excavator, a bulldozer, a loader and the like bears a cycle load with complex change, often bears impact and overload, such as a boom of a crawler crane, bears complex alternating stress mixed by stress ratios of 0.1, -0.2, -0.5, -1 and the like, the maximum impact overload born by the Q890D serving as a boom material reaches 900MPa, the metal structural member is recycled 300 ten thousand times under low stress to generate failure, and the fracture analysis finds that the main fracture form is fatigue fracture. It is counted that 50% -90% of various mechanical failures are caused by fatigue, most of the mechanical failures are suddenly broken, and as the existing machinery is developed to high speed and large-scale, many parts run under severe working conditions such as high temperature, high pressure, heavy load and the like, and fatigue failure accidents are more endless. The yield and tensile strength of high-strength steel such as Q355, Q460, Q550 and Q890 which are commonly used at present meet the national standard, but the problem of low fatigue strength exists, and the service life of the whole machine is directly influenced, so that a steel material with better performance needs to be developed.

The related art improves the mechanical properties of steel by adding various alloying elements. For example, chinese patent application (CN 103741037A) describes a high-strength fatigue-resistant steel pipe material and a preparation method thereof, wherein the high-strength fatigue-resistant steel pipe material comprises the chemical components of ：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：0.03-0.06％、Nb：0.02-0.04％、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≤0.025％、S≤0.01％, mass percent and the balance of Fe. The invention has the advantages that the alloy elements are more and high in content, and the cost of steel is greatly increased due to the addition of four rare earth elements, for example, the cost of per ton of steel is increased by 500 yuan for every 1 percent of V, and the cost of per ton of steel is increased by 3820, 260 yuan, 8700 yuan and 1050 yuan for every 1 percent of rare earth element Po, la, nd, lu. The preparation process adopts a heat treatment mode to improve the fatigue performance, and the total temperature rise and fall processes is 13 times, the time for one 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%, the impact energy is 218J at 0 ℃, the price cost per ton of steel is more than 1000 yuan higher than that of the steel with the same grade, the price is higher, the performance has no outstanding characteristics, and the large-scale popularization and the application in practice are difficult.

Disclosure of Invention

The invention provides low carbon steel with innovative components and structures. 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 are free of mixed crystals. The grain size deviation between the surface and the core of the low carbon steel product is lower than 0.5 level, and the whole grain size reaches 9.0-10.5 level.

In a first aspect, the present application provides a steel material having the following ：C：0.03～0.13％,Mn：0.6～1.40％,Si：0.15～0.30％,Nb：0.010～0.020％,Ni：0.10～0.30％,Ti：0.015～0.030％,Cr≤0.25％,Al：0.015～0.060％,N：0.01～0.02％,V≤0.20％,P＜0.015％,S＜0.020％, chemical components, the balance being 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 volume content of ferrite in the low carbon steel is 80% to 95% (e.g., 80%, 85%, 90%, or 95%), the volume content of pearlite is 3% to 15% (e.g., 5%, 10%, 15%), and the content of cementite precipitated along grain boundaries is 0.5 to 3% (e.g., 1%, 2%, 3%).

The steel material is innovative in composition, contains no Po, la, nd, lu, mo elements, and greatly reduces the content of V element to less than or equal to 0.20%, so that the cost of the material is greatly reduced.

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

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

C：0.03～0.13％,Mn：0.6～1.40％,Si：0.15～0.30％,Nb：0.010～0.020％,Ni：0.10～0.30％,Ti：0.015～0.030％,Cr≤0.25％,Al：0.015～0.060％,N：0.01～0.02％,V≤0.20％,P＜0.015％,S＜0.020％, The balance of Fe and acceptable impurities;

S2) forging a raw steel billet;

S3) hot rolling the product of the last step, and cooling to below 50 ℃ after hot rolling (for example, below room temperature) to obtain a hot rolled plate;

s4) cold rolling the product of the last step to obtain a cold-rolled sheet.

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

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

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

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

In some embodiments, in step S3, the hot rolling is performed at 10-30% per pass and the total deformation is 70-90%.

In some embodiments, the sheet is obtained after hot rolling and has a thickness of 10 to 150mm, for example 50 to 100mm.

In some embodiments, in step S3, the cooling rate is 1-10deg.C/S.

In some embodiments, in step S3, cooling is performed 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 includes air cooling or air cooling. Air cooling is cooling in air. Air cooling is cooling in a flowing gaseous cooling medium.

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

In some embodiments, in step S4, the total deformation is from 50 to 95% for each cold rolling pass from 5 to 25%.

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

In some embodiments, the method of producing low carbon steel further comprises step S5, peening the product of the previous step.

In some embodiments, in step S5, the peening is laser peening, the laser monopulse energy being 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 laser peening techniques common in the art. For example, any of the laser peening techniques described in the following documents (Shikun. Laser shock peening technique [ M ]. Beijing: national defense industry Press, 2020.11.).

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) Tensile strength is 736-852 MPa;

(2) Lower yield strength is 552-618 MPa;

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

(4) 229-247.5J of impact energy;

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

(6) The fatigue limit strength is 421-512 MPa 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 grade.

Description of the terms

"Acceptable impurities" refers to impurities that are permitted to exist in the steel material in accordance with international standards, national standards, industry standards, and the like, related in the art. In some embodiments, acceptable impurities may be considered unavoidable impurities. In some embodiments, the acceptable impurities have substantially no substantial effect on the properties of the steel material,

Ferrite is an interstitial solid solution formed by dissolving carbon in alpha-Fe, and is a body-centered cubic lattice.

Pearlite is a eutectoid mixture of ferrite and cementite.

The beneficial effects of the invention are that

One or more embodiments of the invention 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) Steel materials have reduced costs.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

fig. 1 is a metallographic photograph of the steel material of 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 they are 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 C：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：0:15％,P：0.010％,S：0.15％, of Fe and unavoidable impurities in percentage by mass of chemical components.

S1) smelting: smelting according to the component proportion, and obtaining a raw material ingot after continuous casting;

S2) forging: freely forging the cast ingot, wherein the forging ratio is 4.5;

s3) hot rolling: hot rolling at 1180 deg.c to 20% in each pass and total deformation of 80%, cooling to room temperature at 8 deg.c/s and product thickness of 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 with a laser peening energy of 5J. The low carbon steel plate is obtained, and the thickness of the product is 6mm.

Example 2

The low-carbon steel comprises C：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％, of Fe and unavoidable impurities in percentage by mass of chemical components.

S1) smelting: smelting according to the component proportion, and obtaining a raw material ingot after continuous casting;

s2) forging: freely forging the cast ingot, wherein the forging ratio is 3.5;

s3) hot rolling: hot rolling at 1080 ℃ with 10% of each pass and 70% of total deformation, and cooling to room temperature at a speed of 2 ℃/s, wherein the thickness of the product is 30mm;

S4) cold rolling: 10% of each cold rolling pass, 50% of total deformation and 4mm of product thickness;

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

Example 3

The low-carbon steel comprises C：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％, of Fe and unavoidable impurities in percentage by mass of chemical components.

S1) smelting: smelting according to the component proportion, and obtaining a raw material ingot after continuous casting;

S2) forging: freely forging the cast ingot, wherein the forging ratio is 4;

S3) hot rolling: hot rolling at 1120 deg.c with 30% deformation amount of 90% in each pass and final cooling at 5 deg.c/s to room temperature and product thickness of 80mm;

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

S3) shot blasting: the obtained cold-rolled sheet was subjected to laser peening with a laser peening energy of 6J. The low carbon steel plate is obtained, and the thickness of the product is 6mm.

Comparative example 1

Refer to the patent application CN103741037A specification [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 was Fe.

The preparation method of the comparative example 1 comprises the following steps:

1) The chemical components require that the prepared furnace burden is added into an electric arc furnace for smelting and continuously cast into round billets;

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 straightening, flaw detection, marking, packaging and other subsequent processes are carried out on the heat-treated pipe, so that a finished product is obtained.

The addition of rare earth elements and noble metal elements in comparative example 1 leads to an increase in the cost of the steel, and 3) the heat treatment process in the preparation method is complicated, the heat preservation time is long, and the cooling mode is complicated, so that the application of the alloy is limited.

The raw material cost of comparative example 1 is 700 to 1200 yuan per ton, compared with the raw material cost of example 1.

Comparative example 2

A steel sheet was prepared with reference to the scheme 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 is Fe.

S1) smelting: smelting according to the component proportion, and obtaining a raw material ingot after continuous casting;

S2) forging: freely forging the cast ingot, wherein the forging ratio is 4.5;

s3) hot rolling: hot rolling at 1180 deg.c to 20% in each pass and total deformation of 80%, cooling to room temperature at 8 deg.c/s and product thickness of 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 with a laser peening energy of 5J. The low carbon steel plate is obtained, and the thickness of the product is 6mm.

Analytical detection

1. Tissue analysis

The microstructure of the low carbon steel sheet of example 1 is shown in fig. 1. As shown in fig. 1, the phase structure of the low carbon steel sheet of example 1 is mainly: 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 whole grain size reaches 9.0 grade-10.5 grade. The grain size deviation of the surface and core of the steel sheet is lower than 0.5 grade.

According to detection, in the embodiment 1-3, the volume content of ferrite is 80% -95%, the volume content of pearlite is 3% -15%, and the content of cementite precipitated along a grain boundary is 0.5% -3%.

2. Analysis of mechanical Properties

Mechanical property analysis was performed on the low carbon steel sheets of examples 1 to 3. Tensile strength, lower yield strength and elongation after fracture are tested according to GB/T228.1-2021, impact energy is tested according to GB/T229-2020, hardness is tested according to GB/T230.1-2018, fatigue limit strength is tested according to GB/T3075-2021, stress ratio is 0.1, grain size is tested according to GB/T6493-2017, grading is carried out by adopting a intercept point method, repeatability and reproducibility of a grading result are less than +/-0.5 level, a surface grain size testing position is less than 0.5mm from the surface of a sample, and a core grain size testing position is the center position of the thickness of a plate. The results of the mechanical property analysis 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 break, impact energy, fatigue limit strength; but also has a smaller surface grain size and core grain size; but also has 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 respective embodiments may be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions falling within the scope of the claims.

Claims (16)

1. A low-carbon alloy steel comprises the following ：C：0.03～0.13％,Mn：0.6～1.40％,Si：0.15～0.30％,Nb：0.010～0.020％,Ni：0.10～0.30％,Ti：0.015～0.030％,Cr≤0.25％,Al：0.015～0.060％,N：0.01～0.02％,V≤0.20％,P＜0.015％,S＜0.020％, percent of Fe and acceptable impurities, wherein the low-carbon alloy steel comprises 80-95 percent of ferrite, 3-15 percent of pearlite and 0.5-3 percent of cementite precipitated along grain boundary.

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

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

C：0.03～0.13％,Mn：0.6～1.40％,Si：0.15～0.30％,Nb：0.010～0.020％,Ni：0.10～0.30％,Ti：0.015～0.030％,Cr≤0.25％,Al：0.015～0.060％,N：0.01～0.02％,V≤0.20％,P＜0.015％,S＜0.020％, The balance of Fe and acceptable impurities;

S2) forging a raw steel billet;

s3) hot rolling the product of the last step, and cooling to below 50 ℃ after hot rolling to obtain a hot rolled plate;

s4) cold rolling the product of the last step to obtain a cold-rolled sheet.

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 billet is ferrite and pearlite.

4. The method according to claim 2, wherein in step S2, the forging is free forging and the forging ratio is3 to 5.

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

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

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

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

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

10. The method according to claim 2, wherein in step S4, the total deformation is between 50 and 95% for each cold rolling pass between 5 and 25%.

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

12. The method of claim 2, wherein the method of producing low carbon steel further comprises

And S5, shot blasting is carried out on the product in the last step.

13. The method of claim 12, wherein the peening process is laser peening, the laser monopulse energy being 2 to 6J.

14. The method according to claim 12, wherein in the step S3), the product of the previous step is hot rolled, and the hot rolled product is cooled to a temperature below room temperature to obtain a hot rolled sheet.

15. A low carbon alloy steel prepared by the method of any one of claims 2 to 14, wherein the ferrite content is 80 to 95% by volume, the pearlite content is 3 to 15% by volume, and the cementite content precipitated along grain boundaries is 0.5 to 3%.

16. The low carbon alloy steel of claim 15, having one or more of the following mechanical properties:

(1) Tensile strength is 736-852 MPa;

(2) Lower yield strength is 552-618 MPa;

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

(4) 229-247.5J of impact energy at 0 ℃;

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

(6) The fatigue limit strength is 421-512 MPa 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 grade.