CN117418162A

CN117418162A - Steel for anti-fatigue pipe and preparation method thereof

Info

Publication number: CN117418162A
Application number: CN202311290447.2A
Authority: CN
Inventors: 俞城双; 张�杰; 李秋晨; 张靖波; 王宏; 王广义
Original assignee: Zhejiang Laifual Harmonic Drive Co ltd
Current assignee: Zhejiang Laifual Harmonic Drive Co ltd
Priority date: 2023-10-08
Filing date: 2023-10-08
Publication date: 2024-01-19

Abstract

The invention provides steel for an anti-fatigue pipe, which comprises the following components in percentage by mass: c:0.04-0.06%, si:0.20 to 0.44 percent of Mn:1.00-1.10%, zr:0.02-0.8%, tc:0.01-0.06%, ti:0.01-0.02%, cr:0.10-0.30%, ni:0.10-0.30%, W:0.05-0.25%, P: < 0.005%, S: less than 0.005% and the balance of Fe and unavoidable impurities. The invention also provides a preparation method of the steel for the anti-fatigue pipe, which comprises the following steps: s1, molten iron pretreatment; s2 smelting and forging: s3, heating; s4, rolling for at least 4 times; s5, cooling: and (5) performing water quenching treatment on the rolled steel plate.

Description

Steel for anti-fatigue pipe and preparation method thereof

Technical Field

The invention relates to the field of steel manufacturing, in particular to steel for an anti-fatigue pipe and a preparation method thereof.

Background

In recent years, with the increasing demand of special steel and the continuous progress of various technological technologies such as exploration and exploitation, higher requirements are put on the fatigue resistance of steel. Particularly in the exploitation field of oil gas resources, the requirement on the fatigue resistance of steel is more severe.

Due to the complex environment and climate, steel materials used for offshore operation bear the influence of wind, wave, current, ice, earthquake and other loads at all times. Collisions between steel products can also occur. The steel product can generate wave frequency vibration, vortex-induced vibration, parametric vibration and the like, and the wave frequency vibration, the vortex-induced vibration, the parametric vibration and the like can cause fatigue damage and fracture failure of the steel, so that huge economic loss is brought to engineering, and serious secondary disasters are caused to natural environment. Therefore, there is a need to develop a steel material having high fatigue resistance, which has excellent fatigue resistance on the basis of satisfying the toughness.

Disclosure of Invention

A first object of the present invention is to provide a steel for pipes having high fatigue resistance.

A second object of the present invention is to provide a method for producing steel for pipes having high fatigue resistance.

The invention is realized by the following technical scheme:

the steel for the anti-fatigue pipe comprises the following components in percentage by mass:

c:0.04-0.06%, si:0.20 to 0.44 percent of Mn:1.00-1.10%, zr:0.02-0.8%, tc:0.01-0.06%, ti:0.01-0.02%, cr:0.10-0.30%, ni:0.10-0.30%, W:0.05-0.25%, P: < 0.005%, S: less than 0.005% and the balance of Fe and unavoidable impurities.

The austenite grain size of the steel for fatigue resistance is 8-12 microns.

The volume fraction of the superfine crystal ferrite is 30-60%.

The preparation method of the steel for the anti-fatigue pipe comprises the following steps:

s1, molten iron pretreatment;

s2 smelting and forging:

s3, heating;

s4, rolling for at least 4 times;

s5, cooling: and (5) performing water quenching treatment on the rolled steel plate.

The pretreatment comprises KR desulfurization; after KR desulfurization, the S content is lower than 0.002%;

the final forging temperature of the forging is higher than 950 ℃;

the heating temperature is 1050-1100 ℃ and the heating time is 100-120min;

the initial rolling temperature of the rolling is 980-1010 ℃ and the final rolling temperature is 760-830 ℃.

The rolling adopts two-stage rolling, wherein the first stage rolling is rough rolling, the initial rolling temperature of the rough rolling is 980-1000 ℃, the final rolling temperature of the rough rolling is 790-800 ℃, and the accumulated deformation of the final 2-3 passes is more than 40%;

the second stage is finish rolling, the finish rolling start temperature is 1000-1010 ℃, the finish rolling finish temperature is 800-830 ℃, and the accumulated deformation is more than 55%.

Compared with the prior art, the invention has the advantages that:

1. the invention ensures that the microstructure of the steel is ultrafine austenite by controlling the element types, element contents and the rolling and cooling processes of the tube steel. Acicular ferrite and ultrafine grain polygonal ferrite are further introduced into the structure, and the proportion of a high orientation difference interface in the structure is increased, so that the inhibition effect on fatigue crack growth is improved, and the fatigue resistance of the steel for the pipe is improved.

2. According to the invention, on the basis of Zr microalloying, tc microalloying is matched, and through composite precipitation and secondary precipitation of a Tc-containing second phase, the strength of a softening area of a steel welding joint is improved, stress concentration at the position is avoided, and the fatigue resistance of a welding seam is improved.

Drawings

FIG. 1 is a photograph showing the result of 100-fold metallographic structure examination of the steel for fatigue resistance pipe prepared in example 1;

FIG. 2 is a photograph showing the result of 500-fold metallographic structure examination of the steel for fatigue resistance pipe prepared in example 1;

FIG. 3 is a photograph showing the result of 100-fold metallographic structure examination of the steel for fatigue resistance pipe prepared in example 2;

FIG. 4 is a photograph showing the result of 500-fold metallographic structure examination of the steel for fatigue resistance pipe prepared in example 2;

FIG. 5 is a photograph showing the result of 100-fold metallographic structure examination of the steel for fatigue resistance pipe prepared in example 3;

FIG. 6 is a photograph showing the result of 500-fold metallographic structure examination of the steel for fatigue resistance pipe prepared in example 3;

FIG. 7 is a photograph showing the result of 100-fold metallographic structure examination of the steel for fatigue resistance pipe prepared in example 4;

FIG. 8 is a photograph showing the result of 1000 times of the metallographic structure test of the steel for fatigue resistance pipe prepared in example 4;

FIG. 9 is a photograph showing the result of 100-fold metallographic structure examination of the steel for fatigue resistance pipe prepared in example 5;

FIG. 10 is a photograph showing the result of 1000-fold metallographic structure examination of the steel for fatigue resistance pipe prepared in example 5;

FIG. 11 is a photograph showing the result of 100-fold metallographic structure examination of the steel for fatigue resistance pipe prepared in example 6;

FIG. 12 is a photograph showing the result of 1000-fold metallographic structure examination of the steel for fatigue resistance pipe prepared in example 6.

Detailed Description

The invention provides steel for an anti-fatigue pipe, which comprises the following chemical components in percentage by mass: c:0.04 to 0.06 percent, si:0.20 to 0.44 percent, mn:1.00 to 1.10 percent, zr: 0.02-0.08%, tc:0.03 to 0.06 percent of Ti:0.01 to 0.02 percent, cr:0.10 to 0.30 percent of Ni:0.10 to 0.30 percent, W:0.05 to 0.25 percent, P: < 0.005%, S: less than 0.005% and the balance of Fe and unavoidable impurities. At present, the existing steel for the pipe is difficult to have good toughness and high fatigue resistance.

The invention ensures that the microstructure of the steel is ultrafine austenite by controlling the element types, element contents and rolling and cooling processes of the pipe steel, further introduces acicular ferrite and ultrafine grain polygonal ferrite into the microstructure, accurately regulates and controls the proportion of each phase in the microstructure, and improves the toughness and fatigue resistance of the pipe steel.

The reason why the composition of the cast slab is limited in the steel for fatigue resistance tube and the method for producing the same according to the present invention will be described, and the composition is expressed in% by mass only.

C: carbon is an element for ensuring the strength of the steel plate, and forms carbide with zirconium and scandium to delay austenite recrystallization so as to refine grains; the content of the carbon element has a large influence on the impact toughness of the steel, and the welding performance is obviously damaged when the content is too high, so that the content of C is controlled to be 0.04-0.06%.

Si: silicon is generally used as a deoxidizer in steelmaking, and molten steel is easy to oxidize when the silicon content is lower than 0.2%; silicon is also a solid solution strengthening element, but a large amount of silicon is generally disadvantageous in terms of welding properties, and Si content should be controlled to be less than 0.4% in order to secure toughness of steel. Therefore, the Si content is controlled to be 0.20 to 0.44%.

Mn: manganese has solid solution strengthening effect, can compensate for the reduction of yield strength caused by the reduction of carbon content, can improve the toughness of steel and reduce ductile-brittle transition temperature; manganese can reduce the transformation temperature of steel during cooling, and has a refining effect on the grain size of ferrite; too high manganese content can increase center segregation of the controlled rolling steel plate, and the welding performance is not good; therefore, the Mn content is controlled to be 1.00 to 1.10%.

Zr: zirconium is a key microalloying element, and when zirconium can control steel rolling, strain is induced to separate out nanoscale Zr-containing second phase particles, so that obvious precipitation strengthening effect is generated; the strength of a softening area of a steel ring welding joint for the pipe can be improved through secondary precipitation of a Zr-containing second phase in a welding heat affected zone, and stress concentration at the position is avoided, so that the fatigue resistance of a pipe ring welding joint is improved; when the zirconium content is less than 0.02%, the effect of improving the strength of the softened region is not obvious enough; at the same time, the upper limit should be controlled at 0.08% for cost and effect overflow. Tc: tc is a critical microalloying element. Tc can prevent the growth of austenite grains, and in the process of controlling rolling and reheating, the carbon and nitride of undissolved microalloy elements Tc, zr and Ti can obviously prevent the coarsening process of the austenite grains through a mechanism of pinning grain boundaries by particles; tc can delay the recrystallization of deformation gamma, and micro-alloy carbon and nitride particles precipitated by solute atom dragging and strain induced precipitation of solid solution micro-alloy elements Tc, zr and Ti can obviously prevent the recrystallization of deformation gamma under the pinning action of grain boundary and subgrain boundary in the controlled rolling process of the steel plate, so that a fine phase change tissue is obtained through the phase change of unrecrystallized gamma; tc can delay the phase transformation process of 'gamma-alpha', and in the cooling process after high-temperature deformation, micro-alloy elements Tc, zr and Ti can block new phase formation in grain boundary segregation, so that the phase transformation temperature of 'gamma-alpha' is reduced, polygonal ferrite phase transformation is inhibited, and acicular ferrite formation is promoted.

Ti: stable TiN is formed at high temperature, and austenite grains are restrained from growing up in the reheating process; the excessive content can form large-size precipitated phases, which affect the toughness of the steel; the Ti content is controlled to be 0.01-0.02%, namely, the micro-titanium treatment is carried out.

W: tungsten can reduce the transformation temperature of supercooled austenite, inhibit the formation of polygonal ferrite and promote acicular ferrite transformation; in the Zr-containing pipeline steel, W can improve the solid solubility of Zr (C, N) in austenite, reduce the precipitation temperature of Zr (C, N) and enable more Zr (C, N) to be precipitated in low temperature alpha, thereby improving the precipitation strengthening effect of Zr (C, N); carbide forming elements can be fused into the lattice of the microalloy carbonitride in the welding thermal cycle process to reduce mismatch energy, thereby promoting the precipitation of the microalloy carbonitride; if the W content is less than 0.05%, the effect of W is low; if the W content exceeds 0.25%, the weldability of the steel sheet, particularly the toughness under high heat input welding, is impaired; therefore, the W content is controlled to be 0.05-0.25%.

Ni: as a supplemental element to molybdenum, the effect on the phase change process is similar to molybdenum; ni can improve the low-temperature toughness of the material, so that the Ni content is controlled to be 0.1-0.3%.

Cr: as a supplemental element to molybdenum, the effect on the phase change process is similar to molybdenum. Cr can improve the hardenability of the material and can improve the strength of the material in the form of carbide, and if the Cr content is less than 0.1%, it is difficult to exert its effect, but the Cr content exceeds 0.3%, which reduces the toughness of the steel and increases the manufacturing cost of the material, so that the Cr content is controlled to 0.1 to 0.3%.

P: phosphorus is an impurity element in steel, and can impair toughness of steel for pipes; therefore, the P content is controlled to be 0.005% or less. S: sulfur is an impurity element in steel, and sulfide inclusions are formed to become a crack source; therefore, the S content is controlled to be 0.005% or less.

The invention also provides a preparation method of the steel for the pipe, which is used for preparing the steel for the pipe and comprises the following steps of:

step 1: and (3) molten iron pretreatment: impurity elements in steel are reduced through molten iron pretreatment, and S content is ensured to be lower than 0.002% after KR desulfurization;

step 2: smelting and forging: molten steel is poured into a continuous casting blank through converter smelting and external refining;

step 3: heating: and heating the casting blank in a heating furnace at 1050-1100 deg.c for 1-2 hr.

Step 4: rolling for at least 4 times: rolling and cooling the continuous casting billet to obtain finished steel;

specifically, in the step 4, a two-stage rolling method is adopted for control rolling, the method is divided into a first-stage rolling and a second-stage rolling, the first-stage rolling is rough rolling, the rough rolling is divided into 3-pass rolling, the initial rolling temperature of rough rolling is 980-1000 ℃, the final rolling temperature of rough rolling is 760-830 ℃, and the accumulated deformation of 2-3 passes is more than 40%, so that recrystallized austenite is fully refined through rough rolling; the second stage is rolling, the rolling temperature is 1000-1010 deg.c, the rolling temperature is 800-830 deg.c, the accumulated deformation is greater than 55%, and the finishing is to provide enough nucleation sites for the ferrite phase transition.

S5, performing water quenching treatment on the rolled steel plate.

The microstructure of the steel is ultrafine austenite, acicular ferrite and ultrafine grain polygonal ferrite are further introduced into the microstructure, the volume fraction of the ultrafine grain ferrite is 15-20%, and the average grain size of the ultrafine grain ferrite is less than or equal to 6 mu m. The austenite refinement in the rough rolling stage and the austenite full flattening in the finish rolling stage are key for obtaining the superfine ferrite in the dual-phase structure, and meanwhile, the proportion of the superfine ferrite is regulated and controlled by regulating the cooling temperature, and the acicular ferrite transformation is controlled by further regulating the final cooling temperature; in the aspect of alloy elements, the austenite grain refinement and acicular ferrite transformation effects similar to those of high Zr steel can be achieved by increasing the content of TC and reducing the corresponding Zr content, and meanwhile, the problem of softening a heat affected zone of subsequent pipeline steel welding can be effectively solved by the TC element.

The steel for the pipe prepared by the invention has the yield strength of 495-550 MPa, the tensile strength of 500-701 MPa, the impact energy at minus 20 ℃ of more than or equal to 350J, the fatigue strength at 107 cycles of more than or equal to 350MPa, and simultaneously has lower fatigue crack expansion rate, and the heat affected zone of the ring welding has no obvious softening phenomenon; the high-strength and high-toughness heat-resistant steel has good fatigue resistance and heat-affected zone softening resistance on the basis of meeting the requirement of good toughness.

The advantages of the invention in terms of precise control of the elemental chemistry, content and manufacturing process parameters will be demonstrated in the following specific examples and comparative examples.

Example 1

A steel for fatigue-resistant pipe comprises the following chemical components in weight: c:0.046%, si:0.31%, mn:1.01%, zr:0.50%, TC:0.01%, ti:0.010%, cr:0.1%, ni:0.1%, W:0.06%, P:0.003%, S:0.003% of Fe and the balance of unavoidable impurities. The preparation method comprises the following steps:

step 1: and (3) molten iron pretreatment: impurity elements in steel are reduced through molten iron pretreatment, and S content is ensured to be lower than 0.0015% after KR desulfurization;

step 3: heating: and heating the casting blank in a heating furnace at 1050 ℃ for 1 hour.

Step 4: rolling for 5 times: rolling and cooling the continuous casting billet to obtain finished steel;

specifically, in the step 4, firstly, rough rolling is performed in the first stage, the rough rolling is divided into 3 passes, the initial rolling temperature of the rough rolling is 980 ℃, the final rolling temperature of the rough rolling is 790 ℃, and finally, the accumulated deformation of 2 passes is more than 40%, and recrystallized austenite is fully refined through rough rolling; and then performing finish rolling in a second stage, wherein the finish rolling start temperature is 1000 ℃, the finish rolling finish temperature is 800 ℃, the accumulated deformation is more than 55%, and enough nucleation positions are provided for the post ferrite transformation through finish rolling.

S5, performing water quenching treatment on the rolled steel plate. And (3) precipitating ultrafine grain ferrite in the billet structure in the quenching water treatment.

The steel sheet for a pipe prepared in this example had a yield strength of 502MPa, a tensile strength of 589MPa, an impact energy of 406J at-20℃and a fatigue strength of 369MPa at 107 weeks, and a fatigue crack growth rate equation of da/dN=1.28X10 ^-12 (ΔK) ^4.87 The method comprises the steps of carrying out a first treatment on the surface of the The heat affected zone of the girth weld has no softening phenomenon.

Example 2

A steel for fatigue-resistant pipe comprises the following chemical components in weight: c:0.058%, si:0.40%, mn:1.02%, zr:0.07%, TC:0.045%, ti:0.015%, cr:0.24%, N i:0.25%, W:0.23%, P:0.003%, S:0.002%, the balance being Fe and unavoidable impurities. The preparation method comprises the following steps:

step 3: heating: and heating the casting blank in a heating furnace at 1100 ℃ for 2 hours.

specifically, in the step 4, firstly, rough rolling is performed in the first stage, the rough rolling is divided into 3 passes, the initial rolling temperature of the rough rolling is 1000 ℃, the final rolling temperature of the rough rolling is 800 ℃, and finally, the accumulated deformation of 2 passes is more than 45%, and recrystallized austenite is fully refined through rough rolling; and then performing finish rolling in a second stage, wherein the finish rolling start temperature is 1000 ℃, the finish rolling finish temperature is 830 ℃, the accumulated deformation is more than 55%, and enough nucleation positions are provided for the post ferrite transformation through finish rolling.

The steel sheet for a pipe prepared in this example had a yield strength of 525MPa, a tensile strength of 630MPa, an impact energy of 390J at-20℃and a fatigue strength of 375MPa at 107 weeks, and a fatigue crack growth rate equation of da/dN=3.23×10 ^-12 (ΔK) ^4.90 The method comprises the steps of carrying out a first treatment on the surface of the The heat affected zone of the girth weld has no softening phenomenon.

Example 3

A steel for fatigue-resistant pipe comprises the following chemical components in weight: c:0.05%, si:0.39%, mn:1.04%, zr:0.8%, TC:0.018%, ti:0.02%, cr:0.25%, ni:0.15%, W:0.06%, P:0.003%, S:0.002%, the balance being Fe and unavoidable impurities. The preparation method comprises the following steps:

step 3: heating: heating the casting blank in a heating furnace at 1100 ℃ for 1.5 hours; the steel is heated to generate plastic deformation.

specifically, in the step 4, firstly, rough rolling is performed in the first stage, the rough rolling is divided into 3 passes, the initial rolling temperature of the rough rolling is 990 ℃, the final rolling temperature of the rough rolling is 800 ℃, and finally, the accumulated deformation of 2 passes is more than 50%, and recrystallized austenite is fully refined through rough rolling; and then performing finish rolling in a second stage, wherein the finish rolling start temperature is 1000 ℃, the finish rolling finish temperature is 830 ℃, the accumulated deformation is more than 55%, and enough nucleation positions are provided for the post ferrite transformation through finish rolling.

The steel sheet for a pipe prepared in this example had a yield strength of 494MPa, a tensile strength of 565MPa, an impact energy of 352J at-20℃and a fatigue strength of 378MPa at 107 cycles, and a fatigue crack growth rate equation of da/dN=1.77×10 ^-12 (ΔK) ^4.97 The method comprises the steps of carrying out a first treatment on the surface of the The heat affected zone of the girth weld has no softening phenomenon.

Example 4

A steel for fatigue-resistant pipe comprises the following chemical components in weight: c:0.060%, si:0.37%, mn:1.05%, zr:0.050%, tc:0.01%, ti:0.014%, cr:0.20%, N i:0.19%, W:0.18%, P:0.003%, S:0.002%, the balance being Fe and unavoidable impurities. The preparation method comprises the following steps:

step 3: heating: and heating the casting blank in a heating furnace at 1100 ℃ for 1 hour.

The steel plate for the pipe, which is prepared by the embodiment, has the yield strength of 542MPa, the tensile strength of 655MPa, the impact energy of 387J at minus 20 ℃, and good strength and toughness. Meanwhile, the 107-week fatigue strength is 383MPa, and the fatigue crack growth rate equation is da/dN=1.86×10 ^-12 (ΔK) ^4.90 The method comprises the steps of carrying out a first treatment on the surface of the The heat affected zone of the girth weld has no softening phenomenon.

Example 5

A steel for fatigue-resistant pipe comprises the following chemical components in weight: c:0.048%, si:0.21%, mn:1.08%, zr:0.52%, TC:0.04%, ti:0.015%, cr:0.21%, ni:0.18%, W:0.10%, P:0.003%, S:0.002%, the balance being Fe and unavoidable impurities. The preparation method comprises the following steps:

S5, performing water quenching treatment on the rolled steel plate.

The steel sheet for a pipe prepared in this example had a yield strength of 587MPa, a tensile strength of 526MPa, an impact energy of 3996J at-20℃and a fatigue strength of 367MPa at 107 weeks, and a fatigue crack growth rate equation of da/dN=

2.76×10 ^-12 (ΔK) ^4.98 The method comprises the steps of carrying out a first treatment on the surface of the The heat affected zone of the girth weld has no softening phenomenon.

Example 6

A steel for fatigue-resistant pipe comprises the following chemical components in weight: c:0.040%, si:0.30%, mn:1.07%, zr:0.7%, TC:0.04%, ti:0.015%, cr:0.15%, ni:0.11%, W:0.20%, P:0.003%, S:0.002%, the balance being Fe and unavoidable impurities. The preparation method comprises the following steps:

step 3: heating: and heating the casting blank in a heating furnace at 1005 ℃ for 2 hours.

S5, performing water quenching treatment on the rolled steel plate.

The steel sheet for a pipe prepared in this example had a yield strength of 517MPa, a tensile strength of 701MPa, an impact energy of 317J at-20℃and a fatigue strength of 338MPa at 107 cycles, and a fatigue crack growth rate equation of da/dN=

2.05×10 ^-12 (ΔK) ^4.98 The method comprises the steps of carrying out a first treatment on the surface of the The heat affected zone of the girth weld has no softening phenomenon.

Comparative example 1

The present comparison provides a steel comprising, by weight: c:0.042%, si:0.30%, mn:1.08%, zr:0.73%, ti:0.012%, cr:0.15%, ni:0.11%, W:0.12%, P:0.003%, S:0.002%, the balance being Fe and unavoidable impurities. The preparation method comprises the following steps:

step 3: heating: heating the casting blank in a heating furnace at 1000 ℃ for 1 hour;

S5, performing water quenching treatment on the rolled steel plate.

The steel plate prepared in the comparative example has the yield strength of 497MPa, the tensile strength of 586MPa, the impact energy of 391J at minus 20 ℃, and good strength and toughness. Meanwhile, the fatigue strength at 107 weeks is 344MPa, and the fatigue crack growth rate equation is da/dN=2.02X10-12 (delta K) 4.99; softening occurs in the fine grain region of the ring welding heat affected zone.

The comparative example does not contain TC element, zr element is not in the content range required by the invention, the 107-week fatigue strength of the finally prepared steel plate is 340Mpa, which is lower than that of the steel prepared by the invention, and softening phenomenon occurs in the ring welding heat affected zone, thus seriously affecting the service safety.

Comparative example 2

The present comparison provides a steel comprising, by weight: c:0.050%, si:0.33%, mn:1.06%, TC:0.035%, ti:0.017%, cr:0.14%, ni:0.13%, W:0.15%, P:0.004%, S:0.001%, the balance being Fe and unavoidable impurities. The preparation method comprises the following steps:

S5, performing water quenching treatment on the rolled steel plate.

The yield strength of the steel plate prepared in the comparative example is 233MPa, the tensile strength is 500MPa, the impact energy at minus 20 ℃ is 350J, the fatigue strength at 107 weeks is 196MPa, and the fatigue crack propagation rate equation is da/dN=

8.68×10 ^-12 (ΔK) ^4.96 The method comprises the steps of carrying out a first treatment on the surface of the The heat affected zone of the girth weld has no softening phenomenon. The comparative example does not contain Zr element, and thus the fatigue crack growth rate is significantly increased.

Comparative example 3

A steel for fatigue-resistant pipe comprises the following chemical components in weight: c:0.046%, si:0.30%, mn:1.10%, ti:0.015%, cr:0.14%, ni:0.12%, W:0.13%, P:0.003%, S:0.002%, the balance being Fe and unavoidable impurities. The preparation method comprises the following steps:

step 3: heating: and (3) placing the casting blank into a heating furnace for heating, wherein the heating temperature is 1000 ℃, and the heat preservation time is 1 hour.

specifically, in the step 4, firstly, rough rolling is performed in the first stage, the rough rolling is divided into 3 passes, the initial rolling temperature of the rough rolling is 1000 ℃, the final rolling temperature of the rough rolling is 800 ℃, and finally, the accumulated deformation of 2 passes is more than 35%, and recrystallized austenite is fully refined through rough rolling; and then performing finish rolling in a second stage, wherein the finish rolling start temperature is 1000 ℃, the finish rolling finish temperature is 830 ℃, the accumulated deformation is more than 55%, and enough nucleation positions are provided for the post ferrite transformation through finish rolling.

S5, performing water quenching treatment on the rolled steel plate.

The steel plate for pipe manufactured in this comparative example had a yield strength of 367MPa, a tensile strength of 276MPa, an impact energy of 188J at-20 ℃ and a fatigue strength of 207MPa at 107 weeks, and a fatigue crack growth rate equation of da/dN=9.99X10 ^-12 (ΔK) ^5.02 The method comprises the steps of carrying out a first treatment on the surface of the The heat affected zone of the girth weld has no softening phenomenon.

In comparative example 1, the fatigue strength was lowered by the absence of the TC element, and softening was mainly caused in the fine grain region of the girth weld heat affected zone.

In comparative example 2, zr element is not contained, and the rough rolling deformation amount in the preparation process is less than 40%, resulting in insufficient degree of refinement of polygonal ferrite grains; meanwhile, the phase transformation driving force is insufficient, so that the volume fraction of ferrite is outside the required range of the invention, and finally, the fatigue strength is low, and the fatigue crack growth rate is obviously increased.

Comparative example 3 does not contain Zr element and Tc element, and fatigue crack growth rate is remarkably increased, and comprehensive fatigue resistance is lowered.

The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present invention are intended to be included in the scope of the present invention.

Claims

1. A steel for an anti-fatigue pipe is characterized in that,

the composition comprises the following components in percentage by mass:

2. A steel for fatigue resistance according to claim 1, wherein,

the austenite grain size of the steel for fatigue resistance is 8-12 microns.

3. A steel for fatigue resistance according to claim 1, wherein,

the volume fraction of the superfine crystal ferrite is 30-60%.

4. A method for producing a steel for an anti-fatigue pipe according to any one of claim 1 to 3,

the method comprises the following steps:

s1, molten iron pretreatment;

s2 smelting and forging:

s3, heating;

s4, rolling for at least 4 times;

5. A method for producing a steel for an anti-fatigue pipe according to claim 4,

the final forging temperature of the forging is higher than 950 ℃;

the heating temperature is 1050-1100 ℃ and the heating time is 100-120min;

6. A method for producing a steel for an anti-fatigue pipe according to claim 4,

the rolling adopts two stages of rolling, wherein the first stage of rolling is rough rolling, and the second stage of rolling is finish rolling.

7. A method for producing a steel for an anti-fatigue pipe according to claim 6,

the initial rolling temperature of the rough rolling is 980-1000 ℃, and the final rolling temperature of the rough rolling is 790-800 ℃.

8. A method for producing a steel for an anti-fatigue pipe according to claim 7,

the accumulated deformation of the last 2-3 times of rolling in the rough rolling is more than 40%.

9. A method for producing a steel for an anti-fatigue pipe according to claim 6,

the finish rolling temperature is 1000-1010 ℃, and the finish rolling temperature is 800-830 ℃.

10. A method for producing a steel for an anti-fatigue pipe according to claim 9,

the accumulated deformation of the last 2-3 times of rolling in the finish rolling is more than 55%.