阅读说明：本技术 一种高强度抗疲劳无缝钢管及其制造方法 (High-strength anti-fatigue seamless steel tube and manufacturing method thereof ) 是由 张春霞 刘耀恒 张忠铧 于 2019-09-27 设计创作，主要内容包括：本发明公开了一种高强度抗疲劳无缝钢管,其化学元素质量百分比为：C：0.15～0.30％,Si：0.4～1％,Mn：1.3％～2％,N：0.001～0.01％；此外还含有V、Nb、Ti的至少其中一种,其含量满足0.65＞V％×3.5+Nb％×6.8+Ti％×12.5＞0.25；余量为Fe和其他不可避免的杂质。此外,本发明还公开了一种制造方法,其包括步骤：(1)制得管坯；(2)将管坯加热,然后经穿孔、连轧制成荒管；(3)将荒管冷却到650℃以下后,再加热到840～1000℃,保温一段时间后出炉,经张力减径或定径工序后结束轧制,钢管结束轧制时的温度不低于780℃；(4)轧后钢管自由空冷。(The invention discloses a high-strength anti-fatigue seamless steel tube, which comprises the following chemical elements in percentage by mass: c: 0.15-0.30%, Si: 0.4-1%, Mn: 1.3% -2%, N: 0.001-0.01%; in addition, at least one of V, Nb and Ti is contained, and the content of the V, Nb and Ti satisfies 0.65 to V percent multiplied by 3.5 to Nb percent multiplied by 6.8 to Ti percent multiplied by 12.5 to 0.25; the balance being Fe and other unavoidable impurities. In addition, the invention also discloses a manufacturing method, which comprises the following steps: (1) preparing a tube blank; (2) heating the tube blank, and then perforating and continuously rolling to prepare a pierced billet; (3) cooling the pierced billet to below 650 ℃, then heating to 840-1000 ℃, keeping the temperature for a period of time, discharging, finishing rolling after a tension reducing or sizing procedure, wherein the temperature of the steel tube is not lower than 780 ℃ when the rolling is finished; (4) and (4) freely cooling the rolled steel pipe in air.)

1. A high-strength anti-fatigue seamless steel pipe is characterized by comprising the following chemical elements in percentage by mass:

c: 0.15-0.30%, Si: 0.4-1%, Mn: 1.3% -2%, N: 0.001-0.01%; in addition, at least one of V, Nb and Ti is contained, and the content of the V, Nb and Ti satisfies 0.65 to V percent multiplied by 3.5 to Nb percent multiplied by 6.8 to Ti percent multiplied by 12.5 to 0.25; the balance being Fe and other unavoidable impurities.

2. The high-strength fatigue-resistant seamless steel pipe according to claim 1, wherein each element of the other inevitable impurities satisfies at least one of: less than or equal to 0.008 percent of S, less than or equal to 0.02 percent of P and less than or equal to 0.006 percent of O.

3. The high-strength fatigue-resistant seamless steel pipe according to claim 1, wherein the microstructure is ferrite + pearlite.

4. A high strength fatigue resistant seamless steel tube according to claim 3, wherein the pearlite inter-lamellar average spacing is <200 nm.

5. The high strength fatigue resistant seamless steel tube as claimed in claim 1, wherein the full wall thickness cross-sectional grain size is > 7 grade.

6. The high strength fatigue resistant seamless steel tube of claim 1, wherein the depth of the fully decarburized layers of the inner and outer surfaces is <0.3 mm.

7. The high-strength fatigue-resistant seamless steel pipe as claimed in any one of claims 1 to 6, wherein the yield strength in the controlled rolling state or normalized state is 500MPa or more, and the fatigue life is 100X 10 or more⁴Next, the process is carried out.

8. The method for manufacturing a high-strength fatigue-resistant seamless steel pipe as claimed in any one of claims 1 to 7, wherein the manufacturing method does not include a quenching and tempering heat treatment step, and the method includes the steps of:

(1) preparing a tube blank;

(2) heating the tube blank, and then perforating and continuously rolling to prepare a pierced billet;

(3) cooling the pierced billet to below 650 ℃, then heating to 840-1000 ℃, keeping the temperature for a period of time, discharging, finishing rolling after a tension reducing or sizing procedure, wherein the temperature of the steel tube is not lower than 780 ℃ when the rolling is finished;

(4) and (4) freely cooling the rolled steel pipe in air.

9. The method according to claim 8, wherein in the step (3), the holding time is not less than (0.5 x t) min, wherein t represents the wall thickness of the steel pipe and the unit parameter is mm.

10. The manufacturing method according to claim 8, wherein in the step (2), the tube blank is heated to 1150 to 1280 ℃ and kept for 1 to 4 hours before piercing and continuous rolling.

Technical Field

The invention relates to a steel pipe and a manufacturing method thereof, in particular to a seamless steel pipe and a manufacturing method thereof.

Background

Semitrailers are trailers whose axles are located behind the center of gravity of the vehicle (when the vehicle is evenly loaded) and which are equipped with coupling devices that transmit horizontal and vertical forces to the tractor, and are heavy transport vehicles which are connected to the head of the semitrailer by means of towing pins. Compared with a single automobile, the semitrailer can improve the comprehensive economic benefit of road transportation. The transportation efficiency can be improved by 30-50%, the cost is reduced by 30-40%, and the oil consumption is reduced by 20-30%. And thus the demand thereof has been increasing in recent years. The semitrailer axle is placed behind the center of gravity of the vehicle, and is equipped with a coupling device capable of transmitting horizontal or vertical force to a tractor, its main bearing component is rear axle, mainly bears weight of carriage, and in the course of running of vehicle it is required to bear periodic pressure load, and its related standard JT/T475 also provides its vertical bending fatigue evaluation method, and its standard requirements for fatigue life is not less than 80X 104 times.

The traditional semi-trailer axle is usually manufactured by welding a steel plate into a pipe after being bent and welding upper axle heads at two ends, but the manufacturing method has more problems such as: the process is complex, the integral stability is poor, and the fatigue life fluctuation is large. Therefore, in recent years, some axle manufacturing enterprises adopt seamless steel pipes to be directly hot-formed into axle blanks, and then other accessories are welded for use.

However, the seamless steel pipe in the above-described manufacturing method has a difficulty in improving the performance because the structure performance control similar to the TMCP technology cannot be achieved during rolling, and in general, the seamless steel pipe as the axle tube needs to be achieved by heat treatment for hardening and tempering (i.e., quenching and tempering) in order to achieve high strength (e.g., 500MPa or more). Due to the fact that the inner diameter and the wall thickness of the whole length of the machined axle are changed, the whole uniformity of the axle after quenching and tempering heat treatment is poor, and the whole bearing capacity and fatigue resistance of the axle are affected.

For example: chinese patent publication No. CN101892441A, published 24/11/2010, entitled "an ultra-fine grain semitrailer axle tube material and an axle tube processing method" discloses an ultra-fine grain semitrailer axle tube material and an axle tube processing method. In the technical scheme disclosed in the patent document, the outer wall spray cooling and the inner wall residual heat tempering are performed by using the residual heat after the steel pipe is rolled, so that the strength and the toughness of the steel pipe are improved.

In view of this, it is desirable to obtain a seamless steel pipe which can have high strength and high fatigue resistance.

Disclosure of Invention

An object of the present invention is to provide a high-strength fatigue-resistant seamless steel pipe having high strength and excellent fatigue resistance.

In order to achieve the purpose, the invention provides a high-strength anti-fatigue seamless steel pipe, which comprises the following chemical elements in percentage by mass:

c: 0.15-0.30%, Si: 0.4-1%, Mn: 1.3% -2%, N: 0.001-0.01%; in addition, at least one of V, Nb and Ti is contained, and the content of the V, Nb and Ti satisfies 0.65 to V percent multiplied by 3.5 to Nb percent multiplied by 6.8 to Ti percent multiplied by 12.5 to 0.25; the balance being Fe and other unavoidable impurities.

In the high-strength fatigue-resistant seamless steel tube of the present invention, the design principle of each chemical element is as follows:

c: in the high-strength fatigue-resistant seamless steel pipe, the C is beneficial to improving the strength of the steel, but can also reduce the ductility and toughness of the steel. In order to ensure the obdurability matching of the steel grade and keep the required microstructure as ferrite and pearlite, the mass percent of C in the high-strength fatigue-resistant seamless steel pipe is limited to be 0.15-0.30%.

Si: in the high-strength fatigue-resistant seamless steel pipe according to the present invention, Si is an element introduced by a deoxidizer in the steel, and contributes to suppressing the oxygen content in the steel and increasing the tendency of ferrite formation, so that the Si content is controlled to 0.4% by mass or more in the embodiment of the present invention, but if the Si content exceeds 1% by mass, the tendency of cold embrittlement of the steel is significantly increased. Based on the above, the high-strength fatigue-resistant seamless steel pipe of the present invention is limited to 0.4 to 1% by mass of Si.

Mn: in the high-strength fatigue-resistant seamless steel pipe according to the present invention, Mn has advantageous effects of enlarging the austenite phase region, refining grains, and the like, and in the present case, since the mass percentage of C is limited to a low level, the solid solution strengthening effect is improved by adding Mn, but at the same time, considering that the mass percentage of Mn exceeds a certain amount, the tendency of forming structures such as bainite and martensite during cooling of the steel is also increased, and the hot workability of the steel is also significantly affected. Based on the above, the mass percent of Mn in the high-strength fatigue-resistant seamless steel pipe is controlled to be 1.3-2%.

N: in the high-strength fatigue-resistant seamless steel pipe, the strength and the hardness of the steel can be effectively improved by containing a trace amount of N in the steel, but too high mass percent of N can cause more inclusions to form, so that the performance of the steel is not facilitated. Based on the above, the mass percent of N in the high-strength fatigue-resistant seamless steel pipe is controlled to be 0.001-0.01%;

in addition, the high-strength fatigue-resistant seamless steel pipe further comprises at least one of V, Nb and Ti, and the content of the at least one of V, Nb and Ti is more than 0.65 and less than V% and less than 3.5 and less than Nb% and less than 6.8 and less than Ti% and less than 12.5 and less than 0.25.

In the above formula, V%, Nb%, and Ti% represent the mass percentages of the corresponding elements, respectively, and when the formula is substituted, the substituted value is a value before the percentile, for example, when the mass percentage of V is 0.06%, the substituted value of V is 0.06.

In the technical scheme of the invention, V, Nb and Ti are all strong carbide forming elements, and are combined with carbon and nitrogen in steel to form carbonitride which is precipitated at high temperature, thereby being beneficial to refining crystal grains and improving the obdurability of the steel. According to a great deal of experimental research of the inventor, the obvious grain refining effect can be obtained by adding at least one of V, Nb and Ti elements and enabling the content of the V, Nb and Ti elements to reach a certain level. In addition, when the content of the elements exceeds a certain level, coarse carbides are easily formed, so that the plasticity and toughness of the steel are not facilitated. Based on this, the content of the above elements is controlled to satisfy 0.65 > V%. times.3.5 + Nb%. times.6.8 + Ti%. times.12.5 > 0.25.

Further, in the high-strength fatigue-resistant seamless steel pipe according to the present invention, each element of the other inevitable impurities satisfies at least one of the following: less than or equal to 0.008 percent of S, less than or equal to 0.02 percent of P and less than or equal to 0.006 percent of O.

S: s is a harmful element in steel, and the existence of S has adverse effects on the corrosion resistance, the hot workability, the toughness and the like of the steel, so that the mass percent of S is controlled to be less than or equal to 0.008 percent in the technical scheme of the invention. Preferably, the mass percent of S can be further controlled to be less than or equal to 0.005 percent.

P: p is a harmful element in steel, and the existence of P has adverse effects on the corrosion resistance, the toughness and the like of the steel, so that the P is controlled to be less than or equal to 0.02 percent by mass in the technical scheme of the invention. Preferably, the mass percent of P can be further controlled to be less than or equal to 0.018 percent.

O: o exists in steel in various oxide inclusions, the existence of the inclusions has adverse effects on the hot workability and the ductility and toughness of the steel, and in order to ensure the final performance, in the technical scheme of the invention, the mass percent of O is controlled to be less than or equal to 0.006 percent. Preferably, the mass percent of O can be controlled to be less than or equal to 0.004 percent.

Further, in the high-strength fatigue-resistant seamless steel pipe according to the present invention, the microstructure is ferrite + pearlite.

Furthermore, in the high-strength fatigue-resistant seamless steel pipe, the average spacing between pearlite layers is less than 200 nm.

Furthermore, in the high-strength fatigue-resistant seamless steel tube, the full-wall thickness section grain size is more than 7 grades, so that the obdurability and the fatigue life of the high-strength fatigue-resistant seamless steel tube are ensured.

Furthermore, in the high-strength fatigue-resistant seamless steel tube, the depth of the full decarburized layer on the inner surface and the outer surface is less than 0.3mm, so that the strength, toughness and fatigue life of the high-strength fatigue-resistant seamless steel tube are ensured.

Furthermore, in the high-strength anti-fatigue seamless steel pipe, the yield strength of the controlled rolling state or the normalized state is more than or equal to 500MPa, and the fatigue life is more than or equal to 100 multiplied by 10⁴Next, the process is carried out.

Accordingly, another object of the present invention is to provide the above-mentioned method for producing a high-strength fatigue-resistant seamless steel pipe, which is high in strength and excellent in fatigue resistance.

In order to achieve the above object, the present invention provides the above method for manufacturing a high-strength fatigue-resistant seamless steel pipe, which does not include a quenching and tempering heat treatment step, and which includes the steps of:

(1) preparing a tube blank;

(2) heating the tube blank, and then perforating and continuously rolling to prepare a pierced billet;

(3) cooling the pierced billet to below 650 ℃, then heating to 840-1000 ℃, keeping the temperature for a period of time, discharging, finishing rolling after a tension reducing or sizing procedure, wherein the temperature of the steel tube is not lower than 780 ℃ when the rolling is finished;

(4) and (4) freely cooling the rolled steel pipe in air.

In the manufacturing method, because the manufacturing method does not need quenching and tempering heat treatment, the production flow can be simpler, and the problems of dimensional precision change and poor straightness caused by quenching and tempering heat treatment can be avoided. And because the seamless steel pipe is cooled in a wider cooling speed range, a uniform structure of ferrite and pearlite can be stably obtained, the overall uniformity and the surface decarburized layer level of the obtained high-strength fatigue-resistant seamless steel pipe are better than those of a quenched and tempered product, the performance is more stable, and the seamless steel pipe is more suitable for axle products with thickened sections.

In addition, in the technical scheme of the invention, the temperature of the steel pipe after finishing rolling is not lower than 780 ℃ so as to ensure that the structure after finishing rolling is maintained in a full austenite structure state.

Further, in the manufacturing method of the invention, in the step (3), the heat preservation time is not less than (0.5 x t) min, wherein t represents the wall thickness of the steel pipe, and the unit parameter is mm.

Further, in the manufacturing method of the invention, in the step (2), the tube blank is heated to 1150-1280 ℃ and kept for 1-4 hours, and then the tube blank is perforated and continuously rolled.

In the scheme, the heating temperature of the tube blank is controlled to be not lower than 1150 ℃ in consideration of the conditions of different hot rolling units so as to ensure that the tube blank has enough deformation force, but if the temperature exceeds 1280 ℃, the coarsening and the overburning of crystal grains are easy to occur. Similarly, the heat preservation time is less than 1h, which cannot ensure the heating uniformity, and the heat preservation time is more than 4h, which is easy to cause the problems of coarsening and overheating of crystal grains. Therefore, in some preferred embodiments, in the step (2), the tube blank is heated to 1150-1280 ℃ and kept for 1-4 h before piercing and continuous rolling.

Compared with the prior art, the high-strength anti-fatigue seamless steel pipe and the manufacturing method thereof have the advantages and beneficial effects as follows:

the high-strength anti-fatigue seamless steel pipe has ultrahigh strength and anti-fatigue performance, the yield strength of the controlled rolling state or normalized state is more than or equal to 500MPa, and the fatigue life is more than or equal to 100 multiplied by 10⁴Next, the process is carried out.

In addition, the manufacturing method does not need quenching and tempering heat treatment during manufacturing, has simple production flow, and does not have the problems of dimensional precision change, poor straightness and the like caused by quenching and tempering heat treatment.

In addition, the manufacturing method of the invention can stably obtain a uniform ferrite plus pearlite structure because the seamless steel pipe is cooled in a wider cooling speed range, and the obtained high-strength fatigue-resistant seamless steel pipe has better overall uniformity and surface decarburized layer level than a quenched and tempered product, has more stable performance and is more suitable for axle products with thickened sections.

Drawings

FIG. 1 is a metallographic structure diagram of a high-strength fatigue-resistant seamless steel tube according to example A.

Detailed Description

The high strength fatigue resistant seamless steel pipe and the method for manufacturing the same according to the present invention will be further explained and illustrated with reference to specific examples, which, however, should not be construed to unduly limit the technical aspects of the present invention.

Examples A-F and comparative examples a-e

The high strength fatigue resistant seamless steel tubes of examples a-F were made using the following steps:

(1) the tube blank was produced by smelting and casting according to the chemical composition shown in table 1.

(2) And heating the tube blank to 1150-1280 ℃, keeping for 1-4 h, and then perforating and continuously rolling to obtain a pierced billet.

(3) Cooling the pierced billet to below 650 ℃, then heating to 840-1000 ℃, keeping the temperature for a period of time, discharging, finishing rolling after a tension reducing or sizing procedure, wherein the temperature of the steel pipe when finishing rolling is not lower than 780 ℃, and the heat preservation time is not more than (2 x t) min, wherein t represents the wall thickness of the steel pipe, and the unit parameter is mm.

(4) And (4) freely cooling the rolled steel pipe in air.

Table 1 lists the mass percentages of the chemical elements of the high-strength fatigue-resistant seamless steel pipes of examples A to F and the conventional steel pipes of comparative examples a to e.

Table 1 (wt%, balance Fe and unavoidable impurities other than P, S and O)

Table 2 lists specific process parameters for the high strength fatigue resistant seamless steel pipes of examples A-F and the conventional steel pipes of comparative examples a-e.

Table 2.

In order to verify the working effect of the present case and to prove the excellent effect of the present case compared to the prior art, the high strength fatigue resistant seamless steel pipes of examples a to F and the conventional steel pipes of comparative examples a to e were sampled for performance testing. Meanwhile, the high-strength fatigue-resistant seamless steel pipes of examples A to F and the conventional steel pipes of comparative examples a to e were processed into axles according to a conventional process, and then fatigue properties were evaluated according to JT/T475 standards.

The strength data is obtained by processing the manufactured steel pipe into an API arc-shaped sample, and averaging after testing according to an API standard;

the microstructure is obtained by taking a full-wall-thickness sample from a sample tube, grinding and polishing the sample tube, corroding the sample tube by using 4% nitric acid alcohol, and then photographing and analyzing the sample tube under a metallographic microscope, wherein the average pearlite lamella spacing data is obtained by averaging 50 measurement data.

Table 3 lists the test results for the high strength fatigue resistant seamless steel pipes of examples A-F and the conventional steel pipes of comparative examples a-e.

Table 3.

As can be seen from Table 3, the yield strength in the controlled rolling state or the normalized state of each example of the present invention is not less than 500MPa, and the fatigue life is not less than 100X 10⁴Next, the process is carried out. The microstructure of each example of the present application was ferrite + pearlite, and the pearlite lamellar average distance<200nm, full wall thickness, cross section grain size > 7 grade, and full decarburized layer depth on inner and outer surfaces<0.3mm。

Contrary to the comparative examples, the conventional steel pipes in comparative examples a to c cannot obtain sufficient strength or fatigue life because the alloying elements do not meet the ranges defined in the present specification. In addition, in comparative example c, since the cooling temperature before reheating was too high, the transformation was not completed, and finally the effect of the reheated austenitized refined structure was not significant, and the grains and pearlite lamellae coarsened, affecting the toughness and fatigue life of the steel pipe. In comparative example d, since the finish rolling temperature was too low, proeutectoid ferrite was precipitated, the microstructure was not uniform, and the fatigue life was reduced. In comparative example e, however, the heating temperature was too high, resulting in too deep surface decarburized layer and coarse grains, which also decreased fatigue life.

FIG. 1 is a typical metallographic structure diagram of a high-strength fatigue-resistant seamless steel pipe according to example A.

As shown in fig. 1, in the high-strength fatigue-resistant seamless steel pipe of example a, the microstructure thereof was ferrite + pearlite.

In conclusion, the high-strength anti-fatigue seamless steel pipe has ultrahigh strength and anti-fatigue performance, the yield strength of the controlled rolling state or normalized state is more than or equal to 500MPa, and the fatigue life is more than or equal to 100 multiplied by 10⁴Next, the process is carried out.

In addition, the manufacturing method does not need quenching and tempering heat treatment during manufacturing, has simple production flow, and does not have the problems of dimensional precision change, poor straightness and the like caused by quenching and tempering heat treatment.

In addition, the manufacturing method of the invention can stably obtain a uniform ferrite plus pearlite structure because the seamless steel pipe is cooled in a wider cooling speed range, and the obtained high-strength fatigue-resistant seamless steel pipe has better overall uniformity and surface decarburized layer level than a quenched and tempered product, has more stable performance and is more suitable for axle products with thickened sections.

From the above, it can be seen that the steel for hot rolling axle of the present invention has the characteristics of high strength and excellent formability, and the steel for hot rolling axle of the present invention has good cold workability and high elongation.

In addition, the steel for the hot rolling axle can be used without heat treatment, has low manufacturing cost, does not need a complex cooling control technology after hot rolling, can be realized by adopting a common laminar cooling process, and is easy to produce.

It should be noted that the prior art in the protection scope of the present invention is not limited to the examples given in the present application, and all the prior art which is not inconsistent with the technical scheme of the present invention, including but not limited to the prior patent documents, the prior publications and the like, can be included in the protection scope of the present invention.

In addition, the combination of the features in the present application is not limited to the combination described in the claims of the present application or the combination described in the embodiments, and all the features described in the present application may be freely combined or combined in any manner unless contradictory to each other.

It should also be noted that the above-mentioned embodiments are only specific embodiments of the present invention. It is apparent that the present invention is not limited to the above embodiments and similar changes or modifications can be easily made by those skilled in the art from the disclosure of the present invention and shall fall within the scope of the present invention.