CN114619004B

CN114619004B - Rare earth microalloyed seamless steel tube for cold drawn high-strength hydraulic cylinder barrel and preparation method thereof

Info

Publication number: CN114619004B
Application number: CN202210185119.5A
Authority: CN
Inventors: 张学颖; 米永峰; 姜海龙; 姚晓乐; 郭智韬; 宋江波
Original assignee: Baotou Iron and Steel Group Co Ltd
Current assignee: Baotou Iron and Steel Group Co Ltd
Priority date: 2022-02-28
Filing date: 2022-02-28
Publication date: 2024-06-11
Anticipated expiration: 2042-02-28
Also published as: CN114619004A

Abstract

The invention discloses a rare earth microalloyed cold drawn high strength seamless steel tube for a hydraulic cylinder barrel, which comprises the following chemical elements in percentage by mass: c0.19-0.25%; si 0.20-0.35%; mn 1.50-1.80%; p is less than or equal to 0.018 percent; s is less than or equal to 0.010 percent; cr is less than or equal to 0.25%; v is 0.14 to 0.20 percent; re is less than or equal to 0.002%; the balance of Fe and unavoidable impurities, the mass fraction is 100%, and a preparation method thereof is also disclosed. The cold-drawn seamless tube for the high-strength hydraulic cylinder barrel, which has better tensile strength, yield strength and elongation and has V-shaped full-size longitudinal impact energy higher than 120J in an experimental environment of minus 20 ℃, is produced by the processes of steelmaking, tube rolling, heat treatment and the like.

Description

Rare earth microalloyed seamless steel tube for cold drawn high-strength hydraulic cylinder barrel and preparation method thereof

Technical Field

The invention relates to the field of metallurgical materials, in particular to a rare earth microalloyed seamless steel tube for a cold drawn high-strength hydraulic cylinder barrel and a preparation method thereof.

Background

In the last decade, the global engineering machinery industry has presented a steadily evolving situation. Along with the rapid development of the construction of various important infrastructures in China, the traditional market steadily increases, the demand of domestic engineering machinery steadily increases, and simultaneously, higher requirements are put forward on technical indexes such as energy consumption, strength and stability of the engineering machinery. The hydraulic cylinder is used as an important part of engineering machinery, has extremely high requirements on buffering, high load, high frequency and stability, and uses a cold-drawn seamless steel tube as the most important raw material of the hydraulic cylinder, so that the important parameters such as precision, strength, service life and the like of the hydraulic cylinder are directly determined.

In the development process of engineering machinery and special vehicle industry, the supply of key accessories such as hydraulic cylinders, hydraulic valves, hydraulic pumps and the like has become the bottleneck of the development of the engineering machinery industry in China. The cylinder barrel of the hydraulic cylinder in the domestic engineering machinery industry is commonly made of 20, 45, 27SiMn, 25Mn and the like, and the aim of improving the strength performance of the material is fulfilled by improving the carbon content of the material, or the performance of steel is improved by adding elements such as C, mn, si and the like. The adoption of the method improves the strength of the material to meet the strength requirement of mechanical design, but increases the carbon and silicon contents in the steel, which inevitably increases the carbon equivalent of the material, thereby affecting the welding performance. In the processing process of the oil cylinder, the complex section and the connecting size are inevitably welded, the outer surface of the oil cylinder is connected with more structural members in many cases, and pre-welding preheating and post-welding tempering are often impossible. If the welding performance of the oil cylinder material is poor, potential safety hazards can be brought to engineering machinery.

Therefore, the development of the seamless steel tube for the hydraulic cylinder barrel with low carbon equivalent and reasonable strong plastic matching and excellent impact toughness has become a hot spot developed by steel tube manufacturers. The seamless steel tube for the cold-drawing hydraulic cylinder barrel and the production method thereof not only improve the grade of seamless tube products and optimize the product structure, but also bring great economic and social benefits to enterprises.

Disclosure of Invention

The invention aims to provide a rare earth microalloying cold drawing high strength seamless steel pipe for a hydraulic cylinder and a preparation method thereof, wherein a single strengthening element vanadium is added on the basis of low carbon steel, and a target value of 560MPa of tensile strength (Rm) is produced through processes of steelmaking, pipe rolling, heat treatment and the like, and an actual measurement value is more than 700 MPa; the target value of the yield strength (Rp0.2) is more than 400MPa, the measured value is more than 500MPa, the target value of the elongation (A) is more than 17%, and the measured value is 26%; a cold-drawn seamless tube for a V-shaped full-size high-strength hydraulic cylinder barrel with the longitudinal impact energy higher than 120J in an experimental environment at-20 ℃.

In order to solve the technical problems, the invention adopts the following technical scheme:

The invention relates to a rare earth microalloying cold drawing high strength seamless steel tube for a hydraulic cylinder barrel, which comprises the following chemical elements in percentage by mass: c0.19-0.25%; si 0.20-0.35%; mn 1.50-1.80%; p is less than or equal to 0.018 percent; s is less than or equal to 0.010 percent; cr is less than or equal to 0.25%; v is 0.14 to 0.20 percent; re is less than or equal to 0.002%; the balance of Fe and unavoidable impurities, and the mass fraction is 100 percent.

Further, the chemical elements and the mass percentages thereof are as follows: c0.20%; si 0.30%; mn 1.63%; p0.018%; s0.010%; cr 0.25%; v0.14%; re 0.02%; the balance of Fe and unavoidable impurities, and the mass fraction is 100 percent.

Further, the chemical elements and the mass percentages thereof are as follows: c0.21%; si 0.35%; mn 1.70%; p0.015%; s0.008%; cr 0.23%; v0.15%; re 0.02%; the balance of Fe and unavoidable impurities, and the mass fraction is 100 percent.

Further, the chemical elements and the mass percentages thereof are as follows: c0.22%; si 0.29%; mn 1.59%; p0.011%; s0.008%; cr 0.25%; v0.16%; re 0.02%; the balance of Fe and unavoidable impurities, and the mass fraction is 100 percent.

Further, the chemical elements and the mass percentages thereof are as follows: c0.23%; si 0.28%; mn 1.56%; p0.018%; s0.005%; cr 0.24%; v0.14%; re 0.02%; the balance of Fe and unavoidable impurities, and the mass fraction is 100 percent.

Further, the chemical elements and the mass percentages thereof are as follows: c0.22%; si 0.36%; mn 1.72%; p0.013%; s0.004%; cr 0.25%; v0.16%; re 0.02%; the balance of Fe and unavoidable impurities, and the mass fraction is 100 percent.

Carbon (C): as the most economical and basic strengthening element in the steel, the strengthening element has obvious effect on improving the strength of the steel through solid solution strengthening and precipitation strengthening, but the excessively high carbon content has adverse effects on the elongation, toughness and weldability of the steel, the invention properly controls the carbon content, improves the toughness and weldability of the steel while guaranteeing the strength, and the C content is 0.19-0.25 percent for the invention.

Silicon (Si): the steel mainly exists in a solid solution state, mainly is solid solution-strengthened, and no carbonitride is formed, so that the volume fraction of ferrite and the ferrite structure can be remarkably improved. For the purposes of the present invention, si content is from 0.20 to 0.35%.

Manganese (Mn): mn can greatly improve the strength and toughness of the steel grade through solid solution strengthening, is the most main and economical strengthening element for compensating the strength loss caused by the reduction of the content of C, is also an effective deoxidizer, has the effect of S removal, but too high Mn can promote the formation of carbide, thereby reducing the toughness of the steel grade; mn can be infinitely miscible with gamma-Fe, so that the gamma region is enlarged, the hardenability of steel is increased, but too high Mn has the tendency of increasing the growth of austenite, and is easy to cause coarse grains, so that the steel has overheat sensitivity and tempering brittleness, and the welding performance of the steel is reduced. Thus, for the purposes of the present invention, the Mn content ranges from 1.50 to 1.80%.

Chromium (Cr): cr can improve the thermodynamic stability of steel, and chromium mainly plays a role in solid solution strengthening in the steel, enlarges an austenite region, is favorable for forming pearlite and increasing the percentage of pearlite in the steel, and can reduce the lamellar spacing of the pearlite and thin cementite in the pearlite. Thereby improving the strength of the steel. However, too high a Cr content results in a decrease in the weldability of the steel grade, and therefore, the Cr content is less than or equal to 0.25%.

Vanadium (V): v is the most main alloy element, and vanadium can refine grains, improve the strength and yield ratio after normalizing and the low-temperature toughness, and improve the welding performance of steel. Vanadium has extremely strong affinity with carbon, nitrogen and oxygen, and forms corresponding stable compounds with the vanadium, and the main function of the vanadium is to refine the structure and grains of steel. Reduces the overheat sensitivity of the steel and improves the strength and toughness of the steel. Accordingly, V is 0.14 to 0.20% in the present invention.

Rare earth (Re): the addition of proper rare earth alloy is favorable for deoxidation, desulfurization and gas removal, reduces the influence of harmful elements, obviously improves the toughness, wear resistance and corrosion resistance of the steel, and improves the welding performance and low-temperature performance of the steel.

A preparation method of a seamless steel tube for a rare earth microalloyed cold drawn high strength hydraulic cylinder barrel comprises the following steps:

The steelmaking production process comprises the following steps: molten iron pretreatment, converter smelting, LF refining, VD degassing and round billet continuous casting; the molten iron of the incoming material must be pretreated so as to ensure the quality of the molten iron supplied to the converter; in order to inhibit the gas content in the material, the ferrosilicon, ferromanganese, ferrochromium and ferrovanadium must be deoxidized and alloyed before being added; converter endpoint control target: c is more than or equal to 0.06 percent, P is less than or equal to 0.010 percent, and tapping temperature is 1610-1630 ℃; smelting by adopting a single slag process, wherein the final slag alkalinity is more than or equal to 3.0; slag must be blocked during tapping, and slag must be removed after slag blocking failure; in the LF refining step, slag making, desulfurizing, component adjusting and heating are carried out according to the components and the temperature of the molten steel of the converter, deoxidation is enhanced, white slag is produced, the holding time of the white slag is more than or equal to 20min, and the slag condition is regulated according to the situation so as to ensure the tapping of the white slag; adding ferrovanadium in the middle and later stages of refining, performing component fine adjustment in the later stage of refining, and adding rare earth alloy in proportion; the target value of VD deep vacuum degree is less than or equal to 0.06KPa, the deep vacuum time is more than or equal to 15 minutes, after VD is finished, a proper amount of high-calcium wire is fed, and Ar is blown in a soft mode after wire feeding for not less than 15 minutes, so that lower gas content in the material is ensured; in the continuous casting process, an electromagnetic stirring process is adopted, the superheat degree delta T of molten steel is less than or equal to 25 ℃, proper pulling speed is selected according to the sections of different round billets, the round billets are subjected to slow cooling in a slow cooling pit, the pit entering temperature is more than 600 ℃, and the slow cooling time is not less than 48 hours; the method is used for obtaining the high-quality round billet with low P, low S and uniform components;

the pipe rolling process comprises the following steps: round billet sawing, annular furnace heating, perforation, PQF continuous rolling, tension reducing and cooling; the temperature of the heat preservation section of the annular furnace is about 1260 ℃, and the temperature of the perforated round billet is about 1220 ℃; the inlet temperature of continuous rolling is about 1100 ℃; the temperature after fixed tension is reduced is 850-950 ℃; the high-precision high-quality pipe bodies with different sizes are obtained through a three-roller retained mandrel continuous rolling unit PQF combined with a high-end hot rolling control technology;

the heat treatment process comprises the following steps: normalizing treatment, namely normalizing and air cooling is adopted; normalizing temperature is 900+/-10 ℃, and preserving heat for 25-35 minutes.

Furthermore, the dephosphorization pressure of the high-pressure water after normalizing is more than or equal to 12MPa, the straightening force is strictly controlled during straightening after normalizing, the requirement of the bending degree of the steel pipe is ensured, and the conditions of concave correction, elliptic correction and crack correction are not required to occur.

Compared with the prior art, the invention has the beneficial technical effects that:

the invention provides a seamless steel tube for a cold-drawn hydraulic cylinder barrel and a preparation method thereof, wherein alloy elements are reasonably selected and the content ratio of the elements is proper, so that the steel has lower carbon equivalent, is easy to produce and low in cost, and the steel tube has higher strength, excellent low-temperature impact toughness and high dimensional accuracy by reasonable smelting continuous casting process, rolling process and heat treatment process. The invention is the most main raw material of the high-strength hydraulic cylinder, can be widely applied to industries such as engineering machinery, metallurgical machinery, plastic machinery, petrochemical machinery, light industrial machinery, aerospace, ships, marine engineering equipment and the like, and has the characteristics of easy production, low cost and excellent performance.

Drawings

The invention is further described with reference to the following description of the drawings.

FIG. 1 shows the metallographic structure of a steel pipe after heat treatment production.

Detailed Description

The steel pipe material obtained according to the invention is exemplified by the production specification phi 273 x 16mm, and the chemical composition is shown in table 1:

TABLE 1 statistical results of chemical compositions of the inventive steel pipes wt%

Examples	C	Si	Mn	P	S	Cr	V	Re (addition)
									1	0.20	0.30	1.63	0.018	0.010	0.25	0.14	0.02
2	0.21	0.35	1.70	0.015	0.008	0.23	0.15	0.02
									3	0.22	0.29	1.59	0.011	0.008	0.25	0.16	0.02
4	0.23	0.28	1.56	0.018	0.005	0.24	0.14	0.02
									5	0.22	0.36	1.72	0.013	0.004	0.25	0.16	0.02

The chemical components of the steel pipe completely meet the requirements of the invention on steel types, the contents of P and S are lower, the component design requirements are met, and the table 1 shows that the component content deviation of each furnace is small, and the stable component content is beneficial to the temperature control during the heat treatment, thereby providing preconditions for the good organization and performance of the pipe.

The steelmaking process comprises the following steps: the steel pipe with the specification of phi 273 multiplied by 16mm is produced, the section of a continuous casting round billet is phi 390mm, and the arc radius of a sector section of a steelmaking continuous casting machine of a steel-clad steel pipe company is 12m. In order to overcome the problem that microcracks on the surface of a round billet are easy to generate when a round billet with a large section is produced with a small arc radius, particularly steel grade containing V alloy elements and sensitive to the microcracks is adopted, a series of measures such as proper V content and proportion are adopted; continuous casting is carried out at a stable pulling speed, and the temperature of a straightening section of a continuous casting blank is ensured to be not less than 900 ℃; a weak and uniform secondary cooling system is adopted; proper casting powder is selected, so that centering and arc aligning precision of the casting machine is improved; after the casting blank is taken off line, the round blank enters a slow cooling pit for slow cooling, and the pit entering temperature is more than 600 ℃ so as to eliminate the structural stress and the thermal stress. By the measures, the round billet with high quality is obtained.

The pipe rolling process comprises the following steps: round billet sawing, annular furnace heating, perforation, PQF continuous rolling, tension reducing (sizing) and cooling. The round billet is heated in an annular furnace, the furnace temperature is 1280 ℃, the heating temperature deviation of the pipe billet is +/-10 ℃, the furnace time is not suitable for overlong, the perforation adopts a low-speed biting and high-speed rolling process, the temperature after the perforation is 1220 ℃, the temperature after the perforation is 1100 ℃, the temperature after sizing is 920 ℃, cooling and sawing.

And (3) heat treatment: normalizing treatment is adopted. The actual condition that the specification is larger is combined with the field device and the test steel tube specification of phi 273 mm, and the normalizing process is designed to be 900 ℃. The normalizing heat-preserving time is too short, and the temperature uniformity when the steel pipe is heated is negatively affected, so that the temperature is preferably not less than 30 minutes.

The geometric dimension of the steel pipe of the invention:

The subsequent cold drawing of the product users has higher requirements on surface quality and the geometric dimension of the finished product pipe, and a series of measures are adopted to control in the production process: when in perforation, the stability of pushing steel biting, perforation, holding a roller for holding a pipe and throwing steel is strictly controlled; rough rolling is carried out in an austenite recrystallization region, so that the large reduction is achieved as much as possible in order to fully refine original austenite grains, and the total deformation of the rough rolling stage is increased under the condition of allowing equipment parameters; when the steel tube is deformed in the finish rolling stage of the non-recrystallized zone, the rolling reduction of a plurality of passes before finish rolling is properly increased to ensure the uniformity of the structure of the steel tube in the wall thickness direction, and tubular control is carried out in the last 3 and 4 passes; in order to ensure the quality of the outer surface of the steel pipe and prevent the occurrence of surface defects such as pitting surface, the high-pressure water dephosphorization pressure after continuous rolling, sizing and normalizing is required to be more than or equal to 11MPa. The measured non-roundness and wall thickness non-uniformity of the steel pipe does not exceed 70% -80% of the tolerance of the outer diameter and the wall thickness. The tolerance of the outer diameter (D) of the steel pipe is +/-1 percent D, and the uneven degree of the wall thickness (S) is less than or equal to +/-8%S. The steel pipe has good surface quality and high dimensional accuracy, is easy for the subsequent cold drawing process of the steel pipe, and meets the requirement of high-accuracy dimension.

The mechanical properties of the steel pipes of the present invention are shown in Table 2. As shown in Table 2, the method of the invention can well meet the requirements of high-strength steel pipes, steel pipes with the specification of phi 273 multiplied by 16mm have high strength and excellent low-temperature impact toughness, and the longitudinal impact at minus 20 ℃ is more than 120J.

TABLE 2 mechanical Properties of the inventive Steel pipes

The grain sizes of inclusions and structures of the steel pipes of the present invention are shown in Table 3.

TABLE 3 grain size of impurities and structures of the steel pipes of the present invention

Note that: f represents ferrite, and P represents pearlite.

After the heat treatment, the steel pipe of example 1 was sampled for metallographic analysis, and the metallographic structure was as shown in FIG. 1 below. As can be seen from fig. 1, the metallographic structure of the steel pipe is that fine net-shaped proeutectoid ferrite is uniformly distributed on the pearlite matrix.

The seamless steel tube for the cold-drawing hydraulic cylinder barrel with the specification phi 273 multiplied by 16mm, which is produced by the invention, has the advantages of low carbon equivalent of steel types, easy production, low cost, high strength, excellent low-temperature impact toughness and high dimensional accuracy by reasonable smelting continuous casting process, rolling process and heat treatment process due to reasonable selection of alloy elements and proper element content proportion. The product of the invention is the most main raw material of the high-strength hydraulic cylinder, can be widely applied to industries such as engineering machinery, metallurgical machinery, plastic machinery, petrochemical machinery, light industrial machinery, aerospace, ships, marine engineering equipment and the like, and has the characteristics of easy production, low cost and excellent performance.

The above embodiments are only illustrative of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention, and various modifications and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope defined by the claims of the present invention without departing from the design spirit of the present invention.

Claims

1. A preparation method of a rare earth microalloyed cold drawn high strength seamless steel tube for a hydraulic cylinder barrel is characterized by comprising the following chemical elements in percentage by mass: c0.19-0.25%; si 0.20-0.35%; mn 1.50-1.80%; p is less than or equal to 0.018 percent; s is less than or equal to 0.010 percent; cr is less than or equal to 0.25%; v is 0.14 to 0.20 percent; re is less than or equal to 0.002%; the balance of Fe and unavoidable impurities, wherein the mass fraction is 100 percent;

The preparation method comprises the following steps:

2. The method for preparing the seamless steel tube for the rare earth microalloyed cold drawn high strength hydraulic cylinder barrel according to claim 1, which is characterized by comprising the following chemical elements in percentage by mass: c0.20%; si 0.30%; mn 1.63%; p0.018%; s0.010%; cr 0.25%; v0.14%; re 0.02%; the balance of Fe and unavoidable impurities, and the mass fraction is 100 percent.

3. The method for preparing the seamless steel tube for the rare earth microalloyed cold drawn high strength hydraulic cylinder barrel according to claim 1, which is characterized by comprising the following chemical elements in percentage by mass: c0.21%; si 0.35%; mn 1.70%; p0.015%; s0.008%; cr 0.23%; v0.15%; re 0.02%; the balance of Fe and unavoidable impurities, and the mass fraction is 100 percent.

4. The method for preparing the seamless steel tube for the rare earth microalloyed cold drawn high strength hydraulic cylinder barrel according to claim 1, which is characterized by comprising the following chemical elements in percentage by mass: c0.22%; si 0.29%; mn 1.59%; p0.011%; s0.008%; cr 0.25%; v0.16%; re 0.02%; the balance of Fe and unavoidable impurities, and the mass fraction is 100 percent.

5. The method for preparing the seamless steel tube for the rare earth microalloyed cold drawn high strength hydraulic cylinder barrel according to claim 1, which is characterized by comprising the following chemical elements in percentage by mass: c0.23%; si 0.28%; mn 1.56%; p0.018%; s0.005%; cr 0.24%; v0.14%; re 0.02%; the balance of Fe and unavoidable impurities, and the mass fraction is 100 percent.

6. The method for preparing the seamless steel tube for the rare earth microalloyed cold drawn high strength hydraulic cylinder barrel, which is disclosed in claim 1, is characterized in that the requirement on the dephosphorization pressure of high-pressure water after normalizing is more than or equal to 12MPa, the straightening is required after normalizing, the straightening force is strictly controlled during straightening, the requirement on the bending degree of the steel tube is ensured, and the conditions of concave correction, elliptic correction and crack correction are not required.