CN114752855B

CN114752855B - 460 MPa-grade economical low-yield-ratio low-crack-sensitivity structural steel and manufacturing method thereof

Info

Publication number: CN114752855B
Application number: CN202210379130.5A
Authority: CN
Inventors: 孙宪进; 白云; 赵乾; 苗丕峰; 诸建阳; 许峰; 张建
Original assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Current assignee: Jiangyin Xingcheng Special Steel Works Co Ltd
Priority date: 2022-04-12
Filing date: 2022-04-12
Publication date: 2023-09-15
Anticipated expiration: 2042-04-12
Also published as: CN114752855A

Abstract

The application relates to 460MPa grade economical low yield ratio low crack sensitivity structural steel and a manufacturing method thereof, wherein the chemical components of the steel plate are 0.03-0.05 wt.% of C, 0.20-0.30 wt.% of Si, 1.20-1.50 wt.% of Mn, 0.02-0.04 wt.% of Al, 0.035-0.045 wt.% of Nb, 0.01-0.02 wt.% of Ti, 0.15-0.25 wt.% of Cr, less than or equal to 0.15 wt.% of pcm, and the balance Fe and unavoidable impurities; has a single-phase polygonal ferrite + fine MA structure. The thickness of the product is 10-20mm, the yield strength is more than or equal to 460MPa, the impact energy at minus 40 ℃ is more than or equal to 300J, the elongation after break A50 is more than or equal to 0.40, and the yield ratio is less than or equal to 0.80. The application obtains a single-phase polygonal ferrite and fine MA structure by utilizing on-line enhanced cooling, and simultaneously realizes stress relief treatment through a low-temperature straightening process to obtain the low yield ratio and low crack sensitivity structural steel plate with good low-temperature toughness.

Description

460 MPa-grade economical low-yield-ratio low-crack-sensitivity structural steel and manufacturing method thereof

Technical Field

The application belongs to the technical field of iron-based metallurgy, and relates to 460 MPa-level low-yield-ratio low-crack-sensitivity structural steel and a manufacturing method thereof.

Background

With the continuous development of infrastructure construction, super-large steel structure engineering construction represented by the Kong Zhu Australian bridge and the Hangzhou Bay bridge is more and more, and stricter requirements are put forward on the performance of high-strength structural steel; mainly has the characteristics of low yield ratio and easy welding on the basis of ensuring high strength. Therefore, in recent years, structural steel sheets having a yield strength of 420MPa or more, a low yield ratio, and a low crack sensitivity have become a development hot spot. The yield ratio refers to the ratio of the yield strength to the tensile strength of a material, and the higher the tensile strength is under the premise of consistent yield strength grade, the lower the yield ratio is.

In the design of the low yield ratio method developed at present, most of the methods adopt a component design method of adding noble alloy elements such as Ni, mo and the like, and the dual-phase structure low yield ratio structural steel plate is obtained through controlled rolling and controlled cooling, and the defects are high production cost and poor economy.

For example, patent publication No. CN109550806A provides a method for producing a 460 MPa-grade low-yield structural steel plate, wherein the element components are C0.05-0.10%, si 0.10-0.50%, mn 1.20-2.00%, nb 0.02-0.045%, ti0.005-0.025%, cr 0.40-1.00%, ni 0.05-0.20%, cu 0.10-0.5%, mo 0.08-0.25%, als0.010-0.050%, and the balance Fe and unavoidable impurities. The yield ratio of the structural steel plate is less than or equal to 0.85, and the method utilizes an online controlled rolling and cooling process to obtain the bainitic+ferrite dual-phase structure. The patent publication No. CN111979481A provides a thin-specification low-yield-ratio high-strength structural steel and a production method thereof, wherein the steel plate adopts the composition design of increasing Mn and Cr elements and reducing Nb and Ti elements, and comprises the following chemical components in percentage by mass: c:0.06-0.08%, si:0.15-0.25%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, ni:0.2-0.4%, mo:0.1-0.2%, al:0.01-0.045%, mn+Cr:1.90-2.20%, nb+Ti:0.035-0.05%, and the balance Fe and other unavoidable impurities, adopting a rolling cooling process of high-temperature finish rolling and variable speed cooling after rolling to obtain a ferrite-bainite dual-phase structure, wherein the yield strength is 520-570MPa, the tensile strength is 670-760MPa, the yield ratio is 0.69-0.79, and the production thickness is 8-16mm. Patent publication No. CN112501496a provides a dual-phase low yield ratio steel sheet, the element composition is C:0.037-0.056%, si:0.15-0.20%, mn:1.28-1.58%, P is less than or equal to 0.015%, S is less than or equal to 0.008%, nb:0.022-0.042%, ti:0-0.015%, al:0.01-0.045%, no noble alloy element is added, and a quasi-polygonal ferrite and bainite dual-phase structure is obtained, and finally, the thickness is less than or equal to 24mm, the yield strength is 380-460MPa, the tensile strength is 550-660MPa, the elongation A is more than or equal to 23%, and the longitudinal impact power is more than or equal to 200J at minus 40 ℃. Although no noble alloy element is added, the control thought of the metallographic structure of the steel is still to adopt a method of controlling the metallographic structure to be a double-phase structure for production, and the manufacturing process still adopts a rolling and cooling control mode. The patent publication No. CN112048675A provides a granular bainite high-strength steel plate with low yield ratio used in a low-temperature environment and a manufacturing method thereof, wherein the chemical components (wt%) of the granular bainite high-strength steel plate are C0.05-0.11, si 0.20-0.50, mn 1.00-1.40, al 0.02-0.04, nb 0.01-0.03, ti 0.01-0.03, ni 0.80-1.30, mo 0.30-0.60, cr 0.30-0.60, B0.0008-0.0020, S less than or equal to 0.003 and P less than or equal to 0.015, and the granular bainite high-strength steel is obtained by adopting a rolling and heat treatment method, the yield strength is more than or equal to 500MPa, and the yield ratio is less than or equal to 0.70. The method still adopts the steps of adding noble alloy elements such as Ni, mo and the like into a structure, and adopting a quenching and tempering heat treatment process for production on the manufacturing method.

Disclosure of Invention

The application aims to provide an economic low yield ratio low crack sensitivity structural steel plate with yield strength of 460MPa and a manufacturing method thereof. In the aspect of element component design, noble alloy elements such as Ni, mo and the like are not required to be added, and regulation and control for obtaining a ferrite-bainite dual-phase structure are not performed in the production method.

The technical scheme adopted by the application is as follows: 460MPa grade economical structural steel with low yield ratio and low crack sensitivity comprises the following chemical components of 0.03-0.05 wt.% of C, 0.20-0.30 wt.% of Si, 1.20-1.50 wt.% of Mn, 0.02-0.04 wt.% of Al, 0.035-0.045 wt.% of Nb, 0.01-0.02 wt.% of Ti, 0.15-0.25 wt.% of Cr, less than or equal to 0.15 wt.% of pcm, and the balance of Fe and unavoidable impurities. The effect and content selection reasons of all key components contained in the application are specifically described as follows:

c: the most critical elements affecting the structure regulation and the weldability in the steel have good solid solution strengthening effect when the content is high, and have great contribution to the strength, but have damage to the weldability and the low-temperature toughness; when the content is low, the solid solution strengthening effect is weak, the strength is low, and if other noble alloy elements are added, the economical efficiency is reduced. In the patent, the weldability and the influence on the phase change under the ultra-fast cooling are considered, meanwhile, the required tissue regulation and control needs are combined, the ultra-low carbon design is adopted, and the C content selection range is 0.03-0.05%.

Si: the main deoxidizing element can form a substitutional solid solution, which is beneficial to the regulation and control of the yield ratio; however, the Si content is too high, so that fayalite is easy to form, the surface quality of the steel plate is affected, and the Si content is selected to be 0.20-0.30%.

Mn: the main solid solution strengthening elements in the steel improve the strength and toughness of the steel in a solid solution strengthening mode, and are beneficial to control of the yield ratio; however, mn is also an element for improving hardenability, and martensite is obtained when Mn is too high, and the application adopts a design of medium and low Mn in combination with the process adopted by the application, and the reasonable selection range is 1.20-1.50%.

Al: the main deoxidizing element can form AlN to refine grains. The Al content of the application is selected to be 0.02-0.04%.

Nb, ti: the most important fine-grain element in the steel, nb can obviously improve the austenite recrystallization temperature of the steel, and enlarge the range of a non-recrystallized zone, thereby refining the prior austenite grain size; forming fine Nb (C, N) and TiN precipitated phases when rolling in an unrecrystallized area, and refining ferrite grains; considering comprehensively, the Nb content of the application is selected from 0.035 to 0.045 percent, and the Ti content is selected from 0.01 to 0.02 percent.

A manufacturing method of a 460 MPa-grade economical low-yield-ratio low-crack-sensitivity structural steel plate comprises the following process steps: in the steelmaking process, a converter smelting, LF+RH vacuum degassing treatment and slab continuous casting process are preferably adopted to produce continuous casting billets with the thickness of more than 150 mm; after the continuous casting billet is inspected, charging and reheating are carried out to ensure that the structure is uniformly and completely austenitized, elements are fully dissolved, preferably, a continuous casting billet heating furnace with the thickness of more than 150mm is used for 150-170min, the soaking section heat preservation temperature is 1120-1180 ℃, and the heat preservation time is more than or equal to 15min, so as to obtain more uniform prior austenite grain size. The rolling stage adopts a high-temperature rolling process, the initial rolling temperature is 1030-1120 ℃, the final rolling temperature is 880-950 ℃, and the rolling pass is preferably controlled to be 6-8 times; slightly staying the rolled steel plate for waiting for 10-50s; through stay in the austenite temperature interval, austenite recrystallization is recovered and stabilized, and uniform and stable austenite structure required by phase change is provided for subsequent direct accelerated cooling. After the steel plate stays, on-line direct accelerated cooling is carried out, the cooling start temperature is 860-900 ℃, the cooling speed is 20-30 ℃/s, and the final cooling temperature is 200-300 ℃; at the beginning of the transformation stage, a polygonal ferrite structure is obtained, as the transformation progresses, due to the fact that the carbon content in the transformed ferrite is low, the concentration of carbon elements in the non-transformed structure is far greater than that of a target component, at a relatively high cooling speed, an MA structure is obtained by the post-transformation structure, and by strictly controlling the cooling temperature and the cooling speed and combining the dynamic CCT transformation curve characteristics under the element component design, the polygonal ferrite+MA structure is finally obtained. And (3) after the steel plate is directly subjected to accelerated cooling treatment, straightening treatment is immediately carried out, straightening is carried out repeatedly for three times at the temperature of 150-250 ℃, and the internal stress of the steel plate at a high cooling speed is released through repeated straightening, so that an ideal finished steel plate is obtained.

Compared with the prior art, the application has the main differences that:

(1) the application provides an economic component design, which is different from the prior art, removes noble Ni, mo and other alloy elements, reduces the content of Mn element, and has remarkable progress in the aspects of energy conservation and consumption reduction.

(2) Based on the design of economical components, a set of economic low yield ratio low crack sensitivity structural steel plate with good low temperature toughness is creatively provided, wherein the single-phase polygonal ferrite and fine MA structure is obtained by utilizing on-line strong cooling equipment, and meanwhile, the stress relief treatment is realized by a low temperature straightening process.

Drawings

FIG. 1 is a photograph showing the microstructure of a 15mm steel plate in the example of the present application;

FIG. 2 is a photograph showing the microstructure of a 20mm steel plate in the example of the present application;

Detailed Description

The present application is described in further detail below in connection with the following examples, which are to be understood as being exemplary and not limiting of the technical solution of the present application.

Examples 1-3:

according to the chemical composition range and the manufacturing method of the application, the 460MPa grade economic structural steel plate with low yield ratio and low crack sensitivity is manufactured through the process steps of converter smelting, LF refining, RH vacuum degassing, slab continuous casting, continuous casting blank inspection and cleaning, casting blank heating, high-pressure water descaling, rolling, cooling, temperature straightening and the like.

The specific process of the heating, rolling and cooling stages is as follows: heating the continuous casting billet to 1120-1180 ℃, wherein the total heating time is 165min (example 1), 168min (example 2) and 159min (example 3), and the soaking period heat preservation time is 20min (example 1), 18min (example 2) and 17min (example 3), and descaling the continuous casting billet by using high-pressure water after discharging the continuous casting billet; then rolling was performed at an initial rolling temperature of 1100 ℃ (example 1), 1095 ℃ (example 2) and 1080 ℃ (example 3), rolling passes of 8 passes (example 1), 7 passes (example 2) and 6 passes (example 3), respectively, final rolled steel sheet thicknesses of 10mm (example 1), 15mm (example 2) and 20mm (example 3), respectively, final rolling temperatures of 885 ℃ (example 1), 910 ℃ (example 2) and 945 ℃ (example 3), post-rolling residence times of 10s (example 1), 20s (example 2) and 50s (example 3), and post-rolling rapid cooling was entered at an initial temperature of 864 ℃ (example 1), 880 ℃ (example 2) and 895 ℃ (example 3), respectively, and cold speeds of 30 ℃/s (example 1), 25 ℃/s (example 2) and 22 ℃/s (example 3), final cold temperatures of 261 ℃ (example 1), 246 ℃ (example 2) and 220 ℃ (example 3). Straightening was then carried out at 190 ℃ (example 1), 220 ℃ (example 2) and 200 ℃ (example 3) to obtain the final finished steel sheet, and specific rolling and cooling measures were shown in the following table.

The chemical compositions of the steel plates prepared in the examples are shown in Table 1, the rolling and cooling of the steel plates are shown in Table 2, the mechanical properties are shown in Table 3, and the microstructure of the steel plates is shown in FIGS. 1-2.

Table 1 chemical composition (wt.%) of the steel sheet of example

Table 2 example process for rolling and cooling steel sheet

Examples

Thickness of (L)

Start rolling temperature

Finishing temperature

Residence time

Cooling temperature

Final cooling temperature

Cooling speed

1

10mm

1100℃

885℃

10s

864℃

261℃

30℃/s

2

15mm

1095℃

910℃

20s

880℃

246℃

25℃/s

3

20mm

1080℃

945℃

50s

895℃

220℃

22℃/s

TABLE 3 mechanical Properties of the Steel sheets of examples

While the preferred embodiments of the present application have been described in detail, it is to be clearly understood that the same may be varied in many ways by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A460 MPa grade economical low yield ratio low crack sensitivity structural steel is characterized in that: the steel plate comprises the following chemical components of 0.03-0.05 wt.% of C, 0.20-0.30 wt.% of Si, 1.20-1.50 wt.% of Mn, 0.02-0.04 wt.% of Al, 0.035-0.045 wt.% of Nb, 0.01-0.02 wt.% of Ti, 0.15-0.25 wt.% of Cr, less than or equal to 0.15 wt.% of pcm, and the balance of Fe and unavoidable impurities; has a single-phase polygonal ferrite + fine MA structure;

the manufacturing method of the steel plate comprises the following steps of

(1) Smelting and casting molten steel: smelting molten steel conforming to chemical components, and casting the molten steel into a casting blank;

(2) heating a casting blank: heating the casting blank in a furnace, and fully dissolving elements in solid and fully austenitizing the structure;

(3) high-temperature rolling: the initial rolling temperature is 1030-1120 ℃ and the final rolling temperature is 880-950 ℃; the steel plate stays for waiting after rolling, and the stay time is controlled to be 10-50s;

(4) and (5) accelerated cooling: after the steel plate stays, the steel plate is cooled in an online acceleration way, the cooling temperature is 860-900 ℃, the cooling speed is 20-30 ℃/s, and the final cooling temperature is 200-300 ℃;

(5) straightening the steel plate after cooling treatment, wherein the straightening temperature is as follows: and (5) straightening back and forth at 150-250 ℃.

2. The 460 MPa-grade economical low yield ratio low crack sensitivity structural steel according to claim 1, wherein: the thickness of the product is 10-20mm, the yield strength is more than or equal to 460MPa, the impact energy at minus 40 ℃ is more than or equal to 300J, the elongation after break A50 is more than or equal to 0.40, and the yield ratio is less than or equal to 0.80.

3. A method of making the 460 MPa-grade economical low yield ratio low crack susceptibility structural steel of claim 1, characterized by: comprises the following steps of

4. The 460 MPa-level economical low yield ratio low crack sensitivity structural steel manufacturing method according to claim 3, wherein: the molten steel smelting in the step (1) sequentially comprises top-bottom converting, LF+RH refining and continuous casting blank with the thickness of 150mm is produced by adopting a continuous casting process.

5. The 460 MPa-level economical low yield ratio low crack sensitivity structural steel manufacturing method according to claim 3, wherein: the heat preservation temperature of a soaking section for heating the casting blank in the step (2) is 1120-1180 ℃, and the heat preservation time is more than or equal to 15min; and the continuous casting blank with the thickness of 150mm is in a furnace for 150-170min.

6. The 460 MPa-level economical low yield ratio low crack sensitivity structural steel manufacturing method according to claim 3, wherein: and (3) rolling the casting blank with the thickness of more than 150mm in 6-8 times to produce the steel plate with the thickness of 10-20 mm.