CN112375977A - Rare earth microalloyed seamless steel tube for Q390 steel grade structure and production method thereof - Google Patents

Abstract

The invention discloses a seamless steel tube for a rare earth microalloyed Q390 steel grade structure and a production method thereof, wherein the chemical components of the seamless steel tube for the structure comprise C: 0.16-0.20, Si: 0.20-0.30, Mn: 1.20-1.30, P: less than or equal to 0.020 and S: less than or equal to 0.010, Al: 0.02-0.05, Cr: 0.10-0.20, Ti: 0.010-0.030, V: 0.08-0.10, Nb: 0.025-0.040, RE: 0.008-0.015 wt%, and Fe and inevitable impurities as the rest. The seamless steel pipe for the Q390 steel grade structure provided by the invention has excellent low-temperature-resistant toughness, and can meet the use requirements under different working conditions (especially low-temperature working conditions).

Description

Rare earth microalloyed seamless steel tube for Q390 steel grade structure and production method thereof

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to a seamless steel tube for a rare earth microalloyed Q390 steel grade structure and a production method thereof, in particular to a seamless steel tube for a Q390 steel grade structure with a wall thickness of more than 16mm and a production method thereof.

Background

At present, the demand of structural seamless steel pipes is increasing, but the chemical components of the structural seamless steel pipes are not specified clearly, and the existing structural seamless steel pipes in the market have various types and types, but basically have the defects of poor welding performance or poor low-temperature toughness resistance, so that the service of the structural seamless steel pipes under the low-temperature condition is limited. For example, CN104451411A discloses a seamless steel pipe containing rare earth for Q420 structure, which has an impact toughness of only about 80J at-40 ℃, and limits the application range of the seamless steel pipe for structure.

Disclosure of Invention

In view of one or more of the problems in the prior art, an aspect of the present invention provides a seamless steel tube for a rare earth microalloyed Q390 steel grade structure, the chemical composition of which comprises, in mass percent, C: 0.16-0.20, Si: 0.20-0.30, Mn: 1.20-1.30, P: less than or equal to 0.020 and S: less than or equal to 0.010, Al: 0.02-0.05, Cr: 0.10-0.20, Ti: 0.010-0.030, V: 0.08-0.10, Nb: 0.025-0.040, RE: 0.008-0.015 wt%, and Fe and inevitable impurities as the rest.

The invention also provides a production method of the seamless steel tube for the rare earth microalloyed Q390 steel grade structure, which comprises the following process steps: molten iron pretreatment → smelting in a top-bottom combined blown converter → refining in an LF furnace → VD vacuum treatment → round billet continuous casting → heating of pipe blank → perforation → continuous rolling pipe → stretch-setting and diameter reduction → cold bed → sawing → heat treatment → straightening; wherein:

after the step of the molten iron pretreatment process, the content of S in the molten iron is reduced to be below 0.050%;

in the smelting process step of the top-bottom combined blown converter, 10-15% of scrap steel is added into molten iron, a single slag process is adopted for smelting, and the final slag alkalinity and the end point target are controlled as follows: c, tapping is more than or equal to 0.10 percent; deoxidizing and alloying in the tapping process, wherein the final deoxidation adopts an aluminum deoxidation process, slag is blocked or removed in the tapping process, and white ash blocks are added after the alloy is added in the tapping process;

in the LF furnace refining process steps: blowing argon normally in the whole refining process as required, heating and raising the temperature from 1520 +/-10 ℃ to 1620 +/-10 ℃ in a mode of gradually increasing the temperature raising speed from low grade to high grade; carrying out slagging desulfurization, component adjustment and heating operation according to the components and the temperature of the molten steel of the converter; adopting white slag making operation;

the VD vacuum treatment process comprises the following steps: the vacuum degree is less than or equal to 0.10KPa, the deep vacuum time is more than or equal to 10 minutes, after the deep vacuum treatment is carried out for 10 minutes, the fixed-length silicon-calcium wires are fed, the rare earth ferroalloy is added, and then the argon blowing is carried out for more than 15 minutes;

the round billet continuous casting process comprises the following steps: adopting low pulling speed, constant pulling speed control and electromagnetic stirring process, wherein the pulling speed is controlled to be 0.9m/min-1.2 m/min; controlling the superheat degree of the molten steel to be less than or equal to 30 ℃; straightening a casting blank, and cutting the casting blank into round pipe blanks;

the heat treatment system in the heat treatment process steps is as follows: normalizing at 900-920 ℃, keeping the temperature for 70-90 min, and cooling in air.

Based on the technical scheme provided by the technical scheme, by reasonably designing chemical components, adopting MnVTiRE steel component design and optimizing the heat treatment process steps, on the premise of ensuring the strength, the seamless steel pipe for the structure with the Q390 steel grade wall thickness of more than 16mm and excellent low-temperature toughness is obtained, and the impact toughness at minus 40 ℃ is detected to reach more than 150J, so that the use requirements under different working conditions (particularly low-temperature working conditions) can be met.

Detailed Description

The invention aims to provide a seamless steel tube for a Q390 steel grade (the wall thickness is more than 16mm) structure with excellent low temperature resistance toughness and a production method thereof. The object of the present invention is achieved by the following embodiments.

The seamless steel pipe for the Q390 steel grade structure comprises the following chemical components in percentage by mass: c: 0.16-0.20, Si: 0.20-0.30, Mn: 1.20-1.30, P: less than or equal to 0.020 and S: less than or equal to 0.010, Al: 0.02-0.05, Cr: 0.10-0.20, Ti: 0.010-0.030, V: 0.08-0.10, Nb: 0.025-0.040, RE (Ce): 0.008-0.015 wt%, and Fe and inevitable impurities as the rest.

The production method of the seamless steel pipe for the Q390 steel grade structure comprises the following process steps: molten iron pretreatment → smelting in a top-bottom combined blown converter → refining in an LF furnace → VD vacuum treatment → round billet continuous casting → heating of pipe blank → perforation → continuous rolling pipe → stretch-setting and diameter reduction → cold bed → sawing → heat treatment → straightening; wherein:

after the step of the molten iron pretreatment process, the content of S in the molten iron is reduced to be below 0.050%;

in the smelting process step of the top-bottom combined blown converter, 10-15% of scrap steel is added into molten iron, a single slag process is adopted for smelting, and the final slag alkalinity and the end point target are controlled as follows: c, tapping is more than or equal to 0.10 percent; deoxidizing and alloying in the tapping process, wherein the final deoxidation adopts an aluminum deoxidation process, slag is blocked or removed in the tapping process, and white ash blocks are added after the alloy is added in the tapping process;

in the LF furnace refining process steps: blowing argon normally in the whole refining process as required, heating and raising the temperature from 1520 +/-10 ℃ to 1620 +/-10 ℃ in a mode of gradually increasing the temperature raising speed from low grade to high grade; carrying out slagging desulfurization, component adjustment and heating operation according to the components and the temperature of the molten steel of the converter; adopting white slag making operation;

the VD vacuum treatment process comprises the following steps: the vacuum degree is less than or equal to 0.10KPa, the deep vacuum time is more than or equal to 10 minutes, after the deep vacuum treatment is carried out for 10 minutes, the fixed-length silicon-calcium wires are fed, the rare earth ferroalloy is added, and then the argon blowing is carried out for more than 15 minutes;

the round billet continuous casting process comprises the following steps: adopting low pulling speed, constant pulling speed control and electromagnetic stirring process, wherein the pulling speed is controlled to be 0.9m/min-1.2 m/min; controlling the superheat degree of the molten steel to be less than or equal to 30 ℃; straightening a casting blank, and cutting the casting blank into round pipe blanks; making a pipe for the casting blank which is qualified in inspection and has the sulfur mark not greater than 2.0 level;

the tube making process is as follows;

continuously checking the temperature of each section of a preheating section, a heating section, a soaking section and the like of the annular heating furnace, wherein the temperature of each section of the annular heating furnace is controlled as shown in the following table 1;

table 1: temperature control of each section of annular heating furnace

The computer control system records the heating temperature of each section on line, and requires to control the temperature of the preheating section and the soaking section well, thereby ensuring thorough and uniform heating without overburning. The heating tool must be measured before use, and the treatment roller way is inspected before rolling to avoid scratching. Rolling the heated tube blank into a seamless steel tube, and performing thermal sampling for at least one time in each batch to check the geometric dimension;

the heat treatment and straightening process comprises the following steps: normalizing at 900-920 ℃, keeping the temperature for 70-90 min, and cooling in air. After heat treatment, the grain size can reach 8 grades, and the structure is ferrite plus pearlite.

The present invention will be described in detail below with reference to specific examples, which are intended to facilitate understanding of the present invention and are not intended to limit the present invention.

Examples

Seamless steel pipes for Q390 grade steel structures with a specification of 426X 20mm were produced according to the chemical compositions of examples 1 to 5 listed in Table 2 below according to the method provided above. The mechanical properties of the seamless steel pipes for Q390 steel grade structures produced in each example (wherein the impact toughness specimen size is 10X 55mm) are shown in Table 3 below.

Table 2: chemical composition and content (%)

Examples	C	Si	Mn	P	Al	Cr	S	V	Nb	Ce	Ti
												Example 1	0.17	0.25	1.22	0.017	0.025	0.15	0.008	0.09	0.025	0.008	0.022
Example 2	0.17	0.30	1.21	0.013	0.031	0.11	0.007	0.10	0.033	0.011	0.021
												Example 3	0.19	0.27	1.30	0.014	0.035	0.15	0.010	0.08	0.035	0.015	0.012
Example 4	0.20	0.21	1.25	0.016	0.027	0.17	0.010	0.09	0.040	0.008	0.028
												Example 5	0.16	0.25	1.21	0.017	0.035	0.20	0.007	0.08	0.027	0.011	0.015

Table 3: mechanical properties of seamless steel pipes for Q390 steel grade structures in each example

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (2)

1. The seamless steel tube for the rare earth microalloyed Q390 steel grade structure is characterized by comprising the following chemical components in percentage by mass: 0.16-0.20, Si: 0.20-0.30, Mn: 1.20-1.30, P: less than or equal to 0.020 and S: less than or equal to 0.010, Al: 0.02-0.05, Cr: 0.10-0.20, Ti: 0.010-0.030, V: 0.08-0.10, Nb: 0.025-0.040, RE: 0.008-0.015 wt%, and Fe and inevitable impurities as the rest.

2. A method of producing a seamless steel tube for a rare earth microalloyed Q390 steel grade structure as claimed in claim 1, which includes the steps of: molten iron pretreatment → smelting in a top-bottom combined blown converter → refining in an LF furnace → VD vacuum treatment → round billet continuous casting → heating of pipe blank → piercing → continuous rolling pipe → stretch-setting and diameter reduction → cooling bed → sawing → heat treatment → straightening, wherein:

after the step of the molten iron pretreatment process, the content of S in the molten iron is reduced to be below 0.050%;

in the smelting process step of the top-bottom combined blown converter, 10-15% of scrap steel is added into molten iron, a single slag process is adopted for smelting, and the final slag alkalinity and the end point target are controlled as follows: c, tapping is more than or equal to 0.10 percent; deoxidizing and alloying in the tapping process, wherein the final deoxidation adopts an aluminum deoxidation process, slag is blocked or removed in the tapping process, and white ash blocks are added after the alloy is added in the tapping process;

in the LF furnace refining process steps: blowing argon normally in the whole refining process as required, heating and raising the temperature from 1520 +/-10 ℃ to 1620 +/-10 ℃ in a mode of gradually increasing the temperature raising speed from low grade to high grade; carrying out slagging desulfurization, component adjustment and heating operation according to the components and the temperature of the molten steel of the converter; adopting white slag making operation;

the VD vacuum treatment process comprises the following steps: the vacuum degree is less than or equal to 0.10KPa, the deep vacuum time is more than or equal to 10 minutes, after the deep vacuum treatment is carried out for 10 minutes, the fixed-length silicon-calcium wires are fed, the rare earth ferroalloy is added, and then the argon blowing is carried out for more than 15 minutes;

the round billet continuous casting process comprises the following steps: adopting low pulling speed, constant pulling speed control and electromagnetic stirring process, wherein the pulling speed is controlled to be 0.9m/min-1.2 m/min; controlling the superheat degree of the molten steel to be less than or equal to 30 ℃; straightening a casting blank, and cutting the casting blank into round pipe blanks;

the heat treatment system in the heat treatment process steps is as follows: normalizing at 900-920 ℃, keeping the temperature for 70-90 min, and cooling in air.