CN104087826A - Large aperture thin-wall X65 level heat expanding seamless steel tube and production method - Google Patents

Abstract

The invention relates to a large aperture thin-wall X65 level heat expanding seamless steel tube and a production method. The outer diameter D is 406-609mm with the tolerance being +/-0.75%D and the wall thickness S is 6.35-9.53mm with the tolerance being +/-12.5%S. The large aperture thin-wall X65 level heat expanding seamless steel tube comprises the following components in percentage by mass: 0.24-0.28% of C, 1.25-1.40% of Mn, 0.10-0.13% of V, 0.01-0.04% of Al, 0.45-0.60% of Si, less than or equal to 0.025% of P, less than or equal to 0.015% of S, less than or equal to 0.001% of B and the balance of Fe and inevitable impurities. The production method comprises the following steps: first, smelting scrap steel into molten steel; then dosing required alloys to obtain the molten steel which meets the requirements of steel tube components; producing a circular blank by adopting an EBT-LF-VD-CCM process; carrying out perforation-continuous rolling-sizing-straightening-saw cutting by a 340 continuous casting unit to obtain a mother tube for heat expansion; then, carrying out heat expansion by using a local medium frequency induction heating heat expander, wherein the heat expansion temperature is below an AC1 line; carrying out weak atomizing water cooling at a 300mm section after the steel tube is heated to expand to obtain an induction coil so as to obtain the required large aperture thin-wall seamless steel tube.

Description

Large-caliber thin-walled X65 level hot-expanding seamless steel tubes and production method

Technical field

The present invention relates to seamless steel tube production technical field, particularly a kind of large-caliber thin-walled X65 level hot-expanding seamless steel tubes and production method.

Background technology

In seamless steel tube production process, as 406 ㎜ * 6.35 ㎜, 508 ㎜ * 6.35～7.0 ㎜, 609.6 ㎜ * 9.53 ㎜ specification steel pipe's production mainly adopt, local Frequency Induction Heating heat expands technique to large-diameter thin-wall seamless steel pipe, this steel tube performance will reach X65 level, conventionally adopt two kinds of methods: the one, fall C and add micro alloying element V, Nb, Ti, then by modified thermal treatment, meet the mechanical property of steel pipe, but this production method can make steel pipe deform in modified process, when serious, cause waste product; The 2nd, improve C, Mn content, by the female Guan Houzai heat of hot rolling, expand and become a useful person, although adding of C, the raising of Mn content and microalloy element improves the tensile strength of hot finished steel pipe and yield strength, but unit elongation reduces, cost up, meanwhile, affect the welding property of steel pipe, and API5L(45 ^th) stipulate in PSL1 X65 standard: C≤0.28%, Mn≤1.40%, if C reduces, Mn can increase, but maximum is no more than 1.75%.When the female Guan Re of this hot rolling expands, if do not taken appropriate measures, its tensile strength and yield strength also can decline to some extent.Therefore, must select suitable steel grades, repave the weak atomization water-cooled while expanding with Steel Pipe Heat, make this hot-expanding pipe be heated near the AC1 temperature of this steel grade or carry out press working during following a certain temperature, then after slowly cooling to certain temperature with plug, air cooling is to room temperature, this special low temperature deformation annealing process is owing to being in below the austenite recrystallization temperature of steel, and metallic carbide dissolve difficulty, makes the strength of materials increase.

Summary of the invention

The object of the invention is to overcome the above-mentioned deficiency of prior art and a kind of large-caliber thin-walled X65 level hot-expanding seamless steel tubes and production method are provided.

Technical scheme of the present invention is: a kind of large-caliber thin-walled X65 level hot-expanding seamless steel tubes, and its outer diameter D is: 406 ~ 609 ㎜, tolerance is: +/-0.75%D, wall thickness S is: 6.35 ~ 9.53 ㎜, tolerance is: +/-12.5%S; Composition, in quality %, specifically has: C:0.24～0.28, Mn:1.25～1.40, V: 0.10～0.13, Al:0.01～0.04, Si:0.45～0.60, P≤0.025, S≤0.015, B≤0.001, all the other are Fe and inevitable impurity.

In mentioned component:

C is carbide forming element, and certain C content can improve intensity and the hardness of matrix, but the unit elongation of the high meeting reduction of C content steel unfavorable to welding, API5L X65 PSL1 stipulates C≤0.28(Wt%).

Mn makes up pipe line steel because C content reduces, to cause the most economical strengthening element of loss of strength, Mn can be dissolved in ferrite makes ferrite strengthening, also can be dissolved in cementite, improve its hardness, Mn can also increase and refine pearlite, improve intensity and the hardness of steel, can improve the hot strength of material, but too high levels reduces the thermal conductivity of steel.

Si can be dissolved in ferrite makes it strengthening, improves intensity and the hardness of steel pipe.

V has slight thinning microstructure and medium precipitation strength effect, in the process of cooling of pipe line steel after rolling, separates out V(C, N) produce precipitation strength, thus improve the intensity of steel, wherein the effect of VN is greater than NbN and TiN.

Al can strengthen deoxidation and the crystal grain thinning of steel, and the intensity that is conducive to steel improves.

The present invention also provides a kind of production method of large-caliber thin-walled X65 level hot-expanding seamless steel tubes, and by controlling suitable C, Mn, V, Al, Si content, Steel Pipe Heat adopts atomized water cooling while expanding, and makes the physicochemical property of tube material reach API5L(45 ^th) PSL1 X65.Its concrete production method is as follows:

First smelting scrap steel is become to molten steel, then with addition of required alloy, obtain conforming with the molten steel of steel pipe composition requirement, adopt EBT → LF → VD → CCM explained hereafter circle blank, perforation → tandem rolling → sizing → alignment → sawing by 340 tandem rolling units obtains female pipe for heat expansion, by local Frequency Induction Heating thermal expansion machine, carrying out heat again expands, heat expands temperature below AC1 line, actual hot-expanding pipe temperature is controlled at 710 ~ 730 ℃, at steel pipe, add when thermal expansion goes out 300 ㎜ section after ruhmkorff coil and carry out weak atomization water-cooled, obtain needed large-diameter thin-wall seamless steel pipe.

The heat of carrying out large-caliber thin-walled X65 level hot-expanding seamless steel tubes provided by the invention no longer needs to heat-treat after expanding, and has guaranteed the stability of steel pipe apparent size, has reduced manufacturing cost simultaneously.

The present invention compared with prior art has following features:

The present invention is by the Composition Design to large-caliber thin-walled X65 level hot-expanding seamless steel tubes, when expanding, heat adopts weak atomization water-cooled explained hereafter, hot-expanding pipe does not need to carry out the modified thermal treatment of off-line, not only reduced cost, and the waste product that apparent size distortion seriously causes while having avoided because of thermal treatment, thereby obtain the X65 PSL1 weldless steel tube that physicochemical property is good.

Embodiment

Embodiment mono-,

A large-caliber thin-walled X65 level hot-expanding seamless steel tubes, its outer diameter D is: 406 ㎜, tolerance is: +/-0.75%D, wall thickness S is: 6.35 ㎜, tolerance is: +/-12.5%S; Composition, in quality %, specifically has: C:0.24～0.26, Mn:1.25～1.30, V: 0.10～0.12, Al:0.010～0.025, Si:0.45～0.50, P≤0.025, S≤0.015, B≤0.001, all the other are Fe and inevitable impurity.

Its concrete production method is as follows:

First smelting scrap steel is become to molten steel, then with addition of required alloy, obtain conforming with the molten steel of steel pipe composition requirement, adopt EBT → LF → VD → CCM explained hereafter circle blank, perforation → tandem rolling → sizing → alignment → sawing by 340 tandem rolling units obtains female pipe for heat expansion, by local Frequency Induction Heating thermal expansion machine, carrying out heat again expands, heat expands temperature below AC1 line, actual hot-expanding pipe temperature is controlled at 710 ~ 730 ℃, at steel pipe, add when thermal expansion goes out the 300mm section after ruhmkorff coil and carry out weak atomization water-cooled, obtain needed large-diameter thin-wall seamless steel pipe.

The mechanical property of steel pipe is in Table 1.

Table 1 mechanical properties of pipe

Material	σs（Mpa）	σb（Mpa）	δ（%）
				The large-caliber thin-walled hot-expanding seamless steel tubes of X65 level	470~520	560~630	≥32
The requirement of PSL1 X65 grade standard	≥450	≥535	≥28

Embodiment bis-,

A large-caliber thin-walled X65 level hot-expanding seamless steel tubes, its outer diameter D is: 609 ㎜, tolerance is: +/-0.75%D, wall thickness S is: 9.53 ㎜, tolerance is: +/-12.5%S; Composition, in quality %, specifically has: C:0.26～0.28, Mn:1.30～1.40, V: 0.12～0.13, Al:0.025～0.040, Si:0.50～0.60, P≤0.025, S≤0.015, B≤0.001, all the other are Fe and inevitable impurity.

Its concrete production method is as follows:

First smelting scrap steel is become to molten steel, then with addition of required alloy, obtain conforming with the molten steel of steel pipe composition requirement, adopt EBT → LF → VD → CCM explained hereafter circle blank, perforation → tandem rolling → sizing → alignment → sawing by 340 tandem rolling units obtains female pipe for heat expansion, by local Frequency Induction Heating thermal expansion machine, carrying out heat again expands, heat expands temperature below AC1 line, actual hot-expanding pipe temperature is controlled at 710 ~ 730 ℃, at steel pipe, add when thermal expansion goes out the 300mm section after ruhmkorff coil and carry out weak atomization water-cooled, obtain needed large-diameter thin-wall seamless steel pipe.

The mechanical property of steel pipe is in Table 2.

Table 2 mechanical properties of pipe

Material	σs（Mpa）	σb（Mpa）	δ（%）
				The large-caliber thin-walled hot-expanding seamless steel tubes of X65 level	470~520	560~630	≥32
The requirement of PSL1 X65 grade standard	≥450	≥535	≥28

Claims (2)

1. a large-caliber thin-walled X65 level hot-expanding seamless steel tubes, its outer diameter D is: 406 ~ 609 ㎜, tolerance is: +/-0.75%D, wall thickness S is: 6.35 ~ 9.53 ㎜, tolerance is: +/-12.5%S, it is characterized in that: composition, in quality %, specifically has: C:0.24～0.28, Mn:1.25～1.40, V: 0.10～0.13, Al:0.01～0.04, Si:0.45～0.60, P≤0.025, S≤0.015, B≤0.001, all the other are Fe and inevitable impurity.

2. a kind of large-caliber thin-walled X65 level hot-expanding seamless steel tubes according to claim 1, is characterized in that: its concrete production method is as follows:

First smelting scrap steel is become to molten steel, then with addition of required alloy, obtain conforming with the molten steel of steel pipe composition requirement, adopt EBT → LF → VD → CCM explained hereafter circle blank, perforation → tandem rolling → sizing → alignment → sawing by 340 tandem rolling units obtains female pipe for heat expansion, by local Frequency Induction Heating thermal expansion machine, carrying out heat again expands, heat expands temperature below AC1 line, actual hot-expanding pipe temperature is controlled at 710 ~ 730 ℃, at steel pipe, add when thermal expansion goes out 300 ㎜ section after ruhmkorff coil and carry out weak atomization water-cooled, obtain needed large-diameter thin-wall seamless steel pipe.