CN102534429A - High-strength low-yield ratio X90 hot-rolled steel plate and production method thereof - Google Patents

Abstract

The invention provides a high-strength low-yield ratio X90 hot-rolled steel plate and a production method thereof, and belongs to the technical field of high-strength pipeline steel production. The hot-rolled steel plate comprises the following chemical constituents by weight percent: 0.02 to 0.07 percent of C, 0.10 to 0.40 percent of Si, 1.40 to 1.54 percent of Mn, 0 to 0.012 percent of P, 0 to 0.003 percent of S, 0.02 to 0.06 percent of Alt, 0.05 to 0.10 percent of Nb, 0.008 to 0.040 percent of Ti, 0.20 to 0.35 percent of Cr, 0.20 to 0.35 percent of Mo, 0 to 0.008 percent of N, 0 to 0.0002 percent of H, and Fe and unavoidable impurity elements in balancing amount. The production method comprises the following steps: revolving furnace smelting, outside furnace refining, heating, dephosphorizing, rolling, super-fast cooling and the like. The hot-rolled steel plate has the advantages that the tenacity of the product is excellent; the weldability and the self-crack arrest capability are favorable; and the engineering construction cost can be reduced.

Description

HS low yield strength ratio X90 hot-rolled steel sheet and working method thereof

Technical field

The invention belongs to the high-strength line-pipe steel production technical field, particularly relate to a kind of HS low yield strength ratio X90 hot-rolled steel sheet and working method thereof, be used for the transport pipe construction of oil, Sweet natural gas.

Background technology

The world energy sources pipe-line construction is towards long distance, strong, the high-pressure delivery development of superelevation; Progress along with X100 and X120 exploitation; 2002, API and ISO formulated new job simultaneously, its objective is the superstrength grade of steel that in API 5L and ISO 3183, increases from X90 to X120.These three steel of X90, X100 and X120 have been put into the API Spec 5L pipeline steel tube standard the 44th edition of issue in 2007, and the strong pipe line steel of superelevation has strided forward major step to its final practical application.

In recent years, China has obtained major progress in the exploitation of X70/X80 high-strength line-pipe steel, at international pipeline circle from becoming the leader with the runner.Answer China's Economic development requirement at present, have every year the source of the gas amount of nearly 1,100 hundred million m3 be badly in need of to carry, and along with the rapid raising of Xinjiang gas maked coal production capacity, the source of the gas amount is still increasing.Be badly in need of building up the requirement that gas transmission is satisfied in many pipework during " 12 ".And because Hexi Corridor restricted width, land acquisition, resident's resettlement, with aspects such as local government's coordinations, operation maintenance, must most reduce number of tubes to greatest extent, raising single tube transport capacity.Therefore improving pipe-line transportation pressure, grade of steel and wall thickness becomes essential technological line.And aspect the exploitation of superstrength pipeline steel tube, China with abroad in weldability with from having a long way to go aspect the researchs such as arrest toughness.

For exploring the required high-new pipe line steel tackling of key scientific and technical problems scheme of the extensive pipe-line construction of China of formulating; During the 2010-2011; Inside and outside pipeline industry of organizing nation of group of CNPC and metallurgy industry expert hold repeatedly technological demonstration meeting, gas pipe line Intensity Design coefficient during China " 12 " and X90/X100 high-strength line-pipe steel Application and Development are studied great special project be expounded through peer review.Expert group has proposed valuable advices and suggestion to technical indicator setting, innovation system construction, safeguards etc.; Suggestion " research of gas pipe line Intensity Design coefficient " and " X90/X100 high-strength line-pipe steel technological development application " problem is set up the project as early as possible; Carry out the design in early stage and the X90/X100 technical preparation of western three-way one-level area 0.8 design ratio, and consider to carry out extensive pipe-line construction in China.One type of regional design ratio of gas pipe line improves 0.08 percentage point, can practice thrift the tubing consumption and reduce engineering construction cost 10%.The development and application of the strong X90/X100 pipe line steel of superelevation can effectively improve pipeline operation efficiency, reduces thickness of steel pipe, reduces engineering cost.

Though three superstrength pipe line steel rank X90, X100 and X120 have been put into API5L and ISO 3183 standards simultaneously in 2007, its progress has nothing in common with each other.X90 is the middle grade of steel of X80 and X100 strength grade, the thing that the development and application of X90 is seemingly natural, however practical situation are really not so.In the numerous pipeline academic conference in the whole world, can't see paper and the relevant report of relevant X90 all the time, yet the research and development of X100 and X120 once become focus, and accomplishing the construction of some test sections in succession.

Consider China's practical situation, in the exploitation that should fully pay attention to X90 aspect the superstrength Pipeline Steel Development.As being feasible from X80 to make a leapleap forward ideal transition point and through-station of X100, and itself also has good economic benefits with the exploitation of X90.Therefore develop the X90 pipe line steel and the Technology thereof of good-toughness, significant.

Summary of the invention

The object of the present invention is to provide a kind of HS low yield strength ratio X90 hot-rolled steel sheet and working method thereof, toughness of products is good, and has good weldability and from the crack arrest ability, can reduce the engineering construction cost.

Said steel plate chemical ingredients of the present invention is: C:0.02～0.07%, Si:0.10～0.40%, Mn:1.40～1.54%, P :≤0.012%; S :≤0.003%, Alt:0.02～0.06%, Nb:0.05～0.10%; Ti:0.008～0.040%, Cr:0.20～0.35%, Mo:0.20～0.35%; N :≤0.008%, H :≤0.0002%, surplus is Fe and inevitable impurity element; Be weight percentage.

Adopt above-mentioned chemical composition design, through two stages controlled rolling+supper-fast cooling technology, the present invention has prepared the X90 steel plate, and ys reaches more than the 625MPa, and tensile strength is more than 695MPa, and yield tensile ratio is below 0.91;

Summer is than impacting toughness :-20 ℃, and full-scale 10 * 10 * 55mm v-notch sample, Charpy-V impact power (CNV) >=320J, the summer is than impacting shear area >=90%.

Block hammer performance :-20 ℃, the total wall thickness sample shear area (DWTT SA) >=85% of dropping hammer.

Preparing method of the present invention comprises operations such as converter smelting, external refining, heating, de-scaling, rolling, supper-fast cooling; The following technical parameter of control in technology:

(1) steel billet is heated to 1150-1220 ℃, the steel billet upper and lower surfaces temperature difference≤20 ℃;

(2) steel billet carries out high-pressure water descaling, and the de-scaling water pressure is controlled at 21～26MPa;

(3) steel billet is rolled in two stages; The fs start rolling temperature is controlled at 1050-1100 ℃; Temperature is treated in the centre, and time of staying temperature is controlled at 100-200s, and the subordinate phase start rolling temperature is controlled at 870-900 ℃; Finishing temperature is controlled at 821-850 ℃ of scope, and subordinate phase single pass draft all is controlled at the 10-30% scope;

(4) carry out supper-fast cooling behind the hot-rolled steel plate, final cooling temperature is controlled at 300-400 ℃, and speed of cooling is controlled at 31-40 ℃/s.

The formation main points of content of the present invention are based on following understanding:

The C element is effective to improving armor plate strength; But its low-temperature impact toughness and weldableness thereof have been reduced simultaneously; Because the strong X90 pipe line steel of superelevation requires relatively strictness to toughness levels and weldability, so the content of carbon is controlled at than in low carbon content 0.02～0.07% scope.

Mn improves intensity through solution strengthening, also can reduce γ-α transformation temperature, and then the refinement ferrite crystal grain.But well-known, Mn is prone to segregation element, can cause the strand center segregation serious; And cause steel plate heart portion banded structure serious; Cause anisotropy, cause impact fracture layering or brittle failure to occur, reduce the low-temperature flexibility performance and the anti-HIC performance of steel plate greatly; Especially for the superstrength steel grade, it is harmful to low-temperature impact toughness to add too much Mn.

The bainitic transformation control element that Mo is stronger.In high strength microalloy steel, add an amount of Mo element and just can obtain tangible bainite structure, because of phase transformation changes to the low temperature direction, can make the further refinement of phase-change organization simultaneously, significantly improve the toughness and tenacity of steel, also can effectively reduce yield tensile ratio simultaneously.In the strong X90 pipe line steel of superelevation, through adding a certain amount of Mo alloy, realize the phase transformation strengthening effect, improve the strength stability and its low-temperature impact toughness of raising of X90 pipe line steel.Therefore Mo content is controlled at 0.20～0.35% scope among the present invention, has obtained tiny and uniform bainite structure and good toughness and tenacity.

The Cr alloy has the effect of similar Mo alloy; Can suppress proeutectoid ferrite and generate, move the ferritic phase varied curve, realize the phase transformation strengthening effect to the lower right; Reduce starting temperature of transformation simultaneously; The refinement bainite structure improves the strength stability and its low-temperature impact toughness of raising of X90 pipe line steel, and significantly reduces the yield tensile ratio of material.The present invention has carried out a large amount of tests, and through adding different Cr content, find: be accompanied by the raising of the content of Cr, the tensile strength of steel plate increases substantially, and the yield tensile ratio of material obviously reduces, and sees shown in the accompanying drawing 3.Therefore Cr content is controlled at 0.20～0.35% scope among the present invention, is not influencing under the flexible prerequisite, has obtained the low yield strength ratio of X90 pipe line steel, the most important thing is that the Cr alloy is very cheap, and is favourable to reducing cost.

The present invention adopts the foundation of this production technique to be:

Through the homogeneity of control slab heating temperature and upper and lower surfaces temperature, effectively control the size and the homogeneity of original austenite grains, be that follow-up operation of rolling plate shape control is favourable simultaneously.Facts have proved,,, in the operation of rolling, occur easily upwarping or the phenomenon of button down, cause steel-fastening or milled sheet shape too poor, useless or accident occur rolling when the steel billet upper and lower surfaces temperature difference during greater than 30 ℃ for the HS steel grade;

A high-pressure water descaling is adopted in steel billet tapping back; Control de-scaling water pressure is effectively removed the iron scale of billet surface at 21～26MPa, helps the accurate measurement of steel billet temperature on the one hand; Can avoid being pressed into of operation of rolling iron scale on the other hand, cause the plate surface quality problem;

Control fs start rolling temperature and finishing temperature make abundant refinement of austenite crystal and homogenizing; Subordinate phase adopts low temperature controlled rolling, control start rolling temperature and finishing temperature, and the single pass draft of assurance subordinate phase is in the 10-30% scope; Make full use of the low temperature controlled rolling and depress effect greatly; In hardened austenite inner accumulation dislocation, for follow-up phase transformation provides more forming core point, finally through rolling back entry fast; Obtain refinement, uniform bainitic transformation tissue, improve the intensity and the low-temperature flexibility of X90 steel plate.

Go into water temp, final cooling temperature and speed of cooling through the control steel plate, utilize the limit cooling power of ultrafast cool equipment, fully the crystal grain of refinement steel plate; Make the toughness and tenacity of steel plate reach a coupling preferably; Tensile strength is high, and yield tensile ratio is low, and the summer is than impacting good-toughness.

X90 hot-rolled steel sheet performance of the present invention reaches following level:

(1) tensile property: ys reaches>=625MPa, and tensile strength reaches>=695MPa, and yield tensile ratio reaches≤0.91 scope.

(2) toughness properties: 10 * 10 * 55mm sample summer of-20 ℃ than v-notch ballistic work more than 320J ,-20 ℃ block hammer performance (DWTT) average shear area >=85%.

The invention has the advantages that: X90 steel plate provided by the invention has from arrest toughness and good weldableness, can be widely used in the oil and gas pipeline engineering construction, and the construction cost that reduces line of pipes is had obvious effect.

Description of drawings

Fig. 1 is an optics Electronic Speculum organization chart of the present invention.

Fig. 2 is an ESEM organization chart of the present invention.

Fig. 3 for different Cr content among the present invention to the steel plate effects of tensile strength.

Embodiment

The HS low yield strength ratio X90 hot-rolled steel sheet and the working method thereof of good-toughness are smelted in 100 tons of converters according to the present invention, and controlled rolling is carried out in refining on 100 tons of RH refining furnaces on the 4300mm milling train, on ultrafast cold UFC, control cold.Through embodiment the present invention is done further description below.Embodiment light plate chemical ingredients is seen table 1, and the embodiment process system is seen table 2, and the embodiment mechanical property is seen table 3:

The embodiment chemical ingredients

Table 1. X90 hot-rolled steel sheet of the present invention embodiment chemical ingredients (wt%)

The embodiment process system

Table 2. X90 hot-rolled steel sheet of the present invention embodiment process system

The embodiment mechanical property

The metallographic structure of the X90 hot-rolled steel sheet that the present invention produces is even, tiny bainite structure form, with reference to accompanying drawing 1,2.Embodiment steel plate mechanical property is as shown in table 3 below.

Table 3. embodiment X90 hot-rolled steel sheet mechanical property

The present invention is through adopting special alloy formula; Utilize ultrafast device for cooling (UFC), realize the very low temperature phase transformation, fully refinement phase-change organization; Improve the intensity and the toughness of X90 pipe line steel; Have from arrest toughness and good weldableness, can be widely used in the oil and gas pipeline engineering construction, the construction cost that reduces line of pipes is had obvious effect.

Claims (3)

1. HS low yield strength ratio X90 hot-rolled steel sheet, it is characterized in that: said steel plate chemical ingredients is: C:0.02～0.07%, Si:0.10～0.40%, Mn:1.40～1.54%; P :≤0.012%, S :≤0.003%, Alt:0.02～0.06%, Nb:0.05～0.10%; Ti:0.008～0.040%, Cr:0.20～0.35%, Mo:0.20～0.35%; N :≤0.008%, H :≤0.0002%, surplus is Fe and inevitable impurity element; Be weight percentage.

2. the HS low yield strength ratio X90 hot-rolled steel sheet of good-toughness as claimed in claim 1, it is characterized in that: the performance of steel plate is:

Ys reaches more than the 625MPa, and tensile strength is more than 695MPa, and yield tensile ratio is below 0.91;

Summer is than impacting toughness :-20 ℃, and full-scale 10 * 10 * 55mm v-notch sample, Charpy-V impact power (CNV) >=320J, the summer is than impacting shear area (SA) >=90%;

Block hammer performance :-20 ℃, the total wall thickness sample shear area (DWTT SA) >=85% of dropping hammer.

3. the preparation method of the described HS low yield strength ratio of claim 1 an X90 hot-rolled steel sheet comprises operations such as converter smelting, external refining, heating, de-scaling, rolling, supper-fast cooling, it is characterized in that: the following technical parameter of control in the technology:

(1) steel billet is heated to 1150-1220 ℃, the steel billet upper and lower surfaces temperature difference≤20 ℃;

(2) steel billet carries out high-pressure water descaling, and the de-scaling water pressure is controlled at 21～26MPa;

(3) steel billet is rolled in two stages; The fs start rolling temperature is controlled at 1050-1100 ℃; Temperature is treated in the centre, and time of staying temperature is controlled at 100-200s, and the subordinate phase start rolling temperature is controlled at 870-900 ℃; Finishing temperature is controlled at 821-850 ℃ of scope, and subordinate phase single pass draft all is controlled at the 10-30% scope;

(4) carry out supper-fast cooling behind the hot-rolled steel plate, final cooling temperature is controlled at 300-400 ℃, and speed of cooling is controlled at 31-40 ℃/s.

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