CN104278204A

CN104278204A - Molybdenum-free pipe coiled plate with excellent low-temperature fracture toughness and production method thereof

Info

Publication number: CN104278204A
Application number: CN201310285066.5A
Authority: CN
Inventors: 张英慧; 黄国建; 安晓光; 黄明浩; 孔祥磊
Original assignee: Angang Steel Co Ltd
Current assignee: Angang Steel Co Ltd
Priority date: 2013-07-08
Filing date: 2013-07-08
Publication date: 2015-01-14
Anticipated expiration: 2033-07-08
Also published as: CN104278204B

Abstract

The invention discloses a molybdenum-free pipe coiled plate with excellent low-temperature fracture toughness and a production method thereof. The pipe coiled plate comprises, by weight, 0.02-0.08% of C, 0.10-0.50% of Si, 1.50-1.75% of Mn, less than or equal to 0.020% of P, less than or equal to 0.005% of S, 0.03-0.08% of Nb, 0.010-0.050% of V, 0.005-0.050% of Ti, 0.10-0.50% of Cr, 0.010-0.050% of Als, less than or equal to 0.0080% of N, and the balance Fe and inevitable impurities. The production method comprises the following steps of molten iron pretreatment, converter smelting, external refining, continuous casting, casting blank heating, controlled rolling, controlled cooling, and coiling.

Description

A kind of pipeline roll bending excellent without molybdenum low temperature fracture toughness and production method thereof

Technical field

The invention belongs to high-strength low-alloy steel field, relate to specifically a kind of without molybdenum, there is good low temperature fracture toughness L485MB hot-rolled coil and production method thereof.

Background technology

Sweet natural gas, as the geseous fuel of a kind of high fuel value and relative clean environmental protection, is one of important energy source pillar of national economy.In recent years, along with Sweet natural gas exploitation, exploit to desert, the remote districts such as polar region and ocean extend, long distance pipeline not only will through tundra, the landslide geology such as band, seismic zone and the very complicated area of weather condition, to the reliability of pipe line steel and cost-effectiveness requirement high.

LNG(natural gas liquids) become a kind of major way of China's inlet natural gas, domestic LNG(natural gas liquids) receiving station's building-up work moves forward steadily, for ensureing that long distance carries out the high-pressure delivery of combustion gas safely, pipeline needs to possess good crack arrest characteristic, and these provide opportunity for we develop low-temperature flexibility pipe line steel.

Simultaneously, because of steel industry starting material as iron ore, coal price rise steadily, steel industry production cost constantly increases, under these circumstances, exploitation low-alloy, high strength, high tenacity Hi-grade steel pipe line steel just become the Main Means reducing production cost, so also can create more economic benefit for enterprise.

So far, consult domestic patent documentation in X70/L485MB pipe line steel, the patents list retrieving the degree of correlation larger is as follows:

1) grant number is CN1746326, name is called the Chinese patent of " acicular ferrite type X70 pipe line steel and the manufacture method thereof with high arrest toughness ", and its chemical composition is C 0.020-0.060%, Si 0.100-0.500%, Mn 1.45-1.75%, P 0.004-0.012%, S≤0.002%, Nb 0.050-0.080%, Ti 0.005-0. 025%, V 0.010-0.060%, Mo 0.10-0.30%, Cu≤0.30%, Ni≤0.30%, Ca 0.0015-0.0040%, N≤0.0080%, Al _total0.015-0.045%, this Composition Design not only increases production cost, but also only can meet the requirement of-15 DEG C of DWTT fracture toughness propertyes;

2) publication number is CN1927486A, in embodiment described in the Chinese patent that name is called " manufacturing technique of low compression ratio high grade pipe line steel ", X70 pipe line steel composition is C 0.03-0.06%, Si 0.15-0.3%, Mn 1.55-1.60%, P < 0.01%, S < 0.002%, Nb 0.03-0.05%, Ti 0.015-0.025%, Mo 0.15-0.25%, only can meet-15 DEG C of DWTT SA >=90%;

3) publication number is CN101684539A, name is called the Chinese patent of " a kind of thick-specification high-tenacity X 70 acicular ferrite pipe line steel and manufacture method ", its chemical composition is C 0.03-0.06%, Si 0.15-0.25%, Mn 1.55-1.75%, P 0.012-0.020%, S≤0.003%, Cu 0.20-0.35%, Cr 0.20-0.35%, Nb 0.06-0.08%, Ti 0.01-0.02%, Als≤0.050%, Mo 0.20-0.30%, only meets-15 DEG C of DWTT SA >=90%;

4) publication number is CN101519752A, name is called the Chinese patent of " low-carbon high-niobium chromium series high strength high tenacity pipeline steel roll and manufacture method thereof ", X70 pipe line steel chemical composition C 0.01-0.06% described in this patent, Si 0.10-0.40%, Mn 1.00-1.80%, P≤0.018%, S≤0.004%, Ti 0.005-0.030%, Nb 0.08-0.18%, Cu≤0.30, Mo 0.08-0.20%, Cr 0.10-0.35%, Al 0.01-0.06%, N 0.002-0.008%, adding of Mo and Cu alloy not only increases design cost, and, it only can meet-10 DEG C of DWTT SA >=90%,

5) application number is CN201110147542.8, name is called the Chinese patent of " a kind of low-cost X 70 pipeline steel plate and preparation method thereof ", chemical composition C 0.061-0.095%, Si 0.10-0.45%, Mn 1.45-1.85%, P≤0.014%, S≤0.004%, Alt0.01-0.06%, Nb 0.02-0.039%, Ti 0.01-0.02%, N≤0.008%, although it adopts without molybdenum Composition Design, still only meet-15 DEG C of DWTT SA >=90%;

6) application number is CN201110369856.2, in the Chinese patent that name is called " a kind of pipeline steel X 70 hot-rolled plate containing Cr and production method ", chemical composition C 0.030-0.080%, Si 0.10-0.40%, Mn 1.55-2.00%, P≤0.015%, S≤0.0050%, Nb 0.035-0.060%, Ti 0.008-0.025%, Alt 0.020-0.060%, N≤0.008%, although it adopts without molybdenum Composition Design, it also only meets-15 DEG C of DWTT fracture toughness property index requests;

7) application number is CN200910011961.1, name is called the Chinese patent of " a kind of high-strength economical X 70 pipeline steel hot-rolling flat plate and production method thereof ", chemical composition C 0.02-0.08%, Si 0.10-0.35%, Mn 1.40-1.70%, P≤0.020%, S≤0.005%, Nb 0.04-0.07%, Ti 0.008-0.030%, Als 0.020-0.045%, although it adopts without the economical Composition Design of molybdenum, add Ni simultaneously, Cr, one or more elements of Cu, wherein Ni≤0.30, Cr≤0.20, Cu≤0.20, only can meet-15 DEG C of DWTT fracture toughness property index requests,

8) patent publication No. is JP2003064418(A), KR20030053767(A), UA12217(U) and foreign patent CA2775043(A1) in, all containing one or more alloying constituents in Mo, Ni, Cu, only meet-15 DEG C of DWTT SA >=85%.

The X70/L485MB pipe line steel that patent describes in sum only meets-15 DEG C and above DWTT fracture toughness property index request, all do not possess-20 DEG C of DWTT fracture toughness property crack arrest abilities, therefore, the pipe line steel of exploitation-20 DEG C and following excellent in low temperature toughness is significant.

Summary of the invention

The object of the invention is to for the problems referred to above, provide a kind of pipeline roll bending excellent without molybdenum low temperature fracture toughness, its feature is that alloy content is low ,-20 DEG C of DWTT excellent in low temperature toughness, and its-25 DEG C of DWTT SA >=90%.

The object of the invention is to be achieved through the following technical solutions.

A kind of pipeline roll bending excellent without molybdenum low temperature fracture toughness and production method Composition Design alloy content low, chemical component weight percentage ratio is: C 0.02-0.08%; Si 0.10-0.50%; Mn 1.50-1.75%; P≤0.020%; S≤0.005%; Nb 0.03-0.08%; V 0.010-0.050%; Ti 0.005-0.050%; Cr 0.10-0.50%; Als 0.010-0.050%; N≤0.0080%, surplus is Fe and is inevitably mingled with.

Wherein principal element content proportion design principle is as follows:

C content of the present invention is 0.02-0.08%, and carbon is the strengthening element of economy the most basic in steel, have obvious effect, but the raising of carbon content can worsen its toughness and weldability by solution strengthening and precipitation strength to raising pipeline steel strength; Reduce carbon content, not only can prevent the generation of niobium carbide, during heating of plate blank, have more content of niobium to be dissolved in austenite, can ensure that steel has high toughness, plasticity, excellent welding property and hic resistance and anti-SSC ability simultaneously.Low-carbon (LC) can also reduce segregation.

Si content of the present invention is 0.10-0.50%, plays solution strengthening and improves steel tensile strength.

Mn content of the present invention is 1.50-1.75%.Manganese compensates the loss of strength caused because carbon content reduces in pipe line steel.High Mn can promote acicular ferrite nucleating, and high Mn/C ratio can improve yield strength and impelling strength, reduces the size of carbide precipitate, promotes precipitation strength effect.

Nb content of the present invention is 0.03-0.08%.Niobium can improve austenite recrystallization temperature, realizes high temperature rolling, can reduce mill load like this and enhance productivity.Like this can by postponing austenite to ferritic transformation, improve NbC in the volume fraction of bainite and ferrite and separate out and obtain additional strengthening effect, finally obtain high strength, mechanical property that high tenacity coordinates.

V content in the present invention is 0.010-0.050%.Vanadium has higher precipitation strength effect and more weak Grain Refinement Effect, and in the present invention's design during Nb, V, Ti tri-kinds of microalloy element compound uses, wherein vanadium mainly improves the intensity of steel by precipitation strength.

Ti content in the present invention is 0.005-0.050%.Titanium is strong nitrogen killer, in the process of sheet billet continuous casting, utilizes titanium fixed nitrogen can form TiN precipitated phase that is tiny, high-temperature stable, the Austenite Grain Growth that this particle can effectively stop strand to reheat to cause.

Cr content of the present invention is 0.10-0.50%.Chromium can suppress the formation of proeutectoid ferrite, extend the incubation period of ferrite forming core, reduce the growth rate of ferrite crystal grain, and it is less to the postponement of bainite transformation, reduce the temperature of the maximum velocity of transformation of bainite, make more easily bainite transformation to occur under identical cooling conditions, in addition, chromium also has solution strengthening, and acidic conditions reduces the effect of corrosion speed.

Production method of the present invention adopts the CSP technological process of production, and concrete steps are: hot metal pretreatment-converter smelting-external refining-continuous casting-strand heating-controlled rolling-controlled cooling model-batch, and Working Procedure Controlling level is as described below with effect.

Hot metal pretreatment Main Function in the present invention improves Molten Steel Cleanliness, reduces and reduce in molten iron to be mingled with and foreign matter content, for follow-up finished product mechanical property is prepared.

In casting process in the present invention, drop into slighter compress, center porosity and segregation can be reduced.Continuously cast bloom casting speed control is at 1.0-2.0m/s, and slab thickness is 135-170 mm.

External refining operation in the present invention comprises RH+LF two treating processess.By RH process, reduce gas content, [H]≤10ppm; During LF process, carry out line feeding Ca process, line feeding amount >=800m, make the abundant nodularization of inclusion, thus ensure that finished product clamp foreign material are all not more than 2.0 grades.

Strand in the present invention mainly adopts the temperature dress technique of more than 550 DEG C, and slab heating temperature controls at 1100-1250 DEG C, is more than 150 minutes in stove soaking time.

The operation of rolling in the present invention comprises roughing and finish rolling, and before roughing, ensure plate surface quality through dephosphorize by high pressure water, roughing starts temperature and controls more than 1000 DEG C, and take vertical, horizontal tandem rolling, draught is more than 55%; It is 1050-950 DEG C that finish rolling starts rolling temperature, and finishing temperature is 900-750 DEG C, and previous three passes adds up draught up to more than 70%; Section cooling section takes collector to concentrate cooling, and cooling rate is 10-25 DEG C/s, and coiling temperature is within the scope of 600-450 DEG C, and air cooling is to room temperature subsequently.

Production technique of the present invention illustrates:

Slab heating temperature is 1100 ~ 1250 DEG C.For making the Secondary phase particle such as alloy element Nb, V, Ti fully separate out, playing the effect of refined crystalline strengthening, Nb, V, Ti alloy back dissolving in strand be made as far as possible in steel.1180 DEG C time, Nb precipitation particles most of back dissolving in strand.1250 DEG C time, the Nb precipitation particles back dissolving degree in steel close to saturated, and Heating temperature more than 1250 DEG C after, original austenite grains degree will be grown up rapidly, therefore determines that slab heating temperature is 1100 DEG C ~ 1250 DEG C.

Finish rolling start rolling temperature is higher than 1000 DEG C, and the not easily refinement of finished product crystal grain, refined crystalline strengthening effect is bad.Lower than 950 DEG C, then increase the load of finishing stand, easily cause industrial accident; Regulation finishing temperature, more than 750 DEG C, can be avoided making mill load excessive in two-phase region rolling, and it is interval to avoid the restive texturing temperature of template, and can reduce steel plate and indulge lateral performance difference.But finishing temperature is higher than 900 DEG C, grain refining is not enough, affects strengthening effect.

The L485MB hot-rolled coil of the excellent in low temperature toughness that the present invention produces, from Composition Design cost, replaces Mo with Nb and does not add Ni, Cu alloying element, thus decreasing alloy designs cost; Simultaneously by taking corresponding production and rolling technology design, it is made to reach API 5L standard-required, especially-25 DEG C of DWTT SA >=90%, not only meet the need of market, for enterprise brings certain economic benefit and social benefit, and contribute for the development of domestic low-temperature flexibility pipe line steel.

Accompanying drawing explanation

Fig. 1 is the organization chart of embodiment 1;

Fig. 2 is embodiment 1-25 DEG C of DWTT fracture micro-appearance figure.

Embodiment

Introduce the embodiment that L485MB hot-rolled coil is concrete below, embodiment chemical composition is in table 1, and technique implementation status is in table 2, and mechanical property is in table 3.

Table 1 L485MB hot-rolled coil embodiment chemical composition (wt%)

Sequence number	C	Si	Mn	P	S	Nb	V	Ti	Cr	Als	N
												1	0.046	0.35	1.72	0.012	0.003	0.071	0.023	0.015	0.21	0.018	0.0048
2	0.054	0.37	1.70	0.013	0.002	0.056	0.021	0.023	0.18	0.037	0.0056
												3	0.062	0.38	1.63	0.015	0.002	0.064	0.035	0.012	0.20	0.029	0.0033
4	0.058	0.38	1.68	0.011	0.002	0.045	0.041	0.022	0.35	0.045	0.0028
												5	0.046	0.45	1.71	0.013	0.004	0.050	0.045	0.037	0.47	0.027	0.0026
6	0.028	0.28	1.58	0.010	0.002	0.038	0.040	0.025	0.37	0.021	0.0067
												7	0.078	0.25	1.58	0.008	0.003	0.047	0.039	0.018	0.38	0.035	0.0048
8	0.023	0.49	1.73	0.011	0.004	0.062	0.038	0.034	0.38	0.041	0.0055
												9	0.045	0.36	1.69	0.009	0.002	0.059	0.029	0.049	0.45	0.045	0.0044
10	0.067	0.18	1.53	0.014	0.003	0.035	0.031	0.026	0.28	0.040	0.0037

Note: surplus is iron and inevitable impurity.

Table 2 L485MB hot-rolled coil embodiment production technique

Sequence number	Specification, mm	Heating temperature, DEG C	Finish rolling entrance, DEG C	Finish to gauge, DEG C	Cooling rate, DEG C/s	Batch, DEG C
							1	8	1100-1250	1020	850	25	450-600
2	8	1100-1250	980	820	18	450-600
							3	8	1100-1250	1000	800	15	450-600
4	10	1100-1250	1050	780	10	450-600
							5	10	1100-1250	950	750	15	450-600
6	10	1100-1250	1024	831	22	450-600
							7	12	1100-1250	1037	798	17	450-600
8	12	1100-1250	1029	820	20	450-600
							9	12.5	1100-1250	1010	817	14	450-600
10	12.5	1100-1250	989	825	19	450-600

Table 3 L485MB hot-rolled coil embodiment 30 ° of direction mechanical properties

Note: tension specimen adoption rate sample.

Fig. 1 is the acicular ferrite structure of L485MB hot-rolled coil, and Fig. 2 is L485MB hot-rolled coil fracture micro-appearance.

Claims

1. without the pipeline roll bending that molybdenum low temperature fracture toughness is excellent, it is characterized in that: chemical component weight percentage ratio is: C0.02%-0.08%; Si0.10%-0.50%; Mn1.50%-1.75%; P≤0.020%; S≤0.005%; Nb0.03%-0.08%; V0.010%-0.050%; Ti0.005%-0.050%; Cr0.10%-0.50%; Als0.010%-0.050%; N≤0.0080%, surplus is Fe and is inevitably mingled with.

2. a pipeline roll bending production method excellent without molybdenum low temperature fracture toughness according to claim 1, comprise hot metal pretreatment-converter smelting-external refining-continuous casting-strand heating-controlled rolling-controlled cooling model-batch, it is characterized in that: external refining comprises RH+LF, RH process ensures [H]≤10ppm; During LF process, carry out line feeding Ca process, line feeding amount >=800m, ensure that finished product clamp foreign material are all not more than 2.0 grades; Continuously cast bloom casting speed control is at 1.0-2.0m/s, and slab thickness is 135-170 mm; Strand adopts the temperature dress technique of more than 550 DEG C, and slab heating temperature controls at 1100-1250 DEG C, is more than 150 minutes in stove soaking time; Roughing starts temperature and controls more than 1000 DEG C, and take vertical, horizontal tandem rolling, draught is more than 55%; It is 1050-950 DEG C that finish rolling starts rolling temperature, and finishing temperature is 900-750 DEG C, and previous three passes adds up draught up to more than 70%; Section cooling section takes collector to concentrate cooling, and cooling rate is 10-25 DEG C/s, and coiling temperature is at 600-450 DEG C, and air cooling is to room temperature subsequently.