CN103042039A - Controlled rolling and cooling process for Cr-containing economic X70 pipeline hot-rolled steel coil plate - Google Patents

Abstract

The invention discloses a controlled rolling and cooling process for a Cr-containing economic X70 pipeline hot-rolled steel coil plate. The controlled rolling and cooling process for the Cr-containing economic X70 pipeline hot-rolled steel coil plate is characterized by including the steps: (1) soaking at the heating temperature of 1150-1210 DEG C for not shorter than 120 minutes; (2) distributing rough rolling passes and using 8-10 passes for rough rolling, wherein deformation of each pass is required to be within the range of 10%-20%, and deformation of the last three rough rolling passes is within the range of 10%-20%; (3) distributing finish rolling passes, wherein the rolling temperature of the first pass of finish rolling is not higher than 1050 DEG C, the deformation of the last finish rolling pass is less than 8%, the accumulated deformation of the last two passes is less than 16%, the temperature of final finish rolling ranges from 770 DEG C to 850 DEG C; (4) immediately implementing laminar cooling at the cooling speed higher than 20-25 DEG C/s after finish rolling; and (5) after laminar cooling, coiling to the coil plate via a coiling machine at the coiling temperature of 300-400 DEG C.

Description

The cooling controlling and rolling controlling process that contains Cr economical X 70 pipeline steel hot-rolling coiled sheet

Technical field

The invention belongs to the pipe line steel production technical field, particularly the cooling controlling and rolling controlling process of X70 line steel hot rolling coiled sheet.

Background technology

Produce the Composition Design that the X70 pipe line steel generally adopts ' Nb+Mo ' both at home and abroad, to obtain acicular ferrite structure; Obtain higher low-temperature impact toughness on the one hand, on the other hand, reduce Bauschinger effect, that is, and the decline of material yield strength character behind the minimizing tubulation.In fact, in the industrial production of X70 pipe line steel, even adopt molybdenum element also can not can obtain uniform acicular ferrite structure fully, also can't avoid the generation of Bauschinger effect fully.When serious, the matrix of X70 pipe line steel coiled sheet is the line and staff control of ferrite, granular bainite and a small amount of acicular ferrite of polygon form, and the drop-out value of yield strength makes the yield strength of X70 steel pipe be near or below lower limit 485MPa near 100MPa before and after the coiled sheet tubulation.In addition, in the manufacturing of X70 coiled sheet, adopt molybdenum element, although can suppress polygonal ferrite forms, be more convenient for obtaining acicular ferrite structure, so that manufacturing process is simple and direct feasible, still, the shortcoming of this way also clearly, the molybdenum of every adding 0.10% in steel improves 220～250 yuan of ton steel production costs.

Summary of the invention

The technical problem to be solved in the present invention provides a kind of cooling controlling and rolling controlling process of the Cr of containing economical X 70 pipeline steel hot-rolling coiled sheet, in the situation that satisfy X70 line steel hot rolling coiled sheet performance, significantly reduces production costs.

For solving the problems of the technologies described above, the invention provides a kind of cooling controlling and rolling controlling process of the Cr of containing economical X 70 pipeline steel hot-rolling coiled sheet, it is characterized in that, the chemical component weight percentage (%) of described coiled sheet is: C 0.05-0.075%, Si 0.10%-0.35%, Mn 1.00-1.65%, Nb 0.050-0.080%, Ti 0.010-0.025%, Cr 0.30-0.4%, surplus is iron and inevitable impurity; The cooling controlling and rolling controlling process of described coiled sheet is:

(1) heating-up temperature is 1150～1210 ℃, and soaking time is no less than 120 minutes,

(2) roughing rolling pass is distributed: use 8～10 passage roughing, every time deflection requires between 10～20%, the deflection 17-20% of last 3 passages of roughing,

(3) finish rolling rolling pass is distributed: finish rolling the first passage rolling temperature is not higher than 1050 ℃, and last pass deformation of finish rolling is less than 8%, and last two passage cumulative deformations are less than 16%, 770 ℃-850 ℃ of finish rolling finishing temperatures,

(4) implement immediately laminar flow cooling after the finish rolling, cooldown rate is greater than 20-25 ℃/s,

(5) through after the laminar flow cooling, coil into coiled sheet through coiling machine, coiling temperature 300-400 ℃.

Design philosophy of the present invention is:

Technical scheme of the present invention has following three main points: (1) adopts the low-carbon (LC) Composition Design, carries out Nb-microalloying, adds the chromium element more than or equal to 0.30%; (2) target is to obtain evenly tiny acicular ferrite structure, contains a small amount of granular bainite microstructure, to improve obdurability; (3) reduce to greatest extent S, P, N content by the super clean smelting, reduce the Grain Boundary Segregation of manganese sulfide inclusion and phosphorus with further raising low-temperature impact work.The present invention does not contain the elements such as molybdenum, nickel, copper, vanadium.

The process system of the controlled rolling of X70 pipe line steel of the present invention and control cooling is:

(1) heating-up temperature is 1150～1210 ℃, and soaking time is no less than 120 minutes.

(2) roughing rolling pass is distributed: use 8～10 passage roughing.Every time deflection requires between 10～20%.For refine austenite crystal grain, the deflection of last 3 passages of roughing requires close to 20%; For avoiding roll-force excessive, the deflection of last 3 passages of roughing requires to be not more than 20%.

(3) finish rolling rolling pass is distributed: use hot continuous rolling.Finish rolling the first passage rolling temperature is not higher than 1050 ℃.Require last pass deformation of finish rolling less than 8%, last two passage cumulative deformations are less than 16%.The finish rolling finishing temperature is not higher than 850 ℃, is not less than 770 ℃.Adopt TMCP heat engine tool controlled rolling technique, do not allow arbitrary frame not depress the sky mistake, also do not adopt HTP high temperature rolling technique.

(4) implement immediately the laminar flow cooling after the finish rolling.Between laminar flow cooling and last passage of finish rolling, without other technological measures that specially increases, separate out control phase transformation control, ultrafast cooling device etc. such as relaxation.Cooldown rate is greater than 20 ℃/s.

(5) through after the laminar flow cooling, coil into coiled sheet through coiling machine.The coiling temperature scope is not higher than 400 ℃, is not less than 300 ℃.

The foundation of the TMCP process system of X70 pipe line steel of the present invention is:

X70 pipe line steel of the present invention adopts the mode of ' controlled rolling+acceleration cooling ' to produce, and the acceleration after it is accumulated and roll by the distortion in austenite recrystallization district Deformation recrystallization, austenite non-recrystallization district cools off to obtain best grain refining effect.Microscopic structure is controlled and crystal grain thinning, lower temperature region in austenite recrystallization district and austenite non-recrystallization district is carried out multi-pass rolling, carry out higher cooling velocity (〉=20 ℃/S) under, deformed austenite is changed into tiny uniformly take acicular ferrite as main body, contain the heterogeneous structure that a small amount of granular bainite forms.

The present invention has following technique effect:

(1) X70 pipe line steel of the present invention has more stable intensity and excellent low-temperature impact toughness.

(2) crystallite dimension of X70 pipe line steel of the present invention is tiny, 12～13 grades of grain sizes.

(3) microscopic structure of X70 pipe line steel of the present invention is acicular ferrite, contains a small amount of granular bainite, has quasi-polygonal ferrite and the martensite/austenite of minute quantity.

(4) the yield strength representative value of X70 coiled sheet of the present invention is 530MPa, tensile strength representative value 650MPa, and-20 ℃ of summers are 400J(10 * 10 * 55mm) than V-type ballistic work representative value.Behind the tubulation, the yield strength representative value of economical high tenacity X70 pipe is 510MPa, tensile strength representative value 645MPa.-20 ℃ of Charpy impact sections of shear (SA%) 100% of coiled sheet and steel pipe ,-15 ℃ of DWTT are 100%.

(5) show through the batch production practice, the composition that this patent is designed and technique can reduce cost and steady production X70 pipe line steel coiled sheet effectively, have solved simultaneously Bauschinger effect obviously and the higher problem of alloy designs cost.

Description of drawings

Below in conjunction with accompanying drawing to the detailed description of the invention:

Fig. 1: the 11.1mmh slab is rolled up 1/4 thickness place microscopic structure.

Fig. 2: the 17.5mm slab is rolled up 1/4 thickness place microscopic structure.

The specific embodiment

The chemical composition scope of pipe line steel according to the present invention, through 300 tons of converter smeltings, through ladle argon-blown, the refining of LF stove, RH application of vacuum and continuous casting, again after the heating, enter two frame R1 and R2 roughing, carry out the controlled rolling of heat engine tool through 7 frame 2250mm tandem rolling unit production lines again, roll rear employing pipe line steel steel high strength cooling technique, hot rolling thickness specification 11.1mm, 17.5mm.

The chemical composition of X70 pipe line steel of the present invention sees Table 1, TMCP heat engine tool controlled rolling process system and sees Table 2, and performance sees Table 3～table 5.

Being mingled with of X70 pipe line steel of the present invention, microscopic structure and grain size see Table 6～table 7.

The chemical composition of table 1 X70 pipe line steel of the present invention, wt%

Retort number	Rolling lot number	C	Si	Mn	P	S
							12304041	H120868000	0.075	0.12	1.12	0.014	0.0013
12303829	H120810760	0.051	0.35	1.61	0.013	0.0005
							12303322	H120852020	0.063	0.20	1.38	0.010	0.0007
12303972	H120851580	0.067	0.25	1.55	0.010	0.0007

The chemical composition of continued 1 X70 pipe line steel of the present invention, wt%

Retort number	Rolling lot number	Nb	Ti	N	Als	Cr
							12304041	H120868000	0.067	0.0202	0.0050	0.022	0.35
12303829	H120810760	0.079	0.0248	0.0044	0.024	0.38
							12303322	H120852020	0.051	0.0114	0.0047	0.024	0.31
12303972	H120851580	0.061	0.0137	0.0047	0.023	0.33

The TMCP process system of table 2 X70 pipe line steel of the present invention

The service check result of table 3 X70 pipe line steel of the present invention

Impact property (7.5 * 10 * 55mm) (with rolling to becoming the 30o direction) of table 4 X70 volume of the present invention

Impact property (10 * 10 * 55mm) (with rolling to becoming the 30o direction) of table 5 X70 volume of the present invention

The field trash type (rank) of table 6 X70 of the present invention

The microscopic structure of table 7 X70 of the present invention and grain size

Lot number	Microscopic structure	Prior austenite grain size (level)
			H120868000	Acicular ferrite+granular bainite	13.0
H120810760	Acicular ferrite+granular bainite	12.5
			H120852020	Acicular ferrite+granular bainite	12.0
H120851580	Acicular ferrite+granular bainite	12.0

Claims (1)

1. cooling controlling and rolling controlling process that contains Cr economical X 70 pipeline steel hot-rolling coiled sheet, it is characterized in that, the chemical component weight percentage (%) of described coiled sheet is: C 0.05-0.075%, Si 0.10%-0.35%, Mn 1.00-1.65%, Nb 0.050-0.080%, Ti 0.010-0.025%, Cr 0.30-0.4%, surplus is iron and inevitable impurity; The cooling controlling and rolling controlling process of described coiled sheet is:

(1) heating-up temperature is 1150～1210 ℃, and soaking time is no less than 120 minutes,

(2) roughing rolling pass is distributed: use 8～10 passage roughing, every time deflection requires between 10～20%, the deflection 17-20% of last 3 passages of roughing,

(3) finish rolling rolling pass is distributed: finish rolling the first passage rolling temperature is not higher than 1050 ℃, and last pass deformation of finish rolling is less than 8%, and last two passage cumulative deformations are less than 16%, 770 ℃-850 ℃ of finish rolling finishing temperatures,

(4) implement immediately laminar flow cooling after the finish rolling, cooldown rate is greater than 20-25 ℃/s,

(5) through after the laminar flow cooling, coil into coiled sheet through coiling machine, coiling temperature 300-400 ℃.

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