CN100463993C - Low carbon equivalent micro-alloy steel pipe and on-line normalizing process thereof - Google Patents

Abstract

The invention discloses a on-line normalizing craft of low carbon equivalent microalloy steel pipe, which comprises the following steps: setting the mass percent of steel element as: 0.10-0.14 C, 0.15-0.35 Si,1.30-1.50 Mn, P<=0.015, S<=0.005, Ni<=0.25, Mo<=0.08, Cu<=0.20, 0.020-0.050 Al, 0.05-0.10 V, 0.02-0.06 Nb, Ti<=0.04 and surplus Fe; smelting steel; shaping pipe; processing the pipe; getting the product. This craft can make each index meet the demands of API 5L PSL2 and SSL-5L-95-2 technical regulation, which can save the preparing cost.

Description

Low carbon equivalent micro-alloy steel pipe and online normalizing process thereof

Technical field

The present invention relates to a kind of steel pipe and production technique thereof, particularly a kind of low carbon equivalent micro-alloy steel pipe and online normalizing process thereof.

Background technology

Development along with world economy and petroleum prospecting, drilling and transport trade, the quickening of the general layout process of global economy economic integration, above high grade of steel line pipes such as exploitation X42, X46, X52, X56 and even X60, especially the tube product that adapts to the high added value pipeline of different zones particular requirement, all significant for optimizing product structure and opening up the domestic and foreign markets.According to the different requirements of different zones, tube product also will reach the different standards that require of different zones except satisfying the API5L standard, also will be applicable to the environmental requirement of different areas simultaneously.

For example the SSL-5L-95-2 standard in Iran zone indicates clearly the regulation except intensity, hardness, unit elongation etc. are often referred to, and also other acceptance index such as the chemical ingredients of steel pipe, carbon equivalent, yield strength variation range (narrow), impelling strength, yield tensile ratio, condition of delivery, body size, pipe end geometric accuracy has been proposed more strict index.Specific targets are in detail to following degree:

1, chemical ingredients and carbon equivalent see Table 1:

Table 1 API 5L PSL2 class and Iranian standard SSL-5L-95-2 X52 grade of steel (Wt%)

Element	C	Si	Mn	P	S	Nb+V+Ti	B	Ceq
									Max	0.15	0.35	1.50	0.025	0.005	0.12	0.0005％	0.42

Carbon equivalent calculation formula: Ceq=C+Mn/6+ (Cr+Mo+V)/5+ (Cu+Ni)/15

2, every mechanical property requirements sees Table 2:

Table 2 mechanical property requirements

3, condition of delivery: normalizing or as-normalized condition delivery.

4, steel pipe geometrical dimension:

External diameter tolerance: pipe end :-0.4mm～+ 1.59mm, body: ± 0.75%.

Ovality :≤0.5%

Wall thickness tolerance :-12.5%～+ 15%

Straight degree :≤0.15%

Groove: root face: 1.59mm ± 0.79mm

Chamfering: 30 (0～+ 5 °)

5, other requirements:

Remanent magnetism requires: each port of steel pipe is along circumferentially surveying 4 points at least, and measurement point is answered uniform distribution.When using the Hall gaussmeter to measure, the mean value of four measuring value should not surpass 30 Gausses (3.0mT), and single value is no more than 35 Gausses (3.5mT).

Summary of the invention

For solving the problem that exists in the above-mentioned technology; the purpose of this invention is to provide a kind of low carbon equivalent micro-alloy steel pipe and online normalizing process thereof; be beneficial to adapt to the code requirement of different zones, improve the quality of steel grade and the online normalizing process that adapts to this steel grade quality.

For achieving the above object, technical solution of the present invention provides a kind of low carbon equivalent micro-alloy steel pipe, its steel grades of % is by weight: C:0.10～0.14, Si:0.15～0.35, Mn:1.30～1.50, P :≤0.015, S :≤0.005, Ni :≤0.25, Mo :≤0.08, Cu :≤0.20, Al:0.020～0.050, V:0.05～0.10, Nb:0.02～0.06, Ti :≤0.04, and all the other are Fe.

A kind of online normalizing process of producing above-mentioned low carbon equivalent micro-alloy steel pipe also is provided, and its technology may further comprise the steps:

The smelting of steel: steel scrap, sponge iron and molten iron enter refining furnace and carry out external refining, sampling analysis be fused into molten steel in 150 tons of ultra-high power electric arc furnaces after, and according to analytical results, adjust the content of steel interalloy element; The Clean Steel six machines waterborne six stream curved type continuous caster continuous castings of outgas through the high vacuum degassing stove and to handle the stove high vacuum degassing, take off S, remove inclusion, feeding behind the silk become qualified steel billet.

The moulding of pipe: when steel billet is heated to more than 1280 ℃ in ring furnace; wear into hollow billet by diescher piercer; be rolled into hollow forging through Φ 250mmMPM seven frame retained mandrel continuous mills again; hollow forging is cooled to below 550 ℃ by chain type cooling bed, enters process furnace and carries out reheat (online normalizing), enters 14 frame sizing mills then and carries out hot size; steel pipe is after being cooled to the normal temperature state on the cold bed; crop end enters the vertical cross-roll straightening machine aligning of 6 rollers, enters middle database through behind the magnetic leakage detection.

The processing of pipe: the steel pipe that comes out from middle database; the test pressure of Yao Qiuing carries out the water test as agreed; qualified steel pipe enters the next procedure scale and cuts; pipe end adverse slope mouth; survey then and grow, weigh, spray mark, be coated with rust-inhibiting paint, dry, wear tin hat, go into readys for delivery such as stockyard after becoming qualified product.

Effect of the present invention is to replace the off-line normalizing process by online normalizing process; the every index of the mechanical property of steel pipe all satisfies API 5L PSL2 class and Iranian standard SSL-5L-95-2 demand of technical standard; can reach the effect of off-line normalizing process; saved production cost again; and carbon equivalent has played multiple useful effect also less than 0.42%.

Embodiment

In conjunction with the embodiments low carbon equivalent micro-alloy steel pipe of the present invention and online normalizing process thereof are illustrated.

Low carbon equivalent micro-alloy steel pipe of the present invention hangs down the steel (S≤0.005%) of S content when smelting, more strict than common steel grade.The steel grades of % low carbon equivalent micro-alloy steel pipe is by weight: C:0.10～0.14, Si:0.15～0.35, Mn:1.30～1.50, P :≤0.015, S :≤0.005, Ni :≤0.25, Mo :≤0.08, Cu :≤0.20, Al:0.020～0.050, V:0.05～0.10, Nb:0.02～0.06, Ti :≤0.04, and all the other are Fe.

(359 ~ 430MPa), also requirement can not be above 0.42% for carbon equivalent simultaneously at 71MPa in order to guarantee the yield strength variation range; The geometrical dimension of steel pipe requires need adjust tube rolling part processing parameter than common steel tube strictness; Also will solve owing to adopt magnetic disc suspending, steel pipe is magnetized easily, the remanent magnetism problem; Thereby need on rolling technology, propose a kind of rational operational path and reach the mechanical performance index requirement.

Domestic production X52 grade of steel line pipe is to adopt the off-line normalizing process at present, also can reach the various mechanical performance indexs of Iranian code requirement, but its production process complexity, cycle are long, cost is high (have bad luck expense and thermal treatment expense and add up to 400 yuan/ton).And online normalizing process is that hollow forging is warmed up to 920 ℃ from 500 ℃～550 ℃, online normalizing (normalizing) technology of finishing, and reached the effect same of off-line normalizing.Thereby utilized the waste heat of hollow forging, saved the energy, need not outwards have bad luck, saved overhead charges and shortened the production cycle.The expense of online normalizing is 100 yuan/ton, compares with the off-line normalizing and saves 300 yuan/ton.

With the X52 grade of steel φ 168.3 * 7.1mm specification among the production TPCO-03158E is example, and the main technique step of its production is as follows:

1, the smelting of steel

At existing steel-making, continuous casting process characteristics, adopt low-carbon (LC) to contain manganese steel and be the basis, be aided with the steel grade design that microalloy is strengthened, through rational technology controlling and process, make molten steel composition even, the inside and outside quality of continuously cast bloom meets the requirement of pipeline steel rolling, and tissue that its each element of while is a steel pipe and final performance play a role and get ready.Strengthen intensity and the toughness index that guarantees material for main means with solution strengthening, dispersion-strengthened and crystal grain.Guaranteeing under the prerequisite of material property comprehensively, avoiding as far as possible and using the higher alloying element of carbon equivalent contribution.Guarantee the basic intensity and the toughness of material with the composition combination of lower carbon content and higher manganese content, improve the toughness index of material by the microalloy strengthening principle of carbide forming element V element.

In order to improve the mechanical property of steel pipe, the present invention carries out following technology: the steelworks batching is selected the high-quality steel scrap for use, and every stove should add 45 tons of sponge iron at least, and 45 tons of molten iron are to guarantee the molten steel purity.Tapping forward direction ladle bottom adds two tons of high-quality sweetening agents, and guarantees slag free tapping.In tapping process, add ferromanganese, ferro-vanadium, enter the lower limit of scope of design to guarantee composition to molten steel.

Contain dimension for producing low S,, reduce the impurity element in the steel as far as possible adopting heavy-duty waste steel 40%+30% sponge iron+30% molten iron on the raw material choice.Require the electric furnace slag free tapping simultaneously, add the high-quality sweetening agent in tapping forward direction ladle, refining will have been made alkaline white slag desulfurization ((CaO)+[S]=(CaS)+[O]), and carries out the desulfurization of VD high vacuum degassing and handle.

In order to satisfy the mechanical property requirements of steel pipe, chemical composition design to steel grade is as follows: C:0.10～0.14, Si:0.15～0.35, Mn:1.30～1.50, P :≤0.015, S :≤0.005, Ni :≤0.25, Mo :≤0.08, Cu :≤0.20, Al:0.020～0.050, V:0.05～0.10, Nb:0.02～0.06, Ti :≤0.04, and all the other are Fe.Wherein carbon equivalent Ceq can estimate according to formula.By estimating that we learn carbon equivalent Ceq value between 0.36%～0.41%,, reached the purpose and the effect of low-carbon-equivalent less than 0.42% requirement in the Iranian standard SSL-5L-95-2 standard.

Molten steel is after concise stove carries out alloy fine setting, heats up, and Ying Jing (VD) vacuum outgas is handled, and vacuum pressure remains on below the 0.5Torr, high vacuum time 〉=8 minute.Guarantee that molten steel S content reaches below 0.005%, thereby adapt to the Middle East sour environment.

First straightening roller do not have draught behind the continuous casting, goes out two cold house's temperature and is not less than 1000 ℃, guarantees the inside and outside quality of strand, thereby waters out up-to-standard strand.During the smelting of steel, batching adds sweetening agent when electric furnace steel tapping meticulously, guarantees slag free tapping, VD stove high vacuum time 〉=10 minute, S in the final steel≤0.005%, carbon equivalent Ceq≤0.42.The smelting component of part heat (batch) number sees Table 3.

The smelting component (Wt%) of table 3 part heat (batch) number

Heat (batch) number	C	Si	Mn	P	S	Ni	Cr	Mo	Cu	Al	V	Nb	Ti	C.e.q
															043776	0.11	0.17	1.36	0.011	0.004	0.04	0.02	0.02	0.12	0.011	0.05	0.01	0.01	0.37
043777	0.11	0.22	1.43	0.013	0.004	0.04	0.02	0.01	0.11	0.005	0.05	0.01	0.01	0.37
															043778	0.11	0.20	1.41	0.010	0.005	0.04	0.02	0.01	0.10	0.009	0.05	0.01	0.01	0.37
043779	0.14	0.20	1.40	0.013	0.005	0.04	0.02	0.01	0.11	0.010	0.05	0.01	0.01	0.40
															043780	0.12	0.19	1.40	0.011	0.004	0.04	0.02	0.01	0.11	0.009	0.05	0.01	0.01	0.38
043781	0.12	0.20	1.43	0.011	0.004	0.04	0.02	0.01	0.11	0.010	0.05	0.01	0.01	0.38
															043783	0.12	0.20	1.35	0.010	0.003	0.04	0.03	0.01	0.13	0.010	0.05	0.01	0.01	0.37
043825	0.12	0.20	1.39	0.011	0.004	0.04	0.02	0.01	0.11	0.010	0.05	0.01	0.01	0.38
															043826	0.12	0.19	1.35	0.011	0.004	0.04	0.04	0.02	0.09	0.013	0.05	0.01	0.01	0.38
043827	0.13	0.18	1.38	0.014	0.004	0.04	0.02	0.02	0.11	0.012	0.05	0.01	0.01	0.39
															043828	0.12	0.20	1.42	0.014	0.003	0.04	0.03	0.02	0.11	0.007	0.05	0.01	0.01	0.39
043829	0.12	0.20	1.43	0.015	0.004	0.04	0.03	0.02	0.10	0.008	0.05	0.01	0.01	0.39

By optimization to steel grades, add microalloy element V simultaneously, every mechanical performance index of steel all reaches good effect.Yield strength is controlled in the 70MPa variation range, and ballistic work all more than 100J, shear than reaching 100% by section.Occurrence sees Table 4:

The mechanical property of table 4 part heat (batch) number

Heat (batch) number	Yield strength	Tensile strength	Yield tensile ratio	δ％	Hardness I interior 1	Hardness I interior 2	Hardness I interior 3	0 ℃ of AK (J) is vertical full-scale	Section is sheared and is compared %
										043776	384	526	0.73	37	189	189	192	111	100
043777	392	528	0.74	38	162	164	175	102	100
										043778	398	536	0.74	37	165	168	172	107	100
043779	401	540	0.74	39	193	205	199	114	100
										043780	400	535	0.75	37	189	183	183	105	100
043781	406	535	0.76	37	198	192	183	108	100
										043783	403	535	0.75	37	189	197	194	114	100
043825	389	522	0.75	38	196	199	199	109	100
										043826	400	544	0.74	34	178	166	165	115	100
043827	396	533	0.74	36	163	165	166	121	100
										043828	395	531	0.74	36	172	179	176	111	100
043829	393	529	0.74	36	176	178	177	113	100

2, the moulding of pipe:

In the tube rolling process, the operational path of selecting for use is: when steel billet is heated to more than 1280 ℃, wear into hollow billet by diescher piercer in ring furnace, be rolled into hollow forging through Φ 250mm MPM seven frame retained mandrel continuous mills again.Hollow forging is cooled to below 550 ℃ at chain type cooling bed; go into process furnace and carry out reheat (online normalizing); online normalizing temperature is 920 ℃; that is: use online normalizing process and replaced traditional normalizing process; the performance index that normalizing process can reach have been reached; reduce production process, saved production cost.Steel pipe carries out hot size, cooling, crop end, straightener aligning then, enters middle database through behind the magnetic leakage detection.

For the intensity and impelling strength and the shearing ratio that improve steel, adopting online normalizing temperature is 920 ℃.

In order to guarantee the geometrical dimension of steel pipe, the rolling groove of steel pipe is optimized, for example 114.3, external diameter such as φ 168.3 selects 181 passes for use, φ 219.1 external diameters are selected 235 passes for use.Reducing mill stand is also than producing the many of common steel tube simultaneously.

With φ 210 * 7800mm steel billet is example, the continuously cast bloom sawing of φ 210 * 7800mm is become the length of 3900mm, go into that rotary heating furnace is diathermanous comes out of the stove to 1270 ℃, after dephosphorize by high pressure water and centering, send into the hollow billet that becomes Φ 220 * 32mm with the diescher piercer pierced billet of big godet; Dephosphorization and protection and dephosphorize by high pressure water are sprayed through borax respectively in the inside and outside surface of hollow billet, and seven frame retained mandrels (diameter of mandrel is Φ 166.6) the tandem rolling unit of sending into 181 passes again extends rolling; Hollow forging passes through reheating furnace after taking off pipe by three frame three-roller type winding arbor extraction press groups fast.In order to guarantee the every mechanical performance index of steel pipe, set the reheating furnace temperature, the normalizing temperature is 920 ℃.

Behind 14 frame mini-stretch reducing mill group sizings, become the double chi steel pipe (total length is not less than 26000mm) of φ 168.3 * 7.1mm.Two multiple length hollow forgings enter finishing line through the cold bed cooling, are the pipeline section that is not less than 12200mm by the thick scale of gang saw, after aligning and non-destructive test(ing)(NDT) (N10), its outward appearance, external diameter and wall thickness are surveyed sample again, and qualified steel pipe enters middle database.

3, the processing of pipe:

The steel pipe that comes out from middle database enters the light pipe line; is the steel pipe of 12200 ± 600mm at the light pipe line by tube end cutting machine bed and groove machining tool scale; process through the two ends groove; body is by 3165PSI, 10 seconds the water test of pressurize; and through surveying long weighing; after spraying mark, oven dry, band tin hat and pursuing a check, qualified production tube warehouse-in.

During this products production, all adopt the nylon sling lifting, guarantee that steel pipe remanence reaches standard-required.

Table 3 and table 4 reflect the chemical ingredients and the mechanical property of X52 grade of steel φ 168.3 * 7.1mm specification part heat (batch) number among the TPCO-03158E.The every index of composition and mechanical property all satisfies the requirement of API 5L PSL2 class and Iranian standard SSL-5L-95-2 as can be seen from the table.

4, the detection of product and evaluation

X52 grade of steel line pipe is by the test evaluation of metallographic and inclusion, and mechanical property test, geometric parameter and steel pipe remanence (taking a sample test) all can satisfy the requirement of API 5L PSL2 class and Iranian SSL-5L-95-2 standard.

Claims (2)

1. technology of producing low carbon equivalent micro-alloy steel pipe, this technology may further comprise the steps:

The described low carbon equivalent micro-alloy steel pipe steel grades of % by weight is: C:0.10～0.14, Si:0.15～0.35, Mn:1.30～1.50, P :≤0.015, S :≤0.005, Ni :≤0.25, Mo :≤0.08, Cu :≤0.20, Al:0.020～0.050, V:0.05～0.10, Nb:0.02～0.06, Ti :≤0.04, and all the other are Fe;

The smelting of steel: steel scrap, sponge iron and molten iron enter refining furnace and carry out external refining, sampling analysis be fused into molten steel in 150 tons of ultra-high power electric arc furnaces after, and according to analytical results, adjust the content of steel interalloy element; The Clean Steel six machines waterborne six stream curved type continuous caster continuous castings that process high vacuum degassing stove outgases, takes off behind S, removal inclusion, hello the silk become qualified steel billet;

The moulding of pipe: when steel billet is heated to more than 1280 ℃ in ring furnace, wear into hollow billet by diescher piercer, be rolled into hollow forging through Φ 250mm MPM seven frame retained mandrel continuous mills again, hollow forging is cooled to 500 ℃-550 ℃ by chain type cooling bed, enter reheating furnace and be heated to 920 ℃ of online normalizing temperature, enter 14 frame sizing mills then and carry out hot size, steel pipe is after being cooled to the normal temperature state on the cold bed, crop end, enter the vertical cross-roll straightening machine aligning of 6 rollers, enter middle database through behind the magnetic leakage detection;

The processing of pipe: the steel pipe that comes out from middle database; the test pressure of Yao Qiuing carries out the water test as agreed; qualified steel pipe enters the next procedure scale and cuts; pipe end adverse slope mouth; survey then and grow, weigh, spray mark, be coated with rust-inhibiting paint, dry, wear tin hat, go into readys for delivery such as stockyard after becoming qualified product.

2. low carbon equivalent micro-alloy steel pipe that adopts the described prepared of claim 1.