CN102828125A - Strain design based pipe line steel X70 and its manufacturing method - Google Patents

Abstract

The invention discloses strain design based pipe line steel X70 and its manufacturing method. the steel comprises the following ingredients of: by weight, 0.06-0.10% of C, 0.1-0.6% of Si, 1.0-2.5% of Mn, P being less than or equal to 0.015%, S being less than or equal to 0.003%, Cr being less than 0.1%, 0.05-0.35% of Mo, 0.01-0.15% of Nb, 0.005-0.03% of Ti, 0.01-0.06% of Al, one or two components selected from 0-0.5% of Cu and 0-0.5% of Ni, and the balance Fe and unavoidable microscale impurities. The manufacturing method is characterized in that slab heating temperature is 1050-1280 DEG C by a controlled rolling and controlled cooling method; the temperature for controlled rolling in a recrystallization zone is controlled within the range of 900-1250 DEG C; the temperature for controlled rolling in a non-recrystallization zone is controlled within the range of 700-950 DEG C; initial cooling temperature is 650-800 DEG C; finish cooling temperature is 100-500 DEG C; and cooling rate is 5-35 DEG C/s. According to the invention, elements of V, B and the like are not added, and the total amount of Mo, Cu, Cr and Ni is low. In addition, subsequent heat treatment is not required, the process is simple and requires low cost, and production efficiency is high.

Description

A kind of pipeline steel X70 and method of manufacture thereof based on the strain design

Technical field

The present invention has designed a kind of pipeline steel and method of manufacture thereof, particularly a kind of X70 pipeline steel and method of manufacture thereof based on the strain design.The pipe line steel of using the present invention's preparation can be applied to the line pipe that the X70 grade of steels are adopted at polar region, tundra, seismic zone and deep-sea etc., and various pressurized vessel and engineering machinery are with welding steel.

Background technology

In recent years, the variation of energy structure and to the growth of energy demand has greatly promoted the exploration and the exploitation of new hydrocarbon resources.Big reserves oil field of finding at present and natural-gas field are distributed in special geologic condition zones such as polar region, tundra, seismic zone and deep-sea more.Extensive motion at these regional stratums or seabed ocean current; Pipe line steel not only will bear higher interior pressure; Also must have quite high deformability and strain hardening ability simultaneously, to bear axial crushing deformation and the flexural deformation that causes owing to geofault relative movement, seismic wave propagation, liquefaction of soil, bathycurrent.Obviously, lost efficacy no longer by stress control via such geographic pipeline, and by strain control, simple high-intensity high-tenacity can not be guaranteed the safety of pipeline that pipe line steel also should have good Chinese People's Anti-Japanese Military and Political College adaptability to changes.Based on this, should use based on the strained method of design in the steel for pipe selection design to replace method of design based on stress.

Based on the pipeline steel of strain design,, also Chinese People's Anti-Japanese Military and Political College's adaptability to changes of its vertical performance strict regulation have been made except lateral performance (like intensity, yield tensile ratio, unit elongation, ballistic work, the shear area etc. of dropping hammer) satisfies based on the stress design required standard.The canonical parameter that characterizes Chinese People's Anti-Japanese Military and Political College's adaptability to changes has: high uniform elongation (UEL>=10%), low yield strength ratio (Y/T≤0.85) and the stress-strain(ed) curve that does not have yield point elongation (cupola type).

Based on the pipeline steel of strain design is that pipe line steel develops one of challenging field of tool.At present, the pipe line steel of domestic employing TMCP explained hereafter high-intensity high-tenacity is mature on the whole, and particularly " enforcement of a series of key state projects such as West-east Gas, X70, X80 pipe line steel are used on a large scale.But; Present X70, the X80 level pipeline pipeline steel capital are typical perlite or the acicular ferrite structure of lacking; The corresponding plate property of such types of organization has good intensity and toughness coupling, but its plasticity is not enough, and homogeneous deformation unit elongation UEL is not more than 10%; Yield tensile ratio is mostly more than 0.85, have in addition reach 0.92.Adopt the pipe line steel of traditional TMCP explained hereafter, can not satisfy selection standard based on the strain method of design.

Current; Research based on the pipe line steel of strain design all has report both at home and abroad; But there is following problem: composition and method of manufacture that X80 and above rank two-phase pipe line steel thereof are provided like patent US5545270A, US5531842, US5755895A and CN101456034A etc.; The X70 level pipeline pipeline steel is not related to, and added a large amount of high price metallic element Mo, Ni, Cr etc., be not suitable for the production of high performance-price ratio pipe line steel.Particularly patent US5545270A, US5531842 and US5755895A propose to carry out three stage rolling, have increased an intermediate blank and have treated temperature, have reduced production efficiency; Last rolling need between two-phase region, carrying out, because rolling temperature is low, rolling drag height requires harsh to milling train.Paper Development of a high-deformability linepipe with resistance to strain-aged hardening by HOP (heat-treatment on-line process); JFE Technical Report No.12 (Oct.2008); Relate to composition, the process and performance of X70 large-strain pipeline steel; But the acquisition of its Chinese People's Anti-Japanese Military and Political College's strain characteristics has benefited from follow-up HOP technology.

Summary of the invention

In order to overcome the shortcoming of above-mentioned prior art; But technical problem to be solved by this invention provides and a kind ofly satisfies Chinese People's Anti-Japanese Military and Political College's adaptability to changes X70 level pipeline pipeline of carrying geologic condition abominable area hydrocarbon resources and economical and efficient to produce and use steel, has designed a kind of pipeline steel X70 that designs based on strain and preparation method thereof especially.

The composition plan of pipe line steel of the present invention is compared with traditional X-ray 70, adopts alloying elements such as higher carbon content, a spot of selective interpolation Cu, Ni, Mo, Cr, and adds microalloy elements such as minor N b, Ti.Be organized as the heterogeneous structure of polygonal ferrite and bainite.The polygonal ferrite uniform elongation is high, bainite intensity is good, and suitable two-phase volume(tric)fraction coupling can obtain high uniformly extension, suitable intensity, good toughness, high strain-hardening index and low yield tensile ratio simultaneously.

The content range of each composition by weight percentage among the present invention: C0.06%-0.10%, Si0.1%-0.6%, Mn1.0%-2.5%; P≤0.015%; S≤0.003%, Cr＜0.1%, Mo0.05%-0.35%, Nb0.01%-0.15%; Ti 0.005%-0.03%, Al0.01%-0.06%; Contain among Cu, the Ni one or both, Cu 0%-0.5%, Ni 0%-0.5% simultaneously; Surplus is Fe and micro-unavoidable impurities.

Following with the effect of the main moity of pipe line steel X70 among the present invention based on the strain design:

C: most economical, the most basic strengthening element in the steel; Through solution strengthening and precipitation strength the intensity that improves steel there is obvious effect; But raising C content has negative impact to ductility, toughness and the weldableness of steel, and for this reason, the present invention is set at 0.10% with the C upper content limit.Modern age, the evolution of pipe line steel was the process that constantly reduces C content.Reduce the toughness that C content helps to improve steel on the one hand, can improve the welding property of steel on the other hand.Cross when low when C content, can not give full play to the precipitation strength effect of elements such as Nb, the present invention is 0.06% with C content lower limit set.

Si: adding Si is for deoxidation in the steelmaking process and the intensity that improves matrix.If add excessive Si, the toughness of the welded heat affecting zone of mother metal will significantly reduce, and open-air welding procedure performance also can variation.Therefore, Si content is set at 0.01-0.60% in the present invention.

Mn:, be that compensation reduces the main and most economical strengthening element that causes loss of strength in the pipe line steel because of C content through the intensity of solution strengthening raising steel.Mn still enlarges the element of γ phase region, can reduce the γ → α transformation temperature of steel, helps to obtain tiny phase-change product, can improve toughness, the reduction ductile-brittle transition temperature of steel.For the balance between proof strength and the low-temperature flexibility, the minimum content of Mn is set at 1.0%.Improve the content of Mn, the hardenability characteristic of steel increases, and after content is increased to a certain degree, can cause the welding property especially toughness of severe exacerbation welded heat affecting zone that descends.In addition, too high Mn content also can increase the continuously cast bloom center segregation, and the anisotropy of plate property is increased.Therefore, Mn upper content limit of the present invention is designed to 2.5%.

Nb: be one of topmost element in the modern microalloying pipe line steel, fairly obvious to the effect of grain refining.Separate out the austenitic answer of obstruction deformation, recrystallize through NbC strain inducing in the course of hot rolling; Make the rolling deformation austenite structure in non-recrystallization zone when phase transformation, change tiny phase-change product into through controlled rolling and controlled chilling, so that steel has HS and H.T..The present invention cooperates C content to add the effect of an amount of Nb performance NbC, and the present invention chooses Nb content range 0.01%-0.15%.

Ti: be strong solid N element, the stoichiometric ratio of Ti/N is 3.42, utilizes the Ti fixing N about 30ppm in the steel just about 0.01%, when sheet billet continuous casting, can form the TiN precipitated phase of tiny high-temperature stable.Austenite crystal when this tiny TiN particle can suppress the slab reheat is effectively grown up, and helps to improve the solid solubility of Nb in austenite, improves the impelling strength of welded heat affecting zone.When the content low excessively (as being lower than 0.005%) of Als, Ti can form oxide compound, gives birth to the effect that particle can play intracrystalline ferritic forming core core, refinement welded heat affecting zone tissue in these.In order to obtain this effect, to add 0.005%Ti at least.When the Ti addition surpasses certain certain value, the TiN particle will alligatoring, and the precipitation strength effect of TiC manifests, and causes low-temperature flexibility to worsen.Therefore, the present invention chooses Ti content range 0.005%-0.03%.

The existence of Al:Al also has the effect of thinning microstructure normally as the reductor in the steel.But when the content of Al surpasses 0.06%, thereby the amount of aluminum oxide nonmetal inclusion increases the cleanliness factor that reduces steel.Al content crosses that low then deoxidation is insufficient, and easy oxidation element such as Ti will form oxide compound, so the content lower limit set of Al is 0.01%.

Cr, Mo: be to enlarge the γ phase region; Separate out ferritic earlier when postponing γ → α phase transformation and form, promote the principal element that acicular ferrite forms, phase-change organization plays an important role to control, under certain cooling conditions and finishing temperature, adds in the Ultra-low carbon pipe line steel; Just can obtain tangible acicular ferrite and bainite structure; Because of phase transformation changes to the low temperature direction, can make and organize further refinement simultaneously, structure refinement helps the improvement of low-temperature flexibility.Reasonably combined in order to obtain intensity, plasticity and flexible, the present invention chooses Cr＜0.10%, Mo0.05%-0.35%.

Cu, Ni: can improve the intensity of steel through the solution strengthening effect, Cu can also improve the solidity to corrosion of steel simultaneously, and the adding of Ni mainly is to improve Cu in steel, to be prone to the red brittleness that causes, and useful to low-temperature flexibility.In thick specification pipe line steel, also can compensate the strength degradation that water-cooled undercapacity that the increase because of thickness causes causes.The present invention chooses Cu0%-0.50%, Ni0%-0.50%.

P, S: be unavoidable impurities element in the steel, it is low more good more to hope.From the consideration of smelting cost, again can not be unconfined low.Therefore, the present invention is set at 0.015% and 0.003% with P, S upper content limit.Through ultralow S (less than 30ppm) and Ca processing sulfide is carried out inclusion morphology control, can make pipe line steel have high impelling strength.

Therefore; Have characteristics such as high uniform elongation, low yield strength ratio to ferritic+bainite duplex structure; Be the basis with material reinforcement theories such as grain refining, phase transformation strengthening, precipitation strength and dislocations strengthenings, low-carbon (LC), super low sulfur, Nb, Ti combined microalloying, Mo, Cr alloying and the suitable Cu of adding of control tissue, the composition design of Ni have been adopted in the composition design with the X70 of duplex structure pipe line steel.Hot rolling technology has adopted the hot treat mechanically technology of controlled rolling and controlled cooling, carries out the organizational controls of the finished product through reasonable component and technology, to obtain to have the ferritic+bainite structure of HS, H.T., high uniform elongation and low yield strength ratio.

For guarantee lower yield tensile ratio with than the coupling of high-strong toughness; Except selecting duplex structure's design for use; Also adopted two stages controlled rolling technology in the steel plate production process; Wherein the fs rolling be that the recrystallization zone is rolling, the single pass heavy deformation of these stage at least three passages is not less than 15%, reaches the purpose of abundant refinement original austenite grains; Subordinate phase is rolling to be that non-recrystallization zone is rolling; The cumulative deformation in this stage is not less than 60%; Accomplish ferrite crystal grain refinement and intragranular position dislocation density cumulative task, steel plate rolls the back in the laminar flow process of cooling, adopts specified TR to cooperate corresponding speed of cooling.

Pipe line steel of the present invention adopts following operational path: get the raw materials ready → converter or electrosmelting → external refining → casting → slab reheat → controlled rolling → controlled chilling.

Hot rolling technology is controlled as follows:

(1) slab heating temperature: 1050-1280 ℃;

(2) temperature controlling range of recrystallization zone controlled rolling: 900-1250 ℃;

(3) temperature controlling range of non-recrystallization zone controlled rolling: 700-950 ℃;

(4) begin to cool down temperature: 650-800 ℃;

(5) stop cooling temperature: 100-500 ℃

(6) speed of cooling: 5-35 ℃/s

Concrete steps are:

A) handle carrying out soaking after the as cast condition blank in the set component span of control cleaning, temperature is controlled in 1050-1280 ℃ the scope;

B) blank after coming out of the stove is carried out dephosphorize by high pressure water and handle, remove the iron scale that blank is produced in heat-processed;

C) blank after the dephosphorization is carried out the controlled rolling of two stages immediately, promptly the recrystallization zone is rolling rolling with the non-recrystallization district, accurately controlled rolling temperature and pass deformation and cumulative deformation;

D) steel plate after the finish to gauge carries out air cooling and treats that temperature begins to cool down TR to water-cooled, during the austenitic transformation of 30%-70% for analysing granular ferrite earlier;

E) steel plate after the relaxation is carried out the laminar flow cooling, the steel plate air cooling after the water-cooled is to room temperature.In the water-cooled process, remaining austenitic transformation is a bainite structure, finally obtains proeutectoid ferrite+bainite duplex structure.

The steel plate of the proeutectoid ferrite that finally obtains+bainite duplex structure; It is 485-630MPa that its transverse mechanical performance can reach following requirement: ys Rt0.5; Tensile strength Rm is 570-760MPa; Yield tensile ratio Rt0.5/Rm≤0.80 ,-20 ℃ of ballistic work CVN>=200J ,-20 ℃ of DWTT shear area SA>=85%.Vertical mechanical property of steel plate can reach following requirement: homogeneous deformation elongation UEL>=10%; Ys Rt0.5>=400MPa; Tensile strength Rm>=550MPa; Yield tensile ratio Rt0.5/Rm≤0.80, stress-strain(ed) curve do not have yield point elongation and Rt1.5/Rt0.5>=1.15, and wherein Rt1.5 is that total elongation is 1.5% pairing stress value.

The invention has the advantages that:

(1) adopts low-carbon (LC) to add Mn, selectively add Cu, Ni, Mo, Cr, do not add the economical composition design of V, reduced production cost effectively;

(2) method of employing two stages controlled rolling, promptly the recrystallization zone is rolling rolling with the non-recrystallization district.In the deformation process, adopt suitable texturing temperature and deflection, make austenite crystal obtain effective refinement; The intermediate blank air cooling is treated thermophase, and niobium carbonitride second is separated out obviously mutually, and austenite grain boundary obtains effective pinning, and crystal grain has good stability, and tangible grain coarsening phenomenon can not take place;

(3) after the finish to gauge, steel plate carries out air cooling and treats temperature, and the temperature of steel plate before the cooling of entry laminar flow is reduced to ferritic and separates out the following 10-70 of temperature Ar3 ℃, and the austenitic transformation that makes 30%-70% in the steel plate is the good polygonal ferrite of plasticity;

(4) steel plate of treating after the temperature carries out the laminar flow order but; The speed of cooling scope is controlled at 5-35 ℃/s; Final cooling temperature is controlled in the 100-500 ℃ of scope, guarantees that remaining austenitic transformation is a bainite structure in the water-cooled process; The polygonal ferrite of separating out earlier can obviously not grown up, and finally obtains polygonal ferrite+bainite duplex structure;

(5) the cooled steel plate air cooling of laminar flow is to room temperature, and intensity and plasticity index are good.It is 485-630MPa that the transverse mechanical performance of steel plate can reach following requirement: ys Rt0.5, and tensile strength Rm is 570-760MPa, yield tensile ratio Rt0.5/Rm≤0.80 ,-20 ℃ of ballistic work CVN>=200J ,-20 ℃ of DWTT shear area SA>=85%.Vertical mechanical property of steel plate can reach following requirement: homogeneous deformation elongation UEL>=10%; Ys Rt0.5>=400MPa; Tensile strength Rm>=550MPa, yield tensile ratio Rt0.5/Rm≤0.80, stress-strain(ed) curve does not have yield point elongation and Rt1.5/Rt0.5>=1.15.

Through using this patent, production that can economical and efficient is used steel based on the X70 level pipeline pipeline of strain design.The advantage of this patent is selectively to add alloying elements such as Cu, Cr, Ni, Mo, and each alloying element total amount has reduction in various degree, and does not need subsequent heat treatment, so ME is simple, cost is lower.Use the X70 pipe line steel that the present invention produces, except the requirement of strength that can satisfy traditional X-ray 70, also have the characteristic of low yield strength ratio and high uniformly extension, be applied to the security that the X70 line pipe will increase substantially the pipeline operation.

Embodiment

Below in conjunction with embodiment the present invention is further specified:

The chemical ingredients of embodiment 1-12, Comparative Examples 13-16, processing parameter and results of property are shown in table 1-4.

1. chemical ingredients

The chemical ingredients of embodiment 1-12 and Comparative Examples 13-16 (wt%) is like table 1.

Table 1 chemical ingredients (wt%)

	C	Si	Mn	P	S	Ti	Nb	Cu	Ni	Cr	Mo	Al
													1	0.06	0.33	1.68	0.01	0.003	0.017	0.03	0.24	0.23	0.09	0.05	0.04
2	0.06	0.26	1.64	0.01	0.003	0.012	0.04	0.15	0.15	0.09	0.09	0.03
													3	0.07	0.42	1.55	0.01	0.003	0.015	0.03	0	0.45	0.05	0.05	0.03

4	0.07	0.35	1.52	0.01	0.003	0.015	0.04	0.45	0	0.09	0.05	0.03
													5	0.10	0.25	1.72	0.01	0.003	0.015	0.03	0.20	0.20	0.05	0.05	0.03
6	0.09	0.30	1.58	0.01	0.003	0.015	0.04	0.20	0.20	0	0.15	0.03
													7	0.06	0.32	1.27	0.01	0.003	0.015	0.03	0.22	0.18	0.05	0.05	0.03
8	0.06	0.30	1.85	0.01	0.003	0.015	0.04	0.22	0.20	0	0.15	0.03
													9	0.07	0.30	1.50	0.01	0.003	0.015	0.03	0	0.20	0.09	0.10	0.03
10	0.07	0.25	1.65	0.01	0.003	0.015	0.05	0.15	0	0.09	0.10	0.03
													11	0.07	0.30	1.50	0.01	0.003	0.015	0.03	0.15	0.20	0.09	0.10	0.03
12	0.07	0.25	1.65	0.01	0.003	0.015	0.05	0.15	0.15	0.09	0.10	0.03
													13	0.02	0.25	1.65	0.01	0.003	0.015	0.05	0.15	0	0.60	0.10	0.03
14	0.05	0.30	1.50	0.01	0.003	0.015	0.03	0.15	0.20	0.10	0.10	0.03
													15	0.06	0.25	1.65	0.01	0.003	0.015	0.05	0.15	0.15	0	0.15	0.03
16	0.11	0.25	1.65	0.01	0.003	0.015	0.05	0.15	0.15	0	0.55	0.03

2. hot rolling technology

Operational path is following: get the raw materials ready → converter or electrosmelting → external refining → casting → slab reheat → controlled rolling → controlled chilling.

The processing parameter of embodiment 1-12, Comparative Examples 13-16 is seen table 2.

Table 2 processing parameter

3. results of property

Carry out mechanics, summer ratio impact, DWTT experiment respectively, the horizontal plate property test-results of embodiment 1-12, Comparative Examples 13-16 is as shown in table 3, and vertically performance is as shown in table 4.

Table 3 transverse mechanical results of property

	Ys MPa	Tensile strength MPa	Yield tensile ratio	Unit elongation A50%	Ballistic work J-20 ℃	?SA％-20℃DWTT
							1	570	760	0.75	35.9	331	90
2	531	708	0.75	40.9	336	90
							3	485	703	0.69	39.3	348	90
4	496	689	0.72	41.5	318	90
							5	490	650	0.75	39.3	340	90
6	595	744	0.80	41.8	292	90
							7	509	679	0.75	40.2	296	90
8	491	691	0.71	41.0	337	90
							9	495	685	0.72	38.6	277	90
10	555	730	0.76	41.9	287	90
							11	610	760	0.8	42.0	266	90
12	573	735	0.78	35.3	345	90
							13	435	600	0.73	40.1	333	90
14	599	722	0.83	38.7	317	90
							15	588	683	0.86	39.4	264	90
16	589	720	0.82	39.8	291	90

Table 4 is the mechanics results of property vertically

Claims (5)

1. pipeline steel X70 and method of manufacture thereof based on a strain design, the content range of its composition be by weight percentage: C0.06%-0.10%, Si0.1%-0.6%; Mn1.0%-2.5%, P≤0.015%, S≤0.003%; Cr＜0.1%, Mo 0.05%-0.35%; Nb0.01%-0.15%, Ti 0.005%-0.03%, Al0.01%-0.06%; Contain among Cu, the Ni one or both, Cu 0%-0.5%, Ni 0%-0.5% simultaneously; Surplus is Fe and micro-unavoidable impurities.

2. the pipeline steel X70 based on strain design according to claim 1, what it is characterized in that said steel is organized as ferritic+bainite duplex structure.

3. method of manufacture according to the said pipeline steel X70 based on strain design of claim 1～2; It is characterized in that operational path is for getting the raw materials ready → converter or electrosmelting → external refining → casting → slab reheat → controlled rolling → controlled chilling; Wherein, slab heating temperature is 1050-1280 ℃; The temperature controlling range of recrystallization zone controlled rolling is 900-1250 ℃; The temperature controlling range of non-recrystallization zone controlled rolling is 700-950 ℃; Beginning to cool down temperature is 650-800 ℃; Stopping cooling temperature is 100-500 ℃; Speed of cooling is 5-35 ℃/s.

4. the method for manufacture of the pipeline steel X70 based on strain design according to claim 3; It is characterized in that the blank after the heating is carried out carrying out the controlled rolling of two stages immediately after dephosphorize by high pressure water is handled; The single pass heavy deformation of fs at least three passages is not less than 15%, and the cumulative deformation of subordinate phase is not less than 60%.

5. the method for manufacture of the pipeline steel X70 based on strain design according to claim 3 is characterized in that the steel plate after the finish to gauge is controlled cold relaxation to water-cooled begins temperature, and the austenitic transformation that makes 30%-70% is for analysing granular ferrite earlier; In the water-cooled process, making remaining austenitic transformation is bainite, obtains proeutectoid ferrite+bainite duplex structure.