CN1351187A - Process for preparing high-cleanness, high-strength and high-toughness steel for gas delivering pipeline - Google Patents

Abstract

A high-cleaness high-strength high-toughness steel for gas-delivery pipeline contains C (0.066-0.086%), Si (0.139-0.339%), Mn (1.23-1.43%), Ti (0.009-0.029%), Nb (0.03-0.05%), V (0.03-0.05%), S (less than 0.0008%), P (less than 0.0015%), O (less than 15 PPm), N (less than 30 PPm) and Fe (rest). It is made up by hot rolling. Its microscopic structure is acicular ferrite AF+less quasi-polygonal ferrite + very little pearlite P + M/A cells. Its advantages are high strength, very high low-temp impact toughness and very high resistance to stress corrosion of hydrogen sulfide.

Description

A kind of preparation method of high-cleanness, high-strength and high-toughness steel for gas delivering pipeline

The invention belongs to the field of High-Strength Low-Alloy rolling controlled and cooling controlled steel, be mainly used in and make high pressure, big caliber petroleum gas delivering pipe line steel.

Oil and gas is the important component part of national economy, is the basic substance of social development.By 2010, the crude oil in China breach reaches 7,000 ten thousand tons every year, the Sweet natural gas breach reaches the 40-50 billion cubic meter, for this reason, China has formulated in this year that " the grand strategy and policy of West-east Gas; will lay thousands of kilometers gas transmission line from West to East will be set up from external simultaneously to thousands of kilometers domestic line of pipes, introduce the external energy.Because the line of pipes major part all will be passed through ice box, the region complexity is carried cost in order to reduce oil gas on the way, in accordance with international practices, all will adopt big caliber, the high pressure line of big throughput rate is carried, this just requires the line of pipes steel satisfying under the condition of intensity, has splendid toughness.For carrying acid gas also to require it to have very high anti-H with pipe line steel ₂The S corrosive nature.Domestic gas transmission line the longest, that pressure is the highest, performance is best is capital, an X60 Shan gas transmission line at present, its main sheet material is produced by Baoshan Iron ﹠ Steel Group Corp., though capital, X60 Shan pipeline steel has higher intensity, toughness and good welding property, but its S, P, O, the N total amount is higher, the mechanical controlled rolling technology of heat (TMCP) is simple, and the pipe line steel of acquisition is organized as ferrite+perlite, is difficult to satisfy the requirement of the big caliber line of pipes of high pressure of higher category with steel.

The object of the present invention is to provide the production process system of a kind of super purified high-strong toughness X70 level High Pressure Gas Transmitting Pipeline with steel, the structural state of its product is the heterogeneous structure based on acicular ferrite AF, has simultaneously stronger anti-H again having higher-strength and flexible ₂S corrodibility.

The invention provides a kind of preparation method of high-cleanness, high-strength and high-toughness steel for gas delivering pipeline, the chemical component weight per-cent of steel is: C 0.066～0.086%, and Si 0.139～0.339%, and Mn 1.23～1.43%, Ti0.009～0.029%, Nb 0.03～0.05%, and V 0.03～0.05%, S＜0.0008%, P＜0.0015%, O＜15PPm, N＜30PPm, all the other are iron Fe; It is characterized in that hot mechanical controlled rolling process system (TMCP) is as follows:

1) rolling pass is distributed: 60-44-32-22-12-8 is totally five roads, and in the austenite recrystallization district+non-recrystallization district multi-pass controlled rolling and controlled cooling, rolling-900 ℃～830 ℃ finish to gauges-500 of-1150 ℃ of open rollings-1000 of 1200 ℃ of heating ℃～950 ℃ ℃～400 ℃ of ends are cold;

2) type of cooling: 15～30 ℃/s of water-cooled.

The present invention has carried out ultra-pure purification at capital, former X60 Shan gas transmission line on the basis of steel, and the foundation of carrying out ultrapure clean processing is:

S in the steel, P are harmful elements, and when particularly the content of S was higher, obviously the toughness of reduction steel and anti-H 2 S stress corrosion and anti-hydrogen caused the ability of bringing out crackle.

The foundation of the TMCP technology that the present invention adopts is: tissue is controlled and crystal grain thinning, utilize promptly that to carry out multi-pass in the lower temperature region in austenite recrystallization district and austenite non-recrystallization district rolling, and strengthen last pass deformation, cooperate again medium speed of cooling (15-30 ℃/s), can obtain heterogeneous structure, and crystal grain obtains refinement based on the perlite P+M/A constituent element of acicular ferrite AF+a spot of quasi-polygonal ferrite+minute quantity.

The present invention provides a kind of new structural state promptly to the X70 level high-pressure natural gas line of pipes of ultrapure clean smelting with steel:

The perlite P+M/A constituent element of a spot of quasi-polygonal ferrite+minute quantity of acicular ferrite AF+.

Adopt the foundation of this heterogeneous structure to be: thin non-disperse distributing cementite and the martensite island of waiting in the axonometer columnar ferrite AF matrix that more than the upper bainite formation temperature, forms, its substructure has higher dislocation desity; The heterogeneous structure structure that this kind tissue and tiny quasi-polygonal ferrite F form has higher intensity and toughness.Acicular ferrite AF has the characteristic of continuous surrender, the more important thing is that acicular ferrite AF can weaken the yield strength that causes because of Bauschinger effect and reduce.Acicular ferrite AF has the comprehensive action of rolling reinforcement and phase transformation strengthening, has overcome the weakness of ferrite F+ perlite P pipe line steel, can produce thicker, intensity rank and the higher sheet material of toughness.

In a word, pipe line steel of the present invention is compared with capital, existing X60 Shan pipe line steel and is had following advantage:

1) pipe line steel of the present invention has higher intensity and very high low-temperature impact toughness, also has good anti-H 2 S stress corrosion ability simultaneously.

2) grain-size of pipe line steel of the present invention is significantly less than capital, X60 Shan pipe line steel, and average grain size reaches about 4um.

3) the over-all properties σ of pipe line steel of the present invention _s=574～589MPa, σ _b=640～659MPa, δ ₅₀=20.9～24.7%, Ψ=78.3～79.1, CVN _{-20 ℃}=337～408J/mm ², CVN _{-50 ℃}=319～336J/mm ², CVN _{-80 ℃}=314～345J/mm ²

Below by embodiment in detail the present invention is described in detail.

Accompanying drawing 1 is the metallographic structure photo of X70 pipe line steel.

Embodiment

The chemical ingredients scope of pipe line steel according to the present invention adopts vacuum induction melting, forges and be processed into 60 * 80 * 140 square billet, carries out hot mechanical controlled rolling and controlled cooling on small section mill, simulates in constant-temperature oven at last and batches, and is rolled into the thick sheet material of 8mm.Its chemical ingredients sees Table 1, and the TMCP process system sees Table 2, and mechanical property sees Table 3, and Fig. 1 is seen in metallographic structure.

The chemical ingredients of table 1, embodiment pipe line steel

Grade of steel	????C	????Si	????Mn	????Ti	????Nb	????V	????S	????P	??O (ppm)	??N (ppm)
											????E1	??0.076	??0.26	?1.47	??0.020	??0.049	??0.049	??0.0006	??0.0010	??10	??28
????E2	??0.077	??0.25	?1.28	??0.027	??0.045	??0.053	??0.0006	??0.0010	??11	??18

Table 2, TMCP process system

Test piece number (Test pc No.)	??60～44	??44～32	??32-22	??22-12	??12-8	Cooling time	Speed of cooling	Final cooling temperature
									Open rolling		Treat temperature		Finish to gauge
	??E11	??1129	??1059	??1000										??900	??17	??30	??386
??E12						??1128		??947	??920	??850	??14	??27	??470
	??E21	??1134	??1095	??1003										??902	??16	??29	??434
??E22						??1110	??1080	??950		??852	??13	??32	??435

Table 3 mechanical property of materials test-results

Test piece number (Test pc No.)	????σ s????MPa	????σ b????MPa	????Y·R	????δ 50????％	????Ψ ????％	??CVN ??-20℃ ??J/mm 2	??CVN ??-50℃ ??J/mm 2	??CVN ??-80℃ ??J/mm 2
									????E11	????589	????659	????0.89	????20.9	????79.0	????394	????336	????342
????E12	????574	????644	????0.89	????23.8	????78.5	????408	????335	????345
									????E21	????574	????648	????0.89	????24.7	????79.1	????361	????330	????328
????E22	????585	????640	????0.91	????23.0	????78.3	????337	????319	????314

Claims (1)

1, a kind of preparation method of high-cleanness, high-strength and high-toughness steel for gas delivering pipeline, the chemical component weight per-cent of steel is: C 0.066～0.086%, and Si 0.139～0.339%, and Mn 1.23～1.43%, Ti0.009～0.029%, Nb 0.03～0.05%, and V 0.03～0.05%, S＜0.0008%, P＜0.0015%, O＜15PPm, N＜30PPm, all the other are iron Fe; It is characterized in that hot mechanical controlled rolling process system (TMCP) is as follows:

1) rolling pass is distributed: 60-44-32-22-12-8 is totally five roads, and in the austenite recrystallization district+non-recrystallization district multi-pass controlled rolling and controlled cooling, rolling-900 ℃～830 ℃ finish to gauges-500 of-1150 ℃ of open rollings-1000 of 1200 ℃ of heating ℃～950 ℃ ℃～400 ℃ of ends are cold;

2) type of cooling: 15～30 ℃/s of water-cooled.

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