CN100392132C

CN100392132C - Steel for low temperature and high tenacity structure use and its production method

Info

Publication number: CN100392132C
Application number: CNB2005100247768A
Authority: CN
Inventors: 王巍
Original assignee: Baoshan Iron and Steel Co Ltd
Current assignee: Baoshan Iron and Steel Co Ltd
Priority date: 2005-03-30
Filing date: 2005-03-30
Publication date: 2008-06-04
Anticipated expiration: 2025-03-30
Also published as: CN1840725A

Abstract

The present invention relates to low-temperature structural steel with high tenacity. The low-temperature structural steel with high tenacity has the chemical compositions of 0.04 wt% to 0.08 wt% of C, 0.60 wt% to 0.80 wt% of SiO, 1.65 wt% to 2.15 wt% of Mn, 0.055 wt% to 0.75 wt% of Nb, 0.010 wt% to 0.020 wt% of Ti, 0.025 wt% to 0.045 wt% of Al<t>, P<=0.012 wt%, S<=0.003 wtT, O<=0.0015 wtT, 0.008 wt% to 0.012 wt% of N, Fe and inevitable impurities. The manufacturing method of the present invention comprises the following steps: smelting with a converter or an electric furnace; refining with a vacuum furnace; casting; billet reheating with the heating temperature of 1130 DEG C to 1170 DEG C; rolling; quick cooling; TMCP and finishing, wherein the total deformation rate is more than or equal to 55% in the three previous times of rolling, and the deformation rate is from 25% to 33% in the last time of the rolling; after rolled and waited for 30 seconds to 50 seconds, the chemical components are quickly cooled at the speed of 15 DEG C/S to 30 DEG C/S, and the final cooling temperature is between 350 DEG C and 450 DEG C. Noble elements, such as Ni, Mo, etc., do not need to be added to the present invention. The processes of TMCP and RPC are used for production. The present invention has the advantage of simple production process. Only rolling and cooling after the rolling need to be controlled.

Description

A kind of steel for low temperature and high tenacity structure use and manufacture method thereof

Technical field

The invention belongs to the structure iron field, particularly a kind of steel for low temperature and high tenacity structure use and manufacture method thereof.

Background technology

Along with long-distance transportation demands such as petroleum gas, Sweet natural gas are constantly increased, the manufacturing of liquefying plant and storage facilities needs increasing low temperature resistant high-intensity high-tenacity steel.Except higher intensity (the yield strength 〉=390MPa), also will have good low-temperature flexibility.According to general standard, the design use temperature is lower than-110 ℃, even reaches-165 ℃.

Table 1 is concrete regulation and the of the present invention contrast (do not comprise NV9Ni steel, in table last column be the present invention designed steel grade) of Veritas (DNV) Classification of Vessel standard to low temperature and ultralow-temperature flexibility steel mechanical property and design effort temperature.

Table 1:DNV classification society rule is to the regulation of the mechanical property of very low temperature steel design temperature and steel

Analyze as can be known from table 1, because these steel require to have at low temperatures toughness preferably, the production method that common hot rolling C-Mn structure iron is commonly used is all to add higher Ni (more valuable element, about 150000 yuan/ton in steel.Effect: improve hardening capacity, reduce martensite point, increase the formation tendency of residual austenite, and increase the low-temperature flexibility that ferrite matrix cleavage ability is improved matrix by influence to chemical ingredients.In addition, the strand that contains nickel steel forms the iron scale that is difficult to removal easily when heating, must adopt mechanical workout or emery wheel etc. to carrying out pre-cleaning in the surface, perhaps before the steel billet heating, will wrap up iron sheet and handle, to prevent in heat-processed, further producing iron scale.Therefore, the heating rolling operation that contains nickel steel is very complicated and loaded down with trivial details) and Cr (the strong reduction bainite transformation point temperature that do not wait of content, weak reduction martensite point temperature improves bainite hardening capacity and intensity) or Mo (more valuable element, about 650000 yuan/ton.Improve hardening capacity, the solution strengthening ferrite, form stable carbide, crystal grain thinning) etc. element, perhaps do not add or Ni, Cr above few adding the or Mo element and carry out repeatedly thermal treatment (as normalizing, normalizing+tempering, or quenching+tempering etc., technology is numerous and diverse, and is time-consuming), thereby the ferrite that obtains refinement adds bainite structure, makes final product have better strength and toughness under lower temperature.In a word, the composition of existing low temperature and high tenacity structure steel and complete processing complexity, cost height.

Summary of the invention

The object of the present invention is to provide a kind of steel for low temperature and high tenacity structure use and production method thereof, this steel has good toughness under ultralow temperature, can be used to make liquefied gas storage, the engineering of under low temperature or ultralow temperature, working and physical construction and liquefied petroleum gas (LPG), natural gas liquids hull structure, substitute high Ni quenched and tempered steel, its production technique is simplified (only need controlled rolling and roll after cold soon), thereby the production cost of very low temperature steel is reduced significantly, and efficient is improved simultaneously.

The very low temperature steel that uses adopts the production of high Ni hardening and tempering process usually at present, and complex process and cost are very high.For example; minimum design effort temperature is-105 ℃ a 5Ni steel (containing 5%Ni); need carry out normalizing adds tempering or quenching and adds tempering and handle; and must carry out special processing and protection to billet surface owing to the high easily oxidation of Ni content; therefore operation is very complicated, and the manufacturing cost of steel plate is about more than 20,000 yuan.The present invention is designed does not contain the Ni high-strength steel, only need carry out Nb and Ti microalloying.This steel has good toughness under ultralow temperature, can be used to make liquefied gas storage, the engineering of under low temperature or ultralow temperature, working and physical construction and liquefied petroleum gas (LPG), natural gas liquids hull structure, substitute high Ni quenched and tempered steel, its production technique is simplified (only need controlled rolling and roll after cold soon), thereby the production cost of very low temperature steel is reduced significantly, and efficient is improved simultaneously.

For achieving the above object, technical scheme of the present invention is a kind of steel for low temperature and high tenacity structure use, its chemical ingredients: (wt%)

C 0.04～0.08

Si 0.60～0.80

Mn 1.65～2.15

Nb 0.055～0.075

Ti 0.010～0.020

Al _T 0.025～0.045

P ≤0.012

S ≤0.003

O ≤0.0015

N 0.008～0.012

All the other are Fe and inevitable impurity.

The manufacture method of a kind of steel for low temperature and high tenacity structure use of the present invention, it comprises the steps,

A. smelt, cast, converter or electrosmelting, vacuum oven refining;

B. steel billet reheat, Heating temperature: 1130～1170 ℃, soaking time: 0.8～1.2 minute * base thickness (mm);

C. rolling, start rolling temperature: 1000～1050 ℃, steel billet is single pass deformation rate 〉=30% more than 1000 ℃, at accumulative total deflection 〉=50% more than 950 ℃, 850 ℃ of less-than cumulation deflection 〉=70%, finish to gauge previous three passes total deformation rate 〉=55%, last pass deformation rate 25～33%, finishing temperature: 750～780 ℃;

D. cooling, rolling ends be 30～50 seconds of air cooling afterwards, cool off final cooling temperature then fast according to the speed of 15～30 ℃/S: 350～450 ℃.

Beneficial effect of the present invention

1. need not to add noble elements such as Ni, Mo;

2. because steel grade of the present invention adopts TMCP (hot mechanical CONTROL PROCESS)+RPC (relaxation is separated out the control phase transformation) explained hereafter, in order to increase the density of separating out of Nb, it separates out granularity refinement, thus further refinement bainite and ferritic structure, so the add-on of Nb and N is suitably improved;

3. steel grade production technique of the present invention is simple, only need carry out controlled rolling and roll postcooling, in order to increase the separating out of Nb, the bainite structure of refinement simultaneously, before entry is cold soon, carry out 30～50 seconds relaxation.

4. the calculating by model and the checking of test, the microstructures Control of steel is polygonal ferrite+bainite, and the polygonal ferrite ratio is: 8～15%, ferrite crystal grain diameter≤8 micron.

The present invention can be used to make minimum temperature and reach-120 ℃ of high-strength steel that ultralow-temperature flexibility is good (excellent weldability of steel) under the situation of not adding valuable nickel element, brings the beneficial effect of following aspect thus:

The manufacturing cost of steel reduces significantly.According to the technology of generally using at present, impact test temperature need be added about 5% nickel element for-120 ℃ very low temperature steel, if by 120,000 yuan of/ton calculating (the product recovery rate of nickel is calculated by 92%), only this item is promptly saved 652 yuan of/ton steel of cost;

The strand that contains nickel steel must adopt mechanical workout or emery wheel etc. to carrying out pre-cleaning in the surface, removes the serious iron scale in surface.In addition, before the steel billet heating, to wrap up iron sheet and handle, to prevent in heat-processed, further producing iron scale.Therefore, it is very complicated and loaded down with trivial details to contain the heating rolling operation of nickel steel.The present invention then need not to carry out extra cleaning and safeguard procedures fully.

Contain nickel steel and need carry out normalizing, normalizing+tempering or quenching+temper, complex procedures, the cycle is longer, has increased manufacturing cost simultaneously again, technology provided by the invention then need not to carry out any thermal treatment fully, has simplified manufacturing process, has reduced production cost, has shortened the manufacturing cycle.

Description of drawings

Fig. 1 is a process flow sheet of the present invention.

Fig. 2 is test temperature-ballistic work of the present invention (laterally) relation curve (embodiment 5).

Embodiment

Embodiment sees Fig. 1, table 2.

The steel grade of the present invention design do not need to add elements such as top valuable Ni, Cr or Mo, it is (very cheap only to need to increase very cheap Si a little.Solution strengthening reduces the bainite transformation point, and the bainite C curve is moved to right, suppressing supercooled austenite decomposes, increase residual austenite volume fraction and stable austenite, promote the formation of rich carbon austenitic film between the ferrite in the bainite, improve toughness), Mn is (cheap.The strong bainite point that reduces, the weak martensite point that reduces, improve hardening capacity and intensity) and micro-Nb and Ti (Nb and Ti are micro alloying elements, can be by separating out growing up of control crystal grain, improve intensity) etc. element and certain cooling controlling and rolling controlling process (TMCP), promptly can satisfy the requirement that under lower temperature, has better strength and toughness.Table 3 is the synopsis of the present invention and documents.

As can be seen from Table 3, low temperature structure steel in the past, perhaps (1) adds noble elements such as higher Ni, Cr or Mo on chemical ingredients, and the complicated heat treatment operation of minimizing back, perhaps do not add or add less noble elements such as Ni, Cr or Mo, will adopt complicated heat treatment operation such as normalizing, tempering at postorder.

The present invention does not then need to add valuable Ni, Cr or Mo element, only need suitably improving under the situation of cheap Si and Mn, add the extremely Nb and the Ti of trace, and in rolling and cooling, adopt comparatively easy technologies such as TMCP and RCP, do not need follow-up complicated thermal treatment, promptly can reach the effect of front.

Fig. 2 is that steel plate (embodiment 5) the series of temperatures summer is than V-type transverse impact curve.As seen when test temperature reached-120 ℃, the ballistic work of steel still satisfied at the toughness reguirements under this temperature (more than 27 joules), reached the low-temperature flexibility level of relevant criterion fully.

Claims

1. steel for low temperature and high tenacity structure use, its chemical ingredients: (wt%)

C 0.04～0.08

Si 0.60～0.80

Mn 1.65～2.15

Nb 0.055～0.075

Ti 0.010～0.020

Al _T 0.025～0.045

P ≤0.012

S ≤0.003

O ≤0.0015

N 0.008～0.012

All the other are Fe and inevitable impurity.

2. the manufacture method of a steel for low temperature and high tenacity structure use as claimed in claim 1, it comprises the steps,

A. smelt, cast by described composition;

B. steel billet reheat, Heating temperature: 1130～1170 ℃, soaking time: 0.8～1.2 minute * the base thickness that calculates with millimeter;

C. rolling, start rolling temperature: 1000～1050 ℃, steel billet is single pass deformation rate 〉=30% more than 1000 ℃, at accumulative total deflection 〉=50% more than 950 ℃, 850 ℃ of less-than cumulation deflection 〉=70%, finish to gauge previous three passes total deformation rate 〉=55%, last pass deformation rate 25～33%, finishing temperature: 750～780 ℃; .