CN104109818A - Hot-rolled flat plate of large-wall thickness deep-sea pipe steel and manufacturing method thereof - Google Patents

Abstract

The invention discloses a hot-rolled flat plate of large-wall thickness deep-sea pipe steel and a manufacturing method thereof, and belongs to the technical field of low-carbon microalloyed steel. The hot-rolled flat plate comprises, by weight, 0.025-0.045% of C, 0.10-0.35% of Si, 1.10-1.40% of Mn, less than or equal to 0.015% of P, less than or equal to 0.003% of S, 0.04-0.07% of Nb, less than or equal to 0.06% of V, 0.010-0.020% of Ti, 0.15-0.40% of Ni, less than or equal to 0.20% of Cr, less than or equal to 0.08% of Mo, 0.010-0.040% of Al and the balance Fe and unavoidable impurities, wherein a ratio of Al/N is greater than or equal to 2. The manufacturing method comprises the following steps of blast furnace molten iron collection, pre-desulphurization of blast furnace molten iron, smelting by a converter, LF+RH refining, plate blank continuous casting, plate blank heating, rolling by 4300 rolling mill, ACC fast-cooling, stack cooling, sampling and examination, and warehousing and transportation. The hot-rolled flat plate has stable mechanical property indexes, good plasticity-toughness matching and excellent corrosion resistance. The hot-rolled flat plate subjected to UOE molding pipe-preparation has performances reaching to an X70 level.

Description

A kind of large wall thickness deep-sea is hot rolled slab and manufacture method thereof for pipe line steel

Technical field

The invention belongs to low-carbon micro steel-alloy technical field, particularly relate to a kind of large wall thickness deep-sea pipe line steel hot rolled slab and manufacture method thereof, be applicable to deep-sea oil gas transport pipe.

Background technology

Along with the high speed development of world economy and the exhaustion of land Energy resources, offshore oil and gas exploitation has become upsurge, pipe-line construction to ocean, seismic zone, polar region frozen soil etc. the severe area of environment extend.At present, existing more than 100 countries in the whole world are carrying out offshore oil gas prospecting, wherein over half at deep-sea.Limited by exploration, laying, detection, pipeline material technology and equipment condition, China's pelagic realm petrol resources exploitation is in the starting stage, only the pipeline of Li Gulf, South Sea project carries out pipeline laying in the depth of water of 1500m, the above domestic report of succeeding in developing that there is no of pipe line steel in 3000 meters, deep-sea.China's deep-sea oil gas exploitation is faced with very urgent situation, and particularly at the South Sea, hydrocarbon storage amount is very abundant, and the status in China energy strategy is very crucial.Concerning steel enterprise, accelerate research and development large wall thickness deep-sea pipe line steel, boosting country south sea petroleum strategic importance is great.

Deep-sea uses pipe line steel thickness generally more than 30mm, special area even exceedes 40mm, the Pipeline Steel Plate that requires high strength, excellent low-temperature flexibility and low yield strength ratio, especially thickness to be greater than 40mm to obtain along thickness of slab direction uniformly tissue and desirable DWTT performance very difficult.

Retrieve pertinent literature and the patented technology before patent of the present invention, announced, as Chinese patent CN102409224 Granted publication " hot-rolled steel sheet and the production method for thick specification subsea pipeline steel of excellent in low temperature toughness ", the continuously cast bloom specification using is not announced, steel plate thickness only arrives 36.3mm, still cannot meet consumers' demand in special marine site, and alloying constituent is higher, expensive; And for example Chinese patent CN102676925 Granted publication " a kind of large wall thickness subsea pipeline steel plate and production method thereof ", this alloy formula adopts C:0.06～0.07%, M0:0.15%, infiltrate into steel plate heart portion completely for ease of rolling, Heating temperature is up to 1235 DEG C, and higher Heating temperature is unfavorable to low-temperature flexibility,-20 DEG C of Charpy-V impact powers are on the low side, be only 300J, adopt in addition 300mm thickness continuously cast bloom, the Submarine Pipeline compression ratio of producing thicker specification is limited.

Summary of the invention

The object of the present invention is to provide a kind of large wall thickness deep-sea pipe line steel hot rolled slab and manufacture method thereof, design and rolling technology by reasonable component, use 400mm continuously cast bloom to produce large wall thickness deep-sea pipe line steel hot rolled slab, product thickness reaches 40mm, not only product over-all properties meets the demands, and has good low-temperature flexibility and corrosion resistance.Steel plate is taking ferrite and granular bainite duplex structure as main, and homogeneous microstructure is tiny, and grain fineness number is more than 13 grades, and through-thickness is organized as Figure 1-3.

The composition (by weight percentage) of hot rolled slab of the present invention is:

C:0.025-0.045%, Si:0.10-0.35%, Mn:1.10-1.40%, P≤0.015%, S :≤0.003%, Nb:0.04-0.07%, V :≤0.06%, Ti:0.010-0.020%, Ni:0.15-0.40%, Cr :≤0.20%, Mo :≤0.08%, Al:0.010-0.040%, Al/N >=2, surplus is Fe and inevitable impurity.

Composition Design of the present invention is based on following understanding:

C: for ensureing that large wall thickness deep-sea pipe line steel has excellent welding property and good low-temperature flexibility, carbon content need be strict controlled in below 0.06%.

Si is effective deoxidant element, can also play strengthening effect, but Si too high levels can make plasticity and the toughness drop of steel, and therefore setting its scope is 0.15%～0.40%.

Mn is solution strengthening element important in steel, can reduce transformation temperature, and thinning microstructure substructure is improved toughness in strengthening steel plate; Meanwhile, can improve hardening capacity.If manganese too high levels is unfavorable to welding and toughness.

P, S are detrimental impurity element, adopt calcium to process and PURITY STEEL PRODUCTION TECHNOLOGY, strictly control the inclusion such as phosphorus, sulphur in steel.

Nb, Ti are solution strengthening elements, are again carbonitride forming elements, in heating steel billet and the operation of rolling, pinning austenite grain boundary also stops austenite crystal excessively to be grown up, but its too high levels can affect toughness and weldability, meanwhile, Carbonitride Precipitation increases Properties of HIC resistance also harmful.

Cr can effectively increase the hardening capacity of steel, improves mechanical property, but too high levels has disadvantageous effect to material weldability.

Ni, Cu play solution strengthening effect, can also improve solidity to corrosion, and Ni can also improve the low-temperature flexibility of steel simultaneously.

The existence of N can worsen the toughness of mother metal and welded heat affecting zone, and its content is no more than 0.006% and is advisable.

The production of hot rolled slab of the present invention comprises: blast-melted → molten iron pre-desulfurization → converter smelting → LF+RH refining → sheet billet continuous casting → heating of plate blank → 4300 mill milling → ACC cooling → cooling in heap → sampling fast, inspection → warehouse-in, shipping.

At slab casting+controlled rolling+Controlled cooling process, in process, control parameter and be:

(1) the chemical composition smelting molten steel by steel plate is poured into the thick continuously cast bloom of 400mm;

(2) by walking beam heating furnace by heating steel billet to 1170～1220 DEG C of design temperatures, heat-up time, 280-450min, ensured steel billet abundant austenitizing;

(3) steel billet enters 4300mm mill milling after coming out of the stove, and adopts recrystallization zone+non-recrystallization district two stage rolling when rolling, and doubly, rough rolling step and finish rolling stage parameter are as follows for the 2-3 that holding gauge is finished product thickness:

Rough rolling step: start rolling temperature: 1000-1100 DEG C, end temp: >=980 DEG C, roll speed: 1.0-3.5m/s, rolling torque: 2000-3200kNm; Tiny for obtaining, uniform microstructure, roughing needs bonding pass deformation rate 10%-30%.

The finish rolling stage: adopt low temperature open rolling, start rolling temperature: 760-820 DEG C, finishing temperature: 750-800 DEG C, roll speed: 2.0-4.0m/s.

(4) rolling rear steel plate, to enter ACC laminar flow cooling, begins to cool down temperature and be controlled at 740-790 DEG C, and final cooling temperature is controlled at 200-350 DEG C, and rate of cooling is controlled at 15-20 DEG C/s;

(5) the cooling rear stacking slow cooling of steel plate, heap cool time 12-24 hour.

The large wall thickness deep-sea pipe line steel of producing by above-mentioned operation, steel plate thickness specification reaches 40mm; Mechanical property of steel plate index is stable, and plasticity, toughness coupling better, have good resistance to corrosion, and steel plate performance after UOE moulding tubulation reaches X70 level.

Brief description of the drawings

Fig. 1 is the line steel hot rolling flat plate surface metallographic structure of large wall thickness deep-sea.

Fig. 2 is large wall thickness deep-sea line steel hot rolling flat plate thickness 1/4 place's metallographic group.

Fig. 3 is the line steel hot rolling flat plate thickness 1/2 place metallographic structure of large wall thickness deep-sea.

Fig. 4 is large wall thickness deep-sea line steel hot rolling flat plate stress strain curve shape.

Embodiment

According to the present invention, large wall thickness deep-sea pipe line steel hot rolled slab and manufacture method thereof smelted, and is cast into the continuously cast bloom of 400mm × 2200mm × 2850mm in 100 tons of converters, on 4300mm Heavy Plate Rolling Line, is rolled.Chemical composition is as shown in table 1, and process system is as shown in table 2, and strength property is as shown in table 3, and toughness properties is as shown in table 4, and steel plate CTOD inspection is as shown in table 5, and antiacid assay is as shown in table 6, and steel plate performance after UOE moulding tubulation is as shown in table 7.

The chemical composition wt% of table 1 steel plate

C	Si	Mn	P	S	Al	Nb	Ni	V	Ti	Cr	Cu	N	H
														0.043	0.25	1.32	0.008	0.001	0.037	0.044	0.285	0.038	0.015	0.23	0.21	0.004	0.0001

Table 2 process system

Table 3 armor plate strength performance

The large wall thickness of the present invention deep-sea pipe line steel manufacture method stress strain curve is continuously the domed shape of surrender, has lower yield tensile ratio, and stress strain curve as shown in Figure 4.

Table 4 steel plate toughness properties

Table 5CTOD assay

The anti-HIC of table 6, SSC assay

Performance after table 7 steel plate tubulation

The present invention is by adopting low temperature to depress greatly and very low temperature phase transformation, fully refinement phase-change organization, obtain the large wall thickness subsea pipeline steel plate taking ferrite+bainite duplex structure as matrix, there is high strength and good low-temperature flexibility, advance deep-sea oil gas strategy significant to country.

Claims (2)

1. a large wall thickness deep-sea pipe line steel hot rolled slab, is characterized in that, the composition of this hot rolled slab is by weight percentage: C:0.025-0.045%, Si:0.10-0.35%, Mn:1.10-1.40%, P≤0.015%, S :≤0.003%, Nb:0.04-0.07%, V :≤0.06%, Ti:0.010-0.020%, Ni:0.15-0.40%, Cr :≤0.20%, Mo :≤0.08%, Al:0.010-0.040%, Al/N >=2, surplus is Fe and inevitable impurity.

2. a production method for hot rolled slab described in claim 1, technique comprises: blast-melted → molten iron pre-desulfurization → converter smelting → LF+RH refining → sheet billet continuous casting → heating of plate blank → 4300 mill milling → ACC cooling → cooling in heap → sampling fast, inspection → warehouse-in, shipping; It is characterized in that, at slab casting+controlled rolling+Controlled cooling process, the technical parameter of controlling in process is:

(1) the chemical composition smelting molten steel by steel plate is poured into the thick continuously cast bloom of 400mm;

(2) by walking beam heating furnace by heating steel billet to 1170～1220 DEG C of design temperatures, heat-up time, 280-450min, ensured steel billet austenitizing;

(3) steel billet enters 4300mm mill milling after coming out of the stove, and adopts recrystallization zone+non-recrystallization district two stage rolling when rolling, and doubly, rough rolling step and finish rolling stage parameter are as follows for the 2-3 that holding gauge is finished product thickness:

Rough rolling step: start rolling temperature: 1000-1100 DEG C, end temp: >=980 DEG C, roll speed: 1.0-3.5m/s, rolling torque: 2000-3200kNm; Roughing needs bonding pass deformation rate 10%-30%;

The finish rolling stage: adopt low temperature open rolling, start rolling temperature: 760-820 DEG C, finishing temperature: 750-800 DEG C, roll speed: 2.0-4.0m/s;

(4) rolling rear steel plate, to enter ACC laminar flow cooling, begins to cool down temperature and be controlled at 740-790 DEG C, and final cooling temperature is controlled at 200-350 DEG C, and rate of cooling is controlled at 15-20 DEG C/s;

(5) the cooling rear stacking slow cooling of steel plate, heap cool time 12-24 hour.