7ni steel plate and method for producing and using the same

Abstract

The application discloses a 7Ni medium plate and a production method and application thereof, and comprises the following steps: hot metal pretreatment, converter smelting, LF and RH / VD refining, continuous casting, heating furnace heating, rolling, MULPIC cooling, finishing and heat treatment. The surface of the casting blank is ground, polished and sprayed with an anti-oxidation coating before heating, and low-temperature steel burning of the heating furnace is combined, so that the iron oxide skin pressure and heavy skin defects on the surface of the steel plate are effectively reduced; large reduction rolling is carried out in the rough rolling process, and the starting rolling temperature and the final rolling temperature are controlled in the finish rolling process, so that the grain size is effectively controlled; the one-time quenching + tempering process is adopted in the heat treatment process, and the online quenching is used to replace the offline quenching, so that the quenching process is reduced compared with the conventional quenching + quenching + tempering process, the heat treatment process is shortened, the production cost is effectively reduced, and the production capacity of the heat treatment production line is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel smelting, and more particularly to a 7Ni steel medium plate, a production method and application thereof. BACKGROUND

[0002] With the rapid increase of energy consumption, over-reliance on coal resources has caused serious air pollution, and large-scale use of clean energy natural gas has become an inevitable development trend. The proportion of natural gas in primary energy consumption will continue to increase, and offshore imported liquefied natural gas (LNG) accounts for 50% of the imported amount, for which a large number of offshore ship LNG storage tanks, land LNG storage tanks, new energy vehicle fuel tanks, and inland shipping fuel tanks need to be built, and a large amount of LNG storage tank steel is needed, and the future market is huge.

[0003] Nickel-saving 7Ni steel alloy has relatively low cost, but its various physical and chemical properties are good, and can meet the requirements of LNG storage tank steel, and is the main reserve material for LNG storage tank steel at present. The common production method of 7Ni steel is to adopt quenching + quenching + tempering for heat treatment after hot rolling, which not only increases the production cost but also occupies the heat treatment production line, which is not conducive to the improvement of yield.

[0004] Therefore, it is of great significance to develop a low-cost and high-efficiency production method of 7Ni steel medium plate for low-temperature pressure vessels. SUMMARY

[0005] Therefore, the present application provides a 7Ni steel medium plate, a production method and application thereof, which optimizes the controlled rolling and controlled cooling process, simplifies the heat treatment process, and reduces the production cost of 7Ni steel.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A production method of a 7Ni steel medium plate, the production process comprising molten iron pretreatment, converter smelting, LF and RH / VD refining, continuous casting, heating furnace heating, rolling, MULPIC cooling, finishing, and heat treatment, and the key process steps comprising:

[0008] The surface of the casting blank is polished before entering the heating furnace, so that the surface of the casting blank is smooth without obvious pits, protrusions and scratches, and the upper and lower surfaces are sprayed with an oxidation-resistant coating, the heating temperature in the heating furnace is 1120-1220℃, and the holding time is 150-300min;

[0009] The rolling process is two-stage rolling, the single pass reduction rate of the spread stage of the rough rolling process is 10% to 20%, and the rolling times of the single pass reduction rate are greater than or equal to 2 times; the single pass reduction rate after spreading is 20% to 40%, and the rolling times of the single pass reduction rate are greater than or equal to 2 times; the rough rolling temperature is 850 to 950 DEG C, the finish rolling temperature is 700 to 840 DEG C, and the rolling is followed by controlled cooling;

[0010] The heat treatment adopts a quenching + tempering process, the quenching temperature is 650 to 700 DEG C, and the tempering temperature is 530 to 590 DEG C.

[0011] Preferably, the chemical composition of the 7Ni steel is as follows: C 0.03% to 0.13%, Mn 0.30% to 0.90%, Si 0.05% to 0.30%, Ni 6.50% to 7.50%, P≤0.010%, S≤0.008%, V≤0.03%, Mo 0.10% to 0.30%, and the balance is Fe and inevitable impurity elements.

[0012] Preferably, the anti-oxidation coating is one or more of aluminum silicate fiber, rare earth oxide, and aluminum oxide powder, and the thickness is 1 to 3 mm.

[0013] Preferably, the rough rolling temperature is greater than or equal to 1050 DEG C.

[0014] Preferably, in the controlled cooling process, the steel plate with a thickness of 6 to 15 mm is air-cooled after rolling, and the steel plate with a thickness greater than or equal to 15 mm is online quenched after rolling, the Mulpic cooling water amount is as follows: 60 to 150 L / s on the upper and lower sides of the A zone, 200 to 500 L / s on the upper and lower sides of the B, C and D zones, the roll speed is 0.5 to 2.0 m / s, and the re-red temperature is less than or equal to 200 DEG C.

[0015] The application also provides a 7Ni steel plate prepared by the production method, and application of the 7Ni steel plate in the preparation of a low-temperature pressure container.

[0016] According to the above technical solution, compared with the prior art, the application provides a 7Ni steel plate, a production method and application thereof, and has the following beneficial effects:

[0017] In the production method of the present application, the surface scale of the steel plate is effectively reduced by surface grinding, polishing and spraying anti-oxidation coating, and the surface quality of the steel plate is significantly improved by low-temperature burning; the large reduction rolling in the rough rolling process promotes dynamic recrystallization, the surface and core of the intermediate billet are refined, the rolling-in and rolling-out temperatures are controlled in the finish rolling process, the grain size is effectively controlled, and the microstructure with good strength and toughness matching is obtained; the good plate shape is obtained by air cooling for the steel plate with a thickness of 6-15 mm, in addition, the microstructure mainly composed of martensite is obtained for the thin plate under air cooling, the microstructure mainly composed of martensite is obtained for the steel plate with a thickness of ≥15 mm by on-line quenching, and the plate shape deterioration problem caused by uneven cooling is reduced; the one-time quenching + tempering process is adopted in the heat treatment, the one-time quenching process is reduced, the heat treatment process is shortened, the production cost is effectively reduced, and the production capacity of the heat treatment production line is increased. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the provided drawings.

[0019] Fig. 1 The microstructure diagram of the 7Ni steel in the embodiment 1 of the present application is shown in the figure.

[0020] Fig. 2 The microstructure diagram of the 7Ni steel in the embodiment 2 of the present application is shown in the figure. DETAILED DESCRIPTION

[0021] The technical solutions of the present application will be described clearly and completely in combination with the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0022] In the following embodiments 1-3, the chemical composition of the steel is as follows: C 0.07%, Mn 0.56%, Si 0.12%, Ni 7.0%, P 0.004%, S 0.002%, V≤0.01%, Mo=0.27%, and the rest is Fe and inevitable impurity elements;

[0023] The smelting process is as follows: hot metal pretreatment, converter smelting stirring dephosphorization and decarburization, P is 90 ppm, C is 0.04%, LF furnace refining desulfurization and adding nickel plate and other alloy to adjust alloy composition, S is 20 ppm, VD furnace vacuum treatment, vacuum degree is 0.3 torr, vacuum pumping and vacuum holding time is 7 min and 23 min respectively, 260*2270 mm section continuous casting, drawing speed is 0.95 m / min, after offline after 24 h.

[0024] Example 1

[0025] 14 mm thick 7Ni steel plate production, before entering the heating furnace, the surface of the casting blank is polished and polished, the surface of the casting blank is smooth, and there is no obvious defect, the upper and lower surfaces are sprayed with 2 mm of aluminum oxide powder anti-oxidation coating, the heating temperature in the heating furnace is 1123℃, and the holding time is 260 min;

[0026] The rolling process is two-stage rolling, the rough rolling opening temperature is 1095℃, the rough rolling is 9 passes, the single pass reduction rate of the spreading stage is 16% and 14% respectively, and a total of 2 passes are rolled; the first and second passes after spreading are 36% and 28% respectively, and a total of 7 passes are rolled in longitudinal rolling; the intermediate blank thickness is 60 mm; the fine rolling opening temperature is 873℃, the final rolling temperature is 756℃, and the rolling is air cooled after rolling;

[0027] The heat treatment adopts one-time quenching + tempering process, the quenching temperature is 672℃, the holding time is 24 min, the tempering temperature is 565℃, and the holding time is 30 min.

[0028] Example 2

[0029] 25 mm thick 7Ni steel plate production, before entering the heating furnace, the surface of the casting blank is polished and polished, the surface of the casting blank is smooth, and there is no obvious defect, the upper and lower surfaces are sprayed with 3 mm of aluminum silicate fiber anti-oxidation coating, the heating temperature in the heating furnace is 1150℃, and the holding time is 186 min;

[0030] The rolling process is two-stage rolling, the rough rolling opening temperature is 1134℃, the rough rolling is 7 passes, the single pass reduction rate of the spreading stage is 17% and 13% respectively; the first and second passes after spreading are 32% and 27% respectively, and a total of 5 passes are rolled in longitudinal rolling; the intermediate blank thickness is 80 mm; the fine rolling opening temperature is 892℃, the final rolling temperature is 774℃, and the rolling is online quenching cooling after rolling, the Mulpic cooling water amount is: 90 L / s on the upper and lower of A zone, 300 L / s on the upper and lower of B, C and D zones, the roll speed is 1.5 m / s, and the re-red temperature is ≤200℃;

[0031] The heat treatment adopts one-time quenching + tempering process, the quenching temperature is 692℃, the holding time is 45 min, the tempering temperature is 583℃, and the holding time is 50 min.

[0032] Example 3

[0033] 50mm thick 7Ni steel plate production, before entering the heating furnace, the surface of the casting blank is polished and polished, so that the surface of the casting blank is smooth and has no obvious defects, the upper and lower surfaces are sprayed with 1mm of aluminum oxide powder anti-oxidation coating, the heating temperature in the heating furnace is 1168℃, and the holding time is 286min;

[0034] The rolling process is two-stage rolling, the rough rolling opening temperature is 1148℃, the rough rolling is 5 passes, the single pass reduction rate of the spreading stage is 16% and 14% respectively, the first and second passes after spreading have a reduction rate of 33% and 22% respectively, and the longitudinal rolling is 3 passes in total; the intermediate blank thickness is 110mm; the finish rolling opening temperature is 915℃, and the finish rolling temperature is 822℃, after rolling, on-line quenching cooling is performed, the Mulpic cooling water amount is: 70L / s on the upper and lower sides of the A zone, 400L / s on the upper and lower sides of the B, C and D zones, and the roll speed is 1.0m / s, the re-red temperature is ≤200℃;

[0035] The heat treatment adopts one-time quenching + tempering process, the quenching temperature is 659℃, the holding time is 78min, the tempering temperature is 542℃, and the holding time is 66min.

[0036] The microstructure diagram of the 7Ni steel prepared in Example 1-2 is shown in FIG. 1. Figs. 1-2 The mechanical property detection results and the reverse transformation austenite content of the 7Ni steel prepared in Example 1-3 are shown in Table 1.

[0037] Table 1: Mechanical properties and reverse transformation austenite content

[0038]

[0039] From the mechanical property detection results, it can be known that the yield strength of the steel plate obtained by the method of the present application in Example 1-3 is ≥620MPa, the tensile strength is ≥700MPa, the total elongation is ≥21%, and the impact energy at -196℃ is ≥150J.

[0040] In the present specification, each embodiment is described in a progressive manner, and each embodiment focuses on the difference from other embodiments, and the same or similar parts between each embodiment can be referred to each other.

[0041] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for producing a 7Ni steel plate, the production flow comprising hot metal pretreatment - converter smelting - LF and RH / VD refining - continuous casting - heating furnace heating - rolling - MULPIC cooling - finishing - heat treatment, characterized in that, The 7Ni steel has the following chemical components by weight percentage: C 0.03%-0.13%, Mn 0.30%-0.90%, Si 0.05%-0.30%, Ni 6.50%-7.50%, P≤0.010%, S≤0.008%, V≤0.03%, Mo 0.10%-0.30%, and the balance of Fe and inevitable impurities; the thickness of the medium plate is≥15mm, and the production key process steps include: Before entering the heating furnace, the surface of the casting blank is polished and polished until the surface of the casting blank is smooth without obvious pits, protrusions and scratches, the upper and lower surfaces are sprayed with an anti-oxidation coating, the heating temperature in the heating furnace is 1120-1220℃, and the holding time is 150-300min; The rolling process is two-stage rolling, the single pass reduction rate of the spreading stage in the rough rolling process is 10%-20%, and the rolling times of the reduction rate are≥2; the single pass reduction rate after spreading is 20%-40%, and the rolling times of the reduction rate are≥2; the rough rolling temperature is 850-950℃, the finish rolling temperature is 700-840℃, and the controlled cooling is performed after rolling; In the controlled cooling process, the on-line quenching after rolling is performed, the Mulpic cooling water amount is: 60-150L / s in the upper and lower A zone, 200-500L / s in the upper and lower B, C and D zones, the roller speed is 0.5-2.0m / s, and the re-red temperature is≤200℃; The heat treatment adopts the quenching+tempering process, the quenching temperature is 650-700℃, and the tempering temperature is 530-590℃.

2. The production method of a 7Ni steel plate according to claim 1, characterized in that, The anti-oxidation coating is one or more of aluminum silicate fiber, rare earth oxide and aluminum oxide powder, and the thickness is 1-3mm.

3. The production method of a 7Ni steel medium plate according to claim 1, characterized in that, The rough rolling open rolling temperature is≥1050℃. 4.A 7Ni steel medium plate prepared by the method of any one of claims 1-3. 5.The use of the 7Ni steel medium plate prepared by the method of any one of claims 1-3 or the 7Ni steel medium plate of claim 4 in the preparation of a low-temperature pressure vessel.

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