WO2022100056A1 - Crack arrest steel plate for bca2-grade container ship and manufacturing method for crack arrest steel plate - Google Patents

Abstract

The present invention relates to the technical field of steel production. Disclosed is a crack arrest steel plate for a BCA2-grade container ship. The crack arrest steel plate comprises the following chemical components by mass percentage: 0.04%-0.10% of C, 1.60%-2.00% of Mn, 0.30%-0.60% of Ni, 0.005%-0.05% of Nb, 0.005%-0.02% of Ti, 0.015%-0.060% of Al, 0.01%-0.25% of Cr, 0.10%-0.35% of Cu, 0.10%-0.40% of Si, not more than 0.010% of P, not more than 0.004% of S, and the balance being Fe and other inevitable impurities. Ferrite is induced to be separated out by means of grain boundary deformation, generation of carbide at the grain boundary is suppressed, the crack initiation probability is reduced, and the crack initiation energy is increased; and coarse carbide particles between bainite strip bundles are refined, the amount of coarse carbide is reduced, the length of a crack propagation path is increased, the brittle crack propagation resistance is effectively increased, and thus the crack arrest toughness is remarkably improved.

Description

A kind of BCA2 container ship crack arrest steel plate and its manufacturing method technical field

The invention relates to the technical field of iron and steel production, in particular to a crack arrest steel plate for BCA2 container ships and a manufacturing method thereof.

Background technique

The International Association of Classification Societies stipulates in UR W31 that after the thickness of the crack arrest steel plate for container ships exceeds 80mm, its crack arrest toughness should meet the BCA2 level, that is, the crack arrest toughness Kca ≥ 8000N/mm ^1.5 at -10℃, and in 2021 Effective January 1.

For steel plates above 80mm, due to the relatively small compression ratio and the small controlled cooling rate, it has been difficult for the conventional TMCP process to improve the crack arrest performance of the steel plate.

Studies have shown that there are many factors affecting the crack arrest performance of steel plates. Grain size, volume fraction of each phase, pearlite quantity, precipitation carbide quantity and location, and rolling texture all show different effects. Alloy design and active control for the above factors can effectively improve the crack arrest performance of steel plates.

The patent with publication number "JP2017-186614" discloses a thick steel plate with a thickness greater than 70mm and excellent crack arrest performance and its manufacturing method, and specifies that the structure within 5mm forms a structure extending in the rolling direction. The ratio is more than 1.5; the average bainite grain size of the 1/4t part of the plate thickness is below 25.0μm, and the average bainite grain size of the 1/2t part of the plate thickness is less than 35.0μm; the 1/4t part of the plate thickness The ferrite fraction is 15.0% to 40.0%, and the ferrite fraction of the 1/2t part of the plate thickness is 10.0% to 40.0%. In addition, at each plate thickness position, the total area of the structure other than ferrite and bainite is less than 5% (including 0%), and tempering treatment at 350 to 650°C is required after the accelerated cooling is completed.

The patent with the application number "201280007816.6" discloses a method for manufacturing a thick steel plate, an evaluation method and an evaluation device for the propagation stop performance of long brittle cracks, and a two-phase rolling control texture technology, which is difficult to produce and efficient. Significantly lower and less suitable for commercial applications. The patent with the application number "201580070867.7" discloses a high-strength steel with excellent brittle crack growth resistance and a manufacturing method thereof. The high-content precious metal Ni is used to toughen the matrix, and the production cost is greatly increased. At the same time, it is necessary to use a 400mm Thick billets, without general production conditions.

The patent with the application number of "201910149978.7" discloses a low alloy cost, high crack arrest extra-thick steel plate and a manufacturing method thereof, which adopts three-stage rolling. The cumulative reduction ratio of the second stage is ≥50%, and the third stage is in the two-phase region, and the cumulative reduction ratio is ≥28%. The total compression ratio of the steel plate is required to be greater than or equal to 3.5, and there is no general production condition; the production process is complex, and the rolling efficiency is low, which on the contrary brings the disadvantage of rising comprehensive costs.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides a BCA2 grade container ship crack arrest steel plate, whose chemical composition and mass percentage are as follows: C: 0.04%-0.10%, Mn: 1.60%-2.00%, Ni: 0.30%-0.60% , Nb: 0.005% ~ 0.05%, Ti: 0.005% ~ 0.02%, Al: 0.015% ~ 0.060%, Cr: 0.01% ~ 0.25%, Cu: 0.10% ~ 0.35%, Si: 0.10% ~ 0.40%, P ≤0.010%, S≤0.004%, the balance is Fe and other inevitable impurities.

The technical scheme that the present invention is further limited is:

The chemical composition and mass percentage of the aforementioned BCA2 container ship crack arrest steel plate are as follows: C: 0.05%-0.09%, Mn: 1.70%-2.00%, Ni: 0.35%-0.58%, Nb: 0.012% ～0.045%, Ti: 0.009%～0.018%, Al: 0.020%～0.050%, Cr: 0.03%～0.22%, Cu: 0.12%～0.30%, Si: 0.12%～0.35%, P≤0.008%, S ≤0.002%, the balance is Fe and other inevitable impurities.

The chemical composition and mass percentage of the aforementioned BCA2 grade container ship crack arrest steel plate are as follows: C: 0.04%, Mn: 1.70%, Ni: 0.35%, Nb: 0.012%, Ti: 0.012%, Al: 0.020 %, Cr: 0.01%, Cu: 0.30%, Si: 0.40%, P: 0.009%, S: 0.003%, and the balance is Fe and other inevitable impurities.

The chemical composition and mass percentage of the aforementioned BCA2 container ship crack arrest steel plate are as follows: C: 0.09%, Mn: 1.85%, Ni: 0.50%, Nb: 0.030%, Ti: 0.005%, Al: 0.030 %, Cr: 0.10%, Cu: 0.20%, Si: 0.10%, P: 0.004%, S: 0.002%, and the balance is Fe and other inevitable impurities.

The chemical composition and mass percentage of the aforementioned BCA2 container ship crack arrest steel plate are as follows: C: 0.07%, Mn: 2.00%, Ni: 0.58%, Nb: 0.045%, Ti: 0.020%, Al: 0.050 %, Cr: 0.22%, Cu: 0.10%, Si: 0.25%, P: 0.006%, S: 0.001%, and the balance is Fe and other inevitable impurities.

The aforementioned crack arrest steel plate for a BCA2 container ship has a thickness of 80-100 mm.

Another object of the present invention is to provide a method for manufacturing a crack arrest steel plate for a BCA2 container ship, comprising the following steps:

S1. The 320mm thick slab is heated at 1080～1180℃, after descaling, the first stage rough rolling is carried out at 1000～1150℃ to refine the grain size d to 25～40μm;

d=343ε ₁ ^-0.5 d ₀ ^0.4 exp(-55000/RT), where d ₀ =100μm, ε ₁ is the cumulative strain, R is the gas constant, and T is the kelvin temperature;

S2. When the temperature at 1/4 of the thickness of the billet to be warmed is in the range of Ar ₃ ～Ar ₃ +30[Ni], the second-stage finishing rolling is performed, and the total accumulated strain ε ₂ >0.50, and the deformation-induced ferrite must be satisfied. Condition d/ε ₂ <60 μm;

[Ni] is the Ni content, the unit is %;

S3. Immediately control cooling after finishing the second stage, the cooling rate is greater than 2°C/s, cooled to below 450°C, and pile-cooled for more than 60 hours to obtain a steel plate.

The beneficial effects of the present invention are:

(1) The present invention induces ferrite precipitation in grain boundary deformation, suppresses the generation of carbides at grain boundaries, reduces crack initiation probability, and increases crack initiation energy; refines coarse carbide particles between bainite strands and reduces coarse carbonization Increase the number of materials, increase the length of the crack propagation path, effectively increase the brittle crack propagation resistance, and thus significantly improve the crack arrest toughness;

(2) composition design of the present invention has the following advantages:

C is the most effective strengthening alloying element. It improves the hardenability and also increases the ductile-brittle transition temperature. Under the condition of ensuring strength, reducing the C content as much as possible is conducive to reducing the ductile-brittle transition temperature;

Mn is the most effective element to increase the strength in the case of low carbon. When the content exceeds a certain content, the effect of stabilizing the supercooled austenite is strong, and the bainite transformation temperature is shifted to the low temperature region, which effectively refines the bainite strands and reduces the effective Grain size; if the content is further increased, the segregation of Mn in the slab will increase, resulting in abnormal low-toughness structure after local material transformation, which damages the crack arrest toughness; the composition fluctuation of Mn element is used to match the appropriate non-recrystallization temperature. It can induce fine ferrite in the relatively Mn-depleted region, transfer the C element into the remaining austenite, and also create favorable dynamic conditions for the refined bainite transformation and reduce the bainite strips. The number of coarse carbides between bundles improves the carbide morphology;

Cr, Cu, and Ni are also stable supercooled austenite elements, which improve the hardenability and toughen the matrix, and effectively reduce the ductile-brittle transition temperature;

As harmful elements, P and S elements should be as low as possible from the point of view of clean steel. Considering the overall economy, the content of P is less than 0.008%, and the content of S is less than 0.002%.

(3) There are small deformation-induced ferrite formations at the prior austenite grain boundaries at 1/6 to 2/5 of the thickness of the steel sheet of the present invention, which effectively inhibits the formation of coarse carbides at the grain boundaries; austenite crystallites There is also deformation-induced ferrite on the deformation zone formed in the grains, which effectively separates the coarse grains of prior austenite. After controlled cooling, the bainite surrounds the deformation to induce ferrite nucleation and growth, and it is difficult for carbides to form in the shell. Produced between strands of ingots;

(4) Compared with the conventional process, the 80-100mm thick steel plate of the present invention has a smaller size and a smaller number of carbides, which greatly improves the propagation resistance of brittle cracks;

(5) The steel plate of the present invention has high strength and excellent low temperature toughness, and realizes the economical and efficient production of high crack arrest toughness and extra-thick crack arrest steel plate for container ships; it can use small compression ratio casting billets, and has less restrictions on production conditions.

Description of drawings

FIG. 1 is a photo of the microstructure at 1/4 of the thickness of the steel sheet of the present invention.

Detailed ways

A kind of BCA2 grade container ship crack arrest steel plate provided in the example, the composition is shown in Table 1, Tables 2 to 4 are the manufacturing process of the steel plate of the embodiment, and Table 5 is the performance parameter of the steel plate of the embodiment.

Table 1 Chemical composition unit: w.t.%

serial number	Plate thickness/mm	C	Si	Mn	P	S	Cr	Ni	Cu	Nb	Ti	Alt
Example 1	80	0.04	0.40	1.70	0.009	0.003	0.01	0.35	0.30	0.012	0.012	0.020
Example 2	90	0.09	0.10	1.85	0.004	0.002	0.10	0.50	0.20	0.030	0.005	0.030
Example 3	100	0.07	0.25	2.00	0.006	0.001	0.22	0.58	0.10	0.045	0.020	0.050

Table 2

serial number	Plate thickness/mm	Heating temperature/℃	Cumulative strain ε 1	Grain size d/μm
Example 1	80	1180	0.74	26.52
Example 2	90	1100	0.27	33.67
Example 3	100	1080	0.41	25.45

table 3

*A _r3 =910-273C-74Mn-56Ni-16Cr-9Mo-5Cu

Table 4

serial number	Cooling rate/℃	Red back temperature/℃	Heap cooling time/h
Example 1	4.1	430	61
Example 2	3.5	380	72
Example 3	2.5	351	65

table 5

Through the observation and analysis of the initiation and propagation process of brittle cracks in the crack arrest steel plate, it is found that the coarse carbide particles at the grain boundaries are the main origin of brittle crack initiation. The cracks connect with the cracks initiated by grain boundary carbides to form macroscopic cracks. As shown in Figure 1, the present invention suppresses the precipitation of coarse carbides at the grain boundary by inducing the production of ferrite through deformation, changes the nucleation position of bainite in the austenite, and improves the quantity and morphology of carbides between the bainite strands. The brittle crack propagation resistance of the steel plate is improved, and the 460MPa container ship crack arrest steel plate that meets the BCA2 level is obtained, with a maximum thickness of 100mm. The yield strength of the steel plate is ≥460MPa, the tensile strength is 570-720MPa, the single value of Charpy impact energy at -60℃ in the center of the plate thickness is greater than or equal to 200J, and Kca(-10℃)≥8000N/mm ^3/2 .

In addition to the above-described embodiments, the present invention may also have other embodiments. All technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims (7)

1. A BCA2 grade container ship crack arrest steel plate, characterized in that its chemical composition and mass percentage are as follows: C: 0.04%-0.10%, Mn: 1.60%-2.00%, Ni: 0.30%-0.60%, Nb: 0.005% ～0.05%, Ti: 0.005%～0.02%, Al: 0.015%～0.060%, Cr: 0.01%～0.25%, Cu: 0.10%～0.35%, Si: 0.10%～0.40%, P≤0.010%, S ≤0.004%, the balance is Fe and other inevitable impurities.
2. A BCA2 grade container ship crack arrest steel plate according to claim 1, characterized in that: its chemical composition and mass percentage are as follows: C: 0.05%-0.09%, Mn: 1.70%-2.00%, Ni: 0.35%- 0.58%, Nb: 0.012% to 0.045%, Ti: 0.009% to 0.018%, Al: 0.020% to 0.050%, Cr: 0.03% to 0.22%, Cu: 0.12% to 0.30%, Si: 0.12% to 0.35% , P≤0.008%, S≤0.002%, the balance is Fe and other inevitable impurities.
3. A BCA2 grade container ship crack arrest steel plate according to claim 1, characterized in that: its chemical composition and mass percentage are as follows: C: 0.04%, Mn: 1.70%, Ni: 0.35%, Nb: 0.012%, Ti : 0.012%, Al: 0.020%, Cr: 0.01%, Cu: 0.30%, Si: 0.40%, P: 0.009%, S: 0.003%, and the balance is Fe and other unavoidable impurities.
4. A BCA2 grade container ship crack arrest steel plate according to claim 1, characterized in that: its chemical composition and mass percentage are as follows: C: 0.09%, Mn: 1.85%, Ni: 0.50%, Nb: 0.030%, Ti : 0.005%, Al: 0.030%, Cr: 0.10%, Cu: 0.20%, Si: 0.10%, P: 0.004%, S: 0.002%, and the balance is Fe and other unavoidable impurities.
5. A BCA2 grade container ship crack arrest steel plate according to claim 1, characterized in that: its chemical composition and mass percentage are as follows: C: 0.07%, Mn: 2.00%, Ni: 0.58%, Nb: 0.045%, Ti : 0.020%, Al: 0.050%, Cr: 0.22%, Cu: 0.10%, Si: 0.25%, P: 0.006%, S: 0.001%, and the balance is Fe and other unavoidable impurities.
6. A crack arrest steel plate for BCA2 container ships according to claim 1, characterized in that the thickness of the steel plate is 80-100 mm.
7. A kind of manufacture method of BCA2 grade container ship crack arrest steel plate, it is characterized in that: be applied to any one of claim 1-6, comprise the following steps:

   S1. The 320mm thick slab is heated at 1080～1180℃, after descaling, the first stage rough rolling is carried out at 1000～1150℃, and the grain size d is refined to 25～40μm;

   d=343ε ₁ ^-0.5 d ₀ ^0.4 exp(-55000/RT), where d ₀ =100μm, ε ₁ is the cumulative strain, R is the gas constant, and T is the kelvin temperature;

   S2. When the temperature at 1/4 of the thickness of the billet to be warmed is in the range of Ar ₃ ～Ar ₃ +30[Ni], the second-stage finishing rolling is performed, and the total accumulated strain ε ₂ >0.50, and the deformation-induced ferrite must be satisfied. Condition d/ε ₂ <60 μm;

   [Ni] is the Ni content, the unit is %;

   S3. Control cooling immediately after finishing the second stage, the cooling rate is greater than 2°C/s, cool to below 450°C, and stack for more than 60 hours to obtain a steel plate.

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