WO2017206418A1

WO2017206418A1 - Normalized-condition delivered 180-200 mm-thick eh36 steel plate and preparation method therefor

Info

Publication number: WO2017206418A1
Application number: PCT/CN2016/102366
Authority: WO
Inventors: 刘朝霞; 阮小江; 苗丕峰; 赵孚; 白云; 刘俊
Original assignee: 江阴兴澄特种钢铁有限公司
Priority date: 2016-05-31
Filing date: 2016-10-18
Publication date: 2017-12-07
Also published as: CN105839003A; CN105839003B

Abstract

A normalized-condition delivered 180-200 mm-thick EH36 steel plate and a preparation method therefor. Chemical components of the steel plate are based on the national standard GB712 or classification society rules, Al is utilized to substitute the addition of element Ti, and a relative high content of V is added. The preparation method comprises: electric furnace smelting, LF refining, VD refining, die casting, ingot heating, cogging rolling, controlled slow cooling, billet heating, rolling, normalizing and the like that are performed in sequence. The obtained steel plate does not have an obvious gradient structure in a thickness direction. The steel plate employs a mixed structure mainly consisting of ferrite pearlite, supplemented by a small amount of bainite. Microscopic structures are fine and uniform and have an average grain size of 8-12 µm. The yield strength ranges from 380 MPa to 430 MPa, the tensile strength ranges from 550 MPa to 600 MPa, and the ductility is moderate. The steel plate has an impact toughness value greater than or equal to 60 J at a temperature of -40ºC at a 1/4 point and a 1/2 point, and has an excellent comprehensive mechanical property.

Description

180~200mm thick EH36 steel plate with normal fire delivery and preparation method thereof

Technical field

[0001] The invention belongs to the field of steel metallurgy, and particularly relates to a special thick 180~200mm EH36 steel which is delivered in a normal state and a production method thereof.

Background technique

[0002] At present, when it comes to the safety of marine operations, offshore enterprises still adopt foreign imports for the special thick plates of key parts such as 180~200mm EH36. The main reason is that there are very few enterprises in China that produce steel plates with a thickness of 180 to 200 mm. For the EH36 marine engineering steel plate delivered in high standard, the domestic technical reserve is insufficient.

[0003] At present, there are two major difficulties in the production of high-strength and extra-thick steel plates for marine engineering: 1. In order to meet the requirements of welding and low-temperature toughness, it is necessary to ensure the design of low-carbon equivalent components, so it must be matched with high-quality ultra-thickness. Slabs or steel ingots, etc. Increase the compression ratio to ensure the strength of the steel plate. 2. Products with a thickness of 150mm or more No existing codes and standards can be followed. The maximum thickness of steel plates covered by the eight countries in the world's nine-nation classification society is 100mm, the Norwegian Classification Society (DNV) is 150mm thick, and the national standard GB712~201 1 corresponds to a maximum thickness of 150mm. In the JIS classification and national standard GB712, the production of EH 36 steel grade is mainly controlled by the rolling, TMCP, hot rolling, normalizing rolling, normalizing and so on. At present, the offshore shipbuilding enterprises are still based on the composition design and requirements applicable to the product specifications of 6~100mm or 6~150mm to produce EH36 steel plates of 180~200mm, ie without changing the alloy composition (guaranteing low carbon equivalent) and delivery status. Under the premise, we purchase high-strength homogeneous steel sheets of extra thick series.

[0004] The object of the present invention is to use normalizing production without additional precious alloys and still using low carbon equivalent chemical composition to ensure the welding performance of the steel, and to redesign the steel plate production process for the thicker thickness of the EH36 steel plate. Ensure the uniformity of the tissue produced.

technical problem

[0005] The object of the present invention is to provide a normal fire delivery 180~200mm for the above prior art.

Preparation method of extra thick EH36 steel plate. The steel ingot of ≥900mm thickness is selected, and the ingot is rolled into the intermediate billet by the billet. The compression ratio of the thickness of the intermediate blank to the finished steel is 2.0 2.5, and the intermediate billet is controlled to be rolled to the thickness of the finished product. The steel ingot billet + controlled rolling production method is equivalent to two austenite recrystallization of the billet. The uniformity of the properties of the final large-thickness steel sheet in the thickness direction is ensured, in particular, the 1/2 thickness is ensured. The invention is from the blank to the finished steel, and the compression ratio is ≥ 4.5, and the method is suitable for the conventional thickness. The standard ingredients of EH3 6 still apply to the present invention.

Problem solution

Technical solution

[0006] The technical solution adopted by the present invention to solve the above problems is: a 180 200 mm thick E H36 steel plate delivered in a normal fire state, the chemical composition of the steel plate is based on the national standard GB712 or the classification society specification, and the A1 is used instead of the micro The element Ti prevents the Ti from being precipitated with other elements such as Nb 0 N; the element V is added to facilitate the hydrogen expansion control of the extra-thick plate, and the chemical composition by weight percentage is: C: 0.11 - 0.18%, Si: 0.15 0.50% Mn: 1.30 1.60<3⁄4 P: <0.0070%, S: <0.0030%, Nb: 0.010 0.050<3⁄4 V 0.0 30 A1: 0.050 0.070<3⁄4 Ni: 0.10 0.40<3⁄4 Cr: 0.10 0.20<3⁄4, the balance is Fe and inevitable Impurity element.

[0007] Preferably, the chemical composition of the steel sheet is C: 0.17% by weight, Si: 0.25%, Mn: 1.55%

P: <0.0060%, S: <0.0020%, Nb: 0.035%, V 0.065%, A1: 0.060%, Ni: 0.30%, Cr: 0.15%, and the balance is Fe and an unavoidable impurity element.

[0008] The steel plate does not have a distinct gradient structure in the thickness direction, and the steel plate structure is a mixed structure in which ferrite pearlite is mainly a small amount of bainite, and the average grain size is 8 12 μηι. Yield strength transverse tensile properties are 38 0 430 MPa, tensile strength 550 600 MPa, elongation ≥ 21 < 3⁄4, steel plate at 1/4 thickness, 1/2 thickness at -40 ° C impact toughness ≥ 60 J

[0009] The design principle of the steel composition of the present invention is:

[0010] The addition of C can increase the hardenability of steel, especially the production of medium and heavy plates, which can significantly improve the strength of normalized steel, but excessive C content is not conducive to the ultra-low temperature impact properties of steel, low temperature strain efficiency, welding Performance and corrosion resistance, so the carbon content in the present invention is controlled to low carbon control, between 0.11 and 0.18%

[0011] Si is mainly used for deoxidation. Although it is determined according to different smelting methods, it is necessary to obtain a good steel sheet performance, which must be above 0.15%, but if it exceeds 0.50%, it will cause segregation and damage of the heart. Welding performance, so the upper limit is specified as 0.50% [0012] Mn has a function of delaying the transformation of austenite to ferrite in the steel, and is advantageous for refining ferrite to improve strength and toughness. When the content of manganese is low, the above effects are not significant, and the strength and toughness of the steel sheet are low. If it is too high, it will cause segregation of continuous casting billet, poor toughness and weldability. The upper limit of manganese content is 1.60%, so the comprehensive addition of alloy is considered in the present invention, and the amount of manganese added is specified. It is in the range of 1.30~1.60<3⁄4.

[0013] The solute drag effect of Nb and the pinning action of Nb(C,N) on the austenite grain boundary inhibit the recrystallization of deformed austenite, expand the austenite non-recrystallization interval, and reduce the production of extra-thick plates. Stay warm. The precipitates are formed after cooling or tempering, so that the strength and toughness are improved, and the corrosion resistance of the steel can be improved. When the addition amount is less than 0.020%, the effect is not obvious, and the toughness is greater than 0.050%, which causes surface cracks in the continuous casting billet. Therefore, the present invention stipulates that the niobium content should be in the range of 0.020 to 0.050%.

[0014] V is an excellent deoxidizer for steel, which is an effective refining of grain elements and improves the strength and toughness of steel. In normalized steel, V is a precipitation strengthening element, and it is beneficial for the thick plate to expand hydrogen during the slow cooling process. The addition amount is greater than 0. 080%, the toughness is lowered, and the center segregation of the thick plate is remarkable. Therefore, the present invention stipulates that the niobium content should be in the range of 0.030 to 0.080 < 3⁄4.

[0015] A1 is used to fix the nitrogen element in the steel, and is added by replacing the micro-element Ti with A1 to prevent the Ti from being precipitated with other elements such as Nb, 0, N to form a prismatic hard large inclusion. Etc., resulting in unstable impact performance. At the same time, the content of A1 is too high, which easily leads to blockage of the crystallizer riser and formation of large A1 oxide. In the present invention, the aluminum content is specified to be 0.050 to 0.070%.

[0016] Ni is an element which improves the hardenability of steel, and is also the most commonly used element for effectively improving the low temperature toughness of steel. In addition, the combination of residual Cr and P in the steel will help to improve the corrosion resistance of the steel, but the upper limit of the classification society is 0.40%, in order not to exceed the requirements of the classification society. Therefore, in the present invention, the nickel content is specified to be 0.15 to 0.40 < 3⁄4.

[0017] Cr is an element which improves the hardenability of steel, and can suppress the formation of polygonal ferrite and pearlite, promote the transformation of bainite or martensite at a low temperature, and increase the strength of steel. However, if the Cr content is too high, it will affect the toughness of the steel and cause temper brittleness. The requirements of the classification society are not more than 0.20%. Therefore, the chromium content in the present invention is controlled to be 0.10 to 0.20 < 3⁄4.

[0018] Although P can improve the corrosion resistance, it lowers the low temperature toughness and hinders the weldability, and is not suitable for the structural steel. The present invention is controlled by steel ingots and is controlled to be 0.0070% or less. [0019] The formation of MnS inclusions in S also causes center segregation and adversely affects corrosion resistance. The present invention provides that it is controlled to be 0.0030% or less.

[0020] The method for preparing the 180-200 mm thick EH36 steel sheet which is delivered in the normalized state includes the following steps, [0021] (1) smelting process:

[0022] Selecting high-quality pig iron and scrap steel as raw materials for smelting, selecting high-quality steelmaking raw materials, raw materials are sequentially smelted by electric furnace, LF refining, VD

Refining, die casting, control of five harmful residual elements: 8≤0.0030<3⁄4, P<0.0070%, H<0.00015%, O<0.0015%, N<0.0050%; Ensure inclusions A, B, C in the finished steel sheet The total level of class D is below level 3.0;

[0023] In order to inhibit the looseness and segregation inside the steel ingot, the molten steel casting superheat degree is 25~40 ° C, and the casting process adopts full argon gas protection, and is cast into a flat steel ingot of ≥900 mm thickness;

[0024] After the steel ingot is uncapped, the belt is molded into a slow cooling pit for slow cooling and hydrogen expansion of 48 to 72 hours;

[0025] after the slow cooling, the surface is cleaned, and the steel ingot riser is removed after cleaning;

[2] (2) Steel ingot blanking process:

[0027] The steel ingot is heated to 1230~1260 ° C in a soaking furnace, the steel ingot insulation is 10~15 min / cm, and after dewatering, the scale is rolled by high pressure water, and then the billet is rolled into a middle billet, and the thickness of the intermediate billet is Satisfying the compression ratio between the thickness and the finished product is between 2.0 and 2.5; the intermediate blank after the blank is added with a cover and slow cooling for more than 48 hours;

[0028] (3) Rolling process:

[0029] The intermediate billet is heated to 1180 to 1250 ° C, and the intermediate billet is heated to a temperature of l l 14 min/cm to sufficiently dissolve the alloy elements in the steel to ensure uniformity of composition and properties of the final product. After the steel billet is discharged, it is descaled by high pressure water, and then subjected to two-stage controlled rolling of rough rolling + finishing rolling: the rolling temperature of rough rolling is 1050~1100 °C, rolling with large reduction, rolling is not carried out. Rolling, maintaining full longitudinal rolling, to ensure that each pass is set as much as possible according to the maximum rolling capacity. After the rough rolling, the three-pass single pass reduction ratio is 10~15%; the finishing rolling temperature is 850~920°C, and the thickness is rolled to the finished product. After finish rolling, ACC accelerated cooling is performed, and the cooling red return temperature is 630. ~700 ° C;

[0030] (4) Normalizing heat treatment process:

[0031] After rolling, the steel sheet is subjected to normalizing heat treatment, and the normalizing temperature is 880 to 920 ° C, and the holding temperature is 1.5 to 2.2 min/mm. Specifically, the continuous furnace is used for normalizing heat treatment of the steel plate, and the normalizing temperature of the continuous furnace is 880 to 920 ° C. Lmin/mm _{。 The} furnace is heated to the normal temperature of the steel plate is 1.6~2.2min/mm _; or the soaking furnace is used for the normal heat treatment of the steel plate, the normalizing temperature of the soaking furnace is 880-920 ° C, and the heat preservation time is 1.5~2. lmin/mm.

Advantageous effects of the invention

Beneficial effect

[0032] The invention is based on the design principle of carbon-manganese steel composition, and does not additionally increase precious alloys such as Ni and Cu, thereby saving alloy cost. Low carbon equivalent, welded enamel can still match the welding materials and welding process of ordinary EH36.

[0033] The molten steel smelting method of the present application has the advantages of low residual elements and high cleanliness of molten steel, and is applicable to the production of other high-standard extra-thick steel grades.

[0034] The method of the invention is carried out by steel ingot billet + controlled rolling, and the austenite recrystallization heat treatment is involved in the rolling process, so that the original austenite grains in the material are more uniform and fine. The heating temperature of the billet reaches 1230-1 260 °C, which effectively improves the segregation of the ingot core. This is an important prerequisite for ensuring the uniformity and uniformity of the final thick plate. The intermediate billet heating temperature is 1180-1250 °C, which is beneficial to the austenite recrystallization. At the same time, the reheating temperature of the intermediate billet is not as high as the heating temperature of the ingot billet, in order to ensure that the austenite is not recrystallized. As for roughening.

[0035] The slab after rolling is processed by the normalizing process, and the process plan required by the classification society's specifications is not changed, making the user more acceptable. It also overcomes the shortcomings of prior art quenching and tempering, NAC and other processes for processing thick plates with large gradients in the thickness direction and poor performance.

[0036] The extra-thick EH36 ship plate steel produced under the condition of the invention has good toughness, and the steel plate does not have obvious gradient structure in the thickness direction, and the steel plate structure is mainly composed of ferrite pearlite, and a small amount of bainite is supplemented. Mixed organization. The microstructure was fine and uniform, and the average grain size of the steel sheet was measured by the cross-sectional method to be 8-12 μη. Brief description of the drawing

DRAWINGS

1 is a metallographic structure at a thickness of 1/4 of a steel plate in Embodiment 1 of the present invention, which is a mixed structure in which ferrite pearlite is mainly a small amount of bainite structure;

2 is a metallographic structure of a steel sheet at a thickness of 1/2 in Example 1 of the present invention, which is a mixed structure in which a ferrite pearlite is mainly a small amount of bainite structure.

BEST MODE FOR CARRYING OUT THE INVENTION BEST MODE FOR CARRYING OUT THE INVENTION

[0039] The present invention will be further described in detail below with reference to the embodiments of the drawings.

[0040] Preparation method of extra thick EH36 steel:

[0041] (1) Using high-quality scrap steel as smelting raw materials, using high-quality steelmaking raw materials, smelting two furnaces, 50 tons per furnace. The molten steel is sequentially smelted by electric furnace, LF refining, VD

Refining, steady casting into 4 steel ingots, 25 tons per steel ingot, the three steel ingots used in the present invention are used as Examples 1 to 3, respectively. The ingot section is larger than 900mm to ensure a compression ratio of more than 4.5 with the final product. Control the five harmful residual elements of molten steel: 8≤0.0030<3⁄4, P is 0.0070%, H is 0.00012%,

0 is 0.0010% and N is 0.004%. Taking into account the need to allow the inclusions to fully float and control the internal porosity of the ingot, segregation requirements for superheat, casting at 25-40 ° C superheat, the casting is argon gas protection, cast into a flat steel ingot ≥ 900mm thick. After the steel ingot is uncapped, it is molded into a slow cooling pit for 48-72 hours of slow cooling and hydrogen expansion. After the slow cooling, the surface of the steel ingot is cleaned. In this embodiment, the steel ingot does not need to be cleaned with temperature, and the steel ingot riser is removed after cleaning. The smelting components of the steel ingots of the respective examples are shown in Table 1.

[0042] Table 1 Example Chemical composition of EH36 steel plate for marine engineering (wt<3⁄4)

[] [Table 1]

[0043]

[0044] (2) The cleaned ≥900mm steel ingot is heated to 1230-1260 ° C in the soaking furnace, and the ingot is heated to 13 min/cm, and then descaled by high pressure water after being discharged, and then the billet is rolled into the middle. The billet ensures a compression ratio of the thickness of the intermediate blank to the thickness of the finished product of 2.0-2.5. After the blank is obtained, the intermediate blank is taken off the line, and the cover is slowly cooled for about 48 hours, and the upper blank of the other steel grades is topped and covered.

[0045] The intermediate blank is sent to a step-type heating furnace, heated to 1180-1250 ° C, and the intermediate billet is heated to a temperature of l l-14 min / cm, so that the alloying elements in the steel are fully dissolved to ensure the composition of the final product. And uniformity of performance. Steel billet After de-pressing, it is descaled by high-pressure water and then subjected to two-stage controlled rolling of rough rolling + finishing rolling: the rolling temperature of rough rolling is between

1050-1100 °C, rolling with large reduction, rolling 吋 does not carry out rolling and rolling, maintaining full vertical rolling, to ensure that each pass is set as much as possible according to the maximum rolling capacity. The single pass reduction ratio of the last three passes of rough rolling is 10-15%; the finishing rolling temperature is between 850 and 920 °C, after finishing rolling to the finished product thickness, it is sent to the ACC unit for accelerated cooling, and the cooling red temperature is cooled. For 630-700. C.

[0046] (3) Normalizing treatment: The homogenizing furnace is used for normalizing treatment, the normalizing temperature is controlled to be 890-910 ° C, and the thermal insulation is 2.0 min/mm soil for 5 min.

[0047] Examples 1 to 3 are extra-thick EH36 plates of 180-200 mm, and the total class of inclusions A, B, C, and D is controlled at 2.0. In the case of extra-thick plates, the uniformity of the steel plate in the thickness direction is directly related to the performance of the steel. The uniform structure is the safety guarantee for the normal use and service of the steel plate.

[0048] The present invention detects the performance of the extra-thick EH36 plate at 1/2, Table 2, from the tensile properties of the steel plate, the transverse tensile properties of the yield strength of the steel plate are between 380 and 430 MPa, and the tensile strength is between Between 550 and 600 MPa, the elongation is moderate, all of which are above the requirements of GB712. The tensile properties of the steel sheet at a thickness of 1/2 are slightly lower than the thickness of 1/4, but the difference is not large. The low-temperature impact toughness of the steel sheets of the examples was as shown in Table 3, and the impact toughness value of -40 ° C at 1/4 of the thickness of the steel sheet and 1/2 was ≥ 60 J.

Table 2 Tensile properties of various embodiments of the present invention

[]

Table 3 Impact performance of various embodiments of the present invention

In addition to the above-described implementations, the present invention also includes other embodiments, where equivalent transformations or equivalents are employed. The technical solutions formed by the alternatives are all within the scope of the claims of the present invention. Embodiments of the invention

[0052] The description paragraphs of the embodiments of the present invention are entered here.

Industrial applicability

[0053] Enter the paragraph of industrial applicability description here.

Sequence table free content

[0054] Type the sequence table free content description paragraph here.

Claims

Claim [Claim 1] A 180~200mm thick EH36 steel plate delivered in a normalized state, characterized in that: the chemical composition of the steel plate is based on the national standard GB712 or classification society specifications, and A1 is used to replace the trace element Ti to Prevent Ti from compound precipitation with other elements such as Nb, O, and N; Add element V to facilitate hydrogen expansion control of extra thick plates. The chemical composition in weight percentage is: C: 0.11-0.18%, Si: 0.1 5~0.50<¾, Mn: 1.30~1.60<¾, P: <0.0070%, S: <0.0030%, Nb: 0.010~0.050<¾, V: 0.030~0.080<¾, A1: 0.050~0.070<¾, Ni: 0.10~ 0.40%, Cr: 0.10-0.20%, the balance is Fe and inevitable impurity elements. [Claim 2] The 180~200mm thick EH36 steel plate delivered in a normalized state according to claim 1, characterized in that: the chemical composition of the steel plate in weight percentage is C: 0.17%, Si: 0.25%, Mn: 1.55%, P: <0.0060%, S: <0.0020%, Nb: 0.035%, V: 0.065%, Al: 0.060%, Ni: 0.30%, Cr: 0.15%, the balance is Fe and inevitable impurity elements . [Claim 3] A method for preparing a 180~200mm thick EH36 steel plate delivered in a normalized state according to claim 1 or 2, characterized by: including the following steps,

(1) Smelting process:

High-quality pig iron and scrap steel are selected as smelting raw materials, and high-quality steel-making raw and auxiliary materials are selected. The raw materials are smelted by electric furnace, LF refining, and VD in sequence.

Refining and molding, control of five harmful residual elements: 8≤0.0030<¾, P<0.0060%, H<0.00015%, O<0.0015%, N<0.0050%; ensure inclusions A, B, C, The overall level of Category D is below 3.0;

In order to suppress looseness and segregation inside the steel ingot, the superheat of molten steel casting is 25~40°C. The entire casting process is protected by argon gas, and the flat steel ingot is cast into a ≥900mm thick flat steel ingot; after the steel ingot is uncapped, it is brought into the slow cooling pit with the mold for 48~72 seconds. Small-scale slow cooling hydrogen expansion;

After slow cooling, the surface is cleaned, and after cleaning, the riser of the steel ingot is cut off;

(2) Steel ingot opening process:

The steel ingot is heated to 1230~1260°C in a soaking furnace. The heat preservation time of the steel ingot is 10~15min/cm. After being discharged from the furnace, it is descaled with high-pressure water and then rolled into an intermediate billet. The thickness of the intermediate billet is The compression ratio between the thickness of the finished product and the thickness of the finished product is between 2.0 and 2.5; the intermediate blank after the blank is rolled off the line is covered and slowly cooled for more than 48 hours;

(3) Rolling process:

The intermediate billet is heated to 1180~1250°C, and the heating time of the intermediate billet is 11~14min/cm. After the steel billet is released from the furnace, it is descaled by high-pressure water, and then carries out two-stage controlled rolling of rough rolling + finishing rolling: rough rolling and simultaneous rolling The temperature is 1050~1100°C, large reduction is used for rolling, no steel transfer rolling is performed during rolling, full longitudinal rolling is maintained, and the reduction rate of the three single passes after rough rolling is 10~15%; finish rolling The joint rolling temperature is 850~920°C, and the rolling is to the finished product thickness. After the finishing rolling is completed, ACC accelerated cooling is performed, and the cooling return temperature is 630~700°C;

(4) Normalizing heat treatment process:

After rolling, the steel plate is subjected to normalizing heat treatment, the normalizing temperature is 880~920°C, and the holding time is 1.5~2.2min/mm°

[Claim 4] The 180~200mm thick EH36 steel plate delivered in a normalized state according to claim 1 or 2, characterized in that: the steel plate does not have an obvious gradient structure in the thickness direction, and the steel plate structure is ferrite pearlite A mixed structure consisting mainly of a small amount of bainite and a small amount of bainite, with an average grain size of 8~12μm°

[Claim 5] The 180~200mm thick EH36 steel plate delivered in the normalized state according to claim 1 or 2, characterized in that: the yield strength, the transverse tensile property is 380~430MPa, and the tensile strength is 550~6OOMPa, The elongation is ≥21%, and the -40°C impact toughness value of the steel plate at 1/4 thickness and 1/2 thickness is ≥60 J.

[Claim 6] The method for preparing a 180~200mm thick EH36 steel plate delivered in a normalized state according to claim 3, characterized in that: a continuous furnace is used for normalizing heat treatment of the steel plate, and the normalizing temperature of the continuous furnace is 880~ 920°C, the time from entering the furnace to coming out of the furnace is 1.6~2.2min/mm; or use a soaking furnace to normalize the steel plate, the normalizing temperature of the soaking furnace is 880-920°C, and the holding time is 1.5~2.1min /mm°