CN114645191B - Low-cost high-toughness high-weldability high-strength ship board and preparation method thereof - Google Patents
Low-cost high-toughness high-weldability high-strength ship board and preparation method thereof Download PDFInfo
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Abstract
The invention provides a low-cost high-toughness high-weldability high-strength ship board and a preparation method thereof, wherein the preparation method of the low-cost high-toughness high-weldability high-strength ship board comprises the following steps: the weight percentage Wt of the chemical components of the ship plate is C:0.06 to 0.10%, si:0.15 to 0.40%, mn: 1.35-1.50%, P is less than or equal to 0.020%, S is less than or equal to 0.008%, nb:0.025 to 0.040%, ti:0.018 to 0.020%, alt: 0.020-0.040, less than or equal to 0.006 percent of N and the balance of Fe and inevitable trace elements; the process route of the preparation method of the low-cost high-toughness high-weldability high-strength ship plate comprises the following steps: the method comprises the following steps of molten iron pretreatment, converter smelting, LF refining, RH refining, whole-process protective casting, slab heating, descaling, rough rolling, finish rolling, pre-straightening, ultra-fast cooling, straightening, air cooling and steel plate inspection. The invention has better comprehensive performance.
Description
Technical Field
The invention relates to the field of steel rolling, in particular to the field of production of structural steel for ship and ocean engineering, and especially relates to a low-cost high-toughness high-weldability high-strength ship plate and a preparation method thereof.
Background
With the development of large ships, the demand for large, high-rise and complex hull welding structures is increasing, and the requirements for strength, ductility, weldability and low-temperature toughness of steel for ships are increasing. The high-strength ship plate steel is mainly used for manufacturing hulls, decks and the like of ocean, coastal and inland shipping ships. Therefore, the requirements for materials are also becoming more stringent, such as excellent toughness, weldability, strain aging sensitivity, and uniformity of properties. The traditional high-strength ship plate mainly comprises medium carbon plus alloy elements (such as Mn, nb, ti, ni, cr, mo and the like), controlled rolling and heat treatment processes, and although the structure can be homogenized and the low-temperature toughness is improved, the carbon equivalent is high, the weldability is poor, the production period is long, and the cost is high.
With the development of controlled rolling and controlled cooling technology, controlled rolling and controlled cooling processes of low C + Mn + Al + Ti or low C + Mn + Nb + V + Ti + Ni or low carbon + Mn + Nb + V + Ti or low carbon + Mn + Nb + V and other component systems are gradually developed, although better weldability and obdurability can be obtained, the alloy cost is high or the control difficulty is large or the internal performance of thick steel plates is difficult to guarantee. The structure obtained in the above way is mainly massive ferrite + pearlite or polygonal ferrite + pearlite, and the improvement of the comprehensive performance has limitation.
In summary, the following problems exist in the prior art: the prior ship steel has poor strength, plasticity and toughness, weldability and low-temperature toughness, or has high cost and difficult production control.
Disclosure of Invention
The invention provides a low-cost high-toughness high-weldability high-strength ship board and a preparation method thereof, so that the ship board has better comprehensive performance and lower production cost.
Therefore, the invention provides a preparation method of a low-cost high-toughness high-weldability high-strength ship plate, which comprises the following steps:
the weight percentage Wt of the chemical components of the ship plate is C:0.06 to 0.10%, si:0.15 to 0.40%, mn: 1.35-1.50%, P is less than or equal to 0.020%, S is less than or equal to 0.008%, nb:0.025 to 0.040%, ti:0.018 to 0.020%, alt: 0.020-0.040, less than or equal to 0.006 percent of N and the balance of Fe and inevitable trace elements;
the process route of the preparation method of the low-cost high-toughness high-weldability high-strength ship plate comprises the following steps: the method comprises the following steps of molten iron pretreatment, converter smelting, LF refining, RH refining, whole-process protective casting, slab heating, descaling, rough rolling, finish rolling, pre-straightening, controlled cooling (adopting ultra-fast cooling) after rolling, straightening, air cooling and steel plate inspection.
Further, the rough rolling: the longitudinal, transverse and longitudinal continuous rolling mode is adopted, the rough rolling finishing temperature is more than or equal to 1000 ℃, the single-pass reduction of the middle pass is more than or equal to 20mm, and the cogging thickness is 2-3.5 times of the thickness of the finished product.
Further, finish rolling: low-temperature section rolling, the accumulated reduction rate is more than 65 percent, the finish rolling start temperature is 900-950 ℃, and the finish rolling temperature is 810-850 ℃. Continuous rolling, and no temperature reduction during the passage.
Further, the ultra-fast cooling is carried out, wherein the starting cooling temperature is more than or equal to 730 ℃, the temperature of red return is 580-630 ℃, and the cooling speed is 13 ℃/S-35 ℃/S.
Furthermore, the cooling water group number is started according to the temperature of red returning, and a sectional cooling or back-end cooling, low steel plate running speed, high water flow and high water pressure cooling strategy is adopted, so that the surface layer of the steel plate forms an imitated crystal form F + GB, and meanwhile, the cooling uniformity in the thickness direction is increased, and the reduction of the banded structure is reduced.
Further, slab continuous casting: the casting process keeps constant drawing speed; the dynamic soft reduction is used, the reduction interval is 0.5-1.2, and the reduction is 5.0 mm.
Further, LF molten steel refining treatment: after the final alloying, the medium-strength argon blowing or strong argon blowing time of more than 3min must be ensured, and the TiFe must be added after the white slag or the transparent glass slag or the light dark green slag is manufactured.
Further, RH molten steel refining treatment: the sedation time is 18 min-35 min.
The invention also provides a low-cost high-toughness high-weldability high-strength ship plate, which comprises the following chemical components in percentage by weight: 0.06 to 0.10%, si:0.15 to 0.40%, mn: 1.35-1.50%, P is less than or equal to 0.020%, S is less than or equal to 0.008%, nb:0.025 to 0.040%, ti:0.018 to 0.020%, alt: 0.020-0.040, less than or equal to 0.006 percent of N and the balance of Fe and inevitable trace elements; the carbon equivalent CEV is less than or equal to 0.34, and the ratio of the surface layer imitated crystal form F + GB is 28% of the thickness of the steel plate.
Further, the thickness of the ship plate is 6-50mm.
The carbon equivalent CEV of the obtained low-cost high-toughness high-weldability high-strength ship board is less than or equal to 0.34The ratio of the layer imitated crystal form F and GB is 28% of the thickness of the steel plate. The yield strength ReH is 474-490 MPa, the tensile strength Rm is 550-580 MPa, the elongation A after fracture is 24.0-27.0%, and the V-shaped impact work (longitudinal) AKV at the temperature of-60 DEG C 2 190-323J, transverse V-shaped impact power AKV 2 170J-297J, qualified cold bending, 40-73% of Z-direction performance, and-60 ℃ strain aging impact energy (longitudinal) AKV 2 120-230J, and the steel plate has better comprehensive performance.
According to the invention, elements such as Ni or V or Cr or Mo and the like are not required to be added, a subsequent heat treatment process is not required, and a crystal-like F + GB + PF + AF + P structure (F is ferrite, P is pearlite, GB is granular bainite, and AF is acicular ferrite) is formed through design and optimization of components and a controlled rolling and cooling process, so that good comprehensive performance is obtained, and stable production of the product is realized.
Drawings
FIG. 1 is a photomicrograph of the metallographic structure of the surface layer of the ship plate according to example 1 of the present invention; the surface layer is of an imitated crystal form F + GB, and the thickness of the imitated crystal layer is 14mm;
FIG. 2 is a high magnification photograph of the metallographic structure of the surface layer of the ship plate according to example 1 of the present invention;
FIG. 3 is a photograph of the metallographic structure of a quarter of the thickness of the plate of the ship in example 1 of the present invention; mainly comprises the following steps: f + AF + PF + a small amount of P;
FIG. 4 is a photograph of the metallographic structure of the core of the ship in example 1 of the present invention; the center part does not have F or P banded structures, and a B segregation zone is 0.5 grade;
FIG. 5 is a photograph of the metallographic structure of the center of the boat plate in example 1 of the present invention; the metallographic structure is as follows: f + GB + P
FIG. 6 is a photomicrograph of the metallographic structure of the surface layer of the boat deck in example 2 of the present invention; the surface layer is of an imitated crystal form F + GB, and the thickness of the imitated crystal layer is 2.5mm;
FIG. 7 is a high magnification photograph of a metallographic structure of a surface layer of a ship plate according to example 2 of the present invention; FIG. 8 is a photograph of the metallographic structure of a quarter of the thickness of the boat plate in example 2 of the present invention; mainly comprises the following steps: f + PF + a small amount of P,
FIG. 9 is a photograph of the metallographic structure of the core of the ship's board in example 1 of the present invention; the center part does not have F or P banded structures, and a B segregation zone is 0.5 grade;
FIG. 10 is a photograph of the metallographic structure of the center of the boat plate in example 1 of the present invention; the metallographic structure is as follows: f + GB + P;
FIG. 11 is a photograph of the metallographic structure of the surface layer of the ship plate in example 5 of the present invention;
FIG. 12 is a photograph of the metallographic structure of the core of a ship in accordance with example 5 of the present invention;
FIG. 13 is a photograph or schematic illustration of a weld tensile failure location for a boat deck of example 2; the weld tensile failure location was outside the weld (the weld tensile failure location was 28.7mm from the weld);
FIG. 14 is a photograph of the impact fracture morphology at different locations of the welded joint of the ship plate of example 2.
Detailed Description
In order to more clearly understand the technical features, objects, and effects of the present invention, the present invention will now be described with reference to the accompanying drawings.
The invention provides a low-cost high-toughness high-weldability high-strength ship board and a preparation method thereof. The yield strength ReH of the product is more than or equal to 420MPa, the tensile strength Rm is more than or equal to 530MPa, the elongation A after fracture is more than or equal to 21 percent, and the longitudinal impact energy AKV at the temperature of minus 60 DEG C 2 The cold bending is not less than 150J, the cold bending is qualified, the performance in the thickness direction is superior to Z35 grade, and the carbon equivalent Ceq is not more than 0.35.
The technical scheme adopted is as follows: a ship plate with low cost, high toughness, high weldability and high strength is prepared from the following chemical components (weight percentage Wt): 0.06 to 0.10%, si:0.15 to 0.40%, mn: 1.35-1.50%, P is less than or equal to 0.020%, S is less than or equal to 0.008%, nb:0.025 to 0.040%, ti:0.015 to 0.020%, alt: 0.020-0.040, less than or equal to 0.006N, and the balance of Fe and inevitable trace elements. Ceq is: 0.30-0.35.
Further, the ship plate with low cost, high toughness, high weldability and high strength comprises the following chemical components in percentage by weight: 0.06 to 0.09%, si:0.15 to 0.40%, mn: 1.35-1.50%, P is less than or equal to 0.020%, S is less than or equal to 0.008%, nb:0.025 to 0.035%, ti:0.015 to 0.018%, alt: 0.020-0.040, less than or equal to 0.006N, and the balance of Fe and inevitable trace elements. Ceq is: 0.32-0.34.
A manufacturing method of a low-cost high-toughness high-weldability high-strength ship plate comprises the following process routes: molten iron pretreatment → converter smelting → LF refining → RH refining → whole course protective casting → slab heating → descaling → rough rolling → finish rolling → pre-straightening → ultra-fast cooling → straightening → air cooling → steel plate inspection → warehousing.
1. Smelting molten steel in a converter:
ensuring that S in the molten iron is less than or equal to 0.01Wt%; argon is blown from bottom in the whole smelting process;
2. LF molten steel refining treatment:
and after the last alloying, the medium-strength argon blowing or strong argon blowing time of more than 3min must be ensured. The TiFe is added after the white slag, the transparent glass slag or the light greenish black slag is manufactured.
3. RH molten steel refining treatment: the sedation time is 18 min-35 min.
4. Slab continuous casting:
the casting process stabilizes the pulling speed and keeps the pulling speed constant; the dynamic soft reduction is used, the reduction interval is 0.5-1.2, and the reduction is about 5.0 mm.
5. Heating the plate blank:
the heating temperature is 1130-1240 ℃, and the heating time is more than or equal to 210min.
6. Rolling:
two-stage rolling, no rolling mill cooling water is used in the whole process, and high-pressure descaling is performed according to actual spraying. (1) rough rolling: and carrying out austenite recrystallization rolling by adopting a longitudinal, transverse and longitudinal rolling mode, high-temperature rapid rolling and large reduction so as to transfer the deformation to the center of the blank. The initial rolling temperature is 1110-1170 ℃, the final rolling temperature of rough rolling is more than or equal to 1000 ℃, and the single-pass reduction of the middle pass is more than or equal to 20mm. The cogging thickness is 2-3 times of the thickness of the finished product. (2) finish rolling: mainly rolling in an austenite non-recrystallization region of a low-temperature section to promote the formation of a small-grain imitated crystal form F. Meanwhile, in order to improve the low-temperature impact toughness of the steel plate, enough pass reduction rate is ensured, the accumulated reduction rate is more than 65 percent, the rolling temperature of finish rolling is 900-920 ℃, and the final rolling temperature is 810-830 ℃. And (3) continuously rolling, and keeping the rolling rolls between the passes for cooling.
7. And (3) cooling:
after finish rolling, the steel enters a (ultra-fast cooling) cooling zone as fast as possible, and the precipitation of massive ferrite and the recovery softening of work hardening are avoided. The starting cooling temperature is more than or equal to 730 ℃, and the temperature of red return is 580-630 ℃. And starting the cooling water group number according to the temperature of red returning, and adopting a sectional cooling or back-end cooling, low steel plate running speed, high water flow and high water pressure cooling strategy to form an imitated crystal form F + GB on the surface layer of the steel plate and increase the cooling uniformity in the thickness direction so as to reduce the banded structure and improve the strength and toughness and uniformity of the thickness directional performance of the steel plate.
Compared with the conventional ferrite and pearlite steel, the grain boundary imitating ferrite/granular bainite complex phase structure has better toughness matching and deformation cooperativity. The existence of a proper amount of grain boundary-simulated ferrite with relatively small grain size increases the coordinated deformation capability of a complex phase structure, improves the crack forming work, simultaneously bends and bifurcates a crack expanding path, passivates the tip of a microcrack, and enhances the crack stopping performance of steel. The use of Granular Bainite (GB) instead of pearlite has a higher strength than pearlitic steels of the same carbon content. Based on a high-purity steel smelting technology and a medium plate ultra-fast cooling technology, the invention obtains an imitation crystal F + GB + PF + AF + P structure by developing a low C + Mn + Nb + Ti component system and a rolling and cooling control process, so that the material has high weldability, good low-temperature toughness, strong plasticity, strain aging sensitivity and uniform performance.
The ship board with low cost, high toughness, high weldability and high strength, which is obtained by the invention, has the carbon equivalent CEV less than or equal to 0.34, and the content of the surface layer crystal-like form F + GB reaches 28% of the thickness of the steel plate. The yield strength ReH is 474-490 MPa, the tensile strength Rm is 550-580 MPa, the elongation A after fracture is 24.0-27.0%, and the V-shaped impact energy (longitudinal) AKV at-60 DEG C 2 190-323J, transverse V-shaped impact power AKV 2 170J-297J, qualified cold bending, 40-73% of Z-direction performance, and-60 ℃ strain aging impact energy (longitudinal) AKV 2 120-230J, and the steel plate has better comprehensive performance.
According to the invention, elements such as Ni or V or Cr or Mo and the like are not required to be added, a subsequent heat treatment process is not required, and a crystal-like F + GB + PF + AF + P structure is formed through design and optimization of components and a controlled rolling and controlled cooling process, so that good comprehensive performance is obtained, and stable production of the product is realized.
The ultrahigh-strength ship plate with high toughness and high weldability comprises FH420, FH420-Z25 and FH420-Z35.
The ultrahigh-strength ship plate with high toughness and weldability comprises steel with the grade lower than FH420 series, such as AH 40-FH 40, AH 36-FH 36, AH 32-FH 32 and the like.
The thickness of the ultrahigh-strength ship plate with high toughness and high weldability is less than or equal to 50mm, for example, 18-50mm.
The following are specific examples of the invention: the production method of the ultrahigh-strength ship plate with high toughness and high weldability adopts the following component proportion and specific process. Wherein, table 1 shows the composition (in weight percent) and carbon equivalent CEV of the steels of the respective examples. Tables 2 and 3 show the rolling and cooling process parameters for the compositions of the examples described in Table 1, tables 4 and 5 show the mechanical properties and structure for the examples, and tables 6-1 and 6-2 show the welding properties. FIGS. 1, 2, 3, 4 and 5 are metallographic structure photographs of different portions of example 1; FIGS. 6, 7, 8, 9 and 10 are metallographic photographs of different portions of example 2; fig. 11 and 12 are photographs of the metallographic structure of the surface layer and the core of the example.
Table 1: chemical composition (wt%) and carbon equivalent Ceq of product
Table 2: specific rolling process parameters for each example
The initial rolling temperature of rough rolling is 1110-1180 ℃, continuous rolling is carried out in a longitudinal-transverse-longitudinal mode, and widening passes are widened by 2 passes by using plane shape control. And (4) finish rolling is carried out continuously for 8 times of longitudinal rolling.
Table 3: specific Cooling Process parameters for Each example
And (3) cooling in sections or in the back section, giving a certain relaxation time to the steel plate, and accelerating cooling after the crystal-like form F is separated out on the surface layer.
Table 4: mechanical properties obtained for the examples
Table 5: thickness-wise uniformity of properties and strain-aged impact obtained in examples 1 and 2
Tables 6-1 and 6-2: welding Properties obtained in example 2
The welding test adopts a submerged arc automatic welding process, the welding wire for the test is a submerged arc welding wire for a low-alloy high-toughness ship, the diameter of the welding wire is 3.2mm, and the welding input heat is 50KJ/cm. The mechanical property test sample of the welded joint is prepared according to the Material and welding Specification 2009 of the Chinese classification society of Ship. Tensile tests, bending tests and impact tests of the welded joint were carried out according to GB/T228-2010 metallic material tensile test, GB/T232-1999 metallic material bending test method and GB/T229-2007 metallic material Charpy pendulum impact test method, as shown in tables 6-1 and 6-2. In the welded joint tensile test, the performance of the steel plate is higher than the specified value of the base material FH 420.
TABLE 6-1 tensile test results of welded joints
The ship plate submerged arc automatic welding joint is subjected to a-40 ℃ impact test in combination with the common environment of steel for ships and ocean engineering, and the impact test result is shown in the table 6-2 and the figure 14. As can be seen from Table 6-2, the impact toughness of the steel plate at the joint line and the base material meets the requirement of GB/T712 (i.e. the average impact energy is not less than 42J), and the steel plate has better impact toughness.
TABLE 6-2 weld joint impact test results
The ship plate submerged arc automatic welding joint is subjected to a cold bending test, the diameter of a positive and negative bending core is 2a, the diameter of a side bending core is 3a, the cold bending test result is shown in tables 6-3, and the steel plate bending is qualified.
TABLE 6-3 Cold bending test results
| Thickness/mm | Welding method | Positive curve | Reverse bend | Lateral bending |
| 25mm | Transverse direction | Qualified | Qualified | Qualified |
Fig. 13 is a photograph of the welded tensile failure location of the ship plate of example 2, which is 28.7mm away from the welded joint. FIG. 14 is a photograph of impact fracture morphology at different locations of a welded joint of a ship plate of example 2. The impact toughness of the steel plate at different positions from the welded joint can change under the influence of welding, and the appearance of the impact fracture shown in FIG. 14 shows that after welding, the impact toughness of a welding zone and a welding affected zone at-40 ℃ is better.
The above description is only an exemplary embodiment of the present invention, and is not intended to limit the scope of the present invention. In order that the components of the present invention may be combined without conflict, it is intended that all equivalent changes and modifications made by those skilled in the art without departing from the spirit and principles of the present invention shall fall within the protection scope of the present invention.
Claims (4)
1. The preparation method of the low-cost high-toughness high-weldability high-strength ship plate is characterized by comprising the following steps of:
the ship plate comprises the following chemical components in percentage by weight: 0.06% -0.0897%, si:0.15% -0.40%, mn: 1.35-1.50%, P is less than or equal to 0.020%, S is less than or equal to 0.008%, and Nb: 0.025-0.0379%, ti:0.015% -0.0171%, alt: 0.020-0.040 percent, less than or equal to 0.006 percent of N and the balance of Fe and inevitable trace elements;
the process route of the preparation method of the low-cost high-toughness high-weldability high-strength ship plate comprises the following steps: the method comprises the following steps of molten iron pretreatment, converter smelting, LF refining, RH refining, whole-process protective casting, slab heating, descaling, rough rolling, finish rolling, pre-straightening, controlled cooling after rolling, straightening, air cooling and steel plate inspection, wherein the controlled cooling after rolling is carried out by adopting ultra-fast cooling;
rough rolling: carrying out austenite recrystallization rolling by adopting a longitudinal, transverse and longitudinal continuous rolling mode and high-temperature rapid rolling and large rolling reduction, so that deformation is transferred to the center of a blank; the initial rolling temperature is 1110-1170 ℃, the rough rolling finishing temperature is more than or equal to 1000 ℃, and the single-pass rolling reduction of the middle pass is more than or equal to 20mm; the cogging thickness is 2~3 times of the thickness of the finished product;
finish rolling: rolling in an austenite non-recrystallization region of a low-temperature section to promote the formation of a crystal-grain-size-reduced form F, and simultaneously ensuring sufficient pass reduction rate for improving the low-temperature impact toughness of the steel plate; the accumulated reduction rate is more than 65 percent, the rolling temperature of fine rolling is 900-950 ℃, and the final rolling temperature is 810-850 ℃; continuous rolling, and no stay between passes for cooling;
starting the number of cooling water groups according to the temperature of red return, and adopting a cooling strategy of back-end cooling, low steel plate running speed, high water flow and high water pressure to form an imitated crystal form F + GB on the surface layer of the steel plate and increase the cooling uniformity in the thickness direction so as to reduce the banded structure;
the thickness of the ship plate is 50mm; in the latter stage cooling, the cooling temperature: 731 ℃, red return temperature: 627 ℃, steel plate running speed: 0.94m/s, water pressure: 0.16MPa, water flow: 120m 3 H; cooling rate: the temperature of the mixed gas is 32 ℃/s,
the carbon equivalent CEV of the ship plate is less than or equal to 0.34, and the ratio of the surface layer imitated crystal form F + GB is 28% of the thickness of the steel plate;
the central metallographic structure is as follows: f + GB + P.
2. The method for manufacturing a low-cost high-toughness high-weldability high-strength ship plate as claimed in claim 1, wherein slab casting: the casting process keeps constant drawing speed; the dynamic soft reduction is used, the reduction interval is 0.5-1.2, and the reduction is 5.0 mm.
3. The method for manufacturing the low-cost high-toughness high-weldability high-strength ship plate as claimed in claim 1, wherein the LF molten steel refining treatment comprises the following steps: after the last alloying, the medium-strength argon blowing or strong argon blowing time of more than 3min must be ensured, and the TiFe must be added after white slag or transparent glass slag or light dark green slag is manufactured.
4. The method for manufacturing a low-cost high-toughness high-weldability high-strength ship plate as claimed in claim 1, wherein the RH molten steel refining treatment comprises: the sedation time is 18min to 35min.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202211385032.9A CN116200671A (en) | 2022-02-11 | 2022-02-11 | Low-cost high-toughness high-weldability high-strength ship plate |
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| CN114672722A (en) * | 2022-01-27 | 2022-06-28 | 唐山中厚板材有限公司 | Steel plate for ship plate and production method thereof |
| CN115094331B (en) * | 2022-07-18 | 2023-05-09 | 柳州钢铁股份有限公司 | Low-cost Q690 steel plate and production method thereof |
| CN115354230A (en) * | 2022-08-30 | 2022-11-18 | 重庆钢铁股份有限公司 | Low-carbon high-manganese microalloying thermo-mechanical rolling production method for E40-grade ship plate |
| CN115652211B (en) * | 2022-11-08 | 2023-11-10 | 鞍钢股份有限公司 | Economical 420 MPa-level steel plate cooling uniformity control method for engineering structure |
| CN117701999B (en) * | 2024-02-06 | 2024-04-30 | 北京科技大学 | Thick high-toughness ocean engineering structural steel and preparation method thereof |
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| CN107164696A (en) * | 2017-04-19 | 2017-09-15 | 唐山钢铁集团有限责任公司 | One kind can the high-strength deck of boat EH40 of Large Heat Input Welding and its production method |
| WO2019105055A1 (en) * | 2017-11-29 | 2019-06-06 | 南京钢铁股份有限公司 | S355g10+m wide and heavy steel plate having low-temperature toughness for ocean engineering, and method for manufacturing same |
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| CN1113975C (en) * | 2000-09-08 | 2003-07-09 | 清华大学 | Heterogeneous low-carbon air-cooled granular bainite/crystalloid ferrite steel |
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