CN111363967A - High-strength and high-toughness CrMo series connecting rod steel and manufacturing method thereof - Google Patents
High-strength and high-toughness CrMo series connecting rod steel and manufacturing method thereof Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 129
- 239000010959 steel Substances 0.000 title claims abstract description 129
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 34
- 229910001149 41xx steel Inorganic materials 0.000 title claims abstract description 25
- 238000003723 Smelting Methods 0.000 claims abstract description 31
- 238000005096 rolling process Methods 0.000 claims abstract description 19
- 238000001816 cooling Methods 0.000 claims abstract description 17
- 238000007670 refining Methods 0.000 claims abstract description 17
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 16
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 12
- 238000005266 casting Methods 0.000 claims abstract description 12
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 10
- 239000000126 substance Substances 0.000 claims abstract description 10
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 9
- 238000007872 degassing Methods 0.000 claims abstract description 8
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 8
- 239000012535 impurity Substances 0.000 claims abstract description 7
- 229910052802 copper Inorganic materials 0.000 claims abstract description 6
- 238000000034 method Methods 0.000 claims description 59
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 58
- 230000008569 process Effects 0.000 claims description 37
- 229910052786 argon Inorganic materials 0.000 claims description 29
- 238000007664 blowing Methods 0.000 claims description 23
- 238000010079 rubber tapping Methods 0.000 claims description 20
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 17
- 239000000463 material Substances 0.000 claims description 16
- 239000002893 slag Substances 0.000 claims description 13
- 238000010583 slow cooling Methods 0.000 claims description 12
- 238000009749 continuous casting Methods 0.000 claims description 11
- 238000009489 vacuum treatment Methods 0.000 claims description 11
- 238000001514 detection method Methods 0.000 claims description 9
- 238000010438 heat treatment Methods 0.000 claims description 9
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 6
- 229910052742 iron Inorganic materials 0.000 claims description 6
- 238000005496 tempering Methods 0.000 claims description 6
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 5
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 5
- 239000011575 calcium Substances 0.000 claims description 5
- 229910052791 calcium Inorganic materials 0.000 claims description 5
- 238000010791 quenching Methods 0.000 claims description 5
- 230000000171 quenching effect Effects 0.000 claims description 5
- 239000002994 raw material Substances 0.000 claims description 5
- 230000009467 reduction Effects 0.000 claims description 5
- 238000002791 soaking Methods 0.000 claims description 5
- 239000011593 sulfur Substances 0.000 claims description 5
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 4
- 238000005070 sampling Methods 0.000 claims description 4
- 238000006477 desulfuration reaction Methods 0.000 claims description 3
- 230000023556 desulfurization Effects 0.000 claims description 3
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- 239000007788 liquid Substances 0.000 claims description 3
- 238000003756 stirring Methods 0.000 claims description 3
- 238000012938 design process Methods 0.000 abstract description 2
- 230000003749 cleanliness Effects 0.000 description 5
- 238000013461 design Methods 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- 238000005275 alloying Methods 0.000 description 4
- 239000000956 alloy Substances 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
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- 229910052750 molybdenum Inorganic materials 0.000 description 3
- 229910052759 nickel Inorganic materials 0.000 description 3
- 238000005452 bending Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000009863 impact test Methods 0.000 description 2
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- 230000001502 supplementing effect Effects 0.000 description 2
- 238000007546 Brinell hardness test Methods 0.000 description 1
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- 229910052760 oxygen Inorganic materials 0.000 description 1
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Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Treatment Of Steel In Its Molten State (AREA)
Abstract
The invention relates to high-strength and high-toughness CrMo series connecting rod steel and a manufacturing method thereof, wherein the steel comprises the following chemical components in percentage by mass: c: 0.38-0.43%, Si: 0.15-0.35%, Mn: 0.75-1.00%, Cr: 0.80-1.10%, P: less than or equal to 0.015%, S: less than or equal to 0.010 percent, Ni: 0.20-0.40%, Cu: less than or equal to 0.20 percent, Mo: 0.15-0.25%, Al: 0.010-0.040 percent, less than or equal to 0.0015 percent of [ O ], lessthan or equal to 0.0075 percent of [ N ], lessthan or equal to 0.0002 percent of [ H ], and the balance of Fe and inevitable impurities. The manufacturing method comprises smelting, casting, rolling, cooling and post-treatment. The smelting comprises electric furnace smelting, LF furnace refining and VD furnace degassing treatment; through reasonable component design and production process, the steel has high strength, plasticity, toughness and purity.
Description
Technical Field
The invention belongs to the technical field of steel for automobiles, and particularly relates to high-strength high-toughness CrMo series steel for a connecting rod and a manufacturing method thereof.
Background
The connecting rod is an important part of the engine, and the output and the sales rate of the connecting rod are obviously increased along with the rapid development of the engine industry. The connecting rod does complex planar motion in the engine body, bears very high periodic impact force, inertia force and bending force in the working process, and the high-performance engine with small volume, high power and low oil consumption puts higher and more updated requirements on the connecting rod, and has high strength and rigidity, high toughness, purity and fatigue performance. For the quenched and tempered steel for the connecting rod, carbon quenched and tempered steel is generally adopted for a low-power engine, and alloy quenched and tempered steel is adopted for a high-power engine.
The connecting rod is a key part of an automobile engine, the quality of the connecting rod directly influences the performance of the engine, the requirements on the purity, the comprehensive mechanical property and the fatigue property of steel are strict, and the surface and the interior of the steel are almost free of defects. The existing steel for the connecting rod is mainly used for cracking the connecting rod, the high-performance quenched and tempered steel for the connecting rod is few, and the steel for the connecting rod and the manufacturing method thereof are provided according to the performance requirements of high strength, high plasticity, high toughness and high purity of the steel for the connecting rod.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a high-strength high-toughness CrMo connecting rod steel and a manufacturing method thereof, which control the cleanliness of steel and optimize the structure and performance homogeneity of the material by controlling the chemical components of the material and a reasonable production process, so that the material obtains excellent mechanical property, fatigue property and high internal and external quality.
In order to achieve the purpose, the invention adopts the following technical scheme:
a high-strength and high-toughness CrMo series steel for connecting rods comprises the following chemical components in percentage by mass: c: 0.38-0.43%, Si: 0.15-0.35%, Mn: 0.75-1.00%, Cr: 0.80-1.10%, P: less than or equal to 0.015%, S: less than or equal to 0.010 percent, Ni: 0.20-0.40%, Cu: less than or equal to 0.20 percent, Mo: 0.15-0.25%, Al: 0.010-0.040 percent, less than or equal to 0.0015 percent of [ O ], lessthan or equal to 0.0075 percent of [ N ], lessthan or equal to 0.0002 percent of [ H ], and the balance of Fe and inevitable impurities.
The invention adopts Mn, Cr, Ni and Mo multi-alloying to improve the strength, plasticity and impact toughness of the material, so that the steel has good comprehensive mechanical property and moderate hardness, adopts low P, S and gas component design to ensure the cleanliness of the steel, improves the fatigue property of the steel, reduces the cold brittleness of the steel, refines crystal grains by Al, and finally obtains good comprehensive property of the material.
One of the technical characteristics of the invention lies in the reasonable component design, and adopts the component design of Mn, Cr, Ni and Mo multi-alloying, low P, S and [ O ], [ H ], and proper amount of Al.
The comprehensive mechanical property of the steel is improved by adopting a multi-alloying method, and the Mn: 0.75-1.00%, Cr: 0.80-1.10%, Ni: 0.20-0.40%, Mo: 0.15-0.25%, and ensures that the steel has good plasticity and impact toughness while ensuring the strength of the steel; in order to ensure high cleanliness and low cold brittleness of steel, the design of low P, S and low gas components is adopted, and the ratio of P: less than or equal to 0.015%, S: less than or equal to 0.010 percent, less than or equal to 0.0015 percent of [ O ], and less than or equal to 0.0002 percent of [ H ]; in order to refine crystal grains and improve the comprehensive performance of steel, Al: 0.010-0.040%.
In view of stability of the properties of the steel material and cost, it is preferable that the high toughness CrMo-based steel for connecting rods has the following chemical components in percentage by mass: c: 0.39-0.41%, Si: 0.19 to 0.25%, Mn: 0.85-0.90%, Cr: 0.94-1.00%, P: less than or equal to 0.015%, S: less than or equal to 0.010 percent, Ni: 0.20-0.30%, Cu: less than or equal to 0.20 percent, Mo: 0.20-0.25%, Al: 0.015-0.040%, less than or equal to 0.0015% of [ O ], lessthan or equal to 0.0070% of [ N ], lessthan or equal to 0.00015% of [ H ], and the balance of Fe and inevitable impurities.
In a preferred embodiment, the high-toughness CrMo-based steel for a connecting rod is a round steel, and more preferably, the specification of the steel for a connecting rod is Φ 20mm to Φ 120 mm.
As a preferable mode, the high-strength and high-toughness CrMo steel for connecting rods has the yield strength of not less than 800MPa, the tensile strength of not less than 930MPa, the elongation after fracture of not less than 18 percent, the reduction of area of not less than 54 percent, the impact energy at minus 46 ℃ of not less than 80J, and the hot-rolled hardness of the steel for connecting rods is 200-HB 269; preferably, after the thermal refining, the yield strength of the steel for the connecting rod is 830-870MPa, the tensile strength is 970-1000MPa, the elongation after fracture is 19-23%, the reduction of area is 56-65%, the impact energy at-46 ℃ is 90-120J, and the hot-rolled hardness of the steel for the connecting rod is 200-255 HB.
The second technical characteristic of the invention is that reasonable production technology is adopted, the purity of steel is improved, the comprehensive mechanical property and fatigue property of steel are ensured, and the steel meets the requirements of use conditions.
The invention also provides a manufacturing method of the high-strength and high-toughness CrMo connecting rod steel, the chemical composition design requirement of the CrMo connecting rod steel is as above, and the manufacturing method sequentially comprises the working procedures of smelting, pouring, rolling, cooling and post-treatment; the smelting process sequentially comprises the sub-processes of electric furnace smelting, LF furnace refining and VD furnace degassing treatment.
In the manufacturing method of the steel for the CrMo connecting rod with high strength and toughness, as a preferable embodiment, in the electric furnace smelting sub-process, the adding amount of molten iron accounts for more than or equal to 40 percent (such as 45 percent, 50 percent, 55 percent, 60 percent, 65 percent, 70 percent, 75 percent, 80 percent and 85 percent) of the total mass of the electric furnace smelting raw materials, the tapping end point [ C ] of the electric furnace is more than or equal to 0.10 percent by weight, and [ P ] is more than or equal to 0.010 percent by weight; the tapping temperature is 1630-1670 ℃, and slag-forming materials are added according to 12-16 kg/t steel (such as 13kg/t steel, 14kg/t steel and 15kg/t steel); more preferably, the adding amount of the molten iron accounts for 60-80% of the total mass of the smelting raw materials of the electric furnace; 0.11-0.15 wt% of electric furnace tapping terminal point [ C ]; the tapping temperature is 1640-1660 ℃; the slag making materials are added according to 13-15 kg/t steel.
In the above method for producing a high-toughness CrMo connecting rod steel, as a preferred embodiment, the LF furnace refining sub-step includes: controlling the slag alkalinity to be more than or equal to 3.0, and carrying out deoxidation and desulfurization operation to control the sulfur content in the steel to be less than 0.008 wt%; before sampling for the first time, feeding an aluminum wire, controlling the total aluminum content in the steel to be 0.025-0.040 wt%, and keeping the white slag for not less than 30 min; feeding a calcium wire according to the steel thickness of 1.5-3.0 m/t before LF tapping; more preferably, the slag alkalinity of the LF refining is controlled to be more than or equal to 4.0, and more preferably 4.0-4.5; the sulfur content is controlled to be below 0.005 wt%; the white slag is kept for 30-40 min; and feeding a calcium wire according to the steel thickness of 1.5-2.0 m/t before LF tapping.
In a preferred embodiment of the method for producing a high-toughness CrMo connecting rod steel, the vacuum treatment step of the VD furnace degassing step is performed in such a manner that the holding time of the vacuum degree of 67Pa or less is not less than 12 minutes (for example, 13 minutes, 14 minutes, 15 minutes, 17 minutes, 20 minutes); after VD vacuum treatment, the soft argon blowing time is not less than 20 minutes (such as 22min, 25min, 28min, 30min, 40min and 50 min); more preferably, the maintaining time of the vacuum degree below 67Pa is 12-15min, and the soft argon blowing time after VD vacuum treatment is 25-35min (such as 26min, 28min, 32min, 34 min).
In order to ensure the purity of the steel material, the method for manufacturing the CrMo connecting rod steel with high strength and toughness further comprises the step of slagging off before molten steel enters the VD furnace between the LF furnace refining sub-process and the VD furnace degassing treatment sub-process.
According to the manufacturing method of the steel for the CrMo connecting rod with high strength and toughness, as a preferred embodiment, in the smelting process, the whole smelting process adopts argon blowing control, and the flow of argon is reasonably controlled in different stages of different sub-processes, so that molten steel can be fully stirred and is not exposed, the uniformity of chemical components and temperature of the molten steel is ensured, the chemical reaction is accelerated, harmful gas and impurities are removed, and the molten steel is purified, so that the uniformity and cleanliness of steel are improved; more preferably, the argon flow rate is 500-600 NL/min (such as 520NL/min, 540NL/min, 560NL/min and 580NL/min) when electric furnace smelting tapping is carried out, and the argon flow rate is 10-30 NL/min (such as 12NL/min, 15NL/min, 20NL/min, 25NL/min and 28NL/min) before and after the electric furnace smelting tapping is carried out; in LF furnace refining, the argon blowing flow rate in the molten steel component adjusting process (i.e. the alloy supplementing process according to the primary sampling result) is 500-600 NL/min (such as 520NL/min, 540NL/min, 560NL/min and 580NL/min), and the argon blowing flow rate in other LF furnace refining processes is 30-80 NL/min (such as 32NL/min, 35NL/min, 40NL/min, 50NL/min, 60NL/min, 70NL/min, 75NL/min and 78 NL/min); in the degassing treatment of the VD furnace, the flow rate of argon is 40-80 NL/min (such as 45NL/min, 50NL/min, 60NL/min, 70NL/min, 75NL/min and 78NL/min) when the vacuum degree is below 67Pa during the VD vacuum treatment, and the flow rate of argon is 10-30 NL/min (such as 12NL/min, 15NL/min, 20NL/min, 25NL/min and 28NL/min) when soft blowing is carried out after the VD vacuum treatment.
The manufacturing method of the steel for the CrMo connecting rod with high strength and toughness is a preferred embodiment, in the pouring process, a casting blank is poured by adopting continuous casting, the whole process of the continuous casting process is protected and poured, a crystallizer and a tail end are adopted for electromagnetic stirring, the liquid level of the crystallizer fluctuates +/-2 mm, the pouring is carried out by adopting a low superheat degree (namely, the superheat degree is 20-30 ℃) at 20-30 ℃, the temperature of tundish molten steel is controlled to be 1513-1523 ℃ (such as 1515 ℃, 1518 ℃ and 1520 ℃) according to different blank types, the drawing speed is controlled to be 0.50-1.10 m/min (such as 0.60m/min, 0.70m/min, 0.80m/min, 0.90m/min and 1.00m/min) according to different blank types, in order to ensure the quality of the casting blank, the drawing speed of the blank is controlled to be not less than 900 ℃ (such as 910 ℃, 920 ℃, 930 ℃, 950 ℃ and 980 ℃, more preferably, the drawing speed is controlled according to different blank types, the drawing speed of 260mm × mm blank is controlled to 0.50-0.60 m/min, the drawing speed of the blank is controlled to 84 mm and the drawing speed of the blank is controlled to be not.
In a preferred embodiment of the method for producing a high-toughness CrMo connecting rod steel, in the rolling step, the soaking temperature of the heating furnace is controlled to be 1200 to 1250 ℃ (for example 1205 ℃, 1210 ℃, 1220 ℃, 1230 ℃, 1240 ℃ and 1245 ℃) and the heating time is 2.5 to 4.0 hours (for example, 3 hours and 3.5 hours); the initial rolling temperature is 1080-1170 ℃ (such as 1100 ℃, 1120 ℃, 1140 ℃ and 1160 ℃) and the final rolling temperature is 950-1050 ℃ (such as 960 ℃, 980 ℃, 1000 ℃, 1020 ℃ and 1040 ℃). More preferably, the soaking temperature is 1220-1250 ℃, the heating time is 3.5-4.0 hours, the initial rolling temperature is 1120-1150 ℃, and the final rolling temperature is 960-980 ℃.
In the above method for producing a high-toughness CrMo connecting rod steel, in a preferred embodiment, the cooling step includes cooling the rolled steel material in an upper cooling bed, and controlling the temperature of a lower cooling bed at 700 to 730 ℃ (for example, 705 ℃, 710 ℃, 715 ℃, 720 ℃, 725 ℃); placing into a cooling bed, collecting into a slow cooling pit, slowly cooling, and discharging at a temperature not more than 100 deg.C (such as 90 deg.C, 80 deg.C, 70 deg.C, 60 deg.C, 50 deg.C, 40 deg.C) to obtain hot rolled round steel. More preferably, the temperature of the lower cooling bed is controlled to be 710-730 ℃.
In a preferred embodiment of the method for producing a high-toughness CrMo connecting rod steel, the post-treatment step includes: and (3) straightening the hot-rolled round steel out of the slow cooling pit, treating surface iron oxide scales, and performing ultrasonic flaw detection, wherein the round steel meeting the requirement of ultrasonic flaw detection that the diameter of a flat bottom hole is not more than phi 2mm is a qualified product.
The process conditions not limited in the above manufacturing method can be referred to the conventional techniques in the art.
Compared with the prior art, the invention has the beneficial effects that:
1) according to a plurality of strengthening mechanisms, the steel for the connecting rod is designed by adopting a multi-alloying method, so that the steel has good strength, good plasticity and toughness are ensured, and the requirements of the using conditions of the connecting rod are met;
2) in the production process, harmful elements such as P, S, O and the like are controlled in a lower range through the optimization of the manufacturing process and the strict control of the process, so that the purity of the steel is greatly improved; the steel has good internal and external quality, machinability and performance stability through processes of slow cooling, flaw detection and the like;
3) the invention meets the performance requirements of high strength, high plasticity, high toughness and high purity of the steel for the connecting rod through reasonable component design and production process; compared with the conventional products in the field, the obtained hot-rolled round steel has the advantages that the plasticity index can be improved by more than 30 percent and the toughness index can be improved by more than 40 percent through a proper heat treatment process.
Detailed Description
The technical solution of the present invention is further described in detail by way of examples below.
Examples 1 to 3:
a high-strength and-toughness CrMo connecting rod steel is prepared through smelting in UHP ultrahigh-power electric furnace, LF refining, VD vacuum degassing, continuous casting, rolling, slow cooling and flaw detection. Examples 1-3 are specific illustrations of how the invention can be practiced in the production of phi 100mm gauge steel.
The steel comprises the following components in percentage by mass:
c: 0.39-0.41%, Si: 0.19 to 0.25%, Mn: 0.85-0.90%, Cr: 0.94-1.00%, P: less than or equal to 0.015%, S: less than or equal to 0.010 percent, Ni: 0.20-0.30%, Cu: less than or equal to 0.20 percent, Mo: 0.20-0.25%, Al: 0.015-0.040%, less than or equal to 0.0015% of [ O ], lessthan or equal to 0.0070% of [ N ], lessthan or equal to 0.00015% of [ H ], and the balance of Fe and inevitable impurities.
The production process comprises the following steps:
(1) smelting
Smelting in an electric furnace, wherein the molten iron is added with the mass accounting for 60-80% of the total mass of the raw materials, the tapping end point of the electric furnace (C) is 0.11-0.15 wt%, and the tapping end point of the electric furnace (P) is less than or equal to 0.010 wt%. Tapping temperature is 1640-1660 ℃, and slag-forming materials are added according to 13-15 kg/t steel.
And LF refining controls slag alkalinity to be 4-4.5, enhances deoxidation and desulfurization operations, and controls sulfur content to be below 0.005 wt%. Before sampling for the first time, feeding an aluminum wire, controlling the total aluminum content in the steel to be 0.025-0.040 wt%, and keeping the white slag for 30-40 min. And feeding a calcium wire according to the steel thickness of 1.5-2.0 m/t before LF tapping.
In order to ensure the purity of the steel, the molten steel is subjected to slagging off before entering a VD furnace. The vacuum degree is less than 67Pa, and the holding time is 12-15 minutes. And after VD vacuum treatment, the soft argon blowing time is 25-35 minutes.
Argon blowing control is adopted in the whole smelting process, the argon blowing flow is 500-600 NL/min when the electric furnace steel is tapped, and the argon blowing flow is 10-30 NL/min before and after the steel is tapped; argon blowing flow in the LF refining alloy supplementing process is 500-600 NL/min, and the rest time is 30-80 NL/min; the flow rate of argon gas under 67Pa is 40-80 NL/min, and the flow rate of argon gas blown during soft blowing is 10-30 NL/min.
(2) Pouring
Casting blanks are cast by adopting continuous casting, the whole process of the continuous casting process is protected for casting, a crystallizer and a tail end are adopted for electromagnetic stirring in the continuous casting, the fluctuation of the liquid level of the crystallizer is +/-2 mm, the casting is carried out by adopting the low superheat degree at the temperature of 20-30 ℃, the temperature of a tundish is controlled to be 1513-1523 ℃, a blank mold of 260mm × 300mm is controlled, the casting speed is 0.55-0.60 m/min, and the temperature of the casting blanks entering a withdrawal and straightening machine is more than or equal to 920 ℃, so that the.
(3) Rolling of
The soaking temperature of a heating furnace is controlled to be 1220-1250 ℃, the heating time is 3.5-4.0 hours, the initial rolling temperature is 1120-1150 ℃, the final rolling temperature is 960-980 ℃, the temperature of a lower cooling bed is controlled to be 710-730 ℃, the steel is collected into a slow cooling pit for slow cooling after being placed on the cooling bed, and the pit discharging temperature is not more than 100 ℃ to prepare the hot rolled round steel. The hot rolling hardness of the prepared round steel is 230-255 HB.
(4) Flaw detection
After the hot-rolled round steel is taken out of the slow cooling pit, full-automatic ultrasonic flaw detection is carried out through straightening and surface iron scale treatment, the bending degree of the steel is not more than 2.5mm/m, the diameter of a flat bottom hole of the ultrasonic flaw detection is not more than phi 2mm, and finally the round steel is obtained.
The specific process parameters are shown in tables 1-4. Table 1 shows the chemical compositions of the steels for connecting rods in the embodiments 1-3, Table 2 shows key process parameters in the smelting and continuous casting processes, Table 3 shows the argon blowing control condition in the smelting process, and Table 4 shows key process parameters in the rolling and slow cooling processes.
Table 1 steel for connecting rod example chemical composition (weight,%)
TABLE 2 Key technological parameters of smelting and continuous casting
TABLE 3 argon blowing control during smelting
TABLE 4 Key Process parameters for the Rolling and Slow Cooling Process
The results of the performance test of the steel products of examples 1 to 3 in each furnace are shown in tables 5 and 6.
Table 5 shows the results of the measurement of non-metallic inclusions and grain size in the finished steel products, in which the method of measuring non-metallic inclusions was ASTM E45 method A and the method of measuring grain size was ASTM E112.
Table 6 shows the mechanical properties of the quenched and tempered steel, wherein the quenching and tempering system comprises 830-860 ℃/30min oil quenching and 580-650 ℃/60min tempering; after quenching and tempering, the sample blank is subjected to tensile test, impact test and Brinell hardness test according to GB/T2975, GB/T228, GB/T229 and GB/T231.1 standards respectively, wherein the impact test temperature is-46 ℃.
TABLE 5 examination results of non-metallic inclusions and grain size
TABLE 6 mechanical Properties after hardening and tempering
As can be seen from examples 1-3, the connecting rod has the advantages of stable control of steel components, high cleanliness of steel and uniform and fine crystal grains. The material has good plastic toughness performance on the premise of keeping higher strength, the elongation after fracture is not less than 19%, the reduction of area is not less than 56%, and the impact energy at minus 46 ℃ is basically about 100J. Under the same quenching and tempering system, the elongation of the conventional material (42CrMo) is 12-15%, and the impact energy is 40-60J; compared with the conventional material, the comprehensive performance of the steel for the connecting rod in the embodiment is greatly improved, wherein the plasticity index (calculated by elongation) can be improved by more than 30%, and the toughness index (calculated by impact energy) can be improved by more than 40%.
While the preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art. Therefore, the appended claims should be construed to include preferred embodiments and all such variations and modifications as fall within the scope of the invention.
Claims (10)
1. The high-strength and high-toughness CrMo steel for the connecting rod is characterized by comprising the following chemical components in percentage by mass: c: 0.38-0.43%, Si: 0.15-0.35%, Mn: 0.75-1.00%, Cr: 0.80-1.10%, P: less than or equal to 0.015%, S: less than or equal to 0.010 percent, Ni: 0.20-0.40%, Cu: less than or equal to 0.20 percent, Mo: 0.15-0.25%, Al: 0.010-0.040 percent, less than or equal to 0.0015 percent of [ O ], lessthan or equal to 0.0075 percent of [ N ], lessthan or equal to 0.0002 percent of [ H ], and the balance of Fe and inevitable impurities.
2. The steel for a high-strength and high-toughness CrMo connecting rod as claimed in claim 1, wherein the steel for a connecting rod comprises the following chemical components in percentage by mass: c: 0.39-0.41%, Si: 0.19 to 0.25%, Mn: 0.85-0.90%, Cr: 0.94-1.00%, P: less than or equal to 0.015%, S: less than or equal to 0.010 percent, Ni: 0.20-0.30%, Cu: less than or equal to 0.20 percent, Mo: 0.20-0.25%, Al: 0.015-0.040 percent, less than or equal to 0.0015 percent of [ O ], lessthan or equal to 0.0070 percent of [ N ], lessthan or equal to 0.00015 percent of [ H ], and the balance of Fe and inevitable impurities;
preferably, the steel for the connecting rod is round steel, and the specification of the steel for the connecting rod is phi 20 mm-phi 120 mm.
3. The steel for a CrMo connecting rod with high strength and toughness as claimed in claim 1 or 2, wherein the yield strength of the steel for a connecting rod after quenching and tempering treatment is not less than 800MPa, the tensile strength is not less than 930MPa, the elongation after fracture is not less than 18%, the reduction of area is not less than 54%, the impact energy at-46 ℃ is not less than 80J, and the hot-rolled hardness of the steel for a connecting rod is 200-269 HB;
preferably, after the thermal refining, the yield strength of the steel for the connecting rod is 830-870MPa, the tensile strength is 970-1000MPa, the elongation after fracture is 19-23%, the reduction of area is 56-65%, the impact energy at-46 ℃ is 90-120J, and the hot-rolled hardness of the steel for the connecting rod is 200-255 HB.
4. The method for manufacturing the steel for the high-toughness CrMo connecting rod, according to claim 1, is characterized by comprising the steps of smelting, casting, rolling, cooling and post-treatment in sequence; the smelting process sequentially comprises the sub-processes of electric furnace smelting, LF furnace refining and VD furnace degassing treatment.
5. The manufacturing method according to claim 4,
in the electric furnace smelting sub-procedure, the proportion of the molten iron in the total mass of the electric furnace smelting raw materials is more than or equal to 40 percent, the electric furnace tapping end point [ C ] is more than or equal to 0.10wt percent, and [ P ] is less than or equal to 0.010wt percent; the tapping temperature is 1630-1670 ℃, and slag-forming materials are added according to 12-16 kg/t steel;
preferably, the adding amount of the molten iron accounts for 60-80% of the total mass of the smelting raw materials of the electric furnace; the electric furnace tapping end point [ C ] is 0.11-0.15 wt%; the tapping temperature is 1640-1660 ℃; the slag making materials are added according to 13-15 kg/t steel.
6. The manufacturing method according to claim 5,
in the LF furnace refining sub-process, controlling the slag alkalinity to be more than or equal to 3.0, and carrying out deoxidation and desulfurization operation to control the sulfur content in the steel to be less than 0.008 wt%; before sampling for the first time, feeding an aluminum wire, controlling the total aluminum content in the steel to be 0.025-0.040 wt%, and keeping the white slag for not less than 30 min; feeding a calcium wire according to the steel thickness of 1.5-3.0 m/t before LF tapping;
preferably, the slag alkalinity of the LF refining is controlled to be greater than or equal to 4.0, and more preferably 4.0-4.5; the sulfur content is controlled to be below 0.005 wt%; the white slag is kept for 30-40 min; and feeding a calcium wire according to the steel thickness of 1.5-2.0 m/t before LF tapping.
7. The manufacturing method according to claim 6,
slag skimming before molten steel enters the VD furnace is further included between the LF furnace refining sub-process and the VD furnace degassing sub-process;
in the vacuum treatment process of the VD furnace degassing treatment sub-process, the holding time of the vacuum degree below 67Pa is more than or equal to 12 minutes; after VD vacuum treatment, the soft argon blowing time is not less than 20 minutes;
preferably, the maintaining time of the vacuum degree below 67Pa is 12-15min, and the soft argon blowing time after VD vacuum treatment is 25-35 min.
8. The manufacturing method according to claim 4,
in the smelting process, the whole smelting process adopts argon blowing control, and the argon flow is reasonably controlled in different stages of different sub-processes;
preferably, the argon blowing flow rate is 500-600 NL/min during electric furnace smelting and tapping, and the argon blowing flow rate is 10-30 NL/min before and after the electric furnace smelting and tapping; in the LF furnace refining, except for the argon blowing flow rate of 500-600 NL/min in the process of adjusting the components of the molten steel, the argon blowing flow rate of other processes is 30-80 NL/min; and in the VD vacuum treatment process, the flow of argon is 40-80 NL/min when the vacuum degree is below 67Pa, and the flow of argon blowing is 10-30 NL/min when soft blowing is carried out after VD vacuum treatment.
9. The manufacturing method according to claim 4,
in the pouring process, continuous casting is adopted to pour a casting blank, the whole process of the continuous casting process is protected to pour, a crystallizer and a tail end are adopted for electromagnetic stirring in the continuous casting, and the fluctuation of the liquid level of the crystallizer is +/-2 mm; pouring at a low superheat degree of 20-30 ℃, controlling the temperature of tundish molten steel to be 1513-1523 ℃, and controlling the drawing speed to be 0.50-1.10 m/min according to different blank shapes; the temperature of the casting blank entering the tension leveler is more than or equal to 900 ℃;
preferably, the drawing speed is controlled according to different blank types, wherein the drawing speed of a blank type of 260mm × 300mm is controlled according to 0.50-0.60 m/min, and the drawing speed of a blank type of 180mm × 220mm is controlled according to 0.95-1.10 m/min;
more preferably, the temperature of the casting blank in the tension leveler is more than or equal to 920 ℃;
preferably, in the rolling procedure, the soaking temperature of the heating furnace is controlled to be 1200-1250 ℃, and the heating time is 2.5-4.0 hours; the initial rolling temperature is 1080-1170 ℃, and the final rolling temperature is 950-1050 ℃;
more preferably, the soaking temperature is 1220-1250 ℃, the heating time is 3.5-4.0 hours, the initial rolling temperature is 1120-1150 ℃, and the final rolling temperature is 960-980 ℃.
10. The manufacturing method according to claim 4,
in the cooling procedure, the rolled steel is cooled on an upper cooling bed, and the temperature of a lower cooling bed is controlled to be 700-730 ℃; after the steel is placed on a cooling bed, the steel is collected into a slow cooling pit for slow cooling, the pit discharging temperature is not more than 100 ℃, and hot rolled round steel is prepared; preferably, the temperature of the lower cooling bed is controlled to be 710-730 ℃;
the post-treatment process comprises the following steps: and (3) straightening the hot-rolled round steel out of the slow cooling pit, treating surface iron oxide scales, and performing ultrasonic flaw detection, wherein the round steel meeting the requirement of ultrasonic flaw detection that the diameter of a flat bottom hole is not more than phi 2mm is a qualified product.
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