CN111621720A - Austenite alloy steel and preparation method thereof - Google Patents
Austenite alloy steel and preparation method thereof Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- 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
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- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- 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
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- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
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- C—CHEMISTRY; METALLURGY
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- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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Abstract
The invention relates to an austenite-bainite alloy steel and a preparation method thereof, wherein the alloy steel comprises the following components in percentage by mass: c: 0.26 to 0.35; si: 1.66 to 1.84; mn: 1.70-1.90; p: less than or equal to 0.014; s: less than or equal to 0.014; cr: 1.11 to 1.29; mo: 0.35 to 0.45; v: 0.08 to 0.15; the balance of Fe and inevitable gaseous impurity elements; the alloy steel also comprises the following components: less than or equal to 0.30; cu: not more than 0.30, wherein the gas impurity elements are strictly controlled: the content of [ O ] is less than or equal to 10ppm, the content of [ H ] is less than or equal to 1.0ppm, and the content of [ N ] is less than or equal to 70 ppm. The preparation process comprises material preparation, electric furnace or converter smelting, external refining, continuous casting process and heat treatment process. In the quality components of the austenite-bainite alloy steel, the content of C exceeds the conventional content of C in alloy steel, martensite still does not appear, bainite can be generated, the prepared alloy steel has high strength, good plasticity and toughness and certain intergranular corrosion resistance, and the service life of the alloy steel is prolonged.
Description
Technical Field
The invention relates to the field of material preparation, in particular to an austenite-bainite alloy steel and a preparation method thereof.
Background
Along with the development of the railway industry of China towards heavy load and high speed, higher and higher requirements are put forward on the strength, toughness, impact property and the like of steel used for railway rails and parts. The high manganese steel which is used in large quantity at present is increasingly difficult to meet the requirements of railway development at present, particularly for railway turnout parts with poor service conditions, the combined turnout is converted into an integral turnout, and the alloy steel used is required to have higher strength, toughness and impact property. Usually, to obtain a fine structure, Nb is usually added during the smelting process, and the resulting compounds can effectively hinder the movement of recrystallized grain boundaries in the subsequent deformation process of the alloy steel matrix. However, Nb element itself is a precious metal element, and is expensive, and the cost is increased when it is used in actual production. In addition, the alloy steel is required to avoid the phenomena of oxide, nitride, hydrogen embrittlement and the like as far as possible in the forming and service processes.
As early as 80 s in the last century, the United states developed a bainite steel rail named Titan and successfully applied to high-speed rails. The bainite steel rail has the advantages of good obdurability, wear resistance, long service life and the like, the tensile strength reaches 1400 MPa, and the elongation can reach more than 15%. The related test results show that the service life of the bainite steel rail is several times longer than that of the pearlite steel rail, all mechanical performance indexes are more excellent, and the excellent indexes completely meet the development requirements of heavy haul railways. With the increase of railway transportation capacity, pearlite steel rails with the tensile strength of 980MPa level face the bottleneck that the existing transportation capacity cannot be borne, so that the research and development of high-strength bainite steel rails with the tensile strength of more than 1200MPa level become a middle weight.
Patent CN 201510919742.9 provides an alloy system and a heat treatment method of bainite steel rail thereof, and the bainite steel rail, wherein the components of the alloy system are as follows by mass percent: c: 0.22 to 0.27; si: 1.65 to 1.85; mn: 1.60 to 1.80; cr: 1.30 to 1.90; mo: 0.25 to 0.85; ni: 0.25 to 0.95; v: 0.040 to 0.060 or Nb: 0.020 to 0.040, P: less than or equal to 0.015, S: less than or equal to 0.015; the balance of Fe and inevitable impurity elements; wherein the impurity elements are strictly controlled: (1) gas content: the [ H ] of molten steel is less than or equal to 2.0ppm, the [ H ] of casting blank is less than or equal to 1.5ppm, the [ O ] is less than or equal to 25ppm, and the [ N ] is less than or equal to 70 ppm; (2) residual elements: al is less than or equal to 0.006 wt.%, Cu is less than or equal to 0.15 wt.%, Sn is less than or equal to 0.010 wt.%, and Sb is less than or equal to 0.010 wt.%. After heat treatment, the austenite structure is refined, and the segregation and unevenness of elements and microstructures are eliminated, so that a fine and uniform lower bainite structure is obtained after cooling phase transformation, and a high-strength bainite steel rail is obtained. But the elongation of the steel rail is more than 15%, and the toughness improvement capacity is still limited. And the steel rail needs to have certain corrosion resistance (mainly the capability of resisting intercrystalline corrosion) when in use so as to prolong the service life of the steel rail.
Titanium has strong affinity with elements such as nitrogen, oxygen, carbon and the like, so that the titanium can be used as a good deoxidizer and an effective element for fixing nitrogen and carbon, and the titanium and the carbon easily form titanium carbide which has strong binding force, stability and difficult decomposition and has the function of preventing crystal grains from growing. Since the affinity between titanium and carbon is much greater than the affinity between chromium and carbon, titanium with carbon fixed therein is commonly used in stainless steels to eliminate depletion of chromium at grain boundaries, thereby eliminating or reducing the tendency of stainless steels to intergranular corrosion. Titanium is also one of the strong ferrite forming elements, significantly raising the temperature of steels a1 and A3. For common low alloy steel, titanium can improve the plasticity and toughness of the steel, and forms titanium carbide with carbon to inhibit dislocation movement, thereby improving the strength of the steel. After heat treatment, the crystal grains are refined, and the precipitated carbide also can obviously improve the plasticity and impact toughness of the steel. Titanium with about 5 times of carbon content is generally added into high-chromium stainless steel, so that the corrosion resistance and toughness of the steel can be improved, the tendency of crystal grain growth of the steel at high temperature can be inhibited, and the welding performance of the steel can be improved.
The copper has the outstanding effect of improving the atmospheric corrosion resistance of common low-alloy steel, and particularly when the copper is used together with phosphorus, the strength and yield ratio of the steel can be improved by adding the copper without adverse effect on welding performance. The steel rail steel containing 0.20-0.50 wt.% of copper has a corrosion resistance life 2-5 times that of a common carbon steel rail. The austenitic stainless steel containing 2-3 wt.% copper can effectively resist the corrosivity of sulfuric acid, phosphoric acid, hydrochloric acid and the like, and can keep certain stability under the stress corrosion condition.
Disclosure of Invention
The invention provides an austenite-bainite alloy steel, which is prepared by utilizing the technologies of electric furnace/converter steelmaking, external refining, vacuum oxygen blowing decarburization and the like and adding a proper heat treatment process, and has the properties of high strength, good plasticity and toughness, high hardness, better intergranular corrosion resistance and the like, and the obtained indexes completely meet the service performance of a heavy haul railway.
The technical scheme of the invention is as follows:
an austenite-bainite alloy steel, the structure of which comprises austenite and bainite, is characterized in that the components of the alloy steel calculated according to the mass percentage comprise: c: 0.26 to 0.35; si: 1.66 to 1.84; mn: 1.70-1.90; p: less than or equal to 0.014; s: less than or equal to 0.014; cr: 1.11 to 1.29; mo: 0.35 to 0.45; v: 0.08 to 0.15; the balance being Fe and unavoidable gaseous impurity elements.
Preferably, the alloy steel further comprises the following components: less than or equal to 0.30; cu: less than or equal to 0.30.
Preferably, the inevitable gaseous impurity elements need to be strictly controlled: the content of [ O ] is less than or equal to 10ppm, the content of [ H ] is less than or equal to 1.0ppm, and the content of [ N ] is less than or equal to 70 ppm.
Preferably, the content of Ti and Cu in the alloy steel is 0.1-0.2 and 0.1-0.25 respectively according to the mass percentage.
The preparation method of the austenite-bainite alloy steel comprises the following steps:
s1: preparing materials, namely weighing corresponding materials according to the components of the alloy steel, and putting the materials into an electric furnace or a converter for smelting;
s2: smelting in an electric furnace or a converter, starting a power supply, baking the furnace and materials, heating to 1700-1750 ℃, preserving heat for 4-6 hours, transferring slag-stopping tapping into a ladle after the materials are completely melted, and preparing for external refining;
s3: and (3) refining outside the furnace, after smelting in an electric furnace or a converter, deoxidizing, desulfurizing, dephosphorizing, decarburizing and degassing a steel ladle by using an LF + VOD/RH refining method.
S4: continuous casting process, after external refining, the molten steel is continuously cast into steel billets for forming;
s5: forging the cast steel billet into an alloy steel sample, adjusting the temperature to 930-960 ℃ for austenitizing, preserving the heat for 1-2 h, then quickly cooling to 520 ℃ at the speed of 1.6 ℃/s, preserving the heat for 15-30 min, slowly cooling to the martensite phase transition temperature which is above 320 ℃, preserving the heat for 15-30 min, and finally air cooling to room temperature to obtain the alloy steel containing residual austenite and lower bainite tissues;
the step S5 further comprises tempering treatment, wherein the tempering heating temperature is 330 +/-10 ℃, the heat is preserved for 1-2 hours, and then air cooling is carried out; cooling to room temperature to finish the preparation of the austenite-bainite alloy steel.
Preferably, the step S3 of refining outside the furnace uses synthetic slag to perform deoxidation, desulfurization and dephosphorization in the ladle, wherein the synthetic slag is CaO-Al2O3And (4) slag system.
Preferably, the martensitic transformation temperature is 340 ℃.
Compared with the prior art, the invention has the following technical effects:
(1) the alloy steel of the invention contains C content exceeding that of the conventional alloy steel, wherein the C content is as follows: 0.26-0.35 still does not generate martensite, bainite can be generated, and the prepared alloy steel has high strength, good plasticity and toughness and certain intergranular corrosion resistance.
(2) The alloy steel with the austenite and bainite tissues as main tissues is obtained by the preparation process of the alloy steel, the austenite is a fine-grained tissue and shows good plasticity and toughness, and the bainite is a lower bainite tissue and has high strength.
(3) The added titanium element in the alloy steel improves the tensile strength and the toughness of the alloy steel at room temperature and low temperature, and the added copper element improves the intergranular corrosion resistance of the alloy steel and prolongs the service life of the alloy steel.
(4) The heat treatment process of the invention can obtain the lower bainite structure without salt bath isothermal treatment.
Detailed Description
The austempered steel alloy of the present invention and the method for producing the same will be described in detail with reference to the following embodiments.
Example 1
An austenitized steel alloy, said steel alloy comprising austenite and bainite, said steel alloy comprising, in mass percent: c: 0.32 of; si: 1.84; mn: 1.70; p: 0.014; s: 0.014; cr: 1.11; mo: 0.35; v: 0.15; ti: 0.10 to 0.20; cu: 0.10 to 0.25; the balance being Fe and unavoidable gaseous impurity elements.
The inevitable gaseous impurity elements need to be strictly controlled: the content of [ O ] is less than or equal to 10ppm, the content of [ H ] is less than or equal to 1.0ppm, and the content of [ N ] is less than or equal to 70 ppm.
The contents of Ti and Cu in the alloy steel are preferably 0.2 and 0.25, respectively, in terms of mass percentage.
A preparation process of austenite-bainite alloy steel comprises the following specific steps:
(1) preparing materials, namely weighing corresponding materials according to the alloy steel components in the embodiment 1, wherein the total weight of the materials is calculated according to 500Kg, and putting the weighed materials into an electric furnace or a converter for smelting;
(2) smelting in an electric furnace or a converter, starting a power supply, baking the furnace and materials, heating to 1700-1750 ℃, preserving heat for 4-6 hours, transferring slag-stopping tapping into a ladle after the materials are completely melted, and preparing for external refining.
(3) After the smelting in an electric furnace or a converter, the synthetic slag is added into a steel ladle by using an LF method to remove impurity elements such as oxygen, sulfur, phosphorus and the like, then oxygen is blown into the molten steel by using a VOD method under the vacuum condition and argon is applied for stirring for decarburization, finally the molten steel is sucked into a vacuum chamber by using an RH method, argon is introduced into the molten steel, the mixture of the molten steel and the argon entering the vacuum chamber releases gas under the action of high vacuum, meanwhile, the molten steel becomes molten steel beads, and the molten steel beads become smaller molten steel beads in the process that the gas to be removed in the molten steel beads is released into the vacuum under the action of the high vacuum, so that a good degassing effect is realized.
(4) The continuous casting process includes the steps of after external refining, pouring molten steel in a ladle into a tundish, distributing the molten steel into each crystallizer by a water gap in the tundish, forming a casting, quickly solidifying and crystallizing to form a billet, and adjusting parameters of the crystallizer to prevent the casting blank from generating defects such as stripping, bulging, cracks and the like.
(5) And (2) respectively forging the cast steel billets into two samples with the section sizes of 25mm multiplied by 25mm and 130mm multiplied by 180mm, regulating the temperature to 930-960 ℃ for austenitizing, preserving the heat for 1-2 h, quickly cooling to 520 ℃ at the speed of 1.6 ℃/s, preserving the heat for 15-30 min, slowly cooling to 340 ℃ above the martensite phase transition temperature (320 ℃), preserving the heat for 15-30 min, and finally air cooling to room temperature to obtain the alloy steel containing the residual austenite and the lower bainite structure. In order to improve the stability of the retained austenite and increase the strength and toughness of the alloy steel, the alloy steel sample subjected to the heat treatment is tempered, the tempering heating temperature is 330 +/-10 ℃, the temperature is kept for 1-2 hours, and then air cooling is carried out. Cooling to room temperature to finish the preparation of the austenite-bainite alloy steel.
In the prior art, the method for obtaining the lower bainite is to carry out salt bath isothermal treatment above the martensite transformation temperature, the salt bath has the defects of energy consumption and long treatment time, the heat treatment process in the invention does not need the salt bath, a billet is firstly heated to more than 900 ℃ for austenitizing, then is quickly cooled to more than 500 ℃, and then is slowly cooled to more than 500 DEG C
And finally, air cooling the lower bainite transformation area to room temperature to obtain a lower bainite structure.
In the step (3), the external refining is carried out, synthetic slag is used for deoxidation, desulfurization and dephosphorization in a steel ladle, and the synthetic slag is CaO-Al2O3And (4) slag system.
Example 2
The difference from the embodiment 1 is that the austenite-bainite alloy steel has a structure comprising austenite and bainite, and the composition of the alloy steel comprises the following components in percentage by mass: c: 0.30; si: 1.75; mn: 1.80; p: 0.007; s: 0.007; cr: 1.2; mo: 0.40; v: 0.12; ti: 0.10 to 0.20; cu: 0.10 to 0.25; the balance being Fe and unavoidable gaseous impurity elements. In addition, the contents of Ti and Cu in the alloy steel are preferably 0.15 and 0.18, respectively, in terms of mass percentage.
The alloy steel comprises the following components:
the C is a strong-gap solid solution strengthening element and is important for the strength, hardness and toughness of the steel. As the carbon content increases, the strength, hardness of the steel increases, and toughness and weldability decrease. Carbon is an element that stabilizes austenite because it has a high solubility in austenite and a low solubility in ferrite. When the carbon content is lower, the typical bainite structure of the bainite steel is obviously reduced, and the content of granular bainite is increased; the content of acicular bainite in the structure gradually increases as the carbon content increases.
Si can inhibit carbide precipitation and promote the alloy steel to form a carbide-free bainite structure, and meanwhile, when the Si reaches a certain amount, the content of residual austenite and the stability of the residual austenite can be improved. Si is a non-carbide-forming element, and when the content is small, a non-metallic inclusion is formed, which suppresses the coarsening of austenite grains. When the content reaches a certain amount, it is soluble in solid solution, promoting austenite grain coarsening.
Mn is a weak carbide forming element, can remarkably improve the hardenability of the bainite steel compared with Mo, is beneficial to air-cooling self-hardening of the bainite steel, and can remarkably reduce the bainite transformation starting temperature Bs.
The Cr can increase the sudden permeability of steel, and can shift the C curve to the right, delay the transformation of high-temperature region greatly and have little influence on medium-temperature region, increase the incubation period of transformation of super-cooled austenite and slow down the transformation speed. Cr can enhance the hardenability and the tempering stability of steel, and the content of Cr in low alloy steel is generally less than 2 percent, and the high Cr content can increase the tempering brittleness of the steel.
Mo has strong solute dragging effect, can remarkably delay ferrite phase change and inhibit precipitation of carbides.
The role of V, which is usually added to the steel as a microalloying element, is that of a strong carbonitride forming element, with C
N, O, etc. have very strong affinity and are capable of forming stable carbides and nitrides. Among the various strong nitride-forming elements, V has the highest solid solubility in steel, and when the temperature is lower than 900 ℃, the carbonitride of V, i.e., all of it is dissolved in austenite. The dispersed V solid solution blocks the growth of crystal grains and plays a role in precipitation strengthening. V can improve the hardenability of the bainitic steel and refine the prior austenite grains. The V microalloying can improve the strength and hardness of the steel and improve the ductility and toughness of the steel, so that the steel has better wear resistance.
Ti has a strong affinity with elements such as C, N, O, Si, and can generate carbon and nitride, thereby acting as precipitation strengthening. When the Ti content is 0.08% or less, the effect of refining crystal grains is exhibited, and when the Ti content is 0.08% or more, the effect of precipitation strengthening is mainly exhibited.
According to the preparation process of the austenite-bainite alloy steel provided by the invention, the performance of the produced alloy steel meets the following indexes: the tensile strength is more than 1530 MPa; the elongation is more than 16 percent; the reduction of area is more than 52 percent; normal temperature impact toughness (20 ℃) is more than 100J/cm2(ii) a Low temperature impact toughness (40 ℃ below zero) is more than 60J/cm2(ii) a The cross section hardness of the alloy steel is 45-50 HRC; the width of the corrosion groove is less than 0.003667 mm.
Table 1 alloy steel composition (mass%, wt.%)
Table 1 gives the composition of the alloy steels in examples 1, 2 compared to comparative examples 1, 2 and 3 (mass percent, wt.%); table 2 shows a table comparing the properties of the various alloys of examples 1, 2 with those of comparative examples 1, 2 and 3. By comparing table 1 and table 2, it is found that the strength of the alloy steel and the toughness at normal temperature and low temperature can be significantly improved by increasing the mass percent of the carbon element and adding the titanium element, and the tendency of intergranular corrosion resistance is also improved to a certain extent, that is, the width of the corrosion groove is reduced after the alloy steel is corroded by the sulfuric acid aqueous solution for 10 min. The addition of copper also improves the performances obviously, and particularly improves the intercrystalline corrosion resistance obviously. Meanwhile, titanium and copper elements are added, and the performances are further improved, so that the titanium and copper elements have a remarkable effect on the performance of the alloy steel.
TABLE 2 comparison of alloy steel properties for various compositions
By adopting the technical scheme provided by the invention, the obtained alloy steel has high strength, good plasticity and toughness and certain intergranular corrosion resistance, the service life of the alloy steel is prolonged, and the development requirement of a heavy haul railway is completely met.
The specific embodiments are only for explaining the invention, and the invention is not limited thereto, and those skilled in the art can make modifications without inventive contribution to the present embodiments as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the invention.
Claims (8)
1. An austenite-bainite alloy steel, the structure of which comprises austenite and bainite, is characterized in that the components of the alloy steel calculated according to the mass percentage comprise: c: 0.26 to 0.35; si: 1.66 to 1.84; mn: 1.70-1.90; p: less than or equal to 0.014; s: less than or equal to 0.014; cr: 1.11 to 1.29; mo: 0.35 to 0.45; v: 0.08 to 0.15; the balance being Fe and unavoidable gaseous impurity elements.
2. The austempered steel alloy of claim 1 further comprising in its composition Ti: less than or equal to 0.30; cu: less than or equal to 0.30.
3. Austempered steel alloy according to claim 1 characterized in that said unavoidable gaseous impurity elements require strict control: the content of [ O ] is less than or equal to 10ppm, the content of [ H ] is less than or equal to 1.0ppm, and the content of [ N ] is less than or equal to 70 ppm.
4. The austempered steel alloy according to claim 1, wherein the contents of Ti and Cu in the alloy steel are respectively 0.1-0.2 and 0.1-0.25 in percentage by mass.
5. A method for preparing an austempered steel alloy according to any of claims 1 to 3, characterized in that the preparation method comprises the following steps:
s1: preparing materials, namely weighing corresponding materials according to the components of the alloy steel, and putting the materials into an electric furnace or a converter for smelting;
s2: smelting in an electric furnace or a converter, starting a power supply, baking the furnace and materials, heating to 1700-1750 ℃, preserving heat for 4-6 hours, transferring slag-stopping tapping into a ladle after the materials are completely melted, and preparing for external refining;
s3: and (3) refining outside the furnace, after smelting in an electric furnace or a converter, deoxidizing, desulfurizing, dephosphorizing, decarburizing and degassing a steel ladle by using an LF + VOD/RH refining method.
6, S4: continuous casting process, after external refining, the molten steel is continuously cast into steel billets for forming;
s5: forging the cast steel billet into an alloy steel sample, adjusting the temperature to 930-960 ℃ for austenitizing, preserving the heat for 1-2 h, then quickly cooling to 520 ℃ at the speed of 1.6 ℃/s, preserving the heat for 15-30 min, slowly cooling to the martensite phase transition temperature, above 320 ℃, preserving the heat for 15-30 min, and finally air cooling to room temperature to obtain the alloy steel containing residual austenite and lower bainite tissues;
and the step S5 further comprises tempering treatment, wherein the tempering heating temperature is 330 +/-10 ℃, the heat preservation is carried out for 1-2 hours, then air cooling is carried out, and the preparation of the austenite-bainite alloy steel is finished when the austenite-bainite alloy steel is cooled to room temperature.
7. The method for preparing austempered steel alloy steel according to claim 4, wherein the step S3 of refining outside the furnace uses synthetic slag for deoxidation, desulfurization and dephosphorization in a ladle, wherein the synthetic slag is CaO-Al2O3And (4) slag system.
8. The method of manufacturing an austempered steel alloy according to claim 4 wherein the martensitic transformation temperature is 340 ℃.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
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2019
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| CN103429766A (en) * | 2011-05-30 | 2013-12-04 | 塔塔钢铁有限公司 | Bainitic steel of high strength and high elongation and method to manufacture said bainitic steel |
| WO2017082421A1 (en) * | 2015-11-13 | 2017-05-18 | 日本精工株式会社 | Multi-row ball bearing |
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