MICROALLOY CARBON STEEL FOR PASSENGER CAR HUB BEARINGS AND METHOD FOR MANUFACTURING THE SAME

Abstract

A steel, including: between 0.45 and 0.70 wt. % of carbon, between 0.10 and 0.50 wt. % of silicon, between 0.30 and 0.70 wt. % of manganese, between 0.20 and 0.60 wt. % of chromium, less than or equal to 0.025 wt. % of phosphorus, between 0.003 and 0.030 wt. % of sulfur, less than or equal to 0.1 wt. % of molybdenum, less than or equal to 0.2 wt. % of nickel, less than or equal to 0.04 wt. % of aluminum, less than or equal to 0.3 wt. % of copper, less than or equal to 0.001 wt. % of calcium, less than or equal to 0.003 wt. % of titanium, less than or equal to 0.001 wt. % of oxygen, less than or equal to 0.04 wt. % of arsenic, less than or equal to 0.03 wt. % of tin.

Claims

1. A steel, comprising: between 0.45 and 0.70 wt. % of carbon; between 0.10 and 0.50 wt. % of silicon; between 0.30 and 0.70 wt. % of manganese; between 0.20 and 0.60 wt. % of chromium; less than or equal to 0.025 wt. % of phosphorus; between 0.003 and 0.030 wt. % of sulfur; less than or equal to 0.1 wt. % of molybdenum; less than or equal to 0.2 wt. % of nickel; less than or equal to 0.04 wt. % of aluminum; less than or equal to 0.3 wt. % of copper; less than or equal to 0.001 wt. % of calcium; less than or equal to 0.003 wt. % of titanium; less than or equal to 0.001 wt. % of oxygen; less than or equal to 0.04 wt. % of arsenic; less than or equal to 0.03 wt. % of tin; less than or equal to 0.005 wt. % of antimony; less than or equal to 0.002 wt. % of lead; and the balance being iron and inclusions.

2. The steel of claim 1, wherein a length of a single inclusion is less than or equal to 3 mm.

3. The steel of claim 1, wherein nonmetallic inclusions in the steel according to ISO 4967 A meet the following requirements: Type A thin inclusions are less than or equal to 2.0; Type A thick inclusions are less than or equal to 1.5; Type B thin inclusions are less than or equal to 1.5; Type B thick inclusions are less than or equal to 0.5; Type C thin inclusions and thick inclusions are zero; Type D thin inclusions are less than or equal to 1.0; Type D thick inclusions are less than or equal to 0.5; and Type Ds inclusions are less than or equal to 1.0.

4. The steel of claim 1, wherein a tensile strength of the steel is higher than or equal to 780 Megapascal; a hardness of the steel is smaller than or equal to 255 HBW. Jominy of the steel salsifies J1.0, J2.060 HRC, J3.058 HRC, and J4.055 HRC.

5. A method for manufacturing steel, the method comprising: smelting steel in an electric arc furnace or a converter; refining the steel ladle refining; performing vacuum degassing or Ruhrstahl Heraeus (RH) vacuum degassing; continuously casting the steel; continuously rolling the steel; sawing the steel; stacking and cooling the steel; finishing the steel; detecting flaw on a steel surface and inside the steel; and packaging the steel; wherein when the steel is smelted in the electric furnace or a converter, carbon content at an output of the electric furnace or the converter is controlled to be higher than or equal to 0.10 wt. %; phosphorus content at the output of the electric furnace or the converter is controlled to be less than or equal to 0.020 wt. %; slag tapping is prevented; quantity of aluminum and iron added to the steel is determined by the carbon content at the output, and aluminum content of a first sample when the first sample arrived at a refining furnace is controlled between 0.040 and 0.070 wt. %; in the refining process, refining slag is in a ternary slag system, and micro-positive pressure is maintained in the refining furnace; aluminum and silicon carbide are used to perform combined deoxidation; in the refining slag, wt. % FeO+wt. % MnO is less than 1%, and aluminum content is maintained between 0.025 and 0.045 wt. %; in the vacuum degassing or Ruhrstahl Heraeus (RH) vacuum degassing, processing time is prolonged to increase agitated gas flow in vacuum; following the vacuum degassing, soft argon blowing is performed; the continuous casting is under antioxidant protection, and yields a 300 mm340 mm or larger continuous casting billet; and the continuous casting billet is moved to a heating furnace to be heated to a temperature between 1050 and 1250 C.; the temperature is kept and the continuous casting billet stays in the heating furnace for more than 3 hrs; phosphorus in the continuous casting billet is removed using pressurized water; the continuous casting billet is rolled to yield 48-100 bars, wherein a rough rolling start temperature is higher than 950 C., and a finish rolling temperature is higher than 800 C.; following the continuous rolling, the steel is sawed, cooled, straightened, and detected flaw to yield a target product.

6. The method of claim 5, wherein the continuous casting uses both mold electromagnetic stirrer (M-EMS) and final electromagnetic stirrer (F-EMS); especially, electromagnetic stirrers are applied at a final stage of solidification; overheat pouring in the continuous casting is under 35 C.; the steel is cooled in a secondary cooling section, and growth of the continuous casting billet is controlled so that carbon content at a central carbon segregation area is less than or equal to 10% of normal carbon content of smelted steel.

7. The method of claim 5, wherein the steel prepared by the method comprises between 0.45 and 0.70 wt. % of carbon, between 0.10 and 0.50 wt. % of silicon, between 0.30 and 0.70 wt. % of manganese, between 0.20 and 0.60 wt. % of chromium, less than or equal to 0.025 wt. % of phosphorus, between 0.003 and 0.030 wt. % of sulfur, less than or equal to 0.1 wt. % of molybdenum, less than or equal to 0.2 wt. % of nickel, less than or equal to 0.04 wt. % of aluminum, less than or equal to 0.3 wt. % of copper, less than or equal to 0.001 wt. % of calcium, less than or equal to 0.003 wt. % of titanium, less than or equal to 0.001 wt. % of oxygen, less than or equal to 0.04 wt. % of arsenic, less than or equal to 0.03 wt. % of tin, less than or equal to 0.005 wt. % of antimony, and less than or equal to 0.002 wt. % of lead; iron and inclusions.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] For further illustrating the invention, experiments detailing a steel for hub bearing and a method for manufacturing the steel are described below.

[0044] Chemical compositions (wt. %) of the steel for hub bearing in the examples and chemical compositions (wt. %) of steel G55 and steel C56E2 (as a comparison) which are commonly used in the market are shown in Table 2 and Table 3:

TABLE-US-00002 TABLE 2 Example C Si Mn P S Cr Mo Ni Al Steel 1 0.56 0.30 0.58 0.013 0.004 0.35 0.01 0.03 0.015 Steel 2 0.57 0.28 0.59 0.011 0.004 0.35 0.02 0.04 0.017 Steel 3 0.57 0.28 0.58 0.013 0.004 0.36 0.01 0.03 0.018 Domestic steel G55 4 0.55 0.27 0.80 0.012 0.001 0.08 0.01 0.03 0.022 Foreign steel C56E2 5 0.56 0.28 0.79 0.010 0.002 0.10 0.01 0.03 0.018

TABLE-US-00003 TABLE 3 Example Cu As Sn Sb Pb Ca Ti O Steel 1 0.06 0.0046 0.0067 0.0011 0.001 0.0001 0.0007 0.00058 Steel 2 0.07 0.0045 0.0067 0.0012 0.001 0.0002 0.0008 0.00059 Steel 3 0.06 0.0043 0.0067 0.0010 0.001 0.0001 0.0008 0.00058 Domestic steel G55 4 0.05 0.0046 0.0050 0.0013 0.001 0.0004 0.0006 0.00057 Foreign steel C56E2 5 0.06 0.0049 0.0044 0.0013 0.001 0.0003 0.0009 0.00062

[0045] A method for manufacturing the steel for hub bearing comprises: smelting steel in an electric furnace or a converter; refining the steel; performing vacuum degassing or Ruhrstahl Heraeus (RH) vacuum degassing; continuously casting the steel; continuously rolling the steel; sawing the steel; stacking and cooling the steel; finishing the steel; detecting flaw on a steel surface and inside the steel; packaging the steel.

[0046] Specifically, molten iron, scrap, deoxidant, refractory, and other raw materials used in the method are in high quality. When the steel is smelted in the electric furnace or a converter, carbon contents at an output of the electric furnace or the converter in the three examples are 0.25wt. %, 0.29 wt. %, and 0.30 wt. %, respectively; phosphorus contents at the output of the electric furnace or the converter of the three examples are0.012wt. %, 0.010 wt. %, and 0.012 wt. %, respectively. Aluminum contents in the steel when the refining process is finished are controlled to be 0.025 wt. %, 0.02 wt. %, and 0.027 wt. %, respectively. The overheating continuous casting is controlled to be at 22 C., 20 C., 21 C. in the examples, respectively. The heating temperature of the continuous rolling is controlled to between 1050 and 1250 C. The temperature is kept and the continuous casting billet stays in the heating furnace for more than 3 hrs. Scale in the continuous casting billet is removed using pressurized water; the continuous casting billet is rolled in a 17-stand continuous rolling mill, where a rough rolling start temperature is higher than 950 C., and a finish rolling temperature is higher than 800 C. Following the continuous rolling, the steel is sawed, cooled, straightened, and detected flaw to yield a target product.

[0047] Comparison of mechanical properties of steel in the examples is shown in Table 4:

TABLE-US-00004 TABLE 4 Tensile End End End End strength Hardness quenching quenching quenching quenching Example (MPA) (HBW) J1.0(HRC) J2.0(HRC) J3.0(HRC) J4.0(HRC) Steel 1 835 241 62 61 60 58 Steel 2 840 239 62 61.5 60 58 Steel 3 837 240 62 61 59.5 57 Domestic steel G55 4 794 230 61 60.5 59 55 Foreign steel C56E2 5 805 234 61 60 59 56

[0048] As shown in Table 4, in terms of strength, hardness, toughness, abrasive resistance, and hardenability, the steel for hub bearing in the examples of the invention equal to or is slightly better than existing steel for hub bearing.

[0049] In addition, carbon content tested at a central carbon segregation area of the steel in the examples is less than 10% of normal carbon content of smelted steel, thus the central carbon segregation is obviously controlled, and the microstructure uniformity of steel is ensured.

[0050] Non-metallic inclusions in the steel in the examples meet the requirements in Table 1. Meanwhile, Macroscopic defects of the steel in the examples are detected according to a high-frequency impregnating flaw detection method SEP 1927, and a length of single inclusion is less than or equal to 3 mm.

[0051] Unless otherwise indicated, the numerical ranges involved in the invention include the end values. While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.