Metal treatment – Stock – Ferrous
Reexamination Certificate
2000-04-05
2002-05-07
Wyszomierski, George (Department: 1742)
Metal treatment
Stock
Ferrous
C420S042000, C420S055000, C060S272000
Reexamination Certificate
active
06383310
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an exhaust equipment member such as an exhaust manifold, a turbine housing, etc. for automobile engines, an internal combustion engine system using such an exhaust equipment member, and a method for producing such an exhaust equipment member.
Prior Art
Exhaust equipment members such as exhaust manifolds, turbine housings, etc. for automobiles are conventionally made of heat-resistant cast iron such as NI-RESIST cast iron (Ni—Cr—Cu austenitic cast iron), heat-resistant ferritic cast steel, etc. Though the NI-RESIST cast iron has relatively good high-temperature strength at an exhaust gas temperature of up to 900° C., it does not have enough durability at a temperature of 900° C. or higher. Also, the heat-resistant ferritic cast steel is poor in a high-temperature strength at an exhaust gas temperature of 950° C. or higher.
There is a heat-resistant, austenitic cast steel as a material more resistant to a high temperature than heat-resistant cast iron such as NI-RESIST cast iron and heat-resistant ferritic cast steel. For instance, Japanese Patent Laid-Open No. 54-96418 discloses a heat-resistant, austenitic cast steel comprising by weight 0.1-1.5% of C, 0.5-5.0% of Si, less than 2.5% of Mn, 15-35% of Cr, and 8-45% of Ni, 0.5-3.0% of W, 0.2-5.0% of Nb, or further 0.5-2.0% of Mo and 0.05-0.25% of S, the balance being substantially Fe. This Japanese laid-open application shows in Examples a heat-resistant, austenitic cast steel having a composition comprising by weight 0.12-1.42% of C, 0.23-0.73% of Si, 0.77-0.83% of Mn, 0.87-1.62% of Mo, 24.8-25.3% of Cr, 19.6-20.3% of Ni, 0.86-1.6% of W, 0.21-1.33% of Nb, and 0.08-16% of S, the balance being substantially Fe. Because this cast steel contains S, it exhibits improved cuttability, a high-temperature tensile strength of 10.6-15.4 kg/mm
2
at 1000° C., and a weight loss by oxidation of 1.7-8.3 mg/(dm
2
·hr) at 900° C.
The present applicant proposed heat-resistant, austenitic cast steels durable in use at a high temperature of 900° C. or higher (Japanese Patent Laid-Open Nos. 5-5161 and 7-228948).
Japanese Patent Laid-Open No. 5-5161 discloses a heat-resistant, austenitic cast steel having a composition comprising by weight 0.20-0.60% of C, 2.00% or less of Si, 1.00% or less of Mn, 15-30% of Cr, 8-20% of Ni, 2-6% of W, 0.2-1.0% of Nb, and 0.001-0.01% of B, the balance being substantially Fe and inevitable impurities, which has excellent high-temperature strength even after subjected to repeated heat cycles of heating up to higher than 900° C. and cooling, and an exhaust equipment member made of such heat-resistant austenitic cast steel. This Japanese laid-open application shows in EXAMPLE a composition comprising by weight 0.19-0.49% of C, 0.87-1.06% of Si, 0.46-0.59% of Mn, 18.82-28.20% of Cr, 8.26-18.84% of Ni, 2.02-5.03% of W, 0.28-0.98% of Nb, and 0.002-0.008% of B, the balance being substantially Fe and inevitable impurities, or further 0.49-0.55% of Mo and/or 4.50-18.74% of Co. EXAMPLES of this Japanese laid-open application show that the heat-resistant austenitic cast steel had a 0.2-% yield strength of 33-62 MPa, a tensile strength of 59-31 MPa and an elongation of 27-40% at 1050° C. Also, they show that when the thermal fatigue life of this austenitic cast steel was measured on a round rod test piece having a gauge length of 20 mm and a diameter of 10 mm in the gauge length under the conditions of the lowest heating temperature of 150° C., the highest heating temperature of 1000° C., and each one cycle of 12 minutes in a state where the elongation and shrink of the test piece by heating were mechanically completely constrained, the number of cycles was 88-195 until the thermal fatigue failure took place. Further, they show that the weight loss by oxidation after kept at 1000° C. for 200 hours was 15-50 mg/cm
2
.
Japanese Patent Laid-Open No. 7-228948 discloses a heat-resistant, austenitic cast steel with excellent castability and cuttability having a composition comprising by weight 0.2-1.0% of C, 2% or less of Si, 2% or less of Mn, 15-30% of Cr, 8-20% of Ni, 1-6% of W, 0.5-6% of Nb, 0.01-0.3% of N, and 0.01-0.5% of S, C—Nb/8 being 0.05-0.6%, and the balance being substantially Fe and inevitable impurities, and an exhaust equipment member made of such austenitic cast steel. This Japanese laid-open application shows in EXAMPLE a composition comprising by weight 0.21-0.80% of C, 0.52-1.11% of Si, 0.51-1.05% of Mn, 16.55-21.02% of Cr, 8.45-18.55% of Ni, 1.02-5.80% of W, 0.68-6.95% of Nb, 0.03-0.14% of N, and 0.03-0.41% of S, C—Nb/8 being 0.12-0.58%, and the balance being substantially Fe and inevitable impurities. The heat-resistant austenitic cast steel in this EXAMPLE had a 0.2-% yield strength of 55-80 MPa, a tensile strength of 62-125 MPa and an elongation of 26-75% at 1000° C. Also, when the thermal fatigue life of this austenitic cast steel was measured on a round rod test piece having a gauge length of 25 mm and a diameter of 10 mm in the gauge length under the conditions of the lowest heating temperature of 150° C., the highest heating temperature of 1000° C., and each one cycle of 12 minutes in a state where the elongation and shrink of the test piece by heating were mechanically completely constrained, the number of cycles was 145-210 until the thermal fatigue failure took place. Further, it exhibited a weight loss by oxidation of 18-50 mg/cm
2
when kept in the air at 1000° C. for 200 hours.
In most automobile engines, gasoline is mixed with air in an intake manifold or a collector as an air-intake member and then supplied to a combustion chamber of the engine. In this structure, if gasoline or a mixture of gasoline and air leaks from the intake manifold or the collector by the collision of an automobile, it may be ignited. To prevent such an accident, air-intake members such as an intake manifold or a collector are connected to the engine on the rear side, while exhaust equipment members such as an exhaust manifold and a turbine housing are connected to the engine on the front side.
Recently, further reduction of an exhaust gas and improvement in fuel efficiency are increasingly demanded for the purpose of maintaining global environment. Thus, progress has been achieved in increase in the output of engines and the combustion temperature, resulting in the development and wide spreading of so-called direct-injection engines having combustion chambers into which gasoline is directly injected. In this direct-injection engine, because gasoline is directly introduced into a combustion chamber from a fuel tank, only the slightest amount of gasoline would leak if the automobile collided, resulting in little likelihood that the collision leads to a large accident. Accordingly, instead of the conventional arrangement that the exhaust equipment members such as an exhaust manifold and a turbine housing are disposed in front of the engine while the air-intake members such as an intake manifold or a collector are disposed on the rear side of the engine, the air-intake members may be disposed in front of the engine to supply a cooled air to the combustion chamber of the engine, while the exhaust equipment members are disposed on the rear side of the engine, so that they are directly connected to an exhaust gas-purifying apparatus to improve the initial performance of an exhaust gas-purifying catalyst in the exhaust gas-purifying apparatus.
When the exhaust equipment members such as an exhaust manifold and a turbine housing are disposed on the rear side of the engine, the surface temperatures of the exhaust equipment members are elevated because the exhaust equipment members are less likely to be brought into contact with the wind during the driving of an automobile. Thus, the exhaust equipment members need high durability at a high temperature.
The exhaust equipment members such as an exhaust manifold and a turbine housing are presently required to have enough durability to an exhaust gas at temperatures exceeding 1000° C., or near 1050° C., or further near 1100° C. Further,
Hayashi Keijiro
Itoh Kenji
Otsuka Koki
Takahashi Norio
Hitachi Metals Ltd.
Sughrue & Mion, PLLC
Wyszomierski George
LandOfFree
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