WO2009002013A1

WO2009002013A1 - Cast iron for turbine housing/exhaust manifold

Info

Publication number: WO2009002013A1
Application number: PCT/KR2008/002435
Authority: WO
Inventors: Je Won Han; Yun Taek Kim
Original assignee: Borgwarner Inc.
Priority date: 2007-06-22
Filing date: 2008-04-29
Publication date: 2008-12-31
Also published as: KR20080112843A

Abstract

The cast iron for the turbine housing/exhaust manifold according to the present invention comprises carbon, silicon, phosphorus, manganese, and magnesium components, and includes from 0.5 to 2 wt % of vanadium (V), from 0.5 to 3 wt % of molybdenum (Mo), and from 0.1 to 2 wt % of nickel (Ni). According to the cast iron for the turbine housing/exhaust manifold of an automobile, there is an advantageous effect of improving the thermal deformation characteristic and increasing the high-temperature oxidation resistance, by modifying the constituent elements of the alloy for the turbine housing/exhaust manifold at high temperature.

Description

Description CAST IRON FOR TURBINE HOUSING/EXHAUST MANIFOLD

Technical Field

[1] The present invention relates to cast iron for the turbine housing/exhaust manifold, and in particular, it relates to cast iron for turbine housing/exhaust manifold with improved characteristics such as thermal conductivity, thermal expansion, thermal shock, thermal deformation, etc. at high temperature by modifying the constituent elements of an alloy for the turbine housing/exhaust manifold which is used at high temperature, and with increased high-temperature oxidation resistance.

[2]

Background Art

[3] Most of the materials which are presently used as the automobile engine exhaust system material are the FCD-H and FCD-50HS materials, and to this date, such materials have been suitably used in the present situation where the output and exhaust gas temperature is not very high.

[4] However, due to the increase of the recent automobile engine displacement and the improved output, the exhaust gas temperature has increased sharply, and as such, when a gasoline engine is operated at the maximum temperature of about 1000 ⁰C, or when a diesel engine is operated at about 830 ⁰C, the thermal load on the parts such as the exhaust manifold and the turbine housing becomes very great.

[5] The greatest problem caused by the exhaust temperature rise is the problem of thermal deformation of the material, wherein the exhaust manifold which alternates between regions of high temperature and low temperature is accompanied by thermal expansion and thermal shrinkage depending on situation, which can cause surface oxidation wrinkles by such thermal deformation, and which can progress and develop into a penetration crack.

[6] Such oxidation wrinkles and penetration crack frequently occur at the relatively less sturdy port part or the merging part, and this is thought to be partly affected by the fact that the port part is thin and the structural imbalance due to cooling.

[7] Accordingly, as the high-speed performance improves through exhaust temperature increase, there have been attempts to gradually raise the exhaust temperature of the engine, and therefore, there is an urgent need to develop heat-resistant cast iron material having superior thermal deformation and oxidation resistance characteristics that can support such attempts.

[8] Moreover, the conventional materials for the turbine housing/exhaust manifold have been inexpensive materials in the operation range of less than 800 ⁰C such as GGV, HiSiMo, Super-HiSiMo, SiMoCr, etc.; however, as even diesel engines use 800 ~ 830 0C pursuant to the tightened regulations for engine output and exhaust gas, it has become necessary to use the D5S material.

[9] However, the D5S material contains 30 ~ 35 wt % of nickel (Ni), and due to the sudden rise of the Ni price recently, there has been substantial concern over the cost of materials.

[10]

Disclosure of Invention Technical Problem

[11] The present invention was devised taking into consideration the aforementioned concerns, and its object is to provide cast iron for the turbine housing/exhaust manifold with improved thermal deformation and enhanced high-temperature oxidation resistance characteristics, by modifying the constituent elements of an alloy for the turbine housing/exhaust manifold which is used at high temperature.

[12]

Technical Solution

[13] Further object of the present invention is to provide cast iron for the turbine housing/ exhaust manifold with improved mechanical characteristics at high temperature, by including vanadium (V; 0.5 ~ 2.0 wt %), molybdenum (Mo; 0.5 ~ 3.0 wt %), and nickel (Ni; 0.1 ~ 2.0 wt %) components to the turbine housing/exhaust manifold material.

[14] Further object of the present invention is to add vanadium (V) and molybdenum

(Mo) to GGV instead of using expensive Ni, whereby mechanical properties of matter required for high-temperature operating environment can be attained.

[15] In order to achieve the aforementioned objects, the cast iron for the turbine housing/ exhaust manifold according to the present invention comprises carbon, silicon, phosphorus, manganese, and magnesium components, and includes from 0.5 to 2 wt % of vanadium (V), from 0.5 to 3 wt % of molybdenum (Mo), and from 0.1 to 2 wt % of nickel (Ni).

[16] Said cast iron is characterized in that it has thermal resistance at the temperature of from 600 ⁰C to 900 ⁰C.

[17] Said cast iron is characterized in that its high-temperature tensile strength at 700 ⁰C is

140 N/mm².

[18] Said cast iron is characterized in that its high-temperature tensile strength at 800 ⁰C is from 75 to 80 N/mm².

[19] Said cast iron is characterized in that its elongation at 800 ⁰C is from 35 to 45 %.

[20] Said cast iron is characterized in that its yield point at 800 ⁰C is at least 55 N/mm². [21] Said cast iron is characterized in that its thermal conductivity is from 20 to 40 W/mk.

[22] Said cast iron is characterized in that its weight increase due to thermal oxidation is

16 mg/cm².

[23] Said cast iron is characterized in that its thermal expansion at 800 ⁰C is from 0.5 to

1.5 %.

[24] As seen hereinabove, according to the cast iron for the turbine housing/exhaust manifold of an automobile, there is an advantageous effect of improving the thermal deformation characteristics and enhancing the high-temperature oxidation resistance characteristics, by modifying the constituent elements of an alloy for the turbine housing/exhaust manifold which is used at high temperature.

[25] The cast iron for the turbine housing/exhaust manifold according to the present invention has the advantageous effect of improving the mechanical characteristics at high temperature, by including vanadium (V; 0.5 ~ 2.0 wt %), molybdenum (Mo; 0.5 ~ 3.0 wt %), and nickel (Ni; 0.1 ~ 2.0 wt %) components to the turbine housing/exhaust manifold material.

[26] Moreover, since the present invention uses vanadium (V) and molybdenum (Mo), instead of expensive Ni, while having the mechanical properties of matter required for high-temperature operating environment, there is an advantageous effect of reducing the cost of manufacturing.

[27]

Advantageous Effects

[28] As described hereinabove, according to the cast iron for the turbine housing/exhaust manifold of an automobile according to the present invention, there are advantageous effects of improving the thermal deformation characteristics and increasing the high- temperature oxidation resistance, by modifying the alloy for the turbine housing/ exhaust manifold which is used at high temperature.

[29]

Brief Description of the Drawings

[30] Fig. 1 is a drawing showing the tensile strength of the cast iron and an embodiment according to present invention.

[31] Fig. 2 is a drawing showing the elongation of the cast iron according to the present invention.

[32] Fig. 3 is a drawing showing the yield point characteristics of the cast iron according to the present invention.

[33] Fig. 4 is a drawing showing the thermal conductivity characteristics of the cast iron according to the present invention.

[34] Fig. 5 is a drawing showing the thermal oxidation characteristics of the cast iron according to the present invention.

[35] Fig. 6 is a drawing showing the thermal expansion characteristics of the cast iron according to the present invention. [36] Fig. 7 is a drawing showing the E-modulus characteristics of the cast iron according to the present invention. [37]

Mode for the Invention

[38] Hereinbelow, the present invention is described in greater detail. [39] Hereinbelow, there is provided explanation for the reasons for limiting the composition and the scope of the cast iron according to the present invention.

[40] In addition, the cast iron according to the present invention comprises carbon, silicon, phosphorus, manganese, and magnesium components, and includes from 0.5 to 2 wt % of vanadium (V), from 0.5 to 3 wt % of molybdenum (Mo), and from 0.1 to 2 wt % of nickel (Ni).

[41] The following shows the composition and the scope of each cast iron according to the present invention.

[42] [43] Table 1 [Table 1]

[44] 1) Molybdenum (Mo) (0.5) ~ (3) wt % [45] From 0.3 to 3.5 wt % of molybdenum (Mo) can be added to the cast iron of the present invention, and preferably, from 0.5 to 3.0 wt % can be added.

[46] The molybdenum which is added to the cast iron in the manner described above can enhance the high-temperature tensile strength, the creep property, and the rupture strength of the cast iron and improve the oxidation resistance by forming a protective film at high temperature.

[47] However, toughness and shock resistance at low temperature can be reduced. Accordingly, the content of molybdenum in the cast iron is preferably from 0.5 to 3 wt %.

[48] 2) Vanadium (V) (0.5) ~ (2) wt % [49] From 0.3 to 2.5 wt % of vanadium (V) can be added to the cast iron of the present invention, and preferably, from 0.5 to 2.0 wt % can be added. The vanadium which is added to the cast iron in this manner can prevent oxidation at high temperature and deformation at high temperature of the cast iron of the present invention

[50] 3) Silicon (Si) (4) ~ (4.6) wt % [51] From 3 to 5 wt % of the silicon component can be added to the cast iron of the present invention, and preferably, from 4 to 4.6 wt % can be added.

[52] As more of the silicon (Si) component is added, it is possible to obtain the advantageous effects such as thermal resistance, improvement in structural properties, etc., of the iron cast.

[53] In addition, it has an important advantageous effect on the properties of the ferritic spherical graphite cast iron. It is possible to improve the dimensional stability of the cast iron by raising the transition temperature of ferrite/austenite together with carbon, and it is possible to improve the oxidation resistance by forming a protective film at high temperature on the surface of the cast iron by the Si + O₂ →SiO₂ reaction of the silicon.

[54] On the other hand, if the silicon (Si) range is insufficient, the matrix structure of the cast iron does not turn into ferrite and perlite may exist instead. Accordingly, while the temperature of perlite rises, and when it rises above 650 ⁰C, it leads to decomposition which can be the cause of the thermal expansion of the cast iron.

[55] Accordingly, for the reasons described above, if too much silicon (Si) is added, brittleness is increased. Therefore, it is preferable to limit the silicon content to the (4) ~ (4.6) wt % range.

[56] More specifically, if the silicon (Si) component is added in excess of 4 wt %, a Fe₂

SiO₄ layer forms in an iron oxide (FeO) oxidized layer; however, this layer is very fine so that it can decrease the progression of oxidation; and if the silicon (Si) component is added in the range of 4 ~ 4.6 wt %, there is an advantageous effect of mitigating the catalytic attack according to high-temperature oxidation scale.

[57] 4) Carbon (C) (3) ~ (3.6) wt %

[58] From 2.5 to 4.0 wt % of carbon can be added to the cast iron according to the present invention, and preferably, from 3 to 3.6 wt % of carbon can be added.

[59] The carbon content of from 3 to 3.6 wt % is preferable due to the fact that much silicon component is added to the cast iron, and if the carbon content exceeds this range, it can lead to the production of a hypereutectic composition.

[60] Accordingly, even though the carbon content which is added to the cast iron can improve the hardness of the cast iron, it can reduce the corrosion resistance of the cast iron; and as such, it is preferable to add from 3 to 3.6 wt %.

[61] 5) Nickel (Ni) (0.1) ~ (2.0) wt %

[62] From 0.1 to 2.5 wt % of the nickel component can be added to the cast iron according to the present invention, and preferably, from 0.1 to 2.0 wt % can be added.

[63] The nickel (Ni) component which is added to the cast iron can improve the corrosion resistance of the material, and can toughen the quality of the cast iron. Moreover, if the nickel component is added in excess of a predetermined amount, it can reduce the thermal expansion coefficient of the cast iron. [64] Accordingly, it is preferable to add from 0.1 to 2.0 wt % of the nickel component to the cast iron.

[65] 6) Manganese (Mn) not exceeding (0.3) wt %

[66] The manganese (Mn) in an amount not exceeding 0.5 wt % can be added to the cast iron according to the present invention, and preferably, 0.3 wt % of the manganese component can be added. [67] The manganese component can improve the hardness and the high-temperature tensile strength of the cast iron, and can improve the toughness of the cast iron. [68] Accordingly, it is preferable to add the manganese component in an amount not exceeding 0.3 wt %.

[69] 7) Phosphorus (P) not exceeding 0.047 wt %, sulfur (S) not exceeding 0.02 wt %

[70] The cast iron according to the present invention can be formed by adding a number of constituent elements. Accordingly, as a number of constituent elements are admixed, a number of impurities can be added to the cast iron. [71] However, it can be difficult to completely eliminate the impurities, and as such, it is important to minimize the content of the impurities. It is thus possible to reduce the corrosion resistance and the strength of the cast iron, and it is preferable to minimize the content of phosphorus and sulfur which can be the cause of various brittleness. [72] Accordingly, the phosphorus content which is added to the cast iron is preferably not in excess of 0.047 wt %, and the sulfur content is preferably not in excess of 0.02 wt

%. [73] Hereinbelow, the present invention is described in greater detail by referring to its embodiments. [74] However, these embodiments are used only for the purpose of describing the present invention in greater specificity, and it is to be understood that the scope of the present invention is not limited by these embodiments. [75] The following comparative examples and embodiments are the representative materials of the cast iron for the turbine housing/exhaust manifold which are presently used under the temperature condition of less than 800 ⁰C. [76] Embodiment

[77] As described above, the cast iron according to the present invention, i.e., GGV-VMo, comprises carbon (C) (3 ~ 3.6) wt %, silicon (Si) (4 ~ 4.6) wt %, manganese (Mn) not exceeding (0.3) wt %, phosphorus (P) not exceeding 0.047 wt %, sulfur (S) not exceeding 0.02 wt %, magnesium not exceeding (0.05) wt %, molybdenum (Mo) (0.5

~ 3) wt %, nickel (Ni) from 0.1 to 2 wt %, and vanadium (V) from 0.5 to 2 wt %. The cast iron of the present invention, the remainder of which comprises impurities and Fe, is used to fabricate an exhaust manifold through the conventional method. [78] Comparative Example [79] The conventional GGV does not have a name according to a formal standard concerning material names, and each company calls it differently by slightly modifying the constituent elements with respect to the heat resistant ductile cast steel. As what is conventionally called CGI (compacted graphite iron) in the U.S.A. was slightly improved into a turbine housing material, it has come to be called GGV in Germany.

[80] The GGV (Gusseisen mit Vermikular graphit: the German name for cast iron with vermicular graphite) of the comparative example comprises carbon (C) (3 ~ 3.6) wt %, silicon (Si) (4 ~ 4.6) wt %, manganese (Mn) not exceeding (0.3) wt %, phosphorus (P) not exceeding 0.047 wt %, sulfur (S) not exceeding 0.02 wt %, magnesium not exceeding (0.05) wt %, molybdenum (Mo) (0.4 ~ 0.7) wt %, and nickel not exceeding (0.60) wt %. The GGV alloy of the present invention, the remainder of which comprises impurities and Fe, is used to fabricate an exhaust manifold through the conventional method.

[81] Properties of Matter Characteristics and Results

[82] Pursuant to the testing standards set forth in the German Industrial Standard (DIN EN

1002-1) and the Korean Industrial Standard KSD 0801 ~ 0811, the properties of matter characteristics and results with respect to the above embodiment and comparative example are discussed hereinbelow.

[83] A rectangular specimen with k = 5.65, D = 10 + 0.075 mm, S₀ = 78.5 mm², and L_c =

55 mm is used as the specimen for the embodiment and the comparative example, and this specimen was used to measure the tensile strength, the elongation, the yield point, etc. of the cast iron by using different measuring devices for each property.

[84] In addition, as for the reference for measuring the properties of matter of the cast iron of the present invention, if the exhaust gas temperature rises higher than 950 ⁰C, the temperature of the exhaust system (i.e., the cast iron) can rise up to 800 ⁰C, which is lower by about -100 ⁰C.

[85] Accordingly, in the present experiment, the thermal strength with respect to the materials of the embodiment and the comparative example is from 600 ⁰C to 800 ⁰C.

[86] Fig. 1 to Fig. 7 are drawings showing the characteristics of the cast iron according to the present invention.

[87] Fig. 1 is a drawing showing the tensile strength of the cast iron according to the present invention and that of the comparative example.

[88] The high-temperature tensile strength test of the cast iron (GGV-VMo) according to the present invention was performed according to temperature, which showed the characteristics of 140 N/mm² at 700 ⁰C and 75 ~ 80 N/mm² at 800 ⁰C. That is, it was determined to have similar or favorable high-temperature tensile strength compared to the conventional GGV.

[89] Fig. 2 is a drawing showing the elongation of the cast iron according to the present invention.

[90] Referring to Fig. 2, it can be seen that the elongation of the cast iron according to the present invention is about 40% at 800 ⁰C, and that its elongation characteristic is almost identical in comparison to the elongation characteristic of the conventional GGV.

[91] Fig. 3 is a drawing showing the yield point characteristic of the cast iron according to the present invention.

[92] Referring to Fig. 3, it can be seen that the cast iron of the present invention shows the characteristic of about 55 N/mm² at 800 ⁰C, and that it has very similar yield point characteristic compared to that of the conventional GGV.

[93] Fig. 4 is a drawing showing the thermal conductivity characteristic of the cast iron according to the present invention.

[94] Referring to Fig. 4, it can be seen that the cast iron according to the present invention shows the thermal conductivity characteristic of about 30 W/mk, and that this is an improvement in comparison to the conventional GGV.

[95] This shows that the thermal relief characteristic of the cast iron with respect to its surroundings has improved, whereby its ability to maintain the shape of the cast iron from thermal shock has improved.

[96] Fig. 5 to Fig. 7 are drawings showing the characteristics of the cast iron according to the present invention with respect to its thermal oxidation, thermal expansion, and E- modulus.

[97] Referring to Fig. 5, from the data measured during 100 hours at 750 ⁰C, it can be seen that the thermal oxidation characteristic of the cast iron according to the present invention is that the weight increase from thermally oxidating for 100 hours is 16 mg/ cm², which shows that it does not become oxidized even at high temperature for thermal oxidation, compared to the conventional GGV.

[98] Accordingly, it can be seen that the cast iron has improved oxidation resistance even at high temperature.

[99] Referring to Fig. 6, it can be seen that the cast iron according to the present invention has thermal expansion characteristic of 5 mm at 800 ⁰C which corresponds to thermal expansion of 1.25%, and that it has lower thermal expansion compared to the conventional GGV. As described, it can be seen that, as the thermal expansion is measured low, the cast iron has improved characteristics such as the deformation of the case iron due to thermal expansion at high temperature.

[100] Referring to Fig. 7, it can be seen that the E-modulus of the cast iron according to the present invention is measured as 50 GPa at 800 ⁰C, and that this is similar characteristic compared to the conventional GGV.

Claims

[1] Cast iron for the turbine housing/exhaust manifold, comprising the one selected carbon, silicon, phosphorus, magnesium and combinations thereof, and including from 0.5 to 2 wt % of vanadium (V), from 0.5 to 3 wt % of molybdenum (Mo), and from 0.1 to 2 wt % of nickel (Ni). [2] The cast iron for the turbine housing/exhaust manifold as claimed in claim 1, characterized in that, said cast iron has thermal resistance at the temperature of from 600 ⁰C to 900 ⁰C. [3] The cast iron for the turbine housing/exhaust manifold as claimed in claim 1, characterized in that, the high-temperature tensile strength of said cast iron is 140 N/mm² at 700 ⁰C. [4] The cast iron for the turbine housing/exhaust manifold as claimed in claim 1, characterized in that, the high-temperature tensile strength of said cast iron is from 75 to 80 N/mm² at

800 ⁰C. [5] The cast iron for the turbine housing/exhaust manifold as claimed in claim 1, characterized in that, the elongation of said cast iron is from 35 to 45 % at 800 ⁰C. [6] The cast iron for the turbine housing/exhaust manifold as claimed in claim 1, characterized in that, the yield point of said cast iron is at least 55 N/mm² at 800 ⁰C. [7] The cast iron for the turbine housing/exhaust manifold as claimed in claim 1, characterized in that, the thermal conductivity of said cast iron is from 20 to 40 W/mk. [8] The cast iron for the turbine housing/exhaust manifold as claimed in claim 1, characterized in that, the weight increase due to thermal oxidation of said cast iron is 16 mg/cm². [9] The cast iron for the turbine housing/exhaust manifold as claimed in claim 1, characterized in that, the thermal expansion of said cast iron is from 0.5 to 1.5 % at 800 ⁰C.