Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
1999-08-17
2003-03-25
King, Roy (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S662000, C148S612000
Reexamination Certificate
active
06537397
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing an Fe-based member having a high Young's modulus and an Fe-based member having a high Young's modulus and a high toughness.
2. Description of the Related Art
There is a conventionally known method for enhancing the Young's modulus of an Fe-based member, which is to compound a dispersing material such as a reinforcing fiber, reinforcing granules and the like having a high Young's modulus to a matrix for the Fe-based member.
However, the known method suffers from problems that the dispersing material is coagulated in the matrix, and that when the surface properties are poor, the toughness of the Fe-based member is largely injured.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a producing process of the above-described type, wherein a particular metallographic structure can be produced by subjecting an Fe-based material having a particular composition to a particular treatment, thereby mass-producing an Fe-based member having a high Young's modulus, a high toughness or a toughness required for practical use.
To achieve the above object, according to the present invention, there is provided a process for producing an Fe-based member having a high Young's modules, comprising a first step of subjecting an Fe-based material comprising
0.6% by weight≦carbon (C)≦1.9% by weight
silicon (Si)<2.2% by weight
0.9% by weight≦manganese (Mn)≦1.7% by weight
0.5% by weight≦nickel (Ni)≦1.5% by weight and
the balance of iron (Fe) including inevitable impurities, to a thermal treatment at a heating temperature T
1
set in a range of T
S
<T
1
<T
L
wherein T
S
represents a solidus temperature for the Fe-based material and T
L
represents a liquidus temperature, and under a cooling condition set at a quenching level, and a second step of subjecting the resulting Fe-based material to a thermal treatment at a heating temperature T
2
set in a range of Te1<T
2
<Te2 wherein Te1 represents a eutectic transformation-starting temperature, and Te2 represents a eutectic transformation-finishing temperature, and for a heating time t set in a range of 60 min≦t≦180 min.
If the Fe-based material having the above-described composition is subjected to the thermal treatment at the first step, the solidified structure is transformed into a primary thermally treated structure. The primary thermally treated structure is comprised of a matrix comprising martensite, a large number of massive residual &ggr; phases, a large number of intermetallic compound phases and the like. If the conditions are changed at the first step, the primary thermally treated structure cannot be produced. In the quenching, the cooling rate CR is set higher than a usual oil-cooling level or a forcibly air-cooling level, and thus, at CR≧250° C./min. For this quenching, for example, an oil-cooling, a water-cooling or the like may be used.
If the Fe-based material having the primary thermally treated structure is then subjected to the thermally treatment at second step, the primary thermally treated structure is transformed into a secondary thermally treated structure. The secondary thermally treated structure is comprised of a matrix, for example, comprising an &agr; phase, a large number of fine carbide granules, a large number of massive precipitated &ggr; phases and the like. Fine short fiber-shaped carbide phases may be included in the secondary thermally treated structure in some cases.
In the secondary thermally treated structure, the fine carbide granules contribute to an enhancement in Young's modulus of the Fe-based member, and the precipitated &ggr; phases contribute to an enhancement in toughness of the Fe-based member.
If the heating temperature T
2
is lower than Te1 or the heating time t is shorter than 60 minutes at the second step, the fine division and dispersion of the carbide cannot be achieved sufficiently. On the other hand, if the heating temperature T
2
is higher than Te2 or the heating time t is longer than 180 minutes at the second step, the graphitization is advanced excessively, and the coagulation of the carbide is produced.
Carbon (C) in the composition of the Fe-based material produces the fine carbide granules which contribute to an enhancement in Young's modulus. To increase the amount of fine carbide granules produced, it is necessary to add a larger amount of carbon(C), and hence, the lower limit of the C content is set at 0.6% by weight. On the other hand, if C>1.9% by weight, not only the carbide content but also the graphite content are increased and further, a eutectic graphite phase is precipitated. For this reason, the Fe-based member is embrittled.
Silicon (Si) serves to promote the deoxidation and the graphitization and is dissolved as a solid solution into the &agr; phase to reinforce the &agr; phase. In addition, silicon (Si) has an effect of increasing the difference &Dgr;T between the eutectic transformation starting temperature Te1 and the eutectic transformation finishing temperature Te2, namely, widening the range of the heating temperature T
2
at the second step. Therefore, it is desired to increase the silicon content, but if the silicon content is increased, the graphite content is increased because of the larger C content. Thus, the Si content is set at Si<2.2% by weight, preferably, at Si≦1.0% by weight.
Manganese (Mn) has an effect of promoting the deoxidation and the production of carbide and increasing the above-described temperature difference &Dgr;T. Nickel (Ni) which is another alloy element has an effect of inhibiting the production of carbide. Therefore, the lower limit value of the Mn content is set at 0.9% by weight in order to overcome such effect of nickel (Ni) to promote production of carbide. On the other hand, if Mn>1.7% by weight, the Fe-based member is embrittled.
Nickel (Ni) is a &ggr;-phase producing element, and has an effect of permitting a small amount of precipitated &ggr; phases to exist at ambient temperature to confine impurities in the precipitated &ggr; phases, thereby enhancing the toughness of the Fe-based member. To provide such an effect, it is desirable to set the Ni content at about 1% by weight. In addition, nickel (Ni) exhibits a significant effect of increasing the temperature difference &Dgr;T. However, when the nickel(Ni) content is set at Ni<0.5% by weight, the above effects cannot be obtained. On the other hand, even if the nickel content is set at Ni>1.5% by weight, the increment of the temperature difference &Dgr;T is not varied.
In addition, according to the present invention, there is provided a process for producing an Fe-based member, wherein the heating temperature relative to the liquidus temperature T
L
is set at T
1
>T
L
and a quenching similar to that described above is carried out at a first step, and then, a second step similar to that described above is carried out, as well as a process for producing an Fe-based member, wherein the heating temperature relative to an Acm temperature and the solidus temperature T
S
is set in a range of T
A
≦T
1
≦T
S
at a first step, and the second step similar to that described above is carried out.
Even with these processes, a thermally treated structure similar to the above-described secondary thermally treated structure can be produced.
Further, according to the present invention, there is provided a process for producing an Fe-based member having a high Young's modulus and a high toughness, comprising a first step of subjecting an Fe-based material comprising
0.6% by weight≦carbon (C)≦1.9% by weight
silicon (Si)<2.2% by weight
0.9% by weight≦manganese (Mn)≦1.7% by weight
0.5% by weight≦nickel (Ni)≦1.5% by weight
Ni (% by weight)/Mn (% by weight)≦1.12 and
the balance of iron (Fe) including inevitable impurities, to a thermal treatment at a heating temperature T
1
set at T
1
≧T
A
wherein T
A
represents an
Armstrong Westerman & Hattori, LLP
Honda Giken Kogyo Kabushiki Kaisha
King Roy
Wilkins, III Harry D.
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