JP2021154329A - Forging material, forging component and method for production of forging component - Google Patents

Abstract

To provide a forging material and forging component having excellent forgeability and capable of exerting superior wear resistance after the forging process and carburized quenching/tempering treatment, and to provide a method for production of the forging component.SOLUTION: A forging material in one embodiment of this invention is the material by lateral extrusion and comprises outside and inside steel materials having a prescribed chemical composition. In the place at which the forging material is laterally extruded, the areas S1 and S2 of the outside and inside steel materials in a face perpendicular to the axial direction of the forging material satisfy 0.90≥S2/(S1+S2). In the deformation resistance obtained at a strain rate 10 s-1 in an edge face binding compression test, the deformation resistances σ'1 and σ'2 of the outside and inside steel materials in an equivalent plastic strain of 1.5 satisfy σ'1×S1/(S1+S2)+σ'2×S2/(S1+S2)≤750[MPa].SELECTED DRAWING: Figure 1

Description

The present invention relates to a forging material, a forged member, and a method for manufacturing the forged member.

Of the steel forged members used in machines, automobiles, etc., bearings, gears, etc. that require particularly high wear resistance are, for example, carburized, hardened, and tempered using chrome steel specified in JIS G4053 as a material. It is used after processing. In addition, some forged members are made of high carbon chrome steel specified by JIS G4805 and tempered. These forged members are subjected to quenching and tempering treatment after heating the steel material to a high temperature in which the steel material has a single-phase region of austenite or a two-phase region of austenite and cementite, and the surface layer has a high hardness of 550 HV or more to achieve high wear resistance. I'm getting sex. Such forged members are required to be resistant to wear caused by contact and sliding with other members at a high surface pressure.

As a means for improving the wear resistance of the forged member, there is a method of increasing the C concentration of the surface layer portion by carburizing, quenching and tempering treatment, or a method of using high carbon steel as a material (forging material) of the forged member. Further, alloy tool steel, the method as high-speed tool steel, the Cr, Mo, V, and W was added to the forging material, the hard alloy carbides than cementite (Mo 2 _C, WC, etc.) dispersed in the steel It has been known.

For example, in Patent Document 1, steel to which a large amount of C, Cr, Mo, V, W, and Co is added is subjected to charcoal-burning and tempering treatment, and wear resistance, particularly wear resistance at a high temperature of 300 ° C to 400 ° C. Inventions for improving the above are described.

According to Patent Document 2, steel containing a large amount of Cr, Mo, and V is subjected to charcoal-burning and tempering treatment to set the area ratio of carbides existing in the region from the surface to a depth of 50 μm to 6 to 25%. , Inventions for improving abrasion resistance have been described.

Japanese Unexamined Patent Publication No. 7-019252 Japanese Unexamined Patent Publication No. 2015-105419

However, the prior art described in Patent Document 1 and Patent Document 2 has a drawback that the molding load at the time of forging is high and the die life is short because the content of the alloy component in the forging material is high.

The present invention has been made in view of the above circumstances, and is a forging material and a forging member having excellent forging property and capable of exhibiting excellent wear resistance after forging and charcoal-burning and tempering. It provides a method of manufacturing this forged member.

The gist of the present invention is as follows.
(1) The forging material according to one aspect of the present invention is a forging material by lateral extrusion, which comprises an outer steel material and an inner steel material, and the composition of the outer steel material is mass%, and C: 0. 15 to 0.40%, Si: 0.05 to 0.50%, Mn: 0.25 to 1.50%, Cr: 0.05 to 1.50%, P: 0.001 to 0.030% , S: 0.005 to 0.025%, Al: 0.005 to 0.100%, N: 0.001 to 0.025%, V: 0.50 to 3.00%, and Mo: 0. It contains 80 to 6.00%, the balance is composed of Fe and impurities, and the composition of the inner steel material is, in terms of mass%, C: 0.05 to 0.30%, Si: 0.05 to 0.35%. , Mn: 0.25 to 1.00%, Cr: 0.01 to 1.50%, P: 0.001 to 0.030%, S: 0.005 to 0.025%, Al: 0.005 The shaft of the forging material where the forging material is laterally extruded, containing ~ 0.100% and N: 0.001 to 0.025%, the balance consisting of Fe and impurities. The area S1 of the outer steel material and the area S2 of the inner steel material on the plane perpendicular to the direction satisfy Equation 1, and the deformation resistance obtained ^{at the strain rate 10s -1 in the end face restraint compression test.} The deformation resistance σ'1 of the outer steel material and the deformation resistance σ'2 of the inner steel material in No. 5 satisfy Equation 2.
0.90 ≧ S2 / (S1 + S2) <Equation 1>
σ'1 x S1 / (S1 + S2) + σ'2 x S2 / (S1 + S2) ≤750 [MPa] <Equation 2>
(2) In the forging material according to (1) above, the composition of the outer steel material is mass%, B: 0 to 0.0050%, Nb: 0 to 0.100%, Ti: 0 to 0.100. %, And one or more selected from the group consisting of REM: 0 to 0.020% may be further contained.
(3) In the forging material according to (1) or (2) above, the clearance between the outer steel material and the inner steel material may be 0.1 mm to 2 mm.
(4) In the forging material according to any one of (1) to (3) above, the outer steel material may have a bonderube-treated film.
(5) The forged member according to another aspect of the present invention has a base formed by the outer steel material and the inner steel material having the composition according to the above (1) or (2), and outward from the base. It is provided with a protruding portion, and the protruding portion is projected from a portion of the outer steel material in the base portion and protrudes from the portion of the inner steel material in the base portion, and is in the outer protrusion portion. It is provided with an inner protrusion that fills at least a part of the space, and the thickness of the outer protrusion is 0.5 mm or more.
(6) In the forging member according to the above (5), the ratio R _P of the outer area S _{P 1} and the area S _{P 2} of the inner steel steel at the root of the protruding portion, in said base portion, said protrusion wherein the section near the ratio R _B of the outer surface area S _{B 1} of the steel product and the area S _{B 2} of the inner steel may fulfill the following equation 3 to equation 5.
_RP = _SP 2 / ( _SP 1 + _SP 2) <Equation 3>
_{R B = S B 2 / (} S B 1 + S B 2) < Formula 4>
_{| (R P -R B) /} R P | ≦ 5% < Formula 5>
(7) In the forged member according to (5) or (6) above, the Vickers hardness of the outer protrusion may be 740 HV or more.
(8) The method for manufacturing a forged member according to another aspect of the present invention is the method for manufacturing a forged member according to any one of (5) to (7) above, and is described in (1) to (4) above. ), The forging material is provided with a step of forging the forging material and a step of carburizing, quenching and tempering the forged material, and the forging is performed on the side of the forging material with respect to the forging material. The base portion and the projecting portion are formed by the side extrusion, and the projecting portion is in a state where the inner protrusion is inserted into the outer protrusion at the time of the side extrusion, and the protrusion is formed. , 0.90 ≧ S2 / (S1 + S2) is satisfied.

According to the present invention, there is provided a forging material and a forging member having excellent forging property and capable of exhibiting excellent wear resistance after forging and carburizing, quenching and tempering, and a method for manufacturing the forged member. Can be done.

It is a perspective view of an example of the forging material of this invention. It is sectional drawing of an example of the forging material of this invention. It is sectional drawing of an example of the forging material of this invention. It is sectional drawing of an example of the forging material of this invention. It is a schematic diagram of an example of the forged member of this invention. It is a figure explaining the shape of the forging material of an Example and the forging member formed by forging the forging material. However, (a) a front view of the forging material before forging, (b) a front view of the forged member formed by forging, and (c) the same plan view are shown. It is a figure explaining (a) the shape of the test piece used for the end face restraint compression test, and (b) the shape of the jig used. It is a figure explaining the shape of the Nishihara type wear test piece.

According to the prior art, in order to increase the wear resistance of the forged member, it is necessary to increase the amount of alloying elements having the effect of strengthening the steel. On the other hand, in order to improve the workability at the manufacturing stage of the forged member, it is necessary to reduce the hardness of the material (forging material) of the forged member, and for that purpose, it is necessary to reduce the amount of alloying elements. .. According to the prior art, it has been difficult to satisfy these two requirements at the same time.

In the present invention, the following four points are adopted as means for solving the problems described in detail.
1. 1. The forging material was a composite material composed of an outer steel material and an inner steel material.
2. In the outer steel material of the forging material, the composition was designed to contain alloy carbide-forming elements such as Mo and V. The outer steel material of the forging material constitutes the surface layer portion of the forging member after forging. Therefore, by controlling the components of the outer member of the forging material as described above, the wear resistance of the forging member can be ensured.
3. 3. In the inner steel material of the forging material, the content of alloying elements such as Mo and V was lower than that of the outer steel material. As a result, the forming load can be reduced when the forging material is forged.
4. If a large plastic deformation is caused in the composite material composed of the outer steel material and the inner steel material, the outer steel material may be broken. Therefore, the ratio of the cross-sectional area S1 of the outer steel material to the cross-sectional area S2 of the inner steel material is set within a predetermined range. Further, it was decided that the deformation resistance of the outer steel material and the deformation resistance of the inner steel material satisfy a predetermined relationship. This makes it possible to apply forging processes that form complex shapes, such as lateral extrusion, to composite materials.

The forging material 1 according to one aspect of the present invention obtained by the above findings is a forging material by lateral extrusion, and includes an outer steel material 11 and an inner steel material 12, and the composition of the outer steel material 11 is as follows. By mass%, C: 0.15 to 0.40%, Si: 0.05 to 0.50%, Mn: 0.25 to 1.50%, Cr: 0.05 to 1.50%, P: 0.001 to 0.030%, S: 0.005 to 0.025%, Al: 0.005 to 0.100%, N: 0.001 to 0.025%, V: 0.50 to 3. It contains 00% and Mo: 0.80 to 6.00%, the balance is composed of Fe and impurities, and the composition of the inner steel material 12 is by mass%, C: 0.05 to 0.30%, Si: 0.05 to 0.35%, Mn: 0.25 to 1.00%, Cr: 0.01 to 1.50%, P: 0.001 to 0.030%, S: 0.005 to 0. A location where 025%, Al: 0.005 to 0.100%, and N: 0.001 to 0.025% are contained, the balance is composed of Fe and impurities, and the forging material 1 is laterally extruded. In the above, the area S1 of the outer steel material 11 and the area S2 of the inner steel material 12 on the plane perpendicular to the axial direction of the forging material 1 satisfy Equation 1, and the deformation obtained ^{at the strain rate 10s -1 in the end face restraint compression test.} In terms of resistance, the deformation resistance σ'1 of the outer steel material 11 and the deformation resistance σ'2 of the inner steel material 12 at the equivalent plastic strain of 1.5 satisfy Equation 2.
0.90 ≧ S2 / (S1 + S2) <Equation 1>
σ'1 x S1 / (S1 + S2) + σ'2 x S2 / (S1 + S2) ≤750 [MPa] <Equation 2>
First, the forging material according to the present embodiment will be described in detail below.

(Steel component)
The chemical components of the outer steel material 11 and the inner steel material 12 constituting the forging material 1 according to the present embodiment will be described. The proportions (%) of each element shown below mean mass%. In the chemical composition of the outer steel material and the inner steel material, some elements have the same numerical range, and some elements have different numerical ranges. In the following description, the reasons for limiting the content of each chemical component will be described.

C (outer steel material): 0.15 to 0.40%
C (inner steel material): 0.05 to 0.30%
Carbon (C) is an essential element for ensuring the strength of steel materials. The outer steel material of the forging material, which constitutes the surface layer portion of the forged member after forging, needs to have a hardness of 740 HV or more after charcoal-burning and tempering in order to realize high wear resistance. If the C content of the outer steel material is less than 0.15%, the required strength cannot be obtained. On the other hand, if the C content of the outer steel material exceeds 0.40%, the forgeability of the outer steel material deteriorates. Therefore, the C content of the outer steel material is set to 0.15 to 0.40%. The C content of the outer steel material may be 0.18% or more, 0.20% or more, or 0.25% or more. The C content of the outer steel material may be 0.38% or less, 0.35% or less, or 0.30% or less.

On the other hand, the base material of the forged member does not need to have high wear resistance. Therefore, in the inner steel material of the forging material, which constitutes the base material portion of the forging member after forging, the forging property required for the forging material is prioritized. Therefore, the C content of the inner steel material is set to 0.05 to 0.30%. The C content of the inner steel material may be 0.08% or more, 0.10% or more, or 0.15% or more. The C content of the inner steel material may be 0.28% or less, 0.25% or less, or 0.20% or less.

Si (outer steel material): 0.05 to 0.50%
Si (inner steel material): 0.05 to 0.35%
Silicon (Si) is an element for suppressing the transition of ε-carbide precipitated during tempering to coarse cementite and significantly increasing the temper softening resistance of low-temperature tempered martensitic steel. In the outer steel material, if the Si content is less than 0.05%, the above effect cannot be exhibited. On the other hand, if the Si content of the outer steel material exceeds 0.50%, an oxide layer is formed on the surface layer during the carburizing, quenching and tempering treatment, and the peeling life of the surface starting point is shortened. Therefore, the Si content of the outer steel material of the forging material, which constitutes the surface layer portion of the forging member after forging, is set to 0.05 to 0.50%. The Si content of the outer steel material may be 0.08% or more, 0.10% or more, or 0.20% or more. The Si content of the outer steel material may be 0.45% or less, 0.40% or less, or 0.30% or less.

On the other hand, the inner steel material for forging does not require high temper softening resistance, and forging property and machinability during machining are prioritized. Therefore, the Si content of the inner steel material is set to 0.05 to 0.35%. The Si content of the inner steel material may be 0.08% or more, 0.10% or more, or 0.15% or more. The Si content of the inner steel material may be 0.32% or less, 0.30% or less, or 0.25% or less.

Mn (outer steel material): 0.25 to 1.50%
Mn (inner steel material): 0.25 to 1.00%
Manganese (Mn) is an element that enhances hardenability, suppresses red-hot brittleness, and improves hot ductility. If the Mn content of the outer steel material is less than 0.20%, the above effect cannot be exhibited. On the other hand, if the Mn content of the outer steel material exceeds 1.50%, an effect commensurate with the content cannot be expected. Therefore, the Mn content of the outer steel material is set to 0.25 to 1.50%. The Mn content of the outer steel material may be 0.25% or more, 0.30% or more, or 0.40% or more. The Mn content of the outer steel material may be 1.40% or less, 1.30% or less, or 1.20% or less.

On the other hand, the inner steel material for forging does not need to have high hardenability, and forging property and machinability during machining are prioritized. If the Mn content of the inner steel material exceeds 1.00%, the forgeability deteriorates. Therefore, the Mn content of the inner steel material is set to 0.25 to 1.00%. The Mn content of the inner steel material may be 0.25% or more, 0.30% or more, or 0.40% or more. The Mn content of the inner steel material may be 0.90% or less, 0.80% or less, or 0.70% or less.

Cr (outer steel material): 0.05 to 1.50%
Cr (inner steel material): 0.01 to 1.50%
Chromium (Cr) is a useful element that enhances the hardenability of steel materials and at the same time forms hard carbides to improve wear resistance. If the Cr content of the outer steel material is less than 0.05%, the effect of improving hardenability cannot be obtained. On the other hand, when the Cr content of the outer steel material exceeds 1.50%, not only the forgeability and machinability deteriorate, but also coarse carbides are formed at the austenite grain boundaries during the carburizing, quenching and tempering treatment. Therefore, the Cr content of the outer steel material is set to 0.05 to 1.50%. The Cr content of the outer steel material may be 0.10% or more, 0.20% or more, or 0.30% or more. The Cr content of the outer steel material may be 1.30% or less, 1.10% or less, or 1.00% or less.

On the other hand, the inner steel material does not need high hardenability and abrasion resistance, and forgeability and machinability at the time of processing parts are prioritized. Cr is also an element that stabilizes cementite, and is added in a small amount in order to leave a small amount of nuclei necessary for the formation of spheroidal cementite during spheroidizing annealing. If the Cr content of the inner steel material is less than 0.01%, the effect is small. On the other hand, if the Cr content of the inner steel material exceeds 1.50%, the forgeability and machinability deteriorate. Therefore, the Cr content of the inner steel material is set to 0.01 to 1.50%. The Cr content of the inner steel material may be 0.10% or more, 0.15% or more, or 0.20% or more. The Cr content of the inner steel material may be 1.20% or less, 1.00% or less, or 0.80% or less.

P (outer steel material and inner steel material): 0.001 to 0.030%
Phosphorus (P) is an element contained as an impurity. P segregates at the grain boundaries and lowers the grain boundary strength. Therefore, the P content should be as low as possible. Therefore, the upper limit of the P content in both the outer steel material and the inner steel material is set to 0.030% or less. The preferable upper limit of the P content is 0.020% or less. The preferred upper limit of the P content in both the outer and inner steels is 0.018%, 0.015%, or 0.010%. On the other hand, although P can be reduced in the steelmaking process, if it is less than 0.001%, the manufacturing cost is high, and if it is less than 0.001%, the grain boundary strength is not significantly improved. Therefore, the lower limit of the P content in both the outer steel material and the inner steel material may be 0.001% or more, 0.002% or more, or 0.005% or more. The numerical range of the P content may be different between the outer steel material and the inner steel material.

S (outer steel and inner steel): 0.005 to 0.025%
Sulfur (S) improves the machinability of the forging material. Therefore, 0.005% or more of S is contained in both the outer steel material and the inner steel material. However, if the S content is too large, S that is not fixed by Mn is generated as FeS at the grain boundaries, so that the hot ductility is lowered. In addition, the wear resistance is lowered due to the large amount of MnS produced. Therefore, the upper limit of the S content in both the outer steel material and the inner steel material is set to 0.025% or less. Therefore, the S content of both the outer steel material and the inner steel material is set to 0.005 to 0.025%. The S content of the outer steel material and the inner steel material may be 0.008% or more, 0.010% or more, or 0.015% or more. The S content of the outer steel material and the inner steel material may be 0.022% or less, 0.020% or less, or 0.018% or less. The numerical range of the S content may be different between the outer steel material and the inner steel material.

Al (outer steel material and inner steel material): 0.005 to 0.100%
Aluminum (Al) has a deoxidizing effect, and at the time of heat treatment, it combines with N to form AlN, thereby preventing coarsening of austenite grains and increasing toughness. If the Al content of the outer steel material and the inner steel material is less than 0.005%, these effects are not exhibited. On the other hand, when the Al content of the outer steel material and the inner steel material exceeds 0.100%, the above effect is saturated. Therefore, the Al content of both the outer steel material and the inner steel material is set to 0.005 to 0.100%. The Al content of the outer steel material and the inner steel material may be 0.008% or more, 0.010% or more, or 0.015% or more. The Al content of the outer steel material and the inner steel material may be 0.080% or less, 0.060% or less, or 0.050% or less. The numerical range of the Al content may be different between the outer steel material and the inner steel material.

N (outer steel material and inner steel material): 0.001 to 0.025%
Nitrogen (N) has the effect of preventing coarsening of austenite grains and increasing toughness by combining with Al and V to form a nitride. If the N content of the outer steel material and the inner steel material is less than 0.001%, the effect is small. On the other hand, when the N content of the outer steel material and the inner steel material exceeds 0.025%, the above effect is saturated. Therefore, the N content of both the outer steel material and the inner steel material is set to 0.001 to 0.025%. The N content of the outer steel material and the inner steel material may be 0.002% or more, 0.005% or more, or 0.010% or more. The N content of the outer steel material and the inner steel material may be 0.022% or less, 0.020% or less, or 0.018% or less. The numerical range of the N content may be different between the outer steel material and the inner steel material.

V (outer steel material): 0.50 to 3.00%
Vanadium (V), like Mn and Cr, enhances the hardenability of steel. V is a useful element that further combines with C to form hard and fine carbides to improve wear resistance, and to refine crystal grains to improve toughness. If the V content of the outer steel material is less than 0.50%, the effect of improving wear resistance cannot be exhibited. On the other hand, when the V content of the outer steel material exceeds 3.00%, the forgeability and machinability deteriorate. Therefore, the V content of the outer steel material is set to 0.50 to 3.00%. The V content of the outer steel material may be 0.60% or more, 0.80% or more, or 1.00% or more. The V content of the outer steel material may be 2.50% or less, 2.00% or less, or 1.50% or less.

Mo (outer steel material): 0.80 to 6.00%
Molybdenum (Mo) is a useful element that enhances the hardenability of steel materials and at the same time forms hard carbides to improve wear resistance. If the Mo content of the outer steel material is less than 0.80%, the above effect cannot be exhibited. On the other hand, when the Mo content of the outer steel material exceeds 6.00%, the forgeability and machinability deteriorate. Therefore, the Mo content of the outer steel material is set to 0.80 to 6.00%. The Mo content of the outer steel material may be 1.00% or more, 1.20% or more, or 1.50% or more. The Mo content of the outer steel material may be 5.00% or less, 4.00% or less, or 3.00% or less.

The rest of the chemical composition of the outer and inner steels is iron (Fe) and impurities. Impurities are ores and scraps used as raw materials for steel, or components mixed from the environment of the manufacturing process, etc., and are permitted components within a range that does not impair the characteristics of the forging material according to the present embodiment. means. Further, the outer steel material may further contain an optional element described below. However, the forging material according to the present embodiment can solve the problem without containing these optional elements. Therefore, the lower limit of the content of the optional element is 0%.

(Arbitrary selective element of outer steel material)
B (outer steel material): 0 to 0.0050%
Boron (B) enhances the hardenability of steel with only a slight solid solution in austenite. Therefore, it may be contained in the outer steel material in order to efficiently obtain the martensite structure during charcoal-burning and tempering. On the other hand, if B is contained in the outer steel material in an amount of more than 0.0050%, a large amount of BN is formed and N is consumed, which may lead to coarsening of austenite grains. Therefore, the B content of the outer steel material may be 0 to 0.0050%. The B content of the outer steel material may be 0.0005% or more, 0.0010% or more, or 0.0015% or more. The B content of the outer steel material may be 0.0045% or less, 0.0040% or less, or 0.0030% or less.

Nb (outer steel material): 0 to 0.100%
Niobium (Nb) is an element that combines with N and C in steel to form a carbonitride. This carbonitride pins the austenite grain boundaries, which in turn suppresses grain growth and prevents texture coarsening. In order to obtain the effect of preventing the coarsening of the structure, the outer steel material may contain 0.100% or less of Nb. On the other hand, if Nb is contained in the outer steel material in an amount of more than 0.100%, the forgeability may be significantly deteriorated due to the increase in the hardness of the material. Therefore, the Nb content of the outer steel material may be 0 to 0.100%. The Nb content of the outer steel material may be 0.005% or more, 0.010% or more, or 0.020% or more. The Nb content of the outer steel material may be 0.090% or less, 0.080% or less, or 0.070% or less.

Ti (outer steel material): 0 to 0.100%
Titanium (Ti) is an element that combines with N and C in steel to form a carbonitride. This carbonitride pins the austenite grain boundaries, which in turn suppresses grain growth and prevents texture coarsening. In order to obtain the effect of preventing the coarsening of the structure, the outer steel material may contain 0.100% or less of Ti. On the other hand, if Ti is contained in the outer steel material in an amount of more than 0.100%, the forgeability may be significantly deteriorated due to the increase in the hardness of the material. Therefore, the Ti content of the outer steel material may be 0 to 0.100%. The Ti content of the outer steel material may be 0.005% or more, 0.010% or more, or 0.020% or more. The Ti content of the outer steel material may be 0.090% or less, 0.080% or less, or 0.070% or less.

REM (outer steel material): 0 to 0.020%
Rare earth element (REM) is a general term for a total of 17 elements, including 15 elements from lanthanum with atomic number 57 to lutetium with atomic number 71, scandium with atomic number 21 and yttrium with atomic number 39. The REM content is the total value of the contents of these elements. When REM is contained in the outer steel material, the elongation of MnS particles is suppressed during rolling. However, if the REM content exceeds 0.020%, a large amount of sulfide containing REM may be generated, and the machinability of the steel may deteriorate. Therefore, the REM content of the outer steel material may be 0 to 0.020%. The REM content of the outer steel material may be 0.002% or more, 0.005% or more, or 0.008% or more. The REM content of the outer steel material may be 0.018% or less, 0.015% or less, or 0.010% or less.

Next, the configurations of the outer steel material and the inner steel material other than the chemical components will be described.
The outer steel material 11 is a hollow steel material, and the inner steel material 12 is arranged inside the outer steel material 11. When the forging material 1 according to the present embodiment is subjected to lateral extrusion, it is preferable that the inner steel material 12 is, for example, a steel bar and the outer steel material 11 is a pipe-shaped material, as shown in FIG. By laterally extruding the forging material 1 shown in FIG. 1, the forging member 2 shown in FIG. 5 can be obtained.

(Outer steel material)
The outer steel material 11 constitutes a surface layer portion that is a portion that slides in contact with another steel member in the forging member 2 obtained by processing the forging material 1 according to the present embodiment. Therefore, the outer steel material 11 of the forging material 1 according to the present embodiment must cover the sliding portion of the surface of the forging member. The outer steel material 11 is required to have high wear resistance after charcoal-burning and tempering. Therefore, as described above, the outer steel material 11 contains a hard alloy carbide-forming element such as Cr and Mo and a high concentration of C, and has a Vickers hardness of 740 HV or more after charcoal-burning and tempering under predetermined conditions. If the Vickers hardness of the outer steel material 11, which corresponds to the surface layer portion of the forging material, is less than 740 HV after charcoal-burning and tempering under predetermined conditions, the wear resistance of the surface layer portion cannot be ensured. However, the hardness of the outer steel material 11 at the stage before charcoal-burning and tempering is not particularly specified. At the stage before forging, the hardness of the outer steel material 11 is preferably low in consideration of workability.

Further, the cross-sectional area ratio of the outer steel material 11 is also important. If lateral extrusion is performed in a thin portion where the area ratio of the outer steel material 11 is less than 10%, the outer steel material 11 is destroyed during forging. Therefore, at the laterally extruded portion, the area S1 of the outer steel material and the area S2 of the inner steel material on the plane perpendicular to the axial direction of the forging material 1 must satisfy the formula 1.
0.90 ≧ S2 / (S1 + S2) <Equation 1>
It is not necessary that the equation 1 is satisfied over the entire area of the forging material 1. It suffices that Equation 1 is satisfied at least at a portion that is greatly deformed by forging, that is, a portion that is laterally extruded. For example, as shown in FIG. 2, the ratio of the area S1 of the outer steel material 11 to the area S2 of the inner steel material 12 may be uniform. On the other hand, when the forging material 1 is for forging by lateral extrusion, it is sufficient that the formula 1 is satisfied at least at the position where the forging material 1 is laterally extruded. Therefore, for example, as shown in FIG. 3, the outer steel material 11 may be arranged as a part of the forging material 1. In the forging material 1 of FIG. 3, the formula 1 is not satisfied at both ends thereof, but the outer steel material 11 is arranged at the side-extruded portion, and the formula 1 may be satisfied at this portion. .. Further, as shown in FIG. 4, for example, it is not hindered that both ends of the outer steel material 11 have a tapered shape. Even in the forging material 1 of FIG. 4, the formula 1 is not satisfied at both ends thereof, but it is sufficient that the outer steel material 11 is arranged at the side-extruded portion and the formula 1 is satisfied at this portion. ..

The upper limit of S2 / (S1 + S2) may be changed according to the shape of the forged member. For example, S2 / (S1 + S2) may be less than 0.88, less than 0.85, or less than 0.80. For example, when manufacturing an automobile spider from the forging material 1, it is considered preferable to set S2 / (S1 + S2) to less than 0.90 from the viewpoint of ensuring the thickness of the outer protrusion 241.

On the other hand, if the cross-sectional area ratio of the outer steel material is too large, the ratio of the outer steel material 11 having a high deformation resistance to the forging material 1 becomes excessive. Therefore, the forging property of the forging material 1 deteriorates and the die load increases. The mold load is greatly affected by the deformation resistance of each of the outer steel material 11 and the inner steel material 12 in addition to the cross-sectional area S1 of the outer steel material 11 and the cross-sectional area S2 of the inner steel material 12. The strain generated on the surface layer of the laterally extruded shaft of the forged member 2 formed by the lateral extruding process like the cross shaft joint is 1.2 to 1.7. If the deformation resistance of the forging material in this range exceeds 750 [MPa], the molding load becomes high and the die life is significantly shortened. Therefore, the cross-sectional area S1 of the outer steel material 11, the deformation resistance σ'1 at which the equivalent plastic strain amount of the outer steel material 11 is 1.5, the area S2 of the inner steel material 12, and the equivalent plastic strain amount of the inner steel material 12 are 1.5. It is necessary that the deformation resistance σ'2 to be satisfied satisfies Equation 2.
σ'1 x S1 / (S1 + S2) + σ'2 x S2 / (S1 + S2) ≤750 [MPa] <Equation 2>
Here, the deformation resistance is the result when the end face restraint compression test is performed at a ^{strain rate of 10s -1.}

The outer steel material 11 may be surface-treated. For example, the outer steel material 11 may have a bonderube-treated film. The bonderube-treated film is a lubricating film obtained by treatment with a zinc phosphate-based chemical conversion film and a soap-based lubricant. Usually, the bonderube film has a three-layer structure of a phosphate film, unreacted soap (for example, sodium stearate), and a metal soap formed between them ("Lubrication Technology for Cold Forging" Akio Shimizu, See Shaped Materials, Shaped Material Center, 2010, Vol.51, No.10, pp. 24-25, etc.). The bonderube treatment film improves mold release and prevents damage to the mold due to heat and contact pressure generated during cold forging.

The thickness of the outer steel material 11 is not particularly specified as long as the above-mentioned cross-sectional area requirement is satisfied, but may be, for example, 0.5 mm or more, 1.0 mm or more, or 1.5 mm or more at the laterally extruded portion. .. In other words, it may be specified that the outer steel material 11 is provided with a portion having a thickness of 0.5 mm or more, 1.0 mm or more, or 1.5 mm or more. Further, the thickness of the outer steel material 11 may or may not be uniform along the circumferential direction. If the thickness of the outer steel 11 is not uniform along the circumferential direction, the thickness of the thinnest portion along the circumferential is 0.5 mm or more, 1.0 mm at the laterally extruded portion of the outer steel 11. It may be more than or equal to 1.5 mm or more.

(Inner steel)
The entire surface of the inner steel material 12 in the forging material 1 of the present embodiment does not necessarily have to be covered with the outer steel material 11. The inner steel material 12 may be exposed on a surface that does not come into contact with other parts (see FIG. 3). For example, the inner steel material 12 may be exposed in the direction of the central axis in the cross shaft joint made of the forging material 1 of the present embodiment, but since wear resistance is not required for this portion, the inner steel material 12 is exposed. You may be. Further, a cavity may be provided inside the inner steel material 12. When such a forging material is subjected to lateral extrusion, it is considered that the inner cavity of the inner steel 12 is filled with the inner steel 12 and disappears before the lateral extrusion shaft is formed. Therefore, the area of the cavity is not included in the area S2 of the inner steel material 12 on the plane perpendicular to the axial direction of the forging material 1 described above.

A clearance may be provided between the outer steel material 11 and the inner steel material 12. By providing the clearance, it becomes easy to carry out the step of arranging the outer steel material 11 inside the inner steel material 12, and the manufacturing efficiency of the forging material 1 is improved. Further, during lateral extrusion, the clearance is filled with the outer steel material 11 and the inner steel material 12, so that the clearance does not interfere with the production of the forged member 2. The size of the clearance is not particularly limited, and can be appropriately determined according to the shapes of the outer steel material 11 and the inner steel material 12. For example, the clearance may be 0.1 mm to 2.0 mm.

The size of the forging material 1 (specifically, the outer diameter of the side-extruded portion, which is a portion subject to large deformation due to forging) is not particularly limited. For example, when the forging material 1 is subjected to cold forging, it is desirable that the outer diameter of the forging material 1 is within the range of φ20 mm to φ55 mm in consideration of workability. On the other hand, if the forging material 1 is subjected to hot forging, it is considered that even if the size of the forging material 1 exceeds the above range, the forging equipment will not be loaded.

The shape of the forging material 1 can also be appropriately selected depending on the intended purpose. In FIG. 1, the forging material 1 and the inner steel material 12 have a round bar shape, but the forging material 1 and / or the inner steel material 12 may have a square bar shape. In this case, the "diameter" (including both the inner diameter and the outer diameter) of the forging material 1, the outer steel material 11, and the inner steel material 12 means a circle-equivalent diameter.

Next, the forged member 2 according to another aspect of the present invention will be described. As shown in FIG. 5, the forged member 2 according to the present embodiment includes a base portion 23 formed of an outer steel material 21 and an inner steel material 22, and a protruding portion 24 protruding outward from the base portion 23. The protrusion 24 is projected from the outer protrusion 241 protruding from the outer steel 21 portion in the base 23 and the inner steel 22 portion in the base 23, and is formed in at least a part of the space in the outer protrusion 241. It is integrally molded with the filled inner protrusion 242, and the thickness of the outer protrusion 241 is 0.5 mm or more.

(Forged member)
The forging member 2 is formed by forging the forging material 1 of the present embodiment. The forged member of the present embodiment includes a base portion 23 formed of an outer steel material 21 and an inner steel material 22, and a protruding portion 24 protruding outward from the base portion 23. The components of the outer steel material 21 and the inner steel material 22 of the forging member 2 are the same as the components of the outer steel material 21 and the inner steel material 22 of the forging material 1 described above. Further, the protruding portion 24 is projected from a portion of the outer protruding portion 241 projecting from a predetermined portion of the outer steel material 21 forming the base portion 23 and a portion of the inner steel material 22 forming the base portion 23, and is projected from the portion of the outer protruding portion 241. It is integrally molded with the inner protrusion 242 filled in at least a part of the space inside. Here, the inner protrusion 242 forming the protrusion 24 may be filled in the entire space in the outer protrusion 241 but does not necessarily have to be filled in the entire space in the outer protrusion 241. It may be a state in which a part of the outer protrusion 241 is inserted, that is, a space is formed between the outer protrusion 241 and the inner protrusion 242.

The thickness of the outer protrusion 241 is 0.5 mm or more. Thereby, sufficient wear resistance can be obtained. The thickness of the outer protrusion 241 may be 0.6 mm or more, 0.8 mm or more, or 1.0 mm or more. It is not necessary to specify the upper limit of the thickness of the outer protrusion 241, but for example, the thickness may be specified as 5.0 mm or less, 4.0 mm or less, or 3.0 mm or less.

Further, it is more preferable that the forged member 2 satisfies the following formulas 3 to 5.
_RP = _SP 2 / ( _SP 1 + _SP 2) <Equation 3>
_{R B = S B 2 / (} S B 1 + S B 2) < Formula 4>
_{| (R P -R B) /} R P | ≦ 5% < Formula 5>
Here, the symbols in the formulas 3 to 5 indicate the following items.
At the base 23,: S _P 1: the area _S P 2 of the outer steel 21 at the root of the protruding portions 24: the area _R P of the inner steel 22 at the root of the protrusion 24: _{S P} 1 and _S ratio of _P 2 _S B 1 area of the outer steel 21 in the vicinity of the projecting portion 24 _S B 2: at the base 23, the area _R B of the inner steel 22 in the vicinity of the projecting portion 24: ratio of _{S B} 1 and _{S B} 2

In forging 2 Formula 3 Formula 5 is satisfied, the ratio _{R P} and _{R B} are substantially equal. It is considered that such a forged member 2 is forged so as to suppress the breakage of the outer steel material 21 in the forged member 2.

Further, in the outer protrusion 241 it is estimated that the ratio between the area of the outer steel material 21 and the area of the inner steel material 22 inherits the ratio in the above-mentioned forging material 1. Therefore, similarly to the forging material 1, it may be defined as 0.90 ≧ _{R P. 0.88> R P, 0.85> R} P, or 0.80> may be _{R P.}

In the forged member 2, the Vickers hardness of the outer steel material 21 is preferably 740 Hv or more. As a result, the wear resistance of the forged member 2 is further enhanced. The Vickers hardness of the outer steel material 21 is the Vickers hardness at a position at a depth of 50 μm from the surface of the outer steel material 21. The load for measuring the Vickers hardness of the outer steel material 21 is 2.94 N.

Types of forged members include, for example, spiders for automobile parts, other inner races, tripods, gears, and the like. FIG. 5 shows a spider formed by laterally extruding the forging material 1 according to the present embodiment. The central portion corresponds to the base portion 23, and the bearing portion protruding outward from the peripheral surface of the base portion 23 corresponds to the protruding portion 24.

(Manufacturing method of forged parts)
Hereinafter, a method for manufacturing a forged member using the forging material of the present embodiment will be described. The method for manufacturing the forged member according to the present embodiment includes a step of forging the forging material 1 according to the present embodiment and a step of carburizing, quenching and tempering the forged material 1 for forging. The processing was lateral extrusion with respect to the forging material 1, and the base 23 and the protrusion 24 were formed by the lateral extrusion. In the protrusion 24, the inner protrusion 242 entered the outer protrusion 241 during the lateral extrusion. In this state, the protruding portion 24 is provided at a position where 0.90 ≧ S2 / (S1 + S2) is satisfied. Hereinafter, this manufacturing method will be described in detail.

As described above, the forging material 1 of the present embodiment is obtained by inserting the steel material having the chemical composition of the inner steel material 12 inside the steel material having the chemical composition of the outer steel material 11. For example, in the case of the embodiment shown in FIGS. 1 and 2, the inner steel material 12 is, for example, a cylinder, and the outer steel material 11 has an inner diameter substantially the same as the outer diameter of the inner steel material and a length (height) substantially the same in the axial direction. ) Is cylindrical. In the forging material 1 shown in FIGS. 1 and 2, the relationship of 0.90 ≧ S2 / (S1 + S2) is satisfied over the entire length thereof.

Then, both ends (upper and lower ends) of the forging material 1 in the axial direction are sandwiched and forged by lateral extrusion to form the base portion 23 and the protruding portion 24. By performing lateral extrusion, predetermined portions of the outer steel material 11 (21) and the inner steel material 12 (22) are extruded in a direction intersecting the axis. Therefore, the outer protrusion 241 is formed on the outer steel 11 (21), and the inner protrusion 242 is formed on the inner steel 12 (22). At this time, the inner steel material 12 (22) is extruded into the outer protrusion 241, and the inner protrusion 242 is in the space inside the outer protrusion 241. Therefore, the protruding portion 24 is formed by integrally molding the outer protruding portion 241 and the inner protruding portion 242.

As described above, the shape of the forging material 1 is not limited to that exemplified in FIGS. 1 and 2, but with respect to the forging material 1 having other shapes as exemplified in FIG. 3 or FIG. Also, lateral extrusion can be carried out as appropriate. In this case, it is necessary to provide the protruding portion at a position where 0.90 ≧ S2 / (S1 + S2) is satisfied. For example, when the forging material 1 shown in FIG. 3 is forged by lateral extrusion, it is necessary to design the die so that the portion where the protrusion 24 is provided coincides with the portion where the outer steel material 11 is arranged. .. As a result, the outer steel material 21 can be prevented from breaking at the protruding portion 24, and the thickness of the outer protruding portion 241 of the protruding portion 24 can be set to 0.5 mm or more.

In addition, after the forging process, the forged member is charcoal-burned and tempered. As a result, the hardness of the outer steel material 21 can be increased, and the wear resistance of the forged member 2 can be ensured.

(Carburizing process)
After the forging process, the forged member is carburized at 850 to 1100 ° C. The carburizing treatment is a treatment utilizing the diffusion phenomenon of carbon. For example, when gas carburizing is performed, a hydrocarbon gas such as acetylene, propane and ethylene is used. If the carburizing temperature is less than 850 ° C., a long time heat treatment is required to diffuse sufficient carbon into the forged member, which increases the cost. On the other hand, if the carburizing temperature exceeds 1100 ° C., significant coarse graining and grain mixing will occur. Therefore, carburizing is carried out in a temperature range of 850 to 1100 ° C. In order to reduce the cost, suppress coarse graining, and suppress grain mixing at a higher level, it is preferable to carry out the carburizing temperature in the temperature range of 900 to 1050 ° C. The carburizing treatment may be vacuum carburizing or plasma carburizing.

(Holding process)
After the carburizing and before quenching, it may be held at a predetermined temperature for a certain period of time. The purpose of holding for a certain period of time after carburizing is to prevent quench cracking and reduce strain during quenching. The retention temperature is 850 ° C. or higher for 10 minutes or longer in order to diffuse C efficiently. On the other hand, even if it is retained at a temperature higher than 900 ° C. for more than 60 minutes, the effects of preventing quench cracking and reducing strain during quenching are saturated. Therefore, the upper limit of the retention temperature may be 900 ° C. Further, the upper limit of the retention time may be 60 minutes.

(Quenching process)
After the carburizing treatment is completed, quenching is performed from a temperature range of 850 to 1100 ° C. Quenching is performed after the carburizing treatment in order to improve the hardness by using the surface structure as martensite. If the quenching temperature is less than 850 ° C., the proportion of the soft phase such as the ferrite phase may increase, and a sufficient martensite area ratio cannot be secured, so that the hardness of the steel decreases.

On the other hand, when the quenching temperature is higher than 1100 ° C., significant coarse graining and grain mixing occur. Therefore, the quenching temperature is preferably 850 ° C to 1100 ° C. Further, as a quenching method, oil quenching having excellent cooling characteristics is preferable, but quenching with water is also possible, and if it is a small gear, quenching with a high-pressure inert gas is also possible.

(Tempering process)
After quenching, tempering is performed at 130 to 200 ° C. When the tempering temperature is 130 ° C. or higher, tempered martensite having high toughness can be obtained. Further, by setting the tempering temperature to 200 ° C. or lower, it is possible to prevent a decrease in hardness due to tempering. In order to achieve each of these effects at a higher level, it is preferable that the tempering temperature is 150 to 180 ° C. By going through this tempering step, the forged member according to the present embodiment can be obtained.

In the forged member of the present embodiment, the composition and hardness change rapidly at the boundary between the outer steel material constituting the surface layer portion and the inner steel material constituting the base material portion, and therefore, depending on the thickness of the surface layer portion and the usage conditions. , It is conceivable that the boundary will be the starting point of destruction. In such a case, in the forged member, the component is changed stepwise by sandwiching a layer having an intermediate component between the outer steel material and the inner steel material, or the component is continuously changed by performing diffusion treatment at a high temperature. It is possible to take measures such as forging.

In order to confirm the effect of the present invention, a forging member was manufactured from the forging material according to the present invention and the forging material outside the scope of the present invention, and the predetermined performance was evaluated.

First, steels having the chemical components shown in "outer steel material" and "inner steel material" in Table 1 were melted and billets were produced by continuous casting. In Table 1, the underlined values are outside the scope of the present invention. Further, in Table 1, the content of the element not intentionally added is indicated by the symbol “−”.

Next, the billet was hot-rolled to produce a round bar having a diameter of 55 mm. Further, the round bar was subjected to spheroidizing annealing (SA).

An outer steel material having the chemical components shown in "outer steel material" in Table 1 and having an outer diameter of 50 mm and an inner diameter of 44.7 mm was produced from a round bar after spheroidizing annealing (after the SA step). Further, a rod-shaped inner steel material having the chemical composition shown in "inner steel material" in Table 1 and having an outer diameter of 44.7 mm was produced from a round bar after spheroidizing annealing (after the SA step).

However, in Example 1 of the present invention in Table 1, the inner diameter of the outer steel material and the outer diameter of the inner steel material are 47.5 mm, and in Comparative Example 10, the inner diameter of the outer steel material and the outer diameter of the inner steel material are 48 mm. Increased the proportion of. Further, in Example 8 of the present invention, the inner diameter of the outer steel material and the outer diameter of the inner steel material are set to 41 mm, and in Comparative Example 9, the inner diameter of the outer steel material and the outer diameter of the inner steel material are set to 31.6 mm, so that the ratio of the inner steel material is increased. Reduced. Further, Comparative Example 18 made of a single steel material was also prepared. The manufacturing methods of these examples will be described later.

Next, with the inner steel material inserted inside the outer steel material, lateral extrusion is performed (for a single steel material in Comparative Example 18), and the crosses shown in FIGS. 6 (B) and 6 (C) are cross-shaped. A shaft-shaped forged member was formed. When the maximum load at the time of molding was 324 kN or less, it was judged to be acceptable as having excellent forgeability. Further, when the maximum load at the time of molding exceeds 324 kN, it is judged to be inferior in forgeability and rejected.

Further, from the r / 2 position of the round bar (position at a depth of 1/2 of the radius r of the round bar) after the spheroidizing annealing (after the SA step), the compression test piece with the end face restraint groove of FIG. 7 is prepared. bottom. The compression test piece with end face restraint groove is a test piece having a diameter of 8 mm and a length of 12 mm centered on the diameter R / 2 position, and the longitudinal direction of the round bar test piece is parallel to the forging and stretching axis of the round bar having a diameter of 55 mm. Met. The notch shape is described in "Cold Installation Test Method", Cold Forging Material Strength Group, Plasticity and Machining, vol. 22. no. According to the notch of the No. 1 test piece described on page 241, p139.

For each steel, three compression test pieces with end face restraint grooves shown in FIG. 7A were prepared. For the cold compression test, Thermec Master Z (registered trademark) manufactured by Fuji Radio Industrial Co., Ltd. was used. The jig used was made by JIS SKH51 and has an end face restraint groove of φ40 mm × L50 mm (see FIG. 7 (b)). The strain rate when the test piece was compressed was 10 s- ¹ , and cold compression was performed at a compressibility of 75% or more, and then the deformation resistance at which the equivalent plastic strain amount was 1.5 was determined.

The relationship between the deformation resistance σ'1 where the area S1 of the outer steel material and the equivalent plastic strain amount is 1.5 and the deformation resistance σ'2 where the area S2 of the inner steel material and the equivalent plastic strain amount is 1.5 is as follows σ' 1 × S1 / (S1 + S2) + σ'2 × S2 / (S1 + S2) ≦ 750 [MPa]
When the condition is satisfied, it is judged to be acceptable as being within the scope of the present invention.

The wear resistance was evaluated by the Nishihara type wear test. However, this wear test cannot be performed on the manufactured forged member. When the Nishihara-type wear test piece shown in FIG. 8 is manufactured from the forged member, the outer steel material slips, so that the test piece cannot be rotated to cause sliding. Therefore, in order to simulate the outer steel material of the forged member, the Nishihara type wear test piece (evaluation material) shown in FIG. 8 was manufactured by machining from the steel material having the same chemical composition as the outer steel material. These test pieces were subjected to charcoal-burning and tempering treatment under the conditions shown in Table 2.

Next, the weight of the Nishihara-type wear test piece before the wear test was measured, and under the conditions of slip rate 9.1%, oil lubrication 2 cc / min, surface pressure 1.5 MPa, rotation speed 100 rpm, and mating material JIS G4805 SUJ2. , The wear test was carried out for 4 hours. Then, the weight of the Nishihara-type wear test piece was remeasured, and the weight of the Nishihara-type wear test piece before and after the test was calculated. The Nishihara-type wear test was carried out three times at the same level, and the average value of the wear weight was calculated. When the average value of the wear weight was less than 9 mg, it was judged to be acceptable as having excellent wear resistance. Further, when the average value of the wear weight was 9 mg or more, it was judged to be inferior in wear resistance and rejected. If the average value of the wear weight is less than 9 mg, the thickness of the wear area should be sufficiently smaller than the thickness of the outer steel material of the forged member. Therefore, it can be considered that the forged member provided with the outer steel material having the same composition as the steel material that passes the above-mentioned judgment criteria is excellent in wear resistance.

Comparative Example 18 is composed of a single steel material. The outer diameter was the same as the outer diameter of the outer steel materials of Examples 1 to 17 described above. The manufacturing method was the same as the manufacturing method of the inner steel materials of Examples 1 to 17 described above. This was laterally extruded under the same conditions as in Examples 1-17. Then, the abrasion resistance was evaluated and the hardness was measured by the same method as in Examples 1 to 17.

Further, the forged member is also subjected to charcoal-burning and tempering treatment under the conditions shown in Table 2, and the lateral extrusion shaft is formed at a depth of 50 μm on the outer surface in the radial direction on the plane perpendicular to the longitudinal direction. The Vickers hardness was measured with a test force of 2.94 N in accordance with JIS Z 2244. When the Vickers hardness of the surface layer portion was 740 HV or more, it was judged to be acceptable as being within the range of the present invention.

No. in Table 1 1 to 8 are examples of the present invention, and others (No. 9 to 18) are comparative examples. Table 3 shows the area ratio of the inner steel material, σ, maximum forming load, wear weight, and hardness after carburizing, quenching, and tempering of the outer steel material in these invention examples and comparative examples. In Table 3, values outside the scope of the invention and values that do not meet the pass / fail criteria are underlined. In addition, "σ" in Table 3 is a value obtained by σ'1 × S1 / (S1 + S2) + σ'2 × S2 / (S1 + S2).

In the forging materials of Examples 1 to 8 of the present invention, the chemical composition was within the range of the present invention, S2 / (S1 + S2) was 90% or less, and σ was 750 MPa or less. Therefore, in the forging materials of Examples 1 to 8 of the present invention, the forming load at the time of lateral extrusion was suppressed. Further, the forged members obtained from the forging materials of Examples 1 to 8 of the present invention had a small wear weight and were excellent in wear resistance. Therefore, from the forging materials of Examples 1 to 8 of the present invention, it was possible to obtain a forged member having excellent forging property and exhibiting excellent wear resistance after forging and charcoal-burning and tempering.

On the other hand, in the forging material of Comparative Example 9, the area ratio occupied by the outer member was too large, and σ exceeded 750 MPa, so that the forming load at the time of lateral extrusion became excessive.
In the forging material of Comparative Example 10, the thickness of the outer member was too small, so that the outer member cracked during lateral extrusion. Therefore, the forging member could not be manufactured from the forging material of Comparative Example 10.
In the forging material of Comparative Example 11, the carbon content of the outer steel material was excessive. Therefore, in Comparative Example 11, σ exceeded 750 MPa, and the molding load at the time of lateral extrusion became excessive.
The forging material of Comparative Example 12 had an excess of carbon content in the inner steel material. Therefore, in Comparative Example 12, σ exceeded 750 MPa, and the molding load became excessive at the time of lateral extrusion.
The forging material of Comparative Example 13 had a insufficient Si content in its outer steel material. Therefore, the forged member obtained from the forging material of Comparative Example 13 lacked wear resistance.
The forging material of Comparative Example 14 had a insufficient Mn content in the outer steel material. Therefore, the forged member obtained from the forging material of Comparative Example 14 lacked wear resistance.
The forging material of Comparative Example 15 had a insufficient Cr content in the outer steel material. Therefore, the forged member obtained from the forging material of Comparative Example 15 lacked wear resistance.
The forging material of Comparative Example 16 had a insufficient V content in its outer steel material. Therefore, the forged member obtained from the forging material of Comparative Example 16 lacked wear resistance.
The forging material of Comparative Example 17 had a insufficient Mo content in its outer steel material. Therefore, the forged member obtained from the forging material of Comparative Example 17 lacked wear resistance.
The forging material of Comparative Example 18 is made of a single steel material, and its chemical composition is close to that of the outer steel material of the present invention. However, the amount of V is smaller than that of the outer steel material of the present invention. During the lateral extrusion of Comparative Example 18, the forming load was not excessive, but the forged member obtained from the forging material of Comparative Example 18 lacked wear resistance.

According to the present invention, there is provided a forging material and a forging member having excellent forging property and capable of exhibiting excellent wear resistance after forging and carburizing, quenching and tempering, and a method for manufacturing the forged member. Can be done. As a result, the effect of extending the life of the die by suppressing the forming load during forging can be obtained. Therefore, the present invention has high industrial applicability.

1 Forging material 11 Outer steel 12 Inner steel 2 Forged member 21 Outer steel 22 Inner steel 23 Base 24 Protruding part 241 Outer protrusion 242 Inner protrusion 242

Claims (8)

A material for forging by side extrusion, which includes an outer steel material and an inner steel material.
The composition of the outer steel material is mass%,
C: 0.15 to 0.40%,
Si: 0.05 to 0.50%,
Mn: 0.25 to 1.50%,
Cr: 0.05 to 1.50%,
P: 0.001 to 0.030%,
S: 0.005 to 0.025%,
Al: 0.005 to 0.100%,
N: 0.001 to 0.025%,
V: 0.50 to 3.00%, and Mo: 0.80 to 6.00%
Containing, the balance consists of Fe and impurities,
The composition of the inner steel material is mass%.
C: 0.05 to 0.30%,
Si: 0.05 to 0.35%,
Mn: 0.25 to 1.00%,
Cr: 0.01 to 1.50%,
P: 0.001 to 0.030%,
S: 0.005 to 0.025%,
Al: 0.005 to 0.100%, and N: 0.001 to 0.025%,
Containing, the balance consists of Fe and impurities,
At the location where the forging material is laterally extruded, the area S1 of the outer steel material and the area S2 of the inner steel material on the plane perpendicular to the axial direction of the forging material satisfy Equation 1.
In the deformation resistance obtained at a strain rate of 10s ^-1 in the end face restraint compression test, the deformation resistance σ'1 of the outer steel material and the deformation resistance σ'2 of the inner steel material at an equivalent plastic strain of 1.5 are given by Equation 2. Forging material that meets the requirements.
0.90 ≧ S2 / (S1 + S2) <Equation 1>
σ'1 x S1 / (S1 + S2) + σ'2 x S2 / (S1 + S2) ≤750 [MPa] <Equation 2> The composition of the outer steel material is mass%,
B: 0 to 0.0050%,
Nb: 0 to 0.100%,
Ti: 0 to 0.100%, and REM: 0 to 0.020%,
The forging material according to claim 1, further containing one or more selected from the group consisting of. The forging material according to claim 1 or 2, wherein the clearance between the outer steel material and the inner steel material is 0.1 mm to 2 mm. The forging material according to any one of claims 1 to 3, wherein the outer steel material has a bonderube-treated film. A base portion formed of the outer steel material and the inner steel material having the composition according to claim 1 or 2, and a protruding portion protruding outward from the base portion are provided.
The projecting portion is projected from the outer protrusion portion protruding from the outer steel material portion in the base portion and from the inner steel material portion in the base portion, and is filled in at least a part of the space in the outer protrusion portion. With an inner protrusion,
A forged member characterized in that the thickness of the outer protrusion is 0.5 mm or more. The ratio R _P between the area S _{P 2} of the inner steel and an area S _{P 1} of the outer steel at the root of the protrusion,
In the base, and the ratio R _B of the area of the outer steel S _{B 1} and the area S _{B 2} of the inner steel in the protrusions vicinity, claim 5, characterized in that satisfies the following formula 3 Formula 5 Forged member described in.
_RP = _SP 2 / ( _SP 1 + _SP 2) <Equation 3>
_{R B = S B 2 / (} S B 1 + S B 2) < Formula 4>
_{| (R P -R B) /} R P | ≦ 5% < Formula 5> The forged member according to claim 5 or 6, wherein the Vickers hardness of the outer protrusion is 740 HV or more. The method for manufacturing a forged member according to any one of claims 5 to 7.
The step of forging the forging material according to any one of claims 1 to 4 and
The process of charcoal-burning and tempering the forged material and
With
The forging is lateral extrusion with respect to the forging material.
The base and the protrusion are formed by the lateral extrusion.
The protruding portion is in a state in which the inner protrusion is inserted into the outer protrusion at the time of lateral extrusion.
A method for manufacturing a forged member, wherein the protruding portion is provided at a position where 0.90 ≧ S2 / (S1 + S2) is satisfied.

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