TECHNICAL FIELD
[0001]
The present invention relates to a non-thermal refined nitrocarburized
component. Specifically, the present invention relates to a non-thermal refined
nitrocarburized component having a high bending fatigue strength and an excellent
bending strai ghtening property.
[0002]
The "non-thermal refined nitrocarburized component" denotes a component
subjected to a nitrocarburizing "treatment without being subjected to a
"quenching-tempering treatment" that is a so-called "thermal refining treatment" after
being machined. Hereinafter, the "component subjected to the nitrocarburizing
treatment" is referred to simply as a "nihocarburized component".
BACKGROI.JND ART
[0003]
Crankshafts, connecting rods, and the like used in automobiles, industrial
machines, and construction machinery etc. are produced by being subjected to a
nitrocarburizing treaÍment without being subjected to a thermal refining treatment of
quenching-tempering after being forged and machined into a desired shape.
Particularly, in production of automobile components that require a high fatigue strength
and a high wear resistance, treatments, such as an induction hardening treatment and a
nitrocarburizing treatment that are a casehardening treatment, are carried out after
forging and machining in most cases.
[0004]
The "nitrocarburizing treatment" performs a cementation treatment on nitrogen
and carbon at a temperature of atr Al transformation point or less, and has such major
/v
characteristics that have a low heat-treatment temperature and a smaller heat treatment
strain than that in the "induction hardening treatment". A "compound layer" (layer
formed of precipitated nitride such as Fe:N) observed as a white portion through etching
using nital is formed in a surface layer of the component subjected to the
nitrocarburizing treatment. A "diffusion layer" is formed between the above
compound layer and a base metal (hereinafter referred to as "base material").
[0005]
The nitrocarburizing treatment causes a small heat treatment strain, but cannot
eliminate this strain, and thus brings not a small bad influence on dimensional accuracy.
Particularly, even a slight deterioration of dimensional accuracy becomes a crucial
matter in a crankshaft or the like that is a rotational shaft component. Hence, it is
required to perform bending-straightening after the nitrocarburizing treatment so as to
improve the dimensional accuracy.
[0006]
Unfortunately, cracks may be generated from the surface layer if the
nitrocarburized component is subjected to the bending-straightening. Hence, a
nitrocarburized component, such as a crankshaft, is required to experience no cracks
even if being subjected to bending-straightening, that is, to have an excellent bending
straightening property as well as a high bending fatigue strength.
[0007]
In the following description, the nitrocarburized component may be
represented by a crankshaft in some cases.
[0008]
Because of current demand for consideration to the environments, a crankshaft
that is a major component of an engine is also oriented to reduction in weight and size
without exclusion, and has been required to have an extremely high bending fatigue
strength of 800 MPa or more, for example.
[000e]
In the light of cost reduction, resource saving, and others, there has been
increased demand for a non-thermal refined crankshaft without being subjected to a
/s
"quenching-tempering treatment'r (thermal refining treatment) during the production
thereof.
[0010]
ln order to secure the above bending fatigue strength of 800 MPa or more in a
non-thermal refined crankshaft, it is required to set hardness at a position of 0.05 mm
from the surface of the component (also referred to as a "surface-layer hardness",
hereinafter) to be at least 410 or more in terms of a Vickers hardness (refened to as a
"HV hardness", hereinafter) after the nitrocarburizing treatment.
[0011]
However, in the case of setting the HV hardness at a position of 0.05 mm from
the surface of the crankshaft to be 410 ormore, cracks are likelyto be generated in the
surface layer if the bending straightening is performed. Conducting a bending fatigue
test on such a crankshaft results in fatigue fractures initiated from the above cracks.
[0012]
In addition, as described above, there has been increased demand for further
reduction in weight of a crankshaft, and thus further more flexibiiity has been required
in crankshaft shape designing. Consequently, steel material for a crankshaft is required
to have a bending straightening property high enough for a crankshaft having a shape
likely to exhibit a greater bending than that in a conventional art during the
nitrocarburi zing To be bending-straightened.
[0013]
Accordingly, there has been extremely strong demand for a crankshaft having a
sufficient bending straightening property in addition to a bending fatigue strength as
high as 800 MPa or more.
[0014]
To meet the above demand, for example, JP2002-2269394 (Patent Document
1) discloses a "non-thermal refined steel for nitrocarburizing", 'wherein the steel
contains, in massTo, C:0.2to 0.6%o, Si: 0,05 to 1.ÙYo, Mn: 0.25 To 1.0%o, S: 0.03 to 0.2o/o,
Cr:0.2Yo or less, s-Al: 0.045% or less, Ti: 0.002 to 0.010%, N: 0.005 to 0.025Yo, and O:
0.001 to 0.005%, and further contains one or more type.s of elements selected from Pb:
/+
0.01 to 0.40o/o, Ca: 0.0005 to 0.0050%, and Bi: 0.005 to 0.40% if necessary satisfies
conditions: 0.12 x Tio/o < Oo/o < 2.5 x Ti%o, and 0.04 x N% < Oo/o < 0.7 x N%, and
includes a balance made of Fe and unavoidable impurities, wherein a micro-structure
after hot forging is a mixed structure of ferrite and perlite.
[001s]
JP2007-I773094 (Patent Document 2) discloses a crankshaft made of a steel
whose surface is subjected to a nitriding treatment or a niffocarburizing treatment, the
crankshaft including a pin section and ajournal section. The steel contains, as an alloy
element, C: 0.07 mass% or more to 0.1,2 masso/o or less, Si: 0.05 masso/o or more to 0.25
masso/o or less, Mn: 0.1 masso% or more to 0.5 mass% or less, Cu: 0.8 masso/o or more to
1.5 mass% or less, Ni: 2.4 masso/o or more to 4.5 mass% ot less, Al: 0.8 mass% or more
to 1,5 mass% or less, Ti: 0.5 masso% or more to 1.5 mass% or less, and further contains
oneormoretypesof elementsselected"fromS: 0.01 mass%ormoreto0.l0masso/0, Ca:
0.0010 masso/o or more to 0.0050 masso/o if necessary and includes a balance made of
Fe and unavoidable impurities. For the crankshaft, each steel specimen taken from a
center part of the steel that is affected by no influence of the nitriding treatment is
subjected to a solid solution treatment at 1200oC for one hour, and thereafter, is cooled
at an appropriate cooling speed of 0.3"C/seconds or more to l.5oC/seconds or less
within a temperature range from 900oC or more to 300'C or less, thereby setting a ratio
of bainite in the steel micro-structure to be 80% or more, and setting the HV hardness to
be 200 or more to 300 or less; each internal hardness of the pin section and the journal
section that are subjected to the nitriding treatment or the nitrocarburizing treatment is
set to be 350 or more to 500 or less in terms of the HV hardness; and the HV hardness at
a position of 0.05 mm from the surface is 650 or more to 950 or less.
[0016]
ln JP20l2-260054 (Patent Document 3), the present inventors have proposed a
"non-thermal refined nitrided crankshaft" wherein a steel material of a base metal
contains, in masso/0, C:0.25 to 0.60Yo, Si: 0.10 To 7.\Yo, Mn: 0.60 to 2.0o/o, P: 0.08% or
less, S: 0,10% or less, Al: 0.05% or less, Cr: 0.20 lo l.}Yo, and N: 0.0030 to 0.0250Yo,
includes a balance made of Fe and impurities, and satisfies 40 - C + 2Mn + 5.5Cr >
{ç
43.0; and the HV hardness at a depth of 0.05 mm from the surface is 380 to 600, and at
least each of a pin fillet section, a journal fillet section, and a pin section has a
compound-layer depth of 5 pm or less.
[00 17]
This non-thermal refined nitrided crankshaft may further contain one or more
types of elements selected from Cu, Ni, Mo, V Ti, and Ca, and in this case, it is
neces sary to s atis fy 140 - C+2Mn+5 . 5 Cr+26Mo>4 3 . 0l .
[00 I 8]
In JP2011-42846A (Patent Document 4), the present inventors have further
proposed a "thermal refined nitrocarburized component", wherein a steel material of a
base metal contains, in mass%, C: 0.25 to 0.40Yo, Si: 0.10 to 0.35%, Mn: 0.60 to 1.0%o,
P: 0.08% or less, S: 0.10% or less, Al: 0.05% or less, Cr: 0.30 to l.70Yo, and N: 0.0030
to 0.0250o/o, and includes a balance made of Fe and impurities; and the HV hardness at a
position of 0.05 mm from the surface is 400 to 600, and a compound-layer depth at a
stress concentrated region is 5 ¡rm or less.
[001e]
The thermal refined nitrided component may fuither contain one or more types
of elements selected from Cu, Mo, V Ni, and Ti.
LIST OF PRIORART DOCUMENTS
PATENT DOCUMENT
[0020]
Patent Document l: JP2002-226939A
Patent Document 2: JP2007-177309A
Patent Document 3: JP20l2-260054
Patent Document 4: JP20IL-428464
DISCLOSURE OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE iNVENTION
1002ll
lu
With the chemical composition described in Patent Document 1, it is not
possible to attain a suffrcient surface-layer hardness. Hence, the bending fatigue
strength is too low to reach 800 MPa, as shown in an example of Patent Document 1.
10022)
With the chemical composition described in Patent Document 2, the
surface-layer hardness after the nitrocarburizing treatment becomes too high, as shown
in an embodiment thereof. Hence, it is hard to tell that a sufficient bending
straightening property is secured during performing the bending straightening treatment.
[0023]
With the chemical composition described in Patent Document 3, it is possible
to attain a high fatigue strength and a high bending straightening properfy, as shown in
an embodiment thereof. However, a crankshaft has been oriented to reduction in
weight and size, and requires more sèvere fatigue strength and bending straightening
property.
[0024]
The thermal refined nitrocarburized component disclosed in Patent Document
4 is excellent in bending straightening property after the nitrocarburizing treatment, and
has a bending fatigue strength as high as 800 MPa or more in the bending fatigue test,
Accordingly, this component is usable as a component, such as a crankshaft, in
automobiles, industrial machines, and construction machinery, for example, and
contributes to reduction in weight and size. Unfortunately, in the invention of Patent
Document 4, subsequent to the machining, a thermal refining treatment of quenching
and tempering is required before the nitrocarburizing treatment.
[002s]
An object of the present invention, which has been made in order to solve the
problems above, is to provide a non-thermal refined nitrocarburized component
excellent in bending straightening property, and having a fatigue strength as high as 800
MPa or more in the bending fatigue test.
MEANS FOR SOLVING THE PROBLEMS
fr
[0026]
In order to solve the aforementioned problems, the present inventors have
conducted various studies. As a result, the following points l) to 7) were found.
[0027]
1) A thin sheet specimen was collected from a surface layer of each steel
material subjected to the nitrocarburizing treatment, and a tension test was conducted on
each specimen; and as a result, specimens whose compound layers were removed
exhibited greatly enhanced tension in the tension test, compared with that of specimens
whose compound layers were not removed.
[0028]
2) As a result of observation on a fracture surface of each thin sheet specimen
after the tension test, the specimens whose compound layers were not removed had
fracture surfaces where brittle fractures were generated in the compound layers, thus
initiating cracking; contrary to this, the specimens whose compound layers were
removed had ductility fracture surfaces.
[002e]
3) If the compound layer in the surface layer of the steel material subjected to
the nitrocarbunzing treatment is removed, the fracture morphology during the
bending-straightening is changed from the brittle fractures starting from the compound
layer to the ductility fractures. Accordingly, it is possible to enhance the bending
straightening property of the nitrocarburized component.
[0030]
4) Meanwhile, in the bending fatigue strength, there is little difference between
before and after the removal of the compound layer. In the case of the non-thermal
refined nitrocarburized component, if the hardness at a position of 0.05 mm from the
component surface is 410 or more in terms of the HV hardness, and if the hardness at a
position of 1.0 mm from the component surface (hereinafter, also referred to as "internal
hardness") is 200 or more in terms of the HV hardness, and the metal micro-structure of
the base metal (hereinafter, also referred to as "base material micro-structure") is bainite
micro-structure, it is possible to stably attain a high bending fatigue strength of 800
îs
MPa or more.
[003 1]
5) ln the non-thermal refined component, an endurance ratio (fatigue
strength"/tensile strength) of the base metal is lower than that in the thermal refined
component. Therefore, the non-thermal refined component has a lower fatigue
strength of the base metal than that of the thermal refined component even if the
non-thermal refined component has an internal hardness equivalent to that of the
thermal refined component. In particular, when the internal hardness of the
non-thermal refined nitrocarburized component is as low as less than 200 in terms of the
HV hardness and the base material micro-structure is dominantly made up of a mixed
strucfure of fenite and pearlite (hereinafter, referred to as a "ferrite-pearlite
micro-structure"), even if the surface-layer hardness is as high as 410 or more in terms
of the HV hardness, a fracture initiated from an internal part may take place during the
fatigue test, which makes it hard to attain a fatigue strength as high as 800 MPa or more.
[0032]
6) It is possible to substantially secure a sufficient bending straightening
property by removing the compound layer in the surface layer of the nitrocarburized
component even if the surfaceJayer hardness after the nitrocarburizing treatment is 410
or more in terms of the HV hardness.
[0033]
7) However, in the case of a crankshaft shape that requires a high bending
straightening property, if the surfaceJayer hardness of the nitrocarburized component
becomes more than 480 in terms of the HV hardness, it may be hard to attain a
suffrcient bending straightening property even if the compound layer is removed.
[0034]
The present invention has been accomplished based on the above findings, and
the gist lies in a non-thermal refined nitrocarburized component as follows.
[003s]
(l) A non-thermal refined nitrocarburized component, comprising a steel
material of a base metal, the steel material having a chemical composition consisting of:
fq
by mass%,
C: 0.35 to 0,50%;
Si: 0.10 to 0.35%;
}¿4n:2.3 to 2.8Yo;
S: 0.01% or less;
N: 0.0030 to 0.02500/o;
Cu: 0 to 1.0%;
Mo: 0 to 0.3Yo;
Ni: 0 to 0.5%;
Ti: 0 to 0.020Yo, and
the balance: Fe and impurities, wherein .
Fn1 shownbythebelow described Formula Ii] satisfres 3.10 < Fnl < 6.00, and
the impurities include P: 0.08% or less; Al: 0.05% or less; and Cr: less than
0.20%o, and wherein
at a stress concentrated region,
an HV hardness at a position of 0.05 mm from a surface is 4 10 to 480,
an HV hardness at a position of 1.0 mm from the surface is 200 or more,
a compound-layer depth is 5pm or less, and
a metal micro-structure of the base metal is a bainite micro-structure:
Fnl : (0.316C + 0.122) x (0.7Si + 1) x (5.1Mn - l.l2) x (0.364Ni + 1) x
(2.16Cr + 1) x (3Mo + 1) ...[],
where an symbol of an element in Formula [1] indicates a content of the element in steel
in mass%.
[0036]
(2) The non-thermal refined nitrocarburized component as set forth in the
above (l), wherein the chemical composition of the steel material of the base metal
contains, in masso/o, one or more types of elements selected from
Cu: 0.05 to 1.0% and
Mo: 0.05 to 0.3%o.
[0037]
(3) The non-thermal refined nitrocarburized component as set forth in the
above (1) or (2), wherein the chemical composition of the steel material of the base
metal contains, in masso/0, one or more types of elements selected from
Ni: 0.05 to 0.5% and
Ti: 0.005 to0.020%.
[0038]
The term "impurities" denotes those impurities which come from ores and
scraps as row materials, manufacturing environments, and so on during industrially
producing steel materials.
[003e]
The "stress concenhated region" denotes a region where fatigue fractures are
generated due to bending or cracking is caused while carrying out the bending
straightening. As a specific exâmple thereof, if the "non-thermal refined
nitrocarburized component" is a crankshaft having a shape as shown in Figure 1, the
"stress concentrated region" represents a "pin fillet section" or a 'Joumal fillet section"
of the crankshaft.
ADVANTAGEOUS EFFECTS OF THE INVENTION
[0040]
The non-thermal refined nitrocarburized component of the present invention is
excellent in bending straightening property after the nitrocarburizing treatment, and has
a bending fatigue strength as high as 800 MPa or more in the bending fatigue test;
therefore, this non-thermal refined nitrocarburized component is usable as a component,
such as a crankshaft, in automobiles, industrial machines, and construction machinery
and is capable of realizing reduction in weight and size of components used threrein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041]
[Figure 1] Figure I is a drawing exemplifying a part of a crankshaft as a non-thermal
refined nitrocarburized component, and explaining a "pin fillet section" and a 'Joumal
t(
fillet section" equivalent to a "stress concentrated region" ofthe crankshaft.
[Figure 2] Figure 2 is a drawing showing a shape of a grooved Ono-type rotating
bending fatigue test specimen used in Example; and a unit of measurement in the
drawing is "mm".
[Figure 3] Figure 3 is a drawing showing a shape of a four-point bending test specimen
used in Example; and a unit of measurement in the drawing is "mm".
fFigure 4] Figure 4 is a drawing showing a target surface to be examined of a four-point
bending test specimen used in Examples.
[Figure 5] Figure 5 is a drawing schematically showing measurement positions of
hardness in the Vckers hardness test in a four-point bending test specimen used in
Examples.
lFigure 6l Figure 6 is a drawing schematically showing measurement positions of
compound-layer depth in a four-point bending test specimen used in Examples.
MODE FOR CARRYING OUT THE INVENTION
[0042]
Each requirement of the present invention will be described in detail,
hereinafter. It should be noted That "%o" for a content of each element denotes
"mass%".
[0043]
(A) Chemical composition of steel material of base metal:
C: 0.35 to 0.50%
C has an action to improve the internal hardness, and enhance the bending
fatigue strength. The C content is required to be 0.35% or more in order to attain a
desired bending fatigue strength. However, an excessive C content results in an
excessively high surface-layer hardness, so that it is hard to attain a suffrcient bending
straightening property even if the compound-layer depth at the stress concentrated
region is 5 pm or less. Hence, the C content is set to be 0.35 to 0.50%. The C
content is preferably 0.38% or more, and preferably 0.45% or less.
[0044]
IL
si: 0.10 to 0.350/o
Si is an element necessary for deoxidation during melting the steel, and the Si
content of at least 0.10% is required for obtaining the above effect. However, an
excessive content of Si causes excessive deterioration of the bending straightening
property even if the compound-layer depth at the stress concentrated region is 5 pm or
less. Hence, the Si content is set to be 0.10 to 0.35%. The Si content is preferably
0.15% or more, and preferably 0.30% or less.
[004s]
Mn: 2.3 to 2.8o/o
Mn is an element having a deoxidizing action similar to Si. Mn also has an
action to increase a solute nitrogen content in the su¡face layer during the
nihocarburizing to improve the surface-layer hardness, thereby enhancing the bending
fatigue strength. In order to exert thiS effect, the Mn content is required tobe2.3o/o or
more. On the other hand, the Mn content of more lhan 2.8Yo causes an excessively
high surface-layer hardness, which excessively deteriorates the bending straightening
property even if the compound-layer depth at the stress concentrated region is 5 pm or
iess. Accordingly, the Mn content is set to be 2.3 to 2.8%. The Mn content is
preferably 2.4%o or more, and preferably 2.7%o or less.
[0046]
S: 0.10% or less
An effect to improve machinability can be attained by actively containing S.
However, the S content of more than 0.10% significantly deteriorates the bending
fatigue strength and the bending straightening property, Accordingly, the S content is
set to be 0.10% or less. It is preferable to set the S content to be 0.08% or less. In
order to attain the effect to improve machinability, it is preferable to set the S content to
be 0.04% or more.
[0047]
N: 0.0030 to 0.0250%
N is an element to improve the bending fatigue strength and the bending
straightening property. In order to attain this effect, the N content is required to be
t1t3f
0.0030% or more. On the other hand, the N content of more than 0.0250%o rather
safurates this effect. Accordingly, the N content is set to be 0.0030 to 0.0250%, The
N content is preferably 0.0080% or more, and preferably 0.0220% or less.
[0048]
Cu: 0 to 1.0%
Cu is an element to improve the internal hardness, and enhance the bending
fatigue strength. Hence, Cu may be contained as needed. However, the Cu content
of more than LlYo deteriorates hot workability. Accordingly, the amount of Cu to be
contained is set to be 1.0% or less. The amount of Cu is preferably 0.4o/o or less, and
more preferably 0.3% or less.
[004e]
In order to stably attain the above effect, it is preferable to set the amount of Cu
to be 0.05% or more, and more preferably 0.10lo or more.
[00s0]
Mo: 0 to 0.3%o
Mo has an action to strengthen ferrite, and improve the internal hardness to
enhance the bending fatigue strength. Hence, Mo may be contained as needed.
However, an excessive Mo content of more than 0.3Yo rather saturates the above effect,
only to deteriorate economic efficiency. Accordingly, the amount of Mo to be
contained is set to be 0.3% or less. The amount of Mo is preferably 0.20lo or less.
[00s 1]
ln order to stably attain the above effect, the amount of Mo is preferably 0.05%
or more, and more preferably 0.1olo or more.
l00s2l
Any one type selected from Cu and Mo, or two types selected from Cu and Mo
in combination may be contained. The total content when these elements are
contained in combination may be l.3Yo, and preferably 0.3% or less,
[00s3]
Ni: 0 to 0.5%
Ni is an element to improve toughness, and enhance the bending straightening
r+
property. Accordingly, Ni may be contained as needed, However, the Ni content of
more than 0.5%o ra|her saturates the above effect, only to deteriorate the economic
efficiency. Hence, the amount of Ni to be contained is set to be 0.5% or less. The
amount of Ni is preferably 0.3o/o or less, and more preferably 0.2% or less.
[00s4]
In order to stably attain the above effect, the amount of Ni is preferably 0.05%
or more, and more preferably 0.08% or more.
[0055]
ln the case of containing Cu, it is likely to cause hot cracking called "Cu
checking", and in order to prevent this, it is preferable to contain Cu in combination
with Ni in a manner as to satisfy Ni/Cu > 0.5.
[00s6]
Ti: 0 to 0.020o/o
Ti is an element that forms nitride, and refines grains to hinder propagation of
cracking during the bending-straightening, thereby enhancing the bending straightening
property. Accordingly, Ti may be contained as needed, However, the Ti content of
more than 0.020% generates coarse nitride, and significantly deteriorates the bending
straightening property even if the compound-layer depth at the stress concentrated
region is 5 ¡rm or less. Accordingly, the amount of Ti to be contained is set to be
0.020% or less. The amount of Ti is preferably 0.015% or less.
[0057]
In order to stably attain the above effect, the amount of Ti is preferably 0.005%
oT more.
[00s8]
Any one type selected from Ni and Ti, or two types selected from Ni and Ti in
combination may be contained. The total content when these elements are contained
in combination may be 0.520%o, and preferably 0,30% or less.
[005e]
Fn 1 : within range of 3. I 0 to 6.00
ln the non-thermal refined nitrocarburized component according to the present
w /tç
invention, Fnl represented bythe below described Formula [1] is within a range of 3,10
to 6.00:
Fnl : (0.316C + 0.122) x (0.7Si + 1) x (5.1Mn - LIz) x (0.364Ni + 1) x
(2.l6Cr + 1) x (3Mo + 1) ...[1],
where an symbol of an element in Formula [1] indicates a content of the element in steel
in mass%,
[0060]
Fnl is an index relating to the base material micro-structure. Any of C, Si,
Mn, Ni, Cr, and Mo improves hardenability of steel. If Fnl is 3.10 or more, the
hardenability of steel material becomes suffrciently high, and the base material
micro-structure becomes a bainite micro-structure, which allows to impart a high
endurance ratio to the base material. However, if Fnl becomes more than 6.00, the
base material micro-structure becomeb a martensite micro-structure, and the hardness
becomes excessively high, thus adversely affecting the bending straightening property.
Hence, Fnl is set to be 3.10 < Fni < 6.00. Fnl is preferably 3.50 or more, and is also
preferably 5.00 or less.
[0061]
The non-thermal refined nitrocarburized component according to the present
invention includes a steel material of a base metal having a chemical composition
consisting of each element described above, with the balance being Fe and impurities,
where the impurities include P: 0.08% or less; Al: 0.05% or [ess; and Cr: less than
0.20%.
[0062]
P: 0.08% or less
P is an impurity contained in the steel, and deteriorates the bending fatigue
strength. Particularly, the P content of more than 0.08% significantly deteriorates the
bending fatigue strength. Accordingly, the P content is set to be 0.08% or less, It is
preferable to set the P content to be 0.04% or less.
[0063]
Al: 0.05% or less
,F lø
Al is an impurity contained in the steel. An excessive Al content deteriorates
the bending straightening property. Particularly, the S content of more than 0.05%
significantly deteriorates the bending straightening property even if the compound-layer
depth at the stress concentrated region is 5 pm or less. Accordingly, the Al content is
set to be 0.05% or less. TheAl content is preferably 0.03% or less.
[0064]
Cr: less lhan0.20o/o
Cr is an impurity contained in the steel. Containing Cr may excessively
increase the surfacelayer hardness, which deteriorates the bending straightening
property; thus it is preferable to set the Cr content to be as small as possible.
Accordingly, the Cr content is set to be less than 0.20Vo. The Cr content is preferably
0.10% or less.
[006s]
(B) Hardness, compound-layer depth, and micro-structure:
In the non-thermal refined nitrocarburized component according to the present
invention, (1) at a stress concentraied region, the HV hardness at a position of 0.05 mm
from a surface, that is, the HV hardness in a surface layer is 410 to 480; the HV
hardness at a position of 1.0 mm from the surface, that is, the HV hardness at an intemal
part is 200 or more; the compound-layer depth is 5pm or less, and (2) the metai
micro-structure of the base metal is a bainite micro-structure.
[0066]
(B-1) SurfaceJayer hardness at steel concentrated region
In order to attain a fatigue strength as high as 800 MPa or more, it is necessary
that the HV hardness in the surface layer at a stress concentrated region is 410 or more.
On the other hand, if the HV hardness in the surface layer at the stress concentrated
region is more than 480, in the case of using a crankshaft shape to likely cause a gïeater
bending than that of a conventional art during the nitrocarburizing, it may be hard to
attain a practically suffrcient bending straightening property even if the compound-layer
depth at the stress concentrated region is 5 pm or less.
[0067]
Fw
Accordingly, in the non-thermal refined nitrocarburized component according
to the present invention, the HV hardness at a position of 0.05 mm from the surface at
the stress concentrated region is set to be 410 to 480, The HV hardness at a position of
0.05 mm from the surface at the stress concentrated region is preferably 420 or more,
and preferably 470 or less.
[0068]
(B-2) Intemal hardness at the stress concentrated region:
In the non-thermal refined nitrocarburized component, since the endurance
ratio of the base metal is lower than that in the thermal refined nitrocarburized
component, at the stress concentrated region, the fatigue strength of the base metal
becomes lower than that in the thermal refined nitrocarburized component even if the
non-thermal reftned nitrocarburized component has an intemal hardness equivalent to
that of the thermal refined nitrocarburized component. Consequently, in the
non-thermal refined nitrocarburized component, at the stress concentrated region, in the
case of having an HV hardness of less than 200 at the internal part, even if the
non-thermal refined nitrocarburized component has an intemal hardness equivalent to
that of the thermal refined nitrocarburized component, and also has a surface-layer
hardness as high as 410 or more in terms of the HV hardness, fatigue fractures initiated
from the intemal part may be caused, which makes it hard to attain a high fatigue
strength of 800 MPa or more.
[006e]
Accordingly, in the non-thermal refined nitrocarburized component according
to the present invention, the HV hardness at a position of 1.0 mm from the surface at the
stress concentrated region is set to be 200 or more. The HV hardness at a position of
1.0 mm from the surface at the stress concentrated region is preferably 210 or more, and
preferably 320 or less in the light of machinability.
[0070]
(B-3) CompoundJayer depth at the stress concentrated region:
By setting the compound-layer depth at the stress concentrated region to be
thinner, it is possible to improve the bending straightening property without
V /tg
deteriorating the bending fatigue strength. However, it is hard to expect significant
improvement of the bending straightening property if the compound layer whose depth
is more than 5 pm still remains.
[0071]
Accordingly, in the non-thermal refined nitrocarburized component according
to the present invention, the compound-layer depth at the stress concentrated region is
set to be 5 pm or less. The compound-layer depth at the stress concentrated region is
preferably 3 pm or less, and it is most preferable to have no compound layer, that is,
have a compound-layer depth of 0 ¡rm.
10072J
(B-4) Metal micro-structure of base metal:
As described above, the metal micro-structure (base material micro-structure)
of the base metal of the non-thermal reirned nitrocarburized component according to the
present invention, which has a steel material of a base metal having the chemical
composition described in the above section (A), is a bainite micro-structure. The
bainite micro-sffucture as used herein refers to a metal micro-strucfure of the base metal
of which 80% or more is bainite micro-structure.
[0073]
As described above, since a non-thermal refined nitrocarburized component
has a lower endurance ratio of the base material compared with a thermai refined
nitrocarburized component, even if it has an internal hardness equal to that of the
thermal refined nitrocarburized component at a stress concentrated region, the fatigue
strength of the base material will become lower than that of a therrnal reftned
nitrocarburized component. However, when the base material micro-structure of the
non-thermal refined nitrocarburized component is a bainite micro-structure, the
endurance ratio of the base material becomes higher compared with a case i¡ which the
base material micro-structure is a ferrite-pearlite micro-structure. Hence, a bainite
type non-thermal refined steel can attain a higher fatigue strength compared with a
ferrite-pearlite type non-thermal refined steel which has the same internal hardness at a
stress concentrated region.
v't1
100741
A component which satisfies the above described conditions (B-1) to (B-4) can
be obtained in such a manner that a steel material that satisfies the chemical
composition specified by the present invention is hot-forged at a temperature of 1000'C
or more into a hot forged product having a shaft diameter of 8 to 80 mm; then after
being allowed to cool and machined, the product is subjected to a nitrocarburizing
treatment by being retained for two hours in an atmosphere where an RX gas and
ammonia gas are mixed at a mixfure ratio of 1: I at a temperature of 600oC, and then
cooled in an oil having a temperature of 90'C; and subsequently the stress concentrated
region thereof is ground through machining such as lapping.
[007s]
The above mentioned "RX gas" is one type of a modified gas, and represents a
brand name of this gas.
[0076]
Specifically, representing a crankshaft as an example of the non-thermal
refined nítrocarburized component, for example, this crankshaft can be obtained in such
a manner that a starting material that satisfres conditions on the chemical composition
specified by the present invention is hot-forged into a crankshaft, this crankshaft is
machined, and thereafter this crankshaft is subjected to the nitrocarburizing treatment to
retain the crankshaft for two hours in an atmosphere where an RX gas and an ammonia
gas are mixed at a mixture ratio of 1:1 at a temperature of 600'C, and then cooled in an
oil having a temperature of 90oC, and subsequently, the pin fillet section and the joumal
fillet section are ground through machining using a lapping machine or the like.
100771
Hereinafter, although the present invention will be described in detail by way
of Examples, the present invention will not be limited to those Examples.
EXAMPLE
[0078]
Each of Steels A to N having respective chemical compositions shown in Table
v' 9-Õ
I was melt in a 70t convertor, subjected to continuous casting, and further subjected to
blooming into a cast piece having a cross sectional dimension of 180 mmx 180 mm.
[007e]
Subsequently, each cast piece was hot-forged under the conditions that a
heating temperature was 1200"C, and a finishing temperature was 1000 to 1050'C into
a steel bar having a diameter of 90 mm. Each steel bar after the hot-forging was
cooled in the atmosphere down to a room temperature through allowing cooling.
[0080]
In Table l, each of Steels A to H is a steel having chemical composition within
the range specified by the present invention, and each ofSteels I to N is a steel having
chemical composition out of the range specified by the present invention.
T<) -¿-
[0081]
[Table 1]
Steel
A
B
C
D
E
F
G
HI
J
KL
M
N
C
0.36
0.48
0.4r
0.43
0.40
0.41
0.37
0.36
+0.19
0.37
0.36
0.36
0.36
0.49
Si
0.21
0.14
0.32
0.20
0.1s
0.22
0.t7
0.15
0.11
0.20
0.18
0.22
0.14
0.30
Mn
2.72
2.42
2.32
2.48
2.44
2.42
2.40
2.3s
2.50
*2.25
*3.10
2.45
2.30
2.77
Chemical composition (mass%) Balance: Fe and impurities
S
0.070
0.042
0.066
0.062
0.07s
0.066
0.050
0.0ss
0.06s
0.068
0.060
0.060
0.066
0.062
Fn1:(0.316C+0.122)x(0.7Si+1)x(5.lMn-1.12)x(0.364Ni+1)x(2.16Cr+l)x(3Mo+1)
A mark (*) represents deviation from the chemical composition specified bv the Dresent invention
N
0.013s
0.0170
0.0r80
0.017s
0.01s0
0.0160
0.016s
0.0180
0.0185
0.0170
0.0175
0.0190
0.0185
0.017s
Cu
Table 1
0.20
0.19
Mo Ni Ti
0.0t2
0.11
0.10
0.09
P
0.017
0.020
0.018
0.018
0.010
0.016
0.011
0.022
0.010
0.015
0.014
0.012
0.02r
0.018
001PF268
AI
0.0(
0.0,
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0_0
0.0:
0.0
0.0
0.0
)7
,-2
l4
l2
t1
t0
t4
t0
t1
t2
¿0
t5
t5
t8
Cr
0.04
0.09
0.14
0.06
0.10
0.09
0.11
0.04
0.19
0.13
0.10
+0.29
0.03
0.18
Fn1
3.75
4.03
4.30
3.83
3.78
4.03
3.80
4.09
3.22
3.6r
4.74
4.97
*2.92
*6.05
'/ z^
100821
Each steel bar having a diameter of 90 mm obtained in this manner was heated
up to a temperature of 1200oC, and then hot-forged at a finishing temperature of 1000 to
1050"C into a steel bar having a diameter of 50 mm. Each finished steel bar was
cooled down to a room temperature through allowing cooling in the atmosphere.
[0083]
ln each of Steels A to N, a grooved Ono-type rotating bending fatigue test
specimen having a shape shown in Figure 2 was cut out in parallel to the forging axis
from an Dl4 part ("D" represents a diameter of a steel bar) of each steel bar as
hot-forged having a diameter of 50 mm, and a four-point bending test specimen having
a shape shown in Figure 3 was also cut out in the same manner as this grooved
Ono-fype rotating bending fatigue test specimen,
[0084]
In the test specimen in Figure 2, the groove bottom of the R3 is equivalent to
the stress concentrated region. Similarly, in the test specimen in Figure 3, the notch
bottom of the R3 is equivalent to the stress concentrated region.
[008s]
Each grooved Ono-type rotating bending fatigue test specimen and each
four-point bending test specimen, which were obtained in the above manner, were
respectively subjected to the nitrocarburizing treatment to retain each test specimen for
two hours in an atmosphere where the RX gas and the ammonia gas are mixed at a
mixfure ratio of 1:1 at a temperature of 600'C; and thereafter, was cooled in the oil
having a temperafure of 90oC.
[0086]
In Test No. 1 to Test No. 14, subsequent to the nitrocarburizing treatment,
electrolytic grinding was further carried out at the gtoove bottom of each grooved
Ono-type rotating bending fatigue test specimen, and at the notch bottom of each
four-point bending test specimen, with a target grinding depth of 0.03 mm under the
following conditions.
[0087]
F 2-e
- Electrolytic solution: perchloric acid (HCIO+): acetic acid (CH:COOH) : 1:9
- Current value: 0.144
- Grinding area:
Ono-type rotating bending fatigue test specimen: 160 mm2
Four-point bending test specimen: 96 mm2
- Grinding time period:
Ono-type rotating bending fatigue test specimen: 970 seconds
Four-point bending test specimen: 590 seconds
[0088]
In TestNo. 15 and TestNo. 16, subsequent to the nitrocarburizing treatment,
electrolytic grinding was fi¡rther carried out at the groove bottom of each grooved
Ono-type rotating bending fatigue test specimen, and the notch bottom of each
four-point bending test specimen, with atargel grinding depth of 0.015 mm under the
following conditions.
[008e]
- Electrol¡ic solution:perchloric acid (HCIO+): acetic acid (CHTCOOH): 1:9
- Current value: 0.144
- Grinding area:
Ono-type rotating bending fatigue test specimen: 160 mm2
Four-point bending test specimen: 96 mm2
- Grinding time period:
Ono-type rotating bending fatigue test specimen: 490 seconds
Four-point bending test specimen: 300 seconds
[00e0]
Using the specimens as nitrocarburized (Test No. 17) and the specimens further
subjected to the electrolytic grinding after the nitrocarburizing treatment (Test No. I to
Test No. 16) obtained in the above manner, a study of the bending fatigue strength by
the Ono{ype rotating bending fatigue test, and a study of the bending straightening
property by the four-point bending test were respectively carried out.
[00e1]
7L+
Further, using the Ono-type rotating bending fatigue test specimens and the
four-point bending test specimens, which were as nitrocarburized (Test No. 17) or
subjected to electrolytic grinding after the nitrocarburizing treatment (Test No. 1 to Test
No. 16), the surface-layer hardness (i.e., hardness at a position of 0.05 mm from the
surface of each specimen), the intemal hardness (i.e., hardness at aposition of 1.0 mm
from the surface of each specimen), and the compoundJayer depth at the groove bottom
and the notch bottom, which were stress-concentrated regions, were studied. Further
the base material micro-structure was studied as well.
[00e2]
The details of each study will be described, hereinafter.
[00e3]
(1) Study ofbending fatigue strength:
The Ono-type rotating bending fatigue test was carried out at a room
temperature, in the atmosphere, under completely reversed bending at a rotational rate
of 3000 rpm so as to study the bending fatigue strength (refened to as "6w",
hereinafter).
[00e4]
The target ow was set to be 800 MPa or more.
[00es]
(2) Study of bending straightening property:
A strain gauge of 2 mm was adhesively bonded to the notch bottom of each
four-point bending test specimen, and bending-straightening strain was applied to this
specimen until the gauge was broken, A read value of the gauge at the moment when
the gauge was broken was evaluated as the bending straightening property.
[00e6]
The target value of the bending straightening property was set to be 22000 p
(equivalent to the bending-straightening strain of 2.2%) or more.
[00e7]
(3) Surface-layer hardness and internal hardness at stress concentrated region
The Ono-type rotating bending fatigue test specimen was cut such that a cross
.zr L5
"!
section that passes through the central portion of the specimen and is parallel with the
longitudinal direction of the specimen appears. Further, the four-point bending test
specimen was cut such that a cross section that is parallel with the longitudinal direction
of the specimen and is perpendicular to the direction of the groove appears. Then, to
employ each cut surface as a target surface to be examined, after the vicinity of the
groove of the R3 of the Ono-type rotating bending fatigue test specimen and the vicinity
of the notch of the R3 of the four-point bending test specimen were embedded in resin,
the aforementioned surface was polished to be mirror-finished; and subsequently the
surface-layer hardness at the stress concentrated region (hereinafter, simply referred to
as the "surface-layer hardness) and the internal hardness at the stress concentrated
region (hereinafter, simply referred to as the "intemal hardness") were studied using a
Vickers hardness meter. The target surface to be examined of the four-point bending
test specimen is shown in Figure 4. The target surface to be examined is similar for
the case of the Ono-type rotating bending fatigue test specimen (not shown).
l00e8l
As for hardness, in conformity to the "Vickers hardness test - Test method"
described in JIS Z 2244:2009, the HV hardness at any six points respectively at a
position of 0.05 mm and a position of 1.0 mm from the groove bottom of the R3 and the
notch bottom of the R3 were measured with a test force of 2.94N using a Vickers
hardness meter, and the measured values were arithmetically averaged to evaluate the
surface-layer hardness and the intemal hardness. Figure 5 schematically shows the
measurement positions of hardness in the four-point bending test specimen. The
measurement positions are similar for the target surface to be examined of the Ono-type
rotating bending fatigue test specimen (not shown).
[00ee]
(4) Compound-layer depth at the stress concentrated region:
The compound-layer depth at the stress concentrated region (hereinafter,
simply refened to as "compound-layer depth") was studied using each of the test
specimens embedded in the resin that were used in the above (3).
[0100]
v'zÇ
Specifically, each test specimen embedded in the resin was polished once again,
etched with nital, and then any five visual fields at the groove bottom of the R3 and any
five visual fields at the notch bottom of the R3 were respectively observed with an
optical microscope with magnification of 400x; and portions observed to be white were
deterrnined as the "compound layers", and the depths of these layers were measured,
and arithmetically averaged as the compound-layer depth. The measurement positions
of the compound-layer depth in the four-point bending test specimen are schematically
shown in Figure 6. The measurement positions are similar for the target surface to be
examined of the Ono-type rotating bending fatigue test specimen (not shown).
[0101]
(5) Base material micro-structure:
The base material micro-structure was studied using each of the test specimens
embedded in resin that were used in the studies described in (3).
[0r02]
Specifically, the base material micro-structure was observed by an optical
microscope at a magnification of 400 times by using a test specimen which was etched
with nital as described above.
[0103]
Table 2 shows, in summary results of each study described above. ln Table 2,
in a base material micro-structure described as "bainite", a bainite micro-structure
accounts for 80 7o or more of the base material micro-structure; in one described as
"ferrite-pearlite", a ferrite-pearlite micro-structure accounts for 80% or more of it, and
in one described as "martensite", a martensite micro-structure accounts for 80% or more
of it.
[0104]
,zLr +
[Table 2]
Test
No.
Steel
Grooved Ono-tyoe rotatine bendins fatizue test specimen
Compound
Layer
depth
(pm)
I
2
3
4
5
6
7
8
9
10
1l
t2
13
l4
l5
t6
t7
A
B
C
D
E
F
G
H
*I
*J
r.K
)FL
,l.M
r.N
A
B
C
Surface
Layer
hardness
(HV
hardness)
2
I
3
0
2
J
0
I
I
0
2
2
2
I
*11
*10
*21
internal
hardness
(HV
hardness)
433
435
415
440
44s
461
451
440
435
*405
*5 l0
*505
412
*540
440
445
42s
base material
micro-structure
244
260
235
26s
270
280
290
235
*195
240
28s
27s
2t0
295
245
260
238
Table
bainite
bainite
bainite
bainite
bainite
bainite
bainite
bainite
bainite
bainite
bainite
bainite
ferrite-pearlite
* martensite
bainite
bainite
bainite
A mark (*) represents deviation from the requirement specified by the present invention
A mark (#) represents that the value does not satisfu the tarset value.
ow
(MPa)
Compound
Layer
Depth
(pm)
840
880
810
890
880
900
880
860
#180
#790
920
900
#770
920
840
870
810
Surface
Layer
hardness
(HV
hardness)
Four-ooint bendins test
2
I
J
0
2
3
0
1
I
0
3
2
I
I
*12
*9
*20
lnternal
hardness
(HV
hardness)
431
434
4t6
436
444
465
452
440
433
*406
*512
*505
4t3
*542
441
444
428
sDecl
base material
micro-structure
men
243
2,6t
234
264
211
280
291
233
* 198
242
282
277
2r0
299
244
260
235
001PF268
bainite
bainite
bainite
bainite
bainite
bainite
bainite
bainite
bainite
bainite
bainite
bainite
*fenite-pearlite
*martensite
bainite
bainite
bainite
Bending
Straightening
property
(p)
29800
29s00
27200
30200
26000
24s00
27000
28000
29500
33500
#16s00
#16000
32400
#13500
#14000
#13s00
#15000
/2L/g
[010s]
As shown in Table 2, in the cases of Test No. I to Test No, 8 that satisff the
conditions specified by the present invention in the chemical cornposition of the steel
material of the base metal, the surface-layer hardness, the internal hardness, and the
compound-layer depth as well as the base material micro-structure, it is apparent that
the target values of the ow and the bending straightening property were both satisfied,
and these cases arc excellent in bending fatigue characteristics and bending
straightening property,
[0106]
To the contrary, in the cases of Test No. 9 to Test No. 14, the respective
chemical compositions of Steel I to Steel N deviate from the conditions speciflred by the
present invention, and thus these cases are poorer in bending fatigue characteristics or
bending straightening property.
l0r07l
Specifically, in the case of Test No. 9, the C content of Steel I that is the steel
material of the base metal is less than the range specified by the present inventíon.
Consequently, the internal hardness of the Ono-type rotating bending fatigue test
specimen is as low as 195 in terms of the HV hardness, and the ow does not satisff the
target value of 800 MPa or more; thus this case is poor in bending fatigue
characteristics.
[0108]
ln the case of Test No. 10, the Mn content of Steel J that is the steel material of
the base metal is less than the range specified by the present invention. Consequently,
the surface-layer hardness of the Ono-type rotating bending fatigue test specimen is as
low as 405 in terms of the HV hardness, and the ow does not satisff the target value of
800 MPa or more; thus this case is poor in bending fatigue characteristics.
[010e]
ln the case of Test No. I 1, the Mn content of Steel K that is the steel material of
the base metal is more than the range specified by the present invention. Consequently,
although the compound-layer depth is as small as 3 pm, the surface-layer hardness of
/2Ly q
the four-point bending test specimen is as high as 512 in terms of the HV hardness, and
the bending straightening property does not satisfli the target value of 22000 p or more
in terms of the read value of the gauge; thus this case is poor in bending straightening
property.
[0rr0]
. In the case of Test No. 12, the Cr content of Steel L that is the steel material of
the base metal is more than the range specified by the present invention. Consequently,
although the compound-layer depth is as small as 2 ¡tm, the surface-layer hardness of
the four-point bending test specimen is as high as 505 in terms of the HV hardness, and
the bending straightening property does not satisfy the target value of 22000 p or more
in terms of the read value of the gauge; thus this case is poor in bending straightening
property.
[0111]
In the case of Test No. 13, Fnl of Steel M, which is the steel materiai of the
base metal, is less than the range specified by the present invention. Consequently, the
base material micro-structure becomes a ferrite-pearlite micro-structure, and although
the surface-layer hardness in the Ono-type rotating bending fatigue test specimen is as
high as 412 inHV hardness, and the internal harness is 210 in HV hardness, the bending
fatigue strength ow does not satisfy the target value of 800 MPa or more, thus
exhibiting poor bending fatigue characteristics.
[0112]
In the case of Test No. 14, Fnl of Steel N, which is the steel material of the
base metal, is more than the range specified by the present invention. Consequently,
the base material micro-structure becomes a martensite micro-structure, and although
the compound layer depth is as low as I ¡rm, the surface-layer hardness of the four-point
bending test specimen is as high as 542 in terms of HV hardness, and the bending
straightening property does not satisfy the target value of 22000 p or more in terms of
the read value of the gauge, thus exhibiting poor bending straightening property.
[0113]
In the cases of Test No. 15 to Test No. 17, the compound-layer depth of the
?f
3O
four-point bending test deviates from the condition specified by the present invention;
thus these cases are poor in bending straightening property.
[0114]
In the case of Test No. I 5, although Steel A that is the steel material of the base
metal has chemical composition within the range specified by the present invention, the
compound-layer depth of the four-point bending test specimen is as high as 12 pm, and
the bending straightening property does not satisff the target value of 22000 p or more
in terms of the read value of the gauge; thus this case is poor in bending straightening
property.
[011s]
ln the case of Test No. 16, although Steel B that is the steel material of the base
metal has chemical composition within the range specified by the present invention, the
compound-layer depth of the four-point bending test specimen is as high as 9 pm, and
the bending straightening property does not satisfy the target value of 22000 F or more
in terms of the read value of the gauge; thus this case is poor in bending straightening
property.
[01 I 6]
In the case of Test No. 17, although Steel C that is the steel material of the base
metal has chemical composition within the range specified by the present invention, the
compound-layer depth of the four-point bending test specimen is as high as 20 pm, and
the bending straightening property does not satisfy the target value of 22000 p or more
in terms of the read value of the gauge; thus this case is poor in bending straightening
property.
INDUSTRIAL APPLICABILITY
[01 I 7]
The non-thermal refined nitrocarburized component of the present invention is
excellent in bending straightening property after the nitrocarburizing treatment, and has
a bending fatigue strength as high as 800 MPa or more in the bending fatigue test;
therefore, this non-thermal refined nitrocarburized component is usable as a component,
/f3t
such as a crankshaft, in automobiles, industrial machines, or construction machinery,
and this component is capable of attaining reduction in weight and size.
/93r L

claims.
l. A non-thermal refined nitrocarburized component, comprising a steel material
of a base metal, the steel material having a chemical composition comprising: by
masso/0,
C: 0.35 to 0.50%o;
Si: 0.10 to 0.35%o;
Mn: 2.3 to2.8Yo;
S: 0.01% or less;
N: 0.0030 to 0.02500/o;
Cu: 0 to l.0%;
Mo: 0 to 0.3o/o:
Ni: 0 to 0.5%;
Ti: 0 to 0.020%o; and
the balance: Fe and impurities, wherein
Fnl shown by the below described Formula [1] satisfies 3.10 < Fnl < 6.00, and
the impurities include P: 0.08% or less; Al: 0.05% or less; and Cr: less than
0.20Yo, and wherein
at a stress concentrated region,
an HV hardness at a position of 0.05 mm from a surface is 410 to 480,
an HV hardness at a position of 1.0 mm from the surface is 200 or more,
a compound-layer depth is 5¡rm or less, and
a metal micro-structure of the base metal is a bainite micro-structure:
Fnl : (0.316C + 0.122) x (0.7Si + l) x (5.1Mn - 1.12) x (0.364Ni + l) x
(2.l6Cr + l) x (3Mo + 1) ...[],
where an symbol of an element in Formula [1] indicates a content of the element in steel
in masso/0.
2. The non-thermal refined nitrocarburized component according to claim 1,
wherein
3e
the chemical composition of the steel material of the base metal contains, in
masso/0, one or more types of elements selected from
Cu: 0.05 to l.0ol0, and
Mo: 0.05 to 0.3o/o.
3. The non-thermal refined nitrocarburized component according to claim 7 or 2,
wherein
the chemical composition of the steel material of the base metal contains, in
mass%0, one or more types of elements selected from
Ni: 0.05 to 0.5o/o, and
Ti: 0.005 fo 0.020%.