JP3368735B2 - High strength, low ductility non-heat treated steel - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, low-ductility non-heat treated steel, and more specifically, it requires high strength but does not require ductility, and rather can be cold split at room temperature. The present invention relates to a high-strength, low-ductility non-heat treated steel which has a flat brittle fracture surface and is suitable as a steel for connecting rods and connecting rod caps of automobile engines.

[0002]

2. Description of the Related Art A connecting rod (commonly known as connecting rod) body 1 and a connecting rod cap (commonly known as connecting rod cap) 2 shown in FIG. 1, which are parts of an automobile engine or the like, are conventionally hardened after being hot forged in another process. After being tempered, it was subjected to bolt hole machining and finish shaping by machining, and then joined and assembled by a bolt 3 to a crankshaft having a complicated shape.

However, recently, reflecting the severe economic situation, the movement for reducing the manufacturing cost of various automobile parts has become active, and this movement is no exception in engine parts.

For this reason, the connecting rod body 1 and the connecting rod cap 2 are integrally formed by hot forging and subjected to heat treatment for quenching and tempering, or hot forging, as a measure for reducing the manufacturing cost. After cooling, it is divided into a connecting rod body 1 and a connecting rod cap 2, and the joints (joining surfaces) are not machined for finishing shaping, and are assembled to the crankshaft with bolts 3 for assembly. That method is being considered. in this way,
The processing of the bolt holes is performed before or after dividing the integrally molded material.

As a method of dividing the integrally formed connecting rod body 1 and the connecting rod cap 2 described above, for example, a jig is inserted to give a force acting in the direction shown by the arrow in FIG. 1 to divide the connecting rod body 1 and the connecting rod cap 2. Can be considered. In this method, it is extremely important to flatten the dividing surface divided into the connecting rod body 1 and the connecting rod cap 2.

However, the steel (J
If it is integrally formed by hot forging using IS standard S45C or S48C equivalent steel etc. as it is, and then is divided into the connecting rod body 1 and the connecting rod cap 2 at room temperature, the dividing surface looks like a candy or gum is cut into pieces. There is a problem that a so-called "ductile fracture surface" cannot be obtained and a flat "brittle fracture surface" cannot be obtained, and a finish shaping process by machining must be performed. If the above division is performed at a low temperature (for example, liquid nitrogen temperature), brittle fracture occurs and a flat brittle fracture surface can be easily obtained, but it is technically easy to keep the temperature low in an actual operation line where a large amount of products flow. However, there is a problem that the cost for constructing and maintaining the equipment will increase, which does not necessarily lead to cost reduction.

On the other hand, since the heat treatment after integrally forming by hot forging is costly, there is a demand for a new type of steel in which the heat treatment can be omitted.

As a non-heat treated steel in which heat treatment as a heat treatment performed after hot rolling or hot forging can be omitted, for example, "non-heat treated high strength steel" is proposed in Japanese Patent Laid-Open No. 5-195140. . However, the non-heat treated steel described in this publication is a high-strength non-heat treated steel of the type that prevents cracks on the bloom surface during continuous casting. Therefore, when the above-mentioned proposed steel is used as the steel for the connecting rod body 1 and the connecting rod cap 2, the desired strength can be obtained, but the connecting rod body 1 and the connecting rod cap 2 can be formed on the connecting rod body 1 and the connecting rod cap 2 at room temperature after being integrally molded as described above. With respect to the method of dividing, the ductility is too great to obtain a brittle fracture surface. Therefore, it is necessary to perform finish shaping by machining.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and has a tensile strength equal to or higher than that of conventional steel, and a hot forged integrally formed material is obtained at room temperature by the method as described above. It is an object to provide a high-strength, low-ductility non-heat treated steel in which the fracture surface when divided by is a flat brittle fracture surface.

[0010]

Means for Solving the Problems The present inventor has obtained the following findings as a result of various studies to solve the above problems.

The fracture modes of non-heat treated steel containing more than 0.70% by weight of C at room temperature include the following fn1, fn2 and fn.
Correlation with 3. Then, “fn1 ≧ 0” and “fn2
Brittle fracture is promoted when at least one of ≦ 0 ”and“ fn3 ≧ 0 ”is satisfied. However, fn1 = N-0.1Al-0.002, fn2 = N-0.3Ti, fn3 = N-0.5Al-0.3Ti-0.15Nb-
0.3V-1.3B-0.002, In addition, the element symbol in the formula of fn1 to fn3 represents the content in the weight% of the element.

The above-mentioned fn1 ≧ 0, fn2 ≦ 0 and fn
When at least one of 3 ≧ 0 is satisfied and the elongation value of the steel material at the room temperature tensile test is 10% or less, the room temperature split surface of the hot forged integrally formed material is a flat brittle fracture surface.

In addition to the above (at least one of fn1 ≧ 0, fn2 ≦ 0, and fn3 ≧ 0 is satisfied, and the elongation value of the steel material is 10% or less when subjected to a tensile test at room temperature), hot forged integral If a notch of 0.5 mmR or less is provided on at least a part of the molding material to be divided, the integral molding material can be easily divided at room temperature by applying a slight force, and the division surface is further improved. It is a flat and brittle fracture surface.

When the chemical composition of the steel is within a specific condition range, the tensile strength of the non-heat treated steel can be arranged by the following fn4. When this value is 0 or more, the tensile strength of 800 MPa or more can be obtained. fn4 = C + (Si / 10) + (Mn / 5) + (5Cr
/22)+1.65V-(5S/7)-0.8, Note that the element symbol in fn4 also represents the content of the element in% by weight. Strictly controlling the chemical composition of the steel, and at least one of the above fn1 ≧ 0, fn2 ≦ 0 and fn3 ≧ 0 and the elongation value of the steel material when subjected to a room temperature tensile test ≦ 10%,
Also, if the condition of fn4 ≧ 0 can be satisfied, a flat brittle fracture surface can be obtained by division at room temperature and high strength can be obtained. Therefore, the connecting rod body 1 and the connecting rod cap 2 having the desired tensile strength of 800 MPa or more can be manufactured by the new process described above. In this case, the inside of the large end hole, which is the part of the integrally molded material desired to be divided (N in FIG. 1).
By providing a notch of 0.5 mmR or less in at least a part of the (part), the connecting rod body 1 and the connecting rod cap 2 described above can be manufactured more easily and reliably.

Even if the C content is more than 0.70% by weight, if the C content is about 1.20% by weight or less, the above fn1 ≧ 0, fn2 ≦ 0 and fn3 ≧ 0.
If at least one of the above is satisfied, the hot workability does not deteriorate much as compared with the case of the low C steel.

The present invention based on the above findings is described in the following (1)-
The high strength and low ductility non-heat treated steel described in (3) is the gist.

(1) C: 0.70% to 1.20% by weight, Si: 1.50% or less, Mn: 0.3
0-2.00%, P: 0.15% or less, S: 0.10%
Below, Cu: 0.20% or less, Ni: 0.50% or less,
Cr: 0.02 to 2.00%, Mo: 0.50% or less,
V: 0.50% or less, Nb: 0.17% or less, Ti:
0.20% or less, B: 0.0100% or less, Al: 0.
100% or less (excluding 0.005% or less) , N:
0.030% or less, Pb: 0.30% or less, the balance consisting of Fe and unavoidable impurities, and fn1 ≧
0, fn2 ≤ 0 and fn3 ≥ 0 are satisfied, and fn4 ≥ 0 is satisfied.
Low ductility non-heat treated steel .

(2) In% by weight, C: exceeds 0.70%
Up to 1.20%, Si: 1.50% or less, Mn: 0.3
0 to 2.00%, P: 0.15% or less (however, 0.04%
% Or more), S: 0.10% or less, Cu: 0.20
% Or less, Ni: 0.50% or less, Cr: 0.02 to 2.
00%, Mo: 0.50% or less, V: 0.50% or less,
Nb: 0.17% or less, Ti: 0.20% or less, B:
0.0100% or less, Al: 0.100% or less, N:
0.030% or less, Pb: 0.30% or less, and the balance
The part is composed of Fe and unavoidable impurities, and fn1 ≧
0, satisfying at least one of fn2 ≦ 0 and fn3 ≧ 0
And high strength characterized by fn4 ≧ 0
Low ductility non-heat treated steel.

(3) In% by weight, C: exceeds 0.70%
Up to 1.20%, Si: 1.50% or less, Mn: 0.3
0-2.00%, P: 0.15% or less, S: 0.10%
Below, Cu: 0.20% or less, Ni: 0.50% or less,
Cr: 0.02 to 2.00%, Mo: 0.50% or less,
V: 0.50% or less, Nb: 0.003 to 0.17%
Ti: either 0.005 to 0.20% or both
B, 0.0100% or less, Al: 0.100% or less
Lower, including N: 0.030% or less, Pb: 0.30% or less
And the balance consists of Fe and unavoidable impurities.
At least one of fn1 ≧ 0, fn2 ≦ 0, and fn3 ≧ 0
Is satisfied, and fn4 ≧ 0 is satisfied.
High strength, low ductility non-heat treated steel. Hereinafter, the above (1) to (3)
The items described in (1) to (3) are referred to as inventions.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the chemical composition of steel in the present invention as described above will be explained below. In addition, "%" means "weight%."

C: C has a function of imparting desired static strength to steel and promoting brittle fracture at room temperature. In particular, fn1 ≧ 0, f
In the steel satisfying at least one of n2 ≦ 0 and fn3 ≧ 0, brittle fracture at room temperature is extremely promoted when C exceeds 0.70%. On the other hand, if the content exceeds 1.20%, the deformation resistance during hot becomes large and a large processing facility is required, and further, the above-mentioned fn1 ≧ 0, fn
Even when at least one of 2 ≦ 0 and fn3 ≧ 0 is satisfied, the hot workability is deteriorated, and cracks are likely to occur during hot working. Therefore, the content of C is set to more than 0.70% and up to 1.20%. In order to secure further stable hot workability, the upper limit of the C content is 1.1.
It is preferably 0%.

Si: Si may not be added. If added, it not only promotes deoxidation of steel, but also has the effect of improving hardenability. In order to surely obtain these effects, the Si content is preferably 0.05% or more. However, if its content exceeds 1.50%, the hot workability is extremely deteriorated and cracks are likely to occur during hot working. Therefore, the Si content is set to 1.50% or less. The upper limit of the Si content is 1.00 in order to secure further stable hot workability.
It is desirable to set it as%.

Mn: Mn is necessary for deoxidation and has the action of improving hardenability and improving static strength. However, if the content is less than 0.30%, the desired effect cannot be obtained, and 2.00%
%, The hot workability will deteriorate, so the content was made 0.30 to 2.00%.

P: P may not be added. If added, it has the effect of causing grain boundary embrittlement and lowering ductility, so it is effective in obtaining a flat brittle fracture surface by the above-described division method at room temperature. To ensure this effect, P is 0.005%
The above content is preferable. However, if the content exceeds 0.15%, the hot workability deteriorates significantly. Therefore, P in the invention of (1) and the invention of (3)
Content of 0.15% or less, in the invention of (2)
P content is 0.15% or less (however, 0.04% or more
Except) . In order to secure stable hot workability, the P content in the invention of (1) and the invention of (3) is more preferably 0.10% or less.

S: S may not be added. If added, it has the effect of causing grain boundary embrittlement and lowering the ductility, so that it is effective in obtaining a flat brittle fracture surface by the above-described division method at room temperature, similar to P. Further, S has a function of improving the machinability at the time of drilling a bolt hole. In order to surely obtain these effects, the content of S is preferably 0.005% or more. However, if the content exceeds 0.10%, the hot workability deteriorates significantly. Therefore, the upper limit of the S content is set to 0.
It was set to 10%.

Cu: Cu need not be added. If added, it has the effect of enhancing hardenability and improving static strength. In order to reliably obtain this effect, the content of Cu is preferably 0.01% or more. However, if the content exceeds 0.20%, the hot workability is deteriorated and cracks are generated during hot rolling or hot forging. Therefore, the Cu content is 0.2
It was set to 0% or less.

Ni: Ni may not be added. If added, it has the effect of enhancing hardenability and improving static strength. To ensure this effect, the Ni content is preferably 0.01% or more. However, if the content exceeds 0.50%, ductility and toughness increase, and a flat brittle fracture surface cannot be obtained. Therefore, the Ni content is set to 0.50% or less.

Cr: Cr has the effect of improving the hardenability and the static strength. However, if the content is less than 0.02%, the desired effect cannot be obtained, and if it is more than 2.00%, the effect is saturated, and only the cost increases and the economic efficiency is impaired. Therefore, the content is set to 0.02 to 2.00%. The Cr content is preferably 0.10% or more.

Mo: Mo may not be added. If added, it has the effect of improving hardenability and strength. In order to surely obtain this effect, the Mo content is preferably 0.01% or more. However, even if the content exceeds 0.50%, the above effect is saturated, so that only the cost increases and the economical efficiency is impaired. Therefore, the content of Mo is set to 0.50% or less. The Mo content is more preferably 0.05% or more.

V: V may not be added. If added, it has the effect of increasing strength. To ensure this effect, V is 0.005
It is preferable that the content be at least%. But 0.5
Even if the content is more than 0%, the above effect is saturated, and only the cost increases and the economic efficiency is impaired. Furthermore, the hot workability is deteriorated. Therefore, the V content is set to 0.50% or less.

Nb: Nb may not be added. If added, it has the effect of increasing strength. To ensure this effect, Nb is 0.0
The content is preferably 03% or more. But,
Even if the content exceeds 0.17%, the above effect is saturated,
Only the cost will rise and the economic efficiency will be impaired. Further, the hot workability is deteriorated. Therefore, from (1)
The content of Nb in the invention of Akira and (2) is 0.17%.
Below. In the invention of (3), 0.003
~ 0.17% Nb and 0.005-0.20% Ti
Either one or both were included. In addition,
In order to secure more stable hot workability, the upper limit of the Nb content is preferably 0.10%.

Ti: Ti may not be added. If added, it has the effect of increasing strength. Further, it has an effect of affecting the fracture mode of the non-heat treated steel at room temperature and promoting brittle fracture through the fn2 and fn3. To ensure these effects,
The Ti content is preferably 0.005% or more. However, if the content exceeds 0.20%, the hot workability deteriorates. Therefore, the invention of (1) and
In the inventions of (2) and (2), the Ti content is set to 0.20% or less. In the invention of (3), 0.005 to
0.20% Ti and 0.003-0.17% Nb
Either one or both of them are included. In order to secure more stable hot workability, the content of Ti is preferably 0.10% or less.

B: B may not be added. If added, it has the effect of improving hardenability and increasing strength. In order to surely obtain this effect, the content of B is preferably 0.0003% or more. However, if its content exceeds 0.0100%, not only the effect of improving the hardenability is saturated, but also the hot workability is significantly deteriorated. Therefore, the content of B is set to 0.0100% or less.

Al: Al may not be added. If added, it stabilizes the deoxidation of the steel and homogenizes it, and also has the effect of forming nitrides to refine the crystal grains and increase the strength. Further, it affects the fracture mode of non-heat treated steel at room temperature, and the fn1,
It has the effect of promoting brittle fracture through fn3. In order to reliably obtain these effects, the content of Al is preferably 0.005% or more. However, if the content exceeds 0.100%, the hot workability is deteriorated. Therefore, A in the invention of (2) and the invention of (3)
In the invention of (1), the content of 1 is 0.100% or less .
Al content of 0.100% or less (however, 0.00
5% or less) .

N: N may not be contained. If it is contained, it has the effect of forming nitrides and carbonitrides to refine the crystal grains and increase the strength. Further, in relation to Ti, Al, Nb, etc., it affects the fracture morphology of non-heat treated steel at room temperature.
When at least one of ≧ 0, fn2 ≦ 0 and fn3 ≧ 0 is satisfied, it has an effect of promoting brittle fracture. In order to surely obtain these effects, it is desirable that the content of N be 0.0030% or more. However, in general, in melting steel, in order to contain N in excess of 0.030%, special melting raw materials, equipment and technology are required, resulting in cost increase and economic loss. Inter-workability may be deteriorated. Therefore, the content of N is set to 0.030% or less.

Pb: Pb may not be contained. If contained, it has the effect of improving the machinability during bolt hole processing. In order to reliably obtain this effect, the Pb content is preferably 0.01% or more. However, if Pb is contained in an amount of more than 0.30%, the hot workability is deteriorated and cracks are generated during hot rolling or hot forging. Therefore, the Pb content should be 0.30.
% Or less.

Fn1, fn2, fn3: C exceeding 0.70%, Mn exceeding 0.30%, 0.0
The fracture mode of the non-heat treated steel containing 2% or more of Cr at room temperature can be summarized by the above-mentioned fn1, fn2 and fn3.
Brittle fracture is promoted when at least one of ≧ 0, fn2 ≦ 0 and fn3 ≧ 0 is satisfied. And fn1 ≧ 0,
satisfying at least one of fn2 ≦ 0 and fn3 ≧ 0,
In addition, when the elongation value of the steel material when subjected to the normal temperature tensile test is 10% or less, the room temperature split fracture surface of the hot forged integrally formed material becomes a flat brittle fracture surface, which is desired by the new process as described above. It is possible to manufacture a connecting rod body and a connecting rod cap having a tensile strength of 800 MPa or more, which is the strength. Therefore, fn
It is specified to satisfy at least one of 1 ≧ 0, fn2 ≦ 0 and fn3 ≧ 0.

The upper limit of the value of fn1 is not particularly limited, and may be 0.028 which is the upper limit value obtained from fn1.

The lower limit of the value of fn2 is not particularly limited, and may be the lower limit value of -0.06 obtained from fn2.

The upper limit of the value of fn3 is not particularly limited, and may be 0.028 which is the upper limit value obtained from fn3. In this case, fn1 = fn3.

Further, fn3 uses fn1, and fn3 =
fn1- (0.4Al + 0.3Ti + 0.15Nb +
0.3V + 1.3B). Therefore, f
When n3 ≧ 0, fn1 ≧ 0 is always satisfied.

The relation between fn2 and fn3 is as follows: fn3 = fn2- (0.5Al + 0.15Nb + 0.3
V + 1.3B + 0.002), and therefore fn2 ≦ 0 and fn3 ≧ 0 are not satisfied at the same time. From this, the promotion of brittle fracture in the case of fn2 ≦ 0 is based on the formation of carbides and carbonitrides of Ti, and the promotion of brittle fracture in the case of fn3 ≧ 0 and fn1 ≧ 0 is a so-called “free solid state”. It is considered that it is largely based on the "melted N".

Fn4: 800M required as a connecting rod body and a connecting rod cap only when the chemical composition of steel is strictly controlled and the value of fn4 is set to 0 or more.
A tensile strength of Pa or higher can be imparted to non-heat treated steel. Therefore,
Let fn4 ≧ 0. There is no particular upper limit to this value,
It may be the maximum value (value close to 2.23) obtained from fn4.

The steel having the above-mentioned chemical composition is melted by a usual method, and then, for example, by hot rolling and forging by a usual method, the connecting rod body 1 and the connecting rod cap 2 are connected to each other. After being molded into, it is subjected to bolt hole processing. Then, the connecting rod body 1 and the connecting rod cap 2 are divided at room temperature by the method described above. In addition,
If necessary, a notch of 0.5 mmR or less may be provided in at least a part of the inside (N portion in FIG. 1) of the large end hole which is a portion to be divided into the one body. Next, the connecting rod body 1 and the connecting rod cap 2 which are divided are connected to the crankshaft with bolts 3 and assembled.

[0045]

EXAMPLE Steels having the chemical compositions shown in Tables 1 to 3 were melted in a test furnace by a usual method. Steels 1 to 3 in Tables 1 and 2
0 is the steel of the present invention, and steels 31 to 44 in Table 3 are comparative steels in which any of the components thereof is out of the range of the content specified in the present invention.

Next, these invented steels and comparative steels were formed into billets by a usual method, heated to 1250 ° C., and then hot forged into a round bar having a diameter of 30 mm at a temperature of 1200 to 950 ° C., Then, it was cooled to room temperature by air.

A JIS No. 4 test piece was cut out from the thus-obtained hot-forged round bar and a tensile test was conducted at room temperature. Furthermore, the state of the fracture surface after the room temperature tensile test was observed with a scanning electron microscope (SEM).

The surface of the round bar hot forged to 30 mm was visually observed to confirm the presence of forging cracks.

Tables 4 and 5 show the results of the tensile test at room temperature, the results of observation of fracture surfaces and the results of confirmation of forging cracks.

In the steels 1 to 30 of the present invention, forging cracks did not occur, and the desired 800MP was obtained.
A tensile strength of a or more and an elongation of 10% or less were obtained, and the fracture surfaces after the room temperature tensile test were all flat brittle fracture surfaces (see Table 4).

On the other hand, among the comparative steels in which any of the components deviates from the content range specified in the present invention, the C content,
Si amount, P amount, S amount, V amount, Nb amount, Ti amount, B amount, A
Among the inventions in which the amount of l and the amount of Pb are (1) to (3) respectively
31-34 , which is higher than the highest specified value in
Also, hot forging cracks were observed in the steels 36 to 41.
In the steel 35 in which the Ni content deviated a little from the specified value of the present invention, the room temperature elongation exceeded 10%, and the fracture surface after the room temperature tensile test was a ductile fracture surface. Steel 42 and 43 are fn1 ≧ 0, fn2 ≦
Neither 0 nor fn3 ≧ 0 was satisfied, and since the room temperature elongation exceeded 10%, all fracture surfaces after the room temperature tensile test were ductile fracture surfaces. Since the steel 44 had a negative value of fn4, the tensile strength did not reach the target 800 MPa (see Table 5 above).

Then, using the steels 2 and 12 which are the steels of the present invention shown in Table 1 above as raw materials, by a normal hot forging method, 20 connecting bodies each of which the connecting rod body 1 and the connecting rod cap 2 are connected are formed. Each was hot formed. In addition, after hot forming, 5 out of each 20
A notch of 0.3 mmR was made in the N portion of FIG. Then, a split test was performed on the connecting rod body 1 and the connecting rod cap 2 at room temperature by the method described above. As a result, it was found that a flat brittle fracture surface was obtained in all 20 of both steels and that they could be used without finish shaping by machining. In addition, it was particularly easy to divide each of the five notched steel bodies.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

[Table 5]

[0058]

EFFECTS OF THE INVENTION By using the high-strength, low-ductility non-heat treated steel according to the present invention, it is possible to manufacture the connecting rod body and the connecting rod cap by a new process at a low cost, and the industrial effect is great.

[Brief description of drawings]

FIG. 1 is a diagram showing details of a connecting rod.

Claims (3)

(57) [Claims] 1. C: in excess of 0.70% by weight, 1.20
%, Si: 1.50% or less, Mn: 0.30-2.
00%, P: 0.15% or less, S: 0.10% or less, C
u: 0.20% or less, Ni: 0.50% or less, Cr:
0.02-2.00%, Mo: 0.50% or less, V:
0.50% or less, Nb: 0.17% or less, Ti: 0.2
0% or less, B: 0.0100% or less, Al: 0.100
% Or less (excluding 0.005% or less) , N: 0.0
30% or less, Pb: 0.30% or less, and the balance is F
e and unavoidable impurities, fn1 ≧ 0, fn2 ≦ 0
And satisfying at least one of fn3 ≧ 0, and fn
High-strength, low-ductility non-heat treated steel characterized by 4 ≧ 0. However, fn1 = N-0.1Al-0.002, fn2 = N-0.3Ti, fn3 = N-0.5Al-0.3Ti-0.15Nb-
0.3V-1.3B-0.002, fn4 = C + (Si / 10) + (Mn / 5) + (5Cr
/22)+1.65V-(5S/7)-0.8, In addition, the element symbol in a formula represents the content in the weight% of the element. 2. % By weight, C: exceeds 0.70% and 1.20
%, Si: 1.50% or less, Mn: 0.30-2.
00%, P: 0.15% or less (however, 0.04% or more
Excluding), S: 0.10% or less, Cu: 0.20% or less,
Ni: 0.50% or less, Cr: 0.02 to 2.00%,
Mo: 0.50% or less, V: 0.50% or less, Nb:
0.17% or less, Ti: 0.20% or less, B: 0.01
00% or less, Al: 0.100% or less, N: 0.030
% Or less, Pb: 0.30% or less, and the balance is Fe and
And unavoidable impurities, fn1 ≧ 0, fn2 ≦ 0 and
At least one of fn3 ≧ 0 is satisfied, and fn4 ≧
High strength and low ductility characterized by being 0 Non-heat treated steel. However
Then fn1 = N-0.1Al-0.002, fn2 = N-0.3Ti, fn3 = N-0.5Al-0.3Ti-0.15Nb-
0.3V-1.3B -0.002, fn4 = C + (Si / 10) + (Mn / 5) + (5Cr
/22)+1.65V -(5S / 7) -0.8, In addition, the element symbol in the formula is the content of the element in% by weight.
Represent 3. % By weight, C: more than 0.70% and 1.20
%, Si: 1.50% or less, Mn: 0.30-2.
00%, P: 0.15% or less, S: 0.10% or less, C
u: 0.20% or less, Ni: 0.50% or less, Cr:
0.02-2.00%, Mo: 0.50% or less, V:
0.50% or less, Nb: 0.003 to 0.17% and T
i: either 0.005 to 0.20%, or both,
B: 0.0100% or less, Al: 0.100% or less,
Contains N: 0.030% or less, Pb: 0.30% or less
However, the balance consists of Fe and unavoidable impurities, and fn1 ≧
0, satisfying at least one of fn2 ≦ 0 and fn3 ≧ 0
And high strength characterized by fn4 ≧ 0
Low ductility non-heat treated steel. However, fn1 = N-0.1Al-0.002, fn2 = N-0.3Ti, fn3 = N-0.5Al-0.3Ti-0.15Nb-
0.3V-1.3B -0.002, fn4 = C + (Si / 10) + (Mn / 5) + (5Cr
/22)+1.65V -(5S / 7) -0.8, In addition, the element symbol in the formula is the content of the element in% by weight.
Represent