JPH11279698A - Non-heat treated steel for hot forging with easy fracture separation and its products - Google Patents

Abstract

(57) [abstract] (with correction) [PROBLEMS] To form an ingot material by hot forging into a machine structural part shape and use it without tempering, and to use it after separating into two or more parts and combining them. Provided is a non-heat-treated steel for hot forging, which can be separated by rupture, does not cause plastic deformation of a fracture surface, and has high fatigue strength of a material, and a connecting rod for an engine using the steel. SOLUTION: C: 0.2 to 0.6% by weight, Si:
0.1-3.0%, Mn: 0.1-1.8%, Cr:
0.1-1.0%, V: 0.1-0.5%, P: 0.0
5 to 0.20%, As: 0.0001 to 0.020%,
Sb: 0.001 to 0.020%, Sn: 0.005 to
0.030%, (However, As + Sb + Sn ≦ 0.03
0%) sol-Al: 0.005 to 0.045%, N: 0.
A non-heat treated steel for hot forging having an alloy composition of 005 to 0.030%, with the balance being substantially Fe, and having a hardness of 35 HRC or less after hot forging.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-heat treated steel for hot forging, which can be easily broken and separated, and a product thereof, particularly a connecting rod for an internal combustion engine.

[0002]

2. Description of the Related Art For example, in order to manufacture a connecting rod for an automobile engine, as shown in FIG. 1, a blank having a shape gradually increasing from a narrow end to a wide end is formed by hot forging or the like. Formed by means, a small-diameter hole (21) through which the pin of the piston passes is made in the narrow end (2), and a large-diameter hole (11) for grasping the crankshaft is made in the wide end (1). In this method, a screw hole is cut through the two parts of the main body (3) and the half ring (4), and the hole is fixed by a bolt (5). However, this method not only cuts off excess material as a cutting margin in the cut portion, but also requires finishing the separation surface by cutting or polishing after cutting, which increases the number of steps and increases the cost.

As a solution to this problem, in recent years, the cutting of the wider portion of the forged product has been replaced with a break, and the cut surface has been combined and fixed with bolts.
With this method, the original shape is reproduced by combining the irregular fracture surfaces, so there is no need to cut the screw hole so that it penetrates the two parts. For example, as shown in FIG. If the screw hole (6) is used, there is an advantage that the other may be a straight hole (7).

[0004] In a mechanical part of a type in which such a forged part is broken, divided into two parts, and recombined,
While it is first required that it be easy to break and break from where expected, mass-produced machine parts, such as connecting rods, in particular, must not be very hard. As is well known, hard materials have poor machinability and low productivity.

[0005] As a means for obtaining a material which is easy to break, sintering a metal powder and forging a sintered product into a part having low toughness may be considered. The knot forging itself is a complicated process and low productivity,
With regard to cost, it is difficult to obtain the effect of improvement.

A component obtained by hot forging a general ingot material has a hardness of 18 to 35 HR used as steel for machine structural use.
Since it has sufficient toughness in the range of C, if it is divided by fracture, large plastic deformation occurs in the fracture surface unlike a powder sintered product, and it is difficult to accurately match the separated fracture surface. .

[0007]

SUMMARY OF THE INVENTION It is a general object of the present invention to form an ingot material into a shape for a machine structure by hot forging and to use it without heat treatment. Non-heat treated steel for hot forging that can be used to separate by breaking rather than cutting, so that the plastic deformation of the fracture surface does not matter, while the fatigue strength of the material can be obtained sufficiently high Is to provide.

It is a specific object of the present invention to provide a mechanical part, especially a connecting rod for an engine, made using this material.

[0009]

The non-heat treated steel for hot forging which achieves the general object of the present invention has a C: 0.2 to 0.2% by weight.
0.6%, Si: 0.1 to 3.0%, Mn: 0.1 to
1.8%, Cr: 0.1 to 1.0%, V: 0.1 to 0.
5%, P: 0.05 to 0.20%, and As:
0.0001-0.020%, Sb: 0.0001-
0.020%, and Sn: 0.0005 to 0.030
%, So that As + Sb + Sn ≦ 0.030%, sol-Al: 0.005 to 0.045% and N: 0.005 to 0.030%, and the balance is substantially Fe And the hardness after hot forging is 35 HRC or less.

[0010] A non-heat treated steel product for hot forging that achieves the specific object of the present invention is made of a non-heat treated steel for hot forging having the above-mentioned alloy composition and easy to break and is subjected to impact after forming. This is a product that is used in combination with a fracture surface by fracture and separation, and a specific example is a connecting rod for an internal combustion engine.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The non-heat treated steel for hot forging according to the present invention, which is easy to fracture and separate, has a Pb: 0.
3% or less, S: 0.2% or less, Te: 0.3% or less, C
a: 0.01% or less, and Bi: 0.30% or less 1
It may be an alloy composition containing two or more species.

The function of each alloy component and the reason for limiting the composition range will be described below.

C: 0.2-0.6% C is an element necessary for securing the strength, and therefore, it must be contained in an amount of 0.2% or more. But,
If the content is too large, the hardness becomes too high and the machinability decreases, so the content is set to 0.6% or less.

Si: 0.1-3.0% In addition to acting as a deoxidizing agent, Si forms a solid solution in ferrite and improves the ferrite strength of the soft layer which is the main cause of plastic deformation during fracture separation. Increase the brittle fracture rate,
Improve the adhesion of the fracture surface. In order to obtain this effect, the content needs to be 0.10% or more. On the other hand, if the content is too large, the hardness becomes too high, thereby reducing the machinability and deteriorating the hot workability. Therefore, the upper limit of the addition amount is 3.0%.

Mn: 0.1-1.8%, Cr: 0.1-1.0% Mn and Cr are effective components for securing strength, and Mn is also a deoxidizing agent. In order to obtain such effects, both require addition of 0.1% or more. If it is added excessively, bainite is generated during air cooling after forging, and the hardness becomes too high, thereby significantly reducing machinability.
Therefore, the upper limit of the addition amount is 1.8% for Mn and 1.0% for Cr.

V: 0.1 to 0.5% V is an essential component for non-heat treated steel. Like Si, it is an element that strengthens ferrite, improves the adhesion of the fracture surface, and greatly contributes to the improvement of the fatigue strength. This effect can be obtained by adding 0.1% or more, but adding a large amount excessively increases the hardness, deteriorates machinability, and is disadvantageous in terms of cost. From this viewpoint, 0.5% is the limit of the addition amount.

P: 0.05 to 0.20% P is known as an element which segregates at the grain boundary and lowers the toughness, and its content is usually kept low. The steel is actively used for the purpose of causing grain boundary destruction and improving the adhesion of the fracture surface. This effect can be obtained in the presence of a small amount of about 0.05%. On the other hand, even if a large amount is added, the effect is saturated and the hot workability is lowered.

As: 0.0001-0.020%, S
b: 0.0001 to 0.020%, and Sn: 0.0
005 to 0.030% by As + Sb + Sn ≦ 0.03
0% In general, the content of AS, Sb and Sn as impurities that impair toughness and hot workability even in a small amount is usually kept low. In the present invention, since these elements have an effect of greatly improving the adhesion of the fracture surface, P
In conjunction with, is actively used. The effect is A
s is 0.0001%, Sb is 0.0001%, and Sn is 0.0005%. Even if it is added in a large amount, its effect is saturated and the adverse effect of reducing hot workability becomes remarkable.
b is 0.020%, Sn is 0.030%, and As + Sb + Sn is 0.030%.
Not to exceed.

Sol-Al: 0.005 to 0.045% Acid-soluble Al forms nitrides with N in the steel and is finely dispersed to suppress the growth of crystal grains during hot forging. To ensure this effect, the presence of 0.005% or more is required. Even if present in a large amount, the effect is saturated, so that the addition is limited to the upper limit of 0.045% or less.

N: 0.005 to 0.030% N forms a nitride with Al and acts to suppress the growth of crystal grains during the hot forging described above. For that, 0.005
% Or more is required. This effect is due to the above A
As with l, the addition amount is saturated with an increase in the addition amount. Therefore, the addition amount is selected in the range up to the upper limit of 0.030%.

Pb: 0.3% or less, S: 0.2% or less,
Te: 0.3% or less, Ca: 0.01% or less, and B
i: One or more of 0.30% or less These are all machinability improving elements, and when high machinability is required in the processing of a forged product, they can be appropriately selected and added. Recommended. However, if the amount of addition is excessive, the hot workability and the fatigue limit are reduced, so the addition should be made within the above-mentioned limits.

It is necessary that the hardness after hot forging is not more than 35 HRC in order to guarantee the ease of machining.
This can be easily realized by appropriately selecting the amounts of the components that affect the hardness, such as C, Si, Mn, and Cr.

[0023]

EXAMPLES Steel having an alloy composition (% by weight, balance Fe and impurities) shown in Table 1 (Example) and Table 2 (Comparative Example) was melted in a vacuum induction furnace and cast into a 50 kg ingot.

Table 1 (Example) No. CSiMnPCrVAsSbSnsS-AlN, etc.1 0.25 0.61 0.62 0.102 0.20 0.25 0.0005 0.0004 0.0011 0.019 0.009 2 0.35 0.60 0.61 0.101 0.20 0.24 0.0005 0.0004 0.0012 0.021 0.009 3 0.45 0.60 0.60 0.103 0.20 0.25 0.0005 0.0006 0.0011 0.021 0.008 4 0.34 2.49 0.61 0.101 0.19 0.25 0.0005 0.0005 0.0010 0.020 0.011 5 0.35 0.60 1.52 0.098 0.20 0.25 0.0005 0.0005 0.0009 0.020 0.010 6 0.35 0.60 0.60 0.102 0.80 0.24 0.0005 0.0003 0.0008 0.021 0.011 0.7 0.3 0.59 0.060 0.20 0.25 0.0005 0.0004 0.0008 0.022 0.011 8 0.34 0.59 0.61 0.184 0.20 0.25 0.0005 0.0006 0.0009 0.018 0.010 9 0.35 0.60 0.61 0.102 0.20 0.40 0.0005 0.0006 0.0011 0.019 0.010 10 0.35 0.60 0.60 0.097 0.21 0.25 0.0012 0.0004 0.0011 0.019 0.009 11 0.35 0.61 0.60 0.098 0.20 0.25 0.0005 0.0011 0.0011 0.021 0.011 12 0.36 0.61 0.60 0.102 0.20 0.25 0.0005 0.0006 0.0019 0.020 0.012 13 0.35 0.60 0.60 0.100 0.20 0.26 0.0005 0.0005 0.0011 0.036 0.011 14 0. 35 0.60 0.60 0.101 0.20 0.25 0.0005 0.0005 0.0010 0.018 0.025 15 0.35 0.60 0.61 0.101 0.20 0.25 0.0005 0.0004 0.0010 0.018 0.011 Bi 0.1 16 0.35 0.60 0.61 0.100 0.20 0.25 0.0005 0.0006 0.0009 0.020 0.011 S 0.05 Pb 0.1 17 0.34 0.61 0.60 0.100 0.21 0.25 0.0005 0.0006 0.0009 0.021 0.012 S 0.05 Te 0.013 18 0.35 0.60 0.60 0.100 0.20 0.25 0.0005 0.0006 0.0008 0.021 0.009 S 0.05 Pb 0.15 Ca 0.002 Table 2 (Comparative Example) No. C Si Mn P Cr V As Sb Sns-Al N Other A 0.10 0.60 0.60 0.101 0.20 0.25 0.0005 0.0004 0.0010 0.024 0.009 B 0.71 0.60 0.59 0.099 0.20 0.25 0.0005 0.0005 0.0010 0.023 0.010 C 0.35 4.01 0.60 0.099 0.20 0.25 0.0005 0.0004 0.0011 0.023 0.010 D 0.35 0.60 0.60 0.003 0.20 0.25 0.0005 0.0005 0.0011 0.022 0.010 0.23 0.660 0.60 0.19 0.26 0.0005 0.0005 0.0012 0.022 0.011 F 0.36 0.60 2.00 0.100 0.20 0.25 0.0005 0.0005 0.0011 0.021 0.011 G 0.35 0.60 0.60 0.100 1.20 0.25 0.0005 0.0006 0.0010 0.020 0.012 H 0.35 0.60 0.60 0.102 0.20 0.05 0.0005 0.0007 0.0010 0.020 0.011 I 0.36 0.62 0.60 0.101 0.20 0.60 0.0005 0.0007 0.0011 0.022 0.010 J 0.36 0.60 0.61 0.100 0.20 0.25 0.0250 0.0005 0.0010 0.022 0.010 K 0.35 0.60 0.60 0.098 0.20 0.25 0.0005 0.0253 0.0012 0.023 0.009 L 0.35 0.61 0.60 0.100 0.205 0.26 0.0037 0.022 0.011 M 0.35 0.60 0.60 0.100 0.21 0.25 0.0015 0.0014 0.0011 0.021 0.011 N 0.35 0.60 0.60 0.100 0.20 0.25 0.0010 0.0010 0.0019 0.022 0.009 O 0.35 0.60 0.61 0.102 0.20 0.24 0.0005 0.0004 0.0012 0.022 0.010 Pb 0.35 P 0.35 0.60 0.60 0.101 0.20 0.25 0.0005 0.0004 0.0011 0.021 0.009 S 0.30 Bi 0.32 Q 0.35 0.60 0.61 0.101 0.20 0.24 0.0005 0.0005 0.0012 0.021 0.009 S 0.10 Pb 0.35 R 0.35 0.25 0.80 0.015 0.10 0.10 − − − 0.0020 0.010 Hot roll the above ingot at 1200 ° C. The material was 50 mm square. After keeping this material at 1200 ° C. for 60 minutes, it was forged into a round bar having a diameter of 22 mm and cooled to room temperature. A test piece was cut out from the obtained round bar having a diameter of 22 mm, and the hardness HRC and the elongation at break were measured.
Elongation at break is notch depth 1 mm, notch angle 60 degrees, notch bottom radius 0.2 mm, notched, minimum part diameter 8 mm
Is the amount of permanent deformation when the tensile test piece is broken at room temperature at a tensile speed of 10 mm / sec. As will be easily understood, it can be said that the smaller the amount of deformation, the higher the adhesion of the fracture surface of the two parts obtained by fracture.

The above results are shown in Tables 3 and 4, together with the presence or absence of cracks during hot forging.

Some of the samples were subjected to a drill test under the following conditions to evaluate the machinability. Together,
The results are shown in Tables 3 and 4. The machinability data in the table is No.
This is a relative value with the value of 2 being 100. Tool: SKH51 Feed: 0.1mm / rev Hole depth: 10mm Tool life evaluation: Cannot be cut.

Table 3 (Example) No. Hot forging crack Hardness HRC Elongation at break (mm) Machinability 1 None 18.8 0.22-2 -2 None 22.9 0.13 100 3 None 28.2 0 0.000 None 29.7 0.00-5 None 30.4 0.00-6 None 29.8 0.00-7 None 23.6 0.09-8 None 23.4 0.07-9 None 31.2 0.00-10 None 23.7 0.11-11 None 22.3 0.17-12 None 22.7 0.11-13 None 23.2 0.12-14 None 23.9 0. 06-15 None 24.3 0.04 334 16 None 22.7 0.07 251 17 None 23.6 0.14 262 18 None 24.5 0.11 451 Table 4 (Comparative example) No. Hot forging crack Hardness HRC Elongation at break (mm) Machinability A None 12.0 0.54-B None 38.4 0.00-C Yes 35.4 0.00-D No 23.8 1.23-E Yes 23.1 0.00-F No 38.7 0.00-G No 38.5 0 .00 -H None 15.6 0.90 -I None 39.0 0.00 -J Yes 25.6 0.16 -K Yes 22.6 0.27 -L Yes 23.0 0.26 -M Yes 23.2 0.18 -N Yes 24.6 0.13 361 O Yes 23.6 0.07 -P Yes 24.2 0.09 512 Q Yes 22.1 0.09 431 R No 16.8 21-As can be seen from the data in Table 3, all of the steels 1 to 18 having the alloy composition according to the present invention have an appropriate hardness, a small breaking elongation, and no cracks during forging. .
Steels 15 and 18 have improved machinability by adding free-cutting elements without impairing hot workability. On the other hand, each steel of the comparative example did not achieve the expected results as shown in the data of Table 4.

Specifically, first, steel A has a large elongation at break because of low C content and insufficient hardness. Steel B is
Conversely, the C content is high and too hard. Although data is not shown, it is naturally predicted that the machinability is low. Steel C also
Since the amount of Si is excessive, it is hard, and the properties are the same as those of steel B. Steel D has a low P content and therefore a large elongation at break. This is presumably because grain boundary strength fracture is unlikely to occur. Contrary to this, steel E has too much P, and hot workability is impaired, so that forging cracks occur. Steels F and G have too high contents of Mn or Cr and are high in hardness. It is thought that bainite was generated during cooling, and the machinability is expected to be poor. Steel H has a low V content, low ferrite hardness, and large elongation at break. Since the steel I has too much V and has too high hardness, the machinability is low.
Steels J, K and L have too high contents of As, Sb or Sn and have poor hot workability. Steels M and N are As + S
Since b + Sn exceeds 0.03%, the hot workability is still poor. Steels O, P and Q are Pb, S
Alternatively, the Bi content is high and there is a problem in hot workability.

Although steel R is a known steel type, it has a composition without addition of As, Sb, and Sn, which is one of the features of the present invention, so that the elongation at break is too large, and parts used in combination after fracture separation are used. Not suitable for the manufacture of

[0030]

The non-heat treated steel for hot forging according to the present invention positively utilizes P and As, Sb and Sn, which are excluded as unfavorable components in ordinary steel for machine structural use, and uses an appropriate amount of each. By the addition, a forged product which is easy to break, has small breaking elongation, and therefore has high adhesion of the fracture surface was successfully obtained. The hardness of this steel can be suppressed to a limit advantageous for machining by appropriately selecting the amount of the alloy component. Machinability can be improved by adding a free-cutting element without impairing hot workability. In this way, the non-heat treated steel for hot forging of the present invention is suitable as a material for mechanical parts used in combination after breaking and separating, especially for connecting rods of engines.

[Brief description of the drawings]

FIG. 1 shows an example of a connecting rod which is a typical product made of the non-heat treated steel for hot forging of the present invention.
FIG. 4 is a plan view showing a joint part with a part broken.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wide end 11 Large diameter hole 2 Narrow end 21 Small diameter hole 3 Main body 4 Half ring 5 Bolt 6 Screw hole 7 Straight hole

Claims (4)

[Claims] C. 0.2 to 0.6% by weight, Si:
0.1-3.0%, Mn: 0.1-1.8%, Cr:
0.1-1.0%, V: 0.1-0.5%, P: 0.0
5 to 0.20%, and As: 0.0001 to 0.
020%, Sb: 0.0001 to 0.020%, and Sn: 0.0005 to 0.030%, As + Sb + S
n ≦ 0.030%, and sol-A
l: 0.005 to 0.045% and N: 0.005 to
Non-temper for hot forging easy to break and separate, characterized by having an alloy composition containing 0.030% and the balance substantially consisting of Fe and having a hardness of 35 HRC or less after hot forging. steel. 2. In addition to the alloy component according to claim 1, P
b: 0.3% or less, S: 0.2% or less, Te: 0.3%
Or less, Ca: 0.01% or less, and Bi: 0.30%
A non-heat-treated non-heat treated steel for hot forging, which has an alloy composition containing one or more of the following, and is easily fracture-separated. 3. A non-heat treated steel for hot forging, which is easy to fracture and has the alloy composition according to claim 1 or 2, is used as a material.
A product that is given a shock after molding to break and separate, and then used in combination with each other. 4. The product of claim 3, which is a connecting rod for an internal combustion engine.