JPH0533101A - Non-heat treated steel for induction hardening crankshafts - Google Patents

Abstract

(57) [Summary] [Purpose] A non-heat treated steel for induction hardening crankshafts that does not require quenching and tempering, has a large difference in hardness due to the difference in cooling rate due to dimensional differences, and has excellent workability. I will provide a. [Composition] The material composition of the non-heat treated steel for crankshafts,
C: 0.40 to 0.52% by weight, Si: 0.10.
.About.0.40%, Mn: 1.00 to 1.50%, S: 0.
010 to 0.070%, Cr: 0.40 to 0.70%,
Pb: 0.02-0.35%, Ca: 0.0005-
0.0100%, O: 0.0040% or less, Al: 0.
025% or less, N: 0.005 to 0.015%, and the balance substantially Fe.

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 induction hardening crankshafts.

[0002]

2. Description of the Related Art Since a crankshaft receives a large inertial force, bending force, and torsional force, it is required to have strength and rigidity to withstand them. Therefore, as a material for such a crankshaft, a material obtained by tempering structural carbon steel (S45C, etc.) has been conventionally used.

In this case, the concrete manufacturing process of the crankshaft is such that after the steel material is forged, it is subjected to a heat treatment, that is, after quenching and tempering, it is mechanically processed, then induction hardened, and then ground. It will go through the process.

By the way, the tempering process consisting of quenching and tempering is a complicated process including a number of steps including the additional steps. Therefore, if a non-heat treated material that does not undergo quenching / tempering can be used as such a crankshaft material,
It is desirable because the manufacturing process of the crankshaft can be simplified.

Conventionally, non-heat treated steel is a steel to which elements such as V and Nb are added in a small amount, and carbides and nitrides are precipitated during air cooling after forging to increase hardness after cooling. It was done.

[0006]

However, in the case of the crankshaft, the dimensions vary greatly depending on the position, so that the cooling rate of each part becomes non-uniform during cooling, and carbides and nitrides of V, Nb, etc. There is a problem that the degree of precipitation becomes uneven and the difference in hardness becomes large.

[0007]

SUMMARY OF THE INVENTION The present invention provides such a V,
The purpose of the present invention is to provide a non-heat treated steel for crankshafts that can secure hardness without the addition of Nb and the like and that the difference in hardness does not increase due to the difference in dimensions. Is C: 0.40-0.
52%, Si: 0.10 to 0.40%, Mn: 1.00
˜1.50%, S: 0.010 to 0.070%, Cr:
0.40 to 0.70%, Pb: 0.02 to 0.35%,
Ca: 0.0005 to 0.0100%, O: 0.004
0% or less, Al: 0.025% or less, N: 0.005-
The material is composed so that 0.015% and the balance substantially consist of Fe.

The present invention does not add microalloys such as V and Nb, but adds C, Mn and Cr and adjusts the components to impart the required hardness to the matrix itself.

In the case of the heat-treated steel made of the medium carbon steel, the hardness of the central portion is lower than the hardness of the surface layer portion. On the other hand, according to the present invention, when the required hardness is secured by adding C, Mn, Cr and the like and adjusting the components, the hardness becomes substantially constant from the surface layer portion to the central portion in the air-cooled state after forging.

Therefore, if the hardness of the surface layer is made equal to that of the case of the heat-treated steel, the hardness of the central portion becomes harder, which causes a problem in workability.

In order to solve this, it is effective to add a free-cutting element. However, in the present invention, S, Pb,
It has been found that the combined addition of Ca is preferable.

[0012] These S and Pb form inclusions and cause a decrease in strength. In the present invention, Cr,
Mn has the effect of increasing the hardness of the matrix and the function of improving the toughness, and by doing so, it is possible to prevent the strength from decreasing due to inclusions such as S and Pb.

According to the present invention, in addition to the effect that the complicated heat treatment that has been conventionally required can be omitted, the difference in hardness due to the difference in dimensions, that is, the difference in cooling speed, in manufacturing the crankshaft can be reduced. In addition, the workability is good and the crankshaft can be manufactured at low cost.

Next, the reasons for limiting each component in the present invention will be described in detail. C, Mn, and Cr are elements necessary for adjusting the hardness after forging. C is necessary to secure the surface hardness after induction hardening, and the appropriate range is 0.40
It is 0.52%.

Mn and Cr increase the hardness of the matrix, improve the toughness, and prevent the strength from being lowered by inclusions such as S and Pb. The lower limits are 1.0% and 0.4, respectively.
Must be set to%.

On the other hand, if added in a large amount, bainite is formed to lower the strength and machinability.
It is necessary to set it to 5% and 0.7%.

S, Pb, and Ca are for ensuring workability. Appropriate values are S: 0.010 to 0.070%, Pb: 0.02 from the viewpoint of influence on strength and improvement of workability.
˜0.35%, Ca: 0.0005 to 0.0100%.

From the viewpoint that O and Al bring out the machinability improving effect of Ca and at the same time reduce the hard inclusions which are the starting points of fatigue, their upper limits are 0.0040%, 0.
It was set to 025%.

[0019]

EXAMPLES In order to further clarify the characteristics of the present invention, examples thereof will be described in detail below. The materials having the chemical components shown in Table 1 were melted in a 2 ton arc furnace, refined in a ladle, and cast into an ingot. This was hot-rolled to obtain a round bar having a diameter of 100 mm, and the round bar was used as a raw material, heated to 1200 ° C., forged round bar having a diameter of 25 mmφ and 50 mmφ, and air-cooled. In Table 1, C-1 to C-4 are comparative materials, of which C-4 was subjected to quenching at 850 ° C. and tempering at 600 ° C. after forging.

The obtained stepped round bar has hardness, machinability,
When the impact value and hardness after induction hardening were measured,
The results shown in Table 2 were obtained.

[0021]

[Table 1]

[0022]

[Table 2]

As can be seen from the results in Table 2, the steel of the present invention (N
In the case of o.1 to No.4), the hardness HRC20 to 29 required for the crankshaft is satisfied, and the impact value is also sufficient.

Further, the hardness after induction hardening is equivalent to C-4 in the case of the steel of the present invention, and the machinability is comparative material C.
It is superior to -4 and is effective in reducing the processing cost of the crankshaft.

C-1 has a C content less than the lower limit and lacks hardness, and C-2 has a C content higher than the upper limit and has a low impact value.

C-3 does not contain a free-cutting element and has poor drilling workability as compared with the refining material of C-4.

The embodiment of the present invention has been described in detail above, but this is merely an example, and the present invention can be configured in a mode in which various modifications are made based on the knowledge of those skilled in the art without departing from the spirit of the invention. is there.

Claims (1)

Claims: 1. C: 0.40 to 0.52% Si: 0.10 to 0.40% Mn: 1.00 to 1.50% S: 0.010 on a weight basis. 0.070% Cr: 0.40 to 0.70% Pb: 0.02 to 0.35% Ca: 0.0005 to 0.0100% O: 0.0040% or less Al: 0.025% or less N: 0.005 to 0.015% Non-heat treated steel for induction hardened crankshafts, the balance being substantially Fe.