JPS59232252A - Carburizing steel - Google Patents

Abstract

PURPOSE:To manufacture a carburized steel with high surface hardness by preparing a steel contg. specified percentages of C, Mn, Cr, Si and Al and by carburizing it to form a carburized surface layer contg. precipitated fine spheroidal carbides. CONSTITUTION:A steel consisting of, by weight, 0.1-0.3% C, 0.2-1.5% Mn, 1- 3% Cr (Mn+Cr<=3%), 0.5-1.5% Si and/or 0.2-1.5% Al and the blance Fe with impurities or further contg.one or more among 0.1-0.5% each of Mo, V, Ti, Zr and Nb+Ta is prepd. The steel is worked and carburized in an atmosphere having about 1.0-2.5% carbon potential to obtain structural parts having superior pitting resistance, fatigue strength and high dimensional accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a carburizing steel, and in particular to a carburizing steel that has a high hardness of the carburized layer on the surface after carburizing treatment and is suitable as a material for carburized parts with excellent pitting resistance and fatigue strength. It is something.

Conventionally, mechanical structural parts, such as gears, connecting rods, pinions, racks, bearings, bearing races, steering parts, etc., are often carburized to increase the surface l14 abrasion resistance and fatigue strength.

Conventionally, the materials for parts to which such carburizing treatment is applied include 5c14, SCr material, 30M material specified by JIS,
SMn material.

Structural steels such as SNC material and SNCM material are usually used.

On the other hand, in recent years, efforts have been made to reduce the weight of automobile parts, especially in order to improve the driving performance and fuel economy of automobiles. There is also a growing demand for miniaturization of power drain system parts. However, when the above-mentioned conventional structural steel is subjected to normal carburizing treatment, there is a problem that sufficient strength cannot be obtained, especially when the parts are downsized.

Therefore, it is desired to increase the strength of miniaturized parts, especially pitting resistance and fatigue strength.
It has also been considered to perform excessive carburization to increase surface hardness in order to improve pitting properties. However, when attempting to perform excessive carburization on conventional structural steel that has been used in two series, it is necessary to ensure that the carbon potential of the atmosphere is approximately 3% or more.
There was a problem in that the workability of the carburizing process was significantly lowered.

Special-purpose steels have been developed that are characterized by excessive carburization with such high carbon potential, but these are intended for large parts such as rolling rolls, and they contain large amounts of Cr and Mo. In addition to being expensive, especially when this special purpose steel is applied to small parts such as automobile parts, it has a high content of Cr and Mo. Therefore, since the hardenability is too good, the center of the part is hardened during the carburizing process, and when applied to gears, for example, there is a problem that residual stress at the root of the tooth decreases, resulting in a decrease in strength.

This invention was made by focusing on the above-mentioned conventional problems, and the carbon potential of the carburizing atmosphere is 2,
To obtain carburized parts that can be excessively carburized even when subjected to a normal carburizing treatment of about 5% or less, can significantly increase surface hardness, and have excellent pinching resistance and fatigue strength. The purpose is to provide carburizing steel that can be carburized.

The carburizing steel according to the present invention has C: 0.1-0 in weight percent.
．． 3%, Mn: 0.2 to 1.5%, Cr: 1 to 3%, and contains Mn+Cr≦3%, furthermore, Si: 0.5 to 1
．． 5%, AM: one or two of 0.2-1.5%
Contains seeds, if necessary, Mo: 0.1 to 0.5%.

V: 0.1-0.5%, Ti: 0.1-0.5%, Zr
: 0.1 to 0.5%, Nb+Ta (including the case where either one is O): 1 or 2 of 0.1 to 0.5%
If necessary, Cu: 1.5% or less, Ni: 2% or less to further increase strength, Cu: 5% or less to improve weather resistance, and machinability. Improved metal C3: 0, 4% or less, Pb: 0.4%
below.

Bi: 0.4% or less, Se: 0.4% or less.

Te: 0.1% or less, Ta: 0.5% or less, Ca: 0.01% or less, REM: to control the form of sulfide.
N: 0.1% or less, to control crystal grains. O1～
0.03% is appropriately selected and contained, and if necessary, B:O, 0O05% or less, to prevent coarsening of crystal grains.
To improve fatigue strength and cold forging property (0): 0.
0.0030% or less, more preferably 0.0020% or less,
S: O,0O10% or less, Sn which is a carburizing inhibiting element,
Sb, As, Zn: appropriately regulated to 0.0050% or less,
It is characterized in that fine spherical carbides are precipitated in the carburized layer after carburizing in a carburizing atmosphere with the balance consisting of Fe and impurities, more preferably a carbon potential of 1.0 to 2.5%.

Next, the reason for limiting the component range (wt%) of the carburizing steel according to the present invention will be explained.

C: 0.1-0.3% C is an element to be included in order to obtain the strength required for structural parts and surface hardness after carburizing treatment, but as mentioned above, the content is less than 0.1%. If it exceeds 0.3%, the toughness and cold forgeability will deteriorate, so the required strength and surface hardness cannot be obtained, so the content is set in the range of 0.1 to 0.3%.

Mn: 0.2 to 1.5% Mn is effective as a deoxidizing and desulfurizing element during steel making, but if it is less than 0.2%, the above deoxidizing and desulfurizing effects are small, and the carburizing treatment Sufficient surface hardness cannot be obtained. On the other hand, if it exceeds 1.5%, it becomes difficult to control hardenability and workability and machinability deteriorate. Therefore, the Mn content was set in the range of 0.2 to 1.5%. In order to obtain such an effect, the content is 1% or more. However, if the Cr content becomes too large, it becomes difficult to control the hardenability, so it is set in the range of 1 to 3%.

M n + Cr≦3% If the Mn and Cr contents are too high, it becomes difficult to control the hardenability of the steel as described above, and for example, when applied to gears, the hardenability is excessive and the tooth root Since the residual stress in the steel decreases and the strength decreases, it is necessary to set an upper limit for the total amount of Mn and Cr, and the total of Mn and Cr is set to 3% or less.

St: 0.5 to 1.5%, one or two types of A Bunji 0.2 to 1.5% Both Si and An precipitate carbides to ensure sufficient hardness of the carburized layer. , and for this purpose, S
It is necessary to contain 0.5% or more of t and 0.2% or more of An. However, if the content is too high, the toughness will deteriorate, so Si should be kept at 1.5% or less, and A
fl also needs to be 1.5% or less.

Mo: 0.1-0.5%, V: Q, l-0.5%, Ti
:0.1~0.5%, Zr:0.1~0.5%, Nb+
Ta: One or more of 0.1 to 0.5% Mo, V, Ti, Nb, and Ta are all effective in preventing coarsening of austenite crystal grains during carburizing treatment at high temperatures. Since these are elements, it is preferable to contain each of them in an amount of 1% or more, if necessary.

However, if the content exceeds 0.5% of each, the effect of preventing crystal grain coarsening will decrease, so
O, 5% (including the case where either one of Nb and Ta is O).

In addition to the above-mentioned basic elements, the steel for carburizing according to the present invention contains Cu: 1.5 to further increase the strength.
% or less, it is also desirable to contain Ni: 2% or less,
In order to improve weather resistance, it is also desirable to contain Cu: 5% or less, and in order to improve machinability, S: 0
．． 4% or less, Pb: o, 4% or less, Bi: 0.4% or less.

Se: 0.4% or less, Te: 0.1% or less.

It is also desirable to contain Ta: 0.5% or less, and in order to control the form of sulfides, Te: 0.1% or less, C
It is also desirable to contain it in a range such as a: 0.01% or less, REM: 0.1% or less, and in order to control crystal grains,
It is also desirable to contain N: 0.01 to 0.03%, and further, in order to prevent coarsening of crystal grains, B: 0.01% to 0.03% is contained.
(0): 0.0030% or less, more preferably 0.0005% or less, in order to improve fatigue strength and cold forging property
．． 0020% or less.

It is also desirable to regulate S: to 0.0010% or less, Sn, which is an element that inhibits carburization: 0.005% or less, Sb: 0
．． 005% or less, As: 0.005% or less, Zn: 0.005% or less, As: 0.005% or less, Zn: 0.
It is also desirable to regulate it to 0.005% or less.

Structural parts such as gears, ball joints, drive shafts, camshafts, steering parts, bearings, and bearing races are formed using the steel whose composition has been adjusted in this way, and then, more preferably, the carbon potential of the carburizing atmosphere is reduced to 1. By performing carburizing treatment in an atmosphere with a concentration of .0 to 2.5%, fine spherical carbides are precipitated in the carburized layer on the surface, resulting in high surface hardness and excellent pitting resistance and fatigue strength. , obtaining structural parts with good dimensional accuracy. Here, it is more desirable that the carbon potential of the carburizing atmosphere is 1.0 to 2.5%.
This is because if the carbon potential is too low, excessive carburization becomes difficult and it becomes impossible to increase the surface hardness by carburizing.On the other hand, if the carbon potential is too high, the usual simple carburizing treatment is not possible and the processing cost becomes extremely high. To become.

Examples of the present invention will be described below along with comparative examples.

After melting steel with the chemical composition shown in Table 1, it is made into an ingot, then bloomed and rolled into a product with a diameter of 25ml and a length of 11° and a length of 75mm.
+++++11 test pieces were produced. Next, each test piece was placed in a carburizing atmosphere with a carbon potential shown in Table 2.
Heating at 25℃ for 5 hours → 830'C! Cold sleeves (oil temperature 70°C)
) → Heating at 170°C for 1 hour → Carburizing and quenching was performed under the conditions of air cooling, and the structure of the carburized layer of each specimen was observed, and the hardness of the carburized layer at a depth of 0.1 mm from the surface layer was measured. . The results are shown in Table 2.

Table 1 Table 2 As is clear from Tables 1 and 2, the steels for carburizing (Nos. 2 to 10) according to the present invention had a carburizing effect when carburized in a carburizing atmosphere with a carphone potential of 1.25%. To,
Fine spherical carbides are precipitated in the carburized layer, and the hardness of the carburized layer is extremely large.The results show that when applied to gears, etc., the pitting resistance and fatigue strength can be significantly increased. Ta. On the other hand, it was also found that if the carbon potential in the carburizing atmosphere was too low, an increase in surface hardness due to excessive carburization could not be obtained.

Furthermore, steels that do not satisfy the composition range of this invention (No.
In 1), the carbon potential in the carburizing atmosphere is 1.
Even at 25%, no excessive carburized layer was formed and sufficient surface hardness could not be obtained.

As explained hereafter, the carburizing steel according to the present invention contains C: 0.1-0.3%, Mn: 0.2-1 in weight percent.
．． 5%, Cr: 1-3% and includes Mn+Cr≦3%, furthermore, Si: 0.5-1.5%, A text = 0.2-1
．． 1 or 2 of 5%, if necessary, Mo:
0.1-0.5%, V: 0.1-0.5%, Ti: 0.
1-0.5%, Zr: 0.1-0.5%, Nb+Ta:
It contains one or more of O, 1 to 0.5%, and the remainder consists of Fe and impurities, and fine spherical carbides are precipitated in the carburized layer after carburizing treatment, so the carburizing atmosphere is Excessive carburizing is possible even when performing normal carburizing treatment with a carbon potential of 2.5% or less, and this excessive carburizing can significantly increase surface hardness, improving pitting resistance and fatigue strength. excellent kiya,
It is possible to obtain carburized parts such as connecting rods, pins, ons, racks, bearings, bearing races, steering parts, etc., and even when these parts are miniaturized based on the demand for weight reduction, it is possible to perform normal carburizing treatment. This has significant effects, such as the fact that it can be made to have sufficiently excellent strength, and there is no need to carry out special carburizing treatment to carry out excessive carburizing as in the past.

Procedural Sleeve Letter (Spontaneous) June 20, 1980 Patent Office Wakasugi YF + 1 Husband 2 Invention 0 Name 72, Charcoal Servant 3 Relationship with the amended person case Applicant for the watch, m! l II: F, Hoshizaki-cho, Mon-ku, Nagoya, Aichi Prefecture■
Out 66 Suzuji m''”5 (Name) (371) Representative of Daido Shutsuri Co., Ltd. Autumn 1) True bullet 4, agent 6 Number of inventions increased by amendment 7, inventions with 1 word on 4 sides subject to amendment Detailed Explanation Column 8, Contents of Amendment As shown in Attachment 1, the following has been added between lines 15 and 16 on page 14 of the specification.

"Next, sooting tends to occur when the carbon potential is increased in general gas carburizing, but this type of sooting does not occur in vacuum carburizing, so
It is possible to increase carbon potential relatively easily. Therefore, from this point of view, it is more desirable to perform vacuum carburizing when excessive carburizing is performed, and J′! : Examples in the case of air carburizing will be explained together with comparative examples.

First, No., l, 2, 5, 6 shown in Table 1
, 8.

Test specimens with a diameter of 25 mm and a length of 75 mm prepared from No. 10 steel in the same manner as in the Examples and Comparative Examples were subjected to vacuum carburizing treatment in an immersion atmosphere with a carbon potential of 1.7%. In this vacuum carburizing process, in the above atmosphere,
The conditions were as follows: heating at 1040°C for 1.5 hours → quenching at 830°C oil cooling → tempering at 170°C for 1 hour. Thereafter, the carburized layer of each test piece was observed by group Fa, and the hardness of the carburized layer at a depth of 0.1 mm from the surface layer was measured. The results are shown in Table 3.

Table 3 As shown in Table 3, in the carburizing steel according to the present invention, fine spherical carbides were precipitated in the carburized layer even when vacuum carburizing was performed in a carburizing atmosphere with a carbon potential of 1.7%. It was confirmed that the hardness of the carburized layer was sufficient, and it was also confirmed that when the steel for carburizing according to the present invention is excessively carburized using 4' (dry carburizing). In the case of the comparative example, coarse net-like carbides precipitated due to high-temperature carburizing treatment, and the hardness of the carburized layer was also low, which was an unfavorable result.''

Claims (2)

[Claims] (1) In weight%, C: O, 1-0.3%, Mn: 0.2
~1.5%, Cr: 1~3%, and M n + Cr≦
3%, and further contains one or two of Si: 0.5-1.5%, A-20.2-1.5%, and the remainder is Fe and impurities, and is carburized. A carburizing steel characterized by the precipitation of fine spherical carbides in the subsequent carburized layer. (2) In weight%, C: 0.1-0.3%, Mn+0.2
~1.5%, Cr: 1-3%, and M n + Cr≦
Contains 3%, and further includes Si: 0.5 to 1.5%, A:
One or two of 0.2 to 1.5%, and Mo
:O, 1-0.5%. V: 0.1-0.5%, Ti: 0.1-0.5%, Zr
:0.1~0.5%, Nb+Ta:01~0.5%, the balance is Fe and impurities, and fine spherical carbides are formed in the carburized layer after carburizing. Steel for carburizing characterized by precipitation.