JPS5946301B2 - Steel for cold forging with excellent machinability and its manufacturing method - Google Patents

Description

Detailed Description of the Invention The present invention relates to steel for machine structural use, more specifically carbon steel, manganese steel, nickel-chromium steel, chromium-molybdenum steel, nickel, chromium-molybdenum steel, manganese-chromium steel, molyftene steel. , relates to steels with improved machinability and cold forgeability, such as nickel-1-molybdenum steels.

S is known as an element that impairs the cold forgeability of steel.

S in steel is easily stretched into a string shape along the forging direction during hot working (exists in the form of sulfides such as MnS, and these sulfides impair cold forgeability. Therefore, conventionally, low sulfur steel has been exclusively used as steel for cold forging by performing a desulfurization treatment during melting.However, low sulfur steel has the problem of poor machinability. The inventors of the present application investigated various component compositions in order to solve the above problem, and found that when Te was included depending on the S content, %T
When e/%S is larger than 0.04, sulfides such as MnS do not elongate in the forging direction, the anisotropy of mechanical properties becomes small, and furthermore, cold forgeability is excellent and machinability is improved. found a steel that was equivalent to or better than sulfur free-cutting steel and filed an application (Japanese Patent Application No. 114554/1983), and as a result of further research on improving cold forgeability, they found a steel with a low sulfur content. (S: 0.04% or less), %Te/%S
It has been discovered that cold forgeability can be markedly improved without deteriorating rigidity by making S and Te a composite metal with a content of 0.04% or more and further suppressing O and N. This was proposed as Japanese Patent Application No. 54-28619.

The present inventors have further completed the steel of the present invention, which suppresses the formation of Al2O3 by lowering the AI of the steel of Japanese Patent Application No. 54-28619 and further improves cold forgeability. That is, the gist of the present invention is firstly a cold forging steel with excellent machinability, which is characterized by having the following composition. (1) C: 0.6% or less, Sl: 0.5%
Hereinafter, Mn: 2.0% or less, S: 0.003 to 0.
04%, Te: 0.03% or less (however, %Te/%S:
0.04 or more), Al: less than 0.01%, N: 0.02
% or less, 0:0.003% or less, the remainder substantially consisting of Fe.

(2) C: 0.6% or less, Si: 0.5% or less, Mn:
2.0% or less, S2 0.003-0.04%, Te: 0
．． 03% or less (however, %Te/%S: 0.04 or more)
Al: less than 0.0t%, N: 0.02% or less, 0:0.
003% or less, further Ni: 4.5% or less, Cr: 3
．． 5% or less, MO: 1.0% or less, and the remainder substantially consists of Fe.

(3) C: 0.6% or less, Si: 0.5% or less, Mn:
2.0% or less, S: 0.003-0.04%, Te: 0
．． 03% or less (however, %Te/%S: 0.04 or more)
Al: less than 0.01%, N: 0.02% or less, 0:0.
003% or less, V: 2.0% or less, Nb: 0.5
% or less, Ti: 0.5% or less, B: 0.01% or less, Z
Contains one or more of r: 0.5% or less,
The remainder consists essentially of Fe.

(4) C: 0.6% or less, Si: 0.5% or less, Mn: 2.0% or less, S: 0.003 to 0.04
%, Te: -0.03% or less, (however, %Te/%
S: 0.04 or more), Al: less than 0.01%, N: 0.
02% or less, 0:0.003% or less, and further Pb:0.
01-0.30%, Se: 0.00:3-0.10%
, Bi: 0.01-0.30%, Ca: 0.0002
-0.01:% of one or more of these, with the remainder essentially consisting of Fe. (5) C: 0.6% or less,
Si: 0.5% or less, Mn: 2.0% or less, S: 0
．． 003 to 0.04%, Te: 0.03% or less (however, %Te/%S: 0.04 or more), Al: 0.01%
One or more of the following: N: 0.02% or less, 0: 0.003% or less, Ni: 4.5% or less, Cr: 3.5% or less, MO: 1.0% or less and V
: 2.0% or less, Nb: 0.5% or less, Ti: 0.5
% or less, B: 0.01% or less, Zr: 0.5% or less, and the remainder substantially consists of Fe.

(6) C: 0.6% or less, Si: 0.5% or less, Mn:
2.0% or less, S: 0.003-0.04%, Te
:? 0.03% or less (however, %Te/%S: 0.04
or more), Al: less than 0.01%, N: 0.02% or less,
0: 0.003% or less, further Ni: 4.5% or less,
Contains one or more of Cr: 3.5% or less, MO: 1.0% or less, and the remainder substantially consists of Fe.

(7) C: 0.6% or less, Si: 0.5% or less, Mn:
2.0% or less, S: 0.003-0.04%, Te
: 0.03% or less, (but %Te/%S: 0.04 or more), Al: less than 0.01%, N: 0.02% or less, O
: 0.03% or less, V: 2.0% or less, Nb: 0
．． 5% or less, Ti: 0.5% or less, B: 0.01% or less, Zr: 0.5% or less, and one or more of P
b: 0.01-0.3%, Se: 0.003-0.1
0%, Bi: 0.01-0.30%, Ca: 0.00
Contains one or more of 02 to 0.01%,
The remainder consists essentially of Fe.

(8) C: 0.6% or less, Si: 0.5% or less, Mn: 2.0% or less, S: 0.003 to 0.04
%, Te: 0.03% or less, (However, %Te/%S: 0
．． 04 or higher), Al: less than 0.01%, N: 0.02%
Below, 0: 0.003% or less, further Ni: 4.
5% or less, Cr: 3.5% or less, MO: 1.0% or less, V: 2.0% or less, Nb:
0.5% or less, Ti: 0.5% or less, B: 0.01% or less, Zr: 0.5% or less, and one or more of them;
Pb: 0.01-0.30%, Se: 0.003-0
．． 10%, Bi: 0.01-0.30%, Ca: 0
．． 0002 to 0.01%, and one or more of them;
Pb: 0.0i~0.3%, Se: 0.00:3-0
．． 10%, Bi: 0.01-0.30%, Ca: 0
．． 0002 to 0.01%, and the remainder essentially consists of Fe.

The gist of the present invention also extends to the following method suitable for producing the above-mentioned cold forging steel with excellent machinability.

(9) C: 0.6% or less, Si: 0.5% or less, Mn
: 2.0% or less, S: 0.003 to 0.04%, Al2 less than 0.01%, N: 0.02% or less, 0: 0.003
% or less, with the remainder substantially consisting of Fe, and in the process, during or after vacuum degassing,
By introducing a non-oxidizing gas into the molten steel and forcibly stirring it, large non-metallic inclusions are floated and separated, and then Te is reduced to 0.
0.03% or less and %Te/%S: 0.04 or more is added to the molten steel and uniformly dispersed in the molten steel.

Next, the reasons for limiting the composition of the steel of the present invention will be explained.

C: 0.6% or less It is an element necessary to ensure strength, but if it is contained in a large amount, toughness will decrease and cold forgeability will deteriorate, so 0.6%
Limited to the following.

Si: 0.5% or less It is effective as a deoxidizing element and is necessary to prevent the occurrence of surface defects in steel ingots, but if it is contained in a large amount, the toughness decreases and the base becomes hard, making it difficult to cold forge. Since the properties deteriorate, the content was limited to 0.5% or less.

Mn: 2.0% or less In addition to improving hardenability, it forms sulfides such as MnS and has the effect of preventing hot embrittlement caused by S, but if it is contained in a large amount, machinability deteriorates, so 2.0% Limited to the following.

S: 0.0003-0.04% To improve machinability, at least 0.003% is necessary.

However, if it is contained in a large amount, cold forgeability deteriorates, so the upper limit is set at 0.04%, and the range is 0.003 to 0.04%.
And so. Te: 0.03% or less S: 0.003 to 0.0
In order to obtain the necessary %Te/%S to suppress the elongation of sulfides such as MnS in steel containing 4%, it is desirable to contain a large amount, but even if the content is too large, the cooling Since the effect on the forgeability is not significantly improved, the upper limit was set at 0.03%.

%Te/%S: 0.04 or more The situation in which the elongation of sulfides such as MnS is suppressed as %Te/%S increases is as shown in Figure 1, and when this value is 0.04 or more, If you do, you will definitely get the desired effect.

0: 0.0030% or less Te is a harmful element as it generates oxides that become starting points for cracks during cold forging, and in order to fully exhibit Te's effect of improving cold forgeability, the content must be reduced to 0.0030% or less. It is necessary to keep it below 0.030%.

Especially when the cold working rate is extremely high, 0.0020
% or less. N: 0.020% or less An element that increases the deformation resistance of steel and reduces cold forgeability, and the content must be as low as possible, with an upper limit of 0.02%.
It was set to 0%.

In addition, when taking a particularly high cold working rate, the content should be reduced to 0.
．． It is preferable to set it to 0.015% or less. Al: 0.01
It was set to be less than 0.01 because it combines with oxygen to form hard Al2O3, which tends to become a starting point for cracks that occur during cold forging, and also wears out tools during cutting.

When the cold forging processing rate is particularly high, it is preferable to reduce the amount to 0.007% or less. Ni: 4.5% or less, Cr: 3.5% or less, MO: 1.0% or less The above three elements are elements necessary to improve toughness and temper softening resistance in the steel of the present invention. However, even if it is contained in a large amount, the effect does not improve proportionally, so Ni is 4
．． If necessary, the content may be selectively contained within the range of 5% or less, 3.5% or less for Cr, and 1.0% or less for MO.

B: 0.010% or less, V: 2.0% or less, Ti: 0.
5% or less, Nb: 0.5% or less, Zr: 0.5% or less These elements can improve the crystal structure or heat treatment characteristics by adding them to the basic component steel of previous revision 1). Therefore, it is more advantageous to include it selectively.

However, in order to avoid impairing the characteristics of the basic components, which have low sulfide expansion and excellent cold forgeability,
The content must be within the above range. Note that the above effects can be obtained from Ni, Cr, MO, Pb, S, as shown in the examples.
e, Bi. It was confirmed that this could also be obtained when a certain amount of Ca was selectively included. Pb: 0.01-0.30
%, Se: 0.003-0.10%, Bi: 0.0
1 to 0.30%, Ca: 0.0002 to 0.01% All of the above elements are effective in improving machinability in the steel of the present invention, but if they are contained in large amounts, cold Since forgeability deteriorates, Pb is 0.01 to 0.30% and S
e is 0.003 to 0.10%, Bi is 0.01 to 0.3
0%, and Ca is in the range of 0.0002 to 0.01%, and may be selectively contained as necessary.

Next, the present invention will be explained in detail with reference to Examples.

Example Alloy components other than Te, Pb, Bi, and Ca were adjusted to predetermined amounts in an experimental arc furnace, transferred to a vacuum degassing treatment container, and degassed, and then a porous plug was installed at the bottom. The molten steel was transferred to a ladle, and while forced stirring was performed by blowing argon gas into the molten steel from the porous plug, Te was adjusted to a value of %Te/%S of 0.04 or more depending on the S in the molten steel. Added so that

Thereafter, predetermined amounts of Pb, Bi, and Ca powder were added to the molten steel as required while blowing argon gas into the molten steel through a porous plug.

Note that Pb, Bi, and Ca can also be added to the melt flow when the melt is transferred to a ladle equipped with a gas blowing device after vacuum degassing treatment. A melting pot containing Te and optionally Pb, Bi, and Ca was heated to 1.
It was cast into a 3 ton pot block.

Next, this steel ingot is finished at a temperature of 950℃ or higher and a forging ratio of approximately 10.
Various test pieces were taken from the steel material obtained by hot rolling so as to have a value of 0 or more.

The composition of each sample material is shown in Table 1. In Table 1,
The specimens marked with * are comparative examples.

The scope of the claims of the present invention to which each sample material belongs is indicated in the claim column. Properties of sulfides In order to investigate the properties of sulfides in each sample material, the length (L) and width (W) of 200 sulfides were measured within a certain microscope field, and the length ratio (L/ The average value of W) was calculated and the results are also listed in Table 1.

Furthermore, the relationship between %Te/%S and the length ratio of sulfides is shown in FIG. Most of these sulfides are MnS, and it can be seen from this figure that when %Te/%S is greater than 0.04, the length ratio of the sulfides becomes 5 or less. Cold forgeability
Mvt test pieces of φ30 x 50 were created from test materials (partially used as rolled) that had been heat-treated suitable for each steel type in order to examine cold forgeability, and the processing rates were 60% and 65%, respectively. %, 70%
200 specimens were cold forged (amp set) for each level, and the presence or absence of cracks was observed using a 2.0x microscope. Table 2 shows the percentage of crack occurrence in the number of sample materials (200 pieces).

As is clear from the table, the crack occurrence rate of the steel of the present invention is much lower than that of the comparative steel, and the steel has excellent cold forgeability. Machinability The test materials shown in Table 2 were tested under the cutting conditions shown in Table 3 to examine their machinability.

The results are also listed in Table 2.

From the cutting test results shown in Table 2, it can be seen that the steel of the present invention has superior stiffness compared to the comparative steel.

As explained above, the steel of the present invention can be used in place of conventional steel for cold forging in order to contain appropriate amounts of Te and S.
By setting Te/%S to 0.04 or more and further limiting N and 0 to appropriate ranges, spindle-shaped sulfides can be effectively generated, and cooling can be achieved by lowering the Al content and reducing Al2O3. It is characterized by further improved forgeability and improved machinability, and has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the effect of %Te/%S ratio on sulfide morphology.

Claims (1)

[Claims] 1 C: 0.6% or less, Si: 0.5% or less, Mn: 2
．． 0% or less, S: 0.003-0.04%, Te: 0.
03% or less (however, %Te/%S: 0.04 or more),
Al: less than 0.01%, N: 0.02% or less, O: 0.
A steel for cold forging with excellent rigidity, characterized in that the remainder is substantially composed of Fe at 0.003% or less. 2 C: 0.6% or less, Si: 0.5% or less, Mn: 2
．． 0% or less, S: 0.003-0.04%, Te: 0.
03% or less (however, %Te/%S: 0.04 or more),
Al: less than 0.01%, N: 0.02% or less, O: 0.
003% or less, further Ni: 4.5% or less, Cr: 3.
5% or less, Mo: 1.0% or less, and the remainder substantially consists of Fe. A cold forging steel with excellent rigidity. 3 C: 0.6% or less, Si: 0.5% or less, Mn: 2
．． 0% or less, S: 0.003-0.04%, Te: 0.
03% or less (however, %Te/%S: 0.04 or more),
Al: less than 0.01%, N: 0.02% or less, O: 0.
003% or less, V: 2.0% or less, Nb: 0.5
% or less, Ti: 0.5% or less, B: 0.01% or less, Z
A cold forging steel with excellent machinability, characterized by containing one or more of r: 0.5% or less, with the remainder essentially consisting of Fe. 4 C: 0.6% or less, Si: 0.5% or less, Mn: 2
．． 0% or less, S: 0.003-0.04%, Te: 0.
03% or less (however, %Te/%S: 0.04 or more),
Al: less than 0.01%, N: 0.02% or less, O: 0.
003% or less, further Pb: 0.01 to 0.30%, S
e: 0.003-0.10%, Bi: 0.01-0.3
0%, Ca: 0.0002 to 0.01%, and the remainder is substantially Fe. Cold forging steel with excellent machinability. . 5 C: 0.6% or less, Si: 0.5% or less, Mn: 2
．． 0% or less, S: 0.003-0.04%, Te: 0.
03% or less (however, %Te/%S: 0.04 or more),
Al: less than 0.01%, N: 0.02% or less, O: 0.
003% or less, further Ni: 4.5% or less, Cr: 3.
5% or less, Mo: one or more of 1.0% or less, V: 2.0% or less, Nb: 0.5% or less, Ti:
0.5% or less, B: 0.01% or less, and Zr 0.5% or less. Steel for cold forging. 6 C: 0.6% or less, Si: 0.5% or less, Mn: 2
．． 0% or less, S: 0.003-0.04%, Te: 0.
03% or less (however, %Te/%S: 0.04 or more),
Al: less than 0.01%, N: 0.02% or less, O: 0.
003% or less, further Ni: 4.5% or less, Cr: 3.
5% or less, Mo: 1.0% or less, Pb: 0.01 to 0.3%, Se: 0.003
~0.10%, Bi:0.01~0.30%, Ca:0
．． A steel for cold forging having excellent rigidity, characterized in that the steel contains one or more of the following: 7 C: 0.6% or less, Si: 0.5% or less, Mn: 2
．． 0% or less, S: 0.003-0.04%, Te: 0.
03% or less (however, %Te/%S: 0.04 or more),
Al: less than 0.01%, N: 0.02% or less, O: 0.
003% or less, V: 2.0% or less, Nb: 0.5
% or less, Ti: 0.5% or less, B: 0.01% or less, Z
r: one or more of 0.5% or less and Pb:
0.01-0.3%, Se: 0.003-0.10%,
Bi: 0.01-0.30%, Ca: 0.0002-0
．． A steel for cold forging with excellent rigidity, characterized in that the steel contains one or more of the following: 8 C: 0.6% or less, Si: 0.5% or less, Mn: 2
．． 0% or less, S: 0.003-0.04%, Te: 0.
03% or less (however, %Te/%S: 0.04 or more),
Al: less than 0.01%, N: 0.02% or less, O: 0.
003% or less, further Ni: 4.5% or less, Cr: 3.
5% or less, Mo: 1.0% or less, V: 2.0% or less, Nb: 0.5% or less, Ti
: 0.5% or less, B: 0.01% or less, Zr: 0.5%
One or more of the following and Pb: 0.01~
0.30%, Se: 0.003-0.10%, Bi: 0
．． 01-0.30%, Ca: 0.0002-0.01%
A steel for cold forging with excellent rigidity, characterized in that it contains one or more of the following, with the remainder essentially consisting of Fe. 9 C: 0.6% or less, Si: 0.5% or less, Mn: 2
．． 0% or less, S: 0.003-0.04%, Al: 0.
0.01% or less, N: 0.02% or less, N: 0.003% or less, with the remainder substantially consisting of Fe, and in the process, during vacuum degassing or after degassing, in the molten steel. By introducing a non-oxidizing gas and forcibly stirring, large non-metallic inclusions are floated and separated, and then Te is reduced to 0.03
% or less and %Te/%S: 0.04 or more is added in an amount of 0.04 or more and homogeneously dispersed in molten steel.