JPH06145908A - Calcium free cutting stainless steel - Google Patents

Abstract

PURPOSE:To improve the machinability off stainless steel and to maintain its corrosion resistance by adding specified amounts of Ca and Al to an alloy contg. specified amounts of Cr and Fe and specifying the content of oxygen. CONSTITUTION:An alloy is constituted of, by weight, 10 to 30% Cr, and balance Fe with impurities. In this alloy, 10 to 100ppm Ca and 50 to 150ppm Al are added and the content of 0 is regulated to 50 to 150ppm to satisfy the conditions of Ca/O >=0.5 and Al/O >=0.5 by atomic ratios. Thus, at least 20% of oxide inclusions is occupied by gehlenite, 2CaO.Al2O3.SiO2. Thus, the deterioration in its corrosion resistance is prevented, and the effect of improving its machinability can be fulfilled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in calcium free-cutting stainless steel, which provides a stainless steel which has improved machinability and maintained corrosion resistance.

[0002]

2. Description of the Related Art Corrosion resistance decreases when S or Te is added to improve the machinability of steel. Therefore, an appropriate amount of Ca is added as a means for improving the machinability without significantly lowering the corrosion resistance. Has been. Ca forms a low-melting-point oxide inclusion, which has a lubricating effect on the cutting tool, which is the main mechanism for improving machinability.

However, in stainless steel, Ca
It cannot be said that the effect of improving the machinability due to the addition of is very high. Among oxide inclusions of Ca, those having a relatively low melting point and useful for improving machinability are anorthite CaO.A.
Although it is l ₂ O ₃ .2SiO ₂ (which has a lubricating effect on the tool in the temperature range of 1400 to 1600 ° C.), it is considered that a large amount of Cr is present in the stainless steel, which prevents the formation of anorthite.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide calcium free-cutting stainless steel in which Ca is added to stainless steel to prevent deterioration of its corrosion resistance and improve machinability. is there.

[0005]

The calcium free-cutting stainless steel according to the present invention is basically an alloy containing Cr: 10 to 30% (weight%, the same applies hereinafter), with the balance being Fe and impurities, Ca: 10 to 100 ppm and Al: 50
~ 150ppm added and O content 50 ~ 15
Restricted to 0 ppm, atomic ratio Ca / O ≧ 0.5 and Al
By satisfying the condition of /O≧0.5, at least 20% of the oxide-based inclusions can be made into a grenite 2CaO · Al.
It is characterized in that ₂ O ₃ · SiO ₂ is occupied.

The steel type which is the basis of the steel contained in this embodiment is, for example, martensitic or ferritic stainless steel such as JIS SUS403, 410, 430.

Another embodiment is Cr: 10 to 30% and N
In an alloy containing i: 6 to 20% and the balance of Fe and impurities, Ca: 10 to 100 ppm and Al: 50
~ 150ppm added and O content 50 ~ 15
Restricted to 0 ppm, atomic ratio Ca / O ≧ 0.5 and Al
By satisfying the condition of /O≧0.5, at least 20% of the oxide-based inclusions can be converted into the grenite 2CaO · A.
1 ₂ O ₃ · SiO ₂ is occupied.

An example of this kind of steel foundation is JIS SU.
There are austenitic stainless steels such as S201, 304, 303.

Still another embodiment is Cr: 10 to 30%,
Ni: 6 to 20%, Mo: 5.0% or less, C
u: 5.0% or less and N: 0.5% or less, and an alloy containing one or more of Ca and 10 to 100 ppm and Al: 50 to 15 with the balance being Fe and impurities.
0ppm added and O content 50-150ppm
Regulated in terms of atomic ratio, Ca / O ≧ 0.5 and Al / O ≧
By satisfying the condition of 0.5, at least 20% of the oxide-based inclusions can be converted into the grenite 2CaO.Al ₂ O ₃
・ Characterized by occupying SiO ₂ .

[0012] To give an actual example of the basis of the steel of this aspect, it is a duplex stainless steel such as JIS SUS316, 317.

[0011]

The role of the element added in each of the above stainless steels and the reason for limiting the composition range are known for stainless steels. That is, Cr: 10 to 30% is necessary for obtaining corrosion resistance that can be said to be stainless steel. Ni: 6 to 20% is also a component for enhancing the corrosion resistance as stainless steel and for obtaining strength, toughness and other desired physical properties. Mo: 5% or less is added to improve hardenability and stabilize the passive state. Cu: 5% or less is added for the purpose of improving corrosion resistance. Also, N:
0.5% or less is an additive intended for stabilizing the austenite phase, refining crystal grains due to formation of nitride, and increasing strength due to age precipitation hardening after solution treatment.

By adding Ca, Gerenite 2CaO
In order to generate Al ₂ O ₃ .SiO ₂ , as described above, Ca: 10 to 100 ppm and Al: 50 to 15 ppm.
0ppm is added, and the O content in impurities is 50 to 15
Restricted to 0 ppm, Ca / O ≧ 0.5 and Al / O
It is necessary to satisfy the condition of ≧ 0.5. The reason for this is
This is because, as shown in FIG. 1, generation of gehlenite exists in a region where both Ca / O and Al / O are larger than 0.5. Further, it should be within the area between the two straight lines shown in FIG. 1, that is, 0.7 (Al / O) ≦ (Ca / O) ≦ 1.5 (Al /
If the condition of (O) +0.25 is satisfied, most of the oxide-based inclusions containing Ca are present as gehlenite, which is preferable, but if 20% or more of the oxide-based inclusions are occupied by gehrenite,
The desired tool lubrication effect is obtained.

In the improvement of machinability by oxide inclusions, there exists an optimum oxide melting point Q _M that maximizes the tool life, and it is expressed as Q _M = 1.67Q _C (Q _C is the cutting temperature). It is known that

The cutting temperature depends on the cutting speed. For example, when the cutting speed is 100 m / min in SUS304, the cutting temperature Q _C is within 900 ° C. and the above Q _M is 1.
It will be about 500 ° C. Gohrenite is 1400-1
The melt viscosity at 600 ° C. becomes suitable for the tool lubrication action.

[0015]

[Example] SUS304 was melted by the AOD method.
After decarburization and chromium reduction, slag is removed and C
Slag deoxidation was performed using the strongly basic slag of /S=3.0. Next, add Al when tapping the steel, and then add C
a was added to adjust the components. A Ca-Si wire feeder was used to add Ca.

For comparison, SUS304 with Al added and with Ca added were also melted.
The contents (ppm) of the components related to the oxide-based inclusions in the five samples in total are shown in Table 1.

Table 1 ward No. Ca 1 Al 2 O Example 1 59 82 72 〃 2 68 91 89 89 〃 3 66 103 101 101 Comparative Example 4 36 19 129 〃 5 5 <20 115 Each of the above samples was cut, and oxide inclusions appearing in the cross section were cut. , EPMA. Table 2 shows the ratio of the constituents of the inclusions. In the table, the data represented by means the composition of each of the inclusions when the inclusions are composed of two oxide-based composites.

Table 2 Section No. CaO SiO ₂ Al ₂ O ₃ Cr ₂ O ₃ MgO MnO Estimated melting point ratio Example 1 38 28 27 1 1 0 1520 − 2 39 19 41 0 2 0 1580 6 0 0 20 0 30 0 2100 4 3 32 20 36 0 6 6 1580 3 3 2 70 0 24 1 2100 7 4 19 35 2 13 2 10 1960 − 5 0 0 22 39 0 32 2100 − To check the machinability, each sample is turned and It was drilled and evaluated by tool wear (cutting time 30 minutes) and drill life (cutting speed 15 m / min). The result
It shows in Table 3.

Table 3 ward No. Flank wear Rake face wear Drill life Example 1 0.081 mm 0.031 mm 370 mm 〃 2 0.078 0.012 300 〃 3 0.102 0.018 300 Comparative example 4 0.102 0.062 270 〃 5 5.0. 150 0.130 200 Regarding the corrosion resistance, the tests shown in Table 4 were performed on the test pieces of each sample to examine the degree of rusting and the corrosion reduction.

Table 4 Section No. Wet fountain Spray Room temperature 1% Hydrochloric acid Room temperature 5% Sulfuric acid Boiling 5% Sulfuric acid Example 1 AB AB A A A A 〃 2 AB AB A A A A 〃 3 AB AB A A A A Comparative example 4 AB AB A A A A 〃 5 AB A B A A A A (Evaluation) Wetting test / salt spray test: rusting amount A-AB-B-C-D None Slightly present Overall corrosion test: Weight loss g / m ² · hr 0. 1-1.0 1.0-10 10-100 ABC

[0021]

According to the present invention, it has been possible to solve the problems, which were conventionally considered difficult, of improving the machinability and maintaining the corrosion resistance of stainless steel.

[Brief description of drawings]

FIG. 1 Al / O and Ca / O for the formation of oxide-based inclusions gehlenite in steel as intended in the present invention.
A graph showing the conditions of and.

Claims (3)

[Claims] 1. An alloy containing Cr: 10 to 30% (weight%, the same applies hereinafter), with the balance being Fe and impurities, Ca: 10 to 100 ppm and Al: 50 to 150.
While adding ppm, the O content is regulated to 50 to 150 ppm, and the atomic ratio of Ca / O ≧ 0.5 and Al / O ≧
By satisfying the condition of 0.5, at least 20% of the oxide-based inclusions can be converted into the grenite 2CaO.Al ₂ O ₃
-Calcium free-cutting stainless steel characterized by being occupied by SiO ₂ . 2. Cr: 10 to 30% and Ni: 6 to 2
In an alloy containing 0% and the balance being Fe and impurities, Ca: 10 to 100 ppm and Al: 50 to 150
While adding ppm, the O content is regulated to 50 to 150 ppm, and the atomic ratio of Ca / O ≧ 0.5 and Al / O ≧
By satisfying the condition of 0.5, at least 30% of the oxide-based inclusions can be converted into gehlenite 2CaO.Al ₂ O ₃
-Calcium free-cutting stainless steel characterized by being occupied by SiO ₂ . 3. Cr: 10-30%, Ni: 6-20
%, And Mo: 5.0% or less, Cu: 5.0% or less, and N: 0.5% or less of one or more alloys, with the balance being Fe and impurities, Ca: 1
Oxidation by adding 0 to 100 ppm and Al: 50 to 150 ppm, regulating the O content to 50 to 150 ppm, and satisfying the conditions of Ca / O ≧ 0.5 and Al / O ≧ 0.5 in atomic ratio. At least 3 inclusions
Calcium free-cutting stainless steel characterized by occupying 0% of Gerenite 2CaO ・ Al ₂ O ₃・ SiO ₂ .