JP3483800B2 - Free-cutting stainless steel with excellent outgassing properties - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a free-cutting stainless steel having excellent outgas characteristics.

[0002]

2. Description of the Related Art Conventionally, general-purpose SUS416 and SUS43
In S-containing free-cutting stainless steels such as 0F and SUS303, S mainly forms sulfide MnS together with Mn in the steel, and this sulfide exhibits effects such as improvement of chip disposability and reduction of cutting resistance. Improve machinability. Further, S has a great effect of improving the life of the turning tool especially over a wide cutting speed as compared with Pb, which is also a free cutting element, and has a feature that it is difficult to substitute with other free cutting elements.

On the other hand, MnS is generally inferior in corrosion resistance to the stainless steel matrix, and has a drawback that it easily becomes a starting point of corrosion. Therefore, the general-purpose S-containing free-cutting stainless steel was inferior in rust resistance as compared with the steel containing no S. In addition to free-cutting stainless steel, which is often used as a material for precision machine parts, in recent years, not only the corrosion resistance of the stainless steel material itself is good, but also MnS contained in the steel reacts with moisture in the air. It is also required that the materials around precision machine parts are not corroded by hydrogen sulfide gas (outgas) generated by the above. From such a point, CAMPS-ISIJ vol. 10 (1997) p
1271 and the like, as an S free-cutting stainless steel with improved corrosion resistance and outgas characteristics, the amount of Mn in the steel is reduced and sulfides are converted from MnS to Cr-rich (Cr,
A steel type changed to Mn) S has been developed and put into practical use.

[0004]

However, in free-cutting stainless steel in the normal composition range, reducing Mn not only changes the sulfide composition, but also changes the composition of the unavoidably formed oxide. Let Conventionally, SUS41
In S-containing free-cutting stainless steels such as No. 6, SUS430F, and SUS303, it is known that the effect of improving machinability is greater when MnS is a granular type and the degree of stretching is smaller.
Therefore, JP-A-8-193249 and JP-A-8-2
As disclosed in Japanese Patent No. 60102, at the time of steel making, dissolved oxygen is increased and MnS is controlled so as to have a granular form.

At this time, Mn silicate is often formed as an oxide in free-cutting stainless steel having a general composition range. Like sulfides, Mn silicate is rich in ductility and rarely causes problems in product characteristics. On the other hand, when Mn is reduced in order to change the sulfide composition to (Cr, Mn) S, the composition of the oxide changes, and the produced oxide is hardly stretched by hot working. These oxides that remain in the form of lumps in the product not only accelerate the tool wear during cutting to shorten the life, but also have a very large demerit that they are exposed on the cutting surface and deteriorate the surface finish.

[0006]

[Means for Solving the Problems]
As a result of the inventors' earnest development,
Softening so that it stretches hot due to changes in composition
Is necessary, the alloy element amount range is limited, and the oxide is S
When it is controlled to a specific composite type composition containing i, Cr, Al, etc.
In this case, a soft oxide that has a low melting point and is stretched hot is formed.
And found out. The gist of the invention is (1)% by weight, C: 0.50% or less, Si: 0.15
~ 1.00%, Mn: 1.00% or less, S: 0.05 ~
0.50%, Cr: 10.00 to 30.00%, Al:
0.005% or less, O: 0.005 to 0.040%, balance
Part consists of Fe and unavoidable impurities, and
Weight ratio of Cr and Mn contained in existing sulfide inclusions
Oxide having Cr / Mn of 1 or more and existing in steel
Of the inclusions, if they are spindle-shaped or spherical, they are long
For diameters and linear ones, the length should be 10 μm or more.
At least 50% or more of certain oxides
Is, by weight%, 30% ≦ SiO₂≦ 70%, 10% ≦ M
nO ≦ 30%, 20% ≦ Al₂O ₃+ Cr₂O₃≤50
% Free cutting with excellent outgas characteristics
Stainless steel.

(2)% by weight, C: 0.50% or less, S
i: 0.15 to 1.00%, Mn: 1.00% or less,
S: 0.05 to 0.50%, Cr: 10.00 to 30.
00%, Al: 0.005% or less, Ca: 0.0005
-0.01%, O: 0.005-0.040%, the balance being Fe and unavoidable impurities, and the weight ratio of Cr and Mn Cr contained in the sulfide inclusions present in the steel Cr
/ Mn is 1 or more, and among oxide-based inclusions present in the steel, at least the number of oxides having a major axis in the case of a spindle or a spherical one and a length of 10 μm or more in the case of a linear one The proportion of 50% or more is 20% ≦ SiO ₂ ≦ 70%, 10% ≦ Al ₂ O ₃ by weight%.
+ Cr ₂ O ₃ ≦ 50%, 10% ≦ CaO ≦ 50%, which is a free-cutting stainless steel with excellent outgas characteristics.

(3) In the above (1) or (2), further, in weight%, Ni: 20.00% or less, Mo: 3.0.
0% or less, Cu: 4.00% or less, Ti: 1.00% or less, Nb: 1.00% or less, N: 0.50% or less, B:
0.02% or less, Se: 0.30% or less, Te: 0.3
It is a free-cutting stainless steel excellent in outgas characteristics, characterized by containing one or more of 0% or less and Pb: 0.30% or less.

The present invention will be described in detail below. In the present invention, Cr and Mn contained in the sulfide-based inclusions
The weight ratio of Si and M that are oxide forming elements
The addition amount of n, Al, and Ca is regulated, and the oxide is SiO ₂ −.
It is characterized by changing the softness that can be stretched between the heat composite of _{MnO-Cr 2 O 3 -Al 2} O 3 (-CaO). Therefore, these oxides can be rendered harmless during rolling, cutting, and surface finishing. As a result, it is possible to obtain a stainless steel which has a small amount of so-called outgas, which is a phenomenon in which inclusions in the steel material react with H ₂ O to generate hydrogen sulfide gas, and which has excellent machinability and finish of the cut surface. .

Included in sulfide inclusions present in steel
The reason why the weight ratio Cr / Mn of Cr and Mn is 1 or more is as follows.
If it is less than 1, the corrosion resistance of sulfide inclusions decreases and the rust resistance
This is because the outgas characteristics deteriorate. Also in the steel
Of the existing oxide inclusions, spindle-shaped or spherical
In the case of, the major axis is 1 and in the case of linear, the length is 1 each
50% in at least the number ratio of oxides of 0 μm or more
The above is, by weight%, 30% ≦ SiO.₂≦ 70%,
10% ≦ MnO ≦ 30%, 20% ≦ Al₂O₃+ Cr₂
O₃≦ 50% range, or 20% ≦ SiO₂≦ 70
%, 10% ≦ Al ₂O₃+ Cr₂O₃≦ 50%, 10%
If ≦ CaO ≦ 50%, the oxide is hot rolled.
It does not deteriorate the cutting surface finish of the product.
Absent. If the oxide composition deviates from this range, it will be near the rolling temperature.
If it is poor in deformation, it may not be stretched at all and the surface quality may deteriorate.
Let me down.

Further, when Ca is added, it is usually easy to react with S to produce CaS. Since CaS is spherical and finely dispersed, it may be used for free-cutting steel for machine structural members that needs to suppress anisotropy of mechanical properties. However, CaS has extremely strong reactivity with water, and corrosion resistance,
As with MnS, the outgas characteristics are adversely affected. Therefore, by limiting the lower limit of the amount of O and fixing Ca as an oxide, the amount of Ca existing as a sulfide is limited.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the content of each component element of the present invention will be described below. C: 0.50% or less C is an element necessary for increasing strength. However, in order to improve the corrosion resistance, the smaller the amount, the better.
It was set to 50%. Si: 0.15-1.00% Si is an element necessary as a deoxidizing element at the time of steel making, and is also necessary for making an oxide a suitable composition. However, if too much, the annealing hardness will be increased and the workability will be impaired.
The range was 0.15-1.00%.

Mn: 1.00% or less Mn is a deoxidizing element like Si, and at the same time, it is important as an element affecting the sulfide composition in this component system. However, if the Mn content is large, the Mn concentration in the sulfide increases and the corrosion resistance and the outgas characteristics deteriorate, so the upper limit value was made 1.00%. S: 0.05 to 0.50% S forms a sulfide and is extremely effective in improving machinability.
If it is too large, the machinability improving effect is saturated and the hot workability is deteriorated, so the range was made 0.05 to 0.50%.

Cr: 10.00 to 30.00% Cr is a basic element of stainless steel and imparts corrosion resistance. In addition, it reacts with S in the present component system to provide high Cr and low M.
It forms an n-type sulfide to improve the corrosion resistance and outgassing properties of the sulfide itself. Therefore, the range is from 10.00 to
It was set to 30.00%. Al: 0.005% or less Al is a strong deoxidizing element and, at the same time, has a great influence on the oxide composition, and when it contains an appropriate amount, it is a composite oxide excellent in hot ductility even if the Mn concentration is low. To generate. If the amount is too large, the oxide becomes a hard oxide of Al ₂ O ₃ single phase and the deformability during hot working decreases, so it appears in a large area on the cutting surface of the product and the surface finish deteriorates, It reduces the amount of dissolved oxygen during manufacturing and deteriorates machinability. Therefore,
The upper limit value was 0.005%.

Ca: 0.0005 to 0.01% Ca is an extremely strong deoxidizing element, and at the same time has a great influence on the oxide composition. A complex type oxide suitable for finish is produced. If the amount is too large, the oxide becomes a hard oxide with a high CaO concentration and the deformability during hot working decreases, so it appears in a large area on the cutting surface of the product, deteriorating the surface finish and reducing the dissolved oxygen. Resulting in reduced machinability. Therefore,
The range was made into 0.0005-0.01%.

O: 0.005-0.040% O is too fine because dissolved oxygen is too small due to excessive addition of a deoxidizing element during steelmaking, and the sulfides tend to be hot-stretched and become too fine. The shape is unsuitable for improving machinability. Further, when Ca is added, Ca, which is a deoxidizing element, does not react with O to form a sulfide having a high Ca concentration, and the desired corrosion resistance and outgas characteristics cannot be obtained. If it is too large, the machinability improving effect is saturated, and the amount of oxide only increases. Therefore,
The range was made 0.005-0.040%.

Ni: 20.00% or less Ni is a strong austenite forming element and is mainly added to austenitic stainless steel and some martensitic steels. More than a certain amount is required for non-magnetic applications,
Furthermore, it has the effect of improving the corrosion resistance to non-oxidizing acids. However, from the viewpoint of cost, the upper limit was set to 20.00%. Mo: 3.00% or less Mo is an element necessary for improving the corrosion resistance. However, if the amount is too large, an embrittlement phase is deposited to deteriorate the corrosion resistance and mechanical properties. Therefore, the upper limit is set to 3.00%.

Cu: 4.00% or less Cu is mainly solid-dissolved in austenite and improves corrosion resistance.
Effective in improving cold workability. However, excessive addition deteriorates the hot workability, so the upper limit was made 4.00%. Ti: 1.00% or less Ti improves the corrosion resistance by forming Ti carbide, and is also advantageous for improving the strength by precipitating an intermetallic compound. But,
If it is too large, it becomes brittle, so the upper limit was made 1.00%.

Nb: 1.00% or less Nb is a strong carbide-forming element, which suppresses the formation of Cr carbide by forming Nb carbide and improves the corrosion resistance. However, if too large, the hot workability is deteriorated, so the upper limit was made 1.00%. N: 0.50% or less N is useful for improving corrosion resistance and strength. However, excessive addition causes defects in the steel ingot, so the upper limit is 0.5.
It was set to 0%.

B: 0.02% or less B is an appropriate addition, and particularly improves the hot workability of austenitic stainless steel. However, if too large, it worsens, so the upper limit was made 0.02%. Se: 0.30% or less Se reacts with Mn, Cr or the like to form a non-metallic inclusion, and improves machinability, similar to S. However, excessive addition causes the effect to be saturated and deteriorates the hot workability, so the upper limit is set to 0.
It was set to 30%.

Te: 0.30% or less Te, like S and Se, improves machinability by forming inclusions. However, excessive addition deteriorates the hot workability because the effect is saturated, so the upper limit was made 0.30%. Pb: 0.30% or less Pb is present in the steel alone or dispersed in the form of adhering to inclusions, and is dissolved during cutting to have an effect as a lubricant and an effect of improving chip crushability. Excessive addition causes saturation of the machinability improvement effect and inhibition of hot workability, so the upper limit was made 0.30%.

[0022]

EXAMPLES Hereinafter, examples of the present invention will be specifically described. 19Cr ferritic stainless steel was melted in a vacuum induction furnace. Table 1 shows the chemical composition obtained by adjusting the amount of addition of the above elements after adjusting this component except for Si, Mn, Al and Ca. Diameter of these components 160m
A steel ingot of m was forged to a diameter of 15 mm at 1200 ° C., cut in parallel to the forging direction, and the morphology of inclusions was observed using an optical microscope and an electron microscope. Arbitrarily select 10 oxide inclusions having a length of 10 μm or more in the longitudinal direction, and use the ratio of the minor axis to the minor axis length of these oxide inclusions and the degree of deformation (major axis / minor axis). Was measured. The results are shown in Table 2. Furthermore, the composition of the same oxide was investigated using an energy dispersive X-ray analyzer (EDX).

Further, the forged material having a diameter of 15 mm and 800 ° C.
It was annealed for 2 hours and subjected to corrosion resistance and outgas test. Corrosion resistance test is 20 ℃ at 90% relative humidity
The temperature rising and cooling from −2 hours to 50 ° C.-4 hours was repeated 20 times, and the rusting condition of the surface of the test piece was observed. For the outgas test, the test piece, pure water, and silver plate were heated to 80 ° C
After 20 hours, due to the change in color of the silver plate,
The amount of hydrogen sulfide gas generated was evaluated. That is, hydrogen sulfide reacts with silver to change the silver plate to blackish brown, and the degree of discoloration increases as the amount of hydrogen sulfide outgas increases.

As a machinability evaluation, a drill piercing test was conducted. Using a SKH51 straight shank drill with a diameter of 5 mm, thrust 414 N, peripheral speed 18.7 m / m
Under a constant thrust of in and a constant circumferential velocity, a cross section of a test piece having a diameter of 15 mm was perforated perpendicularly, and the machinability was evaluated for the time (seconds) required to reach a depth of 10 mm. That is, the better the machinability, the shorter the drilling time.

[0025]

[Table 1]

[0026]

[Table 2]

The results of various tests are shown in Table 1. N shown in Table 1
o1 to 8 are examples of the present invention, and Nos. 9 to 16 are comparative examples. In Nos. 1 to 8, since the compositions of sulfide and oxide are appropriately controlled, excellent machinability is ensured, corrosion resistance and outgas characteristics are excellent, and the oxide is stretched. Is also good. On the other hand, Comparative Example No9
Is due to a conventional steelmaking method, and since Al and Ca are not added, the produced oxide is close to SiO ₂ and does not stretch by hot working, but remains in a lump form, thus reducing the surface finish. When Al is excessively added as in Comparative Example No. 10,
When the amount of O is greatly reduced, the produced oxide is Al ₂ O ₃
Become the subject. For this reason, the amount of oxides decreases, but the machinability deteriorates due to the poor sulfide shape.

When only Ca is added as in Comparative Example No. 11, the produced oxide is mainly CaO--SiO ₂ ,
It remains without stretching due to hot working. Furthermore, in the case of Comparative Example No. 12 in which the amount of Si is small, the produced oxide is Cr ₂ O ₃ −.
It is MnO and remains undeformed because it is hard. Even in the case of Comparative Example No. 13 containing appropriate amounts of Al and Ca, if the amount of Si is small, the Si concentration in the oxide will be low, and the composition will not be optimal for hot ductility. Comparative Example No. 14 has a high Mn and an appropriate oxide composition, but since the Mn concentration in the sulfide is high,
It has poor corrosion resistance and outgassing properties, and has no advantages over conventional steel. Comparative Example No. 15 has a small amount of S and has no effect of improving machinability. Comparative Example No. 16 has an appropriate oxide composition,
Since the amount of O is small, the sulfide is significantly stretched during hot working, resulting in poor machinability.

[0029]

INDUSTRIAL APPLICABILITY As described above, the present invention has an extremely excellent effect that it is possible to provide a material having excellent machinability in which corrosion resistance and outgas characteristics are improved by controlling sulfide morphology. .

Claims (3)

(57) [Claims] 1. By weight%, C: 0.50% or less, Si: 0.15 to 1.00%, Mn: 1.00% or less, S: 0.05 to 0.50%, Cr: 10 0.000 to 30.00%, Al: 0.005% or less, O: 0.005 to 0.040% The balance consists of Fe and unavoidable impurities, and the sulfide having a major axis of 10 μm or more existing in steel. For at least 90% or more of the systematic inclusions, the sulfide-based inclusions have a Cr / Mn weight ratio of Cr / Mn of 1 or more, and are oxide-based inclusions present in the steel. Among them, the spindle-shaped or spherical-shaped one has a major axis, and the linear-shaped one has a length of 10 μm or more.
And 30% ≦ SiO ₂ ≦ 70%, 10% ≦ MnO ≦ 30
%, 20% ≦ Al ₂ O ₃ + Cr ₂ O ₃ ≦ 50%, a free-cutting stainless steel with excellent outgas characteristics. 2. By weight%, C: 0.50% or less, Si: 0.15 to 1.00%, Mn: 1.00% or less, S: 0.05 to 0.50%, Cr: 10 0.000 to 30.00%, Al: 0.005% or less, Ca: 0.0005 to 0.01%, O: 0.005 to 0.040% The balance consists of Fe and unavoidable impurities, and steel For at least 90% or more of the sulfide inclusions having a major axis of 10 μm or more, the weight ratio Cr / Mn of Cr and Mn contained in the sulfide inclusions is 1 or more, In addition, the composition of the oxide inclusions present in the steel that are 50% or more in at least the number ratio of oxides having a long diameter in the case of spindle or spherical ones and 10 μm or more in the case of linear ones But% by weight
And 20% ≦ SiO ₂ ≦ 70%, 10% ≦ Al ₂ O ₃ +
Cr ₂ O ₃ ≤ 50%, 10% ≤ CaO ≤ 50%, a free-cutting stainless steel with excellent outgas characteristics. 3. The method according to claim 1 or 2, further comprising, by weight, Ni: 20.00% or less, Mo: 3.00% or less, Cu: 4.00% or less, Ti: 1.00% or less. , Nb: 1.00% or less, N: 0.50% or less, B: 0.02% or less, Se: 0.30% or less, Te: 0.30% or less, Pb: 0.30% or less 1 Free-cutting stainless steel with excellent outgas characteristics, which is characterized by containing two or more kinds.