JP2001234298A - AUSTENITIC Ca-ADDED FREE CUTTING STAINLESS STEEL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an austenitic stainless steel improved in machinability without deteriorating corrosion resistance. SOLUTION: The austenitic free cutting stainless steel has a composition consisting of, by weight, <=0.15% C, 0.2-1.0% Si, 0.2-2.0% Mn, 8.0-15.0% Ni, 16.0-20.0% Cr, 0.0003-0.008% Al, 0.001-0.01% Ca, 0.005-0.020% O and the balance Fe with inevitable impurities. Moreover, this steel has a composition which contains, besides the above, <=0.05% S and either or both of <=3.0% Mo and <=4.0% Cu, further contains either or both of <=0.2% N and <=0.01% B, and further contains one or more kinds among <=1.0% Ti, <=1.0% Nb, <=1.0% V, <=1.0% W, <=1.0% Ta and <=1.0% Zr and in which, besides the above, the weight ratio of Ca to Al, Ca/Al, in the steel is regulated to 0.2-5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic free-cutting stainless steel by adding Ca.

[0002]

2. Description of the Related Art Generally, austenitic stainless steels such as SUS304 and SUS316 are widely used in various fields because of their excellent corrosion resistance, ductility, toughness and weldability. However, because of high ductility, easy work hardening, low thermal conductivity, etc., in cutting, the wear of the cutting tool is large, and the chip disposability is poor,
Machinability is inferior to carbon steel and low alloy steel. In order to make up for these disadvantages, free-cutting stainless steels such as SUS303 and SUS316F, which are improved in machinability by adding free-cutting elements such as S, are also standardized in JIS, and are used in household electric appliances and OA equipment. It is frequently used for small cutting parts and parts that emphasize decorativeness.

[0003] S reacts with elements such as Mn in steel to form sulfides such as MnS, and these sulfides act as a source of stress concentration during cutting, thereby suppressing tool wear due to a reduction in cutting resistance. And an effect of improving machinability such as improvement in chip handling. However, since the sulfide generated in the free-cutting stainless steel is more easily corroded than the stainless steel matrix, it becomes a starting point of rust and pitting corrosion and deteriorates corrosion resistance.

[0004] On the other hand, as a method for improving machinability, a method using a Ca-containing oxide generated by performing Ca treatment during deoxidation has been known for a long time. Among the Ca-containing oxides, a low melting point oxide composition called anorthite or gehlenite has a large machinability improving effect, but anorthite having a low melting point is particularly preferred. It is said that the low-melting oxide is softened by the heat generated at the time of cutting and has an action of suppressing wear because it is adhered and protected on the tool surface.

[0005]

However, unlike carbon steel and low alloy steel, in austenitic stainless steel containing a relatively large amount of alloying elements such as Cr and Ni, the oxidation of Cr, Mn, Si and the like depends on the components. There are few prior art examples showing a component system that may generate oxides and generate oxides suitable for improving machinability. In JP-A-6-145908, Al: 50 to 150 ppm, Ca: 1
Under the conditions of 0 to 100 ppm and Ca / O ≧ 0.5 and Al / O ≧ 0.5 in atomic ratio, gehlenite is generated, and a tool lubrication effect is obtained. However, in this patent, while recognizing the effect of improving the machinability of anorthite itself, it is stated that the formation of anorthite is prevented in stainless steel in which a large amount of Cr is present. It focuses only on the range.

Further, in Japanese Patent Application Laid-Open No. Hei 9-137254, malleable low-melting lime aluminosilicate type oxide together with manganese sulfide acts as a solid lubricant and has an effect of suppressing tool wear. It indicates that there is. In this patent, as a component system for obtaining the above performance,
Oxide constituent elements include Si and Ca, O content and Ca
Although the / O ratio is controlled, there is no mention of a suitable amount of Al which has a large effect on the lime aluminosilicate type oxide composition.

[0007]

Means for Solving the Problems The inventors of the present invention have made intensive developments to solve the above-mentioned problems, and as a result, in austenitic stainless steel, the amounts of Al, Ca and the like have been variously changed to change the oxide composition. As a result of investigating various properties such as machinability and the like, a suitable component system for generating an oxide effective for improving machinability could be found. The gist of the invention is as follows: (1) By weight%, C: 0.1% or less, Si: 0.2 to
1.0%, Mn: 0.2 to 2.0%, Ni: 8.0 to 1
5.0%, Cr: 16.0 to 20.0%, Al: 0.0
003 to 0.008%, Ca: 0.001 to 0.01
%, O: 0.005 to 0.020%, the balance consisting of Fe and unavoidable impurities.

(2) In addition to the component (1), S:
An austenitic Ca-added free-cutting stainless steel containing 0.05% or less. (3) In addition to the component (1) or (2), Mo:
3.0% or less, Cu: 4.0% or less, one or two of them
An austenitic Ca-added free-cutting stainless steel containing a seed. (4) In addition to the above components (1) to (3), N: 0.2
% Or less, B: Austenitic Ca-added free-cutting stainless steel containing one or two of 0.01% or less.

(5) In addition to the components (1) to (4), Ti: 1.0% or less, Nb: 1.0% or less, V:
1.0% or less, W: 1.0% or less, Ta: 1.0% or less, and Zr: 1.0% or less. Free-cutting stainless steel. (6) In addition to the components (1) to (5), Ca in steel
Austenitic Ca-added free-cutting stainless steel, wherein the weight ratio of Al and Al is 0.2 to 5 Ca / Al.

Hereinafter, the present invention will be described in detail. In the austenitic stainless steel, as described above, the low melting point type oxide containing Al, Ca, etc. can be generated to improve the machinability by adjusting the alloy components. It has been found that it is important to control Al at a lower concentration and in a narrower range than before, and then to add Ca. In addition, the control of the amount of O is also important. When the amount of O is less than 0.005%, the amount of oxide is small and the contribution to the improvement in machinability is poor. It has also been found that high melting point oxides mainly composed of Cr and Cr are apt to be generated and the effect of improving machinability is lost.

Furthermore, it has been found that it is effective to control the weight ratio of Ca to Al within a certain range in order to more stably produce an oxide having a suitable composition. That is, the Ca / Al ratio should be suppressed to between 0.2 and 5,
If the Ca / Al ratio is less than 0.2, the Al ₂ O ₃ concentration is high and a high melting point type oxide is produced, so that the effect of improving machinability is lost. Therefore, the effect of improving machinability is poor because of the deviated oxide composition.
Thus, in the present invention, it has been clarified that an oxide effective for improving machinability can be generated by finely controlling the component elements in the Al concentration region lower than the range conventionally considered. It is another object of the present invention to provide an austenitic stainless steel having improved machinability without deteriorating corrosion resistance.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the composition of the present invention will be described below. C: 0.1% or less C is an element necessary for increasing the strength. However, since it is an element that deteriorates corrosion resistance, its upper limit is 0.1%.
And Si: 0.2 to 1.0% Si is usually added for deoxidation, and in particular, in the present invention, is an element necessary for forming a low melting point type oxide. However, if it is less than 0.2%, the effect as a deoxidizing agent is weak, and if it exceeds 1.0%, toughness is reduced. Therefore, the range is set to 0.2 to 1.0%.

Mn: 0.2 to 2.0% Mn is used as a deoxidizing agent in steel making, like Si. Further, it reacts with S to generate sulfide. But 0.2%
If less than 2.0%, it is not sufficient to exhibit the above-mentioned function.
Exceeds the range, the corrosion resistance is impaired.
2.0%. Ni: 8.0 to 15.0% Ni is an essential element for the austenitic stainless steel and is an element that stabilizes the austenite phase.
If the content is less than 8.0%, the austenite phase is not stable, so the lower limit was made 8.0%. In addition, since Ni is an expensive element, the upper limit is set to 15.0%.

Cr: 16.0 to 20.0% Cr is a basic element of stainless steel, and imparts corrosion resistance by forming an oxide film on the surface. If it is less than 16.0%, it is insufficient to secure corrosion resistance, and if it exceeds 20.0%, it becomes expensive. Therefore, the range was set to 16.0 to 20.0%. Al: 0.0003% to 0.008% Al is a powerful deoxidizing element, and is an extremely important element in controlling the oxide composition in the present invention. But,
If it is less than 0.0003%, it is insufficient for controlling the oxide composition,
If the content exceeds 0.008%, a hard oxide is formed and the machinability is impaired. Therefore, the range is 0.0003 to 0.00
8%.

Ca: 0.001 to 0.01% Ca is a strong deoxidizing element.
Is an important element as well. In order to form an oxide having a composition effective for improving machinability, the effect is not effective at less than 0.001%, it is difficult to add over 0.01%, and at the same time, the corrosion resistance due to the generation of a large amount of sulfides. Due to deterioration, the range was made 0.001 to 0.01%. O: 0.005 to 0.020% Most of O becomes an oxide at room temperature and is dispersed in steel. In the present invention, it has been clarified that the machinability can be remarkably improved by the delicate control of deoxidizing elements such as Al and Ca and the presence of an appropriate amount of O. For this purpose, 0.005% Less than 0.02 is less effective.
If it exceeds 0%, a high-melting-point oxide mainly composed of Mn or Cr is formed to deteriorate machinability.
05 to 0.020%.

S: 0.05% or less S forms sulfide and is extremely effective in improving machinability.
However, in the present invention, the upper limit is set to 0.05% in order to suppress deterioration of corrosion resistance. Mo: 3.0% or less Mo has an effect of improving corrosion resistance. However, the addition of a large amount leads to an increase in cost, so the upper limit was made 3.0%.

Cu: 4.0% or less Cu forms a solid solution in austenite ground to improve corrosion resistance and lower deformation resistance. However, the addition exceeding 4.0% deteriorates hot workability. Therefore, the upper limit was set to 4.0%. N: 0.2% or less N is a strong austenite-forming element and has an effect on improving corrosion resistance and strength. However, if it exceeds 0.2%, hot workability deteriorates, so the upper limit is made 0.2%.

B: 0.01% or less B is austenitic and improves hot workability. However, if it is too much, it will worsen. Therefore, the upper limit is set to 0.
01%. Ti: 1.0% or less, Nb: 1.0% or less, V: 1.0
%, W: 1.0% or less, Ta: 1.0% or less, Z
r: 1.0% or less Ti, Nb, V, W, Ta, and Zr all generate carbides and improve corrosion resistance. However, the addition exceeding 1.0% saturates the effect and deteriorates the hot workability. Therefore, the upper limit was set to 1.0% in each case.

Ca / Al: 0.2-5 Ca and Al are contained in stainless steel as described above.
It is an element necessary for generating a low melting point oxide containing Ca and the like. This oxide improves tool life by adhering to a working tool during cutting to protect the tool surface and to suppress mechanical wear of the tool. It is important to control Al in a trace amount range and to add Ca on it in order to generate an oxide of a suitable composition,
It is effective to control the important ratio of Ca and Al within a certain range. If the Ca / Al ratio is less than 0.2, Al ₂
A high melting point type oxide is generated with a high O ₃ concentration, and the machinability improving effect is lost. Also, when the Ca / Al ratio exceeds 5, the machinability improving effect is poor because of the deviated oxide composition. Become. Therefore, the range was set to 0.2 to 5.

[0020]

EXAMPLE An austenitic stainless steel having the components shown in Table 1 was melted using an experimental furnace. 120 ingots made
The steel bar was forged at 0 ° C. and subjected to a solution heat treatment of water cooling at 1100 ° C. and subjected to various tests. First, cut the plane parallel to the forging direction,
The polished and observed oxide-based inclusions were analyzed for oxide composition using an energy dispersive X-ray analyzer.
Next, the forged material having a diameter of 60 mm was turned by a lathe as described below, and the wear amount of the tool flank and the rake face was measured. On the other hand, a corrosion test specimen having a diameter of 12 mm × 21 mm was prepared and subjected to a corrosion resistance test described below. Table 2 shows the results.

[0021]

[Table 1]

[0022]

[Table 2]

(1) Tool wear test Tool material type: P20 Wind speed: 200, 250 m / min Depth of cut: 1.0 mm Feed: 0.2 mm / rev Lubricating oil: None Evaluation: Tool flank and rake after 10 minutes turning Surface wear (2) Corrosion resistance test Cycle wet test: 90% RH, Δ (20 ° C.-1.5
h) ← → (70 ° C.-4.5 h)｝ × After 20 cycles, the surface of the test piece was observed for rust.

As shown in Table 1, invention steel Nos.
Produces an oxide having an appropriate composition, and has improved machinability while maintaining good corrosion resistance. Comparative steel No14
Is a normal SUS30 containing no Al and Ca
4, and the generated oxide is mainly composed of Si and Mn, and has no effect of suppressing tool wear. Comparative steel No.15
As described above, when Al is contained but Ca is not contained, an oxide containing Al is generated, but the effect of suppressing tool wear is small. Comparative steel No. 16 was a case where strong deoxidation with Al was performed, but was mostly an oxide containing Al, and rather accelerated flank wear because of a hard oxide.

Comparative steel No. 17 does not contain Al but contains Ca, and produces an oxide mainly composed of Si and Ca.
The effect of suppressing tool wear is poor. Like comparative steel No.18,
Even when Ca is included, when excessive Al is included, the oxide becomes high in Al concentration, and a tendency to promote wear is observed.
Comparative steel No. 19 contained appropriate amounts of Al and Ca, but had a high dissolved oxygen content. In this case, mainly Mn was used.
And an oxide composed of Cr as a main component, and wear is promoted.

Comparative steel No. 20 is SUS303 containing 0.15% of S. Although machinability is good, corrosion resistance is slightly inferior due to relatively high sulfide content. Comparative steel No. 21 is SUS303 in which S was further increased to 0.33%.
Due to the large amount of sulfide, tool wear is suppressed compared to the invention steel, but corrosion resistance is very poor. Comparative steel No. 22 is SUS316 subjected to normal Al deoxidation. An oxide having a high Al concentration is generated, and the machinability is not good. Comparative steel N
o23 is SUS316F which has been Al-deoxidized, and the tool wear is suppressed by the influence of S, but the corrosion resistance is somewhat poor.

[0027]

As described above, according to the present invention, it is possible to provide a free-cutting stainless steel having improved machinability without deteriorating the corrosion resistance, and has an extremely excellent effect.

Claims (6)

[Claims] C: 0.1% or less, Si: 0.2 to 1.0%, Mn: 0.2 to 2.0%, Ni: 8.0 to 15.0%, by weight% Cr: 16.0 to 20.0%, Al: 0.0003 to 0.008%, Ca: 0.001 to 0.01%, O: 0.005 to 0.020% From the balance Fe and inevitable impurities An austenitic Ca-added free-cutting stainless steel, characterized in that: 2. In addition to the component of claim 1, S: 0.05
% Of austenitic C
a Free-cutting stainless steel added. 3. An austenitic Ca additive characterized by containing one or two of Mo: 3.0% or less and Cu: 4.0% or less in addition to the components of claim 1 or 2. Free-cutting stainless steel. 4. An austenitic Ca additive comprising one or two of N: 0.2% or less and B: 0.01% or less in addition to the components of claim 1 to 3. Free-cutting stainless steel. 5. In addition to the components of claims 1 to 4, Ti: 1.0% or less, Nb: 1.0% or less, V: 1.0% or less, W: 1.0% or less, Ta: Austenitic Ca-added free-cutting stainless steel containing one or more of 1.0% or less and Zr: 1.0% or less. 6. In addition to the components of claims 1 to 5, C in steel
An austenitic Ca-added free-cutting stainless steel, wherein the weight ratio of a to Al is Ca / Al: 0.2 to 5.