JPS62278252A - Free-cutting austenitic stainless steel - Google Patents

Abstract

PURPOSE:To improve machinability without deteriorating hot workability nor causing food sanitation problems, by adding, as free-cutting elements, Sn and Bi to an austenitic stainless steel. CONSTITUTION:As austenitic stainless steel excellent in corrosion resistance and machinability, a steel material which has a composition consisting of, by weight, <0.2% C, <2.0% Si, <10% Mn, 7.5-30.0% Cr, <40.0% Ni, 0.005-0.50% Bi, 0.005-0.70% Sn, 0.0005-0.10% B, <0.20% P, <0.40% S, <0.02% O, <0.10% N, and the balance Fe or further containing 1 or >=2 kinds among 0.005-0.50% Zr, 0.005-0.50% REM, <0.09% Ca, 0.05-0.5% Al, 0.05-3.0% Nb, 0.05-0.5% Ta, 0.05-2.0% Ti, and 0.05-0.5% V or <5.0% Mo and/or <4.0% Cu independently or in combination is developed. Since harmful Pb as free-cutting component is not contained in the above steel, free-cutting austenitic stainless steel free from food sanitation problems as well can be obtained.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention' [Objective of the Invention] (Field of Industrial Application) The present invention relates to an austenitic free-cutting stainless steel having excellent corrosion resistance and machinability. Pb as a component
The present invention relates to an austenitic stainless free-cutting steel that can be suitably used as a material for food equipment, which requires not only corrosion resistance but also particularly food hygiene safety.

(Conventional technology) Stainless steel is a metal material with excellent heat resistance and corrosion resistance, but this stainless steel generally has high viscosity and poor thermal conductivity, and chips easily adhere to tools during cutting. , machining is often difficult. Therefore,
S, Pb, Bi.

Research and development has been conducted to improve machinability by adding free-cutting elements such as Te and Se, and so-called free-cutting stainless steels have come to be used for various purposes.

(Problem to be solved by the invention) However, although the machinability of this type of free-cutting stainless steel is improved by adding the above-mentioned free-cutting elements, conversely, the machinability is improved due to the addition of the above-mentioned free-cutting elements. There is a problem in that hot workability deteriorates due to this. In particular, austenitic stainless steel originally does not have very good hot workability, and there is a problem in that hot workability becomes even worse when free-cutting elements are added.

In addition, since stainless steel has excellent corrosion resistance, it is used in a wide range of applications that require corrosion resistance, and austenitic stainless steel in particular has poorer corrosion resistance, making it a material suitable for a wide range of applications. It is. However, the inclusion of the above-mentioned free-cutting elements may limit its uses. For example, when used as a material for food equipment, the addition of S, Pb, Te, Se, etc. causes corrosion resistance and food hygiene problems, and the addition of Pb in particular cannot be used due to food hygiene problems. There was a problem.

On the other hand, since Bi is an element used in pharmaceuticals and cosmetics, it has been considered optimal for free-cutting stainless steel for food equipment, but the addition of Bi significantly reduces hot workability. There was also the problem that it was not possible to add too much.

(Purpose of the Invention) The present invention has been made by focusing on the problems of the prior art described above. In particular, in austenitic stainless steel whose corrosion resistance has deteriorated, even if Sn is added as a free-cutting element, the heat Austenite does not significantly deteriorate machinability, has improved machinability compared to Bi alone, and also has no food hygiene problems and can be suitably used as a material for food equipment. The purpose is to provide free-cutting stainless steel.

[Structure of the invention] (Means for solving the problems) The austenitic stainless free-cutting steel according to the present invention contains 1% by weight, C: 0.2% or less, Si: 2.0% or less, M
n: 10, 0% or less, Cr: 7.5-30.0%
, Ni: ~40.0% or less, Bi: 0.005-0.
50%, Sn: 0.005-0.70%, B: 0.0o
05-0.10% and if necessary Zr: 0.005
~0.50%, REM: 0.005~0.50%, Ca
: 0.09% or less, AM: 0.05-0.5%, Nb:
0.05-3.0%, Ta: 0.05-0.5%, Ti
: 0.05 to 2.0%, ■ One or more selected from 0.05 to 0.5%, MO; 5.0% or less, Cu: 4. One or two types selected from 0% or less, Zarani P: 0.20% or less, S
: 0, 40% or less, O: 0, 02% or less, N
: 0.10% or less, the balance being Fe and impurities.

The reason for limiting the component range (wt%) of the austenitic stainless free-cutting steel according to the present invention will be explained below.

C: 0.2% or less C is a strong austenitizing element, but from the viewpoint of corrosion resistance, the smaller the content, the better it is, especially in austenitic stainless steel, it is preferably 0.2% or less.

Si + 2.0% or lessSi is an element that acts as a deoxidizing agent during steel melting, and is effective in increasing oxidation resistance, but it is a ferrite-forming element, and too much will reduce toughness, so the upper limit should be set. is set to 2.0%.

Mn・10.0% or less Mn forms a compound with S, Se, etc., and is an effective element for preventing red-hot brittleness. Further, since Mn is an austenitizing element and is cheaper than Ni, it can be included as a replacement element for N1, but since adding a large amount reduces machinability, the upper limit is set at 10.0%.

Cr; 7.5 to 30.0% Cr is a basic element of austenitic stainless steel, and is added to improve corrosion resistance and oxidation resistance. And the content range required for this is 7.5-30.0%
It is.

Ni: 40.0% or less Ni is a preferable and important additive element for stainless steel, and is an effective element for forming a stable austenite phase and improving the corrosion resistance and toughness of steel. However, if too much is added, machinability deteriorates and it becomes expensive, so the upper limit is set at 40.0%.

Bi: 0.005 to 0.50% Bi is an element that is effective in improving machinability and poses no problem in terms of food hygiene. .005%
or more. However, if a large amount of B is contained, the hot workability will be significantly reduced, and even if B is contained, sufficient hot workability cannot be obtained, so the upper limit is set to 0.50%.

Sn: 0.005 to 0.70% Sn is also an effective element for improving machinability, so in order to give free machinability to austenitic stainless steel, it is added Contain .005% or more. However, if contained in a large amount, hot workability will be reduced, so the content should be 0.70% or less.

B: O, 0O05~0.10% B is one of the important elements in the austenitic free-cutting stainless steel according to the present invention, and prevents the deterioration of hot workability due to the combined addition of Bi and Sn to improve stiffness. It is an effective element for In order to obtain such an effect, it is necessary to add 0.0005 to 0.10%.

Zr: 0.005~0.50%, REM: 0.005~
0.50%, Ca: 0.09% or less, Ai: 0.0
5-0.5%, Nb: 0.05-3.0%, Ta: 0.
05-0.5%, Ti: 0, 05-2.0%
, V: one or more selected from 0.05 to 0.5% Zr, REM (one or more rare earth elements), Ca, AM, Nb, Ta, Ti, V Both are effective elements for improving hot workability. That is, these elements have the effect of fixing O and N in the steel, and depending on one element, also fixing S, thereby improving hot workability. Furthermore, Ai, Nb, Ta, Ti, V, etc. also have the effect of improving corrosion resistance, strength, etc.

Therefore, in order to obtain such an effect, one or more kinds may be contained within the above range, if necessary. In this case, the upper limit of each element was regulated in consideration of machinability and cost.

One or two types selected from Mo: 5, 0% or less, Cu: 4.0% or less. Since both Mo and Cu are elements that improve corrosion resistance, one of these may be used as necessary. Alternatively, it is also good to add two types. In this case, Mo strengthens the passive film in Cr-Ni stainless steel and improves corrosion resistance, but it is harmful if added in large amounts, so 5.0%
If a large amount of Cu is added, hot workability is reduced, so the content must be 4.0% or less.

P: 0.20% or less If a large amount of P is contained, hot workability will be impaired, so the upper limit is set to 0.20%.

S: 0.40% or less S is an element that imparts free machinability to steel, but if added in a large amount, it reduces hot workability and corrosion resistance, so the upper limit is set to 0.40%. In particular, when high corrosion resistance is required, such as in food equipment, it is preferably 0.002% or less.

0: 0.02% or less ○ remains in the steel as an oxide and is harmful to corrosion resistance as well as hot workability, so the upper limit is set to 0.02%.

N: 0.10% or less It has the effect of Nl + nut-resistant soybeans, but if it is contained in a large amount, it inhibits the hot workability improvement effect of B, so 0.10% is the upper limit.

In particular, for austenitic stainless steel whose hot workability is not so good, the content is more preferably 0.05% or less.

(Examples and Comparative Examples) Inventive steels Nos. 1 to 14 and comparative steels Nos. 15 to 20 with chemical components shown in Table 1 were melted in a 2-ton arc furnace and refined in a ladle refining device (GRA F). After that, it was cast to obtain a 2-ton steel ingot.

Then, after heating each of the steel ingots to about 1250"C,
It was rolled into a 1400 mm square billet, and hot workability was evaluated during this rolling. At this time, the evaluation of hot workability was carried out by an appearance test to observe the surface condition of each billet to check for billet cracks, and a hot tensile test (1250 'C)
Judgment was made based on the rupture area (%). These results are shown in Table 2.

Next, to evaluate the machinability of each test steel, each billet was
It was determined based on the drillability (cutting speed at which the tool life is 1000 mm) of a material that was forged into a round bar with a diameter and subjected to solution treatment. The cutting conditions at this time are shown in Table 3. Further, the machinability evaluation test is also shown in Table 2.

Table 3: Corrosion resistance was measured by immersing the same materials used in the machinability test in the various solutions shown in Table 4, and measuring t' in the corroded area 1ij].
It was fixed at 11. The results are also shown in Table 2, and as shown in Tables 1 and 2, the invention steels No. 1 to 14 all have excellent hot workability comparable to comparative steel No. 15.16. It can be seen that rolling blooming by normal hot rolling is possible. On the other hand, comparative steels Nos. 17 to 20 containing Bi and/or Sn but not containing B have poor hot workability, and large cracks occur during hot rolling, and the hot rupture area of area is also small. Recognize.

In addition, the present invention steels No. 1 to 14 are all comparative steel No.
It has better machinability (drillability) than No. 15 and No. 16. Furthermore, the invention steel Nos. 1 to 14 are also excellent in corrosion resistance. From this, unreleased 'J]tLI
It is clear that Nos. 1 to 14 are excellent in all of hot workability, machinability and corrosion resistance,
In particular, since it does not contain P'b, it is suitable as a material for food equipment.

[Effects of the Invention] As explained above, the austenitic stainless steel according to the present invention contains 1% by weight, C'02% or less, Si:
2.0% or less, Mn: 10.0% or less, Cr: 7.5~
30.0%, Ni: 40.0% or less, Bi: 0.005
~0.50%, Sn: 0.005~0.70%, B: 0
．． 0005 to 0.10% and Zr: 0.0% as necessary.
005-0.50%, REM: 0.005-0.50%
, Ca: 0.09% or less, AM: 0.05 to 0.5%,
Nb: 0.05-3.0%, Ta: 0.05-0.5%
, T i :0.05~2.0%, V:0.05~
One or more types selected from 0.5%, also as necessary Mo: 5, 0% or less, Cu: 4
．． One or two types selected from 0% or less, P: 0.20% or less, S/0.40% or less, O: 0.0
2% or less, N: 0.10% or less, and the remainder consists of Fe and impurities, so it has excellent hot workability, machinability, and corrosion resistance, and can be rolled by normal hot rolling. Since it is possible to bloom, it reduces manufacturing costs, and its excellent machinability allows it to be easily formed into parts by cutting.It also has excellent corrosion resistance, and especially contains Pb. This has the great effect of not causing any food hygiene problems and making it suitable as a material for food equipment.

Claims (4)

[Claims] (1) In weight%, C: 0.2% or less, Si: 2.0% or less, Mn: 10.0% or less, Cr: 7.5 to 30.0%, Ni: 40.0% or less, Bi: 0.005-0.50%, Sn: 0.005-0.70%, B: 0.0005-0.10%, P: 0.20% or less, S: 0.40% or less, O : 0.02% or less, N: 0.10% or less, the remainder being Fe and impurities. (2) In weight%, C: 0.2% or less, Si: 2.0% or less, Mn: 10.0% or less, Cr: 7.5 to 30.0%, Ni: 40.0% or less, Bi: 0.005-0.50%, Sn: 0.005-0.70%, B: 0.0005-0.10%, and Zr: 0.005-0.50%, REM: 0.0
05-0.50%, Ca: 0.09% or less, Al: 0.
05-0.5%, Nb: 0.05-3.0%, Ta: 0
．． 05-0.5%, Ti: 0.05-2.0%, V: 0
．． One or more selected from 05 to 0.5%, P: 0.20% or less, S: 0.40% or less, O: 0.02% or less, N: 0.10% or less, An austenitic stainless free-cutting steel characterized by the remainder being Fe and impurities. (3) In weight%, C: 0.2% or less, Si: 2.0% or less, Mn: 10.0% or less, Cr: 7.5 to 30.0%, Ni: 40.0% or less, Bi: 0.005-0.50%, Sn: 0.005-0.70%, B: 0.0005-0.10%, and Mo: 5.0% or less, Cu: 4.0% or less One or two selected from among: P: 0.20% or less, S: 0.40% or less, O: 0.02% or less, N: 0.10% or less, and the balance consists of Fe and impurities. Characteristic austenitic stainless free-cutting steel. (4) In weight%, C: 0.2% or less, Si: 2.0% or less, Mn: 10.0% or less, Cr: 7.5 to 30.0%, Ni: 40.0% or less, Bi: 0.005-0.50%, Sn: 0.005-0.70%, B: 0.0005-0.10%, and Zr: 0.005-0.50%, REM: 0.0
05-0.50%, Ca: 0.09% or less, Al: 0.
05-0.5%, Nb: 0.05-3.0%, Ta: 0
．． 05-0.5%, Ti: 0.05-2.0%, V: 0
．． One or more types selected from 05 to 0.5%, further one or two types selected from Mo: 5.0% or less, Cu: 4.0% or less, P: 0.20 % or less, S: 0.40% or less, O: 0.02% or less, N: 0.10% or less, the balance being Fe and impurities.