JPH032351A - Free cutting steel - Google Patents

Abstract

PURPOSE:To improve cold workability and pressure resistance by regulating O content to a specific value or below and controlling the shape of sulfide in a free cutting steel having a specific composition. CONSTITUTION:This free cutting steel has a composition consisting of, by weight, <=0.20% C, <=0.10% Si, <=2.0% Mn, <=0.10% P, 0.15-0.40% S, <=0.0080% O, and the balance Fe and containing, if necessary, 0.03-0.35% Pb and/or 0.005-0.500% of one or more elements among Bi, Te, Se, Sn, Zr, B, and Ca and also has a structure in which sulfides of 0.5-5.0mu length and 0.5-3.0mu width comprise >=80% of the whole of sulfides. This free cutting steel has superior cold workability and pressure resistance as well as superior machinability. In the above composition, excessive growth of sulfides takes place if O content is in excess, and, as a result, cold workability is deteriorated and pressure leakage is brought about from the boundaries between the sulfides and a matrix.

Description

[Detailed description of the invention] [Purpose of the invention]

(Industrial Application Field) The present invention is applicable to telephones, radios, stereos, and televisions. Various parts in a wide range of fields, such as telecommunication mechanical parts such as videos, precision mechanical parts such as watches and copy computers, pressure equipment parts such as air cylinders and oil cylinders, transport@mechanical parts such as automobiles and bicycles, etc., such as gears, Shafts, pins, screws, nuts, nozzles,
This relates to free-cutting steel that has excellent cold workability and is used as a material for nipples, valves, etc. (Prior art) Conventionally, the materials for the various parts illustrated above include:
Machine structural steels such as SC material, SCM material, SCr material, and S0M material are used, and carbon tone S is used to improve their machinability. Carbon steel 10 pb, carbon steel + S + Pb, alloy condition S. Alloy steel + pb, alloy steel + S + Pb, carbon steel + Ca + (
S)+ (Pb), alloy condition〇a+ (S)+(P b
) and other combinations have been used as appropriate. (Problems to be solved by the invention) Steels with improved machinability of carbon steels and alloy steels,
As mentioned above, in manufacturing the various parts illustrated,
It was usual to perform 4j'J machining, but in recent years, there has been a demand for manufacturing by forming with high productivity by cold forging (cold plastic working) and then finishing by cutting. Materials for various parts are now required to have excellent not only machinability but also cold workability. However, while the above-mentioned conventional free-cutting steel has excellent machinability, when used for example in the above-mentioned pressure equipment parts,
Problems include pressure leaks and poor cold workability due to excessively large sulfides. (9. Purpose of the present invention) The present invention was made in view of the above-mentioned conventional problems, and in particular, by using a composite free-cutting steel of sulfur and sulfur/lead, a certain level of machinability is secured, and a cooling process is achieved. The object of the present invention is to provide free-cutting steel that has improved machinability and does not cause pressure leaks.

[Structure of the invention]

(Means for Solving the Problems) The free-cutting steel with excellent cold workability according to the present invention has, in weight %,
C: 0.20% or less, Si: 0.10% or less, M n
+ 2, 0% or less, P: o, 10% or less, S: 0.1
5 to 0.40%, O: 0.0080% or less, Pb: 0.03 to 0.35% as necessary, B as necessary
one or more selected from i, Te, Se, Sn, Zr, B, Ca, total 20,005 to 0.5
00%, the balance consists of Fe and impurities, and 80% or more of the total sulfide has a length of 0.5 to 5.0 μm and a width of 0.5 to 5.0 μm.
It is characterized by having a structure in which Cu in the impurity is within a range of 3.0 gm. The total content of Ni, Cr, and Mo should be 1.0% or less, and 80% or more of the total sulfide should have a length of 0.5 to 5.0%.
It is characterized in that it is in the range of .mu.m and @0, 5 to 3, 0 .mu.m, and is distributed within the range of 5 to 30 in loOpmz. Next, the reason for limiting the composition (weight %) and sulfide form of the free-cutting steel having excellent cold workability and pressure resistance according to the present invention will be explained. C: 0.20% or less C is an element useful for ensuring the strength of the various mechanical parts listed above, and the content is about the same as that of conventional low carbon sulfur and sulfur 6-lead composite free-cutting steels. There is. but,
If too much, machinability deteriorates, so the content was set to 0.20% or less. Si: 0.10% or less Si is used as a deoxidizing agent during melting in ordinary steel, but this Si is a matrix (ferrite) strengthening element and is not suitable for deformation in order to improve cold workability. Since it is an element that has a negative effect by increasing the resistance, 1. In the free-cutting steel according to the present invention, it is necessary to further improve its machinability and to further improve its cold 1f (I) workability. Therefore, it was decided to keep the St content to a trace amount or impurity level, and it was regulated to 0.10% or less. Mn: 2, 0% or less Mn acts as a deoxidizing agent during steel making, and also acts as a ) and has the effect of stabilizing it, so it is more desirable to contain it in an amount of 0.3% or more.
If it is too large, machinability deteriorates, so it is set at 2.0% or less. P: 0.10% or less P has the effect of increasing the hardness after cold drawing and improving machinability when performing cold drawing, so if necessary, for example, 0.03% or more. Although it is desirable to contain it, if it is contained in a large amount, the toughness is reduced, so the content is set to 0.1 θ% or less. S: 0.15-0.40% S is an element that should be suppressed for the purpose of improving cold workability, but it is an effective element for improving the machinability of steel and is the basis of free-cutting steel. Since it is an element that becomes , it was contained in an amount of 0.15% or more. However, if the content is too large, the strength and toughness will decrease, so the content should be 0.40% or less. Pb: 0.03-0.35% Pb is an effective element for improving the machinability of steel, so it is good to include it at 0.03% or more as necessary.
However, if the amount is too large, manufacturing defects may occur due to sweating of Pb, so even if Pb is included, it must be kept at 0.35% or less. 0: 0.0080% or less If the 0 content is too high, sulfides will grow too much, deteriorating cold workability and causing pressure leaks from the interface between the sulfide and the matrix. The amount was limited to an extremely small amount of 0.0080% or less. One or more selected from Bi, Te, Se, Sn, Zr, B, Ca in total 20,005~o,
soo% Bi, Te, Se, Sn, Zr, B, and Ca are all effective elements for improving the machinability of steel, and
Zr, Te, and Ca are elements that are effective in improving the morphology of sulfides present in steel, so if necessary, one or more of these may be contained in a total amount of 0.005% or more. Good too. However, if it is too large, it may actually reduce machinability or hot workability, so even if it is included, it is preferable that the total amount of these elements is 0.500% or less. Cu, Ni, Cr, MO (7) total is 1.0% or less Cu
, Ni, Cr, and Mo are elements that are easily mixed in during manufacturing, but these are all unnecessary elements in carbon steel-based free-cutting steel, so the total of these should be 1.0% or less. It is more desirable. The free-cutting steel according to this proposal has the above-mentioned chemical composition, and more than 80% of the total sulfides have a length of 0.5 to 5.0 mm.
μm and the width is within the range of 0.5 to 3.0 μm, but in particular, Mn, which is a typical component of sulfide, is
If the length and width of S are too large, it will have a negative effect on cold workability and will cause pressure leaks when used in pressure equipment parts, while if it is too small, it will not have a good effect on machinability. Since it is undesirable, more than 80% of the total sulfide
has a length of 0.5 to 5.0 μm and a width of 0.5 to 3.0 Bm
It was regulated to be within the range of More preferably, 80% or more of all sulfides have a length of 0.5 to 5.071 m and a width of 0.5 to 3.0 μm, and there are 5 to 30 sulfides in 100 gm2. It is better to have a distribution such that the number of sulfides is too large, and it is not very desirable for the purpose of improving cold workability. is not very desirable. (Action of the invention) The free-cutting steel according to the present invention has a chemical composition limited as described above and a sulfide morphology controlled as described above, and is different from conventional sulfur and sulfur/lead composites. By applying oxygen reduction measures to free-cutting steel and controlling the form of sulfides, we improved cold workability and pressure resistance, and also reduced Si, which is a matrix-strengthening element that has a negative effect on cold workability. Because of this, it has the effect of ensuring sufficient machinability and extremely excellent cold workability. (Example) After melting steel with the chemical composition shown in Table 1, it is made into an ingot with a diameter of 1
After making a 1 mm polished steel bar, we investigated the sulfide morphology and sulfide distribution amount of the 6 steel, and the critical compressive strain (cross nHO/H) when simply upset-processed from the height Ho to the height H.
Furthermore, the machinability was investigated under the conditions shown in Table 2. These results are also shown in Table 1. The cold workability and machinability were evaluated using the cold workability index and machinability index based on Comparative Example 1. Table 2: Machinability evaluation test conditions As is clear from the results shown in Table 1, conventional free-cutting steel (
Although the machinability was slightly lower than that of Comparative Example 1 (standard), it was recognized that the cold workability was considerably improved, and the various machine parts listed earlier were manufactured by cold working with excellent productivity. It was subsequently confirmed that this is a free-cutting steel that is extremely suitable for finishing by cutting.

【Effect of the invention】

The free-cutting steel according to the present invention has, in weight percent, C: 0.20% or less, Si: O, 10% or less, Mn = 2.0% or less, and P: 0.
．． 10% or less, S2 0.15-0.40%, O: 0.0
080% or less, Pb: 0.03 to 0.35 as necessary
%, as well as Bi, Te, Se, and Sn. Total of one or more selected from Zr, B, and Ca: 0.005 to 0.500%, the balance consisting of Fe and impurities, and 80% or more of the total sulfide has a length of 0.5
~ 5.0 μm and a width within the range of 0.5 to 3.0 gm, it has excellent machinability and cold workability. For example, Gears, shafts, pins, screws, nuts, nozzles. It has the great effect of being an extremely excellent material for forming various mechanical parts such as nipples, valves, cylinders, etc. by cold plastic working with excellent productivity and then finishing them by cutting. Patent applicant: Daido Steel Co., Ltd.

Claims (1)

[Claims] (1) In weight%, C: 0.20% or less, Si: 0.10
% or less, Mn: 2.0% or less, P: 0.10% or less, S
: 0.15-0.40%, O: 0.0080% or less, the balance consists of Fe and impurities, and 80% or more of the total sulfide has a length of 0.5-5.0 μm and a width of 0.5-5.0 μm. 3.0μm
A free-cutting steel with excellent cold workability that is within the range of . (2) In weight%, C: 0.20% or less, Si: 0.10
% or less, Mn: 2.0% or less, P: 0.10% or less, S
:0.15~0.40%, Pb:0.03~0.35%
, O: 0.0080% or less, the balance consists of Fe and impurities, and 80% or more of the total sulfide has a length of 0.5 to 5.0μ
A free-cutting steel with excellent cold workability, characterized in that the width is within the range of 0.5 to 3.0 μm. (3) In weight%, C: 0.20% or less, Si: 0.10
% or less, Mn: 2.0% or less, P: 0.10% or less, S
: 0.15 to 0.40%, O: 0.0080% or less, and the total of one or more selected from Bi, Te, Se, Sn, Zr, B, Ca: 0.005 to 0
．． 500%, the balance is Fe and impurities, and more than 80% of the total sulfide has a length of 0.5 to 5.0 μm and a width of 0.5 μm.
A free-cutting steel with excellent cold workability, characterized in that the diameter is within the range of 5 to 3.0 μm. (4) In weight%, C: 0.20% or less, Si: 0.10
% or less, Mn: 2.0% or less, P: 0.10% or less, S
:0.15~0.40%, Pb:0.03~0.35%
, O: 0.0080% or less, and Bi, Te, Se,
One or two selected from Sn, Zr, B, Ca
Total of species or more: 0.005 to 0.500%, the balance consists of Fe and impurities, and more than 80% of the total sulfide has a length of 0.
．． A free-cutting steel with excellent cold workability, characterized by having a diameter of 5 to 5.0 μm and a width of 0.5 to 3.0 μm. (5) Claims (1), (2), and (3), characterized in that the total content of Cu, Ni, Cr, and Mo in the impurities is 1.0% or less. or No. (4)
Free-cutting steel with excellent cold workability as described in any of the above. (6) More than 80% of all sulfides have a length of 0.5 to 5.0μ
m and within the width range of 0.5 to 3.0 μm and 100
Claims (1) and (2), characterized in that they are distributed in the range of 5 to 30 in μm^2;
The free-cutting steel with excellent cold workability according to any one of item (3), item (4), or item (5).