JPH0772322B2 - Free cutting steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention is a free-cutting steel used as a material for precision small parts used in a wide range of fields such as automobiles and home electric appliances. It is about.

(Prior Art) Conventionally, a low carbon free-cutting steel is often used as a material for precision small parts used in the above-mentioned automobiles, home electric appliances, and the like. Lead (Pb), calcium (Ca), sulfur (S) and sulfur complex, sulfur-special element complex, lead-sulfur complex, tellurium (Te), quaternary (Pb + S + Te + X), etc. was there.

Then, specifically, there was a free-cutting steel in which Pb and Bi were added in combination in order to improve the machinability of low-carbon sulfur free-cutting steel, for example.

(Problems to be solved by the invention) In the free-cutting steel in which Pb and Bi are added together to such low carbon sulfur free-cutting steel, in the tool life, cutting resistance, chip crushability, surface roughness, etc. Among the machinability evaluated, when focusing on the finish surface roughness, which is particularly important for low carbon free-cutting steel, the presence or absence of adhesion of the constituent cutting edge is an important factor.

However, in the conventional case, the same amount of S and Pb and
Even for free-cutting steel with a combination of Bi and Bi, it is said that the built-up edge will be attached during cutting and the finished surface roughness will be poor, or the built-up edge will be good during cutting without the built-up edge being attached. There is a problem in that the roughness of the finished surface may not be constant in some cases.

(Object of the Invention) The present invention has been made by paying attention to the above-mentioned conventional problems, and it is possible to always obtain good finished surface roughness when cutting is performed under practical cutting conditions. The purpose is to provide free-cutting steel.

[Structure of the Invention] (Means for Solving the Problems) The present invention, even when the same amount of S and Pb and Bi are added in combination to improve the machinability in low carbon steel,
As a result of earnest research on the cause of sticking or non-sticking of the constituent cutting edges during cutting, it was found that P and N in the steel had a great influence on the roughness of the finished surface, leading to completion. It is a thing.

That is, the free-cutting steel according to the present invention has a C: 0.05% by weight.
~ 0.15%, Si: 0.05% or less, Mn: 0.80 to 1.50%, P: 0.040
~ 0.090%, S: 0.100-0.400%, Bi: 0.005-0.15%, Pb:
0.10 to 0.35%, N: 0.0065 to 0.015%, O: 0.004 to 0.030
%, Al: 0.002% or less and P + 6N: 0.08 to 0.13%, balance F
It is characterized by comprising e and impurities.

Next, the reasons for limiting the composition range (% by weight) of the free-cutting steel according to the present invention will be described.

C: 0.05 to 0.15% C is an element necessary for ensuring the strength and wear resistance of precision small parts such as automobiles and home electric appliances, and therefore is set to 0.05% or more. However, as the C content increases, the strength and wear resistance improve, but the machinability decreases, and the oxygen content decreases and the sulfide becomes finer to increase the tool wear, resulting in the machinability. Is 0.15%.

Si: 0.05% or less Si is a deoxidizing element, but if it is too much, the amount of oxygen will be too low and the sulfide will be thin, the wear of the tool will be large and the machinability will decrease, so it was made 0.05% or less. .

Mn: 0.80 to 1.50% When Mn is too small, the hot workability is deteriorated, and the MnS amount is decreased to reduce the machinability. However, if it is too large, the amount of deoxidation increases, and the amount of oxygen in the steel becomes too small, which reduces machinability, so it was made 1.50% or less.

P: 0.040 to 0.090% P is an element that affects the presence or absence of adhesion of the constituent cutting edge during cutting together with N and has the effect of improving machinability, so it was set at 0.040% or more. However, if too much, the hot workability deteriorates, so it was set to 0.090%.

S: 0.100 to 0.400% Bi: 0.005 to 0.15% Pb: 0.10 to 0.35% S, Bi, Pb are all effective elements for improving the machinability of steel, and reduce cutting resistance to reduce tool life. Is an effective element to increase the. Of these elements, S acts effectively under cutting conditions on the high speed side, and Pb acts effectively under cutting conditions on the low speed side, so that stable cutting can be performed under a wide range of cutting conditions. The three elements of S, Bi and Pb were added to the composite. In order to obtain such an effect of improving machinability, S is 0.100% or more and Bi is 0.005%.
As described above, Pb is set to 0.10% or more.

However, if the contents of these machinability improving elements are too high, the hot workability is impaired, so S is 0.400% or less and Bi is 0.15%.
Hereinafter, Pb is set to 0.35% or less.

N: 0.0065 to 0.015% N is an element that is likely to be contained during the melting of steel, and is an element that affects the adhesion of the constituent cutting edges during cutting together with P. If the N content is too low, the value of P + 6N Since the amount of P contained for securing the amount will increase, the P content is set to 0.0065% or more so that the P content can be made appropriate. But,
If the amount of N is too large, it may cause troubles in steel making, so it was set to 0.015% or less.

O: 0.004 to 0.030% If the O content is too small, the sulfide becomes fine and wear of the tool is increased to reduce the machinability, so the content was made 0.004% or more. However, if the amount is too large, the amount of oxide produced increases and the tool life is shortened, so the content was made 0.030% or less.

Al: 0.002% or less Al is an element having a deoxidizing action, and if the Al content is too large, the amount of oxygen decreases, the sulfide becomes fine and the tool wear becomes large, and as a result, the machinability deteriorates. It was set to 0.002% or less.

P + 6N: 0.08 to 0.13% As mentioned above, this invention is particularly important for low carbon free-cutting steel among machinability evaluated by tool life, cutting resistance, chip crushability, surface roughness, etc. In order to improve the roughness of the finished surface, it was confirmed that the adhesion of the constituent cutting edge during cutting is an important factor, and P and N contained in the steel indicate whether the constituent cutting edge adheres during the cutting process. It was completed by discovering that it has a large effect on the finish surface roughness. In this case, P
When + 6N is lower than 0.08%, the built-up edge will adhere during cutting and deteriorate the roughness of the finished surface. Therefore, it is necessary to set it to 0.08% or more. It has been confirmed that it is necessary to set it to 0.13% or less because the tool wear increases and the finished surface roughness deteriorates.

Then, in order to satisfy P + 6N in the range of 0.08 to 0.13%,
When the amount of P is increased and the amount of N is decreased, P has a deoxidizing action and reduces the amount of oxygen like Si and Al, and the amount of N is an element that easily enters steel and is small. Doing so causes an increase in cost, and since N acts 6 times, it is rather desirable to reduce the P amount and adjust the N amount within the above range.

(Example) A low carbon steel having the chemical composition shown in Table 1 is melted and melted in a 2ton arc furnace, cast into a 2ton steel ingot, and hot rolled to obtain a wire coil having a diameter of 12 mm, which is drawn and straightened. Then, a round bar having a diameter of 12 mm was obtained.

Next, the round bar made of steel having each of the above chemical components was cut under the conditions shown in Table 2, and the surface finish roughness (Rmax (μm)) of the 1000th work piece was examined. The results are also shown in Table 1.

As shown in Table 1, in Comparative Steel No. 5, the O content is too large, so the amount of oxides is large and the amount of P + 6N is too large, so the wear of the tool is large and the finish of the work piece is rough. Is a large value. Further, in Comparative Steel No. 6, the N content is small and the P + 6N amount is 0.070%, which is too small, so that the component cutting edge is attached during cutting and the finished surface roughness is increased. Furthermore, in Comparative Steel No. 6, it was confirmed that the Si content and the Al content were too large, so that the O content was small, the sulfide was thin, the tool was worn out, and the finished surface roughness was also increased. .

On the other hand, in the present invention steels Nos. 1 to 4 which satisfy the compositional requirements of the free-cutting steel according to the present invention, tool wear is small and
It was confirmed that the finished surface roughness of the 00th processed product was small.

[Advantages of the Invention] As described above, the free-cutting steel according to the present invention is, by weight%, C: 0.05 to 0.15%, Si: 0.05% or less, and Mn: 0.80 to 1.
50%, P: 0.040 to 0.090%, S: 0.100 to 0.400%, Bi: 0.005
~ 0.15%, Pb: 0.10 ~ 0.35%, N: 0.0065 ~ 0.015%, O: 0.
004 to 0.030%, Al: 0.002% or less and P + 6N: 0.08 to 0.1
Since it consists of 3% and the balance Fe and impurities, it is possible to prevent the constituent cutting edges from adhering during cutting under practical cutting conditions, and the finished surface roughness of the workpiece is always good. It is possible to have a very excellent effect.

Claims (1)

[Claims] 1. By weight%, C: 0.05 to 0.15%, Si: 0.05% or less, Mn: 0.80 to 1.50%, P: 0.040 to 0.090%, S: 0.100 to 0.400%, Bi: 0.005 to 0.15%, Free-cutting steel characterized by Pb: 0.10 to 0.35%, N: 0.0065 to 0.015%, O: 0.004 to 0.030%, Al: 0.002% or less and P + 6N: 0.08 to 0.13%, balance Fe and impurities.