JPS613872A - Free-cutting austenitic stainless steel having excellent drawability - Google Patents

Abstract

PURPOSE:To prevent cracking of an S-contg. free-cutting austenitic stainless steel during drawing by decreasing the content of C and N in said steel and controlling the total content of Ni and Cu to a specific value. CONSTITUTION:The total content of C and N as the component to affect drawing crackability of the S-contg. free-cutting austenitic stainless steel contg., by weight %, <0.05% C, <1.00% Si, <2.00% Mn, 8-11% Ni, 17-19% Cr, 0.20-0.40% S, <0.04% N, 0.25-1.00% Cu or further 0.1-0.6% Mo is controlled to <=0.07% and the Cu which decreases work hardenability by the synergistic effect with Ni is incorporated therein at >=9.50% in terms of Ni+2Cu. The generation of a drawing crack in the austenitic stainless steel provided with the excellent free-cutting property by the addition of S is decreased by adjusting the content of the above-mentioned impurities and additive elements.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a free-cutting austenitic stainless steel mesh having excellent drawing workability.

Austenitic stainless steel is corrosion resistant and heat resistant
.

Because of its excellent properties, it is used in a wide range of fields as structural members and mechanical parts.

Machine parts such as bolts, nuts, screws, shafts, and pins are drawn into the specified shape and then finished into products by cutting, which improves the productivity of the cutting process in some applications. Because, S, Se
Free-cutting austenitic stainless steel containing free-cutting elements such as Pb is used.

However, in steels containing about 0.20% S, such as 5US303, which is a typical free-cutting austenitic stainless steel, sulfides spread in the rolling direction tend to become starting points for cracks during cold working. , has the problem of significantly reducing cold working 41.

Therefore, in order to prevent the occurrence of cold working cracks, free-cutting austenitic stainless steels have been used in which the machinability is sacrificed and the S spacing is reduced to 0.05 to 0.20%.

On the other hand, austenitic stainless steel is a steel that generates martensite during cold working and is easily work hardened.

This tendency also applies to austenitic stainless steels.
The smaller the Cr content and the lower the austenite stability, the greater the cold work cracking caused by work hardening.

In particular, when the amount of deformation of the surface layer is large, such as during drawing, only the surface layer undergoes significant work hardening, resulting in a large difference in hardness between it and the inside, and large residual stress exists in the surface layer. Therefore, cracks during drawing process are likely to occur.

In this way, conventional S free-cutting austenitic stainless steels reduce the amount of S, sacrificing machinability, and the work hardening properties of austenitic stainless steels themselves cause drawing cracks, resulting in poor machinability and poor machinability. I was not satisfied with either sex.

The object of the present invention is to obtain an inexpensive free-cutting austenitic stainless steel having excellent drawing workability and eliminating the drawbacks of conventional steels.

The present inventors investigated the influence of C+N and Ni+ 2 Cu on the drawing cracking of S-containing austenitic stainless steel, the interaction between C+N and Ni+ 2 Cu, and the
As a result of extensive research into the balance of Ni, Mn, C, N, Cu, etc., we succeeded in developing the steel of the present invention.

That is, 0.30 Si -1,6Mn -18Cr
-0,25S steel with 0 to 0.15% C+N,
Ni+2C: Tests were conducted with u varying from 8.0 to 12°0%.
The amount and the amount of Ni+ 2 Cu were found. As is clear from Figure 1, as the amount of C0N decreases, Ni+
As the amount of 2cU increases, the incidence of drawing cracks decreases. That is, when the amount of C+N is 0.07% or less and the amount of Ni4-2Cu is 9.50% or more, no drawing cracks occur.

This is due to a decrease in work hardenability due to a decrease in C+Nl and a decrease in Nl.
By stabilizing the austenite phase by increasing the amount of i-1-2Cu, the formation of martensite during drawing was suppressed, and the occurrence of drawing cracks was prevented.

From Figure 1, a and the necessary N are required to prevent cracking during drawing process.
By finding the minimum content of i+Cu, it was possible to obtain free-cutting austenitic stainless steel at low cost.

Figure 2 shows 0.02C-0,30Si-1,6Mn-8,
The effect of Cu on drawing cracking in 5N+ -01Cr -0,3O3-0,OIN steel was investigated, and Fig. 3 shows the influence of Cu on drawing cracks in 0.02G-0,30Si.
L6Mn-8,5Ni-18Cr-0,5Cu-
The influence of S on drawing cracking in 0, 01N steel was investigated. As is clear from Figure 2.3, by having the above composition, C4 is 0.25 to 1
．． It has been found that drawing process cracks do not occur when the S content is 0% or when the S content is increased to 0.40%.

In this way, the steel of the present invention has a C of 0.05% or less and a Si of 1.0%.
0% or less, Mn 2.0% or less, Ni 8.0 to L1.
0%, Cr 17.0-19.0%, S 0.20-0
．． 40%, N 0.04% or less, Cu 0.25-],
00%, and C1N 0.07% or less, Ni
+ 2Cu 9.5% or more, and if necessary, M
By containing o'0.1 to 0.6%, it is inexpensive,
It has excellent drawing workability and free machinability.

Like N, C is an element that improves work hardening properties, thereby deteriorating drawing workability, and also forms chromium carbide, reducing corrosion resistance. In the present invention, it is desirable to reduce this as much as possible. It was set to 0.05% or less.

Si is a necessary element for deoxidation during steel manufacturing, but the presence of more than necessary impairs drawing workability due to solid solution strengthening.
It also reduces hot workability, so the upper limit is set to 1.0.
It was set to 0% or less.

Like Si, Mn is used as a deoxidizing agent and is also an element that stabilizes the austenite phase. It is also an element that combines with S to produce MnS and improves machinability. However, if it is contained in a large amount, hot workability is reduced, so the upper limit was set at 2.00%.

Ni is an important element for improving corrosion resistance, lowering the hardness of the matrix, and at the same time stabilizing the austenite phase, and must be contained in an amount of 8.0% or more. However, since Ni is an expensive element, its content should be kept to the minimum necessary, and the upper limit was set at 11.0%.

Cr is the most important element for improving corrosion resistance.
It is necessary to contain at least 17.0% or more. However, if the content increases, the ferrite-austenite balance in the high temperature range will be disrupted, resulting in a significant decline in hot workability and also reducing drawing workability, so the upper limit should be set at 1.
It was set at 9.0%.

S is extremely effective as an element for improving machinability in austenitic stainless steel, and the machinability improves as the content increases, so it must be contained in an amount of 0.20% or more. However, since S is an element that degrades corrosion resistance and also reduces hot workability and cold workability, the upper limit is set to 0.
It was set at 40%.

Like C, N improves work hardenability, and Cu
Due to the synergistic effect with i, the work hardenability is reduced, and the fourth
As is clear from the figure, the most important aspect of the present invention is to reduce the difference in hardness between the surface layer and the center during drawing, prevent cracking during drawing, and further improve machinability and corrosion resistance. element with at least 0.
It is necessary to contain 25% or more, and the lower limit is set to 0.25%. However, if it is contained in a large amount, hot workability will be significantly impaired due to red heat brittleness, so the upper limit was set at 1.00%.

MO is an element that increases corrosion resistance and must be contained in an amount of 0.10% or more. However, since Mo is an expensive element, the upper limit was set to o and eo%.

As for C + N, as mentioned above, both C and N are elements that deteriorate drawing workability by increasing work hardening properties, and if the sum of C + N exceeds 0.07%, drawing cracks are likely to occur. It is desirable to lower the upper limit to 0 as much as possible.
．． It was set at 0.7%.

Ni + 2 Cu is an important element in the present invention, which reduces work hardenability due to the synergistic effect of Ni and Cu and prevents pultrusion cracking.If the sum of Ni + 2Cu is 9.5% or less, pultrusion cracking will occur. Since this is likely to occur, the lower limit was set at 9.5%.

Next, the characteristics of the steel of the present invention will be clarified by comparing it with conventional steel and comparative steel through examples.

Table 1 shows the chemical composition of these test steels.

In Table 1, A-Ell is conventional steel 5US303, F
The steel is a comparative steel, and G-Qil is a steel of the present invention.

Table 2 shows the incidence of drawing cracks, machinability, and corrosion resistance after the test steels in Table 1 were heated at 1050°C for 30 minutes and subjected to solid solution treatment of W and Q. be.

Regarding the incidence of cracking during drawing process, a sample material of 1 Ommφ which was pickled with 5% sulfuric acid and further pickled with nitric-fluoric acid was tested at 8.5 m.
This figure shows the crack occurrence rate when the sample was drawn into a hexagonal shape (area reduction rate of 20.3%), and a lubricating oil for drawing was used as the lubricant.

Regarding machinability, we prepared five pieces of 40mmφX]Omm materials, used a 5φ5KH9 straight drill as the cutting tool, and measured the drill drilling time at a rotation speed of 114 Orpm and a thrust of 30kg (weight free fall method). It is expressed as an index with a certain A steel set as 100.

Regarding corrosion resistance, the corrosion weight loss when immersed in boiling 5% sulfuric acid solution at 611r is shown.

As is known from Table 2, conventional steels A and B are C
Due to the high +N content of 0.12% and 0.09%, the ζ drawing crack occurrence rate is as high as 56.17%, and AW! Sli is 0. ] Due to the small amount of 5%, machinability is also low. Also, regarding C steel, C
Due to the low U content of 0.05%, the occurrence rate of drawing cracks is as high as 35%, and for D, E, and F steels, the occurrence rate of drawing cracks is 12 to 50% due to the low Ni+2Cu content. %, which was high.

In contrast, the steels G to Q, which are the steels of the present invention, are C4-No.
, 07% or less, Ni + 2 Cu 9.5% or more,
By reducing work hardening properties, J'
In the steel of the present invention, Si was increased to 0.20 to 0.40%, but no drawing cracks caused by S were generated. In addition, machinability is 1.3 to 1.6% compared to conventional steel A steel by increasing S (J to 0.20 to 0.40%).
It has twice the machinability and also has corrosion resistance of 0.20 to 0.40%, which contains a large amount of S, but the corrosion loss is 320 to 587 g1rd・h, which is the conventional steel A steel. It was almost equivalent.

As described above, the steel of the present invention is an austenitic stainless steel that has corrosion resistance equivalent to that of conventional steel and has excellent drawing workability and machinability.

As mentioned above, in order to prevent the occurrence of drawing cracks, the steel of the present invention has the content of elements that increase work hardenability such as C and N as low as possible, and alloys that reduce work hardenability such as Ni and Cu. By containing the minimum required amount of S, it improves drawing workability at a low cost, and prevents cracking caused by S, so it is possible to add the necessary amount of S, and has excellent machinability, making it highly practical. It is something.

[Brief explanation of drawings]

Figure 1 shows the effects of C-1-N and Ni+2 on drawing cracking.
Figure 2 is a diagram showing the influence of Cu, and Figure 2 is a diagram showing the relationship between the occurrence rate of pultrusion cracks and Cu, and Figure 3 is a diagram showing the relationship between pultrusion cracks and S. Figure 4 shows the influence of Ni and Cu on the hardness after drawing as C0N('ya
) S(y,)

Claims (1)

[Claims] 1. C 0.05% or less, Si 1.00% or less, Mn 2.00% or less, Ni 8.0 to 11.0%, C
r17.0-19.0%, S0.20-0.40%, N
Contains 0.04% or less, Cu 0.25 to 1.00%,
A free-cutting austenitic stainless steel with excellent drawing workability, characterized in that it contains 0.07% or less of C+N, 9.50% or more of Ni+2Cu, and the remainder consists of Fe and impurity elements. 2. Weight ratio: C 0.05% or less, Si 1.00% or less, Mn 2.00% or less, Ni 8.0 to 11.0%, C
r17.0-19.0%, S0.20-0.40%, N
Contains 0.04% or less, Cu 0.25 to 1.00%,
Furthermore, 0.1 to 0.6% of Mo is contained, and C+N0
．． A free-cutting austenitic stainless steel with excellent drawing workability, characterized by having a Ni+2Cu content of 0.07% or less, a Ni+2Cu content of 9.50% or more, and the remainder consisting of Fe and impurity elements.