JPS6369950A - Nonmagnetic austenitic stainless steel having high hardness - Google Patents

Abstract

PURPOSE:To attain reduction in the amounts of expensive components and to improve the nonmagnetism and hardness, by adding no Mo unlike SUS 316 steel and specifying the amounts of Mn, Cr, Cu and N in a balanced state. CONSTITUTION:The compsn. of an austenitic stainless steel is composed of, by weight, <=0.15% C, <=1.5% Si, 0.5-6.0% Mn, 17-23% Cr, 10-15% Ni, 0.1-3.0% Cu, <0.20-0.35% N and the balance Fe. In the steel, the solid soln. hardening action of N is effectively utilized, so high strength and hardness are obtd. by intense working. In order to improve the hot workability without deteriorating various characteristics such as high nonmagnetism, high strength and hardness, 0.001-0.020% in total of Ca and rare earth metals and/or 0.0005-0.015% B may be added to the above-mentioned compsn.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a hot working method that can obtain high hardness by cold working or further aging treatment and maintain sufficiently low magnetic permeability. This invention relates to non-magnetic austenitic stainless steel with improved workability.

[Conventional technology]

In recent years, with the rapid development and spread of magnetic recording devices and electronic equipment, there has been an increasing demand for non-magnetic steel with extremely low magnetic noise. The conditions that non-magnetic steel must meet as a constituent material for this type of equipment are as follows.

(A) Must have sufficient non-magnetic performance even under severe cold working.

(B) Must have sufficient strength.

(C) The price is low.

(D) When welded, the magnetic permeability of the welded part is low.

Particularly recently, thin-walled pipes are increasingly being used for rotating shafts and tape guide posts, and the materials used for these parts are also subject to the conditions listed above.
4. Excellent abrasion resistance has become an essential condition.

Currently, non-magnetic steels include 5US304W4, 5US305fi, and 5U, which have stable austenite properties against processing.
Austenitic stainless steels such as S316 steel are the mainstream.

However, 5US304 Rust is a meta-stabilized austenitic stainless steel and undergoes martensitic transformation even with slight cold working, leading to an increase in magnetic permeability, which poses a problem as a non-magnetic steel.

Well, SUS 305m, SUS 316ff4, austenite stability against processing is 20%.
SUS 316 steel has excellent properties as a non-magnetic steel, but has the disadvantage of being very expensive, since it has a high Ni content, and contains MO, although it has excellent properties as a non-magnetic steel. Furthermore, these hooks have poor wear resistance because high hardness cannot be obtained even by cold working.

On the other hand, as an example of the prior art, JP-A-54-8'1916
However, since this steel is based on 5US304fi, it has low Nl and Cr (Cu and N are not actively added, so SUS 316 has poor non-magnetic performance.

[Problem that the invention seeks to solve]

As mentioned above, when conventional non-magnetic steels are subjected to severe cold working, their magnetic permeability increases due to insufficient austenite stability, and high hardness cannot be obtained, resulting in poor wear resistance. SUS 316 steel has a problem in that it is very expensive because it contains Mo.

The purpose of the present invention is to solve the problems of the above-mentioned prior art, and to
In contrast to S316 steel, no Mo is added, and Mn, Cr, and C
By balancing u and N under optimal conditions, it has non-magnetic performance superior to conventional non-magnetic steel, and by applying cold workability or aging under appropriate conditions, it has high strength and high hardness. Non-magnetic austenitic stainless steel that can provide high wear resistance and improved hot workability to increase productivity and manufacturing cost.
To provide a non-magnetic austenitic stainless steel that is cheaper than 316M.

[Means and effects for solving the problems] The above objects of the present invention are achieved by the following two inventions. The gist of the first invention is as follows (that is, in terms of weight ratio, C: 0.15% Si: 1.5% or less Mn = 0, 5-6, 0% Cr: 17 -23% Ni: 10-15% Cu: 0.1-3.0% N: Contains more than 0.207. to 35% or less, and the remainder consists of Fe and inevitable impurities. It is a high-hardness non-magnetic austenite stainless steel.

The gist of the second invention is as follows.

That is, in addition to the same basic components as the first invention, Ca and rare earth metal R (hereinafter referred to as REM): 0.001~
0.20%, B: 0.0005 to 0.015% High hardness non-magnetic austenitic stainless steel characterized by containing one or more selected from among them, with the remainder consisting of Fs and inevitable impurities. It is steel.

The present invention uses steel plates and steel strips obtained by the normal manufacturing process of ingots having the above components, that is, hot rolling - sintering pure pickling → cold rolling → annealing pickling, and processes them as necessary. After processing such as welding and welding, cold working is performed to obtain high strength and high hardness, and then further cold working is performed at 450 to 600°C for 1
It is a non-magnetic austenitic stainless steel that can be aged for 0 minutes or more to achieve strength and hardness that cannot be obtained by cold working alone.

When non-magnetic materials are used as parts and constituent materials of various 8i devices, they are subjected to cutting, machining, processing to obtain strength (for example, drawing), welding, etc.

On the other hand, it is generally known that austenitic stainless steel undergoes martensitic transformation through hard working and becomes magnetic.

For example, 5US316 steel, which is commonly used in this type of application, has a CGS of approximately 1.005 in the annealed state.
(5000e magnetization), but this has a magnetic permeability of 20
% or more, the magnetic permeability is 10% cold rolling.
CG3 units tend to rapidly increase at a rate of 0.01 or more.

The present inventors focused on these points and aimed to obtain a material that can maintain excellent non-magnetic performance even when subjected to severe cold working for the purpose of increasing strength and #4 abrasion resistance. With this goal in mind, various studies were conducted on the magnetic permeability of austenitic stainless steels made of various components and cold rolled into annealed steel plates.

In the present invention, based on the results, we considered the processing stability of non-magnetic performance, and in order to obtain high non-magnetic performance, high strength, and high hardness at the same time, we actively added N to enhance its solid solution hardening effect. Because it is effectively utilized, by undergoing severe processing,
High strength and hardness can be obtained.

Moreover, as a result of research, it has been found that by further aging this at a temperature of 450 to 600°C for 10 minutes or more, high strength and hardness that cannot be obtained by cold working alone can be obtained.

As will be described later, the present inventors focused on the fact that hot workability is poor in component systems that emphasize non-magnetic properties, high strength, and high hardness, and as a result of repeated research on this point, the first invention In the component system shown in , the strength within the crystal grains of the slab becomes higher relative to the grain boundaries due to the solid solution hardening effect, so S, P
It was found that this is due to the remarkable hot embrittlement effect caused by the segregation of impurities such as in the grain boundaries. Therefore, as a result of repeated research on methods to improve hot workability without impairing properties such as high non-magnetic performance, high strength, and high hardness, we found that Ca, RE
It has been found that addition of M, B, etc. is most effective.

Next, the reason for limiting each component element in the present invention will be explained.

C: C is one of the effective elements that has the effect of stabilizing austenite against processing, and also has a large solid solution hardening effect as well as a precipitation hardening effect as a carbide, so it is desirable to add a large amount. However, if the content exceeds 0.015%, the processability and corrosion resistance deteriorate, so the upper limit was set at 0.15%.

Sl: Si acts as a deoxidizer, but is also a ferrite-forming element, and its content exceeding 15% promotes the formation of δ-ferrite and σ phase, leading to an increase in magnetic permeability, so it was limited to 15% or less.

Mn: Like Ni, Cu, and N, Mn has a strong effect of stabilizing austenite (and is an essential element for the nonmagnetic steel of the present invention. Furthermore, in the present invention, considering corrosion resistance, Cr 1
Since the content is as high as 7 to 23%, it is necessary to add at least 0.5% or more in order to suppress the production of δ ferrite. On the other hand, if the Mn content exceeds 60%, the yield of Mn during melting will decrease and the price will increase, and the ductility of the material will decrease, impairing manufacturability and workability, and the austenite stabilizing effect will decrease. is also saturated, so set the upper limit to 60%.
and was limited to a range of 0.05 to 60%.

Cr: Cr not only has the effect of stabilizing austenite against processing, but is also an important constituent element of stainless steel, and in order to maintain corrosion resistance, the content is preferably 17% or more. On the other hand, Cr is a ferrite-forming element like Si, and its presence in large amounts promotes the formation of ferrite phase, leading to a sudden increase in magnetic permeability and Mn1, an austenite stabilizing element.
There is also a limit to the amount of Cu and N added, so the upper limit is set at 23%.
and was limited to a range of 17% to 23%.

Ni: Ni is a strong austenite stabilizing element, the most important element in stably obtaining non-magnetism, and has the effect of improving corrosion resistance and cold workability. However, along with MO, it is an expensive element, and in order to reduce manufacturing costs, the lower limit was set at 10% without deteriorating the non-magnetic performance.
Considering the addition of Cu and N, the upper limit was set at 15%.

Cu: Cu is an element that stabilizes austenite like MnXNi and Cr5N, and has the effect of improving cold forgeability.
In the present invention, - is the main element, and in order to fully exhibit its effect, the lower limit is set to 0.1%. However, 30
Even if the content exceeds 0.1%, the effect will be saturated and it will cause cracking of the weld, and will also cause grain boundary embrittlement at high temperatures and deteriorate hot workability, so the upper limit is set at 30%.
It was limited to a range of 30%.

N: Similar to Mn, Ni, Cr, and Cu, N has a stabilizing effect on austenite and has a large solid solution hardening effect, and is an advantage of the present invention because it improves non-magnetic performance and at the same time provides high strength and hardness. It is an extremely important element, and in order to fully exhibit its effects, it must be added in an amount exceeding at least 0.20%. However, if the content exceeds 0.035%, blowholes will occur during melting and the integrity of the steel ingot will be impaired.
．． It was limited to 35% or less.

The above-mentioned limited amounts of C, Si, Mn, Cr, Ni1Cu, and N are the basic components of the high hardness nonmagnetic steel according to the present invention, and since the solid solution hardening effect of N is effectively utilized, The composition has a high intracrystalline strength, which reduces the relative strength of the grain boundaries, making cracks more likely to occur during hot working, improving hot workability without compromising nonmagnetic performance, strength, or hardness. Therefore, Ca, REM, and B may be further added. The reason for this limitation is as follows.

CaSREM: In order to fully exhibit the above hot workability improving effect, Ca and REM must be added in a total amount of 0.001% or more. However, if the total amount exceeds 0.020%,
Many oxide inclusions are formed, which deteriorates cleanliness, deteriorates corrosion resistance, and makes melting difficult, so the upper limit is set at 0.020% in total, and 0001 to 0.020%.
limited to the range of

B: B also has the effect of improving hot workability, but if it is less than 0.0005%, it will not have a sufficient effect, and if it is added in excess of 0.015%, weldability will deteriorate and the hot workability improvement effect will be saturated. Upper limit is 0.015%, range is 0.0005-0
．． It was limited to 0.015%.

Note that when Ca and REM are added, it is desirable to suppress the solid solution oxygen to a sufficiently low level in order to fully exhibit their effects.

〔Example〕

Table 1 shows the chemical compositions of the first and second invention steels of the present invention and comparative steels. The first adjustable A1 is 19Cr-12
This is a steel based on Nifi with increased amounts of Cu and N added. A2 increases the amount of C, Cu, and N, and at the same time
This steel has increased the amount of Mn to the maximum of 56%, fully demonstrating the stabilizing effect of non-magnetic performance of Mn. A3 is a steel that further reduces the Ni content to 104%, making it cheaper. B1, B3, and B4 of the second invention are steels with improved hot workability (addition of Ca, REM, and B) compared to A1 to A3, and B2 has a Mn content of 33%. In addition, the amount of Cr was increased to 22%.
This steel contains 0.0034% B in order to increase the B content, stabilize non-magnetism, and improve hot workability. on the other hand,
Comparative steels C1 to C3 are each JIS standard steel SUS 3
04 Tsuba, SUS 305 containing 0.0027% B
steel and SUS 316 steel.

These inventive steels and comparative steels were cast into a 150 kg steel ingot (by high-frequency vacuum melting), hot-rolled, cold-rolled, and then made into steel plates with a thickness of 071111I and solution-treated at 1100°C for 5 minutes. was applied.

The non-magnetic performance was evaluated by cold rolling the sample material to 500 (
Os) The magnetic permeability during magnetization was measured, and a cold rolling ratio-magnetic permeability curve was drawn and compared.

The tensile test was conducted according to JISZ-2241.

The hardness characteristics in the cold-worked state and the hardening characteristics due to aging were evaluated based on the Vickers hardness of the plate surface of a solution-treated steel plate cold-rolled at a rolling rate of 60% and the hardness of a 60% cold-rolled plate.
This was done by comparing the Vickers hardness of the plate surface of plates that were aged at 00°C for 1 hour. In addition, the evaluation of hot workability is
An ingot with a thickness of 50m and a width of 1501III11 was heated to 1250℃.
The tests were conducted to determine the presence or absence of edge cracks when hot-rolled to a thickness of 4 mm, and the cross-sectional shrinkage rate of a fracture test piece in a hot tensile test of a round bar.

FIG. 1 shows the change in magnetic permeability (in CG3 units) of the sample material with respect to the cold rolling rate. Comparison fic 1 is a metastable austenitic stainless steel, and the increase in magnetic permeability is sensitive to cold working, and although it is not shown in Figure 1, even at a cold working rate of 10%, the magnetic permeability is already 14. The non-magnetic properties are extremely poor. This is because austenite is unstable, so even a slight amount of cold working produces martensite, leading to an increase in magnetic permeability.

Comparative steels C2 and C3 maintain low magnetic permeability in the solution state up to a cold rolling reduction of about 20%, but beyond this point, the magnetic permeability rapidly increases, and both C2 and C3 reach a low permeability at a rolling reduction of 60%. The magnetic coefficient exceeds 1015.

In contrast, the steel of the present invention has a low magnetic permeability of 35
% or more, and moreover, the rolling ratio is 60%.
It can be seen that the magnetic permeability of this steel is as low as 101 or less, making it extremely excellent as a non-magnetic steel.

Finally, A2, A3, B2 to B4 maintain their magnetic permeability in the solution state up to a rolling reduction of 53% or higher, and among them, A2 and B3 are extremely excellent, with no increase in magnetic permeability observed at all even at a rolling reduction of 60%. There is. In addition to increasing the amount of Mn, these include Cr and Cu.
This was achieved by increasing the amount of N added in order to simultaneously obtain high non-magnetic performance, high strength, and high hardness.

Among them, A3 and B4 have high properties as shown in the figure despite reducing the amount of Ni, so they are extremely effective steels in that they can obtain high nonmagnetism at a lower cost. .

Next, Table 2 shows the mechanical properties of the test materials, the Vickers hardness of the plate surface of the 60% cold rolled material, the hardness after aging, and the presence or absence of edge cracking during hot rolling.

Present invention tr4A1-A3, B1-B4 (7) Tensile strength 1. t, about 60 kg/mm for comparison W4C1 to C3
2, it is 73 kg/m+w2 or more, and especially in B4 with N amount of 0.30%, it is 86.5 kg/m
+n+*2 strength is obtained.

Looking at the plate surface Vickers hardness of the 60% cold-rolled material in the cold-rolled state, comparative tr4C2 and C3 have a hardness of 370 or less, whereas the steel of the present invention has a high hardness of 400 or more. C1 is 4
It has a high hardness of 42, but this is because austenite is unstable and is hardened because a large amount of martensite is generated by 60% cold rolling. Therefore, it is a high hardness non-magnetic steel. However, it is unsuitable in terms of non-magnetic properties.

Table 2 In contrast, the steel of the present invention has both nonmagnetism and high hardness, characteristics that are difficult to obtain with conventional stainless steel.

In addition, when looking at the Vickers hardness of a 60% cold-rolled material at 500°C for 1 hour, an increase in surface hardness was observed for both the inventive steel and the comparative steel compared to the cold-rolled state. reactor. However, when comparing the values, the values of comparison@C2 and C3 are 392.429, respectively, whereas the values of the invention steel are 47.
3 or more, and B4 in particular has a high hardness of 500 breaths.

Next, if we look at the presence or absence of edge cracks due to hot rolling, comparison jjlc
1 is low in Ni and N, and C2 contains B, so no edge cracking is observed, but Ca.

Comparison tMC with the first invention steel without the addition of REM and B
In No. 3, edge cracking occurred, indicating poor hot workability. On the other hand, in the second invention steel, no edge cracking was observed at all, and good hot workability was obtained due to the addition of Ca, REV, and B.

Furthermore, in order to examine the above-mentioned hot workability improvement effect in more detail, a hot tensile test was conducted using the heat pattern shown in FIG. 2, and the results are shown in FIG.

In FIG. 3, the shaded area indicates the range of the results of the second adjustable range 81 to B4. According to the findings of the present inventors, in this test method, it has been found that when the cross-sectional shrinkage rate is about 60% or more, no edge cracking occurs during hot rolling and good hot workability is exhibited.

Since the first shot cutting A1 and A3 do not aim to improve the hot workability described above, A1 has a tensile temperature of 1100°C or lower,
Further, in A3, the cross-sectional shrinkage rate was less than 60% at 1150° C. or lower, indicating poor hot workability. In particular, the hot shrinkage rate is poor at tensile temperatures around 1000°C, which indicates hot embrittlement due to impurities such as S and P, and these steels are not suitable for high strength. As a result, the strength of the grain boundaries was relatively reduced, and hot embrittlement appeared more prominently.

On the other hand, 81 to B4, which had improved hot workability without impairing nonmagnetic properties and hardness properties,
As shown in the shaded area in the figure, no embrittlement was observed near 1000°C, and the cross-sectional shrinkage was approximately 60% or more up to the tensile temperature of 800°C, indicating good hot workability. . For comparison, the data for Bl, B4 and C3 are shown in Figure 3, but C3 is still slightly higher than 1000.
A brittle region appears around ℃, and the cross-sectional shrinkage rate is also less than 60%.

〔Effect of the invention〕

As is clear from the above examples, the present invention limits the components of the nonmagnetic steel, particularly by balancing Mn, Cr, Cu, and N under optimal conditions, thereby increasing the stability of nonmagnetic properties and at the same time achieving high strength. This relates to an unprecedented new austenitic stainless steel that has high hardness and improved hot workability without sacrificing these properties.
In addition to improving the properties, we were able to obtain high properties at a low cost by reducing manufacturing costs by improving hot workability.

By subjecting the steel of the present invention to cold working and further aging under appropriate conditions, it was possible to simultaneously obtain high magnetic properties and high strength and high hardness.

Therefore, the steel of the present invention can be widely used in members that require non-magnetic properties, high strength, or wear resistance, such as constituent materials for magnetic recording devices and electronic equipment, and constituent materials for large-scale magnetic devices.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between cold rolling reduction and magnetic permeability.
The figure is a diagram showing the heat pattern of the hot tensile test, and FIG. 3 is a diagram showing the relationship between the tensile temperature and cross-sectional shrinkage rate of the hot tensile test.

Claims (2)

[Claims] (1) Weight ratio C: 0.15% or less Si: 1.5% or less Mn: 0.5-6.0% Cr: 17-23% Ni: 10-15% Cu: 0.1-3 .0% N: A high hardness nonmagnetic austenitic stainless steel characterized by containing more than 0.20% and 0.35% or less, with the remainder consisting of Fe and inevitable impurities. (2) Weight ratio: C: 0.15% or less Si: 1.5% or less Mn: 0.5-6.0% Cr: 17-23% Ni: 10-15% Cu: 0.1-3 .0% N: Contains more than 0.20% and 0.35% or less, and further includes Ca and rare earth metals: 0.001 to 0.020% B in total.
: 0.0005 to 0.015% of one or more selected from the group consisting of: 0.0005 to 0.015%, and the remainder being Fe and inevitable impurities.