JPH0426740A - High strength non-magnetic steel - Google Patents

Abstract

PURPOSE:To easily obtain a high strength non-magnetic steel excellent in hot workability, ductility after cold working and corrosion resistance at a low cost by specifying the compsn. constituted of C, Si, Mn, S, Cr, Ni, Mo, N, Ca, Mg and Fe. CONSTITUTION:This is a high strength non-magnetic steel contg., by weight, <=0.2% C, 0.1 to 2% Si, 0.5 to <4% Mn, <=0.01% S, 20 to 40% Cr, 5 to 15% Ni, 1.5 to 5% Mo, 0.6 to 1.5% N and one or more kinds of 0.001 to 0.02% Ca and 0.001 to 0.02% Mg, furthermore contg., at need, one or more kinds of <=3% Cu and <=5% W and/or one or more kinds of <=2% Nb and <=2% V and the balance Fe with inevitable impurities. The steel is a metallic material combining high strength of about >=1800kgf/mm<2> 0.2% proof stress, good hot workability, excellent ductility after cold working, excellent corrosion resistance, sufficient economical advantage or the like.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a non-magnetic stainless steel that has excellent strength, hot workability, corrosion resistance such as pitting corrosion resistance and sulfuric acid resistance, and ductility after cold working. It is related to.

<Prior art and its problems> Currently, stainless steel has good corrosion resistance and N
Since it is a cheaper material than i-alloys and Ti materials, it has a wide range of uses in various fields, but it has some disadvantages compared to Ti and Ti alloys in terms of strength, especially specific strength.
This was a major obstacle to expanding demand in fields that place importance on this, such as the aircraft industry.

However, so-called "metastable stainless steels" (for example, 5US301 steel), which ensure high strength by causing martensitic transformation through cold working, and those that combine precipitation hardening with martensite after quenching have been developed. Although so-called "PH stainless steels" and the like have been developed to ensure this, all of these materials have magnetism and cannot be used as non-magnetic materials, so their uses are inevitably limited.

In addition, Ni-based alloys such as "Inconel 718 (trade name)", which has γ' precipitated on austenite, are known as non-magnetic materials that can achieve high strength, but these Ni-based alloys are expensive. Therefore, it could not be said to be an industrially versatile material.

Against this background, attempts have recently been made to increase the strength of stainless steel by adding N (nitrogen), such as 5US30.
Materials such as 4N2 have been developed, but none of these materials actually contain N in excess of 0.5% (hereinafter, percentages representing component proportions are expressed as weight percentages). Also, the strength was insufficient. This is because if an excessively large amount of N is added to stainless steel, the heat treatment temperature to dissolve nitrides into austenite single phase becomes too high, and it also causes a great disadvantage in terms of workability.
This is because industrial production of the desired material becomes extremely difficult.

As mentioned above, the development of new materials in recent years has been remarkable, but there are still materials that have even better properties such as strength, hot workability, ductility, and corrosion resistance, as well as advantages in terms of productivity and price. At present, it has not been possible to fully meet recent demands for metal materials that have both

Therefore, based on the above situation, the present invention aimed to:
For example, non-magnetic materials required for aircraft materials etc.
0.2χ Crab resistance High strength of 180 kgf/- or more, good hot workability, and excellent ductility after cold working.

The object of the present invention was to provide a metal material that has both excellent corrosion resistance and sufficient economic advantages.

Means for Solving the Problems> As a result of repeated research and repeated numerous experiments in order to achieve the above object, the present inventors found that [Basically, among the non-magnetic materials that have excellent strength and corrosion resistance, they are inexpensive. For stainless steel, which is relatively advantageous in many aspects, adding N is the most effective and economical way to significantly increase its strength while maintaining its non-magnetism.If the chemical composition of stainless steel is devised and adjusted, it can be used industrially A large amount of N can be dissolved in solid solution at a temperature below 1250℃, and by adjusting the chemical composition and increasing the N content, strength, hot workability, ductility after cold working and strain aging,
We have come to the conclusion that it is possible to create a high-strength non-magnetic steel with excellent corrosion resistance such as pitting corrosion resistance and sulfuric acid resistance.

The present invention was made based on the above findings, etc. [Stainless steel, C: 0.2% or less, St: 0.1 to 2%.

Mn: 0.5% or more and less than 4%, s: 0. ot%
below.

Cr: 20-40%, Ni: 5-15%
.

Mo: 1.5~5%, N: 0.6~
Contains 1.5%, Ca: O, 001-0.02%, Mg:
Also contains one or more of 0.001 to 0.02%,
Alternatively, Cu: 3% or less, W: 5% or less.

By configuring the composition to include one or more of Nb: 2% or less, V: 2% or less, and the remainder consisting of Fe and unavoidable impurities, it is non-magnetic and has excellent strength, hot workability, and cold workability. It is characterized by having good ductility after processing and corrosion resistance.

Hereinafter, in the stainless steel according to the present invention, the reason why the content ratio of each component is numerically limited as described above will be explained together with its effect.

a) C A certain amount of C contributes to the strengthening of austenite together with N, but if the content exceeds 0.2%, solid solution of nitrides becomes difficult, so the upper limit of the C content is set. It was set at 0.2%.

b) 5t Si is an essential component as a deoxidizing agent and also contributes to the strengthening of austenite, but it is difficult to manufacture industrially to keep its content below 0.1%; .0%
The Si content was limited to 0.1 to 2.0% because if the Si content exceeds 2.0%, the effect of increasing the solid solution temperature of nitrides becomes significant, and it also becomes a factor in producing ferrite.

c) Mn Mn is also an element that has a deoxidizing effect, but the more important point is that it is an austenite-forming element and that it works extremely effectively in increasing the solid solubility of N. However, the Mn content is 0.
．． If the content is less than 5%, the desired effect cannot be obtained; on the other hand, if the content is 4% or more, not only does the hot workability tend to decrease, but also the ductility of cold-worked materials and strain-aged materials is affected. Since there are concerns about negative effects, the Mn content should be reduced to 0.
It was limited to 5% or more and less than 4%.

d) SS Since S is the main cause of deteriorating the hot workability of steel, the lower it is, the better it is as an impurity element, but economic considerations and fixation by addition of Ca or Mg should be possible to the extent possible. Therefore, the upper limit of the S content was set at 0.01%.

e) Cr Cr is a main element supporting the corrosion resistance of the steel of the present invention, and is an essential component for increasing the solid solubility of N and lowering the nitride solid solution temperature. However, the content is 20%
If the content is less than 40%, the desired effect cannot be obtained, while if the content exceeds 40%, hot working becomes difficult.
The content was set at 20-40%.

f) Ni is essential as an austenite-forming element, and from this point of view it is necessary to add 5% or more, but on the other hand, if its content exceeds 15%, the effect of lowering the solid solubility of N becomes noticeable. Therefore, the Ni content is 5 to 15%.
It was determined that

g) M.

Mo is an essential element for improving the ductility of cold-worked materials and strain-aged materials related to the steel of the present invention, and also has the effect of improving corrosion resistance, increasing the solid solubility of N, and reducing the solid solution temperature of nitrides. Although it is a useful element that has the effect of increasing the amount of carbon, if its content is less than 1.5%, the desired effect due to the above function cannot be obtained. However, on the other hand, Mo is also a ferrite-forming element, and if it is contained in an amount exceeding 5%, there is a concern that the austenite phase may become unstable. Therefore, the Mo content was determined to be 1.5 to 5%.

h) N N is an essential component for austenite formation and strengthening, but if its content is less than 0.5%, the desired high strength (0.2χ crab resistance 180 kgf/- or more) cannot be achieved. On the other hand, if the content exceeds 1.5%, nitrides will not be completely dissolved even in the chemical composition steel specified in the present invention, resulting in poor mechanical properties (elongation, cold rollability, cold workability). etc.), and also makes hot working difficult. Therefore, the N content was determined to be 0.5 to 1.5%.

The solid solution temperature T('C) for dissolving nitrides in manufacturing the steel of the present invention is Tr('C)≦T(
'C)≦1200°C. here,
T r ('C) is a value determined by the calculation formula % formula %), and if the solution temperature is lower than this value, sufficient solid solution of nitrides cannot be expected.
It is industrially unfavorable to raise the temperature higher than 00°C in terms of equipment and energy consumption.

It goes without saying that the "high-pressure dissolution method" is effective as a means of containing N at a high concentration.

i) Ca and Mg Since Ca and Mg are essential components to reduce the adverse effects of S that deteriorates the hot workability of steel, one or both of them are added, but their content is The amount is 0. oo
If it is less than i%, the effect of improving hot workability is not sufficient;
If each content exceeds 0.02%, it will cause a decrease in hot workability, so the content of each should be reduced to 0.
．． It was limited to 0.001% to 0.02%.

j) Cu, and W These elements have the effect of improving the corrosion resistance of stainless steel, so one or two of these elements may be added as necessary, but other elements may have their own reasons for limiting their content. It will be explained in detail along with the effect of.

Cu Cu is an austenite-forming element and does not show a significant decrease in nitrogen solid solubility like Ni, so it is an effective component for securing the austenite phase, but if it is contained in an amount exceeding 3%, The Co content was determined to be 3% or less since this would lead to a decrease in hot workability.

Although W is a component that does not significantly affect the nitride solid solution temperature, it is also a ferrite-forming element, so the W content was determined to be 5% or less.

k) Nb, and ■ Each of these has the effect of increasing N solubility, so one or two types of these are added as necessary, but they tend to form nitrides that cannot be solid-solubilized, and if added in large amounts, ferrite Therefore, the contents of both ■ and Nb were determined to be 2% or less.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

<Example> First, each steel having the composition shown in Table 1 was melted, and the 0.2χ yield strength, nitride solid solution temperature (minimum temperature required to dissolve nitrides in austenite) ), magnetic permeability, hot workability, elongation and pitting corrosion resistance at 20°C of "70% cold-rolled material" and "strain-aged material obtained by heating this cold-rolled material for 4 minutes at 600°C and then air cooling", and The sulfuric acid properties were investigated.

The 0.2χ proof stress is obtained by annealing the hot-worked material above the nitride solid solution temperature, applying 70% cold working, and then holding it at 600°C for 4 minutes before air cooling. Measurements were made using the test piece.

In addition, magnetic permeability was measured using a low permeability needle.

Hot workability was determined by making a test piece of 811φ from the ingot.
After holding it at 250°C for 20 seconds, it was cooled to 1050°C at a cooling rate of 10°C/second, and at the moment it reached 1050°C, a tensile test was performed at a strain rate (1) of 1.7 s-' to determine. .

The pitting corrosion resistance was evaluated using a 0.5 mol NaCl aqueous solution (7
The pitting potential was measured at 0°C.

The sulfuric acid resistance was evaluated by examining the corrosion loss in a boiling 5% sulfuric acid aqueous solution.

These results are shown in Table 2. Regarding hot workability, ○...Cross-sectional shrinkage rate = 80% or more, Δ...Cross-sectional shrinkage rate: 50% or more and less than 80%.

×... Sectional shrinkage rate: less than 50% It was displayed in

As is clear from the results shown in Table 2, all stainless steels according to the present invention are non-magnetic, have a low nitride solid solution temperature, and have excellent strength with a 0.2χ crab resistance of 180 kgf/- or more. , it can be confirmed that in addition to good hot workability and excellent ductility after cold working and strain aging, it also has very excellent corrosion resistance.

Summary of Effects> As explained above, the present invention has extremely useful effects industrially, such as making it possible to easily and inexpensively provide non-magnetic stainless steel with excellent strength workability and corrosion resistance. brought about.

Applicant: Nippon Stainless Co., Ltd.

Claims (4)

[Claims] (1) Weight percentage: C: 0.2% or less, Si: 0.1-2%, Mn: 0.5% or more and less than 4%, S: 0.01% or less, C
Contains r: 20-40%, Ni: 5-15%, Mo: 1.5-5%, N: 0.6-1.5%, and Ca: 0.001-0.02%. Mg: 0.001~0
．． A high-strength non-magnetic steel characterized in that it also contains one or more of the following: (2) Weight percentage C: 0.2% or less, Si: 0.1-2%, Mn: 0.5% or more and less than 4%, S: 0.01% or less, C
r: 20-40%, Ni: 5-15%, Mo: 1.5-5%, N: 0.6-1.5%. Contains Ca: 0.001-0.02%, Mg: 0.001-0
．． High-strength non-magnetic material characterized by containing one or more of 02% and one or more of Cu: 3% or less and W: 5% or less, with the remainder consisting of Fe and unavoidable impurities. steel. (3) Weight percentage C: 0.2% or less, Si: 0.1-2%, Mn: 0.5% or more and less than 4%, S: 0.01% or less, C
Contains r: 20-40%, Ni: 5-15%, Mo: 1.5-5%, N: 0.6-1.5%, and Ca: 0.001-0.02%. Mg: 0.001~0
．． High-strength non-magnetic material characterized by containing at least one of 0.02% and at least one of Nb: 2% or less and V: 2% or less, with the remainder consisting of Fe and inevitable impurities. steel. (4) Weight percentage: C: 0.2% or less, Si: 0.1-2%, Mn: 0.5% or more and less than 4%, S: 0.01% or less, C
Contains r: 20-40%, Ni: 5-15%, Mo: 1.5-5%, N: 0.6-1.5%, and Ca: 0.001-0.02%. Mg: 0.001~0
．． 02%, one or more of Cu: 3% or less, W: 5% or less, and one or more of Nb: 2% or less, V: 2% or less, A high-strength nonmagnetic steel characterized in that the remainder consists of Fe and inevitable impurities.