JPS59222558A - Corrosion resistant steel with high strength - Google Patents

Abstract

PURPOSE:To obtain a corrosion resistant steel with high strength suitable for use as the material of a member for aeronautical apparatus, etc. by blending austenite forming elements with ferrite forming elements in a well-balanced state and by adding a proper amount of Cu. CONSTITUTION:This corrosion resistant steel with high strength consists of, by weight, <=0.15% C, <=1% Si, <=2% Mn, 9-15% Cr, 6-11% Ni, 1-4% Mo, 0.1- 5% Cu, 0.5-2% Al, 0.001-0.1% N and the balance Fe with inevitable impurities or further contains one or more among 0.02-0.4% Nb, 0.02-0.4% V, 0.01- 0.3% Ti, <=0.01% B and 0.01-0.3% Zr according to need. The steel having said composition is provided with >=about 150kgf/mm.<2> high tensile strength by simple soln. heat treatment and aging. The steel has superior corrosion resistance, especially resistance to corrosion due to hydrochloric acid and sulfuric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides materials that require high strength and high corrosion resistance;
For example, regarding high-strength corrosion-resistant steel that can be used as a material for aircraft equipment parts, chemical plant parts, coastal structure parts, etc., the tensile strength L of 50 kgf/mm2 or more can be achieved by a single solution treatment. The present invention relates to high-strength corrosion-resistant steel that provides strength and excellent corrosion resistance.

In recent years, as the fields in which stainless steel is used have expanded, high strength and corrosion resistance have often been required.

Among conventional stainless steels, martensitic stainless steels can be hardened by heat treatment and thus have high strength, but they do not have sufficient corrosion resistance and have poor workability. In addition, austenitic stainless steel has excellent corrosion resistance, but since it does not harden through heat treatment, the usual method is to harden it through cold working5 to increase its strength, so it is severely restricted as a structural steel. Ta.

On the other hand, precipitation hardening stainless steel has been developed as a steel that combines the high strength of martensitic stainless steel and the high corrosion resistance of austenitic stainless steel to solve these problems. This precipitation-hardening stainless steel is made by adding a third element to Fe-Cr-Ni steel, subjecting it to solution treatment, and then forming it to increase its strength by utilizing the precipitation hardening phenomenon caused by aging treatment. It was planned. Most of the precipitation hardening stainless steels currently in use are martensitic or semi-martensitic.
The former is a single treatment type (e.g. 17-4PH) in which martensite is formed by solution treatment and hardened by one aging treatment, and the latter is austenitic by solution treatment, followed by intermediate heat treatment or cold treatment. This is a dual treatment type (for example, 17-7PH) in which martensite is formed by processing and then precipitation hardening treatment is performed, but in both cases, the strength and hardness are excellent, but the corrosion resistance is poor, especially in the latter case. This has the problem of being complicated.

On the other hand, in order to develop steel with high strength and excellent corrosion resistance,
Although this is not necessarily impossible due to the addition of large amounts of expensive alloying elements, it has had the problem of being naturally restricted from being used as an industrial structural material for economic reasons.

This invention was made by focusing on these conventional problems, and by adjusting the austenite-forming elements and ferrite-forming elements in a well-balanced manner and adding an appropriate amount of Cu, a material with high strength and excellent corrosion resistance was developed. The aim is to provide inexpensive high-strength, corrosion-resistant steel.

That is, the high-strength corrosion-resistant steel of the present invention has, in weight percent, C;
0.15% or less, 5il1% or less, Mn; 2% or less, C
r: 9-15%, Ni: 6-11%, Mo: 1-4%,
Cu; 0.1-5%, AM; 0.5-2%, N, 0.0
01-0.1%, Nb, 0
．． 02-0.4%, further as necessary, V, 0.02
~0.4%.

Ti; 0.01 to 0.3%, B, 0.01% or less, Zr
; 0.01 to 0.3% of one or more of them, the balance being Fe and unavoidable impurities.

The high-strength corrosion-resistant steel according to the present invention has a tensile strength of 150 kgf/mm2 or more and excellent corrosion resistance (especially hydrochloric acid corrosion resistance and sulfuric acid corrosion resistance) by applying a single solution treatment. It is suitable as a material for, for example, fasteners for aircraft equipment and parts for petrochemical equipment, which require high strength and excellent corrosion resistance.

The reason why the component range of the high-strength corrosion-resistant steel according to the present invention is limited as described in the claims is as follows.

C, 0.15% or less C, together with N, is a strong austenite-forming element and is an element that improves the strength of martensite, but if it is too large, Cr carbides will precipitate at the austenite grain boundaries,
Since it deteriorates corrosion resistance, it needs to be 0.15% or less. On the other hand, if the C content is extremely low, it tends to produce δ ferrite, so it is more preferable to set it to 0.02% or more.

5il1% or lessSi is an element that is added to molten steel and has a deoxidizing effect, but if it exceeds 1%, it promotes the formation of δ ferrite and deteriorates corrosion resistance, and also coarsens crystal grains and impairs toughness. cormorant.

Therefore, the Si content was limited to 1% or less. In addition, 0.1% or more is required for deoxidation during melting and refining, but
When copper is melted by vacuum melting, it may be lower than 091%.

Mn: 2% or less Mn is an element that is added to molten steel and has a deoxidizing and desulfurizing effect, but if it exceeds 2%, retained austenite is generated and the strength is reduced. Therefore, the Mn content was limited to 2% or less. In addition, although 0.1% or more is required for deoxidation and desulfurization, it may be even lower than 0.11% when steel is produced by vacuum melting.

,) Cr; 9 to 15% Cr is an element that imparts corrosion resistance, but if it is less than 9%, such an effect cannot be obtained and the corrosion resistance deteriorates, so it is necessary to make it 9% or more. On the other hand, from the compositional balance of austenite-forming elements such as C and Ni and ferrite-forming elements such as Mo and Nb, when Cr exceeds 15%, it promotes the formation of δ ferrite and deteriorates corrosion resistance. Therefore,
The Cr content was limited to a range of 9 to 15%.

Ni; 6 to 11% Ni is a basic element constituting the steel of the present invention together with Cr, Mo, and AQ, and is an element that coexists with these elements and imparts strength and corrosion resistance. However, if it is less than 6%, such an effect cannot be obtained, and the formation of δ ferrite is promoted, resulting in deterioration of corrosion resistance.

Moreover, when it exceeds 11%, the strength decreases due to an increase in retained austenite. Therefore, the Ni content should be reduced from 6 to 11%.
limited to the range of

Mail~4% MO is an important element that finely precipitates an intermetallic compound with Ni through aging treatment after solution treatment, hardens the steel, and imparts corrosion resistance. However, if it is less than 1%, such an effect is not sufficient, and if it exceeds 4%, there is an increased tendency for δ ferrite to be produced and the cost becomes high. Therefore, M
The O content was limited to a range of 1 to 4%.

Nb, 0.02-0.4% Nb generates carbides and contributes to the prevention of intergranular corrosion, and also has a low tendency to combine with O and N to generate inclusions, thereby suppressing a decrease in cleanliness. Since it is an element that contributes to obtaining stable strength and toughness values, it is further added to the first invention depending on the purpose of use. In this case, in order to obtain the above-mentioned effect, it is necessary to add 0.02% or more, but if it is too much, the toughness and corrosion resistance will deteriorate, so 0.02% or more is necessary.
It should be 4% or more.

V, 0.02-0.4%, Ti; 0.01-0.3%,
B, 0.01% or less, Zr; 0.01・~0.3%
One or more of these, V, Ti, B, and Zr, all refine crystal grains and cause intergranular corrosion, Ti forms carbides to prevent intergranular corrosion, and Zr causes sulfide. Because it has the effect of controlling the shape of objects and improving toughness,
It is added to the first invention depending on the purpose of use, etc., but if it is less than the above component range, such effects cannot be obtained sufficiently, and on the other hand, if it exceeds the above component range, it will promote the formation of δ ferrite. At the same time, large carbonitrides are formed, which deteriorates corrosion resistance and toughness. Therefore, V, Ti, B, Zr
One or more of the following: 0.02 to 0.4
%, Ti: 0.01 to 0.3%, B: 0.01% or less, Zr: added in the range of 0.01 to 0.3%.

Cu: 0.1 to 5% Cu is an important element in the present invention, and is an effective element for improving corrosion resistance against sulfuric acid and hydrochloric acid and at the same time causing precipitation hardening to increase strength. However, if it is less than 0.1%, this effect is small, and if it exceeds 5%, retained austenite is generated, which reduces strength and impairs hot workability. Therefore, the Cu content was limited to a range of 0.1 to 5%.

Sentence A: 0.5 to 2% AM is an important element that imparts strength to the steel of the present invention, and like Mo, it hardens the steel by finely precipitating intermetallic compounds with Ni during aging treatment. . However, if it is less than 0.5%, this effect is not sufficient, and if it exceeds 2%, it is a strong ferrite-forming element, so even if it is adjusted with other elements, it will produce δ ferrite and reduce corrosion resistance. become.

Therefore, the An content was limited to a range of 0.5 to 2%.

N, O, OO1~0.1% N, along with C, is a strong austenite-forming element, and from the component balance, o is
, ooi% or more can be added. however,
If the amount added exceeds 0.1%, toughness and corrosion resistance will be reduced. Therefore, the N content is 0.001 to 0.1%.
limited to the range of

In addition, in addition to the components listed in -1-, Ta may be included.
Although it is possible to further improve the prevention of intergranular corrosion due to the formation of carbides,
In this case, in order to obtain such an effect, the content should preferably be 0.02% or more, and if it is too large, the toughness and corrosion resistance will decrease, so the content should be 0.4% or less.

Steel composed of the above-mentioned composition ranges is melted into specified compositions in an electric furnace or vacuum melting furnace, etc., and after forming the molten steel into an ingot, it is formed into bars, plates, etc. by hot forging or hot rolling. be done.

The steel thus obtained has a tensile strength of 150 kgf/2'' or more after RG-treatment with temporary solid solution treatment, and has excellent corrosion resistance, particularly against sulfuric acid and hydrochloric acid.

The solution treatment described above is performed by heating to a high temperature, for example, around 925° C., to austenite, and then cooling in air, oil, or water to change the matrix structure to martensite. On the other hand, in the case of prescription processing,
After solution treatment of steel, the elements (Cu, Cu,
Mo.

AJI) is precipitated as a secondary phase and hardened. The high-strength corrosion-resistant steel of this invention thus has Ni, Cr,
, Mo and A are used as basic components and Cu is further added to achieve both high strength and high corrosion resistance through a single solution treatment.

(Example) First, copper having the chemical composition shown in Table 1 was melted in a vacuum melting furnace and then formed into an ingot, and each steel ingot was forged and drawn to obtain a test material. next,
Each sample material was subjected to solid solution treatment under conditions of heating and holding at 925° x t hr and cooling with oil, and then heated at 538°C, x 4 h.
Aging treatment was performed under conditions of heating and holding and then air cooling. Thereafter, each sample material was subjected to a tensile test and a corrosion test. Among these, the tensile test was conducted by cutting JIS No. 4 test pieces from each sample material at room temperature, and measuring 0.2% proof stress, tensile strength,
The elongation and aperture were measured. Corrosion tests were conducted by immersion in a 1% hydrochloric acid solution for 6 hours at room temperature, in a 5% sulfuric acid solution for 6 hours at room temperature, and at 5%
Sulfuric acid solution! A 6-hour immersion test was conducted during the night, and the high content loss after each test was investigated.The results are shown in Table 2.

As is clear from Tables 1 and 2, test material No.
Sample No. 1 has too little Cu content, so its corrosion resistance is extremely poor, and Sample No. 8 has too much Cu content, so it has good corrosion resistance but low strength, whereas fiNo. It can be seen that samples Nos. 2 to 7 and Nos. 9 to 15 have high strength and significantly improved corrosion resistance, particularly resistance to sulfuric acid and hydrochloric acid.

As explained above, according to the high-strength corrosion-oriented steel according to the present invention, by adjusting the austenite-forming elements and ferrite-forming elements in a well-balanced manner and adding an appropriate amount of Cu, temporary solution treatment can be achieved. Tensile strength 150
It has the remarkable effect of having high strength of kgf/mm2 class or higher and excellent corrosion resistance.

, 1 Patent No. 31 Applicant Daido Steel Co., Ltd. Representative Patent Attorney Yutaka Oshio Procedural Amendment (Voluntary) June 2, 1982 Commissioner of the Patent Office Kazuo Wakasugi 1 Indication of Case Submitted June 1, 1988 Patent application 2, title of the invention - high strength corrosion resistant steel 3, relationship with the person making the amendment 41 Patent applicant address: Mr. 66 Kade, Hoshizaki-cho, Minami-ku, Nagoya, Aichi Prefecture
Name) (371) Daido Special Steel Co., Ltd. Representative Autumn 1) Seiyu 4, agent L Karike, J-sumi's Yokugo IDLE match 3n, % man V drinking 4'' and went to 〃■8.

Claims (4)

[Claims] (1) In weight%, C: 0.15% or less, Si: 1% or less, Mn: 2% or less, Cr: 9-15%, Ni: 6-11
%, Mo; 1 to 4%, Cu; 0.1 to 5%, A; 0.
5-2%, N: 0.001-0.1%, balance Fe and unavoidable impurities. (2) In weight%, C: 0.15% or less, Si: 1% or less, Mn: 2% or less, Cr: 9-15%, Ni: 6-11
%, Mo; 1-4%, Cu; 0.1-5%, Text A; 0.
5-2%, N; 0.001-0.1%, Nb, 0.0
A high-strength corrosion-resistant steel characterized by comprising 2 to 0.4%, the balance being Fe and unavoidable impurities. (3) In weight%, C: 0.45% or less, Si: 1% or less, Mn: 2% or less, Cr: 9 to 15%, Ni: 6 to 11
%, Mo: 1-4%, Cu: 0.1-5%, A text
; 0.5-2%, N; 0.001-0.1%, and V; 0.02-0.4%, Ti; 0
, 01-0.3%, B; 0.01% or less, Zr;
A high-strength, corrosion-resistant steel comprising one or more of 0.01 to 0.3%, the balance being Fe and unavoidable impurities. (4) In weight%, C: 0.15% or less, Si: 1% or less, Mn: 2% or less, Cr: 9-15%, Ni: 6-11
%, Mo; 1-4%, Cu; 0.1-5%, Text A; 0.
5-2%, N: o, ooi~0.1%, Nb; 0.02
~0,4%, and ■;0,02~0.4%, Ti;0
．． 01-0.3%, B, 0.01% or less, Zr; 0.0
A high-strength, corrosion-resistant steel comprising one or more of 1 to 0.3%, the balance being Fe and unavoidable impurities.