JPS6299443A - Stainless steel - Google Patents

Abstract

PURPOSE:To provide superior high strength, high toughness and corrosion resistance by using conventional 17-4PH steel as a base, improving strength by means of an intermetallic compound of Al and Ti and also of carbides of Mo, W, V, etc., and also improving impact value by means of B, Nb and V. CONSTITUTION:The stainless steel has a composition consisting of, by weight, 0.02-0.2% C, <2% Si, <3% Mn, 2.5-4.5% Cu, 2.5-5% Ni, 13-18% Cr, 0.5-2.5% Mo, 0.05-1% Nb+Ta, 0.0001-0.05% B, 0.002-0.05% N, and the balance Fe with inevitable impurities, or further containing 1 or >=2 kinds among 0.5-2.5% Al, 0.1-1% Ti, <1% V and <1% W and having the balance Fe with inevitable impurities.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a precipitation hardening stainless steel that has high strength, high toughness, and excellent corrosion resistance, and is used, for example, in turbine blades, bomb shuffles, The present invention relates to precipitation hardening stainless steel used as a material for disc rotors and various other mechanical structural parts that require high strength, high toughness, and corrosion resistance.

(Prior Art) Cr-Ni stainless steel has a matrix structure such as austenite, martensite, austenite + ferrite, etc. depending on its composition, processing, and heat treatment conditions.

Steel types to which precipitation hardening elements such as Nb, Ta, Cu, Be, and P are added are called precipitation hardening stainless steels.
It is useful as a material that has both corrosion resistance and high strength.

Among these, representative martensitic precipitation hardening stainless steels are 17-4PH and 15-5PH stainless steels, which are widely used as materials for structural materials such as aircraft, corrosion-resistant springs, valves, impellers, etc.

(Problems to be Solved by the Invention) These martensitic precipitation hardening stainless steels have a tensile strength of at most 150 kgf/mm', and the impact value at that time is 2 kgf-m/Cm2 or less, and the strength is Although the toughness is high to some extent, the toughness cannot be said to be very good. Furthermore, hot workability is quite poor, and sufficient care must be taken during manufacturing. This is C
Since the target is precipitation hardening due to u, the Cu content is 3 to 5.
The main reason for this is that it is as high as %.

This invention was made by focusing on the two problems of the conventional method.It has excellent hot workability, is easy to manufacture, and has a tensile strength of approximately 150 to 170 kg f/.
m m ' or more' and the impact value is about 2,5~3k
The object of the present invention is to provide a precipitation hardening type stainless steel which has a corrosion resistance of 5 US 304 or higher and a corrosion resistance of 5 US 304 or higher.

[Structure of the invention] (Means for solving the problem) The stainless steel according to the present invention has a content of 1% by weight and a C: 0.0.
2-0.2%, Si: 2.0% or less, Mn: 3.0% or less, Cu: 2.5-4.5%, Ni: 2.5-5.0%
, Cr: 13.0-18.0%, Mo: 0.5-2.5
%, Nb+Ta+0.05-1.0%, B:0.000
1 to 0.05%, N: 0.002 to 0.15%, and if necessary Al: 0.5 to 2.5%, Ti: 0
．． 1-1.0%, V:1. O% or less, W: 1.0% or less, one or more of the following, and if necessary - (
It is characterized by consisting of one or two of Mg: 0.01% or less, Ca: 0.01% or less, the balance being Fe and inevitable impurities, and has high strength, high toughness, and corrosion resistance. This is an excellent martensitic precipitation hardening stainless steel.

Next, the reason for limiting the composition range (wt%) of the precipitation hardening stainless steel according to the present invention will be described.

C: 0.02-0.2% C is the most fundamentally important element necessary to increase strength and hardness at room and high temperatures. That is, to increase the strength of steel, first of all it is necessary to increase the C content. Therefore, C is at least 0.02%.
- is required. However, if it exceeds 0.2%, Cr
Since it reacts with carbide-forming elements such as , Mo, etc. and deteriorates corrosion resistance, the limit is set at 0.2%.

Si: 2.0% or more Si improves the 1lVIJ8 properties of steel and also
However, if it exceeds 2.0%, the crystal grains become coarse and the toughness becomes low F, so 2.0% was set as the -1- limit.

Mn: 3, 0% or less Like Si, Mn stabilizes 0 in steel as inclusions and improves mechanical properties, but since it is a strong austenite-forming element, 3.0% is If it exceeds 3.0%, retained austenite will form and the structure will become unstable.
was set as the upper limit.

Cu: 2.5-4.5% Cu is one of the important elements of the stainless steel according to the present invention. In other words, Cu significantly improves strength by precipitation hardening (precipitating a phase).
must be contained in an amount of at least 2.5%. However, if it exceeds 4.5%, hot workability decreases and there is a risk of cracking during hot working, and a large amount of Cu may lower the Ms point and generate retained austenite. Therefore, the upper limit of Cu was set to 4.5%. Note that Cu also has a rating of 2.5 to 4.
5% is mandatory.

Ni: 2.5 to 5.0% Ni is an important element in the stainless steel according to the present invention, and since it contains Cu, it is an element absolutely necessary to prevent the occurrence of cracks during hot working. This Ni improves the impact value by -1, and at the same time plays an important role in ensuring corrosion resistance and strength. However, if it is less than 2.5%, it cannot fulfill its role sufficiently, and on the other hand, if it exceeds 5.0%, it is a strong austenite-forming element, which lowers the Ms point to near room temperature, and depending on the components, O' If the temperature is below C, sufficient quenching will not be possible, so in this invention, the appropriate amount of Ni is set to 2.
The content is 5 to 5.0%, more preferably 2.5 to 4.5%.

Cr:13. O~18.0% Cr is also a basic element of the stainless steel according to this invention,
It is an essential element for ensuring corrosion resistance of 9+1& and toughness.

This Cr creates carbides with C to improve strength! i, do it. From the viewpoint of corrosion resistance, at least 13.0% Cr is required, but if it exceeds 18.0%, it is a strong ferrite (ferrite) forming element, so it leads to the formation of δ ferrite, which improves corrosion resistance, toughness and fatigue. Because there is a sufficient risk of deterioration of characteristics, the second limit is 18.0%.
And so.

Mo: 0.5-2.5% MO is a strong carbide-forming element and is an important element for improving strength. Additionally, it is an essential element because it has the ability to significantly improve corrosion resistance. In order to obtain these effects, at least 0.5% is required. However, since it is a strong ferrite-forming element, if it exceeds 2.5%, there will be a problem of the formation of δ-ferrite, leading to a decrease in toughness, so the upper limit was set at 2.5%.

Nb+Ta: 0.05-1.0% Nb and Ta are carbide forming elements, and combine with Cr <C
Nb reacts preferentially and becomes stable.

It produces Ta carbide, prevents the reduction of Cr in the matrix, and provides good corrosion resistance. Also, Nb.

Since Ta refines crystal grains and improves toughness and ductility, it is an essential element in the stainless steel according to the present invention. In order to fully satisfy these performances, at least 0.05% of Na+Ta (including the case where one of them is less than the effective amount) is required. However, since adding a large amount may generate a large amount of giant carbides, the upper limit was set at 1.0% for Nb+Ta. In addition, Nb+
A more preferable content of Ta is 0.1 to 0.5%.

B: 0.0001 to 0.05% B is an important element that contributes to strengthening grain boundaries, improving hot pressability, ensuring toughness, and improving high-temperature strength. In order to bring about these effects, at least o, o
ooi% or more-L is required.

However, if it exceeds 0.01%, a large amount of Fe2B is generated and hot workability is significantly inhibited, so the upper limit is set at 0.01%.
And so. In addition, the more preferable content of B is 0.0005
~0.0015%.

N: 0.002-0.15% N is similar to C and is an element that contributes to strength, toughness, and corrosion resistance by forming nitrides, and these effects are 0.002% or more. Obtained in two. Note that this N is an element that is always contained in normal manufacturing. In this case, if the N content exceeds 0.15%, there will be problems with gas generation during welding, and since it is a strong austenite-forming element, it will lower the Ms point and cause instability of the structure, resulting in poor strength and toughness. There are concerns about deterioration.

There are some planets where it is less than 0.15%. And more preferably N-containing 7i1. is set to 0.005 to 0.050%.

A type: 0.5 to 2.5% A type is an effective element for creating an intermetallic compound with the amount of N and measuring the strength. In order to obtain such an effect, at least 0.5% or more is required. However, since An is a strong ferrite-forming element, adding a large amount will produce δ-ferrite, leading to a decrease in toughness, so the limit of An is set to 2.5%. It should be noted that if the amount of A added increases, it tends to coarsen the crystal grains, so it is more preferably 1.0 to 2.0%.

Ti: 0.1-1.0% Ti is similar to Nb and Ta, preferentially forms carbides and contributes to improving corrosion resistance. It also improves toughness by making crystal grains finer. Furthermore, Ti forms a strong intermetallic compound with Ni and is also involved in ensuring strength. However, if a large amount of Ti is added, the cleanliness will be significantly impaired, so 0.
It is added in an amount of 1 to 1.0%, more preferably 0.2 to 0.5%.

V: 1.0% or less W: 1.0% or less v, W is a strong carbide-forming element and is an effective element for ensuring strength. However, since adding a large amount leads to a decrease in corrosion resistance and ductility, the second limit for both ■ and W is 1.0
%. Further, more preferable ranges are V: 0.5% or less and W: 0.5% or less.

Mg: 0.01% or less Ca: 0.01% or less Mg and Ca are both elements that improve hot workability. However, if added in large amounts, the cleanliness of the steel will deteriorate, leading to a decrease in strength and toughness, so 0.01% each
Hereinafter, each content is more preferably 0.002 to 0.006%.

It goes without saying that it is desirable that P, S, and 0 be as low as possible.

(Example) Next, the features of the stainless steel according to the present invention will be explained in detail using examples.

Table 1 shows the chemical composition of the steel of the present invention and that of the comparative steel, with Pl being 17-4PH as a standard and M
O is added, and Ca and Mg are also added.

P2 is Pl with high C and Nb content, and P3 is Pl with high C and Nb content.
This is the result of adding sentence A to the above. P4 is a slightly smaller amount of Pl and an increased amount of B, and P5 is Nb,
P6 has an increased amount of B, and P6 has a significantly increased amount of Cr, Mo, and N. Pl is intended to lower the amount of C to the lower limit and add AJI and Ti to strengthen precipitation hardening, and P8 is made by further adding W and ■.

Therefore, we investigated the tensile properties and impact values of these materials at room temperature after undergoing solution heat treatment and precipitation hardening treatment.

Corrosion loss (corrosion resistance) with 5% H2SO4 purified sulfuric acid was determined. These results are shown in Table 2.

The heat treatment conditions are 1050 except for 5US304.
°C oil cooling → 480 °C air cooling.

As shown in Table 2, as per P3〈A9. Alone and P
7. As shown in P8, the tensile strength of the composite with Al and Tr exceeds 170 kgf/mm2, and the tensile strength is 4 ft, which is higher than that of 17-4PH. That is, in this invention, conventional 17-4PH steel is used as a standard, and Al.

Strength improvement due to intermetallic compounds formed by Ti, M
-1B, Nb
, increasing the SEI value by V, etc., ensuring strength by N,
This is an attempt to improve hot workability by adding B, Ca, and Mg.

Figure 1 is 17-4PH,! 1-P8 shows the relationship between tensile strength, yield strength, impact value and aging temperature at room temperature. Also, Figure 2 shows 17-4PH, P3, and P7.

The impact transition curve is shown with P8 as a representative, and it can be seen from the above two figures that the steel of the present invention is a high-strength, high-toughness steel.

"Effects of the Invention" As explained above, the stainless steel according to the present invention contains 1% by weight, C: 0.02 to 0.2%, and Si+2.0%.
% or less, Mn: 0, 3% or less, Cu: 2.5~
4.5%, Ni: 2.5-5.0%, Cr: 13.0-
18.0%, Mo: 0.5-2.5%, Nb+Ta:
0.05-1.0%, B: 0.0001-0.05%
, N: 0.002-0.15%, and A sentence = 0.5-2.5% as necessary, Ti: 0.1-1.0%,
V: 1.0% or less, W: 1.0% or less, one or two types of insert-1-1 Mg: 0.01 as required
% or less, Ca: 0.01% or less, and the remainder consists of Fe and unavoidable impurities, so it has high strength, high toughness, and excellent corrosion resistance, such as , turbine blades (stationary blades, rotor blades), pump shafts, disc rotors, 1f11 corrosion springs, and other mechanical structural parts that require high strength, high toughness, and corrosion resistance. This will bring about a positive effect.

[Brief explanation of drawings]

Figure 1 shows the tensile strength of 17-4PH and P8 at room temperature.
Graph showing the relationship between yield strength and impact value and aging temperature, 2nd
The figure is 17-4. P H, P3, P7. It is a graph which shows the impact transition curve of P8. Patent Applicant Daido Steel Co., Ltd. Representative Patent Attorney Ko Shio Fyo Figure 1

Claims (4)

[Claims] (1) In weight%, C: 0.02-0.2%, Si: 2.
0% or less, Mn: 3.0% or less, Cu: 2.5 to 4.5
%, Ni: 2.5-5.0%, Cr: 13.0-18.
0%, Mo: 0.5-2.5%, Nb+Ta: 0.05
~1.0%, B: 0.0001~0.05%, N: 0.
0.002 to 0.15%, the balance being Fe and unavoidable impurities. A precipitation hardening stainless steel having high strength, high toughness, and excellent corrosion resistance. (2) In weight%, C: 0.02-0.2%, Si: 2.
0% or less, Mn: 3.0% or less, Cu: 2.5 to 4.5
%, Ni: 2.5-5.0%, Cr: 13.0-18.
0%, Mo: 0.5-2.5%, Nb+Ta: 0.05
~1.0%, B: 0.0001~0.05%, N: 0.
002-0.15%, and Al: 0.5-2.5%,
Ti: 0.1-1.0%, V: 1.0% or less, W: 1.
Precipitation hardening stainless steel with high strength, high toughness, and excellent corrosion resistance, characterized by comprising one or more of 0% or less, the balance being Fe and unavoidable impurities. (3) In weight%, C: 0.02-0.2%, Si: 2.
0% or less, Mn: 3.0% or less, Cu: 2.5 to 4.5
%, Ni: 2.5-5.0%, Cr: 13.0-18.
0%, Mo0.5~2.5%, Nb+Ta:0.05~
1.0%, B: 0.0001-0.05%, N: 0.0
02-0.15%, and Mg: 0.01% or less, Ca
: High strength characterized by consisting of one or two of 0.01% or less, the balance being Fe and unavoidable impurities;
Precipitation hardening stainless steel with high toughness and excellent corrosion resistance. (4) In weight%, C: 0.02-0.2%, Si: 2.
0% or less, Mn: 3.0% or less, Cu: 2.5 to 4.5
%, Ni: 2.5-5.0%, Cr: 13.0-18.
0%, Mo: 0.5-2.5%, Nb+Ta: 0.05
~1.0%, B: 0.0001~0.05%, N: 0.
002-0.15%, and Al: 0.5-2.5%,
Ti: 0.1-1.0%, V: 1.0% or less, W: 1.
One or more of 0% or less, and further Mg:
Precipitation hardening stainless steel with high strength, high toughness, and excellent corrosion resistance, characterized by comprising 0.01% or less, one or two of Ca: 0.01% or less, the balance being Fe and unavoidable impurities. steel.