JPH0639661B2 - Hot-worked high chromium alloy steel with excellent high temperature corrosion resistance and high temperature strength - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Object of the Invention" The present invention relates to the idea of hot-working high chromium alloy steel excellent in high temperature corrosion resistance and high temperature strength, and relates to hot working high chromium alloy steel excellent in high corrosion resistance and high temperature strength. In order to provide steel having excellent toughness, properties such as high temperature corrosion resistance and high temperature strength are secured, and hot workability such as torsion is improved.

Industrial field High chromium alloy steel.

Conventional technology There are many alloy steels that have excellent strength and corrosion resistance when including cast materials, but the number is extremely limited when they are forged materials or pipe materials. In many cases, this is mainly because the hot workability is poor even if casting can be performed, and the work cannot be economically performed. However, the following methods are available to improve the hot workability of these alloy steels.

Secondary dissolution such as ESR is performed.

Deoxidize and desulfurize.

Add trace elements such as Ca and Mg.

That is, various processes, equipments, etc. have been developed even today, and even if the workability is still insufficient even if the measures are taken, the measures are taken. It should be noted that Japanese Patent Publication No. 51-46729 discloses that elements such as Ti and Zr are added to high chromium alloys. Also in JP-A-53-108821, Cr:
Steel has been announced in which the addition range of Ni, Si, Mn, Al, C, etc. is specified for 30 to 47%.

Problems to be Solved by the Invention Although the method as described above is important, it is difficult to stably introduce light elements such as Ca and Mg into the furnace, and reliably improve hot workability. Requires more ingenuity.

In particular, it is known that nitrogen impairs hot workability in a high chromium alloy system. Japanese Patent Publication Sho 51-4
The addition of the element according to 6729 is not sufficient, even if it has some effect. It is difficult to obtain a high chromium alloy steel having excellent hot workability without impairing heat resistance, high temperature strength, corrosion resistance, weldability and the like.

The one disclosed in JP-A-53-108821 is as described above.
Even if Ni, Si, Mn, Al, C, etc. are specified, their contents are high as is clear in the examples, and they are manufactured by as-casting, and hot working such as hot rolling. It was impossible.

"Structure of the Invention" Means for Solving Problems C: 0.01 to 0.2 wt%, Si: 0.5 wt% or less, Mn: 0.3 wt% or less, Cr: 22 to 38 wt%, Ni + Co: 30 wt % To 65 wt% or less, Mo + W: 0.1 to 3.0 wt%, Ti + Nb: 0.03 to 1.0 wt%, Al: 0.01 to 0.3 wt%, S: 0.01 wt% or less, Ca + Mg: 0.01 wt% or less, Zr + Hf + Y: 0.002 to 0.2 wt%, N: 0.05 wt% or less, O: 0.015 wt% or less, the balance being Fe and unavoidable impurities, and the formula below. The value of the workability parameter Ze due to
A hot-working high chromium alloy steel excellent in high temperature corrosion resistance and high temperature strength, which is characterized by being within +0.02.

Action Each component is selected within the above composition range, and the workability parameter Ze is set within the range of -0.02 to +0.02, thereby inhibiting the high strength and high corrosion resistance of this kind of high chromium alloy. Without significantly increasing the hot workability. That is, particularly for Si, Mn, and Al, the upper limits thereof are set to 0.5 wt%, 0.3 wt%, and 0.3 wt%, so that forging and pipe forming, which are processed under high temperature conditions, can be advantageously performed.

To further explain the present invention as described above, in the present invention, heat resistance in high chromium alloy steel, high temperature strength,
Oxygen, silicon, manganese, aluminum, etc., which are harmful to hot working, can be controlled without impairing the original properties such as corrosion resistance and weldability, and a high chromium alloy steel with excellent hot workability can be obtained. It was done like this.

That is, first, the reasons for limiting the component composition in the present invention are as follows. In the following, wt% is simply referred to as "%".

C: 0.01 to 0.20%.

In order to obtain high temperature strength, at least 0.01% is necessary, but in a high chromium alloy such as the present invention, this C impairs weldability and workability, so the upper limit is 0.20%. .

Si: 0.5% or less.

This Si is not a particularly necessary element in the constitution, but since it is mixed in from the scrap during melting, the upper limit is 0.5% from the viewpoint of weldability and phase stability.

Mn: 0.3% or less.

This Mn is also not particularly necessary in the structure, but it is also mixed when scrap is used, and the upper limit was made 0.3% from the viewpoint of oxidation resistance.

Cr: 22-38%.

22% or more is required to secure excellent high temperature corrosion resistance.

However, if this Cr exceeds 38%, the toughness and workability are significantly impaired, so it is necessary to set this to the upper limit.

Ni + Co: more than 30% and 65% or less.

Ni and Co act in substantially the same way, these are 30% in order to stabilize the austenitic structure of high chromium materials.
It is necessary to exceed.

However, it is not economical to use 65% or more of these elements, so this is the upper limit.

Ti + Nb: 0.03 to 1.0%.

A small amount of Ti and Nb increases the high-temperature strength and also improves the workability, so it is necessary to contain 0.03% or more.
However, excessive addition impairs the toughness, so the upper limit is 1.0%.

Al: 0.01 to 0.3%.

Al is required as a degassing agent, and it is necessary to make it a minimum of 0.01%. However, if the content exceeds 0.3%, the toughness is impaired, so it is necessary to set this to the upper limit.

Ca + Mg: 0.01% or less.

These Ca and Mg are effective for improving the workability, and the addition of either or both of them in the range of 0.01% or less further improves the torsion test result and the like.

Zr + Y + Hf: 0.002-0.2%.

These materials also act in the same manner, and even when added in a very small amount, the high temperature strength and hot workability are remarkably improved.
It is necessary to add at least 0.002%. However, addition of 0.2% or more impairs weldability, so a maximum of 0.2%
Should be%.

S: 0.01% or less.

In order to improve the workability aimed at by the present invention, it is preferable that the amount is as small as possible, and 0.01% or more is harmful.

N: 0.05% or less.

In a high chromium austenitic steel, this N seriously impairs hot workability. However, if it dissolves in the atmosphere, N
Is included, but the upper limit should be 0.05%.

O: 0.015% or less.

The removal of oxides is indispensable in order to ensure the hot workability, high strength, and high corrosion resistance characteristics of the steel of the present invention. Therefore, the upper limit of oxygen should be 0.015% or less. is necessary.

Mo + W: 0.1-3.0% Mo and W work in the same way. Minimum to increase high temperature strength
0.1% is necessary, but if it exceeds 3.0%, the phase stability is impaired, so the upper limit is made 3.0%.

The balance is Fe and inevitable impurities, but in the present invention, the workability parameter Ze needs to satisfy Ze = −0.02 to +0.02, and this workability parameter Ze is calculated by the following equation. To be

Example A concrete production example of the present invention and a comparative example thereof will be described below.

The present inventors alloys A to U and comparative alloys a to h obtained by melting and hot rolling using an atmospheric furnace and a vacuum furnace have the chemical compositions shown in Table 1. The results of the inter-twist test are also shown in Table 1.

That is, in all of the alloys of the present invention, the workability parameter Ze is -0.0
It is within the range of 2 to 0.02, and the breaking rotation number in the torsion test is 8 or more, and most of it is 15 to 20. On the other hand, in the comparative alloy, the workability parameter Ze is out of the above range and the torsion test result is 6 or less.

The attached drawings show the relationship between the above torsion test results and the machinability parameter Ze as a chart. As is clear from this figure, the machinability sharply improves in the range of Ze from -0.02 to 0.02. What is done is clear.

The alloy A of the present invention and the conventional SU shown in Table 1 are typically used.
The creep rupture properties and high temperature corrosion performance of S347 and Ion Colloid 800 are shown in Table 2 below. It is clear that the present invention is superior in any of them, and according to the present invention, strength and corrosion resistance are excellent. It was confirmed that the workability can be greatly and accurately improved without impairing the above.

"Effects of the Invention" When the present invention as described above is used, the hot workability of the high chromium alloy of this kind is improved and improved accurately without impairing its properties such as high strength and high corrosion resistance. Various products can be advantageously manufactured by forging and other economical hot working, and this is an invention that has a great industrial effect.

[Brief description of drawings]

The drawings illustrate embodiments of the present invention, including the workability parameters and 110 for the invented alloys and the comparative alloys.
It is a chart which summarized and showed the torsion test result in 0 degreeC.

Claims (1)

[Claims] 1. C: 0.01 to 0.2 wt%, Si: 0.5 wt% or less, Mn: 0.3 wt% or less, Cr: 22 to 38 wt%, Ni + Co: more than 30 wt% and 65 wt% or less, Mo + W : 0.1 to 3.0 wt%, Ti + Nb: 0.03 to 1.0 wt%, Al: 0.01 to 0.3 wt%, S: 0.01 wt% or less, Ca + Mg: 0.01 wt% or less, Zr + Hf + Y: 0.002 to 0.2 wt%, N: 0.05 wt% or less, O: 0.015 wt% or less, the balance consisting of Fe and inevitable impurities, and the value of the workability parameter Ze according to the following formula -0.02
A hot-working high chromium alloy steel excellent in high temperature corrosion resistance and high temperature strength, which is characterized by being within +0.02.