JPS5881955A - Heat resistant steel for high temperature gas furnace - Google Patents

Abstract

PURPOSE:To provide heat resistant steel for a high temp. gas furnace with enhanced corrosion resistance and high temp. strength in an inert gas, by a method wherein a specific amount of C, Si, Mu, Cu, Ni, Al, Mo are contained and Ti and Nb are further added to reduce the amount of Cr. CONSTITUTION:This heat resistant steel for high temp. gas furnace consists of, on the wt. basis, 0.02-0.2% C, 0.05-2.0% Si, 0.05-2.0% Mn, 8-15% Cr, 8- 13.5% Ni, 0.3% or less Al, 3.5-8% Mo, 0.01-0.1 Ti and Nb respectively added alone or compositely and the remainder Fe and inevitable impurities. This constituent steel is one of which the amounts of Cr and Ni are reduced and a specific amount of Mo, Ti, Nb are added. By this composition, heat resistant steel for the high temp. gas furnace having excellent corrosion resistance and high temp. strength in an impure helium gas is inexpensively obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to heat resistance for high temperature gas furnaces. More specifically, the present invention relates to a heat-resistant steel for high-temperature gas furnaces that has excellent corrosion resistance and high-temperature strength in impure inert solids.

The structure for the remote temperature gas furnace is made of Hastelloy for the high temperature parts.
Ni-based superalloys mainly composed of X alloys are being used, but most of these materials contain 20%
Contrary to common knowledge in oxidizing gases, it does not have sufficient oxidation resistance in impure helium because it contains a large amount of chromium.

In this case, the 1lj1f property can be improved by adding appropriate amounts of silicon and manganese, but this is still not sufficient. Furthermore, since these alloys generally contain high amounts of alloying elements such as molybdenum, tungsten, and nickel, these alloys generally have the disadvantage of low commercial prices.

The purpose of the present invention is to make up for these drawbacks by developing a high-temperature steel that uses an inexpensive iron base and has better oxidation resistance than Hastelloy-X alloy and commercial strength comparable to that of Steroidy-X alloy. The purpose of the present invention is to provide heat-resistant materials for gas furnaces.

As a result of intensive research, the inventors of the present invention have found that the carbon 0.0
2-02% by weight, silicon 0.05-20% by weight, manganese 0.05-2.0% by weight, black 8-15% by weight,
Nickel 87-13.5! t%, aluminum 0.3% by weight or less, molybdenum 3.5 to 8% by weight, titanium and niobium in the range of 0.01 to 1.0% by weight each, singly or in combination, and the remainder added by melting. This objective was achieved by creating a heat-resistant steel for high-temperature gas furnaces that has excellent oxidation resistance and high-temperature strength in impure helium gas, which contains unavoidable impurities and iron.

Therefore, in achieving the present invention, the present inventors determined the optimum alloy composition range in consideration of the following points. I will explain in detail.

(1) If the carbon content is less than 0.02% by weight, no reinforcement by carbide can be expected, and if it is more than 0.2% by weight, it will be difficult to adjust the grain size, so the carbon content should be 0.02 to 0.2% by weight.
shall be.

(2) Silicon: 0.05-2% by weight. Silicon is an indispensable element as a deoxidizing agent, and is also an effective element for peeling off films in impure helium, but if it is contained in a large amount of 2% by weight or more, non-metallic inclusions will increase, so the upper limit must be set. is 2% by weight. Also, 0.05% by weight
The following effects cannot be expected.

(3) Manganese: o, 05-2% by weight. Manganese is not only effective as a deoxidizing agent together with silicon, but also forms chromium-manganese spinel oxide with chromium in impure helium, contributing to oxidation resistance.
Machining more than % by weight impairs workability. Moreover, if it is less than 0.005% by weight, no effect can be expected.

(4) Chromium: 8-15% by weight. In impure helium, the oxidation resistance is good even if the chromium content is low, but if the chromium content is less than 8% by weight, the strength of the austenitic base cannot be maintained.1. Further, the strengthening effect of carbides cannot be expected. Moreover, if the amount of chromium exceeds 15% by weight, the oxidation resistance in impure helium will deteriorate, so the upper limit is set at 15% by weight.

(5) 28-13.5% by weight of nickel. In order to stabilize the austenite base, a nickel addition of 8% by weight or more is required, and for the purpose of supplying an inexpensive iron-based material, the upper limit of nickel is set at 13.5% by weight.

(6) Aluminum = 3% by weight or less, aluminum is effective as a deoxidizing agent, but if it is added in excess of 03% by weight, internal oxidation becomes significant.

(7) Molybdenum = 3.5 to 8% by weight, if molybdenum is less than 35% by weight, the austenitic area will not be strengthened.
Furthermore, if Mo6C and F'e2Mo phases do not provide precipitation strengthening effects, and if more than 8% by weight of molybdenum is added in total, it will be difficult to stabilize the austenite base in this alloy yarn and the toughness will decrease, so the upper limit should be set at 8%. The amount is expressed as %.

(8) Titanium and niobium fl 0.01-1.0
Each may be added singly or in combination within a range of weight percent.

Even a very small amount of titanium or niobium can control the shape and size of the carbide. In order to achieve the effect of finely dispersing carbides, it is necessary to add at least 0.011 ton of either titanium or niobium, and the effect is further strengthened by adding bonding, but when each is over 100%, Complete book on weldability and manufacturability.

(9) Remaining! ll: Iron except for impurities. Smelting the thin side of the above composition range to produce a 10-meter steel ingot,
After further solid solution treatment, it is placed near the high temperature gas furnace (
Freep rupture wiping tests and corrosion tests were conducted in IJ helium gas. An example of measuring the amount of impurities in helium gas is as follows. Hydrogen 205° Methane 5,0095,0
022ppmb 02 Below detection limit. The test results are shown in Table 1 along with the chemical composition.

High chromium content ratio I! ! ! 2. Button 1. Compared to conventional steel, the oxidation weight gain of the shaft of the present invention is significantly smaller. As is clear from the table, the creep rupture strength in impure helium can be obtained by adding several percent or more of molybdenum, and the strength can be further increased by adding trace amounts of titanium and niobium, either singly or in combination. Although it is an iron-based heat-resistant button 1 containing only a small amount of alloying elements, it exhibits strength comparable to Hastelloy-X alloy, which is a conventional Ni-based alloy. Naturally, since this TM is stabilized with Austinite '1, its U properties after aging are lower than that of Incoloy 80, which is the conventional steel.
It shows values equal to or higher than those of the 0 alloy and the Hanuteroi X alloy.

An example is shown in Table 2.

The present invention is based on the fact that corrosion resistance is better in impure helium with a lower Or. However, reinforcement with Mo and T1Nb, which are well known in the atmosphere, are methods for increasing creep strength in impure helium. The strengthening effect is based on the fact that it can be used even in impure helium, but the key point of the present invention is to significantly reduce chromium, a ferrite stabilizing element normally contained in heat-resistant forceps 1, in order to improve corrosion resistance. By reducing the amount of nickel, which is an expensive austenite stabilizing element, and adding molybdenum, titanium, and niobium, which are ferrite stabilizing elements but have strong strengthening effects, we have created a steel that is inexpensive and excellent in impure helium. Our goal is to provide the following.

The Kokyo Gas Reactor Heat Resistance U1 of the present invention is required to have excellent corrosion resistance and high-temperature strength in low-level construction such as lumbar tubes in breeder reactors, control rods in high-temperature gas reactors, duct breaks, and intermediate heat exchangers. It can be used as a structural part ladle.

It is well known that low chromium materials have a corrosion resistance of 75% in impure helium, but this is a new fact that is contrary to the common knowledge in strongly oxidizing atmospheres such as the air.

On the other hand, with regard to the creep strength in the atmosphere, it is well known to add molybdenum as a reinforcing effect, and to add trace amounts of T1 and Nb alone or in combination. However, in helium containing impurities, a unique corrosion reaction occurs during the creep test, so the creep strength enhancement effect in the atmosphere cannot be directly utilized. In other words, in impure helium, where common sense regarding corrosion in the atmosphere does not apply, the common sense in the atmosphere regarding the reinforcing effect of creep has no basis. To ask for the price,
A new technological range that cannot be inferred from behavior in the atmosphere,
It can be said that the patent applicant Japan Atomic Energy Research Institute

Claims (1)

[Claims] Carbon 0.02-0.2% by weight, silicon 0.05-2.
0% by weight, manganese 005-20% by weight, chromium 8-1
5% by weight, nickel 8-13.5% by weight, aluminum 0.3% by weight or less, molybdenum 35-8% by weight, titanium and niobium each in the range of 001-10% by weight, singly or in combination, and the remainder A heat-resistant steel for still-temperature gas furnaces that has excellent oxidation resistance and high-temperature strength in impure helium gas, which is made of impurities and iron that are unavoidable during melting.