JPH03120335A - High nickel iron-base alloy for casting - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance, strength and hot formability in the high nickel iron-base alloy by specifying C, Si, Mn, P, S, Ni, Cr, Mo, Cu, Tl, Nb and Fe. CONSTITUTION:The high nickel iron-base alloy is formed from a compsn. constituted of <=0.05% C, <=1% Mn, <=0.03% P, <=0.03% S, 38 to 46% Ni, 19.5 to 23.5% Cr, 2.5 to 3.5% Mo, 1.5 to 3% Cu, 0.6 to 1.2% Tl, 0.15 to 0.8% Nb and the balance Fe as well as satisfying 5 to 20 Nb/C. The cast material constituted of the above high nickel iron-base alloy has high corrosion resistance and high strength. The alloy furthermore has hot formability required for molding a special shaped tube.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high nickel iron-based alloy, and more particularly to a high nickel iron-based alloy for casting which has improved corrosion resistance while maintaining hot formability.

[Conventional technology]

“Incoloy 825” (38
~46Ni-19,5~23.5Cr-2,5~3.5
Mo-1,5-3Cu-0,6-1.2Ti-Fe)(
Hereinafter, r I N825J) is generally formed into a predetermined product shape by rolling, forging, or the like. High nickel alloys tend to have poor hot forgeability, but this alloy has a
．． The addition of 6 to 1.2% Ti provides good hot workability, and the plastic processed product can be used in applications that require high corrosion resistance and high strength, such as piping components for sour oil wells. has been done.

The above IN825 alloy is an alloy that can be manufactured into pipe materials and the like by casting, but unlike hot plastic processed products, the corrosion resistance and strength of cast products are not sufficient. As an improvement material, Ti
Instead of the addition of 0.068% to 1.1% of Nb, an alloy (hereinafter referred to as rNb-containing rN825J) has been proposed.

[Problem to be solved by the invention]

The Nb-containing 1N825 alloy is an alloy that makes it possible to manufacture cast products that have both corrosion resistance and strength. When producing a T-shaped tube by subjecting it to hot mass processing, cracks are likely to occur and it is extremely difficult to form it into a predetermined shape. In addition, Ti0.6-1.
Cast pipes made of INB25 alloy containing 2% are fully capable of being formed into T-shaped pipes, etc., but as mentioned above, there are problems with corrosion resistance, strength, etc.

The present invention has been made in view of the above, and provides a high nickel iron-based alloy for casting that has excellent corrosion resistance and hot formability when the cast product is formed into a T-shaped pipe or the like.

[Means and effects for solving the problems] The high nickel iron-based alloy for casting of the present invention has C: 0°05% or less, Si:
1% or less, Mn: 1% or less, pro.

0.03% or less, S: 0.03% or less, Ni: 38-46
%, Cr: 19.5-23.5%, Mo:
2, 5-3, 5%, Cu: 1.5-3%.

Ti: 0.6-1°2%, Nb: 0.15-0.8%
, the remainder substantially consists of Fe, and the Nb/C ratio is 5 to 20.

The reasons for limiting the components of the high nickel iron-based alloy for casting of the present invention are as follows.

C: 0.05% or less C has the effect of increasing the strength of the alloy, but on the other hand, it causes a decrease in corrosion resistance, so the upper limit is set at 0.05% to ensure corrosion resistance.

Si: 1% or less St has a deoxidizing effect on the molten alloy and has the effect of improving castability. For this purpose, it is sufficient to add up to 1%, and there is no need to exceed that amount.

Mn: 1% or less Mn has a deoxidizing effect on the molten alloy and also has the function of fixing S as MnS. The amount added for this purpose is sufficient to be up to 1%, and there is no need to exceed it.

P: 0.03% or less, S: 0.03% or less P and S are impurities that cause a decrease in the corrosion resistance of the alloy.
．． If it does not exceed 0.3%, there will be no substantial adverse effects.

Ni: 38-46% Ni is one of the basic elements of the alloy of the present invention, and forms a stable austenite matrix. Addition of Nt is effective in strengthening passivation and corrosion resistance against solutions containing chloride ions and non-oxidizing acids, and increasing the amount increases resistance to stress corrosion cracking. However, when added in a large amount, the effect is almost saturated, and adding more than that impairs economic efficiency. Therefore, it is set at 38 to 46%.

Cr: 19.5 to 23.5% Cr is an element necessary for passivation of the alloy, and is highly effective in increasing resistance to oxidizing acids and improving pitting corrosion resistance. Coexistence with Mo provides sufficient resistance to pitting corrosion, etc. within the range of 19.5 to 23.5%, and the effect hardly changes even if the amount is increased beyond this range. For this reason,
It is set to 19.5 to 23.5%.

Mo: 2.5-3.5% Mo increases strength by solid solution strengthening of the matrix and the formation of carbides, and also has effects such as stabilizing the passive state and improving pitting corrosion resistance in corrosive environments containing chlorine ions. have However, addition of large amounts increases stress corrosion cracking susceptibility. For this reason, 2.
5 to 3.5%.

Cu; 1.5 to 3% Cu is effective in solid solution strengthening of the base, improving corrosion resistance against non-oxidizing acids, etc. Further, in coexistence with Mo, it shows a great effect on improving pitting corrosion resistance. On the other hand, when a large amount is added, the toughness of the base decreases. Therefore, it is set at 1.5 to 3%.

Ti: 0.6 to 1.2% Ti is effective in promoting passivation, improving intergranular corrosion resistance, etc. In addition, strength is increased by finely precipitating as carbides. However, if too much is added, the toughness and weldability will be reduced.

Therefore, it is set at 0.6 to 1.2%.

Nb: 0.15-0.8% Nb is effective in improving corrosion resistance, especially intergranular corrosion resistance, without impairing the hot workability of the alloy, by adding Nb in combination with Ti. Further, Nb becomes fine carbides and preferentially precipitates on dislocations, increasing the strength. This effect can be obtained by adding 0.15% or more. The effect can be enhanced by increasing the amount of Ni added, but if the amount is too large, the weldability and hot workability tend to decrease, so the upper limit is set at 0.8%. In addition, from the viewpoint of improving intergranular corrosion resistance by adding Nb, the Nb/C ratio is 5.
It is preferable to set it as above. However, even if the ratio exceeds about 20, the effect hardly changes.

The cast material made of the high nickel iron-based alloy of the present invention, for example, the centrifugally cast pipe material, is heat treated at a temperature of about 105''.
Solution treatment is carried out by heating and holding at ±50°C for an appropriate time (for example, 2 to 3 hours) and then cooling with water. The cast material has both the high corrosion resistance and high strength necessary as a piping component for sour oil wells, and has good hot formability that can withstand forming processes such as T-shaped pipes by hot mold forming. are doing.

The high nickel iron-based alloy of the present invention is also used for casting clad products in combination with other metals. A typical example is a two-layer pipe in which an outer layer made of carbon steel (for example, APIX60, etc.) and an inner layer made of the high nickel iron-based alloy of the present invention are laminated concentrically by centrifugal casting. It will be done.

After solution treatment of the inner layer (high nickel iron base metal), the outer layer (carbon steel) is tempered by quenching (95
0”C±30゛C, water cooling or air cooling) and tempering treatment (6
By subjecting the inner layer to a temperature of 70°C±30°C (air cooling), the required strength is imparted to the outer layer without causing any unfavorable changes in the material properties of the inner layer.

〔Example〕

Pipe material made of high nickel iron-based alloy by centrifugal force casting (outer diameter: TS", wall thickness: 1.6', pipe length near 00 m)
m) was cast and subjected to a hot forming test of a T-shaped tube by mass forming. In addition, the test tube was subjected to solution treatment (1050'C).
After annealing with X2Hr/water cooling) and 600%XIHr/air cooling, intergranular corrosion test and JIS
A tensile test was conducted using Z2241. Note that the annealing treatment described above is a heat treatment equivalent to stress relief annealing performed on the welded portion in actual piping construction.

After heating the test tube to 1000°C ± 25°C in a furnace, we formed an opening with a diameter of 6 inches on the tube wall using the ball punching method.

In accordance with the ASTM A262 C method, the test piece was immersed in a 65% nitric acid solution (boiling) for 48 hours.
The test was repeated several times, and the corrosion weight loss after the test was measured.

Table 1 shows the chemical composition of the test tube materials as well as the test results. Black 11 and 12 are invention examples, No. 101, Na1
02 is a comparative example, Comparative Example No. 101 is an example of a conventional Nb-containing IN825 material for casting, and Nα102 is an example of a conventional Ti-containing IN825 material for hot working.

In the table, the "X" mark in the "Hot forming process test J column" indicates that cracking has occurred.
The ○ mark means that the specified T-shaped tube was formed without any cracks or the like. In addition, rMPYJ in the "grain boundary corrosion test" column is the thickness reduction (mi1/year) calculated from the amount of weight loss of the test piece due to corrosion.

Disaster 1 Carbon m (C: 0.2O-Qo,
26%.

Mn:1. O~1.35%, P:0.01~0.
03%, s:o, ot~0.03%, API X6
A two-layered tube having a laminated structure of an outer layer made of a nickel-based iron-based alloy and an inner layer made of a high-nickel iron-based alloy was obtained, and a T-shaped tube was formed under the same hot forming conditions as in Example 1. .

In addition, the test tube material was subjected to solution treatment (1050'c
r/water cooling) and further quenching (
950'CX2Hr/water cooling) and tempered 690'CX
3Hr / air cooling), and annealing 600'CX I
After cooling], the inner layer (high nickel iron-based alloy layer) was subjected to the same intergranular corrosion test and tensile test as in Example 1. Note that, as described in Example 1, the above-mentioned annealing treatment is a heat treatment assuming stress relief treatment for the welded portion of the pipe material.

Table 2 shows the chemical composition of the test tube materials as well as the test results. In the table, Nα21 and Nα22 are invention examples, No. 201~
203 is a comparative example. Comparative example Nα201 is a material equivalent to conventional Nb-containing lN825 for casting, Na 202 and No. 2
03 is an example in which the inner layer is made of a material equivalent to Ti-containing IN825 for conventional hot working. In the table, O and × marks in the "hot forming test" column and rMPY in the "intergranular corrosion test" column have the same meanings as above.

As shown in Examples 1 and 2 above, conventional casting N
N(11nt(
Although the intergranular corrosion resistance of Nα201 (single-layer pipe) and Nα201 (double-layer pipe) is good, cracks occur during the forming process of T-shaped pipes. Used No. 102 (single layer tube) and No.
202. Although k203 (double-layer pipe) exhibits good hot formability, it is significantly inferior in intergranular corrosion resistance. On the other hand,
Invention example No. 11. No. 12 (single layer tube) and N
o, 21.

22 (double-layer pipe) has good hot formability, and can be formed into a specified T-shaped pipe without cracking.
Moreover, the corrosion loss in the intergranular corrosion environment is negligible, and it has good corrosion resistance.

〔Effect of the invention〕

The cast material made of the high nickel iron-based alloy of the present invention has both high corrosion resistance and high strength, and also has hot formability necessary for forming irregularly shaped pipes such as T-shaped pipes.

Therefore, the high nickel iron-based alloy of the present invention is useful for producing cast products such as pipe materials that require high corrosion resistance and high strength, such as piping components for sour oil wells.

Claims (1)

[Claims] 1, C: 0.05% or less, Si: 1% or less, Mn: 1%
Below, P: 0.03% or less, S: 0.03% or less, Ni
:38-46%, Cr:19.5-23.5%, Mo:
2.5-3.5%, Cu: 1.5-3%, Ti: 0.6
1.2%, Nb: 0.15-0.8%, the balance substantially consisting of Fe, and a Nb/C ratio of 5-20.