JPS62179878A - Production of ni alloy clad steel sheet having no surface flaw - Google Patents

Abstract

PURPOSE:To produce an Ni alloy clad steel sheet without having surface flaws by using a precipitation hardening type Ni alloy added with specific component elements as a cladding metal and subjecting the same to hot rolling under specific conditions. CONSTITUTION:The product clad steel sheet is produced by combining the cladding metal consisting of the Ni alloy with a base metal consisting of a carbon steel or low-alloy steel. The precipitation hardening type Ni alloy which contains 20-80wt% Ni and 15-25wt% Cr, is controlled in the content of S and P to <=0.005wt% S and <=0.008wt% P, respectively and is added with 1 or >=2 kinds among 0.005-0.01wt% Ca, 0.004-0.008wt% Mg, 0.015-0.02wt% La, and 0.01-0.015wt% Y is used as the cladding metal. The cladding metal is combined with the base metal by a welding assembly method, explosive cladding method, etc., by which the clad stock is obtd. The stock is subjected to hot rolling under the conditions of 1,000-1,150 deg.C heating temp. and >=920 deg.C finishing temp, by which the Ni alloy clad steel sheet having no surface flaws is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing a Ni-base alloy clad steel plate, and more particularly to a method for manufacturing a Ni-base alloy clad steel plate free from surface defects.

(Conventional technology) Ni-based alloys, especially precipitation-hardened Ni-based alloys C and below, simply referred to as Ni-based alloys, exhibit excellent corrosion resistance and high-temperature strength, and have recently been used in various chemical industrial materials. It has come to attract attention as an oil well material and line pipe material for oil fields and gas fields, which contain corrosive elements such as CI-*Coz+) Its.

However, single-base alloys include Cr, Ni, and even Nb, Ti,
Since it contains a large amount of 10 etc., it is extremely expensive as a material, and its use as a cladding material has been considered (
Ru. In other words, the material is composited to separately ensure corrosion resistance and strength as a structural material. Specifically, the interior of the material is made of carbon steel.

This method uses low-alloy steel and places Ni-based alloy only on the surface layer, which is a useful method for cost reduction.

(Problems to be Solved by the Invention) However, when such a Ni-based alloy clad steel plate is actually manufactured, the following problems arise.

There are several methods for manufacturing clad steel plates, but from the viewpoint of cost, the welding assembly-rolling joining method or the explosive crimping (tJj bonding) method is particularly advantageous. However,
When such a method is applied to the production of Ni-based alloy clad steel sheets, the following problems arise. That is, welding assembly-
In both the rolling bonding method and the explosion bonding method, the final step in the manufacturing process involves hot rolling to finish the base material-laminated material laminate (hereinafter referred to as cladding material) to a specified thickness. However, Ni-based alloys have very poor hot workability;
For this reason, if hot rolling is performed in manufacturing the clad steel sheet, cracks and surface flaws will occur.

For these reasons, it is extremely difficult to manufacture high-quality, defect-free products at a high yield with respect to Ni-based alloy clad steel plates.

An object of the present invention is to provide a method for manufacturing a Ni-based alloy clad steel sheet without producing surface defects by applying a weld assembly-roll joining method or an explosion bonding method.

(Means and effects for solving the problem) As a result of detailed experiments and investigations by the present inventors, it has become clear that the following two points are the causes of poor workability of Ni-based alloys in hot conditions. Ta.

■Ni-based alloys include γ' (Nis(Al, Ti)), γ
” (Ni3Nb), which maintains high temperature strength and creep resistance, but this γ°,
On the other hand, the precipitation of the γ′″ ordered phase causes hardening of the inside of the crystal grains, resulting in embrittlement due to intergranular cracking. This embrittlement is observed in the temperature range of around 700 to 900°C. be.

■Also, even in the high temperature range of 1150℃ or higher, N
i-based alloys become brittle. This phenomenon causes sulfides and phosphides to melt at grain boundaries, leading to embrittlement due to exfoliation cracks at grain boundaries.

The present invention is based on the above facts ① and ②, and hot rolling is carried out during the production of Ni-based alloy clad steel sheets while avoiding embrittlement of the Ni-based alloy. In the production of Ni-based alloy clad steel sheets involving hot rolling, S and P are each set to S≦
0. O05wL%, P≦0.008wt%, Ca O,005~0.01wt%, Mg 0.00
4~0.008wt%, LaO, 015~0.02w
t%, yo, ot~o.

Using a Ni-based alloy containing one or more of
The gist of the present invention is a method for producing a Ni-based alloy clad steel sheet, which is carried out at a finishing temperature of 920° C. or higher.

In short, the method of the present invention described above consists of: (1) Ni as a bonding material;
Lower S and P 1 in the base alloy and change S to Ca+Mg, La
By fixing with +Y, the Ni-based alloy is prevented from becoming brittle due to the melting of phosphides and Ni sulfides at grain boundaries during the rolling process. Temperature range exceeding 70
By adopting a heating temperature and finishing temperature that do not fall within the temperature range of about 0 to 900°C, rolling of the Ni-based alloy in a embrittled state is avoided, thereby producing Ni-based alloy clad steel sheets without surface flaws or cracks. This made manufacturing possible.

Hereinafter, the method of the present invention will be explained specifically and in detail.

- Regarding the materials used, first, the base material is carbon steel or low alloy steel. The steel type is selected taking into account the intended use of the clad steel plate, and has the required properties other than corrosion resistance (strength,
toughness, etc.). For materials other than carbon steel and low-alloy steel, the cost increases and the economic benefits as cladding materials are diminished.

Next, as a laminating material, Ni20~80wt%, Cr
A Ni-based alloy containing 15 to 25 wt%, that is, a precipitation hardening Ni-based alloy, in which S and P as impurities are restricted to S≦0.005wt% and P≦0.008wt%, respectively. 0.01wt%, Mg 0.
004~0.008wt%+LaO,015~0.0
An alloy containing one or more of 2 wt% and 01 to 0.015 wL% of YO is used. Regarding each of the above components, the basic component is Ni = an essential element for austenitizing the structure, and is also essential from the viewpoint of improving corrosion resistance and maintaining strength. 20-[%necessary*
Basically, Ni1i can be added to any amount, but the upper limit is set to 80 wt%, especially considering the relationship with the Cr content.

Cr: An essential element for ensuring corrosion resistance, and for this purpose at least 15 wt% is required; however, if it exceeds 25 wt%, intermetallic compounds are likely to form, causing deterioration of workability.

Next, regarding impurities and additive components, these are the first characteristic points of the present invention, and are as follows.

P and S: Form phosphides and Ni sulfides, respectively, and precipitate at grain boundaries, causing embrittlement due to melting of phosphides and N1 sulfides in high temperature ranges exceeding about 1150°C. To avoid this embrittlement, P≦0.008 wt%.

S≦0. It is necessary to set it to O05twt%.

Ca, Mg, La, Y: the above S is 0.005 wt%t
Even if it is reduced to %, it is not sufficient to completely prevent the precipitation of Ni sulfide at grain boundaries. These additional elements have the meaning of supplementing this point, and are for fixing S in the grains. One or more of these elements may be added. Below each of the above lower limit values, the fixing effect of S will be insufficient, and addition of stars exceeding the upper limit value will cause S≦0.0.
Not only is it excessive compared to the condition of 0.05 wt%, but it also causes welding defects during welding work.

Regarding other components of the Ni-based alloy, MO is an element effective for corrosion resistance and strength, and is added as necessary. However, if its addition exceeds 2iwt%, intermetallic compounds will precipitate, resulting in adverse effects on workability.

5olA j! , Ti+Nb: These elements are elements that harden the material by precipitating the γl and γII phases, and at least one element needs to be added in a precipitation hardening type Ni-based alloy. 0.1 wt%, 0.2 wt, respectively
%, less than 0.2 wt%, precipitation hardening effect is not sufficiently observed; Qwt%, 6. Ow
When L% is exceeded, the hardening of the material becomes excessive, and even if the method based on the present invention is employed, surface flaws and cracks due to rolling cannot be prevented completely.

Si: Added as necessary to deoxidize and improve corrosion resistance and oxidation resistance, but if the amount exceeds 2wt%, workability deteriorates due to precipitation of intermetallic compounds, and weldability also deteriorates. There will be negative effects.

Mn = may be added for deoxidation and desulfurization,
Unless the amount is 111 t% or less, weldability will deteriorate.

- Obtain a cladding material using the base material 1 laminated material shown above.

Either welding assembly or explosion bonding method may be used to obtain the cladding material. In either case, Ni insert material (Ni7i) is interposed between the base material and the mating material as usual. To prevent carbon in the material from diffusing into the laminated material side and deteriorating its original performance, especially corrosion resistance.

In the welding assembly, the base material and the mating material are overlapped with the Ni insert material in between, and then welded at the four circumferential end faces to assemble them into one piece.

Similarly, the explosion bonding method uses Ni inserts, +
They are stacked together via a wire and then directly explosively bonded.

What is obtained by welding assembly is a mere laminate of the base material and the composite material, whereas what is obtained by the explosion bonding method is a product in which the base material and the composite material have already been joined metallurgically. Material refers to both.

・This rad material is then hot rolled and finished to a predetermined thickness. Rolling is done at a heating temperature of 1000-1150℃
, the finishing temperature shall be 920°C or higher. In the case of a cladding material obtained by welding assembly, it goes without saying that a vacuum degassing treatment (to eliminate air between each layer to ensure mutual bonding by rolling) is performed before rolling.

Regarding the heating temperature as the rolling condition, this is 1150
If the temperature exceeds .degree. C., even the Ni5 alloy having the above-mentioned composition may become brittle, making it difficult to avoid surface flaws due to rolling. In addition, if it is less than 1000℃, the finishing temperature is 920℃.
It becomes impossible to secure temperatures above ℃. Therefore, 1000-115
The temperature was 0°C.

If the finishing temperature is lower than 920° C., the Ni-based alloy used as the laminated material will become embrittled due to the precipitation of r + and γ′ ordered phases in this case as well, and there is a risk that surface flaws will be caused by rolling. Therefore, the lower limit was set at 920°C.

Rolling is performed within a range that satisfies these temperature conditions, but if it is not possible to secure the necessary rolling reduction with just one heating, heating is performed in between and the heating and rolling are repeated. This may be repeated multiple times.

(Example) The conditions of S, Pg, and additional elements (Ca, Mg, La, Y) were set using the precipitation hardening type Ni-based alloy (trade name: IncoFuru 825, equivalent to IncoFuru 718) shown in Table 1. As shown in Table 2, variously modified alloys were mechanically ground to a plate thickness of 5+n, and this was used as a bonding material, and a 150 IJ thick Ni foil was used as an insert material to form a plate J! ! They were assembled by welding onto a 95 am low alloy steel base material, vacuum degassed, and then hot rolled at various heating and finishing temperatures shown in Table 2 to give a plate thickness of 20 mm.

The surfaces of the various clad steel plates obtained were polished with emery paper, and then subjected to puff polishing.
The number of flaws existing within 1 oaJ area of the surface was investigated to evaluate the occurrence of surface flaws.

The results were as shown in the left column of Table 2.

As is clear from the same table, based on the present invention, the laminated material contains S≦0.005wt%, P≦0.008wt%, Ca 0.005-0.01wt%, Mg 0.
004-0.008wt%, LaO, 015-0.0
Using a Ni-based alloy to which one or more of 2 wt% and 01 to 0.015 wt% of YO is added, the heating temperature during rolling is 1000 to 1150 °C, and the finishing temperature is 920 °C or higher. Satisfied invention example (6) ~
In (15) and (31) to (40), there were no surface flaws in the laminated materials.

In contrast, comparative examples (1) to (5), (16) to (
25) and (26) to (30) are cases in which at least one of the component conditions of the laminated material and the temperature conditions of hot rolling are outside the scope of the present invention, but these all cause surface defects on the laminated material. The occurrence of was observed.

In this example, Inconel 825° Inconel 71
Although only the case using a Ni-base alloy based on an alloy equivalent to Inconel 751°Ni+mon is shown,
ic 80^, Rene 41. Pryromet
The inventors have confirmed that the present invention is equally effective when a precipitation hardening Ni-based alloy equivalent to No. 860 is used.

(Effects of the Invention) As is clear from the above description, the present invention reliably prevents surface flaws from occurring in the Ni-based alloy in the production of Ni-based alloy clad steel sheets that involve hot rolling, and achieves high quality. This has the effect of enabling stable production of Ni-based alloy clad steel sheets, and therefore greatly contributes to improving the production yield and reducing costs of Taland steel sheets.

Claims (1)

[Claims] (1) When manufacturing a finished clad steel plate by hot rolling from a clad material made by combining a base material made of carbon steel or low alloy steel with a composite material made of a Ni-based alloy,
As a laminating material, Ni20~80wt%, Cr15~2
5wt%, S and P each S≦0.005wt%,
Regulate P≦0.008wt% and Ca0.005~0
．． 01wt%, Mg0.004-0.008wt%, L
a0.015-0.02wt%, Y0.01-0.01
Precipitation hardening type N with 5 wt% of one or more added
Using an i-based alloy, hot rolling is performed at a heating temperature of 1000 to 115
A method for producing a Ni-based alloy clad steel sheet free of surface defects, characterized in that the method is carried out under conditions of 0° C. and a finishing temperature of 920° C. or higher.