JPH0723524B2 - Hot working method for Cu-containing Ni-based alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is known as a hot working method for Cu-containing Ni-based alloys intended to prevent hot work cracking, particularly as an alloy in which hot work cracking frequently occurs. This is a hot working method for Cu-containing Ni-based alloys to prevent hot work cracking, which is characterized by performing cold working by pressing or rolling on Cu-containing Ni-based alloys such as JIS H4551 as a pretreatment. .

(Prior Art) For example, a Cu-containing Ni-based alloy defined as JIS H4551 has been used in a large amount as a corrosion resistant material in the field of chemical industry from the viewpoint of its excellent corrosion resistance today, and it is typically the following first It has the composition shown in the table.

However, when hot working is performed directly from the continuous casting slab to the product size, this system alloy frequently suffers from bald defects on the surface and cracks or crack defects called edge cracks on the side surfaces, making it difficult to mass produce products.

Therefore, in the past, of course, a flaw removal process was provided prior to hot working, and hot working was divided into several steps and carried out little by little.
The flaw removal process was performed every time a flaw was generated. Normally, hot rolling is repeated 20 times at each processing rate of about 20%, or at the beginning, the processing rate is 20 to 30%, and thereafter, the processing rate is increased once or more. It was

As is clear from the above, such a conventional method has a high risk of leaving flaws at the time of flaw removal and not only deteriorates the quality of the product, but also repeats hot working and flaw removal, resulting in extremely high operating costs. It will be very expensive.

By the way, in order to prevent surface cracks or surface defects observed during hot working of steel materials, it has been practiced to lower the heating temperature or to apply an antioxidant or the like to the material to be hot rolled (Example: JP JP-A-56-26603 and JP-A-59-56519
issue). Particularly, in JP-A-59-56519, Ni20-45%, Cr6%
A method of coating a high Ni-base alloy steel containing the following with an antioxidant to prevent edge cracks and surface defects during hot rolling is disclosed.

On the other hand, in Japanese Patent Laid-Open No. 58-19428, at the time of hot extrusion of a continuous cast material of stainless steel, the continuous cast material is heated and hot worked in advance to refine the structure of a surface layer having a thickness of at least 3 mm from the surface. , It is disclosed that hot extrusion is continued, but this will destroy the strong directional continuous casting structure found in continuous casting materials and obtain hot extrusion characteristics equivalent to those using hot rolled materials. It is what

It is also disclosed that prior to the above-mentioned hot working performed in advance, cold working such as shot blasting of the material end face is performed in order to prevent streak defects at the tip of the extruded material. It is also a pre-treatment of the treatment and aims to eliminate the anisotropy at the very surface of the material due to grain refinement.

(Problems to be Solved by the Invention) The object of the present invention is to prevent Cu from containing hot work.
It is to provide a hot working method for a base alloy.

Another object of the present invention is to prevent hot work cracking by reducing the number of times of surface maintenance as much as possible, and if possible, producing a product by one hot rolling at a large work rate of, for example, 60% or more. It is to provide a hot working method for Cu-containing Ni-based alloys.

(Means for Solving the Problems) As a result of intensive studies made by the present inventors in order to achieve the above-mentioned objects, as a result of the conventional use of an antioxidant, the present alloy has a high sensitivity to intergranular oxidation. However, while the hot working temperature was lowered, we focused on the fact that the segregation of Cu at the grain boundaries reduced the ductility of the grain boundaries. Perform cold working on the Cu-containing Ni-based alloy at the stage, accumulate strain inside the slab, use this strain as the driving force, and recrystallize the surface layer part with particularly high strain during heating during the subsequent hot working. By refining the structure, Cu segregation effectively disappears and the ductility of grain boundaries is improved to an unexpected degree, which greatly improves the hot workability of this Cu-containing Ni-based alloy. I found out what to do. Based on this, various basic tests were subsequently carried out, and the processing rate was 60%.
The present invention has been completed by confirming that the present alloy having good surface quality can be produced even by only one hot working with a large working rate of at least%.

Here, the gist of the present invention is Cu of the following alloy composition
As a pretreatment for the hot working of the Ni-containing alloy containing, cold working is performed to refine the structure of the surface layer part to prevent Cu segregation to grain boundaries, and then hot working is performed. This is a hot working method for Cu-containing Ni-based alloys to prevent cracking defects at the time.

C: 0.30% or less, Si: 0.50% or less, Mn: 2% or less, Cu: 28.0 to 34.0%, Fe: 2.5% or less, balance Ni As described above, the pretreatment cold working condition adopted in the present invention is press. Alternatively, the rolling rate is 5%, preferably 10
% Or more is added, and the cold work rate is defined as follows.

Cold working ratio _{= (H 1 -H 2) /} H 1 × 100 (%) H 1 = thickness before working, H ₂ = plate thickness after working Furthermore, as the hot working method forging, pressing and rolling There is. Preferably, hot working is performed at a large working rate so that a final product can be obtained by one hot working. The processing rate at that time is generally 60% or more.

Regarding the Cu-containing Ni-based alloy of the present system alloy, the crack sensitivity increases as the Fe content increases, but according to the present invention,
Even if the maximum amount of impurities such as Fe is mixed within the allowable specification range,
A product with a good quality appearance is obtained.

The mechanism of effectively preventing cracking during hot working according to the present invention has not been clarified yet, but in the case of a continuously cast slab, it can be considered as follows.

In the as-cast state, it is noticeable at the grain boundaries of coarse crystal grains.
Cu segregation is observed and the strength difference between the grain boundary and the matrix is large, leading to fine cracking during hot working. Therefore, as in the present invention, by cold working to recrystallize it and refine it, the new grain boundaries inevitably have reduced or disappeared Cu segregation, and the relative strength of the grain boundaries and the matrix becomes small, and As is generally said, the decrease in crack susceptibility due to grain refinement acts synergistically with the above effects,
It is considered that hot workability is improved to an unexpected degree.

The Cu-containing Ni alloy targeted by the present invention is, by weight%, C: 0.30% or less, Si: 0.50% or less, Mn: 2% or less, Cu: 28.0 to 34.0%, Fe: 2.5% or less, balance Ni, Is a Ni alloy.

Therefore, in its preferred embodiment, the present invention is
, C: 0.30% or less, Si: 0.50% or less, Mn: 2% or less, Cu: 28.0 to 34.0%, Fe: 2.5% or less, the balance Ni, as a pretreatment for hot working of Ni-based alloys. Rate 5%
It is characterized by performing the above cold working and refining the structure of the surface layer portion to prevent Cu segregation to the grain boundaries, and then performing hot working, containing Cu for the purpose of preventing crack defects during hot working. This is a hot working method for Ni-based alloys.

Here, the reason why each alloy component is selected in the preferred embodiment as described above is as follows.

C (carbon): The C component is a preferable element as an alloy component because it has a deoxidizing action on the molten alloy and an action to increase the strength of the alloy.
If the content is more than 30%, an excessive amount of C will be precipitated at the crystal grain boundaries and the workability will be deteriorated. Therefore, the C content is preferably limited to 0.30% or less.

It should be noted that even if a small amount of C is contained, the above effect can be obtained to some extent, but it is preferable that the content of C be 0.05% or more.
Is good to contain.

Si and Mn (silicon and manganese): These components each effectively act as a deoxidizer for the molten alloy, but the Si content exceeds 0.50% and the Mn content exceeds 2%. And the ductility of the alloy is extremely reduced, the Si content is 0.50% or less, and
It is preferable to limit the Mn content to 2% or less.

Even if the content of these elements (remaining amount of deoxidation) is about traces, it goes without saying that a sufficient deoxidation effect can be obtained.

Cu (copper): The Cu component has the function of forming a solid solution in Ni to improve the corrosion resistance, but if its content is less than 28.0%, the corrosion resistance of the alloy against non-oxidizing acids is not sufficient, while 34.0% Beyond Cu
However, the Cu content is 2
It is preferably set to 8.0 to 34.0%.

Fe (iron): The Fe component also has an effect of improving the corrosion resistance of the alloy and is preferable as an alloying element. However, if it exceeds 2.5%, the ductility may decrease, so Fe is included. The amount should be 2.5% or less.

Even if the Fe content is very small, the effect of improving the corrosion resistance can be obtained, but it is preferable to secure the content of 0.5% or more.

Next, the present invention will be further described with reference to examples.

Example Five Cu-containing Ni-based alloys having the compositions shown in Table 2 and varying the Cu and Fe contents were melted. Among them, the sample materials No. 1 to 4 are small ingots (10k
g), Specimen No. 5 was melted into a continuous cast slab with a thickness of 150 mm and a width of 1050 mm.

The surface of each of these test materials was cut and removed to collect test materials. For continuous cast slabs, test materials were collected from columnar crystal parts.

After slab care for each test material, cold rolling was performed by the method of the present invention at a cold working rate of 3.6 to 14.4%, and then 1
It was heated to 100 ° C and hot worked at a working rate of 60%. The target dimensions and shape were obtained by hot rolling once. The antioxidant was applied during the hot working.

As a comparative example, an antioxidant was applied after maintenance by a conventional method, and then hot working was performed immediately under the same conditions.

The occurrence of surface defects in the hot-rolled material thus obtained was examined. The results are summarized in Table 3. In the table, a cold working rate of 0% is a conventional method in which cold working is not performed. Further, in the method of the present invention, as the cold working rate, a level of approximately 5% at which uniform microfabrication of the surface layer portion was observed by macrostructure observation,
And two higher levels of 10-15%.

As is clear from the results shown in Table 3, in the conventional method, cracks were found on both the surface and side surfaces of all the test materials. On the other hand, no cracks were observed in any of the methods of the present invention.

FIG. 1 is a graph summarizing the above results, and it can be seen that cracking is substantially prevented when the processing rate is 5% or more, preferably 10% or more.

Next, in order to observe the state of microstructure refinement by macroscopic observation, first, heat treatment was performed under the conditions of 1100 ° C. × 1 Hr and WQ, assuming heating after cold working and during hot rolling thereafter.

The results are shown in FIG. 2 of the accompanying drawings as a macrostructure photograph. With cold rolling as it is, changes in the structure due to cold rolling are hardly observed, but with as-heat treated, recrystallization from the surface layer proceeds as the cold reduction increases, and the recrystallized region increases. ing. However, when the processing rate is the lowest, 3.61%, coarse crystals remain in the surface layer. On the other hand, when the processing rate is 5.00% or more, no coarse crystals remain and it can be said that the structure is refined.

FIG. 3 is a microstructure photograph after the cold working and heating to 1100 ° C. for the purpose of refining the crystal, and it can be seen that the segregation of Cu at the grain boundaries has substantially disappeared.

On the other hand, FIG. 4 shows Cu of the material shown in FIG. 3 by X-ray diffraction method.
In the analysis examples of Ni and Ni, it can be seen that neither Cu nor Ni is segregated at all.

FIG. 5 is shown for comparison and is a photograph of the same microstructure as in FIG. 3 when cold working is not performed, and Cu is segregated at the grain boundaries. FIG. 6 is a graph showing an example of analysis of Cu and Ni by the X-ray diffraction method at this time, and it can be seen that Cu is significantly segregated.

(Effect) As described in detail above, the Cu-containing Ni-based alloy, which has been conventionally counted as one of so-called difficult-to-machine materials as an alloy that frequently causes hot work cracking, can be extremely easily and conventionally manufactured by the method of the present invention. The hot working can be easily performed by simply performing the cold working once before the heating without any change of the equipment, and the profit is great. In addition, since the reduction rate can be made large, hot working can be done in a single step, and operating profits are large.

[Brief description of drawings]

FIG. 1 is a graph showing the influence of the workability of cold rolling on the occurrence of cracks; FIG. 2 is the change in structure depending on the workability of cold rolling when cold rolling and heat treatment are performed. FIG. 3 is a microstructure photograph of the hot-worked material obtained by the present invention; FIG. 4 is a graph showing an example of Cu and Ni analysis of the material of FIG. 3; A microstructure photograph of the hot-worked material without cold working; and FIG. 6 are graphs showing Cu and Ni analysis examples of the material of FIG.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoichiro Shintani 2-12-1 Minatomachi, Joetsu City, Niigata Prefecture, Japan Naoetsu Research Institute, Japan Stainless Co., Ltd. (72) Inventor Tsuyoshi Sanada 2-12 Minatomachi, Joetsu City, Niigata Prefecture No. 1 Japan Stainless Steel Co., Ltd. Naoetsu Works (72) Inventor Yutaka Kimami 2-12-1, Minatomachi, Joetsu City, Niigata Prefecture Japan Stainless Steel Co., Ltd. Naoetsu Works (72) Inventor Tsuruta 2 Minatomachi, Joetsu City, Niigata Prefecture No. 12-1 Japan Stainless Steel Co., Ltd. Naoetsu Works

Claims (1)

[Claims] 1. A Cu-containing Ni-based alloy consisting of C: 0.30% or less, Si: 0.50% or less, Mn: 2% or less, Cu: 28.0 to 34.0%, Fe: 2.5% or less and the balance: Ni. As a pretreatment of the hot working, the cold working with a working rate of 5% or more is performed to refine the structure of the surface layer portion to prevent Cu segregation to grain boundaries, and then hot working is performed. Cu content to prevent cracking defects during hot working
Hot working method for Ni-based alloys.