JPS61144283A - Production of clad material - Google Patents

Abstract

PURPOSE:To secure the corrosion resistance of the austenitic material in clad materials without spoiling the performance of the steel of base materials by treating with rapid cooling the austenitic material of the specified composition after re-heating at the specified temp. again after its rapid cooling treatment. CONSTITUTION:A hot working is performed with heating to the temp. of more than 1,000 deg.C the preparatory clad material consisting of the base material of the carbon steel of less than 0.3% C or low alloy steel and the austenitic material containing Ni, Cr, Mo and further more than one kind of Ti and Nb. It is treated with rapid cooling from the temp. of more than 800 deg.C with the state as it is after the hot work. It is then treated with rapid cooling after reheating to the temp. of 880-960 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a cladding material, which includes Ni, Cr, and Mo, which have good corrosion resistance, and further includes one of Ti and Nb.
The present invention relates to a method for manufacturing a cladding material of an austenitic material containing more than one species.

(Prior art) In recent years, as the energy situation has become tighter, oil and gas wells have become deeper and the environment has become increasingly harsh.
H2S), carbon dioxide gas (C02), chlorine ions <CI-)
Drilling, transportation, and storage of crude oil and natural gas containing highly corrosive substances have become commonplace, and accordingly, metal materials with high strength and corrosion resistance suitable for use in such environments are being developed. requested.

Conventional low-alloy steels cannot withstand use in such harsh environments due to their corrosion resistance, so in order to meet this demand, there has been a recent trend toward using higher grade corrosion-resistant abrasives, such as austenitic stainless steels. High-alloy materials such as Incoloy, Incoloy, and Hastelloy (all trade names) are beginning to be adopted.

By the way, since high alloying of such materials always involves an increase in cost, economic disadvantages are unavoidable. Furthermore, since these materials are austenitic stainless steels or alloys, their strength is low if they are solution-treated, which is the usual manufacturing method to ensure corrosion resistance.
Therefore, in order to ensure the required strength, it was customary to further cold-work the steel after solution treatment.

(Problems to be solved by the invention) However, according to the experiments and research of the present inventors, H2
The main type of corrosion in the S-Co2-Cl- environment is so-called stress corrosion cracking (hereinafter abbreviated as "scc"), but the corrosion behavior of SCC in this case is completely different from that of general corrosion. There is. In other words, while general SCC is deeply related to the presence of Cl-, H2S-C02-C
In the l- environment, Cl- as well as
In fact, the important fact has become clear that the influence of H2S is even greater than that, and that the above-mentioned cold working significantly deteriorates the resistance to corrosion in this H2S-C02-Cl- environment.

(Means for Solving the Problem) Therefore, the present inventors aimed to develop an inexpensive material with excellent strength and corrosion resistance without cold working the austenitic material. Focusing on the fact that it depends only on the properties of the surface, and after conducting various experiments and research, we found that the desired purpose could be achieved by cladding with austenitic material.

This cladding material is formed by using an austenitic material as a composite material, and on the other hand, using a steel such as carbon steel or low-alloy steel that has the desired strength and toughness as a base material, and hot processing and crimping the two. It is then processed into a product. However, as already mentioned, austenitic materials do not have the desired corrosion resistance unless they are subjected to solution treatment after forming. Therefore, to ensure corrosion resistance, it is sufficient to perform solution treatment on the formed cladding material, but in general, treatment at temperatures of 100°C or higher is required to sufficiently solutionize austenitic materials. When heated to a high temperature, the austenite grains of the base metals of carbon steel and low alloy steel become coarser, resulting in a problem of extremely poor toughness.

On the other hand, in order to ensure the toughness of the base metal, it is sometimes used as rolled or after being cooled to room temperature after rolling and then reheated to a low temperature range below 1000°C and quenched.
In that case, deterioration of the corrosion resistance of the austenitic material is inevitable.

In response to the above-mentioned current situation, the inventors of the present invention set out to provide a method for manufacturing a crund material that can ensure the corrosion resistance of the austenitic material that is the laminated material without impairing the performance of the steel that is the base material. As a result of further investigation, the following findings were obtained.

(Al austenitic materials can be hot worked at high temperatures and then rapidly cooled directly from a temperature of 800°C or higher to obtain a good structure in which carbides and precipitates are dissolved in the austenite matrix.

(bl) If an austenitic material containing one or more of Ti and Nb is further heated to a temperature of 880 to 960°C and then rapidly cooled, the C dissolved in solid solution in the austenite becomes Ti and Corrosion resistance is stable because it precipitates as Nb carbide and undergoes so-called stabilization treatment.

fc) The quenching treatment after reheating to a temperature of 880 to 960°C in the above [bl] is a quenching treatment for the steel that is the base material, and this temperature is below the so-called crystal grain coarsening starting temperature. Therefore, this fine-grained steel exhibits a fine-grained structure, especially at low CJg where the C content is about 0.06% by weight or less.
Good strength and toughness can be obtained even after quenching.

(d) If the base material is steel with a C content of about 0.06% by weight or more, the toughness will deteriorate if it is left quenched from a temperature of 880 to 960°C, that is, if it is quenched. Toughness can be recovered by tempering at a temperature below Ac1 point.

The above tempering treatment is also effective for low C steel with an IEL C content of about 0.06% by weight or less.

(fl Furthermore, even if the above-mentioned tempering treatment is performed on the steel that is the base material, the austenitic material that is the bonding material has been stabilized, so its corrosion resistance will not deteriorate.

Thus, the present inventors have completed the present invention based on the above findings, and the present invention includes a base material that is carbon steel or low alloy steel with C:Q of 3% or less, and further contains Ni, Cr, and Mo. A preliminary cladding material consisting of a composite material of austenitic materials containing at least one type of Ti and Nb is heated to a temperature of 1000°C or higher and hot worked, and after hot working it is heated to a temperature of 800°C or higher as it is. The toughness and strength of the base material are impaired by quenching from a temperature of The gist of this is to ensure excellent corrosion resistance of the laminated material portion.

Here, the austenitic material that is the laminating material is Ni,
It is necessary to use a material containing Cr, Mo, and at least one of Ti and Nb, but H2SC02-CI!
- In order to obtain excellent SCC resistance in the environment, it is preferable to contain Ni at 30% or more, Cr at 20% or more, and Mo at 2.5% or more by weight. On the other hand, Ti and Nb are added to stabilize solid solution C as TiC and NbC, and it is desirable that the amount of addition satisfies at least the following formula % (%). Since addition deteriorates hot workability, the upper limit is 3% for Ti and 3% for N.
It is best to set b to about 5%. For the stabilization of C, T
The effect of Nb is greater than that of i.

Further, carbon steel or low alloy steel with C: O, a% or less preferably has C: 0.06% or less, but C: 0.06
%, in order to prevent deterioration of toughness due to quenching, it is preferable to perform tempering at an Ac point of 4 or less.

Here, in a broad sense, "low alloy steel" is a flame consisting of 5% or less of constituent elements and the remainder Fe.

Note that the preliminary clamp material assembled prior to hot working is constructed by pasting the base material and the mating material together at appropriate positions by means such as welding.

This preliminary cladding material is then crimped by hot working,
This results in an integrally constructed cladding material.

゛Of course, this cladding material may be a steel plate or a steel pipe, and may also have a nickel layer at the interface between the base material and the composite material.

′″′″ゝ゛1j′″＊O'fff(lJsFlc"=
la1mIu-El.

Previously, it was performed after reheating and solution treatment, in which the material was cooled in the atmosphere to room temperature and then reheated to a high temperature and rapidly cooled, but according to the present invention, solution treatment can be performed subsequent to hot working. Therefore, the secondary effect is that the thermal energy for heating to and holding the solution temperature can be reduced.

(Function) In the present invention, the lower limit heating temperature for hot working the cladding material is set at 1000°C, because heating in a low temperature range below this temperature increases the deformation resistance of the material. In addition to making machining difficult, hot workability deteriorates due to insufficient solid solution of carbides and precipitates into the austenite matrix in the laminated material. In the method of directly quenching after processing, if the heating temperature is less than 1000° C., the desired microstructure cannot be obtained, leading to deterioration of SCC resistance.

However, the upper limit temperature for heating prior to hot working is not specified, and it is sufficient to set the temperature at which hot brittleness does not occur during material processing. Temperature at which the aperture value in a high temperature tensile test is 50% or more (e.g. 1200 to 1250"C)
If you choose , there will be no problem with the base material.

On the other hand, the reason why the lower limit temperature for starting rapid cooling after hot working is set to 800°C is that if the starting temperature for rapid cooling is set lower than this temperature, slow cooling will be carried out to that temperature.
This is because if the material is slowly cooled to less than 00° C., grain boundary carbides may precipitate in the austenitic material that is the mating grain, resulting in deterioration of SCC resistance.

Furthermore, during the reheating and rapid cooling process, the upper and lower limits of the heating temperature were set to 960°C and 880°C, respectively, because at temperatures below 880°C, the austenitic material that is the laminated material
This is because the fixation or stabilization treatment of solid solution C by Ti'PtJb may not be performed sufficiently, resulting in deterioration of SCC resistance.On the other hand, at temperatures exceeding 960°C, the base material steel becomes coarse grained. This is because the toughness may deteriorate.

Furthermore, in order to improve the toughness of the base metal, which is carbon steel or low alloy steel, it may be tempered at a temperature below Ac1 point, but if the tempering temperature exceeds Ac1 point, the strength and toughness will deteriorate. Since the variation becomes large, the upper limit temperature for tempering is set as the Ac work point.

In addition, if the austenitic material used as the laminating material in the present invention further contains Cu as a component element, it has better SCC resistance, but since adding a large amount of Cu deteriorates hot workability, its upper limit is preferably about 3%.

As mentioned above, we chose carbon steel or low-alloy steel for the base material in order to ensure strength and toughness as a cladding material, and we also made the carbon content 0.3% or less. This is to obtain good toughness.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

A base material of low alloy steel and carbon steel with a thickness of 70 mm having the composition shown in Table 1, and a composite material of austenitic material with a thickness of 6.5 mm having the composition shown in Table 2. After cleaning the joint surfaces, the art materials were bonded together and spot welded to obtain a preliminary cladding material, which was then hot rolled under the conditions shown in Table 3 to form a cladding material with a thickness of 12 mm, also under the conditions shown in the same table. Heat treatment was performed and the cladding material was molded.

The strength of the clad material thus obtained and the toughness of the base material are also shown in Table 3.

From the results shown in Table 3, it is clear that the treatment according to the present invention provides a rad material with good base material toughness.

Next, for the alloys with mating row numbers B-1 to B-3 shown in Table 2, plates were produced under the conditions shown in Table 4, and from the obtained plate material, a thickness of 2 mm was formed perpendicular to the rolling direction. 10mm width,
A 751-length specimen was taken and subjected to the SCC test.

Here, the SCC test was conducted using a three-point support beam jig 1O schematically shown in the attached drawing, and applied a tensile force equivalent to 0.2% proof stress to the above test piece (S) via each fulcrum 1 and 12.13. 10% with added stress, 5 atm H2S, 15 atm CO2
The test piece was immersed in a NaCl solution (temperature 200°C) for 20 days, and the SCC resistance was evaluated by observing the presence or absence of cracks on the test piece surface after the test. Similarly, Table 4 summarizes the manufacturing conditions of the plate materials, as well as the 0.2% yield strength and SCC test results.

According to the results shown in Table 4, it is clear that even if the treatment according to the present invention is performed, the corrosion resistance of the austenitic material used as the laminated material is good. From the results shown in Tables 3 and 4, it can be easily seen that the cladding materials treated according to the present invention have poor strength, toughness, and corrosion resistance.

(Effects) As explained above, the effects of the present invention are very large, and its industrial value is high.

[Brief explanation of the drawing]

The attached drawing is a schematic explanatory diagram showing a three-point support beam jig for SCC test for plate-shaped test pieces. S: Test piece 10; 3-point support beam jig 11: Fulcrum 12:〃 13:〃 Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent attorney Do Hirose - (1 person) S: 1 ball sound 1o: a7 ! , Sarashita now heem mud smell 11: support, 12: ga 13:.

Claims (2)

[Claims] (1) Cladding consisting of a base material of carbon steel or low alloy steel with C: 0.3% or less and a composite material of an austenitic material containing Ni, Cr, Mo and also one or more of Ti and Nb. In the method for manufacturing the material, a pre-clad material made by combining the base material and the composite material is heated to a temperature of 1000°C or higher, hot worked to form a cladding, and after hot working, the material is heated to a temperature of 800°C or higher in that state. Rapidly cooled from a temperature of
A method for producing a cladding material, which is then reheated to a temperature of 880 to 960°C and then rapidly cooled. (2) A cladding made of a base material of carbon steel or low alloy steel with C: 0.3% or less and a composite material of an austenitic material containing Ni, Cr, Mo, and also one or more of Ti and Nb. In the method for manufacturing the material, a pre-clad material made by combining the base material and the composite material is heated to a temperature of 1000°C or higher, hot worked to form a cladding, and after hot working, the material is heated to a temperature of 800°C or higher in that state. Rapidly cooled from a temperature of
A method for producing a cladding material, characterized in that the material is then reheated to a temperature of 880 to 960°C, rapidly cooled, and further tempered at a temperature below the Ac_1 point of the base material.