JPS649391B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing corrosion-resistant alloy steel. The corrosive environments in which metal materials are used have tended to become more severe in recent years.For example, chemical plants are experiencing higher temperatures, higher pressures, and higher concentrations of chlorides, and oil, gas, and geothermal wells are also experiencing corrosion. With the deepening of wells, the temperature and pressure at the bottom of wells are increasing, and the concentration of chlorides is increasing, and the concentrations of hydrogen sulfide, carbon dioxide, etc. are also increasing. In response to these increasingly severe corrosive environmental conditions, the metal materials used therein have properties such as pitting corrosion resistance and stress corrosion cracking resistance (hereinafter referred to as "SCC resistance").
is required, and for this reason chromium is used for pitting resistance.
Materials to which molybdenum, etc. are added, and nickel, etc. for SCC resistance are being used. The use of high alloy steels known as Incoloy, Hastelloy, etc., is also being considered as a steel material. As mentioned above, there is a trend toward increasing the amount of nickel added to corrosion-resistant alloy steel to improve SCC resistance, and increasing chromium and molybdenum to improve pitting corrosion resistance, but the amount of each alloying element added varies individually. Materials are determined based on the effect of elements on solidification phenomena, and the mutual optimum balance of alloying elements such as nickel, chromium, and molybdenum is quantitatively considered in order to improve SCC resistance and pitting corrosion resistance. Not yet known. Furthermore, one of the most important elements in actual product manufacturing
Thermal history, especially solution treatment conditions and SCC resistance
At present, the interaction between corrosion resistance and pitting corrosion resistance has not been sufficiently elucidated. On the other hand, high nickel alloy steels tend to develop hydrogen embrittlement during cold working, and for example, Hastelloy, which exhibits sufficient SCC and pitting corrosion resistance, will develop hydrogen embrittlement. High alloy steel used in severe corrosive environments is required to have hydrogen embrittlement resistance as well as pitting corrosion resistance and SCC resistance, but to date, no alloy steel with excellent overall performance has been known. The present invention was created in view of the current situation, and aims to elucidate the interaction of alloying elements with respect to SCC resistance, pitting corrosion resistance, and hydrogen embrittlement resistance, and the relationship between these and solution treatment (or quasi-solution treatment) treatment conditions. However, it has excellent SCC resistance comparable to conventional so-called Incoloy and Hastelloy.
We have succeeded in producing a corrosion-resistant alloy steel that not only has high corrosion resistance and pitting corrosion resistance, but also has hydrogen embrittlement resistance. That is, in the present invention, C: 0.03wt% or less,
Si: 2wt% or less, Mn: 2wt% or less, P: 0.02wt%
Below, S: 0.01wt% or less, Ni: 30 to 60wt%,
Cr: 22~35wt%, Mo: 10wt% or less, Ti: 0.5~
3.0wt%, N: 0.01wt% or less, and in addition, contains one or more of the following: 2wt% or less of Cu, 0.1wt% or less of Ca, 1wt% or less of Nb, and the balance is iron and A composition consisting of unavoidable impurities, where the Δ ₁ value determined by Δ ₁ = Cr+1.5Mo−100C+30N is 25 or more, and Δ ₂ =Ni−[(Cr+1.5Mo−20) ² /12−30C−10N ] An alloy steel having a composition with a Δ ₂ value of 15 or more is subjected to solution treatment or semi-solution treatment at a temperature range of 1000°C or more. The reasons for limiting the component composition and heat treatment conditions of the present invention will be explained in detail below. The reasons for limiting the component composition of the present invention are as follows. Some say that C is effective in suppressing intragranular SCC, but if the C content exceeds 0.03wt%, grain boundary SCC may occur.
High Ni content tends to occur, especially when C solid solubility decreases
This risk increases with alloys. There is also the problem that carbide precipitates can easily become a starting point for pitting corrosion.
For this reason, the upper limit of C is limited to 0.03 wt% or less. Si is necessary as a deoxidizing component and is an effective element for improving SCC resistance, but if it exceeds 2wt%, it deteriorates hot workability, and therefore its upper limit is
It is defined as 2wt%. Like Si, Mn has a deoxidizing effect. This Mn is
It has almost no effect on SCC properties, but if it exceeds 2wt%, precipitates such as manganese sulfide tend to become a starting point for pitting corrosion, so the upper limit is set at 2wt%. Since P as an unavoidable impurity has the effect of increasing SCC susceptibility, it must be reduced as much as possible, and therefore its upper limit is set at 0.02 wt%. S as an unavoidable impurity has the effect of deteriorating hot workability and creates manganese sulfide, etc., which deteriorates pitting corrosion resistance, so its upper limit is set at 0.01 wt%. Ni is an effective element for improving SCC resistance, and its effect becomes noticeable when the content is 30 wt% or more. On the other hand, even if the content exceeds 61 wt%, no further effect can be expected, and on the contrary, it will impair economic efficiency. Cr is an effective element for improving the corrosion resistance of high alloy steel, especially by strengthening the passive film. In order to obtain sufficient pitting corrosion resistance, a content of 22 wt% or more is required, but if the content exceeds 35 wt%, it is difficult to avoid deterioration of hot workability. It is determined to be 35wt%. Mo is about 1.5 times as effective as Cr in strengthening the passive film, but if its content exceeds 10wt%, it easily forms a σ phase that deteriorates corrosion resistance during hot processing. Therefore, the upper limit is 10wt
%. Although N improves pitting corrosion resistance, the steel of the present invention has sufficient pitting corrosion resistance even without a nitrogen component. On the contrary, N
If it exceeds 0.01wt%, it will have an adverse effect on SCC resistance, and therefore the upper limit is set at 0.01wt%. Ti has the effect of improving hot workability, fixing C and suppressing grain boundary SCC, and has the effect of effectively suppressing hydrogen embrittlement in high Ni alloys. It is necessary to contain more than wt%. However, if it exceeds 3wt%, hot cracking occurs and the metal structure becomes unstable, so the upper limit is set at 3wt%. Figure 1 shows the results of investigating the effects of Ni _and Ti content on hydrogen cracking. Sodium chloride, 0.5% acetic acid in contact with iron,
Judgment was made based on the presence or absence of cracks after 300 hours. As is clear from the figure, even in the high Ni range where hydrogen cracking is likely to occur, hydrogen embrittlement resistance is appropriately obtained by containing 0.5% or more of Ti. One or more of Cu, Nb, and Ca components may be contained. Among these components, Cu
is helpful to improve the corrosion resistance of the material, but 2wt
If it exceeds %, it will lead to deterioration of hot workability.
The upper limit is set at 2wt%. In addition, Nb and Ca have the effect of improving hot workability, and Nb has the effect of fixing C and, as a result, suppressing grain boundary SCC. Although each ingredient exhibits such effects,
It is sufficient if Ca is 0.1 wt% or less and Nb is 1 wt% or less, and no further effect can be expected even if the content exceeds these upper limits. Therefore, these are Ca
0.1wt%, Nb can be contained up to 1wt%. In the present invention, in addition to the compositional conditions of the component elements as described above, the following conditions are further applied: Δ ₁ =Cr+1.5Mo−100C+30N _Δ2 =Ni−[(Cr+1.5Mo−20) ² /12−30C −10N] It is necessary to adjust each component value so that the Δ ₁ value and Δ ₂ value defined by each equation satisfy Δ ₁ 25 and Δ ₂ 15, respectively. Furthermore, in the present invention, after the alloy steel having the above-mentioned composition conditions is melted, so-called solution treatment or quasi-solution treatment is performed in the steps after the hot rolling step. It is necessary to do this in the area. In the present invention, while regulating the composition conditions using the above Δ ₁ value and Δ ₂ value,
The processing temperature of solution treatment (or quasi-solution treatment)
By setting the temperature to 1000°C or higher, excellent pitting corrosion resistance and SCC resistance can be obtained. In addition,
The quasi-solution treatment described above refers to a treatment in which the dissolution of carbide in the structure progresses, although not completely, and the non-uniformity of the component elements becomes uniform. Figure 2 shows the influence of _Δ1 value on pitting corrosion resistance at 950
The pitting corrosion susceptibility was investigated in relation to the solution or quasi-solution treatment temperature at 50°C or higher. (2g/m ² /h, <2g/m ² /h). In addition, Figure 3 shows the effect of _Δ2 value on SCC resistance in relation to solution treatment or quasi-solution treatment temperature at 950°C or higher. It was immersed in a magnesium chloride solution boiling at 154°C and judged by the presence or absence of cracks after 600 hours. According to these test results, the pitting corrosion resistance shown in Figure 2 is poor in the range of Δ ₁ <25;
Further, even in the range of Δ ₁ 25, good results are not necessarily obtained if the heat treatment temperature is less than 1000°C. Further, regarding the SCC resistance shown in FIG. 3, the SCC resistance is excellent in the range of Δ ₂ 15, and no SCC cracking occurs even when the heat treatment temperature is 1000° C. or higher. Therefore, taking all of these into account, in order to ensure the pitting corrosion resistance and SCC resistance that are the objectives of the present invention, the composition conditions should be set to Δ ₁ 25,
It can be seen that it is necessary to set Δ ₂ 15 and to perform solution treatment or solution treatment at a temperature of 1000° C. or higher. The solution treatment or quasi-solution treatment described above can be performed at various stages after hot working, such as hot rolling-cold rolling-solution treatment or quasi-solution treatment, hot rolling-solution treatment. or quasi-solution treatment-
Various processes such as cold rolling can be used. Also, after solution treatment (or quasi-solution treatment), solid solution C
A heat treatment, a so-called stabilization treatment, can be performed to stabilize the structure by changing it from a supersaturated state to a saturated state.In this case, for example, hot rolling - solution treatment - cold rolling - stabilization treatment can be performed. , hot rolling - solution treatment - stabilization treatment - cold rolling, hot rolling -
Cold rolling-solution treatment-cold rolling-stabilization treatment,
The following steps can be taken. Here, the quasi-solution treatment is a heat treatment that progresses the dissolution of carbide in the structure to a certain extent, thereby achieving uniformity of component elements (including uniformity of microscopic component concentration). This is as described above, and the structure obtained in this manner becomes similar to a homogenized and stabilized structure through solution treatment and stabilization treatment. In addition, in the process shown above, cold rolling is performed between the solution treatment and stabilization treatment, and this cold rolling
Since the precipitation of NbC, TiC, etc. is promoted, a more stable structure can be obtained. [Example] Table 1 shows the chemical components of the invention steels (A-1 to A-15) and comparative steels (B-1 to B-7). All of these were manufactured on a normal stainless steel production line, and after hot rolling, annealing, and cold rolling,
Solution treatment or quasi-solution treatment was performed by heating in a temperature range of 950 to 1100°C for 10 to 30 minutes and rapidly cooling. Note that under some conditions, solution treatment or quasi-solution treatment was performed at a stage corresponding to the above-mentioned annealing step, and heat treatment after cold rolling was omitted. Since the position of the heat treatment in the process or the holding time in the heat treatment do not affect the results, these items were omitted. Test results regarding the pitting corrosion resistance and SCC resistance of each sample steel are also shown in Table 1.

【table】

[Table] *3 Hydrogen cracking test results: ○No cracking, ●Cracking As is clear from the table, all of the steels of the present invention are excellent in terms of pitting corrosion resistance, SCC resistance, and hydrogen embrittlement resistance. It can be seen that, in contrast to the comparative steel, at least one property was adversely affected. As described above, according to the present invention, pitting corrosion resistance,
Elucidating the interactions of alloying elements on SCC resistance and hydrogen embrittlement resistance and their relationship with heat treatment conditions,
By selecting them within a specific range, it has become possible to manufacture alloy steel with excellent pitting corrosion resistance, SCC resistance, and hydrogen embrittlement resistance, and the industrial effects associated with this type of alloy steel have been made possible. This is a great invention.

[Brief explanation of drawings]

Figure 1 shows the influence of Ni and Ti contents on hydrogen cracking. FIG. 2 shows the influence of the Δ ₁ value on pitting corrosion resistance in relation to the heat treatment temperature. FIG. 3 shows the influence of Δ ₂ value on SCC resistance in relation to heat treatment temperature.

Claims (1)

[Claims] 1 C: 0.03wt% or less, Si: 2wt% or less, Mn:
2wt% or less, P: 0.02wt% or less, S: 0.01wt% or less, Ni: 30 to 60wt%, Cr: 22 to 35wt%, Mo:
10wt% or less, Ti: 0.5-3.0wt%, N: 0.01wt%
Below, in addition to these, 2wt% or less of Cu,
A composition containing one or more of Ca of 0.1wt% or less and Nb of 1wt% or less, with the balance consisting of iron and unavoidable impurities, and _Δ1 = Cr + 1.5Mo - 100C + _30N . Alloy steel having a composition with a Δ 2 value of 25 or more and a Δ ₂ value of 15 or more obtained by Δ ₂ = Ni−[(Cr+1.5Mo−20) ² /12−30C−10N] at a temperature of 1000°C or more. A method for producing a corrosion-resistant alloy steel, the method comprising solution treatment or quasi-solution treatment in a temperature range of .