JPS61559A - Steel having resistance to erosion by hydrogen - Google Patents

Abstract

PURPOSE:To obtain a high toughness and high ductility steel having resistance to erosion by hydrogen by adding specified percentages of C, Si, Mn, Mo, Ni and Al to Fe. CONSTITUTION:The steel consisting of, by weight, 0.05-0.15% C, 0.15-0.35% Si, 0.3-0.9% Mn, 0.4-0.6% Mo, 0.01-0.11% Ni, 0.001-0.01% Al and the balance Fe with impurities is manufactured. It is desirable that the amounts of P and S among the impurities in the steel are restricted to <=about 0.035% each. The erosion of the steel by hydrogen is thus prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a hydrogen corrosion resistant steel that has improved hydrogen corrosion resistance and has a matrix having high mechanical properties of high toughness and high ductility.

[Conventional technology]

For equipment used in the oil refining industry, chemical industry, coal liquefaction, gasification, etc. under both temperature and high pressure hydrogen environments, for example piping systems such as pressure vessels, this is created based on actual equipment accident cases and actual plant usage results. 1/2 Mo steel is used based on the so-called Nelson diagram. However, 1/2M
otil is used in areas where stress concentration is likely to occur due to adjacent structurally unstable welds and other materials of different materials. Due to necessity, actual operating conditions tend to be higher in temperature and pressure, so accidents due to hydrogen erosion occur frequently on the safe side of the limit line, and solving this problem is an important issue.

After this hydrogen erosion has undergone a specific incubation period, it suddenly becomes ductile and
This is a phenomenon in which toughness and strength decrease.

That is, among materials used for pressure vessels and the like, carbon steel and low alloy steel are particularly used at high temperatures and high pressures (300°C to 600°C).

When exposed for a long time in an environment of 10 to 600 (9 f/crl), hydrogen diffused inside the material reacts with carbides contained in the alloy to produce hydrocarbons (methane → CH4), which form crystals. Bubbles are generated and grow by trapping at grain boundaries and the interface between nonmetallic inclusions and the steel matrix.
Cracks occur due to their connection.

Currently, as a measure to prevent this type of hydrogen attack from reducing ductility and toughness, low alloy steels such as 2'% Cr-IMo castings used in high-temperature environments (300 to 600°C) such as pressure vessels are being Measures such as the addition of Cr, Mo, and rare earth elements are taken to precipitate stable carbides in IJ NOx and prevent the generation and production of methane bubbles that become the nucleus of hydrogen attack. On the other hand, in 1/2 Mo steel, there is a reduction in trace impurities such as p and s and the amount of carbon, but with the current refining steelmaking technology, it is extremely difficult to remove any further impurities, and the reduction in the amount of carbon can also be achieved at high temperatures. It is impossible to suppress the hydrogen corrosion to a level lower than strength problems such as creep, and this hydrogen corrosion has not yet been completely prevented.

[Problem that the invention seeks to solve]

Therefore, in order to prevent hydrocarbon gas generation, Ni and AA'i, which are elements that promote carbon graphitization, are added in appropriate amounts at the time of manufacturing the material to diffuse carbon into the grain boundaries and increase carbon The object of the present invention is to provide a steel capable of suppressing the gasification reaction of hydrogen and hydrogen, thereby preventing the occurrence of hydrogen corrosion.

[Failure to solve the problem]

Therefore, the hydrogen corrosion resistant steel of the present invention has a weight ratio of 1.

C: 005-0.15%, Si: 0.15-0
．． 35%, Mn: 0.3-0.9%.

Mo: 0.4~0.6%, Ni: 0.01~
Q, 11%, AQ: 0.001 to 0.01% The remainder essentially consists of Fe.

Furthermore, this steel plate can prevent hydrogen corrosion even in the weld heat affected zone, which has inferior hydrogen corrosion resistance compared to the base metal.

In other words, hydrogen corrosion in the weld heat-affected zone is caused by the coarsening of crystal grains due to welding heat input during welding and the formation of thermodynamically unstable carbides. A
By controlling the addition of g and 'i, hydrogen attack can be prevented.

The reasons for limiting the numerical values of the present invention will be explained below.

[C] C is an element necessary to increase tensile strength, but if it exceeds 0.15%, it promotes temper embrittlement and deteriorates weldability and toughness of the material. In addition, if it is less than 005%, sufficient strength at room temperature and high temperature cannot be obtained, so 005 to 01
It was limited to a range of 5 inches.

[Si'3Sl is a solid solution strengthening element for ferritic iron, and its reduction may reduce the strength at room temperature and high temperature, and is also an element that promotes temper embrittlement. Furthermore, since core materials are mainly used in welded parts of piping systems, it is necessary to increase their high-temperature strength to avoid thermal fatigue and other effects of concentration of mental energy. Therefore, from the viewpoint of high temperature strength, it is 0.15% or more.

Further, in order to prevent embrittlement during tempering, it was limited to 035 or less.

[Mn:] Mn is an element necessary to fix S, which is a harmful element in steel, and to obtain strength. Moreover, if it exceeds 0.9%, weldability will deteriorate. Therefore, in order to fix S, it was set to 0.3% or more and 0.9% or less from the viewpoint of weldability.

[Mo:] Mo is an element necessary to increase strength and toughness. That is, 0.4% or more to obtain strength and toughness.

Furthermore, since it increases the susceptibility to tempering embrittlement and is expensive, it is limited to 0.6% or less.

IJJi) Ni is an element necessary to obtain toughness at low temperatures and to reduce susceptibility to hydrogen embrittlement.

Since it is a powerful element that promotes graphitization of carbon, it inhibits the stability of carbides and has a very effective catalytic action in hydrocarbon production reactions.

It is harmful because it accelerates hydrogen corrosion and also segregates at grain boundaries during tempering embrittlement. Therefore, 001% for low temperature toughness
In addition, in order to prevent hydrogen corrosion and temper embrittlement,
It was limited to 0.01% to 0.11%.

[AOAQ is an element that improves toughness by refining the austenite grain size9, but on the other hand, it also causes a decrease in creep strength, promotes graphitization, and has a negative effect on hydrogen attack, so AOAQ of 0001 to 0.01% is range. From the above point, it is more practically effective to set FiAlo to 0.005% or less.

CP, SIP, and S are elements contained as impurities in steel, and since they have a negative effect on the deterioration of ductility and toughness, it is better to minimize them as much as possible, but since their contamination during the refining and steelmaking process of the material is unavoidable, they are included in the present invention. The amount is not particularly limited. However, from the above point of view, it is desirable that each content be 0.035% or less.

〔Example〕

The present invention will be described in detail below based on experimental results.

The chemical compositions of the test materials are shown in Table 1.
/2 Steel plate A-M based on Mo steel with changes in Ni and AAi, which is heat-treated to correspond to the thermal cycle of the weld heat affected zone (HAZ) shown in Table 2, and the HAZ equivalent material shown in Table 2. Two types of base materials were used for each, including a base material that had been subjected to general heat treatment.

The test materials subjected to the heat treatment shown in Table 2 are subjected to G and E type step cooling shown in Figure 2 to further reduce embrittlement. Bright heat treatment inside (
Po5t weldheat treatment) is an annealing treatment for the purpose of stress relief.

In the evaluation test, an autoclave with a high temperature and high pressure hydrogen atmosphere was used, and hydrogen exposure treatment was performed under the conditions shown in Figure 3, followed by a tensile test at room temperature.

Hydrogen erosion performance was investigated.

Figures 1 and 4 show the tensile strength of the base material.

FIG. 3 is a diagram showing the influence of Ni and AC on the drawing ratio of test materials that differ in the harmfulness of hydrogen exposure treatment. If you look at the aperture ratio,
For sample materials E, F, and G with Ni: 0.15 or higher, a significant decrease in drawing ratio is observed as the Ni content increases. Similar to Ni, AA also has test materials J, L, and J of 0.021 or higher.
, M, the aperture ratio decreases as AC increases.

Looking at the tensile strength, as well as the drawing ratio, a decrease in strength is seen in specimens E, F, G, and J, as well as in L and M as Ni and Ai increase.

Furthermore, FIGS. 5 and 6 are diagrams showing the influence of N1 and AP on the tensile strength and drawing ratio of HAZ-equivalent materials.

The same tendency as that of the base material is observed for the HAZ-equivalent material, but the degree of mechanical property deterioration is more significant in the HAZ-equivalent material. That is, sample materials E, F, and G, as well as J and K, have a large amount of Ni or AA.

In contrast, in L and M, the reduction in drawing ratio was extremely significant, whereas in sample materials A and B according to the present invention with appropriate amounts of Ni and AA.
, C, D, H and ■ have low sensitivity to hydrogen corrosion.

Table 1 Chemical composition of sample materials Table 2 Heat treatment conditions for sample materials

[Brief explanation of drawings]

Figures 1, 4UA, 5 and 6 are mechanical property graphs showing the effects of the present invention, Figure 2 is a graph showing step cooling heat treatment conditions, and Figure 3 is a hydrogen exposure test graph. This is a process diagram showing the process. Ni content〃) Fig. 1 Chiang Lan Fig. 3 Country Fig. 4 Skin content and percentage) Fig. 5 = 343

Claims (1)

[Claims] Weight ratio: C: 005-0.15%, Si: 0.15-0
．． 35%, Mn: 0.3-0.9%, Mo: 0.4-0
．． 6%, Ni: 0.01-0.11%, Al: 0.00
1 to 0.01, the remainder being essentially Fe.