KR100330453B1 - Cr-Mo-V Alloy Steel for Pressure Vessel - Google Patents

Abstract

The present invention relates to chromium-molybdenum-vanadium steel for pressure vessels, by weight% C 0.10 to 0.17%, Mn 0.30 to 0.70%, Si 0.05 to 0.20%, Cr 2.00 to 3.50%, Mo 0.60 to 1.20% , W 0.80% or less, Ni 0.05 to 0.25%, V 0.25 to 0.35%, Nb 0.01% or more and 0.05% or less, Ti 0.005 to 0.03%, B 0.0005 to 0.002%, Ca 0.0005 to 0.015%, Al 0.01 to 0.04%, P 0.015% or less, S 0.01% or less, the balance is composed of Fe and other unavoidable impurities, and contains 0.80wt% ≤ Mo + 0.5W ≤ 1.20wt%, high temperature strength, impact toughness, temper brittleness and resistance to hydrogen erosion Because of this high chromium-molybdenum for pressure vessel, which is suitable for pressure vessels using high temperature and high pressure hydrogen of 450 ℃ or higher in heavy oil decomposition and desulfurization process of oil refinery, and easy to manufacture because of excellent weldability. Provides vanadium steel.

Description

Chromium-molybdenum-vanadium steel for pressure vessels {Cr-Mo-V Alloy Steel for Pressure Vessel}

The present invention relates to chromium-molybdenum-vanadium steel for pressure vessels, and particularly, chromium-mol which can be used in a temperature range of at least 450 ° C as a steel for pressure vessels using high-temperature and high-pressure hydrogen such as petroleum refining and heavy oil decomposition. The present invention relates to a ribidenium-vanadium steel.

In recent years, plants using hydrogenation processes, such as petroleum refining and heavy oil decomposition, have tended to be more large, high temperature and high pressure to improve efficiency. Accordingly, the chromium-molybdenum steel pressure vessel conventionally used in the plant needed to be designed thicker. However, in order to satisfy the design conditions, not only the wall thickness becomes so thick that it is almost impossible to manufacture, but also there is a risk of material damage caused by hydrogen (hereinafter referred to as 'hydrogen erosion').

The present invention has been made to solve the above problems, the object of the invention is to improve the erosion resistance and high temperature strength significantly by adding an element such as vanadium to chromium-molybdenum steel, improve the weldability It is to provide a chromium-molybdenum- vanadium steel for the pressure vessel that can facilitate the.

The present invention steel is designed to maximize the mutual synergy of various alloying elements and minimize the mutual suppression effect. Therefore, if the composition of each element is optimally designed, the resistance to hydrogen erosion is increased, the hardenability is increased, and uniform bainite structure can be obtained up to the center of the ultra-thick material with a thickness of 450 mm, the weldability is increased, and the productivity is improved. Since the fineness is ensured toughness, it can be used as a material of the high-pressure, high-pressure vessel.

To this end, the alloy steel of the present invention by weight% C 0.10 to 0.17%, Mn 0.30 to 0.70%, Si 0.05 to 0.20%, Cr 2.00 to 3.50%, Mo 0.60 to 1.20%, W 0.80% or less, Ni 0.05 to 0.25 %, V 0.25-0.35%, Nb 0.01% or more, 0.05% or less, Ti 0.005-0.03%, B 0.0005-0.002%, Ca 0.0005-0.015%, Al 0.01-0.04%, P 0.015% or less, S 0.01% or less The part is composed of Fe and other unavoidable impurities, and has a composition including 0.80 wt% ≦ Mo + 0.5W ≦ 1.20 wt%.

The characteristic and role of the said element which comprises this invention steel are demonstrated as follows.

1) Carbon (C) improves the hardenability to ensure homogeneous mechanical properties to the center of thick steel, and precipitates carbide during heat treatment to increase the strength of the material. However, if the content is less than 0.10 wt%, the required high temperature strength cannot be obtained. If the content exceeds 0.17 wt%, the weldability is lowered, making the pressure vessel very difficult. For this reason, it is preferable to limit to 0.10 to 0.17 wt%.

2) Manganese (Mn) plays an important role as an alloying element to improve the hardenability during the maintenance of strength and heat treatment. Therefore, in order to secure weldability, at least 0.30wt% is required to reduce the carbon content, but if it exceeds 0.70wt%, the resistance to temper brittleness is impaired together with silicon (Si), so the range of 0.30 to 0.70wt% is preferable. .

3) Phosphorus (P) is an element that is inevitably mixed during steelmaking, which plays a role in tempering brittleness during heat treatment or high temperature use. Therefore, it is preferable to keep it as low as possible, but the maximum value is 0.015wt% in consideration of economic cost in manufacturing process. Shall be.

4) Sulfur (S) is an element that is inevitably mixed during steelmaking. It is a harmful element that impairs impact toughness and harms weldability. Therefore, it is preferable to keep it as low as possible, but the maximum value is 0.01wt% in consideration of economic cost in the manufacturing process. Shall be.

5) Silicon (Si) is an element that acts as a deoxidizer to remove oxygen in molten steel during steelmaking. If it is less than 0.05 wt%, deoxidation may be insufficient, and if it exceeds 0.2 wt%, coarsening of carbides may occur. The range of 0.05-0.20 wt% is preferable because it promotes the drop in high temperature strength or the increase in temper brittleness.

6) Chromium (Cr) plays an important role in suppressing the erosion by hydrogen. In order to use in a hydrogen atmosphere of 450 ℃ or more is required at least 2wt%, and exceeds 3.5wt% high temperature strength is drastically dropped.

7) Molybdenum (Mo) is effective in increasing the high temperature strength and resistance to temper brittleness. However, if the content is less than 0.6wt%, the high temperature strength is lowered at around 500 ° C, and if the content is more than 1.2wt%, the weldability is deteriorated.

8) Tungsten (W) plays a role similar to Mo as an effective element in increasing high temperature strength and resistance to temper odor. That is, molybdenum (Mo) and tungsten (W) are the same group elements on the periodic table of elements, and show similar characteristics in ferritic steels. However, tungsten is about twice as heavy as Mo, so about twice as much weight is required to achieve the same effect. Therefore, a coefficient of 0.5 is required for W in the sense of equivalence. On the other hand, although the two elements show a similar effect, they are not exactly the same, and thus the type and growth of precipitates formed during long-term use at high temperatures. The speed is slightly different, resulting in a slightly different effect on long-term creep rupture strength, etc. As such, there is an optimum range of additions for tungsten and Mo, which show appropriate effects due to differences between the two elements, while similarities between the two elements. As a result, there is also an optimal range of addition in the overall concept. Tungsten alone is 0.80wt% or less to sufficiently exhibit the above effects, and if it exceeds this, the weldability is impaired. In addition, as a total of (Mo + 0.5W), it is necessary to control to 0.80-1.20 wt%. This is because when it is less than 0.8 wt%, the above effects are hardly exhibited sufficiently, and when it exceeds 1.2 wt%, the weldability tends to be deteriorated.

9) Nickel (Ni) has the effect of improving the hardenability and toughness in the heat treatment process similar to Mn, but inhibits the high temperature strength, it is preferable to maintain within the range of 0.05 ~ 0.25 wt%.

10) Vanadium (V) is an important element that increases the high temperature strength by depositing fine carbides and fixes carbon to increase resistance to hydrogen erosion. However, if the amount is less than 0.25wt%, the effect is weak, and the effect of increasing the high temperature strength is reduced to the peak of 0.3wt%, and if it contains a large amount, hot cracking is likely to occur during welding, so it is limited to 0.25 ~ 0.35wt%. .

11) Niobium (Nb) forms fine carbides to prevent toughness due to grain coarsening during heat treatment at high temperatures. However, since it is hardly effective at 0.01 wt% or less and impairs weldability when it is added, it is good to contain it in the range of 0.01 wt% or more and 0.05 wt% or less.

12) Titanium (Ti) reacts with nitrogen (N) contained in molten steel together with aluminum (Al) to indirectly work to improve the hardenability of the material by boron (B) by reducing the nitrogen. If the Ti content is less than 0.005wt%, it is difficult to expect the effect, and if it contains 0.03wt% or more, nonmetallic inclusions are generated and the impact toughness worsens. Therefore, the Ti content is preferably limited to 0.005 to 0.03wt%.

13) Since aluminum (Al) has strong affinity with oxygen, it is added for the purpose of combining oxygen with molten steel and removing oxygen in the form of aluminum oxide, but some of the remaining amount reacts with nitrogen together with titanium to form fine nitrides. By contributing to the refinement of grains and reducing the solid solution nitrogen, it is possible to maximize the effect of improving the hardenability of boron (B). However, if it is less than 0.01wt%, the effect is insignificant, and if too much, the toughness of the impact deteriorates, so it should not exceed 0.04wt%.

14) Boron (B) is an alloying element that can dramatically improve the hardenability by adding a very small amount. However, if the content of boron (B) in the steel is less than 0.0005wt%, this effect is not obtained. If the content is more than 0.002wt%, the hot workability and weldability are deteriorated. However, since boron cannot be expected to form nitrides in combination with solid nitrogen, it is necessary to increase the activity of solid boron by adding Ti, Al, etc., which are more strongly bonded to solid nitrogen than boron.

15) Calcium (Ca) is an element that dramatically improves the weldability by adding a very small amount. However, if the effect is less than 0.0005wt%, the effect is hardly expected, and if it exceeds 0.015wt%, the cleanliness of the steel may be impaired and adversely affected. Therefore, it is necessary to limit the amount to 0.0005 ~ 0.015wt%.

Hereinafter, an embodiment of the present invention steel will be described.

First, after oxidation in an electric furnace, the ASEA-SKF secondary ladle refining furnace was subjected to reduction refining and coagulated into 80 tons ingot by vacuum oil removal degassing. The ingot was forged into a shell form of 1,750 mm, 2,410 mm and 3,500 mm in length by a 10,000-ton press, then quenched at 1000 to 1050 ° C, quenched at 910 to 960 ° C, and tempered at 660 ° C. Processed.

Table 1 below shows the chemical composition of the prototype thus produced, and Table 2 shows the mechanical performance and weldability of the prototype. As shown in Table 2, it can be seen that the high temperature strength is large enough to be used as a pressure vessel for high temperature and high pressure, the mechanical properties in the thickness direction are uniform, and fracture toughness is large. In addition, since the weldability is excellent, the production can be expected to be easy.

According to the present invention having the above-described configuration, since the high temperature strength and impact toughness is high, and the resistance to temper brittleness and hydrogen erosion is high, a pressure vessel using high-temperature, high-pressure hydrogen, such as heavy oil decomposition and desulfurization of the refinery, It is suitable as a material and has an advantage of being easy to manufacture because of its excellent weldability.

In addition, it is possible to ensure a sufficient curing ability to produce a uniform bainite structure from the surface to the center during the heat treatment process can achieve the effect that the quality of the final product is uniformly excellent.

Claims (1)

By weight% C 0.10 to 0.17%, Mn 0.30 to 0.70%, Si 0.05 to 0.20%, Cr 2.00 to 3.50%, Mo 0.60 to 1.20%, W 0.80% or less, Ni 0.05 to 0.25%, V 0.25 to 0.35%, Nb greater than 0.01% and 0.05% or less, Ti 0.005 to 0.03%, B 0.0005 to 0.002%, Ca 0.0005 to 0.015%, Al 0.01 to 0.04%, P 0.015% or less, S 0.01% or less, the balance consisting of Fe and other unavoidable impurities And, chromium-molybdenum-vanadium steel for pressure vessels containing 0.80 wt% ≦ Mo + 0.5W ≦ 1.20wt%.