KR20210143116A - Use of a steel material - Google Patents

Abstract

The present invention relates to the use of steel for manufacturing sour gas resistant members for energy generation, tubes, tanks, pipelines for gas or other fluids, components in contact with hydrogen, bipolar plates of fuel cells, and heat exchangers. The steel is the high manganese-containing austenitic steel made of 0.02-0.12 wt% of carbon, 0.05-0.5 wt% of nitrogen, 10-20 wt% of manganese, 10-20 wt% of chrome, and the remainder consisting of iron and common impurities. The present invention provides the austenitic steel with low cost.

Description

Use of steel {USE OF A STEEL MATERIAL}

The present invention starts from an austenitic stainless steel St 1.4404 according to the material information data of Deutsche Edelstahlwerke dated June 8, 2016. These special steels can be useful in many areas of application. A major disadvantage of such steels is that they contain a high proportion of nickel as an alloying element, say in the order of 10 to 13 weight percent. This causes a significant increase in the price of the product due to the high nickel price, and consequently the use of this material is not considered in many applications due to the high price.

It is an object of the present invention to provide a low-cost austenitic steel which allows such steel grades to be used in new areas of use.

Accordingly, the present invention provides sour gas resistant members for energy generation, tubes, tanks, pipelines for gas or other fluids, parts in contact with hydrogen, bipolar plates of a fuel cell and heat exchangers. It proposes a new use of a steel material for manufacturing, wherein the steel material has the following components:

● 0.02 to 0.12% carbon,

● 0.05 to 0.5% nitrogen

● 10-20% manganese;

● 10 to 20% chromium;

• Residual iron with common impurities

(expressed in weight percent) is a high manganese containing austenitic steel.

According to the present invention, a nickel-free high manganese-containing austenitic steel is provided which is exceptionally useful for the intended use and thus allows the material to be used also in new areas of application.

This so-called high manganese austenite has sufficient corrosion resistance and good formability, in particular cold formability, wherein the steel can be introduced into new areas of application due to its low cost composition.

The steel may further have one or more additional components in addition to the components presented, namely

● silicone up to 0.8%;

● copper up to 4%;

● Nickel up to 4%;

● Molybdenum up to 2%;

● up to 0.05% phosphorus;

● up to 0.05% sulfur;

● Titanium up to 0.5%;

● Niobium up to 0.5%;

● Have at least one of up to 0.5% vanadium.

In principle, all are expressed in weight percent.

In order to optimize ductility and improve corrosion resistance, the addition of nickel is made only exceptionally and in small amounts. The percentage of nickel can be set to zero only if the improved corrosion resistance is waived.

Preferably the components of the alloying elements are:

● 0.05 to 0.08% carbon,

● 0.08 to 0.15% nitrogen;

● 13 to 17% manganese;

● 13 to 17% chromium;

● 1-2% nickel;

and preferably

● silicone from 0.1 to 0.2;

● 1 to 2% copper;

● up to 0.2% molybdenum,

and as acceptable impurities.

● up to 0.005% sulfur;

● up to 0.02% phosphorus;

● up to 0.5% titanium;

● up to 0.5% niobium,

● up to 0.5% vanadium,

• Residual iron (expressed as a percentage by weight), optionally with common impurities.

The steel material presented preferably has the following mechanical and technical properties:

tensile strength R _m = 500 to 800 MPa,

yield strength R _{p 0,2} = 200 to 500 MPa,

Elongation at break A80 = at least 42%.

In this case, particularly preferably, the material contains less than 5% strain-induced martensite under the main use of the TWIP-mechanism in cold forming.

Another special thing is that the technical properties of the steel are set by rolling of the material by a suitable degree of rolling and/or by annealing the material at a suitable annealing temperature.

1 is a Schaeffler-Deron-diagram.

Influence of elements:

In the case of alloying elements, a distinction must be made in principle whether they are carbide formers, austenite formers or ferrite formers, or for what purpose they are alloyed into steel.

Each individual element, in proportion, gives the steel certain properties. When a plurality of elements are present, the effect may increase . However, there are alloy variants in which single elements do not influence themselves in the same direction with respect to a particular behavior, but rather act in opposition to each other.

The alloying elements present in the steel are merely prerequisites for the intended properties; Machining and heat treatment only achieve these properties.

carbon (C)

Generally:

Carbon is the most important and most influential alloying element in steel. Each unalloyed steel contains, in addition to carbon, silicon, manganese, phosphorus and sulfur, which are unintentionally added during manufacture. The addition of additional alloying elements to achieve special effects and the intentional increase of the manganese content and the silicon content result in alloyed steels. As the C-content increases, the strength and hardenability of the steel increase, while the extensibility, forgeability, weldability and workability (by cutting tool) of the steel decrease. Corrosion resistance to water, acids and hot gases is practically unaffected by carbon.

The proportion of carbon in the concept according to the invention is kept relatively low, resulting in an optimal ratio between strength and extensibility. The goal is to achieve maximum formability. In turn, carbon is an austenite former.

Manganese (Mn)

Generally:

- Mn very strongly reduces the critical cooling rate and thus increases the hardenability

- yield strength and strength increase with Mn-addition

- a content exceeding 4% forms a brittle martensitic structure even at slower cooling

- Steels with a Mn-content exceeding 12% are at the same time austenitic steels at a high C-ratio, since Mn significantly broadens the γ-region.

Mn is an austenite former and is mainly used in accordance with the present invention as a cheaper replacement for Ni. Therefore, a ratio of 10 to 20% is also used in this concept.

Chromium (Cr)

Generally:

- Reduces the critical cooling rate required for martensite formation

- Increase hardenability and improve heat treatment

- Cr increases the scaling resistance

- Cr shrinks the γ-region and thus expands the ferrite region; Stabilizes austenite with austenitic Cr-Mn-steels or Cr-Ni-steels

- chromium forms a layer of chromium oxide from a mass fraction of 10.5%, as a result of which further oxidation is prevented; If such an oxide layer is damaged, the blank metal comes into contact with the atmosphere and a new passivating layer is automatically formed, ie the layer is self-healing.

According to the present invention, the main task of Cr is to prevent corrosion. In order to increase corrosion protection, a Cr-content of 14 to 16 % is used here, since in this concept the product has to be used in corrosive media.

Nickel (Ni)

Generally:

Nickel belongs to alloying elements that promote solidification after a stable iron-carbon system. By reducing the critical cooling rate, nickel increases full hardening and full heat treatment. In addition, nickel increases viscosity, grain refinement, and reduces overheating sensitivity, among other things, especially in the low temperature range. 18/10 chromium-nickel steel (1.4301) belongs to representative steels of corrosion-resistant austenitic steels.

As already mentioned, nickel is a relatively expensive alloying element, and according to the invention its proportion is replaced by manganese. However, the viscosity may increase by a predetermined ratio, and the stability of austenite may be positively affected. Continuing, nickel has a positive effect on corrosion resistance.

Nitrogen (N)

Generally:

Nitrogen acts similarly to carbon as an austenite former. However, the lower maximum solubility of iron in nitrogen is significantly higher than that of iron in carbon. By alloying other elements, or by vacuum nitriding, the nitrogen content in the steel can be significantly increased, and some of the nickel in austenitic steels can replace the effect of carbon and reduce carbon.

According to the present invention, nitrogen is used as a substitute for carbon and improves corrosion resistance. Nitrogen continues to act as a replacement for the austenite former, nickel.

Austenite formers:

These are alloying elements that expand the austenite zone and stabilize the austenite. Ni, Co, Mn, N and C are the most important representative elements. The structure of the resulting high-alloy steels shown by the Schaeffler-Deron-diagram can be determined according to the chemical composition. As shown in the figure, in this diagram the austenite formers are opposite the ferrite formers.

Claims (5)

of steel for manufacturing sour gas resistant members for energy generation, tubes, tanks, pipelines for gas or other fluids, parts in contact with hydrogen, bipolar plates of fuel cells and heat exchangers For use,
The steel contains the following components:
● 0.02 to 0.12% carbon,
● 0.05 to 0.5% nitrogen
● 10-20% manganese;
● 10 to 20% chromium;
• Residual iron with common impurities
High manganese-containing austenitic steels with (expressed in percent by weight), steels. According to claim 1,
The steel has one or more further components of the following further components, namely
● silicone up to 0.8%;
● Nickel up to 4%;
● Molybdenum up to 2%;
● up to 0.05% phosphorus;
● up to 0.05% sulfur;
● Titanium up to 0.5%;
● Niobium up to 0.5%;
● Use of steels, having at least one of up to 0.5% vanadium. 3. The method of claim 1 or 2,
The steel has the following mechanical and technical characteristics:
tensile strength R _m = 500 to 800 MPa,
yield strength R _{p 0,2} = 200 to 500 MPa,
The use of steels with an elongation at break A80 = at least 42%. 4. The method according to any one of claims 1 to 3,
The use of a steel, wherein the material contains less than 5% strain-induced martensite under the sole use of the TWIP-mechanism in cold forming. 5. The method according to any one of claims 1 to 4,
The use of a steel, wherein the technical properties of the steel are established by rolling of the material to a suitable degree of rolling and/or by annealing the material at a suitable annealing temperature.

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