EP3913104A1 - Use of a steel material - Google Patents

Abstract

The invention relates to the use of a steel material for the production of sour gas-resistant parts for power generation, pipes, tanks, pipelines for gases or other fluids, components that come into contact with hydrogen, bipolar plates of fuel cells and heat exchangers, the steel material having the following components has: high manganese content austenitic steel with (data in percent by weight) • 0.02 to 0.12% carbon, • 0.05 to 0.5% nitrogen, • 10 to 20% manganese, • 10 to 20% chromium, • the remainder iron with common impurities.

Description

The invention is based on a stainless austenitic steel St 1.4404 according to the material data sheet of the Deutsche Edelstahlwerke from 08.06.2016. Such a stainless steel should be useful for many areas of application. The main disadvantage of this steel is that it contains a high proportion of nickel as an alloying element, on the order of 10 to 13 percent by weight. Due to the high nickel prices, this leads to a considerable increase in the price of the product, so that due to the high price, the use of this material for many areas of application is out of the question.

The aim of the invention is to provide an inexpensive austenitic steel which makes these steel qualities accessible to new areas of application.

• 0,02 bis 0,12 % Kohlenstoff,
• 0,05 bis 0,5 % Stickstoff,
• 10 bis 20 % Mangan,
• 10 bis 20 % Chrom,
• Rest Eisen mit üblichen Verunreinigungen.

Accordingly, the invention is a new use of a steel material for the production of sour gas-resistant parts for power generation, pipes, tanks, pipelines for gases or other fluids, components coming into contact with hydrogen, bipolar plates of fuel cells and heat exchangers, whereby the steel material has the following components:
high manganese content austenitic steel with (data in percent by weight)

• 0.02 to 0.12% carbon,
• 0.05 to 0.5% nitrogen,
• 10 to 20% manganese,
• 10 to 20% chromium,
• The remainder is iron with the usual impurities.

According to the invention, a nickel-free austenitic steel with a high manganese content is specified, which is extremely useful for the specified use and thus also makes the material accessible for new areas of application.

Such a so-called high manganese austenite is sufficiently corrosion-resistant and easily formable, in particular cold-formable, with the steel being able to be used in new areas of application due to its inexpensive composition.

• bis zu 0,8 % Silizium,
• bis zu 4 % Kupfer,
• bis zu 4 % Nickel,
• bis zu 2 % Molybdän,
• höchstens 0,05 % Phosphor,
• höchstens 0,05 % Schwefel,
• bis zu 0,5 % Titan,
• bis zu 0,5 % Niob,
• bis zu 0,5 % Vanadium.

In addition to the specified components, the steel material can also have at least one further component, namely

• up to 0.8% silicon,
• up to 4% copper,
• up to 4% nickel,
• up to 2% molybdenum,
• not more than 0.05% phosphorus,
• not more than 0.05% sulfur,
• up to 0.5% titanium,
• up to 0.5% niobium,
• up to 0.5% vanadium.

All data are always in percent by weight.

The addition of nickel is only intended as an exception and in small amounts in order to optimize the ductility properties and improve the corrosion resistance. If the improved corrosion resistance is dispensed with, the proportion of nickel can remain set to zero.

• 0,05 bis 0,08 % Kohlenstoff,
• 0,08 bis 0,15 % Stickstoff,
• 13 bis 17 % Mangan,
• 13 bis 17 % Chrom,
• 1 bis 2 % Nickel,

sowie vorzugsweise

• 0,1 bis 0,2 Silizium,
• 1 bis 2 % Kupfer,
• maximal 0,2 % Molybdän,

und als zulässige Verunreinigungen

• höchstens 0,005 % Schwefel,
• höchstens 0,02 % Phospor,
• höchstens 0,5 % Titan,
• höchstens 0,5 % Niob,
• höchstens 0,5 % Vanadium
• Rest Eisen gegebenenfalls mit üblichen Verunreinigungen.

Angaben in Gewichtsprozent)The components of alloy elements are preferred as follows:

• 0.05 to 0.08% carbon,
• 0.08 to 0.15% nitrogen,
• 13 to 17% manganese,
• 13 to 17% chromium,
• 1 to 2% nickel,

as well as preferably

• 0.1 to 0.2 silicon,
• 1 to 2% copper,
• maximum 0.2% molybdenum,

and as permissible impurities

• not more than 0.005% sulfur,
• not more than 0.02% phosphorus,
• not more than 0.5% titanium,
• not more than 0.5% niobium,
• at most 0.5% vanadium
• The remainder is iron, possibly with the usual impurities.

Data in percent by weight)

• Zugfestigkeit R_m = 500 bis 800 MPa,
• Streckgrenze R_p 0,2 = 200 bis 500 MPa,
• Bruchdehnung A80 = mindestens 42 %.

The specified steel material preferably has the following mechanical technological 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%.

It is particularly preferred that the material contains less than 5% deformation-indexed martensite in the case of cold deformation using predominantly the TWIP mechanism.

A special feature is also seen in the fact that the technological properties of the steel material are set by rolling the material with a suitable degree of rolling and / or annealing the material at a suitable annealing temperature.

Influence of the elements:

In the case of alloying elements, a basic distinction must be made as to whether they are carbide, austenite or ferrite formers and for what purpose they are added to the steel.

Each individual element gives the steel certain specific properties depending on its proportion. If several elements are present, the effect can be increased. However, there are alloy variants in which the individual elements with regard to a certain behavior do not exert their influence in the same direction, but can counteract each other.

The presence of the alloying elements in the steel only provides the prerequisite for the desired properties; this can only be achieved through processing and heat treatment.

Carbon (C)

Generally:
Carbon is the most important and most influential alloying element in steel. In addition to carbon, every unalloyed steel contains silicon, manganese, phosphorus and sulfur, which are unintentionally added during manufacture. The addition of further alloying elements to achieve special effects as well as the deliberate increase in the manganese and silicon content leads to alloyed steel. With increasing C content, the strength and hardenability of the steel increase, whereas its elongation, forgeability, weldability and machinability (using cutting tools) are reduced. The corrosion resistance to water, acids and hot gases is practically not influenced by the carbon.

In the concept according to the invention, the proportion of carbon is kept relatively low, so that an optimal relationship between strength and elongation is obtained. The aim is to achieve maximum formability. Furthermore, carbon is an austenite former.

Manganese (Mn)

• Mn setzt die kritische Abkühlungsgeschwindigkeit sehr stark herab und erhöht damit die Härtbarkeit
• Streckgrenze und Festigkeit werden durch Mn-Zusatz erhöht
• Gehalte über 4% führen auch bei langsamer Abkühlung zur Ausbildung von sprödem martensitischem Gefüge
• Stähle mit Mn-Gehalten über 12% sind bei gleichzeitigem hohem C-Anteil austenitisch, weil Mn den γ-Bereich erheblich ausweitet.

Generally:

• Mn greatly reduces the critical cooling rate and thus increases the hardenability
• Yield strength and strength are increased by adding Mn
• Contents above 4% lead to the formation of a brittle martensitic structure even with slow cooling
• Steels with an Mn content of more than 12% are austenitic with a high C content at the same time, because Mn considerably expands the γ range.

Mn is an austenite former and is mainly used according to the invention as a cheaper substitute for Ni. This is why a proportion of 10-20% is used in this concept.

Chromium (Cr)

• Setzt die für die Martensitbildung erforderliche kritische Abkühlgeschwindigkeit herab
• Erhöht Härtbarkeit und verbessert Vergütbarkeit
• Cr erhöht Zunderbeständigkeit
• Cr schnürt das γ-Gebiet ab und erweitert dadurch den Ferritbereich; stabilisiert jedoch den Austenit in austenitischen Cr-Mn- bzw. Cr-Ni-Stählen
• Chrom bildet ab 10,5 % Massenanteil eine Chromoxid-Schicht, wodurch weitere Oxidation verhindert wird. Wird diese Oxidschicht beschädigt, gelangt blankes Metall in Kontakt mit der Atmosphäre, und es bildet sich automatisch eine neue passivierende Schicht, d. h., die Schicht ist selbstheilend.

Generally:

• Reduces the critical cooling rate required for martensite formation
• Increases hardenability and improves temperability
• Cr increases scale resistance
• Cr constricts the γ region and thereby expands the ferrite range; however, it stabilizes the austenite in austenitic Cr-Mn or Cr-Ni steels
• Chromium forms a chromium oxide layer above 10.5% by mass, which prevents further oxidation. If this oxide layer is damaged, bare metal comes into contact with the atmosphere and a new passivating layer is automatically formed, ie the layer is self-healing.

According to the invention, the main task of Cr is to protect against corrosion. Since in this concept the product is to be used in a corrosive medium, a Cr content of 14-16% is used here in order to obtain increased corrosion protection.

Nickel (Ni)

Generally:
Nickel is one of the alloying elements that promote solidification according to the stable iron-carbon system. By reducing the critical cooling rate, nickel increases the hardening and tempering. Nickel also increases the toughness, especially in the low temperature range, has a grain-refining effect and reduces the sensitivity to overheating. The 18/10 chrome-nickel steel (1.4301) is one of the main representatives of corrosion-resistant austenitic steels.

As already mentioned, nickel is a relatively expensive alloying element and, according to the invention, the proportion here is replaced by manganese. However, a certain proportion can increase the toughness and also have a positive influence on the stability of the austenite. Furthermore, nickel has a positive effect on corrosion resistance.

Nitrogen (N)

Generally:
Nitrogen acts as an austenite former in a similar way to carbon. The lower maximum solubility of the However, iron for nitrogen is significantly larger than that for carbon. By adding other elements or applying nitrogen pressure, the nitrogen content in the steel can be increased significantly, some of the nickel in austenitic steels replaces the effect of carbon and the carbon content can be reduced.

According to the invention, nitrogen serves as a substitute for carbon and improves corrosion resistance. Furthermore, nitrogen acts as a substitute for the autenite former nickel.

Austenite formers:

Alloying elements that expand the austenite area and stabilize the austenite. Ni, Co, Mn, N and C are the most important representatives. With the help of the Schaeffler DeLong diagram, the resulting structure of high-alloy steels can be determined based on the chemical composition. In this diagram, the austenite formers are opposed to the ferrite formers, as shown in the drawing.

Claims (5)

Use of a steel material for the production of sour gas-resistant parts for power generation, pipes, tanks, pipelines for gases or other fluids, components that come into contact with hydrogen, bipolar plates of fuel cells and heat exchangers, the steel material having the following components:
high manganese content austenitic steel with (data in percent by weight) • 0.02 to 0.12% carbon, • 0.05 to 0.5% nitrogen, • 10 to 20% manganese, • 10 to 20% chromium, • Remaining iron with usual impurities. Use according to claim 1,
wherein the steel material has at least one of the further components, namely • up to 0.8% silicon, • up to 4% nickel, • up to 2% molybdenum, • a maximum of 0.05% phosphorus, • a maximum of 0.05% sulfur, • up to 0.5% titanium, • up to 0.5% niobium, • up to 0.5% vanadium. Use according to claim 1 or 2,
characterized in that the steel material has the following mechanical technological 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%. Use according to one of claims 1 to 3,
characterized in that the material contains less than 5% deformation-indexed martensite in the case of cold deformation using the TWIP mechanism alone. Use according to one of claims 1 to 4,
characterized in that the technological properties of the steel material are adjusted by rolling the material with a suitable degree of rolling and / or annealing the material at a suitable annealing temperature.

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