EP4296393A1 - Acier allié trempant au bore, en particulier acier pour trempe et revenu - Google Patents

Acier allié trempant au bore, en particulier acier pour trempe et revenu Download PDF

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Publication number
EP4296393A1
EP4296393A1 EP22180813.2A EP22180813A EP4296393A1 EP 4296393 A1 EP4296393 A1 EP 4296393A1 EP 22180813 A EP22180813 A EP 22180813A EP 4296393 A1 EP4296393 A1 EP 4296393A1
Authority
EP
European Patent Office
Prior art keywords
weight
steel
grains
grain size
optionally
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22180813.2A
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German (de)
English (en)
Inventor
Volker Block
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Saarstahl AG
Original Assignee
Saarstahl AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Saarstahl AG filed Critical Saarstahl AG
Priority to EP22180813.2A priority Critical patent/EP4296393A1/fr
Priority to PCT/EP2023/065501 priority patent/WO2023247214A1/fr
Publication of EP4296393A1 publication Critical patent/EP4296393A1/fr
Pending legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron

Definitions

  • the invention relates to a boron-alloyed steel, in particular tempered steel, and a manufacturing process therefor.
  • Boron alloy steel is known through use.
  • boron is a cost-effective means of increasing the hardenability of steel, as it has a comparatively strong effect even at low levels. Without countermeasures, boron forms boron nitrides with the nitrogen contained in the steel and is then no longer available to increase hardenability.
  • boron-alloyed steels are alloyed with titanium, as titanium binds nitrogen present in the steel. Boron-alloyed steel is usually also alloyed with aluminum.
  • Aluminum forms aluminum nitrides with nitrogen, which contribute significantly to the development of good fine grain resistance, which has a positive effect on the mechanical properties. The formation of aluminum nitrides and that of titanium nitrides compete with each other.
  • unset aluminum forms oxides, which have a negative impact on the degree of purity and mechanical properties.
  • the invention is based on the object of creating a boron-alloyed steel by means of which workpieces can be produced which have a longer service life.
  • this object is achieved by a steel with the following composition: - C: 0.1 - 0.6% by weight, -Si: 0.05 - 1.5% by weight, -Mn: 0.3 - 1.8% by weight, - B: 0.001 - 0.005% by weight, -Ti: 0.01 - 0.06% by weight, - optional Nb: 0.01 - 0.05% by weight, - optional Cr: 0.1 - 1.2% by weight, - optional Ni: 0.1 - 1.5% by weight, - optional Mon: 0.01 - 0.5% by weight, -Al: ⁇ 0.005% by weight, - N: ⁇ 0.007% by weight, -P: ⁇ 0.02% by weight, -S: ⁇ 0.04% by weight, -Cu: ⁇ 0.3% by weight, - Rest: iron and manufacturing-related impurities.
  • the steel according to the invention has both good fine-grain resistance and good through-hardenability.
  • the other properties of the steel do not change or change only very slightly compared to the known boron-alloyed steels with a larger Al content.
  • the low aluminum content or its avoidance results in an improvement in the degree of purity compared to boron-alloyed steels with a higher Al content. This measure largely prevents the aluminum from forming inclusions in the form of Al 2 O 3 or compounds with other oxides such as MgO, which can lead to precipitation. Workpieces made from steel have a longer service life due to their higher purity.
  • the steel has an Al content of at most 0.004% by weight, preferably at most 0.003% by weight. This allows a further improvement in the degree of purity to be achieved. This is, for example, by switching from aluminum deoxidation to silicon deoxidation possible.
  • aluminum is only present as a production-related impurity, preferably with a content of ⁇ 0.001% by weight.
  • Silicon is alloyed into the steel according to the invention in amounts of 0.05 - 1.5% by weight. Silicon increases the yield strength of the steel. Up to the claimed maximum content of 1.5% by weight, the increase in yield strength occurs without a negative impact on ductility. Higher levels can lead to greater decarburization, which is undesirable. However, for many applications it has proven to be sufficient to only provide a maximum of 0.7% by weight of silicon in the composition.
  • silicon acts as a deoxidizing agent, whereby the above-mentioned properties of the steel can be achieved, in particular even at particularly low Al contents of at most 0.003% by weight. In order to achieve a sufficiently large deoxidizing effect of the silicon in the composition, Si contents of at least 0.2% by weight, particularly preferably of at least 0.3% by weight, are preferably set.
  • the carbon content in steel is crucial for its strength.
  • the required strength can be adjusted in the required range of 0.1 - 0.6% by weight.
  • Preferably 0.15 - 0.45% by weight of carbon is provided.
  • the manganese serves to increase the strength of the ferrite and increases the hardenability of the steel.
  • Manganese is added in amounts of 0.3 - 1.8% by weight. Above levels of 1.8% by weight, manganese has a negative effect on the toughness of the steel due to segregation. For most applications it has proven to be advantageous for increasing strength and hardenability to provide manganese in contents of 0.4 - 1.5% by weight.
  • boron is expediently provided in the steel.
  • the maximum boron content is preferably 0.005% by weight. At higher contents, the hardenability-increasing effect deteriorates again because boron carbides are formed.
  • Titanium is intended as an alloying element in amounts of 0.01 - 0.06% by weight because it has a higher affinity for nitrogen than boron and binds nitrogen by forming titanium nitride and avoids the formation of boron nitride.
  • the titanium nitride formed also contributes to the fine grain resistance of the steel. It has proven to be particularly advantageous if the ratio of titanium to nitrogen content is Ti/N ⁇ 3.0, preferably Ti/N ⁇ 3.5.
  • Niobium can optionally be alloyed into the steel in amounts of 0.01 - 0.05% by weight, preferably 0.02 - 0.03% by weight. It has been shown that steel can be given particularly good fine-grain resistance during heat treatment by adding niobium and the formation of carbides associated with its effect as an alloying element. By adding 0.01 - 0.05% by weight of niobium, the fine grain resistance mentioned above can be achieved with annealing times of up to 60 minutes at annealing temperatures of up to 950 °C. Niobium is expediently alloyed in amounts of at least 0.02% by weight so that the effect on fine grain resistance can be adjusted particularly reliably.
  • chromium can optionally be provided to increase the hardenability, preferably in the claimed range of 0.1 to 1.2% by weight.
  • Nickel leads to a significant improvement in the toughness of the steel and increases its hardenability.
  • Nickel can optionally be alloyed into the steel according to the invention in amounts of 0.1 - 1.5% by weight. If good notched impact strength is required at low temperatures of up to -20 °C, in particular up to -40 °C, a nickel content of at least 0.5% by weight, preferably at least 1% by weight, of nickel is expediently provided.
  • Molybdenum can optionally be alloyed into the steel according to the invention in amounts of 0.01 - 0.5% by weight.
  • the use of molybdenum as an alloying element increases hardenability. If at least 0.3% by weight of molybdenum is preferably provided in the alloy, the so-called temper embrittlement, in which a drop in notched impact energy values occurs at tempering temperatures of around 550 ° C, can be avoided.
  • the nitrogen content contained in the steel due to the process is expediently a maximum of 0.007% by weight. Accordingly, the titanium content required to bind the nitrogen can be kept low.
  • a maximum content of 0.02% by weight is intended for phosphorus in order to avoid an embrittling effect.
  • the sulfur content of the steel is a maximum of 0.04% by weight.
  • the steel expediently contains at least 0.015% by weight of sulfur.
  • the S content is at most 0.01% by weight, which has a particularly positive effect on the impact work.
  • the maximum content of copper in the alloy is preferably 0.3% by weight, particularly preferably ⁇ 0.1% by weight.
  • the steel is intended for producing a long product, preferably a strand, a rod or a wire.
  • the steel expediently forms a semi-finished product.
  • grain sizes or distribution of grain sizes in accordance with DIN EN ISO 643: 2020 - 03 are present in the steel: at least 90% of the grains have a grain size number of ⁇ 5, a maximum of 10% of the grains have a grain size number of 3 or 4 and there are none Grains with a grain size number of ⁇ 2.
  • oil is used as the hardening medium.
  • Other typical hardening media are water or water-polymer solutions.
  • the steel which preferably contains 0.01 - 0.05% by weight of niobium, has such fine grain stability that after annealing 950 °C for a period of 30 minutes and subsequent hardening, preferably after annealing for a period of 60 minutes and subsequent hardening, in which the steel has the following grain sizes or distribution of grain sizes in accordance with DIN EN ISO 643: 2020 - 03: at least 90% of the grains have a grain size number of ⁇ 5, a maximum of 10% of the grains have a grain size number of 3 or 4 and there are no grains with a grain size number of ⁇ 2.
  • the steel is expediently annealed at temperatures of 850 °C - 900 °C before hardening.
  • Table 1 shows the compositions of various steels. The main difference between the steels is their aluminum and niobium content.
  • the steel "Saar 1" serves as a reference. It is a boron-alloyed tempered steel that has 0.031% aluminum by weight and therefore a comparatively high aluminum content. The niobium content is 0.001% by weight.
  • the steel Saar 2 according to the invention has a significantly lower aluminum content of 0.003% by weight and is therefore almost aluminum-free. This steel also has a niobium content of 0.001% by weight.
  • the Saar 3 steel according to the invention has the same aluminum content of 0.003% by weight of aluminum as the Saar 2 steel.
  • the Saar 3 steel differs from the "Saar 2" steel in that it has a significantly higher niobium content of 0.024% by weight.
  • Fig. 1 shows the grain size development for the steels Saar 1, Saar 2 and Saar 3 after 30 minutes of annealing at various temperatures between 880 °C and 950 °C.
  • the steel Saar 2 according to the invention is fine-grain stable up to 930 ° C with an annealing time of 30 minutes and thus at least achieves the fine-grain resistance of the reference variant Saar 1, which is fine-grain stable up to 910 ° C.
  • the Nb-alloyed steel Saar 3 has a resistance to fine grains even up to 950 °C.
  • both the reference steel Saar 1 and the steel Saar 2 according to the invention are fine-grain stable with a holding time of one hour at annealing temperatures of up to 910 ° C.
  • the Nb-alloyed steel Saar 3 has fine-grain resistance for annealing temperatures of up to 950 °C with a holding time of up to one hour.
  • the investigations show that the steel according to the invention is at least equal to the standard steel in terms of fine-grain resistance and an additional fine-grain stabilizing effect can be achieved by adding niobium.
  • Tables 2 to 4 show the results of the determination of mechanical properties of the steels Saar1, Saar 2 and Saar 3, namely elastic limit R p0.2 , tensile strength R m and elongation at break A5, after treatment with different tempering temperatures between 400 and 600 ° C.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
EP22180813.2A 2022-06-23 2022-06-23 Acier allié trempant au bore, en particulier acier pour trempe et revenu Pending EP4296393A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP22180813.2A EP4296393A1 (fr) 2022-06-23 2022-06-23 Acier allié trempant au bore, en particulier acier pour trempe et revenu
PCT/EP2023/065501 WO2023247214A1 (fr) 2022-06-23 2023-06-09 Acier allié au bore, en particulier acier traité thermiquement

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP22180813.2A EP4296393A1 (fr) 2022-06-23 2022-06-23 Acier allié trempant au bore, en particulier acier pour trempe et revenu

Publications (1)

Publication Number Publication Date
EP4296393A1 true EP4296393A1 (fr) 2023-12-27

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EP22180813.2A Pending EP4296393A1 (fr) 2022-06-23 2022-06-23 Acier allié trempant au bore, en particulier acier pour trempe et revenu

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EP (1) EP4296393A1 (fr)
WO (1) WO2023247214A1 (fr)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3773500A (en) * 1970-03-26 1973-11-20 Nippon Steel Corp High tensile steel for large heat-input automatic welding and production process therefor
US4029934A (en) * 1973-08-20 1977-06-14 British Steel Corporation Welding, and a steel suitable for use therein
EP0857794A1 (fr) * 1997-02-10 1998-08-12 Kawasaki Steel Corporation Feuillard d'acier, laminé à froid aet procédé de fabrication
EP1780293A2 (fr) * 2005-10-28 2007-05-02 Saarstahl AG Procédure de fabrication de la matière brute de l'acier par déformer ä chaud

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3773500A (en) * 1970-03-26 1973-11-20 Nippon Steel Corp High tensile steel for large heat-input automatic welding and production process therefor
US4029934A (en) * 1973-08-20 1977-06-14 British Steel Corporation Welding, and a steel suitable for use therein
EP0857794A1 (fr) * 1997-02-10 1998-08-12 Kawasaki Steel Corporation Feuillard d'acier, laminé à froid aet procédé de fabrication
EP1780293A2 (fr) * 2005-10-28 2007-05-02 Saarstahl AG Procédure de fabrication de la matière brute de l'acier par déformer ä chaud

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WO2023247214A1 (fr) 2023-12-28

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