Classifications

• • 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
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • 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
  • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
• • 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
  • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/001—Austenite
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/002—Bainite

Definitions

• the invention relates to a steel alloy for a low alloy, high strength and at the same time tough steel with excellent wear resistance according to claim 1.
• the invention relates to tubes made of this alloy, strips, and sheets of which z. B. components for the automotive industry, such as body panels,
• Wear plates made of this alloy can be used for excavator buckets. Also, such steels are used for applications where suddenly occurring
• Impact energies must be absorbed, e.g. as bulletproof armor.
• Tubes made from this alloy can be designed as welded, hot or cold strip or seamless tubes, which may occasionally have deviating from the circular cross-sections.
• Construction tubes or sheets of this steel alloy can also be used for highly stressed welded steel structures, for example in crane, bridge, ship, hoist and truck construction.
• Characteristic of these steels is e.g. a strength of 1000 to about 2000 MPa, depending on the strength of an elongation at break of at least 5% and a very finely (nano-) structured bainitic structure with shares of retained austenite.
• Carbide-free bainitic steels for rails are e.g. known from DE 696 31 953 T2.
• the steel alloy disclosed therein in addition to additions of manganese, chromium and other elements such as molybdenum, nickel, vanadium, tungsten, titanium and boron, a silicon content between 1 and 3%.
• This steel is designed for the requirements of highly wear-stressed rails, but for tapes, sheets and tubes for the stated application uneconomical or not applicable, since in addition to the requirements for wear resistance, both the strength and toughness requirements are met.
• the cross-sectional dimensions of the rails differ significantly from those of the strips, sheets and tubes due to their compact cross-section, which means that the alloy concept can be adapted to the material properties to be achieved after the Air cooling of the steel required.
• a disadvantage of the known steel is also the expensive addition of titanium and other alloying elements such as nickel, molybdenum and tungsten.
• Another problem with the known steel is that no information is made on the nitrogen content, which exerts a negative influence on the material properties, in particular with aluminum additions by the formation of aluminum nitrides.
• Notched impact strength at -20 ° C at least 15 J
• the object of the invention is to provide a steel alloy for a low-alloy, high-strength, tough and wear-resistant carbide bainitic steel for the production of strips, sheets and tubes, on the one hand cheaper than the known steel alloys and on the other hand uniform, the requirements of the material properties such Strength, elongation at break, toughness etc. guaranteed. moreover These material properties should be achieved by air hardening even when cooling to still air.
• Remaining iron with melting impurities with optional addition of one or more elements of Mo, Ni, Co, W, Nb, Ti, or V as well as Zr and rare earths with the proviso that to avoid primary excretions of AIN the condition
• rare earths and reactive elements such as Ce, Hf, La, Re, Sc and / or Y can be alloyed with a total of up to 1 wt .-%.
• Cooling in air has a strength (R m ) of more than 1250 MPa, an elongation at break of more than 12% and a toughness (KBZ) at -20 ° C of at least 15 J (see Table 1).
• the structure consists of carbide-free bainite and retained austenite with a content of at least 75% bainitic ferrite, at least 10% retained austenite and up to a maximum of 5% martensite (or martensite phase and / or decomposed austenite).
• the steel alloy according to the invention is based on the development of the
• chromium in the range from 0.10 to 2.00 wt.%, Moreover, the kinetics of ferrite formation can be decisively controlled so that the formation of coarse polygonal ferrite grains, which can negatively influence the material properties, is effectively avoided.
• Crucial here is the interaction of aluminum and chrome. While aluminum accelerates ferritic and bainitic transformation, the addition of chromium retards ferritic transformation (see Figure 2). Through a specific combination of these two elements, both the kinetics of ferrite and bainite formation can be controlled.
• the nitrogen content be as specified Upper limit of 0.025 wt .-%, better still 0.015 wt .-%, or optimally 0.010 wt .-% does not exceed the number and size of harmful aluminum nitrides as
• AI x N ⁇ 5 x 10 "3 (wt .-%) must be fulfilled.
• the investigated alloy compositions and the determined mechanical characteristics are given in Table 1. All samples were heated to about 950 ° C and then cooled in still air or accelerated. The required cooling rate is made dependent on the sheet thickness and the composition. As the results of the mechanical sampling show, the required properties could not be achieved with the test melt 14 because of the too low Cr content.
• the test melt 6 according to the invention fulfilled the requirements because of the larger sheet thicknesses of 12 mm only by accelerated cooling. Typical temperature profiles for cooling in still air or with quenching are shown in FIG.
• Substructure (such as subgrains) with fine lamellar microstructure is outlined in FIG. Nb (C, N) precipitation stabilizes the former austenite grain structure.
• TRIP Transformation Induced Plasticity
• Carbon for reasons of sufficient strength of the material, the minimum content should not be less than 0.10% by weight. In view of a sufficiently low martensite start temperature and thus the setting of a very fine microstructure but still good weldability, the carbon content should not exceed 0.70 wt .-%. Carbon contents between 0.15 and 0.60% by weight have been found to be favorable, optimal properties being achieved when the carbon content is between 0.18 and 0.50% by weight.
• Aluminum / silicon the essential element to achieve the required
• the aluminum content should be at least 0.05% by weight, but not more than 3.00% by weight, since otherwise coarse polygonal ferrite grains may be produced which again impair the mechanical properties.
• silicon may additionally be added in amounts of from 0.25 to 4.00% by weight. Good material properties are achieved at aluminum contents of between 0.07 and 1.55% by weight and optimally between 0.09 and 0.75% by weight. Corresponding silicon contents are from 0.50 to 1.75% by weight or between 0.75 and 1.50% by weight.
• the selective addition of chromium of at least 0.10 to 2.00 wt .-%, the ferritic conversion can be delayed and controlled by combining with aluminum, both the kinetics of ferrite and bainite formation targeted.
• Advantageous chromium contents are 0.10 to 1.75% by weight or between 0.10 and 1.50% by weight.
• Manganese the manganese addition in the range of 1.00 to 3.00% by weight results, depending on the respective requirements of the steel alloy, from a compromise between strength which can be achieved by higher additions and one
• the manganese content should be between 1.50 and 2.50 wt.% Or between 1.70 and 2.50 wt.%.
• Niobium / nitrogen adjust the niobium content from 0.001 to 0.50 wt.% To ensure the formation of Nb (C, N).
• the resulting grain refining contributes to a significant improvement in toughness properties.
• Advantageous niobium contents are from 0.001 to 0.10 or 0.001 to 0.05 wt .-% with advantageous nitrogen contents of 0.001 to 0.015 or 0.002 to 0.010 wt .-%.
• micro-alloying elements based on vanadium can be added to 0.20% by weight and / or titanium to 0.10% by weight. It should be a Summengehalt at Ti, V of max. 0.20 wt .-% and Ni, Mo, Co, W, Zr a Summengehalt of max. 5.50 wt .-% are maintained. In order to be able to exploit the effect of these alloying elements, a minimum content of 0.01% by weight should be maintained in each case.
• Rare earths and reactive elements the optional addition of rare earths and reactive elements such as Ce, Hf, La, Re, Sc and / or Y can be used to set a targeted fin spacing and thus to further strength / and
• Toughening in amounts of up to 1 wt .-% take place. If necessary, a total amount of 20 ppm should be added.
• the martensite starting temperature shall be determined as follows:
• cementite formation must be suppressed. This is achieved by a targeted alloy with Si and Al, since both elements have a very low solubility in cementite. For this, the following condition must be observed:
• Austenitization of the steels of the invention can be achieved (see Figure 1).
• the microstructure of the steel according to the invention consists of bainitic ferrite and retained austenite lamellae. It may have fractions of up to 5% martensite (or martensite / austenite phase and / or decomposed austenite).
• the two most important parameters of the microstructure, which significantly influence the mechanical properties of the steel, are the fin spacing and the proportion of retained austenite. The smaller the fin spacing and the higher the proportion of retained austenite, the higher the strength and elongation at break of the material become. In order to achieve the required high strength of the material of at least 1250 up to 2500 MPa, the average fin spacing should be less than 750 nm, advantageously less than 500 nm.
• a residual austenite content of at least 10% and a martensite proportion of at most 5% should be present.
• the average former Austenitkornucc should not exceed a value of 100 ⁇ .
• the microstructure is very fine, the microstructural constituents can hardly be differentiated by light microscopy, so that a combination of electron microscopy and X-ray diffraction can be used on a case-by-case basis.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Heat Treatment Of Sheet Steel (AREA)

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• 2013
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