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
  • C22C38/40—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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C33/00—Moulds or cores; Details thereof or accessories therefor
  • B29C33/38—Moulds or cores; Details thereof or accessories therefor characterised by the material or the manufacturing process
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/005—Heat treatment of ferrous alloys containing Mn
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/008—Heat treatment of ferrous alloys containing Si
• • 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
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0242—Flattening; Dressing; Flexing
• • 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
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0263—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • 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
  • C22C38/18—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
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • 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
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • 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
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
• • 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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets

Definitions

• the present invention relates to a high-strength steel intended in particular for the manufacture of large-sized parts such as mold parts for plastics, tooling parts such as dies, or wear parts such as moldings. parts intended to resist abrasion.
• the mechanical parts that are subjected to high forces or very high wear stresses must be made in steels having high mechanical strengths corresponding to hardnesses between 300 and 500 HB, but which however, they must remain sufficiently stubborn, machinable, weldable, etc.
• These parts are, in general, obtained by cutting and machining of sheets or thick blocks.
• a block that is generally parallelepipedic shape is obtained by forging an ingot.
• a sheet is obtained by rolling an ingot or a slab.
• the thickness is the smallest dimension. For blocks or sheets considered here, the thickness is greater than 10 mm and can reach 1 meter.
• the object of the present invention is to remedy these drawbacks by proposing a steel which makes it possible to obtain high mechanical characteristics of up to 400HB, or even 450 HB, even at the heart of very massive parts, while presenting variations in hardness due to relatively small segregations.
• the subject of the invention is a high-strength steel whose chemical composition comprises, by weight: 0.03% ⁇ C ⁇ 0.2%
• the chemical composition satisfies one or more of the following conditions:
• the chemical composition is such that:
• the invention also relates to a block or a steel sheet according to the invention, which has a thickness greater than 10 mm, and a bainitic structure, martensito-bainitic or martensitic and whose hardness difference between the harder zones and the Less hard zones of the block or sheet, resulting from the segregated veins, is less than about 20% of the average hardness of the block.
• the invention finally relates to a method for producing a steel block or sheet according to the invention, according to which, after being shaped by hot-deformation by hot forging or by rolling, quenching is carried out by cooling with air or austenitization followed by quenching by air cooling.
• the invention is particularly suitable for the manufacture of sheets or blocks whose thickness is greater than 10 mm and in general greater than 20 mm. This thickness may exceed 100 mm and even exceed 150 mm, 300 mm or even 500 mm. It can reach 1 meter.
• the attached figure is a graph showing the carbon content to be targeted according to the desired hardness for a high-characteristic steel according to the invention, after an income at 550 ° C. (curve 1) or after an income below 500 ° C. (curve 2), for a basic composition: 0.15% of silicon, 3.3% of manganese, 3% of chromium, 0.25% of molybdenum and for blocks which have been cooled in air after normalization at 900 ° C.
• the thickness being greater than 10 mm and up to 500 mm or even more than 1 meter, and for the average hardness to be very homogeneous between the core and the surface, it is necessary to use a steel whose hardenability is sufficient to obtain a homogeneous structure without the need to quench in a quenching medium too brutal. Indeed, the more the quench medium is brutal, the more the variations in cooling rates inside the block are important and, as a result, the greater the risk of obtaining structural heterogeneity are important. On the other hand, when quenchability is sufficient, cooling in air, and in particular in still air, which leads to relatively modest differences in cooling between the surface and the core makes it possible to obtain a satisfactory structure which is then very homogeneous. Naturally, these quenching conditions do not have a direct bearing on the problem of local variations in hardness resulting from segregations.
• the over-hardening in veins corresponds to the difference between the average hardness of the veins and that of the surrounding matrix excluding veins. Comparing these measurements between two-by-two castings, we can deduce the contribution to over-curing in veins attributable specifically to the segregation of each alloying element.
• the part of over-curing in veins attributable to an element is the result of the segregation of this element, that is to say, by definition, the product of the nominal content of this element by its segregation rate. Therefore, the elements will be validly compared as to their harmfulness in this respect.
• this element has the main effect of acting on the hardness of the martensite, so its content is chosen according to the level of hardness that is desired get on the pieces.
• To determine the carbon content as a function of the desired hardness it is possible, for example, to divide the hardness scale by 40HB slices, between 320HB and 440HB. These fields correspond roughly to conventional areas of use of abrasion-resistant steels or tool steels.
• the following carbon content ranges, from 0.03% to 0.06% carbon, from 0.07% to 0.15%, from 0.16% to 0.20% carbon may also be considered.
• Each of these carbon content domains corresponds, for a given heat treatment, a hardness range.
• the level of hardness for one in identical carbon is not the same.
• the lowest hardness range corresponds to the lowest carbon content and the highest hardness range to the highest carbon content.
• the boundaries of these carbon content areas corresponding to the hardnesses vary slightly depending on the contents in the other alloying elements and depending on the cooling rate, and also depending on the heat treatment that is performed on the parts.
• FIG. 1 shows the evolution of the hardness as a function of the carbon content for blocks which have been air-cooled after normalization at 900 ° C. following preliminary hot rolling.
• the blocks received an income for one at 480 0 C and for the second at 550 ° C.
• the block which has been returned to the temperature of 480 0 C has a hardness of 360HB for a carbon content of 0.1% while the same steel returned at 550 0 C has a hardness of 320 HB only.
• the block returned to 480 ° C has a hardness of the order of 440HB while the block which has been returned to 560 0 C has a hardness of
• the minimum carbon content of 0.03% corresponds to a value below which the hardening segregation and the interest attached to its reduction become low. It will be noted that the hardnesses obtained vary little by the application of an income when its temperature does not exceed substantially 480 ° C. These results are also applicable to sheets.
• This element which serves in particular to deoxidize the liquid steel bath during the preparation has a content in general greater than 0.025% and preferably greater than 0.05% or even may exceed 0.1%. However, the content of this element must remain less than 0.49%, and preferably remain less than 0.35%, better still less than 0.19%, and, if this is possible taking into account the deoxidation requirements of the bath , stay below 0.1%.
• silicon is an element that tends to increase very significantly the massive segregation at the head of the ingot (so-called major segregation), which is then used to feed the segregated veins which are all the more important than the segregation at the head ingot is important.
• silicon tends to degrade the thermal conductivity of steel, which may be unfavorable in certain applications such as, in particular, molds for molding plastics.
• silicon has a detrimental effect on the susceptibility to reversible brittleness, which must be taken into consideration, especially when the cooling rates of the products are low, which is the case for the applications concerned for this steel.
• This element has a favorable effect on the quenchability and, because of its tendency to form carbides, has a favorable effect on the resistance to the softening with the income, and the effect of over-hardening on the segregated veins is much less marked than that of molybdenum or tungsten it must be added in contents preferably of greater than 1% and better still greater than 2.5%, but must remain below 5%, and preferably below 3.5 % and better still be between 2.7% and 3% in order to obtain both sufficient quenchability, satisfactory softening resistance and at the same time without leading to excessive over-hardening of the segregated areas.
• Molybdenum and tungsten these two elements, which have a very marked tendency to form carbons favorable to a good resistance to the softening of the yield, nevertheless have the disadvantage of having a very important effect on the hardening of segregated areas. Also, since tungsten has the same effect as molybdenum at 2% of tungsten per 1% of molybdenum, the sum Mo + W / 2 will be limited to 1%, preferably to 0.5% or even 0.3%. %, maximum.
• Vanadium, Niobium Since these elements have extremely adverse effects on the hardness of segregated zones, the steel will not be the subject of voluntary additions of vanadium or niobium which may, however, exist as residual , the vanadium content must remain below 0.010% and better still, less than 0.005%, and the niobium content must remain less than 0.050% and better still, less than 0.010%.
• this element has a very favorable effect on hardenability and also has the advantage of having a very modest effect on the super-hardness of segregated zones. Therefore, it is used preferentially to obtain quenchability. Also, the manganese content is between 3% and 4% so that the combined effect of manganese and carbon on quenchability is sufficient.
• This element has a favorable effect on the quenchability and a modest effect on the super-hardness of the segregated zones. However, this element is very expensive, so its content is less than 0.9% and preferably less than 0.5% and more preferably is only at residual levels.
• copper the content of this element, which is often present in the form of a residual, must remain less than 0.9%, preferably less than 0.4% and more preferably still less, less than 0.2%, since this element has no particularly favorable effect on the properties of the steel in question.
• aluminum this element which has a favorable effect on the deoxidation of the liquid steel bath during production and which, in the solid state, makes it possible to control the size of the austenitic grain by formation of aluminum nitride, has a content of less than 0.1%. When it is desired to globulise sulphides if formed and which can form elongated networks sources of loosening, it is preferred to add 0.040 to 0.60% aluminum.
• sulfur, Se, Te sulfur, which is an impurity always present at least in the trace state, can have a favorable effect on the machinability. However, if the contents are too high it has an adverse effect on the toughness, and possibly on the polishing ability of the steels.
• Selenium and tellurium have effects comparable to that of sulfur at the rate of 2 parts of selenium for 1 part of sulfur or 3 parts of tellurium for 1 part of sulfur. Also, especially for applications requiring good polishability, the sum S + Se / 2 + Te / 3 is in trace state or greater than 0.005%, but remains, in any case, less than 0.020 %.
• the rest of the composition consists of iron and impurities resulting from the elaboration.
• the blank thus obtained which constitutes a steel block or sheet is then used either in the raw state of rolling or forging, or after a heat treatment adapted to the intended use that the skilled person knows to choose.
• the raw state of rolling or forging is used in particular for applications such as the manufacture of parts intended to withstand wear in the mineral industry or public works, applications in which the cost of steel is an element very important of the choice.
• the pieces, sheets or rough blocks of forging or rolling possibly cut or pre-machined are austenitized by heating at a temperature above the temperature AC 3 , and in general of the order of 900 0 C and then quenched by cooling in the air, especially in calm air, or possibly in a quenching medium having a somewhat faster cooling but without this being desired.
• This austenitization followed by air cooling has the advantage of reinforcing the ratio of the yield strength to the tensile strength.
• the quenching treatment may, if appropriate, be carried out directly in the hot shaping by hot plastic deformation, if this has been carried out under appropriate temperature conditions.
• Blocks or sheets that are hot deformation hot when they are re-austenized and cooled slowly can advantageously be subjected to a heat treatment of tempering at a temperature greater than 450 0 C but less than 550 0 C.
• Such a treatment of income that does not significantly change the hardness, to the advantage of reducing the level of residual stress in the bins or parts as they are directly derived from previous treatments.
• the re-austenization and slow cooling treatment has the advantage over the hot shaping raw state of relaxing at least a portion of the residual stresses.
• the treatment of income may have the advantage of further strengthening a little the ratio of the yield strength to the tensile strength.
• the treatment of income can be replaced by a relaxation treatment at a temperature of between 150 ° C. and 250 ° C.
• Such relaxation treatment does not lead to appreciable variations in hardness. In contrast, in general, it leads to a significant improvement in toughness, which is useful both to facilitate the implementation of products and secondly to improve the service life of parts.
• Such a treatment is particularly suitable for parts intended to work in conditions which require a high resistance to metal-on-metal friction wear encountered in the mechanical engineering industry, or abrasive wear which the we meet in public works, in mines or quarries.
• two steel castings marked 1 and 2 have been made, which have been compared with steels marked C1 and C2, given by way of comparison.

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