FR2651507A1 - THERMALLY TREATED STEEL WITH IMPROVED MECHANICAL-TECHNOLOGICAL PROPERTIES OF MATERIAL. - Google Patents

Abstract

a) Heat-treated steel, with improved mechanical-technological material properties. b) Steel characterized in that the steel has a resistance and a heterogeneous structure on the cross section, in which only the peripheral zone is in the normalized state. c) The invention relates to a heat-treated steel with improved mechanical-technological material properties

Description

"Heat-treated steel with mechanical properties-

  The invention relates to a steel with improved material properties, mainly in the dimensional range of wire types and fine steels, which is advantageously usable especially as

than steel construction.

  The particular development of processes and products in the field of heat treatment and heat treatment of steel forming has led to the production and use of a series of

  of steels having a mechanical strength and a structural

  determined in cross-section, corresponding to the conditions of use and

  implemented in practice. These are

  take, for example, ribbed concrete steels for unstretched reinforcement, in particular for lattice

  welded (DD-A-106 661). Concrete steels of this type

  eg, hardened thermally by intense cooling, from the high temperature of forming, are

  as a function of the cooling intensity

  a more or less thick peripheral zone,

  strongly tempered and returned, and a ferritic heart

  that-pearlitic practically unchanged. This is by

  consequently a partially treated steel having

  vanting mechanical-technological properties of material, which stands out in particular also

by a good weldability.

  High-strength steel, also treated

  partially in the peripheral area, in particular concrete steel or primary

  drawing, having improved material properties.

  is characterized in that the ash has a heterogeneous distribution of the mechanical strength on

  the cross-section, in which a layer

  tensitic strength is found in the area of

  transition between the outer layer with reduced resistance

  te and the less hard core area (DD-C-268 258). The structure of this steel is due to the fact that the outer peripheral layer, just like the layer of

  the highly resistant transition zone is mainly

  consists of differently annealed martensite, while the central zone is pearlite

  or ferrite and pearlite with definite proportions

of bainite.

  In addition, a very resistant steel is known,

  in particular a steel for prestressed concrete, with

  improved resistance to corrosion cracking under

  stress and delayed failures (DD-C-267 513).

  With a homogeneous chemical composition and a continuous quenching and tempering on the cross-section (including the core), the steel is characterized in that it has in the central zone a strength of 450 MPa higher than in the peripheral area and the ratio of the elastic limit Rpo, o01 to the

  tensile strength Rm ranges from 0.70 to 0.85. The neck-

  the peripheral device has a value of 0.05

  higher with respect to the ratio Rpo0.01 to Rm.

  An advantageous improvement of this high-strength steel, having a continuous martensitic structure on the cross-section, is due to the fact that this steel consists of several layers in its zone

  the strength of steel increasing

  dually towards the heart and reaching a maximum in the heart (C21D / 316556.8). The number of

  layers in the peripheral area as well as their ex-

  tension in relation to the superficial part of the

  cross section of the heart, and the temperature

  dual income, can be freely chosen in

certain limits.

  Since the steels indicated more

  may be produced with their heterogeneous structure

  gene from the high temperature forming, the

  conception, repeatedly supported in the literature.

  specialization, according to which the heat treatment

  classical mechanics of high-temperature steels, mal-

  convincing economic benefits, it is obvious that

  clearly not applicable to conventional treatment

  Tempering and tempering (A. Randak et al., Stahl und Eisen (Iron and Steel) 85 (1965) 22, p.1452) is at the same time thus refuted. The disadvantage, however, is that in particular at the high temperatures of rolling

  the initial structure is not always optimal.

  male for the hardening of steels, according to their chemical composition. With regard to homogeneity and

  at the grain size of the austenite, it would be

  to submit to a preliminary standardization

  rolled steel for tempering treatment and

  came. The defined structural state of the perlite stage which can thus be achieved should be sought both as an intermediate stage for subsequent heat treatments (for example for quenching and tempering treatment) and as advantageous also as a state of the art. use (eg for structural steels) because, at the fineness of grain corresponding to the Hall-Petch relation, is particularly related a

  noticeable increase in the elastic limit

  you. This, however, is opposed by the objective concept that a steel normally annealed in the sense of the term can not be produced from the high rolling temperature (A. Randak et cool., Stahl und Eisen

(1965) 22, p. 1457).

  The object of the invention is to improve the mechanical and technological properties of materials, in particular

  concrete steels and structural steels

  heat-truction, to expand the possibilities of

  the use, for material, technological and economic reasons, of steel of this type, and

  to enable their production on production lines

wire and fine steels.

  The object of the invention is to develop a steel whose mechanical and technological characteristics of material are improved by the fact that with respect to the structure of concrete steels, is

  established an advantageous intermediate state for the

  subsequent thermal hardening, or, in view of the

  structure of purely ferritic structural steels

  The advantages of these pearlitic materials are that their structural state is to be achieved in direct relation with the thermal hardening or in the form of a heat treatment separated from the steel.

the rolling cycle.

  This object is achieved according to the invention, by the

  steel has a resistance and a

  terogens on the cross section, in which

  only the peripheral zone is in the normal

  sé. The structure of this steel is characterized by

  that as a structural steel it is

  It has a non-standardized ferritic-pearlitic central zone surrounded by a standardized ferritic-pearlitic peripheral zone. On the other hand, the structure of this steel is characterized by the fact that, as steel for heat-hardened concrete, it consists of a non-standardized central ferritic-pearlitic zone which is surrounded by a peripheral zone.

  than normalized and then soaked and returned.

  The thickness of this peripheral layer is determined, in addition to the technological parameters,

  from the point of view of the material in particular by the re-

  lation of the point Ms, at the temperature Ac3. The temperature

  A3 decreases with increasing C content in steels, but also with

  temperature Ms, the adjustment possibilities of the

  layer thickness, as regards the material, are limited when one focuses only on the martensitic conversion. The maximum achievable surface area of the normalized layer is then

about 15 to 20%.

  The present invention is illustrated using

  of the descriptive and nonlimiting example below.

Example

  The example of a non-alloy weldable steel having a C content of 0.23%, an Ac3 temperature of 840 C, an MS temperature of 430 ° C and a diameter of 25 mm, will reveal the possibilities and limits

of the material according to the invention.

  The formation of the normal peripheral layer

  of this steel was directly carried out in the rolling cycle, in that the rolled steel was for a short time surface-cooled with

  a great intensity, by which, from a tempera-

  rolling temperature of 1080 C, in the zone

  device leads to a Y - a - Y conversion.

  finished with subsequent equilibration of the temperature of the peripheral part and the core at 870 C. After the subsequent cooling to the air, the structure of the

  this steel consists of a normal peripheral layer

  ferritic-pearlitic seam about 1 mm thick

  and a non-normal ferritic-pearlitic core zone

  Lisée. Another sample of this steel, after

  temperature equilibrium at 870 C was again

  calf hardened intensely on the surface for a short

  duration, with the balancing temperature now reaching

  600 C. The initial peripheral layer already

  mated then consisted of martensite returned to

fine structure.

Claims (1)

R E V E N D I C A T I ONS   1) Heat treated steel characterized   improved mechanical-technological material ticks   in the dimensional range of wire types and fine steels, which is particularly advantageously   for use as a structural steel,   rised in that steel has a resistance and a structural   heterogeneous shape on the cross-section, in the-   which only the peripheral zone is in the state standardized.   ) Heat treated steel according to   claim 1, characterized in that it is constituted   ferritic-pearlitic core zone   which is surrounded by a ferriti- that-pearlitic normalized.   ) Heat treated steel according to   claim 1, characterized in that as steel   thermally hardened for concrete, it consists of   a non-standard ferritic-pearlitic central zone surrounded by a standardized peripheral zone and   then quenched and tempered.