DD159183A1 - METHOD FOR THE HEAT TREATMENT OF HIGH-ALLOY STAINLESS STEEL TOMBURNING DURING GLOWING - Google Patents

Abstract

The invention relates to a method for the pretreatment of scale and oxide layers on high alloyed stainless steels to improve their treatability and is applicable in the production of hot or cold rolled high-alloy steel sheets u. strips and in the manufacture of wire in the steel industry. The aim of the invention is to develop a method by which the poor treatability of stainless steel scale is eliminated and the resulting low plant capacity is increased. According to the invention, the object is achieved in that the application of the media takes place immediately before the calcination, a Zundervor treatment is achieved during the Gluehungen and the transformation of Walzzunders in Gluehzunder disturbed by the existing salt layers, modified or severely hampered.

Description

Process for the heat treatment of high-alloy. Stainless steel scale during the annealing

The invention relates to a method for the pretreatment of scale and oxide layers on high-alloy stainless steels to improve their treatability and is applicable to 'the. Production of hot- or cold-rolled high-alloy steel sheets and strips and in the production of wires, from stainless steel in the steel industry, »

The production of high-alloy, cold-rolled stainless steel strip or sheet of excellent flatness, defined geometry and mechanical properties as well as certain micro-purity occurs by cold working hot-rolled materials. Prior to cold forming, the v / alzzle layer formed during the hot rolling process on the runout must be removed from the surface of the bar. * By incorporating alloying elements. of the steel in the scale, complex, sparingly soluble or admissible oxide mixtures are formed on the rolling stock surface. Before the actual cold forming of the stainless steel strips, the production stages are annealing (austenitizing, recrystallization) and descaling. The annealing is carried out under air atmosphere at about _e 1000 °. To achieve a defect-free cold strip surface, the mill scale layer must be removed before forming

· «. 2 ~

become; This is done inter alia by pickling. In this method, the two processes, heat treatment and pickling run separately on different plants or plant parts or _e one after the other, on a corresponding scale from plant. During annealing microstructure formation is · in addition to the desired structural changes, bz? / _E structural relaxation in the continuous flow process or in Haubenglühverfahren the hot rolling scale layer ever. changed to annealing atmosphere and cooling in an undefined way "The incipient annealing κ; Under layer is by the thermochemical effects based descaling with combination of different Vorbeizen - salt bath melt (mixtures of KaETO, Boras, ITaOH, other oxidizing salts, reducing salt mixtures NaOH + or KOH + HaH ₂ ), acid mixtures (mixtures of

HCL, H ₂ PO ^) and finished stains with mixed acids,. (Mixtures of MO ₇ , HF, H ₂ SO ₄ , HCL, H ^ PO ^ and other additives) difficult to attack and remove, whereby relatively large exposure times are required and low throughput speeds in the 'plants follow _e

Japanese Patent Specification 49555/73 describes a process for the production of steel coils of low-alloyed steels having excellent pickability. Here, salt mixtures are applied to the steel surface as thin layers immediately after heat deformation in order to form easily accessible scale layers No. 50396 discloses another method of pretreating low-alloy steels with good pickling properties. In this case, the medium is applied to both sides of the coiled tape .and additionally there is a closure of a hinge side to prevent "the" air circulation. The medium becomes one after rolling up. Coil applied by various methods, including dipping. «

d) Aim of the invention

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The aim of the invention is to develop a process by which the poor pickability of Edelstablzun is eliminated and the resulting low plant capacity is increased.

the invention;

The object of the invention is to find a method at Y / elchera the Ent igniter ung hot-rolled, annealed Bdelstahlbänder by the application of Salzgeraischen done more effectively and an increase in capacity is guaranteed »Invention according to the object is achieved in that the application of the media directly before the annealing, an ignition treatment is achieved during the annealing process and the transformation of the mill scale into annealing scale,

disturbed, modified or strongly impeded by the existing salt layers «

On both scaled surfaces of stainless steel strips or sheets, media are applied prior to annealing, the main components of which are salts or. Saizgeraische of the alkalis or. Alkaline earth metals with oxidizing or disruptive properties are (eg hydroxides, nitrates, carbonates, boron compounds, oxides, chlorides, ammonium compounds), The application is carried out by »spraying, spraying, dipping, scattering, melting, so da.3 a uniformly thin salt or , Salt mixture film remains on the collar surface. The application can be carried out in aqueous solution, in solutions of other organic or inorganic solvents or in powder form. The strip temperature should be so high that the solvent evaporates sufficiently quickly and uniformly, but must not be so high that insufficient wetting or The amount of salt applied should be between * Ö, 2 and 2.0 g / m ² on each side and the belt temperature 60 - 90 ⁰ G.

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The invention will be explained in more detail below with reference to several exemplary embodiments.

The examples relate to a combined pickling annealing section of a bell annealing plant for the treatment of austenitic and ferritic stainless steels. '.

example 1

The steel strip is supplied with the medium by means of a device. Moreover, the steel strip passes through a supporting roller into the annealing furnace. Here is the. Heat treatment of the steel and a thermochemical thermomechanical seeding of the medium, the temperature should be> 600 ⁰ C and the residence time 2l 2 min. be. The steel strip is then cooled, "the salt mixture being removed, and then further working according to the technologies known per se, a similar process being also applicable to wire and sheet metal production.

Example 2

The example relates to heat treatment of ferritic chromium steels in the hood furnace, before the heat treatment process, the hot strip on a Umwekelanläge is wrapped, thereby the tape is applied on both sides with the medium * During annealing occurs at annealing temperatures> 600 °, a thermal influence of the scale , In the subsequent pickling process, salt bath treatment can be dispensed with, or the reaction time can be considerably shortened.

Example 3

In addition, it is possible to apply after the v / armwalzprozeß prior to the reeling salt mixtures that produce an easily accessible mill scale.

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Claims (3)

• · '. ·'. "25.%. Ml Claim ^ // 1. A method for heat treatment of hochlegier.tem stainless steel scale during annealing for the purpose of improvement of the pickling characterized _f that prior to the austenitic-Bierungsgluhung austenitic stainless steels in Durchlaufpro ~ process on the strip surfaces media applied consisting of salts of alkali, alkaline earth or boron compounds, be used to anneal the strips « 2. Method according to item 1, characterized in that the O
is between 0.2 and 2.0 g / m on each side. Characterized *** in that the medium is applied in aqueous solutions, in other organic or inorganic solvents, in powder form from the melt, by dipping or spraying, 4 "process according to Pk't * 1 characterized in that the strip temperature is selected so that a uniform film is formed and sufficient wetting occurs through the medium * A method for heat treating hbchiegiertem stainless steel igniter during the annealing for the purpose of improving their pickling, characterized in that hot rolled ferritic stainless steels prior to the recrystallizing annealing. in the hood furnace before pickling with media consisting of salts and alkalis, alkaline earths or boron compounds, applied and then annealed. 6. Method according to item 5, characterized in that the 2 ' , between 0.2 and 2 _$ 0 g / m per side and by spraying, spraying or dipping when wrapping the bundles is applied as a uniform film. 7 «Method according Pkt« 1 characterized in that the media are applied after hot rolling.