DD285534A7 - CHEMICAL MEASURING METHOD FOR IMPROVING THE PHYSICO-CHEMICAL SURFACE TEXTURE OF METALLIC MATERIALS - Google Patents

Abstract

The invention relates to a chemical measuring method for assessing the physico-chemical surface properties of metallic materials which have been claimed in some way (eg mechanically by machining). While it is the object of the invention, with little technical effort to assess the physico-chemical state of the surface to make it the most effective, most material-saving and to achieve a high product quality best technologies in terms of further use of these components with respect to corrosion, wear, pickling behavior, liability applied Layers, Schweisz- and Loetbarkeit u. ae. Their task is to use a single measuring method to assess the surface in terms of its utility value properties in a complex manner or to optimize the technology for further processing steps. According to the invention, the reaction layer thickness is determined from the surface to be examined by time-tracking of the soldering behavior in an electrolyte solution, and the magnitude of this value is concluded after appropriate calibration for physico-chemical properties. Metalloberflaeche; Material testing, chemical; Analysis; Surface texture, physico-chemical; microhardness; pickling behavior; Corrosion; Defect density; Layers; Liability; Schweiszbarkeit; solderability}

Description

of the dissolving metal, the amount of metal is determined at the time at which, after an initial increase in the dissolution rate and subsequent stagnation or reduction thereof, the rate of dissolution rapidly increases again. From the determined amount of metal, the thickness of the oxidic reaction layer can be calculated assuming a uniform Abtrag.

The electrolyte used is, for example, a solution of the disodium salt of ethylenediaminetetraacetic acid (EDTA). To increase the precision of the measurement, depending on the material and the nature of the preceding mechanical stress, a pH value is set at which the release curve has the most favorable evaluation form. The prior knowledge of the magnitude of the reaction layer thickness reduces the investigation effort. So z. For example, for turned, unalloyed steels (layer thickness 0.1 ... 0.4 μm) a pH value of 4 is best.

When investigating the dissolving behavior of machined metallic surfaces in complexing agent solutions of different pH values, but also in acids or inhibitor-containing acids, it was surprisingly found that characteristic curves can be generated when the metal in solution is detected over time, from whose course the oxidic reaction layer thickness is estimated can be. The rate of dissolution initially increases, reaches relatively constant values at a low level, and then rises more sharply after the oxide reaction layer has been removed. In this case, the reaction layer is to be understood as meaning the outer oxidic layer formed by the introduction of energy (eg thermally, mechanically), which, for B. when cutting steel, a thickness between 0.1 and 0.5 mm achieved.

The local dissolution rate, despite the use of different erosive electrolytes, reflects the impurity intensity and thus the structure of the edge zone. Surprisingly, other chemical parallel or subsequent reactions as well as the roughness of the surface do not have a dominating effect on the dissolution rate.

It has further been surprisingly found that the thickness of this layer corresponds to the most diverse physico-chemical properties of the surface surface layer, such as. Microhardness, solidification depth, defect density and distribution. Rust and pickling behavior, solderability and weldability as well as adhesion of subsequently applied metallic or non-metallic coatings. Thus, this size is suitable for the complex characterization of physicochemical surface properties (virtually non-destructive, as only a maximum of 1 μm removal). The cause of these correlations appears to be that the reaction layer formation significantly affects the impurity trajectory and density in the underlying zone. Thus, for oxidation, necessary diffusion of metal atoms into the surface defects will remain unaffected. In addition to the reaction layer thickness itself, the defect density and distribution essentially influences the physicochemical properties of the surface layer of the surface. So z. B. thickens! Reaction layers unraveled steels raised both on a high defect density in the edge region as well as a large penetration of these disorders. Accordingly, the size and depth of the stated physical and chemical properties of the surface layer are also. With different preprocessing, e.g. The different relationships between reaction layer thickness and the individual physico-chemical surface properties can be different. However, these can be quantified in any case by calibration or definition of limit values.

Ausführungsbeisplel The invention will be explained in more detail with reference to embodiments. example 1

A shaft made of steel C 60 with different cutting speeds was turned outwards. As the following table shows, there is a clear correlation between the determined reaction layer thickness d and physical (microhardness HVo, oo6, solidification depth VT, distance of the largest defect density from the surface d _F ) and chemical (frequency of rust Hn after 90 hours at 95% relative humidity, average Pickling rate v _L in 1N H ₂ SO ₄ ) Activation of the metal surface:

d (mm) HV _0AM6 VT (Mm) d _F (mm) H _N (%) VI (mg.cm " ² .h" ¹ ) 0.40 480 80 7-8 29.2 1.6 0.33 380 65 3.5-4.5 15.4 0.7 0.30 350 58 1.5-2.5 12.1 0.45 0.31 360 60 about 2 13.7 0.5

To determine the reaction layer thickness, this was carried out in a 0.1 M EDTA solution (disodium salt of

Ethylenediaminetetraacetic acid) having a pH of 4 in solution going iron spectrally determined as a function of time. The reaction layer thickness d was calculated from the plateau of the curve obtained.

Example 2

A steel C45 shaft was externally rotated in otherwise constant cutting conditions with different wear conditions of the bit. Analogously to Example 1, a connection between those mediated reaction layer thickness d and properties of Oberflächenrondschichtermittolt could be (MikrohärteHVo.oos.'Abstandder greatest defect density from said Oberflächedf; rust degree of frequency H _n after 150 hours at 95% relative humidity, mean pickling speed v _L in 30% igerHjSO, |):

d (mm) HVO, oos df (mm) H _N (%) V ₁ (mg · cm -2. "-ι 0.14 195 1.5-2.5 5.1 1.7 0.18 245 2-3 10.4 1.9 0.20 270 2-3 12.1 2.0 0.38 510 4-5 24.3 2.5

The determination of the reaction layer thickness is carried out analogously to Example 1. Example 3

Guideways made of hardened steel 100 Cr β were milled with superhard composite material 10 under different cutting conditions. The following values were obtained for reaction layer thickness d, pickling rate v _L in 1N H ₂ SO ₄ , microhardness HV ₀ , ooe and the degree of solidification in the boundary layer VG:

d (pm) VI (mg-crn " ¹ * h" ¹ ) HVoxwe VG 0.2 0.28 602 1.11 0.12 0.15 587 0.92

In addition, significant differences in wettability with certain oils were found. The reaction layer thickness determination was carried out analogously to Example

Example 4 It was the material AIMg 3 rotated with variously worn chisels. There could be a correspondence between Reaction layer thickness, pickling rate in 8% HCl and the microhardness or the degree of solidification in the surface layer

be determined.

The reaction layer thickness determination was carried out analogously to Example 1, but at a pH of Example 5

The steel 16 MnCr 5 was ground with corundum grinding wheel of various kinds. Again, a relationship between reaction layer thickness d, pickling rate v _L in 1N H ₂ SO ₄ and microhardness HV ₀ , 005 has been found. In this case, however, there is an indirect proportionality:

α (μιη) VI (mg.cm " ² .h" ¹ ) HVO, OO6 0.44 0.25 190 0.33 0.4 225 0.26 0.5 240

The reaction layer thickness determination was carried out analogously to Example

Example β

Cylindrical steel pins of C 60 with different reaction layer thickness, produced by turning at different Cutting speeds were diffusion welded with GGL 25 casting. There could be a correspondence between Reaction layer thickness, various physicochemical properties of the surface layer and the strength of the Welded joints are determined. The reaction layer thickness determination is carried out analogously to Example Example 7 Steel strip strips of St38 were oxidized to different degrees by heat treatment. With the help of the invention Solution could be set limits of the reaction layer thickness, where the surface under certain Soldering is solderable or not. The reaction layer thickness was determined analogously to Example 1. Example 8

Twisted surfaces of carbon steel C 60 with different reaction layer thickness were coated with nitro combination paint. It was possible to establish a clear correspondence between the determined reaction layer thickness and the adhesion of the lacquer layer, determined by the crosshatch method. The determination of the reaction layer thickness was carried out analogously to Example

Claims (3)

1. Chemical measuring method for assessing the physico-chemical surface quality of metallic materials, using aqueous electrolytes and per se known analysis method, characterized in that the examined rust-and fat-free surface exposed in an electrolyte and from the time course of the dissolving metal the amount of metal is determined at the time at which, after an initial increase in the dissolution rate and subsequent stagnation or reduction thereof, the dissolution rate increases sharply again. 2. Chemical measuring method according to claim 1, characterized in that a solution of the disodium salt of ethylenediaminetetraacetic acid (EDTA) is used as the electrolyte. 3. Chemical measuring method according to claim 2, characterized in that to increase the precision of the measurement depending on the material and the nature of the preceding mechanical processing, an optimum pH of the electrolyte is adjusted. Field of application of the invention The invention relates to a chemical measuring method for assessing the physico-chemical surface properties of metallic materials in order to individually or complexly assess utility value characteristics determined for a direct intended use with a single method of analysis or the technology for further processing steps (mechanical, thermal, chemical, e.g. B. when applying layers or soldering and welding) set. Characteristic of the known technical solutions As a measure of the quality of metallic surfaces of technicians so far mainly the geometric surface shape (roughness, waviness) is used. However, this is not sufficient for many applications, especially with regard to the future increasing demands on the quality of metallic surfaces. On the contrary, it is also necessary to use the physico-chemical properties. Increasingly, although very complex measurement methods for the detection of individual physical-chemical surface properties are used. However, it has long been considered in the art as a defect that biw no complex method. no representative value exists for the assessment of the physico-chemical surface properties. (H. Weber, T. Loladze: Basics of Spanens, Verlag Technik, Beriin 1986) Although a complex parameter for surface properties is also the contact angle of drops of certain Prüfflüssigkeiten on surfaces, with its help, for example, the adhesion of paint layers with metal surfaces before Coating is forecasted. However, the relationships are not always clear. First of all, this is due to the fact that the interactions between test liquid and metal can be different than those between paint and metal, and secondly, generally only the surface tension on thinnest surface layers determines the contact angle. However, this does not capture the effects of underlying layers, which are currently exert a dominant influence on physico-chemical properties. The application of complexing agents in electrolytes for the method according to the invention tangential applications is limited to the removal of rust and scale (DE-OS 2949466, US 3492238, EP 0086245). The use thus relates only to iron materials and also does not serve the measurement of the thickness of the thinnest, metallic-looking oxide Reuktionsschichten and thus the assessment of the physicochemical surface texture after mechanical, thermal u.a. Stress. Object of the invention The aim of the invention is to assess the physico-chemical surface quality of metallic materials with a single measurement method in order to use the most effective, material-saving and best to achieve a high product quality technologies with respect to the further use or use of the components with respect to corrosion, wear, pickling behavior, Adhesive strength applied layers, solderability and weldability, inter alia set. Explanation of the essence of the invention The invention has for its object to provide a chemical measuring method for assessing the physico-chemical surface quality of metallic materials, especially iron materials, the universal for various types of previous types of stress and different materials for complex testing of the surface, preferably in terms of corrosion and pickling behavior, the Microhardness, the depth of consolidation, the defect density and distribution, the weldability and solderability and the expected adhesion of metallic and non-metallic coatings can be used. According to the invention, the object is achieved by using aqueous electrolytes and per se known analytical methods characterized in that exposed to be examined rust and fat-free surface in an electrolyte and from the time course