DE10156326B4 - Process for surface decoration and surface hardening of ferrometallic parts - Google Patents

Abstract

Process for the surface decoration and surface hardening of ferrometallic parts, in which the parts to be hardened are heated in a carbon-donating, calcium-phosphate-containing, low-oxygen medium at least to the austenitizing temperature and then quenched in water, characterized in that the following process steps are carried out:
- Enveloping (2) the parts with lattice-like formwork elements made of largely inert material with numerous lattice meshes, a distance of 0.5 to 3 mm being left between the formwork elements and the surface sections of the parts to be hardened;
- Embedding (3) the coated parts in a coal mixture granulate of charcoal and animal coal in a largely airtight container, the coal mixture granules also being introduced into the distance between the formwork elements and the surface sections of the parts to be hardened;
- Uniform heating (4) of the filled insert container to a target temperature above the austenitizing temperature;
- Maintaining (5) the target temperature for a given austenitizing time, which is determined as a function of the mass and the desired carburizing depth of the parts to be hardened;
- Rapid cooling (6) of the insert container to a stabilizing temperature which is equal to the austenitizing temperature or is up to 100 K below this;
Maintaining this stabilization temperature for 10 to 30 minutes;
- Positioning the closed opening of the insert container directly on the water surface of a quench bath;
- Quenching (7) the parts to be hardened by opening and emptying the insert container into the quenching bath, the parts with the formwork elements and the carbon mixture granulate falling into the quenching bath.

Description

The present invention relates to a method of surface decoration and for surface hardening of ferrometallic parts, in which the parts to be hardened are in a carbon-emitting Calcium phosphate-containing, low-oxygen medium in the range of the austenitizing temperature of the respective ferrometallic material heated and then in oxygen-rich water. The surface treatment takes place through the formation of interfering corrosion protection layers.

The procedure described here is ultimately based on an austenitization process with targeted cooling. Such Processes are also known under the terms colored hardness or colored case hardening. They are used, for example, when hardening of weapon parts and their simultaneous aesthetic design. colorful Hardened Parts are used especially on hunting and sports weapons, at where the optical design plays an important role. The procedure let yourself but also for other iron parts, even if it is primarily about achieving an aesthetic Effect through special coloring (marbling) and hardly at all increase the degree of hardness this part goes.

In the EP 0 647 726 A1 , A method for treating parts is specified, in which the parts are hardened in an oven at hardening temperatures by introducing a reaction gas and blued homogeneously. It is generally known that ferrous materials can be hardened by temperature treatment if suitable reaction conditions are created which allow a structural change. There are generally various methods for increasing the surface hardness of ferrometallic parts.

At A. N. Minkewitsch, “CHEMICAL-THERMAL SURFACE TREATMENT VON STAHL ", published by VEB Verlag Technik Berlin 1953, pages 91-104, is the use of steel in solid carbons for the purpose the material hardening described. As a basic component for a solid carburizing agent charcoal is given. So-called coal mixes are also called Accelerators such as barium carbonate or sodium carbonate and others Components added. The method described in this document is, however, only based on the increase the surface hardness the insertion of steel in solid carbons. To achieve a visually appealing design through special coloring, the publication is not received.

AT 150 984 describes a procedure for case hardening of corrosion resistant Chromium steel with a chromium content of 8% to 20% and a carbon content from 0 to 25%, which is also due to the increase in Targets surface hardness. Coal is used as the coaling agent, which has a high absorbance has. The possibility a targeted color design of the hardened surfaces not treated.

In addition to the technical aspect of increase the surface hardness plays in surface treatment of certain ferrometallic parts also an aesthetic one Effect a role. Visible iron parts should depend on the application get an attractive appearance. With the so-called bluing or Coloring tarnish the metal surfaces slightly bluish. If iron parts at elevated Temperature more spherical Exposed to air form on the surfaces of the Part layers of oxides, sulfides, carbonates and possibly chlorides. This blue color is occasionally evoked to look like it to achieve.

In contrast, in so-called multi-color hardening (colored hardening) one Coloring aimed at, in which different colors (e.g. yellow, Reddish brown, blue, gray) are present and these colors in a marble-like Structure on the surface the parts are distributed. The color spectrum and the color structure can be adjusted using the Process parameters can be influenced.

The so-called colored hardening is Hardly used nowadays because it is technologically difficult to master is and in the past above all using experience was executed. Few documents have been preserved, the details of such Colorful hardening process describe. In the book “Die Modern Rifle Manufacturing ", Friedrich Brandeis, Bernhard Friedrich Voigt Verlag, 1881, page 345 ff., Explains that for steeling or Insertion (i.e. colored hardness) animal coal (mainly charred Leather) is used. The insertion occurs accordingly in special Iron boxes, who filled with this coal become. The sealed insert box is then heated, whereby uniform heating is to take place. Finally should include the parts The leather coal is ejected into a quench bath to the parts to deter there. This old publication also states that the Coloring depends on various factors and it has many years of experience needed to get good results. A sure reworkable However, no method can be inferred from this prior art.

The object of the present invention therefore consists in a method of surface decoration and for hardening of ferrometallic parts with which the so-called colorful hardships simple and predictable with essentiallyachievable results can. In particular, it should make it possible the parts to be hardened on all desired surface sections on the one hand a sufficient degree of hardness lend and on the other hand a multicolored decorative surface design to give.

• – Umhüllen der Teile mit gitter- oder gazeförmigen Schalelementen aus weitgehend inertem Material mit zahlreichen Gittermaschen, wobei zwischen den Schalelementen und den zu härtenden Oberflächenabschnitten der Teile ein Abstand von 0,5 bis 3 mm belassen wird;
• – Einbetten der umhüllten Teile in einem Kohlegemischgranulat aus Holzkohle und tierischer Kohle (Knochenkohle) in einem weitgehend luftdicht abgeschlossenen Einsatzbehälter, wobei das Kohlegemischgranulat auch in den Abstand zwischen den Schalelementen und den zu härtenden Oberflächenabschnitten der Teile eingebracht wird;
• – gleichmäßiges Erwärmen des gefüllten Einsatzbehälters auf eine Zieltemperatur oberhalb der Austenitisierungstemperatur;
• – Aufrechterhalten der Zieltemperatur für eine vorgegebene Austenitisierungszeit, die in Abhängigkeit von der Masse und dem ferrometallischen Werkstoff der zu härtenden Teile bestimmt ist;
• – schnelles Abkühlen des Einsatzbehälters auf eine Stabilisierungstemperatur, die gleich der Austenitisierungstemperatur ist oder bis 100 K unter dieser liegt,
• – Aufrechterhalten dieser Stabilisierungstemperatur für 10 bis 30 Minuten;
• – Positionieren der verschlossenen Öffnung des Einsatzbehälters unmittelbar an der Wasseroberfläche eines Abschreckbades;
• – Abschrecken der zu härtenden Teile durch Öffnen und Entleeren des Einsatzbehälters in das Abschreckbad, wobei die Teile mit den Schalelementen in das Abschreckbad fallen.

This object is achieved by the method according to the invention, which comprises the following steps:

• - Encasing the parts with lattice or gauze-shaped formwork elements made of largely inert material with numerous lattice meshes, a distance of 0.5 to 3 mm being left between the formwork elements and the surface sections of the parts to be hardened;
• - Embedding the coated parts in a coal mixture granulate made of charcoal and animal coal (bone coal) in a largely airtight sealed container, the coal mixture granules also being introduced into the distance between the formwork elements and the surface sections of the parts to be hardened;
• - uniform heating of the filled insert container to a target temperature above the austenitizing temperature;
• - Maintaining the target temperature for a predetermined austenitization time, which is determined depending on the mass and the ferrometallic material of the parts to be hardened;
• Rapid cooling of the insert container to a stabilization temperature which is equal to the austenitizing temperature or is up to 100 K below this,
• Maintaining this stabilization temperature for 10 to 30 minutes;
• - Positioning the closed opening of the insert container directly on the water surface of a quench bath;
• - Quenching the parts to be hardened by opening and emptying the insert container into the quenching bath, the parts with the formwork elements falling into the quenching bath.

It has been shown that when the aforementioned Process steps understandable results in colored hardening can be. Uniform surface decorations and sufficient degrees of hardness for the ferrometallic parts.

The use of grid-shaped formwork elements, which the ones to be hardened Wrapping parts with the result that at the moment the insert container is emptied into the quench bath holds the coal mixture particles long enough to be hardened Adhere parts to the desired chemical reactions in the quench bath trigger, which cause the desired coloring. It is also advantageous by positioning the opening of the insert container immediately on the water surface of the quench bath to keep the period in which the ones to be hardened Parts of the atmosphere are exposed. Since the insert container during the heating of the Parts are essentially airtight and the coal granulate an inert atmosphere inside the insert container generated, can the parts despite increased Temperature does not react with oxygen, which is essential for the hardening process. Otherwise, an exclusive color reaction with the This enables oxygen in the quenching water and prevents scaling.

Especially when using Parts with a low carbon content in the iron material it is advantageous to harden the Parts before the actual color hardening undergo a carburizing process in which the parts in one Aufkohlungsbehälter be surrounded with carburizing granules and to a carburizing temperature from 900 ° C up to 960 ° C heated and subsequently cooled slowly become. Close to that the above Process steps to carry out the color hardening. This enables particularly high degrees of hardness and carburization depths achieve that with the materials mentioned only when executing the colorful cure not possible would. In modified embodiments can the carburizing steps also directly into the colored hardness process to get integrated.

It is particularly beneficial if the formwork elements are formed by a stainless steel gauze, whereby the mesh has an opening diameter should have from about 1 mm to 3 mm. The ones to be hardened Parts are wrapped in the stainless steel mesh, too here the distance between the formwork element and those to be hardened Sharing is maintained. The stainless steel mesh usually shows sufficient inherent stability on to ensure this distance if it is loose around the parts is placed. At higher Accuracy requirements can but also spacer elements can be used that have a defined Ensure clearance between the gauze and the surfaces of the parts. It can but also winding devices are used, for example through suitable forms the automated wrapping of the parts and maintaining the necessary Ensure distance for example, by directly introducing a predetermined one Coal granulate layer thickness between formwork element and iron part. ever after used carbon granulate (granulate size) it is possible without further ado the individual carbon grains through the wrapping of the parts with the stainless steel net let the net mesh trickle to the distance between formwork element and partial surface fill sufficiently with the coal mixture. The coal mixture can but also during of the wrapping process be introduced.

According to a preferred embodiment, the insert container is made entirely of stainless steel. This material is particularly suitable because Even at the required austenitizing temperatures, there is no significant outgassing of material or oxidation reactions that would impair the process. In modified embodiments, other materials could also be used. For example, ceramic containers would be suitable. The same criteria apply to the material selection for the formwork elements, with flexible formwork elements being particularly suitable for adapting to different shapes of parts to be hardened. However, if there are constant shapes at larger parts numbers, the formwork elements can also consist of harder materials with an adapted shape. For example, it would be conceivable to produce special sleeves made of ceramic materials or stainless steel, which also have numerous meshes or holes and are adapted to the special shape of the parts to be hardened. Particularly good results in terms of both hardening and surface design are achieved if the coal mixture has a mixing ratio of bone coal to charcoal such as 40:60 based on the mass fraction.

Preferably the water in the quench bath in which the parts are quenched prior to quenching 8 ° C to 10 ° C tempered and enriched with oxygen. Technical oxygen is preferred finely divided into the quenching bath until there is a Oxygenation of about 150-200 comes. Through the crowd of the fed It is also oxygen possible, the resulting colors on the surface of the to be hardened Affect parts. When about 5-10 liters of oxygen per minute are introduced into a volume of water of about 70 liters, adjusts itself a few minutes, an oxygen concentration that, above all the formation of brown tones on the surfaces which results in parts. If the oxygen supply is the same Framework conditions on 10-30 Increased 1 per minute, mainly blue and violet colors are achieved. The one for achieving the desired one Color reaction in percent oxygen content refers on the oxygen content of the quenching water without enrichment, which corresponds to 100% oxygen content.

To achieve uniform colors it is advantageous to harden the Parts before color hardening polish or treat with glass bead blasting (grain size 0 - 50 μm) and degrease carefully. Can be used as a polishing agent Polishing discs are used. Good degreasing results are achieved if the parts are treated in an ultrasonic bath with acetone, isopropanol or soda solution become.

To hardness tensions of the treated Parts and damage to avoid the surface layers causing the coloring, it is particularly convenient to hardened Dry parts after quenching at about 150 ° C and then with to be provided with a transparent lacquer layer which at the same time Color brilliance increases. While the drying process at the temperature mentioned occurs at the same time to a certain structural normalization and thus to relax the materials. The protective layer can for example, consist of a transparent, scratch-resistant thermal lacquer.

The heat treatment of the to be hardened Divide in one if possible evenly heated Oven, in particular electrically heated convection ovens advantageous are. Moreover it is appropriate to Oven before loading the filled one setter already at a temperature of about 50-100 K below the austenitizing temperature preheat. Further advantages, details and further developments result from the following description of a preferred embodiment of the method according to the invention, with reference to the drawing.

The only figure shows a schedule a preferred embodiment a method of surface decoration and for hardening of ferrometallic parts.

Before the start of the actual colouration process pretreatment of the items to be hardened is normally carried out Parts in step 1. For this purpose, the parts are polished to a high gloss and / or glass bead blasted, there a later one mechanical surface treatment not possible anymore is. Otherwise, would the applied layers of paint are destroyed. They also have to Share carefully be degreased. You can do this for example in an ultrasonic bath with acetone, isopropanol or 10% soda solution degreased and aftertreated with distilled (deionized) water become. Satisfactory results are achieved when the ultrasonic bath to about 60 ° C up to 80 ° C heated and the degreasing is carried out for about 15 to 20 minutes. After degreasing the parts are dried, for example in a forced air oven at temperatures of around 30 ° C up to 60 ° C.

In step 2, formwork elements are attached to the parts to be hardened, which are later to hold the carbon granulate for a certain time on the surface of the parts for chemical reactions. At the same time, they must not significantly delay the ingress of water as a quenching medium. The formwork elements are arranged on the parts in such a way that the individual areas of the parts cool down as evenly and quickly as possible during the quenching process in order to avoid the occurrence of so-called soft spots caused by the Leidenfrost phenomenon. To do this, the quenching water must be led to the surface of the parts quickly and evenly. At the same time, the formwork elements must ensure sufficient adhesion of the carbon granulate so that the metal oxide layers can be formed, which are responsible for the coloring. Different aids are possible as formwork elements, for example perforated sheets made of stainless steel, which have holes with a diameter of 1 mm to 3 mm. Such perforated sheets are particularly suitable for attachment to parts to be hardened with regular, visible outer surfaces. If parts that have relatively irregular shapes are to be treated, for example weapon parts to be hardened, it is often more expedient to use stainless steel mesh or stainless steel gauze as formwork elements. Such fabrics are flexible and can be easily adapted to any shape. In all cases, care must be taken to ensure that the formwork elements are spaced from the surface of the parts, at least in the areas to be hardened, in order to insert at least a thin layer of carbon granulate between the formwork elements and the surface of the parts and to avoid washing off due to bubbles during the quenching process ,

In step 3 below the ones to be hardened Parts in the insert container arranged. It is advantageous to use a cylindrical stainless steel container setter to be used, since this guarantees heat transfer well and the cylindrical shape, on the other hand, ensures uniform heating on all sides filled Allows parts. The parts are essentially arranged centrally in the container and must be on all sides be surrounded by the coal mixture, which consists of charcoal and animal Coal exists. It is particularly useful the use of a coal mixture of bone coal and charcoal, at a mixing ratio of 40:60 percent by weight and a grain size of the coal granulate of 0.1 mm to 2 mm. The coal granulate is slightly compacted, especially around ensure that there is sufficient coal granule between the formwork element and the surface the one to be hardened Parts arrived. The granulate layer surrounding each part should at least have a thickness of 20 mm to 40 mm in order to be sufficient during the hardening process Carburization in the surface layers to achieve and thereby ensure a reducing environment. The densified layers of coal can supply oxygen prevent effectively. Moreover is caused by the sufficiently thick layers of coal granules an undesirable excessive heating of the surface areas the one to be hardened Parts avoided.

To evenly deter individuals later To allow sections of the parts the parts should preferably be arranged in the insert container in such a way that the temperature differences that occur when the hot part enters do not generate excessive material stress in the quench bath, which could lead to delays. In particular larger parts are therefore in the insert container positioned that with the section of the larger cross section first in immerse the quench bath.

After complete assembly, the stainless steel container is also with a stainless steel lid is closed to during the subsequent heat treatment largely exclude the ingress of oxygen into the container and a higher one Partial pressure inside the tank to achieve.

In step 4, the parts are up to warmed to reach a target temperature. The target temperature corresponds at least the material-specific austenitizing temperature and is usually above 720 ° C.

In step 5 below, the heat treatment or austenitizing takes place. As is known, the conversion of ferrite into the so-called austenite (γ-iron) takes place above approximately 720 ° C. (AC ₁ ). Depending on the mass and the desired carburization depth of the parts to be hardened, this temperature is maintained for about 20-60 minutes.

The peculiarity of colored hardening is that that partial austenitizing and carburizing in one heat treatment have to be done to the components as possible to be able to deter without warping. When carburizing depths are required (greater than 0.05 mm) and higher hardness values (greater than 400 HV1), separate carburizing must be carried out beforehand. Done in step 6 a cooling of the Parts to a stabilizing temperature that is equal to the austenitizing temperature or can be up to 100 K lower. On the one hand, the stabilization temperature so chosen be that a complete reconversion austenite is avoided. On the other hand, the delay in hardness, that occurs when quenching, if possible be kept small, which can be achieved by a lower starting temperature is. The stabilization temperature is maintained for about 10 to 30 minutes again dependent the mass and the material of the parts to be hardened. Because the reverse conversion of austenite takes place especially during slow cooling processes cooling down from the target temperature to the stabilization temperature if possible done quickly. For example, this can be done by opening the Oven reached.

In step 7, the treated parts are then quenched in a quenching bath. The desired colors on the surface are created during this quenching process. This creates metal oxide layers, which cause interference effects of the light on the polished component surface, which become visible as color gradients with a marble-like structure due to different layer thicknesses. When quenching, it must be avoided that the parts come into contact with atmospheric oxygen, which would result in immediate surface oxidation (scaling). For this purpose, the insert container with its opening immediately above the water surface of the quench bath. The opening of the insert container is then released by removing the lid, so that the parts contained in the insert container, the formwork elements attached to them and the carbon granulate fall into the quenching bath without delay. In the quenching bath, the desired chemical reactions that form the metal oxide layers occur on the surface of the hot parts. In order to achieve the special color effects, the carbon granulate must be held on the surface of the parts at least during the first cooling period before being washed off, which is ensured by the formwork elements.

To achieve particularly good (multi-colored) color effects achieve, it is advantageous to use the water of the quench bath Enrich oxygen before quenching parts. Good results are achieved when about 10-30 liters per minute in a quench bath with a water volume of 60 - 80 1 can be initiated via a period of about 3 minutes. For better oxygen distribution in the quench water So-called bubble stones are used, which in the oxygen Introduce small gas bubbles into the water. That way an oxygen enrichment of about 180 ° can be achieved. This oxygen content stays for largely constant for a few minutes during which the quenching process execute is. The quench bath is preferably at a temperature of 8-10 ° C.

In step 8, post-treatment can be carried out the hardened Parts done. The parts are immediately after the quenching process removed from the quench bath. The formwork elements can then be removed. The parts are then preferably in a convection oven at about 150 ° C over 2 to Dried and relaxed for 3 hours. A special color brilliance of the surface layers can reach if a transparent lacquer layer (e.g. zapon lacquer, thermal lacquer) is applied. Moreover is an improved corrosion protection and increased abrasion resistance of the metal oxide layers formed.

The method shown can be used modified embodiments be changed in detail, if this is necessary due to the properties of the parts to be treated is.

Claims (15)

Process for the surface decoration and surface hardening of ferrometallic parts, in which the parts to be hardened are heated in a carbon-releasing, calcium-phosphate-containing, low-oxygen medium at least to the austenitizing temperature and then quenched in water, characterized in that the following process steps are carried out: 2 ) the parts with lattice-shaped formwork elements made of largely inert material with numerous lattice meshes, a distance of 0.5 to 3 mm being left between the formwork elements and the surface sections of the parts to be hardened; - embed ( 3 ) the coated parts in a coal mixture granulate made of charcoal and animal coal in a largely airtight sealed insert container, the coal mixture granulate also being introduced into the distance between the formwork elements and the surface sections of the parts to be hardened; - even heating ( 4 ) the filled insert container to a target temperature above the austenitizing temperature; - maintain ( 5 ) the target temperature for a given austenitization time, which is determined depending on the mass and the desired carburization depth of the parts to be hardened; - rapid cooling ( 6 ) of the insert container to a stabilization temperature which is equal to the austenitization temperature or is up to 100 K below this; Maintaining this stabilization temperature for 10 to 30 minutes; - Positioning the closed opening of the insert container directly on the water surface of a quench bath; - Scare off ( 7 ) the parts to be hardened by opening and emptying the insert container into the quenching bath, the parts with the formwork elements and the carbon mixture granulate falling into the quenching bath. A method according to claim 1, characterized in that the to be hardened Parts before wrapping with the formwork elements in a carburizing container with carburizing granules to a carburizing temperature of 900 ° C to 960 ° C for a carburizing time of Warmed for 60 to 120 minutes and subsequently cooled slowly become. A method according to claim 1 or 2, characterized in that the formwork elements by a stainless steel gauze with a mesh size of 1 to 3 mm are formed, which is wrapped around the parts to be hardened. A method according to claim 1 or 2, characterized in that the formwork elements are made of perforated stainless steel plates, their holes have a diameter of 1-3 mm and the spacers on the to be hardened Parts are attached. A method according to claim 1 or 2, characterized in that the formwork elements are made of ceramic and match the shape of the one to be hardened Parts are adjusted. Method according to one of claims 1 to 5, characterized in that the parts are embedded in a completely stainless steel insert container. Method according to one of claims 1 to 6, characterized in that that the coal mixture granulate consists of bone coal and charcoal with a mixing ratio of 40:60 percent by mass and a grain size of 0.5-2 mm. Method according to one of claims 1 to 7, characterized in that that the target temperature for 20–60 minutes is maintained. Method according to one of claims 1 to 8, characterized in that that the quench bath is at a temperature of before the parts are quenched 8 ° C to Cooled to 10 ° C and is enriched with oxygen. A method according to claim 9, characterized in that 10–30 liters of oxygen per minute in 70 liters of water as a quenching medium finely divided until an oxygen concentration of 150-180 is reached. Method according to one of claims 1 to 10, characterized in that that the parts to be hardened before colored hardening polished and / or glass bead blasted and degreased. become. A method according to claim 11, characterized in that with Acetone, isopropanol or soda solution degreased in an ultrasonic bath. Method according to one of claims 1 to 12, characterized in that that the hardened parts dried at 150-180 ° C after quenching and be relaxed and then with a transparent Corrosion protection layer covered become. Method according to one of claims 1 to 13, characterized in that that the warming of the to be hardened Parts in an evenly heated Oven takes place before opening the insert container filled with the parts a temperature of 50-100 K is preheated below the austenitizing temperature. Method according to one of claims 1 to 14, characterized in that that the insert container before emptying with its opening 1–5 cm above the water surface the quench bath is positioned.