NO309045B1 - Corrosion-resistant alloy and method for producing corrosion-resistant materials for cutting devices - Google Patents

Abstract

Corrosion-resistant alloy having a hardness of more than 54 HRC consists of (in wt.%):0.40-0.85 C, up to 1.0 Si,, up to 1.4Mn, 16.0-19.0 G, 0.8-1.5 Mo, 0.05-0.2 V, up to 0.18 Ti, 0.12-0.29 N, with the proviso that Ni max is 0.25, Co max. is 0.20, Cu max is 0.25, and Ni + Co + Cu, max is 0.48. The sum of the concn. of C and N is 0.61-0.95. Also claimed is the mfr. of a corrosion-resistant cutting tool.

Description

The present invention relates to a corrosion-resistant alloy according to the preamble to claim 1. Furthermore, the invention relates to a method for producing cutting materials with high hardness and high bending strength according to the preamble to claim 4.

Within the food and beverage industry, corrosion-resistant alloys are required, especially for cutting materials, which must resist chemical attacks particularly well and must not cause any changes in taste or shorten the shelf life of food products and the like. For medical instruments as well, the highest possible corrosion resistance and good polishing ability of the material used for the purpose is required. In both types of application, a high material toughness is also required as well as hardness and good sharpening without burrs, whereby, however, no particularly high demands are placed on the wear resistance of the material.

Non-rusting steel, i.e. iron base alloys with a Cr content of approx. 13$, for example DIN material No. 1.4110, is successfully used for cutting devices. However, because the corrosion resistance of such materials, especially in chlorine-containing environments, is not always sufficient, alloys with approx. 18$ Cr content for use, for example material No. 1.4112, which due to a higher Cr concentration shows an increased resistance to chemical attack. Alloys with approx. However, 18$ Cr and over 0.85$ C have the disadvantage that in the case of coarse carbide precipitations, albeit with increased wear resistance and hardness for the material, the bending strength and polishability may be impaired. Attempts have already been made to use a steel with approx. 15$ Cr as well as 0.3$ C alloyed with 0.3$ N as materials for cutting devices. In the production of these steels, however, on the one hand, expensive pressure melting methods must be used, which entails financial disadvantages, on the other hand, the corrosion resistance and grindability as well as the bending strength of the material cannot always provide sufficiently good values.

It has also been found that, despite the high Cr contents of corrosion-resistant alloys and the passive layer formed thereby on the surface of the parts, allergic reactions can possibly be induced by contact with too high a concentration of Ni and/or Co and/or Cu with the skin of living beings.

The task of the invention is now to provide a particularly corrosion-resistant, as well as acceptable for skin contact alloy with high hardness, good polishing ability and particularly high flexural toughness with high fracture resistance, which can also be used in chlorine-containing media. Furthermore, the invention aims to provide a method for the production of corrosion-resistant cutting materials for the food industry and for medical instruments, with which the disadvantages according to the state of the art can be overcome.

The task is solved by a material according to the characteristic features of claim 1. Advantageous embodiments are specified in the subclaims.

The further objectives are solved by a method of the initially mentioned type with the characteristic features in claim 4, whereby further embodiments are specified in the subclaims.

The advantages achieved with the invention consist in particular in that the composition of the alloy is ensured by a low total carbide proportion of low carbide grain size as well as a high matrix hardness and thereby a good machinability and polishability and especially a good bending strength. Thereby, it is important that in the concentration limits the sum of the contents of carbon and nitrogen lies within a specific range. It was surprisingly found that with a steel with a chromium content of approx. 17.5$, the chromium concentration in the matrix is increased by adding nitrogen and thus the corrosion resistance can be improved, whereby the carbon concentration can be reduced without having to accept reduced hardness. The reasons for this are still not completely scientifically clear, however, it is assumed by the inventors that at a nitrogen content of greater than 0.1, especially greater than 0.12, fine nitrides and/or carbonitrides are formed, preferably of the elements from groups IV and V in the periodic table, for example vanadium, which causes a significant reduction of the carbide grain size. In the case of a fine grain structure with the hardness-increasing elements carbon and nitrogen in combination, the matrix hardness and matrix toughness are increased as well as their Cr concentration and the formation of coarse, sharp-edged carbides is avoided.

If, however, a higher nitrogen content is set than approx. 0.29 wt-# in the alloy, coarse, needle-shaped nitrides can occur and a transformation of austenite into martensite is prevented, which has a very unfavorable effect on the application properties of the material. The highest corrosion resistance at the best material properties was found in the range of the above nitrogen contents at carbon concentrations between 0.4 and 0.85 wt-#, when the sum of carbon and nitrogen contents is in the range from 0.61 to 0.95.

In a method for the production of corrosion-resistant cutlery, the advantages achieved by the invention are essentially that the alloys can be produced economically and by heat treatment of the knife and instruments produced therefrom, the best performance properties for the parts are achieved. It is therefore important that the alloying technical prerequisites are met and that a homogeneous annealing structure is produced by a solution annealing treatment. Also of particular importance is a soft annealing of the material around the Å3 point for the alloy before austenitizing, in order to equalize with increased intensity the precipitation and transformation kinetics during subsequent cooling. A subsequent tempering treatment is carried out at a relatively low temperature and serves in particular to relax the material.

In order to achieve uniform heat removal from the surface of the parts by intensified cooling from the austenitizing temperature and to avoid a thermally conditioned deformation of the material due to inhomogeneous stresses, it may be advantageous for the cooling to take place between two stabilizing plates. This cooling or "Quetten" method has proven particularly beneficial for the production of knives with a large surface area and a complicated cutting shape.

In a further preferred embodiment of the method, after hardening, at least one cooling treatment of the material is carried out, in order to also convert any portion of residual austenite remaining in the structure into martensite.

In clinical investigations, it has been established that at a content of less than 0.25 wt-# Ni, less than 0.20 wt-# Co and less than 0.25 wt-# Cu, especially at a total content of Ni+Co+Cu of below 0.48$ in the alloy, practically no allergic reactions occur on the skin of living beings, whereby, however, in the case of particular sensitivity somewhat lower concentrations of the above-mentioned elements completely exclude hypersensitivity reactions.

The invention is explained in more detail with the help of some examples from the experimental series.

Here is indicated

table 1 is a listing of the experimental materials and table 2 is a compilation of the performance characteristics of the cutting products produced from the materials using different heat treatment parameters.

Claims (8)

1. Corrosion-resistant alloy suitable as cutting parts with a hardness greater than 54 HRC, good polishing ability and high flexural strength containing essentially the elements carbon, silicon, manganese, chromium, molybdenum, vanadium, nitrogen as well as iron and manufacturing-related impurities, characterized by a proportion by weight # on under the assumption that the contents of Nine maximums add up to 0.25 Co maximum amounts to 0.20 Cu maximum amounts to 0.25 Ni + Co + Cu maximum amounts to 0.48 and the sum of the concentrations of carbon and nitrogen gives a value of at least 0.61 and at most 0.95. 2. Alloy according to claim 1, characterized in that the contents in weight # constitute Nine maximum 0.15 Cu maximum 0.15 Ni + Co + Cu maximum 0.24. 3. Alloy according to one of claims 1 or 2, characterized in that the sum of the concentration of carbon and nitrogen gives a value of at least 0.66 and at most 0.84. 4. Process for the production of corrosion-resistant cutting parts with a hardness of 54 to 61 HRC and high flexural toughness, especially for the food industry and for medical instruments from an alloy containing essentially the elements carbon, silicon, manganese, chromium, molybdenum, vanadium, nitrogen and iron and production-related pollutants, characterized by the fact that an alloy is produced with proportions in weight # of under the assumption that the contents of Nine maximums add up to 0.25 Co maximum amounts to 0.20 Cu maximum amounts to 0.25 Ni + Co + Cu maximum amounts to 0.48 and the sum of the concentrations of carbon and nitrogen gives a value of at least 0.61 and at most 0.95, and the material is preferably subjected to a deformation, at least a solution annealing treatment at a temperature higher than 1065°C, after which it is produced from the alloy the part or the tool, in particular the cutting material in the raw state, is soft annealed in the region of the A3 point of the alloy, preferably at a temperature between 800 and 880°C, then cooled at low intensity, heated again and austenitized in a temperature range from 940 to 1060°C and then cooled with increased intensity, after which at least one tempering treatment is carried out at a temperature between 165 and 385°C and a finishing treatment of the cutting part is carried out. 5. Method according to claim 4, characterized in that the alloy is produced with a Ni content by weight of a maximum of 0.15 Cu maximum 0.15 Ni + Co + Cu maximum 0.24 and/or a total value for the concentration of C+N of 0.66 to 0.84. 6. Method according to one of claims 4 or 5, characterized in that the cooling of the parts is carried out with increased intensity in the "Quetten" method, optionally with water, preferably with compressed air, especially with oil. 7. Method According to one of claims 4 to 6, characterized in that the austenitizing of the parts is carried out in a temperature range between 960 and 1050°C, preferably at 980 to 1030°C. 8. Method according to one of claims 4 to 7, characterized in that after the cooling with increased intensity of the austenitizing temperature, the part is subjected to a deep-freeze treatment at a temperature below minus 55°C, preferably below minus 70°C.