EP0694622B1 - Corrosion resistant alloy and method for making corrosion resistant cutting tools - 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 invention relates to a corrosion-resistant alloy. Furthermore, the invention relates to a method for Production of cutlery with high hardness and great flexural strength.

In the food and luxury food industry are becoming corrosion-resistant Alloys, especially for cutlery, which chemical Resist attacks particularly well and none at all Changes in taste and shortening the shelf life of food and Like. May effect. It is also the highest possible for medical instruments Corrosion resistance and good polishability of the used Required. With both types of use there is also a high Material toughness as well as hardness and burr-free good sharpenability are required, whereby however, no particularly high demands on the wear resistance of the Material.

Stainless steels, i.e. iron-based alloys with a Cr content of around 13%, e.g. DIN material no. 1.4110, are used successfully for cutlery used. However, because the corrosion resistance of such materials, especially in an environment containing chlorine ions, is not always sufficient, alloys with approx. 18% Cr content, e.g. Material No. 1.4112 for Use which increased due to a higher Cr concentration Resistant to chemical attack. Alloys with approx. 18% Cr and However, above 0.85% C have the disadvantage that, in particular, through coarse Carbide deposits, although with increased wear resistance and hardness of the Material, the bending toughness and the polishability can be reduced. An attempt has already been made to use a steel with approx. 15% Cr and 0.3% C, which with 0.3% N is alloyed to be used as the material for the cutlery. When generating this However, steels have to be used on the one hand, expensive pressure melting processes, what brings economic disadvantages, on the other hand, the corrosion resistance and grindability and the flexural toughness of the material are not always deliver sufficiently good values.

DE-C-3 901 470 relates to a corrosion-resistant, high-strength martensitic cold work steel. JP-A-2-166 228 relates to a high-carbon stainless steel with excellent quenching hardness, wear resistance and corrosion resistance.

It was also found that despite the high Cr contents of corrosion-resistant alloys and therefore on the surface of the parts formed passive layer of these, if necessary, by a too high Concentration of Ni and / or Co and / or Cu on contact with the skin of Living things can cause allergic reactions.

The object of the invention is now to provide a particularly corrosion-resistant alloy which is compatible with skin contact and which has high hardness, good polishability and, in particular, high flexural strength with high fracture resistance, which can also be used in media containing chlorine ions.
The invention further aims to provide a method for producing corrosion-resistant cutlery for the food industry and for medical instruments, with which the disadvantages of the known cut parts are eliminated.

The task is carried out with a corrosion-resistant alloy Claim 1 solved. Advantageous configurations are specified in the subclaims.

The other goals are with a procedure solved according to claim 4, wherein their further developments are specified in the subclaims.

The advantages achieved by the invention are in particular that the Composition of the alloy with a low total carbide content low Carbide grain sizes as well as a high matrix hardness and therefore a good grinding and This ensures polishability and, in particular, good bending toughness important that in the concentration limits the sum of the contents of carbon and nitrogen are in a certain range. It was surprising found that the steel with a chromium content of about 17.5% Chromium concentration in the matrix increased by alloying with nitrogen and thus the corrosion resistance can be improved, without The carbon concentration can be reduced. The reasons for this have not yet been scientifically clarified, but it is by the Inventors assumed that with a nitrogen content of at least 0, 12, fine nitrides and / or carbonitrides, preferably the Elements of the IV and V group of the periodic system, e.g. Vanadium, be formed, which is a substantial reduction in carbide grain size cause. Through a fine grain structure with the hardest elements Carbon and nitrogen in combination are both the matrix hardness and Matrix toughness and their Cr concentration increased and a formation of avoided rough sharp-edged carbides.

However, if the nitrogen content is higher than 0.29% by weight in the alloy set, coarse acicular nitrides can arise and a conversion of the Austenites in martensite are hindered, which is extremely detrimental to the Usage properties of the material affects. The highest Corrosion resistance with the best material properties was in the area of Nitrogen contents above at carbon concentrations between 0.4 and 0.85 % By weight if the sum of carbon and nitrogen content in the Range is from 0.61 to 0.95.

In a process for producing corrosion-resistant cutlery, the Advantages achieved by the invention can be seen essentially in the fact that alloys can be produced economically and by heat treatment The knives and instruments made from it have the best usage properties Parts can be reached. It is important that the alloy engineering Requirements are given and that by solution annealing a homogeneous structure is achieved. It is also of particular importance a soft annealing of the material around the A3 point of the alloy in front of you Austenitize to the excretion and transformation kinetics in subsequent cooling with increased intensity. A subsequent tempering treatment is carried out at a comparatively low temperature carried out and serves in particular to relax the material.

To ensure even heat dissipation from the surface of the parts when intensified cooling to reach the austenitizing temperature and a thermal distortion of the material due to inhomogeneous stresses avoid it can be beneficial if a cool down between two stabilizing plates. This cooling or squeezing process has proven to be particularly cheap for the production of large-area knives with complicated Cutting edge shape highlighted.

According to a further preferred embodiment of the method, after Hardened at least one freeze treatment of the material any remaining austenite in the structure also in Convert martensite.

Clinical investigations have shown that a content of less than 0.25% by weight of Ni, below 0.20% by weight of Co and below 0.25% by weight of Cu, in particular with a total content of Ni + Co + Cu of less than 0.48% by weight of the alloy practically no allergic skin reactions of living things occur, whereby however, with special sensitivity somewhat lower concentrations above Exclude elements of hypersensitivity reactions completely.

Tabelle 1 eine Auflistung von Versuchswerkstoffen und

Tabelle 2 eine Zusammenstellung der Gebrauchseigenschaften der aus den Werkstoffen gefertigten Schneidwaren bei Anwendung unterschiedlicher Wärmebehandlungsparameter.

The invention will be explained in more detail with the aid of a few examples from the test series.
Show it

Table 1 a list of test materials and

Table 2 shows a summary of the performance characteristics of the cutlery made from the materials when using different heat treatment parameters.

Claims (8)

1. A corrosion-resistant alloy, tolerated by the skin on contact, with a hardness of more than 54 HRC, good polishability and a high level of toughness, comprising the following elements in wt.%:

   C = 0.40 to 0.85

   Si = up to 1.0

   Mn = up to 1.4

   Cr = 16.0 to 19.0

   Mo = 0.8 to 1.5

   V = 0.05 to 0.2

   Nb = up to 0.15

   Ti = up to 0.18

   N = 0.12 to 0.29

   remainder iron and production-related impurities,
   with the proviso that

   Ni = at most 0.25

   Co = at most 0.20

   Cu = at most 0.25

   Ni + Co + Cu = at most 0.48

   and the sum of the concentrations of carbon and nitrogen gives a value of at least 0.61, but at most 0.95.
2. An alloy according to claim 1, characterised by the following contents in wt.%:

   Ni = at most 0.15

   Cu = at most 0.15

   Ni + Co + Cu = at most 0.24.
3. An alloy according to either one of claims 1 and 2, characterised in that the sum of the concentrations of carbon and nitrogen gives a value of at least 0.66 and at most 0.84.
4. A method of manufacturing corrosion-resistant cutting implements, tolerated by the skin on contact, with a hardness of 54 to 61 HRC and a high level of toughness, in particular for the food industry and for medical instruments, from an alloy comprising the following elements in wt.%:

   C = 0.40 to 0.84

   Si = up to 1.0

   Mn = up to 1.4

   Cr = 16.0 to 19.0

   Mo = 0.8 to 1.5

   V = 0.05 to 0.2

   Nb = up to 0.15

   Ti = up to 0.18

   N = 0.12 to 0.29

   remainder iron and production-related impurities,
   with the proviso that

   Ni = at most 0.25

   Co = at most 0.20

   Cu = at most 0.25

   Ni + Co + Cu = at most 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, preferably during deformation, undergoes at least one solution heat treatment at a temperature of more than 1065°C, after which the part or workpiece formed from the alloy, in particular the cutting implement in the crude state, is soft-annealed in the region of the A3 point of the alloy, preferably at a temperature between 800°C and 880°C, then cooled with low intensity, subsequently reheated and, in a temperature range from 940°C to 1060°C, austenitised and then cooled with higher intensity, followed by at least one tempering treatment at a temperature between 165°C and 385°C and by finishing of the cutting implement.
5. A method according to claim 4, characterised in that the alloy is produced with the following contents in wt.%:

   Ni = at most 0.15

   Cu = at most 0.15

   Ni + Co + Cu = at most 0.24

   and/or a total value of the concentrations of C+N of 0.66 to 0.84.
6. A method according to either one of claims 4 and 5, characterised in that the cooling of the parts with higher intensity is carried out by a chilling method, optionally with water, preferably with compressed air, in particular with oil.
7. A method according to any one of claims 4 to 6, characterised in that the austenitisation of the parts is carried out in a temperature range between 960°C and 1050°C, preferably from 980°C to 1030°C.
8. A method according to any one of claims 4 to 7, characterised in that, after cooling with higher intensity from the austenitisation temperature, the part undergoes deep-cooling treatment at a temperature of below -55°C, preferably below -70°C.