KR20070017983A - Steel alloy for cutting details - Google Patents

Abstract

The present invention has the following composition (wt%), C 0.40 to 0.60, Si 0.1 to 1.0, Mn 0.3 to 1.0, Cr 12 to 15, Mo 2.5 to 4.0, Ni 0 to 1.0, Co 0 to 4.0, N 0.15 -0.20, the balance is composed of not only Fe but also commonly occurring impurities, and it has a hardness exceeding 56 HRC without deep cooling, as well as PRE exceeding 25 defined as PRE =% Cr + 3.3 ·% Mo + 16 ·% N It's about the steel alloys you get. In addition, the steel alloy includes carbides, nitrides and / or carbonitrides whose maximum diameter does not exceed 5 μm. This steel alloy has surprisingly been found to be very suitable as a cutting material for many cutting operations.

Description

Steel Alloys for Fine Cutting {STEEL ALLOY FOR CUTTING DETAILS}

The present invention relates to a steel alloy for fine cutting, among other requirements, a great demand for corrosion resistance and hardness.

The fine part of the material must be able to be made by photo etching, and in order to meet these requirements, a very special combination of properties is required according to the discussion below.

Hardness is very important when first studying the requirements for materials suitable for cutting tools. Higher hardness materials are more resistant to plastic deformation, which is the general erosion mechanism of the cutting edge, and these materials can easily bend or deflect under stress. In addition, materials with higher hardness are more resistant to abrasion and therefore the blade will remain sharp longer, or in other words, have better blade durability. An additional advantage of harder materials is that the generally visible reduction in toughness provides improved burr breaking in mechanical grinding and polishing, so sharp edges can be obtained. For blades with demand for blade durability and the possibility of mechanical sharpening, the minimum value of the hardness of the material is 56 HRC (hardness at Rockwell C-scale. This is approximately 615 HV 1 Kg measured at Buckers hardness at 1 kg load). Corresponds to).

A factor that more strongly affects the blade durability of the material is the presence of hard particles of the material (carbide, nitride, carbonitride, hereinafter referred to as carbonitride). Increasing volume fraction of carbonitride provides a material with better edge durability. However, there are limitations to consider the possibility of remaking really sharp edges by machining or photoetching. In the mechanical processing of blades with small blade angles (<30 °), experiments have shown that carbonitrides larger than 10 μm in diameter (also applied to slag and inclusions) cause abrasion, blade damage, and rapid fading of the inherent sharpness. Shows that In the manufacture of blades by etching, the demand is increasing. In photoetching suitable for the production of composite microparts of thin materials, the material surface portion is protected by a protective film. In unprotected areas, etching media sprayed onto the surface (eg HCl and FeCl) ₃ ) is made by a chemical process. Due to the different electrochemical properties of the bulk body and the carbonitride, the etching will be accelerated at the boundary between the bulk body and the carbonitride. This involves the risk that carbonitrides are etched out of the material. In order to ensure that this phenomenon does not adversely affect the finished product, carbonitrides larger than 5 μm in diameter should be avoided in the material. A common cause of large carbonitrides is the alloying of very powerful carbon precursors, for example vanadium, so it is desirable to avoid this type of alloying element. Another cause of large carbonitrides is inadequate process control when casting and thermally processing materials. Large (Φ> 10 μm) carbonitrides on all angled major carbides formed in the casting also limit the possibility of polishing the material to polish.

At the onset of corrosion in martensitic stainless chromium steel, this corrosion is the most common pitting corrosion type. The three most important alloying elements for controlling this type of corrosion are chromium, molybdenum and nitrogen. Frequently used anticorrosion methods are PRE values (anticorrosion equivalents), and PRE =% Cr + 3.3 ·% Mo + 16 ·% N. The experiment shows that the PRE-value according to the above formula should be at least 25 for martensitic chromium steel in order to obtain sufficient corrosion resistance in the environment of chloride ion.

Further requirements for the material in the cost-effective and quality assurance method according to the invention are a continuous process comprising an austenitic, quench furnace and final tempering furnace to convert to martensite (strip width up to 1000 mm). And the width of the strip should be at least 15 μm). In the austenitic system, the carbonitrides of the material dissolve somewhat and the content of alloying elements increases in the matrix. In order for this dissolution to be even (enable for good dimensional tolerances) and to occur within a short time (high productivity), the size distribution is controlled by a small size (Φ <5 μm) of carbonitride and also by a precisely controlled manufacturing process. And uniformity is required. The manufacturing process for the material involves the melting of the raw material in an electric arc, alternatively in a high frequency furnace. The content of carbon in the material can be controlled by the selection of raw materials or by carbon removal in one of the AOD (Argon Oxygen Decarburization) and Creusot Loire Uddehelom (CLU) or in the refining process. Alternatively, the material can be re-dissolved in a second metallurgical process such as VIM (Vacuum Induction Melting), VAR (Vacuum Arc Remelting), ESR (Electroslag Remelting) have. Casting can be carried out by conventional methods or continuous casting in an ingot. The first strong shrinkage is made in the warm state, after which the material is spheroidized. Cold rolling is then performed in a number of stages including the intermediate annealing process. The material can be delivered to the consumer in cold rolled, annealed or hardened and tempered form. As noted above, stainless martensitic chromium steels have an advantage over austenitic materials for the production of microparts by photochemical processes. These advantages are, among others, that the material after curing has very good flatness and no deformation. The material also has good productivity in this type of processing.

In order to meet the above requirements and to enable simultaneous production of the finished material in the form of a strip in a cost effective manner, very accurate optimization is also required for all alloying elements and process parameters. For a moderate level of production cost, it is required that the material be produced by a normal (unpressurized) metallurgical process. This will substantially limit the content of nitrogen up to 0.20% by weight in a well controlled process. Therefore, the content of nitrogen should be between 0.15 and 0.20 weight%. In the hardened form, the hardness of the material is determined by the weight percent content of the actual phase (carbon + nitrogen), and it is possible to obtain a hardness of 56 HRC or more without deep freezing while sufficiently maintaining the volume fraction of carbide for edge durability. To ensure that the sum of (carbon + salso) is greater than 0.55% by weight, the content of carbide precursors such as chromium and molybdenum must be high. This entails that the content of carbon is generally at least 0.40% by weight and the ratio of carbon to nitrogen must be greater than two. With a relatively high carbon content, the carbon activity should be limited to avoid the formation of primary carbides in the solids, which solids keep the silicon content low, i.e. 0.1 to 1.0% by weight, preferably 0.1 to 0.80 It is provided in weight%, most preferably 0.15 to 0.55 weight%. In curing, the material is austenized at 950-1150 ° C., preferably 1000-1070 ° C., and then quenched to room temperature (suitable for oil between cooling clamps or by compressed air). Temper at about 200 ° C. to achieve hardness in excess of 56 HRC. An additional increase in hardness of about 2 HRC is obtained by quenching to −80 ° C. before tempering.

     Sufficient amount of chromium must be added to the material to form a corrosion resistant oxide film on the material surface, but the high chromium content again increases the risk of forming large primary carbides, which should be avoided. Therefore, the content of chromium should be 12 to 15% by weight, preferably 13 to 15% by weight, most preferably 14 to 15% by weight. Thereafter, a sufficient amount of molybdenum is added to PRE> 25. The appropriate content of Mo is 2.5 to 4.0% by weight, preferably 2.6 to 4.0% by weight, most preferably 2.6 to 3.0% by weight. Due to the high addition of molybdenum and nitrogen, there is a risk that the thermal properties of the material will deteriorate, and in order to limit this risk, other elements with similar effects must be kept at a minimum level-for example, the copper content It should not be more than 0.1 wt%. Nickel and cobalt are expensive alloy materials and are stable in common metallurgical processes, which means that their contents accumulate over time in the production of steel based on recycled steel. For stainless steels, there is a limit on the nickel content of up to 1% by weight for materials not classified as potentially carcinogenic and allergic in accordance with Euro directive 99/45 / EC. And therefore this content is the maximum content of nickel in the alloy according to the patent. Preferably, nickel is not actively added to the material and, in other words, the nickel content is determined to be 0.7% by weight in order to avoid austenite stabilization which may result. The alloy also contains 0.1 to 1.0% by weight, preferably 0.4 to 0.8% by weight, most preferably 0.4 to 0.7% by weight of Mn, with Mn being another element that stabilizes austenite. The maximum content of cobalt is 4% by weight and, on the one hand, due to cost, on the other hand, is intended to avoid the accumulation of cobalt too fast in the treatment of recycled steel, which is dependent on elements that are generally seen as impurities in stainless steel. Belongs to. Preferably, despite the increase in elemental collisions at the martensite formation temperature, cobalt is not actively added to the material and the content of cobalt is at most 0.5% by weight. Therefore, the addition of cobalt may allow more phase transformation to move towards martensite upon cooling after curing.

In view of today's standard materials, it is known that few meet the requirements of HRC> 56 and PRE> 25. In adding the demand for carbides with φ <5 μm, there is no standard that satisfies this requirement. For example, the material of AISI 440 C meets only the hardness requirements. According to the above, in order to satisfy the requirements of the PRE value and the carbide, only the austenitic double material is possible, but hardness and blade durability are inadequate.

According to embodiments of other patent specifications in this field, four things are particularly noted. DE-A-39 01 470, among others, refers to materials suitable for razor blades and knives. However, the patent shows pressurized metallurgy to obtain a nitrogen content of at least 0.20% by weight, so that the carbon content is up to twice the nitrogen. Also mentioned are two experimental alloys with hardness lower than 600 HV. The patent also shows the addition of low content of vanadium. Thus, the material will not meet the above mentioned hardness and avoidance requirements of the alloying element vanadium, and also the production cost will be very high. According to EP-A-638 658, vanadium is used to obtain strong secondary hardening due to high temperature tempering, which can be an advantage if the material is coated or used at high temperatures. However, if the material is etched into the final shape or used to produce a very sharp blade, the opposite is true according to the above. The patent states that, unlike 5 μm, which is mentioned as the maximum limit according to the invention, the maximum allowable size of carbide is 40 μm. EP-A-750 687 describes the maximum content of (carbon + nitrogen) as 0.55% by weight, which is considered to be the minimum content for obtaining sufficient hardness according to the invention. This was confirmed by the fact that the objective of hardness of EP publication was HRC> 50 and that the experimental alloy which reached the highest hardness was 56.3 HRC (this is only after tempering for 1 hour at 180 ° C). This limited hardness, combined with a small portion of residual carbide, results in inadequate blade durability for blade devices with high demands. First of all, the patent specification also focuses on articles which have an extremely high demand for corrosion resistance, because copper is also added, and thus hardness and heat workability have been overlooked. With respect to patent specification US-A-6 235 237, all of which relate to ski river blades with the need for damping, the combination of high chromium with low molybdenum and low nitrogen According to embodiments of the patent specification, blade durability is inadequate for blade devices that provide a hardness lower than 50 HRC, and therefore require high blade durability.

It is a first object of the present invention to provide a new steel alloy that can overcome all the problems of the prior art mentioned above.

In particular, it is an object of the present invention to provide a steel alloy having a hardness of 56 HRC or more, excellent corrosion resistance and which can be machined by photoetching.

In a surprising way to those skilled in the art, the above and further objects are achieved by providing a steel alloy having the following composition (% by weight), with a hardness exceeding 56 HRC without deep cooling, as well as PRE =% Cr + 3.3.% Mo A PRE exceeding 25 specified by + 16% N can be obtained:

C 0.40 to 0.60

Si 0.1 ~ 1.0

Mn 0.3 ~ 1.0

Cr 12-15

Mo 2.5 ~ 4.0

Ni 0 ~ 1.0

Co 0 ~ 4.0

N 0.15-0.20

The balance to 100% consists of iron and impurities which are usually generated by the raw material and / or the manufacturing process. Preferably, the hleo size of carbides, nitrides and carbonitrides is Φ <5 μm, to reduce the risk of blades associated with problems during austenitization and to enable dissolution of carbides, nitrides and carbonitrides.

Preferably, the steel alloy according to the invention has the following composition (% by weight), as well as the balance consisting of Fe and commonly occurring impurities:

C 0.42-0.60

Si 0.15 ~ 0.80

Mn 0.4 ~ 0.8

Cr 13 ~ 15

Mo 2.6 ~ 4.0

Ni 0 ~ 0.7

Co 0 ~ 0.5

N 0.15-0.20

Or more preferably, the steel alloy according to the invention has the following composition (% by weight), as well as the balance consisting of Fe and commonly occurring impurities:

C 0.42-0.50

Si 0.15 ~ 0.55

Mn 0.4 ~ 0.7

Cr 14-15

Mo 2.6 ~ 3.0

Ni 0 ~ 0.7

Co 0 ~ 0.5

N 0.15-0.20

The materials produced according to the present invention are for example used in applications such as knives in the food industry, which have high demands on hardness and blade durability along with corrosion resistance due to the environment containing chloride ions as well as corrosive dishwashing detergents. It is particularly suitable for use. Other areas are dry knives as well as dry / wet shaving and surgical cutting edges. Further areas of application of the new material are, for example, doctor blades in the paper industry (known as coater blades) and creping blades as well as doctor blades in the printing industry.

Among others, the choice of the method of producing the material depends on the desired material volume, the maximum allowable production cost and the slag purity requirements. Consumer needs, such as hardening, tempering and cold rolled final products, respectively, also naturally affect. However, the manufacturing process will always involve metallurgical processes under normal atmospheric pressure (1 atm = 1 bar). Metallurgical processes include melting in electric arc furnaces or high frequency furnaces. The carbon content is controlled by alloy material or carbon removal in AOD or CLU or other refining processes. The content of nitrogen is controlled by using the form of gas or alloying material of nitrogen. Alternatively, the material may be remelted in a second metallurgical process such as VIM, VAR, ESR, and the like. Casting is made via ingot or continuous casting, which is followed by hot working in strip form. After hot working, the material is spheroidized and then cold rolled over several steps to the desired thickness, including an intermediate recrystallization annealing operation. In response to consumer desire for hardened and tempered shipping end products, hardening is in the form of austenizing, quenching (for phase change to martensite) and final tempering in a protective atmosphere, with a continuous strip process for desired hardness. Happens. The material is then cut to the desired width or flat to length according to consumer needs. The final product can be produced by any conventional process from, for example, strip material cured by photoetching and molding or cold rolled strip material by punching / cutting, forming, curing, tempering and final polishing. It is also possible to sell materials in the form of wires, tubes or ingots.

1 shows an overview between three comparative examples for hardness / blade durability and corrosion resistance.

2 shows the CPP test results of alloy 1 and two comparative examples.

Figure 3 shows the hardness according to the tempering temperature for the alloy 1 and three comparative examples.

4 shows CPP corrosion resistance and hardness for Alloy 1 and two comparative examples.

5 shows a micrograph of alloy 1 according to the invention showing the microstructure of the composition.

6 shows a micrograph of a comparative example showing a micrograph of the composition.

7 shows a comparison between Alloy 1 and two comparative examples for hardness level and structure.

Example  One

Alloy 1, a melt of this material, is produced from 10 tonnes of CLU-metallurgy. The material is ingot cast and hot rolled and then cold rolled to intermediate annealing to a thickness suitable for evaluation. The melt of the invention has the composition shown in Table 1 of Alloy 1. Materials according to the present disclosure are compared in three kinds: Comparative Examples 1 to 3. Nominal compositions of Comparative Examples 1-3 are also given in Tables 1-3.

Table 1. Nominal composition by weight of test melts and weight% of Comparative Examples 1-3.

An overview between the comparative examples is shown in FIG. 1 and shows not only the influence of alloying elements C, N and Mo, but also the corrosion resistance against hardness.

Table 2. Test results according to ISO 8442.1 and ISO 8442.5.

In order to evaluate the cutting force and corrosion resistance of the material in accordance with the teachings of the present invention, six blades were produced and evaluated by ISO 8442.1 and ISO 8442.5. Three blades (A-C) are produced from the material of alloy 1, cured at 1055 ° C. to a hardness between 58-58.5 HRC, deep-cooled and tempered at 275 ° C. The three blades D-F are also cured at 1080 ° C. to have a hardness between 58-58.5 HRC, deep-cooled and tempered at 230 ° C. to produce a composition according to Comparative Example 1. All blades are ground and finished with the same equipment to produce similar blades and end products. The test results are shown in Table 2.

The corrosion test according to ISO 8442.1 shows that the material according to the present passes the test despite the fact that Comparative Example 1 failed the test. The results of the blade test according to ISO 8442.5 are at the same level for the new grade and comparative example 1.

Example  2

Corrosion properties of the material of this disclosure are measured by anode polarization / CPP (Critical pitting potential) and compared with Comparative Example 1 and Comparative Example 2. Samples were obtained from Alloy 1, Comparative Examples 1 and 2, and all compositions are given in Table 1. According to the advantages of each alloy, the sample of alloy 1 was cured at 1035 ° C., the sample of Comparative Example 1 was cured at 1080 ° C., and the sample of Comparative Example 2 was cured at 1030 ° C. Tempering in all grades was at 225 ° C. All surfaces of the sample were finished with 600 grit wet grinding. The test solution was 0.1% NaCl, the test was made at 20 ° C. and the potential of the sample increased to 75 mV / min starting at -600 mV. Nitrogen gas bubbles in the solution to reduce oxygen levels. The criterion used to start pitting is I> 10 μm / cm 2. The results of the test are shown in FIG.

Example  3

Curing tests were performed on the material of Alloy 1 and compared with the usual data of Comparative Examples 1, 2 and 3. Alloy 1 cured at 1035 ° C., quenched to 20 ° C., and also hardened to 1055 ° C. followed by deep cooling at −70 ° C. The hardness is shown in Figure 3 according to the tempering temperature after 30 minutes of tempering.

Alloy 1 has a higher hardness than Comparative Examples 1 and 2 at all common tempering temperatures in the range of 175-450 ° C. The hardness of alloy 1 at tempering temperatures above 225 ° C. is also higher than comparative example 3 because of the tempering resistance of alloy 1 with a high alloy composition of molybdenum and nitrogen, which makes alloy 1 less sensitive at high temperatures. Improved tempering resistance of Alloy 1 This bonus is very advantageous for products with, for example, PVD coated surfaces or PTEE surfaces.

Example  4

In FIG. 4, Alloy 1 is compared with Comparative Example 1 and Comparative Example 2 for corrosion resistance and hardness. All samples were tempered at 225 ° C. and heat treated as described above. It is desirable for the composition to have not only high hardness but also high corrosion resistance. It is shown by the arrow in FIG. 4 showing the preferred direction of the physical property. It can be readily seen that Alloy 1 of the present invention combines the improved hardness compared to Comparative Example 1 with the improved corrosion resistance compared to Comparative Example 2.

A general micrograph of the material of alloy 1 in the annealed state is a ferrite-based microstructure of irregularly distributed secondary carbides, nitrides and carbonitrides. In addition, the microstructure of Alloy 1 is free of primary carbides, nitrides and carbonitrides larger than 5 μm in diameter. The general structure of Alloy 1 is shown in FIG. 5, in which the cross section was polished, etched and polished and then micrographed at 1000 magnification. Etching was done in incidental addition, hydrochloric acid and 4% picric acid. The average diameter of carbide nitride and / or carbonitride was estimated to be about 0.4 μm.

In blade applications where inner sharp edges are produced by mechanical methods or etching, the structure without primary carbides larger than 5 μm in diameter needs to be avoided from falling off or etching defects. The general structure of the comparative example 3 is shown in FIG. 6 as a comparison of the micrograph taken on the same conditions.

In FIG. 7, the hardness level and the structure are compared with respect to Alloy 1, Comparative Example 1 and Comparative Example 3 of the present invention.

Example  5

Since the properties of the steel are highly dependent on the curing conditions, the estimates obtained from the basic chemical composition may be wrong. Using the ThermoCal software to calculate the average value at a precomputed titration temperature is one way to more accurately calculate the final properties, which has been applied to alloys 2-6 and 1 as well as Comparative Examples 1-3. The compositions of alloys 2-6 are given in Table 3 and the calculation results are shown in Table 4.

The database used is TCFE3. The optimal curing temperature chosen is used for modeling different grades. Curing temperature, PRE value and M _s The outgoing is calculated from the austenitic composition of the wt% of the interstitial nitrogen and carbon. The calculated% of phase of M ₂₃ C ₆ in the equilibrium of the austenitic phase is also important for wear and blade durability. The equilibrium discussed above is used for PRE. M _s Is calculated using Andrew's formula as follows:

M _s = 539-423 * C-30.4 * Mn-12.1 * Cr-17.7 * Ni-7.5 * Mo +

                    (-423 * N-7.5 * Si + 10 * Co)

Table 3. Weight% Compositions of Alloys 2-6.

The comparison between Alloy 1 and Comparative Example 1 shows that the steel according to the invention has a significantly higher PRE value but at the same time also has a certain amount of carbonized comparable invasive contents, which results in a markedly increased hardness and blade formation. Make steel with corrosion resistance Comparative Example 2 is close to steel alloy 1 in PRE, but with lower predetermined amount of invasive contents of the matrix, lower hardness and internal blade properties can be inferred with lower predetermined amount of carbide phase. These data correspond to the actual measurements of the above example. Alloy 1, M _s The temperature is lower than both Comparative Example 1 and Comparative Example 2 but has the same range as Comparative Example 3, and has a known good hardenability, but significantly higher carbide content leads to coarser microstructure as shown before FIG. .

Table 4. Results of Thermo-Calc calculations.

Alloys 2 to 6 are another possible embodiment of the composition according to the present invention, and the physical properties will be different even if the chemical composition is slightly different. Alloys 2 and 4 are PRE, intrusive contents and M _s Has comparable values for, which leads to similar corrosion resistance and hardness and hardenability, but results in about twice the amount of M ₂₃ C ₆ carbide of alloy 4, but the blade durability is higher in this grade. The highest penetration content and the highest expected hardness in the matrix are obtained in alloy 3, which still has sufficient hardenability due to the addition of cobalt. Alloy 5 also has a higher amount of cobalt compared to alloy 6, which improves hardenability without drastic changes in other properties.

Claims (11)

Has the following composition (% by weight), C 0.40 to 0.60 Si 0.1 ~ 1.0 Mn 0.3 ~ 1.0 Cr 12-15 Mo 2.5 ~ 4.0 Ni 0 ~ 1.0 Co 0 ~ 4.0 N 0.15-0.20 The balance is composed of not only Fe but also commonly occurring impurities and is characterized by obtaining a PRE exceeding 25 specified as PRE =% Cr + 3.3 ·% Mo + 16 ·% N as well as a hardness exceeding 56 HRC without deep cooling. Steel alloys. The steel alloy according to claim 1, wherein C = 0.42 to 0.60 wt%, preferably 0.42 to 0.50 wt%. The steel alloy according to claim 1 or 2, wherein Si = 0.15 to 0.80% by weight, preferably 0.15 to 0.55% by weight. The steel alloy according to any one of claims 1 to 3, wherein Mn = 0.4 to 0.8% by weight, preferably 0.4 to 0.7% by weight. The steel alloy according to any one of claims 1 to 4, wherein Cr = 13 to 15% by weight, preferably 14 to 15% by weight. The steel alloy according to any one of claims 1 to 5, wherein Mo = 2.6 to 4.0% by weight, preferably 2.6 to 3.0% by weight. The steel alloy comprising carbides, nitrides and / or carbonitrides, wherein the maximum diameter of the carbides, nitrides and / or carbonitrides does not exceed 5 μm. Steel alloy. Knives such as knives and caving knives suitable for the food industry, comprising a steel alloy according to any one of claims 1 to 7. A cutting blade for dry or wet shaving, comprising the steel alloy according to any one of claims 1 to 7. A surgical cutting tool, for example a scalpel, the cutting tool comprising a steel alloy according to any one of claims 1 to 7. A doctor blade or creping blade, comprising a steel alloy according to any one of claims 1 to 7, doctor blade or creping blade.

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