EP1052304B1 - Martensitic corrosion resistant chromium steel - Google Patents

Abstract

A corrosion resistant martensitic chromium steel, having a specified carbon/nitrogen ratio and a fine homogeneous microstructure, is new. A novel corrosion resistant martensitic chromium steel has the composition (by wt.) 0.2-0.4% C, 0.15-0.5% Si, 0.15-0.6% Mn, 12.0-15.0% Cr, NOTGREATER 0.28% Ni, 0.05-0.19% N, balance Fe and impurities, the C/N ratio being greater than 2.0.

Description

The invention relates to a corrosion resistant chromium steel with 12 to 15 Wt .-% chromium.

Steels alloyed with 12 to 15% by weight chromium are found in the modern one Technology a large field of application. Alloys of this type exhibit in the significant rust resistance and mechanical properties can by respective alloying measures and by thermal Compensation treatment of the material can be adjusted within wide limits.

12-15% chromium steels with 0.25-0.40 wt% carbon have long been known and found, for example, in the steel - iron list among the Material numbers 1.2083, 1.2316, 1.4028. As a purpose are for it Plastic molds and springs and piston rods specified.

For particular uses, however, is usually the property profile of the Material of essential importance, so that the manufacturers in increasing Measures the demand for an improvement of the material properties in their Entity is asked. In other words, the hardness, the tempering, the Temperature resistance, corrosion resistance, homogeneity of the Gefüges, the polishability and the like of known steels are each be increased or improved, so that an application according use of a new expensive type of alloy can be omitted.

From DE 39 01 470 C1 is known, a molybdenum-containing chrome steel 0.2 to 0.7 wt .-% nitrogen zuzulegieren to its corrosion resistance significantly increase. Although such alloys are corrosion-chemically improved, but can lower hardness, a deteriorated polishability and have low structural homogeneities, because in comparison with the Carbon content is given a high nitrogen concentration.

One use of molybdenum, tungsten, nickel, vanadium and 0.2 to 1.0 Wt .-% nitrogen-containing corrosion-resistant chromium steel, the one is subjected to special heat treatment, for tools and objects with high strength at room temperature and at 500 ° C is known from DE 42 12 966 C1 became known. This alloy is due to vanadium or vanadium and niobium nitride precipitates have high heat resistance and the like Wear resistance, whose deteriorated polishing ability as well Microstructure homogeneity due to high nitrogen concentrations the usability of the material.

In EP 0994199 A1, which represents prior art under Art. 54 (3) EPC, is a steel, which consists of (in% by weight) 0.30% carbon, 0.12% nitrogen, 0.30% silicon, 0.42% Manganese, 13.4% chromium, 0.28% nickel, balance iron and unavoidable impurities and has a martensite of 98.2% by volume.

For engine gaskets, according to JP-A-7278758, a high-strength corrosion-resistant material was used Steel with the best spring and fatigue characteristics and high Stress corrosion cracking resistance proposed. This steel has contents in% by weight from 0.1 to 0.5 C, ≤ 2.0 Si, ≤ 5.0 Mn, 11 to 18 Cr, ≤ 0.01 S, ≤ 0.01 O, 0.01 to 0.2 N and 0.005 H, possesses a structure of high purity with a distance factor of ≤ 0.01% for non-metallic inclusions and is composed in such a way that it out tempered martensite and has a hardness of Hv = 400 to 550. Around To achieve material hardness, it is necessary to heat compensation after a Cold rolling to perform.

From JP-A-8060238 is a martensitic corrosion resistant steel with best Hot workability and high resistance to sulfide-induced stress cracking known. To obtain these properties, the steel consists of% by weight 0.1 to 0.3 C, 0.01 to 1.0 Si, 0.1 to 1.0 Mn, ≤ 0.02 P, ≤ 0.01 S, 11 to 14 Cr, ≤ 0.05 Ni and 0.015 to 0.1 N or 0.001 to 0.3 Ca and / or Mg and / or SE (REM), wherein the Condition 13 x C + 11.5 x N - Cr ≥ - 10.86 must be fulfilled.

The invention is now the task of an economical chrome steel specify a high hardness and temperature resistance at low Corrosive attack, a homogeneous microstructure and improved polishability has.

This object is achieved by a chromium steel according to claim 1.

The advantages thus achieved are essentially to be seen in that at a Corrosion resistance of the heat treated material, which is 17% Cr steels is comparable, whose hardness increases and the long-term tempering behavior is substantially improved, so that at a glass molding pressure, for example in the production of front panels of screens, a much longer service life the tools is achieved. Just as significant are those with the The material according to the invention achieved advantages of a homogeneous microstructure and a particularly good polishability, with these properties in the before use as a glass molded part an improvement in the production quality and can provide a favorable tooling. These benefits are too relevant in the manufacture and use of plastic molds, the improved corrosion resistance of the steel zussätzlich their applicability extended. In this context, the production of lenses and CD's too for which the tools or molds have excellent machinability and have a high surface quality and as long as possible in production to receive.

A morphologically favorable microstructure, in which the matrix hardness is a has high resistance, is characterized by a lack of strong nitride formers, such as was found promoted, with the elements titanium, aluminum, niobium and vanadium are unfavorably effective. However, an aluminum content below 0.05 wt .-% is provide, so as not to tilt the fine-homogeneous Microstructure towards a formation of heterogeneous areas too enable.

Particularly favorable properties of chrome steel can be achieved when the concentration of carbon is 0.25 to 0.30 wt%.

If, by way of limitation, the concentration of nitrogen is 0.07 to 0.15 Wt .-%, preferably 0.08 to 0.12 wt .-%, is certainly one outstanding polishability of the material with favorable mechanical and corrosion-chemical parameters adjustable.

The material quality can be further increased according to the invention if the chromium steel has a maximum concentration of molybdenum plus (tungsten x 0.5) of not more than 0.20 and / or the highest contents Titanium 0.01, preferably 0.006% by weight Aluminum 0.05, preferably 0.025% by weight Niobium 0.01 preferably 0.006% by weight be.

In the following the invention will be explained in more detail by means of test results. Table 1 lists tested materials with their chemical composition. alloy C Si Mn Cr Not a word Ni V W Ti al Nb N 1 0.21 0.25 0.29 13.01 0.01 0.08 0.02 <0.05 nb 0.02 nb 0.05 2 0.20 0.25 0.32 12.87 0.03 0.10 0.01 <0.05 nb 0.02 nb 0.11 3 * 0.31 0.27 0.31 12.96 0.02 0.09 nb <0.05 <0.005 0.02 nb 0.12 4 0.30 0.31 0.32 13.03 <0.02 0.10 0.03 0.05 <0.005 0.02 0.02 0.16 5 0.32 0.26 0.32 12.92 <0.02 0.10 nb <0.005 <0.005 0.02 nb 0.21 6 0.40 0,44 0.30 12,97 <0.02 0.08 nb nb nb nb nb 0.01 7 0.31 0.35 0.31 13.01 0.08 0.09 nb nb nb nb nb 0.01 8th 0.33 0.46 0.26 12.67 0.10 0.2 nb 0.05 nb 0.03 nb 0.01 9 0.39 0.28 0.29 13.02 0.03 0.3 0.02 nb nb nb nb 0.06 10 * 0.40 0.31 0.31 12.98 0.06 0.10 nb nb nb nb nb 0.11 11 0.41 0.27 0.29 12,99 0.06 0.09 nb nb nb nb nb 0.14 12 0.35 0.31 0.35 16.51 1.10 0.78 0.03 0.06 nb nb 0,006 0.02 13 0.36 0.25 0.31 16,72 1.12 0.76 0.03 0.05 nb nb nb 0.18

The alloy 1 corresponds to DIN material number 1.2082, the alloys 6 and 9 correspond to the material number 1.2083, the alloy 7 corresponds to the Material number 1.4028 and finally alloy 12 is the material number 1.2316 to assign. These DIN materials are for comparison with the alloy composition according to the invention.

Tab. 2 shows for the listed alloys from Table 1 the results in terms of mechanical properties, corrosion resistance, polishability and dimensional stability in the heat treatment for comparative analysis, wherein for the overall assessment of the material properties, a ratio was determined, indicating the material quality can serve. alloy Mech. [%] Kormsionsbest. [%] Polished garage [%] Dimensional change [%] identification number comment 1 60 60 120 90 3.3 DIN 1.2082 2 70 70 110 100 3.5 Versuchleg. 3 * 160 100 160 140 5.6 Versuchleg. 4 - - - - - Versuchleg. 5 80 120 120 100 4.2 Versuchleg. 6 100 50 60 80 2.9 DIN 1.2083, 7 90 60 100 100 3.5 DIN 1.4028, 8th 95 70 100 100 3.7 Versuchleg. 9 110 50 70 80 3.1 DIN 1.2083, 10 * 120 70 80 90 3.6 Versuchleg. 11 110 80 70 70 3.3 Versuchleg. 12 70 100 40 50 2.6 DIN 1.2316, 13 70 160 50 60 3.4 Versuchleg. In the production of the key figures, the procedure was as follows: The material which had the best material values overall (alloy 3) was excluded. Of the remaining test alloys, the highest property value of each type was assessed as 100% and the remaining individual values of the materials in relation to this 100%. The percentage properties of the best or of an alloy 3 according to the invention were then also determined on this basis. To represent the characteristic number characterizing the material quality as a whole, a summation of the percentage individual values and a division of this sum by 100 were carried out.

The trial alloy 4 yielded, apparently due to the high Nitrogen content, a porous or leaky block structure and must in the to be left out of comparative consideration.

Leg. 1 und 2 : Zu geringe Härteannahme durch den zu geringen Kohlenstoffgehalt.

Leg. 3: Optimal durch optimale Abstimmung der Legierungselemente und Stickstoff; patentgemäße Legierung

Leg. 5: Über Druckumschmelzen hergestellt, zu hoher Restaustenitanteil wirkt sich negativ auf die Maßänderungsstabilität aus.

Leg. 6 und 9: Norm-Werkstoff; ungünstige Mikrostruktur (Karbidbelegungen an den Korngrenzen und sog. Stringers), daraus folgen auch ungünstige Korrosionsbeständigkeit, Polierbarkeit und Maßänderungsstabilität.

Leg. 7 und 8: Norm- Werkstoff; durch geringeren Kohlenstoff gleichmäßigere Karbidverteilung, d.h. günstigere Polierbarkeit und Maßänderungsstabilität (weil kein Restaustenit), jedoch unzureichende Korrosionsbeständigkeit.

Leg. 10: Korrosionsbeständigkeit ist besser im Vergleich mit Leg. 6 und 9, aber duch zu hohen C-Gehalt auch ungünstige Karbidverteilung, was sich schlecht auf die Polierbarkeit und Maßänderungsstabilität auswirkt.

Leg. 11: Korrosion ist im Vergleich mit Leg. 10 besser, aber C+ N ist zu hoch, d.h, der Restaustenitanteil ist zu hoch, d.h. schlechter Einfluß auf die Polierbarkeit und Maßänderungsstabilität.

Leg. 12: Norm-Werkstoff mit 17% Cr. Ungünstige Gefügeausbildung, d.h. schlechte Polierbarkeit und Maßänderungsstabilität, auch schlechte mechanische Eigenschaften, die Korrosionsbeständigkeit ist durch den hohen Cr-Gehalt gut.

Leg. 13: Aufgestickte Variante der Leg. 12, sehr gute Korrosionsbeständigkeit, Gefügeeigenschaften werden durch N jedoch nur unzureichend verbessert.

The results of the investigation are justified in the following:

Leg. 1 and 2: Too little hardening due to the low carbon content.

Leg. 3: Optimal through optimal matching of the alloying elements and nitrogen; patented alloy

Leg. 5: Produced by pressure remelting, too high residual austenite content has a negative effect on dimensional stability.

Leg. 6 and 9: standard material; unfavorable microstructure (carbide deposits at the grain boundaries and so-called stringer), which also results in unfavorable corrosion resistance, polishability and dimensional stability.

Leg. 7 and 8: standard material; more uniform carbide distribution due to lower carbon, ie more favorable polishability and dimensional stability (because no retained austenite), but insufficient corrosion resistance.

Leg. 10: Corrosion resistance is better compared to Leg. 6 and 9, but Duch too high C content and unfavorable carbide distribution, which has a bad effect on the polishability and dimensional stability.

Leg. 11: Corrosion is in comparison with Leg. 10 is better, but C + N is too high, ie the residual austenite content is too high, ie a bad influence on the polishability and dimensional stability.

Leg. 12: standard material with 17% Cr. Unfavorable microstructure, ie poor polishability and dimensional stability, even poor mechanical properties, the corrosion resistance is good because of the high Cr content.

Leg. 13: Embroidered variant of Leg. 12, very good corrosion resistance, structural properties are improved by N but insufficient.

Based on the hardness and tempering behavior (Fig. 1), the long-term behavior (Fig.2), a corrosion test (FIG. 3), a comparison of micrographs (FIG 4a, 4b) and a Polierfähigkeitsprüfung (Figure 5) is an inventive Alloy 3 compared to standard alloys.

From Fig. 1 it can be seen that in comparison with the standard alloys 7 and 9 the Alloy 3 has a higher hardness over the entire tempering range. The reason for this behavior is in the balance of the Alloy elements to each other or the favorable interaction of activities to see the elements in conjunction with nitrogen. A high hardness capacity an annealing temperature of 200 ° C is for example for low tempered corrosion-resistant plastic molds of advantage.

Fig. 2 shows the dependence of the hardness of the annealing time and gives a very good long-term behavior of a leg according to the invention. 3 at 550 ° C, that is, one particular suitability of this material for higher loads Working temperatures over long periods, such as in Glaspreßformen given is. This favorable material property can be economically advantageous for Reduced cycle time are used, that is, with the same service life of Tool is this at a higher temperature in use.

In Fig. 3 is comparative to standard alloys, the corrosion resistance of Leg. 3 shown. In this case, the inventive alloy 3 reaches the Corrosion resistance of a 17% chromium steel (material number 1.2316).

From Figs. 4a and 4b it can be seen that the inventive Alloy 3 a morphologically much more uniform microstructure formation than the standardized, as good polishable valid material DIN 1.4028 has. That's it synergetically the effect or interaction of the alloying elements with the Nitrogen decisive.

In Fig. 5 is apparent from comparative polishing ability studies the advantage of an alloy 3 according to the invention is shown, in particular has this favorable property due to a special structural homogeneity.

Claims (4)

1. Martensitic corrosion resistant chromium steel which comprises in % by weight: 0.2 to 0.4 % of carbon 0.15 to 0.5 % of silicon 0.15 to 0.6 % of manganese 12.0 to 15.0% of chromium optionally 0.01% of titanium in maximum optionally 0.05% of aluminium in maximum optionally 0.01% of niobium in maximum as well as optionally molybdenum and/or tungsten, the maximum concentration of molybdenum plus (tungsten x 0.5) amounting to 0.28 % by weight in maximum, optionally 0.01 % of vanadium in maximum 0.28% of nickel in maximum 0.07 to 0.15% of nitrogen, the balance being iron and impurities which are due to preparation, with the proviso that the ratio of carbon/nitrogen is above a value of 2.0, a steel being excluded which consists (in % by weight) of 0.30% of carbon, 0.12% of nitrogen, 0.30% of silicon, 0.42% of manganese, 13.4% of chromium, 0.28% of nickel, the balance being iron and inevitable impurities, and which comprises a proportion of martehsite of 98.2 % by volume.
2. Chromium steel according to claim 1, characterised in that the concentration of carbon amounts to 0.25 to 0.30 % by weight.
3. Chromium steel according to claim 1 or 2, characterised in that the concentration of nitrogen amounts to 0.08 to 0.12 % by weight.
4. Chromium steel according to any of claims 1 to 3, characterised in that the maximum contents of titanium amounts to 0.006 % by weight of aluminium to 0.025 % by weight, and of niobium to 0.006 % by weight.

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