DE1208502B - Austenitic steel containing nitrogen - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

C22c

German class: 40 b -39/14

Number:
File number:
Registration date:
Display day:

1 208 502
B 76832 VI a / 40 b
May 19, 1964
5th January 1966

It is known that the yield strength of austenitic steels is relatively low in the quenched state. For 18/8 Cr-Ni steel it is in the range from 25 to 35 kp / mm ² and in Cr-Mn steels, even with a higher carbon content, it hardly reaches more than 45 kp / mm ² . For many purposes, however, austenitic steels with the highest possible yield strength are required.

Various measures are known to increase the yield strength. For example, precipitation hardening is often provided so that yield strengths of up to 100 kp / mm ² can be achieved. However, precipitation-hardened austenitic steels have the disadvantage of poor toughness and reduced corrosion resistance. In particular, such steels are very sensitive to stress corrosion. '.; ■, ■ '. ^! . . '"

As a further measure to increase the strength and, in particular, the yield point, the the high workability of austenitic steels used in cold forming. Unfortunately one is Cold deformation not applicable in many cases.

The strength-increasing effect of nitrogen has also been known for a long time. With the usual nitrogen contents of about 0.25%, an increase in the yield strength of about 10 to 15 kp / mm ² can be achieved, so that yield strengths of about 50 kp / mm ² can be achieved by adding nitrogen. In nitrogen-alloyed, austenitic steels, it is also possible to further increase the yield strength by cold working, with the toughness properties being sufficiently retained. For example, with cap rings made of nitrogen-alloyed, austenitic Mn-Cr steels, yield strengths of up to 110 kp / mm ^{2 are} achieved after quenching and cold forming.

The addition of nitrogen is generally carried out using nitrogen-containing Cr and Mn alloys, but it has also been proposed to carry out the nitrogenization of the steel via the gas phase, where the dependence of the nitrogen solubility on the pressure and composition of the gas atmosphere and must be taken into account by the composition of the steel. The pressure conditions When the steel solidifies, attention must also be paid to ensure that it is sufficiently pore-free Blocks are obtained. In this way, austenitic steels with nitrogen contents of up to 0.6% has been produced, and proposals are known, nitrogen levels up to 0.7% and up to, respectively Use 1% to take advantage of nitrogen as an alloying element. In addition to the nitrogenous, austenitic steel

Applicant:.

Gebr. Böhler & Co. Aktiengesellschaft, Vienna;
Branch: Gebr. Böhler & Co.
Aktiengesellschaft Vienna,
Büderich sales office

Named as inventor:
Dipl.-Ing. Dr. mont. Joseph Frehser,
. Dipl.-Ing. Christian Kubisch, 1-Kapf enberg (Austria) - -

Claimed priority: .

Austria from '24. May 1963 (A4193 / 63)

improvement of the strength properties, nitrogen not only stabilizes the austenite, but it also improves the strength properties of the steel at elevated temperatures as well its toughness properties, the good corrosion behavior being essentially retained.

The limitation of the maximum nitrogen content to 0.7 to 1% was initially due to the Difficulties in achieving higher nitrogen contents with open melting of the steel. Furthermore were Test results of samples made of austenitic steels are known, which are embroidered in the solid state became. It was found, however, that the strength at nitrogen contents of 0.7 to 1.3% begins to fall sharply again and the steels become extremely brittle.

Surprisingly, experiments with austenitic steels have now been carried out under increased nitrogen pressure melted and poured off, with also the solidification of the blocks under increased Atmospheric pressure, show that, however, at even higher nitrogen contents no drop in the Strength and no sudden embrittlement occurs. Rather, both strength and yield strength increase up to nitrogen contents of 3% steadily, while the toughness as it is in the elongation and Constriction values are expressed, drops only slowly at high nitrogen contents and even with 3% nitrogen is still so high that the usability of such steels is ensured. For example causes the nitrogen content to increase from 1 to 3% in a steel with about 0.04% C,

S «■ ι-; λ " · ^:. \ · Λν fw'i 509 777/359

Claims (1)

3 4 0.50% Si, 18% Mn, 2% Ni and 21% Cr are to be taken into account. The nitrogen accumulation The strength of the melt would increase from 75 kp / mm ² to 131 kp / mm ^{2 by introducing stick-} with a decrease in elongation from 42% to 15%. material into the melt or into the slag or through Individual results even suggest that nitrogen-containing slag formers are still being used the upper limit for the stick- 5 that can still be used is accelerated, substance content is around 5% nitrogen. .Because of the fact that the alloys with low The subject matter of the invention is accordingly a selection of the alloy known in the art with more nitrogen content. nitic steel with a high yield point and good constituents can be highly according to the invention Toughness properties that produce up to 0.6% C, 5 to solid steels, which in addition to the high elongation 40% Cr, up to 30% Mn, up to 5% Mo, up to 20% Ni io limit and non-magnetizability also special and 1.3 to 5% nitrogen, the remainder iron with the higher corrosion resistance and high temperature strength Contains borrowed impurities. exhibit. Due to their good toughness properties Other elements can still up to izu th and their work hardening ability can through 1.5% Si, Co, Cu, W, V, Ti, Ta, Nb individually or too - cold forming a further increase in strength several exist. 15 or an increase in the yield point can be achieved. The specified "compositions therefore represent the field of application of the invention framework values, and the respective combination of steel is very wide. It can always be offset wherever it is corrosion resistance and / or austenitic, This means that the austenite-forming iron non-magnetizability in the cold or in the heat, such as C, nitrogen, Mn, Ni, and the ferrite-forming elements such as Cr , Si, Mo, W, is borrowed against each other, such as for cap rings, must be weighed against each other.
not be explained in more detail. _ ... In the manufacture of steels according to the invention, 25.
it has been shown that in order to avoid too long the 1st; Nitrogen-containing, austenitic steel with melting times is most favorable, the highest possible yield strength and good toughness inherent high nitrogen content initially with hooves of stick shafts, consisting of up to 0.6% C, 5 to. Substance-containing F-Cr or Fe-Mn alloys in the 40% Cr, up to 30% Mn, up to 5% Mo, up to the melt and only the 30 20% Ni, 1.3 to 5 % Nitrogen, the remainder essentially being added by means of gaseous nitrogen ~ _-. borrowed iron and common impurities,
2. Steel according to claim 1, this additional dependence of the solubility of nitrogen in steel borrowed up to 1.5% Si, Co, Cu, W ₅ V, Ti, Ta, melt on the partial pressure of nitrogen above which Nb contains individually or in groups. 509 777/359 12.65 0 Bundesdruckerei Berlin