DE1433107B2 - NITRIDE CONTAINING CARBON STEEL - Google Patents

Description

The invention relates to a nitride-containing unalloyed Steel with good ductility and high strength in a wide temperature range, i.e. both at Room temperature on the one hand as well as on the other hand at increased or decreased temperature.

Steels of this type are already known. For example, from German patent specification 954 508 shows that the properties of such steels depend to a large extent on the structure of the structure. This is particularly important for the formation of high-strength steels with high workability and fluidity Structure be very fine-grained, which is achieved according to the patent mentioned that the steel Aluminum and nitrogen is added in such amounts that in the finished steel at least 0.01 to at most 0.30% aluminum nitride are contained.

In practice it has proven to be extremely difficult, in some cases even impossible, to meet this dosage requirement to be met exactly. This is because, in addition to nitrogen, in molten steel there is always also it still contains oxygen, a substance that inevitably forms with the added aluminum reacts from aluminum oxide, which then on the one hand in an uncontrollable manner the aluminum nitride content lowered in the finished steel and which, on the other hand, is in the form of different sizes Deposits agglomerations in the structure. These alumina deposits then lead to defects in the structure, where the strength of the steel is considerable is reduced. ' »

It is from the "Handbuch der Sonderstahlkunde" by E. Houdremont, 1956, pp. 1318 and 1329 It is also known that, similar to aluminum nitride, the nitrides of the metals titanium, zirconium as well as Vanadium work. A closer examination has shown that these metals, in addition to the nitrogen present in the melt reacts to a considerable extent with oxygen and carbon, so that here, too, there are the already mentioned difficulties with the exact dosage of the nitrides.

The following should also be noted: The nitride-forming Elements that can be used as additives to steel alloys must be divided into two Groups are divided. The first group contains those elements whose nitrides are in solid steel are practically insoluble and are therefore primarily used as denitration agents. to this group includes, for example, titanium and zirconium. The second group includes those Metals, for example aluminum, whose nitrides have a certain temperature-dependent solubility in the solid Have steel. It has been shown that the nitrides of these elements not only bind the nitrogen, but also develop other beneficial effects in steel, such as the Improve cold toughness.

In this prior art, the task is to provide an unalloyed, fine-grained, ductile, in particular To propose cold-tough and high-strength steel, whose fine-grain structure is carried out in a known manner Addition of a nitride former has been generated. This nitride former should, however, in contrast to the known Nitride formers react practically completely with the nitrogen present and are therefore easy to dose as well as have no tendency to form oxide agglomerates inside the structure.

This object is achieved according to the invention in that a nitride-containing carbon steel is proposed which is characterized by the fact that it consists of

less than 0.35% carbon,

less than 0.035% sulfur,

less than 0.035% phosphorus,

less than 1.0% manganese,

less than 0.5% silicon,

0.015 to 0.090% beryllium nitride,

The remainder is iron and impurities from the smelting process consists.

Surprisingly, it has been shown that beryllium has the properties mentioned in an advantageous manner Wise united in itself, with the fact that this element as well as aluminum is part of the above second group of nitride formers belongs, the nitride thus a certain temperature-dependent Has solubility in solid steel. In contrast to aluminum, however, beryllium has practically no tendency to Oxide formation in steel, so that it is particularly suitable for the purpose in question.

To produce the steel according to the invention, the procedure can be, for example, that scrap of the appropriate composition is first melted down under oxidizing conditions in an electric arc furnace and then deoxidized with ferrosilicon and ferromanganese. Then nitrogen is blown into the steel bath for about 6 minutes at a pressure of about 5 kp / cm ² and finally 0.10% beryllium is added before casting.

The required nitrogen can also be used in other ways, for example as a master alloy, for example in the form Manganese nitride or the like, are introduced into the steel. In what way the melt embroidered does not play a role in the context of the invention.

Table 1 gives the composition of two experimentally melted steels according to the invention again.

Table 1

Carbon ...

silicon

manganese

phosphorus

sulfur

aluminum

beryllium

nitrogen

Beryllium nitride

Steel 1

0.09

0.34

0.60

0.013

0.025

0.006

0.119

0.001

0.016

Steel 2

0.07

0.31

0.65

0.015

0.022

0.006

0.120

0.017

0.024

All contents are given in percent by weight.

The steel that has been embroidered and mixed with beryllium is then poured off in a known manner. After casting, the blocks are brought to a temperature

^Co temperature heated from 1150 to 125O ⁰ C and finally forged at a final temperature of 850 ^{0 C.} The steel is ^{then heated again to 95O 0} C and then either cooled in air or quenched in oil.

6.5 In Table 2 the mechanical properties of steels treated in this way are summarized and with compared to a normal killed carbon steel with 0.13% C.

Tabel

Steel 1

Steel 2

Comparative steel

Tensile strength, kp / mm ²

Yield point, kp / mm ²

Elongation in%

Constriction in%

Impact value, kp · m / cm ²

Tr 15 in ⁰ C

Trsin ⁰ C

46.5 to 46.9 36.5 to 37.0 39.0 to 40.0 70.0 to 74.0

33.0 -100 46.7
38.0
39.0
79.0
31.0

-100

- 70

44

30th

28

57
8.0
-47
-30

It can be seen that the steels composed according to the invention, in addition to increased strength higher and lower temperatures also have increased ductility. This is evident in the lowering of the transformation temperature of the notched impact values, as can be seen from the figures of FIG Drawing can be seen. It represent

F i g. 1 the temperature dependency of the notched impact values measured according to C har ρ y for the steels 1 and 2 given above as well as for a killed carbon steel with 0.13 ° / ₀ C in the normalized and rolled condition,

F i g. 2 the dependence of the shear fracture ratio on the temperature for the same steels,

F i g. 3 the dependence of the impact value on the temperature for steel 1, once in the annealed and oil-quenched and once in the annealed and air-cooled state,

F i g. 4 the dependence of the impact value on the temperature for steel 2, once in the annealed and oil-quenched and once in the annealed and air-cooled state.

In Fig. 1, the measuring temperature in ⁰ C is plotted on the ordinate and the notched impact value measured according to C har ρ y in kp · m / cm ² on the abscissa. Curve 1 corresponds to the measured values on steel 1 and curve 2 to those on steel 2 in Table 1.

Curve 3 corresponds to a carbon steel with 0.13 ° / ₀ C in the normalized and curve 4 to the same steel in the rolled state. It can be seen that the steep slope of the curves for the beryllium nitride-containing steels is strongly shifted towards lower temperatures, which corresponds to a corresponding improvement in the cold toughness.

In Fig. 2 is the temperature in ° C on the ordinate and the shear fracture ratio in percent is plotted on the abscissa. The curves wear the same Numbering as in FIG. 1. Also for the values shown here, the steep drop in the curves is for the Steels 1 and 2 containing beryllium nitride have been shifted significantly towards lower values.

In Fig. 3, the temperature in ⁰ C is again plotted on the ordinate and the notched impact value in kg · m / cm ² on the abscissa. The curves shown were made on steel 1 according to the table «! measured, namely curve 5 on samples after a heat treatment at 950 ° C and quenching in oil, and curve 6 on samples after a heat treatment at 950 ⁰ C (1 hour) and then cooling in air. It can be seen that the oil quenched steels have better properties than the air quenched steels.

F i g. 4 gives in the same representation as FIG. 3 the corresponding values for steel 2 in table 1 again. Here, too, it can be seen that the oil-quenched steel has better values than the air-cooled steel having.

Claims (1)

Claim: Nitride-containing carbon steel, characterized in that it consists of less than 0.35 ° / ₀ carbon,
less than 0.035 ° / ₀ sulfur,
less than 0.035 ° / ₀ phosphorus,
less than 1.0 ° / ₀ manganese,
less than 0.5 ° / ₀ silicon,
0.015 to 0.090% beryllium nitride, The remainder consists of iron and impurities from the melting process. 1 sheet of drawings