DE2263576A1 - WEAR-RESISTANT FAST-WORKING STEEL WITH GOOD GRINDABILITY AND HIGH TOUGHNESS - Google Patents

Description

German stainless steel works
Company with limited liability

415 Krefeld, Oberschlesienstraße 16

Wear-resistant high-speed steels with good grindability and high toughness.

High speed steels are characterized by a high level of wear resistance up to working temperatures of 600 C. You owe this property the highly tempering-resistant, martensitic matrix into which the Ledeburitic solidification., hard carbides are embedded.

It was recognized early on that by increasing the proportion of hard carbides in the structure the wear resistance can be increased. This finding was supported by increased vanadium contents of up to 5% technically used with an appropriately adjusted carbon content. Such steels have a high resistance to wear, but because of their high proportion of mostly coarse shapes Vanadium carbide, which has a hardness of around 3000 HV, is difficult to grind and is not very tough.

More recently, the carbide content and thus the wear resistance have been increased by increasing the carbon content. Examples of this are the steels with the AISI designation M 41 to M 45, which have a vanadium content of 1 to 2% and a carbon content of 1.1 to 1.2%. In the meantime, however, it has been found that when the carbon content is increased, instead of the usual high-speed _{steel carbide M ß} C, rod-shaped carbides of the M ₃ C type occur (DEW-Technischeberichte 12 (1972), p. 111/33), which due to their hardness of approx 2000 HV and theirs

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unfavorable external shape grindability and toughness are also disadvantageous influence. The task of developing high-speed steels with high wear resistance combined with good grindability and toughness is therefore still unsolved.

The present invention provides a fine solution to this problem. She goes from the surprising finding that if certain alloy regulations are adhered to, a coordination of the alloying elements Contain carbon, tungsten, molybdenum and vanadium with the silicon content, the carbide content in the structure can be increased without Carbides are formed whose shape and hardness impair grindability and toughness. By the inventive coordination of the mentioned Alloy elements, a peritectoid carbide conversion is made possible, which leads to fine and evenly distributed carbides and thus improving grindability and toughness.

By adding precisely matched amounts of silicon, it is possible to increase the carbon content and thereby adjust it so that Although the carbide M2C is formed during solidification, it is unstable and when heated prior to hot forming, it completely disintegrates into the carbides MC and MgC in a peritectoid reaction, which in occur in the desired shape and distribution.

According to the invention is for a high speed steel with high wear resistance with good toughness and machinability, consisting of 0.8 to 1.8% C, 3.5 to 10% Cr, 1 to 13% W, 1 to 10% Mo, 0.5 to 5% V, 0 to 10% Co, the remainder iron with the usual impurities caused by the melting process suggested the silicon content according to the formula% Si - 2, 7 (% C) - 0, 1 (% W) - 0, 14 (% Mo) - 0, 5 (% V) + 0, 3 to be determined with the stipulation of a minimum content of 0.5% Si. As a result, the silicon content is matched to the content of the other alloy elements in such a way that the formation of undesired M2C- ^ carbides is safely prevented. An increase in the silicon content beyond the value resulting from the above relationship leads to an undesirable one Carbide formation and thus an impairment of the steel shafts. This is because coarsely formed ones arise during solidification Primary carbides of the type MgC and MC.

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The significance of the invention is to be based on some microstructure recordings made on three experimental melts of the steel S 2-9-1-8 (M 42 type), whose chemical composition is shown in Table 1, are explained in more detail: "" .- '■ ·

Table 1
Chemical composition in wt .- ^

1 1 3 1 C. 0 Si 4th Cr 1 W. 9 Mon 1 V 8th Co stole Steel 2 1
(invented
moderate) , 08 1 , 26 5 , 89 1 , 35 9 , 24 1 , 18 8th , 21 stole , 09 2 , 07 5 , 11 1 , 48 9 , 41. 1 , 24 7th , 16 , 08 , 82 ■ , 31 , 42 , 16 , 12 , 99

Figure 1 shows that the steel 1 over the rod-shaped M "C-carbide solidified, which remains stable up to high degrees of Vex ° formation (Figs la-c).

Figure 2 shows that steel 2 with a silicon content corresponding to the formula according to the invention also solidifies via the MpC eutectic, but its carbide content is so unstable that it disintegrates as soon as the ingot cools down (Figure 2a). This peritectoid disintegration takes place completely during further hot forming. This results in very fine and evenly distributed carbides of the types M ^ C and MS (Figures 2b and c) _v , which give the steel high wear resistance with good wearability and toughness.

Finally, Figure 3 shows that silicon contents are higher than that calculated according to the formula, lead to a solidification of the steel via the Μ, -C-eutectic, with coarse primary MC-carbides arise (Fig. 3a) · These coarse carbides can also be used with stronger deformation does not completely shatter and lead to an uneven, coarse-grained structure, which the properties of steel adversely affected.

Most conventional high-speed steels have the optimum Carbide formation too low silicon content. When the teaching according to the invention is applied to these steels, there is an improvement the steel properties achieved.

Although increased silicon contents lead to an increase in secondary hardness, however, cause a shift in the secondary hardness maximum

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to lower tempering temperatures. This reduction in the tempering resistance due to silicon is disadvantageous for the use of such steels. Attempts have therefore been made to remedy this disadvantage by further Balance alloying measures. Through extensive research It has been found that the tempering resistance, which is reduced by silicon, can be increased if the chromium content of the steels, which is usually around 4%, is increased to higher values. The optimal one required to ensure resistance to tempering According to a preferred embodiment of the invention, the chromium content should therefore correspond to the silicon content of the steel

% Cr »4 + 2 (% Si)
be linked.

Silicon additions make the steel that is present after hardening Reduced residual austenite content. To weaken this effect, it is therefore advantageous to use the silicon-containing steels according to the invention Add nitrogen to a level of 0.1%.

According to the invention it is possible to use high-speed steels with optimal To generate structure formation and thus excellent performance properties.

High speed steels according to the invention are preferably suitable for Tools that require major grinding work when shaping them are, such as twist drills, taps, dies, broaches, milling cutters and the like.

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Claims (4)

sr claims 1. High speed steel with high wear resistance and good Toughness and machinability consisting of 0.8 to 1.8% carbon, 3.5 to 10% chromium
1 to 13% tungsten 1 to 10% molybdenum 0, 5 to 5% vanadium 0 to 10% cobalt Remainder iron with the usual impurities caused by the melting process, characterized in that the silicon content according to the formula % Si = 2.7 (% C) - 0.1 (% W) - 0.14 (% Mo) - 0.5 (% V) + 0.3 is determined, but is at least 0.5%. 2. High speed steel according to claim 1, characterized in that the chryam content according to the formula % Cr »4 + 2 (% Si)
is matched to the silicon content. 3. High speed steel according to one of claims 1 or 2, characterized characterized in that it contains up to 0.1% nitrogen. 4. Use of Schnellarb eits steels according to one of the claims 1 to 3 for tools whose shaping requires major grinding work, such as twist drills, taps, dies, Broaches, milling cutters and the like. 409828/0475 ' L e r s e i t e