US2229178A - Chromium tungsten molybdenum cobalt alloy steel - Google Patents

Description

Patented Jan. 21, i941 CHROMIUM TUNGSTEN MOLYBDENUM COBALT mor STEEL Leo Kliiger, Vienna, Germany, assignor to Momfina A.-G. fiir kommerzielle und flnanzielle. Angelegenheiten, Zurich, Switzerland No Drawing.

Application July 21, 1939, Serial No.

285,806. In Switzerland July 25, 1938 3 Claims. (Cl. 75-12 8) The invention relates to a chromium tungsten molybdenum cobalt alloy steel in particular for the making of milling tools, and consists in from. 0.25 to 3% of tantalum being added to the alloy.

In making or, respectively casting of tools with sharp edges, cutting edges, corners etc., using steels alloyed with chromium, tungsten, molybdenum and cobalt, a great disadvantage arises owing to the material in the parts of the mould forming the 'edges, cutting edges, comers etc. being chilled. Due to this chilling, effect and to the shrinking occurring after the ensuing congealing, in the cutting places where the metal has receded cavities arise giving cause to a sawlike indentation of the edge, cutting edge etc. requiring very material subsequent working and whose faults sometimes are past help. The loss thereby is very considerable, sufficing to render doubtful the advantages to be gained by casting effect of the casting mould and its disagreeable.

consequence and assures the 100 per cent. formation-of perfectly sharp edges, corners, cutting edges etc. in the moulds, neither poor looking nor showing any other defects. This is because the tantalum is raising the congealing po t or, respectively, delaying the congelation. No sudden chilling of .the metal occurs in the mould, and the formation of cavity-producing elements is avoided. Likewise the structural differences occurring, due to the chilling, in the chilled corners, cutting edges etc. on the one side and in themetal underneath on the other-and which can hardly, be made up for even by subsequent thermic treatment-are avoided, the structure on the contrary becoming completely equal and free of tension due to the addition of the tantalum. which is of particular weight for the subsequent annealing; the qualities of the alloy are improved equally.

= Adding tantalum to the aforesaid basic alloy entails quite a number of unexpected effects of far-reaching importance. ,For instance the sensibility of the alloy towards hardening is decreased to a minimum no changes of volume occurring in the case of sudden fluctuations of temperature. Moreover a fine casting capacity is attained; in this, it came as a surprise that when iron was present in the alloy, the higher carbon content promoting the desired thinness could be maintained in spite of the presence of tantalum, whereas in general it is known from the practice that in adding tantalum toalloys destined for cutting tools the carbon content requires to be decreased. This results in the sharp edges, corners, cutting edges etc. even of the most complicated tools, for instance, milling tools, being completely filled in when casting, the

exterior of the tools being, in consequence, smooth and well-looking. The material is easy to work upon after annealing. A quite peculiar advantage is the elimination of the hardening of the tools entailing so many difficulties, it being possible to harden the alloy in the lower hardening temperature range of from about 900 to about 1200 C. The addition of a small percentage of tantalum to the basic alloy for tools known for itself already therefore represents a technical and economic progress of the utmost importance; due to it it has become possible for the first time fully to eliminate the unequality formerly occurring in alloys of this kind.

The percentage of tantalum, that is, its increase or decrease is most closely interconnected both with the percentage of carbon and molybdenum in the alloyand with the percentage of cobalt; on the one hand it is preferably chosen equal to'the total of the contents in carbon and molybdenum while on the other hand it rises and drops in proportion to the percentage of cobalt. Thus, for instance, a content in cobalt of 1% corresponds with a content in tantalum of 0.25- 0.5%. When the percentage of cobalt is increased to 2% the content in tantalum rises to approximately 0.5-1%.

Apart from iron, the alloy improved by the addition of tantalum essentially contains the following ingredients:

C I Cr W Mo Ta Percent Percent Percent Percent Percent Percent 0. 25-1. 3 2-16 36 0. 25-2. 5 0. 25-6 0. 25-3 The advantages of the addition of tantalum or, respectively their effect upon the alloys mentioned are to a very highdegree increased by even a small addition of copper (OJ-1%) which may partially even replace the tantalum.

If needed other ingredients improving its ef- 'I claim:

1. An alloy steel having percentages in car Icon of from 0.25 to 1.3%, chromium of from 2 to 16%, tungsten of from 3 to 6%, molybdenum of from 0.25 to 2.5%, cobalt of from 0.25 to 3. Analloy steel as claimedin claim 1, in which 6%, tantalum of from 0.25 to 3%,- the balance the content of tantalum is approximately onebeing iron and little quantities of substances third to one-half of the content by weight of ,such as manganese, silicon and vanadium, cobalt.

2. An alloy steel as claimed in claim 1, in which. the contact of tantalum is substantially LEO KLUGER. one-third of the total parts by weight of carbon and molybdenum.