EP0105861B1 - High speed steel alloy - Google Patents

Description

The invention relates to a high-speed steel alloy, u. one that has the carbide-forming elements tungsten, molybdenum, chromium, vanadium and niobium.

Within the framework of high-speed steels, the standardized alloy composition S 6 - 5 - 2 (referred to as M2 according to AISI) with corresponding contents of tungsten, molybdenum, vanadium and chromium is by far the most important with regard to the frequency of their use. In recent years, various attempts have been made to use the alloy elements niobium, which has become the focus of interest not least due to the discovery of new, extensive deposits, in order to enable, in particular, a complete or partial replacement for vanadium as a carbide former in this type of steel . For example, F. Heisterkamp (Metals and Materials, Oct. 1978) referred to alloy variants that differ from the basic type with a content of 2 or 3% niobium with complete replacement of the vanadium or 1% each with partial replacement of this alloy component and have shown good properties. Further work aimed at the partial substitution of tungsten and / or molybdenum with niobium contents of up to about 4% has also already become known; however, the reduction in the tungsten content led to a significant reduction in the hardness values, which is why this route of niobium substitution did not have to be regarded as expedient.

From GB-PS 691 298 is an alloy with in wt .-% 0.5-1.5 C, 0.2-1.5 Si, 0.2-2 Mn, 1-6 Cr, 5-12 Mo , 0 - 5 W, 0.5 - 1.5 V, 0.5 - 4 Nb, rest of iron known. This alloy is aimed exclusively at welding rods, especially for surface build-up welding. In this narrow field of application, there is the advantage that the base body, which has wear-resistant armouring on the outside, has mechanical properties, e.g. Toughness and strength can be selected according to the intended use and therefore the requirements of the alloy for the welding job are low if only the wear and heat resistance requirements are met. However, a welding job requires increased technical effort. The only concrete alloy disclosed in GB-PS does not contain molybdenum and has a tungsten content of 8%, whereby a material is obtained which has a hardness of 40-45 HRC without hardening and only 53 after annealing at 600 ° C HRC.

The invention is based on the unexpected and significant knowledge that it is possible without any restriction to a specific application, without having to accept a loss in hardness, a substantial proportion of the basic composition of the high-speed steel S 6 - 5 - 2 and also of the concrete alloy to save tungsten provided in GB-A 691 298 if a certain amount of vanadium is assigned to a certain niobium content which is kept within relatively low narrow limits and if certain range limits are also observed for the other alloy components.

The characteristic of the high-speed steel alloy according to the invention is that it consists of 0.84 to 1.05% by weight of C, max. 1.0% by weight Si, max. 1.0% by weight Mn, 3.6 to 4.5% by weight Cr, 4.6 to 6.5% by weight Mo, 2.0 to 4.0% by weight W, 0, 5 to 1.6% by weight of V and 0.5 to 1.5% by weight of Nb, remainder Fe and inevitable impurities, the sum of vanadium and niobium in the range of 1 to 2.5% by weight lies.

According to further features of the invention, it is provided that, with a tungsten content of 2.0 to 3.0% by weight, the vanadium content is 1.3 to 1.6% by weight and the niobium content 0.8 to 1.5% by weight. is, the sum of vanadium and niobium being in the range from 1 to 2.5% by weight or that with a tungsten content of more than 3.0 to 4.0% by weight the vanadium content is 0.5 to 1, 5% by weight and the niobium content 0.5 to 1.0% by weight, the sum of vanadium and niobium being in the range from 1 to 2.5% by weight

It is achieved in this way that a maximum result of the technological effects that can be achieved is ensured with a minimum of effort for the carbide-forming elements involved in the alloy structure.

The invention is explained in more detail below on the basis of exemplary embodiments. In Table 1, a different high-speed steel composition corresponding to the basic composition for S 6 - 5 - 2 is compared with four different alloy compositions according to the invention. In addition, the arithmetically required C contents for carbide formation, the differences from the actual C content and the hardening temperatures for the individual steels are given. The hardening temperature was selected in the usual way with the aid of the crack hardness curves and the Snyder-Graff grain number. As is usual with steel analyzes, the composition of the residual portion consisting of Fe and the production-related impurities is not shown separately.

For the investigation of the tool life behavior, side finishing knives (18 mm square: a = 5 °, ß = 74 °, y = 11 °) were made, with which 100 mm thick round rods made of 90 MnV 8 tempered to 1000 N / mm ^{2 were used} at a cutting speed of 24 m / min, a cutting depth of 1.00 mm and a feed of 0.203 mm / rev. The chip length turned down to fretting was measured, with the results of six turning tools of one sample type being averaged in each case. The results are illustrated in Table 2, the hardness temperature used and the hardness values achieved being apparent.

As can be seen from this, the performance of the high-speed steel compositions according to the invention is practically equivalent to or even superior to that of the base material with a corresponding choice of the hardening temperature, which is particularly important in the savings thus achieved. The practical equivalence also resulted from the investigations of the casting and annealing structure carried out with the sample steels as well as the quantity and size distribution of the carbides.

Claims (1)

1. A high speed steel alloy with the carbide forming elements tungsten, molybdenum, chromium, vanadium, and niobium, characterised in that it contains 0.84 to 1.05 wt.% C, max. 1.0 wt.% Si, max. 1.0 wt.% Mn, 3.6 to 4.5 wt.% Cr, 4.6 to 6.5% wt.% Mo, 2.0 to 4.0 wt.% W, 0.5 to 1.6 wt.% V, and 0.5 to 1.5 wt.% Nb, the remainder being Fe and unavoidable impurities, provided that with a tungsten content of 2.0 to 3.0 wt.% the vanadium content is 1.3 to 1.6 wt. % and the niobium content is 0.8 to 1.5 wt.%, and that with a tungsten content of from more than 3.0 to 4.0 wt.% the vanadium content is 0.5 to 1.5 wt.% and the niobium content is 0.5 to 1.0 wt.%, the total content of vanadium and niobium being in the range of 1 to 2.5 wt.% in each case.