US2185616A - High-speed steel - Google Patents

Description

Patented Jan. 2, 1940 UNITED STATES PATENT OFFICE Firth, Pittsburgh,

Pennsylvania Pa., Sterling Steel Company,

assignors to Firtha corporation of No Drawing. Application November 18, 1938;"

Serial No. 241,228

ZCIaims.

In the manufacture of high-speed steels it long has been known that tungsten may be replaced wholly or in part by molybdenum, and such replacement has been recognized to be in a general way valuable, affording tools of superior durability. See Gregg, The Alloys of Iron and Molybdenum, published for the Engineering Foundation, New York and London, 1932, p. 315. It has, however, been additionally found that, in the heat treatment of tools made from molybdenum steel, a softening will occur of the metal on and near the surface; and the softening has been found to 'be due to the burning out of the molybdenum. And it has been deemed advantageous to include in the mix a substantial chromium content, in order to counteract this bad tendency.

We have discovered that, given certain limiting conditions, molybdenum may be the chief and practically the whole substituent for the tungsten of the typical high-speed steel, and chromium may be substantially eliminated. This with the advantage that in the tool produced from the steel greater red-hardness is gained, greater cutting efilciency, and greater length of service. The limiting condition is the presence of boron. If, in a tool steel of otherwise normal mix, in which the carbon content does not exceed 1.00 per cent of the iron, boron be present in an amount ranging fromone quarter to one half of the carbon content, and if the chromium content be reduced to a quantity not exceeding 1.50 per cent, or even eliminated entirely, it becomes possible to produce a tool steelwhose molybdenum content ranges near to 8, say from '7 to 10 per cent, and the tool produced from the steel will have the superiority that has been indicated. The tool maybe treated in the usual manner without loss of hardness in consequence of the escape of molybdenum and of carbon from the surface of the tool. The boron appears to cause a thin film of molybdenum or iron-molybdenum borides on the surface which inhibits the burning out of molybdenum and carbon. As has been indicated, the carbon content should not exceed 1.00 per cent. It will preferably range from .50 to 1.00 per cent.

In the practice of the invention the preparation of the melt is along the usual lines. The molybdenum is introduced in the form of ferromolybdenum, and the boron as ferro-boron or boron carbide. The metallurgist will understand how to proceed in detail. The metal is castandforgcdlnregularprocedureandthe shaped article is subjected to the hardening and tempering steps that are familiar in the art.

Other alloying ingredients used in high-speed steels may be added for their usual efiects. For example, vanadium from .50 to 2.00 per cent increases toughness and raises the drawing temperature. Cobalt can be'added up to 10 per cent. It raises the hardening and drawing temperatures, increases the red-hardness, and toughens the steel. Copper up to 2 per cent helps in the forging and aids in the prevention of demolybdenizing or decarburizing. Nickel up to 5 per cent reduces the hardening temperature and reduces the hardness but does not affect the drawing temperature. It tends to make the alloy tougher. Tungsten in small amounts up to 2 per cent may replace part of the molybdenum but this is not recommended.

This improved steel may contain:

Boron The following are analyses of the non-ferrous contents of seven typical steels of the invention, the quantities of the several contents are given in percentages, relatively to the iron content:

I n IV v -VI VII 1.00 10:;; low low 'ifi .-75 1.25 1120 3:25 1:25

Of these, I, 11, and VI have been found to be most excellent.

Yet another steel was compounded upon the following analysis: carbon .75; silicon .25; manganese low; chromium .65; vanadium 1.25; molybdenum 8.00; cobalt 8.00; boron'.40. This proved to be an excellent high-speed steel. It will be observed of it that whilc the boron content slightly exceeds, it is substantially one half 'of the carbon content. 7

We claim as our invention:

1. A molybdenum tool steel carrying as alloys 5 of the ferrous metal:

Per cent Molybdenum 8.10 Vanadium 1,36 Bor n .22

10 Chromium 1.07 Cobalt 2.59 Carbon .73

2. A molybdenum tool steel carrying as alloys of the ferrous metal ELMER B. WELCH. LEWIS GERALD FIR'I'H.