WO1993002819A1 - High-speed steel manufactured by powder metallurgy - Google Patents

Abstract

The invention relates to a high-speed steel which is manufactured powder-metallurgically and has the following chemical composition in weight-%: 1.3-1.6 C, from traces to max 1.0 Si, from traces to max 1.0 Mn, 3-5 Cr, 4-7 Mo, 4-8 W, 2-4 V, 9-1 Co, balance essentially iron, impurities and accessory elements in normal amounts. The invention also relates to the hardened and tempered tool made of the steel.

Description

HIGH-SPEED STEEL MANUFACTURED BY POWDER METALLURGY.

The present invention relates to a high-speed steel with high hardnes and wear resistance after hardening and tempering. The invention also relates to the hardened and tempered tool made of the steel according to the invention.

The invention particularly aims at providing a high-speed steel havin an improved hot hardness as compared with the commerical high-speed steel which is known under its trade name ASP 3^'0 and which has the nominal composition 1.29 C, .4 Si, .3 Mn, 4.0 Cr, 5.0 Mo, 6.2 W, 8.5 Co, 3.1 V, balance essentially only iron and normally existing impurities. A feature which is particularly characteristic for the p alloy of the invention is that it in comparison with the said ASP 30 has a higher carbon content and a higher cobalt content. This provides a significant increase of the hardness of the steel, although the increase of the contents of carbon and cobalt are compartively small. The increased hardness is due not only to the fact that more carbon increases the carbon content of the steel but also in a co-action between and carbon and cobalt therein that the increased carbon content stimulates the decomposition of retained austenite during tempering after hardening, wherein the carbon content, which otherwise stabilizes the austenite, can be increased and hence also the hardness of the steel.

As far as the composition of the steel of the invention is concerned, reference is made to the accompanying claims.

The composition in weight-% of investigated steels are shown in Table 1. Also the nominal composition of the the commercial steel grade ASP

30 is shown in this table. Balance was iron, impurities and accessory elements in normal amounts. C Si Mn Cr Mo Co weight-%

.23 3.99 5.00 6.30 9.69 3.08

.29 4.00 4.99 6.22 9.57 3.02

.30 3.97 4.98 6.26 9.64 3.03

.3 4.0 5.0 6.2 8.5 3.1

ASP is a registered trade mark of Kloster Speedsteel AB.

All the steels were manufactured powder-metallurgically in the form o 200 kg capsules, which were consolidated to full density through hot isostatic compaction at 1150°C, 1 h and 1000 bar. From this material, rods with the dimension 100 mm 0 were manufactured through hot rolling.

From the manufactured material, there were made test specimens, which were hardened from temperatures varying between 1050 and 1220°C, cooled to room temperature and tempered at temperatures varying between 500 and 600°C.

The best result was achieved with the steel of the invention after hardening from a temperature between 1150 and 1200°C, preferably after hardening from a temperature between 1170 and 1190°C. Thus when hardening steel No. 1 from 1180°C followed by tempering at 560°C, 3 x 1 h, there is achieved a higher hardness than for the commercial steel grade ASP 30 (steel No. 4), an unsignificantly impaired bend rupture strength but the same toughness, as is shown in Table 2. The toughness was measured as the deflection of the test rod at rupture through so-called 4-point-bend-test.

Table 2

Steel HRC RmB F

1 69 4.4 1.8 4 67 4.6 1.8 The investigations imply on one hand that the steel shall have a preferred and a nominal composition, respectively, according to Table 3, and on the other hand that the steel shall be hardened from a temperature between 1150 and 1200°C, preferably from between 1170 and 1190°C, suitably from about 1180°C.

Table 3

balance essentially only iron, impurities and accessory elements in normal amounts.

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Claims

1. High-speed steel, c h a r a c t e r i z e d in that it is manufactured powder-metallurgically and that it has the following chemical composition in weight-%:

1.3 - 1.6 C from traces to max 1.0 Si from traces to max 1.0 Mn

3 - 5 Cr 4 - 7 Mo

4 - 8 W 2 - 4 V 9 - 12 Co

balance essentially only iron, impurities and accessory elements in normal amounts.

2. High-speed steel according to claim 1, c h a r a c t e r i z e d in that it contains:

9.5 - 12 Co

balance essentially only ir n, impurities and accessory elements in normal amounts.

3. High-speed steel according to.claim 2, c h a r a c t e r i z e d in that it has the following nominal composition:

balance essentially only iron, impurities and accessory elements in normal amounts.

4. High speed steel according to claim 3, c h a c r a c t e r i z e d in that it has the following nominal composition:

balance essentially only iron, impurities and accessory elements in normal amounts.

5. Tool with high hardness and wear resistance after hardening and tempering, c h a r a c t e r i z e d in that it is manufactured of a steel having the following composition in weight-%:

balance essentially only iron, impurities and accessory elements in normal amounts, and that the tool is hardened from a temperature between 1150 and 1200°C, preferably from 1170 to 1190°C, suitably fro about 1180°C followed by tempering at a temperature between 500 and 600°C.