Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2001-11-15
2004-11-16
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S246000
Reexamination Certificate
active
06818040
ABSTRACT:
TECHNICAL FIELD
The invention relates to a powder metallurgy manufactured high speed steel with a high content of nitrogen in the form of a body formed through consolidation of alloyed metal powder. The invention particularly relates to a high speed steel suitable for cold work tools intended for applications where the tool is subjected to heavy friction between the working material and the tool resulting in a risk of adhesive wear.
BACKGROUND OF THE INVENTION
Cold work often includes blanking, punching, deep drawing, and other forming of metallic working materials, which usually have the form of sheets or plates, normally at room temperature. For this type of work there are used cold work tools, on which a number of requirements are raised, which are difficult to combine. The tool material shall have a high resistance against abrasive wear, which among other things implies that it hall have an adequate hardness; it shall also have a good resistance against adhesive wear for certain applications; and it shall also have an adequate toughness in its use condition.
For the above and other applications there is to a great extent used a cold work steel which is known under its trade name Sverker 21®, which is a conventionally manufactured steel having the composition 1.55 C, 0.3 Si, 03 Mn, 12.0 Cr, 0.8 Mo, 0.8 V, balance iron and impurities in normal amounts. For cold work tools there is also used the powder metallurgy manufactured tool steel which is known by its trade name Vanadis 4®, which contains 1.5 C, 1.0 Si 0.4 Mn, 8.0 Cr, 1.5 Mo, 4.0 V, balance iron and impurities in normal amounts. Also high speed steels are employed, such as those high speed steels which are known under the trade names ASP®2023 and ASP®2053. The former one has the nominal composition 1.28 C, 4.2 Cr, 5.0 Mo, 6.4 W, 3.1 V, while the latter one has the nominal composition 2.45 C, 4.2 Cr, 3.1 Mo, 4.2 W, 8.0 V, wherein the balance in both the steels is iron, normal amount of Mn and Si and normally existing impurities.
The above mentioned and other steels available on the market place satisfy high requirements on abrasive wear resistance, toughness and other features. However, they do not satisfy high requirements on adhesive wear resistance, which often is a dominating problem in connection with different types of cold forming tool applications, such as pressing of sheets, pipe bending, and cold extrusion. These problems particularly can arise in connection with cold working of sheets of austenitic and ferritic stainless steels, copper, brass, aluminium, and others. The problems can be reduced by lubrication and/or surface coating of the tool surfaces with friction reducing ceramic layers of eg. TiN through PCD or CVD technique, through surface nitriding, or through hard chromium plating, but those are expensive and time consuming problem solutions. In addition, the risk of damages and/or flaking of the depositions is great. If abrasive or adhesive wear damages arise, the repair will be complicated because any defect always will be located on a very stressed part of the tool.
BRIEF DISCLOSURE OF THE INVENTION
It is the purpose of the invention to provide a high speed steel for cold work tools with a very high resistance to adhesive wear in combination with other desirable fires of cold work tools, such as adequate toughness, harness, and resistance to abrasive wear. The steel shall, after pressing the powder to form a consolidated body through hot isostatic compaction (HIP-ing), be able to be hot worked through forging, rolling, and extrusion or be used in the as HIP-ed condition.
These and other objectives can be achieved therein that the high speed steel, with reference to its chemical composition in weight-%
1-2.5 C
1-3.5N
0.05-1.7 Mn
0.05-1.2 Si
3-6 Cr
2-5 Mo
0.5-5 W
6.2-17(V+2Nb)
balance iron and unavoidable impurities in normal amount, wherein the amount of, on one hand, the carbon equivalent, Ceq, expressed as
Ceq
=
C
+
12
14
N
,
and, on the other hand, the vanadium equivalent, Veq, expressed as Ve=V+2 Nb, shall be balanced relative to each other such that the amounts of said elements, expressed in terms of said equivalent, will lie within the area A
1
-B
1
-C
1
-D
1
-A
1
in the system of co-ordinates in
FIG. 1
, in which Ceq/Veq-co-ordinates of the point A
1
-D
1
are
A
1
:4.5/17
B
1
:5.5/17
C
1
:2.5/6.2
D
1
1.5/6.2
and that the high speed steel with reference to its structure, in the hardened and tempered condition of the steel, contain 12-40 vol-% of hard matter consisting of particles of MX-type, which are evenly distributed in the matrix of the steel, M in said matter of MX-type essentially consisting of vanadium and/or niobium, and X consisting of 30-50 weight-% carbon and 50-70 weight-% nitrogen.
In the following, a number of more limited areas will be defined, defining different embodiments and variants of the invention with reference to the relations between carbon equivalent and vanadium equivalent. I the list below, the Ceq/Veq-co-ordinates for all the points which have been indicated in the diagram in
FIG. 1
have been stated.
In this text percentages refer to weight-%, unless otherwise is mentioned
Ceq/Veq-co-ordinates of indicated points in FIG. 1
A1:4.5/17
A2:4.6/17
A3:4.75/17
B2:5.3/17
B1:5.5/17
A1′:4.35/16.5
A2′:4.45/16.5
A3′:4.6/16.5
B2′:5.15/16.5
B1′:5.35/16.5
A1″:4.2/16
A2″:4.3/16
A3″:4.5/16
B2″:5.0/16
B1″:5.2/16
F1″:3.8/14.5
F2″:3.9/14.5
F3″:4.05/14.5
E2″:4.6/14.5
E1″:4.8/14.5
F1′:3.65/14
F2′:3.75/14
F3′:3.9/14
E2′:4.45/14
E1′:4.65/14
F1:3.55/13.5
F2:3.65/13.5
F3:3.8/13.5
E2:4.35/13.5
E1:4.55/13.5
F1′″:3.25/12.5
F2′″:3.35/12.5
F3′″:3.5/12.5
E2′″:4.05/12.5
E1′″:4.25/12.5
F1
IV
:3.1/12
F2
IV
:3.2/12
F3
IV
:3.35/12
E2
IV
:3.9/12
E1
IV
:4.1/12
G1
IV
:2.7/10.5
G2
IV
:2.8/10.5
G3
IV
:2.95/10.5
H2
IV
:3.5/10.5
H1
IV
:3.7/10.5
G1′″:2.55/10
G2′″:2.65/10
G3′″:2.8/10
H2′″:3.35/10
H1′″:3.55/10
G1:2.4/9.5
G2:2.5/9.5
G3:2.65/9.5
H2:3.2/9.5
H1:3.4/9.5
G1′:2.27/9
G2′:2.37/9
G3′:2.52/9
H2′:3.07/9
H1′:3.27/9
G1″:2.15/8.6
G2″:2.25/8.6
G3″:2.4/8.6
H2″:2.95/8.6
H1″:3.15/8.6
D1″:1.85/7.4
D2″:1.95/7.4
D3″:2.10/7.4
C2:2.65/7.4
Cl″:2.85/7.4
D1′:1.75/7
D2′:1.85/7
D3′:2.0/7
C2′:2.58/7
Cl′:2.75/7
D1:1.5/6.2
D2:1.6/6.2
D3:1.75/6.2
C2:2.3/6.2
Cl:2.5/6.2
A number of preferred or conceived embodiments of the invention with reference to the relation between the carbon and vanadium equivalents of the steel within the entire range Veq=6.2−17 (V+2 Nb) are stated in the sub-claims
2
-
5
.
In the following, the election of the different alloy elements and the contents of them will be explained more in detail.
Carbon has two important functions in the steel of the invention. On one hand it shall, together with nitrogen and vanadium and/or niobium, form vanadium and/or niobium carbonitrides; on the other hand carbon shall exist in a sufficient amount in the matrix of the steel in order to provide a desired hardness of the martensite which is obtained after hardening and tempering. More particularly the content of carbon which is dissolved in the matrix should amount to 0.40-0.60%, preferably to 0.47-0.54. From these reasons, carbon shall exist in an amount of at least 1 weight-% and max 2.5 weight-%.
In said hard matter of MX-type, i.e. vanadium and/or niobium carbonitrides, X shall consist of 30-50 weight-% carbon and 50-70 weight-% nitrogen, wherein the ratio weight-% N/weight-% C of the amounts and nitrogen and carbon which are present in said carbonitrides of MX-type shall satisfy the conditions:
1.0
≤
weight
-
%
N
weight
-
%
C
≤
2.3
.
The amount of nitrogen which exist in the steel in its molten state prior to gas granulation and the amount of nitrogen which is added to the steel by n
Sandberg Odd
Westin Leif
Mai Ngoclan
Uddeholm Tooling Aktiebolag
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