Steel material for hot work tools

Details Steel material for hot work tools Steel material for hot work tools

2000-09-22

2002-04-02

Yee, Deborah (Department: 1742)

Alloys or metallic compositions

Ferrous

Chromium containing, but less than 9 percent

C148S333000

Reexamination Certificate

active

06365096

ABSTRACT:

TECHNICAL FIELD
The invention relates to a steel material for hot work tools, i.e. tool for forming or working metals at comparatively high temperatures.
TECHNICAL POSITION
The term ‘hot work tools’ is applied to a great number of different kinds of tools for the working or forming of metals at comparatively high temperatures, for example tools for die casting, such as dies, inserts and cores, inlet parts, nozzles, ejector elements, pistons, pressure chambers, etc.; tools for extrusion tooling, such as dies, die holders, liners, pressure pads and stems, spindles, etc.; tools for hot-pressing, such as tools for hot-pressing of aluminium, magnesium, copper, copper alloys and steel; moulds for plastics, such as moulds for injection moulding, compression moulding and extrusion; together with various other kinds of tools such as tools for hot shearing, shrink-rings/collars and wearing parts intended for use in work at high temperatures. There are a number of standard steel qualities used for these hot work tools, e.g. AISI Type H10-H19, and also several commercial special steels. Table 1 presents some of these standardised and/or commercial hot work steels.
TABLE I
Nominal chemical composition by weight-percentage of known hot work
steels
Steel
Steel type
no.
C
Si
Mn
Cr
Mo
W
Ni
V
Co
Fe
W.nr 1.2344/H13
 1
0.40
1.0
0.40
5.3
1.4
—
—
1.0
—
Bal.
W.nr 1.2365/H10
 2
0.32
0.25
0.30
3.0
2.8
—
—
0.5
—
″
W.nr 1.2885/H10A
 3
0.32
0.25
0.30
3.0
2.8
—
—
0.5
3.0
″
W.nr 1.2367
 4
0.38
0.40
0.45
5.0
3.0
—
—
0.6
—
″
W.nr 1.2889/H19
 5
0.45
0.40
0.40
4.5
3.0
—
—
2.0
4.5
″
W.nr 1.2888
 6
0.20
0.25
0.50
9.5
2.0
5.5
—
10.0
″
W.nr 1.2731
 7
0.50
1.35
0.70
13.0
—
2.1
13.0
0.7
—
″
H42
 8
0.60
0.30
0.30
4.0
5.0
6.0
2.0
″
Com. 1*
 9
0.35
0.1
0.6
5.5
3.0
—
—
0.8
—
″
Com. 2*
10
0.32
0.3
0.6
5.1
2.6
—
—
0.7
—
″
Com. 3*
11
0.39
0.2
0.7
5.2
2.2
—
0.6
0.8
0.6
″
W.nr 1.2396
12
0.28
0.40
0.45
5.0
3.0
—
—
0.7
—
″
W.nr 1.2999
13
0.45
0.30
0.50
3.1
5.0
—
—
1.0
—
″
QRO ® 90*
14
0.39
0.30
0.75
2.6
2.25
—
—
0.9
—
″
CALMAX ® *
15
0.28
0.60
0.40
11.5
—
7.5
—
0.55
9.5
″
H11
16
0.40
1.0
0.25
5.3
1.4
—
—
0.4
—
″
Com. 4*
17
0.37
0.30
0.35
5.1
1.3
—
—
0.5
—
″
Com. 5*
18
0.35
0.17
0.50
5.2
1.6
—
—
0.45
—
″
*Commercially available, non-standard steel. QRO ® 90 and CALMAX ® are registered trademarks of Uddeholm Tooling AB.
DESCRIPTION OF INVENTION
In the first phase of the invention, the steels 1-15 in Table 1 were studied. This study indicated that none of the steels studied satisfied the demands that can be placed on tools for all the different areas of application mentioned above. Consequently, subsequent work concentrated on the development of an alloy primarily intended for die casting of light metals, an area of application where there is a special need of a new steel material with a combination of properties that is better than that currently available using known steels. The objective of the steel material in accordance with the invention is to offer optimal properties in terms of good hardenability and microstructure in order to provide high levels of toughness and ductility also in heavy gauges. At the same time there must be no deterioration of tempering resistance and high temperature strength.
More particularly, a purpose of the invention is to offer a hot work steel with a chemical composition that is such that the steel can satisfy the following demands:
it must have good hot workability in order to thereby get a high yield on manufacture,
it should be capable of manufacture in very heavy gauges, which means thicker than e.g. 760×410 mm or thicker than Ø 550 mm,
it should have very low content of impurities,
it should not contain any primary carbides,
it should have good hot treatment properties, meaning inter alia that it should be capable of being tempered at a moderately high austenitizing temperature,
it should have very good hardenability, i.e. it should be capable of being through-hardened even in the above-mentioned very heavy gauges,
it should be form-stable during heat treatment,
it should have good tempering resistance,
it should have good high-temperature strength,
it should have very good toughness and very good ductility properties in the dimension ranges in question,
it should have good thermal conductivity,
it should not have an unacceptably large coefficient of heat expansion,
it should have good coating properties with PVD/CVD
itriding,
it should have good spark erosion properties, good cutting and welding properties, and
it should have a favourable manufacturing cost
The above-mentioned conditions can be satisfied by the invented steel material for the following reasons: firstly, by the steel alloy having such a basic composition that the material can be processed in order to yield an adequate microstructure with very even distribution of carbides in a ferritic matrix, suitable for further heat treatment of the finished tool; secondly, by the steel material with the said basic composition also having the prescribed low contents of silicon, which is to be regarded as an impurity in the steel of the invention, and also very low contents of the non-metallic impurities nitrogen, oxygen, phosphor and sulphur. Indeed it has long been known that non-metallic impurities, such as sulphur, phosphor, oxygen and nitrogen, involve certain negative effects for many steels, especially regarding the toughness of the steel. This also applies concerning the knowledge that some metals in trace element levels may have negative effects for many steels, such as reduced toughness. For instance, this applies in relation to titanium, zirconium and niobium at small levels. Nonetheless, it has not been possible in the case of most steels, including hot work steel, to improve toughness significantly solely by reduction of contents of impurities of this nature in steel. The study conducted of existing steel alloys has also demonstrated that good toughness cannot be attained solely by optimising the basic composition of the steel alloy. It was only possible to attain the said conditions by a combination of an optimal basic composition and low or very low contents of the said non-metallic impurities, and also preferably a very low content of titanium, zirconium and niobium.
In order to satisfy the above-mentioned conditions the invented steel material has an alloy composition that by weight-percentage essentially consists of:
0.3-0.4 C, preferably 0.33-0.37 C, typically 0.35 C
0.2-0.8 Mn, preferably 0.40-0.60 Mn, typically 0.50 Mn
4-6 Cr, preferably 4.5-5.5 Cr, suitably 4.85-5.15 Cr, typically 5.0 Cr
1.8-3 Mo, preferably max. 2.5 Mo, suitably 2.2-2.4 Mo, typically 2.3 Mo
0.4-0.6 V, preferably 0.5-0.6 V, suitably 0.55 V, balance iron and unavoidable metallic and non-metallic impurities, in connection said non-metallic impurities comprising silicon, nitrogen, oxygen, phosphor and sulphur, which may be included up to the following maximum contents:
max. 0.25 Si, preferably max. 0.20 Si, suitably max. 0.15 Si
max. 0.010 N, preferably max. 0.008 N
max. 10 ppm O, preferably max. 8 ppm O
max. 0.010 P, preferably max. 0.008 P, and
max. 0.010 S, preferably max. 0.0010, suitably max. 0.0005 S
It is preferable that titanium, zirconium and niobium occur in the following maximum contents by weight-%
max. 0.05 Ti, preferably max. 0.01, suitably max. 0.008,
and most preferably max. 0.005,
max. 0.1, preferably max. 0.02, suitably max. 0.010,
and most preferably 0.005 Zr,
max. 0.1, preferably max. 0.02, suitably max. 0.010,
and most preferably max. 0.005 Nb.
As regards the choice of individual desirable alloy elements, it can be briefly stated that the contents of carbon, chromium, molybdenum and vanadium have been chosen so that the steel should have a ferritic matrix in the delivery condition of the material, a martensitic matrix with adequate hardness after hardening and tempering, absence of primary carbides but the existence of secondary precipitated carbides o

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