Metal treatment – Stock – Ferrous
Reexamination Certificate
2000-09-19
2002-02-19
Wyszomierski, George (Department: 1742)
Metal treatment
Stock
Ferrous
C148S545000, C420S010000, C420S012000, C420S015000
Reexamination Certificate
active
06348109
ABSTRACT:
TECHNICAL FIELD
The invention relates to a new steel material which is manufactured in a non-powder metallurgical way, comprising manufacturing of ingots or castings from a melt. The steel material consists of an alloy, which besides iron and carbon, contains chromium, vanadium, and molybdenum as its substantial alloying elements in amounts which are chosen and balanced in such a way that the steel after hardening and tempering has a hardness and a microstructure which makes the material suitable in the first place for cold work tools but also for other applications where high requirements are raised on wear resistance and comparatively good toughness, such as materials for shaping or working ceramic masses, e.g. for tools to be used in the brick-making industry. The invention also relates to the use of the steel material and to a method for the manufacturing of the material, including the method for the heat treatment of the material.
BACKGROUND OF THE INVENTION
In the first place tool steels containing more than 10% chromium, which are manufactured conventionally, are used as materials for cold work tools, on which very high requirements are raised as far as hardness and wear resistance are concerned. The standardised steels AISI D2, D6, and D7, which today are used for abrasive cold work applications, are typical examples of this type of steels. The nominal compositions of these known steels are stated in Table 1.
TABLE 1
Conventional cold work steels - nominal compositions, weight-%
C
Si
Mn
Cr
Mo
W
V
AISI D2
1.5
0.3
0.3
12.0
1.0
—
1.0
AISI D6
2.1
0.3
0.8
12.5
—
1.3
—
AISI D7
2.35
0.3
0.5
12.0
1.0
—
4.0
Like all ledeburitic steels, steels of the above mentioned type solidify through the precipitation of austenite, whereafter M
7
C
3
-carbides are formed in the regions of residual liquid phase. This gives a material which does not satisfy high requirements on some product features which are of significant importance for cold work steels, namely good abrasive wear resistance in combination with good toughness. It is also a drawback with these conventional ledeburitic tool steels that they have a rather bad hot-workability.
As materials for cold work steels there are also used tool steels with high contents of vanadium, which are manufactured powder metallurgically. Those steels which are known by their trade names Vanadis®4 and Vanadis®10 are examples of this type of steels. The nominal compositions of these steels are stated in Table 2.
TABLE 2
Powder metallurgically manufactured cold work steels -
nominal compositions, weight-%, balance Fe and impurities
C
Si
Mn
Cr
Mo
V
Vanadis ® 4
1.5
1.0
0.4
8.0
1.5
4.0
Vanadis ® 10
2.9
1.0
0.5
8.0
1.5
9.8
The above, powder metallurgically manufactured steels offer extremely good combinations of wear resistance and toughness but are expensive to manufacture.
DISCLOSURE OF THE INVENTION
It is a purpose of the invention to provide a new steel material of steel alloy which can be manufactured in a conventional way through the manufacturing of a melt, from which there are cast ingots, which can be hot-worked to the shape of bars, plates, etc, of which there can be manufactured tools or other articles, which can be heat treated for the achievement of a final product having the desired combination of features. The conventional ingot manufacturing can be completed through some subsequent melt-metallurgical process-step, such as e.g. electro-slag-refining (ESR) or, as an alternative process, the building up of ingots of molten metal drops which are caused to solidify, such as according to the process which is known by the name of Osprey.
The field of use of the material of the invention may include anything from wear parts, e.g. within mining industry, to tools within the field of conventional cold work for the manufacturing of tools for blanking and forming, cold extrusion tooling, powder pressing, deep drawing etc, and tools or machine components for forming or working of ceramic masses, e.g. in the brick making industry. In connection herewith it is a particular objective of the invention to provide a material which has a better combination of wear resistance and toughness than conventional ledaburitic cold work steels of type AISI D2, D6, or D7.
Further it is an object of the invention to provide a material of an alloy which has a better hot workability than the said conventional ledaburitic cold work steels, wherein the yield in production in forging shops and rolling mills can be improved and hence also the production economy.
It is also a purpose of the invention to provide a material having good heat treatment properties. Thus it shall be possible to hardened the steel from austenitising temperatures below 1200° C., preferably from temperatures between 900 and 1150° C., typically from 950 to 1100° C. and the steel shall have a good hardenability; a good dimensional stability on heat treatments; and attain a hardness of 55-66 HRC, preferably 60-66 HRC, through secondary hardening.
An acceptable cutability and an acceptable grindability are other desirable features.
These and other aims can be achieved therein that the invention is characterised by what is stated in the appending, independent patent claims.
FIG. 1
illustrates a typical constitutional diagram of an alloy having vanadium, carbon, and molybdenum contents according to the invention and varying chromium contents. The diagram shows the phases in a state of equilibrium at different temperatures. When an ingot or a casting is caused to solidify slowly, the alloy will solidify through a primary precipitation of hard particles of MX-type in molten phase, where M is V and/or Nb, but preferably V, and X is C and/or N, but preferably C. The remaining, residual melt has a comparatively low content of alloying elements and will solidify to form austenite and MX (&ggr;+MX region in the phase diagram). During continued cooling, the &ggr;+MX+M
7
C
3
-region is passed rather quickly, in which region a smaller amount of carbides of M
7
C
3
-type can be precipitated, where M substantially is chromium.
Thus it is typical for the material of the invention that its micro-structure at the temperature 1100° C. in the state of equilibrium consists of austenite in molten phase, and hard particles of MX-type precipitated in the liquid phase, said M being V and/or Nb, but preferably V, and X is C and N, and also, possibly, a smaller amount of secondarily precipitated hard particles, normally max 2%, preferably max 1 vol-%, in the first place M
7
C
3
-carbides, in which M substantially is Cr.
The solidified structure of conventional ledaburitic cold work steel, which typically is lamellar, thus is replaced by an even distribution of hard components of MX-type, more than 50 vol-% of which having sizes within the range 3-20 &mgr;m and, typically a more or less round or elongated, rounded shape and possibly with a smaller amount of lamellar, solidified structure consisting of M
7
C
3
-carbides. After hot-working there is achieved a pronouncedly homogenous and finely dispersed carbide distribution, which is believed to be the main reason why the steel achieves a better hot workability than conventional ledaburitic cold work steels which are manufactured in a non-powder metallurgical way.
In connection with heat treatment comprising hardening and tempering, the material is heated to the &ggr;+MX-region of the phase diagram, wherein any existing M
7
C
3
-carbides, are dissolved and there is again achieved a structure consisting of austenite and hard particles of MX-type distributed in the austenite. At rapid cooling to ambient temperature, the austenite is transformed to martensite. The &ggr;+M+M
7
C
3
-region is passed comparatively quickly, which suppresses the formation of M
7
C
3
-carbides. Therefor it is also typical for the steel material of the invention that it at room temperature has a microstructure consisting of a matrix which substantially consists of martensite and in this matrix 10-40 vol-% and at some preferred embodiments of the inventio
Bednarek Michael D.
Combs-Morillo Janelle
Shaw Pittman LLP
Uddeholm Tooling Aktiebolag
Wyszomierski George
LandOfFree
Steel material and method for its manufacturing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Steel material and method for its manufacturing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Steel material and method for its manufacturing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2984712