|Publication number||US3850621 A|
|Publication date||Nov 26, 1974|
|Filing date||Dec 26, 1973|
|Priority date||Dec 27, 1972|
|Also published as||DE2263576A1, DE2263576B2|
|Publication number||US 3850621 A, US 3850621A, US-A-3850621, US3850621 A, US3850621A|
|Inventors||Haberling E, Kiesheyer H, Weigand H|
|Original Assignee||Deutsche Edelstahlwerke Gmbh|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Referenced by (18), Classifications (10)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent 191 Haberling et al.
1 HIGH-SPEED TOOL STEELS  Inventors: Edmund Haberling; Heinrich Kiesheyer, both of Krefeld; Hanshermann Weigand, Tonisvorst, all of Germany  Assignee: Deutsche Edelstahlwerke Gesellschaft mit beschrankter Haftung, Krefeld, Germany 22 Filed: Dec. 26, 1973 211 Appl. No.: 428,312
 Foreign Application Priority Data Dec. 27, 1972 Germany 2263576  US. Cl. 75/126 A, 75/126 C, 75/126 E, 7 75/126 H, 75/126 .1, 75/126 Q  Int. Cl. C22c 39/14  Field of Search 75/126 A, 126 C, 126 E, 75/126 H, 126 1,126 O  References Cited UNlTED STATES PATENTS 2,241,187 5/1941 De Vries 75/126 0 [451 Nov. 26, 1974 1/1967 Steven 75/126 Q 5/1974 Steven 75/126 A Primary ExaminerL. Dewayne Rutledge Assistant ExaminerArthur J. Steiner Attorney, Agent, or Firm-Cushman, Darby & Cushman  ABSTRACT 3 Claims, 3 Drawing Figures grind and also reduces their toughness.
HIGH-SPEED TOOL STEELS This invention relates to high-speed steels having a high wear resistance combined with good machinability and ductility, and particularly relates to such steels wherein the silicon content is a function of the C/W/Mo/V content.
High-speed tool steels are characterized by high re- 5 I sistance to wear up to working temperatures of 600C.
higher vanadium contents up to 5 percent, and higher corresponding percentages of carbon. Although such steels are highly wear-resisting, their high content of coarse particles of vanadium carbide, which has a hardness of about 3000 Vickers, makes them difficult to Recently the carbide content, and hence the wear resistance, has been raised by increasing the carbon content. Examples embodying such practice are the steels which in the A151 designation are known as M 41 and M 45, and which have vanadium contents of l to 2 percent with carbon contents between 1.1 and 1.2 percent. However it has been found that an increase in carbon leads to the development of spiculate carbides of the type M C, instead of the usual high-speed steel carbide M C (DEW Technical Reports 12, 1972, pp 111/33), and their hardness of around 2000 Vickers and unfavourable shape also adversely affect grindability and ductility.
The present invention is directed to solving the prob- 3 lem ofproducing high-speed tool steels which combine high wear resistance with good grindability and ductility.
The present invention is based on the surprising discovery that provided certain alloying relationships are observed, namely in correlating thesilicon content to Steel No.
. 2. pletely decomposes in a peritectoid reaction to the MC- and M C carbides which then appear in the desired form and distribution.
The invention provides a high-speed tool steel possessing high wear resistance combined with good ductility and machin'ability, consisting essentially of balance iron,
wherein the silicon content is not less than 0.5 percent and is determined by the formula Si 2.7 (%C) 0.1 (%W) 0.14 (%Mo) 0.5 @0113? 9- By the term consisting essentially of in the Specification and claims hereof, is meant that impurities andabove the quantity as hereinbefore set forth leads to an undesirable carbide development and hence to an impairment of the properties of the steel. in such a case coarse primary carbides of the type M C and MC appear.
l sman insla zlsa; H V
The content limits of the silicon that is to be introduced according to the present'specification are calcu-.
' lated from the equation hereinbefore set forth by reference to the limits in the content ranges of the melting y si g aa tsa nattisul rly we!!! The compositions of the examined steels within the ranges embraced by the invention are listed in the ac- C Cr W Mo V C0 Si 1 1.05 4.5 1.3 9.1 1.05 7. balance 1.03 1.10 5.5 1.5 2.5. 1.25 8.4 1.35 2 0.98 4.0 6.2 .0 1.75 .l. balance 0.56 1.03 4.5 6.5 5.25 2.0 0.59 3 0.98 4.0 1.5 8.0 1.75 V .l. balance 0.59 1.03 4.5 1.75 .5 2.0 0.94 4 0.97 5.0 2.5 2.75 2.25 J. balance 0.97 1.03 5.5 2.8 3.0 2.5 1.32
based on thg stated w limits of C. W. Mu. V l g to the w as herein set forth. W W
the contents of the alloying elements carbon. tungsten, molybdenum and vanadium, the carbide proportion in the structure can be increased without the formation of carbides which by reason of their configuration and hardness impair grindability and ductility. This correlation between the said alloying components according to the invention permits a peritectoid carbide reaction to take place which leads to fine and evenly distributed carbides and hence improves grindability and ductility.
The addition of exactly predetermined quantities of silicon according to the invention enables the carbon content to be raised and so adjusted thatalthough the carbide M C does form during solidification, it is so unstable that upon reheating prior to hot forming it comaccompanying drawings at a magnification x 500, of
which FIG. 1 shows that the steel containing 0.26 percent Si solidifies with the formation of the spiculate M C carbide and that this remains stable up to high degrees of deformation (FIGS. la c).
FIG. 2 shows that the Steel 1 having a silicon content according to the'above formula also solidifies via the M C eutectic but that its carbide is so unstable that this already decomposes as the ingot cools (FIG. 2a). This peritectoid decomposition becomes complete in the course of the following hot working process. Very fine and evenly distributed carbides of type M c and MC (FIGS. 2b and c) are formed, which impart to the Steel 1 a high resistance to wear coupled with good grindability and toughness.
FIG. 3 demonstrates that silicon contents exceeding that calculated by the equation according to the invention lead to solidification of Steel 1 via the M C eutectic, giving rise to the appearance of coarse primary MC carbides (FIG. 30). These coarse carbides cannot be fully broken down even by considerable deformation, and they lead to the development of an irregular coarse-grained structure which adversely affects the properties of the said Steel 1.
The majority of conventional high-speed tool steels have silicon contents that are too low for an optimal development of the carbides. If the present invention is applied to such steels their properties are improved, as illustrated by the following results.
With Steel 2, the plastic bending effort in a static bending test was determined. The Steel 2 had been heat-treated as follows: Hardened by oil quenching from 1,200C; tempered at 560C for two periods of one hour. The measured value was 2.5 .I. By comparison the corresponding values of steels similar to Steel 2 but containing only 0.3 percent Si and 1.8 percent Si, were about 2 J.
In order to test ductility and cutting performance planing tests were carried outwith Steel 3. A tool made of the said Steel 3 was hardened by oil quenching from l,200C. and tempered at 550C. for two periods of one hour. The wear on the underface was measured after 1000 strokes (equivalent to 450 metres total length of cut). The wear in Steel 3 was found to be 0.1 mm. Compared with this result steels similar to Steel 3 but containing 0.3 percent and 1.8 percent Si, showed twice as much wear, viz. 0.2 mm.
In a turning test on blanks made of Steel 4, the durability, i.e., the cutting speed in m/min at which the tool failed, i.e.. became useless in 30 minutes machining, was highest with a time of 19.5 m/min when the silicon content had been adjusted to the contents of the other alloying elements according to the invention. The tools made of Steel 4 were hardened by oil quenching from l,200C. and tempered at 540C. for two periods of one hour. However tests on steels of the composition similar toSteel 4, but in one instance containing 1.8 percent Si, and in another instance 0.3 percent Si, gave V60 durability test results of l9 m/min and I8 m/min.
properties is obtained. Increased silicon contents lead to greater hardness but they cause a shift of the secondary hardness maximum to lower annealing temperatures. This reduction in temper stability due to the silicon is a disadvantage in the use of such steels. It has been found that this disadvantage may be overcome by means of further alloying procedures and that the reduction in temper stability due to the silicon can be improved by raising the chromium content of the steels which is normally about 4 percent to higher values.
Thus in a preferred embodiment of the invention the optimum chromium content to ensure stability to temper should be related to the silicon content of the steel by the formula Cr=4 2 (%Si).
Silicon additions reduce the residual austenite which is present after the steels have been hardened. In order to mitigate this effect it is therefore advantageous to introduce into silicon-containing steels according to the invention nitrogen up to 0.] percent.
The present invention enables high-speed tool steels of optimum structure and hence of outstanding applicational properties, such as toughness, wear resistance and grindability to be produced. Despite their improved wear resistance steels composed as proposed by the present invention surprisingly still prove to be readily grindable. Whereas with grinding steels of corresponding other compositions the grinding wheels quickly choked and became blunted causing inadmissible heating and scorching of the ground tools, steels of the proposed composition could be ground substantially without any difficulty.
High-speed tool steels according to the invention are particularly suitable for the making of tools which call for a considerable amount of grinding to give them their final shape, particularly twist drills, taps, cutters, reamers and milling tools.
What is claimed is:
I. A high-speed tool steel possessing high wear resistance combined with good ductility and machinability, consisting essentially of 0.8 to 1.8 '/1 carbon,
3.5 to l0 /1 chromium.
l to l3 tungsten,
l to 10 /1 molybdenum. 0.5 [0 5 71 vanadium. 0 to 10 "/1 cobalt.
wherein the silicon content is not less than 0.5 percent and is determined by the formula Si 2.7 (%C) 0.1 (%W) 0.14 (%Mo) 0.5 (%V) 0.3.
2. A high-speed tool steel according to claim 1, wherein the chromium content is adjusted by reference to the silicon content according to the formula Cr=4+2 (%Si).
3. A high-speed tool steel according to claim 1,
wherein it contains up to 0.l percent nitrogen.
- l l =l
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|U.S. Classification||420/10, 420/37, 420/107, 420/111, 420/12, 420/69|
|International Classification||C22C38/00, C22C38/22|