CA1130117A - High-speed steel tool - Google Patents

Abstract

ABSRACT OF THE DISCLOSURE
A highly wear-resistant rust-proof steel is provided which has high temperature stability and tempering stability for hot and cold working tools, as well as for working parts. The composition of the new high speed steel is as follows:
0.7 to 1.7% of C
0.01 to 0.08% of N
0.02 to 1.5% of B
0.01 to 1.5% of Si 0.01 to 1.0% of Mn 5.0 to 15.0% of Co 3.0 to 7.0% of Cr 13.0 to 20.0% of Mo 0 to 10.0% of W
0 to 5.0% of V
0.02 to 2.0% of Nb and/or of Ta

Description

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HIGH_SP~ED STEEL TOOL

The present invention relates to a highly wear-resistant rust-proof high speed steel of high temperature stability and tempering stab-ility for cold ard hot working tools as well as for working parts According to AISI standards for materials as well as according to ~Stahl_Eisen_Werkstoffblatt~ the alloying range of con~entional high-speed steels is as follows:
0.5 to 3 0% of C
O to 12.0% of Co 3.0 to 5.0% of Cr 0.5 to 12.0% of Mo 1 to 10.0% of V
1 to 19.0% of W
remainder Fe.
Smelting is carried out predominantly in arc furnaces and proces~ng by means of forging, rolling and drawing. The yield becomes sharply reduced as the alloying content ia mcreased. Tempered high-speed steels, therefore, fail to show more than a negligible content of 30% by ~olume of carbide.
In case the processing includes a semi-finished s'teel, i~ alloying content is restricted by its hot workability. This does not apply to the same~extent to the production~proces9es by which parts are produced, such as sintering and compression sintering as well as casting and armour_plating by means of hard-facing,spraylng or dipping. Mentioning these specialized processes~will indicate how *o provide for economy in alloying elements by means of com-,pounding different materials.' According to general op nion~ tool manufac~ure~

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High-speed steels are characterized by high tempering stability and temperature hardness as well as by a high resistance to wear. m e content of chromium in high-speed steels amounts to an average of 4~. This chromium con-tent, in conjunction with carbon, guarantees in a non-ferritic, martensitic structure, being pcor in restaustenite, sufficient hardness and ductility. m e temperature h æ dness is increased by means of fine-grained precipitation of special c æbides of the elements tungsten, molybdenum and vanadium in the mixed-c~ystal alloy. The carbides formed in the solidification of the smelt and in the solid phase, being imbedded in the martensite base material, produ oe a high resistan oe to we æ. A p æ ticularly strong influence on the resistan oe to wear is ascribed to the relatively hard vanadium carbides.
It is the object of the present invention to extend the servi oe life of tools made frcm high-speed, in particul æ hot-w~rked steels, by increasing their tempering stability. Furthermore, in the grinding of tools made from high-speed steel, simplification is to be accomplished and the resistance of the toolto wear is to be improved. Finally, the prcduction costs of the steel are to be reduced by means of a corresponding selection of raw materials, i.e. by the use of the most economical alloying elements.
This object has been achieved according to the present invention by suggesting for cold-and hot-working tools as well as for w,earing parts a highly wear-resistant steel of high temperature stabillty and tempering stability in

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~L3~1L7 the following metals are present in the following percentages by weight:-0.7 to 1.7% of C
0.01 to 0.08% of N
0.02 to 1.5% of B
0.01 to 1.5% of Si 0.01 to 1.0% of Mn 5.0 to 15.0% of Co

3.0 to 7.0% of Cr 13.0 to 20.0% of Mo 0 to 10.0% of W
; 0 to 5.0% of V
0.02 to 2.0% of Nb and/or of Ta remainder Fe.
A presently preferred steel comprises:
0.9 to 1.6% of C
0.01 to 0.08% of N
0.02 to 0.5% of B
0.01 to 1.4% of Si 0.01 to 0.5% of Mn 10.0 to 14.0% of Co 3.0 to 7.0% of Cr 15.0 to 19.0% of Mo 0.5 to 1.5% of V
0.05 to 1.0% of Nb and/or Ta ;:
remainder Fe, the percentages being by weight, providing that the relation of 1.3 ~ Ceff ~ 1.1 ~ CstOi ~ 2 has been met.

~ 1[) , ~3~7 The steel according to the present invention is particularly suitable for producing semi-finished steel and working parts by means of casting processes, including continuous casting as well as by powder-metallurgical processes, including compression sintering which affords the opportunity of adding to the starting powder hard substances, such as Fe3M2, CoMo, Fe3W2, CoW, TiC, WC, TaC, TiN.
According to this invention, provision has-further been made for armour-plating parts of structural steel and of tool steel with the steel according to the present invention. Armour-plating for the pu~pose of ; 10 protecting from wear is conventionally not subjected to any heat treatment.
However, if predetermined combinations of hardness and ductility are required for a specific use, the steel according to the present invention may be treated by heat. A preferred heat treatment comprises either single or multiple annealing at a temperature range of between 500 and 830C.
Although it forms part of the art to replace in high-speed steels part of the tungsten by molybdenum, the tungsten-free high-speed steels according ~i to the present invention are unconventional. It has become apparent that a valuable increase in properties is attained when hot-forming is abandoned and instead casting, welding and sintering processPs are applied. These permit a complete replacement of tungsten in favour of molybdenum. The obvious advantage of such a replacement is to be seen in the lowering of the specific weight of the alloy at a constant content of atom percentage as well as comparatively lower costs of raw materials, even for the same content of mass percentage, i.e.
for approximately ' ;"
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3L3~ 7 double the content of atom percentage.
The mechanical working of tempered steel as well as of steel in the casting or in the sintering process, by means of grinding, for example, will be substantially facilitated, if in addition to the replacement of tungsten by molybdenum in the cemented carbide M6C, the relatively hard vanadium carbide MC is replaced by molybdenum carbide of the types M6C and ~C. Due to a hig~h degree of hardness, vanadium carbide shows a high resistance to wear relative to conventional grinding materials . Table 1 shows a comparison of hard substa~ces in grinding materials and ofcarb~es in high-speed steel.
When high-speed steel was used for machining, no substantial lowering in the behaviour of wear was observed, in spite of a restriction of the special carbides to molybdenum carbides. However, the hardness of the molybdenum carbides and of the martensite steel matrix in the tool did exceed the hardness of the structural constituents inthe working piece.
Since in ppractice such a prerequisite presents itself frequent~r, it was ; assumed that~ in addition to the tempera*ure stability of the steel matrix, the quantity and the distribution are more importan* than the kind of the speclal carbides, as long as structural destruction and reactions by the tool upon the material of the working piece do not develop into dominating~factors of limitation. Bearing this in mind, the highest possible quantity~of fmely distributed molybdenum~carbides has been provided in the high-speed steel.
Vanadium has been retained as an alloying element at a rate which prevents the separate for~ation of vanadium carbide, as far as this is possible, High-speed steels having molybdenum contents of approximately~
13% up~Yard show during tempering in the temperature range of from SOO to . ~ :

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',: : . : ~ : . ' -~L~3~7 700 C, in addition to the depositing of carbide, also a depositing of an inter-mediate phase of Fe3Mo2 type. The maximum vaLue of hardness attainable at a changed tempering temperature is se-t for the speciaL carbides at 550 C and for the intermetaLlic phase at 600 C. A substantially improved te~pering stability (Graph No. 10, page 11 hereof) has been achieved by the overlapping of the depositing temperings across the spe d aL carbide and the intermetallic phase and by the position of the relevant maximum vaLue of hardness which has been dis-placed in the tempering temperature. A comparison was carried out with an S 10-4-3-10 type of steel. The molybdenum content to be set as high as possible for the purpose of increasing the tempering stabiLity had been restricted in the steels tested in the casting stage by the intermetaLlic phase of Fe3Mo2 (Drawing sheet No. 1) which begins to deposit from approximately 20% of Mo upward in the form of coarse platelets when the smelt solidifies. This causes substantial embrittLement of the working materiaL. Any admi~tures of cobalt aLloys for pre-venting the formation of ferrite and for increasing the tempering stability of the ~artensite reinfor oe the tendency to form the intermetallic phase and, there-fore, were restricted to 15% of Co.
The content of silicon must be adapted to the manufacturing pro oe ss.
~p to a content of 1.5% silicon improves the flowing and we-tting properties of the smelt as well as the formation of oxide on the welding material, without any mentionable reduction in temFering stability. Hcwever, there is a decrease in the sin~ring activity of uncased green compacts made from compressed powder.
A low sulphur content is particularly essential in cast structures, in order to obtain good ductile properties. It came as a surprise that the carbon ne oe ssary for acquiring the hardening can, in p æ t, be replaced by boron. In a replacement of this kind, the hardness was increased by approximately ~.5 HR~, independent f m m the tempering temperature, through the addition of 1% of boron.

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.- :, Boron contents of above 1.5g~ have an embrittling effect and sho~d be avoided.
mere is a content of carbon required, in order to prevent any interferenoe with the hardening by carbide depositing at the time of tempering. The car~on con-tent amounted to at least one half of the value of the stoichiometric carbon con-tent, considering the carbide-fonning alloying elements in the steel. me stoichiometric carbon content is represented by the following equation:
% of C toi = 0.06 % of Cr + 0.206 % of V + 0.063 % of Mo + 0.129 % of Nb + 0.066 gO of Ta.
The contents of the partly exchangeable elements of cæbon, boron and nitrogen may be combined to form an effective cæbon content as follows:
% of Ceff = gO of C + 0.86 % of N + 1.11 % of B.

The greatest possible h ædening at the time of tempering requires an effective carbon content of more than 1.3%, preferably more than 1.4%. The ratio of effective and stoichiometric carbon content should for reasons of ductility not substantially exceed a value of 1.1.
- In a cast structure, an addition of boron renders the eutectic carbon mixture coarser and reduoe s the dendrite length (Drawing sheet No. 2). It has thus been unexpected to find during temperature-tool-life torsional tests that the tool- or service-life behaviour of the boron-containing steel is favourable in comparison with non-boron steel (Graph No. 3 on page 13). The service life was considered from the beginning of the test to the beginning of blank braking.
A further improvement in tool-life behaviour has been achieved by minor additions of tantalum or niobium and of nitrogen (Graph No. 3). The tempering stability, increasing with the molybdenum content influences in particulæ the tool-life at a relatively high cutting speed.
In the Graph No. 4 on page 14, Examples 1, 2 and 3 of the steel shcw-ing different alloying contents, the tool life T has been defined in functional .
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~3L3~7 relation to the cutting speed v by the equation of v T = 31.9; T in min.; v in -The T - v curve of the reference steel S 10-4-3~10, material no.
3207.0, has been defined by the equation of v T 99 = 35.5; T in min.;
v in min . The relevant tool life curve shcwn in Illustration No. 6 shows the suFeriority of the introduoed steel over the conventional steel, the v60 discard value, relating to the drilling of a working piece made from 30 CrNiMo 8 is by about 1.5 m~min. comp æ atively greater than that of a conventional tool made from S 10-4-3-10.
Graph No. 5 on page 15, Exa~ple 4, shows a v æ iant of the afore-descri~ed steel and a relatively low dependence of the tool life upon the cutt-ing speed. The T - v curve is represented by the equation of v T l75 = 49.92; T in min.; v in min .

It will have to be observed that in the heat treatment of the intro-duced steel any soft annealing and h ædening treatments will generally be un-necessary. A tempering annealing in the temperature range of the precipitation hardening d oe s effect the desired tempering hardness above that in the cast or welded stage of apprcximately from 60 to 65 HRC. Example 5 of the steel acoord- ~ -ing to the present invention concerns the relation between tempering temperatu4e, ~ ;
hardness and tool or service life in a continuous section. GraFh No. 6 on page 16 re-~eals increasing tempering te~perature above 540 C hardness and tool life decrease. The greatest hardness after tempering at 540 C is to be associated with the lQngest tool life. A c~nparati~ely long tool life :: . . - : ~: : - :. ~ : : ~ : : . :

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was unexpectedly achieved only by the untempered sample which during testing was subjected to an automatic tempering effect by means of heating of the cutter. The temperature hardening, which decreases while thetempering process progresses, is expected to be responsible for the tool life.
Autogenous hard-facing of a higly molybdenous high-speed steel results in an increase in carbon content by appro~aimately 01.%.
Physical properties, such as density and heat expansion coefficient were established in a cast condition of the steel variants according to Examples 1 to 4 and in an annealed condition of the reference steel S 10-4-3-10. The characteristics obtained have been compiled in Table 2. The highly molybdenous steel, in spite of its high alloying content, shows a lower density than the reference steel. In heat expansion, the reference steel shows smaller co-efficients of expansion. The conversion of austenite in the aforenoted steels takes place during heating at between 800 and 900 C.
By comparison, the beginning of the allotropic ~ ~ conversiDn of the higly molybdenous steel is displaced by 30 to 40 C toward higher temperaturés~
Of a substantially greater significance, because of a magnitude of 100 C,1S
the difference in the solid and the liquid temperatures between the highly molybdenous steel and the reference steel. The relatively low solid temperature of approximately 1100 to 1150 C is advantageous in particular for casting and armour_plating; however, it prevents the conventional hardening treatment, As stated above, one tempermg treatment is sufficient for achieving the re~uired values of hardness.
Rust_proofing tests were conducted on the steel according to Example 4 (for composition see Illustration No. 7). Cast samples failed to show any formation of rust at 60 when~immersed in distilled water.

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Table l Comparison of the Vickers Hardness of Hard Substances Hard ~substances Vickers Hardness. Carbides in Vickers Hardness in grinding agents high-speed steel Corundum 1800 M6C (Mo-carbide) 1100 Silicon Carbide 2600 M2C (Mo_carbide) 1500 ~ MC (V-carbide~ 2800 .
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- 10 - '; ' 1~;30~ ~.7 Graph No. 1 Hardnes ~ nt upon tempering temperature Working materials and heat treatment:
(1) corresp. to S 0-18-1-12 ) hard-~aced and tenpered 3 x 1 h (accdg.
to clain) (2) S 10-4-3-10 1230 C 205s/oil and tempered 3 x 2 h (for oomparison) ~ I

A 60 ~ ~ J ~ ~ ~ ~ 640 68 tenpering temperature in C

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~13031 1~7 aph No. 2 Hardness after ~ering deperldent upon the effective carbon content Working materials: According to claims 1 and 2 State: l~ered (1) 540O C 3 x 1 h (2) 600 C 3 x 1 h effective carbon content: % of Cee = g~ of C + 0.86 % of N + 1.11 % of B

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65 ~ =Z.00 2.2 1.00 1.20 1.40 1.60 1.80 2.002.20 % of Ceff in mass per cent -- 12~
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` ~13C~il7 Graph No. 3 Temperature - tool life torsional test for testing the edge-holding prop2rty of boron-free, boron-containing and tantalumrcontaining hiqh-sp~ed st~els .r _ Basic composition: Si Mn Cr M~ V Co 1.3 0.03 4 1.8 1.3 12 Heat treabment: 600 C 3 x 1 h _ Ta= 0.50 _ 0O50 _ _ ~= 1.55 _ 1.56 _ 1.37 _ 1.33 _ O ~ .
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Cutting geom2try: 8 15 90 60 -4 1.0 mm Substance of work pie oe : 30 CrNiM~ 8 Stability: 980 N/mm2 2 Cut or machining section: a x s = 2.0 x 0.45 mm - 13 - ::

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~:~3~ 7 Temperature-tool life torsional test Gra~h_No. 4 _ Test tools: Hard-faced with electrodes of the ccmposition of ~esignat. C B N Si Mn P S Cr Mo V Co Ta Example 1 1.23 0.187 0.030 1.33 0.04 0.008 0.035 3.91 f8.16 1.20 11.81 0.48 Example 2 1.33 0.222 0.031 1.33 0.04 0,.014 0.033 3.91 18.12 1.25 11.77 0.48 Example 3 1.48 0.174 0.042 1.28 0.03 0,.010 0.035 3.67 18.12 1.20 11.77 0.46 Treatment: Autogenously hard-faced onlo basic w~rking material of 49 MnSiNb 3, tempered 600 C 3 x 1 h Referenoe tool: S 10-4-3-10 Heat treatment: 1240 C llOs/oil + 560 C 2 x 1 h } well hardness: 66.5 HRC
200 ~ . _ 150 ~ ~ _ _ _ loo ~ F----~ \I Y ~I ~ 1) Exa~ le ~ 50 .~ ~ "~3) $ == =--~=
I ~-~ S 10-4-3-10 ~ ~
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cutting geomet~ r U~ ~
~, 2021 22 ~3 24 25 26 27 28 29 Cutting speed in m~min Work piece substance: 30 CrNiMo 8 Sta`bility: 980 N/mm2 2 Cut or machining section: a x s = 2.0 x 0.45 mm ,~
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Temperature-tool life torsional test Graph No. S
Test tool: Hard-faced with electrcdes of the composition of Designat. C B N Si Mn P S Cr Mo V Co Ta Example 4 1.17 0.270 0.034 1.21 0.22 0.008 0.012 5.12 17.94 1.29 11.84 0.38 Treatment: Autogenously hard-faced onto basic working material of 49 MnSiNb 3, tempered 600 C 3 x 1 h Reference tool: S 10-4-3-10 Heat treatment: 1240 C 160s/oil + 560 C 2 x 1 h Rockwell har & ess: 66.5 HRC
200 _ _ _ l 150 _ _ ~ _ 100 _ ____ __ __ _ ~ _ Example 4 _ ~ ~ / - I _ ~ ~ ' I --I
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Y IttFing ~eome-try l 1 8~ 15 ~d Cutting speed in m/min Work pieoe substance: 30 CrNiMo 8 Stabi]ity: 980 N/mm2 Cut or machining section: a x s = 2.0 x 0.45 mm2 . ' ' ~ ~ , Graph No. 6 Temperature tool life during torsion test depending upon tempering temperature and hardness . . ~
Test tool: Hard faced with electrodes of the composition of esignat. %C %B ~oN %Si ~OMn %P %S %Cr %Mo %V %Co %I'a Example 5 1.18 0.191 0.049 0.57 0.14 <0.005 0.006 6.04 18.08 1.41 12.91 0.56 Treatment: Autogenously hard~faced onto basic w~rking material of 49 MnNbS
3, untempered and tempered X C 3 x 1 h Reference tool: S 10-4-3-10 Heat treatment: 1240 C 160s/oil + 550 C 2 x 1 h ~Dckwell hardness: 66.5 HRC
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60 62 64 66 68 .70 Hardness in HRC
Work pie~e substance: 30 CrNiMo 8 Stability: 980 N/mm2 Cut or machining section: a x s = 2.0 x 0.45 mm - , ~
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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A highly wear-resistant rust-proof steel of high temperature stability and tempering stability for cold and hot working tools as well as for working parts comprising:
0.7 to 1.7% of C
0.01 to 0.08% of N
0.02 to 1.5% of B
0.01 to 1.5% of Si 0.01 to 1.0% of Mn 5.0 to 15.0% of Co 3.0 to 7.0% of Cr 13.0 to 20.0% of Mo 0 to 10.0% of W
0 to 5.0% of V
0.02 to 2.0% of Nb and/or of Ta remainder Fe, the percentages being by weight.

2. A steel according to Claim 1, characterized by:
0.9 to 1.6% of C
0.01 to 0.08% of N
0.02 to 0.5% of B
0.01 to 1.4% of Si 0.01 to 0.5% of Mn 10.0 to 14.0% of Co 3.0 to 7.0% of Cr 15.0 to 19.0% of Mo 0.5 to 1.5% of V

0.05 to 1.0% of Nb and/or Ta remainder Fe, providing that the relation of 1.3 < Ceff <l-l ' C stoi < 2 has been met.

3. Armour-plating parts made from structural and tool steel of the types defined in Claim 1 and Claim 2.