CORROSION AND FATIGUE RESISTANT CEMENTED CARBIDE PROCESS LINE TOOL

Abstract

A process line tool of a cemented carbide comprising in wt %; about 2.9-11 Ni; about 0.1-2.5 Cr.sub.3C.sub.2; and about 0.1-1 Mo; and a balance of WC, with an average WC grain size less than or equal to 0.5 μm.

Claims

1-13. (canceled)

14. A metal forming tool comprising a composition, the composition comprising, in wt % (weight %): 2.95 to 3.15 Ni; 0.1 to 0.3 Cr.sub.3C.sub.2; 0.1 to 0.3 Mo; and a balance of WC.

15. The metal forming tool according to claim 1, wherein the composition comprises from 95.85 to 96.85 wt % WC.

16. The metal forming tool according to claim 1, wherein the sintered tool has a tungsten carbide average grain size of less than 0.5 microns.

17. The metal forming tool according to claim 1, wherein the sintered tool has a tungsten carbide average grain size of about 0.35 microns.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1: discloses the results of the potentiodynamic sweep tests for sample A, B and C in the examples.

DETAILED DESCRIPTION

[0011] The present disclosure provides a process line tool comprising a composition containing in wt % (weight %): 2.9 to 11 Ni; 0.1 to 2.5 Cr.sub.3C.sub.2 and 0.1 to 2.5 Mo and a balance of WC. Surprising it has been found with the cemented carbide composition disclosed in this application that a significant improvement in corrosion resistance can be achieve whilst still achieving good fatigue resistance.

[0012] According to the present disclosure, the process line tool defined hereinabove or hereinafter is either a rotary cutter knife or metal forming tool. Examples of a metal forming tools, but not limiting to, are can punches, wire drawing dies, tools for stamping, clamping and shaving metals.

[0013] In the present disclosure, Mo as disclosed hereinbefore or hereinafter may be in its elemental or carbide form.

[0014] In one embodiment, the process line tool has a cemented carbide composition comprising from about 9.1 to about 10.1 wt % Ni, such as 9.6 wt %.

[0015] In one embodiment, the process line tool has a cemented carbide composition comprising from about 0.8 to about 1.0 wt % Cr.sub.3C.sub.2, such as 0.9 wt %.

[0016] In one embodiment, the process line tool has a cemented carbide composition comprising from about 0.8 to about 1.0 wt % Mo, such as 0.9 wt %.

[0017] In one embodiment, the process line tool has a cemented carbide composition comprising from about 87.9 to about 89.1 wt % WC, such as 88.6 wt %.

[0018] In one embodiment, the process line tool has a cemented carbide composition comprising in wt %: of: 9.6 Ni; 0.9 Cr.sub.3C.sub.2; 0.9 Mo and 88.6% WC.

[0019] In one embodiment, the process line tool has a cemented carbide composition comprising from about 2.95 to about 3.15 wt % Ni, such as 3.05 wt %.

[0020] In one embodiment, the process line tool has a cemented carbide composition comprising from about 0.1 to about 0.3 wt % Cr.sub.3C.sub.2, such as 0.2 wt %.

[0021] In one embodiment, the process line tool has a cemented carbide composition comprising from about 0.1 to about 0.3 wt % Mo, such as 0.2 wt %.

[0022] In one embodiment, the process line tool has a cemented carbide composition comprising from about 95.85 to about 96.85 wt % WC, such as 96.55 wt %.

[0023] In one embodiment, the process line tool has a cemented carbide composition comprising in wt % of; 3.05 Ni; 0.2 Cr.sub.3C.sub.2; 0.2 Mo and 96.55% WC.

[0024] In one embodiment, the process line tool has a cemented carbide has an average sintered tungsten carbide grain size of less than 0.5 microns, such as an average of about 0.35 μm.

[0025] According to one embodiment, the present disclosure relates to a process line tool, wherein the process line tool is a rotary cutter or metal forming tool, having a composition of from about 9.1 to about 10.1 wt % Ni; from about 0.8 to about 1.0 wt % Cr.sub.3C.sub.2, from about 0.8 to about 1.0 wt % Mo; from about 87.9 to about 89.1 wt % WC and an average sintered WC grain size of less than 0.5 μm. The tool will have typical material properties of: a density from about 14.3 to about 14.5 g/cm.sup.3; a hardness of from about 1450 to 1600 HV30 and toughness from about 9.2 to 10.2 MPa.Math.√m.

[0026] According to another embodiment, present disclosure relates to a process line tool, wherein the process line tool is a metal forming tool, having a composition of from about 2.95 to about 3.15 wt % Ni; from about 0.1 to about 0.3 wt % Cr.sub.3C.sub.2, from about 0.1 to about 0.3 wt % Mo; from about 95.85 to about 97.25 wt % WC and an average sintered WC grain size of less than 0.5 μm. The tool will have typical material properties of: a density from about 15.1 to about 15.4 g/cm.sup.3; a hardness of from about 1850 to 2000 HV30 and toughness from about 5 to 6 MPa.Math.√m.

[0027] Typically grades used in rotary cutting and metal forming applications are submicron grades. Submicron grades give a good combination of high hardness, abrasion resistance and good edge retention properties. Submicron grades are defined a cemented carbide having a sintered tungsten carbide grain size of <1 μm.

[0028] The wear resistance and appropriate corrosion resistance of the cemented carbide grade can be achieved by using a binder formulated from a stainless steel alloy suitably matched to the composition of other steel components of the process line tool in order to minimise galvanic effects and to give superior corrosion resistance. When the cemented carbide component is joined to another stainless steel component it is found that the cemented carbide will corrode preferentially. This is because a galvanic cell is created between the cemented carbide component, the stainless steel and the corroding media. The corroding media may have a pH as low as 2.5 in an extreme case. Therefore the potential difference between the cemented carbide component and the stainless steel is reduced; meaning the driving force for corrosion is reduced.

[0029] It should be appreciated that the following examples are illustrative, non-limiting examples. The compositions and results of the embodiments are shown in Tables 1 and 2 below.

EXAMPLES

[0030] Cemented carbide grades with the compositions shown in table 1 were prepared from powders forming the hard constituents and powders forming the binder. The powders were wet milled together with PEG 34 lubricant and afla anti-flocculating agent until a homogeneous mixture was obtained and granulated by drying. The dried powder was pressed on the Tox press to green bodies before sintering. Sintering was performed at 1360-1410° C. for about 1 hour in vacuum, followed by applying a high pressure, 50 bar Argon, at sintering temperature for about 30 minutes to obtain a dense structure before cooling.

TABLE-US-00001 TABLE 1 Ref A (comparison) B (comparison) C (invention) WC 89.5 89.85 88.6 Starting WC grain 0.8 0.8 0.8 size (μm) Co (wt %) 10 6.6 0 Ni (wt %) 0 2.2 9.6 Mo (wt %) 0 0.2 0.9 Cr.sub.3C.sub.2 (wt %) 0.5 1.15 0.9

[0031] The sintered test coupons have an average tungsten carbide grain size of about 0.35 μm, as measured using the linear intercept method.

TABLE-US-00002 TABLE 2 Ref A B C Density (g/cm.sup.3) 14.4-14.6 14.3-14.6 14.3-14.5 Hardness (Hv30) 1550-1650 1600-1700 1450-1600 Toughness (K1c) 10.5-11.5  9.0-10.0  9.2-10.2 (Palmqvist)

[0032] In the examples the powders were sourced from the following suppliers: Co from Umicore or Freeport, Ni from Inco, Mo from HC Starck and Cr.sub.3C.sub.2 from Zhuzhou or HC Starck.

[0033] The properties in table 2 have been measured according to standards used in the cemented carbide field, i.e. ISO 3369:1975 for the density and ISO 3878:1983 for the hardness. Sintered tungsten carbide grain sizes have been measured using the linear intercept method according to ISO 4499-2:2010.

[0034] Discs were pressed to an approximate diameter of 25 mm and a thickness of 5 mm and supplied with smooth surfaces. Potentiodynamic polarization tests were performed on samples A, B and C at room temperature using a modified ASTM G61 test. ASTM G61 covers a procedure for conducting potential dynamic polarization measurements. Modification was made to the media with the standard 3.5% NaCl solution replaced by aerated HCl with an acidity of pH 2.5. This media is representative of the acidity that the cemented carbide process line tool may need to work in. A further modification compared to the standard test is that an epoxy seal was used rather than a flushed port cell. The epoxy was used to seal the edges of the specimen in order to prevent crevice corrosion. Areas of approximately 5 cm.sup.2 were left exposed. The specimens were cleaned and degreased in acetone in an ultrasonic bath and then dried in air before immersing them in the solution. The test solution was stirred at 600 rpm using a magnetic stirrer. The corrosion potential (E.sub.corr) was monitored for 1 hour before performing the potentiodynamic sweeps in the anodic direction.

[0035] The potentiodynamic polarization sweep test results for sample A, B and C are shown in FIG. 1 and the electrochemical parameters derived from the potentiodynamic tests are shown in table 3.

The potentiodynamic anodic polarization test method is commonly used to rank the resistance of materials to localized corrosion in a given environment. The rationale for this test method is that the application of a positive potential to the specimen provides a driving force for the breakdown of the passive film and thereby initiates localized corrosion. By sweeping the potential at a constant rate in the anodic direction, the susceptibility to localized corrosion of the material can be evaluated from the potential at which the anodic current increases rapidly due to pitting of the surface which is known as the pitting potential, E.sub.p. A more positive pitting potential signified a more corrosion resistant material. For materials with a very high resistance to pitting it is not possible to measure a pitting potential, as instead the entire surface will start to corrode through the passive layer through transpassive corrosion before a pitting potential is reached, this transpassive corrosion of the entire surface tends to occur at very high potentials not usually encountered in real application. The pitting potential has been defined as potential at which the current density first exceeds 0.1 mA/cm.sup.2 during the potential sweep.

TABLE-US-00003 TABLE 3 Sample Ecorr (mV SCE) E.sub.p (mV SCE) A −306 — B −187 347 C 89 >871

[0036] FIG. 1 and table 3 show that sample A has poor corrosion resistance, with no evidence of passivation and active corrosion from the start of the potential sweep. It can also be seen that the corrosion is much improved in sample B, a pitting potential of 347 mV (SCE)

was observed. Further they show that there is significant further improvement in the corrosion resistance for sample C with only transpassive corrosion of the entire surface occurring at very high potentials before any pitting could occur.