Drill bit insert for rock drilling

Abstract

Drill bit insert with a sintered cemented carbide body including a hard phase of tungsten carbide (WC) and a binder phase wherein the cemented carbide comprises 5.0-7.0 wt % Co, 0.10-0.35 wt % Cr, and a Cr/Co weight ratio of 0.015-0.058. The cemented carbide body has a hardness of 1520-1660 Hv30 and a toughness of K1.sub.c10.0 both measured in the bulk at the center of the longitudinal axis through the center of the insert, or 5 mm from any surface of the insert. The insert further has a surface toughness K1.sub.c12.0 measured at 0.5 mm below the surface of the body in a transverse direction to the longitudinal axis the insert. The invention also relates to a drill bit comprising the insert and the use of such a drill bit for drilling.

Claims

1. A drill bit insert for rock drilling comprising a sintered cemented carbide body having a bulk and a surface, and including a hard phase of tungsten carbide (WC) and a binder phase wherein the cemented carbide body comprises: 5.0-7.0 wt % Co, 0.10-0.35 wt % Cr, and balance WC including possible impurities; wherein the cemented carbide body has a Cr/Co weight ratio of 0.015-0.058 and a mean WC grain size of 0.60-0.95 m, wherein the sintered cemented carbide body has a bulk hardness of 1520-1660 Hv30 and a bulk toughness of Kl.sub.c10.0 both measured in the bulk at a measurement point5 mm from the surface of the body, and a mechanically induced surface toughness of Kl.sub.c12.0 measured at a measurement point 0.5 mm below the surface of the body.

2. The drill bit insert according to claim 1, wherein the body comprises 5.4-6.4 wt % Co.

3. The drill bit insert according to claim 1, wherein the body comprises 5.6-6.2 wt % Co.

4. The drill bit insert according to claim 1, wherein the body comprises 0.20-0.30 wt % Cr and/or a Cr/Co weight ratio of 0.031-0.055.

5. The drill bit insert according to claim 1, wherein the body comprises 0.20-0.30 wt % Cr and/or a Cr/Co weight ratio of 0.031-0.042.

6. The drill bit insert according to claim 1, wherein the mean WC grain size of the body is 0.65-0.90 m.

7. The drill bit insert according to claim 1, wherein the mean WC grain size of the body is 0.70-0.90 m.

8. The drill bit insert according to claim 1, wherein the bulk hardness is 1520-1600 Hv30 measured in the bulk at a measurement point5 mm from the surface of the body.

9. The drill bit insert according to claim 1, wherein the surface hardness is 1530-1680 Hv30 measured at a measurement point 0.5 mm below the surface of the body.

10. The drill bit insert according to claim 1, wherein the hardness is 1540-1700 Hv30, measured at a measurement point 0.5 mm below the surface of the body.

11. The drill bit insert according to claim 1, wherein the toughness is Kl.sub.c11.0 measured in the bulk a measurement point5 mm from any the surface of the insert body, and/or Kl.sub.c13.0 measured at a measurement point 0.5 mm below the surface of the body.

12. The drill bit insert according to claim 1, wherein the toughness is Kl.sub.c11.0 measured in the bulk a measurement point5 mm from the surface of the body, and/or Kl.sub.c14.0 measured at a measurement point 0.5 mm below the surface of the body.

13. The drill bit insert according to claim 1, wherein the cemented carbide further comprises a cubic carbides (W.sub.xM.sub.1-x)C phase (M=Ti, Ta, Nb, Zr or Hf) up to 0.2 wt %.

14. A drill bit comprising one or more drill bit inserts according to claim 1.

Description

BRIEF DESCRIPTIONS OF DRAWINGS

(1) FIG. 1. Cross section made through the longitudinal axel (A) at the center of a drill bit insert.

(2) FIG. 2. Toughness increase due to surface treatment of AC9. Here represented by the measured values from inserts having a diameter of 14.5 mm and having a height of 26.2 mm.

(3) FIG. 3. Toughness increase due to surface treatment of AC10. Here represented by the measured values from inserts having a diameter of 14.5 mm and having a height of 26.2 mm.

(4) FIG. 4. Hardness increase due to surface treatment of AC9. Here represented by the measured values from inserts having a diameter of 14.5 mm and having a height of 26.2 mm.

(5) FIG. 5. Hardness increase due to surface treatment of AC10. Here represented by the measured values from inserts having a diameter of 14.5 mm and having a height of 26.2 mm.

(6) FIG. 6. Wear data from in-house testing of AC1, AC2, AC3 and AC4 compositions.

(7) FIG. 7. Test bits used for field testing. Shows major drilling, underground work with COP 44 STD. The Cop 44 is a DTH hammer from the company Atlas Copco.

DETAILED DESCRIPTION OF EMBODIMENTS

(8) The invention is here described in detail in relation to a manufacturing process and examples.

(9) Composition and Powder Preparation

(10) Powder batches with compositions according to Table 1 were made according to established cemented carbide manufacturing processes.

(11) Powders of WC, Co, C and grain refining additives such as Cr.sub.3C.sub.2 and NbC according to the examples in Table 1 were milled in a ball mill for in total 40 to 60 hours. The desired carbon content was adjusted through the addition of granulated carbon powder before milling. The adjustments were based on the analyzed C-content of the WC and the desired total C-content (Cp) of the powder batch. In Table 1 the calculated corresponding Cr and Nb content is listed. The weight of Cr and Nb in grams is listed as Cr.sub.3C.sub.2 and NbC respectively. The corresponding content of Co, Cr and Nb is listed in wt %.

(12) Wet milling conditions was used, using ethanol as milling liquid, with an addition of 2 wt % polyethylene glycol (PEG 3350) as organic binder and 12 kg WC-Co milling balls in a 5 liter mill.

(13) After milling, the slurry was spray-dried in N-atmosphere.

(14) The WC grain size measured as FSSS was before milling about 3 m.

(15) TABLE-US-00001 TABLE 1 Composition of the cemented carbide inserts. Exam- Milling ple Cp WC Co Cr Nb C time (h) AC1 5.83 Balance 6.0 0.15 C-adj. 40 3283 g 210 g 6.04 g 1.30 g AC2 5.83 Balance 6.0 0.30 C-adj. 40 3277 g 210 g 12.08 g 0.98 g AC3 5.83 Balance 6.0 0.15 0.15 C-adj. 40 3277 g 210 g 6.04 g 5.90 g 1.08 g AC4 5.81 Balance 6.0 C-adj. 40 3289 g 210 g 0.59 g AC5 5.85 Balance 5.6 C-adj. 40 3304 g 196 g 0.43 g AC6 5.84 Balance 5.8 C-adj. 40 3296 g 203 g 0.51 g AC7 5.85 Balance 5.85 0.15 C-adj. 40 3289 g 205 g 6.04 g 0.37 g AC8 5.85 Balance 5.6 0.15 C-adj. 40 3289 g 196 g 6.04 g 0.11 g AC9 5.85 Balance 6.0 0.25 C-adj. 60 3289 g 210 g 10.06 g 1.40 g AC10 5.85 Balance 6.0 0.25 C-adj. 60 3289 g 210 g 10.06 g 1.40 g

(16) The compositions according to AC1, AC2, AC3, AC7, AC8, AC9 and AC10 in Table 1 are compositions that are within the scope of the invention. The compositions AC4, AC5 and AC6 in table 1 are comparative examples with compositions that are outside the scope of the present invention.

(17) Pressing of Powder and Sintering

(18) Green bodies were manufactured from the powder by uniaxial pressing. The form was standard mining drill inserts. After pressing the inserts were sintered by using Sinter-HIP in 30 bar Argon-pressure at 1480 C. for 0.5 hour.

(19) The sintered cemented carbide materials are essentially free from chromium carbide precipitations, but precipitations of cubic (W.sub.xNb.sub.1-x)C phase can be found in the sintered structure of AC3.

(20) Grinding

(21) The inserts were grinded to the required diameter by means of centerless grinding. The diameters of the inserts presented in FIGS. 2, 3, 4 and 5, where of approximate diameter 14.5 mm and an approximate height of 26.2 mm.

(22) High Energy Treatment

(23) The inserts were treated with a high energy process in accordance with process disclosed in patent application no. PCT/SE2016/050451 with publication no. WO2016/186558. The drill bit inserts were treated with a high energy treatment process in a centrifuge in order to increase the toughness and hardness. The centrifuge comprises a chamber formed by a stationary side wall and a bottom which is rotatable around a rotation axis, the bottom comprising 6 protrusions which extends between the rotation axis and the side wall, the side wall comprising pushing elements (vertical ridges) arranged around a periphery of the side wall to break the upward and circular motion of the insert bodies. The insert bodies were treated by rotating the bottom of the container with the protrusions around the rotation axis. The insert bodies are then set in motion to collide with each other. The pushing elements breaks the upward and circular motion of the inserts by slightly pushing them from the side wall during the rotation of the bottom. The insert bodies are thus treated in a controlled manner and the combined volume of insert bodies forms a toroidal shape at the lower part of the container where they move around and collide with each other with a limited relative motion to avoid uncontrolled large collisions which tend to give cracks and chippings.

(24) The chamber used was 350 mm, in diameter. The method uses water in the chamber. The process water was mixed with a detergent. To fill the container to a desired level when this small amount of test inserts were treated, cemented carbide bodies of similar or smaller size were added so that the total weight of the treated cemented carbide bodies was about 40 kg. The program used according to this method was divided in several steps according to table 2 and 4.

(25) TABLE-US-00002 TABLE 2 High energy treatment program AC1-AC4 RPM (rotations/minutes] Time [minutes] incl. start/stop 220 20 240 10 280 20 300 60

(26) TABLE-US-00003 TABLE 3 High energy treatment program AC9 RPM (rotations/minutes] Time [minutes] incl. start/stop 220 50 230 30 240 30 250 30

(27) TABLE-US-00004 TABLE 4 High energy treatment program AC10 RPM (rotations/minutes] Time [minutes] incl. start/stop 220 50 230 30 240 30 250 30 280 30 300 90 350 60 380 60

(28) Investigation of Material Properties

(29) After the treatment the drill inserts were investigated to verify the effect. Details on the sintered material properties are shown in Table 5. The hardness is the bulk hardness measured at the center of the insert where the hardness is not much affected by the treatment. The surface hardness is higher according to the high energy treatment.

(30) The addition of niobium in AC3 resulted in a precipitation of trace amounts of brittle cubic carbide phase ((W.sub.xNb.sub.1-x)C). Addition of only chromium did not result in the precipitation of any chromium-carbide containing hard phases. The inserts were investigated using light optical (LOM) and scanning electron microscopy (SEM).

(31) The compositions without Cr, AC4-AC6 would require considerably lower sintering temperature to achieve similar hardness as the compositions that are within the scope of the invention. Even when sintering the AC4 composition at 1400 C. the desired hardness was not reached. Due to the low hardness of AC5 and AC6 these were not field tested.

(32) TABLE-US-00005 TABLE 5 Details on materials produced according to AC 1-10. Coercivity Density Hardness K1.sub.c Sintering Temp. [kA/m] MS* [g/cm.sup.3] [Hv30] [MN*m{circumflex over ()}(3/2)] [ C.] AC1 (comparative) 13.6 88.8 14.92 1515 10.4 1480 AC2 (invention) 13.7 88.8 14.92 1520 10.3 1480 AC3 (invention) 13.9 90.4 14.91 1520 10.3 1480 AC4 (comparative) 12.6 90.4 15.00 1486 11.2 1480 13.3 92.0 14.99 1514 10.2 1400 AC5 (comparative) 11.1 98.4 15.00 1438 11.3 1480 AC6 (comparative) 11.6 87.2 15.06 1469 10.8 1480 AC7 (invention) 13.5 87.2 14.98 1528 10.2 1480 AC8 (invention) 13.3 88.8 14.98 1521 10.4 1480 AC9 (invention) 14.8 90.4 14.90 1564 10.2 1480 AC10(invention) 14.7 90.5 14.90 1562 11.0 1480 *MS = Percentage of magnetic cobalt.

(33) The inserts according to the invention in Table 5 have a mean WC grain size in the range of 0.60-0.95 m.

(34) The toughness and hardness values in Table 5 were measured at the bulk where the material is nearly unaffected by the high energy treatment. The toughness (K1c) of the material was measured using the standard ISO 28079:2009, Palmqvist toughness test for hard metals. Crack length was measured according to method B. For hardness ISO 3878:1983, Hard metalsVickers hardness test, was used. Density is measured according to ISO 3369-1975, Coercivity according to ISO 3326-1975 and MS can be measured according to ASTM B886:2008.

(35) FIG. 1. illustrates a cross section made through the longitudinal axis (A) through the center of a drill bit insert. The insert in FIG. 1 is not to scale and only intended to schematically show the principle for the positions for hardness and toughness measurements. The figure shows indentations for hardness and toughness measurements at 0.5, 1.0 (offset), 2.0, 5.0 and 10.0 mm from the top of the insert surface seen at the top of the figure. The 1.0 mm indent is offset to the longitudinal axis (A) to position it sufficiently far from the 0.5 mm indent. Here it is shown how hardness and toughness is measured in the bulk at the center of the longitudinal axis (A) through the center of the insert, or 5 mm from any surface of the insert, preferably in a transverse direction to the longitudinal axis through the center of the insert. The direction may be perpendicular to the longitudinal axis (A). The measurement position5 mm from any surface of the insert body is preferably used if the diameter and length of the insert is sufficiently large. Otherwise the measurement point for the bulk value should be chosen close to or at the center of the insert along the longitudinal axis (A). The intention is to measure the bulk hardness and toughness at a position where the material is nearly unaffected by the high energy treatment.

(36) It is also shown in FIG. 1. how the hardness and toughness is preferably measured in the surface region, as a measurement value of surface hardness, through an indent positioned at a distance of 0.5 mm from the top surface of the insert in a transverse direction to the longitudinal axis (A). The direction may be perpendicular to the longitudinal axis (A) as shown in FIG. 1. However the surface hardness and toughness can also be measured at other positions around the surface perimeter of the insert.

(37) Also, for the inserts according to the AC9 and AC10 composition, the toughness and hardness of the material through the length of the longitudinal axis of the drill bit inserts was measured. It was found that an increase of surface toughness and hardness had been achieved. The data from the investigation of the toughness of the drill bit inserts can be seen in graph in FIGS. 2, 3, 4 and 5. As seen in FIGS. 2 (AC9) and 3 (AC10) the toughness increases towards the surface and as seen in FIGS. 4 (AC9) and 5 (AC10) the hardness also increases towards the surface.

(38) To the data points in FIG. 2 and FIG. 3, a curve fit toward a point 0.2 mm from the surface has been done with the assumption that the effect of the high energy processing is decaying logarithmically with the distance from the surface. Measurement of toughness (K1.sub.C) from indents with Hv30 cannot be done with good accuracy and repeatability closer than 0.5 mm from the surface. Lower loads like Hv10 or HO results in insufficient crack length for accurate and repeatable measurement of K1c.

(39) Lab Testing: Top-Hammer Percussive Drilling Test in Swedish Hard Granite.

(40) Compositions AC1-AC4 were investigated (AC4 being a standard reference composition for the application).

(41) As can be seen from the results in FIG. 6 the inserts with the AC1, AC2 and AC3 composition were better than the reference. The hardness of the tested drill inserts are in the low range on the specified hardness target for the current invention. From the results of this test it was concluded that 1520 Hv30 should be the low limit for hardness to be part of the scope of the present invention.

(42) Field Test

(43) The test was conducted underground using a DTH 4.75 inch drill bit and an Atlas Copco COP 44 STD hammer.

(44) The drill bit inserts were tested against the best performing bit, with PCD (Poly Crystalline Diamond) coated periphery drill bit inserts and the current wear resistant standard cemented carbide grade containing about 6 wt % Co and no Cr. The test bits had insert made according to the AC9 composition and properties. Both bits were drilled for 800 feet/244 m. The wear of the periphery drill inserts were as expected higher than for the PCD-drill inserts, but the inserts according to AC9 were performing almost as good and well above the expectations. The PCD drill inserts cost roughly 10 times more to produce than the cemented carbide drill inserts according to the present invention. When comparing the wear of the center drill bit inserts it was found that the average diameter of the phase wear (flat spot on the worn insert) was approx. 15 mm (=19 mm) for the current most wear resistant standard Atlas Copco Secoroc grade. Whereas the phase wear of the AC9 drill bit inserts were at an average 1-2 mm. This is shown in FIG. 7 where the bit having PCD coated periphery inserts is shown to the left and the bit having AC9 inserts is shown to the right.

(45) For the purpose of investigating an insert body with a cemented carbide material according to this disclosure ISO 28079:2009, Palmqvist toughness test for hard metals, is preferably used for toughness tests. For hardness ISO 3878:1983, Hard metalsVickers hardness test, is preferably used. For determination of (arithmetic) mean WC grain size value according to this disclosure the linear-intercept technique according to ISO 4499-2:2008 is preferably used. Preferably using SEM micrographs.

(46) Even though the embodiments described in this application relates to percussive drilling the inserts according to the present invention may also be utilized for different types of drill bits used for rotary drilling or a combination of rotary and percussive drilling.

(47) The invention has been described with reference to specific embodiments. It is obvious to a person skilled in the art that other embodiments are possible within the scope of the present invention as defined in the claims. Terms such as comprising, comprised of or including in this application is used in a non-exclusive meaning, such that all comprised or included content may be completed with additional content.