Influence of the cutting edge micro-geometry of PCBN tools on the flank wear in orthogonal quenched and tempered turning M2 steel
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- de Souza, D.J.A., Weingaertner, W.L., Schroeter, R.B. et al. J Braz. Soc. Mech. Sci. Eng. (2014) 36: 763. doi:10.1007/s40430-013-0116-9
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Quenched and tempered high-speed steels obtained by powder metallurgy are commonly used in automotive components, such as valve seats of combustion engines. In order to machine these components, tools with high wear resistance and appropriate cutting edge geometry are required. This work aims to investigate the influence of the edge preparation of polycrystalline cubic boron nitride (PCBN) tools on the wear behavior in the orthogonal longitudinal turning of quenched and tempered M2 high-speed steels obtained by powder metallurgy. For this research, PCBN tools with high and low-CBN content have been used. Two different cutting edge geometries with a honed radius were tested: with a ground land (S shape) and without it (E shape). Also, the cutting speed was varied from 100 to 220 m/min. A rigid CNC lathe was used. The results showed that the high-CBN, E-shaped tool presented the longest life for a cutting speed of 100 m/min. High-CBN tools with a ground land and honed edge radius (S shaped) showed edge damage and lower values of the tool’s life. Low-CBN, S-shaped tools showed similar results, but with an inferior performance when compared with tools with high CBN content in both forms of edge preparation.
KeywordsPCBNEdge geometryGround landHoned edge radiusHigh-speed steel obtained by powder metallurgyOrthogonal longitudinal turning
List of symbols
Depth of cut (mm)
Feed rate (mm−1)
Honed edge radius (mm)
Tool nose radius (mm)
Average flank wear land width (mm)
Cutting speed (m/min)
Chamfer width (mm)
Land angle (°)
Cubic boron nitride
Energy dispersive spectrometry
Polycrystalline cubic boron nitride
Ground land and honed edge
Scanning electron microscope
In order to machine these rings, polycrystalline cubic boron nitride (PCBN) tools are employed due to their mechanical properties, chemical stability and thermal shock resistance. These tools might present coating, chip breakers and customized geometries when demanded by specific applications.
The control over customized cutting geometries is still slightly dominated by tool manufacturers and only recently has been offered in the suppliers’ portfolios. The influence of the tool edge geometry over the machining of sintered, quenched and tempered high-speed steels is not described in the literature.
The main objective of this work is to investigate the influence of the honed edge PCBN tools, with and without a ground land in orthogonal longitudinal turning of quenched and tempered M2 high-speed steels, in terms of the wear behavior.
1.1 PCBN tools
PCBN tools are composed of cubic boron nitrite (CBN) grains in a binder matrix (metal or ceramic) chosen according to the CBN load. Tools with a high CBN content, ranging from 80 to 95 % in weight of CBN, employ a metallic binder. Tools with a CBN content between 40 and 70 % of the tool’s weight usually employ a ceramic binder [16, 19, 34]. PCBN tools are used in the turning of quenched and tempered ferrous materials, mainly for the finishing steps due to their high toughness and thermal stability as well as their lower chemical affinity for ferrous materials . These tools are fragile with a high tendency for fractures. It is necessary that PCBN tools have their edges prepared in order to enable a good performance under these hostile conditions. According to Zareena et al. , the best results for the PCBN tools depend mostly on the tool’s CBN content and binder material.
1.2 Low-CBN tools
Studies on the turning of hardened AISI 52100 by Narutaki and Yamane , Barry and Byrne  and Chou et al. , showed that low-CBN tools had lower wear rate values than tools with a higher CBN content. Bossom  mentions that the wear in low-CBN tools is due to its low thermal conductivity, which retains the heat in the cutting region. Chou et al. , when machining AISI 52100 with low-CBN tools, found the presence of grooves on the flank after a high cutting speed (240 m/min) process. The author concluded that adhesion was the mechanism most responsible for the wear, stating that tools containing lower contents of CBN have better resistance. Luo et al.  and Poulachon et al.  studied the tool wear on low-CBN tools when machining different quenched and tempered steels. Based on the wear grooves observed on the tools’ flank, they concluded that the main mechanism for the CBN tools wear was related to the binder abrasion due to the carbide particles, causing the grains’ pullout. Tool breakage in tools with a low-CBN content and ground land edges was verified by Mahfoudi et al.  when machining AISI 4140, 50 HRC, with vc = 400 m/min, 0.10 mm feed and 1.0 mm cutting depth. Although in some studies the results showed tool breakage, Lahiff et al.  concluded that tools with low-CBN content presented a better performance during turning of hardened materials regarding tool life and surface finishing when compared with tools with a higher load of CBN.
1.3 High-CBN tools
High-CBN tools usually comprised metallic binders such as Co, Al and W. They have higher thermal conductivity, therefore better at dissipating the heat, lowering the temperature in the cutting region . Regarding this difference on thermal conductivity, Bossom  concluded that this was the reason for the lower performance of high-CBN tools during the finishing steps of the turning of hardened materials. Through the study of the flank wear marks on high-CBN tools after turning a hardened and tempered AISI 52100 (61–63 HRC), with the aid of SEM, Chou et al.  concluded that the layers adhered to the tools were tightly bound and that adhesion was the dominant wear mechanism. This type of adhesion in high-CBN tools was also observed by Arsecularatne et al.  when machining AISI D2. Regarding the chipping in PCBN tools, the results encountered by Hodgson et al. , when machining AISI M2 obtained by conventional metallurgy, showed an unsatisfactory performance of the tool due to premature failure of the tool’s cutting edge. The experiments were performed on tools with ground land edges and with cutting speeds ranging from 80 to 120 m/min for a 0.05 mm/rev feed.
1.4 Edge geometry of PCBN tools
The edge comprises the geometric region where the tool’s rake face and flank meet. The edge’s radius defines the sharpness of the tool and it is the region responsible for the actual cutting of the material. Depending on their use, PCBN tools might require further modifications on the edge geometry in addition to the grinding of the face and flank to achieve good results. The modification on the edge shape consists of producing a land and/or a radius on the edge through honing, therefore protecting it from chipping, improving its impact resistance and increasing the tool life . Due to these geometric changes, the heat transfer area from the cutting zone to the cutting edge region increases .
Research reveals that ground land edges might have an influence on the compressive residual stresses during the machining of quenched and tempered materials, as an increase on the chamfer angle causes an increase on these loads [8, 18, 33]. This increase in the chamfer angle promotes the residual compressive stress under the surface, but/and provokes a temperature increase on the tool. In addition to the influence on the compressive residual stresses, the chamfer also influences the machining force.
Tools with honed edges have greater surface contact with workpiece and chip, increasing the heat transfer from the cutting zone to the tool and improving the surface roughness and integrity on the machined workpiece . The purpose of rounding the tool’s edge is to protect the cutting edge from chipping, to improve its impact resistance and to increase the surface area for the heat transfer from the cutting zone [6, 13].
According to Lahiff et al.  and Dogra et al. , the turning of quenched and tempered ferrous materials with the undeformed chip thickness and tool’s edge radius in the same magnitude order, requires tools that can withstand high mechanical and thermal stresses. For these situations the edges should be prepared accordingly, since the process can result in high tensile residual stresses on the workpiece’s surface and also cause sub-surface damage [6, 15, 23]. For fragile tool materials, ground lands and honed edges are used to increase the tool’s life by protecting it against chipping and breakage and increasing its resistance to mechanical and thermal stresses.
1.5 PCBN tool wear mechanisms
PCBN tools are influenced by wear mechanisms such as abrasion , adhesion [7, 17], diffusion , chemical wear [2, 7, 9, 20], adhesion pullout and entrainment in the direction of the cutting speed and chip flow [14, 19, 31, 32]. These wear mechanisms contribute greatly to the flank wear which is the main criterion for determining the tool’s end of life. The flank wear reduces the clearance angle to zero causing an increase in the contact area between the tool flank and the cutting surface, therefore resulting in greater friction and heating in the contact zone. With the increase of the cutting speed, the temperature increases at the interface between the tool and the flank. The cut surface becomes more pronounced . Another type of PCBN tool wear is the crater, which is generally associated with high temperatures and high pressures on the tool–chip interface and decreases the abrasion resistance with the appearance of weaker composites. These composites are generated by the chemical affinity between the different materials in the work area and, being less resistant, are removed by the chip flow on the tool’s surface [10, 20, 27].
1.6 Orthogonal longitudinal turning
The orthogonal longitudinal turning is defined as a machining process with a single-edge cutting tool where the edge is perpendicular to the cutting and feed directions. When orthogonal turning is performed on the machining of a cylinder, there is no influence of the tool’s nose radius on the process and the cutting surface coincides with the machined surface. This process is capable of achieving a surface integrity comparable to those found in ground components .
Turning can be classified as hard turning when machining workpieces have hardness values between 58 and 65 HRC. Some requirements for a successful longitudinal orthogonal turning of quenched and tempered steels are the use of highly precise and rigid machine tools, very hard and resistant tool materials, tool geometry with a negative rake angle and large wedge angle, resistant wedge geometry with appropriate ground land and/or radius, a rigid tool holder and appropriate cutting conditions . PCBN tools can be used to turn quenched and tempered steels either in the form of interchangeable tools with a brazed CBN corner on a carbide substrate or fully in CBN.
The term apparent hardness is used given the lesser resistance encountered by the indenter in parts produced by powder metallurgy. This lower resistance is due to the presence of pores natural to the sintering process. Thus, the lower values of hardness in parts produced by powder metallurgy do not mean necessarily that the functional properties of the material are also affected negatively.
Chemical composition (% weight), density and hardness of sintered M2 high-speed steel
Apparent hardness (HB)
Material properties of the PCBN tools 
Knoop hardness (GPa)
Grain size (μm)
Thermal conductivity (W/mK)
Input variables for the experiments
Cutting edge geometry
Feed, f (mm−1)
Depth of cut, ap (mm)
Cutting speed, vc (m/min)
S (ground land and honed radius)
E (only honed radius)
S (ground land and honed radius)
E (only honed radius)
At the end of each machining experiment, PCBN tools images were obtained on a Zeiss EVO LS15 and a Hitachi TM3000 SEM energy dispersive spectroscopy equipment.
3 Results and discussion
The discussion of the machining results is based on the comparison of the wear progress between different combinations of the input variables.
3.1 Influence of the cutting speed on the flank wear for S-shaped and E-shaped PCBN tools with high CBN content
All the E-shaped tools (CBN200E) reached the stipulated flank wear. The highest number of cuts was obtained with a 100 m/min cutting speed, as shown in Fig. 9b. It can be seen on Fig. 9b that the flank wear is basically the same for every cutting speed for the first 1,560 cuts (or 120 workpieces) approximately. Further cuts presented higher wear in processes with a higher cutting speed.
The results differed from the works of Zhou et al. , Kurt and Seker  and Karpat and Özel , who affirmed that the land helped preventing the occurrence of chipping, and from the work of Klocke and Kratz , who stated the purpose of the land was to protect the edge from chipping.
The observed behavior confirms the results obtained by Hodgson et al.  for the machining of high-speed steels manufactured by conventional processes, where CBN tools with a land presented shorter tool life than tools without it.
The wear behavior of CBN200E tools when machining sintered M2 high-speed steel showed that this edge geometry enables more cuts than the S-shaped tools before the end of life.
3.2 Influence of the cutting speed on the flank wear for S-shaped and E-shaped low-CBN PCBN tools
In relation to honed edge tools (E shape), Lahiff et al.  and Dogra et al.  report that these tools have greater surface contact with the workpiece and chip, increasing the heat transfer from the cutting area to the tool, showing improvement in surface finish and in surface integrity of the machined part. Karpat and Özel  and Dogra et al.  complement that the purpose of the use of honed edge tools (E shape) is also to protect the edge from chipping, improving its impact resistance.
A hypothesis for the shorter life of the low-CBN content tools—for both ground land and honed geometries (S shape) and only honed (E shape)—was the lower hardness and also the low thermal conductivity of the tool (low-CBN content tools have 44 W/mK while high-CBN content tools, 94 W/mK; Table 2). This low thermal conductivity let a greater quantity of heat to be retained in the cutting region, increasing tool wear; a hypothesis also cited by Bossom . For chipping that occurred in high-CBN content tools (CBN200S) and not in low-CBN content tools (CBN10S), the reason given was the higher hardness of the tool provided by most volume of CBN grain in its composition (Table 2), which makes it more susceptible to chipping.
The crater wear was not significant in any of the tools employed and was never a reason for the end of tool’s life.
The E-shaped (only with honed edge) high-CBN PCBN tool (CBN200E) presented the longest tool life in terms of machined parts or cutting steps for the cutting speed range from 100 to 220 m/min. This behavior is related to the greater hardness and better heat dissipation given by the higher CBN content.
The adhesions found on both edge geometries and both PCBN classes throughout the range of cutting speeds had their origin in the workpiece.
The formation of crater wear on the PCBN tools with high CBN content for both edge geometries could be observed. However, this wear was not significant and did not determine the end of the tool life.
The tools with ground land and honed edge radius (S shape) and high CBN content showed chipping in the rake face for all cutting speeds. The damage was influenced by the negative geometry of the land and, therefore, by the higher shear and compressive stresses on the surface.
For the tool with low-CBN content, ground land and honed edge radius (S shape), the tool life increased with the cutting speed for the selected range.
The authors thank the companies Bleistahl Metallurgy Brazil S/A-RS, and Seco Tools, the institutions IttFUSE-UNISINOS-RS, LdSM-UFRGS and SENAI-CETEMP-RS, for the collaboration and support for the realization of this research.