Powder Metallurgical High Speed Steel Research Articles

Cutting performance of coated tools with various adhesion strength quantified by inclined impact tests

Coated tools with PVD-films of almost the same mechanical properties may perform differently. This effect can be attributed to the film adhesion. For highlighting this phenomenon, the adhesion of coatings with practically identical mechanical properties deposited on cemented carbide and powder metallurgical high speed steel inserts was quantified by FEM-based evaluations of inclined impact test and nano-indentation results. Moreover, the films’ mechanical properties were assessed by repetitive nano-impacts. Based on these data and on FEM calculations of the cutting process, the coated tools cutting performance was explained in all investigated material and interrupted cutting process cases.

Adhesion between some tool and work materials in fretting and relation to metal cutting

Adhesion is an important component in the wear of tools and components. Among the methods to quantify adhesion, reciprocating fretting is a possible test method. This paper describes results from reciprocating fretting tests involving cutting tool materials and work materials. Powder metallurgical high speed steel (HSS) tool inserts with and without TiN coating were evaluated for adhesive affinity against a number of aerospace work materials in the form of spherical ended pins in high vacuum. The force required to separate the pin from the flat tool surface obtained from the fretting studies was the parameter used to quantify adhesion. This varied strongly for the different work materials, and TiN coating reduced adhesion appreciably. These results from the fretting studies are discussed in the context of adhesion in metal cutting. While the fretting tests provide a more fundamental information about adhesion, results from milling tests are indicative of the effects of adhesion at stresses and temperature prevalent at tool-chip contact.

Material property database for heat treatment simulation of tool materials

A materials data base has been set up with mechanical, thermophysical and transformation properties of tool and creep resistant steels. In particular powder metallurgical materials have been covered. The intended use of the data is for numerical simulation of heat treatment with focus on computation of residual stresses and distortion in Compound materials (macro composites).The main body of the data was generated in new experiments. In this paper data for the powder metallurgical high speed steel ASP 2060 will be presented. The material properties determined include thermophysical data such as thermal conductivity and specific heat, mechanical data such as yield strength and work hardening rate, and thermal expansion data. Most data were determined at different temperatures and after heat treatments to different microstructures. Additional data added to the database include literature data for elastic properties and transformation induced plasticity.Quenching of a Compound ring consisting of an inner high speed steel and an outer tool steel was simulated numerically using two codes, DistSIMR and Trast7. With the help of a database interface input data adjusted to the formats of the two codes were generated. The results of the simulations showed good agreement between the two models both for the computed residual stresses and distortions, which confirms the reliability of the results.

IMPROVEMENT OF CUTTING TOOLS BY TiN PVD HARD COATING

ABSTRACT A review of recent results obtained in the field of cutting tools improved with a TiN physical vapor deposition (PVD) ion-plated hard coating is presented. Optimization of the tool material, tool surface morphology and interface problems between the TiN coating and the tool surface are discussed in view of their importance in optimum performance tests and the resulting workplace surface quality. The high effectiveness of the TiN PVD coating is demonstrated by selected data from our own data bank and from other sources on six groups of cutting tools, made of high-speed steels (HSS), powder metallurgical high-speed steels (PM-HSS) and of WC based hard metals. We also describe recently introduced, novel hard coatings (TiCN and TiAIN) for cutting tools, and new applications of cutting tools, improved by PVD hard coatings.

Influence of TiN coating on wear of high speed steel at elevated temperature

The friction and sliding wear characteristics have been investigated for one conventional and one powder metallurgical high speed steel (HSS) in both the TiN-coated and the uncoated condition. A crossed cylinders test geometry was used with plain carbon steel as the countermaterial. The influence of countermaterial temperature and intermittent contact was studied. The wear and friction properties have been characterized and the wear mechanisms identified. The most interesting results are the following. The TiN coating substantially reduces the wear rate of HSS when sliding against plain carbon steel at both room temperature and 650 °C. The main contribution to this improvement is the high wear resistance and low friction of the TiN material which withstands the very tough sliding conditions until it is removed by fragmentation. It was also found that both wear rate and friction coefficient are relatively insensitive with respect to HSS grade, countermaterial temperature and contact mode.

The crystallography of secondary carbide precipitation in high speed steel

Precipitation of secondary carbides in a powder metallurgical high speed steel, ASP 23, has been investigated by transmission electron microscopy. Particular attention has been paid to the crystallographic orientation relationships between the precipitated phases and the ferrite matrix. During the hardening treatment prior to tempering, cementite precipitates on prior-austenite grain boundaries and twin boundaries within the martensite plates. The cementite is oriented with respect to one of the adjacent ferrite lattices according to the Bagaryatskii orientation relationship. During tempering at 560°C the cementite coarsens and fine dispersions of MC and M 2C precipitate within the martensite plates. MC obeys the Baker-Nutting orientation relationship while M 2C obeys both the Pitsch-Schrader orientation relationship and another relationship defined by: (0001) M 2C //(021) x; (11¯20) M 2C //(100) x; (¯1100) M 2C //(01¯2) x. The coexistence of both of these orientation relationships for M 2C precipitated in ferrite is explained in terms of the near-coincident site lattice model.

High resolution microanalytical study of precipitation in a powder metallurgical high speed steel

The microstructure of a powder metallurgical high speed steel (ASP 60) has been investigated by combined analytical electron microscopy and atom-probe field-ion microscopy. The compositions of MC and M 6C primary precipitates were determined. The tempering reaction at 560°C was studied in detail and it was shown that extremely fine M 2C precipitates dominated at optimum hardness (3 h). Some fine MC precipitates were also present. The compositions of the secondary carbide precipitates were determined by atom-probe analysis. Overageing at 700°C resulted in the transformation of the fine secondary carbide dispersion to coarse M 6C and M 23C 6 and a change in the matrix morphology from martensitic plates to equiaxed recovered ferrite subgrains.

Use of Powder Metallurgical High Speed Steel in Gear Hobbing and Gear Shaping

A relative new development on the area of high-speed-steels are the powder metallurgical high-speed-steels (PM-HSS). On account of the manufacturing method a nearly homogeneous structure can be obtained. Based on practical knowledge, improved cutting properties, an increased grindability and an insensitiv behaviour during the heat treatment can be expected. In this paper, the application of some differently alloyed PM-steels at the two main methods of gear manufacturing, gear hobbing and gear shaping, is systematically examined and with regard to the economy compared among themselves and with conventionally manufactured high-speed-steels.

Atom-probe microanalysis of a tempered high-speed steel

A powder metallurgical high-speed steel containing (wt%) 2.3C, 4.2Cr, 6.7W, 7.0Mo, 6.4V, and 10.3Co was quenched from 1180°C and triple tempered for 1 hour at 560°C to secondary hardness maximum. Some of the resulting types of carbide precipitates were analysed using atom-probe field-ion microscopy. The following preliminary results were obtained: 1. 1. The martensite contained plate-shaped MC-type precipitates, 1–2 nm thick and up to 20 nm in diameter. The composition obtained corresponds to the approximate formula: (V 0.32Mo 0.39W 0.07Cr 0.21)C 0.86 2. 2. The martensite also contained a high density of thin precipitate platelets, many only a few atomic planes thick and with a largest dimension of typically 5 nm. These precipitates were rich in Fe, Mo and Cr, and their C content suggests a structure M 2C or M 3C. 3. 3. One type of primary carbide, M 6C, was analysed. The composition may be written: (Fe, Co, Cr, Si, V) 3.55(Mo, W) 2.45C which is within the stability range of the η 1-phase.

Atom-probe studies on surface segregation in the binary alloy, tungsten-molybdenum

A powder metallurgical high-speed steel containing (wt%) 2.3C, 4.2Cr, 6.7W, 7.0Mo, 6.4V, and 10.3Co was quenched from 1180°C and triple tempered for 1 hour at 560°C to secondary hardness maximum. Some of the resulting types of carbide precipitates were analysed using atom-probe field-ion microscopy. The following preliminary results were obtained: 1.1. The martensite contained plate-shaped MC-type precipitates, 1–2 nm thick and up to 20 nm in diameter. The composition obtained corresponds to the approximate formula: (V0.32Mo0.39W0.07Cr0.21)C0.862.2. The martensite also contained a high density of thin precipitate platelets, many only a few atomic planes thick and with a largest dimension of typically 5 nm. These precipitates were rich in Fe, Mo and Cr, and their C content suggests a structure M2C or M3C.3.3. One type of primary carbide, M6C, was analysed. The composition may be written: (Fe, Co, Cr, Si, V)3.55(Mo, W)2.45C which is within the stability range of the η1-phase.

Elevated temperature fracture toughness and critical flaw analysis of a powder metallurgical high speed steel

Four point bend tests of a powder metallurgical M3-2PM high speed steel were performed in the temperature range 20 – 600 °C. A critical stress intensity factor was calculated by approximating the fracture initiating inclusion, characterized in a scanning electron microscope, with an elliptical crack with equal extension in the fracture plane. The results fall within the same pattern as previously reported conventional fracture toughness test results, though the scatter is somewhat greater. Additionally, this procedure allows a quantitative reasoning, yielding an estimation of the critical inclusion size distribution.