Influence of surface texture on the galling characteristics of lean duplex and austenitic stainless steels (original) (raw)
Related papers
Lubrication Science, 2012
Adhesive accumulation of work material on the tool surface is today a major problem in many sheet metalforming applications. Different laboratory test methods are used to investigate galling with respect to different tool materials, lubricants and process conditions. In the present study, the galling resistance of a modern nitrogen-alloyed powder metallurgy tool steel and an conventional ingot cast D2 type tool steel was evaluated under lubricated sliding against ferritic stainless steel sheets using a commercial pin-on-disc (POD) and an in-house made slider-on-flat-surface (SOFS) tribotester. The investigated tool steels ranked similarly in terms of galling resistanc in both test methods. However, sliding distances to galling were longer for the SOFS equipment due to continuous sliding on new lubricated sheet surface. Best performance was demonstrated by the powder metallurgy tool steel treated to 65 HRC. Differences in friction behaviour and galling initiation were analysed on the basis of the two different working conditions, i.e. open (SOFS) and closed (POD) tribosystems.
Quantification of galling in sheet metal forming by surface topography characterisation
International Journal of Machine Tools & Manufacture, 1998
One of the major problems in forming of stainless steel sheet is galling due to lubricant film breakdown leading to scoring and bad surface quality. In a Danish research programme new lubricants substituting the normally applied chlorinated paraffin oils are being developed and tested for this purpose. In order to determine the limits of lubrication of these new lubricants, as well as commercial ones already available on the market, two sheet forming tests have been developed. Quantification of the degree of galling is done by roughness measurements on the workpiece surface. In a strip reduction test, this is done by 2D profilometry at strip locations corresponding to different sliding lengths, whereas a deep drawing test is based on 3D roughness mapping of local areas.
High friction and transfer of work material to tool surfaces constitute important industrial problems in forming of many metals and alloys. However, it is very hard to gain a deeper understanding of these phenomena by studying real forming operations. In this paper, we have tried to gain fundamental understanding by avoiding as much as possible of the complexity of real forming. This has been realised by studying the friction and material transfer between well-defined tool material surfaces; uncoated and DLC-coated tool steel, and a needle shaped austenitic stainless steel tip, in situ in the SEM. The tool materials were tested in two conditions; well polished and well polished with local intentional scratches. It was found that work material was immediately transferred to the tool steel surface. When passing an intentional scratch, the local transfer was on a much larger scale, and the friction was higher, but the effect was mostly local. For the polished DLC-coated surface, almost no work material was transferred and the friction was low. An intentional scratch in the polished DLC surface barely influenced the galling behaviour. The present results are discussed in the light of previously published results from an analogous study with aluminium as work material.
Surface and Coatings Technology, 2004
The aim of the present work is to elucidate the influence of surface roughness on the galling properties of coated forming tool steel. The tribological evaluation included TiN, TiB , TaC and WCyC coatings deposited on cold work tool steel. Representing a 2 material difficult to form, austenitic stainless steel was used as a counter-material. A special test configuration made it possible to gradually increase the normal load during forward sliding strokes, and to correspondingly decrease the load during reversed ones. In this investigation, the load was varied between 100 and 1300 N, corresponding to a contact pressure between 2 and 5 GPa. The main observation is that the galling and anti-sticking properties of the tool surface dramatically improve by reducing the surface topography. Consequently, reduced substrate roughness or polishing of the contact surface after coating is highly recommended. However, selection of a carbon-based low-friction coating leads to reduced probability of worked material adhesion even at high surface roughness values and under starved lubrication. ᮊ
Proper coating selection for improved galling performance of forming tool steel
Wear, 2006
The aim of the present work was to investigate and compare different hard coatings as to the tendency for work material adhesion and galling properties when applied on forming tool steel and sliding against different work materials. The surface coatings included were PVD deposited TiN, TiB 2 , VN, TaC and DLC coatings. They were all applied to cold work tool steel. Tribological evaluation was carried out in a load-scanning test rig, with the normal load being gradually increased during each test from 100 to 1300 N (1-3.5 GPa). The coated steel was tested against austenitic stainless steel and alloys of aluminium and titanium.
Acta Polytechnica CTU Proceedings, 2017
The goal of this contribution was to describe parameters of surface integrity of two machined materials; austenite and duplex stainless steel. Residual stresses and presence of straininduced martensite were studied as a function of the side rake angle. Residual stresses of surface and sub-surface layers were determined using X-ray diffraction techniques and hole-drilling method. By using X-ray diffraction, it is possible to determine residual stresses in each phase separately, in comparison with hole-drilling method. The presence of strain-induced martensite was investigated using Barkhausen noise and optical microscope.
Wear, 2010
Two types of powder metallurgical tool steels (i.e. with and without nitrogen) are investigated with respect to their galling related surface properties. Despite similar macrohardness values, Vancron 40 (nitrogen alloyed) exhibits superior wear behaviour as compared to Vanadis 10 (without nitrogen); demonstrating approximately 20 times longer life span when used as die material in powder compaction. The main failure mechanism is mild abrasive wear for Vancron 40 and early severe galling for Vanadis 10. One important difference causing the tribological discrepancy is supposed to be associated with the preferred formation of solid lubricant oxides of the Magnéli type on the Vancron 40 surface as compared to Vanadis 10. The VN precipitates in Vancron 40 have half the thermal conductivity compared to that of the VC precipitates existing in Vanadis 10. Hence, as a result of the local accumulation of frictional heat generated during powder compaction (or any other type of forming process), Magnéli phases of V 2 O 5 and/or VO 2 are more easily formed and maintained on the Vancron 40 surface. With regard to surface oxides, the tool steels were studied by means of X-ray photoelectron spectroscopy (XPS). The tool steel surfaces were examined by means in situ SEM/AFM and electron backscatter diffraction (EBSD) for local adhesion force measurements and understanding the orientation of the phases, respectively. In addition, pin-on-disc wear tests were performed on the tool steels and the worn surfaces were analysed using scanning election microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS).
Wear, 2004
In forming operations, galling is a tribological process associated with pick-up of formed material by the surface of the tool and subsequent damage of the work material surface. In lubricated operations, it is associated to lubricant film breakdown. Currently the main focus in development of forming tools is on improving their galling resistance, mainly by including new forming tool steels, improving surface finish, and applying surface treatments and coatings. However, in order to qualitatively rank the galling resistance of material couples, a proper test method for galling evaluation is needed. During the years several methods for determining the galling resistance have been reported in the literature. In the present investigation three different test methods were compared and evaluated as to their ability to assess the galling tendencies of coated and un-coated forming tool steel. The study included the pin-on-disc configuration, a modified cylinder-on-cylinder test with a spring loading system, and a new load-scanning test method, which involves two crossed cylinders.
Surface treatment of tool steels against galling failure
MATEC Web of Conferences
In the present study two highly alloyed steel grades, intended for cold working applications, were subjected to plane-contact, nonlubricating sliding friction testing in order to estimate the working regions (applied pressure and sliding velocity) that are governed by mild, moderate and severe wear mechanisms, before and after nitrocarburizing. For this purpose, both tool steel grades were initially pre-subjected to the proper heat treatments, in order to achieve a final bulk hardness of 40, 50 and 60 HRC whereas, after heat treatment, half of the material specimens were further subjected to nitrocarburizing surface treatment. The comparative experimental study of heat-treated and heat-/ surface-treated grades within a wide range of applied pressure and sliding velocity values, in combination to the development of a relevant Artificial Neural Network, allowed to determine the areas of recommended operation of such tribosystems. In all cases, the positive influence of the post-harden...