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- Heikkilä, Irma, 1965-, et al.
(författare)
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Clean forming of stainless steel and titanium products by lubricious oxides
- 2012
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Ingår i: Proceedings of NORDTRIB. - Trondheim : NTNU. - 9788214052701
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Konferensbidrag (refereegranskat)abstract
- Big social benefits can be attained through increased use of stainless steel or titanium in new sheet metal applications. Unfortunately, forming of these materials is often a challenging and costly operation, that can lead to environmental and health problems when solving the technical limitations. One possible method to overcome these problems is to use an oxide layer with optimised properties to reduce friction during forming, either as a substitute to lubricants, or acting as a conversion layer for environmental friendly lubricants. The most beneficial group of oxides for low friction is called lubricious oxides with a rutile crystal structure. Oxides of Ti, Mo, V, and Zn can build rutiles under certain contact temperatures during rolling and forming. The aim of this investigation is to evaluate if oxides designed on metal sheets display a lubricious effect under conditions similar to industrial forming processes. Preliminary evaluations show a beneficial influence of two oxides types, on stainless steel and on titanium. More work is needed to test the lubricating effect in other forming operations and to analyse the sustainability aspects for products manufactured with this alternative surface.
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- Heikkilä, Irma, et al.
(författare)
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First experiences on characterization of surface oxide films in powder particles by gd-oes
- 2015
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Ingår i: Proceedings Euro PM 2015. - : European Powder Metallurgy Association (EPMA). - 9781899072477
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Konferensbidrag (refereegranskat)abstract
- The surface characteristics of the powder particles play a key role on the processing of the powders to consolidated products and on the final properties achieved for the material. Characterization of surface oxide films by techniques like XPS and TEM EDS provide reliable information on the surface films, but they are time-consuming methods and the analyzed areas are extremely limited. In this evaluation, the potential of the depth profile analysis by Glow Discharge Optical Emission Spectroscopy (GD-OES) is experimented for Astaloy CrM and 316L powders. The conducted experiments show that the chemical composition and thickness of the surface oxides can be analyzed by GD-OES even for powder materials. Thus, the first results indicate that GD-OES provides a fast method to analyze the surface characteristics of a large number of powder particles during a single measurement.
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- Heikkilä, Irma, 1965-
(författare)
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The Positive Effect of Nitrogen Alloying of Tool Steels Used in Sheet Metal Forming
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sheet metal forming processes are mechanical processes, designed to make products from metal sheet without material removal. These processes are applied extensively by the manufacturing industry to produce commodities such as heat exchangers or panels for automotive applications. They are suitable for production in large volumes.A typical problem in forming operations is accumulation of local sheet material adherents onto the tool surface, which may deteriorate the subsequent products. This tool failure mechanism is named galling. The aim of this work is to explain the mechanisms behind galling and establish factors how it can be reduced.The focus of this work is on the influence of tool material for minimum risk of galling. Experimental tool steels alloyed with nitrogen were designed and manufactured for systematic tribological evaluation. Reference tool materials were conventional cold forming tool steels and coated tool steels. The sheet material was austenitic stainless steel AISI 304, which is sensitive for galling. A variety of lubricants ranging from low to high viscous lubricants were used in the evaluation.The properties of the tool materials were characterized analytically and their tribological evaluation included industrial field tests and several laboratory-scale tests. The testing verified that nitrogen alloying has a very positive effect for improving galling resistance of tool steels. Tool lives comparable to the coated tool steels were achieved even with low viscous lubricants without poisonous additives.The hypothesis used for the explanation of the positive effect of nitrogen alloying is based on the critical local contact temperature at which the lubrication deteriorates. Therefore, the contact mechanism at the tool-sheet interface and the local energy formation were studied systematically. Theoretical considerations complemented with FEA analysis showed that a small size of hard particles with a high volume fraction gives low local contact loads, which leads to low frictional heating. Also, an even spacing between the hard particles and their frictional properties are of importance. Nitrogen alloyed tool steels have these properties in the form of small carbonitrides.The finding of this work can be applied to a wide range of applications that involve sliding metal contacts under severe tribological loading.
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