Isotropy and fatigue

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Isotropy and fatigue
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Isotropic steel: APMS conference
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A lecture given by Peter Olund, at the Adventures in the Physical Metallurgy of Steels (APMS) conference held in Cambridge University. With the focus on steels for bearings, he talks about the role of inclusions in determining the anisotropy of fatigue properties, and of sampling volume effects. The demands of high cleanliness steel constantly increases due to the fact that higher loads are being introduced in the applications. Today there are cases where the elongated sulphide inclusions present in steel with "normal" sulphur content (around 80ppm) will cause premature fatigue failures. A clear trend is therefore reduced sulphur contents in air-melted steels. However, only increasing the desulphurization within the current process window, to produce low sulphur contents (less than 20ppm), will due to thermodynamics drastically increase the number and size of detrimental globular calcium aluminates. Re-melting process has therefore dominated the market for low sulphur steel. Recently, air-melt steel making processes have been developed to produce more isotropic low sulphur steel where the formation of large globular calcium alumina is thermodynamically suppressed. Consequently, steels produced with this process will exhibit more isotropic fatigue properties. In this work fatigue properties has been assessed for steels loaded in different directions with reference to the rolling direction for steels with different level of isotropy. Furthermore, the effect on operation temperature has been taking into account showing that moderate increases in temperature will affect the properties. This influence can be correlated to the microstructural stability, i.e. composition and structure, of the steel.
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at the time that it would I think that the the only thing you can do it at the end of the day you I take the and the planned Kelly's that when lights introduced that applique Ellen USA I worked at about agreed and he's gonna totals about factors that influence fatigue of material thank you thank you very much and it's a pleasure being here thank you very much
for inviting it and considering that it's 50 thousand people looking at you eligible directly but in future I will be Bruce Springsteen who was in the Stockholm a month ago it's only thought about I will talk
about I sought to P and fatigue and it's a bit and different from what we had before we have had a very much about
99 today and this also I think will tying quite well because this is not aspect of it will swing to be considered and I think very much and while the sort of and tell you that then but what they think about we could do in the future also looking into more of these materials when it comes to I was safer teens her eyes mean high-strength high cycle fatigue is also something of I'm not with any any other authors go there because it's so many I don't want but it's all in my own all the people in my group I will also to acknowledge to this work so I will
start to talk about 50 debate in general and they account too the influence of bowls the matrix and
indeed for accepting this this is really something that we we have experience it's very important that really think about those 2 different mechanisms what
already control the fifties is it that the matrix and it is always a different defects could we change the matrix In order to accommodate the feature His 1 Michael structure better than others I think there are I know there are different because we have seen that and those kind of all discussion I think is very important that we start racist start to put more effort and investigate but also of course the defects because they are there and we need to consider a whether
working quite much with very complex and loaded components and what we realize
that a lot of multiplicity data high-strength thing that we see today that you find in the literature it is normally obtained from the most beneficial promised Stephen Hughes supported you directions while a lot of components of a holiday and much more complex than directions which means this anisotropy there think about isotropic properties becomes more and more people the other 1 is the
invisible that Volume I will briefly going to that as well because
many want to have a fatigue limit for that material I want it now and I can say something pick a number because it depends on also loaded volume it's very important when it comes to a defect controlled fatigue especially the high street enhances the last we have
also looked at the beginning in the interest of temperature and all the schools together and because the influence and temperatures also very interesting not of components and they
are not running room temperature there if you want to honest then and the influence of the temperature is becoming more important and I think 1 reason is because we want to have use less material want to put more power in it I think that's the general revenue hard other presenters as well not only scowling still strength because requirements for high-strength more ducked and will sustainable material is out there so I made this
picture and which I think it's somewhat of that this is something we have to consider the matrix and the defects and see that they will also
work together I will give
it a couple times and I think presence of right it gives the impression but what we've seen also is that actually matrix may influence How to defect or generating capacity cracked so it's a bit more complex but I think it gives at least an impression we
have to take those into account when told about
fatigue-and normally try to correlate it we need to have a base and we need to know what you are compared and I
I think 1 extremely good thing is that what and where ,comma maybe he made all these theories about
the size of an inclusion and they're the hardest of material related quite simply a good a lot of good rule of thumb said you can use any 1 rule of thumb is bad the fatigue strength
they're looking at the very simple rotating bending fatigue 2 the hardest
Richardson Wales with industry and of course you see this correlation is quite good but it started
and what we would like to do is going to develop and work with material up in this where it's
got to have a deviation so Of course the reason is as you all know the Matrix will control this part whilst the the
defects will control the sport this challenge is really
hard to win up above this line here which is typical thing that you would like to challenge this is not abating Michaela had more test about them because
what we that it is possible to go on with this sort of
theoretical which is of empirical theoretical simplified and model it is possible and I think that's something will be very interesting for the future that we will work with but also if we want to go up in this high strength levels we also need to consider the defects because they or their and regardless then if we do a material with beautiful matrix Sweeney nite format for 17 months and yet the very nice structure it might fade from the conclusion is that which would be very sad a lot of different
15 mechanism sometimes you difference between contact fatigue and structural fatigue some call
it that I think can yen principle there different test methods but in general mechanism I think it is
fell much the same is true looking in at the material and furniture their point of view I think
counterfeiting is a good way of a review looking at the matrix material what happens with steam matrix because you can see that fight quite good because it's a it's a rather slow process that we see that can run it for a long time and what do you see when you
make a Bowling counterfeiting test now we see something underneath the rolling Raceway we develop what we
call action region which is well accepted we know it's there but what is it I mean this is really the
starting point Florida and I think we have been very very much relying on fracture
mechanics when it comes to and that means we are trying to calculate the fatigue without knowing the course of the initiation and I think what we should dig in all morning investigators wine
history the initiation so this process doesn't happen just for 4 it happens because putting stress there you have a certain temperature and it developed so
it is something that happens the process that happens in the material we have done
this test which is actually tests looking there very much loaded itself
compare that 2 of the same sample but away from that secular tested this rolling bearing material it's a hundred from 6 material at high and high temperature very long time and then you go take the stand
the microscopic and you go and have a look where it's not loaded but if
experiences the same sample now you see the machinery candles tonight is interesting in Carbide's Eisenstein them their democracy the became then In 2 the
doctor what you see you have much
coarser structure something has happened basis this is not this is not the continuum this is
this is not a fracture mechanics process but the crack has formed
this in cup when you see much coarser Michael structure when you see the absence of the retail store so the material is gradually
changing I and my professor when I was at the release to the college hillock was in always also also that it's more energetically their beneficial to go to that and that's I was a standard phrase but it's it's quite good the material want to go to the lowest possible energy and that schools
chaired by stress and temperature goal I think this is this is 15 is stopping all the 15 record and of course
Senor intervene How does different structure respond to this Of course those have
defects and this one's
will enhance because they are awesome strain races putting much more strain putting more energy into the material and promoting this material cables so this the
Met mechanism of 50 that I think is extremely interesting trying to understand they
are other ways fatigue testing you can make structural fatigue I think it's the same make
it looks differently because they are as but if you are you have to have a good life who a few haven't microscope preceding the microscope you can see the same kind of phenomenon you have some kind of all works down all the material in the closing vicinity of the defect
making the things so ICQ decayed material on taking the the practice space where greater crack and then you can start to play around with a fracture
valuation I we made a lot of Lokomotiv testing now I come to 250 and special rotating benefited because it's a fairly simple way of
producing samples to generate a lot of data show time and this is
what we what become come up with 1 thing would enough ,comma with and looking at any it's just support the work on the theory that the nodded the fact more detrimental for 450 and it works quite well
and all this jobs are established from actually experimental test maker of protecting the and then you see how you can increase the strength of fatigue strength if you reduce decree critical different different-sized but of course all captives to some certain points where you have no intrinsic and fatigue the that what's was the capital for high-strength materials but we
are interested in we are talking about the potential is is there are still
a lot of things to do to go "quotation mark we made a lot of tests we'll look at all assessed all of fracture surfaces calculating from what was the smallest possible inclusion at the slowest possible stressed that ever caused 15 it's thousands of samples that great for the commented
titanium should have people there more fitted but that 1 is oxide could quite comfortable so
I hopes to here just just so I would like to send a message but I think that's it this is what I think is very important we should
put more effort into looking into the 50 as the process happening in the material right now I think we are using fracture
mechanics too early we should walk there and we should help the fracture mechanics people got a really good at
calculating cracks when they have a cracked but we have to guide them here the physical metallurgy is I think has a good good knowledge base to drive these kind of investigations and understand this and then don't forget to defect because in the end of the day we also have to to work for this spot was a general
policy and going into more In that isotropic what what we see today is that more and more as I said product or are higher stress in very many different difficult directions is an
example for fuel injection part with you have a hold real area of Holy Land have a chamber there which is subjected to pressure all around 2 thousand baht which
means that in these kind of holes in all directions it will have a very high stress generated which means if you have emanated defects in that region going from from that
they will be potentially costing the that's why we
are trying to get away from From the conventional steam
and developing more and more stadiums that are cleaner and with less than emanated smaller inclusion size these are typical some deformed in the rolling direction the Round Mound words and oxides
if we can make held to another shape there will be more sabbatical and that's
possible and then they need also going for me physical metallurgy stole subtract the process can because I think they
also varied needs to be fed with this kind of information what is really
important for so today we have the possibility to choose by controlling the process good way more defense different ways going from different types of people inclusion
sizes or shapes from apology and composition we
sometimes represented the weekend we can choose how should be set inclusions in order to be asked formats ever possible
going from just low-sulfur steam just lowering the sulfur content might not be sufficient because then we know will end up with quite a big chasm illuminates we need to do something
else and then we can start to make isotropic the electrical and might proper quality which change their compositions into more deformable and an understanding
this buildup up to connect this to their degree reduction
because it withstands also you look at that because that has no other aspects before the material the area
fractions of the Lord size infusions for the most of the
cost of team were reduced because they will be smaller and not not detrimental in whereas if
you you have commenced in more conventional stains they are less prone to we have to do it work
and it's possible to do quite a significant improvements for instance if you look
at the 15 In this case just from taking bending fatigue was seeded marginalized the best there is not the main difference between different themes the has let levels
but even going to transfer restored to have complex then you can really benefit so I sought to appeal should be considered when it's needed we made it quite fun
tests which was very simple but quite illustrative I we know that
it is different depending How big volume that you test what the team
dated and sometimes the people what what is the video image as I said I just pick a number and see the but at the same he we just machine from the same body from samples in different dimensions and then we tested different volumes and
this is the different results so it's quite important because refiners is even more I've made
1 1 consideration when we at directions and volume and this is quite an interesting to have to look at if you have a the most beneficial directions
and you test 100 cubic millimeter now you will run up and you can almost however 15 per cent that served as around 50 % which of the 15 limit at 1300 and if you
run up the difference directions the 50 percent pulled there which is 250 that's a dramatic
difference and you also quite dramatic shift if you go on and test the bigger volume walking test 1 thousand
for a 50 percent it drops down to some rather rare online 100 so take a number last this thing doesn't temperature
which I think is knew well what we think is quite interesting have retrofitted at machines making fatigue testing at elevated temperatures mourners
and this 1 which is really
looking at what happens and the interesting thing is not the the absolute number because that's the number here in many cases represent distinction but this slope that we see here and
I think different kind of material different kind of Mike rastructure will respond differently and this is
1 way or looking at the material how could you make material more prone for more resistant to the temperature I think
1 interesting feature here which is not out Britain I would tell you if you can keep a secret no if you
look at those 2 materials they're from the same he St. place really does he did he treated differently this shows
that you do also in France at the same inclusion population but you have a difference if a which means also the heat
treatment and my construction I don't stop
there I got the one-minute silence but nervous before without
OK and very interesting to at thank you very much and offered into questions that once they're in the middle were aware overseas
operations and I just wanted to know he
said that the Austinite I'm in the complexity of the case due to stress and temperature is exception decaying into eyes and the and highlights of his team was interesting to me that's what we what we assume when we're looking into developed the other microbe we didn't see anything you like you were due more to site at the state's huge thing but I made this a long long desert habitat for transforming than continue to move to the center and had his distress incidents that transformation and rather than just being a temperature treatment and decomposition has a really good question that's what I would like to know what we would like to know because it is not pure the temperature they work together that's what we see and many of which wasn't he just temporary before and make tests it's not the same as testing at a temperature for instance Providence itself 1 way or another if it's dislocation will win its diffusion aid probably some some diffusion we don't they're not fully aware that what we would like to good morning could feasibly be this distressed state of the US tonight it's kind of a really and heads a toned-down version of the kind of client stresses that provoke came to be 2 transformations Mayfield said making site were favorable which transformed into BCC alongside ship I don't know that could be 1 of France's here Have you to sue compared
the mechanical image the during the Cold comes the test of time and we would change the want the AFD should I
struggled with that well not on the only contact with the eye and I made up quite a lot of all work looking into the number of cycles the temperature distress and trying to see what is actually energy that we have put in here and then try to correlate that to happen I think that's something that we will continue to do because I like that I'd be looking at more energy at that point I didn't get any clear when make made a quick-and-dirty I didn't make it a very good relations I think you have to back condition the warning there was
a time when I was what concerned that question we actually published a paper in competition drill sites already this year on the other topic but my question is Is there I'm Have you considered what artifacts of hydrogen engrossed during processing In fatigue life during processing
because this is this is a hot topic in order to steal families I wonder if you have started but no we haven't really is that mean that's a very hot topic in and Of course you see that the choice of a hydrogen in using so what we have done and we are testing on material with Taylor lower constantly the . 5 ppm normal and we haven't that many times the treatments that we have we have not really looking into that thank you the character of what
question why did you choose the temperature use for the rolling contract fatigue tests
100 degrees and how you perform any rolling contributory testing and other temperatures through room temperature and see what is different Yao down we have ever had a simple Rowley complexity of water that was test machine and we have to look at the tempered and you can clearly see present temperature all the material decays and 1 the role contributing another question was why did you choose up 100 Idaho that was started his Seymour effects within a reasonable time I would say and it's not a very high temperature which makes a crazy idea my I question so if
I ever went and understood that you would like to improve the assault of the of the material by reducing the number of it'll be the inclusion in in the steel so by GM the sofa content but
what about the world of the year in any case the oxide content that we that we remain a source of water on the fields during the testing room and in any case would embolden machine of unity of the pieces than he has so far is not often considers there are people in the session of the the absolute right and and what we're doing to reduce the sulfur content we do and also the oxide content and then then you will end up with a much poorer brush with ability so but fortunately we have a very good companies working with machine tools made and the people and their working environment because today you can find this low of receives and you can you can't machinery and but if you need to develop he said that
I have a question this for you at tributes there are understood fuel the anisotropy off the fatigue properties to the island get a chip of the inclusions if it this
rises in your answers yes but what about is there there any effect of crystallographic anisotropy you know that the metal matrix also has so maybe not not what we've seen now coming not not already significant know thank you my
question is of your slide on the relationship between fatigue
life and the size of the
samples yet unity and common sense that and also whether you
have checked what is the body that could actually cost fatigue in relationship with your relationship between oxide sulfides Carbide's I wish the demeanor of the samples size of the samples yes the only what was that that lost 1 if we
have that 1 of Webb looked at
all all the sound that would test the look and we ensure that its inclusion in the schools and the it said it is not the inclusion costing 250 that if it's a surface scratch Latin testicles and we call the I was always this related to the
probability of finding that we didn't inclusion would get raises size Europe OK tallies
Timothy was heard over to people fast questions from that around the world that we got question from the Middle East Argentina In this
2nd sliced there seems to be no falling from the matrix in the trend was direction are they any Of these arrival how would they compare these picture so there
was no then data .period from them metric in the I think means it the will out and now
have there is no because we haven't tested we have concentrated on that strength levels we haven't so far made any Caspersen test in a the hornet's nest and 7 50 so that's still something that we would like to and what about where we will develop a quite good method of testing transfer about splitting up but you make it too but with suspected gently for
forging the flat them would take samples we have very of thank you and the question is Have you observe any fear from 1 . itching regions if you'd be held this it happens this cracked the platform from the northern not is a from adopted reading by itself no no there is "quotation mark the peculiar is even tho I consider thinking
preliminary I'm very surprised nobody has asked the question How did you produce isotropic inflation that's a good thing that's a
good question as the Blues question have no it is a matter of doing working with the pros metallurgy it's not a itself some Nepalese talk about I don't I see a lot of modesty producers are due to the same it's not that we are extremely unique we're doing a good way but we don't have like him the since the simple the new below the market Utah


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