Nobody uses mild steel for their frames and haven't for many decades, if ever.  My middle school (i.e. junior high school) shop teacher used mild steel tubing to make a minibike frame in 1970.  He may have been the last one to ever do it.  

NemadjiMan, on 27 February 2012 - 10:18 AM, said:

Have you ever seen a Matchless frame as used on the G80/G15/N15 models?  Cast steering head and assorted other lugs with steel tubes slip fit and brazed?  Triumphs were the same way.  The Matchless frame weighed 48 lbs.

Contrast.

Most manufacturers used mild steel unless they specifically advertised Reynolds 531 or Chrome-Moly 4130 etc...   IF they had the higher grade of tubing, it was a major advertising point and they used it to say that their procuct was "better" than the competition.  Back in the late '70s early '80s Honda and others used Chrome-Moly tubing in their MX frames and they mentioned it in their ads.  The Brits always mentioned when they used the higher quality tubing in their frames.  If it isn't mentioned, it is probably just mild steel.  Nothing wrong with that, not much difference in strength unless the frames are jigged and heat treated to higher spec levels, which most of them aren't regardless of which tubing was used.  

Your Junior High School shop teacher was doing what Honda and Suzuki and Kawasaki and Yamaha did in the early '70s, using mild steel tubing for his frame.

Swiss

Another thing to take into account when using CF for a frame is the ridgidity of carbon versus aluminum, there could be a lot of unforeseen problems similar to when Honda introduced the first version of the AF in 97.

Swiss, on 28 February 2012 - 07:45 AM, said:

It seems unlikely that only Honda used "better than mild steel" tubing for their frames in the '70s.  Certainly some of the Europeans were.  This would be especially unlikely after they had three or four real MX races under their belts and their darn frames bent and broke.  Every material choice that goes into a dirtbike is not necessarily on the ad sheet.  And every "better than mild steel" tubing alloy doesn't have a cool name like "Reynolds" or "Chrome-Molly" to put into an ad.  Higher strength steel tubing has been commonly available for a LONG, LONG time.

Oh and weren't the '70s "decades" ago anyway??  Like 4 to 5 decades....  

NemadjiMan, on 28 February 2012 - 08:14 AM, said:

Yes, but one's perspective on that sort of thing depends on his age.  If you remember the '70's clearly enough it doesn't always immediately dawn on you that they were 40 years ago.  If you remember the '60's, you weren't really there.

Quote: Nobody uses mild steel for their frames and haven't for many decades, if ever. My middle school (i.e. junior high school) shop teacher used mild steel tubing to make a minibike frame in 1970. He may have been the last one to ever do it

NemadjiMan, on 28 February 2012 - 08:14 AM, said:

Quote: Back in the late '70s early '80s Honda and others used Chrome-Moly tubing in their MX frames and they mentioned it in their ads. The Brits always mentioned when they used the higher quality tubing in their frames

Wow, you are quite selective and misleading in your statements AND your quotes.  Your statement as shown above was that "Nobody uses mild steel for their frames and haven't for many decades, if ever."  Please note clearly the wording "if ever"...  Then I came along and said "Back in the late '70s early '80s Honda and others used Chrome-Moly tubing..."  Which you replied to with the statement: "It seems unlikely that only Honda used "better than mild steel" tubing for their frames in the '70s. Certainly some of the Europeans were."  Please not the differences inour statements.  You seem to say that I said that only Honda used "better than mild steel" tubing -- and I actually said that Honda and others used Chrome-moly tubing.  Earlier I had mentioned the Reynolds 531 which was a high grade of tubing used a LOT by the Brits in their frames.  The term and others would actually include Kawasaki, Yamaha, Suzuki, and the Euros like Ducati, Husky, and various factory and small specialty production shops like out C&J Racing and Champion Racing here in the states, Otus and SGB in France and a number of others.  Lots of the Japanese Factory bikes (and many of them production race bikes) were made with mild steel tubing even if it was around 40 years/4 decades ago.  Not only that but MOST of the current non-aluminum framed trail bikes etc. are STILL made with mild steel tubing!  Understand that these bikes are made to Price Points as the Bean Counters call them.  That means that if you can build it with slightly thicker wall heavier tubing that costs about 1/3 as much as the "better stuff" then that is what you use to keep the Profits flowing!

Mild steel isn't Lead, it isn't soft and doesn't break every time that you go racing with it!  All you do is build the bike with slightly thicker/heavier tubing and it works just fine.  Lots of racing frames have been built with mild steel frame tubing.

Swiss

Things like 1018 steel tubing is an "alloy" as are just about ALL steels.  1018 is considered "mild steel" by most all fabricators and is not a high grade alloy like 4130 or 4140 etc...  The confusion on this may be the idea of what you are considering "mild steel"!  1018, by the way HAS been used to build racing frames by a number of fabricators.  It is considered adequate for racing if the wall thickness is sufficient to handle the loads involved.

Swiss, on 28 February 2012 - 12:21 PM, said:

Price points without sales are meaningless, and when weight becomes a sales point, 1018 is one of the first things out the window.  An example is the steel used in the '03 YZ450 frames that led to that frame being more than 6 pounds lighter than the '02 YZ426 frame. There is, apparently, a mistaken belief held by some that there are only two kinds of steel, and either it's chrome-moly or it's cold rolled junk.  Nothing could be further from the truth.  In fact there are a number of reasons for selecting high strength alloys other than Cr-Mo to do any mass production work with because of Cr-Mo's fussy nature with regard to being welded.  4130, Reynolds 531-853, and other similar alloys require special processing, and are difficult to fabricate with using automated machinery.  There are lots of steels that are far stronger than 1018 that aren't so particular.

Swiss, on 28 February 2012 - 12:21 PM, said:

"...just about all..."?  Please name a steel that is not.

they havent used mild steel in frames for many decades if at all? thats seems odd seeing as i have 2 different frames from 2 different decades in my garage right now and both are mild steel

Honduhminiman, on 28 February 2012 - 05:48 PM, said:

What are they?

I expect nearly all of the play bikes have mild steel frames.  There was a recall on KLX140s that had the dealers welding the frames up in-house.  I'd be a little surprised if they had every tech in the country welding on CrMo frames.

I thought that it was pretty well understood that only the purpose-built race bikes had factory Cr-Mo frames, but perhaps not.

SOAB_465, on 29 February 2012 - 12:05 PM, said:

Honda used to advertise a "medium carbon" steel frame which is not mild steel.  Mild steel is generally considered steel that is not heat-treatable.  That would be steel less than 1.8 wt% carbon or 1018 and lower alloys.  They never really said chrome-moly but I wouldn't be supprised if they were.

And no special tech is required to weld cro-mo frames.  For the longest time, 4130 cro-mo frames were simply welded using an acetylene torch and 4130 filler.  Rapid cooling after tig or mig welding had a tendancy to make the welds brittle which required post weld heat treatment when using 4130 filler.  But... in most cases, it is acceptable to tig or mig cro-mo frames with ER70-S2 which is a mild steel filler.  This gives sufficient mechanical characteristics, in most cases, without post weld heat treatment.

Edited by 1987CR250R, 29 February 2012 - 06:29 PM.

i just did some research and i found out that  my 1992 KX250 frame is actually 4130 steel which is a chromoly alloy.i was mistaken about that. but my 1981 Suzuki GS550 is mild steel as far as i can tell.its not a MX bike which makes a huge difference. its just a cruising bike

1987CR250R, on 29 February 2012 - 06:24 PM, said:

That, and the extremely localized HAZ. But that's what I meant by that.  4130 adds at least two layers of complexity to the production process along with the attendant expense.  The use of a mild steel filler to some extent negates the advantages of the alloy and tends to limit how light it can be made with adequate strength, although it can still be both lighter and stronger than true mild steel.

1987CR250R, on 29 February 2012 - 06:24 PM, said:

i work in a power station welding 833 carbon, B2 and B3 cro mo (aussie standard's may be different to over sea's, but that's 1.25% chome-1% moly and 2.25%chrome and 1% moly respectively), the boiler tubes i repair are only 3mm thick, and hold 2400PSI steam pressure at 500 degree's Celsius, going through hundred's of heat and stress cycles a year without heat treatment at all, and havn't had a weld fail under operating conditions yet, heat treatment's only needed in cases where the steel is thick and act's as a heat sink cooling the weld more quickly then ideal, ie above 8mm in thickness, well above the thickness of a frame, the biggest problem is cro moly is more prone to porosity to the point we're currently trialing a a TGX (flux cored) B3 TIG wire for the root run of our welds to try to combat the problem.

Swiss - sorry for the misquote.  I woulda swore you just said Honda only.  I probably jumped that way 'cause I get tired of hearing about how great Honda engineering is, while deriding the strides other manufacturers have acheived, from some other folks.  My bad.

Seems here that some people want to believe that they have reasonably new bikes in their garages that are built with mild steel tubing.  Jap junk and all that.  Others, like me, want to believe that the engineers went to into their bag of materials options and picked an alloy better than simple CRS steel.  Being an engineer, I cheer for this side.

You can get better steel than plain CRS without spending much money, which is another reason why I lean the direction I do.  The other is that in actual use (especially offroad), manufacturers have a history of suffering frame breakage.  If poorly designed frames cause rider injuries, manufacturers would be liable.  Hence at least one motivation to use better steel alloys.

It's a little unclear to me how anyone can claim that they have a bike in their garage with a mild steel frame, or an existing bike comes with a mild steel frame.  I can see how you would want to believe this though.  You would have to send a sample for material analysis to really determine this.

I guess my last comment would be, thank the AMA for the decades old production rule in MX.  That pretty much assured that we would at least get good materials in most of our dirtbike frames, and not have the factories out there with superior steel alloys (and now aluminum alloys) while us poor joes got copies with inferior materials.

Good discussion though.  I'm learning some stuff from it so, thanks for that.  

There is lots of structural carbon fibre in modern airplanes and they can handle hard landings. My carbon mountain bike (Ibis Mojo) has lasted longer than my titanium mountain bike. It is easier to make Carbon frames any shape that maximizes strength and minimizes weight. So I think there is potential but the cost per gram saved would be very high.