Key steel vs BMS sq bar

[DaveH]

Hi,

Key steel is EN8/EN9 roughly
BMS is EN3,

I have always tended to use Key steel because it seemed to machine better and I thought less prone to warping.

Now in my (as so eloquently pointed out by a member who shall rename nameless - HS93) old age I'm not so sure it is true.

Anyone has any views.  I'd be interested to hear what you you have to say.

For a start is key steel worth the extra cost.
 

DaveH

[John Rudd]

I thought that BMS was EN1A.........

[DaveH]

I thought that BMS was EN1A.........

John,

Nope, EN1A is free cutting, although it may be possible to get 'square section' in EN1A.

Trouble is BMS can be anything you want it to be 
 

DaveH

[John Swift]

I think Bright  Mild Steel covers several grades of steel  including EN1A

EN1A's lead content makes it free cutting  ,

great when machining  but no use if you want to weld it

     John

[Jasonb]

EN1A's lead content makes it free cutting  ,

That if it is leaded EN1A LD, you can also get it without in which case its just EN1A.

You can also get EN1A in black hot rolled form which is not bright.

J

[John Rudd]

I thought that BMS was EN1A.........

John,

Nope, EN1A is free cutting, although it may be possible to get 'square section' in EN1A.

Trouble is BMS can be anything you want it to be 
 

DaveH

Hmmm...misinformed again........

I've had BMS EN1A in round, square and flat form from the suppliers I use..

[DaveH]

I've had BMS EN1A in round, square and flat form from the suppliers I use..

John,

Do you use Key steel? or have you used it?

 
DaveH

[John Rudd]

Yes on both questions...

In fact I have a piece of 1/2 in sq KS under my bench..

[DaveH]

John,

What are your impressions, do you think it cuts "better" - why is it manufactured?

Why not just use "bright mild steel"?,  I am just trying to figure out should I buy key steel or orinary "bright mild steel"

 
DaveH

[John Rudd]

I'm sure the composition of key steel is different to say EN1A, as it has greater shear resistance hence it being used for keys in keyways...Or have I totally misread this thread?

[DaveH]

John,

No - you haven't misread anything, it was just that as an apprentice "2000 years ago" I was told "Use key steel for square and rectangular stock" it is a much better "quality" steel than "bright mild steel". Also I was told it had less of a tendency to warp after machining.

It is something that has stuck with me - I forgot everything else.     

Maybe it was in 1960, I also thought it may have been heat treated but I don't think it is.

If it is just from it's shear strength, I would sooner use a free cutting steel.
 

DaveH

[Pete.]

If it's an important part that mustn't fail I'd go for proper keystock but if it was just some pulley on a polishing machine shaft etc I would just use whatever I could machine to fit the keyslot.

[Anzaniste]

Key steel is a medium carbon steel supplied cold drawn and would have a tensile of 35/45 ton/sq in in old money.
I always remember the rule of thumb that  Mild Steel  had a tensile strength of approximately 30/32 tons/sq in.
Steel below 0.40% carbon, i.e. mild steel will not harden by quenching. Key steel has 0.50% carbon therefore will harden by quenching although not much.

There is a hell of a lot more to it than that but not being that clever I can't remember all I was taught in the olden days!!