BS EN 18 steel equivalent ? 4

[edison123]

Can someone tell me what is equivalent American specification for British (BS) EN 18 steel ?

Is there a conversion table available on the net ?

Thanks

"Most people stop working when they find a job"

 

[Carburize]

The old EN 18 is 4140 without the Mo addition.

 

[edison123]

Thx Carburize.

The chemical analyis by OES gives the following

C - 0.35
Si - 0.26
Mn - 0.77
P - 0.004
Si - 0.004
Cr - 1.15
Ni - 0.02

Mo, Al, Cu, Mg, Zn - none

Does 4140 conform to this ?

"Most people stop working when they find a job"

 

[TVP]

edison123,

Technically, no, 4140 must have 0.15-0.35 Mo. However, 4140 certainly would be an acceptable North American grade to use instead of En 18. The Mo provides additional hardenability, meaning that larger diameter bars or larger parts can be effectively quenched to the same hardness.

 

[Carburize]

4140
C 0.38/0.43
Si 0.15/0.30
Mn 0.75/1.00
Cr 0.80/1.10
Mo 0.15/0.25

 

[edison123]

Thx TVP.

The material EN 18 is for a stud bolt in a hydro generator. This anchors the V blocks between the pole coils of the rotor and hence subject to rotational forces.

Will using 4140 instead of EN 18 affect the performance ?

"Most people stop working when they find a job"

 

[Carburize]

4140 is used extensively for fasteners in North America I supect it might be better than EN 18 in this application.

 

[TVP]

I agree with carburize. Is there a problem with the current stud bolts?

 

[edison123]

TVP

The bolts are to be replaced as part of rehabilitation project and the consultant wanted the US equivalent.

Thank you both for your help.

"Most people stop working when they find a job"

 

[edison123]

One more question

Does 4140 steel requires heat treatment to get hardness or the shaft can be directly used for stud bolts ?

"Most people stop working when they find a job"

 

[CoryPad]

Fasteners typically are heat treated for maximum strength properties. This treatment would be 1) austenitize 2) quench 3) temper

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[edison123]

Thx corypad.

"Most people stop working when they find a job"

 

[edison123]

One more question,

Thread rolling or thread cutting in CNC - Which is better and why ?

Thanks

* Money doesn't grow on tress since the banks own all the branches *

 

[kenvlach]

Rolled threads are generally better. The rolling improves the grain structure vs. applied stresses, increases strength via cold working, gives a more rounded thread root for better fatigue resistance, and doesn't waste (cut) material.
CNC-cut threads may give more precise tolerances, especially in larger sizes > 1".

I suggest also reading
Fatigue life of non standard threads
thread725-148865

 

[TVP]

Thread rolling produces a higher quality thread for the following reasons:

1. Improved surface quality (lower surface roughness)
2. Improved strength and hardness due to strain hardening (cold working)
3. Improved fatigue life due to residual compressive stresses when performed after heat treating
4. Somewhat improved fatigue life due to favorable grain flow/orientation when performed prior to heat treating

An excellent journal article on this subject is "The effect of manufacturing processes on the fatigue
lifetime of aeronautical bolts" from Engineering Failure Analysis 8 (2001) 227-235.

 

[edison123]

Thanks TVP.

So, I will go with rolling.

Corypad's suggestion - 1) austenitize 2) quench 3) temper

This should be done after thread rolling ?



* Money doesn't grow on tress since the banks own all the branches *

 

[Kenneth]

It depends. As noted by TVP, rolling after heat treat (the typical "aerospace" practice, along with using a UNJ thread form) will improve relative fatigue lives, largely due to imparting a residual compressive surface stress that must be overcome before a fatigue crack can inititate/propagate. Heat treat after thread roll will remove those beneficial residual compressive stresses.

If achieving the ultimate attainable fatigue life is not the overriding consideration, then many of the benefits of thread rolling can be obtained by rolling the threads prior to heat treatment (the most common "commercial" fastener practice) without incurring the expense of rolling the material in the heat treated condition, which is typically a job for someone with aerospace threadrolling experience and is more difficult to do with generating unacceptable defects (and is one of the reasons that those aerospace fasteners cost so darn much). Check with your threadroller first to see if he has the experience and equipment to roll material in the heat-treated condition if you decide to have the material rolled in the heat-treated condition.

 

[edison123]

Thx kenneth.

Will heat treatment after rolling result in thread or bolt distortion ?

* Money doesn't grow on tress since the banks own all the branches *

 

[TVP]

Distortion is usually only a problem for very long bolts, and that is related to straightness, not problems with thread geometry.

 

[edison123]

Thx TVP.

I will come back here and let you all know how this turns out.

* Money doesn't grow on tress since the banks own all the branches *