Hardening & Tempering

Posted by Joe on September 11, 1998 at 13:42:07

In Reply to: Re: Raven Finish
posted by Larry Jenkins on September 10, 1998 at 15:50:20

Larry et al
Well, I'll be the first to confess that it has been a long time since this engineer has done anything with hardening & tempering of steel.However, a few quick thoughts come to mind and you'll find a website reference below which will tell you all you want to know (perhaps more than you want to know) about steel and it's structure.
First thought: Dull red depends on a lot of things including background lighting and I wouldn't depend on someone's judgement as to what constitutes "dull".
Second thought: I have a bit of oil hardening tool steel that just arrived from MSC and the instructions for hardening and tempering are
Harden at 1450/1500F Oil Quench
Temper at 300-350 1 hour for RC 62/64
at 400-450 1 hour for RC 58/60
at 800-850 1 hour for RC 48/52
(RC stands for Rockwell C Scale which is a measure of hardness)
Note that 800-850 is roughly a "dull red".Also, I know the fully annealed state for this steel is about RC45.
Sorry to say that temper comes at the expense of hardness.
Third thought: I don't think I would want to mess with any heating of my nuts and bolts to any amount other than to get them off and then throw them away.
The bolting materials of the Model A era were mostly the metal equivalent of the "non-strike" bolts that you can buy at any hardware store today.From my experience in general with machinery I can tell you that this is "none too good".
The common bolts of the Model A were produced as quick as they could pump them out and cooling was often forced (as it is today) in the interests of handing and packaging.In effect, the bolting was to a certain degree quenched and possibly tempered as they sat waiting on top of a full warm bucket or box of bolts waiting to be packaged or plated or used.
Fortunately, most common bolting for the A was simply to hold the pieces together.Engineering sizing for the most part was more a function of "eyeball" and what seemed correct for the pieces.Ole Henry was generous in this regard compared to Chevrolets of the period.
However, I would just as soon use the best possible bolt (read a compromise between historically correct and as strong as possible) in my restoration efforts.By heating and potentially annealing the bolts you may be adversely affecting the maximum possible strength that bolt can provide.
My final thought is do the minimum processing necessary to give the appearance of correctness while preserving the inherent metalurgical correctness of the original bolt.A chemical treatment to achieve a "raven finish" seems to achieve this.
For those like me who wanted to brush up on their theory and practice of hardening of steels, dial into the website below for more of this than you can stand.
Best regards,
Joe
Steel -Microstructure Versus Properties