Our small manufacturing company is taking on a new job that calls for
a product to be manufactured from 420 Stainless Steel.  We have a heat
treating department but have never processed this grade of steel.  We
need to harden the steel and temper it to a final hardness of 51-52
Rockwell "C". It is standard in the heat treating industry to use ASM
International's Heat Treater's Guide
(http://www.asminternational.org/Template.cfm?Section=BrowsebyTopic&template=Ecommerce/ProductDisplay.cfm&ProductID=10852)as
an authority on heat treating questions. My problem is this: The
information given under the section on 420 Stainless Steel appears
ambiguous or contradictory. I have two questions: 1.Assuming I use a
hardening temp of 1850 degrees F and use a fluid bed quench (which is
faster than air and slower than oil)what should I expect to see for a
"as quenched hardness"? 2.What tempering temp should I use to obtain a
final hardness of 51-52 Rockwell "C"?

http://www.azom.com/Details.asp?ArticleID=972
(They use Brinell hardness, but you can convert it here:
http://www.corrosionsource.com/handbook/mat_hard.htm )

Also see:
http://www.stal.com.cn/pdffile/410420425440a.pdf



420 can come in many varieties.  You should probably contact the
manufacturer of the steel to find out what they say their 420 is and
what they recommend for temperatures as well as the entire process
(different steels have different ideal cooling rates, sometimes its
more than just one number)  Even if it truly is "420" with no other
indications, the specs for 420 have a big range for Carbon (one of the
above sources said .15 to .4).