Editing Heat treating (section)

===Case hardening===
[[File:Computerised Heat Treatment Furnance.jpg|thumb|A modern, fully computerised case hardening furnace.|400x400px]]

Case hardening is specified by "hardness" and "case depth". The case depth can be specified in two ways: total case depth or effective case depth. The total case depth is the true depth of the case. For most alloys, the effective case depth is the depth of the case that has a hardness equivalent of HRC50; however, some alloys specify a different hardness (40-60 HRC) at effective case depth; this is checked on a Tukon microhardness tester. This value can be roughly approximated as 65% of the total case depth; however, the chemical composition and hardenability can affect this approximation. If neither type of case depth is specified the total case depth is assumed.<ref name="pmpa" />

For case hardened parts the specification should have a tolerance of at least ±{{convert|0.005|in|mm|abbr=on}}. If the part is to be ground after heat treatment, the case depth is assumed to be after grinding.<ref name="pmpa" />

The [[Rockwell hardness]] scale used for the specification depends on the depth of the total case depth, as shown in the table below. Usually, hardness is measured on the Rockwell "C" scale, but the load used on the scale will penetrate through the case if the case is less than {{convert|0.030|in|mm|abbr=on}}. Using Rockwell "C" for a thinner case will result in a false reading.<ref name="pmpa" />

{| class="wikitable"
|+Rockwell scale required for various case depths<ref name="pmpa" />
|-
! Total case depth, min. [in] !! Rockwell scale
|-
| 0.030 || C
|-
| 0.024 || A
|-
| 0.021 || 45 N
|-
| 0.018 || 30 N
|-
| 0.015 || 15 N
|-
| Less than 0.015 || "File hard"
|}

For cases that are less than {{convert|0.015|in|mm|abbr=on}} thick a Rockwell scale cannot reliably be used, so ''{{visible anchor|file hard}}'' is specified instead.<ref name="pmpa"/> File hard is approximately equivalent to 58 HRC.<ref>Phone interview with the quality control inspector for FPM, Elk Grove Village, IL. 06-21-2010</ref>

When specifying the hardness either a range should be given or the minimum hardness specified. If a range is specified at least 5 points should be given.<ref name="pmpa" />