Our son and I spend quite a bit of time working on cars. We have a good selection of sockets, breaker bars, impact wrenches, extensions, and various accessories.
One of our drawer cabinets contains nothing but chrome-vanadium sockets. (Many of them Craftsman that I’ve owned for over 30 years, BTW.) These have a nice, shiny, chrome finish. Another drawer cabinet contains nothing but chrome-molybdenum (“chrome-moly”) sockets. These have a black finish.
Now I’ve always heard that, when using an electric or pneumatic impact wrench, you should never use a chrome-vanadium socket. This is because chrome-vanadium is harder and more brittle than a chrome-moly socket, and could literally explode when subjected to the stresses of an impact wrench.
O.K., I can understand that. But what socket is best when applying a lot of static torque to a fastener using a long breaker bar? When doing this, I have used chrome-moly sockets, but some folks believe a chrome-vanadium socket is best for this task. Anyone know what the straight dope is on this?
It is true that the chromium-vanadium (Cr-V) sockets are harder and will tend to develop cracks under repeated impact loads, causing them to suffer from corrosion and eventually fracture. They’re great for hand tool use, including with a breaker bar, because they don’t deform or wear as much and can make a tighter grip, and the unbroken surface is highly resistant to corrosion. Chromium-molybednum (Cr-Mo) sockets are not as hard and therefore will tend to wear more with extensive use but are more tolerant to impact loads and will generally not fracture (or at least not without some observable deformation). The black coating you typically see on them is manganese phosphate because Cr-Mo is not nearly as resistant to corrosion, and in marine environments will quickly start to oxidize as the coating wears off.
You can use a breaker bar on each type of socket, but of course applying a breaker or other torque multiplier means that you can more easily develop enough torque to damage the socket (or shear the bolt or stud) without realizing it. In general, under non-impact use the Cr-V socket should last longer without wear, but if it does have tiny fractures or developing corrosion it can fracture unexpectedly under high static torque. I’ve never personally had that happen but then I’m pretty judicious (and liberal with my use of penetrating oil) when using a breaker because the hours spent drilling out a stud or the broken part of a bolt in a blind hole and cleaning/retapping threads cuts into my sacred reading/drinking time.
Stranger