Blade Steel Hardness

[matt321]

How can you tell if a blade is made of harder than avg or softer than avg steel?

[KAV]

Steel hardness is graded by Rockwell scale. This is measured by a machine recording the pressure required to impact a very hard pointed rod and leave a dimple. If you remove the multiple factors; steel type, tempering, forging vs casting vs stock removal, VARIABLE tempering on a individuaul item it is very simple. A 'soft' blade is @ 52-54 Rockwell and a extremely hard one 58-59. Soft will obviously lose an edge faster but is more easily resharpened. Hard will maintain an edge, but may be brittle depending on the application and more difficult to resharpen.

[notthesharpest]

How can you tell if a blade is made of harder than avg or softer than avg steel?

A straight razor, or a double edge?

[matt321]

A straight I mean. Folks often comment on how hard or soft the steel of their razor is. So I was just curious how one would know that without serious testing equipment?

[notthesharpest]

I assume that they can tell by how difficult it is to hone, how little comes off on the stone, and so on. I think they don't know precise figures but are comparing to the other razors they've worked with.

On new custom razors, the maker could tell you exactly what steel he used, and then you would know for sure.

[KAV]

If it's Hollowground the steel is usually very hard. The thin edge profile would 'roll over' to easilly if soft. I suspect people who note soft and hard are going at the hones to much. Any decent blade initially set up properly only requires light touching up and VERY infrequent reprofiling. I've observed countless knives missing 1/4" of original bladestock less than a year old

[matt321]

I've observed countless knives missing 1/4" of original bladestock less than a year old

Ouch.
Anyway, abrasion resistance does not equate to hardness, right?

[drmoss_ca]

Matt,
You can easily estimate hardness by honing quality. The trick is to have honed enough razors to have a feel for what to expect. You may have tried honing a TI or a Wacker, which are very hard steel (Rockwell 63-65), in which case you will know how much easier it is to get an edge on an old W&B (Rockwell low 50's). Then you appreciate why and how the TI keeps its edge for longer!
You are right in separating the qualities of ductility, malleability, and hardness (which itself divides into resistance to scatching, indentation and dynamic or rebound hardness) since they are all different qualities. It seems one might study steel for many years and only scratch the surface, so to speak.

Chris

[matt321]

I've noticed that some tend to develop micro-chips as the apex forms on the hones. I assumed that meant they were brittle and therefore hard. Others seemed to never flake like that, but instead are difficult to achieve a clean edge. Viewed through the loop the edge seems to have a fuzzy border. I assumed those were more plastic and therefore softer.

I don't have a stainless blade, but some threads say they are harder and some say they are softer although more abrasion resistant due to carbides.

[drmoss_ca]

I find that honing stainless is less like abrading away hard steel and more like pushing rubbery tough steel towards the edge. They prefer their own techniques and hones, and it was harder for me to get the knack of honing stainless. I have yet to see any micro-chips on a stainless razor.

Chris

[TstebinsB]

Carbon content plays a role. Razors with a higher carbon content - something like 1% to 1.25% - are more resistant to wear and hold their edge very well.

Friodur Inox razors are made with a soft steel but the blades are cryogenically frozen to give the characteristics of a hard steel. Without that process, the blade would be like the soft, Sheffield razors.

[KAV]

Micro chipping in knives is usually associated with knives of extreme hardness. The chipping actully happens in the final steps which may include a hard ceramic strop or grinding compounds of very fine micron size.
By this time the edge is so thin the structure is compromised with the actual grains tearing apart.
It is also so sharp it actually stops cutting test mediums such as cigarette paper.
Everything in bladeware is a compromise. You can make your own, by finding an edge 'enough' to work without getting into ultimates that ultimately fail.

[matt321]

I have a theory that the harder blades tend to hone up sharp but not necessarily smooth. While the softer blades tend to hone up smooth but not necessarily as sharp.