Gordon England Surface Engineering Forum



Re: Rockwell Vs. UTS


Posted by Gordon England on May 11, 2003 at 18:40:42:

In Reply to: Re: Rockwell Vs. UTS posted by Michael Doyle on May 09, 2003 at 15:23:43:

Hi Michael

I would expect the 304 to be harder than the 420 in this situation. I would stress that conversion comparison between the various hardness test methods is approximate (as is conversion to UTS) and becomes even less reliable for materials other than low alloy steels or where the properties have been dramatically altered by say cold working or as a thermal spray coating.

This can be further complicated by whether the hardness test is measuring microhardness or macrohardness (particle hardness or bulk hardness) and whether the material is homogeneous or heterogeneous in structure. Defining what is micro or macro is grey area, but generally the larger the load and indentation, the better the result for macrohardness and bulk property. UTS comparison in most tables are derived from comparative tests with brinell hardness on steel (best for bulk property). So you can see converting from rockwell C to Brinell then to UTS particularly for unlike materials will introduce even larger errors.

Wear resistance (abrasive) has a relationship with hardness. Again the correlation can be good between some very similar materials like carbon steels, but not necessarily when comparing different materials. Wear resistance is a very complex property with many different modes of operation.

Extreme Comparison:

Hardened steel 55HRC, 275 kpsi UTS, relatively homogeneous.

Thermal spray coating 13Cr steel, 28 HRC (equiv), 40 kpsi (~10kpsi transverse), relatively very heterogeneous, weak particle boundaries, hard and soft particulates, somewhat porous.

In many applications the coating shows equal or superior wear resistance.

As you can see these are complex relationships. Relating them to how a material is finally going to perform in service is not straight forward. Measuring properties like hardness, UTS, Young's Modulus etc.... provide useful guides and in specific materials/applications can provide the overriding factor in predicting performance, but invariably this can not be applied universally to other materials/applications. Sorry, I'm rambling on!

Are you looking at this subject for academic interest or for solving a specific technical problem?

Regards Gordon



Follow Ups:


Surface Engineering Forum

Surface Engineering Message Board Archive

Surface Engineering Message Board Archive Index

Search Message Boards Archives

www.gordonengland.co.uk





GoogleCustom Search

Post A Message!

Gordon England Surface Engineering ForumPlease go to the new Surface Engineering Forum as this old message board is a read only archive. Please copy and paste relevant information or link to the page if you wish to reactivate a thread on the new forum.







Gordon England Independent Thermal Spray Coating Consultant
Telephone: +44 (0)1252 405186

PLEASE CLICK HERE TO EMAIL

Site Links

Introducing

Nature of Thermal Spray Coatings

Surface Engineering in a Nutshell

Surface Engineering Forum

Thermal Spray Gun Repair Service

Plasma Consumable Parts

Thermal Spray Powder Supplies

Applications:

Thermal Spray Coatings on Carbon and Glass Fibre Reinforced Polymers

HVOF Coating of Paper Making Roll

Abradable Coatings

Photomicrographs

Thermal Spray Processes:

Combustion Wire Thermal Spray Process

Combustion Powder Thermal Spray Process

Arc Wire Thermal Spray Process

Plasma Thermal Spray Process

HVOF Thermal Spray Process

Detonation Thermal Spray Process

Plasma Flame Theory

Cold Spray Coating Process



Wear and Use of Thermal Spray Coatings

Corrosion and Use of Thermal Spray Coatings

Glossary of Thermal Spray and Surface Engineering Terms

Image Directory for Thermal Spray Coatings

Plasma Gas Flow Information

Plasma Gas Flow Correction Calculator

Contact Form

Links to other interesting sites related to thermal spray and surface engineering

Reciprocal Links

Periodic Table of the Elements

SI Units

Calculators for Conversion between Units of Measurement

Hardness Testing

Surface Engineering Message Board Archive

Surface Engineering Message Board Archive Index

Search This Site


Photography Gallery2

Photography Gallery3


© Copyright Gordon England