CRS generally has a specific carbon composition, usually 1018/1020 as noted above. HRS is generally supplied as A36, a 'low carbon', steel, which is spec'd by performance, not chemical composition. The carbon content is less controlled and it can vary somewhat. Both of these terms used alone, signify the above. Many steels can be supplied in various forms , as hot rolled, or cold finished, or whatever, but they will also have the grade designation. For example, razor blades are made of high carbon alloy, which may be supplied "cold rolled", but it is definitely not CRS with the low carbon. The usual concept of 'hardening' requires a steel with more carbon then simple CRS or HRS, old wives tales and backyard recipes not withstanding.