What is worth knowing about steel before buying hand tools?
The abbreviations: CrV, CrNI, Cr-Mo or a short description: “tool steel” are placed very often on the hand tool packaging. These descriptions inform the customer of the type of steel of which the product is made. Before buying the tools it is worth noting these marks and getting familiar with their meaning.
In order to interpret properly the afore-mentioned abbreviations the customer should be aware of the fact that steels are classified according to various criteria. A chemical composition is one of them - under this criterion alloy and non-alloy steels are distinguished.
Alloy steel - an alloy of iron and carbon, and specially introduced alloy additions. These additions are present in various quantities - from trace values to several dozen percentage points. As components they are very important because they significantly affect and change steel properties. The most popular alloying elements include: molybdenum, vanadium, aluminium, tungsten, nickel, chromium, manganese, silicon, titanium, niobium and cobalt. In order to increase strength and reduce brittleness the following materials are used in the production of hand tools:
- chrome-vanadium steel (CrV) – with increased corrosion resistance and rust formation. An alloying addition of “chrome” improves significantly steel susceptibility to hardening. An alloying addition of “vanadium” increases steel toughness during heat treating what positively affects high temperature and deformation resistance.
- chrome-nickel steel (CrNI) – with very high resistance to corrosive influences, such as: seawater or sulphuric acid. Besides acid-resistant properties this steel is characterised by heat resistance and creep resistance.
- chrome-molybdenum steel (Cr-Mo) – decidedly the lightest steel which means that the products made of this steel are more durable with lower own weight. An alloying addition of “molybdenum” increases steel expansibility at high temperatures and prevents deformations. The addition increases general steel corrosion resistance in humid and acid environments as well.
Non-alloy (carbon) steel – an alloy of iron and carbon without specially introduced elements. The content of the elements other than carbon is marginal – these are admixtures and impurities. Due to the costs their removal is not worthwhile. In this case the percentage carbon share and alloy heat treating affect non-alloy steel properties and characteristics. Non-alloy steels are generally used to produce components of simple structures and elements requiring high tensile strength (e.g. pressure tanks).
Some hand tools are made of tool non-alloy steel with carbon content within 0,6-1,5%. The working surface of such tools is hard and steel is well hardened.