Industries like forging and die casting rely on tools that are able to withstand extreme pressures and elevated temperatures. And, because of the importance of those tools, the choice of which steel they are made from is vital. H13 tool steel is a material known for having an excellent combination of toughness and a resistance to cracking due to temperature swings.
However, it is not nearly enough to simply choose H13 steel; in order to achieve the material’s full potential and ensure reliable performance, understanding and optimizing its hardness via proper heat treatment and testing is critical. It is not about making the steel hard; it is about making the steel optimally hard for the task at hand.
H13, a hot work tool steel, is tailored to resist softening and maintain its strength even when working within extremely hot environments or with molten metal. To achieve such feats, its formulation consists of a combination of vanadium (V), molybdenum (Mo), and chromium (Cr), which contributes to its heat crack resistance and wear at high temperatures.
Hardness Testing
The method used when verifying if H13 steel has achieved its desired attributes after undergoing heat treatment, is hardness testing. There are two types of hardness testing for H13:
Rockwell hardness testing is widely used for H13 steel because it is non-destructive, quick, and quite straightforward. A hardened steel ball or diamond cone is used as an indenter to make a small indentation on the surface of the steel under controlled load.
Vickers hardness testing is not as common as the Rockwell but offers more precise readings when an analysis of surface hardness is done. A diamond indenter is used to create a pyramid shaped indentation and the size of the resulting indentation is used to calculate the hardness of the steel. It is a method best suited for fine-tuning the heat treatment or when localized areas of a tool is examined.
Optimizing Performance via Heat Treatment
For H13 steel, achieving the right amount of hardness is not only about making the steel as hard as it can be; it is about the right balance of toughness and hardness for the tool’s specific demands. The heat treatment process is somewhat a mixture of both science and art and involves a number of critical steps:
Hardening – The steel is heated to an extremely high temperature in a process called austenitizing, enabling a change in its internal structure. It is then quenched or cooled rapidly, typically in oil or a polymer, in order to lock in a state that is hard but brittle.
Tempering – For H13 steel, this is a highly crucial step. After the steel has been quenched, it is reheated once again but to a lower temperature for a specified length of time, and then cooled again. Through such a process, the steel's brittleness is greatly reduced, its toughness enhanced, and its hardness fine-tuned.
Stress Relieving – At times, there is an additional step involving low-temperature heating used to remove any residual stresses that was introduced during the heat treatment or during manufacturing.
Having hardness testing done at each stage helps to ensure the success of the heat treatment and that the H13 steel has achieved the ideal blend of properties for its intended job. It also helps to extend the tool’s life and aids in reducing manufacturing costs.