Medical Applications of Precipitation Hardening Stainless Steel (Ⅲ)

This article mainly discusses the application of precipitation hardening stainless steel in electrosurgical instruments.

The high frequency current generated by intermittent discharge was originally used for long distance communication. Later the experiment results revealed that the high-frequency current generated heat through the human body without causing electric shock or muscle stimulation. At the beginning of the 20th century, spark discharge currents were used to treat injuries. Today, electrosurgical instruments have been widely used in general surgery for bloodless incisions, removal of visceral masses, treatment and removal of skin disorders, as well as control of bleeding.

Commonly used electrosurgical instruments work like a scalpel, so they are often called “electric knives”. Since high-frequency currents are harnessed to perform their functions, they are also called “high-frequency electric knives.” These instruments are suitable for general surgery, extrathoracic, urology, gynecology and other surgical operations. In surgical clinical surgery, an electric knife can be used for cutting, and electrocoagulation for hemostasis.

In early times, electrocoagulation is generally made of martensitic or austenitic stainless steel, but a common flaw arises by default: during the operation, the device generates heat through high-frequency current. When the heat reacts with human tissue protein, it will cause bonding in the device electrode, causing device failure and even damage to the body tissues.

To cope with this issue, foreign countries use silver-copper alloys or change product structure to solve the bonding problem, which technique is relatively complicated. An alternative technique on trial is to use 17-4 steel as the material to make electrocoagulation. The test results show that the bonding phenomenon is remarkable mitigated. However, the working mechanism behind needs more argumentation. Illustrating with metal heat conduction principle, we know that the bonding is caused by local overheating of the metal during the heating process; from physics’ perspective, the thermal conductivity is a significant factor affecting the local overheating of the metal. As is known, the thermal conductivity of the 17-4 material is 18.4 (W/mk) at 100 °C and 22.7 (W/mk) at 500 °C, superior to that of 304 material.