5 minutes to show you what is "medical stainless steel"
Time : 2022-09-27

Compared with stainless steel for industrial structure, medical stainless steel is required to maintain excellent corrosion resistance in human body to reduce metal ion dissolution, avoid intergranular corrosion, stress corrosion and other local corrosion phenomena, prevent implant failure and fracture, and ensure the safety of implant, so its chemical composition requirements are relatively stricter.

Medical stainless steel, especially implant stainless steel, has higher content of alloy elements such as Ni and Cr than ordinary stainless steel (usually reaching the upper limit requirements of ordinary stainless steel), and lower content of impurities such as S and P than ordinary stainless steel. It is clearly stipulated that the size of non-metallic inclusions in steel should be less than Grade 115 (fine) and Grade 1 (coarse) respectively, while the standard for ordinary industrial stainless steel does not put forward special requirements for inclusions.

In order to avoid intergranular corrosion of medical stainless steel, it is also required to have lower C content. In the early days, it was stipulated that C content should not be higher than 0108% and 0103% (mass fraction). With the progress of metallurgical technology and the improvement of application requirements, in the domestic and international standards for medical stainless steel revised in recent years, all requirements for C content in steel are not higher than 0103% (such as ASTMF138-03, ASTMF139-03, ISO5832-1-2007, GB4234-2003).

316L or 317L austenitic stainless steel commonly used in medical stainless steel has low strength and hardness in the solution state, but its strength and hardness can be improved by cold working deformation. Therefore, surgical implant stainless steel for clinical use is usually in a cold working state (cold working deformation is about 20%) to meet the high strength and hardness required by the implant device, but the cold working state increases the sensitivity of medical stainless steel to stress corrosion and corrosion fatigue damage.

Medical stainless steel has become a widely used medical implant material and medical tool material due to its good biocompatibility, good mechanical properties, excellent resistance to body fluid corrosion, and good processability. Medical stainless steel is widely used to make various artificial joints and fracture internal fixation devices, such as various artificial hip joints, knee joints, shoulder joints, elbow joints, wrist joints, ankle joints and finger joints, various specifications of osteotomy connectors, compression plates, goose head screws, spine screws, bone traction wires, artificial vertebrae, as well as skull plates, artificial vertebrae, etc.

In dentistry, medical stainless steel is widely used in dental inlay, dental orthopedics, root implant and auxiliary devices, such as various crowns, bridges, fixed brackets, clasps, bases, inserts of various specifications, dental arch wires, dentures, and jaw defect repair.

In recent years, the demand for medical stainless steel wire, bar, orthopedic special plate, screw and other semi-finished products with high quality and low price in China's medical device industry has increased significantly, with more than several hundred tons each year. At present, there are only two kinds of medical implant stainless steel standards in China, namely GB4234 (basically equivalent to ISO5832-1 and ASTMF138) and YY060,519-2007 (equivalent to IS05,832-9, corresponding to ASTMF1586). The standardization of medical stainless steel lags far behind the United States (it has revised six kinds of surgical implant stainless steel). Therefore, the revision of new medical stainless steel standards is also an important part of the research and development of medical stainless steel in China in the future.