Stainless steel, also referred to as galvanized iron, is popular among consumers due to its white, glossy texture and resistance to rust. It is used in a wide range of applications including kitchenware, water towers, mechanical parts, aerospace materials, medical devices and the 3C industry. Despite its corrosion resistance, the fatal flaw of stainless steel is its relatively low strength. Volatile nickel prices also have a major impact on the price of nickel-chrome stainless steel. Persistently high prices have limited their development.
The self-drilling screw for example is mainly made by Taiwanese manufacturers from carbon steel or Martensitic (400 series) stainless steel. To satisfy the requirement for high strength and corrosion resistance, two-part self-tapping screws are produced by welding a carbon steel head to a stainless steel shank. Overseas manufacturers have gradually changed to the production of one-piece self-tapping screws as two-part self-tapping screws suffer from high cost of welding and poor anti-corrosion lifetime. All of the high-strength, corrosion-resistant materials used in domestic production of one-piece self-tapping screws are imported from exclusive Japanese suppliers, making them difficult for other manufacturers to obtain. Solving the material problem by overcoming the technical barriers to the development of a high-strength, corrosion-resistant stainless steel is therefore a matter of utmost urgency for the industry.
The “high-nitrogen, low-nickel stainless steel alloy process” developed by Metal Industries Research & Development Centre (MIRDC) used the alloy design and production process to increase nitrogen solubility and reduce nickel content. The alloy that resulted was not only stronger than carbon steel. It had a slow rate of corrosion and lower production costs as well. The addition of nitrogen improved the mechanical properties of stainless steel and made the passivation layer on the surface of the alloy in finely form. This contrasted with the use of high pressure to increase nitrogen solubility during the smelting process. The latter method is not only dangerous but also expensive. MIRDC’s technique increased nitrogen solubility and reduced nickel consumption through the addition of other elements. The chrome-plating and dehydrogenation processes could be eliminated while also extends the service life of the fastener (one-piece self-tapping screw).
The process patent was recognized with a gold medal at “2019 Taiwan Innotech Expo”. The new material is stronger than carbon steel while retaining the corrosion-resistance rivaling that of stainless steel. It can therefore be used in pumps, turbines, marine platforms, ocean current power-generation facilities, and offshore facilities. Future development efforts will focus on marine engineering and facilities. It can also be applied in national defense equipment as well as the petrochemical and medical devices sectors. The value of the industrial chain as a whole will then be enhanced.