鐵素體不銹鋼
Ferritic stainless steel
以鉻為主要合金元素，含Cr量一般在13%--30%之間。具有良好的耐氧化性介質腐蝕的能力和在高溫下耐空氣氧化能力，也可用作耐熱鋼。此種鋼的焊接性能較差。含鉻大于16%時，鑄態組織粗大，在400-525℃及550-700℃之間長期保溫，會出現"475℃"脆性相及σ相，使鋼變脆。475℃脆性與含Cr鐵素體的有序化現象有關。475℃脆性相及σ相脆性，可通過加熱到475℃以上然后快冷來改善。室溫脆性和焊后熱影響區的脆性也是鐵素體不銹鋼的基本問題之一，可采用真空精煉、加入微量元素(如硼、稀土及鈣等)或奧氏體形成元素(如Ni、 Mu、 N、 Cu等)的辦法加以改善。為了改善焊縫區與熱影響區的力學性能，通常還加入少量的Ti和Nb，以阻止熱影響區晶粒長大。常用的鐵素體鋼有ZGCr17和ZGCr28。該類鋼的沖擊韌性低，在很多場合被含高鎳的奧氏體不銹鋼所取代。含Ni量超過2%、含N量超過0.15%的鐵素體鋼有良好的沖擊性能。
With chromium as the main alloy element, the content of Cr is generally between 13% and 30%. It has good corrosion resistance to oxidizing medium and air oxidation resistance at high temperature. It can also be used as heat-resistant steel. The weldability of this kind of steel is poor. When the content of chromium is more than 16%, the as-cast structure is coarse, and the brittle phase and_phase will appear between 400-525 and 550-700 after long-term heat preservation, brittle phase and_phase will appear at 475 to make the steel brittle. The brittleness at 475 C is related to the ordering of ferrite containing Cr. The brittleness of brittle phase and_phase at 475 (?) C can be improved by heating to over 475 (?) C and then rapid cooling. The room temperature brittleness and the brittleness of heat affected zone after welding are also one of the basic problems of ferritic stainless steel, which can be improved by vacuum refining, adding trace elements (such as boron, rare earth and calcium) or austenite forming elements (such as Ni, Mu, N, Cu, etc.). In order to improve the mechanical properties of weld zone and heat-affected zone, a small amount of Ti and Nb is usually added to prevent grain growth in heat-affected zone. Commonly used ferritic steels are ZGCr17 and ZGCr28. This kind of steel has low impact toughness and is replaced by austenitic stainless steel with high nickel content in many cases. Ferritic steels containing more than 2% Ni and 0.15% N have good impact properties.