彎曲度：工字鋼高度小于或等于400MM時，每米彎曲度不得大于1.5MM，總彎曲度不得大于總長度的0.15%。高度大于400MM時，每米彎曲度不得大于1.0MM，總彎曲度不得大于總長度的0.1%。

Bending degree: when the height of the I-steel is less than or equal to 400MM, the bending degree of each meter must not be more than 1.5MM, and the total bending degree should not be more than 0.15% of the total length. When the height is greater than 400MM, the bending degree of each meter must not be more than 1.0MM, and the total bending degree should not be more than 0.1% of the total length.

型材按斷面尺寸可分為大型、中型和小型型材，其劃分常以它們分別適合在大型、中型和小型軋機(jī)上軋制來分類。大型、中型和小型的區(qū)分實(shí)際上并不嚴(yán)格。另外還有用單重（kg/m）來區(qū)分的方法。一般認(rèn)為，單重在5 kg/m以下的是小型材，單重在5～20 kg/m的是中型材，單重超過20 kg/m的是大型材。因此又可以進(jìn)一步分成凸緣型材、多臺階型材、寬薄型材、局部特殊加工型材、不規(guī)則曲線型材、復(fù)合型材、周期斷面型材和金屬絲材等等。簡單斷面型材的橫斷面對稱、外形比較均勻、簡單，如圓鋼、線材、方鋼和扃鋼等。

隨著科學(xué)技術(shù)和工業(yè)的發(fā)展，對材料提出了更高的要求，如更高的強(qiáng)度，抗高溫、高壓、低溫，耐腐蝕、磨損以及其它特殊物理、化學(xué)性能的要求，碳鋼已不能完全滿足要求。

With the development of science and technology and industry, the material has put forward higher requirements, such as higher strength, high temperature, high pressure, low temperature, corrosion resistance, wear and other special physical and chemical properties, carbon steel can not fully meet the requirements.