Factors that increase the cold brittleness of cold-rolled precision bright steel tubes: 1. Solid solution strengthening elements. Phosphorus most strongly increases the toughness-brittle transition temperature; molybdenum, titanium and vanadium also have this effect; elements that have little effect at low content but increase the toughness-brittle transition temperature at high content include silicon, chromium and copper; nickel reduces the toughness-brittle transition temperature; manganese first reduces and then increases the toughness-brittle transition temperature. 2. Elements forming the second phase. Carbon is the most important element that increases the cold brittleness of cold-rolled precision bright steel tubes through the second phase. As the carbon content in cold-rolled precision bright steel tubes increases, the pearlite content in them increases. For every 1% increase in pearlite volume, the toughness-brittle transition temperature increases by an average of 2.2℃. Adding micro-alloying elements such as titanium, niobium and vanadium forms弥散分布的 (dispersedly distributed) nitrides or carbonitrides, causing the toughness-brittle transition temperature of cold-rolled precision bright steel tubes to rise. 3. Grain size affects the toughness-brittle transition temperature. As grains coarsen, the toughness-brittle transition temperature increases. Refining grains reduces the cold brittleness tendency of cold-rolled precision bright steel tubes, which is a widely used method.