Full hard hot dip galvanized steel plate with high strength and good surface quality and production method thereof

Abstract

The invention provides a full hard hot dip galvanized steel plate with high strength and good surface quality, which comprises the following chemical compositions: 0.02 to 0.15 percent of C, 0.15 to 1.50 percent of Mn, 0.05 percent of Si, 0.02 to 0.10 percent of Ti and / or Nb, and the balance of iron and inevitable impurities. A production method comprises processes of smelting, casting, rolling and hot dipping, and is characterized in that: 1) in the smelting process, the content of each alloy element is precisely controlled; 2) in the rolling process, the heating temperature during the hot rolling is between 1,150 and 1,260DEG C, the finish rolling temperature is between 850 and 1,100DEG C, laminar flow after the rolling is quickly concentrated and cooled, the coiling temperature is between 550 and 700DEG C, and the cold rolled reduction ratio is controlled between 60 and 80 percent; and 3) in the hot dipping process, the continuous annealing temperature is controlled between 600 and710DEG C. The production method is suitable for various continuous hot dip galvanizing production lines, and can improve the strength of the full hard hot dip galvanized steel plate. Even if the fullhard hot dip galvanized steel plate is produced on an NOF vertical furnace continuous hot dip galvanizing production line, and no reheating equipment is arranged in a cooling section, defects such asiron leakage, zinc slag and the like generated by adopting a conventional method to produce the steel can also be effectively overcome.

Description

technical field [0001] The invention belongs to the technical field of hot-dip galvanizing, and in particular relates to a full-hard hot-dip galvanized steel sheet with high strength and good surface quality and a production method thereof. Background technique [0002] Full-hard hot-dip galvanized steel sheet is the highest strength level among structural grade continuous hot-dip galvanized steel sheets and steel strips in the existing standards of various countries in the world (ASTM A653 / A653M-2005, EN10326-2004, JIS G3302-2005). As a high-strength steel, in addition to high requirements for its strength in various standards, there are no excessive requirements for its formability, elongation and other indicators, or even no requirements. In this way, it can be produced by directly immersing the cold-rolled sheet in the zinc solution without recrystallization treatment. The full-hard hot-dip galvanized sheets of the existing technology at home and abroad are generally pr...

AI Technical Summary

Problems solved by technology

[0004] (1) It is easy to produce surface quality defects: the annealing temperature of ordinary CQ-grade galvanized steel sheets is generally around 700°C. More, the annealing temperature is lower (not higher than 550°C), resulting in low furnace temperature and flue gas temperature in the non-oxidizing heating section, and the temperature of the flue gas further decreases after reaching the preheating section, and the water in the flue gas is easy to condense on the surface of the steel plate ; Especially when coke oven gas and natural gas are used as fuel gas, the water content in the flue gas is relatively high, and the dew point can reach up to 80°C, and the condensation of water vapor on the surface of the steel plate is more serious; when the thickness of the strip steel is thin and the width is large When the process speed is narrow and the process speed is low, the heat output of the non-oxidation heating section is required to be smaller, the temperature of the flue gas in the non-oxidation heating section is lower, and the condensation of water vapor in the flue gas on the surface of the strip is almost unavoidable

[0005] (2) Low-carbon steel + low-temperature annealing (not higher than 550°C) is used to produce full-hard hot-dip galvanized sheets. Due to the small heat output of the non-oxidizing heating section and the low gas and air flow rates, it is difficult to ensure the positive pressure of the furnace on the environment. The air in the environment is easy to enter the furnace, and the weak oxidizing atmosphere in the non-oxidizing heating section cannot be guaranteed, resulting in oxidation of the strip surface, iron leakage or dezincification

[0006] (3) When the thickness of the strip steel is thinner, the width is narrower, and the process speed is low, the temperature loss of the strip steel passing through the cooling section is relatively large, and the temperature of the strip steel entering the zinc pot is low, which is easy to produce dezincification and zinc dross , sinking roller printing and other defects

But this requires additional investment in equipment, and it will inevitably increase the complexity of the operation when switching between full-hard hot-dip galvanized sheets and ordinary galvanized sheets

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