HIGH-STRENGTH COLD-ROLLED STEEL SHEET SUITABLE FOR CHEMICAL CONVERSION AND METHOD OF ITS PRODUCTION Russian patent published in 2014 - IPC C22C38/14 C21D8/04 

FIELD: metallurgy.

SUBSTANCE: slab made of steel containing in wt %: C: 0.05-0.1, Si: 0.05-0.45, Mn: 2.5-3.5, Al: 0.01-0.08, P: 0.05 or less, S: 0.0050 or less, N: 0.01 or less, Nb: 0.02-0.1, Ti: 0.001-0.05, Fe and unavoidable impurities making the rest Note here that Si/Mn ratio makes 0.02-0.15. Then, it is subjected to hot rolling, pickling and heat treatment at 400-700°C for 0.5-10 hours, as well as cold rolling and annealing. Annealing is performed to final maximum temperature of 760-860°C. Sheet is held at temperature lower than maximum one by 50°C to maximum temperature for 50-100 seconds and cooled, then, down at mean rate of 5-50°C/s. Sheet microstructure comprises 50-80% of ferrite phase and 20-50% of martensite phase over sheet area relative to that of the entire microstructure. Mean grain size of ferrite and martensite phases makes 0.5-3.0 mcm while ferrite grain size-to-martensite grain size makes 0.5-5.0.

EFFECT: required mechanical properties suitability for chemical conversion.

3 cl, 3 tbl, 1 ex