METHOD OF MAKING COLD-ROLLED SHEETS FROM TWO-PHASE STEEL WITH VERY HIGH HARDNESS, AND SHEETS THUS PRODUCED Russian patent published in 2012 - IPC C22C38/58 C21D8/02 C23C2/06 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, particularly, to production of cold-rolled and annealed sheets from two-phase steel.Said steel contains the following substances, in wt %: 0.055≤C≤0.095, 2≤Mn≤2.6, 0.005≤Si≤0.35, S≤0.005, P≤0.050, 0.1≤Al≤0.3, 0.05≤Mo≤0.2, 0.2≤Cr≤0.5, given Cr+2Mo≤0.6, Ni≤0.1, 0.010≤Nb≤0.040, 0.010≤Ti≤0.050, 0.0005≤B≤0.0025, 0.002≤N≤0.007, iron and unavoidable impurities making the rest. Now, semi-finished product is cast. The latter is heated to 1150°C≤T_R≤1250°C and hot-forged at T_PL≥Ar3. Then, coiling is carried out at 500°C≤T_bob≤570°C. Now, descaling is performed as well as cold rolling with reduction of 30-80%. Cold-rolled semi-finished product is heated at the rate of 1°C/s≤V_c≤5°C/s to annealing temperature T_M defined as Ac1+40°C≤T_M≤Ac3-30°C/s whereat said product is cured for 30 s≤t_M≤300 s to produce structure comprising austenite. Thereafter it is cooled down to below Ms at rate V sufficient for conversion of entire amount of austenite in martensite.

EFFECT: high forming qualities, steel hardness of 980 to 1100 MPa.

19 cl, 3 dwg, 4 tbl, 1 ex