METHOD OF THERMAL TREATMENT OF PARTS FROM STRUCTURAL STEEL OF LOWER AND REGULATED HARDENABILITY Russian patent published in 2012 - IPC C21D1/06 C21D1/18 C22C38/50 C22C38/54 

FIELD: metallurgy.

SUBSTANCE: parts of steel containing the following components, wt %: carbon 0.15-1.2, manganese not more than 1.8, silicon not more than 1.8, chrome not more than 1.8, nickel not more than 1.8, molybdenum not more than 0.5, tungsten not more than 1.5, boron not more than 0.007, copper not more than 0.3, aluminium 0.03-0.1, titanium not more than 0.4, vanadium not more than 0.4, nitrogen not more than 0.1, zirconium not more than 0.4, calcium not more than 0.03, sulfur not more than 0.035, phosphorus not more than 0.035, iron and unavoidable admixtures -balance are exposed to volume-surface hardening by volume heating or its working section to temperature of austenitising and cooling with intensity of more than 40,000ccal/m²·hr·°C. The ideal critical diametre is determined from the following expression: Dcr.=K··(1+4,1·Mn)·(1+0,65·Si)·(1+2,33·Cr)·(1+0,52·Ni)·(1+0,27·Cu)·(1+3,14·Mo)·(1+1,05·W)·[1+1,5(0,9-C)]·(1-0,45C')·(1-0,3Ti)·(1-0,35V)·(1-0,25Al), where: K - a coefficient, the value of which depends on a grade of actual austenite grain, [1+1.5(0.9-C)] - a factor, which is taken into account only when there is boron in steel in the amount of 0.002-0.007 wt %, C' - carbon in excessive cementite of hypereutectoid steel.

EFFECT: production of smaller austenite grain and more stable level of hardening.

9 cl, 2 tbl, 6 dwg