STEEL WITH REDUCED HARDENABILITY FOR COIL SPRINGS WITH ROD DIAMETER FROM 24 TO BELOW 27 MM AND SPRING MADE OUT OF IT Russian patent published in 2015 - IPC C22C38/42 F16F1/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to spring steels used to manufacture the coil springs with rod diameter from 24 to below 27 mm for railroad rolling-stock. steel contains carbon, silicon, manganese, chromium, nickel, iron, additionally aluminium, nitrogen, sulphur, phosphorus and copper at following ratio of components, wt %: carbon 0.55-0.60, silicon 0.40-0.60, manganese from 0.15 to below 0.25, aluminium 0.02-0.05, nitrogen 0.004-0.016, sulphur ≤0.015, phosphorus ≤0.020, chromium ≤0.20, nickel ≤0.20, copper ≤0.20, iron - rest. Steel has austenite grain score 11-12, and spring after volume-surface hardening and tempering has in the core the sorbite structure, and on the surface - fine-needled martensite structure.

EFFECT: initial uniform fine grain structure of steel is achieved, this ensures after volume-surface hardening and tempering the optimal spring mechanical characteristics, in particular tensile strength, yield strength and elastic strength.

2 cl, 1 tbl, 1 ex