PURPOSE: To provide an alloy steel for use as track linkage of caterpillen truck having a good quench property and wear resistance to earth and sand by adding a specific amount of Cr, Mo, B to steel having carbon equivalent of less than 0.75.

CONSTITUTION: Title alloy steel consists of C: 0.35W0.50%, Si: 0.60W1.60%, Mn<1.0%, Cr: 0.50W1.0%, Mo<1.0%, B: 0.0005W0.0030%, and the balance Fe. The carbon equivalent of less than 0.75 allows the alloy to be repaired by padding work, produces no quenching cracks and has a good quench property. Its hardness is HRC 50W55, Charpy impact value is 3kgm/cm2 or more, and therefore, this alloy steel is resistant to sand and earth and is suited for track linkage of caterpiller truck.