THIS INVENTION RELATES TO SINTERED METAL ALLOYS SUCH AS IRON BASE ALLOYS CONTAINING COPPER HAVING SIGNIFICANTLY IMPROVED TOUGHNESS CHARACTERISTICS, AND A METHOD FOR MAKING SUCH ALLOYS. A NOVEL STRUCTURE IS PRODUCED CHARACTERIZED BY A NON-HOMOGENEOUS CONCENTRATION OF COPPER SOLID SOLUTION WITHIN THE INDIVIDUAL BASE METAL PARTICLES COMPRISING SAID SINTERED STRUCTURE. SUCH A STRUCTURE IS OBTAINED BY CONTROLLING THE TIME-TEMPERATURE PARAMETERS DURING THE SINTERING AND DIFFUSING STEPS THEREOF. FOR EXAMPLE, SINTERING IS PERFORMED AT A TEMPERATURE LESS THAN THE MELTING POINT OF COPPER; THE DIFFUSION AT A TEMPERATURE RANGING FROM THE MELTING POINT OF COPPER TO LESS THAN THE MELTING POINT OF THE IRON BASE MATERIAL.