Method of making a cemented carbide tool and a cemented tool
According to the present invention there is now provided a cemented carbide body provided with at least one wear resistant layer, which body contains a toughness increasing surface zone. Increase in toughness is obtained due to the presence of a surface zone having increased WC grain size and/or increased Co content. The invention is most suitable for WC—Co cemented carbides. A method for making such bodies is also disclosed.
1. Method for producing a cemented carbide body comprising decarburizing a cemented carbide body containing from about 3 to about 12 weight % binder phase in H 2 +H 2 O or H 2 +CO 2 gas atmosphere at a temperature of from about 900 to about 1290° C., for from about 1 to about 10 h to form an eta phase containing surface zone and then heat treating the body at a heat treating temperature of from about 1350 to about 1450° C., for 10 min–10 h, in a neutral gas atmosphere or vacuum to completely retransform the eta phase or other phases formed during decarburization to WC+Co phase and form a body with a carbon content below the saturation point with an about 5 to about 100 μm thick surface zone having an increased WC grain size relative to a grain size of WC in an interior region of the body, the increased WC grain size present within the entire thickness of the surface zone.
2. The method of claim 1 wherein the decarburizing temperature is from about 1000 to about 1250° C.
3. The method of claim 1 wherein the heat treating temperature is from about 1400 to about 1450° C. and the body is heat treated at the heat treating temperature for from about 0.5 to about 3 h.
4. The method of claim 1 , comprising removing the surface zone at an outermost part of the cutting edge within a distance of 10 to 100 □m measured at a cross section of the cutting edge.
5. The method of claim 1 wherein the cemented carbide body comprises WC—Co.
6. The method of claim 5 wherein the cemented carbide body comprises WC—Co with addition of <3 weight % grain growth inhibitors.
7. The method of claim 6 wherein the cemented carbide body comprises <2.5 weight % grain growth inhibitors.
8. The method of claim 5 wherein the cemented carbide body comprises WC—Co with addition of >zero to <3 weight % grain growth inhibitors.
9. The method of claim 1 wherein the cemented carbide body comprises WC—Co-gamma phase comprising up to about 10 weight % total of at least one of the elements Ti, Ta, Nb, Hf and Zr.
10. The method of claim 1 wherein the cemented carbide body is thereafter further heat treated in a carburizing atmosphere in the temperature range of from about 1200 to about 1370° C. and a time of from about 0.1 to about 2 h.
11. The method of claim 10 wherein the carburizing atmosphere comprises CH 4 +H 2 .
12. The method of claim 10 wherein the cemented carbide body is further heat treated in a neutral gas atmosphere or vacuum at temperatures of from about 1350 to about 1450° C. and a holding time from about 0.1 to about 2 h.
13. The method of claim 12 wherein the cemented carbide body is further heat treated in a carburizing atmosphere such as CH 4 +H 2 , within the temperature range from about 1200 to about 1370° C. and the time from about 0.1 to about 2 h.
14. The method of claim 1 wherein the cemented carbide body is heat treated in neutral atmosphere or vacuum using more than one heat treating temperatures and holding times within the temperature range from about 1360 to about 1450° C. and the time from about 0.1 to about 5 h at each temperature.
15. The method of claim 14 wherein the said body is heat treated in two steps.
16. The method of claim 15 wherein the first heat treating temperature is at least 20° C. lower than the second heat treating temperature.
17. The method of claim 16 wherein the first heat treating temperature is more than 50° C. lower than the second heat treating temperature.