Conventional d r i 11 b i t steels e x h i b i t i ncreased wear and decreased toughness when run a t elevated temperatures i n geothermal wells. B i t s are theref o r e run a t lower speeds and l i g h t e r loads, r e s u l t i n g i n lower penetration rates f o r geothermal d r i l l i n g than f o r conventional rock d r i l l ing. & Carpenter EX-00053, Timken CBS 600, Timken CBS lOOOM and Vasco X-2M steels w i t h improved hot hardness (improved wear resistance), were tested i n

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... on w i t h the steels used f o r cones ( A I S I 4820, 9315 and EX55) and lugs ( A I S I 8620, 9315 and EX55) i n conventional r o l l e r cone rock b i t s . Short-rod f r a c t u r e toughness measurements were made on each o f these steels between room temperature and 400OC. Fatigue crack resistance was determined a t 3OOOC f o r high-temperature steels and a t room temperature f o r conventional steels. Scanning electron microscopy analyses o f the fractured short-rod specimens were correlated with observed crack behavior from the t e s t records. Test r e s u l t s are discussed and steel selections made f o r improved geothermal b i t s . Carpenter EX-00053 and Timken CBS lOOOM steels meet a l l design require-It i s 3 ments f o r use i n s t a b i l i z e r s , lugs and cones a t temperatures t o 400OC. recommended t h a t EX-00053 and CBS lOOOM be manufactured f o r geothermal d r i ll i n g a t the Geysers s i t e .