Abstract A drill string for deep-well drilling, coring and the like is composed of lengths unitarily formed of a nonmagnetic, highnitrogen, chromium-nickel austenitic alloy steel and has a pair of threaded ends matingly engageable with the complementary ends of adjoining lengths and an intermediate or central portion between these ends. The drill-string members are composed of alloy steel containing from trace amounts to 0.07 per cent by weight carbon, trace amounts to 1.00 per cent by weight silicon, 0.50 to 2.00 per cent by weight manganese, 20.0 to 25.0 per cent by weight chromium, 10.0 to 15.0 per cent by weight nickel, 0.05 to 0.50 per cent by weight nitrogen and the balance iron and the usual impurities present in chromium-nickel alloy steels. The drill-string members are resistant to stress corrosion cracking and have their central zones worked (hot/cold working) to a yield point up to 70 kp/mm2 (0.2 percent elongation) while the threaded end portions are hot/cold worked to a yield point above the minimum of (0.2 percent elongation) 70 kp/mm2.
A drill-string length having a central body portion and a pair of complementarily threaded end portions, said portions being formed in one piece from a nonmagnetizable austenitic nickel-chromium steel alloy resistant to stress-corrosion cracking and consisting essentially of trace amounts to 0.07 percent by weight carbon, trace amounts to 1.00 percent by weight silicon, 0.50 to 2.00 percent by weight manganese, 20.00 to 25.00 percent by weight chromium, 10.00 to 15.00 percent by weight nickel, and 0.05 to 0.50 percent by weight nitrogen, the balance being iron and the usual impurities, said central portion being hot/cold worked to a yield point up to 70 kp/mm2 (0.2 percent elongation) and said end portions being hot/cold worked to a yield point of at least 70 kp/mm2 (0.2 percent elongation).
Claim 2
Dependent Claim
127 words
A drill-string length having a central body portion and a pair of complementarily threaded end portions, said portions being formed in one piece from a nonmagnetizable austenitic nickel-chromium steel alloy resistant to stress-corrosion cracking and consisting essentially of trace amounts to 0.07 percent by weight carbon, trace amounts to 1.00 percent by weight silicon, 0.50 to 2.00 percent by weight manganese, 20.00 to 25.00 percent by weight chromium, 10.00 to 15.00 percent by weight nickel, and 0.05 to 0.50 percent by weight nitrogen, the balance being iron and the usual impurities, said central portion being hot/cold worked to a yield point up to 70 kp/mm2 (0.2 percent elongation) and said end portions being hot/cold worked to a yield point of at least 70 kp/mm2 (0.2 percent elongation).
Claim 3
Dependent Claim
42 words
The drill-string length defined in claim 1 wherein said alloy has the following composition: Up to 0.05% Carbon 0.35 to 0.60% Silicon 1.00 to 1.10% Manganese 21.50 to 23.00% Chromium 12.00 to 13.00% Nickel 0.27 to 0.32% Nitrogen Balance Iron and Impurities