HOT-ROLLED STRIP OF HIGH CORROSION RESISTANCE FROM LOW-ALLOY STEEL AND METHOD OF ITS PRODUCTION Russian patent published in 2020 - IPC C22C38/54 C22C38/50 C22C38/32 C22C38/28 C21D8/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to production of hot-rolled strips from low-alloyed steel used for production of electric-welded pipes of main pipelines. Steel has the following chemical composition, wt%: carbon 0.04–0.07, silicon 0.15–0.25, manganese 0.60–0.80, chromium 0.13–0.26, nickel not more than 0.06, copper not more than 0.06, aluminum 0.03–0.06, vanadium not more than 0.06, niobium 0.04–0.06, total content of niobium, vanadium and titanium not more than 0.15, molybdenum not more than 0.01, nitrogen not more than 0.006, boron is not more than 0.0005, calcium is not more than 0.006, sulfur is not more than 0.002, phosphorus not more than 0.012, iron and impurities – the rest. Metallographic structure of the strip contains not more than 10 % pearlite, the rest – ferrite. Score of non-metallic inclusions is not more than 2.5 on average, not more than 3 – on maximum, and point of ferrite grain is not larger than 8.

EFFECT: obtaining strips with yield strength of at least 390 MPa, ultimate strength of at least 480 MPa and KV impact at 0 °C of at least 100 J, as well as high corrosion resistance, in particular when testing for resistance to sulphide cracking at voltage equal to 95 % of the specified minimum yield point, coefficient of sensitivity to cracking (CSR) is not more than 2 %, coefficient of length of cracks (CLR) is not more than 15 %, and factor of thickness of cracks (CTR) is not more than 5 %.

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