Ultra-high strength, weldable steels with excellent ultra-low temperature toughness

Abstract

An ultra-high strength steel having excellent ultra-low temperature toughness, a tensile strength of at least about 930 MPa (135 ksi), and a microstructure comprising predominantly fine-grained lower bainite, fine-grained lath martensite, or mixtures thereof, transformed from substantially unrecrystallized austenite grains and comprising iron and specified weight percentages of the additives: carbon, silicon, manganese, copper, nickel, niobium, vanadium, molybdenum, chromium, titanium, aluminum, calcium, Rare Earth Metals, and magnesium, is prepared by heating a steel slab to a suitable temperature; reducing the slab to form plate in one or more hot rolling passes in a first temperature range in which austenite recrystallizes; further reducing said plate in one or more hot rolling passes in a second temperature range below said first temperature range and above the temperature at which austenite begins to transform to ferrite during cooling; quenching said plate to a suitable Quench Stop Temperature; and stopping said quenching and allowing said plate to air cool to ambient temperature.

Description

field of invention [0001] The invention relates to an ultra-high strength, weldable steel plate with good toughness, and a line pipe manufactured using the steel plate. More particularly, the present invention relates to a weldable low alloy pipeline steel having ultrahigh strength and high toughness, wherein the strength loss in the HAZ is minimized relative to the rest of the pipeline, and to a steel used as A production method of a steel plate for a pipe base material for a pipeline. Background of the invention [0002] A number of terms are defined in the description that follows. For convenience, a glossary is given directly in front of the claims. [0003] Currently, the highest yield strength line pipe in industrial applications has a yield strength of about 550 MPa (80 ksi). Higher strengths, eg up to about 690 MPa (100 ksi), are also commercially available, but to our knowledge, such steels have not been used commercially for pipelines. Additionally, as disclose...

AI Technical Summary

Problems solved by technology

Although ultra-high-strength steels with yield strengths of 830 MPa (120 ksi) or higher have been produced, these steels generally lack the toughness necessary for line pipe and cannot meet the weldability requirements necessary for line pipe because such The material has a relatively high Pcm (a well-known industry term used to denote weldability), with values ​​generally above about 0.35

Images