igh temperature PWHT softening and production method thereof

Abstract

The invention relates to a normalized steel plate having excellent matching of toughness and strength and plasticity, good anti-fatigue and creeping resistance, resistance to high temperature PWHT softening, welding properties, and uniformity of tissue and property along with the direction of thickness of plating. The normalized steel plate can be used for preparing housings of pressure vessels, particularly carcass structures of steam evaporators voltage-stablizers. The resistance to high temperature PWHT softening specially comprises that after the steel plate being processed by the high temperature PWHT (postweld heat treatment) for more than 15 hours at the temperature of no less than 675 DEG C, the parent metal steel plate has the yield strength of no less than 300 MPa, and the tensile strength of no less than 490 MPa. The invention also discloses a preparation method of the steel plate.

Description

technical field [0001] The invention relates to a normalized steel plate with a low carbon equivalent [Ceq=C+Mn / 6+(Cu+Ni) / 15+(Cr+Mo+V) / 5≤0.45%], in particular to a Normalized steel plates for pressure vessel shells softened by high temperature post-weld heat treatment (PWHT). Background technique [0002] The steel plate for heat-resistant pressure vessel shell is a structural material for medium-temperature pressure vessels that requires comprehensive mechanical properties (strength-toughness matching, strong-plasticity matching), welding performance, and stable mechanical properties after high-temperature PWTH. It can be used to make pressure vessels. Components - the carcass structure of the steam evaporator and pressurizer. During the service process of the pressure vessel, the carcass steel plate must not only bear the structural bearing capacity and thermal stress, but also must have high fatigue creep resistance, high temperature PWTH softening resistance and stress ...

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Problems solved by technology

[0003] Traditional heat-resistant pressure vessel normalized steel plates that resist high temperature PWHT softening generally use 0.30-0.50% Mo steel, Cr-Mo series steel, Mn-Ni-Mo steel (see 159-160 Xishan Memorial Technical Lectures, P147- P164; 86~87 Xishan Memorial Technical Lectures, P259~P312), it is inevitable to add a large amount of precious alloying elements such as Cr, Mo, Ni, V, etc. to these steel plates; this not only leads to increased manufacturing costs and increased manufacturing difficulty (Ni Steel plates with high content of , Cr, and Mo elements have poor surface quality of cast slabs, and generally need to go off-line for surface cleaning, and sometimes need to carry out surface coloring penetration PT inspection, slab surface grinding and warm cutting, etc.); Moreover, the alloy content of the steel plate is high, the carbon equivalent Ceq and the welding cold crack sensitivity index Pcm are also high, which brings great difficulties to on-site welding. Preheating is required before welding, heat treatment is required after welding, and the on-site welding environment deteriorates. , Welding efficiency is reduced, processing and manufacturing costs are increased; and problems such as hydrogen corrosion, hydrogen-induced embrittlement, temper embrittlement, lamellar spalling of welded parts, and creep embrittlement are prone to occur during component manufacturing and use

[0004] In the prior art, the accelerated cooling process after normalizing heat treatment is also used to produce low-carbon equivalent and high-temperature PWTH-resistant low-alloy container steel plates, but the steel plate processing and manufacturing process is poor, showing that after high-temperature PWHT, the strength and toughness of the steel plate cannot reach the user Or the requirements of technical standards, the reason is that after the steel plate is accelerated and cooled by normalizing, the obtained microstructure is granular bainite or upper bainite. In addition to the poor intrinsic toughness and plasticity of the steel plate, the more important thing is that The granular bainite or upper bainite obtained by normalizing accelerated cooling has poor thermal stability. In the subsequent high-temperature PWHT process, the structure will be severely degraded, resulting in a sharp decline in the strength and toughness of the steel plate. The method is not suitable for the production of high temperature resistant PWHT low alloy container steel plate, especially under the condition of low carbon equivalent

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