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A ferritic low-temperature steel forging and its low-temperature cryogenic preparation method

A low-temperature steel and ferrite technology, applied in the field of alloy processing, can solve the problems of high energy consumption in liquid nitrogen cryogenics, uncontrollable continuous cooling, retained austenite or M-A islands, etc.

Active Publication Date: 2021-07-09
SHANGHAI JIAOTONG UNIV
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Problems solved by technology

But as a large-scale low-temperature steel forging, due to its large cross-section, there are new problems in the "controlling" and "controlling" aspects of forging and heat treatment: 1. When the minimum critical cooling rate of the forging core is possible, theoretically Obtain tempered martensite or bainite structure with multi-level structure to ensure the impact toughness of the quenched + tempered state at -196°C; II. To avoid the appearance of a large number of irregular retained austenite or M-A islands , to control the reverse transformation of austenite in the original austenite grain boundary or martensite lath interface uniform precipitation in strips, in addition to the introduction of high temperature tempering in the critical zone, cryogenic treatment is also required to ensure that the massive retained austenite as much as possible Decompose completely before final tempering
In the prior art, 9Ni steel low-temperature forgings are mainly processed by liquid nitrogen cryogenic cooling, but the energy consumption of liquid nitrogen cryogenic cooling is high, which greatly increases the production cost, and at the same time, the temperature of liquid nitrogen cryogenic cooling is low (-196 ℃~-150℃), and the uncontrollable continuous cooling makes the treated 9Ni steel low-temperature forgings have a tendency to crack, which poses hidden dangers to the safety of related components

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  • A ferritic low-temperature steel forging and its low-temperature cryogenic preparation method
  • A ferritic low-temperature steel forging and its low-temperature cryogenic preparation method
  • A ferritic low-temperature steel forging and its low-temperature cryogenic preparation method

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preparation example Construction

[0024] The invention provides a ferritic low-temperature steel forging and a low-temperature cryogenic preparation method thereof, comprising the following steps:

[0025] (1) performing homogenization annealing after forging the billet to obtain an annealed forging;

[0026] (2) performing quenching and tempering treatment for the first time on the annealed forging obtained in the step (1) successively to obtain a tempered forging;

[0027] (3) subjecting the tempered forgings obtained in the step (2) to sequentially sub-stage cryogenic treatment at -70 to -85°C, -95 to -105°C and -115 to -130°C to obtain cryogenic forgings;

[0028] (4) The cryogenic forging obtained in step (3) is subjected to a second tempering treatment to obtain a ferritic low-temperature steel forging.

[0029] The invention performs homogenization annealing after forging and molding the billet to obtain an annealed forging.

[0030] In the present invention, the starting temperature of the forging is...

Embodiment 1

[0054] In terms of weight percentage, the composition of ferritic low-temperature steel forgings is: 0.03% C, 0.71% Mn, 0.11% Si, 9.35% Ni, 0.80% Cu and the balance iron.

[0055] The preparation method of the ferritic low-temperature steel forging is as follows:

[0056] (1) After soaking the billet at 1110°C, it is forged and formed. The final forging temperature is 750°C, the cumulative compression ratio is 6, air-cooled to room temperature, then heated to 1110°C and kept for 24 hours, homogenized annealed, and air-cooled to room temperature to obtain Annealed forgings;

[0057] (2) Process the annealed forging obtained in step (1), then raise the temperature to 830°C for heat preservation, and then perform quenching to control the cooling rate of the core of the largest section of the forging to >0.05°C / s (or simulated by furnace cooling) , cooled to room temperature;

[0058] (3) The tempered forging obtained in the step (2) is subjected to cryogenic treatment at -80°C,...

Embodiment 2

[0063] In terms of weight percentage, the composition of ferritic low-temperature steel forgings is: 0.03% C, 0.71% Mn, 0.11% Si, 9.35% Ni, 0.80% Cu and the balance iron.

[0064] The preparation method of the ferritic low-temperature steel forging is as follows:

[0065] (1) After soaking the billet at 1110°C, it is forged and formed. The final forging temperature is 750°C, the cumulative compression ratio is 6, air-cooled to room temperature, then heated to 1110°C and kept for 24 hours, homogenized annealed, and air-cooled to room temperature to obtain Annealed forgings;

[0066] (2) Process the annealed forging obtained in step (1), then raise the temperature to 830°C for heat preservation, and then perform quenching to control the cooling rate of the core of the largest section of the forging to >0.05°C / s (or simulated by furnace cooling) , cooled to room temperature, then heated to 625°C for 4 hours for the first tempering, water cooled to room temperature;

[0067](3) ...

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Abstract

The invention provides a ferritic low-temperature steel forging and a low-temperature cryogenic preparation method thereof, belonging to the technical field of alloy processing. The preparation method provided by the present invention comprises the following steps: performing homogenization annealing on the slab, followed by quenching, first tempering, stepped cryogenic treatment and second tempering to obtain a ferritic low-temperature steel forging, which is stepped and segmented Cryogenic treatment can avoid massive retained austenite in the final state structure, eliminate its adverse effect on toughness, and avoid the risk of cracking and deformation of low-temperature steel, and the formed martensite enriched in solute atoms is very effective for the second tempering The nucleation and final morphology distribution of reverse transformed austenite has a favorable influence in the process. The results of the examples show that the yield strength of the low-temperature steel forging prepared by the present invention is 560-790 MPa, the tensile strength is 750-860 MPa, the elongation is 17-26%, and the V-notch impact energy at -196 °C is 225-225 MPa. 270J.

Description

technical field [0001] The invention relates to the technical field of alloy processing, in particular to a ferritic low-temperature steel forging and a low-temperature cryogenic preparation method thereof. Background technique [0002] Large-scale castings and forgings are widely used in nuclear power, marine equipment, large-scale low-temperature wind tunnels and other fields, and their production technology is the embodiment of the country's manufacturing capacity. As a thick plate material for liquefied natural gas (LNG) storage vessels or transport ships, low-temperature ferritic 9Ni steel has been extensively and systematically studied, and its toughening mechanism has been basically clarified, that is, reverse transformed austenite as a tough phase mainly through Three aspects to improve low temperature (-196°C) toughness: (1) Adding additional ferrite / austenite interface to increase the number of crack transitions or propagation energy; (2) Transformation-induced pla...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C21D6/00C21D6/04C21D1/18C21D1/26
CPCC21D1/18C21D1/26C21D6/001C21D6/005C21D6/008C21D6/04C21D2211/001C21D2211/008
Inventor 刘庆冬张依潇顾剑锋
Owner SHANGHAI JIAOTONG UNIV
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