CN-121992175-A - Green low-carbon production method for directly quenching and tempering HG785 steel plates to replace quenching and tempering

Abstract

The invention discloses a green low-carbon production method for directly quenching and tempering HG785 steel plates instead of quenching and tempering, wherein the thickness of the steel plates is 30-50 mm. The production method provided by the invention has strong universality, low requirements on transformation of the existing medium plate production line (with accelerated cooling and tempering capacity), easy realization of industrialized mass production and remarkable economic and social benefits, and ensures that the mechanical properties of the steel plate reach the standard comprehensively (the yield strength is more than or equal to 785MPa and the impact power stability is more than or equal to 80J at 40 ℃) while realizing green low carbon through the cooperative design of component fine adjustment and gradient quenching and two-phase region coupling tempering, thereby proving that the green production and the product performance improvement can be realized synchronously and further strengthening the practicability and popularization value of the green low carbon technology.

Inventors

• LI ZHONGBO
• WANG YINGJIE
• LIU CHUNXIA
• XU SHAOPU
• YANG DONG
• KANG WENJU
• ZHU XIANXING
• Yuan Gaojian

Assignees

• 南阳汉冶特钢有限公司

Dates

Publication Date

20260508

Application Date

20260126

Claims (1)

1. 1. A green low-carbon production method for directly quenching and tempering HG785 steel plates instead of quenching and tempering is characterized in that the thickness of the steel plates is 30-50mm, the production method comprises the following steps, 1) Smelting and continuous casting, namely smelting molten steel according to the weight percentage, wherein the chemical components of the molten steel meet ：C：0.06-0.10%, Si：0.15-0.35%, Mn：1.40-1.70%, P≤0.015%, S≤0.005%, Nb：0.025-0.045%, Ti：0.008-0.020%, Mo：0.20-0.40%, Cr：0.30-0.60%, Ni：0.30-0.60%, V：0.03-0.06%, B：0.0008-0.0020%, Alt：0.020-0.050%, N≤0.0040%,, and the (Nb+Ti)/(C+N) is between 3.5 and 5.5, the Ti/N is more than 3.5, and the balance is Fe and unavoidable impurities; 2) Heating and rolling, namely heating the continuous casting billet to 1180-1220 ℃, preserving heat to enable microalloy elements to be fully dissolved, firstly performing rough rolling to finish most of deformation in a recrystallization zone, then performing finish rolling, controlling the final rolling temperature to be 830-870 ℃ (in a non-recrystallization zone), and controlling the accumulated reduction rate to be more than or equal to 50 percent so as to obtain a severely deformed non-recrystallized austenitic structure; 3) The direct quenching comprises the steps of immediately entering an accelerated cooling device after rolling, adopting a gradient quenching mode, wherein the surface of the steel plate is cooled to be below 450 ℃ at a cooling speed of more than or equal to 20 ℃ per second in the first stage, the temperature of the core is reduced to be between 600 and 650 ℃ and between Bs and Bf, the water cooling intensity is adjusted in the second stage, the whole (core) of the steel plate is cooled to be below 150 ℃ at a cooling speed of 5 to 15 ℃ per second and is discharged from a quenching area, and the final cooling temperature is controlled to be 80 to 150 ℃; 4) The two-phase area coupling tempering comprises the steps of putting the quenched steel plate into a tempering furnace, tempering according to the following schedule, wherein the first stage is to heat the steel plate to 740-760 ℃ at a temperature rising rate of less than or equal to 5 ℃ per minute, and preserving heat for 10-25 minutes, the second stage is to cool the steel plate to 620-660 ℃ with free cooling or controlled slow cooling rate of less than or equal to 3 ℃ per minute, preserving heat for 40-80 minutes, and the total tempering time (comprising temperature rising and slow cooling in the second stage) is determined according to the thickness of the steel plate per millimeter for 1.5-2.5 minutes; 5) And (5) discharging, and then air cooling or water mist cooling to room temperature to obtain the finished steel plate.

Description

Green low-carbon production method for directly quenching and tempering HG785 steel plates to replace quenching and tempering Technical Field The invention belongs to the technical field of heat treatment of low-alloy high-strength steel plates, and particularly relates to a green low-carbon production method for replacing tempering by direct quenching and tempering of an HG785 steel plate, which adopts a heat treatment production method for replacing traditional offline reheating quenching and tempering (tempering, Q+T) by combining Direct Quenching (DQ) with tempering of a specific system. Background HG785 is high-strength structural steel with yield strength not lower than 785MPa, and is widely applied to key bearing structures of engineering machinery, mining equipment, large bridges and the like. The main flow process for producing the thick high-strength steel plate is quenching and tempering, namely cooling the rolled steel plate to room temperature, then reheating the steel plate to a complete austenitizing temperature (30-50 ℃ above Ac3 in general) in a roller hearth furnace, carrying out quenching after heat preservation, and then carrying out high-temperature tempering to obtain a tempered sorbite structure, thereby realizing the matching of high strength and good toughness. However, the traditional process has the remarkable defects of (1) huge energy consumption, waste heat after rolling is wasted, reheating consumes a large amount of energy sources, (2) long production period, additional heating, heat preservation and multiple transfer time, 3) serious iron scale, large iron scale loss and surface quality caused by reheating, and (4) large equipment investment and occupation, namely high-power roller hearth heat treatment furnace and matched equipment are required to be configured. For energy saving and consumption reduction, a Direct Quenching (DQ) technology has been explored. The principle is that the high temperature waste heat after rolling is utilized to directly carry out on-line quenching, thereby omitting the reheating process. However, when DQ is applied to high-hardenability steel types such as HG785 with the thickness of 30-50mm, the technical bottlenecks are recognized, wherein (1) the cooling uniformity in the thickness direction is difficult to control, namely the cooling rate of the thick plate core is far lower than that of the surface, so that non-target medium-temperature or high-temperature transformation products (such as bainite and pearlite) are easily generated at the core, the uneven structure and the insufficient strength and toughness of the core are easily caused, (2) the quenching stress is extremely large, namely the serious warping and even cracking of the plate are easily caused by the superposition of thermal stress and structural stress generated by direct quenching of the thick plate, and (3) the tempering parameter window is narrow, namely the structure state (usually a mixed structure of martensite and a small amount of bainite) after direct quenching is different from that of single tempered martensite/sorbite after traditional tempering, and the strength and toughness, especially the low-temperature impact toughness fluctuation are difficult to be ensured simultaneously by adopting traditional tempering temperature and time. Therefore, the prior art generally considers that for the HG785 grade steel plate with the thickness of 30-50mm, the direct quenching is difficult and risky to completely replace the tempering process, or the performance (especially the core toughness and the plate shape) does not reach the severe standard, or an extremely complex and expensive super-strong jet cooling system is required, and the industrialized application is limited. Disclosure of Invention In order to solve the technical defects, the invention aims to provide a green low-carbon production method for directly quenching and tempering HG785 steel plates instead of quenching and tempering, which overcomes the prejudice and the obstacle of the prior art, successfully replaces the traditional quenching and tempering by a gradient quenching and two-phase zone coupling tempering process which is unique in component fine tuning and precisely matched with the quenching and tempering process under the condition of not depending on super-strong cooling equipment, and realizes remarkable energy conservation, consumption reduction and efficiency improvement while ensuring the high strength, high toughness and excellent plate shape of the full thickness range (particularly the central part) of the steel plates. In order to achieve the aim, the invention adopts the following technical scheme that the green low-carbon production method for directly quenching and tempering HG785 steel plates instead of tempering comprises the following steps of: 1) Smelting and continuous casting, namely smelting molten steel according to the weight percentage, wherein the chemical components of the