CN109881105B

CN109881105B - Preparation method for obtaining fine-grained austenite structure on surface layer of low-carbon martensite steel plate

Info

Publication number: CN109881105B
Application number: CN201910219598.6A
Authority: CN
Inventors: 衣海龙; 周永康; 毕梦园; 方明阳
Original assignee: Northeastern University China
Current assignee: Northeastern University China
Priority date: 2019-03-22
Filing date: 2019-03-22
Publication date: 2021-11-05
Anticipated expiration: 2039-03-22
Also published as: CN109881105A

Abstract

The invention belongs to the technical field of heat treatment of metal plates and strips, and particularly relates to a heat treatment process method for obtaining a fine-grained austenite structure on the surface layer of a low-carbon martensite steel plate. The first step is as follows: selecting low-carbon martensite steel, and the second step: and heating and rolling the low-carbon martensitic steel in the first step into a steel plate with the thickness of 20-40 mm, wherein the final rolling temperature is 950 +/-20 ℃, and then air-cooling to room temperature. The third step: and (3) putting the cooled steel plate into a heating furnace, heating to 980-1020 ℃, wherein the heating rate is 10 ℃/min, then quickly induction heating the upper surface layer and the lower surface layer of the steel plate to 880-920 ℃, and quickly quenching to room temperature to obtain an original austenite structure with the size not more than 5 mu m on the surface layer of the steel plate. On the premise of not changing the controlled rolling and controlled cooling process of the steel plate, the quenching process is designed into a conventional quenching process and a short-time induction heating quenching process, and on the basis of meeting the requirements of the steel plate quenching process, austenite grains are refined on the surface layer of the steel plate.

Description

Preparation method for obtaining fine-grained austenite structure on surface layer of low-carbon martensite steel plate

Technical Field

The invention belongs to the technical field of heat treatment of metal plates and strips, and particularly relates to a heat treatment process method for obtaining a fine-grained austenite structure on the surface layer of a low-carbon martensite steel plate.

Background

With the continuous expansion of the application range and the application field of the high-performance metal material, higher requirements are put forward on the comprehensive performance and the service performance of medium and heavy plate products. Besides meeting the basic mechanical property index of the steel plate, the steel plate has clear requirements on the crack arrest performance, the wear resistance, the low-temperature toughness and the like of the surface layer. Here, for steel materials, it is important to refine the structure so as to improve both the strength and toughness, and other properties are improved while refining the structure. Aiming at the special performance requirements, the existing surface layer ultrafine grain mechanism is adopted, such as dynamic recovery and recrystallization of ferrite, a large amount of ferrite precipitated from undercooled austenite in the temperature rising process, strain induced ferrite phase transformation and the like, so that a medium plate product with excellent performance can be obtained. However, the current regulation and control means for realizing the ultra-fine grain on the surface layer mainly focuses on the aspects of rolling control and cooling control processes, and is only suitable for part of medium plate products, but for most products, especially for medium plate products delivered in a heat treatment state, the process treatment requirement of the ultra-fine grain on the surface layer cannot be met necessarily, and a feasible process route suitable for the heat treatment process condition needs to be found to realize the regulation and control of the fine grain structure on the surface layer of the medium plate product.

Chinese patent document CN100595292C discloses a high-speed processing method for realizing an ultra-fine grain structure on a surface layer of a metal material, which adopts a mechanical treatment method of high-speed plastic deformation to form submicron or nano grains on the surface layer of the metal material. The microstructure dimensions change in a gradient with increasing depth from the treatment surface. The patent relates to a method for carrying out low-temperature multiple deformation treatment on the surface of a workpiece by utilizing high-speed mechanical motion of a cutter and the surface of a product, wherein the corresponding processing temperature is-196 ℃ to 100 ℃, so that the method cannot be applied to medium plate products with fine-grained surface layers in the application field and the specific process conditions.

Chinese patent documents CN101906519A, CN102828116A, CN103572023B and CN106676240B respectively disclose a method for manufacturing a low yield ratio surface layer ultra-fine grain low-carbon steel thick plate, a surface layer ultra-fine grain high-strength steel plate based on TMCP process and a method for manufacturing the same, a method for manufacturing a low alloy steel thick plate/extra thick plate surface layer ultra-fine grain and a method for manufacturing a surface layer ultra-fine grain ferrite low alloy steel thick plate. In order to finally obtain the fine grain structure on the surface layer, the patents focus on regulating and controlling the cooling path of the intermediate billet, namely, firstly, the surface layer of the intermediate billet is cooled, and then, the second-stage rolling is carried out after temperature return, so that the processes of normal phase transformation and reverse phase transformation of the structure are realized, and the purpose of refining the surface layer structure is further realized. According to the difference of the selected steel types, the specific intermediate billet surface layer cooling termination temperature and the specific intermediate billet surface layer cooling return temperature are different, and both belong to the field of metal plate strip rolling and cooling processes, and if the steel plate obtained by the process control strategy is processed by an off-line quenching process, the fine grain structure on the surface layer of the steel plate is reheated to austenitization and cannot be transmitted to a quenching structure, so that the method cannot be directly applied to the regulation and control process of the fine grain structure on the surface layer of the steel plate under the heat treatment process.

In summary, at present, for medium plate products, the regulation and control process of the fine grain structure of the surface layer of the steel plate under the heat treatment condition is not involved. While meeting the requirements of high-end heat treatment products, a regulating and controlling process for obtaining a fine grain structure on the surface layer of the steel plate based on the heat treatment process condition needs to be developed, so that the product has the comprehensive properties of crack arrest performance, wear resistance, low-temperature toughness and the like, and the added value of the product is improved.

Disclosure of Invention

The invention aims to provide a preparation method for obtaining a fine-grained austenite structure on the surface layer of a low-carbon martensite steel plate, which is mainly characterized in that the fine-grained austenite structure on the surface layer of the steel plate is finally regulated and controlled by regulating and controlling a heat treatment process and only designing a quenching process on the basis of not changing the previous rolling and cooling process.

The technical scheme of the invention is as follows:

a preparation method for obtaining a fine-grained austenite structure on the surface layer of a low-carbon martensite steel plate comprises the following steps:

the first step is as follows: selecting low-carbon martensite steel, wherein the mass percentages are respectively as follows: 0.18-0.22% of C, 0.28-0.32% of Si, 0.45-0.55% of Mn, 0.88-0.92% of Mo, 0.018-0.022% of Nb, less than 0.012% of P, less than 0.01% of S and the balance of Fe.

The second step is that: and (3) heating and rolling the low-carbon martensitic steel in the first step into a steel plate with the thickness of 20-40 mm, wherein the finish rolling temperature is 950 +/-20 ℃, and then air-cooling to room temperature.

The third step: quenching process

And (3) putting the cooled steel plate into a heating furnace, heating to 980-1020 ℃, heating at the rate of 10-15 ℃/min, keeping the temperature for 60min, quenching to room temperature, rapidly induction heating the upper surface layer and the lower surface layer of the steel plate to 880-920 ℃, rapidly quenching to room temperature at the rate of 50 +/-2 ℃/s, and obtaining an original austenite structure with the size not more than 5 mu m on the surface layer of the steel plate.

Further, in the third step, the steel plate is placed into a heating furnace to be heated to 1000 ℃; the upper and lower surface layers of the steel plate are rapidly induction heated to 900 ℃.

The basis for adopting the control method is as follows: for low-carbon martensitic steel, the conventional quenching process is to directly heat the low-carbon martensitic steel to austenitizing temperature, and obtain austenite with uniform section structure after heat preservation treatment for a certain time, and for the low-carbon martensitic steel selected by the invention, the austenite grain size is 20-50 mu m under the quenching process, and the martensite structure is obtained after the quenching process. In the invention, a short-time induction heating quenching process is added on the basis of a conventional quenching process, the temperature of the surface layer of the steel plate can be quickly raised to the austenitizing temperature by induction heating, and meanwhile, the austenite grain size after reverse phase transformation can be effectively refined by quick heating, but the too fast or too slow heating rate is not favorable for the refinement of the austenite grain size, and the refining effect is optimal when the heating rate is 50 ℃/s for the low-carbon martensite steel with the composition. Meanwhile, the induction heating temperature is too high, the austenite grain size is large, when the induction heating temperature is low, the structure of the steel is not completely austenitized, and the final reheating temperature is 900 ℃. Therefore, by the conventional quenching process and the induction heating quenching process, the refinement of the austenitic structure on the surface layer of the steel plate can be realized on the basis of meeting the requirements of the steel plate quenching process.

The invention has the beneficial effects that:

on the premise of not changing the controlled rolling and controlled cooling process of the steel plate, the quenching process is designed into a conventional quenching process and a short-time induction heating quenching process, and austenite grains are refined on the surface layer of the steel plate on the basis of meeting the requirements of the quenching process of the steel plate.

Drawings

FIG. 1 is a diagram showing the structure of austenite grains of the surface layer of a steel sheet obtained according to the present invention.

FIG. 2 is a diagram showing the structure of prior austenite grains in the obtained steel sheet according to the present invention.

Detailed Description

Example 1

Selecting a low-carbon martensite steel blank with the weight percentage of 80mm by 80mm, wherein the components of the low-carbon martensite steel blank comprise, by mass, 0.20% of C, 0.30% of Si, 0.50% of Mn, 0.90% of Mo, 0.02% of Nb0.02%, less than 0.012% of P, less than 0.01% of S and the balance of Fe. Firstly, heating the blank to 1200 ℃, preserving heat for 2 hours, rolling the blank into a steel plate with the thickness of 20mm through multiple passes, wherein the final rolling temperature is 950 ℃, and then cooling the steel plate to room temperature in air. Selecting a hot-rolled steel plate, putting the steel plate into a heating furnace, slowly heating to 1000 ℃, heating at the rate of 10 ℃/min, keeping the temperature for 60min, then quenching to room temperature, then quickly induction heating the upper surface layer and the lower surface layer of the steel plate to 900 ℃, correspondingly heating at the rate of 50 ℃/s, and then quickly quenching to room temperature, finally obtaining an original austenite structure with the size of about 4.5 mu m on the surface layer, wherein the thickness of a fine crystal layer on the surface layer is 3mm, and the grain size distribution of the specific surface layer and the internal original austenite structure is shown in figure 1 and figure 2.

Example 2

The first step is as follows: selecting low-carbon martensite steel blanks of 80mm by 80mm, wherein the low-carbon martensite steel blanks are respectively as follows by mass percent: 0.18 percent of carbon, 0.28 percent of silicon, 0.45 percent of manganese, 0.88 percent of molybdenum, 0.018 percent of niobium, less than 0.012 percent of P, less than 0.01 percent of S and the balance of Fe.

The second step is that: and (3) heating and rolling the low-carbon martensite steel in the first step into a 40mm steel plate, wherein the finish rolling temperature is 930 ℃, and then air-cooling to room temperature.

The third step: quenching process

And putting the cooled steel plate into a heating furnace, heating to 980 ℃, heating at a rate of 10 ℃/min, keeping the temperature for 60min, quenching to room temperature, rapidly induction heating the upper surface layer and the lower surface layer of the steel plate to 880 ℃, heating at a rate of 48 ℃/s, and rapidly quenching to room temperature, wherein the surface layer of the steel plate obtains an original austenite structure with the size of about 4.2 mu m, and the thickness of the fine grain layer of the surface layer is 3 mm.

Example 3

The first step is as follows: selecting low-carbon martensite steel blanks of 80mm by 80mm, wherein the low-carbon martensite steel blanks are respectively as follows by mass percent: 0.22 percent of carbon, 0.32 percent of silicon, 0.55 percent of manganese, 0.92 percent of molybdenum, 0.022 percent of niobium, less than 0.012 percent of P, less than 0.01 percent of S and the balance of Fe.

The second step is that: and (3) heating and rolling the low-carbon martensite steel in the first step into a steel plate with the thickness of 20mm, wherein the finish rolling temperature is 970 ℃, and then air-cooling to room temperature.

The third step: quenching process

And putting the cooled steel plate into a heating furnace, heating to 1020 ℃, wherein the heating rate is 15 ℃/min, keeping the temperature for 60min, quenching to room temperature, rapidly induction heating the upper surface layer and the lower surface layer of the steel plate to 920 ℃, wherein the heating rate is 52 ℃/s, rapidly quenching to room temperature, obtaining an original austenite structure with the size of about 3.9 mu m on the surface layer of the steel plate, and the thickness of the fine grain layer on the surface layer is 2.5 mm.

Claims

1. A preparation method for obtaining a fine-grained austenite structure on the surface layer of a low-carbon martensite steel plate is characterized by comprising the following steps:

the first step is as follows: selecting low-carbon martensite steel, wherein the mass percentages are respectively as follows: 0.18-0.22% of C, 0.28-0.32% of Si, 0.45-0.55% of Mn, 0.88-0.92% of Mo, 0.018-0.022% of Nb, less than 0.012% of P, less than 0.01% of S and the balance of Fe;

the second step is that: heating and rolling the low-carbon martensitic steel in the first step into a steel plate with the thickness of 20-40 mm, wherein the final rolling temperature is 950 +/-20 ℃, and then air-cooling to room temperature;

the third step: quenching process

And (3) putting the cooled steel plate into a heating furnace, heating to 1000 ℃, heating at the rate of 10-15 ℃/min, keeping the temperature for 60min, quenching to room temperature, rapidly induction heating the upper surface layer and the lower surface layer of the steel plate to 900 ℃, heating at the rate of 50 +/-2 ℃/s, and finally quenching to room temperature, wherein the surface layer of the steel plate obtains an original austenite structure with the size not more than 5 mu m.