阅读说明：本技术 一种细化fb2转子钢晶粒的热处理工艺 (Heat treatment process for refining FB2 rotor steel grains ) 是由 彭建强 刘新新 韩亮 徐勤 冯天澍 周立艳 李毅刚 徐佰明 王德彪 于海欧 魏双 于 2020-04-07 设计创作，主要内容包括：一种细化FB2转子钢晶粒的热处理工艺,涉及一种钢热处理工艺。目的是解决现有方法处理得到的FB2转子钢存在粗晶的问题。方法：在700-770℃下保温(0.4-0.6)h/25mm,然后依次经淬火、第1次回火和第2次回火。本发明在700-770℃温度范围内长期保温,将发生珠光体转变,形成与原奥氏体截然不同的固体新相,新相包括铁素体、以及铁素体和细小的M23(C,B)6碳硼化物构成的共析组织,打破了原有的奥氏体晶界,进而消除组织遗传性,使FB2转子钢锻件的晶粒得到细化。本发明适用于FB2转子钢的热处理。(A heat treatment process for refining FB2 rotor steel grains relates to a steel heat treatment process. The method aims to solve the problem that the FB2 rotor steel processed by the existing method has coarse grains. The method comprises the following steps: keeping the temperature at 700-770 ℃ (0.4-0.6) h/25mm, and then sequentially carrying out quenching, 1 st tempering and 2 nd tempering. The invention keeps the temperature for a long time in the temperature range of 700-770 ℃, pearlite transformation occurs, a new solid phase which is completely different from the prior austenite is formed, the new phase comprises ferrite, and a eutectoid structure which is formed by the ferrite and fine M23(C, B)6 carborundum, the prior austenite crystal boundary is broken, the tissue inheritance is eliminated, and the crystal grains of the FB2 rotor steel forging are refined. The invention is suitable for the heat treatment of FB2 rotor steel.)

1. A heat treatment process for refining FB2 rotor steel grains is characterized in that: the heat treatment process for refining the FB2 rotor steel grains is carried out according to the following steps:

firstly, performing preliminary heat treatment: keeping the temperature at 700 and 770 ℃ (0.4-0.6) h/25 mm;

secondly, quenching: preserving the heat at 1090-1110 ℃ (0.9-1.1) h/25mm, and cooling in an oil cooling mode;

third, tempering for the 1 st time: keeping the temperature at 560 ℃ and 580 ℃ for 0.9-1.1 h/25mm, wherein the cooling mode is air cooling;

fourthly, 2 nd tempering: keeping the temperature at 670-.

2. The heat treatment process for refining the grains of the FB2 rotor steel as claimed in claim 1, wherein: step one, the temperature is kept at 740 ℃ for 0.5h/25 mm.

3. The heat treatment process for refining the grains of the FB2 rotor steel as claimed in claim 1, wherein: and step two, preserving heat for 1h/25mm at 1110 ℃, wherein the cooling mode is oil cooling.

4. The heat treatment process for refining the grains of the FB2 rotor steel as claimed in claim 1, wherein: and step three, preserving the heat at 570 ℃ for 1h/25mm, wherein the cooling mode is air cooling.

5. The heat treatment process for refining the grains of the FB2 rotor steel as claimed in claim 1, wherein: and step four, preserving the heat at 680 ℃ for 1h/25mm, and cooling in an air cooling mode.

Technical Field

The invention relates to a steel heat treatment process.

Background

The FB2 rotor steel is 620 ℃ grade rotor steel, and is widely used for 600 ℃ grade and above ultra supercritical steam turbine units at home and abroad. The FB2 rotor steel has excellent creep rupture strength, with a rupture strength of over 100MPa at 620 ℃ and 10 ten thousand hours duration. The excellent creep rupture strength is mainly due to the addition of about 100ppm of B element to the steel. The B element enters into the main strengthening phase M23C6 type carbide of the steel to form M23(C, B)6 type carborundum, thereby inhibiting the aggregation and growth of the strengthening phase carbide, improving the stability of the carbide and obviously improving the creep endurance quality of the steel. Then, M23(C, B)6 type carborides are mainly present at prior austenite grain boundaries, and prior austenite grains are formed in the forging process, are coarse in grains, have strong inheritance and are difficult to eliminate by conventional heat treatment. Therefore, the FB2 steel rotor forging generally has the coarse grain problem, and the impact property of the forging is reduced.

Disclosure of Invention

The invention provides a heat treatment process for refining FB2 rotor steel grains, which aims to solve the problem that FB2 rotor steel obtained by the existing method has coarse grains.

The heat treatment process for refining the FB2 rotor steel grains is carried out according to the following steps:

firstly, performing preliminary heat treatment: keeping the temperature at 700 and 770 ℃ (0.4-0.6) h/25 mm;

secondly, quenching: preserving the heat at 1090-1110 ℃ (0.9-1.1) h/25mm, and cooling in an oil cooling mode;

third, tempering for the 1 st time: keeping the temperature at 560 ℃ and 580 ℃ for 0.9-1.1 h/25mm, wherein the cooling mode is air cooling;

fourthly, 2 nd tempering: keeping the temperature at 670-.

The principle and the beneficial effects of the invention are as follows:

according to the invention, by changing the mode of the preliminary heat treatment, the heat is preserved for a long time within the temperature range of 700-770 ℃, pearlite transformation is generated, a new solid phase which is completely different from the original austenite is formed, the new phase comprises ferrite, and eutectoid tissues formed by the ferrite and fine M23(C, B)6 carboride, the original austenite crystal boundary is broken, the tissue inheritance is eliminated, the crystal grains of the FB2 rotor steel forging are refined, the problem of coarse crystal of steel is solved, and the performance of the forging is improved. The performance indexes of the FB2 rotor steel treated by the method are as follows: the average grain size is not thicker than 2 grade; the impact work Akv is more than or equal to 20J; the ductile-brittle transition temperature FATT50 is less than or equal to 80 ℃.

Drawings

FIG. 1 is a structural morphology diagram of FB2 rotor steel processed by comparative example 1 under a metallographic microscope of 100 times;

FIG. 2 is a structural morphology diagram of FB2 rotor steel processed in example 1 under a metallographic microscope of 100 times;

FIG. 3 is a structural morphology diagram of FB2 rotor steel processed by comparative example 2 under a metallographic microscope of 100 times;

FIG. 4 is a structural morphology diagram of FB2 rotor steel processed in example 2 under a metallographic microscope of 100 times.

Detailed Description

The technical scheme of the invention is not limited to the specific embodiments listed below, and any reasonable combination of the specific embodiments is included.