CN101597682B - Process for ultrafining heat-treatment on crystal grains of axle steel - Google Patents

Abstract

The invention discloses an ultra-fine heat treatment process for axle steel grains, which heats low- and medium-carbon axle steel parts to a temperature near the critical point A _c3 through wave heating to obtain ultra-fine austenite grains. grains and a small amount of refined ferrite, when wave heating is performed, the temperature fluctuation range is required not to exceed A _c3 ±10°C, and the heating time is controlled at 4mm/min according to the effective diameter of the part; when the wave heating is completed, Then increase the heating temperature by 5°C to 10°C, and keep it until the temperature on the entire part cross-section is basically the same, then the parts can be quenched and tempered according to the conventional heat treatment process. In the present invention, the temperature is fluctuated and heated near the critical point A _c3 to obtain ultra-fine austenite grains and a small amount of extremely fine massive ferrite, and then directly quenched to obtain ultra-fine martensite structure plus ultra-fine The multiphase structure of ferrite can significantly toughen and plasticize the material.

Description

Heat treatment process for ultra-fine grain of axle steel

technical field

The invention relates to an ultra-fine heat treatment process for axle steel crystal grains, belonging to the technical field of metal heat treatment.

Background technique

In recent years, with the speed increase of trains, new challenges have been put forward to the performance of locomotives, thus higher requirements have been put forward for the performance of train axles. It is required that the wheels and shafts should have sufficient strength and impact toughness to ensure absolute safety and reliability under the highest speed and load. Wheels and axles are vital components directly related to train safety for high-speed trains. Therefore, all countries in the world attach great importance to the research and development of materials and processes for wheels and shafts. At present, the heat treatment of axles mostly adopts the process route of quenching and tempering heat treatment plus surface strengthening treatment. This method has the following problems. First, the axle has a relatively coarse grain size when it is forged in the early stage, and subsequent heat treatment is prone to tissue inheritance, resulting in a coarse grain size after quenching and tempering heat treatment. The second is that the high temperature in the quenching and tempering heating process leads to the phenomenon of mixed crystals, which reduces the strength and toughness and poses a threat to the safety of train operation. Therefore, the effect of the existing axle steel heat treatment process is still not ideal enough.

Contents of the invention

The purpose of the present invention is to provide an ultra-fine heat treatment process for axle steel grains with smaller grain size, less prone to mixed crystal phenomenon, and higher strength and toughness, so as to overcome the shortcomings of the prior art.

The present invention is realized in the following way: an ultra-fine heat treatment process for axle steel grains of the present invention is to heat the low- and medium-carbon axle steel parts to a temperature near the critical point A _c3 by means of wave heating, so as to obtain ultra-fine Refined austenite grains and a small amount of refined ferrite. When performing wave heating, the temperature fluctuation range is required not to exceed A _c3 ±10°C, and the heating time is controlled at 4mm/min according to the effective diameter of the part; After the wave heating is completed, increase the heating temperature by 5°C to 10°C, and keep the temperature on the entire part section basically the same, then the parts can be quenched and tempered according to the conventional heat treatment process.

When the low and medium carbon axle steel parts are 25CrMoA steel materials, wave heating is performed in the range of 795°C to 815°C.

The austenite grains of the parts can be further refined and the austenite grains homogenized by repeated wave heating and quenching of low and medium carbon axle steel parts.

Due to the adoption of the above-mentioned technical scheme, the present invention aims at the problems existing in the prior art, and adopts the method of wave heating near the critical point. Since high-temperature tempering and austenite transformation are simultaneously produced during the heating process, the nucleation rate is high , the heating temperature is not high, and the ultra-fine grains obtained during phase transformation are not easy to grow, and some untransformed fine ferrite and ultra-fine austenite grains coexist, and direct quenching obtains ultra-fine martensite as the It is mainly composed of a small amount of fine ferrite. This organization has excellent strength and toughness. Therefore, the present invention can obtain superfine austenite grains and a small amount of extremely fine massive ferrite by performing fluctuating heating at a temperature near the critical point _Ac3 , and then directly quench to obtain superfine martensite structure plus The multi-phase structure of ultra-fine ferrite can significantly toughen and plasticize the material. Moreover, in the present invention, after the wave heating is completed, by properly increasing the heating temperature to transform a small amount of ferrite into fine austenite and then quenching, all ultra-fine martensite structures can be obtained, which has a high hardness after tempering. The combination of strength and toughness plays an important role in improving the safety and fatigue life of the axle.

Below is that the grain size contrast of the present invention and traditional technology processing parts is as follows:

Part material: 25CrMoA axle steel

After forging, the austenite grain size after traditional quenching and tempering heat treatment process is 5-7;

The austenite grain size after the heat treatment process of the present invention can reach 10-13 grades.

Through the comparison of the above data, it can be seen that compared with the prior art, the present invention not only has the advantages of ultra-fine grain size of the processed parts and no mixed crystal phenomenon, but also has the advantages of effectively improving the strength of the parts. Advantages of toughness and fatigue life.

Detailed ways

Embodiment of the present invention: when heat-treating low- and medium-carbon axle steel parts, a kind of axle steel grain ultra-fine heat treatment process of the present invention is used for treatment, that is, the low- and medium-carbon axle steel parts are heated by waves Heating to a temperature near the critical point A _c3 to obtain ultra-fine austenite grains and a small amount of refined ferrite. When performing wave heating, the fluctuation range of temperature is required not to exceed A _c3 ±10°C, and according to The effective diameter of the part is to control the heating time at 4mm/min; after the wave heating is completed, the heating temperature is increased by 5°C to 10°C, and when the temperature on the entire part section is basically the same, the part can be treated according to the conventional heat treatment process. Quenching-tempering treatment is carried out.

When the low- and medium-carbon axle steel parts are 25CrMoA steel materials, it is best to heat them with fluctuations in the range of 795 ° C to 815 ° C.

In order to obtain further refined austenite grains and homogenized austenite grains, the low and medium carbon axle steel parts can be repeatedly heated and quenched in the above-mentioned manner.

Claims (2)

1. a process for ultrafining heat-treatment on crystal grains of axle steel is characterized in that: will hang down middle carbon axle steel part and be heated stagnation point A by the mode that heats that fluctuates _C3Near temperature, to obtain super-refinement austenite crystal and a small amount of refinement ferrite, when fluctuating heating, the fluctuation range of temperature requires to be no more than A _C3± 10 ℃, and will be controlled at 4mm/min heat-up time according to the effective diameter of part; After fluctuation heating is finished, again Heating temperature is improved 5 ℃～10 ℃, and remain to temperature on the whole part section when basically identical routinely thermal treatment process part is quenched-temper; Described low in carbon axle steel part be the 25CrMoA steel, in the heating of fluctuating of 795 ℃～815 ℃ scopes.

2. process for ultrafining heat-treatment on crystal grains of axle steel according to claim 1 is characterized in that: the austenite crystal and the homogenizing austenite crystal that come further refinement part by the mode that carbon axle steel part in low is repeated to fluctuate heating and quench.