A q-p heat treatment process for medium carbon alloy steel

Abstract

The invention discloses a Q-P heat treatment process for medium-carbon alloy steel, which comprises the following steps: austenitize the medium-carbon alloy steel at 870-950°C, and then rapidly cool it in a water-based suspension for 1-3s; Keep warm at 100-190°C for 5-15min, then keep warm at 250-280°C for 30-240min, and finally air-cool to room temperature. The medium-carbon alloy steel obtained by the process of the present invention meets the organizational requirements obtained by the ordinary Q-P method, that is, obtains a combination of carbon-poor martensite and high-carbon retained austenite. The hardness of the steel after treatment reaches above 56HRC, which is more than 1.4 times that of the original sample; the bending strength reaches 4009.9MPa, and the deflection reaches 9.2mm.

Description

technical field [0001] The invention belongs to the technical field of heat treatment, and relates to a Q-P heat treatment method for obtaining high bending performance of medium-carbon alloy steel. Background technique [0002] Quenching and partitioning process (Q-P process) is a new process for heat treatment of steel proposed by Speer in 2003. This process is to austenitize steel containing Si or Al, and between Ms and Mf points Quenching at a certain temperature (Quenching temperature, QT), then holding at the same temperature or a higher temperature (Partitioning temperature, PT) for a certain period of time, and finally air cooling to room temperature. The end result is a combination of carbon-poor martensite and carbon-rich retained austenite. Q-P steel is a typical representative of the third generation of advanced high strength steel (AHSS), which has a good combination of strength and toughness. It is based on C-Mn-Si steel, high performance and low price. As a...

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Problems solved by technology

Although this is beneficial to reduce the internal stress of the workpiece and slow down the tendency of cracking, studies have shown that during the quenching process of medium carbon alloy steel, due to the weak cooling capacity of the salt bath, it will lead to martensite and retained austenite. Other phase structures appear, such as pearlite and ferrite, etc., thereby reducing the overall mechanical properties of the workpiece

[0006] 2. High energy consumption of nitrate

Therefore, for large size parts, it is difficult to achieve salt bath insulation

[0007] 3. Nitrate pollutes the environment and harms the human body

For example, after quenching, salt is easy to stick to the workpiece, and the residual salt can cause corrosion, and the cleaning of dead corners such as small holes and threaded holes is more troublesome

In addition, dross is easy to precipitate in the salt bath furnace, and it is difficult to remove when the dross is hard

[0009] To sum up, in the process of Q-P treatment of medium carbon alloy steel, the use of salt bath furnace will cause a series of environmental problems and difficulties in subsequent treatment, and the final obtained structure is also difficult to achieve the required mechanical properties

In addition, there are still big problems in industrial mass production

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