Process analysis of heat treatment of steel-inlaid guide rails using CNC quenching machine tools

In order to improve the positioning accuracy of machine tools and reduce transmission resistance, steel-inlaid guide rails are widely used in machine tools. Heat treatment of steel-inlaid guide rails has also become essential. The heat treatment of steel-inlaid guide rails is mostly carried out by CNC quenching machine tools. Today, I will tell you about the heat treatment process of the SI-220 CNC lathe bed with steel guide rails.

The steel guide rails of the SI-220 CNC lathe bed are made of GCr15 steel. The hardness after heat treatment is required to reach 61-66HRC. The processing process is: forging-normalizing-spheroidizing annealing-rough machining (planing)-stress relief annealing-fine planing, rough grinding, drilling and other fine machining-quenching, Tempering and fine grinding. 

Process specifications for heat treatment of steel-inlaid guide rails by CNC quenching machine tools:

a. Normalizing. When the steel-inlaid guide rail is normalized, the heating temperature is 910°C, the holding time is 1.5 to 2 hours, and it is cooled in flowing air. After normalizing, the grain size of the workpiece should be ≥5, the network carbide should be ≤3, and the hardness should be 270~390HRC.

b. Spheroidizing annealing. Most of the annealing of steel-inlaid guide rails adopts isothermal spheroidizing annealing. The heating temperature is 790~810℃, the holding time is 3~4h, and then the furnace is cooled to 690~710℃, the holding time is 4~6h, and then the temperature is lowered to below 500℃ and air-cooled. . The hardness of the workpiece after spheroidizing annealing is 197-207HBW, and the spheroidization level is 2.

c. Stress relief annealing. The workpiece is hung and heated to 600~650℃, kept warm for 3 hours, and is air-cooled when the furnace temperature is <400℃. Its main purpose is to completely eliminate the residual internal stress of the workpiece being processed.

d.Quenching and tempering at low temperature. When the inlaid steel guide rail is quenched using a CNC quenching machine, the quenching heating temperature is 860°C and the holding time is 40 to 50 minutes. After the oil is cooled to about 170°C, take it out and straighten it while it is hot. Then, perform low-temperature tempering at 140~160℃, and the holding time is 2.5~3h.

When implementing quenching and low-temperature tempering, you should also pay attention to:

1. The workpiece should be preheated at around 600°C and then heated to the quenching temperature.

2. For slender workpieces such as the steel guide rails in this example, they should be hung vertically in a salt bath furnace or pit furnace for heating to reduce deformation caused by their own weight.

3. The workpiece should be tempered at low temperature immediately after quenching. The determination of the tempering temperature should not only consider the hardness, but also take into account the characteristics of the steel and the impact of the tempering temperature on the toughness.

4. The cooling method in this example is essentially an oil quenching and air-cooling dual-medium quenching method. The cooling time in oil should be calculated based on the effective cross-sectional thickness of the workpiece and the content of alloy elements. The effective cross-sectional thickness of 2 to 5mm is 1s. When the oil is cooled to about 170°C and then taken out and then straightened while it is still hot, it actually uses the principle of superplasticity during the martensitic transformation process to deform and straighten.

The heat treatment of steel-inlaid guide rails has always been a matter of concern. The application of CNC quenching machine tools is also becoming more and more common. It is best to use a CNC quenching machine tool to heat treat the steel guide rails. If you want to know more about these two aspects, you can call us for consultation.