Small Caliber Seamless Pipe with Low Hardness after Quenching

Small diameter seamless pipe before going into service need to go through heat treatment, which quenching the main purpose is to improve the mechanical properties of the workpiece to improve its wear resistance, corrosion resistance, toughness and fatigue strength, in order to make small-diameter seamless pipe can be obtained hardness of amatibular bulk organization, to make it rapidly cooled after heating, but also to meet the corrosion resistance of some special steel and ferromagnetic some of the chemical, physical and mechanical properties. Small-caliber seamless pipe quenching process to meet the three conditions: 1. Seamless pipe workpiece cooling to avoid the wave body metamorphosis; 2. The steel hardened, resulting in a modified; 3. The workpiece after the auspicious field treatment, that is to be heated in the field in the field for some time. Quenching is a term we often hear, then the normalization of heat treatment is what? Normalization heat treatment is to heat the workpiece to Aam or A3 above the temperature of 30? -60?, and heat for a period of time until the material is transformed into a uniform after the auspicious field cooling, heat preservation time can be based on the thickness of 25mm temperature 30 minutes estimate. The purpose of the normalization of heat treatment are two, respectively, in order to make the seamless pipe workpiece homogeneity, the material machinability is improved, the casting or rolling structure to adjust the distribution of carbide distribution or size; there is to improve the material Mechanical properties, so that the seamless pipe workpiece grain refinement. In general, the normalization of heat treatment has multiple modified normalization heat treatment, divided into normalization of temperature, the second normalization and two normalization.

Small-caliber seamless pipe production process, sometimes there will be insufficient hardness after quenching. This is a common defect in the heat treatment of quenching. "Under-hardness" is sometimes manifested as the entire small-diameter seamless pipe hardness value is low, sometimes not enough local hardness or have a soft spot. There are many reasons for the lack of hardness of small-diameter seamless pipe during quenching, which is closely related to raw materials, heating process, cooling medium, cooling method, tempering temperature and so on. High quenching temperature can make seamless pipe heating speed, reduce surface oxidation, and can improve work efficiency. In order to make the uniform austenite of seamless pipe, it needs sufficient holding time. If the actual loading capacity, you need to properly extend the holding time. Otherwise, there may be a lack of hardness due to uneven heating. However, holding time is too long, there will also be coarse grains, oxidative decarburization serious shortcomings affect the quenching quality. We believe that if the loading volume is larger than the process documentation, the heating and holding time needs to be extended by 1/5. Once this happens in the production of small-caliber seamless tubes, it must be analyzed in detail before it can be properly addressed against the questions.