For general 304 stainless steel pipe, only before shipping (compression or expansion to the limit position, when the load is about twice the working load) and maximum load test after the maximum load test can be carried out. (or stretching) 304 stainless steel pipe has a certain permanent deformation (generally not more than a few millimeters), the size of the requirements can be used. If suitable for the test, 304 stainless steel pipe has a high enough elastic limit and obvious under the working load, will not produce permanent deformation, but for some high-precision 304 stainless steel pipe (such as measuring instruments with 304 stainless steel pipe), the dimensional stability of 304 stainless steel pipe requirements are higher. Use. 304 stainless steel pipe under long-term load will produce a small amount of permanent deformation due to stress relaxation, even high-precision 304 stainless steel pipe is not acceptable. Resting and heating can overcome these disadvantages. The treatment is to pre-add deformation (elastic deformation) in excess of the working load on the 304 stainless steel pipe, then fixed and heated. The temperature is slightly higher than the working temperature of the thin-walled stainless steel pipe. Insulation 8-24 hours, in the process, 304 stainless steel pipe occurred pre-stress relaxation and permanent deformation, greatly reducing the relaxation of later work, to achieve the purpose of dimensional stability. For high-temperature 304 stainless steel pipe, more relaxation heat treatment is required because the stress relaxation is more serious at high temperatures.

304 stainless steel pipe heat treatment inspection

Post-heat treatment inspection: 304 stainless steel pipe heat treatment should generally be hardness and maximum load test, except for size in accordance with the requirements of the drawings. The key 304 stainless steel pipe needs to be tempered after self-inspection to find small cracks that are not easily detected. In order to check the final quality of 304 stainless steel pipes, it is sometimes necessary to perform a certain number of fatigue tests, generally by applying stresses in excess of the maximum working load and determining the fatigue life (number of stress changes) in a short period of time. It's time to assess the quality of the heat treatment. Some samples are fatigue tested for a certain time under the same conditions as the actual working environment, in order to control the quality of 304 stainless steel pipe, 304 stainless steel pipe will not break during the test.

304 stainless steel pipe quality improvement methods

The current short iron blasting treatment: improve the fatigue life of 304 stainless steel pipe, mainly to improve the surface condition of 304 stainless steel pipe. One of the most widely used is shot blast cleaning, centrifugal shot blast cleaning machine at a speed of about 50-60 meters per second shot from potting iron (or hardened steel balls for better results, recently used glass beads).) Fire the gun. Spring so that the surface layer of plastic deformation and compressive stress, so the 304 stainless steel pipe surface of various defects and stress concentration areas on the fatigue life is greatly reduced, greatly improving the fatigue 304 stainless steel pipe life. Tensile stress applied to the surface of 304 stainless steel pipe, and then shot blasting treatment, the effect is better. Fatigue life of 304 stainless steel pipe after shot blasting can generally be improved by high numbers. Times.

Thermomechanical heat treatment: 304 stainless steel pipe process characteristics are conducive to high-temperature deformation of stainless steel pipe heat treatment. That is, immediately after the hot rolling and deformation to form a thin plate or bar, and then quenched. Thermomechanical heat treatment is applied to the production of automotive steel plate springs. The fatigue life of steel plate springs thermomechanically heat treated under 95 kg/mm2 test stress reaches 1.45 million cycles, which is three times that of steel plate springs. Heat-treated steel plate springs have improved mechanical properties compared to general heat-treated steel plate springs in terms of strength, yield limit, plasticity, toughness, and especially impact toughness.