Vacuum Heat Treatment of Steel Needle Valve

The injector needle valve requires high wear resistance, high strength, high dimensional stability and certain impact toughness, and is made of W18Cr4V steel. The needle valve parts were previously heated in a salt bath furnace and then quenched by oil. The heat treatment caused large deformation and corrosion on the surface. Vacuum heat treatment can significantly reduce the deformation of parts, improve the life of parts, and ensure the quality stability of heat treatment. In industrial production, the application of vacuum heat treatment is more and more extensive, it has many advantages such as no oxidation, no decarburization, smooth surface, small deformation, long service life of processed parts and no pollution.

High-speed steel quenching heating temperature will directly affect its mechanical properties. For steel needle valves, heat and quench at 1265℃~1275℃. Quenched at this temperature, the grain size is 10~11. If the quenching temperature is too low, there are few alloying elements dissolved in the austenite, that is, the alloying degree of the austenite is low, the dispersion of carbides precipitated during tempering is small, and the hardness of the parts is low, the secondary hardening effect is poor, and the hot hardness If the quenching temperature is too high, the grain size of the austenitic product will increase, the workpiece will be easily deformed, the strength and impact toughness will be low, and the wear resistance of the parts will be reduced. 1265℃~1275℃ is the best quenching temperature.

Two preheating is used, the first time is 820℃, and the second time is 1020℃. The heating of parts in vacuum is mainly carried out by means of radiation heat transfer, and the heating speed is slow. The method of high temperature preheating can shorten the heating time, and it is easy to heat evenly during quenching and heat preservation. After the parts are clamped, they are loaded into a special material basket. The furnace load is generally about 7,000 pieces, and the total weight is 115kg (including the weight of the material basket). Preheat at 820°C for 20 minutes, 1020°C for 15 minutes, and 1270°C for 15 minutes. minutes, while properly controlling the heating rate. The heating and holding time should ensure that enough carbides are melted into the austenitic heat without causing excessive grain growth. At a certain temperature, there is an optimum heating time. Excessive heating time will not only no longer increase the alloying degree of austenite, on the contrary, the grains will grow up, which will reduce the mechanical properties of the steel and easily cause the workpiece to be damaged. deformed. If the holding time is too short, the degree of austenite alloying will be insufficient, which will reduce the hot hardness of the parts and affect the hardness uniformity of the parts.

Quenching and cooling adopts air-cooled oil quenching, that is, after the workpiece is transferred to cooling, it is immediately filled with high-purity nitrogen (purity 99.9~99.99%), the pressure is reduced to 7*104Pa, and the workpiece is pre-cooled to below 1000℃ within 90~100s. , and then oil quenched. In this way, the deformation of the parts is reduced, the smoothness of the parts is ensured, and the carbides are not obviously precipitated from the austenite. The hardness of the parts after quenching is 64~65HRC, and the oil temperature is controlled within the range of 30~50℃, and it is stirred.

In order to ensure that the bright and clean surface of the steel needle valve is not damaged after vacuum quenching, so that the workpiece is not oxidized, vacuum tempering is adopted. Tempering is carried out in a vacuum tempering furnace. The mountain is heated very slowly at a low temperature in a vacuum, so nitrogen is backfilled into the furnace during the tempering process, and the pressure is generally 5*104 to speed up the heat transfer rate. We use three tempering process, the first tempering temperature is 350 ℃, holding for 100 minutes, the second is 550 ℃, holding for 90 minutes, the third is 540 ℃, holding 90 minutes. Fully and uniformly tempered, hardness is 63~64HRC

Equipment selection: The VOGQ series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. The good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.