Cleaning:
1. The workpieces and fixtures should be cleaned of oil, residual salt, paint, and other foreign matter before heat treatment.
2. The fixture used for the first time in the vacuum furnace should be degassed and purified in advance at a vacuum level not lower than that required by the workpiece.
Furnace loading:
1. Workpieces that are easily deformed during heat treatment should be heated on a special fixture.
2. The workpiece should be placed in the effective heating zone
Warm-up:
1. For workpieces with complex shapes or sharp changes in cross-section and large effective thickness, preheating should be carried out
2. The preheating methods are: primary preheating is 800℃, secondary preheating is 500~5500℃ and 8500℃. The temperature rise speed of primary preheating should be limited.
heating:
1. Workpieces with grooves and blind holes, castings, and weldments, as well as processed stainless steel workpieces, are generally not suitable for heating in a salt bath furnace.
2. There should be sufficient holding time for heating the workpiece, which can be calculated based on the effective thickness of the workpiece and the conditional thickness (the actual thickness is divided by the shape coefficient of the workpiece)
cool down:
1. When martensitic stainless steel heat-resistant steel is air-cooled, it should be scattered in a dry place
2. Martensitic stainless steel and heat-resistant steel must be quenched and cooled to room temperature before cleaning, cryogenic treatment, or tempering.
3. The workpiece should be tempered in time after quenching. The time interval should generally not exceed 4 hours. If the carbon content (mass fraction of carbon) of the steel used in the workpiece is low and the shape of the workpiece is simple, it should not exceed 16 hours.
4. For welded assemblies composed of martensitic stainless steel and heat-resistant steel, the time interval between welding and subsequent heat treatment should not exceed 4 hours.
Cleanup:
1. According to the requirements and surface conditions of the workpiece, use alkali cleaning, water-soluble cleaning agents, chlorine solvent sandblasting, shot blasting, and other cleaning methods.
2. Generally, pickling is not used for cleaning.
Correction:
1. The workpiece is corrected using static load and is generally not suitable for local knocking.
2. After correction, stress relief annealing should be performed at a temperature lower than the original tempering temperature.
3. For workpieces with complex shapes or strict size requirements, use a shaping fixture combined with tempering to correct after correction.
4. Austenitic stainless steel workpieces should be stress-relieved below 300°C after correction.
Quality inspection:
1. The workpiece shall be inspected according to the items and requirements specified in the corresponding technical documents.
2. When the mechanical properties of the workpiece are unqualified, the heat treatment can be repeated, but the number of repeated quenching or solid solutions generally does not exceed two times. Supplementary tempering of workpieces does not count as repeated processing
3. Martensitic stainless steel and heat-resistant steel workpieces in the quenched state or after low-temperature tempering should be preheated, annealed, or high-temperature tempered before repeated quenching.
4. The original records of heat treatment should be properly kept for future reference.
safety technology:
When heat treating workpieces, the relevant provisions of JB4406-87 “Heat Treatment Safety Technology” must be followed
Post time: Jan-18-2024