1. Carbon steel and low alloy steel (45, T7 has, T8, etc.)
The calculating formula of the traditional carbon steel quenching heating time:
T = k. alpha D (1)
The type of T as the heating time min;
To reflect the status of furnace charging correction coefficient K, usually in the range of 1.0 ~ 1.3 selection;
Alpha for heating coefficient, generally in 0.7 ~ 0.8 mm/min; D for the effective thickness of workpieces.
In actual production, in general, according to the experience and artifacts effective thickness (mm) to calculate the heat preservation time. Such as effective thickness of some 45 # steel workpiece is 60 mm, in air furnace heating quenching heat preservation time is about furnace temperature to the temperature insulation again after 60 min, namely artifacts per 1 mm thickness of effective heat 1 min, this is for a single heat. For mass production, a batch of loading many artifacts, only according to the practical experience to extend the time of heat preservation or through the peephole, observing workpiece burn after appearing again insulation must be asked. Experience has shown that if according to law, 369, for carbon steel, heat preservation time and only 30% of the original traditional heat preservation time. Using box-type furnace heating, for example, 660 mm diameter of 45 steel workpiece, the heat preservation time and need to 60 min x 30% = 20 min.
2. The alloy structural steel (40 cr, 40 MNB, 35 crmo)
For added some alloying elements in the alloy constructional steel and in the process of heat insulation for the carbide homogenization will take time. According to the laws of the 369 alloy structural steel heat insulation can be asked of 60% of the original traditional heat preservation time. For example with the traditional formula of 40 cr insulation when asked if for 100 min, according to the laws of the 369 new insulation when ask for: 100 min x 60% = 60 min.
3. High alloy tool steel (9 sicr, CrWMn, Crl2MoV, W6, project.it, etc.)
For all the steel alloy element content is higher, carbide alloy is more, so need longer time of heat preservation, make its uniformity. The laws of 369 between the traditional heat preservation heat preservation time is 90%.
4. Special performance steel (stainless steel, heat-resistant steel, wear-resistant steel, etc.)
Law of 369 in the steel can be calculated according to the formula of alloy tool steel. Which in the traditional formula of heat insulation time by 90% as a thermal insulation when asked.
5. Preheat the quenching
For large workpiece (effective diameter of 1 m or more) of modified treatment weeken the preheating heat preservation law of 369 asked for
The T1 = 3 d (2)
T2 = 6 d (3)
T3 = 9 d (4)
Type: T1 for preheating time/h for the first time;
T2 for a second heat q/h;
T3 for the final time of heat preservation/h;
D is the thickness/m artifacts.
For phi 475 ~ 1030 mm diameter of large forgings, quench heating when there should be a primary or secondary heating insulation, and the ladder when heated, the maximum temperature difference appears in 400 ~ 560 ℃ and 800 ~ 850 ℃, in the temperature range of heat preservation time applies to preheat the 369 law of hardening. The actual production proves that the furnace for air heating of small and medium-sized parts effective size (500 mm) or less, preheat and heat holding time can be calculated at 369 law.
Second, the 369 law of vacuum heating insulation
The traditional calculation formula of vacuum furnace heating insulation when asked as shown below
T1 = 30 + (1.5 ~ 2) D (5)
T2 = 30 + (1.0 ~ 1.5), D (6)
T3 = 20 + (0.25 ~ 0.5), D (7)
Type: D for artifacts effective thickness/m;
T1 for the first time the preheating time/min;
T2 for a second preheating time/min;
T3 insulation for the final time/min.
Holding time is related to the size of the furnace charging quantity, vacuum furnace heating and heat preservation time of furnace volume, the empirical formula of the relationship between effective factors such as the thickness of workpiece are as follows:
T true 1 = T = 2 T really 3 = o. 4 x G (kg) + D (mm) (8)
Type: G for furnace charging workpiece turnning/kg, other symbolic meaning and before all the same. The type is based on furnace charging quantity in 100 ~ 200 kg, workpiece size around 100 mm.
Workpiece size basic same, neat, and had certain gap (gap put < D), press type calculation of:
G 300 kg or less: T true 1 = T = 2 T really 3 = 30 + D (9)
G = 301-301 kg; T really 1 T true 2 = T = 3 = (30-60) + D (10)
G = 601-900 kg, T true l = T 2: T really 3 = (60-90) + D (11)
G or 901 kg: T true 1 = T = 2 T really 3 = 90 + D (12)
Type: G for furnace charging, the total weight including artifacts, basket, rack and all of the raw material weight (kg);
D for the effective diameter workpiece/mm).
For the strict deformation of mould, because the vacuum furnace at low temperature heat transfer speed is slow, heating insulation for the first time, if the time is too short workpiece surface and center of the temperature difference is too big, may cause thermal stress deformation. As a result, the preheating time should be take upper limit for the first time, in the second preheating take limit, the final heat treatment to remove the limit. For ordinary alloy structural steel workpiece or workpiece deformation is not too strict, preheating time can remove the limit for the first time, and took a ceiling in the final heat. For once a large workpiece, only because of its heated evenly, heat faster, better through burning, the first and second preheating can take lower limit, when heated, finally, take the limit or cap according to the actual requirement. Such not only guarantee the quality of the workpiece after heat treatment requirements, also save the heating time, greatly reduces the cost of production.