Standard (JIS G4404) w /%
Carbon C: 0.90 ~ 1.05
Si Si: ≤ 0.40
Manganese Mn: 0.80 ~ 1.10
Sulfur S: ≤ 0.03
Phosphorus P: ≤ 0.03
Chromium Cr: 0.90 ~ 1.20
Ni: to allow the residual content of ≤ 0.25
Copper Cu: to allow the residual content of ≤ 0.30
Tungsten W: 1.20 ~ 1.60
Mechanical properties:
Hardness: Annealed, 255 ~ 207HB, indentation diameter of 3.8 ~ 4.2mm; quenching, ≥ 62HRC
Heat treatment and microstructure specifications:
Standard heat treatment: quenching, 800 ~ 830 ℃ oil cooling.
Delivery status: delivery of steel in the annealed condition.
Physical properties
Critical point Acl Acm Arl
Temperature (approximate) / ℃ 750 940 710
Thermal processing
SKS31 steel thermal processing are shown in Table 2-13-3.
SKS31 steel thermal processing
Item heating temperature / ℃ start temperature / ℃ termination temperature / ℃ cooling
Steel ingot
Steel billet 1150 - 1200
1100 ~ 1150 1100 ~ 1150
1050 ~ 1100 880 ~ 800
850 to 800 first air-cooled and slow cooling
First air-cooled and slow cooling
In order to reduce or mitigate the carbide network formation, forged as possible after cooling to 650 ~ 700 ℃, and then slow cooling (cold pit, sand cooling or furnace cooling).
SKS31 steel with high hardenability. Since the formation of tungsten carbide in the steel after quenching and tempering of steel with chromium and 9SiCr than the more excess carbon steel and higher hardness and wear resistance. In addition, the tungsten can also help save the small grains, so that the steel is good toughness. Therefore, the cutting tool by the SKS31 steel, less chipping phenomenon, and can better keep the blade shape and size. However, the steel is sensitive to the formation of carbide networks, such networks exist, the tool blade with the danger of falling off, thus shortening the life of the tool, therefore, net carbon steel, must be carried out according to their severity forging and normalizing. The steel used to make at work, cutting edge tools without intense hot and quenching requires no deformation of the measuring and cutting tools, such as making knives, long tap, long reamers, special cutters, die, and other types of special tools, and cutting tool of soft non-metallic materials.
A pre-heat treatment
SKS31 the pre-heat treatment of steel curves shown in Figure 2-13-1 to Figure 2-13-5, before and after annealing phase composition, hardness and microstructure are shown in Table 2-13-4, be noted that: (1 ) annealing holding time in all the charge is heated to annealing temperature of 1 ~ 2h, cooling; isothermal heat of 3 ~ 4h; (2) high-temperature tempering is used to eliminate the cold deformation hardening (as known as recrystallization annealing); eliminate machining before heat treatment stress. After heat treatment the hardness of the low parts in the secondary hardening high-temperature tempering before the insulation is also the first time in full charge after heating to a temperature of 2 ~ 3h; (3) normalizing for the grain refinement of hot steel and eliminate charcoals network; (4) When the steel is lower than 183 HB hardness when annealing, quenching and tempering treatment to improve surface finish machining.
