90CRSI5 is a high-carbon alloy tool steel with good toughness, good tempering stability, and small deformation during heat treatment. The carbides in the steel are evenly distributed, it is not easy to precipitate carbide nets, and it is easy to eliminate normalizing. Through normalizing, the network and coarse carbide structures can be eliminated. However, the compressive strength and wear resistance are insufficient, and the workability is poor. In the decarburized layer with a residual carbon content of 0.6% -0.7% on the surface of the steel, the overheating sensitivity of the surface layer increases due to the reduction of carbides. After normal heating and quenching, the surface hardness can still reach 60-62HRC, but its flexural strength drops by 40% -50%. The grain size of the surface layer reaches 7 grades, and the core is 10 grades.

 
Purpose of use
It is used to manufacture tools with complex shapes, small deformation, high wear resistance and low speed cutting, such as drill bits, threaded tools, reamers, dies, taps, thread rolling plates and thread rolling wheels. (In the case of plastic mold steel, it can be used for ejecting rods to manufacture plastic films with large dimensions, complex shapes and high precision requirements.
 
Chemical composition
Carbon C: 0.85 ～ 0.95
Silicon Si: 1.20 ～ 1.60
Manganese Mn: 0.30 ～ 0.60
Sulfur S: ≤0.030
Phosphorus P: ≤0.030
Chromium Cr: 0.95 ～ 1.25
Nickel Ni: Allow residual content ≤0.25
Copper Cu: Allow residual content ≤0.30
Hardness: Annealing, 241 ～ 197HB, indentation diameter 3.9 ～ 4.3mm; 187 ～ 229HB (for manufacturing thread tools); quenching, ≥62HRC