After quenching and tempering has high hardness and wear resistance, but low thermal rigid, hardenability poor, deformation, low ductility and strength. Used needs to have a high hardness and wear resistance of various tools, such as the shape of a simple mold and punch, metal cutting tools, drilling tools, woodworking cutters, cutters, axes, chisels, hand saws longitudinal and fitter assembly tools, riveting die and other minor tools.
● Chemical Composition:
Carbon C: 0.80 ~ 0.90 Si Si: 0.10-0.35
Manganese Mn: 0.10-0.50
Sulfur S: ≤0.030
Phosphorus P: ≤0.030
Chromium Cr: to allow the residual content of ≤0.25, ≤0.10 (bath quenching steel manufacturing lead time)
Ni: to allow the residual content ≤0.20, ≤0.12 (bath quenching steel manufacturing lead time)
Copper Cu: to allow the residual content of ≤0.30, ≤0.20 (bath quenching steel manufacturing lead time)
Note: Allow the residual content of Cr + Ni + Cu≤0.40 (bath quenching steel manufacturing lead time)
● Mechanical Properties: Hardness: annealing, ≤187HB, indentation diameter ≥4.40mm; quenching, ≥62HRC
● Heat treatment and microstructure specifications: Heat Treatment Specification: Sample quenching 780 ~ 820 ℃, water-cooled.
Thermal processing specification: starting temperature of 1000-1050 ℃, end temperature 850 ℃
Quenching specifications: quenching temperature 730-760 ℃, water-cooled, liquid cooled or water-oil double alkali bath cooling, quenching temperature 57HRC. Tempering temperature 160-180 ℃. [1]
● Production Process
Usually available spring steel furnace, open-hearth, or oxygen converter production; better quality or with a special performance of high-quality spring steel, electric furnace or vacuum furnace slag refining. The main provisions of spring steel elements carbon, manganese, silicon and other content narrower, must strictly control the chemical composition of smelting. Easy to form bubbles and other defects at higher silicon content, after cooling wrought ingot was not easy to produce white spots. Therefore, the smelting of raw materials must be dry, try to remove gas and inclusions, but also to avoid superheat. Spring steel surface decarburization and pay special attention to the quality of the rolling process. When the steel surface decarbonization serious, it will significantly reduce the fatigue limit of steel. For high-silicon spring steel as 70Si3MnA, should be taken to avoid graphitization. Thus, when the thermal processing temperature should not stop rolling low (≥850 ℃), easier to avoid the formation of graphitization temperature range (650 ~ 800 ℃) long residence time. Ma made after core spring spring surface by shot peening make residual compressive stress in order to offset part of the work on the surface stress, inhibit the formation of surface cracks, which can significantly increase the fatigue limit of the spring.
