Method for making an abrasion-resistant steel plate

Method for producing a workpiece of steel which is resistant to abrasion and whose chemical composition comprises, by weight:

• 0.35%≦C≦0.8%
• 0%≦Si≦2%
• 0%≦Al≦2%
• 0.35%≦Si+Al≦2%
• 0%≦Mn≦2.5%
• 0%≦Ni≦5%
• 0%≦Cr≦5%
• 0%≦Mo≦0.50%
• 0%≦W≦1.00%
• 0.1%≦Mo+W/2≦0.50%
• 0%≦B≦0.02%
• 0%≦Ti≦2%
• 0%≦Zr≦4%
• 0.05%≦Ti+Zr/2≦2%
• 0%≦S≦0.15%
• N<0.03%
• optionally from 0% to 1.5% of copper,
• optionally at least one element selected from Nb, Ta and V at contents such that Nb/2+Ta/4+V≦0.5%,
• optionally at least one element selected from Se, Te, Ca, Bi, Pb at contents which are less than or equal to 0.1%,
• the balance being iron and impurities resulting from the production operation, the chemical composition further complying with the following relationships:
• 0.1%≦C−Ti/4−Zr/8+7×N/8≦0.55%
• and:
• Ti+Zr/2−7×N/2≧0.05%
• and:
• 1.05×Mn+0.54×Ni+0.50×Cr+0.3×(Mo+W/2)1/2+K>1.8
• with K=0.5 if B≧0.0005% and K=0 if B<0.0005%, according to which the workpiece is subjected to a thermal quenching processing operation which is carried out in the heat for forming in the hot state, or after austenitization by reheating in a furnace in order to carry out the quenching, the process comprising:
• cooling the workpiece at a mean cooling rate greater than 0.5° C./s between a temperature greater than AC3 and a temperature of from T=800−270×C*−90×Mn−37×Ni−70×Cr−83×(Mo+W/2), with C*=C−Ti/4−Zr/8+7×N/8, to T−50° C.,
• then cooling the workpiece at a core cooling rate Vr<1150×ep−1.7 and greater than 0.1° C./s between the temperature T and 100° C., ep being the thickness of the plate expressed in mm,
• cooling the workpiece as far as ambient temperature.