Cr can increase the hardenability 40Cr seamless steel pipe, improve the strength and stability of tempered steel, with excellent mechanical properties. Large cross-sectional dimension or critical quenching 40Cr seamless, Cr steel should be used. But Cr steel has a second temper brittleness. 40Cr seamless steel pipe tempered quenching and tempering, various parameters have predetermined process card, we realized in practice are:
(1)After quenching 40Cr seamless oil should be cold, 40Cr steel hardenability better cooling can be hardened in oil and 40Cr seamless tube deformation, cracking tendency is small.
(2) After 40Cr seamless quenched hardness is still relatively high, the second tempering temperature will increase 20 ~ 50 ℃, otherwise, hardness decreased difficult.
(3) After tempering 40Cr seamless, complex shape in oil cooling, simple water cooling, in order to avoid a second temper brittleness of. 40Cr seamless steel pipe rapid cooling after tempering, if necessary, and then subjected to stress relieving treatment.
Effect of quenching 40Cr seamless quality, operator level is an important factor, at the same time, there are many reasons for equipment, materials and neuromodulators before processing:
(1) 40Cr seamless transfer from the furnace to the cooling tank slowly, 40Cr seamless tube into the water temperature has dropped below Ar3 critical point, resulting in partial decomposition, 40Cr seamless obtain incomplete hardening organization, reach hardness. So small parts to pay attention to the speed of the cooling liquid, large 40Cr seamless to the cold time to master.
(2) 40Cr seamless tube installed furnace capacity to be reasonable and appropriate level of 1 to 2, 40Cr seamless overlap caused by uneven heating, resulting in uneven hardness.
(3) 40Cr seamless tube into the water arrangement should maintain a certain distance, too close so 40Cr seamless Vicinity vapor membrane rupture blocked, resulting in low 40Cr seamless proximity surface hardness.
(4) Furnace quenching, can not breath after quenching, the degree of decline in the furnace should be considered, midway closed furnace to heat up again, in order to be consistent hardness after quenching 40Cr seamless.
(5) Note that the coolant temperature, 10% brine temperature such as higher than 60 ℃, can not be used. Coolant can not have oil, mud and other impurities, otherwise, there will be insufficient hardness or unevenness.
(6) Unprocessed blank quenching, hardness is not uniform, such as to get good quality quenched and tempered, blank should be rough, bar to forging.