5CrNiMo Steel Heat Treatment Process

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5CrNiMo steel is developed by adding Cr.Ni.Mo on the basis of medium carbon steel.1.5 characteristics of CrNiMo steel.

(1) The carbon content of 5CrNiMo steel is maintained at 0.40% ~0.60%, which can obtain high strength and heat resistance fatigue strength, -fixed hardness and wear resistance, good toughness and heat conduction.

(2) The addition of Cr.Ni.Mo element in 5CrNiMo steel is mainly to improve the hardenability of steel, especially when combined, the hardenability of steel increases greatly.For example, the mold of 300mm* 300mm* 400mm can be quenched thoroughly.At the same time, the three elements were dissolved in iron to strengthen the solution.

(3).In addition to Ni, Cr.Mo element in 5CrNiMo steel can also be dissolved in Fe3C to form (fe.cr.mo)3C, which can improve the hardness and wear resistance of steel.Ni can also strongly improve the toughness and heat resistance fatigue of steel.

(4) M0 element in 5CrNiMo steel can reduce tempering brittleness and refine grain.

(5) Tempering stability of linden steel with Cr.Mo element.

6) The combined action of Cr. Ni makes steel produce antioxidant and corrosion resistance.

(7) When 5CrNiMo steel is quenched, the three elements Cr. Ni. Mo are solidly dissolved in austenite to improve the hardenability of steel.After quenching, the three elements were dissolved in the matrix, which strengthened the matrix and improved the tempering stability of the matrix.During tempering, Cr. Mo element was precipitated by 3C carbide (Fe. Cr. Mo) except Ni.Due to the high tempering temperature and long time required for the precipitation and aggregation of carbides, the thermal stability or heat resistance of steel is formed.The precipitated (fe.cr.mo) 3C carbide and a small amount of the undissolved Mo element carbide during quenching, and then strengthen the matrix structure with good toughness, so that the steel at a certain temperature and maintain a fixed strength, hardness and wear resistance.

(8) a small amount of carbide of Mo element not dissolved in 5CrNiMo steel during quenching prevents the growth of austenite grain, plays a role in refining grain, and makes the steel yield “good strength and toughness.2.5 main chemical components of CrNiMo steel.
0.40% ~ 0.60% C. 0.40% or less Si. 0.50% ~ 0.80% Mn. 0.50% ~ 0.80% Cr. 0.15% ~ 0.30% Mo, 1. 40% ~ 1.80% Ni. S0.030 % P, S 0.030% or less.

Heat treatment of CrNiMo steel
The phase transition points of 5CrNiMo steel are: AC1730°C, Ac3780*C, Ar1680°C . Ms210°C.

The initial forging temperature of 5CrNiMo steel is 1050~1100C, the final forging temperature is 800~850°C, and it is cooled in the pit or in the sand after forging.Common heat treatment process of 5CrNiMo steel

The hardness of heat treatment process parameters requires the process characteristics
Ordinary annealing heating 760~780°C, 4h insulation, furnace cooling to 500°C below the air cooling 197~241HBS Ac1710°C, Ac3770°C, heating temperature above Ac3 line, pearlite structure + block ferrite.

Isothermal annealing heating 850~870°C, heat preservation 3h, 650~680°C isothermal.The temperature was kept for 5 hours, and the furnace was cooled to below 550°C, 197~241HBS AC1710°C, ac3770% C, the heating temperature was above the Ac3 line, and the isothermal temperature was lower than Ar1680°C, so as to obtain pearlite + ferrite structure.

De-stress annealing heating 710~730C, heat preservation 3h, furnace cold to 550°C below the air cooling 197~255HBS to eliminate residual stress, eliminate work hardening.

Quenching heating 820~850° c. heat preservation, oil cooling to 150~180°%, oil output, tempering immediately 54~58HRC heating cr.mn. Si. Ni element and Mo element carbide into the austenite, improve the hardenability, improve the tempering stability.

Heat 880~900°C, oil to 150~180°C, oil output, immediately temper.Tempering for 2h at 420~550°C.Tempering hardness 38~47HRC 62HRC raise the temperature.It is beneficial to improve the hardness and permeability, improve the hardness of martensite, and increase the wear resistance.Secondary tempering medium forging die: heating 520~540*C, holding for 2h, oil cooling, secondary tempering.

Large forging die: heating 560~580°C, holding for 2 hours, oil cooling.Secondary tempering 44~47HRC38~42HRC.
Tempering at a high temperature of 34~37HRC, carbide precipitates out and accumulates.The working part of the tempering temperature some, to maintain high hardness.Enhance wear resistance.The tempering temperature of swallowtail part is higher, which is beneficial to maintain high toughness and prevent the crack of swallowtail part.

Swallowtail part small forging die: heat 640-660c. Heat preservation for 2h, oil cooling.Secondary tempering medium forging die: heat 620~640°C, heat preservation 2h, oil cooling.Secondary tempering 34~37HRC, 31~35HRC.
The lower bainite isothermal quenching was heated to 840~860%C, 160~ 180*C nitrate bath classification, then transferred to 280~300°C nitrate bath isothermal 2h 48~54HRC Ms230C.The thermal stress in the high temperature stage and the phase change stress in the low temperature stage are reduced, and the deformation and cracking are reduced.Avoid the formation of quenching cracks.
Heating 840~860C, oil cooling to about 200°C, oil output, into 280~300°C nitrate bath isothermal 2h.
Heating liquid chromizing at 950°C, holding for 4h, oil cooling.Permeability;15%Cr203+12.5% rare-earth silica-magnesium +72.5% borax 1498HV layer thickness: 0.0081mm. Improved surface hardness, wear resistance and corrosion resistance.
Chromium-vanadium co-osmosis heating 1050°C, 5h insulation, air cooling.Infiltration agent: 50% fe-cr + 43%Al203+ 2%NH4C1+5%V powder 2125HV infiltration layer thickness: 0.020mm. Improve the surface hardness, wear resistance and corrosion resistance.