CN107009094B - The strong high temperature resistant magnesium alloy shell part forging rolling of major diameter superelevation integrates preparation process - Google Patents

Abstract

The invention discloses the strong high temperature resistant magnesium alloy shell part forging rollings of major diameter superelevation to integrate preparation process.Process route is:Semicontinuous electromagnetic casting is machined into ingot blank, homogenizing annealing, multidirectional flat-die forging, machine drilling, ring-rolling and T6 heat treatments.Prepared housing component size is 600 1700mm of outer diameter φ, 35 100mm of wall thickness, 300 700mm of height, and T6 states room temperature is tangential, high to tensile strength >=470MPa, and when elongation >=5%, 200 DEG C is tangential, high to tensile strength >=350MPa, elongation >=7%.The product that the present invention prepares has the features such as large scale, flawless, the room temperature intensity of superelevation and excellent heat resistance, and qualified magnesium alloy shell part can be provided for fields such as aerospaces.

Description

The strong high temperature resistant magnesium alloy shell part forging rolling of major diameter superelevation integrates preparation process

Technical field

The present invention relates to the deformation fields of magnesium alloy, the more particularly to forging deformation and ring of Mg-Gd-Y-Zr magnesium-rare earths Roll deformation field.

Technical background

The structural member important as aerospace field, major diameter housing component are generally prepared by aluminium alloy.But in view of above-mentioned There are urgent loss of weight demands in field, and part aluminium casing part is substituted with the smaller magnesium alloy of density, disappear for reducing fuel Consumption, promotes the speed and flying distance of aircraft, significant.But have using the housing component of magnesium alloy processability qualification Certain difficulty.The special operating environment requirements structural member mechanical property of aircraft is up to standard, heat-resist.But exploitation more at Ripe traditional magnesium alloy, such as Mg-Al-Zn systems, Mg-Zn-Zr systems, generally existing mechanical property is relatively low, and heat resistance difference etc. lacks Point is difficult with the housing component of above-mentioned magnesium alloy processability qualification.Studies have shown that adding rare earth element such as into magnesium alloy Gd, Y, Nd, the alloy systems such as Mg-Gd-Y-Zr designed, can make magnesium alloy obtain very high even superelevation mechanical property and Excellent heat resistance.But rare earth also improves its resistance of deformation while improving magnesium alloy strength and heat resistance, reduces The temperature and velocity window of suitable deformation.Moreover, the special close-packed hexagonal structure of magnesium alloy causes it to be easy in deformation Strong texture is generated, this can limit its ability for continuing deformation.These factors make it difficult to prepare with superhigh intensity, height The magnesium alloy shell part of heat resistance.

Invention content

The purpose of the present invention is provide to cut for the Mg-Gd-Y-Zr housing components with major diameter superhigh intensity high heat resistance Real feasible moulding process, to meet the needs of aerospace field is to high-strength heat-resistant magnesium alloy housing component.It is proposed by the present invention Technique is as follows：

1. preparing magnesium alloy ingot using semicontinuous electromagnetic casting method, specification is φ 340-630mm, length >=2000mm Ingot blank, ingot casting cast after immediately at 150-300 DEG C keep the temperature 12-16h stress relief annealings.

2. keeping the temperature 15-25h at 480-540 DEG C carries out Homogenization Treatments, room temperature is then cooled to the furnace.

3. pair ingot casting carries out railway carriage, flaw detection, sawing machine blanking, it is φ 320-600mm to obtain size, length 800-1200mm's Cylindrical ingot blank.

4. carrying out 10-16h heat preservations to blank in 450 DEG C of -530 DEG C of temperature ranges before forging, and to upper and lower flat anvil in 250- 350 DEG C of temperature ranges are heated；Blank holding temperature is excessively high, has the danger of burning, holding temperature is too low, is easy to cause out It splits, and dynamic recrystallization is less likely to occur.The reason of 450-530 DEG C of selection keeps the temperature blank is that this temperature range both avoided Burning is dangerous, in turn ensures the deformability of alloy, promotes its that dynamic recrystallization, crystal grain thinning occurs.And due to being freely Forging, forging expose in air, and temperature constantly reduces, so needing heated block to keep the temperature forging.Chopping block temperature is too low, no Good heat insulation effect can be played, and chopping block is heated to very high temperature then time consumption and energy consumption, increases process.Chopping block is heated to 250-350 DEG C, preferable heat insulation effect can be not only played, but also is easy to fast implement, improves production efficiency.

5. carrying out 6-10mm/s multi-pass multiway forgings at a slow speed on vertical hydraulic press；Detailed process is:With cylindrical base Material it is high to, arbitrary two vertical radial directions be respectively Z, Y and X-direction.First along Z, Y and X-direction carry out 3-6 passage jumping-ups, Pass deformation is 20-40%, and cylinder blank is pressed into 6 face bodies；Then using a direction in Y or X as axis, compression rib is rolled 6 face bodies are pressed into the faces 10-18 body by angle 2-6 passages, single pass heavy deformation 10-20%；Finally erect jumping-up, drafts 20-40%, It is pressed into approximate cylinder；440-520 DEG C of annealing heat preservation 0.5-2h is melted down, with the height of new cylinder to two after taking-up Arbitrary vertical radial direction is respectively Z, and Y and X-direction repeat above-mentioned forging and intermediate annealing process 1-2 times, and final jumping-up obtains height The approximate cylindrical blank of 300-700mm is spent, it is air-cooled.Forging method in the present invention, in addition in Z, tri- directions Y, X carry out more Passage aximal deformation value forging deformation, other than effective crystal grain thinning.Also using Y or X as axis, compression corner angle are rolled.This mode can Forging surface is enough allowed to obtain enough deflections, and the strong texture that aximal deformation value is brought before can effectively weakening so that forging The deformation of part internal and external parts is uniform, anisotropy very little.Compression corner angle passage is very few or pass deformation is too small, and surface is difficult to obtain Sufficient deformation is obtained, the effect for weakening texture is also bad；It is excessive to compress corner angle passage, forging cooling is apparent, is easy cracking, passage Deflection is excessive, then easy tos produce new texture.Corner angle 2-6 times, pass deformation 10-20% are compressed in the present invention, are ensureing to close Under the premise of gold is indehiscent, surface is made to obtain deflection as much as possible, while strong caused by aximal deformation value before weaken again Strong texture.When forging temperature is too low, need to carry out intermediate annealing to it.Intermediate anneal temperature is excessively high or soaking time is long, Crystal grain is easy excessively to grow up, and damages mechanical property；Annealing temperature is too low or the time is too short, bad to the heat insulation effect of forging, becomes Forging is easy cracking when shape.Intermediate annealing system in the present invention, forging still retains one after making full use of every fire time forging The characteristics of constant temperature is spent, each intermediate annealing suitably reduce temperature, while realizing fully heat preservation to forging, avoid because of temperature The problem of excessive grain caused by excessively high is grown up.

6. the machine drilling at ingot blank center, pore size φ 200-280mm.

7. rolling into shape to one fire time of ingot blank progress or more fiery secondary rings on looping mill, ingot blank is kept the temperature for 460-530 DEG C before looping mill rolling 4-6h, preheating drive roll, embrace roller and upper and lower cone roller at core roller.Drive roll rotating speed is 8-30r/min, the feed of core roller straight line when rolling Speed 0.2-2.0mm/s, upper cone roller along rolled piece height to apply 2-10mm deflections, 250-300 DEG C of roller temperature；Per fire time rolling 450-520 DEG C of heat preservation 0.5-2h is melted down after deflection 20%-60%, rolling；It is deformed, is prepared using the looping mill rolling of different fire time The magnesium alloy shell part of outer diameter φ 600-1700mm, wall thickness 35-100mm, height 300-700mm, are air-cooled to room temperature.It prepares big straight Deflection is big needed for diameter housing component, and deformation time is long, is difficult molding using a fire time looping mill rolling, utilizes more fire time looping mill rollings, equilibrium point With every fire time deflection, molding easy to implement, but intermediate annealing causes crystal grain to be grown up, and can be damaged to performance.Using 450- The intermediate annealing process of 520 DEG C of heat preservation 0.5-2h, and heat preservation is low 10 DEG C more primary than preceding every time, both ensures heat penetration, makes rolled piece It is not easily susceptible to cracking, and inhibits excessively growing up for crystal grain, ensure that mechanical property.Applying height using cone roller when looping mill rolling can to deflection The defects of to avoid generation " fish tail ", but height becomes complicated to the excessive rolled piece stress state that also results in of deflection, magnesium alloy tool There are close-packed hexagonal structure, complicated stress state to easily lead to its cracking, both may be used to the small deformation amount for applying 2-10mm in height With elimination " fish tail " defect, and avoid stress state complex that rolled piece is made to crack.

8. carrying out T6 processing to housing component after forming：Solid solution treatment process is 350-450 DEG C of heat preservation 30-120min, is used Solid solution system in the present invention, the variation of the T4 state strengths of materials is little, and elongation percentage but increases substantially.Then hold higher than this processing range Easily excessive grain is caused to be grown up, damage intensity, then causes the effect for eliminating processing hardening bad less than this range, elongation percentage is promoted Unobvious；Institution of prescription is 200-250 DEG C of heat preservation 10-72h, and aging temp is excessively high or overlong time, and it is excessive to decompose phase size, by force Change effect is bad, and aging temp is too low or the time is too short, long the time required to reaching peak value timeliness, influences production efficiency, strengthens Effect is also restricted.Institution of prescription using the present invention, it is shorter the time required to reaching peak value timeliness, it is also very aobvious to strengthen effect It writes.The T6 heat treating regimes of solution treatment+timeliness in the comprehensive utilization present invention so that housing component has the intensity and Gao Yan of superelevation Malleability.

In the step 4 before multiway forging 480-520 DEG C heat preservation blank 10-14h, in 300-350 DEG C of heated block.

3-6 passage jumping-ups are carried out first along Z, Y and X-direction in the step 5, pass deformation 30-40% will justify Cylindrical workpiece is pressed into 6 face bodies；Then using Y or X as axis, compression corner angle 4-6 passages, pass deformation 15-20%, by 6 face bodies are rolled It is pressed into the faces 14-18 body；Intermediate annealing process is 470-510 DEG C of heat preservation 0.5-1.5h, and intermediate anneal temperature is more primary than preceding every time Low 10 DEG C.

Keep the temperature ingot blank 4-6h in the step 7 at 480-520 DEG C before ring-rolling, when rolling cone roller along rolled piece height to applying Add 2-4mm drafts, intermediate annealing process is 470-510 DEG C of heat preservation 0.5-2h, and heat preservation reduces by 10 than a preceding temperature every time DEG C, finally prepare the housing component that maximum gauge is φ 1700mm.

Solution treatment system is 410-430 DEG C of heat preservation 45-90min in the step 8, and institution of prescription is 210-230 DEG C of guarantor Warm 10-20h.

The main advantages of the present invention

1. pair ingot casting carries out hammer cogging, for the first time using the mode of texturing for rolling compression corner angle, both so that surface of ingot blank Enough deflections are obtained, and are effectively eliminated along Z, the strong texture that Y and X-direction large deformation are brought becomes for subsequent looping mill rolling Shape provides that each position distortions are uniform, the small high-quality forging stock of anisotropy, the strong guarantee success of looping mill rolling.

2. when looping mill rolling by accurately control cone roller along it is high to drafts, both eliminated " fish tail " defect, in turn avoid because Problem of Cracking caused by rolled piece stress complicates；And by using more fire time looping mill rollings, deflection of the equilibrium assignment per fire time and Each intermediate annealing successfully prepares maximum outside diameter φ 1700mm, mechanical property is excellent for the first time than the preceding primary mode for reducing by 10 DEG C Different annular element.

3. by carrying out T6 heat treatment process to rolled piece, to make which give room temperatures tangential, high to tensile strength >=470MPa, It is tangential when elongation >=5%, 200 DEG C, high to tensile strength >=350MPa, the excellent mechanical performance of elongation >=7%.

Description of the drawings

Fig. 1 is the semicontinuous ingot casting figures of φ 450mm used in the present invention；

Fig. 2 is the approximate cylinder forging stock figure of the height 330-500mm prepared by the present invention；

Fig. 3 is the strong high temperature resistant magnesium alloy shell part figure of major diameter superelevation that the present invention prepares.

Specific implementation mode

Embodiment 1

Diameter phi 400mm, long 2500mm, composition Mg-9.20Gd-2.90Y- are prepared first with semicontinuous electromagnetic casting 0.20Ag-0.05Er-0.39Zr (wt.%) ingot casting keeps the temperature 14h stress relief annealings at 225 DEG C, is machined into after casting The ingot blank of diameter phi 380mm, length 800mm, 520 DEG C of heat preservation 15h carry out homogenizing annealing.Hammer cogging, forging are carried out to ingot casting Preceding 490 DEG C of heat preservations ingot blank 10h is made, upper and lower flat anvil is heated to 350 DEG C, 10mm/s is carried out at a slow speed to ingot blank on Vertical Oil press Multi-pass forging deformation, detailed process are：With cylinder blank height to, arbitrary two vertical radial directions be respectively Z, Y and the side X To；First along Z, Y and X-direction carry out 6 passage jumping-ups, and cylinder blank is pressed into 6 face bodies by pass deformation 30%；Then Using Y or X as axis, compression 4 passage of corner angle is rolled, 6 face bodies are pressed into 14 face bodies by pass deformation 20%；Jumping-up is finally erected, is pressed Lower amount 25%, is pressed into approximate cylinder.Melt down 480 DEG C of heat preservation 1h.With the high to arbitrary vertical of new cylinder after coming out of the stove Two radial directions are Z, and Y and X-direction repeat above-mentioned forging technology, the approximate cylinder that height is 330mm are finally pressed into, after forging It is air-cooled to room temperature.The machine drilling at blank center, pore size φ 260mm.480 DEG C heat preservation 6h after, on milling train to ingot blank into The fiery secondary ring of row one rolls into shape, and drive roll rotating speed is 10r/min when rolling, core roller straight line feeding rate 0.4mm/s, cone roller along it is high to Drafts is 2mm, rolling reduction 54%, and 250 DEG C of roller temperature rolls out outer diameter φ 941mm, height 328mm, wall thickness 74mm Housing component, be air-cooled to room temperature.T6 processing is carried out to housing component, solution treatment system is 430 DEG C of heat preservation 1h, then at 210 DEG C Carry out 48h timeliness heat preservations.T6 state tensile mechanical properties are listed in table 1.

Embodiment 2

Diameter phi 450mm, long 2500mm, composition Mg-8.92Gd-2.23Y- are prepared first with semicontinuous electromagnetic casting 0.28Ag-0.12Er-0.36Zr (wt.%) ingot casting is machined into as shown in Figure 1, keeping the temperature 16h stress relief annealings at 200 DEG C Diameter phi 420mm, length are the ingot blank of 1075mm, and the homogenizing annealing of 490 DEG C of heat preservation 20h is carried out to ingot blank.Ingot casting is carried out Hammer cogging, the preceding 520 DEG C of heat preservations ingot blank 10h of forging, upper and lower flat anvil are heated to 325 DEG C, carry out 6mm/s's on Vertical Oil press Multi-pass forging deformation at a slow speed, detailed process are as follows：With cylinder blank height to, arbitrary two vertical radial directions be respectively Z, Y And X-direction；First along Z, Y and X-direction carry out 3 passage jumping-ups, and cylinder blank is pressed into 6 faces by pass deformation 40% Body；Then using Y or X as axis, compression 6 passage of corner angle is rolled, 6 face bodies are pressed into 18 face bodies by pass deformation 20%；Finally erect Jumping-up, drafts 20% are pressed into approximate cylinder.Melt down 510 DEG C of heat preservation 0.5h.With the high to appointing of new cylinder after coming out of the stove Two vertical radial directions of meaning are Z, and Y and X-direction repeat above-mentioned forging technology.500 DEG C of heat preservation 1h are melted down after forging, after coming out of the stove Above-mentioned forging technology is repeated, the approximate cylinder that height is 490mm is finally pressed into, is air-cooled to room temperature.It is mechanical at ingot blank center Perforation, pore size φ 265mm.After 510 DEG C of heat preservation ingot blank 6h, looping mill rolling forming twice is carried out to ingot blank on looping mill.When rolling Drive roll rotating speed is 12r/min, core roller straight line feeding rate 0.2mm/s.First time looping mill rolling deflection is 20%, cone roller along it is high to Drafts is 3mm, and roller temperature is 250 DEG C.First time looping mill rolling terminates 500 DEG C of heat preservation 1h of laggard stove, second of looping mill rolling deflection Be 55%, cone roller along it is high to drafts be 3mm, roller temperature is 280 DEG C, rolls out outer diameter φ 1200mm, height 484mm, wall thickness The housing component of 60mm, is air-cooled to room temperature.It is specific in kind referring to the left sides Fig. 3.T6 processing is carried out to housing component, solution treatment system is 410 DEG C of heat preservation 2h, institution of prescription are 225 DEG C of heat preservation 12h.T6 state tensile mechanical properties are listed in table 1.

Embodiment 3

Diameter phi 450mm, long 2500mm, composition Mg-8.71Gd-2.64Y- are prepared first with semicontinuous electromagnetic casting 0.25Ag-0.12Er-0.35Zr (wt.%) ingot casting keeps the temperature 14h stress relief annealings at 250 DEG C, is machined into diameter phi 420mm, length are the ingot blank of 1075mm, 500 DEG C of heat preservation 15h homogenizing annealings.Hammer cogging is carried out to ingot casting, by ingot before forging Base keeps the temperature 12h at 510 DEG C, heats flat anvil up and down and then carries out the forging multidirectional at a slow speed of 8mm/s on Vertical Oil press to 300 DEG C It makes, detailed process is as follows：With cylinder blank height to, arbitrary two vertical radial directions be respectively Z, Y and X-direction；First along Z, Y and X-direction carry out 4 passage jumping-ups, and cylinder blank is pressed into 6 face bodies by pass deformation 35%；Then using Y or X as axis, Compression 4 passage of corner angle is rolled, 6 face bodies are pressed into 14 face bodies by pass deformation 15%；Finally erect jumping-up, drafts 20%, by it It is pressed into approximate cylinder.Melt down 510 DEG C of heat preservation 1.5h.With the high to arbitrary two vertical radial directions are of new cylinder after coming out of the stove Z, Y and X-direction repeat above-mentioned forging and annealing process 2 times, are finally pressed into the approximate cylinder that height is 500mm, forging terminates After be air-cooled to room temperature, specific material object is shown in 7# in Fig. 2.The machine drilling at blank center, pore size are φ 270mm.490 DEG C of heat preservations After ingot blank 6h, shape is rolled into ingot blank 3 secondary rings of progress on looping mill.Drive roll rotating speed is 16r/min when rolling, and core roller straight line is given Into speed 0.2mm/s.First time rolling reduction is 20%, and cone roller is 2mm to drafts along height, and roller temperature is 270 DEG C, the Looping mill rolling terminates to melt down 480 DEG C of heat preservation 1h.Second rolling reduction is 42%, cone roller along it is high to drafts be 3mm, roll 290 DEG C of temperature, second of looping mill rolling terminate to melt down 470 DEG C of heat preservation 1.5h.Third time rolling reduction is 42%, and cone roller is along high to pressure Lower amount is 3mm, and 300 DEG C of roller temperature rolls out outer diameter φ 1700mm, wall thickness 35mm, and the housing component of height 492mm is air-cooled to Room temperature.It is specific in kind referring to the right sides Fig. 3.T6 processing is carried out to housing component, solution treatment system is 410 DEG C of heat preservation 1.5h, timeliness work Skill is 230 DEG C of heat preservation 12h.T6 state tensile mechanical properties are listed in table 1.

Magnesium alloy shell part mechanical property in 1 embodiment of table

Claims (5)

1. the strong high temperature resistant magnesium alloy shell part forging rolling of major diameter superelevation integrates preparation process, alloy mass percentage composition is：Gd： 8.0-9.6%, Y：1.8-3.2%, Gd content and the ratio of Y contents are：3≤Gd/Y≤5, Zr：0.3-0.7%, Ag：0.02- 0.5%, Er：0.02-0.3%, Ag content and the ratio of Er contents are：1≤Ag/Er≤3, impurity include Fe, Si, Cu, Ni and its His inevitable impurity element, wherein Fe≤0.02%, Si≤0.02%, Cu≤0.005%, Ni≤0.003%, content of impurities No more than 0.1%, remaining is Mg, specifically includes following steps：

A, magnesium alloy ingot is prepared using semicontinuous electromagnetic casting method, specification is φ 340-630mm, the ingot of length >=2000mm Base, ingot casting keep the temperature 12-16h stress relief annealings at 150-300 DEG C immediately after casting；

B, 15-25h is kept the temperature at 480-540 DEG C and carry out Homogenization Treatments, then cool to room temperature with the furnace；

C, railway carriage is carried out to ingot casting, flaw detection, sawing machine blanking, it is φ 320-600mm, the cylinder of length 800-1200mm to obtain size Shape ingot blank；

D, 10-16h is kept the temperature to blank at 450 DEG C -530 DEG C before multiway forging, upper and lower flat anvil is heated, control temperature exists 250-350℃；

E, the multidirectional flat-die forging of multi-pass, detailed process are progress 6-10mm/s at a slow speed on vertical hydraulic press:With cylindrical base Material it is high to, arbitrary two vertical radial directions be respectively Z, Y and X-direction；First along Z, Y and X-direction carry out 3-6 passage jumping-ups, Pass deformation is 20-40%, and cylinder blank is pressed into 6 face bodies；Then using Y or X as axis, compression corner angle 2-6 passages are rolled, 6 face bodies are pressed into the faces 10-18 body by single pass heavy deformation 10-20%；Jumping-up is finally erected, drafts 20-40% is pressed into justifying Cylinder；440-520 DEG C of annealing heat preservation 0.5-2h is melted down, with the high to two arbitrary vertical radial directions of new cylinder after taking-up Respectively Z, Y and X-direction repeat above-mentioned forging and intermediate annealing process 1-2 times, and final jumping-up obtains the circle of height 300-700mm Cylinder blank, it is air-cooled；

F, the machine drilling at ingot blank center, pore size φ 200-280mm；

G, shape is rolled into one fire time of ingot blank progress or more fiery secondary rings, keeps the temperature ingot blank 4-6h for 460-530 DEG C before looping mill rolling, preheating is actively Roller, embraces roller and upper and lower cone roller at core roller；Drive roll rotating speed is 8-30r/min, core roller straight line feeding rate 0.2-2.0mm/ when rolling S, cone roller is along high to application 2-10mm drafts, 250-300 DEG C of roller temperature, per fire time rolling reduction 20%-60%；Rolling knot 450 DEG C of -520 DEG C of heat preservation 0.5-2h are melted down after beam；Using the rolling deformation of primary or more fire time, outer diameter φ 600- are prepared The magnesium alloy shell part of 1700mm, wall thickness 35-100mm, height 300-700mm, are air-cooled to room temperature；

H, T6 heat treatments are carried out to housing component, solid solution system is 350-450 DEG C of heat preservation 30-120min, institution of prescription 200-250 DEG C heat preservation 10-72h；Its T6 states room temperature is tangential, high to tensile strength >=470MPa, tangential, Gao Xiang when elongation >=5%, 200 DEG C Tensile strength >=350MPa, elongation >=7%.

2. preparation process is integrated according to the forging rolling of the strong high temperature resistant magnesium alloy shell part of major diameter superelevation described in claim 1, It is characterized in that：In step D before multiway forging 480-520 DEG C heat preservation blank 10-14h, in 300-350 DEG C of heated block.

3. preparation process is integrated according to the forging rolling of the strong high temperature resistant magnesium alloy shell part of major diameter superelevation described in claim 1, It is characterized in that：3-6 passage jumping-ups are carried out first along Z, Y and X-direction in step E, pass deformation 30-40% will be cylindrical Blank is pressed into 6 face bodies；Then using Y or X as axis, compression corner angle 4-6 passages are rolled, 6 face bodies are pressed by pass deformation 15-20% The faces 14-18 body；Intermediate annealing process is 470-510 DEG C of heat preservation 0.5-1.5h, and intermediate anneal temperature is more primary by low 10 than preceding every time ℃。

4. preparation process is integrated according to the forging rolling of the strong high temperature resistant magnesium alloy shell part of major diameter superelevation described in claim 1, it is special Sign is：Keep the temperature ingot blank 4-6h in step G at 480-520 DEG C before ring-rolling, when rolling cone roller along rolled piece height to applying 2- 4mm drafts, intermediate annealing process is 470-510 DEG C of heat preservation 0.5-2h, and heat preservation reduces by 10 DEG C than a preceding temperature every time, most The housing component that maximum gauge is φ 1700mm is prepared eventually.

5. preparation process is integrated according to the forging rolling of the strong high temperature resistant magnesium alloy shell part of major diameter superelevation described in claim 1, it is special Sign is：Solution treatment system is 410-430 DEG C of heat preservation 45-90min in step H, and institution of prescription is 210-230 DEG C of heat preservation 10- 20h。