110 Questions About Metal Heat Treatment (Part 4)

60.What are the main defects in the ingot?


1) normal segregation

2) inverse segregation

3) specific gravity. Inclusion and porosity.Shrinkage cavity and porosity

61.What principles should be followed in the solid solution treatment process of casting aluminum alloy?

  • Quenching temperature: generally a little lower than the maximum solubility temperature.2. Quenching heating: in order to prevent overheating and deformation of the casting, it is better to use a low temperature below 350, and then with the furnace slowly heating to the quenching temperature.3. Heat preservation time: The heat preservation time is relatively long, generally 3~20h.4. Cooling method: Generally cooling in hot water.

62.Try to explain the means of strengthening different aluminum alloys? What heat treatment is used for the ZL104 gasoline engine to improve its strength?

Deformable aluminum alloy strengthening: cold deformation strengthening (work hardening), heat treatment strengthening (solid-solution + aging strengthening) casting aluminum alloy strengthening: metamorphosis treatment (refinement of tissue), solid-solution + aging, ZL104 aluminum alloy using (535±5) ℃*3h solid solution treatment, (175±5) ℃*9h.The process is based on sand mold casting and the aging time is long. When ZL104 aluminum alloy was aged at 175℃*5h, a GP zone was formed in the matrix and the strengthening operation was significant.

64. What method of grain refinement is usually used in industrial processes to control the grain size of metals as they crystallize?

1. Increase the environmental cooling capacity.2. Chemical metamorphism.3. Increase fluid flow.

65. In order to improve the cutting performance, what heat treatment should be performed on 15Cr, 20Cr2Ni4, 40Cr, 5CrMnMo, GCr15, W18Cr4V steel?

15Cr: Normalizing;20Cr2Ni4: Normalizing + tempering;40Cr: Tempering;5CrMnMo: Annealing;GCr15: Spheroidizing annealing;W18Cr4V: spheroidizing annealing.

66. The hardenability and hardness of steels such as 20, 45, 40Cr, T8, and 65 under normal quenching conditions are analyzed and compared.

Hardenability from high to low: 40Cr, T8, 65, 45, 20;

Hardening from high to low: T8, 65, 45, 40Cr, 20.

67. Can we make cold punching die with W18Cr4V steel? Why?

It can be used to make molds, but it is generally used in molds that require high strength, high wear resistance, and low impact. However, due to its poor toughness, brittle material characteristics, and high price, it is not recommended to be used as a cold punching die.

68.After tempering, the hardness of steel is required to be 217HB ~ 255HB, but the hardness is found to be higher after heat treatment. Can the hardness be reduced by slowing down the cooling speed during tempering? If the hardness is too low after heat treatment, can the hardness be improved by lowering the tempering temperature? Explain why?

No, the tempering temperature needs to be adjusted; No, the tempering temperature should be reduced after re-quenching.

The crankshaft of a medium tractor engine is required to have high strength and good toughness, and the crankshaft journal is required to have good wear resistance (50HRC~55 HRC). (1) Select the material and write the steel number;(2) Formulate a concise process route for processing and manufacturing;(3) Explain the structure of the crankshaft and the surface of the crankshaft journal in the service state.

69.Alloyed carburized carbon steel: 20CrMnMo, 20CrMnTi, 20MnVB

Process line: blanking – forging – normalizing – mechanical processing – carburizing, quenching + low-temperature tempering – shot peening – grinding – finished products

Heart tissue: fine lamellar pearlite; Surface structure: Tempered Martensite

70.What safety measures should I pay attention to when using the saltpeter bath furnace?

Attention must be paid to explosion protection and other safety measures.

In saltpeter bath furnace, any local temperature over 595℃, maybe ignition or explosion, use temperature should be strictly controlled below 550℃.

Nitrate mixtures are oxidized and should not be mixed with materials that are easily oxidized.

Fine carbonized materials should not be used as saltpeter coating, and the pollution of saltpeter bath furnace caused by the accumulation of black on the discharge end of the carburizing furnace must also be avoided.

The maximum temperature of the salt bath is regulated in the treatment of magnesium alloy light metals.

71. When formulating the heat treatment industry, how to calculate the effective thickness of the following shapes of the workpiece?

Round bar shape: calculated by diameter;2 flat workpiece: Calculated by thickness;3 solid cone: the diameter at 1/3 of the height of the big end is calculated; Step axis or section of the workpiece abrupt change: according to the large diameter or large section calculation.

High, delta ↑, Ak↑.

72.What principles should be followed in formulating the solid solution treatment process for casting aluminum alloy?

Answer: (1) the choice of quenching temperature: quenching temperature is generally a little lower than the maximum solubility temperature, so as not to overburn or crack.

(2) Quenching heating mode: In order to prevent overheating and deformation of the casting, it is usually carried out in the air circulation furnace. To prevent deformation, it is better to enter the furnace at a low temperature below 350 degrees, and then slowly heat to the quenching temperature with the furnace.

(3) Heat preservation time: The cast aluminum alloy has a large grain size, the excess phase is difficult to dissolve, and the heat preservation time needs to belong. It is generally 3-20h, and the heat preservation time has little relation with the thickness of the workpiece.

(4) Cooling method: Due to the complex casting shape, many internal defects, and reduced strength and plasticity, the casting will be seriously deformed if the cooling rate is too fast, so the casting should be cooled in hot water after quenching.

73.What is the cause of Swindon liver failure?

The swivel lever is dislocated, and the seven swivel levers are not in the same horizontal plane so that the steel tube cannot be sent to the quenching rotary table smoothly, and the steel tube is easy to be touched and scratched.

Lock failure: Swindon lever is unable to complete a station within the specified time.

Electrical failure: the steel pipe in the discharge table is in place, and the Swieten lever is in the original position without any action either manually or automatically. Moreover, the in-situ light of the operating panel lever is not on, indicating that the Swieten lever is in line switch failure. All the above three situations should be checked and repaired.

74.What is the cause of the failure of the moving door?

Deformation of the moving door. The bottom of the moving door is deformed by grooving so that the moving door cannot complete a station within the specified time.

Operation panel moving door open and close with light button no light display, indicating that moving door line switch fault. When the above two cases occur, we need to find the spot inspection and maintenance.

75.What is the cause of the failure of the quenching rotary device?

Eight dead rotating wheels or the iron chain that drives the quenching rotating bench is stuck, making the instantaneous current load of the frequency conversion motor too large, causing an electric trip, thus causing the quenching rotating bench to stop rotating.

Several iron chains driving the quenching rotary bench to fall off, so that the rotation speed of a group of quenching rotary benches is inconsistent. The above two situations will result in uneven cooling of the steel pipe and severe bending of the steel pipe after water quenching.

76.What is the cause of the failure of the pressing device?

The pressing wheel is badly worn, which may cause the steel tube surface to be bumped and scratched. The pressing wheel should be replaced in time.

The quenching rotary bench steel tube in place light is on, and the pressing wheel does not act, indicating that the pressing device is close to the switch fault, it is necessary to find a spot inspection and maintenance.

77.What is the cause of the failure of the steel pipe placement device?

If the lever deforms and falls off, the existing steel pipe of the quenching rotary bench cannot be detected. If there is no action at the next station, the lever should be replaced in time.

There are steel tubes in the quenching rotary bench, but the lamp is off when the quenching steel tubes in the operation panel are in place. The proximity switch is faulty and should be checked and repaired.

78.What is the cause of the dumping fault?

The flange connecting shaft of the discharging material deforms and falls off, and the steel tube cannot be removed from the quenching rotary bench normally.

The operation panel quenching table tilting up and down with the light button lights are not on, indicating the proximity switch fault, to find a spot inspection and repair.

79.What is the cause of the fault of the line switch connecting the outer water spray baffle?

The lamp with the light button is not on when the water baffle of the operation panel is lifted or lowered, and there is no action for manual operation, indicating that the proximity switch is out of order. It is necessary to find a spot check and repair.

80.What is the cause of the failure of the stepping beam device?

After quenching, the steel pipe has reached the drainage inclined platform, but it is not full. The stepping beam is in the original position without any action of manual or automatic operation. Moreover, the in-situ light of the stepping beam on the operation panel is off, indicating that the proximity switch is out of order.

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