A method for heating a valve plate martensitic stainless steel for a refrigeration compressor

Abstract

The application provides a heating method for refrigeration compressor valve piece martensitic stainless steel, belongs to the technical field of hot working of stainless steel materials, and solves the problem of defects existing in finished products prepared by a traditional martensitic stainless steel heating process.The application comprises the following steps: placing martensitic stainless steel continuous casting billets into a preheating furnace for heating and then discharging; the temperature system of the preheating furnace is as follows: a heat recovery section, a first heating section, a second heating section and a third heating section, and the continuous casting billets are drawn out of the preheating furnace after the end of heating in the third heating section; after heating in the preheating furnace, the martensitic stainless steel continuous casting billets are placed into a heating furnace for heating; and the martensitic stainless steel continuous casting billets are rolled into hot-rolled black coils after heating in the heating furnace, and finished products are prepared.The application effectively improves the segregation degree, eliminates and reduces large-size carbides in the finished products, guarantees the precision and flatness of the hot-rolled plate strip size, and realizes batch stable production of the products through a reasonable continuous casting billet heating method.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hot working of stainless steel materials, and particularly relates to a heating method for a valve sheet of a refrigeration compressor. BACKGROUND

[0002] Martensitic stainless steel refers to stainless steel whose performance is adjusted by adjusting the content of carbon, chromium and other components in the steel and a heat treatment process. After annealing treatment, the main organization thereof is ferrite + carbide; after high-temperature austenitizing, the main organization thereof is martensite after air cooling. Carbon dissolved in high-temperature austenite phase during the period is mainly distributed in the material in the form of (Fe, Cr) carbide, effectively improving the hardness of the material, but too high carbon content will reduce the toughness and plasticity of the material.

[0003] Especially, the martensitic stainless steel involved in the present application is mainly used for manufacturing a valve sheet of a refrigeration compressor. After hot rolling, cold rolling, heat treatment, stamping, quenching and tempering and other series of processes, the valve sheet of the compressor is manufactured. The compressor is a driven fluid mechanical equipment for improving low-pressure gas in a refrigeration system into high-pressure gas, and is the heart of the refrigeration system. The valve sheet is as important as the valve of the human heart for the compressor, and is a key component of the compressor system. For some high-frequency variable frequency refrigeration compressors, the frequency may even reach 150 HZ / S. The compressor valve sheet as the valve not only needs to bear alternating stress and bending stress generated by high-frequency action, but also needs to bear very high suction and discharge pressure to accelerate the circulation of refrigerant. The thinner the valve sheet, the smaller the valve resistance, the lower the power consumption of the compressor, and the more power saving of the refrigeration system. The thickness of the valve sheet is only about 0.1-0.3 mm, and the weight is only about 2-5 g, but it is the most impacted part in the compressor. Therefore, the compressor valve sheet steel must have ultra-high toughness and high-cycle fatigue strength and high impact fatigue strength, and the working environment also has lubricating oil, refrigerant and water vapor, and the long-term working temperature is 180-400 DEG C. The working environment and service conditions require the valve sheet steel to also have high corrosion resistance.

[0004] The martensitic stainless steel involved in the application contains about 0.4% of carbon, is medium-carbon martensitic, chromium is a strong carbide forming element, and the molten steel is easy to form composition segregation between dendrites during the solidification process. If the heating is too fast at the low temperature stage, the organizational stress caused by the segregation in the casting blank will be increased, and the risk of cracks or breakage of the casting blank after heating will occur. Due to the segregation of large-size primary carbides, if the high-temperature diffusion and dissolution are not good during the heating process, the final primary carbides will be inherited to the finished product, causing the poor strength and toughness of the material, and seriously affecting the high-cycle fatigue service life and processing performance of the product. In addition, the compressor has high requirements for air tightness, and accordingly, the size precision and flatness of the valve plate are strictly required. The uneven heating temperature of the casting blank will cause a large thickness difference of the plate and poor flatness, which will be inherited to the downstream processing product, affect the yield of the finished product, and even cause the failure of the compressor and reduce the service life of the refrigeration system. SUMMARY

[0005] The purpose of the application is to provide a heating method for martensitic stainless steel of a valve plate of a refrigeration compressor, so as to solve the problem of defects in the finished product prepared by the traditional martensitic stainless steel heating process.

[0006] The technical scheme of the application is a heating method for martensitic stainless steel of a valve plate of a refrigeration compressor, comprising the following steps: Step one: heating the martensitic stainless steel continuous casting blank in the preheating furnace and then discharging it;

[0007] The temperature system of the preheating furnace is as follows: heat recovery section, first heating section, second heating section and third heating section, and the total heating time is greater than 210 minutes; the heat recovery section and the first heating section are not heated, the continuous casting blank stays for more than or equal to 100 minutes, and the temperature of the continuous casting blank discharged from the first heating section is less than or equal to 400℃; the heating time of the second heating section is greater than 50 minutes, the temperature of the continuous casting blank discharged from the second heating section is less than or equal to 550℃, and the heating rate is less than or equal to 3℃ / min; the heating time of the third heating section is greater than or equal to 60 minutes, the heating rate is less than or equal to 4℃ / min, the continuous casting blank is taken out of the preheating furnace after the heating in the third heating section is completed, and the discharge temperature of the preheating furnace is 680-740℃;

[0008] Step two: placing the martensitic stainless steel continuous casting blank in the heating furnace after the preheating furnace is heated;

[0009] The heating furnace type is: heat recovery section, preheating section, heating section and soaking section, the furnace temperature system is: the heat recovery section is not heated, the preheating section, the upper part of the heating section, the lower part of the heating section, the left upper part of the soaking section, the left lower part of the soaking section, the right upper part of the soaking section, the right lower part of the soaking section are seven positions for seven-section furnace temperature control, wherein the preheating section hearth temperature is 1050-1220 DEG C, the heating time is greater than or equal to 50 minutes; the heating section is controlled separately up and down, the lower part of the heating section temperature is 1270-1290 DEG C, the upper part of the heating section temperature is 1260-1285 DEG C, the heating time of the heating section is greater than or equal to 70 minutes; the temperature of the left upper part of the soaking section, the left lower part of the soaking section, the right upper part of the soaking section and the right lower part of the soaking section is 1268-1280 DEG C, and the heating time is greater than or equal to 80 minutes.

[0010] Step three: the martensitic stainless steel continuous casting billet is rolled into a hot-rolled black roll after heating in the heating furnace, and a finished product is prepared.

[0011] Further, the chemical element composition and mass percentage of the martensitic stainless steel continuous casting billet are as follows: carbon: 0.36-0.43%, silicon: ≤1.0%, manganese: ≤1.0%, phosphorus: ≤0.02, sulfur: ≤0.005%, chromium: 12.00-15.00%, molybdenum: ≤1.5%, vanadium: ≤0.30%, nitrogen: ≤0.2%, and the rest is iron and residual elements.

[0012] Further, in step one, the martensitic stainless steel continuous casting billet is a steel billet directly cast from molten steel by a large-scale arc continuous casting machine, the length of the martensitic stainless steel continuous casting billet is 8000-12000 mm, and the thickness is 160-220 mm.

[0013] Further, in step two, the heat recovery section has no burner and is not heated; the preheating section has 12 burners on both sides, of which 8 are interval control burners; before the martensitic stainless steel continuous casting billet enters the preheating section, the interval control valve is automatically cut.

[0014] Further, in step two, the length and thickness direction temperature difference uniformity of the martensitic stainless steel continuous casting billet is less than or equal to 15 DEG C.

[0015] The beneficial effects of the present application are as follows:

[0016] 1. By closing the preheating furnace preheating section burners, adjusting the preheating furnace three-section heating mode to two-section heating mode, and reasonably setting the heating temperature and heating time of each section, the reasonable control of the low-temperature section heating rate is realized, and problems such as deterioration of composition segregation and increase of organizational stress caused by too fast heating at low temperature stage, and casting billet heating cracks are avoided.

[0017] 2. Through the reasonable distribution of the heating load of the preheating furnace and the heating furnace, the high-temperature diffusion and poor solution during the heating process are prevented, the temperature of the casting blank in the heating section and the soaking section of the heating furnace is ensured to meet the maximum high-temperature solution of primary carbides, the number of large-size primary carbides in rolling and finished products is reduced, the uniform distribution of carbides in finished products is ensured, and the strength and toughness of the products are improved.

[0018] 3. The flame length of the burner in the preheating section of the heating furnace is designed to be the longest, only second to the heating section, the longest flame length and the rigidity of the flame modulation burner must be ensured, the pressure and flow of the gas and air participating in the combustion of the burner must be maximized, and the function of the interval valve is to ensure that each burner operates in the best flame length and rigidity state by adjusting the heating amount of the burner. Through the function of the interval control valve of the preheating section burner in the heating furnace, the problem of short flame and flame floating caused by temperature fluctuation or low load operation of the burner is effectively avoided, and the uniformity of the heating temperature is ensured.

[0019] 4. Through the reasonable setting of the furnace temperature and heating time of each heating section, the automatic control of the interval valve in the preheating section and the separate control of the upper and lower parts of the heating section, the temperature difference in the length direction and the thickness direction of the casting blank is minimized, the surface temperature of the continuous casting blank reaches the target discharge temperature after the preheating section and the heating section, and the uniformity of the thickness direction and the length direction of the casting blank is ≤15℃ through sufficient heat preservation and soaking in the soaking section.

[0020] 5. The uneven heating temperature of the casting blank will cause problems such as poor flatness of the plate and strip during rolling, large differences between the same plates, and uneven distribution of carbides in the local organization of the finished plate and strip. A reasonable heating process ensures the uniformity of the temperature and organization of the plate and strip during the rolling process of the continuous casting blank, realizes the continuity from the continuous casting blank of martensitic stainless steel for refrigeration compressor valve plate to preheating, heating, rough rolling, rolling mill rolling, and coiling, and ensures that the product organization is uniform, the carbides are fine and uniformly distributed, the thickness difference between the same plates meets the requirements of downstream precision rolling processing, and the material has high strength and toughness.

[0021] In this process, molybdenum and vanadium are introduced for alloying. The addition of molybdenum not only makes the material have better corrosion resistance, but also makes the molybdenum carbide difficult to dissolve during heating, so that the steel can maintain fine grains and improve the toughness of the material; the addition of vanadium can inhibit the segregation of carbon and improve the uniformity of the organization.

[0022] The finished product produced by this process has high hardness and toughness, good corrosion resistance to lubricants and cooling media, and good resistance to water vapor corrosion, with a high number of high-cycle fatigue resistance ≥10 7 , high dimensional accuracy and flatness, which is helpful for producing thin compressor valve plates and meets the requirements of long-term stable operation of the compressor with low energy consumption.

[0023] This process effectively improves the degree of segregation, eliminates and reduces large-sized carbides in the finished product, and ensures the dimensional accuracy and flatness of hot-rolled strip. From the perspective of industrial mass production, the process achieves stable mass production of products through a reasonable continuous casting billet heating method. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the heating furnace type;

[0025] Figure 2 This is a carbide microstructure distribution diagram of the finished product obtained in Specific Example 1 of this process;

[0026] Figure 3 This is a diagram showing the carbide microstructure distribution of the finished product obtained using the original process.

[0027] In the diagram: 1-Preheating section burner; 2-Intermittent control burner; 3-Heating section burner; 4-Soaking section burner; 5-Axial burner. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] like Figure 1 As shown, the heat recovery section has no burners. The preheating section has 12 preheating burners 1 on each side, 8 of which are intermittently controlled burners 2. The heating section has heating burners 3 on both sides and an axial burner 5 at the top. The soaking section has soaking burners 4 on both sides. The preheating burners 1 are designed with a flame length second only to the heating burners 3. The intermittent control valve function of the intermittently controlled burners 2 avoids problems such as short flames and flame drift caused by low-load operation of the preheating burners 1, ensuring uniform heating temperature. Through the reasonable distribution of the heating load between the preheating furnace and the heating furnace, the preheating burners 1, heating burners 3, axial burners 5, and soaking burners 4 in the heating furnace operate under optimal heating load conditions, achieving optimal flame length and flame rigidity.

[0030] Example 1

[0031] The chemical element composition and mass percentage of the martensitic stainless steel continuous casting billet are as follows: carbon: 0.36%, silicon: 1.0%, manganese: 1.0%, phosphorus: 0.02%, sulfur: 0.005%, chromium: 12.00%, molybdenum: 1.5%, vanadium: 0.30%, nitrogen: 0.2%, with the remainder being iron and residual elements.

[0032] Martensitic stainless steel continuous casting billets are steel billets cast directly from molten steel using a large arc-shaped continuous casting machine. The length of the martensitic stainless steel continuous casting billet is 8000mm and the thickness is 160mm.

[0033] Step one: the martensitic stainless steel continuous casting billet is placed into a preheating furnace for heating and then taken out;

[0034] The temperature regime of the preheating furnace is: heat recovery section, first heating section, second heating section and third heating section, and the total heating time is 210 minutes; the heat recovery section and the first heating section are not heated, the continuous casting billet stays for 100 minutes, and the temperature of the continuous casting billet taken out of the first heating section is 400℃; the second heating section is heated for 50 minutes, the temperature of the continuous casting billet taken out of the second heating section is 550℃, and the heating rate is 3℃ / min; the third heating section is heated for 60 minutes, the heating rate is 4℃ / min, and the continuous casting billet is taken out of the preheating furnace after the heating in the third heating section is completed, and the temperature of the continuous casting billet taken out of the preheating furnace is 680℃;

[0035] Step two: the martensitic stainless steel continuous casting billet is placed into a heating furnace for heating after the preheating furnace is heated;

[0036] The heating furnace is of the type of: heat recovery section, preheating section, heating section and soaking section, and the furnace temperature regime is that the heat recovery section is not heated, the preheating section, the upper part of the heating section, the lower part of the heating section, the left upper part of the soaking section, the left lower part of the soaking section, the right upper part of the soaking section and the right lower part of the soaking section are seven positions for seven-section furnace temperature control, wherein the hearth temperature of the preheating section is 1050℃, and the heating time is 50 minutes; the heating section is controlled separately in the upper and lower parts, the temperature of the lower part of the heating section is 1270℃, the temperature of the upper part of the heating section is 1260℃, and the heating time of the heating section is 70 minutes; the temperatures of the left upper part of the soaking section, the left lower part of the soaking section, the right upper part of the soaking section and the right lower part of the soaking section are all 1268℃, and the heating time is 80 minutes;

[0037] The heat recovery section has no burner and is not heated; the preheating section has 12 burners on both sides, of which 8 are interval control burners, and the interval control valve is automatically cut before the martensitic stainless steel continuous casting billet enters the preheating section.

[0038] The uniformity of the temperature difference in the length and thickness directions of the martensitic stainless steel continuous casting billet is 15℃.

[0039] Step three: the martensitic stainless steel continuous casting billet is rolled into a black coil with a thickness of 4.5mm after being heated in the heating furnace, and a finished product is prepared;

[0040] Example 2,

[0041] The chemical element composition and mass percentage of the martensitic stainless steel continuous casting billet are: carbon: 0.40%, silicon: 0.9%, manganese: 0.9%, phosphorus: 0.018, sulfur: 0.004%, chromium: 13.00%, molybdenum: 1.4%, vanadium: 0.20%, nitrogen: 0.15%, and the rest is iron and residual elements.

[0042] The martensitic stainless steel continuous casting billet is a billet directly cast from molten steel by a large-scale arc continuous casting machine, the length of the martensitic stainless steel continuous casting billet is 10000mm, and the thickness is 200mm.

[0043] Step one: the martensitic stainless steel continuous casting billet is placed into a preheating furnace for heating and then taken out;

[0044] The temperature system of the preheating furnace is as follows: heat recovery section, first heating section, second heating section and third heating section, and the total heating time is 230 minutes; the heat recovery section and the first heating section are not heated, the continuous casting billet stays for 120 minutes, and the temperature of the continuous casting billet taken out of the first heating section is 380℃; the heating time of the second heating section is 60 minutes, the temperature of the continuous casting billet taken out of the second heating section is 540℃, and the heating rate is 2℃ / min; the heating time of the third heating section is 65 minutes, the heating rate is 3℃ / min, and the continuous casting billet is taken out of the preheating furnace after the heating in the third heating section is completed, and the temperature of the continuous casting billet taken out of the preheating furnace is 710℃;

[0045] Step two: the martensitic stainless steel continuous casting billet is placed into a heating furnace for heating after the preheating furnace heating;

[0046] The heating furnace is of the type of heat recovery section, preheating section, heating section and soaking section, and the temperature system is as follows: the heat recovery section is not heated, the preheating section, the upper part of the heating section, the lower part of the heating section, the left upper part of the soaking section, the left lower part of the soaking section, the right upper part of the soaking section and the right lower part of the soaking section are seven positions for seven-section furnace temperature control, wherein the hearth temperature of the preheating section is 1140℃, and the heating time is 60 minutes; the heating section is controlled separately in the upper and lower parts, the temperature of the lower part of the heating section is 1280℃, the temperature of the upper part of the heating section is 1274℃, and the heating time of the heating section is 75 minutes; the temperatures of the left upper part of the soaking section, the left lower part of the soaking section, the right upper part of the soaking section and the right lower part of the soaking section are all 1274℃, and the heating time is 85 minutes;

[0047] The heat recovery section has no burner and is not heated; the preheating section has 12 burners on both sides, of which 8 are interval control burners, and the interval control valve is automatically cut before the martensitic stainless steel continuous casting billet enters the preheating section.

[0048] The uniformity of the temperature difference in the length and thickness directions of the martensitic stainless steel continuous casting billet is 14℃.

[0049] Step three: the martensitic stainless steel continuous casting billet is rolled into a black coil with a thickness of 4.5mm by a roughing mill and a furnace rolling mill after the heating in the heating furnace, and a finished product is prepared;

[0050] Example 3,

[0051] The chemical element composition and mass percentage of the martensitic stainless steel continuous casting billet are as follows: carbon: 0.43%, silicon: 0.8%, manganese: 0.8%, phosphorus: 0.016, sulfur: 0.003%, chromium: 14.00%, molybdenum: 1.3%, vanadium: 0.1%, nitrogen: 0.1%, and the rest is iron and residual elements.

[0052] The martensitic stainless steel continuous casting billet is a billet directly cast from molten steel by a large-scale arc continuous casting machine, and the length of the martensitic stainless steel continuous casting billet is 12000 mm and the thickness is 220 mm.

[0053] Step one: the martensitic stainless steel continuous casting billet is placed in a preheating furnace for heating and then taken out;

[0054] The temperature system of the preheating furnace is as follows: heat recovery section, first heating section, second heating section and third heating section, and the total heating time is 240 minutes; among them, the heat recovery section and the first heating section are not heated, the billet stays for 130 minutes, and the billet temperature out of the first heating section is 370℃; the second heating section heating time is 70 minutes, the billet temperature out of the second heating section is 530℃, and the heating rate is 2℃ / min; the third heating section heating time is 70 minutes, the heating rate is 2℃ / min, and the billet is taken out of the preheating furnace after the third heating section heating is completed, and the preheating furnace temperature is 740℃;

[0055] Step two: the martensitic stainless steel continuous casting billet is placed in a heating furnace for heating after preheating;

[0056] The heating furnace type is as follows: heat recovery section, preheating section, heating section and soaking section, and the furnace temperature system is as follows: the heat recovery section is not heated, the preheating section, the upper part of the heating section, the lower part of the heating section, the left upper part of the soaking section, the left lower part of the soaking section, the right upper part of the soaking section and the right lower part of the soaking section are seven positions for seven-section furnace temperature control, among them, the preheating section hearth temperature is 1220℃, and the heating time is 70 minutes; the heating section is controlled separately from top to bottom, the lower part of the heating section temperature is 1290℃, the upper part of the heating section temperature is 1285℃, and the heating time of the heating section is 80 minutes; the temperature of the left upper part of the soaking section, the left lower part of the soaking section, the right upper part of the soaking section and the right lower part of the soaking section is 1280℃, and the heating time is 90 minutes;

[0057] The heat recovery section has no burner and is not heated; the preheating section has 12 burners on both sides, among which 8 are interval control burners, and the interval control valve is automatically cut before the martensitic stainless steel continuous casting billet enters the preheating section.

[0058] The uniformity of the temperature difference in the length and thickness directions of the martensitic stainless steel continuous casting billet is 13℃.

[0059] Step three: the martensitic stainless steel continuous casting billet is rolled into a black roll with a thickness of 4.5 mm by a roughing mill and a furnace rolling mill after heating in the heating furnace, and a finished product is obtained;

[0060]

[0061] According to the carbide organization distribution map comparison of Figure 2 and Figure 3 The average size of the carbide of the finished product of the present process embodiment 1 is 1.4 μm, there is no large size carbide above 3.0 μm, the plate difference of the finished product is ≤50 μm, and the maximum unevenness in the longitudinal and transverse directions is not more than 2.5 mm.

[0062] According to the data comparison of Table 1, the finished product prepared by the present production process is superior to the finished product prepared by the original process in the indexes of yield strength, tensile strength, elongation, HV hardness, etc., and is greatly improved compared with the industry standard. The present process method controls the heating process system reasonably, so that the continuous casting billet reaches uniform heating temperature in the heating process, the internal organization of the billet is uniform without stress deformation, the carbide is small and uniformly distributed, there is no chain-shaped segregation band and hidden crack and other organizational defects, the finished product has the advantages of high strength and toughness, high flatness, excellent precision calendering performance, etc., and is suitable for making high-end green energy-saving type refrigeration compressor ultra-thin valve plate.

Claims

1. A heating method for martensitic stainless steel valve plates of a refrigeration compressor, characterized in that: Includes the following steps: Step 1: Place the martensitic stainless steel continuous casting billet into a preheating furnace, heat it, and then remove it from the furnace; The preheating furnace temperature regime is as follows: heat recovery section, first heating section, second heating section, and third heating section, with a total heating time > 210 minutes; the heat recovery section and first heating section are not heated, the continuous casting billet residence time is ≥ 100 minutes, and the temperature of the continuous casting billet exiting the first heating section is ≤ 400℃; the heating time of the second heating section is > 50 minutes, the temperature of the continuous casting billet exiting the second heating section is ≤ 550℃, and the heating rate is ≤ 3℃ / min; the heating time of the third heating section is ≥ 60 minutes, and the heating rate is ≤ 4℃ / min. After the continuous casting billet is heated in the third heating section, it is extracted from the preheating furnace, and the exit temperature of the preheating furnace is 680-740℃. Step 2: After the preheating furnace is heated, the martensitic stainless steel continuous casting billet is placed into the heating furnace for heating; The furnace consists of a heat recovery section, a preheating section, a heating section, and a soaking section. The furnace temperature control system is as follows: the heat recovery section does not supply heat; the preheating section, upper part of the heating section, lower part of the heating section, upper left part of the soaking section, lower left part of the soaking section, upper right part of the soaking section, and lower right part of the soaking section have a seven-segment temperature control. Specifically, the preheating section furnace temperature is 1050-1220℃, with a heating time ≥50 minutes; the heating section is controlled separately for the upper and lower parts, with the lower part of the heating section at 1270-1290℃ and the upper part at 1260-1285℃, with a heating time ≥70 minutes; the upper left, lower left, upper right, and lower right parts of the soaking section all have temperatures of 1268-1280℃, with a heating time ≥80 minutes. Step 3: After being heated in a heating furnace, the martensitic stainless steel continuous casting billet is rolled into hot-rolled black coils to obtain the finished product.

2. A heating method for a martensitic stainless steel valve plate of a refrigeration compressor according to claim 1, characterized in that: The chemical element composition and mass percentage of the martensitic stainless steel continuous casting billet are as follows: carbon: 0.36-0.43%, silicon: ≤1.0%, manganese: ≤1.0%, phosphorus: ≤0.02%, sulfur: ≤0.005%, chromium: 12.00-15.00%, molybdenum: ≤1.5%, vanadium: ≤0.30%, nitrogen: ≤0.2%, with the remainder being iron and residual elements.

3. The heating method for martensitic stainless steel valve plates of a refrigeration compressor according to claim 1, characterized in that: In step one, the martensitic stainless steel continuous casting billet is a steel billet directly cast from molten steel using a large arc-shaped continuous casting machine. The length of the martensitic stainless steel continuous casting billet is 8000-12000mm and the thickness is 160-220mm.

4. The heating method for martensitic stainless steel valve plates of a refrigeration compressor according to claim 1, characterized in that: In step two, the heat recovery section has no burners and does not supply heat; there are 12 burners on each side of the preheating section, of which 8 are intermittently controlled burners. Before the martensitic stainless steel continuous casting billet enters the preheating section, the intermittent control valve is switched to automatic.

5. The heating method for martensitic stainless steel valve plates of a refrigeration compressor according to claim 1, characterized in that: In step two, the temperature difference uniformity in the length and thickness directions of the martensitic stainless steel continuous casting billet is ≤15℃.

Images