CN107937828B

CN107937828B - F6NM martensitic stainless steel cylinder forging and heat treatment method

Info

Publication number: CN107937828B
Application number: CN201711249913.7A
Authority: CN
Inventors: 朱奇锋; 张林洲; 曹雄伟
Original assignee: Baoding Technology Co ltd
Current assignee: Baoding Technology Co ltd
Priority date: 2017-12-01
Filing date: 2017-12-01
Publication date: 2020-10-02
Anticipated expiration: 2037-12-01
Also published as: CN107937828A

Abstract

The invention relates to an F6NM martensitic stainless steel cylinder forging and a heat treatment method, wherein the forging can meet the requirements of high strength and high low-temperature impact toughness, can avoid cracks, and can avoid steel ingot cracking and scrapping during forging, and the heat treatment method comprises the following steps: less than or equal to 0.04 percent of C, 0.30-0.50 percent of Si, 0.70-1.00 percent of Mn, 11.5-13.0 percent of Cr11.5, 3.5-4.5 percent of Ni, 0.50-0.70 percent of Mo0.04-0.1 percent of V, less than or equal to 0.020 percent of P, and less than or equal to 0.010 percent of S. The advantages are that: the F6NM martensitic stainless steel cylinder forging piece with optimized components adopts sectional isothermal slow heating, strictly controls charging temperature, heating speed and heat preservation time, is strictly executed according to a new forging process during forging, and adopts a special heat treatment process of isothermal heating at 550 ℃, air quenching at 1000 ℃ and three tempering at 690 ℃, 630 ℃ and 590 ℃. The inspection size of the produced product meets the requirements of a customer drawing, a sample is taken and sent to a third party for detection, the mechanical properties meet the index requirements, and after multiple production, the mechanical properties are stable, so that the risk of scrapping in the production of F6NM martensitic stainless steel is greatly reduced.

Description

F6NM martensitic stainless steel cylinder forging and heat treatment method

Technical Field

The invention relates to an F6NM martensitic stainless steel cylinder forging with the diameter larger than 953mm and the length larger than 1385mm, which can meet the requirements of high strength and high low-temperature impact resistance, can avoid the generation of cracks and simultaneously avoid the cracking and scrapping of steel ingots during forging, and a heat treatment method thereof, and belongs to the field of manufacturing of stainless steel cylinder forgings.

Background

The F6NM material is a material in American society for testing and materials ASTM A336/A336M-09 alloy steel forging standard for high-temperature pressure-bearing parts, belongs to martensitic stainless steel, and comprises 13% of Cr and 4% of Ni in chemical components, which is equivalent to the national trade mark 0Cr13Ni4 Mo.

The F6NM material is a new type of martensitic stainless steel used to make large castings and forgings. Nowadays, the environmental protection is increasingly strict, the global demand is more and more large, and compared with martensitic stainless steels such as 2Cr13, 3Cr13, 1Cr17Ni2 and the like, the martensitic stainless steels have higher strength and toughness, good corrosion resistance and good weldability, so the martensitic stainless steels are widely applied to the fields of nuclear power engineering components, petrochemical industry, marine equipment, high-pressure pumps, military industry and the like in recent years. However, F6NM martensitic stainless steel has poor thermal conductivity, too high charging temperature or too fast temperature rise, generates large internal stress, generates fine cracks, expands cracks after forging to cause scrap, generates reverse austenite structure after F6NM martensitic stainless steel is subjected to heat treatment, has great influence on performance due to tempering temperature, and is difficult to control mechanical properties.

Disclosure of Invention

The design purpose is as follows: the defects in the background art are avoided, and the F6NM martensitic stainless steel cylinder forging and the heat treatment method are designed, wherein the forged cylinder forging not only can meet the requirements of high strength and high low-temperature impact toughness resistance, but also can avoid cracks and avoid steel ingot cracking and scrapping during forging.

The design scheme is as follows: in order to achieve the above design objectives. In the development process, the application finds that several problems need to be solved to achieve the design purpose of the application.

The technical problem is as follows:

1. the problem of conventional chemical composition can't stably satisfy high strength, high low temperature resistant impact toughness of barrel forging simultaneously is solved.

2. The method solves the problems that the F6NM martensitic stainless steel has poor thermal conductivity, the cracking is caused by overlarge temperature difference between the inside and the outside due to overhigh charging temperature or uneven temperature rise, and the cracking is caused by overlarge temperature difference during forging due to insufficient heat preservation time.

3. The method solves the problems that the forging temperature range of F6NM martensitic stainless steel is small, the plasticity of steel ingots is poor, the steel ingots are very easy to crack during forging, and the rejection rate is high, and the finish forging temperature and the deformation directly influence the grain size and the performance heat treatment effect of products.

4. The method solves the problems that the heat treatment of F6NM martensitic stainless steel can generate reversed austenite structure and the quantity of reversed austenite is difficult to control, and the tempering temperature directly influences the strength of a product and the stability of low-temperature impact.

Secondly, in order to solve the technical problems, the technical problems are solved by the cooperation of optimization of material excellent components, optimization of a heating process, optimization of a forging process and design of a heat treatment process.

1. Material optimization: in order to enable the high strength and the corrosion resistance stability of the F6NM martensitic stainless steel cylinder forging to reach the indexes required by customers, the material is optimized on the basis that the chemical components meet the standard of ASTM A336/A336M-09 alloy steel forging standard for high-temperature pressure-bearing parts.

(1) Carbon (C): is one of the main elements of industrial steel, the performance and structure of the steel are determined by the content and distribution form of carbon in the steel, and the influence of carbon in stainless steel is particularly significant. The effect of carbon on the structure of stainless steel is mainly manifested in two ways, on the one hand, carbon is an element stabilizing austenite and acts to a large extent (about 30 times that of nickel), and on the other hand, carbon and chromium form a complex series of carbides with chromium due to their high affinity. In order to overcome the intergranular corrosion of the F6NM martensitic stainless steel, the carbon content of the steel can be reduced to below 0.04%.

(2) Silicon (Si): is an element forming ferrite, and is a common impurity element in general stainless steel. Therefore, the content is controlled to be 0.30-0.50%.

(3) Manganese (Mn): the function of stabilizing austenite in steel, increasing the stability of austenite, inhibiting the decomposition of austenite, and keeping the austenite formed at high temperature to normal temperature.

Therefore, the content is controlled to be 0.70-1.00%.

(4) Phosphorus (P): in general, phosphorus is a harmful element in steel, increases cold brittleness of steel, deteriorates weldability, decreases plasticity, and deteriorates cold bending property, and therefore, the content of P is controlled to 0.020% or less.

(5) Sulfur (S): sulfur is also a harmful element in general. Hot shortness of the steel occurs, ductility and toughness of the steel are reduced, and cracks are caused during forging. Sulfur also reduces the corrosion resistance of the steel, so the S content is controlled below 0.010%.

(6) Chromium (Cr): chromium is an element determining the property of stainless steel, and chromium as an alloy element promotes the development of contradictory motions in the stainless steel to the advantage of resisting corrosion damage. The chromium content is increased, the requirements of hardness and wear resistance are met, and a certain corrosion resistance function is also considered, so that the Cr content is controlled to be 11.5-13.0%.

(7) Nickel (Ni): nickel is an excellent corrosion-resistant material, and is used as an alloy element in stainless steel, so that the structure of high-chromium steel is changed, and the corrosion resistance and the processing performance of the stainless steel are improved. Therefore, the Ni content is controlled to be 3.5-4.5%.

(8) The trace element V can play the roles of refining the crystal grains of the forging and improving the obdurability, and the trace element V mainly plays the roles of inhibiting the deformation recrystallization of austenite and preventing the crystal grains from growing in the heating process, and carries out precipitation strengthening on the material through the strain induction precipitation of carbon and nitrogen compounds of the trace element V. Therefore, the content of V is 0.04-0.1%

In summary, the optimized chemical compositions are shown in the following table: (mass%)

Optimized chemical components (mass fraction%)

C	Si	Mn	P	S
					≤0.04	0.30～0.50	0.70～1.00	≤0.020	≤0.010
Cr	Ni	Mo	V
					11.5～13.0	3.5～4.5	0.50～0.70	0.04～0.1

2. Optimizing a heating process: the conventional heating process can lead to uneven temperature rise of the steel ingot to generate stress cracks. Strictly controlling the charging temperature to be less than 400 ℃, heating by adopting multi-section isothermal slow heating, wherein the heating speed is less than 60 ℃/h, carrying out isothermal treatment at 650 ℃ and 850 ℃ respectively, reducing the temperature difference between the inside and the outside of the steel ingot, and prolonging the heat preservation time of the initial forging temperature so as to ensure that the steel ingot is fully subjected to uniform austenitization. The innovative post-heating process design is shown in figure 1.

3. Optimizing a forging process: preheating tools such as a special anvil block, a punch and a core rod before forging, and avoiding cracks caused by large temperature difference; the initial forging temperature of the steel ingot is 1220 ℃, the final forging temperature is 850 ℃, because of high alloy elements, the plasticity of the cast steel ingot is poor, the initial forging deformation is not more than 50mm, the cracking is prevented, and a special punch and a core rod are adopted for forging, so that the forging quality is improved, the product allowance is reduced, and the forging time is shortened. The final forging deformation must be more than 12-20%, and the final forging temperature is controlled to 850 ℃, and the suction of coarse crystals or harmful tissues can be caused when the final forging deformation is too small or the final forging temperature is too high, so that the heat treatment performance and the flaw detection are not qualified.

4. Designing a heat treatment process: according to the mechanical properties required by customers, the alloy is characterized by high strength and high low-temperature impact resistance.

The quenching temperature of F6NM is 950-1050 ℃, the martensite is obtained by air quenching and oil quenching, the difference is small, 1000 ℃ air cooling quenching is adopted, 550 ℃ isothermal temperature rise is adopted during heating, and the temperature rise speed is less than or equal to 80 ℃/h; after tempering at 500-700 ℃, the tissues are lath martensite, quenched martensite is formed at 550 ℃, tempered martensite at 560-690 ℃ gradually becomes smaller, and regional martensite appears when 700 ℃ is reached, so the first tempering temperature is set to 690 ℃, fine lath martensite is obtained, and the tempered lath martensite has higher strength but lower low-temperature impact toughness and is unstable after 690 ℃; observing the suction amount of reverse austenite at 550-690 ℃, wherein the suction amount reaches the highest value at 630 ℃, the reverse austenite can reduce the yield ratio and improve the low-temperature impact toughness, so the secondary tempering temperature is set as 630 ℃; in order to stabilize the reversed austenite, the third tempering is carried out, the third tempering temperature is set to be 590 ℃, and the tempering temperature is close to Ac1, so that the structure can be stabilized more from the effects of stress relief, full recovery of the structure, recrystallization and aging precipitation, and the service life of the forge piece is prolonged. The post-innovation heat treatment process curve is shown in fig. 2.

The technical scheme 1: an F6NM martensitic stainless steel cylinder forging, mass percent: less than or equal to 0.04 percent of C, 0.30-0.50 percent of Si, 0.70-1.00 percent of Mn, 11.5-13.0 percent of Cr11.5, 3.5-4.5 percent of Ni, 0.50-0.70 percent of Mo0.04-0.1 percent of V, less than or equal to 0.020 percent of P, and less than or equal to 0.010 percent of S.

The technical scheme 2 is as follows: a forging method of F6NM martensitic stainless steel cylinder forgings is characterized in that tools such as a special anvil block, a punch and a core rod are preheated before forging, and cracks caused by large temperature difference are avoided; the initial forging temperature of the steel ingot is 1220 ℃, the final forging temperature is 850 ℃, because the alloy elements are high, the plasticity of the cast steel ingot is poor, the initial forging deformation is not more than 50mm, the cracking is prevented, a special punch and a core rod are adopted for forging, the forging quality is improved, the product allowance is reduced, and the forging time is shortened; the final forging deformation must be more than 12-20%, and the final forging temperature is controlled to 850 ℃, and the suction of coarse crystals or harmful tissues can be caused when the final forging deformation is too small or the final forging temperature is too high, so that the heat treatment performance and the flaw detection are not qualified.

Technical scheme 3: a heat treatment method of an F6NM martensitic stainless steel cylinder forging is characterized by comprising the following steps: the quenching temperature of F6NM is 950-1050 ℃, the martensite is obtained by air quenching and oil quenching, the difference is small, 1000 ℃ air cooling quenching is adopted, 550 ℃ isothermal temperature rise is adopted during heating, and the temperature rise speed is less than or equal to 80 ℃/h; after tempering at 500-700 ℃, the tissues are lath martensite, quenched martensite is formed at 550 ℃, tempered martensite at 560-690 ℃ gradually becomes smaller, and regional martensite appears when 700 ℃ is reached, so the first tempering temperature is set to 690 ℃, fine lath martensite is obtained, and the tempered lath martensite has higher strength but lower low-temperature impact toughness and is unstable after 690 ℃; observing the suction amount of reverse austenite at 550-690 ℃, wherein the suction amount reaches the highest value at 630 ℃, the reverse austenite can reduce the yield ratio and improve the low-temperature impact toughness, so the secondary tempering temperature is set as 630 ℃; in order to stabilize the reversed austenite, the third tempering is carried out, the third tempering temperature is set to be 590 ℃, and the tempering temperature is close to Ac1, so that the structure can be stabilized more from the effects of stress relief, full recovery of the structure, recrystallization and aging precipitation, and the service life of the forge piece is prolonged.

Compared with the background technology, the F6NM martensitic stainless steel cylinder forging with optimized components is subjected to a large amount of data inquiry and repeated tests, sectional isothermal slow heating is adopted, the charging temperature, the heating speed and the heat preservation time are strictly controlled, the forging is strictly executed according to a new forging process, and the heat treatment adopts a special heat treatment process of isothermal heating at 550 ℃, air quenching at 1000 ℃ and tempering at 690 ℃, 630 ℃ and 590 ℃. The inspection size of the produced product meets the requirements of a customer drawing, a sample is taken and sent to a third party for detection, the mechanical properties meet the index requirements, and after multiple production, the mechanical properties are stable, so that the risk of scrapping in the production of F6NM martensitic stainless steel is greatly reduced.

Chemical composition table of trial-produced steel ingot

Furnace number	C	Si	Mn	P	S
						110-65003	0.035	0.36	0.76	0.016	0.003
110-65004	0.034	0.35	0.75	0.016	0.004
						Furnace number	Cr	Ni	Mo	V
110-65003	12.32	4.22	0.55	0.05
						110-65004	12.29	4.18	0.54	0.06

Mechanical property inspection data sheet

Drawings

FIG. 1 is a schematic view of a F6NM martensitic stainless steel cylinder forging heating process.

FIG. 2 is a schematic view of a heat treatment process of an F6NM martensitic stainless steel cylinder forging.

Detailed Description

Example 1: reference is made to figures 1 and 2. Two furnaces of steel ingots are selected for manufacturing.

1. Chemical composition is shown in the following table-steel ingot chemical composition table.

2. The heating process adopts sectional isothermal slow heating, and strictly controls charging temperature, heating speed and holding time, and the specific process is shown in figure 2.

3. Preheating tools such as a special anvil block, a punch and a core rod before forging, and avoiding cracks caused by large temperature difference; the initial forging temperature of the steel ingot is 1220 ℃, the final forging temperature is 850 ℃, because of high alloy elements, the plasticity of the cast steel ingot is poor, the initial forging deformation is not more than 50mm, the cracking is prevented, and a special punch and a core rod are adopted for forging, so that the forging quality is improved, the product allowance is reduced, and the forging time is shortened. The final forging deformation must be more than 12-20%, and the final forging temperature is controlled to 850 ℃, and the suction of coarse crystals or harmful tissues can be caused when the final forging deformation is too small or the final forging temperature is too high, so that the heat treatment performance and the flaw detection are not qualified. The specific forging implementation process is as follows:

the weight of the cylinder forging piece is 5.72t, 8.5t plum blossom ingots are selected for forging production, and the size diagram of the forging piece blank is as follows; the initial forging temperature is 1220 plus or minus 20 ℃; the finish forging temperature is 850 +/-20 ℃; forging is finished by 4 times; the total forging ratio was 5.0.

Firstly, lightly pressing the surface, chamfering, a riser and an ingot body after the steel ingot is discharged from a furnace, ensuring that the reduction is not more than 50mm, staggering a pouring gate at the water port end, and returning to the furnace for heating;

secondly, hot-staggering a riser of the steel ingot, continuously controlling the rolling reduction to be not more than 50mm, and returning to the furnace for heating;

thirdly, upsetting the blank to H700 mm, punching phi 400mm, and returning to the furnace for heating;

and fourthly, inserting the phi 380mm core rod into the hollow blank, drawing to phi 1030mm, marking and distributing the material, increasing the reduction to 100mm, drawing, pressing the step, rounding to the process size, and finishing.

4. The heat treatment process comprises the following steps: quenching and three times of tempering are adopted for heat treatment, so that the mechanical property of the product is stabilized and the service life of the product is prolonged. The heat treatment process curve is shown in fig. 2.

5. Mechanical property test data is shown in the following table-mechanical property test data table:

6. after flaw detection, the internal quality of the two F6NM martensitic stainless steel cylinder forgings meets the requirements of ASTMA388 ultrasonic flaw detection specifications.

It is to be understood that: although the above embodiments have described the design idea of the present invention in more detail, these descriptions are only simple descriptions of the design idea of the present invention, and are not limitations of the design idea of the present invention, and any combination, addition, or modification without departing from the design idea of the present invention falls within the scope of the present invention.

Claims

1. An F6NM martensitic stainless steel cylinder forging is characterized in that the mass percent is as follows: less than or equal to 0.04 percent of C, 0.30-0.50 percent of Si, 0.70-1.00 percent of Mn, 11.5-13.0 percent of Cr11.5, 3.5-4.5 percent of Ni, 0.50-0.70 percent of Mo0.04-0.1 percent of V, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, and the balance of Fe; the forging method comprises the following steps: strictly controlling the charging temperature to be less than 400 ℃, heating by adopting multi-section isothermal slow heating, wherein the heating speed is less than 60 ℃/h, carrying out isothermal treatment at 650 ℃ and 850 ℃ respectively, reducing the temperature difference between the inside and the outside of the steel ingot, and prolonging the heat preservation time of the initial forging temperature to ensure that the steel ingot is fully subjected to uniform austenitization; preheating a special anvil block, a punch and a core rod tool before forging to avoid cracks caused by large temperature difference; the initial forging temperature of the steel ingot is 1220 ℃, the final forging temperature is 850 ℃, because the alloy elements are high, the plasticity of the cast steel ingot is poor, the initial forging deformation is not more than 50mm, the cracking is prevented, a special punch and a core rod are adopted for forging, the forging quality is improved, the product allowance is reduced, and the forging time is shortened; the final forging deformation is required to be 12-20%, the final forging temperature is controlled to be 850 ℃, coarse grains or harmful tissues are sucked out due to the fact that the final forging deformation is too small or the final forging temperature is too high, and the heat treatment performance and flaw detection are not qualified;

the heat treatment method comprises the following steps: air cooling quenching at 1000 ℃, isothermal temperature rise at 550 ℃ is adopted during heating, and the temperature rise speed is less than or equal to 80 ℃/h; setting the first tempering temperature to 690 ℃, so as to obtain fine lath martensite; setting the second tempering temperature to be 630 ℃; and in order to stabilize the reversed austenite, tempering for the third time is carried out, and the third tempering temperature is set to be 590 ℃, so that the structure can be more stabilized, and the service life of the forge piece is prolonged.

2. The F6NM martensitic stainless steel cylinder forging of claim 1, wherein: c0.035, Si0.36, Mn0.76, Cr12.32, Ni4.22, Mo0.55, V0.05, P0.016 and S0.003.

3. The F6NM martensitic stainless steel cylinder forging of claim 1, wherein: c0.034, Si0.35, Mn0.75, Cr12.29, Ni4.18, Mo0.54, V0.06, P0.016, S0.004.

4. The F6NM martensitic stainless steel cylinder forging of claim 2, wherein: tensile strength Rm 850 MPa; yield strength ReH 693 MPa; elongation A22.0%; the reduction of area is Z71.9%; the impact toughness AKv-73 ℃ is subjected to three-point values of 190J, 188J and 198J.

5. The F6NM martensitic stainless steel cylinder forging of claim 3, wherein: tensile strength Rm 845 MPa; yield strength ReH 690 MPa; elongation A23.0%; the reduction of area Z is 72.5%; the impact toughness AKv is 192J, 190J and 194J at 73 ℃.