Heat treatment method for improving obdurability of 14Cr17Ni2 forge piece

Abstract

The invention belongs to the technical field of forging, and discloses a heat treatment method for improving the obdurability of 14Cr17Ni2 forgings, which comprises the following steps: step 1, quenching: forging a 14Cr17Ni2 stainless steel part, immediately loading the forged 14Cr17Ni2 stainless steel part into a heat treatment furnace, heating to 900-950 DEG C, preserving heat for 2 hours, and then cooling to room temperature; and secondly, tempering is conducted, specifically, the 14Cr17Ni2 stainless steel forge piece treated in the first step is loaded into a tempering furnace, the temperature is increased to 580-600 DEG C, heat preservation is conducted for 4 hours, and then the 14Cr17Ni2 stainless steel forge piece is cooled to the room temperature. According to the method, after-forging heat treatment of the 14Cr17Ni2 stainless steel is optimized, annealing treatment is not carried out after forging, only quenching and tempering treatment is carried out, by controlling the quenching and tempering temperature and time in the quenching and tempering process, good strength and toughness matching is obtained, meanwhile, the hardness can meet the machining requirement, and the machining quality is improved. The requirements for high performance and efficient machining of 14Cr17Ni2 stainless steel tooth and shaft forgings are met, and on the premise that good mechanical performance is obtained, energy is saved, the production period is shortened, and the production cost is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of forging, and in particular relates to a heat treatment method for improving the strength and toughness of 14Cr17Ni2 forgings. Background Art

[0002] 14Cr17Ni2 steel is a widely used stainless steel. It is developed by adding 1.5% to 2.5% Ni to Cr17 stainless steel. It has the characteristics of retaining the corrosion resistance of ferritic stainless steel while having the high strength of martensitic stainless steel.

[0003] Most of the research on the heat treatment process of this material is focused on the influence of forging, quenching and tempering or surface heat treatment on its structure and performance in the final use state. The typical heat treatment system of 14Cr17Ni2 steel bars recommended by GJB2294A is quenching temperature of 950-1040℃, tempering temperature of 275-350℃, tensile strength of not less than 1080MPa, elongation after fracture of not less than 10%, and impact energy of not less than 39J. However, there are few studies on its forging and post-forging heat treatment process. Transmission gears and other important force-bearing parts need to be processed after forging. Therefore, improving the post-forging heat treatment performance of 14Cr17Ni2 steel is crucial to achieve efficient machining and meet the design requirements of parts.

[0004] In the existing manufacturing process, the composition of forgings is optimized, N is added and the Ti content is controlled, which increases the difficulty of smelting and requires specific manufacturers, increasing the production cost. The heat treatment after forging is carried out in two stages: annealing and tempering (including quenching and tempering). Too many heat treatment steps will inevitably lead to excessive energy consumption, extend the production cycle and increase production costs. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the excessive heat treatment steps after forging in the existing manufacturing process will inevitably lead to excessive energy consumption, extend the production cycle and increase production costs.

[0006] In order to solve the above technical problems, the specific technical solutions of the present invention are as follows:

[0007] A heat treatment method for improving the strength and toughness of 14Cr17Ni2 forgings, characterized in that it comprises the following steps:

[0008] Step 1: Quenching:

[0009] After forging, the 14Cr17Ni2 stainless steel parts are immediately placed in a heat treatment furnace, heated to 900-950°C for 2 hours, and then cooled to room temperature;

[0010] Step 2: Tempering:

[0011] The 14Cr17Ni2 stainless steel forgings processed in step 1 are placed in a tempering furnace, heated to 580-600°C and kept for 4 hours, and then cooled to room temperature.

[0012] Preferably, in step one, the heat treatment furnace is heated to 920°C.

[0013] Furthermore, after quenching in step 1, water cooling or oil cooling is performed to room temperature.

[0014] Furthermore, in step 2, the steel is water-cooled to room temperature after tempering.

[0015] Among them, the heat treatment furnace and the tempering furnace are both electric furnaces.

[0016] The invention has the following advantages: the heat treatment after forging of 14Cr17Ni2 stainless steel is optimized, annealing treatment is not performed after forging, only quenching and tempering treatment is performed, and a good match between strength and toughness is obtained by controlling the quenching and tempering temperature and time during the quenching and tempering process, while the hardness can meet the requirements of mechanical processing, meet the requirements of high-performance and high-efficiency mechanical processing of 14Cr17Ni2 stainless steel gear and shaft forgings, save energy while shortening the production cycle and saving production costs on the premise of obtaining good mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the heat treatment system of the present invention. DETAILED DESCRIPTION

[0018] In order to better understand the purpose, structure and function of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings.

[0019] like Figure 1 As shown, the present invention provides a heat treatment process for 14Cr17Ni2 stainless steel forgings, including two processes of quenching treatment and tempering treatment:

[0020] Step 1: quenching: immediately after forging, the 14Cr17Ni2 stainless steel is put into a heat treatment furnace, heated to 900-950°C and kept for 2 hours, and then water-cooled or oil-cooled to room temperature;

[0021] Step 2: tempering. The 14Cr17Ni2 stainless steel forgings processed in step 1 are placed in a tempering furnace, heated to 580-600°C for 4 hours, and then water-cooled to room temperature.

[0022] The 14Cr17Ni2 forging heat treatment process provided by the invention can not only reduce the heat treatment cycle and lower the energy consumption, but also various mechanical properties of the 14Cr17Ni2 forging after the heat treatment can meet the use requirements.

[0023] The delivery state of 14Cr17Ni2 stainless steel bar is annealed. Its material meets the requirements of GJB2294A-2014. After forging, it is first quenched and then tempered. The mechanical properties of its forgings meet the requirements for transmission gears. The tensile strength is not less than 1030MPa, the elongation after fracture is not less than 9%, and the impact energy is not less than 39J. The heat treatment system is as follows Figure 1 As shown. In the quenching treatment, the quenching temperature is 900-950°C, and the holding time of forgings with an effective thickness not exceeding 120 mm is 2 hours, which is suitable for forgings with an effective thickness of 120 mm. The implementation cases of the present invention are all for forgings with an effective thickness of less than 120 mm. The tempering temperature is 580-600°C, and the tempering time is not less than 4 hours.

[0024] Some comparative examples and examples are provided below.

[0025] Embodiment 1:

[0026] Take a forging with a length of 300 mm and a diameter of 80 mm, drill 10 g of sample steel chips 5 mm from the top circle for composition testing, and the measured composition is shown in Table 1:

[0027] Table 1 Chemical composition Unit: mass fraction %

[0028]

[0029] The forgings are heated to 950℃ in an electric furnace, kept at this temperature for 2 hours, and then cooled in a water tank to room temperature. Then the forgings are placed in an electric furnace at 600℃ for 4 hours, and then water-cooled to room temperature.

[0030] The mechanical properties test results are shown in Table 2:

[0031] Table 2 Mechanical properties results

[0032]

[0033] Embodiment 2:

[0034] Take a forging with a length of 300 mm and a diameter of 80 mm, drill 10 g of sample steel chips 5 mm from the top circle for composition testing, and the measured composition is shown in Table 3:

[0035] Table 3 Chemical composition Unit: mass fraction %

[0036]

[0037] The forgings are heated to 900℃ in an electric furnace, kept at this temperature for 2 hours, and then cooled in a water tank to room temperature. Then the forgings are placed in an electric furnace at 580℃ for 4 hours, and then water-cooled to room temperature.

[0038] The mechanical properties test is shown in Table 4:

[0039] Table 4 Mechanical properties results

[0040]

[0041] Embodiment 3:

[0042] Take a forging with a size of 200mm×160×32mm, grind the surface and drill out 10g of sample steel chips for composition testing. The measured composition is shown in Table 5:

[0043] Table 5 Chemical composition Unit: mass fraction %

[0044]

[0045] The forgings are heated to 920℃ in an electric furnace, kept at this temperature for 2 hours, and then cooled in an oil tank to room temperature. Then the forgings are placed in an electric furnace at 600℃ for 4 hours, and then water-cooled to room temperature.

[0046] The mechanical properties test is shown in Table 6:

[0047] Table 6 Mechanical properties results

[0048]

[0049] Embodiment 4:

[0050] Take a forging with a size of 200mm×160×32mm, grind the surface and drill out 10g of sample steel chips for composition testing. The measured composition is shown in Table 7:

[0051] Table 7 Chemical composition Unit: mass fraction %

[0052]

[0053] The forgings are heated to 920℃ in an electric furnace, kept at this temperature for 2 hours, and then cooled in an oil tank to room temperature. Then the forgings are placed in an electric furnace at 600℃ for 4 hours, and then water-cooled to room temperature.

[0054] The mechanical properties test is shown in Table 8:

[0055] Table 8 Mechanical properties results

[0056]

[0057] Comparative Example 1:

[0058] Take a forging with a length of 300 mm and a diameter of 80 mm, drill 10 g of sample steel chips 5 mm from the top circle for composition testing, and the measured composition is shown in Table 9:

[0059] Table 9 Chemical composition Unit: mass fraction %

[0060]

[0061] The forgings are heated to 1000℃ in an electric furnace, kept warm for 2 hours after reaching temperature, then put into a water tank for cooling, and after cooling to room temperature, put back into the electric furnace and heated to 1000℃ with the furnace, kept warm for 2 hours after reaching temperature, then put into a water tank for cooling to room temperature, and then put into an electric furnace at 600℃ for heating for 4 hours, and then air-cooled to room temperature.

[0062] The mechanical properties were tested and the results are shown in Table 10.

[0063] Table 10 Mechanical properties results

[0064]

[0065] Comparative Example 2:

[0066] Take a forging with a length of 300 mm and a diameter of 80 mm, drill 10 g of sample steel chips 5 mm from the top circle for composition testing, and the measured composition is shown in Table 11:

[0067] Table 11 Chemical composition Unit: mass fraction %

[0068]

[0069] The forgings are heated to 1000℃ in an electric furnace, kept warm for 2 hours, then put into a water tank to cool to room temperature, then placed in an electric furnace at 500℃ for 4 hours, and then air-cooled to room temperature.

[0070] The mechanical properties test results are shown in Table 12:

[0071] Table 12 Mechanical properties results

[0072]

[0073] Comparative Example 3:

[0074] Take a forging with a size of 200mm×160×32mm, grind the surface and drill out 10g of sample steel chips for composition testing. The measured composition is shown in Table 13:

[0075] Table 13 Chemical composition Unit: mass fraction %

[0076]

[0077] The forgings are heated to 1000℃ in an electric furnace, kept warm for 2 hours, then put into a water tank to cool to room temperature, then placed in an electric furnace at 550℃ for 4 hours, and then air-cooled to room temperature.

[0078] The mechanical properties test results are shown in Table 14:

[0079] Table 14 Mechanical properties results

[0080]

[0081] Comparative Example 4:

[0082] Take a forging with a size of 260 mm and a diameter of 45 mm, grind the surface and drill out 10 g of sample steel chips for composition testing. The measured composition is shown in Table 15:

[0083] Table 15 Chemical composition Unit: mass fraction %

[0084]

[0085] The forgings are heated to 950°C in an electric furnace, kept warm for 2 hours, then put into a water tank to cool to room temperature, then placed in an electric furnace at 650°C for 4 hours, and then water-cooled to room temperature.

[0086] The mechanical properties test results are shown in Table 16:

[0087] Table 16 Mechanical properties results

[0088]

[0089] The present invention optimizes the heat treatment after forging of 14Cr17Ni2 stainless steel, and only performs quenching and tempering treatment without annealing after forging. By controlling the quenching and tempering temperature and time during the quenching and tempering process, a good match between strength and toughness is obtained, and the hardness can meet the requirements of mechanical processing, and meet the requirements of high-performance and high-efficiency mechanical processing of 14Cr17Ni2 stainless steel gear and shaft forgings, and save energy while shortening the production cycle and saving production costs under the premise of obtaining good mechanical properties. It can be seen from the above embodiments and comparative examples that for forgings of the same size, the forgings treated by the technical solution of the present invention have better performance.

[0090] Although the embodiments of the present invention are described in conjunction with the accompanying drawings, it is apparent to those skilled in the art that several modifications and improvements may be made without departing from the principles of the present invention, and these modifications and improvements should also be considered to fall within the scope of protection of the present invention.

Claims

1. A heat treatment method for improving the strength and toughness of 14Cr17Ni2 forgings, characterized in that: The steps include: Step 1: Quenching: After forging, the 14Cr17Ni2 stainless steel parts are immediately placed in a heat treatment furnace, heated to 900-950°C for 2 hours, and then cooled to room temperature; Step 2: Tempering: The 14Cr17Ni2 stainless steel forgings processed in step 1 are placed in a tempering furnace, heated to 580-600°C and kept for 4 hours, and then cooled to room temperature.

2. The heat treatment method for improving the strength and toughness of 14Cr17Ni2 forgings according to claim 1 is characterized in that: In step 1, the heat treatment furnace is heated to 920°C.

3. The heat treatment method for improving the toughness of 14Cr17Ni2 forgings according to claim 1 is characterized in that: Step 1: After quenching, water cool or oil cool to room temperature.

4. The heat treatment method for improving the strength and toughness of 14Cr17Ni2 forgings according to claim 1 is characterized in that: Step 2: After tempering, water cool to room temperature.

5. The heat treatment method for improving the strength and toughness of 14Cr17Ni2 forgings according to claim 1 is characterized in that: Both the heat treatment furnace and the tempering furnace are electric furnaces.

Images