Heat treatment process for improving impact energy of H13 mandrel

Abstract

The present application relates to a kind of heat treatment processes for improving H13 mandrel impact energy, comprising the following steps: after forging ultrafine treatment, medium frequency quenching, first tempering, second tempering, after forging heat treatment adopts ultrafine treatment process, eliminates reticular structure, obtains good spheroidizing structure, prepares good organizational condition for subsequent quenching and tempering, performance heat treatment adopts medium frequency quenching and tempering, because medium frequency induction coil heating is carried out by skin effect, heating speed is fast, grain is more fine, product heating and cooling stress is small, product straightness is good, using the heat treatment mode of after forging ultrafine treatment+medium frequency quenching and tempering can make the refining steel diameter≤φ200mm specification mandrel obtain higher strength and good impact energy, better solve the problem of low impact energy of H13 mandrel forgings below specification ≤φ200mm of vacuum refining steel production using conventional heat treatment process, meet product design and use requirement, under the premise of strength satisfying design requirement, room temperature average impact energy KV2≥20J.

Description

Technical Field

[0001] This invention belongs to the field of metal heat treatment technology, specifically relating to a heat treatment process for improving the impact energy of H13 mandrels. Background Technology

[0002] Mandrels are the primary tools used in the production of seamless steel pipes on continuous rolling mills. During use, they are subjected to both thermal cyclic stress from rapid cooling and heating and cyclic alternating mechanical stress, resulting in harsh operating conditions that demand high strength and impact toughness from the material. H13 steel is the conventional material for mandrels, and the normal production process involves electroslag remelting, which leads to high production costs. To reduce production costs, mandrels with a diameter ≤ φ200mm are produced from vacuum-refined steel ingots, resulting in lower impact energy, failing to meet the requirement of KV2 ≥ 20J. Currently, there is no technical literature reporting a solution to this technical problem. Summary of the Invention

[0003] The purpose of this invention is to overcome the low impact energy of existing heat treatment processes and provide a heat treatment process for improving the impact energy of H13 mandrels by using post-forging ultrafine treatment and through-heating medium-frequency tempering to meet design and usage requirements.

[0004] The objective of this invention is achieved as follows: a heat treatment process for improving the impact energy of an H13 mandrel, comprising the following steps:

[0005] Step 1) Post-forging ultrafine treatment: Rapid cooling is adopted after forging. The mandrel forging is required to be placed in the annealing furnace at a temperature 50°C below the surface temperature at which martensitic transformation begins (Ms). The temperature is increased at 40-60°C / h to the lower critical temperature (Ar1) ±50°C, and held at the lower critical temperature (Ar1) ±50°C for waiting. Then, it is heated at a rate of 60-80°C / h to 1°C above the lower critical temperature (AC1). Hold at 50℃~200℃. After holding, remove from the furnace and quickly cool to 100℃~150℃ below the martensite transformation temperature before entering the annealing furnace. Heat at 40~60℃ / h to the lower critical temperature (AC1) to the lower critical temperature (AC1) + 30℃ and hold. Then, cool in the furnace at 10~30℃ / h to 30℃~50℃ above the lower critical temperature (Ar1) and hold. Finally, cool in the furnace at 30~50℃ / h to 500℃ before air cooling.

[0006] Step 2) Quenching: The mandrel forgings that have completed Step 1) are rough machined and then transferred to the medium frequency production line. The quenching coil power is 1000±50KW and the speed is 100mm / min~200mm / min. The workpiece is sprayed with water for quenching after it walks out of the quenching coil. The quenching medium is water.

[0007] Step 3) First tempering: Move the mandrel forging from step 2) to the tempering coil. The tempering coil power is 450±50KW and the moving speed is 100mm / min~200mm / min. The workpiece moves out of the tempering coil and begins to be cooled by water spray.

[0008] Step 4) Second tempering: After straightening the mandrel forging from step 3), hoist it to the tempering coil. The tempering coil power is 450±50KW, and the speed is 100mm / min~200mm / min. The workpiece walks out of the tempering coil and begins to be cooled by water spray.

[0009] In step 2), before quenching, the coil temperature needs to be adjusted to meet the quenching temperature requirements using a guide rod of the same specification. The workpiece and the guide rod should be in close contact to avoid temperature fluctuations that could affect the quenching effect.

[0010] In step 2), the medium-frequency quenched furnace is cooled by water spray with a water flow rate of 80±30 m3 / h and a water temperature of no more than 45℃.

[0011] In step 2), the intermediate frequency is 1300 Hz; in step 3), the intermediate frequency is 750 Hz; in step 4), the intermediate frequency is 750 Hz. The intermediate frequency production line is a through-heating intermediate frequency induction heating system.

[0012] The rapid cooling in step 1) is achieved by wind or fog cooling.

[0013] The post-forging heat treatment in step 1) is an ultrafine treatment.

[0014] During the first tempering in step 3), the tempering coil power is 450±50KW and the travel speed is 100mm / min~200mm / min. The workpiece is cooled by water spraying after it walks out of the tempering coil.

[0015] During the second tempering in step 4), the tempering coil power is 450±50KW and the travel speed is 100mm / min~200mm / min. The workpiece is cooled by water spraying after it walks out of the tempering coil.

[0016] The chemical composition of the H13 mandrel forging is: C: 0.32-0.45%; Si: 0.80%-1.20%; Mn: 0.20%-0.50%; Cr: 4.75%-5.50%; Mo: 1.10%-1.75%; V: 0.80%-1.20%; with the balance being Fe and other unavoidable impurities.

[0017] The forging is a forging produced from vacuum-refined steel ingots.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention provides a heat treatment process to improve the impact energy of H13 mandrels, fully tapping the potential of refined H13 steel to achieve the design and usage requirements of mandrel impact energy KV2≥20J, thereby reducing production costs and saving energy. The hot work die steel mandrels involved in this invention are made of American standard H13 material, and through appropriate heat treatment design, meet the design and usage requirements of mandrel forgings.

[0020] The production process of this invention is designed as follows: post-forging ultrafine treatment → medium-frequency quenching + two medium-frequency tempering processes; the implementation of the technical solution mainly lies in controlling the post-forging heat treatment and medium-frequency tempering process. The design of the post-forging heat treatment: The post-forging heat treatment adopts an ultrafine treatment process to eliminate the network structure and obtain a good spheroidized structure, preparing favorable microstructure conditions for the subsequent tempering treatment. The performance heat treatment adopts medium-frequency tempering treatment. Because medium-frequency induction coil heating is achieved through the skin effect, the heating speed is fast, the grains are finer, the heating and cooling stress of the product is small, and the straightness of the product is good. The H13 steel mandrel forgings produced using the process of this invention have a surface hardness HB350~385, a tensile strength of 1150~1215 MPa, and an average room temperature V-notch impact energy KV2≥20J. Detailed Implementation

[0021] Example 1: The mandrel forging material selected is H13, C: 0.36%, Si: 1.05%, Mn: 0.30%, Cr: 5.10%, Mo: 1.35%, V: 1.00%, with the balance being Fe and other unavoidable impurities. The forging with a specification of φ130 is made from vacuum-refined steel ingots.

[0022] Heat treatment includes the following steps:

[0023] Step 1) Post-forging ultrafine treatment: After forging, air cooling is adopted. The mandrel forging is required to be sent into the annealing furnace at a temperature of 30°C above the surface temperature of the martensitic transformation start temperature (Ms). The temperature is increased at 60°C / h to the lower critical temperature (Ar1) + 30°C, and held at the lower critical temperature (Ar1) + 30°C. Then, it is heated at 80°C / h to 150°C above the lower critical temperature (AC1) and held. After holding, it is taken out of the furnace and air-cooled to 100°C below the martensitic transformation start temperature and put into the annealing furnace. The temperature is increased at 60°C / h to the lower critical temperature (AC1) and held. Then, it is furnace-cooled at 30°C / h to 30°C above the lower critical temperature (Ar1) and held. Finally, it is furnace-cooled at 50°C / h to 500°C and air-cooled.

[0024] Step 2) Quenching: The mandrel forgings that have completed Step 1) are rough machined and then transferred to the medium frequency production line. The quenching coil power is 950KW, the speed is 200mm / min, and the medium frequency is 1300HZ. The workpiece is sprayed with water for quenching after it walks out of the quenching coil. The quenching medium is water.

[0025] Step 3) First tempering: Move the mandrel forging from step 2) to the tempering coil. The tempering coil has a power of 400KW, a speed of 200mm / min, and a medium frequency of 750HZ. The workpiece moves out of the tempering coil and begins to be cooled by water spray.

[0026] Step 4) Second tempering: After straightening the mandrel forging from step 3), hoist it to the tempering coil. The tempering coil has a power of 400KW, a speed of 200mm / min, and a medium frequency of 750HZ. The workpiece moves out of the tempering coil and begins to be cooled by water spray.

[0027] The H13 mandrel forgings produced using the above process meet the design requirements in terms of mechanical properties. The average value of the room temperature V-shaped impact energy, KV2, is greater than 20J. The mechanical property test results are shown in the table below.

[0028] Rp 0.2 (MPa) Rm(MPa) A(％) Z(％) KV2(J) Surface hardness Test piece 1 1015 1209 15 49 30 / 28 / 25 355-380HB Test piece 2 1030 1230 14 51 24 / 25 / 26 360-385HB

[0029] Example 2: The mandrel forging material selected was H13, with C: 0.35%, Si: 1.05%, Mn: 0.40%, Cr: 5.05%, Mo: 1.30%, V: 0.95%, and the balance being Fe and other unavoidable impurities. The forging, with a specification of φ200, was made from vacuum-refined steel ingots.

[0030] Heat treatment includes the following steps:

[0031] Step 1) Post-forging ultrafine treatment: After forging, mist cooling is adopted. The mandrel forging is required to be sent into the annealing furnace at a temperature of 50°C above the surface temperature of the martensitic transformation start temperature (Ms). The temperature is increased at 50°C / h to the lower critical temperature (Ar1) + 40°C, and held at the lower critical temperature (Ar1) + 40°C. Then, it is heated at 70°C / h to 170°C above the lower critical temperature (AC1) and held. After holding, it is taken out of the furnace and mist-cooled to 120°C below the martensitic transformation start temperature and put into the annealing furnace. The temperature is increased at 50°C / h to the lower critical temperature (AC1) and held. Then, it is furnace-cooled at 30°C / h to 40°C above the lower critical temperature (Ar1) and held. Finally, it is furnace-cooled at 40°C / h to 500°C and air-cooled.

[0032] Step 2) Quenching: The mandrel forgings that have completed Step 1) are rough machined and then transferred to the medium frequency production line. The quenching coil power is 1050KW, the speed is 100mm / min, and the medium frequency is 1300HZ. The workpiece is sprayed with water for quenching after it walks out of the quenching coil. The quenching medium is water.

[0033] Step 3) First tempering: Move the mandrel forging from step 2) to the tempering coil. The tempering coil has a power of 450KW, a speed of 100mm / min, and a medium frequency of 750HZ. The workpiece moves out of the tempering coil and begins to be cooled by water spray.

[0034] Step 4) Second tempering: After straightening the mandrel forging from Step 3, hoist it to the tempering coil. The tempering coil has a power of 450KW, a speed of 100mm / min, and a medium frequency of 750HZ. The workpiece moves out of the tempering coil and begins to be cooled by water spray.

[0035] The H13 mandrel forgings produced using the above process meet the design requirements in terms of mechanical properties. The average value of the room temperature V-shaped impact energy, KV2, is greater than 20J. The mechanical property test results are shown in the table below.

[0036]

Claims

1. A heat treatment process for improving the impact energy of H13 core rod, characterized in that: It comprises the following steps: Step 1), after forging ultra-fining treatment: after forging, the mandrel forging is sent into the annealing furnace at a temperature of Ms ± 50℃ of the surface martensite transformation starting temperature, and is heated to Ar1 ± 50℃ at a speed of 40-60℃ / h, and is kept at Ar1 ± 50℃, then is heated to AC1 + 150-200℃ above the heating critical temperature at a speed of 60-80℃ / h, and is kept at AC1 + 150-200℃, and is taken out of the furnace and air-cooled to Ms below 100-150℃ after the end of the keeping, and is sent into the annealing furnace at a speed of 40-60℃ / h, and is kept at AC1 + 30℃, then is cooled to Ar1 + 30-50℃ above the cooling critical temperature at a speed of 10-30℃ / h, and is kept at Ar1 + 30-50℃, then is cooled to 500℃ at a speed of 30-50℃ / h, and is taken out of the furnace and air-cooled; the mandrel forging is a forging produced by vacuum refined steel ingot, and has a chemical composition of C: 0.32-0.45%; Si: 0.80-1.20%; Mn: 0.20-0.50%; Cr: 4.75-5.50%; Mo: 1.10-1.75%; V: 0.80-1.20%; and the balance of Fe and other inevitable impurities; Step 2), quenching: the mandrel forging after step 1) is roughly processed, and then is transferred to a transparent medium frequency production line, and a coil temperature is adjusted to meet the quenching temperature requirement by using a same specification lead rod, and the workpiece is tightly connected with the lead rod; The medium frequency frequency is 1300Hz, the quenching coil power is 1000±50kW, the walking speed is 100-200mm / min, the workpiece starts water quenching after walking out of the quenching coil, the quenching medium is water, the water flow is 80±30m³ / h, and the water temperature is not higher than 45℃; Step 3), first tempering: the mandrel forging after step 2) is walked to a tempering coil, the medium frequency frequency is 750Hz, the tempering coil power is 450±50kW, the walking speed is 100-200mm / min, and the workpiece starts water cooling after walking out of the tempering coil; Step 4), second tempering: after the mandrel forging after step 3) is straightened, the mandrel forging is hung in front of the tempering coil, the medium frequency frequency is 750Hz, the tempering coil power is 450±50kW, the walking speed is 100-200mm / min, and the workpiece starts water cooling after walking out of the tempering coil.

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