阅读说明：本技术 一种防止双相不锈钢端面锻造裂纹的成形方法 (Forming method for preventing duplex stainless steel end face from forging cracks ) 是由 张春林 任书旺 申彭洋 赵轶鹏 梁晓辉 于 2020-04-21 设计创作，主要内容包括：一种防止双相不锈钢端面锻造裂纹的成形方法,对双相不锈钢钢锭锻造过程中,将双相不锈钢钢锭加热至1220-1250℃,保温4-6小时后快速出炉,在自由锻锤或压机上进行锻造前,快速对钢锭端面进行淬水急冷；若锻造一次至所需尺寸,即完成锻造过程,若锻造一次之后未达到所需尺寸,将钢锭回炉加热至1200-1230℃,保温2.5－3小时后淬水急冷并再次锻造,重复回炉加热、保温急冷锻造直至到达所需尺寸。通过在双相不锈钢锻造过程中对锻坯端面进行淬水急冷,改变锻坯端面在锻造过程中的受力状态,避免锻坯端面锻造裂纹的产生。提高双相不锈钢材料利用率及锻造成品率,成功生产出内部质量和表面质量良好的双相不锈钢锻件产品,该技术具有明显的经济效益。(A forming method for preventing the end face of the duplex stainless steel from forging cracks is characterized in that in the process of forging the duplex stainless steel ingot, the duplex stainless steel ingot is heated to 1220-1250 ℃, is rapidly discharged after being subjected to heat preservation for 4-6 hours, and is rapidly quenched before being forged on a free forging hammer or a press; if the forging is carried out once to the required size, the forging process is finished, if the required size is not reached after the forging is carried out once, the steel ingot is heated to 1200-1230 ℃ in a return furnace, the temperature is kept for 2.5-3 hours, then quenching water is carried out, the forging is carried out again, and the return furnace heating and the heat-preservation quenching forging are repeated until the required size is reached. The quenching is carried out on the end face of the forging stock in the process of forging the duplex stainless steel, so that the stress state of the end face of the forging stock in the process of forging is changed, and the generation of forging cracks on the end face of the forging stock is avoided. The utilization rate and the forging yield of the duplex stainless steel material are improved, the duplex stainless steel forging product with good internal quality and surface quality is successfully produced, and the technology has obvious economic benefit.)

1. A forming method for preventing forging cracks on the end faces of duplex stainless steel is characterized in that a consumable duplex stainless steel electrode is smelted through a primary smelting process of a medium-frequency induction furnace and a refining process of an argon-oxygen decarburization furnace, and the consumable duplex stainless steel electrode is smelted into a duplex stainless steel ingot through an electroslag remelting process, and the forming method is characterized in that the specific method for forging the steel ingot is as follows:

step S1: in the process of forging the duplex stainless steel ingot, heating the duplex stainless steel ingot to 1220-1250 ℃, preserving heat for 4-6 hours, then quickly discharging the ingot out of the furnace, and quickly quenching the end face of the ingot by quenching before forging on a free forging hammer or a press;

step S2: if the forging is carried out once to the required size, the forging process is finished, if the required size is not reached after the forging is carried out once, the steel ingot is heated to 1200-1230 ℃ in a return furnace, the temperature is kept for 2.5-3 hours, then quenching water is carried out, the forging is carried out again, and the return furnace heating and the heat-preservation quenching forging are repeated until the required size is reached.

2. The forming method for preventing forging cracks of the duplex stainless steel end surface according to claim 1, wherein: the specific method for smelting the consumable duplex stainless steel electrode into the duplex stainless steel ingot by adopting the electroslag remelting process comprises the following steps;

step 1, cleaning oxide skin on the surface of a consumable duplex stainless steel electrode, welding the oxide skin on a false electrode, sending the electrode into a resistance heating furnace, preheating the electrode to 500-600 ℃, and preserving heat for 5-6 hours to remove water on the surface of the electrode;

step 2, baking the slag at 780-820 ℃ for 8-10 hours;

step 3, arc striking and slagging are carried out by adopting a graphite electrode, the baked slag system is added into a crystallizer, slag materials are melted into liquid, and the temperature of the liquid slag is controlled to 1650-;

step 4, moving the consumable duplex stainless steel electrode into a liquid slag bath, and starting electroslag remelting in an atmospheric environment;

and 5, after the consumable duplex stainless steel electrode is melted, slowly cooling the steel ingot in a crystallizer for 40-60 minutes to ensure that liquid metal and molten slag are fully solidified, demoulding the steel ingot, filling the steel ingot into a slow cooling pit, slowly cooling the steel ingot to room temperature, and removing visible defects on the surface of the steel ingot.

Technical Field

The invention belongs to the technical field of special alloy hot-working forming, and particularly relates to a forming method for preventing duplex stainless steel end face forging cracks.

Background

Generally, duplex stainless steel has ferrite phase and austenite phase occupying about half of the solid solution structure, and has both the advantages of ferrite stainless steel and austenite stainless steel. The composite material has good comprehensive mechanical property, higher strength and fatigue strength, good corrosion resistance, fatigue resistance, wear corrosion resistance, high pore corrosion resistance and high crevice corrosion resistance, has low corrosion rate in organic acid and inorganic acid, and is widely applied to industries of oil refining, chemistry, paper pulp and papermaking, chemical fertilizer, sea water desalination, flue gas desulfurization, chemical waste gas treatment, high-strength structural parts and the like. However, the duplex stainless steel has poor thermoplasticity and low forging yield, and the application of the duplex stainless steel is limited to a certain extent.

In the high-temperature forging process of the duplex stainless steel, the duplex stainless steel is in an austenite phase region and a ferrite phase region, strain tends to concentrate in the ferrite phase, the proportion of the two phases and the distribution of elements in the two phases are changed along with the increase of temperature, the ferrite phase is increased, and the plasticity is increased. However, the deformation behaviors of the two phases are different, the main softening process of the ferritic steel during deformation is dynamic recovery during strain, the main softening process of the austenitic steel is dynamic recrystallization, the two-phase softening processes are different, and uneven stress and strain distribution in the duplex stainless steel during forging easily cause crack nucleation and propagation at phase boundaries, so that edge and surface cracks of a workpiece are caused, and particularly end face cracks are serious.

The typical hot working forming process of the current duplex stainless steel comprises the following steps: the steel ingot or the forging stock is heated to 1200-1250 ℃ to ensure that the stress strain is relatively uniform when the two phases deform. And (3) deforming the steel ingot or the forging stock to the shape of a product by adopting a free forging hammer or a press. In the actual hot working process, the 150mm long forging stock with the reserved 100-fold thickness on the end face of the forging stock is not subjected to forging deformation, the end face is used as a fixed rigid end to prevent the forging crack of the end face of the forging stock from occurring, and the undeformed part of the end face is sawn off in the subsequent machining process. The method can effectively avoid end face cracks, but causes material waste and increases production cost. In the patent CN 103121034B super duplex stainless steel ingot hot working cogging, the heating temperature of the duplex stainless steel 2507 is 1180 ℃, and the hot rolling cogging temperature is 1050 and 1150 ℃. The process has the advantages that: the blooming mill is adopted to replace a forging press for hot working cogging, the production period is shortened, and the hot working forming problem of the duplex stainless steel 2507 is solved to a certain extent. The disadvantages of the process are: the method has strict requirements on the steel ingot specification and is not suitable for large-specification steel ingot molding. Secondly, the hot-forming temperature range is narrow, multiple times of heating are needed, the production efficiency is low, the operation is complicated, the requirement on equipment is high, and the control is difficult in the actual production process.

Disclosure of Invention

In order to solve the technical problems, the invention provides a forming method for preventing the forging cracks of the end face of the duplex stainless steel. The utilization rate and the forging yield of the duplex stainless steel material are improved, and the defects of the duplex stainless steel in hot workability are overcome.

In order to realize the technical purpose, the adopted technical scheme is as follows: a forming method for preventing forging cracks on the end faces of duplex stainless steel is characterized in that a consumable duplex stainless steel electrode is smelted through a primary smelting process of a medium-frequency induction furnace and a refining process of an argon-oxygen decarburization furnace, the consumable duplex stainless steel electrode is smelted into a duplex stainless steel ingot through an electroslag remelting process, and the specific method for forging the steel ingot is as follows:

step S1: in the process of forging the duplex stainless steel ingot, heating the duplex stainless steel ingot to 1220-1250 ℃, preserving heat for 4-6 hours, then quickly discharging the ingot out of the furnace, and quickly quenching the end face of the ingot by quenching before forging on a free forging hammer or a press;

step S2: if the forging is carried out once to the required size, the forging process is finished, if the required size is not reached after the forging is carried out once, the steel ingot is heated to 1200-1230 ℃ in a return furnace, the temperature is kept for 2.5-3 hours, then quenching water is carried out, the forging is carried out again, and the return furnace heating and the heat-preservation quenching forging are repeated until the required size is reached.

Further, the specific method for smelting the consumable duplex stainless steel electrode into the duplex stainless steel ingot by adopting the electroslag remelting process comprises the following steps;

step 1, cleaning oxide skin on the surface of a consumable duplex stainless steel electrode, welding the oxide skin on a false electrode, sending the electrode into a resistance heating furnace, preheating the electrode to 500-600 ℃, and preserving heat for 5-6 hours to remove water on the surface of the electrode;

step 2, baking the slag at 780-820 ℃ for 8-10 hours;

step 3, arc striking and slagging are carried out by adopting a graphite electrode, the baked slag system is added into a crystallizer, slag materials are melted into liquid, and the temperature of the liquid slag is controlled to 1650-;

step 4, moving the consumable duplex stainless steel electrode into a liquid slag bath, and starting electroslag remelting in an atmospheric environment; and 5, after the consumable duplex stainless steel electrode is melted, slowly cooling the steel ingot in a crystallizer for 40-60 minutes to ensure that liquid metal and molten slag are fully solidified, demoulding the steel ingot, filling the steel ingot into a slow cooling pit, slowly cooling the steel ingot to room temperature, and removing visible defects on the surface of the steel ingot.

The invention has the beneficial effects that:

compared with the prior art, the invention has the beneficial effects that: the quenching is carried out on the end face of the forging stock in the process of forging the duplex stainless steel, so that the stress state of the end face of the forging stock in the process of forging is changed, and the generation of forging cracks on the end face of the forging stock is avoided. The utilization rate and the forging yield of the duplex stainless steel material are improved, the duplex stainless steel forging product with good internal quality and surface quality is successfully produced, and the technology has obvious economic benefit.

Drawings

FIG. 1 is a graph showing the tensile stress analysis of a single crystal.

Detailed Description

A forming method for preventing the end face of duplex stainless steel from forging cracks adopts the following technical scheme:

firstly, smelting a consumable duplex stainless steel electrode by a primary smelting process of a medium frequency induction furnace and an Argon Oxygen Decarburization (AOD) furnace refining process, wherein the diameter of the electrode is represented by D, and the ratio of the diameter D of the electrode to the diameter D of a steel ingot is 0.7-0.8.

And (II) smelting the consumable duplex stainless steel electrode into a duplex stainless steel ingot by adopting an electroslag remelting process, which comprises the following steps:

cleaning oxide skin on the surface of a consumable duplex stainless steel electrode, welding the oxide skin on a false electrode, sending the electrode into a well-type resistance heating furnace, preheating the electrode to 500-600 ℃, and preserving heat for 5-6 hours to remove water on the surface of the electrode;

secondly, baking the slag at 780-820 ℃ for 8-10 hours;

thirdly, arc striking and slagging are carried out by adopting a graphite electrode, the baked slag system is added into a crystallizer, slag materials are melted into liquid, and the temperature of the liquid slag is controlled to 1650-;

fourthly, moving the consumable electrode into a liquid slag bath, and starting electroslag remelting in an atmospheric environment;

and fifthly, after the electrode is melted, slowly cooling the steel ingot in a crystallizer for 40-60 minutes to ensure that liquid metal and molten slag are fully solidified, loading the steel ingot into a slow cooling pit after demoulding, slowly cooling the steel ingot to room temperature, and removing visible cracks, slag inclusion and other defects on the surface of the steel ingot.

(III) thermodynamic analysis calculation of end face crack formed by steel ingot in forging process

The factors for forming cracks in the forging process are influenced by external conditions besides internal factors, and the conditions for macroscopic damage of the material can be expressed as follows:

σ_cr＝F(σ_ij∫d_ijT)

in the formula: sigma_crCritical tensile stress (or shear critical stress); sigma_ijIs in a stress state; integral multiple of_ijIs strain accumulation; is the strain rate; t is the deformation temperature.

From the above formula, it can be seen that whether cracks can be generated in the forging process is also influenced by the condition of the thermodynamic deformation in addition to the intrinsic factors of the material.

The stretching of the material shows that a slip system is only if it is subjected toThe sliding can be started only when a certain amount of required shearing stress is reached. Stress analysis at the time of single crystal slip was conducted by taking a tensile test as an example, and is shown in FIG. 1. If the cross section area of the sample is F, the sample slides under the action of an external force P, and if the included angle between P and the normal N of the sliding surface is psi and the included angle between P and the sliding direction S is lambda, the tangential component force of P on the sliding surface along the sliding direction is P_τComprises the following steps:

P_τ＝Pcosλ

assuming that the area of the slip plane is F '(F' ═ F/cos ψ), the shear stress τ of P in the slip direction is:

when in useAt the moment, the crystal begins to deform plastically, at which time the shear stress in the slip direction is called the critical shear stress, in τ_kAnd (4) showing.

τ_k＝σ_Scos λ cos ψ or

When a certain slip system in the crystal is subjected to a shear stress greater than the critical shear stress tau_kSlippage begins. Tau is_kWhich represents the resistance of the metal crystal to the slip process and in fact the dislocation motion. For duplex stainless steel, the factors influencing critical shear stress mainly comprise deformation temperature and deformation rate, the higher the metal deformation temperature is, the lower the critical shear stress is, because the higher the temperature is, the larger the kinetic energy of atoms is, the weaker the bonding force among atoms is, and in addition, a new slip system can appear during high-temperature deformation; the larger the deformation rate, the higher the critical shear stress of the metal, and the larger the deformation rate, the simultaneous slip along several crystal planes is caused.

In the patent, the duplex stainless steel belongs to a polycrystal, and for the duplex stainless steel, the orientation of each crystal grain is different, and crystal boundaries exist, and the atomic arrangement at the crystal boundaries is irregular, so that the plastic deformation of each crystal grain is influenced and restricted mutually, therefore, the plastic deformation of the polycrystal is more complicated than that of the single crystal, but the deformation in the range of each crystal grain is similar to that of the single crystal. Therefore, the critical shear stress of the duplex stainless steel can be controlled by controlling the forging deformation temperature and the deformation rate of the duplex stainless steel, thereby avoiding forging cracks.

The control mechanism of the end face crack in the forging process of the duplex stainless steel is consistent with the explanation, the duplex stainless steel is heated to 1220-1250 ℃ in the forging process, the end face of a forging blank is quenched after being discharged from a furnace, the end face temperature is reduced, the critical shear stress in the forging process of the part is improved, the yield strength of the material in the forging process is increased, the local deformation of the part is reduced under the condition of the same forging impact force, namely, a material end face rigid end is artificially manufactured, a certain fixing effect is generated on the end face of the material, the end face forging temperature and the forging deformation rate are reduced, and therefore the end face forging crack in the forging process of the duplex stainless steel is controlled.

Hot working shaping of steel ingot

When the forging heating temperature is more than 1250 ℃, the steel ingot has weaker shear deformation capability and is easy to generate surface and core cracks, and when the forging temperature is lower than 950 ℃, the deformation resistance is sharply increased and the deformation performance of the steel ingot is sharply reduced. Therefore, in order to ensure that the steel ingot has good forming performance and lower deformation resistance and ensure that the forging stock has good surface and core quality, the hot forging and cogging temperature range of the steel ingot is 950-1250 ℃.

And (3) placing the steel ingot into a natural gas heating furnace, heating to 1220-.