High Pressure Heat Treatment - Phase Transformation under Isostatic Pressure in HIP

M. Ahlfors, A. Angré, D. Chasoglou, Linn Larsson
{"title":"High Pressure Heat Treatment - Phase Transformation under Isostatic Pressure in HIP","authors":"M. Ahlfors, A. Angré, D. Chasoglou, Linn Larsson","doi":"10.21741/9781644900031-21","DOIUrl":null,"url":null,"abstract":"Modern HIP furnaces equipped with forced convection cooling enable very fast cooling rates under isostatic pressure. This does not only give shorter HIP cycles and increased productivity but also allows complete heat treatment cycles to be performed in the HIP unit. It has been shown in previous studies that extreme pressures of several thousand bar can push phase transformation towards longer times for the Fe-C system. The new URQ HIP cooling systems give the opportunity to investigate the impact of pressures up to 2000 bar on phase transformation time dependency. A 4340 steel was used in this study and a comparison of austenite phase transformation time at 100 bar and 1700 bar was performed. The study was performed by isothermal heat treatment of specimens for a specific time followed by quenching. To evaluate the influence of pressure on hardenability, the phase fractions were evaluated using grid method on SEM images. The study found significant influence of HIP pressure on the phase transformation kinetics of the material studied. Introduction Hot Isostatic Pressing (HIP) is a process mainly used to consolidate powder into solid highquality parts or to eliminate internal defects in parts produced by casting, additive manufacturing or MIM by applying a high isostatic gas pressure and a high temperature. Traditionally the cooling in the HIP system is relatively slow and could take up to 24 hours. In the mid 1980’s the URC HIP furnaces was introduced with a forced convection cooling technology that significantly decreased the cooling time in the HIP system and thereby reduce the total HIP cycle time by up to 50% [1]. In 2010 the URQ HIP furnaces were introduced with achievable cooling rates up to 3000 K/min. The URQ HIP quenching furnaces gives the possibility to perform traditional heat treatments, e.g. martensitic hardening, in the HIP furnace during the HIP cycle. The forced convection cooling technology (URC, URQ) is based on a wire wound pressure vessel design where a thin cylinder is water cooled from the outside and a wire wound package outside the cooling channels. To protect the pressure vessel from heat during a HIP cycle, an insulated furnace within the pressure vessel is used to achieve high temperature for the load in the hot zone but a cool environment closest to the pressure vessel walls. During the forced convection cooling the hot gas inside the furnace is moved to the outside of the furnace at the same time as the colder gas outside the hot zone is pushed into the furnace chamber. This mixing of gas will lead to a cooling effect and at the same time the hot gas outside the furnace is cooled down by the water-cooled pressure vessel walls like a heat exchanger which adds to the cooling Hot Isostatic Pressing – HIP‘17 Materials Research Forum LLC Materials Research Proceedings 10 (2019) 149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 150 effect. In the case of a URQ furnace a heat exchanger is also placed inside the pressure vessel, outside the furnace, to increase the cooling rate even more. In Figure 1, a schematic image of a URQ furnace during cooling is presented. Figure 1. Schematic image of the cooling in a URQ HIP furnace When looking at performing quenching of a material inside the HIP during a HIP cycle the question came up if the high isostatic pressure on the material during the quenching would make any difference from the conventional quenching methods at atmospheric pressure. A few relatively old geological studies have shown that high pressure during cooling pushes the phase transformation from austenite to pearlite and bainite towards longer times. Most studies have been evaluating very high pressures; 20-42 kbar. Kuteliya et al. studied the effect of 20 kbar hydrostatic pressure on austenite transformation and saw that high pressure slows down the transformation of austenite. [7] In a study made by Radcliffe et al. it was shown that both the initiation and the rate of austenite transformation in iron-carbon alloys are retarded at 42 kbar, relative to the reactions at 1 atm. [8] Austenite – pearlite transformation rates at 34 kbar pressure were studied by Hilliard et al. and it was found that the effect of the pressure was a decrease in transformation rate. [9] A.Weddeling has used the rapid quenching HIP technology to study the influence of high pressure on microstructure. Specimens of low alloyed steel were quenched under pressure in HIP and compared to samples quenched with the same cooling rate in a dilatometer at atmospheric pressure. A certain amount of bainite was formed during quenching but the specimen quenched in the HIP featured less bainite that also had finer structure compared to the dilatometer specimens. These results suggest that the bainite formed under pressure is not only formed later in time but also at lower temperatures at which nucleation is supported and diffusion is retarded compared to bainite formation at higher temperatures. [6] The object of this study was to investigate if a typical HIP pressure of 1700 bar is enough to shift the austenite to pearlite phase transformation towards longer times and if so of what order of magnitude. Shifting the phase transformation towards longer times would imply an increased hardenability which could be very beneficial in industry. Hot Isostatic Pressing – HIP‘17 Materials Research Forum LLC Materials Research Proceedings 10 (2019) 149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 151 For this study, two different steels were studied. For each material a comparison of austenite to pearlite phase transformation time at 100 bar and 1700 bar was performed. The study was performed by isothermal heat treatment of specimens for a specific time followed by quenching. To evaluate the influence of pressure on the hardenability, the phase fractions were evaluated by grid method in SEM together with hardness measurements. See Figure 2 for a schematic presentation of the thermal profiles of the different HIP cycles. Figure 2. Schematic presentation of experimental HIP cycles Experimental Material 4340 Steel 4340, as well denominated 34CrNiMo6 (EN name) and SS 2541, is a widely used steel for quenching and tempering. The chemical composition of the 4340 material used in the study is displayed in Table 1. Table 1. Chemical composition of the 4340 material according to specification. Elements (%) C Mn Si Cr Ni Mo Cu Fe 4340 0.37 0.74 0.26 1.45 1.50 0.19 0.16 bal. TTT diagrams The 4340 material was chosen among several similar steels consulting their Time Temperature Transformation (TTT) diagrams. The factors in favour for 4340 were that it was a fairly common material and that the time to pearlite start was sufficient for the experiments. TTT diagrams for 4340 were found in literature and educational material and additionally JMatPro was used to calculate a diagram. As can be seen in Figure 3 and 4, the TTT diagrams vary quite a bit among themselves and this had to be taken into account deciding isothermal hold time intervals. Hot Isostatic Pressing – HIP‘17 Materials Research Forum LLC Materials Research Proceedings 10 (2019) 149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 152 Figure 3. TTT diagram for 4340 [10]. 1% ferrite at 150 s, 1% pearlite at 2000 s and 99% pearlite at 10000 s at 650 °C. Figure 4. TTT diagram for 4340 with grain size 15 μm, calculated using JMatPro. 0.1% pearlite at 500 s and 99.9% pearlite at 7000 s at 650 °C. Trials Suitable isothermal temperature was selected consulting available TTT diagrams for the material. Subsequently, suitable hold time for the material was also selected based on the TTT diagrams. The HIP cycle is designed so that the material initially is subjected to austenitization temperature, 850 °C, for 15 minutes followed by fast cooling down to selected isothermal temperature, 650 °C, where the material is kept for the chosen hold time followed by rapid quenching to room temperature. The average time to quench the material from 850 to 650 °C in the HIP was 35 seconds measured with the TC in the sample. All HIP cycles were performed at low and high pressure separately. The main challenge for running the HIP cycles was to achieve the same thermal profile for the materials for the two different pressures. All HIP trials were performed with solid cylindrical specimens with size 25x25 mm. Thermocouples were placed in the gas of the HIP furnace hot zone and at least one thermocouple in the center of the specimen for all HIP trials, see Figure 6. The samples were prepared with holes, drilled halfway through the height of the sample in which the thermocouples were placed in order to measure the temperature in the center of the sample. All HIP cycles were performed in the QIH9 URQ HIP at Quintus Technologies AB, Västerås, Sweden, permitting cooling rates of up to 3000 K/min in the gas, i.e. about 45 K/s. Figure 6. Set up of sample with thermocouple in the HIP furnace. Hot Isostatic Pressing – HIP‘17 Materials Research Forum LLC Materials Research Proceedings 10 (2019) 149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 153 Table 3 shows the test matrix of all the trials performed within the project. Typical HIP log curves are presented in Figures 7 and 8, displaying the HIP log curves for 4340 with 3000 s hold time at low and high pressure respectively. The maximum pressure possible to run the rapid quenching feature in the used HIP system is 1700 bar so that pressure was used for the high-pressure cycles of this study. The low-pressure cycles were decided to be run in the HIP as well, in order to make the high and low pressure thermal profiles as similar as possible. To be able to control the HIP temperature and rapidly quench the material 100 bar had to be used as minimum pressure. Table 3. Matrix of the trials performed within the project. Sample Austenitization temperature [°C] Austenitization time [min] Isother m [°C] Pressur e [bar] Hold time [s] 434","PeriodicalId":202011,"journal":{"name":"Hot Isostatic Pressing: HIP’17","volume":"28 1","pages":"0"},"PeriodicalIF":0.0000,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"2","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Hot Isostatic Pressing: HIP’17","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.21741/9781644900031-21","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 2

Abstract

Modern HIP furnaces equipped with forced convection cooling enable very fast cooling rates under isostatic pressure. This does not only give shorter HIP cycles and increased productivity but also allows complete heat treatment cycles to be performed in the HIP unit. It has been shown in previous studies that extreme pressures of several thousand bar can push phase transformation towards longer times for the Fe-C system. The new URQ HIP cooling systems give the opportunity to investigate the impact of pressures up to 2000 bar on phase transformation time dependency. A 4340 steel was used in this study and a comparison of austenite phase transformation time at 100 bar and 1700 bar was performed. The study was performed by isothermal heat treatment of specimens for a specific time followed by quenching. To evaluate the influence of pressure on hardenability, the phase fractions were evaluated using grid method on SEM images. The study found significant influence of HIP pressure on the phase transformation kinetics of the material studied. Introduction Hot Isostatic Pressing (HIP) is a process mainly used to consolidate powder into solid highquality parts or to eliminate internal defects in parts produced by casting, additive manufacturing or MIM by applying a high isostatic gas pressure and a high temperature. Traditionally the cooling in the HIP system is relatively slow and could take up to 24 hours. In the mid 1980’s the URC HIP furnaces was introduced with a forced convection cooling technology that significantly decreased the cooling time in the HIP system and thereby reduce the total HIP cycle time by up to 50% [1]. In 2010 the URQ HIP furnaces were introduced with achievable cooling rates up to 3000 K/min. The URQ HIP quenching furnaces gives the possibility to perform traditional heat treatments, e.g. martensitic hardening, in the HIP furnace during the HIP cycle. The forced convection cooling technology (URC, URQ) is based on a wire wound pressure vessel design where a thin cylinder is water cooled from the outside and a wire wound package outside the cooling channels. To protect the pressure vessel from heat during a HIP cycle, an insulated furnace within the pressure vessel is used to achieve high temperature for the load in the hot zone but a cool environment closest to the pressure vessel walls. During the forced convection cooling the hot gas inside the furnace is moved to the outside of the furnace at the same time as the colder gas outside the hot zone is pushed into the furnace chamber. This mixing of gas will lead to a cooling effect and at the same time the hot gas outside the furnace is cooled down by the water-cooled pressure vessel walls like a heat exchanger which adds to the cooling Hot Isostatic Pressing – HIP‘17 Materials Research Forum LLC Materials Research Proceedings 10 (2019) 149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 150 effect. In the case of a URQ furnace a heat exchanger is also placed inside the pressure vessel, outside the furnace, to increase the cooling rate even more. In Figure 1, a schematic image of a URQ furnace during cooling is presented. Figure 1. Schematic image of the cooling in a URQ HIP furnace When looking at performing quenching of a material inside the HIP during a HIP cycle the question came up if the high isostatic pressure on the material during the quenching would make any difference from the conventional quenching methods at atmospheric pressure. A few relatively old geological studies have shown that high pressure during cooling pushes the phase transformation from austenite to pearlite and bainite towards longer times. Most studies have been evaluating very high pressures; 20-42 kbar. Kuteliya et al. studied the effect of 20 kbar hydrostatic pressure on austenite transformation and saw that high pressure slows down the transformation of austenite. [7] In a study made by Radcliffe et al. it was shown that both the initiation and the rate of austenite transformation in iron-carbon alloys are retarded at 42 kbar, relative to the reactions at 1 atm. [8] Austenite – pearlite transformation rates at 34 kbar pressure were studied by Hilliard et al. and it was found that the effect of the pressure was a decrease in transformation rate. [9] A.Weddeling has used the rapid quenching HIP technology to study the influence of high pressure on microstructure. Specimens of low alloyed steel were quenched under pressure in HIP and compared to samples quenched with the same cooling rate in a dilatometer at atmospheric pressure. A certain amount of bainite was formed during quenching but the specimen quenched in the HIP featured less bainite that also had finer structure compared to the dilatometer specimens. These results suggest that the bainite formed under pressure is not only formed later in time but also at lower temperatures at which nucleation is supported and diffusion is retarded compared to bainite formation at higher temperatures. [6] The object of this study was to investigate if a typical HIP pressure of 1700 bar is enough to shift the austenite to pearlite phase transformation towards longer times and if so of what order of magnitude. Shifting the phase transformation towards longer times would imply an increased hardenability which could be very beneficial in industry. Hot Isostatic Pressing – HIP‘17 Materials Research Forum LLC Materials Research Proceedings 10 (2019) 149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 151 For this study, two different steels were studied. For each material a comparison of austenite to pearlite phase transformation time at 100 bar and 1700 bar was performed. The study was performed by isothermal heat treatment of specimens for a specific time followed by quenching. To evaluate the influence of pressure on the hardenability, the phase fractions were evaluated by grid method in SEM together with hardness measurements. See Figure 2 for a schematic presentation of the thermal profiles of the different HIP cycles. Figure 2. Schematic presentation of experimental HIP cycles Experimental Material 4340 Steel 4340, as well denominated 34CrNiMo6 (EN name) and SS 2541, is a widely used steel for quenching and tempering. The chemical composition of the 4340 material used in the study is displayed in Table 1. Table 1. Chemical composition of the 4340 material according to specification. Elements (%) C Mn Si Cr Ni Mo Cu Fe 4340 0.37 0.74 0.26 1.45 1.50 0.19 0.16 bal. TTT diagrams The 4340 material was chosen among several similar steels consulting their Time Temperature Transformation (TTT) diagrams. The factors in favour for 4340 were that it was a fairly common material and that the time to pearlite start was sufficient for the experiments. TTT diagrams for 4340 were found in literature and educational material and additionally JMatPro was used to calculate a diagram. As can be seen in Figure 3 and 4, the TTT diagrams vary quite a bit among themselves and this had to be taken into account deciding isothermal hold time intervals. Hot Isostatic Pressing – HIP‘17 Materials Research Forum LLC Materials Research Proceedings 10 (2019) 149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 152 Figure 3. TTT diagram for 4340 [10]. 1% ferrite at 150 s, 1% pearlite at 2000 s and 99% pearlite at 10000 s at 650 °C. Figure 4. TTT diagram for 4340 with grain size 15 μm, calculated using JMatPro. 0.1% pearlite at 500 s and 99.9% pearlite at 7000 s at 650 °C. Trials Suitable isothermal temperature was selected consulting available TTT diagrams for the material. Subsequently, suitable hold time for the material was also selected based on the TTT diagrams. The HIP cycle is designed so that the material initially is subjected to austenitization temperature, 850 °C, for 15 minutes followed by fast cooling down to selected isothermal temperature, 650 °C, where the material is kept for the chosen hold time followed by rapid quenching to room temperature. The average time to quench the material from 850 to 650 °C in the HIP was 35 seconds measured with the TC in the sample. All HIP cycles were performed at low and high pressure separately. The main challenge for running the HIP cycles was to achieve the same thermal profile for the materials for the two different pressures. All HIP trials were performed with solid cylindrical specimens with size 25x25 mm. Thermocouples were placed in the gas of the HIP furnace hot zone and at least one thermocouple in the center of the specimen for all HIP trials, see Figure 6. The samples were prepared with holes, drilled halfway through the height of the sample in which the thermocouples were placed in order to measure the temperature in the center of the sample. All HIP cycles were performed in the QIH9 URQ HIP at Quintus Technologies AB, Västerås, Sweden, permitting cooling rates of up to 3000 K/min in the gas, i.e. about 45 K/s. Figure 6. Set up of sample with thermocouple in the HIP furnace. Hot Isostatic Pressing – HIP‘17 Materials Research Forum LLC Materials Research Proceedings 10 (2019) 149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 153 Table 3 shows the test matrix of all the trials performed within the project. Typical HIP log curves are presented in Figures 7 and 8, displaying the HIP log curves for 4340 with 3000 s hold time at low and high pressure respectively. The maximum pressure possible to run the rapid quenching feature in the used HIP system is 1700 bar so that pressure was used for the high-pressure cycles of this study. The low-pressure cycles were decided to be run in the HIP as well, in order to make the high and low pressure thermal profiles as similar as possible. To be able to control the HIP temperature and rapidly quench the material 100 bar had to be used as minimum pressure. Table 3. Matrix of the trials performed within the project. Sample Austenitization temperature [°C] Austenitization time [min] Isother m [°C] Pressur e [bar] Hold time [s] 434
高压热处理-等静压下的相变
配备强制对流冷却的现代HIP炉可以在等静压下实现非常快的冷却速度。这不仅缩短了HIP循环周期,提高了生产率,而且还允许在HIP单元中进行完整的热处理循环。以前的研究表明,几千巴的极端压力可以使Fe-C体系的相变时间延长。新的URQ HIP冷却系统为研究高达2000bar的压力对相变时间依赖性的影响提供了机会。采用4340钢,对其在100bar和1700bar下的奥氏体相变时间进行了比较。对试样进行一定时间的等温热处理,然后淬火。为了评估压力对淬透性的影响,采用网格法对SEM图像进行了相分数评估。研究发现,热挤压压力对所研究材料相变动力学有显著影响。热等静压(HIP)是一种通过施加高等静压气体压力和高温,将粉末固化成固体高质量零件或消除铸造、增材制造或MIM生产的零件内部缺陷的工艺。传统上,HIP系统的冷却速度相对较慢,可能需要长达24小时。在20世纪80年代中期,URC HIP炉引入了强制对流冷却技术,显着减少了HIP系统的冷却时间,从而将总HIP循环时间减少了50%[1]。2010年推出了URQ HIP炉,可实现的冷却速率高达3000 K/min。URQ的HIP淬火炉可以在HIP循环期间在HIP炉中进行传统的热处理,例如马氏体硬化。强制对流冷却技术(URC, URQ)是基于绕线压力容器的设计,其中一个薄圆柱体从外部水冷却,冷却通道外有一个绕线封装。在HIP循环过程中,为了保护压力容器免受热量的影响,在压力容器内使用一个隔热炉来实现热区负载的高温,但最靠近压力容器壁的凉爽环境。在强制对流冷却过程中,炉内的热气体被移动到炉外,同时热区外的冷气体被推入炉膛。这种气体的混合将导致冷却效果,同时炉外的热气体被水冷压力容器壁冷却,就像热交换器一样,增加了冷却热等静压- HIP ' 17材料研究论坛LLC材料研究论文集10 (2019)149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 150效果。在URQ炉的情况下,热交换器也被放置在炉外的压力容器内,以进一步提高冷却速度。图1给出了URQ炉冷却过程的示意图。图1所示。当观察在HIP循环中对HIP内的材料进行淬火时,问题出现了,在淬火过程中材料上的高等静压是否会与传统的常压淬火方法有任何不同。一些较早的地质研究表明,冷却过程中的高压使奥氏体向珠光体和贝氏体相变的时间延长。大多数研究都是评估非常高的压力;20-42千巴。Kuteliya等研究了20kbar静水压力对奥氏体转变的影响,发现高压减缓了奥氏体的转变。[7] Radcliffe等人的一项研究表明,相对于1atm时的反应,铁碳合金在42 kbar时的起始反应和奥氏体转变速度都减慢了。[8] Hilliard等人研究了34 kbar压力下奥氏体-珠光体的相变速率,发现压力的影响是相变速率的降低。[9] A.Weddeling采用快速淬火HIP技术研究了高压对组织的影响。将低合金钢试样在热压下进行淬火,并与在常压下以相同冷却速率在膨胀计中进行淬火的试样进行比较。淬火过程中形成了一定数量的贝氏体,但与膨胀仪试样相比,在HIP中淬火的试样贝氏体较少,且组织更精细。结果表明,与高温下形成贝氏体相比,压力下形成的贝氏体不仅形成时间晚,而且在较低的温度下形成,在较低的温度下形成的贝氏体有利于成核和阻碍扩散。 [6]本研究的目的是研究1700巴的典型静压是否足以使奥氏体相变向珠光体相变转变更长时间,如果是的话,转变的数量级是多少。将相变时间延长意味着淬透性的提高,这在工业上是非常有益的。热等静压- HIP ' 17 Materials Research Forum LLC Materials Research Proceedings (2019) 149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 151在本研究中,研究了两种不同的钢。对每种材料在100 bar和1700 bar下的奥氏体和珠光体相变时间进行了比较。对试样进行一定时间的等温热处理,然后淬火。为了评估压力对淬透性的影响,在扫描电镜中采用网格法对相分数进行了评估,并对硬度进行了测量。图2是不同HIP循环的热分布示意图。图2。4340钢,又称34CrNiMo6 (EN)和SS 2541,是一种广泛使用的淬火和回火钢。研究中使用的4340材料的化学成分如表1所示。表1。4340材料的化学成分符合规范。元素(%)C Mn Si Cr Ni Mo Cu Fe 4340 0.37 0.74 0.26 1.45 1.50 0.19 0.16 bal。参考时间-温度转变(TTT)图,在几种类似的钢中选择了4340材料。对4340有利的因素是,它是一种相当常见的材料,并且从珠光体开始的时间对实验来说是足够的。4340的TTT图可以在文献和教育材料中找到,另外使用JMatPro计算图。如图3和图4所示,TTT图之间的差异很大,在决定等温保持时间间隔时必须考虑到这一点。热等静压- HIP ' 17 Materials Research Forum LLC Materials Research Proceedings 10 (2019) 149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 1524340的TTT图[10]。在650℃下,在150 s时为1%铁素体,在2000 s时为1%珠光体,在10000 s时为99%珠光体。图4。晶粒尺寸为15 μm的4340的TTT图,使用JMatPro计算。0.1%珠光体,500秒,99.9%珠光体,7000秒,650℃。参考现有材料的TTT图,选择合适的等温温度。随后,根据TTT图选择合适的物料保持时间。HIP循环的设计是使材料首先经受850°C的奥氏体化温度15分钟,然后快速冷却到选定的等温温度650°C,在那里材料保持选定的保温时间,然后快速淬火到室温。用样品中的TC测量,在HIP中材料从850℃淬火到650℃的平均时间为35秒。所有HIP循环分别在低压和高压下进行。运行HIP循环的主要挑战是在两种不同压力下实现相同的材料热分布。所有HIP试验均采用尺寸为25x25 mm的实心圆柱形标本进行。热电偶放置在热压炉热区的气体中,在所有热压试验中,至少有一个热电偶放置在试样的中心,见图6。样品准备了孔,在放置热电偶的样品高度的中间钻孔,以便测量样品中心的温度。所有的HIP循环都在瑞典Quintus Technologies AB (Västerås)的QIH9 URQ HIP中进行,允许在气体中高达3000 K/min的冷却速率,即约45 K/s。图6。用热电偶在热压炉中建立试样。热等静压- HIP ' 17 Materials Research Forum LLC Materials Research Proceedings 10 (2019) 149-156 doi: http://dx.doi.org/10.21741/9781644900031-21 153表3显示了项目内进行的所有试验的测试矩阵。典型的HIP测井曲线如图7和图8所示,分别显示了在低压和高压下保持时间为3000 s的4340的HIP测井曲线。在使用的HIP系统中运行快速淬火功能可能的最大压力是1700巴,因此压力用于本研究的高压循环。低压循环也决定在HIP中运行,以使高压和低压热剖面尽可能相似。为了能够控制HIP温度并快速淬火材料,必须使用100 bar作为最低压力。表3。在项目中进行的试验矩阵。 样品奥氏体化温度[°C]奥氏体化时间[min]等m[°C]压力e [bar]保温时间[s
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