20Cr钢渗层碳分布数值模拟系统的研究

通过大量渗碳实验,运用数值模拟和VB6.0程序设计语言等方法开发了20Cr钢渗层碳分布的数值模拟系统,利用该系统用户可直接计算出经不同时间渗碳后的渗碳层深度、表面碳浓度和渗层的碳浓度分布.     

获得高质量齿轮的控制渗碳

渗碳的合金钢齿轮在经过适当的热处理后能够获得最大的负荷能力。为进行高质量的渗碳处理。必须非常仔细地控制渗层深度、渗层显微组织和表面硬度。碳渗入轮齿的深度是气氛碳势、温度、时间和钢的成分的函数。零件渗碳生产之诸多问题中的第一个问题是：如何以及在何处测量渗层深度？     

20CrMnTi钢真空低压渗碳工艺及组织性能研究

研究了20Cr Mn Ti钢真空低压渗碳过程中渗碳温度和渗碳时间对渗层深度、渗层硬度分布和表面碳含量的影响,并分析了碳含量对渗层硬度分布的影响规律,比较了真空渗碳和气体渗碳两种渗碳工艺对盲孔结构的渗碳结果和渗层组织。结果表明,随渗碳温度的升高和渗碳时间的延长,渗层深度和表面碳含量增大,但表面硬度下降。碳含量对渗层硬度分布的分析结果表明,碳质量分数为0.78%时,渗碳层具有最高淬火硬度。对于盲孔结构,相较于气体渗碳,真空渗碳能显著减小渗层深度偏差,并改善渗层组织。     

碳势设定与调节及其对深层渗碳的影响

对20CrNiMo材料运用推杆式连续热处理炉,以氮气、甲醇、丙酮为原料,少量的压缩空气为调节性气体,进行滴注式可控气氛渗碳的试验研究表明,连续渗碳炉各区碳势设定值的合理选择与渗层深度和工艺条件(炉型结构、零件吸碳量多少等)有关;采有较高碳势条件下进行深层渗碳(渗层深度在2.0 mm以上),可以在加快渗碳进程的同时获得较好的渗层碳浓度分布。     

气体渗碳CAD软件的试验验证

用20CrMnTi和20CrMo钢制的试样,根据渗碳层深度分别为1．2mm和1．4mm的齿轮的技术要求,在装备有气体渗碳动态碳势控制CAD软件的渗碳炉上分别进行了试验,对模拟结果进行了验证,证实了该软件功能强劲、控制准确。其表面碳浓度（质量分数）偏差＜0．05％;渗层内的碳浓度梯度曲线平滑,呈“S”平台分布;渗层深度为1．2mm和1．4mm时,渗层深度的偏差＜0．05mm。用该软件设计的渗碳工艺与实际检测结果能很好地吻合。     

20CrMnTi钢渗碳层深度和表层碳浓度分布的数值模拟

研究了常用渗碳钢20CrMnTi以不同工艺渗碳时渗层中碳的分布规律，建立了渗碳层深度与表层碳浓度间的关系，为渗碳工艺参数的优化、渗碳层深度和表层碳浓度分布的精确控制以及渗碳层深度的无损检测提供了理论依据。     

常用渗碳材料渗层碳浓度分布数值模拟系统

建立了不同渗碳条件下渗碳层深度和渗层碳浓度分布模型，通过Visual Basic程序设计语言开发了常用渗碳材料渗层碳浓度分布的数值模拟系统。该系统可方便、快捷地得到在一定工艺条件下相应渗层碳浓度分布和渗碳层深度，为渗碳工艺参数的优化设计和渗碳过程的自动控制提供了重要的参考价值。     

5CrMnMo钢渗碳特性的研究

研究了渗碳温度、炉气碳势对５ＣｒＭｎＭｏ试样渗碳层深，表面碳量的影响以及层深，表面碳量对钢的性能影响，试验表明，５ＣｒＭｎＭｏ钢具有良好的渗碳特性，其最佳渗层深度０．８－１．２ｍｍ，表面碳量应控制在０．８％－１．０％范围，可获得适用于冷镦模具的最佳力学性能。     

18Cr2Ni4WA钢衬套的精密气体渗碳淬火热处理

研究了精密气体渗碳等温淬火工艺对18Cr2Ni4WA钢渗层硬度、深度及显微组织的影响。结果表明,随着总渗碳保温时间的延长,渗层深度增加,但硬度曲线变得平缓;在相同总保温时间的情况下,强渗时间越长,渗层越深;而当扩散时间相同时,强渗时间越长,淬火后表层的硬度较低。优化的精密气体渗碳工艺为:保温温度均为910℃,强渗阶段碳势1.20%,保温3 h;扩散阶段碳势0.80%,保温1 h,渗碳后进行等温淬火,可以获得(1.2±0.1)mm渗层深度。渗碳淬火后渗层组织良好。该工艺成功应用于衬套零件的实际生产,满足了设计要求。     

23Si2MnCrNiMoV钢固体渗碳层的影响因素

研究了渗碳温度、渗碳时间、扩散时间、深冷处理参数对23Si2Mn Cr Ni Mo V钢渗碳层的碳浓度梯度、表层低硬度区深度、有效渗硬层深度(550 HV0.3)、碳扩散距离、微观组织形貌等影响,实验研究的渗碳温度区间为890~970℃,渗碳时间为4~10 h,扩散时间为0~4 h。结果表明,较多的残留奥氏体存在是造成渗碳表层高C低硬度的主要原因,控制C浓度为0.72%~0.86%时,可获得最大硬度,若进一步增加C含量,会形成大量的残留奥氏体,反而降低渗透层的硬度;深冷处理对有效渗硬层深度几乎没有影响,但可使表层低硬度区域从距表面0.7 mm缩至0.3 mm。     

关于渗碳层深度数学模型的研究

本文研究了若干种渗碳钢渗层深度与渗碳时间的关系,对原简单抛物线模型提出了修正,并对修正因子S_o的物理意义及影响因素进行了讨论。文中还研究了碳势对渗层深度的影响的定量规律,并采用数理统计方法进行了显著性分析。     

Corrosion behaviour of low temperature plasma carburised 316L stainless steel in chloride containing solutions

The electrochemical corrosion behaviour of the carburised (expanded austenite) layer on 316L austenitic stainless steel produced by low temperature plasma carburising has been studied in 0.5 M NaCl and 0.5 M HCl + 0.5 M NaCl solutions. The present work focuses on the variation of the corrosion behaviour of the carburised layer with depth from the surface and the effect of carbon concentration on electrochemical behaviour. The results show that the carburised layer has excellent resistance to localised corrosion. There exists a critical carbon concentration, above which the expanded austenite possesses excellent resistance to both metastable pit formation and pit growth.     

Problems and solutions for determination of carbon transfer coefficient β using steel foil carburising method

Abstract

In this paper, the carburising process of steel foil was simulated by numerical method and the carbon transfer coefficient β at the workpiece surface was calculated with the conventional formula for the steel foil carburising test. The results indicated that foil thickness, carburising time and carbon diffusion coefficient in foil apparently affect the calculated carbon transfer coefficient, which always has a smaller value than the preset β value (the true value) and decreases with decreasing carbon diffusion coefficient. This paper suggests that the conventional formula is applicable only when carbon diffusion coefficient in foil is close to infinity; otherwise, the calculated β has obvious error and consequently, gives false information about the influences of other test factors. We propose a new calculation method based on the analytical solution of the diffusion equation during steel foil carburising and a supplementary test, with which the calculated β coefficient is close to the true value, and the carbon diffusion coefficient can be obtained simultaneously.     

Effect of carburising on geometrical control during quenching of martensitic sheet steel channels

The impact of component orientation and selective carburising is examined on the distortion during quenching of post-forming heat-treated (PFHT) channels using three different strength martensitic steel grades. The results show that the minimal, though unpredictable distortion that occurred during quenching of uncarburised channels was confined to either an opening or closing of the channel wall angle. It is also shown that selective carburising on a given surface of the channel will cause a significant change in the shape of the channel during quenching, which is related to the depth of carburising.     

Plasma carburising: exotic with potential

Abstract

Low pressure carburising in combination with high pressure gas quenching has gained an increasing importance in the case hardening of highly stressed components. With the introduction of acetylene as carburising gas and the further development of the systems engineering, this technology has found broad acceptance in the heat treatment industry. Plasma carburising with methane as process gas was first introduced more than 20 years ago but has only been utilised in a few special cases on an industrial scale. The advantage of this type of low pressure carburising is the opportunity to achieve a partial case hardening by simply mechanical masking of the parts to be treated. The ALD Own & Operate GmbH Companies have a 10 year of practical experience with the partial plasma carburising process in the serial production of automotive and aerospace parts. By means of two examples the plasma processes and furnace equipment as well as the masking and the results of the treatment will be presented. Other possible applications of this heat treatment method will also be given.     

Corrosion behaviour of carbon S-phase created on Ni-free biomedical stainless steel

Following the success of forming a carbon S-phase (expanded austenite) surface layer on medical grade Ni-free austenitic stainless steel by DC plasma carburising, the established commercial carburising process Kolsterising® was performed on both Ni-containing (AISI 304) and Ni-free austenitic stainless steels. While the Ni-containing stainless steel responded very well to Kolsterising®, the Ni-free alloy did not. The carbon absorption and the hardness of the Kolsterised® Ni-free alloy are inferior to Kolsterised® AISI 304 Ni-containing stainless steel, however, the hardness of the untreated Ni-free alloy was doubled by Kolsterising®. The response of both Kolsterised® Ni-free and Ni-containing alloys to pitting, crevice corrosion and intergranular corrosion resistance was similar. From this work it can be concluded that the Kolsterised® austenitic stainless steels do not suffer from intergranular corrosion but are susceptible to intragranular pitting when tested in boiling sulphuric acid and copper sulphate solution. It was also observed that Kolsterising® improves significantly the pitting and crevice corrosion resistance of the alloys used in this study.     

Vacuum carburising and high pressure gas quenching technology in automotive industry

Abstract

As the conventional gas carburising furnaces and oil quenching baths used for powertrain parts in the automotive industry have become outmoded, introduction of new equipment and technology is of increasing urgency. Recent demands to improve the mechanical properties of parts and productivity while minimising environmental impact have made vacuum carburising/high pressure gas quenching technology an attractive alternative. However, problems with over carburising and soot in vacuum carburising, and the low cooling ability and high running cost of high pressure gas quenching constitute barriers to adoption of this technology. Attempts to solve these problems by experiments and numerical simulation are reported.     

Development of high performance gas carburising furnace

Abstract

We developed a high performance gas carburising furnace (N-BBH) to overcome the inherent disadvantages of gas carburising furnaces. More than 90% reduction in CO₂ emission was achieved using a small amount of carrier gas in the air tight heating chamber and by precise control of the atmosphere during carburising. No conditioning time was required because the air does not enter either the heating chamber or the pre-chamber when opening the furnace. Carburising speed was higher than that of low pressure carburising because of a high carbon transfer coefficient (β) and high carbon potential (CP). Decreasing the oxidation components, such as CO₂, O₂ and H₂O, and using nitrogen gas or atmospheric gas with high CP, reduced intergranular oxidation 50% or more compared with conventional gas carburising.     

渗碳过程中碳势变化对工件碳浓度的影响

采用剥层分析和模拟试验研究了渗碳过程中的升温、排气、强渗、扩散和降温各阶段的碳势变化对工件渗层最终碳浓度梯度的影响,结果表明,升温、排气和强渗阶段的碳势波动对工件最终表面碳浓度梯度的影响较小,而扩散阶段碳势波动的影响则较大,特别是降温阶段,碳势波动0．1％就会导致自表面至100μm处的渗层中碳浓度变化超过0．05％。