影响奥氏体热作模具钢性能的因素

 在700 ℃下,马氏体型热作模具钢难以工作,奥氏体型热作模具钢具有良好的高温强度。基于均匀设计方法,设计了6种不同成分的试验钢及相应的热处理工艺。试验测定了6种钢的硬度、室温冲击韧性、热稳定性,利用二次型逐步回归分析方法对试验结果进行了建模,得出了三者与成分、工艺之间的回归方程,并与H13钢和DIEVAR钢对比。结果表明：增加Si、Mn、V含量,降低Cr、Mo含量可以提高钢的韧性;同时在所设计的热处理工艺范围内可以使钢的室温冲击功达到300 J;在700 ℃保温20 h,硬度HRC减少1~3。     

H13热作模具钢热处理工艺研究

以热作模具钢的代表——H13热作模具钢的使用条件作为热处理工艺设定参数的主要考虑对象,采用合金化的角度简述合金元素在工件当中的作用,并分析现阶段H13热作模具钢的热处理过程中正火、球化退火、淬火、回火等工艺,以此为出发点,制定并完善了传统的热作模具钢的热处理工艺.     

ZG56CrNiMoV7热作模具铸钢导盘质量控制与热处理

采用中频炉冶炼生产热作模具钢导盘,给出了铸造质量控制与成分控制原则。根据探伤情况,在调质热处理工艺的淬火冷却环节上采用不同介质实现ZG56CrNiMoV7热作模具铸钢导盘的淬火冷却。制定了相应的热处理工艺参数,自己设计专用淬火吊具淬火,成功进行了ZG56CrNiMoV热作模具铸钢导盘的淬火。导盘性能完全满足使用要求,为中频炉冶炼生产大型热作模具铸钢件并采用相应热处理控制技术,提供了重要参数。     

4Cr2WMoVSi热作模具钢的研究与应用

以多元少量的合金化原则设计的4Cr2WMoVSi钢是一种经济型热作模具钢,研究了4Cr2WMoVSi钢的热处理工艺及性能,并与3Cr2W8V钢的热处理工艺和性能作了对比,用4Cr2WMoVSi钢制作了热剪刃,进行了装机使用试验,其使用寿命与3Cr2WSV剪刃的寿命相当,而是5CrW2Si剪刃寿命的3．4倍。     

铝材挤压模R521钢真空热处理工艺研究

探索R521钢热作模具钢的真空热处理工艺以获得更好的机械性能与表面质量。     

热作模具材料的进展

介绍了 1 2种目前在生产上大量使用或推广使用效果较好的热作模具钢 ,并对其化学成分、性能、使用特点及热处理工艺进行了重点阐述。     

国内外热作模具钢的研究进展

介绍了国内外传统和新型热锻、热挤压和压铸用热作模具,以及特殊用途热作模具的钢种和特点;热作模具钢热处理和表面处理技术的研究进展。提高模具钢纯净度、均匀和细化组织,用计算机模拟技术开发热作模具钢新钢种是目前提高热作模具钢寿命的重要方法。     

高热强性热作模具钢SDH3的研究

根据热作模具钢的服役条件,基于成分均匀设计方法设计出一种高硅低钼型热作模具钢SDH3钢(专利钢),并与H13钢进行了室温冲击韧性、回火稳定性和热疲劳性能的对比试验研究,结果表明:热处理后,两种钢冲击韧性相当;620℃下保温22 h后,SDH3钢的硬度值大于35 HRC,比H13钢高4 HRC左右;SDH3钢具有比H13钢更优良的抗热疲劳性能。     

含氮热作模具钢的成分与热处理工艺优化分析

现代金属制造工艺较以往出现了多种变化,技术持续进步,从进一步提升材料质量的角度出发,也有必要继续加强研究。本文以含氮热作模具钢的成分与热处理工艺优化为目标,首先分析含氮热作模具钢的质量影响因素、控制思路等内容,再以此为基础,通过模拟实验的方式,从钒和氮含量控制、淬火和回火温度控制等方面,做材料质量对比分析,服务后续工作。     

含氮热作模具钢的成分与热处理工艺优化分析

现代金属制造工艺较以往出现了多种变化,技术持续进步,从进一步提升材料质量的角度出发,也有必要继续加强研究。本文以含氮热作模具钢的成分与热处理工艺优化为目标,首先分析含氮热作模具钢的质量影响因素、控制思路等内容,再以此为基础,通过模拟实验的方式,从钒和氮含量控制、淬火和回火温度控制等方面,做材料质量对比分析,服务后续工作。     

热处理对低合金耐磨钢K400组织性能的影响

针对低合金耐磨钢的性能要求,以日本住友金属生产的＂Sumihard-K400＂低合金耐磨钢为研究对象,研究了不同淬火温度和回火温度与组织性能的关系,得到硬度、冲击韧性的良好配合,以满足高强度耐磨钢的使用要求。研究结果表明：经淬火加低温回火后的板条马氏体组织与K400原始组织相近。当淬火温度从900℃上升到1 000℃时...     

Upgrading the microstructure and the mechanical properties of cast high speed steel

The main problem of near‐net‐shape cast high speed steel toolings is the bad toughness due to the presence of relatively coarse structure and eutectic brittle carbide network. To overcome this problem intensive secondary cooling in oil immediately after casting was achieved, however special standard tool steels with high amount of austenite stabilizing elements were selected to give austenite + carbide in as‐cast condition. This eliminates the risk of martensitic transformation during intensive secondary cooling. Prespherodisation heat treatment at different temperatures was applied to improve the carbide morphology in cast structures of these steels. This is because traditional hardening of high speed (TS‐1 and TS‐2) cast steels showed severe deterioration in carbide morphology and increased noncoherency with the matrix. In this case, skeleton brittle carbide morphologies were detected in such steels. Impact toughness of prespherodised hardened high speed cast steel (TS‐2) was more or less higher than that of the normally heat treated steel, especially at section sizes lower than 20 mm. Meanwhile the prespherodised steel showed lower toughness at section sizes of more than 20 mm. The hot hardness for the same thickness and test temperature of normally hardened high speed steels was higher to some extent than that for prespherodised and hardened ones. However, the hot hardness increases as the size of sample increases, due to the gross of eutectic and secondary carbide.     

Influence of post weld heat treatment on impact toughness properties of 1Cr0.5Mo and 2.25Cr1Mo steels

The influence of post weld heat treatment on hardness and impact toughness properties of weldments of 1Cr0.5Mo and 2.25Cr1Mo steels has been investigated. Post weld heat treatment significantly reduced the hardness and the impact transition temperature and increased the upper shelf energy. The decrease in hardness was essentially larger for 2.25Cr1Mo than for the other steel, probably due to the presence of martensite in the as-welded condition in the former material. The decrease in the impact transition temperature was largest for 1Cr0.5Mo.     

An Assessment of Vacuum‐Heat‐Treated H11 Hot‐Work Tool Steel using the KIc/HRc Ratio

Charpy V‐notch (CVN) impact‐test values are widely used in toughness specifications for AISI H11 hot‐work tool steel, even though the fracturing energy is not directly related to the tool design. K_Ic, the plain‐strain stress‐intensity factor at the onset of unstable crack growth, can be related to the tool design; however, K_Ic test values are not widely used in toughness specifications. This is surprising since to the designer K_Ic values are more useful than CVN values because the design calculations for tools and dies of high‐strength steels should take into account the strength and the toughness of materials in order to prevent the possibility of rapid and brittle fracture. An investigation was conducted to determine whether standardized fracture‐toughness testing (ASTM E399‐90), which is difficult to perform reliably for hard materials with a low ductility, could be replaced with a so far non‐standard testing method. A particular problem is that the manufacture of the fatigue crack samples is difficult and expensive, and this has promoted the search for alternative fracture‐toughness testing methods. One of the most promising methods is the use of circumferentially notched and fatigue‐precracked tensile specimens. With this technique the fatigue crack in the specimen is obtained without affecting the fracture toughness of the steel, if it is obtained in soft annealed steel, i.e., prior to the final heat treatment. The results of this investigation have shown that using the proposed method it was possible to draw, for the normally used range of working hardness, combined tempering diagrams (Rockwell‐C hardness ‐ Fracture toughness K_Ic ‐ Tempering temperature) for some AISI H11 hot‐work tool steel delivered from three steel plants. On the basis of the combined tempering charts the influence of the processing route on the mechanical properties was investigated. In the same way, vacuum‐heat‐treated tool steels were assessed and their properties expressed as a ratio of the fracture toughness to the hardness (K_Ic/HRc).     

Improvement of Mechanical Properties of Reinforcing Steel Used in the Reinforced Concrete Structures

SAE1010 structural carbon steel, which has a low cost price and wide range of use in the construction industry, has been studied as dual phase (DP) steel subjected to appropriate heat treatment, and its mechanical properties have been investigated under various tempering conditions. Intercritical annealing heat treatment has been applied to the reinforcing steel in order to obtain DP steels with different martensite volume fraction. In addition, these DP steels have been tempered at 200, 300 and 400 °C for 45 min and then cooled to the room temperature. Mechanical properties such as tensile strength, yield strength, reduction in cross-sectional area, total elongation, resilience modulus and toughness have been examined. Furthermore, fractographic examination has been done with scanning electron microscope (SEM) as well as metallographic examination of the steels. As a result of this study, it is found that mechanical properties of DP steel have changed according to the hardness and ratio of martensite phase. In addition, tensile strength, yield strength and resilience modulus of the steels have been reduced. In contrast, the total elongation, reduction of the cross-sectional area and toughness have been increased.     

Influence of Partitioning Effects on the Retained Austenite Content and Properties of Martensitic Stainless Steel

The effect of a quenching and partitioning (Q&P) heat treatment with a quenching temperature (T_Q) range from 20 to 190 °C is investigated for two martensitic stainless tool steels X40Cr14 and “X25CrN13”, focusing on microstructural evolution, hardness, and toughness. The influence on the retained austenite (RA) content, when replacing part of carbon with nitrogen, is of core interest. The amount of RA is analyzed by X-ray diffraction and is additionally proved with electron backscatter diffraction, and the RA content is thermodynamically calculated. Subsequently, the effect of the microstructure on toughness and hardness is investigated. For both steels, the toughness maximum is reached in the region of the RA maximum. The “X25CrN13” attains higher toughness at higher RA contents. Higher RA contents do not benefit X40Cr14. Furthermore, the effect of double tempering at higher tempering temperatures after Q&P on the steels is investigated. Besides RA contents and hardness, dilatometer curves are used to evaluate the formation of fresh martensite in the microstructure. The secondary hardness maximum of “X25CrN13” is reached at 500 °C and that of X40Cr14 is at 480 °C. For double tempering temperature at 520 °C, T_Q has little effect on toughness, and “X25CrN13” shows better values.     

Fracture toughness and fatigue behavior of matrix II and M-2 high speed steels

The effects of heat treatment and of the presence of primary carbides on the fracture toughness,K _Ic and the fatigue crack growth rates,da/dN, have been studied in M-2 and Matrix II high speed steels. The Matrix II steel, which is the matrix of M-42 high speed steel, contained many fewer primary carbides than M-2, but both steels were heat treated to produce similar hardness values at the secondary hardening peaks. The variation of yield stress with tempering temperature in both steels was similar, but the fracture toughness was slightly higher for M-2 than for Matrix II at the secondary hardening peaks. The presence of primary carbides did not have an important influence on the values ofK _Ic of these hard steels. Fatigue crack growth rates as a function of alternating stress intensity, ΔK, showed typical sigmoidal behavior and followed the power law in the middle-growth rate region. The crack growth rates in the near threshold region were sensitive to the yield strength and the grain sizes of the steels, but insensitive to the sizes and distribution of undissolved carbides. The crack growth rates in the power law regime were shifted to lower values for the steels with higher fracture toughness. SEM observations of the fracture and fatigue crack surfaces suggest that fracture initiates by cleavage in the vicinity of a carbide, but propagates by more ductile modes through the matrix and around the carbides. The sizes and distribution of primary carbides may thus be important in the initiation of fracture, but the fracture toughness and the fatigue crack propagation rates appear to depend on the strength and ductility of the martensite-austenite matrix.     

Effects of alloying elements on fracture toughness in the transition temperature region of base metals and simulated heat-affected zones of Mn-Mo-Ni low-alloy steels

This study is concerned with the effects of alloying elements on fracture toughness in the transition temperature region of base metals and heat-affected zones (HAZs) of Mn-Mo-Ni low-alloy steels. Three kinds of steels whose compositions were varied from the composition specification of SA 508 steel (grade 3) were fabricated by vacuum-induction melting and heat treatment, and their fracture toughness was examined using an ASTM E1921 standard test method. In the steels that have decreased C and increased Mo and Ni content, the number of fine M₂C carbides was greatly increased and the number of coarse M₃C carbides was decreased, thereby leading to the simultaneous improvement of tensile properties and fracture toughness. Brittle martensite-austenite (M-A) constituents were also formed in these steels during cooling, but did not deteriorate fracture toughness because they were decomposed to ferrite and fine carbides after tempering. Their simulated HAZs also had sufficient impact toughness after postweld heat treatment. These findings indicated that the reduction in C content to inhibit the formation of coarse cementite and to improve toughness and the increase in Mo and Ni to prevent the reduction in hardenability and to precipitate fine M₂C carbides were useful ways to improve simultaneously the tensile and fracture properties of the HAZs as well as the base metals.     

Effect of Vanadium Microalloying on the HAZ Microstructure and Properties of Low Carbon Steels

Four Steels,C-Mn-0.05V,C-Mn-0.11V,C-Mn-0.03Nb and C-Mn were subjected to heat treatment to simulate the microstructure of a coarse grained heat affected zone (CGHAZ) and an intercritically reheated coarse grained heat affected zone (ICCGHAZ).This involved reheating to 1350°C,rapid cooling (Δt 8/5 =24s) to room temperature and then reheating to either 750°C or 800°C.The toughness of the HAZs was assessed using both Charpy and CTOD tests.Microstructural features were characterised by optical,scanning` and transmission electron microscopy.Fractographic examinations of the Charpy and CTOD specimens were carried out to understand the micromechanism of fracture under different microstructural and test conditions.The CGHAZ toughness was similar for the steels except that Steel C-Mn-0.05V had a slightly lower ITT compared to the others.The toughness deteriorated in the ICCGHAZ for all the steels,again Steel C-Mn-0.05V had a superior toughness compared to the other three steels in both ICCGHAZ conditions.Raising the level of vanadium to 0.11% caused a decrease in ICCGHAZ toughness.Steel C-Mn-Nb exhibited a greater degradation of impact toughness after the intercritical cycles.The presence of M-A constituents was the dominant factor in determining the toughness of the ICCGHAZs.The size and area fraction of the M-A constituents were the smallest in Steel C-Mn-0.05V.Increasing vanadium level to 0.11% resulted in a greater area fraction of the M-A constituents,larger average and maximum sizes of M-A particles,and significantly more fields containing the M-A.The addition of 0.031% Nb produced the largest M-A particles and the greatest area fraction for the steels tested.