Microstructure and Properties of Low Temperature Composite Chromized Layer on H13 Tool Steel

Low temperature composite chromizing is a process composed of a plain ion-carbonitriding or ion-nitriding at 550-580℃, followed by a low-temperature chromizing in a salt-bath of 590℃. The microstructure and properties of the low temperature composite chromized layer on H13 tool steel were investigated using metallography, X-ray diffraction, microanalysis, hardness and wear tests. It was found that this low temperature process was thermo-dynamically and kinetically possible, and the composite chromized layer on H13 steel, with a thickness of 3-6 μm, consisted of three sub-layers (bands), viz. the outer Cr-rich one, the intermediate (black) one, and the inner, original white layer. After chromizing, the former diffusion layer was thickened. The results of X-ray diffraction showed that the composite chromized layer contained such nitrides and carbides of chromium as CrN, Cr2N, (Cr, Fe)23C6, and (Cr, Fe)7C3, as well as plain α-(Fe, Cr). A high surface microhardness of 1450-1550 HV0.025, which is much higher than that obtained by the conventional ion carbonitriding and ion nitriding, was obtained. In addition, an excellent wear resistance was gained on the composite chromized layer.

Study on Heterogeneous Nuclei in Cast H13 Steel Modified by Rare Earth

The dendrite segregation in cast H13 steel was weakened with RE modification treatment. Grain boundary carbide during quenching was also under control and impact toughness was improved greatly. By thermodynamic calculation, analysis of two-dimensional lattice misfitting and electron probe analysis, it is found that Ce2O3 may act as the heterogeneous nuclei of modified cast H13 steel.

Study on primary carbides precipitation in H13 tool steel regarding cooling rate during solidification

This study aims to investigate the primary carbides precipitation in H13 steel solidified at relatively high cooling rates,ranging from 300 to 6,000℃·min^-1,based on in situ observations with a high temperature confocal laser scanning microscope.In the cooling rate range investigated,the solidification microstructure becomes more refined as cooling rate increases and the relationship between the secondary dendrite arm spacing(SDAS),λ2,and cooling rate,.T,can be expressed asλ2=128.45.T-0.124.Regardless of cooling rates,two kinds of primary carbides,i.e.,the Mo-Cr-rich and V-rich carbides,are precipitated along the interdendritic region and most of them are the Mo-Cr-rich carbides.The morphology of Mo-Cr-rich carbide is not obviously influenced by the cooling rate,but that of V-rich carbide is obviously affected.The increasing cooling rate markedly refines the primary carbides and reduces their volume fractions,but their precipitations cannot be inhibited even when the cooling rate is increased to 6,000℃·min^-1.Besides,the segregation ratios(SRs)of the carbides forming elements are not obviously affected by the cooling rate.However,compared with the conventionally cast ingot,the SDAS and primary carbides in the steel solidified at the investigated cooling rates are much finer,morphologies of the carbides have changed significantly,and SRs of the carbides forming elements are markedly greater.The variation of primary carbide characteristics with cooling rate is mainly due to the change in SDAS.

Effect of Thermal Fatigue Loading on Tensile Behavior of H13 Die Steel with Biomimetic Surface

Biomimetic surface is an effective ways to promote the performance grade and applied range of materials without alteringtheir substrate.Many improved properties such as resisting fatigue,enduring wear,etc,have been achieved by applyingbiomimetic morphology or structure to some engineering material surfaces.In this paper,aiming to reveal the relationshipbetween thermal cracking behavior and mechanical properties of engineering materials with biomimetic surface,biomimeticspecimens were fabricated using laser technique by imitating the heterogeneous structure on the surface of plant leaves.Theeffect of thermal fatigue cycling on the tensile properties of H13 die steel specimens with different surfaces (several types ofbiomimetic surfaces and a smooth surface) was compared and investigated.As a result,due to the coupling effects of themorphological features on the surface and the microstructure characteristics within unit zone,these specimens with biomimeticsurface exhibit remarkably enhanced Ultimate Tensile Strength (UTS) and 0.2% Yield Strength (YS) compared with referencespecimens while corresponding ductility remains largely unaffected even heightened,whether the thermal fatigue loads or not.The relative mechanisms leading to these improvements have been discussed.

Influence of Surface Nano-structured Treatment on Pack Boriding of H13 Steel

In order to lower the boriding temperature of hot work steel H13, method of surface mechanical attrition treatment （SMAT）, which can make the grain size of the surface reach nano-scale, was used before pack boriding. The growth of the boride layer was studied in a function of boriding temperature and time. By TEM （transmission electron microscopy）, SEM （scanning electron microscopy）, XRD （x-ray diffraction） and microhardness tests, the grain size, thermal stability of the nano-structured （NS） surface and the thickness,appearance, phases of the surface boride layer were studied. Kinetic of boriding was compared between untreated samples and treated samples. Results showed that after SMAT, the boride layer was thicker and the hardness gradient was smoother. Furthermore, after boriding at a low temperature of 700℃ for 8 h, a boride layer of about 5 μm formed on the NS surface. This layer was toothlike and wedged into the substrate, which made the surface layer combine well with the substrate. The phase of the boride layer was Fe2B. Research on boriding kinetics indicated that the activation energy was decreased for the treated samples.

Laser surface hardening of AISI H13 tool steel

An attempt was made to improve the surface hardness and wear properties of AISI H13 tool steel through solid solution hardening and refinement of microstructures using a 200 W fiber laser as a heat generating source.The hardness of laser melted zone was investigated.In order to identify the effect of heat input on the laser melting zone,scanning conditions were controlled.The results show that,the hardness of as-received AISI H13 tool steel is approximately Hv 240,and the hardness after laser surface heat treatment is around Hv 480-510.The hardening depth and width are increased with the increase in the heat input applied.Application of experimental results will be considered in tooling industry.

Effects of quenching temperature on microstructure and mechanical properties of H13 mandrel steel

Optical microscope, stereomicroscope, scanning electronic microscope （SEM） and mechanical property testing were used to research the effects of different quenching temperatures on the microstructure and mechanical properties of the H13 mandrel steel. The results indicate that following an increase in the quenching ,the degree of alloying is enhanced due to the carbides dissolving gradually in austenite, which improves the hardenability of the specimens, as well as their room and high-temperature strength. At the same time, the fracture toughness increases due to the increment of the martensite number and the interparticle distance of impact toughness. Optimal performance Consequently,the service life of the H13 the carbides. However, extremely coarse grain and martensite can decrease the can be obtained after quenching at 1 060℃ and double tempering at 620℃mandrel steel is extended significantly.

Development of Flow Stress of AISI H13 Die Steel in Hard Machining

An approach was presented to characterize the stress response of workpiece in hard machining, accounting for the effect of the initial workpiece hardness in addition to temperature, strain and strain rate on flow stress in this paper. AISI H13 die steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with experimental data. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response ofAISl H13 die steel with variation of the initial workpiece hardness in hard machining.

Selective laser melting of Fe-Ni-Cr layer on AISI H13 tool steel

An attempt to fabricate Fe-Ni-Cr coating on AISI H13 tool steel was performed with selective laser melting.Fe-Ni-Cr coating was produced by experimental facilities consisting of a 200 W fiber laser which can be focused to 80 μm and atmospheric chamber which can control atmospheric pressure with N2 or Ar.Coating layer was fabricated with various process parameters such as laser power,scan rate and fill spacing.Surface quality and coating thickness were measured and analyzed.Three different surface patterns,such as typeⅠ,typeⅡand type Ⅲ,are shown with various test conditions and smooth regular pattern is obtained under the conditions as 10 μm of fill spacing,50-350 mm/s of scan rate and 40 μm of fill spacing,10-150 mm/s of scan rate.The maximum coating thickness is increased with power elevation or scan rate drop,and average thickness of 10 μm fill spacing is lower than that of 40 μm fill spacing.

Thermal fatigue behavior of niobium microalloyed H13 steel

AISI H13 hot work tool steel is widely used for hot forging, hot-extrusion and die-casting because of its high temperature strength, impact toughness, heat checking resistance and wear resistance, etc. The thermally induced surface damage, i. e., thermal fatigne,is believed to be controlled by the magnitude of the imposed cyclic strain. The thermal fatigue on the surface of hot working die, which is responsible to the initiation of the cracks, is reported to result in more than 80 % of the failure of dies.

Microstructures and properties of Co-based alloy coatings prepared on surface of H13 steel

The Co-based alloy coatings had been prepared by laser cladding and vacuum fusion sintering. Microstructures of the coatings were investigated and the performance of thermal cycling was also tested using scanning electron microscopy （ SEM） and X-ray diffraction （ XRD ）. The results show that the coatings and substrates combine well. The main phase compositions of laser cladding coating are T-Co, Cr23 C6 and Ni2 9 Cro. 7 Feo. 36, while vacuum fusion sintering coating consists of Co, Cr7 C3, and Ni2.9 Cro. 7 Feo. 36. After thermal cycling, the minimum hot cracking width of laser cladding coating is 14 μm; moreover, laser cladding coating maintains high hardness and hot-cracking susceptibility. Those are beneficial to high temperature wear resistance of hot work dies.

FLOW STRESS MODEL FOR HARD MACHINING OF AISI H13 WORK TOOL STEEL

An approach is presented to characterize the stress response of workpiece in hard machining, accounted for the effect of the initial workpiece hardness, temperature, strain and strain rate on flow stress. AISI H13 work tool steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with data collected from published experiments. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response of AISI H13 work tool steel with variation of the initial workpiece hardness in hard machining.

Influence of Deep Cryogenic Treatment (DCT) on Thermo Mechanical Performance of AISI H13 Tool Steel

Deep cryogenic treatment (DCT) is one of the most recent processes being used to treat tool steels. It is a supplementary treatment where components are treated below subzero temperatures for several cryo-soaking hours. This paper focuses on to study the effect of deep cryogenic treatment on Thermo mechanical properties of AISI H-13 tool steel. Deep cryogenic treatment at 32 hours of cryo-soaking time is applied and thermo mechanical performance of tool steel was analyzed by using pin on disk high temperature wear testing and stress rupture testings. The microstructural evolutions during DCT were evaluated by using scanning electron microscope (SEM). It was observed that microstructural modifications like increase in carbide density, fine and uniform martensitic structure during DCT had significantly improved properties.

Effects of carbon,sulphur,phosphorus,and nickel compositions and hot working on thermal fatigue properties of H13 steel

For precise composition control and the selection of hot-w orking operation,effects of carbon（ C）,sulphur（ S）,phosphorus（ P）,and nickel（ Ni） compositions and hot working on thermal fatigue properties of H13 steel under thermal cycling conditions w ere studied by a self-restraint thermal fatigue test. Results show ed that the control of the C content at about 0. 35%,Ni content at about 0. 50%,and S and P contents as low as possible and the forging operation used lead to an improvement of the thermal fatigue resistance of the steel.

热处理对H13热作模具钢的显微结构和性能的影响

研究预备热处理工艺、回火温度及深冷处理对H13热作模具钢的显微结构和力学性能的影响。结果表明,对成分偏析且锻造不足的H13钢,在常规的热处理条件下,适当提高回火温度(如630℃)可部分消除H13钢的带状组织;对该种钢材热处理前进行扩散退火+球化退火预先热处理,能更有效改善其金相组织,较大幅度提高材料的冲击韧度;深冷处理后,残余奥氏体转变为马氏体,同时碳化物分布更加细小、均匀,可进一步提高H13钢的力学性能。

激光增材制造H13钢及回火处理的组织和性能

利用激光增材制造技术成功制备了H13钢,并研究了回火处理对其显微组织和性能的影响。通过光学显微镜、SEM以及XRD衍射仪对各试样进行分析。结果表明,激光增材制造H13钢显微组织主要为马氏体、残余奥氏体以及细小碳化物,回火处理使得马氏体向回火马氏体转变,同时有细小合金碳化物析出。当回火温度超过550℃时,碳化物开始粗化。随回火温度升高,显微硬度呈先升后降的趋势。550℃回火后,试样硬度达到峰值600 HV_(0.3)。摩擦磨损测试结果表明,不同处理状态下各试样主要以粘着磨损为主,同时包含轻微氧化磨损。与沉积态试样相比,550℃回火后,试样耐磨性提高了2倍;650℃回火2 h后,由于基体软化,试样的耐磨性能最差。拉伸测试表明,当回火温度低于550℃时,断口主要以解理断裂为主,550℃回火时抗拉强度最大,为1 928.2 MPa,延伸率为6.4%;当回火温度升高到600~650℃时,断口呈现出韧性断裂,抗拉强度降低,延伸率增大。

H-13钢铸造性能的研究

Ｈ－１３钢是近十几年来应用较为广泛的热作模具钢。几何形状复杂的大、中型模具采用铸造方法制作具有显著的经济效益。可是，目前对Ｈ－１３钢的铸造性能缺乏足够的认识，这方面的研究工作也很少见到报道。为推广应用铸造方法生产Ｈ－１３钢热作模具毛坯，对Ｈ－１３钢的铸造性能作了较为系统的研究，并获得了一组有价值的Ｈ－１３钢铸造性能数据，为高质量的Ｈ－１３钢模具的铸造打下了基础。

热处理工艺参数对H13钢组织和力学性能的影响

利用正交试验法研究了淬火、第一次回火、第二次回火对H13钢组织和性能的影响。结果表明:第二次回火对材料的强度和塑性影响最为显著,其次为淬火,最后是第一次回火;随淬火温度升高,抗拉和屈服强度升高,断面收缩率先升高后降低,伸长率降低;强塑性随第一次和第二次回火温度变化的趋势是一样的,随回火温度升高强度均下降,塑性升高。H13钢淬火后获得板条马氏体,淬火温度升高至1070℃时,马氏体开始明显粗化;回火后马氏体转变为回火马氏体,部分马氏体会产生回复再结晶,在马氏体板条间出现大量碳化物。

QPQ盐浴复合处理对H13钢组织及性能的影响

运用QPQ盐浴复合处理技术对H13钢进行表面强化处理,分析了不同工艺参数对氮化层深度、显微硬度和抗腐蚀性的影响及氮化层显微组织特征。结果表明,在相同的渗氮温度下,渗氮层的深度随渗氮时间的延长而增加,氮化后的材料硬度和耐腐蚀性较渗氮前有较大的提高,氮化3～4h效果最好。

蒸汽氧化处理对H13钢铝合金压铸模具熔损及疲劳性能的影响

将经过蒸汽氧化处理和未处理的H13钢试样进行热疲劳、熔损和熔损-疲劳3种试验,以考核氧化处理对H13钢在铝合金压铸服役过程中的影响。结果表明,经蒸汽氧化表面处理的H13钢耐热疲劳性能不仅没有下降,而且还具有良好的抗熔融铝合金的熔损性能。